Staff directory Jordi Arbiol Cobos

Jordi Arbiol Cobos

ICREA Research Professor and Group Leader
Advanced Electron Nanoscopy



  • A CrMnFeCoNi high entropy alloy boosting oxygen evolution/reduction reactions and zinc-air battery performance

    He, R; Yang, LL; Zhang, Y; Wang, X; Lee, S; Zhang, T; Li, LX; Liang, ZF; Chen, JW; Li, JS; Moghaddam, AO; Llorca, J; Ib, M; Arbiol, J; Xu, Y; Cabot, A Energy Storage Materials; 58: 287 - 298. 2023. 10.1016/j.ensm.2023.03.022.

  • A MOF-Based Spatial-Separation Layer to Enable a Uniform Favorable Microenvironment for Electrochemical CO2 Reduction

    Han, X; Zhang, T; Biset-Peiro, M; Zhao, SQ; Lopez, SM; Daasbjerg, K; Morante, JR; Li, J; Arbiol, J Small Structures; 2023. 10.1002/sstr.202200388.

  • Asymmetrical Plasmon Distribution in Hybrid AuAg Hollow/Solid Coded Nanotubes

    Genç A; Patarroyo J; Sancho-Parramon J; Arenal R; Bastús NG; Puntes V; Arbiol J Nanomaterials; 13 (6): 992. 2023. 10.3390/nano13060992.

  • Author Correction: Reducing charge noise in quantum dots by using thin silicon quantum wells

    Paquelet Wuetz, Brian; Degli Esposti, Davide; Zwerver, Anne-Marije J.; Amitonov, Sergey V.; Botifoll, Marc; Arbiol, Jordi; Sammak, Amir; Vandersypen, Lieven MK.; Russ, Maximilian; Scappucci, Giordano Nature Communications; 14 (1) 2023. 10.1038/s41467-023-37548-z.

  • Constructing an active and stable oxygen electrode surface for reversible protonic ceramic electrochemical cells

    Pei, Kai; Luo, Shunrui; He, Fan; Arbiol, Jordi; Xu, Yangsen; Zhu, Feng; Wang, Yakun; Chen, Yu Applied Catalysis B-Environmental; 330: 122601. 2023. 10.1016/j.apcatb.2023.122601.

  • Engineering of Thermoelectric Composites Based on Silver Selenide in Aqueous Solution and Ambient Temperature

    Nan, Bingfei; Li, Mengyao; Zhang, Yu; Xiao, Ke; Lim, Khak Ho; Chang, Cheng; Han, Xu; Zuo, Yong; Li, Junshan; Arbiol, Jordi; Llorca, Jordi; Ibáñez, Maria; Cabot, Andreu Acs Applied Electronic Materials; 2023. 10.1021/acsaelm.3c00055.

  • Hard superconducting gap in germanium

    Tosato, A; Levajac, V; Wang, JY; Boor, CJ; Borsoi, F; Botifoll, M; Borja, CN; Marti-Sanchez, S; Arbiol, J; Sammak, A; Veldhorst, M; Scappucci, G Communications Materials; 4 (1): 23. 2023. 10.1038/s43246-023-00351-w.

  • Improvement of carbon dioxide electroreduction by crystal surface modification of ZIF-8

    Zhang, T; Liu, H; Han, X; Biset-Peiro, M; Yang, YH; Imaz, I; Maspoch, D; Yang, B; Morante, JR; Arbiol, J Dalton Transactions; 52 (16): 5234 - 5242. 2023. 10.1039/d3dt00185g.

  • In situ construction of graphdiyne based heterojunctions by a deprotection-free approach for photocatalytic hydrogen generation

    Wang, C; Han, X; Xu, Q; Sun, YN; Arbiol, J; Ghazzal, MN; Li, J Journal Of Materials Chemistry a; 11 (7): 3380 - 3387. 2023. 10.1039/d2ta09918g.

  • Is Soft Carbon a More Suitable Match for SiOx in Li-Ion Battery Anodes?

    Sun, Q; Zeng, GF; Li, J; Wang, S; Botifoll, M; Wang, H; Li, DP; Ji, FJ; Cheng, J; Shao, HY; Tian, YH; Arbiol, J; Cabot, A; Ci, LJ Small; 2023. 10.1002/smll.202302644.

  • Metal–organic framework-derived single atom catalysts for electrocatalytic reduction of carbon dioxide to C1 products

    Han, Xu; Zhang, Ting; Arbiol, Jordi Energy Advances; 2023. 10.1039/d2ya00284a.

  • Phosphorous incorporation into palladium tin nanoparticles for the electrocatalytic formate oxidation reaction

    Montana-Mora, G; Qi, XQ; Wang, X; Chacon-Borrero, J; Martinez-Alanis, PR; Yu, XT; Li, JS; Xue, Q; Arbiol, J; Ibanez, M; Cabot, A Journal Of Electroanalytical Chemistry; 936: 117369. 2023. 10.1016/j.jelechem.2023.117369.

  • Reducing charge noise in quantum dots by using thin silicon quantum wells

    Paquelet Wuetz B; Degli Esposti D; Zwerver AJ; Amitonov SV; Botifoll M; Arbiol J; Vandersypen LMK; Russ M; Scappucci G Nature Communications; 14 (1): 1385 - 1385. 2023. 10.1038/s41467-023-36951-w.

  • Selective Ethylene Glycol Oxidation to Formate on Nickel Selenide with Simultaneous Evolution of Hydrogen

    Li, JS; Li, LM; Ma, XY; Han, X; Xing, CC; Qi, XQ; He, R; Arbiol, J; Pan, HY; Zhao, J; Deng, J; Zhang, Y; Yang, YY; Cabot, A Advanced Science; 2023. 10.1002/advs.202300841.

  • Thermoelectric Performance of Surface-Engineered Cu1.5–xTe–Cu2Se Nanocomposites

    Xing, Congcong; Zhang, Yu; Xiao, Ke; Han, Xu; Liu, Yu; Nan, Bingfei; Ramon, Maria Garcia; Lim, Khak Ho; Li, Junshan; Arbiol, Jordi; Poudel, Bed; Nozariasbmarz, Amin; Li, Wenjie; Ibáñez, Maria; Cabot, Andreu Acs Nano; 2023. 10.1021/acsnano.3c00495.

  • Unifying stability and plasmonic properties in hybrid nanoislands: Au–Ag synergistic effects and application in SERS

    Bubaš, Matej; Fabijanić, Ivana; Kenđel, Adriana; Miljanić, Snežana; Spadaro, Maria Chiara; Arbiol, Jordi; Janicki, Vesna; Sancho-Parramon, Jordi Sensors And Actuators B-Chemical; 380: 133326. 2023. 10.1016/j.snb.2023.133326.

  • Unveiling the role of counter-anions in amorphous transition metal-based oxygen evolution electrocatalysts

    Wang X., Han X., Du R., Liang Z., Zuo Y., Guardia P., Li J., Llorca J., Arbiol J., Zheng R., Cabot A. Applied Catalysis B: Environmental; 320 (121988) 2023. 10.1016/j.apcatb.2022.121988.

    At the initial stage of the oxygen evolution reaction (OER) most electrocatalysts undergo structural and chemical surface reconstruction. While this reconstruction strongly influences their performance, it is frequently overlooked. Herein, we analyze the role of the oxidized anions, which is particularly neglected in most previous works. We introduce a range of different anionic groups (Cl-, CH3COO-, NO3-, SO42-) on the surface of an amorphous ZnCoxNiyOz catalyst by a facile proton etching and ion exchange method from a ZIF-8 self-sacrificial template. The structural and chemical properties of the obtained set of materials are thoroughly analysed and correlated with their electrocatalytic performance to study the effect of surface anionic groups, phase transition, metal leaching and defect generation on OER activity. Exploiting the control possibilities provided by the synthesis method here described and employing the uncovered property-performance correlations, the electrocatalyst is optimized. As a result, we produce ZnCo1.25Ni0.73Ox-SO4 catalysts with outstanding OER performances, including a low overpotential of 252 mV at 10 mA cm−2 with a small Tafel slope of 41.6 mV dec−1. Furthermore, this catalyst exhibits remarkable stability with negligible overpotential variation for 100 h. The excellent catalytic properties are rationalized using density functional theory calculations, showing that the surface-adsorbed anions, particularly SO42−, can stabilize the OOH* intermediate, thus enhancing the OER activity. This work offers new insight into the roles of metal leaching and surface-adsorbed anions in the OER progress and facilitates the rational design of highly-efficient electrocatalysts for OER. © 2022 Elsevier B.V.


  • 2D/2D Heterojunction of TiO2 Nanoparticles and Ultrathin G-C3N4 Nanosheets for Efficient Photocatalytic Hydrogen Evolution

    Du R., Li B., Han X., Xiao K., Wang X., Zhang C., Arbiol J., Cabot A. Nanomaterials; 12 (9, 1557) 2022. 10.3390/nano12091557.

    Photocatalytic hydrogen evolution is considered one of the promising routes to solve the energy and environmental crises. However, developing efficient and low-cost photocatalysts remains an unsolved challenge. In this work, ultrathin 2D g-C3N4 nanosheets are coupled with flat TiO2 nanoparticles as face-to-face 2D/2D heterojunction photocatalysts through a simple electro-static self-assembly method. Compared with g-C3N4 and pure TiO2 nanosheets, 2D/2D TiO2/g-C3N4 heterojunctions exhibit effective charge separation and transport properties that translate into outstanding photocatalytic performances. With the optimized heterostructure com-position, stable hydrogen evolution activities are threefold and fourfold higher than those of pure TiO2, and g-C3N4 are consistently obtained. Benefiting from the favorable 2D/2D heterojunction structure, the TiO2/g-C3N4 photocatalyst yields H2 evolution rates up to 3875 μmol·g−1·h−1 with an AQE of 7.16% at 380 nm. © 2022 by the authors. Licensee MDPI, Basel, Switzerland.

  • A Deprotection-free Method for High-yield Synthesis of Graphdiyne Powder with In Situ Formed CuO Nanoparticles

    Li, J; Han, X; Wang, DM; Zhu, L; Ha-Thi, MH; Pino, T; Arbiol, J; Wu, LZ; Ghazzal, MN Angewandte Chemie (International Ed. Print); 61 (43) 2022. 10.1002/anie.202210242. IF: 16.823

  • A High Conductivity 1D π–d Conjugated Metal–Organic Framework with Efficient Polysulfide Trapping-Diffusion-Catalysis in Lithium–Sulfur Batteries

    Yang D., Liang Z., Tang P., Zhang C., Tang M., Li Q., Biendicho J.J., Li J., Heggen M., Dunin-Borkowski R.E., Xu M., Llorca J., Arbiol J., Morante J.R., Chou S.-L., Cabot A. Advanced Materials; 34 (10, 2108835) 2022. 10.1002/adma.202108835. IF: 30.849

    The shuttling behavior and sluggish conversion kinetics of the intermediate lithium polysulfides (LiPS) represent the main obstructions to the practical application of lithium–sulfur batteries (LSBs). Herein, a 1D π–d conjugated metal–organic framework (MOF), Ni-MOF-1D, is presented as an efficient sulfur host to overcome these limitations. Experimental results and density functional theory calculations demonstrate that Ni-MOF-1D is characterized by a remarkable binding strength for trapping soluble LiPS species. Ni-MOF-1D also acts as an effective catalyst for S reduction during the discharge process and Li2S oxidation during the charging process. In addition, the delocalization of electrons in the π–d system of Ni-MOF-1D provides a superior electrical conductivity to improve electron transfer. Thus, cathodes based on Ni-MOF-1D enable LSBs with excellent performance, for example, impressive cycling stability with over 82% capacity retention over 1000 cycles at 3 C, superior rate performance of 575 mAh g−1 at 8 C, and a high areal capacity of 6.63 mAh cm−2 under raised sulfur loading of 6.7 mg cm−2. The strategies and advantages here demonstrated can be extended to a broader range of π–d conjugated MOFs materials, which the authors believe have a high potential as sulfur hosts in LSBs. © 2022 Wiley-VCH GmbH

  • A novel π-d conjugated cobalt tetraaza[14]annulene based atomically dispersed electrocatalyst for efficient CO2 reduction

    Liang Z., Zhang T., Cao P., Yoshida T., Tang W., Wang X., Zuo Y., Tang P., Heggen M., Dunin-Borkowski R.E., Morante J.R., Cabot A., Yamashita M., Arbiol J. Chemical Engineering Journal; 442 (136129) 2022. 10.1016/j.cej.2022.136129. IF: 13.273

    Tetraaza[14]annulenes (TAA) are synthetic macrocycles which are analogue to porphyrins. However, there are almost no reports about the synthesis of polymers based on TAA and neither on their use as electrocatalysts. The study of new catalysts to promote an efficient electrochemical conversion of carbon dioxide to valuable chemicals is a promising approach to relieve the pressure of carbon emissions and realize the carbon cycle. Herein, we first report the synthesis of a novel tetraaza[14]annulene (TAA) based organic polymeric metal complex (PMC) by a non-template method. This PMC is used as ligand to construct a π-d conjugated cobalt coordination polymer (Poly-TAA-Co) with CoN4 structure which is supported on multi-wall carbon nanotubes (CNTs) to work as an atomically dispersed efficient electrocatalyst for the CO2 reduction reaction (CO2RR). The resulting catalyst (Poly-TAA-Co-CNT) exhibits excellent performance, with a 90% CO faradaic efficiency, a low overpotential (390 mV) and good stability in 0.5 M KHCO3 aqueous solution. Density functional theory calculations confirmed that the cobalt tetra[14]annulene is an excellent active site for electrocatalytic CO2RR. This work not only inspires the design of novel TAA based macromolecules, but also paves the way to the development and application of new molecular-based catalysts for electrocatalytic CO2RR. © 2022 The Author(s)

  • Activating the lattice oxygen oxidation mechanism in amorphous molybdenum cobalt oxide nanosheets for water oxidation

    Wang X., Xing C., Liang Z., Guardia P., Han X., Zuo Y., Llorca J., Arbiol J., Li J., Cabot A. Journal of Materials Chemistry A; 10 (7): 3659 - 3666. 2022. 10.1039/d1ta09657e. IF: 12.732

    The cost-effective deployment of several key energy technologies, such as water electrolysis, CO2 electroreduction and metal-air batteries, relies on the design and engineering of cost-effective catalysts able to accelerate the sluggish kinetics of the oxygen evolution reaction (OER). Herein, we detail the synthesis, processing and performance of a cobalt oxide-based OER electrocatalyst with optimized composition, atomic arrangement and nano/microstructure. We demonstrate that doping the cobalt oxide with a higher electronegativity element such as molybdenum promotes the participation of lattice oxygen in the OER. Besides, the processing of the catalyst at moderate temperatures results in an amorphous material with extended compositional and atomic arrangement versatility. Additionally, the catalyst, which is produced through an ion etching assisted strategy using ZIF-67 as a template, displays a highly porous structure in the form of amorphous ultrathin MoCoxOy nanosheets that maximize interaction with the media and facilitate the transport of ions through the electrolyte. After optimizing the molybdenum concentration and structural parameters, the best MoCoxOy catalysts exhibited a low overpotential of 282 mV at 10 mA cm-2 with a reduced Tafel slope of 60.6 mV dec-1, and excellent stability with more than 60 h operation without significant activity decay. © 2022 The Royal Society of Chemistry.

  • Amorphizing noble metal chalcogenide catalysts at the single-layer limit towards hydrogen production

    He Y., Liu L., Zhu C., Guo S., Golani P., Koo B., Tang P., Zhao Z., Xu M., Zhu C., Yu P., Zhou X., Gao C., Wang X., Shi Z., Zheng L., Yang J., Shin B., Arbiol J., Duan H., Du Y., Heggen M., Dunin-Borkowski R.E., Guo W., Wang Q.J., Zhang Z., Liu Z. Nature Catalysis; 5 (3): 212 - 221. 2022. 10.1038/s41929-022-00753-y. IF: 41.813

    Rational design of noble metal catalysts with the potential to leverage efficiency is vital for industrial applications. Such an ultimate atom-utilization efficiency can be achieved when all noble metal atoms exclusively contribute to catalysis. Here, we demonstrate the fabrication of a wafer-size amorphous PtSex film on a SiO2 substate via a low-temperature amorphization strategy, which offers single-atom-layer Pt catalysts with high atom-utilization efficiency (~26 wt%). This amorphous PtSex (1.2 < x < 1.3) behaves as a fully activated surface, accessible to catalytic reactions, and features a nearly 100% current density relative to a pure Pt surface and reliable production of sustained high-flux hydrogen over a 2 inch wafer as a proof-of-concept. Furthermore, an electrolyser is demonstrated to generate a high current density of 1,000 mA cm−2. Such an amorphization strategy is potentially extendable to other noble metals, including the Pd, Ir, Os, Rh and Ru elements, demonstrating the universality of single-atom-layer catalysts. [Figure not available: see fulltext.] © 2022, The Author(s), under exclusive licence to Springer Nature Limited.

  • Author Correction: Sustainable oxygen evolution electrocatalysis in aqueous 1 M H2SO4 with earth abundant nanostructured Co3O4

    Yu, Jiahao; Garcés-Pineda, Felipe A.; González-Cobos, Jesús; Peña-Díaz, Marina; Rogero, Celia; Giménez, Sixto; Spadaro, Maria Chiara; Arbiol, Jordi; Barja, Sara; Galán-Mascarós, José Ramón Nature Communications; 13 (1) 2022. 10.1038/s41467-022-32399-6. IF: 17.694

  • Cobalt Molybdenum Nitride-Based Nanosheets for Seawater Splitting

    Wang, X; Han, X; Du, RF; Xing, CC; Qi, XQ; Liang, ZF; Guardia, P; Arbiol, J; Cabot, A; Li, JS Acs Applied Materials & Interfaces; 14 (37): 41924 - 41933. 2022. 10.1021/acsami.2c09272. IF: 10.383

  • Controlled oxygen doping in highly dispersed Ni-loaded g-C3N4 nanotubes for efficient photocatalytic H2O2 production

    Du R., Xiao K., Li B., Han X., Zhang C., Wang X., Zuo Y., Guardia P., Li J., Chen J., Arbiol J., Cabot A. Chemical Engineering Journal; 441 (135999) 2022. 10.1016/j.cej.2022.135999. IF: 13.273

    Hydrogen peroxide (H2O2) is both a key component in several industrial processes and a promising liquid fuel. The production of H2O2 by solar photocatalysis is a suitable strategy to convert and store solar energy into chemical energy. Here we report an oxygen-doped tubular g-C3N4 with uniformly dispersed nickel nanoparticles for efficient photocatalytic H2O2 generation. The hollow structure of the tubular g-C3N4 provides a large surface with a high density of reactive sites and efficient visible light absorption during the photocatalytic reaction. The oxygen doping and Ni loading enable a fast separation of photogenerated charge carriers and a high selectivity toward the two-electron process during the oxygen reduction reaction (ORR). The optimized composition, Ni4%/O0.2tCN, displays an H2O2 production rate of 2464 μmol g−1·h−1, which is eightfold higher than that of bulk g-C3N4 under visible light irradiation (λ > 420 nm), and achieves an apparent quantum yield (AQY) of 28.2% at 380 nm and 14.9% at 420 nm. © 2022 Elsevier B.V.

  • Critical Role of Phosphorus in Hollow Structures Cobalt-Based Phosphides as Bifunctional Catalysts for Water Splitting

    Zhang W., Han N., Luo J., Han X., Feng S., Guo W., Xie S., Zhou Z., Subramanian P., Wan K., Arbiol J., Zhang C., Liu S., Xu M., Zhang X., Fransaer J. Small; 18 (4, 2103561) 2022. 10.1002/smll.202103561. IF: 13.281

    Cobalt phosphides electrocatalysts have great potential for water splitting, but the unclear active sides hinder the further development of cobalt phosphides. Wherein, three different cobalt phosphides with the same hollow structure morphology (CoP-HS, CoP2-HS, CoP3-HS) based on the same sacrificial template of ZIF-67 are prepared. Surprisingly, these cobalt phosphides exhibit similar OER performances but quite different HER performances. The identical OER performance of these CoPx-HS in alkaline solution is attributed to the similar surface reconstruction to CoOOH. CoP-HS exhibits the best catalytic activity for HER among these CoPx-HS in both acidic and alkaline media, originating from the adjusted electronic density of phosphorus to affect absorption–desorption process on H. Moreover, the calculated ΔGH* based on P-sites of CoP-HS follows a quite similar trend with the normalized overpotential and Tafel slope, indicating the important role of P-sites for the HER process. Moreover, CoP-HS displays good performance (cell voltage of 1.67 V at a current density of 50 mA cm−2) and high stability in 1 M KOH. For the first time, this work detailly presents the critical role of phosphorus in cobalt-based phosphides for water splitting, which provides the guidance for future investigations on transition metal phosphides from material design to mechanism understanding. © 2021 Wiley-VCH GmbH

  • Defect Engineering in Solution-Processed Polycrystalline SnSe Leads to High Thermoelectric Performance

    Liu Y., Calcabrini M., Yu Y., Lee S., Chang C., David J., Ghosh T., Spadaro M.C., Xie C., Cojocaru-Mirédin O., Arbiol J., Ibáñez M. ACS Nano; 16 (1): 78 - 88. 2022. 10.1021/acsnano.1c06720. IF: 15.881

    SnSe has emerged as one of the most promising materials for thermoelectric energy conversion due to its extraordinary performance in its single-crystal form and its low-cost constituent elements. However, to achieve an economic impact, the polycrystalline counterpart needs to replicate the performance of the single crystal. Herein, we optimize the thermoelectric performance of polycrystalline SnSe produced by consolidating solution-processed and surface-engineered SnSe particles. In particular, the SnSe particles are coated with CdSe molecular complexes that crystallize during the sintering process, forming CdSe nanoparticles. The presence of CdSe nanoparticles inhibits SnSe grain growth during the consolidation step due to Zener pinning, yielding a material with a high density of grain boundaries. Moreover, the resulting SnSe-CdSe nanocomposites present a large number of defects at different length scales, which significantly reduce the thermal conductivity. The produced SnSe-CdSe nanocomposites exhibit thermoelectric figures of merit up to 2.2 at 786 K, which is among the highest reported for solution-processed SnSe. © 2022 American Chemical Society. All rights reserved.

  • Direct Observation of the Chemical Transformations in BiVO4 Photoanodes upon Prolonged Light-Aging Treatments

    Arcas R., Cardenas-Morcoso D., Spadaro M.C., García-Tecedor M., Mesa C.A., Arbiol J., Fabregat-Santiago F., Giménez S., Mas-Marzá E. Solar RRL; 6 (7, 2200132) 2022. 10.1002/solr.202200132. IF: 8.582

    Exposing BiVO4 photoanodes to light-aging treatments is known to produce a significant photocurrent enhancement. Until now, the interpretation given to this phenomenon is associated to the formation of oxygen vacancies and little is reported about chemical changes in the material. Herein, the chemical segregation of Bi species toward the surface upon light-aging treatment is demonstrated, which takes place with the concomitant formation of intra-bandgap states associated to the oxygen vacancies. It is further demonstrated that these intra-bandgap states are photoactive and generate photocurrent under infrared excitation. These results highlight the importance of understanding light-induced effects while employing multinary metal oxide photoelectrodes. © 2022 The Authors. Solar RRL published by Wiley-VCH GmbH.

  • Doubling the mobility of InAs/InGaAs selective area grown nanowires

    Beznasyuk D.V., Martí-Sánchez S., Kang J.-H., Tanta R., Rajpalke M., Stankevič T., Christensen A.W., Spadaro M.C., Bergamaschini R., Maka N.N., Petersen C.E.N., Carrad D.J., Jespersen T.S., Arbiol J., Krogstrup P. Physical Review Materials; 6 (3, 034602) 2022. 10.1103/PhysRevMaterials.6.034602. IF: 3.989

    Selective area growth (SAG) of nanowires and networks promise a route toward scalable electronics, photonics, and quantum devices based on III-V semiconductor materials. The potential of high-mobility SAG nanowires however is not yet fully realised, since interfacial roughness, misfit dislocations at the nanowire/substrate interface and nonuniform composition due to material intermixing all scatter electrons. Here, we explore SAG of highly lattice-mismatched InAs nanowires on insulating GaAs(001) substrates and address these key challenges. Atomically smooth nanowire/substrate interfaces are achieved with the use of atomic hydrogen (a-H) as an alternative to conventional thermal annealing for the native oxide removal. The problem of high lattice mismatch is addressed through an InxGa1-xAs buffer layer introduced between the InAs transport channel and the GaAs substrate. The Ga-In material intermixing observed in both the buffer layer and the channel is inhibited via careful tuning of the growth temperature. Performing scanning transmission electron microscopy and x-ray diffraction analysis along with low-temperature transport measurements we show that optimized In-rich buffer layers promote high-quality InAs transport channels with the field-effect electron mobility over 10 000 cm2 V-1 s-1. This is twice as high as for nonoptimized samples and among the highest reported for InAs selective area grown nanostructures. © 2022 American Physical Society.

  • Electrochemical Conversion of Alcohols into Acidic Commodities on Nickel Sulfide Nanoparticles

    Li J., Tian X., Wang X., Zhang T., Spadaro M.C., Arbiol J., Li L., Zuo Y., Cabot A. Inorganic Chemistry; 2022. 10.1021/acs.inorgchem.2c01695.

    The electrocatalytic oxidation of alcohols is a potentially cost-effective strategy for the synthesis of valuable chemicals at the anode while simultaneously generating hydrogen at the cathode. For this approach to become commercially viable, high-activity, low-cost, and stable catalysts need to be developed. Herein, we demonstrate an electrocatalyst based on earth-abundant nickel and sulfur elements. Experimental investigations reveal the produced NiS displays excellent electrocatalytic performance associated with a higher electrochemical surface area (ECSA) and the presence of sulfate ions on the formed NiOOH surface in basic media. The current densities reached for the oxidation of ethanol and methanol at 1.6 V vs reversible hydrogen electrode (RHE) are up to 175.5 and 145.1 mA cm-2, respectively. At these high current densities, the Faradaic efficiency of methanol to formate conversion is 98% and that of ethanol to acetate is 81%. Density functional theory calculations demonstrate the presence of the generated sulfate groups to modify the electronic properties of the NiOOH surface, improving electroconductivity and electron transfer. Besides, calculations are used to determine the reaction energy barriers, revealing the dehydrogenation of ethoxy groups to be more favorable than that of methoxy on the catalyst surface, which explains the highest current densities obtained for ethanol oxidation. © 2022 American Chemical Society.

  • Electrochemical reforming of ethanol with acetate Co-Production on nickel cobalt selenide nanoparticles

    Li J., Wang X., Xing C., Li L., Mu S., Han X., He R., Liang Z., Martinez P., Yi Y., Wu Q., Pan H., Arbiol J., Cui C., Zhang Y., Cabot A. Chemical Engineering Journal; 440 (135817) 2022. 10.1016/j.cej.2022.135817. IF: 13.273

    The energy efficiency of water electrolysis is limited by the sluggish reaction kinetics of the anodic oxygen evolution reaction (OER). To overcome this limitation, OER can be replaced by a less demanding oxidation reaction, which in the ideal scenario could be even used to generate additional valuable chemicals. Herein, we focus on the electrochemical reforming of ethanol in alkaline media to generate hydrogen at a Pt cathode and acetate as a co-product at a Ni1-xCoxSe2 anode. We first detail the solution synthesis of a series of Ni1-xCoxSe2 electrocatalysts. By adjusting the Ni/Co ratio, the electrocatalytic activity and selectivity for the production of acetate from ethanol are optimized. Best performances are obtained at low substitutions of Ni by Co in the cubic NiSe2 phase. Density function theory reveals that the Co substitution can effectively enhance the ethanol adsorption and decrease the energy barrier for its first step dehydrogenation during its conversion to acetate. However, we experimentally observe that too large amounts of Co decrease the ethanol-to-acetate Faradaic efficiency from values above 90% to just 50 %. At the optimized composition, the Ni0.75Co0.25Se2 electrode delivers a stable chronoamperometry current density of up to 45 mA cm−2, corresponding to 1.2 A g−1, in a 1 M KOH + 1 M ethanol solution, with a high ethanol-to-acetate Faradaic efficiency of 82.2% at a relatively low potential, 1.50 V vs. RHE, and with an acetate production rate of 0.34 mmol cm−2 h−1. © 2022 Elsevier B.V.

  • Enabling full-scale grain boundary mitigation in polycrystalline perovskite solids

    Zhao L., Tang P., Luo D., Dar M.I., Eickemeyer F.T., Arora N., Hu Q., Luo J., Liu Y., Zakeeruddin S.M., Hagfeldt A., Arbiol J., Huang W., Gong Q., Russell T.P., Friend R.H., Grätzel M., Zhu R. Science advances; 8 (35): eabo3733. 2022. 10.1126/sciadv.abo3733.

    There exists a considerable density of interaggregate grain boundaries (GBs) and intra-aggregate GBs in polycrystalline perovskites. Mitigation of intra-aggregate GBs is equally notable to that of interaggregate GBs as intra-aggregate GBs can also cause detrimental effects on the photovoltaic performances of perovskite solar cells (PSCs). Here, we demonstrate full-scale GB mitigation ranging from nanoscale intra-aggregate to submicron-scale interaggregate GBs, by modulating the crystallization kinetics using a judiciously designed brominated arylamine trimer. The optimized GB-mitigated perovskite films exhibit reduced nonradiative recombination, and their corresponding mesostructured PSCs show substantially enhanced device efficiency and long-term stability under illumination, humidity, or heat stress. The versatility of our strategy is also verified upon applying it to different categories of PSCs. Our discovery not only specifies a rarely addressed perspective concerning fundamental studies of perovskites at nanoscale but also opens a route to obtain high-quality solution-processed polycrystalline perovskites for high-performance optoelectronic devices.

  • Engineering the Interfacial Microenvironment via Surface Hydroxylation to Realize the Global Optimization of Electrochemical CO2Reduction

    Han X., Zhang T., Biset-Peiró M., Zhang X., Li J., Tang W., Tang P., Morante J.R., Arbiol J. ACS Applied Materials and Interfaces; 14 (28): 32157 - 32165. 2022. 10.1021/acsami.2c09129.

    The adsorption and activation of CO2 on the electrode interface is a prerequisite and key step for electrocatalytic CO2 reduction reaction (eCO2 RR). Regulating the interfacial microenvironment to promote the adsorption and activation of CO2 is thus of great significance to optimize overall conversion efficiency. Herein, a CO2-philic hydroxyl coordinated ZnO (ZnO-OH) catalyst is fabricated, for the first time, via a facile MOF-assisted method. In comparison to the commercial ZnO, the as-prepared ZnO-OH exhibits much higher selectivity toward CO at lower applied potential, reaching a Faradaic efficiency of 85% at -0.95 V versus RHE. To the best of our knowledge, such selectivity is one of the best records in ZnO-based catalysts reported till date. Density functional theory calculations reveal that the coordinated surficial -OH groups are not only favorable to interact with CO2 molecules but also function in synergy to decrease the energy barrier of the rate-determining step and maintain a higher charge density of potential active sites as well as inhibit undesired hydrogen evolution reaction. Our results indicate that engineering the interfacial microenvironment through the introduction of CO2-philic groups is a promising way to achieve the global optimization of eCO2 RR via promoting adsorption and activation of CO2. © 2022 The Authors. Published by American Chemical Society.

  • Enhanced Polysulfide Conversion with Highly Conductive and Electrocatalytic Iodine-Doped Bismuth Selenide Nanosheets in Lithium–Sulfur Batteries

    Li M., Yang D., Biendicho J.J., Han X., Zhang C., Liu K., Diao J., Li J., Wang J., Heggen M., Dunin-Borkowski R.E., Wang J., Henkelman G., Morante J.R., Arbiol J., Chou S.-L., Cabot A. Advanced Functional Materials; 32 (26, 2200529) 2022. 10.1002/adfm.202200529. IF: 18.808

    The shuttling behavior and sluggish conversion kinetics of intermediate lithium polysulfides (LiPS) represent the main obstacles to the practical application of lithium–sulfur batteries (LSBs). Herein, an innovative sulfur host is proposed, based on an iodine-doped bismuth selenide (I-Bi2Se3), able to solve these limitations by immobilizing the LiPS and catalytically activating the redox conversion at the cathode. The synthesis of I-Bi2Se3 nanosheets is detailed here and their morphology, crystal structure, and composition are thoroughly. Density-functional theory and experimental tools are used to demonstrate that I-Bi2Se3 nanosheets are characterized by a proper composition and micro- and nano-structure to facilitate Li+ diffusion and fast electron transportation, and to provide numerous surface sites with strong LiPS adsorbability and extraordinary catalytic activity. Overall, I-Bi2Se3/S electrodes exhibit outstanding initial capacities up to 1500 mAh g−1 at 0.1 C and cycling stability over 1000 cycles, with an average capacity decay rate of only 0.012% per cycle at 1 C. Besides, at a sulfur loading of 5.2 mg cm−2, a high areal capacity of 5.70 mAh cm−2 at 0.1 C is obtained with an electrolyte/sulfur ratio of 12 µL mg−1. This work demonstrated that doping is an effective way to optimize the metal selenide catalysts in LSBs. © 2022 Wiley-VCH GmbH.

  • Extended-SWIR Photodetection in All-Group IV Core/Shell Nanowires

    Luo L., Assali S., Atalla M.R.M., Koelling S., Attiaoui A., Daligou G., Martí S., Arbiol J., Moutanabbir O. ACS Photonics; 9 (3): 914 - 921. 2022. 10.1021/acsphotonics.1c01728. IF: 7.529

    Group IV Ge1-xSnx semiconductors hold the premise of enabling broadband silicon-integrated infrared optoelectronics due to their tunable band gap energy and directness. Herein, we exploit these attributes along with the enhanced lattice strain relaxation in Ge/Ge0.92Sn0.08 core/shell nanowire heterostructures to implement highly responsive room-temperature short-wave infrared nanoscale photodetectors. Atomic-level studies confirm the uniform shell composition and its higher crystallinity with respect to thin films counterparts. The demonstrated Ge/Ge0.92Sn0.08 p-type field-effect nanowire transistors exhibit superior optoelectronic properties achieving simultaneously relatively high mobility, high ON/OFF ratio, and high responsivity, in addition to a broadband absorption in the short-wave infrared range. Indeed, the reduced band gap of the Ge0.92Sn0.08 shell yields an extended cutoff wavelength of 2.1 μm, with a room-temperature responsivity reaching 2.7 A/W at 1550 nm. These results highlight the potential of Ge/Ge1-xSnx core/shell nanowires as silicon-compatible building blocks for nanoscale-integrated infrared photonics. © 2022 American Chemical Society.

  • Glass poling as a substrate surface pre-treatment for in situ metal nanoparticle formation by reduction of metal salt

    Selvam T., Pervan P., Sancho-Parramon J., Spadaro M.C., Arbiol J., Janicki V. Surfaces and Interfaces; 33 (102158) 2022. 10.1016/j.surfin.2022.102158.

    Metal nanoparticles are used in optical coatings and sensors due to their absorption in optical part of spectrum and its sensitivity to the environment induced by localized surface plasmon resonance. Glass is the most common substrate used for optical coatings. However, its surface does not have optimal properties for coating with metal nanoparticles grown in situ by reduction of metal salt. Glass surface optimization methods may involve environmentally hostile chemicals or processes that have time limited or atmosphere sensitive effects. In this study it is demonstrated and discussed effectiveness, mechanisms and advantages of glass poling as pre-treatment method for improving glass surface properties for maximization of coatings plasmonic performance. Pre-treatment of glass surfaces by poling is highly efficient for the purpose. Glass poling quenches ion exchange between metal ions from the solution and alkali ions from glass, favouring nanoparticles formation. Surface prepared in such way is not affected by ageing in normal atmosphere and is effective even after coating with ultrathin dielectric or Cr layers. © 2022 Elsevier B.V.

  • Machine learning in electron microscopy for advanced nanocharacterization: current developments, available tools and future outlook

    Botifoll, M; Pinto-Huguet, I; Arbiol, J Nanoscale Horizons; 7 (12): 1427 - 1477. 2022. 10.1039/d2nh00377e. IF: 11.684

  • Majorana-like Coulomb spectroscopy in the absence of zero-bias peaks

    Valentini M; Borovkov M; Prada E; Martí-Sánchez S; Botifoll M; Hofmann A; Arbiol J; Aguado R; San-Jose P; Katsaros G Nature; 612 (7940): 442 - +. 2022. 10.1038/s41586-022-05382-w. IF: 69.504

  • MOF-Derived Ultrathin Cobalt Molybdenum Phosphide Nanosheets for Efficient Electrochemical Overall Water Splitting

    Wang X., Yang L., Xing C., Han X., Du R., He R., Guardia P., Arbiol J., Cabot A. Nanomaterials; 12 (7, 1098) 2022. 10.3390/nano12071098. IF: 5.076

    The development of high-performance and cost-effective earth-abundant transition metal-based electrocatalysts is of major interest for several key energy technologies, including water splitting. Herein, we report the synthesis of ultrathin CoMoP nanosheets through a simple ion etching and phosphorization method. The obtained catalyst exhibits outstanding electrocatalytic activity and stability towards oxygen and hydrogen evolution reactions (OER and HER), with overpotentials down to 273 and 89 mV at 10 mA cm−2, respectively. The produced CoMoP nanosheets are also characterized by very small Tafel slopes, 54.9 and 69.7 mV dec−1 for OER and HER, respectively. When used as both cathode and anode electrocatalyst in the overall water splitting reaction, CoMoP-based cells require just 1.56 V to reach 10 mA cm−2 in alkaline media. This outstanding performance is at-tributed to the proper composition, weak crystallinity and two-dimensional nanosheet structure of the electrocatalyst. © 2022 by the authors. Licensee MDPI, Basel, Switzerland.

  • Pd2Ga nanorods as highly active bifunctional catalysts for electrosynthesis of acetic acid coupled with hydrogen production

    Wang Q., Liu J., Li T., Zhang T., Arbiol J., Yan S., Wang Y., Li H., Cabot A. Chemical Engineering Journal; 446 (136878) 2022. 10.1016/j.cej.2022.136878.

    The production of hydrogen from water splitting is hampered by the sluggish oxygen evolution reaction (OER). To overcome the OER limitation, herein we propose the electrosynthesis of value-added acetic acid from ethanol as the anodic reaction using high activity catalyts. For this strategy to be cost-effective, we develop a bifunctional catalyst based on Pd2Ga nanorods. Such Pd2Ga/C-based catalyst presents outstanding activity, selectivity and also stability for the electrocatalytic ethanol-to-acetic acid conversion with a current density above 164 mA cm−2 and a mass activity of 1.97 A mg−1Pd. Besides, its activity for hydrogen production is comparable to that of commercial Pt/C catalysts. Using Pd2Ga/C as a bifunctional catalyst for both water reduction at the cathode and ethanol oxidation at the anode, these two coupled reactions are demonstrated to be an energy-efficient approach for the simultaneous production of high purity acetic acid and hydrogen. The assembled electrolyzer requires a small voltage input of 0.62 V to reach a current density of 10 mA cm−2, much lower than that of cells based on commercial Pt/C or Pd/C catalyst. Density functional theory calculations reveal that the high performance of the coupled system relies on a combination of an electronic and bifunctional effect of Ga, reducing the hydrogen-binding energy on the Pd site and at the same time actively participating in the reaction by providing OH− binding sites and reducing the energy barrier of the ethanol oxidation rate-determining step. © 2022

  • Phase Engineering of Defective Copper Selenide toward Robust Lithium-Sulfur Batteries

    Yang D., Li M., Zheng X., Han X., Zhang C., Jacas Biendicho J., Llorca J., Wang J., Hao H., Li J., Henkelman G., Arbiol J., Morante J.R., Mitlin D., Chou S., Cabot A. ACS Nano; 16 (7): 11102 - 11114. 2022. 10.1021/acsnano.2c03788.

    The shuttling of soluble lithium polysulfides (LiPS) and the sluggish Li-S conversion kinetics are two main barriers toward the practical application of lithium-sulfur batteries (LSBs). Herein, we propose the addition of copper selenide nanoparticles at the cathode to trap LiPS and accelerate the Li-S reaction kinetics. Using both computational and experimental results, we demonstrate the crystal phase and concentration of copper vacancies to control the electronic structure of the copper selenide, its affinity toward LiPS chemisorption, and its electrical conductivity. The adjustment of the defect density also allows for tuning the electrochemically active sites for the catalytic conversion of polysulfide. The optimized S/Cu1.8Se cathode efficiently promotes and stabilizes the sulfur electrochemistry, thus improving significantly the LSB performance, including an outstanding cyclability over 1000 cycles at 3 C with a capacity fading rate of just 0.029% per cycle, a superb rate capability up to 5 C, and a high areal capacity of 6.07 mAh cm-2 under high sulfur loading. Overall, the present work proposes a crystal phase and defect engineering strategy toward fast and durable sulfur electrochemistry, demonstrating great potential in developing practical LSBs. © 2022 American Chemical Society.

  • Room temperature aqueous-based synthesis of copper-doped lead sulfide nanoparticles for thermoelectric application

    Li M., Liu Y., Zhang Y., Chang C., Zhang T., Yang D., Xiao K., Arbiol J., Ibáñez M., Cabot A. Chemical Engineering Journal; 433 (133837) 2022. 10.1016/j.cej.2021.133837. IF: 13.273

    A versatile, scalable, room temperature and surfactant-free route for the synthesis of metal chalcogenide nanoparticles in aqueous solution is detailed here for the production of PbS and Cu-doped PbS nanoparticles. Subsequently, nanoparticles are annealed in a reducing atmosphere to remove surface oxide, and consolidated into dense polycrystalline materials by means of spark plasma sintering. By characterizing the transport properties of the sintered material, we observe the annealing step and the incorporation of Cu to play a key role in promoting the thermoelectric performance of PbS. The presence of Cu allows improving the electrical conductivity by increasing the charge carrier concentration and simultaneously maintaining a large charge carrier mobility, which overall translates into record power factors at ambient temperature, 2.3 mWm-1K−2. Simultaneously, the lattice thermal conductivity decreases with the introduction of Cu, leading to a record high ZT = 0.37 at room temperature and ZT = 1.22 at 773 K. Besides, a record average ZTave = 0.76 is demonstrated in the temperature range 320–773 K for n-type Pb0.955Cu0.045S. © 2021 Elsevier B.V.

  • Site-Specific Axial Oxygen Coordinated FeN4 Active Sites for Highly Selective Electroreduction of Carbon Dioxide

    Zhang T., Han X., Liu H., Biset-Peiró M., Li J., Zhang X., Tang P., Yang B., Zheng L., Morante J.R., Arbiol J. Advanced Functional Materials; 32 (18, 2111446) 2022. 10.1002/adfm.202111446. IF: 18.808

    Regulating the coordination environment via heteroatoms to break the symmetrical electronic structure of M-N4 active sites provides a promising route to engineer metal-nitrogen-carbon catalysts for electrochemical CO2 reduction reaction. However, it remains challenging to realize a site-specific introduction of heteroatoms at atomic level due to their energetically unstable nature. Here, this paper reports a facile route via using an oxygen- and nitrogen-rich metal–organic framework (MOF) (IRMOF-3) as the precursor to construct the Fe-O and Fe-N chelation, simultaneously, resulting in an atomically dispersed axial O-coordinated FeN4 active site. Compared to the FeN4 active sites without O coordination, the formed FeN4-O sites exhibit much better catalytic performance toward CO, reaching a maximum FECO of 95% at −0.50 V versus reversible hydrogen electrode. To the best of the authors’ knowledge, such performance exceeds that of the existing Fe-N-C-based catalysts derived from sole N-rich MOFs. Density functional theory calculations indicate that the axial O-coordination regulates the binding energy of intermediates in the reaction pathways, resulting in a smoother desorption of CO and increased energy for the competitive hydrogen production. © 2022 Wiley-VCH GmbH.

  • Stoichiometry modulates the optoelectronic functionality of zinc phosphide (Zn3−xP2+x)

    Stutz E.Z., Ramanandan S.P., Flór M., Paul R., Zamani M., Escobar Steinvall S., Sandoval Salaiza D.A., Xifra Montesinos C., Spadaro M.C., Leran J.-B., Litvinchuk A.P., Arbiol J., Fontcuberta i Morral A., Dimitrievska M. Faraday Discussions; 2022. 10.1039/d2fd00055e.

    Predictive synthesis-structure-property relationships are at the core of materials design for novel applications. In this regard, correlations between the compositional stoichiometry variations and functional properties are essential for enhancing the performance of devices based on these materials. In this work, we investigate the effect of stoichiometry variations and defects on the structural and optoelectronic properties of monocrystalline zinc phosphide (Zn3P2), a promising compound for photovoltaic applications. We use experimental methods, such as electron and X-ray diffraction and Raman spectroscopy, along with density functional theory calculations, to showcase the favorable creation of P interstitial defects over Zn vacancies in P-rich and Zn-poor compositional regions. Photoluminescence and absorption measurements show that these defects create additional energy levels at about 180 meV above the valence band. Furthermore, they lead to the narrowing of the bandgap, due to the creation of band tails in the region of around 10-20 meV above the valence and below the conduction band. The ability of zinc phosphide to form off-stoichiometric compounds provides a new promising opportunity for tunable functionality that benefits applications. In that regard, this study is crucial for the further development of zinc phosphide and its application in optoelectronic and photovoltaic devices, and should pave the way for defect engineering in this kind of material. © 2022 The Royal Society of Chemistry.

  • Sub-nanometer mapping of strain-induced band structure variations in planar nanowire core-shell heterostructures

    Martí-Sánchez S., Botifoll M., Oksenberg E., Koch C., Borja C., Spadaro M.C., Di Giulio V., Ramasse Q., García de Abajo F.J., Joselevich E., Arbiol J. Nature Communications; 13 (1, 4089) 2022. 10.1038/s41467-022-31778-3.

    Strain relaxation mechanisms during epitaxial growth of core-shell nanostructures play a key role in determining their morphologies, crystal structure and properties. To unveil those mechanisms, we perform atomic-scale aberration-corrected scanning transmission electron microscopy studies on planar core-shell ZnSe@ZnTe nanowires on α-Al2O3 substrates. The core morphology affects the shell structure involving plane bending and the formation of low-angle polar boundaries. The origin of this phenomenon and its consequences on the electronic band structure are discussed. We further use monochromated valence electron energy-loss spectroscopy to obtain spatially resolved band-gap maps of the heterostructure with sub-nanometer spatial resolution. A decrease in band-gap energy at highly strained core-shell interfacial regions is found, along with a switch from direct to indirect band-gap. These findings represent an advance in the sub-nanometer-scale understanding of the interplay between structure and electronic properties associated with highly mismatched semiconductor heterostructures, especially with those related to the planar growth of heterostructured nanowire networks. © 2022, The Author(s).

  • Sulfate-Decorated Amorphous-Crystalline Cobalt-Iron Oxide Nanosheets to Enhance O-O Coupling in the Oxygen Evolution Reaction

    Wang, X; Li, JS; Xue, Q; Han, X; Xing, CC; Liang, ZF; Guardia, P; Zuo, Y; Du, RF; Balcells, L; Arbiol, J; Llorca, J; Qi, XQ; Cabot, A Acs Nano; 2022. 10.1021/acsnano.2c12029. IF: 18.027

  • Surface Functionalization of Surfactant-Free Particles: A Strategy to Tailor the Properties of Nanocomposites for Enhanced Thermoelectric Performance

    Chang C., Liu Y., Ho Lee S., Chiara Spadaro M., Koskela K.M., Kleinhanns T., Costanzo T., Arbiol J., Brutchey R.L., Ibáñez M. Angewandte Chemie - International Edition; 61 (35, e202207002) 2022. 10.1002/anie.202207002.

    The broad implementation of thermoelectricity requires high-performance and low-cost materials. One possibility is employing surfactant-free solution synthesis to produce nanopowders. We propose the strategy of functionalizing “naked” particles’ surface by inorganic molecules to control the nanostructure and, consequently, thermoelectric performance. In particular, we use bismuth thiolates to functionalize surfactant-free SnTe particles’ surfaces. Upon thermal processing, bismuth thiolates decomposition renders SnTe-Bi2S3 nanocomposites with synergistic functions: 1) carrier concentration optimization by Bi doping; 2) Seebeck coefficient enhancement and bipolar effect suppression by energy filtering; and 3) lattice thermal conductivity reduction by small grain domains, grain boundaries and nanostructuration. Overall, the SnTe-Bi2S3 nanocomposites exhibit peak z T up to 1.3 at 873 K and an average z T of ≈0.6 at 300–873 K, which is among the highest reported for solution-processed SnTe. © 2022 The Authors. Angewandte Chemie International Edition published by Wiley-VCH GmbH.

  • Sustainable oxygen evolution electrocatalysis in aqueous 1 M H2SO4 with earth abundant nanostructured Co3O4

    Yu J., Garcés-Pineda F.A., González-Cobos J., Peña-Díaz M., Rogero C., Giménez S., Spadaro M.C., Arbiol J., Barja S., Galán-Mascarós J.R. Nature Communications; 13 (1, 4341) 2022. 10.1038/s41467-022-32024-6.

    Earth-abundant electrocatalysts for the oxygen evolution reaction (OER) able to work in acidic working conditions are elusive. While many first-row transition metal oxides are competitive in alkaline media, most of them just dissolve or become inactive at high proton concentrations where hydrogen evolution is preferred. Only noble-metal catalysts, such as IrO2, are fast and stable enough in acidic media. Herein, we report the excellent activity and long-term stability of Co3O4-based anodes in 1 M H2SO4 (pH 0.1) when processed in a partially hydrophobic carbon-based protecting matrix. These Co3O4@C composites reliably drive O2 evolution a 10 mA cm–2 current density for >40 h without appearance of performance fatigue, successfully passing benchmarking protocols without incorporating noble metals. Our strategy opens an alternative venue towards fast, energy efficient acid-media water oxidation electrodes. © 2022, The Author(s).


  • A Direct Z-Scheme for the Photocatalytic Hydrogen Production from a Water Ethanol Mixture on CoTiO3/TiO2Heterostructures

    Xing C., Liu Y., Zhang Y., Wang X., Guardia P., Yao L., Han X., Zhang T., Arbiol J., Soler L., Chen Y., Sivula K., Guijarro N., Cabot A., Llorca J. ACS Applied Materials and Interfaces; 13 (1): 449 - 457. 2021. 10.1021/acsami.0c17004. IF: 9.229

    Photocatalytic H2 evolution from ethanol dehydrogenation is a convenient strategy to store solar energy in a highly valuable fuel with potential zero net CO2 balance. Herein, we report on the synthesis of CoTiO3/TiO2 composite catalysts with controlled amounts of highly distributed CoTiO3 nanodomains for photocatalytic ethanol dehydrogenation. We demonstrate these materials to provide outstanding hydrogen evolution rates under UV and visible illumination. The origin of this enhanced activity is extensively analyzed. In contrast to previous assumptions, UV-vis absorption spectra and ultraviolet photoelectron spectroscopy (UPS) prove CoTiO3/TiO2 heterostructures to have a type II band alignment, with the conduction band minimum of CoTiO3 below the H2/H+ energy level. Additional steady-state photoluminescence (PL) spectra, time-resolved PL spectra (TRPLS), and electrochemical characterization prove such heterostructures to result in enlarged lifetimes of the photogenerated charge carriers. These experimental evidence point toward a direct Z-scheme as the mechanism enabling the high photocatalytic activity of CoTiO3/TiO2 composites toward ethanol dehydrogenation. In addition, we probe small changes of temperature to strongly modify the photocatalytic activity of the materials tested, which could be used to further promote performance in a solar thermophotocatalytic reactor. ©

  • A singlet-triplet hole spin qubit in planar Ge

    Jirovec D., Hofmann A., Ballabio A., Mutter P.M., Tavani G., Botifoll M., Crippa A., Kukucka J., Sagi O., Martins F., Saez-Mollejo J., Prieto I., Borovkov M., Arbiol J., Chrastina D., Isella G., Katsaros G. Nature Materials; 20 (8): 1106 - 1112. 2021. 10.1038/s41563-021-01022-2. IF: 43.841

    Spin qubits are considered to be among the most promising candidates for building a quantum processor. Group IV hole spin qubits are particularly interesting owing to their ease of operation and compatibility with Si technology. In addition, Ge offers the option for monolithic superconductor–semiconductor integration. Here, we demonstrate a hole spin qubit operating at fields below 10 mT, the critical field of Al, by exploiting the large out-of-plane hole g-factors in planar Ge and by encoding the qubit into the singlet-triplet states of a double quantum dot. We observe electrically controlled g-factor difference-driven and exchange-driven rotations with tunable frequencies exceeding 100 MHz and dephasing times of 1 μs, which we extend beyond 150 μs using echo techniques. These results demonstrate that Ge hole singlet-triplet qubits are competing with state-of-the-art GaAs and Si singlet-triplet qubits. In addition, their rotation frequencies and coherence are comparable with those of Ge single spin qubits, but singlet-triplet qubits can be operated at much lower fields, emphasizing their potential for on-chip integration with superconducting technologies. © 2021, The Author(s), under exclusive licence to Springer Nature Limited.

  • Atomically dispersed Fe in a C2N Based Catalyst as a Sulfur Host for Efficient Lithium–Sulfur Batteries

    Liang Z., Yang D., Tang P., Zhang C., Jacas Biendicho J., Zhang Y., Llorca J., Wang X., Li J., Heggen M., David J., Dunin-Borkowski R.E., Zhou Y., Morante J.R., Cabot A., Arbiol J. Advanced Energy Materials; 11 (5, 2003507) 2021. 10.1002/aenm.202003507. IF: 29.368

    Lithium–sulfur batteries (LSBs) are considered to be one of the most promising next generation energy storage systems due to their high energy density and low material cost. However, there are still some challenges for the commercialization of LSBs, such as the sluggish redox reaction kinetics and the shuttle effect of lithium polysulfides (LiPS). Here a 2D layered organic material, C2N, loaded with atomically dispersed iron as an effective sulfur host in LSBs is reported. X-ray absorption fine spectroscopy and density functional theory calculations prove the structure of the atomically dispersed Fe/C2N catalyst. As a result, Fe/C2N-based cathodes demonstrate significantly improved rate performance and long-term cycling stability. Fe/C2N-based cathodes display initial capacities up to 1540 mAh g−1 at 0.1 C and 678.7 mAh g−1 at 5 C, while retaining 496.5 mAh g−1 after 2600 cycles at 3 C with a decay rate as low as 0.013% per cycle. Even at a high sulfur loading of 3 mg cm−2, they deliver remarkable specific capacity retention of 587 mAh g−1 after 500 cycles at 1 C. This work provides a rational structural design strategy for the development of high-performance cathodes based on atomically dispersed catalysts for LSBs. © 2020 Wiley-VCH GmbH

  • Cover Feature: Facing Seawater Splitting Challenges by Regeneration with Ni ? Mo ? Fe Bifunctional Electrocatalyst for Hydrogen and Oxygen Evolution (ChemSusChem 14/2021)

    Ros, Carles; Murcia?López, Sebastian; Garcia, Xenia; Rosado, Marcos; Arbiol, Jordi; Llorca, Jordi; Morante, Joan R. Chemsuschem; 14 (14): 2782 - 2782. 2021. 10.1002/cssc.202101257. IF: 8.928

  • Decoupling the effects of defects on efficiency and stability through phosphonates in stable halide perovskite solar cells

    Xie H., Wang Z., Chen Z., Pereyra C., Pols M., Gałkowski K., Anaya M., Fu S., Jia X., Tang P., Kubicki D.J., Agarwalla A., Kim H.-S., Prochowicz D., Borrisé X., Bonn M., Bao C., Sun X., Zakeeruddin S.M., Emsley L., Arbiol J., Gao F., Fu F., Wang H.I., Tielrooij K.-J., Stranks S.D., Tao S., Grätzel M., Hagfeldt A., Lira-Cantu M. Joule; 5 (5): 1246 - 1266. 2021. 10.1016/j.joule.2021.04.003. IF: 41.248

    Understanding defects is of paramount importance for the development of stable halide perovskite solar cells (PSCs). However, isolating their distinctive effects on device efficiency and stability is currently a challenge. We report that adding the organic molecule 3-phosphonopropionic acid (H3pp) to the halide perovskite results in unchanged overall optoelectronic performance while having a tremendous effect on device stability. We obtained PSCs with ∼21% efficiency that retain ∼100% of the initial efficiency after 1,000 h at the maximum power point under simulated AM1.5G illumination. The strong interaction between the perovskite and the H3pp molecule through two types of hydrogen bonds (H…I and O…H) leads to shallow point defect passivation that has a significant effect on device stability but not on the non-radiative recombination and device efficiency. We expect that our work will have important implications for the current understanding and advancement of operational PSCs. © 2021 Elsevier Inc.

  • Disentangling phonon channels in nanoscale heat transport

    Mukherjee S., Wajs M., De La Mata M., Givan U., Senz S., Arbiol J., Francoeur S., Moutanabbir O. Physical Review B; 104 (7, 075429) 2021. 10.1103/PhysRevB.104.075429. IF: 4.036

    Phonon surface scattering has been at the core of heat transport engineering in nanoscale devices. Herein, we demonstrate that this phonon pathway can be the sole mechanism only below a critical, size-dependent temperature. Above this temperature, the lattice phonon scattering coexists along with surface effects. By tailoring the mass disorder at the atomic level, the lattice dynamics in nanowires was artificially controlled without affecting morphology, crystallinity, chemical composition, or electronic properties, thus allowing the mapping of the temperature-thermal conductivity-diameter triple parameter space. This led to the identification of the critical temperature below which the effects of lattice mass disorder are suppressed to an extent that phonon transport becomes governed entirely by the surface. This behavior is discussed based on a modified Landauer-Datta-Lundstrom near-equilibrium transport model. Besides disentangling the main phonon scattering mechanisms, the established framework also provides the necessary input to further advance the design and modeling of heat transport in semiconductor nanoscale systems. © 2021 American Physical Society.

  • Doping-mediated stabilization of copper vacancies to promote thermoelectric properties of Cu2−xS

    Zhang Y., Xing C., Liu Y., Spadaro M.C., Wang X., Li M., Xiao K., Zhang T., Guardia P., Lim K.H., Moghaddam A.O., Llorca J., Arbiol J., Ibáñez M., Cabot A. Nano Energy; 85 (105991) 2021. 10.1016/j.nanoen.2021.105991. IF: 17.881

    Copper chalcogenides are outstanding thermoelectric materials for applications in the medium-high temperature range. Among different chalcogenides, while Cu2−xSe is characterized by higher thermoelectric figures of merit, Cu2−xS provides advantages in terms of low cost and element abundance. In the present work, we investigate the effect of different dopants to enhance the Cu2−xS performance and also its thermal stability. Among the tested options, Pb-doped Cu2−xS shows the highest improvement in stability against sulfur volatilization. Additionally, Pb incorporation allows tuning charge carrier concentration, which enables a significant improvement of the power factor. We demonstrate here that the introduction of an optimal additive amount of just 0.3% results in a threefold increase of the power factor in the middle-temperature range (500–800 K) and a record dimensionless thermoelectric figure of merit above 2 at 880 K. © 2021 Elsevier Ltd

  • Effect of the Annealing Atmosphere on Crystal Phase and Thermoelectric Properties of Copper Sulfide

    Li M., Liu Y., Zhang Y., Han X., Zhang T., Zuo Y., Xie C., Xiao K., Arbiol J., Llorca J., Ibáñez M., Liu J., Cabot A. ACS Nano; 15 (3): 4967 - 4978. 2021. 10.1021/acsnano.0c09866. IF: 15.881

    Cu2-xS has become one of the most promising thermoelectric materials for application in the middle-high temperature range. Its advantages include the abundance, low cost, and safety of its elements and a high performance at relatively elevated temperatures. However, stability issues limit its operation current and temperature, thus calling for the optimization of the material performance in the middle temperature range. Here, we present a synthetic protocol for large scale production of covellite CuS nanoparticles at ambient temperature and atmosphere, and using water as a solvent. The crystal phase and stoichiometry of the particles are afterward tuned through an annealing process at a moderate temperature under inert or reducing atmosphere. While annealing under argon results in Cu1.8S nanopowder with a rhombohedral crystal phase, annealing in an atmosphere containing hydrogen leads to tetragonal Cu1.96S. High temperature X-ray diffraction analysis shows the material annealed in argon to transform to the cubic phase at ca. 400 K, while the material annealed in the presence of hydrogen undergoes two phase transitions, first to hexagonal and then to the cubic structure. The annealing atmosphere, temperature, and time allow adjustment of the density of copper vacancies and thus tuning of the charge carrier concentration and material transport properties. In this direction, the material annealed under Ar is characterized by higher electrical conductivities but lower Seebeck coefficients than the material annealed in the presence of hydrogen. By optimizing the charge carrier concentration through the annealing time, Cu2-xS with record figures of merit in the middle temperature range, up to 1.41 at 710 K, is obtained. We finally demonstrate that this strategy, based on a low-cost and scalable solution synthesis process, is also suitable for the production of high performance Cu2-xS layers using high throughput and cost-effective printing technologies. ©

  • Effects of solar irradiation on thermally driven CO2 methanation using Ni/CeO2–based catalyst

    Golovanova V., Spadaro M.C., Arbiol J., Golovanov V., Rantala T.T., Andreu T., Morante J.R. Applied Catalysis B: Environmental; 291 (120038) 2021. 10.1016/j.apcatb.2021.120038. IF: 19.503

    Utilization of the renewable energy sources is one of the main challenges in the state-of-the-art technologies for CO2 recycling. Here we have taken advantage of the solar light harvesting in the thermocatalytic approach to carbon dioxide methanation. The large-surface-area Ni/CeO2 catalyst produced by a scalable low-cost method was characterized and tested in the dark and under solar light irradiation conditions. Light-assisted CO2 conversion experiments as well as in-situ DRIFT spectrometry, performed at different illumination intensities, have revealed a dual effect of the incident photons on the catalytic properties of the two-component Ni/CeO2 catalyst. On the one hand, absorbed photons induce a localized surface plasmon resonance in the Ni nanoparticles followed by dissipation of the heat to the oxide matrix. On the other hand, the illumination activates the photocatalytic properties of the CeO2 support, which leads to an increase in the concentration of the intermediates being precursor for methane production. Analysis of the methane production at different temperatures and illumination conditions has shown that the methanation reaction in our case is controlled by a photothermally-activated process. The used approach has allowed us to increase the reaction rate up to 2.4 times and consequently to decrease the power consumption by 20 % under solar illumination, thus replacing the conventional thermal activation of the reaction with a green energy source. © 2021 The Authors

  • Enhanced thermoelectric performance of n-type bi2se3 nanosheets through sn doping

    Li M., Zhang Y., Zhang T., Zuo Y., Xiao K., Arbiol J., Llorca J., Liu Y., Cabot A. Nanomaterials; 11 (7, 1827) 2021. 10.3390/nano11071827. IF: 5.076

    The cost-effective conversion of low-grade heat into electricity using thermoelectric devices requires developing alternative materials and material processing technologies able to reduce the currently high device manufacturing costs. In this direction, thermoelectric materials that do not rely on rare or toxic elements such as tellurium or lead need to be produced using high-throughput technologies not involving high temperatures and long processes. Bi2Se3 is an obvious possible Tefree alternative to Bi2Te3 for ambient temperature thermoelectric applications, but its performance is still low for practical applications, and additional efforts toward finding proper dopants are required. Here, we report a scalable method to produce Bi2Se3 nanosheets at low synthesis temperatures. We studied the influence of different dopants on the thermoelectric properties of this material. Among the elements tested, we demonstrated that Sn doping resulted in the best performance. Sn incorporation resulted in a significant improvement to the Bi2Se3 Seebeck coefficient and a reduction in the thermal conductivity in the direction of the hot-press axis, resulting in an overall 60% improvement in the thermoelectric figure of merit of Bi2Se3 . © 2021 by the authors. Licensee MDPI, Basel, Switzerland.

  • Enhancement of proximity-induced superconductivity in a planar Ge hole gas

    Aggarwal K., Hofmann A., Jirovec D., Prieto I., Sammak A., Botifoll M., Martí-Sánchez S., Veldhorst M., Arbiol J., Scappucci G., Danon J., Katsaros G. Physical Review Research; 3 (2, L022005) 2021. 10.1103/PhysRevResearch.3.L022005. IF: 0.000

    Hole gases in planar germanium can have high mobilities in combination with strong spin-orbit interaction and electrically tunable g factors, and are therefore emerging as a promising platform for creating hybrid superconductor-semiconductor devices. A key challenge towards hybrid Ge-based quantum technologies is the design of high-quality interfaces and superconducting contacts that are robust against magnetic fields. In this work, by combining the assets of aluminum, which provides good contact to the Ge, and niobium, which has a significant superconducting gap, we demonstrate highly transparent low-disordered JoFETs with relatively large ICRN products that are capable of withstanding high magnetic fields. We furthermore demonstrate the ability of phase-biasing individual JoFETs, opening up an avenue to explore topological superconductivity in planar Ge. The persistence of superconductivity in the reported hybrid devices beyond 1.8 T paves the way towards integrating spin qubits and proximity-induced superconductivity on the same chip. © 2021 authors. Published by the American Physical Society.

  • Exploiting the Lability of Metal Halide Perovskites for Doping Semiconductor Nanocomposites

    Calcabrini M., Genç A., Liu Y., Kleinhanns T., Lee S., Dirin D.N., Akkerman Q.A., Kovalenko M.V., Arbiol J., Ibáñez M. ACS Energy Letters; 6 (2): 581 - 587. 2021. 10.1021/acsenergylett.0c02448. IF: 23.101

    Cesium lead halides have intrinsically unstable crystal lattices and easily transform within perovskite and nonperovskite structures. In this work, we explore the conversion of the perovskite CsPbBr3 into Cs4PbBr6 in the presence of PbS at 450 °C to produce doped nanocrystal-based composites with embedded Cs4PbBr6 nanoprecipitates. We show that PbBr2 is extracted from CsPbBr3 and diffuses into the PbS lattice with a consequent increase in the concentration of free charge carriers. This new doping strategy enables the adjustment of the density of charge carriers between 1019 and 1020 cm-3, and it may serve as a general strategy for doping other nanocrystal-based semiconductors. © 2021 American Chemical Society.

  • Facing Seawater Splitting Challenges by Regeneration with Ni−Mo−Fe Bifunctional Electrocatalyst for Hydrogen and Oxygen Evolution

    Ros C., Murcia-López S., Garcia X., Rosado M., Arbiol J., Llorca J., Morante J.R. ChemSusChem; 14 (14): 2872 - 2881. 2021. 10.1002/cssc.202100194. IF: 8.928

    Hydrogen, produced by water splitting, has been proposed as one of the main green energy vectors of the future if produced from renewable energy sources. However, to substitute fossil fuels, large amounts of pure water are necessary, scarce in many world regions. In this work, we fabricate efficient and earth-abundant electrodes, study the challenges of using real seawater, and propose an electrode regeneration method to face undesired salt deposition. Ni−Mo−Fe trimetallic electrocatalyst is deposited on non-expensive graphitic carbon felts both for hydrogen (HER) and oxygen evolution reactions (OER) in seawater and alkaline seawater. Cl− pitting and the chlorine oxidation reaction are suppressed on these substrates and alkalinized electrolyte. Precipitations on the electrodes, mainly CaCO3, originating from seawater-dissolved components have been studied, and a simple regeneration technique is proposed to rapidly dissolve undesired deposited CaCO3 in acidified seawater. Under alkaline conditions, Ni−Mo−Fe-based catalyst is found to reconfigure, under cathodic bias, into Ni−Mo−Fe alloy with a cubic crystalline structure and Ni : Fe(OH)2 redeposits whereas, under anodic bias, it is transformed into a follicular Ni:FeOOH structure. High productivities over 300 mA cm−2 and voltages down to 1.59 V@10 mA cm−2 for the overall water splitting reaction have been shown, and electrodes are found stable for over 24 h without decay in alkaline seawater conditions and with energy efficiency higher than 61.5 % which makes seawater splitting promising and economically feasible. © 2021 Wiley-VCH GmbH

  • Influence of copper telluride nanodomains on the transport properties of n-type bismuth telluride

    Zhang Y., Xing C., Liu Y., Li M., Xiao K., Guardia P., Lee S., Han X., Ostovari Moghaddam A., Josep Roa J., Arbiol J., Ibáñez M., Pan K., Prato M., Xie Y., Cabot A. Chemical Engineering Journal; 418 (129374) 2021. 10.1016/j.cej.2021.129374. IF: 13.273

    The high processing cost, poor mechanical properties and moderate performance of Bi2Te3–based alloys used in thermoelectric devices limit the cost-effectiveness of this energy conversion technology. Towards solving these current challenges, in the present work, we detail a low temperature solution-based approach to produce Bi2Te3-Cu2-xTe nanocomposites with improved thermoelectric performance. Our approach consists in combining proper ratios of colloidal nanoparticles and to consolidate the resulting mixture into nanocomposites using a hot press. The transport properties of the nanocomposites are characterized and compared with those of pure Bi2Te3 nanomaterials obtained following the same procedure. In contrast with most previous works, the presence of Cu2-xTe nanodomains does not result in a significant reduction of the lattice thermal conductivity of the reference Bi2Te3 nanomaterial, which is already very low. However, the introduction of Cu2-xTe yields a nearly threefold increase of the power factor associated to a simultaneous increase of the Seebeck coefficient and electrical conductivity at temperatures above 400 K. Taking into account the band alignment of the two materials, we rationalize this increase by considering that Cu2-xTe nanostructures, with a relatively low electron affinity, are able to inject electrons into Bi2Te3, enhancing in this way its electrical conductivity. The simultaneous increase of the Seebeck coefficient is related to the energy filtering of charge carriers at energy barriers within Bi2Te3 domains associated with the accumulation of electrons in regions nearby a Cu2-xTe/Bi2Te3 heterojunction. Overall, with the incorporation of a proper amount of Cu2-xTe nanoparticles, we demonstrate a 250% improvement of the thermoelectric figure of merit of Bi2Te3. © 2021 Elsevier B.V.

  • Metal Oxide Clusters on Nitrogen-Doped Carbon are Highly Selective for CO2Electroreduction to CO

    Li J., Zitolo A., Garcés-Pineda F.A., Asset T., Kodali M., Tang P., Arbiol J., Galán-Mascarós J.R., Atanassov P., Zenyuk I.V., Sougrati M.T., Jaouen F. ACS Catalysis; 11 (15): 10028 - 10042. 2021. 10.1021/acscatal.1c01702. IF: 13.084

    The electrochemical reduction of CO2 (eCO2RR) using renewable energy is an effective approach to pursue carbon neutrality. The eCO2RR to CO is indispensable in promoting C-C coupling through bifunctional catalysis and achieving cascade conversion from CO2 to C2+. This work investigates a series of M/N-C (M = Mn, Fe, Co, Ni, Cu, and Zn) catalysts, for which the metal precursor interacted with the nitrogen-doped carbon support (N-C) at room temperature, resulting in the metal being present as (sub)nanosized metal oxide clusters under ex situ conditions, except for Cu/N-C and Zn/N-C. A volcano trend in their activity toward CO as a function of the group of the transition metal is revealed, with Co/N-C exhibiting the highest activity at -0.5 V versus RHE, while Ni/N-C shows both appreciable activity and selectivity. Operando X-ray absorption spectroscopy shows that the majority of Cu atoms in Cu/N-C form Cu0 clusters during eCO2RR, while Mn/, Fe/, Co/, and Ni/N-C catalysts maintain the metal hydroxide structures, with a minor amount of M0 formed in Fe/, Co/, and Ni/N-C. The superior activity of Fe/, Co/, and Ni/N-C is ascribed to the phase contraction and the HCO3- insertion into the layered structure of metal hydroxides. Our work provides a facile synthetic approach toward highly active and selective electrocatalysts to convert CO2 into CO. Coupled with state-of-the-art NiFe-based anodes in a full-cell device, Ni/N-C exhibits >80% Faradaic efficiency toward CO at 100 mA cm-2. © 2021 American Chemical Society.

  • Molecular Engineering to Tune the Ligand Environment of Atomically Dispersed Nickel for Efficient Alcohol Electrochemical Oxidation

    Liang Z., Jiang D., Wang X., Shakouri M., Zhang T., Li Z., Tang P., Llorca J., Liu L., Yuan Y., Heggen M., Dunin-Borkowski R.E., Morante J.R., Cabot A., Arbiol J. Advanced Functional Materials; 31 (51, 2106349) 2021. 10.1002/adfm.202106349. IF: 18.808

    Atomically dispersed metals maximize the number of catalytic sites and enhance their activity. However, their challenging synthesis and characterization strongly complicates their optimization. Here, the aim is to demonstrate that tuning the electronic environment of atomically dispersed metal catalysts through the modification of their edge coordination is an effective strategy to maximize their performance. This article focuses on optimizing nickel-based electrocatalysts toward alcohol electrooxidation in alkaline solution. A new organic framework with atomically dispersed nickel is first developed. The coordination environment of nickel within this framework is modified through the addition of carbonyl (CO) groups. The authors then demonstrate that such nickel-based organic frameworks, combined with carbon nanotubes, exhibit outstanding catalytic activity and durability toward the oxidation of methanol (CH3OH), ethanol (CH3CH2OH), and benzyl alcohol (C6H5CH2OH); the smaller molecule exhibits higher catalytic performance. These outstanding electrocatalytic activities for alcohol electrooxidation are attributed to the presence of the carbonyl group in the ligand chemical environment, which enhances the adsorption for alcohol, as revealed by density functional theory calculations. The work not only introduces a new atomically dispersed Ni-based catalyst, but also demonstrates a new strategy for designing and engineering high-performance catalysts through the tuning of their chemical environment. © 2021 The Authors. Advanced Functional Materials published by Wiley-VCH GmbH

  • NbSe2 Meets C2N: A 2D-2D Heterostructure Catalysts as Multifunctional Polysulfide Mediator in Ultra-Long-Life Lithium–Sulfur Batteries

    Yang D., Liang Z., Zhang C., Biendicho J.J., Botifoll M., Spadaro M.C., Chen Q., Li M., Ramon A., Moghaddam A.O., Llorca J., Wang J., Morante J.R., Arbiol J., Chou S.-L., Cabot A. Advanced Energy Materials; 11 (36, 2101250) 2021. 10.1002/aenm.202101250. IF: 29.368

    The shuttle effect and sluggish conversion kinetics of lithium polysulfides (LiPS) hamper the practical application of lithium–sulfur batteries (LSBs). Toward overcoming these limitations, herein an in situ grown C2N@NbSe2 heterostructure is presented with remarkable specific surface area, as a Li–S catalyst and LiPS absorber. Density functional theory (DFT) calculations and experimental results comprehensively demonstrate that C2N@NbSe2 is characterized by a suitable electronic structure and charge rearrangement that strongly accelerates the LiPS electrocatalytic conversion. In addition, heterostructured C2N@NbSe2 strongly interacts with LiPS species, confining them at the cathode. As a result, LSBs cathodes based on C2N@NbSe2/S exhibit a high initial capacity of 1545 mAh g−1 at 0.1 C. Even more excitingly, C2N@NbSe2/S cathodes are characterized by impressive cycling stability with only 0.012% capacity decay per cycle after 2000 cycles at 3 C. Even at a sulfur loading of 5.6 mg cm−2, a high areal capacity of 5.65 mAh cm−2 is delivered. These results demonstrate that C2N@NbSe2 heterostructures can act as multifunctional polysulfide mediators to chemically adsorb LiPS, accelerate Li-ion diffusion, chemically catalyze LiPS conversion, and lower the energy barrier for Li2S precipitation/decomposition, realizing the “adsorption-diffusion-conversion” of polysulfides. © 2021 Wiley-VCH GmbH

  • Nickel Iron Diselenide for Highly Efficient and Selective Electrocatalytic Conversion of Methanol to Formate

    Li J., Xing C., Zhang Y., Zhang T., Spadaro M.C., Wu Q., Yi Y., He S., Llorca J., Arbiol J., Cabot A., Cui C. Small; 17 (6, 2006623) 2021. 10.1002/smll.202006623. IF: 13.281

    The electro-oxidation of methanol to formate is an interesting example of the potential use of renewable energies to add value to a biosourced chemical commodity. Additionally, methanol electro-oxidation can replace the sluggish oxygen evolution reaction when coupled to hydrogen evolution or to the electroreduction of other biomass-derived intermediates. But the cost-effective realization of these reaction schemes requires the development of efficient and low-cost electrocatalysts. Here, a noble metal-free catalyst, Ni1−xFexSe2 nanorods, with a high potential for an efficient and selective methanol conversion to formate is demonstrated. At its optimum composition, Ni0.75Fe0.25Se2, this diselenide is able to produce 0.47 mmol cm−2 h−1 of formate at 50 mA cm−2 with a Faradaic conversion efficiency of 99%. Additionally, this noble-metal-free catalyst is able to continuously work for over 50 000 s with a minimal loss of efficiency, delivering initial current densities above 50 mA cm−2 and 2.2 A mg−1 in a 1.0 m KOH electrolyte with 1.0 m methanol at 1.5 V versus reversible hydrogen electrode. This work demonstrates the highly efficient and selective methanol-to-formate conversion on Ni-based noble-metal-free catalysts, and more importantly it shows a very promising example to exploit the electrocatalytic conversion of biomass-derived chemicals. © 2021 Wiley-VCH GmbH

  • PbS-Pb-Cu xS Composites for Thermoelectric Application

    Li M., Liu Y., Zhang Y., Han X., Xiao K., Nabahat M., Arbiol J., Llorca J., Ibañez M., Cabot A. ACS Applied Materials and Interfaces; 13 (43): 51373 - 51382. 2021. 10.1021/acsami.1c15609. IF: 9.229

    Composite materials offer numerous advantages in a wide range of applications, including thermoelectrics. Here, semiconductor-metal composites are produced by just blending nanoparticles of a sulfide semiconductor obtained in aqueous solution and at room temperature with a metallic Cu powder. The obtained blend is annealed in a reducing atmosphere and afterward consolidated into dense polycrystalline pellets through spark plasma sintering (SPS). We observe that, during the annealing process, the presence of metallic copper activates a partial reduction of the PbS, resulting in the formation of PbS-Pb-CuxS composites. The presence of metallic lead during the SPS process habilitates the liquid-phase sintering of the composite. Besides, by comparing the transport properties of PbS, the PbS-Pb-CuxS composites, and PbS-CuxS composites obtained by blending PbS and CuxS nanoparticles, we demonstrate that the presence of metallic lead decisively contributes to a strong increase of the charge carrier concentration through spillover of charge carriers enabled by the low work function of lead. The increase in charge carrier concentration translates into much higher electrical conductivities and moderately lower Seebeck coefficients. These properties translate into power factors up to 2.1 mW m-1 K-2 at ambient temperature, well above those of PbS and PbS + CuxS. Additionally, the presence of multiple phases in the final composite results in a notable decrease in the lattice thermal conductivity. Overall, the introduction of metallic copper in the initial blend results in a significant improvement of the thermoelectric performance of PbS, reaching a dimensionless thermoelectric figure of merit ZT = 1.1 at 750 K, which represents about a 400% increase over bare PbS. Besides, an average ZTave = 0.72 in the temperature range 320-773 K is demonstrated. © 2021 American Chemical Society.

  • Phase formation and thermoelectric properties of Zn1+xSb binary system

    OSTOVARI MOGHADDAM A., TROFIMOV E., ZHANG T., ARBIOL J., CABOT A. Transactions of Nonferrous Metals Society of China (English Edition); 31 (3): 753 - 763. 2021. 10.1016/S1003-6326(21)65536-X. IF: 2.917

    The phase formation and thermoelectric (TE) properties in the central region of the Zn−Sb phase diagram were analyzed through synthesizing a series of Zn1+xSb (x=0, 0.05, 0.1, 0.15, 0.25, 0.3) materials by reacting Zn and Sb powders below the solidus line of the Zn−Sb binary phase diagram followed by furnace cooling. In this process, the nonstoichiometric powder blend crystallized in a combination of ZnSb and β-Zn4Sb3 phases. Then, the materials were ground and hot pressed to form dense ZnSb/β-Zn4Sb3 composites. No traces of Sb and Zn elements or other phases were revealed by X-ray diffraction, high resolution transmission electron microscopy and electron energy loss spectroscopy analyses. The thermoelectric properties of all materials could be rationalized as a combination of the thermoelectric behavior of ZnSb and β-Zn4Sb3 phases, which were dominated by the main phase in each sample. Zn1.3Sb composite exhibited the best thermoelectric performance. It was also found that Ge doping substantially increased the Seebeck coefficient of Zn1.3Sb and led to significantly higher power factor, up to 1.51 mW·m−1·K−2 at 540 K. Overall, an exceptional and stable TE figure of merit (ZT) of 1.17 at 650 K was obtained for Zn1.28Ge0.02Sb. © 2021 The Nonferrous Metals Society of China

  • Photodehydrogenation of ethanol over cu2o/tio2 heterostructures

    Xing C., Zhang Y., Liu Y., Wang X., Li J., Martínez-Alanis P.R., Spadaro M.C., Guardia P., Arbiol J., Llorca J., Cabot A. Nanomaterials; 11 (6, 1399) 2021. 10.3390/nano11061399. IF: 5.076

    The photodehydrogenation of ethanol is a sustainable and potentially cost-effective strategy to produce hydrogen and acetaldehyde from renewable resources. The optimization of this process requires the use of highly active, stable and selective photocatalytic materials based on abundant elements and the proper adjustment of the reaction conditions, including temperature. In this work, Cu2O-TiO2 type-II heterojunctions with different Cu2O amounts are obtained by a one-pot hydrothermal method. The structural and chemical properties of the produced materials and their activity toward ethanol photodehydrogenation under UV and visible light illumination are evaluated. The Cu2O-TiO2 photocatalysts exhibit a high selectivity toward acetaldehyde production and up to tenfold higher hydrogen evolution rates compared to bare TiO2 . We further discern here the influence of temperature and visible light absorption on the photocatalytic performance. Our results point toward the combination of energy sources in thermo-photocatalytic reactors as an efficient strategy for solar energy conversion. © 2021 by the authors. Licensee MDPI, Basel, Switzerland.

  • Push-Pull Electronic Effects in Surface-Active Sites Enhance Electrocatalytic Oxygen Evolution on Transition Metal Oxides

    Garcés-Pineda F.A., Chuong Nguyën H., Blasco-Ahicart M., García-Tecedor M., de Fez Febré M., Tang P.-Y., Arbiol J., Giménez S., Galán-Mascarós J.R., López N. ChemSusChem; 14 (6): 1595 - 1601. 2021. 10.1002/cssc.202002782. IF: 8.928

    Sustainable electrocatalysis of the oxygen evolution reaction (OER) constitutes a major challenge for the realization of green fuels. Oxides based on Ni and Fe in alkaline media have been proposed to avoid using critical raw materials. However, their ill-defined structures under OER conditions make the identification of key descriptors difficult. Here, we have studied Fe−Ni−Zn spinel oxides, with a well-defined crystal structure, as a platform to obtain general understanding on the key contributions. The OER reaches maximum performance when: (i) Zn is present in the Spinel structure, (ii) very dense, equimolar 1 : 1 : 1 stoichiometry sites appear on the surface as they allow the formation of oxygen vacancies where Zn favors pushing the electronic density that is pulled by the octahedral Fe and tetrahedral Ni redox pair lowering the overpotential. Our work proves cooperative electronic effects on surface active sites as key to design optimum OER electrocatalysts. © 2021 Wiley-VCH GmbH

  • Quasi-double-star nickel and iron active sites for high-efficiency carbon dioxide electroreduction

    Zhang T., Han X., Liu H., Biset-Peiró M., Zhang X., Tan P., Tang P., Yang B., Zheng L., Morante J.R., Arbiol J. Energy and Environmental Science; 14 (9): 4847 - 4857. 2021. 10.1039/d1ee01592c. IF: 38.532

    Although the Faraday efficiencies (FEs) obtained on most of the Ni based single-atom catalysts (Ni-N-C) are satisfactory (generally >90%) for the electrochemical transfer CO2 to CO, their practical application is still limited by their high overpotentials (>600 mV vs. RHE), which implies a higher energy consumption to drive the CO2 RR. In this work, we have prepared a quasi-double star catalyst composed of nearby Ni and Fe active sites via a simple pyrolysis of Ni and Fe co-doped Zn-based MOFs in order to achieve a high selectivity at a low overpotential during the CO2 RR. Specifically, the optimized Ni/Fe-N-C catalyst shows an exclusive selectivity (a maximum FE(CO) of 98%) at a low overpotential of 390 mV vs. RHE, which is superior to both the single metal counterparts (Ni-N-C and Fe-N-C catalysts) and other state-of-the-art M-N-C catalysts. The DFT results further reveal that regulating the catalytic CO2 RR performance via nearby Ni and Fe active sites can potentially break the activity benchmark of the single metal counterparts because the neighboring Ni and Fe active sites not only function in synergy to decrease the reaction barrier for the formation of COOH∗ and desorption of CO∗ in comparison to their single metal counterparts, but also prevent the undesired hydrogen evolution reaction (HER). This work presents a quasi-double-star catalyst composed of two metal sites for high-efficiency CO2 reduction, which paves the way for the rational design of bimetallic catalysts with separated active sites for other reactions. © The Royal Society of Chemistry.

  • Rotated domains in selective area epitaxy grown Zn3P2: Formation mechanism and functionality

    Spadaro M.C., Escobar Steinvall S., Dzade N.Y., Martí-Sánchez S., Torres-Vila P., Stutz E.Z., Zamani M., Paul R., Leran J.-B., Fontcuberta I Morral A., Arbiol J. Nanoscale; 13 (44): 18441 - 18450. 2021. 10.1039/d1nr06190a. IF: 7.790

    Zinc phosphide (Zn3P2) is an ideal absorber candidate for solar cells thanks to its direct bandgap, earth-abundance, and optoelectronic characteristics, albeit it has been insufficiently investigated due to limitations in the fabrication of high-quality material. It is possible to overcome these factors by obtaining the material as nanostructures, e.g. via the selective area epitaxy approach, enabling additional strain relaxation mechanisms and minimizing the interface area. We demonstrate that Zn3P2 nanowires grow mostly defect-free when growth is oriented along the [100] and [110] of the crystal, which is obtained in nanoscale openings along the [110] and [010] on InP(100). We detect the presence of two stable rotated crystal domains that coexist in the structure. They are due to a change in the growth facet, which originates either from the island formation and merging in the initial stages of growth or lateral overgrowth. These domains have been visualized through 3D atomic models and confirmed with image simulations of the atomic scale electron micrographs. Density functional theory simulations describe the rotated domains' formation mechanism and demonstrate their lattice-matched epitaxial relation. In addition, the energies of the shallow states predicted closely agree with transition energies observed by experimental studies and offer a potential origin for these defect transitions. Our study represents an important step forward in the understanding of Zn3P2 and thus for the realisation of solar cells to respond to the present call for sustainable photovoltaic technology. © 2021 The Royal Society of Chemistry.

  • Tailoring plasmonic resonances in Cu-Ag metal islands films

    Bubaš M., Janicki V., Mezzasalma S.A., Spadaro M.C., Arbiol J., Sancho-Parramon J. Applied Surface Science; 564 (150260) 2021. 10.1016/j.apsusc.2021.150260. IF: 6.707

    The plasmonic response of Cu-Ag metal islands films is investigated. Films are obtained by subsequent electron beam deposition of Ag and Cu using different fabrication conditions: deposited mass thickness, substrate temperature and post-deposition annealing in vacuum. Optical properties of films are investigated by spectroscopic ellipsometry and correlated with the structural characterization results obtained by electron microscopy. It is observed that Ag enhances island growth and increases the percolation threshold of Cu films. The localized surface plasmon resonance of isolated particles shows signatures of both Cu and Ag. Moderate thermal annealing enhances island growth and favours Janus-like morphology, increasing the Ag contribution to the surface plasmon resonance. In case of percolated films, annealing-induced dewetting can lead to the appearance of large and irregular particles with a remarkable absorption peak in the near-infrared range. Composition and optical properties of the films can be further modified by Ag partial evaporation upon annealing at high temperatures. The variation of optical properties with aging is related to Cu oxidization and follows different trends depending on the sample morphology. Overall, it is shown that Cu-Ag island films are compelling systems for plasmonic applications, as their optical response can be widely and easily tuned by adjusting fabrication conditions. © 2021 Elsevier B.V.

  • Tubular CoFeP@CN as a Mott–Schottky Catalyst with Multiple Adsorption Sites for Robust Lithium−Sulfur Batteries

    Zhang C., Du R., Biendicho J.J., Yi M., Xiao K., Yang D., Zhang T., Wang X., Arbiol J., Llorca J., Zhou Y., Morante J.R., Cabot A. Advanced Energy Materials; 11 (24, 2100432) 2021. 10.1002/aenm.202100432. IF: 29.368

    The shuttle effect and the sluggish reaction kinetics of lithium polysulfide (LiPS) seriously compromise the performance of lithium–sulfur batteries (LSBs). To overcome these limitations and enable the fabrication of robust LSBs, here the use of a Mott–Schottky catalyst based on bimetallic phosphide CoFeP nanocrystals supported on carbon nitride tubular nanostructures as sulfur hosts is proposed. Theoretical calculations and experimental data confirm that CoFeP@CN composites are characterized by a suitable electronic structure and charge rearrangement that allows them to act as a Mott–Schottky catalyst to accelerate LiPS conversion. In addition, the tubular geometry of CoFeP@CN composites facilitates the diffusion of Li ions, accommodates volume change during the reaction, and offers abundant lithiophilic/sulfiphilic sites to effectively trap soluble LiPS. Therefore, S@CoFeP@CN electrodes deliver a superior rate performance of 630 mAh g−1 at 5 C, and remarkable cycling stability with 90.44% capacity retention over 700 cycles. Coin cells with high sulfur loading, 4.1 mg cm−2, and pouch cells with 0.1 Ah capacities are further produced to validate their superior cycling stability. In addition, it is demonstrated here that CoFeP@CN hosts greatly alleviate the often overlooked issues of low energy efficiency and serious self-discharging in LSBs. © 2021 Wiley-VCH GmbH

  • Tuning the Electronic Bandgap of Graphdiyne by H-Substitution to Promote Interfacial Charge Carrier Separation for Enhanced Photocatalytic Hydrogen Production

    Li J., Slassi A., Han X., Cornil D., Ha-Thi M.-H., Pino T., Debecker D.P., Colbeau-Justin C., Arbiol J., Cornil J., Ghazzal M.N. Advanced Functional Materials; 31 (29, 2100994) 2021. 10.1002/adfm.202100994. IF: 18.808

    Graphdiyne (GDY), which features a highly π-conjugated structure, direct bandgap, and high charge carrier mobility, presents the major requirements for photocatalysis. Up to now, all photocatalytic studies are performed without paying too much attention on the GDY bandgap (1.1 eV at the G0W0 many-body theory level). Such a narrow bandgap is not suitable for the band alignment between GDY and other semiconductors, making it difficult to achieve efficient photogenerated charge carrier separation. Herein, for the first time, it is demonstrated that tuning the electronic bandgap of GDY via H-substitution (H-GDY) promotes interfacial charge separation and improves photocatalytic H2 evolution. The H-GDY exhibits an increased bandgap energy (≈2.5 eV) and exploitable conduction band minimum and valence band maximum edges. As a representative semiconductor, TiO2 is hybridized with both H-GDY and GDY to fabricate a heterojunction. Compared to the GDY/TiO2, the H-GDY/TiO2 heterojunction leads to a remarkable enhancement of the photocatalytic H2 generation by 1.35 times under UV–visible illumination (6200 µmol h−1 g−1) and four times under visible light (670 µmol h−1 g−1). Such enhancement is attributed to the suitable band alignment between H-GDY and TiO2, which efficiently promotes the photogenerated electron and hole separation, as supported by density functional theory calculations. © 2021 Wiley-VCH GmbH.


  • 3D Ordering at the Liquid–Solid Polar Interface of Nanowires

    Zamani M., Imbalzano G., Tappy N., Alexander D.T.L., Martí-Sánchez S., Ghisalberti L., Ramasse Q.M., Friedl M., Tütüncüoglu G., Francaviglia L., Bienvenue S., Hébert C., Arbiol J., Ceriotti M., Fontcuberta i Morral A. Advanced Materials; 32 (38, 2001030) 2020. 10.1002/adma.202001030. IF: 27.398

    The nature of the liquid–solid interface determines the characteristics of a variety of physical phenomena, including catalysis, electrochemistry, lubrication, and crystal growth. Most of the established models for crystal growth are based on macroscopic thermodynamics, neglecting the atomistic nature of the liquid–solid interface. Here, experimental observations and molecular dynamics simulations are employed to identify the 3D nature of an atomic-scale ordering of liquid Ga in contact with solid GaAs in a nanowire growth configuration. An interplay between the liquid ordering and the formation of a new bilayer is revealed, which, contrary to the established theories, suggests that the preference for a certain polarity and polytypism is influenced by the atomic structure of the interface. The conclusions of this work open new avenues for the understanding of crystal growth, as well as other processes and systems involving a liquid–solid interface. © 2020 The Authors. Published by Wiley-VCH GmbH

  • A SnS2 Molecular Precursor for Conformal Nanostructured Coatings

    Zuo Y., Li J., Yu X., Du R., Zhang T., Wang X., Arbiol J., Llorca J., Cabot A. Chemistry of Materials; 32 (5): 2097 - 2106. 2020. 10.1021/acs.chemmater.9b05241. IF: 9.567

    We present a simple, versatile, and scalable procedure to produce SnS2 nanostructured layers based on an amine/thiol-based molecular ink. The ratios amine/thiol and Sn/S, and the reaction conditions, are systematically investigated to produce phase-pure SnS2 planar and conformal layers with a tremella-like SnS2 morphology. Such nanostructured layers are characterized by excellent photocurrent densities. The same strategy can be used to produce SnS2-graphene composites by simply introducing graphene oxide (GO) into the initial solution. Conveniently, the solvent mixture is able to simultaneously dissolve the Sn and Se powders and reduce the GO. Furthermore, SnS2-xSex ternary coatings and phase-pure SnSe2 can be easily produced by simply incorporating proper amounts of Se into the initial ink formulation. Finally, the potential of this precursor ink to produce gram-scale amounts of unsupported SnS2 is investigated. Copyright © 2020 American Chemical Society.

  • A yolk–albumen–shell structure of mixed Ni–Co oxide with an ultrathin carbon shell for high-sensitivity glucose sensors

    Xuan Zhang, Yawei Zhang, Wei Guo, Kai Wan, Ting Zhang, Jordi Arbiol, Yong-Qing Zhao, Cai-Ling Xu, Mao-Wen Xu, Jan Fransaer Materials Advances; 1 (4): 908 - 917. 2020. 10.1039/d0ma00230e.

    Non-enzymatic glucose sensors based on different Co–Ni–C composite materials were developed by pyrolysis of bimetallic or single metal based metal–organic frameworks (MOFs). The structure and composition of the resulting materials were explored by XRD, nitrogen adsorption/desorption isotherms, SEM, HRTEM and STEM-EELS. The electrochemical performance of the bimetallic MOF derived novel yolk–albumen–shell structure of Ni–Co@C (YASNiCo@C) stands out from these materials. The YASNiCo@C electrode exhibited a sensitivity of 1964 μA cm−2 mM−1 with the detection limit of 0.75 μM, a linear range from 5 μM to 1000 μM and good stability for the detection of glucose. These promising electrochemical performances prove that YASNiCo@C is a promising material for glucose sensors. Moreover, the strategy outlined in this work for the design of MOF based nanomaterials can also be used beyond glucose sensors.

  • Bismuth telluride-copper telluride nanocomposites from heterostructured building blocks

    Zhang Y., Liu Y., Calcabrini M., Xing C., Han X., Arbiol J., Cadavid D., Ibáñez M., Cabot A. Journal of Materials Chemistry C; 8 (40): 14092 - 14099. 2020. 10.1039/d0tc02182b. IF: 7.059

    Appropriately designed nanocomposites allow improving the thermoelectric performance by several mechanisms, including phonon scattering, modulation doping and energy filtering, while additionally promoting better mechanical properties than those of crystalline materials. Here, a strategy for producing Bi2Te3-Cu2-xTe nanocomposites based on the consolidation of heterostructured nanoparticles is described and the thermoelectric properties of the obtained materials are investigated. We first detail a two-step solution-based process to produce Bi2Te3-Cu2-xTe heteronanostructures, based on the growth of Cu2-xTe nanocrystals on the surface of Bi2Te3 nanowires. We characterize the structural and chemical properties of the synthesized nanostructures and of the nanocomposites produced by hot-pressing the particles at moderate temperatures. Besides, the transport properties of the nanocomposites are investigated as a function of the amount of Cu introduced. Overall, the presence of Cu decreases the material thermal conductivity through promotion of phonon scattering, modulates the charge carrier concentration through electron spillover, and increases the Seebeck coefficient through filtering of charge carriers at energy barriers. These effects result in an improvement of over 50% of the thermoelectric figure of merit of Bi2Te3. © The Royal Society of Chemistry.

  • Cobalt Hexacyanoferrate as a Selective and High Current Density Formate Oxidation Electrocatalyst

    Han L., González-Cobos J., Sánchez-Molina I., Giancola S., Folkman S.J., Tang P., Heggen M., Dunin-Borkowski R.E., Arbiol J., Giménez S., Galan-Mascaros J.R. ACS Applied Energy Materials; 3 (9): 9198 - 9207. 2020. 10.1021/acsaem.0c01548. IF: 4.473

    Herein we report the selectivity, stability, and electrochemical characterization of cobalt hexacyanoferrate, the Co-Fe Prussian Blue derivative (CoFePB), as a formate/formic acid oxidation electrocatalyst in aqueous media. CoFePB is able to quantitatively catalyze (100% Faradaic efficiency within less than 8% standard error at pH 5) the electrochemical oxidation of formate to CO2 over a pH range of 1-13. This quantitative formate elecrooxidation is possible due to the exclusive selectivity of the catalyst in a wide potential window (from ca. 1.2 to 1.7 V vs RHE), where no other substrate in aqueous conditions is activated: neither other organic molecules, such as alcohols or acids, nor water itself. CoFePB is one of the first heterogeneous noble-metal-free catalysts reported for the electrooxidation of small hydrocarbon molecules. Importantly, the catalyst showed a very high tolerance against surface poisoning during the reaction, as supported by the cyclic voltammetry and electrochemical impedance spectroscopy data, thereby allowing CoFePB to operate at greater current density than state-of-the-art noble metal catalysts. For example, we observed that CoFePB is able to achieve a formate oxidation current ∼10 mA cm-2 at pH 5, 0.4 M formate at 1.4 V vs RHE, whereas a Pt disk and Pd(5%)/C electrodes had currents of 0.4 and 1.4 mA cm-2, respectively, under identical conditions. The remarkable selectivity, stability, and high current density of CoFePB, in contrast to state-of-the-art catalysts based on platinum-group metals, is an important step in the search for inexpensive earth-abundant materials for oxidation of organic molecules for use in liquid fuel cells or for selective organic molecule sensors. Furthermore, because CoFePB is not poisoned by intermediates and can achieve higher current density than Pt or Pd, improvement of the catalyst onset potential can lead to higher power density formate oxidation fuel cells using earth-abundant metals than with Pt or Pd. Copyright © 2020 American Chemical Society.

  • Coherent Epitaxial Semiconductor-Ferromagnetic Insulator InAs/EuS Interfaces: Band Alignment and Magnetic Structure

    Liu Y., Luchini A., Martí-Sánchez S., Koch C., Schuwalow S., Khan S.A., Stankevič T., Francoual S., Mardegan J.R.L., Krieger J.A., Strocov V.N., Stahn J., Vaz C.A.F., Ramakrishnan M., Staub U., Lefmann K., Aeppli G., Arbiol J., Krogstrup P. ACS Applied Materials and Interfaces; 12 (7): 8780 - 8787. 2020. 10.1021/acsami.9b15034. IF: 8.758

    Hybrid semiconductor-ferromagnetic insulator heterostructures are interesting due to their tunable electronic transport, self-sustained stray field, and local proximitized magnetic exchange. In this work, we present lattice-matched hybrid epitaxy of semiconductor-ferromagnetic insulator InAs/EuS heterostructures and analyze the atomic-scale structure and their electronic and magnetic characteristics. The Fermi level at the InAs/EuS interface is found to be close to the InAs conduction band and in the band gap of EuS, thus preserving the semiconducting properties. Both neutron and X-ray reflectivity measurements show that the overall ferromagnetic component is mainly localized in the EuS thin film with a suppression of the Eu moment in the EuS layer nearest the InAs and magnetic moments outside the detection limits on the pure InAs side. This work presents a step toward realizing defect-free semiconductor-ferromagnetic insulator epitaxial hybrids for spin-lifted quantum and spintronic applications without external magnetic fields. Copyright © 2019 American Chemical Society.

  • Engineering grain boundaries at the 2D limit for the hydrogen evolution reaction

    He Y., Tang P., Hu Z., He Q., Zhu C., Wang L., Zeng Q., Golani P., Gao G., Fu W., Huang Z., Gao C., Xia J., Wang X., Wang X., Zhu C., Ramasse Q.M., Zhang A., An B., Zhang Y., Martí-Sánchez S., Morante J.R., Wang L., Tay B.K., Yakobson B.I., Trampert A., Zhang H., Wu M., Wang Q.J., Arbiol J., Liu Z. Nature Communications; 11 (1, 57) 2020. 10.1038/s41467-019-13631-2. IF: 12.121

    Atom-thin transition metal dichalcogenides (TMDs) have emerged as fascinating materials and key structures for electrocatalysis. So far, their edges, dopant heteroatoms and defects have been intensively explored as active sites for the hydrogen evolution reaction (HER) to split water. However, grain boundaries (GBs), a key type of defects in TMDs, have been overlooked due to their low density and large structural variations. Here, we demonstrate the synthesis of wafer-size atom-thin TMD films with an ultra-high-density of GBs, up to ~1012 cm−2. We propose a climb and drive 0D/2D interaction to explain the underlying growth mechanism. The electrocatalytic activity of the nanograin film is comprehensively examined by micro-electrochemical measurements, showing an excellent hydrogen-evolution performance (onset potential: −25 mV and Tafel slope: 54 mV dec−1), thus indicating an intrinsically high activation of the TMD GBs. © 2020, The Author(s).

  • GaAs nanoscale membranes: Prospects for seamless integration of III-Vs on silicon

    Raya A.M., Friedl M., Martí-Sánchez S., Dubrovskii V.G., Francaviglia L., Alén B., Morgan N., Tütüncüoglu G., Ramasse Q.M., Fuster D., Llorens J.M., Arbiol J., Fontcuberta I Morral A. Nanoscale; 12 (2): 815 - 824. 2020. 10.1039/c9nr08453c. IF: 6.895

    The growth of compound semiconductors on silicon has been widely sought after for decades, but reliable methods for defect-free combination of these materials have remained elusive. Recently, interconnected GaAs nanoscale membranes have been used as templates for the scalable integration of nanowire networks on III-V substrates. Here, we demonstrate how GaAs nanoscale membranes can be seamlessly integrated on silicon by controlling the density of nuclei in the initial stages of growth. We also correlate the absence or presence of defects with the existence of a single or multiple nucleation regime for the single membranes. Certain defects exhibit well-differentiated spectroscopic features that we identify with cathodoluminescence and micro-photoluminescence techniques. Overall, this work presents a new approach for the seamless integration of compound semiconductors on silicon. © 2019 The Royal Society of Chemistry.

  • Monodisperse CoSn and NiSn Nanoparticles Supported on Commercial Carbon as Anode for Lithium- And Potassium-Ion Batteries

    Li J., Xu X., Yu X., Han X., Zhang T., Zuo Y., Zhang C., Yang D., Wang X., Luo Z., Arbiol J., Llorca J., Liu J., Cabot A. ACS Applied Materials and Interfaces; 12 (4): 4414 - 4422. 2020. 10.1021/acsami.9b16418. IF: 8.758

    Monodisperse CoSn and NiSn nanoparticles were prepared in solution and supported on commercial carbon black. The obtained nanocomposites were applied as anodes for Li- and K-ion batteries. CoSn@C delivered stable average capacities of 850, 650, and 500 mAh g-1 at 0.2, 1.0, and 2.0 A g-1, respectively, well above those of commercial graphite anodes. The capacity of NiSn@C retained up to 575 mAh g-1 at a current of 1.0 A g-1 over 200 continuous cycles. Up to 74.5 and 69.7% pseudocapacitance contributions for Li-ion batteries were measured for CoSn@C and NiSn@C, respectively, at 1.0 mV s-1. CoSn@C was further tested in full-cell lithium-ion batteries with a LiFePO4 cathode to yield a stable capacity of 350 mAh g-1 at a rate of 0.2 A g-1. As electrode in K-ion batteries, CoSn@C composites presented a stable capacity of around 200 mAh g-1 at 0.2 A g-1 over 400 continuous cycles, and NiSn@C delivered a lower capacity of around 100 mAh g-1 over 300 cycles. Copyright © 2020 American Chemical Society.

  • Phosphorous incorporation in Pd2Sn alloys for electrocatalytic ethanol oxidation

    Yu X., Liu J., Li J., Luo Z., Zuo Y., Xing C., Llorca J., Nasiou D., Arbiol J., Pan K., Kleinhanns T., Xie Y., Cabot A. Nano Energy; 77 (105116) 2020. 10.1016/j.nanoen.2020.105116. IF: 16.602

    Direct ethanol fuel cells (DEFCs) show a huge potential to power future electric vehicles and portable electronics, but their deployment is currently limited by the unavailability of proper electrocatalysis for the ethanol oxidation reaction (EOR). In this work, we engineer a new electrocatalyst by incorporating phosphorous into a palladium-tin alloy and demonstrate a significant performance improvement toward EOR. We first detail a synthetic method to produce Pd2Sn:P nanocrystals that incorporate 35% of phosphorus. These nanoparticles are supported on carbon black and tested for EOR. Pd2Sn:P/C catalysts exhibit mass current densities up to 5.03 A mgPd−1, well above those of Pd2Sn/C, PdP2/C and Pd/C reference catalysts. Furthermore, a twofold lower Tafel slope and a much longer durability are revealed for the Pd2Sn:P/C catalyst compared with Pd/C. The performance improvement is rationalized with the aid of density functional theory (DFT) calculations considering different phosphorous chemical environments. Depending on its oxidation state, surface phosphorus introduces sites with low energy OH− adsorption and/or strongly influences the electronic structure of palladium and tin to facilitate the oxidation of the acetyl to acetic acid, which is considered the EOR rate limiting step. DFT calculations also points out that the durability improvement of Pd2Sn:P/C catalyst is associated to the promotion of OH adsorption that accelerates the oxidation of intermediate poisoning COads, reactivating the catalyst surface. © 2020

  • Rhodium as efficient additive for boosting acetone sensing by TiO2 nanocrystals. Beyond the classical view of noble metal additives

    Epifani M., Kaciulis S., Mezzi A., Zhang T., Arbiol J., Siciliano P., Landström A., Concina I., Moumen A., Comini E., Xiangfeng C. Sensors and Actuators, B: Chemical; 319 (128338) 2020. 10.1016/j.snb.2020.128338. IF: 7.100

    Anatase TiO2 nanocrystals were prepared by solvothermal synthesis and modified by in- situ generated Rh nanoparticles, with a starting nominal Rh:Ti atomic concentration of 0.01 and 0.05. After heat-treatment at 400 °C the TiO2 host was still in the anatase crystallographic phase, embedding Rh nanoparticles homogeneously distributed and whose surface had been oxidized to Rh2O3, as established by X-ray diffraction, Transmission Electron Microscopy and X-ray Photoelectron spectroscopy. Moreover, Rh seemed also homogeneously distributed in elemental form or as Rh2O3 nanoclusters. The acetone sensing properties of the resulting materials were enhanced by Rh addition, featuring a response increase of one order of magnitude at the best operating temperature of 300 °C. Moreover, Rh addition enlarged the detection range down to 10 ppm whereas pure TiO2 was not able of giving an appreciable response already at a concentration as high as 50 ppm. From the sensing data, the enhancement of the sensor response was attributed to the finely dispersed Rh species and not to the oxidized Rh nanocrystals. © 2020 Elsevier B.V.

  • Selective Methanol-to-Formate Electrocatalytic Conversion on Branched Nickel Carbide

    Li J., Wei R., Wang X., Zuo Y., Han X., Arbiol J., Llorca J., Yang Y., Cabot A., Cui C. Angewandte Chemie - International Edition; 59 (47): 20826 - 20830. 2020. 10.1002/anie.202004301. IF: 12.959

    A methanol economy will be favored by the availability of low-cost catalysts able to selectively oxidize methanol to formate. This selective oxidation would allow extraction of the largest part of the fuel energy while concurrently producing a chemical with even higher commercial value than the fuel itself. Herein, we present a highly active methanol electrooxidation catalyst based on abundant elements and with an optimized structure to simultaneously maximize interaction with the electrolyte and mobility of charge carriers. In situ infrared spectroscopy combined with nuclear magnetic resonance spectroscopy showed that branched nickel carbide particles are the first catalyst determined to have nearly 100 % electrochemical conversion of methanol to formate without generating detectable CO2 as a byproduct. Electrochemical kinetics analysis revealed the optimized reaction conditions and the electrode delivered excellent activities. This work provides a straightforward and cost-efficient way for the conversion of organic small molecules and the first direct evidence of a selective formate reaction pathway. © 2020 Wiley-VCH GmbH

  • Semiconductor-Ferromagnetic Insulator-Superconductor Nanowires: Stray Field and Exchange Field

    Liu Y., Vaitiekėnas S., Martí-Sánchez S., Koch C., Hart S., Cui Z., Kanne T., Khan S.A., Tanta R., Upadhyay S., Cachaza M.E., Marcus C.M., Arbiol J., Moler K.A., Krogstrup P. Nano Letters; 20 (1): 456 - 462. 2020. 10.1021/acs.nanolett.9b04187. IF: 11.238

    Nanowires can serve as flexible substrates for hybrid epitaxial growth on selected facets, allowing for the design of heterostructures with complex material combinations and geometries. In this work we report on hybrid epitaxy of freestanding vapor-liquid-solid grown and in-plane selective area grown semiconductor-ferromagnetic insulator-superconductor (InAs/EuS/Al) nanowire heterostructures. We study the crystal growth and complex epitaxial matching of wurtzite and zinc-blende InAs/rock-salt EuS interfaces as well as rock-salt EuS/face-centered cubic Al interfaces. Because of the magnetic anisotropy originating from the nanowire shape, the magnetic structure of the EuS phase is easily tuned into single magnetic domains. This effect efficiently ejects the stray field lines along the nanowires. With tunnel spectroscopy measurements of the density of states, we show that the material has a hard induced superconducting gap, and magnetic hysteretic evolution which indicates that the magnetic exchange fields are not negligible. These hybrid nanowires fulfill key material requirements for serving as a platform for spin-based quantum applications, such as scalable topological quantum computing. Copyright © 2019 American Chemical Society.

  • SnS2/g-C3N4/graphite nanocomposites as durable lithium-ion battery anode with high pseudocapacitance contribution

    Zuo Y., Xu X., Zhang C., Li J., Du R., Wang X., Han X., Arbiol J., Llorca J., Liu J., Cabot A. Electrochimica Acta; 349 (136369) 2020. 10.1016/j.electacta.2020.136369. IF: 6.215

    Tin disulfide is a promising anode material for Li-ion batteries (LIB) owing to its high theoretical capacity and the abundance of its composing elements. However, bare SnS2 suffers from low electrical conductivity and large volume expansion, which results in poor rate performance and cycling stability. Herein, we present a solution-based strategy to grow SnS2 nanostructures within a matrix of porous g-C3N4 (CN) and high electrical conductivity graphite plates (GPs). We test the resulting nanocomposite as anode in LIBs. First, SnS2 nanostructures with different geometries are tested, to find out that thin SnS2 nanoplates (SnS2-NPLs) provide the highest performances. Such SnS2-NPLs, incorporated into hierarchical SnS2/CN/GP nanocomposites, display excellent rate capabilities (536.5 mA h g−1 at 2.0 A g−1) and an outstanding stability (∼99.7% retention after 400 cycles), which are partially associated with a high pseudocapacitance contribution (88.8% at 1.0 mV s−1). The excellent electrochemical properties of these nanocomposites are ascribed to the synergy created between the three nanocomposite components: i) thin SnS2-NPLs provide a large surface for rapid Li-ion intercalation and a proper geometry to stand volume expansions during lithiation/delithiation cycles; ii) porous CN prevents SnS2-NPLs aggregation, habilitates efficient channels for Li-ion diffusion and buffer stresses associated to SnS2 volume changes; and iii) conductive GPs allow an efficient charge transport. © 2020 Elsevier Ltd

  • Stability of Pd3Pb Nanocubes during Electrocatalytic Ethanol Oxidation

    Yu X., Luo Z., Zhang T., Tang P., Li J., Wang X., Llorca J., Arbiol J., Liu J., Cabot A. Chemistry of Materials; 32 (5): 2044 - 2052. 2020. 10.1021/acs.chemmater.9b05094. IF: 9.567

    Intermetallic Pd3Pb nanocrystals with controlled size and cubic geometry exposing (100) facets are synthesized and tested as electrocatalysts for ethanol oxidation in alkaline media. We observe the ethanol oxidation activity and stability to be size-dependent. The 10 nm Pd3Pb nanocrystals display the highest initial current densities, but after few hundred cycles, the current density of smaller nanocrystals becomes much larger. All of the catalysts exhibit a pronounced current decay during the first 500 s of continuous operation, which is associated with the accumulation of strongly adsorbed reaction intermediates, blocking reaction sites. These adsorbed species can be removed by cycling the catalysts or maintaining them at slightly higher potentials for a short period of time to oxidize and later reduce the Pd surface. Such simple cleaning processes, that can be performed during operation breaks without cell disassembly, is sufficient to effectively remove the poisoning species adsorbed on the surface and recover the electrocatalytic activity. Copyright © 2020 American Chemical Society.

  • Synergistic computational-experimental discovery of highly selective ptcu nanocluster catalysts for acetylene semihydrogenation

    Ayodele O.B., Cai R., Wang J., Ziouani Y., Liang Z., Spadaro M.C., Kovnir K., Arbiol J., Akola J., Palmer R.E., Kolen'ko Y.V. ACS Catalysis; 10 (1): 451 - 457. 2020. 10.1021/acscatal.9b03539. IF: 12.350

    Semihydrogenation of acetylene (SHA) in an ethylene-rich stream is an important process for polymer industries. Presently, Pd-based catalysts have demonstrated good acetylene conversion (XC2H2), however, at the expense of ethylene selectivity (SC2H4). In this study, we have employed a systematic approach using density functional theory (DFT) to identify the best catalyst in a Cu-Pt system. The DFT results showed that with a 55 atom system at∼1.1 Pt/Cu ratio for Pt28Cu27/Al2O3, the d-band center shifted -2.2 eV relative to the Fermi level leading to electron-saturated Pt, which allows only adsorption of ethylene via a π -bond, resulting in theoretical 99.7% SC2H4 at nearly complete XC2H2. Based on the DFT results, Pt-Cu/Al2O3 (PtCu) and Pt/Al2O3 (Pt) nanocatalysts were synthesized via cluster beam deposition (CBD), and their properties and activities were correlated with the computational predictions. For bimetallic PtCu, the electron microscopy results show the formation of alloys. The bimetallic PtCu catalyst closely mimics the DFT predictions in terms of both electronic structure, as confirmed by X-ray photoelectron spectroscopy, and catalytic activity. The alloying of Pt with Cu was responsible for the high C2H4 specific yield resulting from electron transfer between Cu and Pt, thus making PtCu a promising catalyst for SHA. © 2019 American Chemical Society.

  • Tin Selenide Molecular Precursor for the Solution Processing of Thermoelectric Materials and Devices

    Zhang Y., Liu Y., Xing C., Xing C., Zhang T., Li M., Pacios M., Yu X., Arbiol J., Arbiol J., Llorca J., Cadavid D., Ibáñez M., Cabot A., Cabot A. ACS Applied Materials and Interfaces; 12 (24): 27104 - 27111. 2020. 10.1021/acsami.0c04331. IF: 8.758

    In the present work, we report a solution-based strategy to produce crystallographically textured SnSe bulk nanomaterials and printed layers with optimized thermoelectric performance in the direction normal to the substrate. Our strategy is based on the formulation of a molecular precursor that can be continuously decomposed to produce a SnSe powder or printed into predefined patterns. The precursor formulation and decomposition conditions are optimized to produce pure phase 2D SnSe nanoplates. The printed layer and the bulk material obtained after hot press displays a clear preferential orientation of the crystallographic domains, resulting in an ultralow thermal conductivity of 0.55 W m-1 K-1 in the direction normal to the substrate. Such textured nanomaterials present highly anisotropic properties with the best thermoelectric performance in plane, i.e., in the directions parallel to the substrate, which coincide with the crystallographic bc plane of SnSe. This is an unfortunate characteristic because thermoelectric devices are designed to create/harvest temperature gradients in the direction normal to the substrate. We further demonstrate that this limitation can be overcome with the introduction of small amounts of tellurium in the precursor. The presence of tellurium allows one to reduce the band gap and increase both the charge carrier concentration and the mobility, especially the cross plane, with a minimal decrease of the Seebeck coefficient. These effects translate into record out of plane ZT values at 800 K. Copyright © 2020 American Chemical Society.

  • Understanding galvanic replacement reactions: the case of Pt and Ag

    Merkoçi F., Patarroyo J., Russo L., Piella J., Genç A., Arbiol J., Bastús N.G., Puntes V. Materials Today Advances; 5 (100037) 2020. 10.1016/j.mtadv.2019.100037. IF: 0.000

    Synthesis of nanocrystals (NCs), where material science elements are addressed with organic chemistry precision techniques, is especially challenging and difficult to control. This difficulty arises from the increased complexity of the mineralization processes and the generation of a liquid-solid interface. These aspects, along with a strong susceptibility to reaction kinetics, ultimately translate into serious challenges for reproducibility and morphological control. By systematically varying the different parameters used to control the morphology of NCs, including complexing agents, coreducers, and cooxidants, the general reaction landscape can be mapped and the most stable and reproducible recipes can be identified. We apply this concept to the model transmetallation reaction between immiscible Pt and Ag forming hollow Pt NCs by galvanic replacement reactions. In this work, 648 synthetic recipes were performed and characterized per duplicate, from which a subset of 307 recipes leading to the controlled formation of hollow NCs were further analyzed to correlate reaction conditions with the final obtained structure and stability (reproducibility). As a result, we present robust general synthetic protocols leading to the ad hoc production of Pt-based hollow NCs with independent control of shell thickness, void size, surface roughness, and degree of porosity. © 2019 The Authors

  • ZnSe/N-doped carbon nanoreactor with multiple adsorption sites for stable lithium-sulfur batteries

    Yang D., Zhang C., Biendicho J.J., Han X., Liang Z., Du R., Li M., Li J., Arbiol J., Llorca J., Zhou Y., Morante J.R., Cabot A. ACS Nano; 14 (11): 15492 - 15504. 2020. 10.1021/acsnano.0c06112. IF: 14.588

    To commercially realize the enormous potential of lithium-sulfur batteries (LSBs) several challenges remain to be overcome. At the cathode, the lithium polysulfide (LiPS) shuttle effect must be inhibited and the redox reaction kinetics need to be substantially promoted. In this direction, this work proposes a cathode material based on a transition-metal selenide (TMSe) as both adsorber and catalyst and a hollow nanoreactor architecture: ZnSe/N-doped hollow carbon (ZnSe/NHC). It is here demonstrated both experimentally and by means of density functional theory that this composite provides three key benefits to the LSBs cathode: (i) A highly effective trapping of LiPS due to the combination of sulfiphilic sites of ZnSe, lithiophilic sites of NHC, and the confinement effect of the cage-based structure; (ii) a redox kinetic improvement in part associated with the multiple adsorption sites that facilitate the Li+ diffusion; and (iii) an easier accommodation of the volume expansion preventing the cathode damage due to the hollow design. As a result, LSB cathodes based on S@ZnSe/NHC are characterized by high initial capacities, superior rate capability, and an excellent stability. Overall, this work not only demonstrates the large potential of TMSe as cathode materials in LSBs but also probes the nanoreactor design to be a highly suitable architecture to enhance cycle stability. © 2020 American Chemical Society.


  • A low temperature solid state reaction to produce hollow MnxFe3-xO4 nanoparticles as anode for lithium-ion batteries

    Yu X., Zhang C., Luo Z., Zhang T., Liu J., Li J., Zuo Y., Biendicho J.J., Llorca J., Arbiol J., Morante J.R., Cabot A. Nano Energy; 66 (104199) 2019. 10.1016/j.nanoen.2019.104199. IF: 15.548

    Hollow MnxFe3-xO4 nanoparticles (NPs) with an average size of 15 nm are produced from the solid state reaction of Fe3O4–Mn3O4 heterostructures. These heterostructures are synthesized through the seeded-growth of Mn3O4 crystal domains on the surface of hollow Fe3O4 NPs obtained by the nanoscale Kirkendall effect. Fe3O4–Mn3O4 heterostructures are subsequently annealed at 500 °C, enough temperature to promote the interfusion of Fe and Mn ions, but without compromising the hollow geometry. MnxFe3-xO4 nanostructures are tested as anode in lithium-ion batteries (LIBs), delivering large lithium storage capacities and high-rate capabilities of 1054 mAh g−1 at 0.1 A g−1 and 369 mAh g−1 at 5 A g−1. Additionally, hollow MnxFe3-xO4 NPs display long cycling stability, with a capacity up to 887 mAh g−1 at 0.3 A g−1 after 450 cycles. The excellent performance of hollow MnxFe3-xO4 NPs as anode for LIBs is associated with their crystal structure, composition, and the presence of carbonized ligands, which further promote electrical conductivity and buffer the volume changes during cycling. Additionally, the small particle size and hollow morphology improves the lithium kinetics, structural stability and cycling performance. © 2019

  • Ballistic InSb Nanowires and Networks via Metal-Sown Selective Area Growth

    Aseev P., Wang G., Binci L., Singh A., Martí-Sánchez S., Botifoll M., Stek L.J., Bordin A., Watson J.D., Boekhout F., Abel D., Gamble J., Van Hoogdalem K., Arbiol J., Kouwenhoven L.P., De Lange G., Caroff P. Nano Letters; 19 (12): 9102 - 9111. 2019. 10.1021/acs.nanolett.9b04265. IF: 12.279

    Selective area growth is a promising technique to realize semiconductor-superconductor hybrid nanowire networks, potentially hosting topologically protected Majorana-based qubits. In some cases, however, such as the molecular beam epitaxy of InSb on InP or GaAs substrates, nucleation and selective growth conditions do not necessarily overlap. To overcome this challenge, we propose a metal-sown selective area growth (MS SAG) technique, which allows decoupling selective deposition and nucleation growth conditions by temporarily isolating these stages. It consists of three steps: (i) selective deposition of In droplets only inside the mask openings at relatively high temperatures favoring selectivity, (ii) nucleation of InSb under Sb flux from In droplets, which act as a reservoir of group III adatoms, done at relatively low temperatures, favoring nucleation of InSb, and (iii) homoepitaxy of InSb on top of the formed nucleation layer under a simultaneous supply of In and Sb fluxes at conditions favoring selectivity and high crystal quality. We demonstrate that complex InSb nanowire networks of high crystal and electrical quality can be achieved this way. We extract mobility values of 10※000-25※000 cm2 V-1 s-1 consistently from field-effect and Hall mobility measurements across single nanowire segments as well as wires with junctions. Moreover, we demonstrate ballistic transport in a 440 nm long channel in a single nanowire under a magnetic field below 1 T. We also extract a phase-coherent length of â&circ;¼8 μm at 50 mK in mesoscopic rings. © 2019 American Chemical Society.

  • Boosting Photoelectrochemical Water Oxidation of Hematite in Acidic Electrolytes by Surface State Modification

    Tang P.-Y., Han L.-J., Hegner F.S., Paciok P., Biset-Peiró M., Du H.-C., Wei X.-K., Jin L., Xie H.-B., Shi Q., Andreu T., Lira-Cantú M., Heggen M., Dunin-Borkowski R.E., López N., Galán-Mascarós J.R., Morante J.R., Arbiol J. Advanced Energy Materials; 9 (34, 1901836) 2019. 10.1002/aenm.201901836. IF: 24.884

    State-of-the-art water-oxidation catalysts (WOCs) in acidic electrolytes usually contain expensive noble metals such as ruthenium and iridium. However, they too expensive to be implemented broadly in semiconductor photoanodes for photoelectrochemical (PEC) water splitting devices. Here, an Earth-abundant CoFe Prussian blue analogue (CoFe-PBA) is incorporated with core–shell Fe2O3/Fe2TiO5 type II heterojunction nanowires as composite photoanodes for PEC water splitting. Those deliver a high photocurrent of 1.25 mA cm−2 at 1.23 V versus reversible reference electrode in acidic electrolytes (pH = 1). The enhancement arises from the synergic behavior between the successive decoration of the hematite surface with nanolayers of Fe2TiO5 and then, CoFe-PBA. The underlying physical mechanism of performance enhancement through formation of the Fe2O3/Fe2TiO5/CoFe-PBA heterostructure reveals that the surface states’ electronic levels of hematite are modified such that an interfacial charge transfer becomes kinetically favorable. These findings open new pathways for the future design of cheap and efficient hematite-based photoanodes in acidic electrolytes. © 2019 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

  • Chromium phosphide CrP as highly active and stable electrocatalysts for oxygen electroreduction in alkaline media

    Liu J., Yu X., Du R., Zhang C., Zhang T., Llorca J., Arbiol J., Wang Y., Meyns M., Cabot A. Applied Catalysis B: Environmental; 256 (117846) 2019. 10.1016/j.apcatb.2019.117846. IF: 14.229

    Catalysts for oxygen reduction reaction (ORR) are key components in emerging energy technologies such as fuel cells and metal-air batteries. Developing low-cost, high performance and stable electrocatalysts is critical for the extensive implementation of these technologies. Herein, we present a procedure to prepare colloidal chromium phosphide CrP nanocrystals and we test their performance as ORR electrocatalyst. CrP-based catalysts exhibited remarkable activities with a limiting current density of 4.94 mA cm−2 at 0.2 V, a half-potential of 0.65 V and an onset potential of 0.8 V at 1600 rpm, which are comparable to commercial Pt/C. Advantageously, CrP-based catalysts displayed much higher stabilities and higher tolerances to methanol in alkaline solution. Using density functional theory calculations, we demonstrate CrP to provide a very strong chemisorption of O2 that facilitates its reduction and explains the excellent ORR performance experimentally demonstrated. © 2019

  • Combined High Catalytic Activity and Efficient Polar Tubular Nanostructure in Urchin-Like Metallic NiCo2Se4 for High-Performance Lithium–Sulfur Batteries

    Zhang C., Biendicho J.J., Zhang T., Du R., Li J., Yang X., Arbiol J., Zhou Y., Morante J.R., Cabot A. Advanced Functional Materials; 29 (34, 1903842) 2019. 10.1002/adfm.201903842. IF: 15.621

    Urchin-shaped NiCo2Se4 (u-NCSe) nanostructures as efficient sulfur hosts are synthesized to overcome the limitations of lithium–sulfur batteries (LSBs). u-NCSe provides a beneficial hollow structure to relieve volumetric expansion, a superior electrical conductivity to improve electron transfer, a high polarity to promote absorption of lithium polysulfides (LiPS), and outstanding electrocatalytic activity to accelerate LiPS conversion kinetics. Owing to these excellent qualities as cathode for LSBs, S@u-NCSe delivers outstanding initial capacities up to 1403 mAh g−1 at 0.1 C and retains 626 mAh g−1 at 5 C with exceptional rate performance. More significantly, a very low capacity decay rate of only 0.016% per cycle is obtained after 2000 cycles at 3 C. Even at high sulfur loading (3.2 mg cm−2), a reversible capacity of 557 mAh g−1 is delivered after 600 cycles at 1 C. Density functional theory calculations further confirm the strong interaction between NCSe and LiPS, and cytotoxicity measurements prove the biocompatibility of NCSe. This work not only demonstrates that transition metal selenides can be promising candidates as sulfur host materials, but also provides a strategy for the rational design and the development of LSBs with long-life and high-rate electrochemical performance. © 2019 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

  • Compositionally tuned Ni x Sn alloys as anode materials for lithium-ion and sodium-ion batteries with a high pseudocapacitive contribution

    Li J., Xu X., Luo Z., Zhang C., Yu X., Zuo Y., Zhang T., Tang P., Arbiol J., Llorca J., Liu J., Cabot A. Electrochimica Acta; 304: 246 - 254. 2019. 10.1016/j.electacta.2019.02.098. IF: 5.383

    Nickel tin alloy nanoparticles (NPs) with tuned composition Ni x Sn (0.6 ≤ x ≤ 1.9) were synthesized by a solution-based procedure and used as anode materials for Li-ion batteries (LIBs) and Na-ion batteries (SIBs). Among the compositions tested, Ni 0.9 Sn-based electrodes exhibited the best performance in both LIBs and SIBs. As LIB anodes, Ni 0.9 Sn-based electrodes delivered charge-discharge capacities of 980 mAh g −1 after 340 cycles at 0.2 A g −1 rate, which surpassed their maximum theoretical capacity considering that only Sn is lithiated. A kinetic characterization of the charge-discharge process demonstrated the electrode performance to be aided by a significant pseudocapacitive contribution that compensated for the loss of energy storage capacity associated to the solid-electrolyte interphase formation. This significant pseudocapacitive contribution, which not only translated into higher capacities but also longer durability, was associated to the small size of the crystal domains and the proper electrode composition. The performance of Ni x Sn-based electrodes toward Na-ion storage was also characterized, reaching significant capacities above 200 mAh g −1 at 0.1 A g −1 but with a relatively fast fade over 120 continuous cycles. A relatively larger pseudocapacitive contribution was obtained in Ni x Sn-based electrodes for SIBs when compared with LIBs, consistently with the lower contribution of the Na ion diffusion associated to its larger size. © 2019 Elsevier Ltd

  • Coordination Polymer to Atomically Thin, Holey, Metal-Oxide Nanosheets for Tuning Band Alignment

    Mofarah S.S., Adabifiroozjaei E., Pardehkhorram R., Assadi M.H.N., Hinterstein M., Yao Y., Liu X., Ghasemian M.B., Kalantar-Zadeh K., Mehmood R., Cazorla C., Shahmiri R., Bahmanrokh G., Bhattacharyya S., Spadaro M.C., Arbiol J., Lim S., Xu Y., Arandiyan H., Scott J., Koshy P., Sorrell C.C. Advanced Materials; 31 (52, 1905288) 2019. 10.1002/adma.201905288. IF: 25.809

    Holey 2D metal oxides have shown great promise as functional materials for energy storage and catalysts. Despite impressive performance, their processing is challenged by the requirement of templates plus capping agents or high temperatures; these materials also exhibit excessive thicknesses and low yields. The present work reports a metal-based coordination polymer (MCP) strategy to synthesize polycrystalline, holey, metal oxide (MO) nanosheets with thicknesses as low as two-unit cells. The process involves rapid exfoliation of bulk-layered, MCPs (Ce-, Ti-, Zr-based) into atomically thin MCPs at room temperature, followed by transformation into holey 2D MOs upon the removal of organic linkers in aqueous solution. Further, this work represents an extra step for decorating the holey nanosheets using precursors of transition metals to engineer their band alignments, establishing a route to optimize their photocatalysis. The work introduces a simple, high-yield, room-temperature, and template-free approach to synthesize ultrathin holey nanosheets with high-level functionalities. © 2019 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

  • Co–Sn Nanocrystalline Solid Solutions as Anode Materials in Lithium-Ion Batteries with High Pseudocapacitive Contribution

    Li J., Xu X., Luo Z., Zhang C., Zuo Y., Zhang T., Tang P., Infante-Carrió M.F., Arbiol J., Llorca J., Liu J., Cabot A. ChemSusChem; 12 (7): 1451 - 1458. 2019. 10.1002/cssc.201802662. IF: 7.804

    Co–Sn solid-solution nanoparticles with Sn crystal structure and tuned metal ratios were synthesized by a facile one pot solution-based procedure involving the initial reduction of a Sn precursor followed by incorporation of Co within the Sn lattice. These nanoparticles were used as anode materials for Li-ion batteries. Among the different compositions tested, Co 0.7 Sn and Co 0.9 Sn electrodes provided the highest capacities with values above 1500 mAh g −1 at a current density of 0.2 A g −1 after 220 cycles, and up to 800 mAh g −1 at 1.0 A g −1 after 400 cycles. Up to 81 % pseudocapacitance contribution was measured for these electrodes at a sweep rate of 1.0 mV s −1 , thereby indicating fast kinetics and long durability. The excellent performance of Co–Sn nanoparticle alloy-based electrodes was attributed to both the small size of the crystal domains and their suitable composition, which buffered volume changes of Sn and contributed to a suitable electrode restructuration. © 2019 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

  • Degradation and regeneration mechanisms of NiO protective layers deposited by ALD on photoanodes

    Ros C., Andreu T., David J., Arbiol J., Morante J.R. Journal of Materials Chemistry A; 7 (38): 21892 - 21902. 2019. 10.1039/c9ta08638b. IF: 10.733

    The use of high pH electrolytes requires protective layers to avoid corrosion in photoanodes based on semiconductors like silicon. NiO is one of the materials that comply with the requirements for transparency, conductivity, chemical stability and catalysis on the surface in contact with the electrolyte. Here, NiO layers have been deposited by atomic layer deposition (ALD) at low temperatures, and their stability is analyzed over 1000 hours. Due to the layer structure characteristics, the best overall performance was achieved at 100 °C deposition temperature. By electrochemical measurements progressive time dependent degradation under anodic working conditions is observed, attributed to the formation of higher nickel oxidation states at the electrode/electrolyte interface as a main degradation mechanism, resulting in an OER overpotential increase. Another minor degradation mechanism affects the optical surface quality and gives rise to a loss of photon absorption efficiency on the scale of hundreds of hours. A regeneration process based on in situ periodic cyclic voltammetry, bringing the electrodes to cathodic conditions every 3, 12 or 48 hours, has been shown to partially reverse the main degradation mechanism achieving 85% stability over 1000 hours in a study with over 10 mA cm-2 photocurrent densities. © 2019 The Royal Society of Chemistry.

  • Engineering surface states of hematite based photoanodes for boosting photoelectrochemical water splitting

    Tang P., Arbiol J. Nanoscale Horizons; 4 (6): 1256 - 1276. 2019. 10.1039/c9nh00368a. IF: 9.095

    Hematite-based photoanodes are promising candidates for photoelectrochemical water splitting. However, the performance of pristine hematite semiconductors is unsatisfactory due to charge recombination occurring at different interfaces: Back contact, bulk and semiconductor/electrolyte interfaces. Increasing efforts have been focused on enhancing the performance of hematite based photoanodes via nanostructure control, doping, heterojunction construction, and surface modification with a secondary semiconductor or an oxygen evolution electrocatalyst. Most of the previous studies attributed the enhanced PEC water splitting performance to the changes in the donor density via doping, the formation of type II heterojunction via a secondary semiconductor coating and the improved water oxidation kinetics via coating oxygen evolution electrocatalysts. However, the role of surface states presented at the semiconductor/electrolyte interfaces of hematite-based photoanodes has been overlooked in previous investigations, which virtually play a critical role in determining the photoelectrochemical water oxidation process. In this review, we summarize the recent progress of various techniques employed for the detection of surface states of hematite photoanodes and highlight the important role of modifying surface states in the development of high performance hematite based photoanodes for photoelectrochemical water splitting application. The challenges and future prospects in the study of hematite based photoanodes are also discussed. © 2019 The Royal Society of Chemistry.

  • Enhanced Hetero-Junction Quality and Performance of Kesterite Solar Cells by Aluminum Hydroxide Nanolayers and Efficiency Limitation Revealed by Atomic-resolution Scanning Transmission Electron Microscopy

    Xie H., Sánchez Y., Tang P., Espíndola-Rodríguez M., Guc M., Calvo-Barrio L., López-Marino S., Liu Y., Morante J.R., Cabot A., Izquierdo-Roca V., Arbiol J., Pérez-Rodríguez A., Saucedo E. Solar RRL; 3 (2, 1800279) 2019. 10.1002/solr.201800279.

    A strategy for interface engineering of hetero-junctions in kesterite solar cells by using Al(OH)3 is demonstrated. The hydroxide nanolayers are prepared via a facile and fast wet chemical route, based on an aqueous solution of aluminum chlorides and thioacetamide. Considerable enhancement of open circuit voltage (Voc) (30–60 mV) and fill factor (FF) (10–20%) after this chemical treatment are observed, achieving a champion conversion efficiency of 9.1% and a champion FF of 70% (among the best FF in kesterite solar cells). The functional mechanism is systematically studied by current-voltage, capacitance-voltage, temperature dependence of current–voltage and photoluminescence measurements, which reveal that Al(OH)3 nanolayers can effectively reduce the interface recombination and largely improve the shunt resistance. Furthermore, atomic resolution high angle annular dark field scanning transmission electron microscopy (HAADF-STEM) evidences the epitaxial relationship of Al(OH)3 with kesterite and CdS, indicating the benign and effective interface passivation achieved by this chemical treatment. Finally, based on HAADF-STEM and electron energy loss spectroscopy mappings, insights into the efficiency limiting and beneficial factors for CZTSSe solar cells, as well as suggestions to further improve both the bulk and related interfaces are presented. © 2018 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

  • From rational design of a new bimetallic MOF family with tunable linkers to OER catalysts

    Zhang X., Luo J., Wan K., Plessers D., Sels B., Song J., Chen L., Zhang T., Tang P., Morante J.R., Arbiol J., Fransaer J. Journal of Materials Chemistry A; 7 (4): 1616 - 1628. 2019. 10.1039/c8ta08508k. IF: 10.733

    Innovative bimetallic MOFs offer more possibilities to further tailor the properties of MOFs, which have attracted great attention for wide applications. However, it is still a great challenge to rationally design bimetallic MOFs due to the lack of a tunable and reasonable hybrid structure architecture. Herein, a new series of bimetallic metal-organic frameworks (MOFs) with tunable pillar linkers were prepared by a one-step synthesis method. These bimetallic MOFs retain the same crystal structure when the mole fraction (based on metal) of the two metals changes from 0 to 1 and both metal ions occupy random nodal positions. The incorporation of a second metal cation has a large influence on the intrinsic properties (e.g. thermal stabilities and band gaps) of the MOFs. Furthermore, these bimetallic MOFs were used as self-sacrificial templates to prepare bimetal oxide catalysts for the oxygen evolution reaction (OER). After pyrolysis, a porous and hierarchical honeycomb-like structure with carbon network covered (bi)metal oxides is formed. Among all the bimetallic MOF-derived catalysts, CoNi1@C showed the best performance for the OER with the lowest Tafel slopes (55.6 mV dec -1 ) and overpotentials (335 mV on a glassy carbon electrode and 276 mV on Ni foam) at a current density of 10 mA cm -2 , which is higher than those of state-of-the-art Co-Ni mixed oxide catalysts derived from MOFs for the OER. Our results indicate that the incorporation of a second metal ion is a promising strategy to tailor the properties of MOFs. More importantly, this new bimetallic MOF family with tunable linkers is expected to serve as a flexible assembly platform to offer broad possibilities for practical applications of MOFs. © 2019 The Royal Society of Chemistry.

  • Ge-Doped ZnSb/β-Zn4Sb3 Nanocomposites with High Thermoelectric Performance

    Ostovari Moghaddam A., Shokuhfar A., Zhang Y., Zhang T., Cadavid D., Arbiol J., Cabot A. Advanced Materials Interfaces; 6 (18, 1900467) 2019. 10.1002/admi.201900467. IF: 4.713

    ZnSb/β-Zn4Sb3 nanocomposites are produced from Zn1.1− xGexSb mixtures using a two-step process. First, proper amounts of the three elements are mixed, melted, and reacted at 800 K. During this process, the nonstoichiometric mixture is crystallized in a combination of ZnSb and β-Zn4Sb3 phases. Then, the material is ball milled and subsequently hot pressed. Through this process, a dense ZnSb/β-Zn4Sb3 composite, consisting of β-Zn4Sb3 nanoinclusions embedded within a ZnSb matrix, is formed. The particular phase distribution of the final ZnSb/β-Zn4Sb3 composites is a consequence of the harder and more brittle nature of ZnSb than Zn4Sb3, which translates into a stronger reduction of the size of the ZnSb crystal domains during ball milling. This small particle size and the high temperature generated during ball milling result in the melting of the ZnSb phase and the posterior crystallization of the two phases in a ZnSb/β-Zn4Sb3 matrix/nanoinclusion-type phase distribution. This particular phase distribution and the presence of Ge result in excellent thermoelectric performances, with power factors up to 1.5 mW m−1 K−2, lattice thermal conductivities down to 0.74 W m−1 K−1, and a thermoelectric figures of merit, ZT, up to 1.2 at 650 K, which is among the highest ZT values reported for ZnSb. © 2019 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

  • Graphene-supported palladium phosphide PdP2 nanocrystals for ethanol electrooxidation

    Liu J., Luo Z., Li J., Yu X., Llorca J., Nasiou D., Arbiol J., Meyns M., Cabot A. Applied Catalysis B: Environmental; 242: 258 - 266. 2019. 10.1016/j.apcatb.2018.09.105. IF: 14.229

    We present a procedure to produce single-phase PdP2 nanocrystals (NCs). The approach involves the reaction of palladium(II) acetylacetonate and hexamethylphosphoroustriamide to nucleate defective Pd5P2 nanoparticles that subsequently, with further phosphorous incorporation, crystallize into PdP2. The synthesized PdP2 NCs were supported on reduced graphene oxide (rGO) and applied as electrocatalysts for ethanol oxidation. The activity of PdP2 toward the ethanol oxidation reaction (EOR) was over a threefold higher than that of Pd NCs prepared under similar conditions. Even better performance was obtained from PdP2 NCs supported on rGO, which showed current densities up to 51.4 mA cm−2 and mass activities of 1.60 A mg-1 Pd, that is 4.8 and 15 times higher than Pd NCs. Besides, PdP2 NCs and PdP2/rGO catalysts showed improved stability during EOR than Pd NCs and Pd/rGO. © 2018 Elsevier B.V.

  • Hierarchical Porous Ni 3 S 4 with Enriched High-Valence Ni Sites as a Robust Electrocatalyst for Efficient Oxygen Evolution Reaction

    Wan K., Luo J., Zhou C., Zhang T., Arbiol J., Lu X., Mao B.-W., Zhang X., Fransaer J. Advanced Functional Materials; 29 (18, 1900315) 2019. 10.1002/adfm.201900315. IF: 15.621

    Electrochemical water splitting is a common way to produce hydrogen gas, but the sluggish kinetics of the oxygen evolution reaction (OER) significantly limits the overall energy conversion efficiency of water splitting. In this work, a highly active and stable, meso–macro hierarchical porous Ni 3 S 4 architecture, enriched in Ni 3+ is designed as an advanced electrocatalyst for OER. The obtained Ni 3 S 4 architectures exhibit a relatively low overpotential of 257 mV at 10 mA cm −2 and 300 mV at 50 mA cm −2 . Additionally, this Ni 3 S 4 catalyst has excellent long-term stability (no degradation after 300 h at 50 mA cm −2 ). The outstanding OER performance is due to the high concentration of Ni 3+ and the meso–macro hierarchical porous structure. The presence of Ni 3+ enhances the chemisorption of OH − , which facilitates electron transfer to the surface during OER. The hierarchical porosity increases the number of exposed active sites, and facilitates mass transport. A water-splitting electrolyzer using the prepared Ni 3 S 4 as the anode catalyst and Pt/C as the cathode catalyst achieves a low cell voltage of 1.51 V at 10 mA cm −2 . Therefore, this work provides a new strategy for the rational design of highly active OER electrocatalysts with high valence Ni 3+ and hierarchical porous architectures. © 2019 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

  • High Magnetic Coercivity in Nanostructured Mn3O4 Thin Films Obtained by Chemical Vapor Deposition

    Bigiani L., Hassan M., Peddis D., Maccato C., Varvaro G., Sada C., Bontempi E., Martí-Sánchez S., Arbiol J., Barreca D. ACS Applied Nano Materials; 2 (3): 1704 - 1712. 2019. 10.1021/acsanm.9b00141. IF: 0.000

    Nanostructured α-Mn3O4 (haussmannite) thin films consisting of evenly interconnected nanoaggregates were prepared on Si(100) substrates by chemical vapor deposition from a Mn(II) diketonate-diamine precursor under different reaction atmospheres (dry vs wet O2) and total operating pressures. The combination of chemico-physical results obtained by the joint use of complementary techniques enabled us to demonstrate the obtainment of high-purity Mn3O4 materials free from other manganese oxide phases, characterized by controllable structural and morphological characteristics as a function of the adopted processing conditions. Magnetic properties were investigated by analyzing temperature dependence (i.e., field-cooled and zero-field-cooled measurements) and field-dependence of the magnetization behavior. The obtained films show bulk-like magnetic properties, together with extraordinarily high low-temperature in-plane coercivities (up to ∼1 T). The possibility to tailor these values by varying the content of microstructural defects may foster the implementation of the obtained films in eventual technological applications. © Copyright © 2019 American Chemical Society.

  • Hollow PdAg-CeO2 heterodimer nanocrystals as highly structured heterogeneous catalysts

    Patarroyo J., Delgado J.A., Merkoçi F., Genç A., Sauthier G., Llorca J., Arbiol J., Bastus N.G., Godard C., Claver C., Puntes V. Scientific Reports; 9 (1, 18776) 2019. 10.1038/s41598-019-55105-x. IF: 4.011

    In the present work, hollow PdAg-CeO2 heterodimer nanocrystals (NCs) were prepared and tested as catalysts for the selective hydrogenation of alkynes. These nanostructures combine for the first time the beneficial effect of alloying Pd with Ag in a single NC hollow domain with the formation of active sites at the interface with the CeO2 counterpart in an additive manner. The PdAg-CeO2 NCs display excellent alkene selectivity for aliphatic alkynes. For the specific case of hydrogenation of internal alkynes such as 4-octyne, very low over-hydrogenation and isomerization products were observed over a full conversion regime, even after prolonged reaction times. These catalytic properties were remarkably superior in comparison to standard catalysts. The promotion of Ag on the moderation of the reactivity of the Pd phase, in combination with the creation of interfacial sites with the CeO2 moiety in the same nanostructure, is pointed as the responsible of such a remarkable catalytic performance. © 2019, The Author(s).

  • Hydrogen photogeneration using ternary CuGaS2-TiO2-Pt nanocomposites

    Caudillo-Flores U., Kubacka A., Berestok T., Zhang T., Llorca J., Arbiol J., Cabot A., Fernández-García M. International Journal of Hydrogen Energy; 2019. 10.1016/j.ijhydene.2019.11.019. IF: 4.084

    In this contribution we synthesized ternary CuGaS2-TiO2-Pt materials. The semiconductor components were surface functionalized with mercapto-alifatic acids to drive their linking and were platinized prior to or after contact between the semiconductors. The corresponding samples were utilized in the photo-production of hydrogen using methanol as a sacrificial agent. The testing under UV and visible illumination conditions together with the calculation of the true quantum efficiency of the process demonstrate the outstanding performance of these ternary materials under sunlight operation. Optimum activity was achieved for samples having a 3 to 5 wt % of the chalcogenide and a selective interaction of the noble metal with the major oxide component. The physico-chemical characterization and particularly the use of photoluminescence spectroscopy showed that photo-activity is controlled by charge separation under illumination, which drives to charge location of electrons and holes in different components of the powders and the efficient use of charge carriers in the chemical reaction. © 2019 Hydrogen Energy Publications LLC

  • III-V Integration on Si(100): Vertical Nanospades

    Güniat L., Martí-Sánchez S., Garcia O., Boscardin M., Vindice D., Tappy N., Friedl M., Kim W., Zamani M., Francaviglia L., Balgarkashi A., Leran J.-B., Arbiol J., Fontcuberta I Morral A. ACS Nano; 13 (5): 5833 - 5840. 2019. 10.1021/acsnano.9b01546. IF: 13.903

    III-V integration on Si(100) is a challenge: controlled vertical vapor liquid solid nanowire growth on this platform has not been reported so far. Here we demonstrate an atypical GaAs vertical nanostructure on Si(100), coined nanospade, obtained by a nonconventional droplet catalyst pinning. The Ga droplet is positioned at the tip of an ultrathin Si pillar with a radial oxide envelope. The pinning at the Si/oxide interface allows the engineering of the contact angle beyond the Young-Dupré equation and the growth of vertical nanospades. Nanospades exhibit a virtually defect-free bicrystalline nature. Our growth model explains how a pentagonal twinning event at the initial stages of growth provokes the formation of the nanospade. The optical properties of the nanospades are consistent with the high crystal purity, making these structures viable for use in integration of optoelectronics on the Si(100) platform. © 2019 American Chemical Society.

  • In Situ Electrochemical Oxidation of Cu2S into CuO Nanowires as a Durable and Efficient Electrocatalyst for Oxygen Evolution Reaction

    Zuo Y., Liu Y., Li J., Du R., Han X., Zhang T., Arbiol J., Divins N.J., Llorca J., Guijarro N., Sivula K., Cabot A. Chemistry of Materials; 31 (18): 7732 - 7743. 2019. 10.1021/acs.chemmater.9b02790. IF: 10.159

    Development of cost-effective oxygen evolution catalysts is of capital importance for the deployment of large-scale energy-storage systems based on metal-air batteries and reversible fuel cells. In this direction, a wide range of materials have been explored, especially under more favorable alkaline conditions, and several metal chalcogenides have particularly demonstrated excellent performances. However, chalcogenides are thermodynamically less stable than the corresponding oxides and hydroxides under oxidizing potentials in alkaline media. Although this instability in some cases has prevented the application of chalcogenides as oxygen evolution catalysts and it has been disregarded in some others, we propose to use it in our favor to produce high-performance oxygen evolution catalysts. We characterize here the in situ chemical, structural, and morphological transformation during the oxygen evolution reaction (OER) in alkaline media of Cu2S into CuO nanowires, mediating the intermediate formation of Cu(OH)2. We also test their OER activity and stability under OER operation in alkaline media and compare them with the OER performance of Cu(OH)2 and CuO nanostructures directly grown on the surface of a copper mesh. We demonstrate here that CuO produced from in situ electrochemical oxidation of Cu2S displays an extraordinary electrocatalytic performance toward OER, well above that of CuO and Cu(OH)2 synthesized without this transformation. © 2019 American Chemical Society.

  • Insight into the Degradation Mechanisms of Atomic Layer Deposited TiO2 as Photoanode Protective Layer

    Ros C., Carretero N.M., David J., Arbiol J., Andreu T., Morante J.R. ACS Applied Materials and Interfaces; 11 (33): 29725 - 29735. 2019. 10.1021/acsami.9b05724. IF: 8.456

    Around 100 nm thick TiO2 layers deposited by atomic layer deposition (ALD) have been investigated as anticorrosion protective films for silicon-based photoanodes decorated with 5 nm NiFe catalyst in highly alkaline electrolyte. Completely amorphous layers presented high resistivity; meanwhile, the ones synthesized at 300 °C, having a fully anatase crystalline TiO2 structure, introduced insignificant resistance, showing direct correlation between crystallization degree and electrical conductivity. The conductivity through crystalline TiO2 layers has been found not to be homogeneous, presenting preferential conduction paths attributed to grain boundaries and defects within the crystalline structure. A correlation between the conductivity atomic force microscopy measurements and grain interstitials can be seen, supported by high-resolution transmission electron microscopy cross-sectional images presenting defective regions in crystalline TiO2 grains. It was found that the conduction mechanism goes through the injection of electrons coming from water oxidation from the electrocatalyst into the TiO2 conduction band. Then, electrons are transported to the Si/SiOx/TiO2 interface where electrons recombine with holes given by the p+n-Si junction. No evidences of intra-band-gap states in TiO2 responsible of conductivity have been detected. Stability measurements of fully crystalline samples over 480 h in anodic polarization show a continuous current decay. Electrochemical impedance spectroscopy allows to identify that the main cause of deactivation is associated with the loss of TiO2 electrical conductivity, corresponding to a self-passivation mechanism. This is proposed to reflect the effect of OH- ions diffusing in the TiO2 structure in anodic conditions by the electric field. This fact proves that a modification takes place in the defective zone of the layer, blocking the ability to transfer electrical charge through the layer. According to this mechanism, a regeneration of the degradation process is demonstrated possible based on ultraviolet illumination, which contributes to change the occupancy of TiO2 electronic states and to recover the defective zone's conductivity. These findings confirm the connection between the structural properties of the ALD-deposited polycrystalline layer and the degradation mechanisms and thus highlight main concerns toward fabricating long-lasting metal-oxide protective layers for frontal illuminated photoelectrodes. Copyright © 2019 American Chemical Society.

  • Ligand-mediated band engineering in bottom-up assembled SnTe nanocomposites for thermoelectric energy conversion

    Ibañ ez M., Hasler R., Genc A., Liu Y., Kuster B., Schuster M., Dobrozhan O., Cadavid D., Arbiol J., Cabot A., Kovalenko M.V. Journal of the American Chemical Society; 141 (20): 8025 - 8029. 2019. 10.1021/jacs.9b01394. IF: 14.695

    The bottom-up assembly of colloidal nanocrystals is a versatile methodology to produce composite nanomaterials with precisely tuned electronic properties. Beyond the synthetic control over crystal domain size, shape, crystal phase, and composition, solution-processed nanocrystals allow exquisite surface engineering. This provides additional means to modulate the nanomaterial characteristics and particularly its electronic transport properties. For instance, inorganic surface ligands can be used to tune the type and concentration of majority carriers or to modify the electronic band structure. Herein, we report the thermoelectric properties of SnTe nanocomposites obtained from the consolidation of surface-engineered SnTe nanocrystals into macroscopic pellets. A CdSe-based ligand is selected to (i) converge the light and heavy bands through partial Cd alloying and (ii) generate CdSe nanoinclusions as a secondary phase within the SnTe matrix, thereby reducing the thermal conductivity. These SnTe-CdSe nanocomposites possess thermoelectric figures of merit of up to 1.3 at 850 K, which is, to the best of our knowledge, the highest thermoelectric figure of merit reported for solution-processed SnTe. © 2019 American Chemical Society

  • MoS x @NiO Composite Nanostructures: An Advanced Nonprecious Catalyst for Hydrogen Evolution Reaction in Alkaline Media

    Ibupoto Z.H., Tahira A., Tang P., Liu X., Morante J.R., Fahlman M., Arbiol J., Vagin M., Vomiero A. Advanced Functional Materials; 29 (7, 1807562) 2019. 10.1002/adfm.201807562. IF: 15.621

    The design of the earth-abundant, nonprecious, efficient, and stable electrocatalysts for efficient hydrogen evolution reaction (HER) in alkaline media is a hot research topic in the field of renewable energies. A heterostructured system composed of MoS x deposited on NiO nanostructures (MoS x @NiO) as a robust catalyst for water splitting is proposed here. NiO nanosponges are applied as cocatalyst for MoS 2 in alkaline media. Both NiO and MoS 2 @NiO composites are prepared by a hydrothermal method. The NiO nanostructures exhibit sponge-like morphology and are completely covered by the sheet-like MoS 2 . The NiO and MoS 2 exhibit cubic and hexagonal phases, respectively. In the MoS x @NiO composite, the HER experiment in 1 m KOH electrolyte results in a low overpotential (406 mV) to produce 10 mA cm −2 current density. The Tafel slope for that case is 43 mV per decade, which is the lowest ever achieved for MoS 2 -based electrocatalyst in alkaline media. The catalyst is highly stable for at least 13 h, with no decrease in the current density. This simple, cost-effective, and environmentally friendly methodology can pave the way for exploitation of MoS x @NiO composite catalysts not only for water splitting, but also for other applications such as lithium ion batteries, and fuel cells. © 2019 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

  • Multilayered Hematite Nanowires with Thin-Film Silicon Photovoltaics in an All-Earth-Abundant Hybrid Tandem Device for Solar Water Splitting

    Urbain F., Tang P., Smirnov V., Welter K., Andreu T., Finger F., Arbiol J., Morante J.R. ChemSusChem; 12 (7): 1428 - 1436. 2019. 10.1002/cssc.201802845. IF: 7.804

    The concept of hybrid tandem device structures that combine metal oxides with thin-film semiconducting photoabsorbers holds great promise for large-scale, robust, and cost-effective bias-free photoelectrochemical water splitting (PEC-WS). This work highlights important steps toward the efficient coupling of high-performance hematite photoanodes with multijunction thin-film silicon photocathodes providing high bias-free photocurrent density. The hybrid PEC-WS device is optimized by testing three types of multijunction silicon photocathodes with the hematite photoanode: amorphous silicon (a-Si:H) tandem: a-Si:H/a-Si:H and triple junction with microcrystalline silicon (μc-Si:H): a-Si:H/a-Si:H/μc-Si:H and a-Si:H/μc-Si:H/μc-Si:H. The results provide evidence that the multijunction structures offer high flexibility for hybrid tandem devices with regard to tunable photovoltages and spectral matching. Furthermore, both photoanode and photocathode are tested under various electrolyte and light concentration conditions, respectively, with respect to their photoelectrochemical performance and stability. A 27 % enhancement in the solar-to-hydrogen conversion efficiency is observed upon concentrating light from 100 to 300 mW cm −2 . Ultimately, bias-free water splitting is demonstrated, with a photocurrent density of 4.6 mA cm −2 (under concentrated illumination) paired with excellent operation stability for more than 24 h of the all-earth-abundant and low-cost hematite/silicon tandem PEC-WS device. © 2019 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

  • On the role of ceria in Ni-Al2O3 catalyst for CO2 plasma methanation

    Biset-Peiró M., Guilera J., Zhang T., Arbiol J., Andreu T. Applied Catalysis A: General; 575: 223 - 229. 2019. 10.1016/j.apcata.2019.02.028. IF: 4.630

    The effect of Ce loading content on Ni-CeO2/Al2O3 catalysts for CO2 plasma methanation was evaluated. Catalysts were prepared by one-pot evaporation-induced self-assembly, Ni content was fixed at 15 wt. %, while CeO2 ranged 0–50 wt. %. The catalysts performances were tested under atmospheric pressure in two operation modes, thermal- and plasma-catalysis. As for conventional thermal catalysis, the catalyst was thermally activated between 200 and 400 °C; while in plasma-catalysis, the catalyst was activated by plasma generated by a dielectric barrier discharges (DBD) reactor. By the application of plasma in the catalyst bed, the reaction temperature was reduced from 350 °C to 150 °C to obtain the same level of conversion than thermal-catalysis. In addition, the incorporation of Ce in Ni-CeO2/Al2O3 led to an improvement of the catalytic performance in both thermal- and plasma-catalysis. Nevertheless, divergences on the optimum Ce content were found. On plasma experiments, the catalyst was more active at a lower amount of CeO2 (˜10 wt.%) with respect to thermal catalysis (˜40 wt.%), reducing the catalyst fabrication cost. Those differences highlights that the CO generated by plasma CO2 dissociation has a significant role for methane production, and thus the need to consider the by-products as reactant for the optimization of catalysts composition for DBD plasma-catalysis. © 2019 Elsevier B.V.

  • Porous NiTiO3/TiO2 nanostructures for photocatatalytic hydrogen evolution

    Xing C., Liu Y., Zhang Y., Liu J., Zhang T., Tang P., Arbiol J., Soler L., Sivula K., Guijarro N., Wang X., Li J., Du R., Zuo Y., Cabot A., Llorca J. Journal of Materials Chemistry A; 7 (28): 17053 - 17059. 2019. 10.1039/c9ta04763h. IF: 10.733

    We present a strategy to produce porous NiTiO3/TiO2 nanostructures with excellent photocatalytic activity toward hydrogen generation. In a first step, nickel-doped TiO2 needle bundles were synthesized by a hydrothermal procedure. Through the sintering in air of these nanostructures, porous NiTiO3/TiO2 heterostructured rods were obtained. Alternatively, the annealing in argon of the nickel-doped TiO2 needle bundles resulted in NiOx/TiO2 elongated nanostructures. Porous NiTiO3/TiO2 structures were tested for hydrogen evolution in the presence of ethanol. Such porous heterostructures exhibited superior photocatalytic activity toward hydrogen generation, with hydrogen production rates up to 11.5 mmol h-1 g-1 at room temperature. This excellent performance is related here to the optoelectronic properties and geometric parameters of the material. © 2019 The Royal Society of Chemistry.

  • Robust one-pot synthesis of citrate-stabilized Au@CeO 2 hybrid nanocrystals with different thickness and dimensionality

    Bastús N.G., Piella J., Perez S., Patarroyo J., Genç A., Arbiol J., Puntes V. Applied Materials Today; 15: 445 - 452. 2019. 10.1016/j.apmt.2019.03.003. IF: 8.013

    Well-defined colloidal Au@CeO 2 hybrid nanocrystals (NCs) comprising different core/shell morphologies have been synthesized via a novel and simple one-pot aqueous approach. The method allows producing hybrid morphologies composed by an active and accessible Au core coated by a porous CeO 2 shell with varying shell thickness and dimensionality by simply adjusting the Au 3+ /Ce 3+ precursor ratio. These hybrid NCs are highly monodisperse and well-dispersed in water, showing intense surface plasmon resonance bands that offer unique opportunities for advanced material applications, such as plasmonics and catalysis. © 2019 Elsevier Ltd

  • Role of Boron and Phosphorus in Enhanced Electrocatalytic Oxygen Evolution by Nickel Borides and Nickel Phosphides

    Masa J., Andronescu C., Antoni H., Sinev I., Seisel S., Elumeeva K., Barwe S., Marti-Sanchez S., Arbiol J., Roldan Cuenya B., Muhler M., Schuhmann W. ChemElectroChem; 6 (1): 235 - 240. 2019. 10.1002/celc.201800669. IF: 3.975

    The modification of nickel with boron or phosphorus leads to significant enhancement of its electrocatalytic activity for the oxygen evolution reaction (OER). However, the precise role of the guest elements, B and P, in enhancing the OER of the host element (Ni) remains unclear. Herein, we present insight into the role of B and P in enhancing electrocatalysis of oxygen evolution by nickel borides and nickel phosphides. The apparent activation energy, Ea*, of electrocatalytic oxygen evolution on Ni2P was 78.4 kJ/mol, on Ni2B 65.4 kJ/mol, and on Ni nanoparticles 94.0 kJ/mol, thus revealing that both B and P affect the intrinsic activity of nickel. XPS data revealed shifts of −0.30 and 0.40 eV in the binding energy of the Ni 2p3/2 peak of Ni2B and Ni2P, respectively, with respect to that of pure Ni at 852.60 eV, thus indicating that B and P induce opposite electronic effects on the surface electronic structure of Ni. The origin of enhanced activity for oxygen evolution cannot, therefore, be attributed to such electronic modification or ligand effect. Severe changes induced on the nickel lattice, specifically, the Ni-Ni atomic order and interatomic distances (strain effect), by the presence of the guest atoms seem to be the dominant factors responsible for enhanced activity of oxygen evolution in nickel borides and nickel phosphides. © 2019 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

  • Seeded-Growth Aqueous Synthesis of Colloidal-Stable Citrate-Stabilized Au/CeO2 Hybrid Nanocrystals: Heterodimers, Core@Shell, and Clover- And Star-Like Structures

    Piella J., Gónzalez-Febles A., Patarroyo J., Arbiol J., Bastús N.G., Puntes V. Chemistry of Materials; 31 (19): 7922 - 7932. 2019. 10.1021/acs.chemmater.9b02005. IF: 10.159

    Well-defined colloidal-stable citrate-stabilized Au/CeO2 hybrid nanocrystals (NCs) with coherent quasi-epitaxial interfaces and unprecedented control of their architectural and morphological characteristics have been synthesized via a novel and straightforward seeded-growth aqueous approach. The synthetic strategy, based on the identification of the experimental conditions under which the heterogeneous nucleation and growth processes of CeO2 onto presynthesized Au are controlled, allows for the fine adjustment of each individual domain in the structure, particularly the size of the Au core (from 5 to 100 nm), the thickness of the CeO2 shell (from 5 to 20 nm), and the growth mode of CeO2 onto Au NCs (from core@shell to heterodimer, clover- and star-like structures). This morphological control is achieved by the rational use of sodium citrate, which plays multiple key roles, as a reducer and stabilizing agent in the preparation of Au NCs, and as a complexing agent of Ce3+ for its controlled oxidation and hydrolysis during the subsequent CeO2 deposition. The resultant Au/CeO2 NCs remain stable and well-dispersed in water, allowing us to study the impact of fine variations of the NC structure on the underlying optical response. This level of morphological control, as well as the ease by which such well-defined nanostructures are produced, opens new opportunities for systematically investigating the interactions between individual components in designing more advanced complex NCs. Remarkably, because no organic solvents are used and no toxic waste is formed during the reaction, the proposed synthesis method can be defined as sustainable, viable, and cost-effective. Copyright © 2019 American Chemical Society.

  • Segregation scheme of indium in AlGaInAs nanowire shells

    Francaviglia L., Tütüncüoglu G., Martí-Sánchez S., Di Russo E., Escobar Steinvall S., Segura Ruiz J., Potts H., Friedl M., Rigutti L., Arbiol J., Fontcuberta I Morral A. Physical Review Materials; 3 (2, 023001) 2019. 10.1103/PhysRevMaterials.3.023001. IF: 2.926

    Quaternary alloys enable the independent optimization of different semiconductor properties, such as the separate tuning of the band gap and the lattice constant. Nanowire core-shell structures should allow a larger range of compositional tuning as strain can be accommodated in a more effective manner than in thin films. Still, the faceted structure of the nanowire may lead to local segregation effects. Here, we explore the incorporation of indium in AlGaAs shells up to 25%. In particular, we show the effect of In incorporation on the energy shift of the AlGaInAs single-photon emitters present in the shell. We observe a redshift up to 300 meV as a function of the group-III site fraction of In. We correlate the shift with segregation at the nanoscale. We find evidence of the segregation of the group-III elements at different positions in the nanowire, not observed before. We propose a model that takes into account the strain distribution in the nanowire shell and the adatom diffusion on the nanowire facets to explain the observations. This work provides novel insights on the segregation phenomena necessary to engineer the composition of multidinary alloys. © 2019 American Physical Society.

  • Selectivity Map for Molecular Beam Epitaxy of Advanced III-V Quantum Nanowire Networks

    Aseev P., Fursina A., Boekhout F., Krizek F., Sestoft J.E., Borsoi F., Heedt S., Wang G., Binci L., Martí-Sánchez S., Swoboda T., Koops R., Uccelli E., Arbiol J., Krogstrup P., Kouwenhoven L.P., Caroff P. Nano Letters; 19 (1): 218 - 227. 2019. 10.1021/acs.nanolett.8b03733. IF: 12.279

    Selective-area growth is a promising technique for enabling of the fabrication of the scalable III-V nanowire networks required to test proposals for Majorana-based quantum computing devices. However, the contours of the growth parameter window resulting in selective growth remain undefined. Herein, we present a set of experimental techniques that unambiguously establish the parameter space window resulting in selective III-V nanowire networks growth by molecular beam epitaxy. Selectivity maps are constructed for both GaAs and InAs compounds based on in situ characterization of growth kinetics on GaAs(001) substrates, where the difference in group III adatom desorption rates between the III-V surface and the amorphous mask area is identified as the primary mechanism governing selectivity. The broad applicability of this method is demonstrated by the successful realization of high-quality InAs and GaAs nanowire networks on GaAs, InP, and InAs substrates of both (001) and (111)B orientations as well as homoepitaxial InSb nanowire networks. Finally, phase coherence in Aharonov-Bohm ring experiments validates the potential of these crystals for nanoelectronics and quantum transport applications. This work should enable faster and better nanoscale crystal engineering over a range of compound semiconductors for improved device performance. © 2018 American Chemical Society.

  • Solution-Processed Ultrathin SnS 2 -Pt Nanoplates for Photoelectrochemical Water Oxidation

    Zuo Y., Liu Y., Li J., Du R., Yu X., Xing C., Zhang T., Yao L., Arbiol J., Llorca J., Sivula K., Guijarro N., Cabot A. ACS Applied Materials and Interfaces; 11 (7): 6918 - 6926. 2019. 10.1021/acsami.8b17622. IF: 8.456

    Tin disulfide (SnS 2 ) is attracting significant interest because of the abundance of its elements and its excellent optoelectronic properties in part related to its layered structure. In this work, we specify the preparation of ultrathin SnS 2 nanoplates (NPLs) through a hot-injection solution-based process. Subsequently, Pt was grown on their surface via in situ reduction of a Pt salt. The photoelectrochemical (PEC) performance of such nanoheterostructures as photoanode toward water oxidation was tested afterwards. Optimized SnS 2 -Pt photoanodes provided significantly higher photocurrent densities than bare SnS 2 and SnS 2 -based photoanodes of previously reported study. Mott-Schottky analysis and PEC impedance spectroscopy (PEIS) were used to analyze in more detail the effect of Pt on the PEC performance. From these analyses, we attribute the enhanced activity of SnS 2 -Pt photoanodes reported here to a combination of the very thin SnS 2 NPLs and the proper electronic contact between Pt nanoparticles (NPs) and SnS 2 . © 2019 American Chemical Society.

  • Superior methanol electrooxidation performance of (110)-faceted nickel polyhedral nanocrystals

    Li J., Zuo Y., Liu J., Wang X., Yu X., Du R., Zhang T., Infante-Carrió M.F., Tang P., Arbiol J., Llorca J., Luo Z., Cabot A. Journal of Materials Chemistry A; 7 (38): 22036 - 22043. 2019. 10.1039/c9ta07066d. IF: 10.733

    We present the synthesis of (110)-faceted nickel polyhedral nanocrystals (NCs) and their characterization as electrocatalysts for the methanol oxidation reaction (MOR). Ni NCs were produced at 180 °C through the reduction in solution of a Ni salt. They were combined with carbon black and Nafion and deposited over glassy carbon to study their electrocatalytic properties. Electrodes based on (110)-faceted Ni NCs displayed a first order reaction with KOH in the concentration range from 0.1 M to 1.0 M. These electrodes were characterized by higher coverages of active species, but lower diffusion coefficients of the species limiting the reaction rate when compared with electrodes prepared from spherical Ni NCs. Overall, electrodes based on faceted Ni NCs displayed excellent performance with very high current densities, up to 61 mA cm-2, and unprecedented mass activities, up to 2 A mg-1, at 0.6 V vs. Hg/HgO in 1.0 M KOH containing 1.0 M methanol. These electrodes also displayed a notable stability. While they suffered an activity loss of ca. 30% during the first 10000 s of operation, afterward activity stabilized at very high current densities, ∼35 mA cm-2, and mass activities, ∼1.2 A mg-1, with only a 0.5% decrease during operation from 20000 to 30000 s. © 2019 The Royal Society of Chemistry.

  • Tailor-made metal-nitrogen-carbon bifunctional electrocatalysts for rechargeable Zn-air batteries via controllable MOF units

    Zhang X., Luo J., Lin H.-F., Tang P., Morante J.R., Arbiol J., Wan K., Mao B.-W., Liu L.-M., Fransaer J. Energy Storage Materials; 17: 46 - 61. 2019. 10.1016/j.ensm.2018.11.034. IF: 0.000

    The majority of chemical syntheses involve the use of catalysts, which play a crucial role in the yield and conversion rates of chemical reactions. In view of the increasing demand for chemical commodities and specialties linked to the growth of the world's population and the living standards, highly efficient and low-cost catalysts are urgently required. The metal-nitrogen-carbon (M-N-C) catalysts family is one of the most promising candidates. In this work, a series of benzene-1,3,5-tricarboxylate linker based metal organic frameworks (MOFs) were used as self-sacrificial templates and tunable platform for designable preparation of M-N-C catalysts. Changing the pillars between the 2D layers and the nature of the metal ions in the pristine MOFs significantly influenced the structure, chemical composition and catalytic activity of the resulting M-N-C catalysts for the oxygen reduction reaction (ORR). Furthermore, the influence of the MOF units on the catalyst performance, the role of the metals in the M-N-C catalysts and the primary catalytically active sites for ORR were explored by a combination of density functional theory (DFT), in-depth structural and chemical/elemental characterizations, and electrochemical studies. Among the prepared catalysts, Co-BTC-bipy-700 exhibited the highest electrocatalytic activity for oxygen reduction reaction (ORR), which showed a larger limiting current density and similar half-wave potentials with less catalyst degradation and much higher methanol tolerance than the commercial Pt/C catalyst. Meanwhile, as a bifunctional electrocatalyst, Co-BTC-bipy-700 catalyst was also employed for oxygen evolution reaction (OER) and demonstrated a lower overpotential (lowered by 140 mV at a current density of 10 mA cm−2) and better durability than IrO2. Furthermore, in terms of device performance, the Zn-air battery enabled by Co-BTC-bipy-700 catalyst reached a maximum specific energy as high as 1009.8 Wh kg−1, which is 76.5% of the theoretical value (1320 Wh kg−1), and demonstrated higher discharge potential and lower charge potential than that based on the Pt/C catalyst. Importantly, the presented strategy for tailor-made M-N-C catalysts by controlling the synthesis of the pristine MOFs could offer a guide map for the future design of M-N-C catalysts family not only for electrochemical reactions but also beyond electrochemistry. © 2018 Elsevier B.V.

  • The Role of Polarity in Nonplanar Semiconductor Nanostructures

    De La Mata M., Zamani R.R., Martí-Sánchez S., Eickhoff M., Xiong Q., Fontcuberta Morral A., Caroff P., Arbiol J. Nano Letters; 19 (6): 3396 - 3408. 2019. 10.1021/acs.nanolett.9b00459. IF: 12.279

    The lack of mirror symmetry in binary semiconductor compounds turns them into polar materials, where two opposite orientations of the same crystallographic direction are possible. Interestingly, their physical properties (e.g., electronic or photonic) and morphological features (e.g., shape, growth direction, and so forth) also strongly depend on the polarity. It has been observed that nanoscale materials tend to grow with a specific polarity, which can eventually be reversed for very specific growth conditions. In addition, polar-directed growth affects the defect density and topology and might induce eventually the formation of undesirable polarity inversion domains in the nanostructure, which in turn will affect the photonic and electronic final device performance. Here, we present a review on the polarity-driven growth mechanism at the nanoscale, combining our latest investigation with an overview of the available literature highlighting suitable future possibilities of polarity engineering of semiconductor nanostructures. The present study has been extended over a wide range of semiconductor compounds, covering the most commonly synthesized III-V (GaN, GaP, GaAs, GaSb, InN, InP, InAs, InSb) and II-VI (ZnO, ZnTe, CdS, CdSe, CdTe) nanowires and other free-standing nanostructures (tripods, tetrapods, belts, and membranes). This systematic study allowed us to explore the parameters that may induce polarity-dependent and polarity-driven growth mechanisms, as well as the polarity-related consequences on the physical properties of the nanostructures. © 2019 American Chemical Society.

  • Tuning transport properties in thermoelectric nanocomposites through inorganic ligands and heterostructured building blocks

    Ibáñez M., Genç A., Hasler R., Liu Y., Dobrozhan O., Nazarenko O., De La Mata M., Arbiol J., Cabot A., Kovalenko M.V. ACS Nano; 13 (6): 6572 - 6580. 2019. 10.1021/acsnano.9b00346. IF: 13.903

    Methodologies that involve the use of nanoparticles as "artificial atoms" to rationally build materials in a bottom-up fashion are particularly well-suited to control the matter at the nanoscale. Colloidal synthetic routes allow for an exquisite control over such "artificial atoms" in terms of size, shape, and crystal phase as well as core and surface compositions. We present here a bottom-up approach to produce Pb-Ag-K-S-Te nanocomposites, which is a highly promising system for thermoelectric energy conversion. First, we developed a high-yield and scalable colloidal synthesis route to uniform lead sulfide (PbS) nanorods, whose tips are made of silver sulfide (Ag2S). We then took advantage of the large surface-to-volume ratio to introduce a p-type dopant (K) by replacing native organic ligands with K2Te. Upon thermal consolidation, K2Te-surface modified PbS-Ag2S nanorods yield p-type doped nanocomposites with PbTe and PbS as major phases and Ag2S and Ag2Te as embedded nanoinclusions. Thermoelectric characterization of such consolidated nanosolids showed a high thermoelectric figure-of-merit of 1 at 620 K. Copyright © 2019 American Chemical Society.

  • Understanding semiconductor nanostructures via advanced electron microscopy and spectroscopy

    Zamani R.R., Arbiol J. Nanotechnology; 30 (26, 262001) 2019. 10.1088/1361-6528/ab0b0a. IF: 3.399

    Transmission electron microscopy (TEM) offers an ample range of complementary techniques which are able to provide essential information about the physical, chemical and structural properties of materials at the atomic scale, and hence makes a vast impact on our understanding of materials science, especially in the field of semiconductor one-dimensional (1D) nanostructures. Recent advancements in TEM instrumentation, in particular aberration correction and monochromation, have enabled pioneering experiments in complex nanostructure material systems. This review aims to address these understandings through the applications of the methodology for semiconductor nanostructures. It points out various electron microscopy techniques, in particular scanning TEM (STEM) imaging and spectroscopy techniques, with their already-employed or potential applications on 1D nanostructured semiconductors. We keep the main focus of the paper on the electronic and optoelectronic properties of such semiconductors, and avoid expanding it further. In the first part of the review, we give a brief introduction to each of the STEM-based techniques, without detailed elaboration, and mention the recent technological and conceptual developments which lead to novel characterization methodologies. For further reading, we refer the audience to a handful of papers in the literature. In the second part, we highlight the recent examples of application of the STEM methodology on the 1D nanostructure semiconductor materials, especially III-V, II-V, and group IV bare and heterostructure systems. The aim is to address the research questions on various physical properties and introduce solutions by choosing the appropriate technique that can answer the questions. Potential applications will also be discussed, the ones that have already been used for bulk and 2D materials, and have shown great potential and promise for 1D nanostructure semiconductors. © 2019 IOP Publishing Ltd.

  • Upscaling high activity oxygen evolution catalysts based on CoFe2O4 nanoparticles supported on nickel foam for power-to-gas electrochemical conversion with energy efficiencies above 80%

    Urbain F., Du R., Tang P., Smirnov V., Andreu T., Finger F., Jimenez Divins N., Llorca J., Arbiol J., Cabot A., Morante J.R. Applied Catalysis B: Environmental; 259 (118055) 2019. 10.1016/j.apcatb.2019.118055. IF: 14.229

    We investigate cobalt ferrite nanoparticles (NPs) supported on large-scale electrodes as oxygen evolution reaction (OER) catalysts. Colloidal CoFe2O4 NPs were loaded on low-cost and high surface area nickel foam (NF) scaffolds. The coating process was optimized for large electrode areas, ensuring a proper distribution of the NPs on the NF that allowed overcoming the electrical conductivity limitations of oxide NPs. We were able to produce CoFe2O4-coated NFs having 10 cm2 geometric surface areas with overpotentials below 300 mV for the OER at a current density of 50 mA/cm2. Such impressively low overpotentials suggested using CoFe2O4 NP-based electrodes within a water electrolysis device. In this prototype device, stable operating currents up to 500 mA at remarkably low cell-voltages of 1.62 and 1.53 V, at ambient and 50 °C electrolyte temperatures, respectively, were reached during operation periods of up to 50 h. The high electrochemical energy efficiencies reached at 50 mA/cm2, 75% and 81% respectively, rendered these devices particularly appealing to be combined with low-cost photovoltaic systems for bias-free hydrogen production. Therefore, CoFe2O4 NP-based electrolysers were coupled to low-cost thin-film silicon solar cells with 13% efficiency to complete a system that afforded solar-to-fuel efficiencies above 10%. © 2019 Elsevier B.V.


  • Colloidal Ni-Co-Sn nanoparticles as efficient electrocatalysts for the methanol oxidation reaction

    Li J., Luo Z., He F., Zuo Y., Zhang C., Liu J., Yu X., Du R., Zhang T., Infante-Carrió M.F., Tang P., Arbiol J., Llorca J., Cabot A. Journal of Materials Chemistry A; 6 (45): 22915 - 22924. 2018. 10.1039/c8ta08242a. IF: 9.931

    The deployment of direct methanol fuel cells requires engineering cost-effective and durable electrocatalysts for the methanol oxidation reaction (MOR). As an alternative to noble metals, Ni-based alloys have shown excellent performance and good stability toward the MOR. Herein, we present a series of Ni3-xCoxSn2 colloidal nanoparticles (NPs) with composition tuned over the entire Ni/Co range (0 ≤ x ≤ 3). We demonstrate electrodes based on these ternary NPs to provide improved catalytic performance toward the MOR in an alkaline medium when compared with binary Ni3Sn2 NPs. A preliminary composition optimization resulted in Ni2.5Co0.5Sn2 NP-based electrodes exhibiting extraordinary mass current densities, up to 1050 mA mg-1, at 0.6 V vs. Hg/HgO in 1.0 M KOH containing 1.0 M methanol. This current density was about two-fold higher than that of Ni3Sn2 electrodes (563 mA mg-1). The excellent performance obtained with the substitution of small amounts of Ni by Co was concomitant with an increase of the surface coverage of active species and an enhancement of the diffusivity of the reaction limiting species. Additionally, saturation of the catalytic activity at higher methanol concentrations was measured for Ni3-xCoxSn2 NP-based electrodes containing a small amount of Co when compared with binary Ni3Sn2 NPs. While the electrode stability was improved with respect to elemental Ni NP-based electrodes, the introduction of small amounts of Co slightly decreased the cycling performance. Additionally, Sn, a key element to improve stability with respect to elemental Ni NPs, was observed to slowly dissolve in the presence of KOH. Density functional theory calculations on metal alloy surfaces showed the incorporation of Co within the Ni3Sn2 structure to provide more effective sites for CO and CH3OH adsorption. However, the relatively lower stability could not be related to CO or CH3OH poisoning. © The Royal Society of Chemistry 2018.

  • Colloidal Ni2-: XCoxP nanocrystals for the hydrogen evolution reaction

    Liu J., Wang Z., David J., Llorca J., Li J., Yu X., Shavel A., Arbiol J., Meyns M., Cabot A. Journal of Materials Chemistry A; 6 (24): 11453 - 11462. 2018. 10.1039/c8ta03485k. IF: 9.931

    A cost-effective and scalable approach was developed to produce monodisperse Ni2-xCoxP nanocrystals (NCs) with composition tuned over the entire range (0 ≤ x ≤ 2). Ni2-xCoxP NCs were synthesized using low-cost, stable and low-toxicity triphenyl phosphite (TPP) as a phosphorus source, metal chlorides as metal precursors and hexadecylamine (HDA) as a ligand. The synthesis involved the nucleation of amorphous Ni-P and its posterior crystallization and simultaneous incorporation of Co. The composition, size and morphology of the Ni2-xCoxP NCs could be controlled simply by varying the ratio of Ni and Co precursors and the amounts of TPP and HDA. Ternary Ni2-xCoxP-based electrocatalysts exhibited enhanced electrocatalytic activity toward the hydrogen evolution reaction (HER) compared to binary phosphides. In particular, NiCoP electrocatalysts displayed the lowest overpotential of 97 mV at J = 10 mA cm-2 and an excellent long-term stability. DFT calculations of the Gibbs free energy for hydrogen adsorption at the surface of Ni2-xCoxP NCs showed NiCoP to have the most appropriate composition to optimize this parameter within the whole Ni2-xCoxP series. However, the hydrogen adsorption energy was demonstrated not to be the only parameter controlling the HER activity in Ni2-xCoxP. © The Royal Society of Chemistry 2018.

  • Colloidal synthesis of CsX nanocrystals (X = Cl, Br, I)

    Shaw P.J., Meyns M., Zuo Y., Grau-Carbonell A., Lagoudakis P.G., Charlton M.D.B., Martí-Sánchez S., Arbiol J., Cabot A., Kanaras A.G. Nanomaterials; 8 (7, 506) 2018. 10.3390/nano8070506. IF: 3.504

    A facile colloidal synthesis of highly ionic cesium halide nanocrystals is reported. Colloidal nanocrystals of CsI, CsCl and CsBr with unprecedentedly small dimensions are obtained using oleylammonium halides and cesium oleate as precursors. The ease and adaptability of our method enables its universalization for the formation of other highly ionic nanocrystals. © 2018 by the authors. Licensee MDPI, Basel, Switzerland.

  • Controllable vapor phase fabrication of F:Mn3O4 thin films functionalized with Ag and TiO2

    Bigiani L., Barreca D., Gasparotto A., Sada C., Martí-Sanchez S., Arbiol J., Maccato C. CrystEngComm; 20 (22): 3016 - 3024. 2018. 10.1039/c8ce00387d. IF: 3.304

    A facile two-step vapor phase synthetic approach is proposed for the fabrication of Mn3O4 thin films chemically modified with fluorine, and eventually functionalized with silver or titania. The adopted strategy exploits the initial chemical vapor deposition (CVD) of Mn3O4 on Si(100) substrates starting from a diamine diketonate Mn(ii) complex, followed by the controlled radio frequency (RF)-sputtering of silver or titania. Complementary analytical techniques were employed to investigate the crystallinity (X-ray diffraction), chemical composition (X-ray photoelectron spectroscopy, secondary ion mass spectrometry, energy dispersive X-ray spectroscopy), morphology and nano-organization (field emission-scanning electron microscopy, atomic force microscopy, transmission electron microscopy) of both pristine and functionalized manganese oxide thin films. Under the adopted operating conditions, the target Mn(ii) complex acted as a single-source precursor for both Mn and F, leading to the formation of phase-pure hausmannite Mn3O4 films characterized by a uniform in-depth fluorine content. In addition, the obtained results gave evidence of the formation of high purity Ag/F:Mn3O4 and TiO2/F:Mn3O4 composites with a close contact between the single constituents. This work outlines an amenable and efficient method for the vapor phase growth of composite Mn3O4-based thin films, which are favorable candidates for diverse technological applications, from photocatalysis to gas sensing. © 2018 The Royal Society of Chemistry.

  • Crystallographically Textured Nanomaterials Produced from the Liquid Phase Sintering of BixSb2-xTe3 Nanocrystal Building Blocks

    Liu Y., Zhang Y., Ortega S., Ibáñez M., Lim K.H., Grau-Carbonell A., Martí-Sánchez S., Ng K.M., Arbiol J., Kovalenko M.V., Cadavid D., Cabot A. Nano Letters; 18 (4): 2557 - 2563. 2018. 10.1021/acs.nanolett.8b00263. IF: 12.080

    Bottom-up approaches for producing bulk nanomaterials have traditionally lacked control over the crystallographic alignment of nanograins. This limitation has prevented nanocrystal-based nanomaterials from achieving optimized performances in numerous applications. Here we demonstrate the production of nanostructured BixSb2-xTe3 alloys with controlled stoichiometry and crystallographic texture through proper selection of the starting building blocks and the adjustment of the nanocrystal-to-nanomaterial consolidation process. In particular, we hot pressed disk-shaped BixSb2-xTe3 nanocrystals and tellurium nanowires using multiple pressure and release steps at a temperature above the tellurium melting point. We explain the formation of the textured nanomaterials though a solution-reprecipitation mechanism under a uniaxial pressure. Additionally, we further demonstrate these alloys to reach unprecedented thermoelectric figures of merit, up to ZT = 1.96 at 420 K, with an average value of ZTave = 1.77 for the record material in the temperature range 320-500 K, thus potentially allowing up to 60% higher energy conversion efficiencies than commercial materials. © 2018 American Chemical Society.

  • Field effect enhancement in buffered quantum nanowire networks

    Krizek F., Sestoft J.E., Aseev P., Marti-Sanchez S., Vaitiekenas S., Casparis L., Khan S.A., Liu Y., Stankevič T., Whiticar A.M., Fursina A., Boekhout F., Koops R., Uccelli E., Kouwenhoven L.P., Marcus C.M., Arbiol J., Krogstrup P. Physical Review Materials; 2 (9, 093401) 2018. 10.1103/PhysRevMaterials.2.093401.

    III-V semiconductor nanowires have shown great potential in various quantum transport experiments. However, realizing a scalable high-quality nanowire-based platform that could lead to quantum information applications has been challenging. Here, we study the potential of selective area growth by molecular beam epitaxy of InAs nanowire networks grown on GaAs-based buffer layers, where Sb is used as a surfactant. The buffered geometry allows for substantial elastic strain relaxation and a strong enhancement of field effect mobility. We show that the networks possess strong spin-orbit interaction and long phase-coherence lengths with a temperature dependence indicating ballistic transport. With these findings, and the compatibility of the growth method with hybrid epitaxy, we conclude that the material platform fulfills the requirements for a wide range of quantum experiments and applications. © 2018 American Physical Society.

  • Growth and Luminescence of Polytypic InP on Epitaxial Graphene

    Mukherjee S., Nateghi N., Jacobberger R.M., Bouthillier E., de la Mata M., Arbiol J., Coenen T., Cardinal D., Levesque P., Desjardins P., Martel R., Arnold M.S., Moutanabbir O. Advanced Functional Materials; 28 (8, 1705592) 2018. 10.1002/adfm.201705592. IF: 13.325

    Van der Waals epitaxy is an attractive alternative to direct heteroepitaxy where the forced coherency at the interface cannot sustain large differences in lattice parameters and thermal expansion coefficients between the substrate and the epilayer. Herein, the growth of monocrystalline InP on Ge and SiO2/Si substrates using graphene as an interfacial layer is demonstrated. Micrometer-sized InP crystals are found to grow with interfaces of high crystalline quality and with different degrees of coalescence depending on the growth conditions. Some InP crystals exhibit a polytypic structure, consisting of alternating zinc-blende and wurtzite phases, forming a type-II homojunction with well (barrier) width of about 10 nm. The optical properties, investigated using room temperature nano-cathodoluminescence, indicate the signatures of the direct optical transitions at 1.34 eV across the gap of the zinc-blende phase and the indirect transitions at ≈1.31 eV originating from the alternating zinc-blende and wurtzite phases. Additionally, the InP nanorods, found growing mainly on the graphene/SiO2/Si substrate, show optical transition across the gap of the wurtzite phase at ≈1.42 eV. This demonstration of InP growth on graphene and the correlative study between the structure and optical properties pave the way to develop hybrid structures for potential applications in integrated photonic and optoelectronic devices. © 2017 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

  • Growth of Au-Pd2Sn Nanorods via Galvanic Replacement and Their Catalytic Performance on Hydrogenation and Sonogashira Coupling Reactions

    Nafria R., Luo Z., Ibáñez M., Martí-Sànchez S., Yu X., De La Mata M., Llorca J., Arbiol J., Kovalenko M.V., Grabulosa A., Muller G., Cabot A. Langmuir; 34 (36): 10634 - 10643. 2018. 10.1021/acs.langmuir.8b02023. IF: 3.789

    Colloidal Pd2Sn and Au-Pd2Sn nanorods (NRs) with tuned size were produced by the reduction of Pd and Sn salts in the presence of size- and shape-controlling agents and the posterior growth of Au tips through a galvanic replacement reaction. Pd2Sn and Au-Pd2Sn NRs exhibited high catalytic activity toward quasi-homogeneous hydrogenation of alkenes (styrene and 1-octene) and alkynes (phenylacetylene and 1-octyne) in dichloromethane. Au-Pd2Sn NRs showed higher activity than Pd2Sn for 1-octene, 1-octyne, and phenylacetylene. In Au-Pd2Sn heterostructures, X-ray photoelectron spectroscopy evidenced an electron donation from the Pd2Sn NR to the Au tips. Such heterostructures showed distinct catalytic behavior in the hydrogenation of compounds containing a triple bond such as tolan. This can be explained by the aurophilicity of triple bonds. To further study this effect, Pd2Sn and Au-Pd2Sn NRs were also tested in the Sonogashira coupling reaction between iodobenzene and phenylacetylene in N,N-dimethylformamide. At low concentration, this reaction provided the expected product, tolan. However, at high concentration, more reduced products such as stilbene and 1,2-diphenylethane were also obtained, even without the addition of H2. A mechanism for this unexpected reduction is proposed. Copyright © 2018 American Chemical Society.

  • High Thermoelectric Performance in Crystallographically Textured n-Type Bi2Te3- xSex Produced from Asymmetric Colloidal Nanocrystals

    Liu Y., Zhang Y., Lim K.H., Ibáñez M., Ortega S., Li M., David J., Martí-Sánchez S., Ng K.M., Arbiol J., Kovalenko M.V., Cadavid D., Cabot A. ACS Nano; 12 (7): 7174 - 7184. 2018. 10.1021/acsnano.8b03099. IF: 13.709

    In the present work, we demonstrate crystallographically textured n-type Bi2Te3-xSex nanomaterials with exceptional thermoelectric figures of merit produced by consolidating disk-shaped Bi2Te3-xSex colloidal nanocrystals (NCs). Crystallographic texture was achieved by hot pressing the asymmetric NCs in the presence of an excess of tellurium. During the hot press, tellurium acted both as lubricant to facilitate the rotation of NCs lying close to normal to the pressure axis and as solvent to dissolve the NCs approximately aligned with the pressing direction, which afterward recrystallize with a preferential orientation. NC-based Bi2Te3-xSex nanomaterials showed very high electrical conductivities associated with large charge carrier concentrations, n. We hypothesize that such large n resulted from the presence of an excess of tellurium during processing, which introduced a high density of donor TeBi antisites. Additionally, the presence in between grains of traces of elemental Te, a narrow band gap semiconductor with a work function well below Bi2Te3-xSex, might further contribute to increase n through spillover of electrons, while at the same time blocking phonon propagation and hole transport through the nanomaterial. NC-based Bi2Te3-xSex nanomaterials were characterized by very low thermal conductivities in the pressing direction, which resulted in ZT values up to 1.31 at 438 K in this direction. This corresponds to a ca. 40% ZT enhancement from commercial ingots. Additionally, high ZT values were extended over wider temperature ranges due to reduced bipolar contribution to the Seebeck coefficient and the thermal conductivity. Average ZT values up to 1.15 over a wide temperature range, 320 to 500 K, were measured, which corresponds to a ca. 50% increase over commercial materials in the same temperature range. Contrary to most previous works, highest ZT values were obtained in the pressing direction, corresponding to the c crystallographic axis, due to the predominance of the thermal conductivity reduction over the electrical conductivity difference when comparing the two crystal directions. © 2018 American Chemical Society.

  • NiSn bimetallic nanoparticles as stable electrocatalysts for methanol oxidation reaction

    Li J., Luo Z., Zuo Y., Liu J., Zhang T., Tang P., Arbiol J., Llorca J., Cabot A. Applied Catalysis B: Environmental; 234: 10 - 18. 2018. 10.1016/j.apcatb.2018.04.017. IF: 11.698

    Nickel is an excellent alternative catalyst to high cost Pt and Pt-group metals as anode material in direct methanol fuel cells. However, nickel presents a relatively low stability under operation conditions, even in alkaline media. In this work, a synthetic route to produce bimetallic NiSn nanoparticles (NPs) with tuned composition is presented. Through co-reduction of the two metals in the presence of appropriate surfactants, 3–5 nm NiSn NPs with tuned Ni/Sn ratios were produced. Such NPs were subsequently supported on carbon black and tested for methanol electro-oxidation in alkaline media. Among the different stoichiometries tested, the most Ni-rich alloy exhibited the highest electrocatalytic activity, with mass current density of 820 mA mg−1 at 0.70 V (vs. Hg/HgO). While this activity was comparable to that of pure nickel NPs, NiSn alloys showed highly improved stabilities over periods of 10,000 s at 0.70 V. We hypothesize this experimental fact to be associated to the collaborative oxidation of the byproducts of methanol which poison the Ni surface or to the prevention of the tight adsorption of these species on the Ni surface by modifying its surface chemistry or electronic density of states. © 2018 Elsevier B.V.

  • Optical Analysis of Oxygen Self-Diffusion in Ultrathin CeO2 Layers at Low Temperatures

    Neuderth P., Hille P., Martí-Sánchez S., de la Mata M., Coll M., Arbiol J., Eickhoff M. Advanced Energy Materials; 8 (29, 1802120) 2018. 10.1002/aenm.201802120. IF: 21.875

    An optical in situ strategy for the analysis of oxygen diffusion in ultrathin ceria layers with a thickness of 2–10 nm at temperatures between 50 and 200 °C is presented, which allows for the determination of diffusion coefficients. This method is based on the sensitivity of the photoluminescence (PL) intensity of InGaN nanowires to adsorbed oxygen. The oxygen diffusion through an ultrathin CeO2 coating deposited on the InGaN nanowires is monitored by analyzing the transient PL behavior of the InGaN nanowires, which responds to changes of the oxygen concentration in the environment when the corresponding oxygen concentration is established at the CeO2/InGaN interface due to diffusion through the coating. Quantitative evaluation of the oxygen diffusion in CeO2 based on a model considering Langmuir Adsorption and recombination yields a diffusion coefficient D of (2.55 ± 0.05) × 10−16 cm2 s−1 at a temperature of 100 °C. Temperature-dependent measurements reveal an Arrhenius type behavior of D with an activation energy of (0.28 ± 0.04) eV. In contrast, no oxygen diffusion is detected for an ultrathin layer (≥5 nm) of Al2O3, which is known as a poor oxygen ion conductor within the analyzed temperature regime. © 2018 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

  • Optical emission of GaN/AlN quantum-wires-the role of charge transfer from a nanowire template

    Müßener J., Greif L.A.T., Kalinowski S., Callsen G., Hille P., Schörmann J., Wagner M.R., Schliwa A., Martí-Sánchez S., Arbiol J., Hoffmann A., Eickhoff M. Nanoscale; 10 (12): 5591 - 5598. 2018. 10.1039/c7nr08057c. IF: 7.233

    We show that one-dimensional (1d) GaN quantum-wires (QWRs) exhibit intense and spectrally sharp emission lines. These QWRs are realized in an entirely self-assembled growth process by molecular beam epitaxy (MBE) on the side facets of GaN/AlN nanowire (NW) heterostructures. Time-integrated and time-resolved photoluminescence (PL) data in combination with numerical calculations allow the identification and assignment of the manifold emission features to three different spatial recombination centers within the NWs. The recombination processes in the QWRs are driven by efficient charge carrier transfer effects between the different optically active regions, providing high intense QWR luminescence despite their small volume. This is deduced by a fast rise time of the QWR PL, which is similar to the fast decay-time of adjacent carrier reservoirs. Such processes, feeding the ultra-narrow QWRs with carriers from the relatively large NWs, can be the key feature towards the realization of future QWR-based devices. While processing of single quantum structures with diameters in the nm range presents a serious obstacle with respect to their integration into electronic or photonic devices, the QWRs presented here can be analyzed and processed using existing techniques developed for single NWs. © 2018 The Royal Society of Chemistry.

  • Optimizing the yield of A-polar GaAs nanowires to achieve defect-free zinc blende structure and enhanced optical functionality

    Zamani M., Tütüncüoglu G., Martí-Sánchez S., Francaviglia L., Güniat L., Ghisalberti L., Potts H., Friedl M., Markov E., Kim W., Leran J.-B., Dubrovskii V.G., Arbiol J., Fontcuberta I Morral A. Nanoscale; 10 (36): 17080 - 17091. 2018. 10.1039/c8nr05787g. IF: 7.233

    Compound semiconductors exhibit an intrinsic polarity, as a consequence of the ionicity of their bonds. Nanowires grow mostly along the (111) direction for energetic reasons. Arsenide and phosphide nanowires grow along (111)B, implying a group V termination of the (111) bilayers. Polarity engineering provides an additional pathway to modulate the structural and optical properties of semiconductor nanowires. In this work, we demonstrate for the first time the growth of Ga-assisted GaAs nanowires with (111)A-polarity, with a yield of up to ∼50%. This goal is achieved by employing highly Ga-rich conditions which enable proper engineering of the energies of A and B-polar surfaces. We also show that A-polarity growth suppresses the stacking disorder along the growth axis. This results in improved optical properties, including the formation of AlGaAs quantum dots with two orders or magnitude higher brightness. Overall, this work provides new grounds for the engineering of nanowire growth directions, crystal quality and optical functionality. © The Royal Society of Chemistry.

  • Passivation layers for nanostructured photoanodes: Ultra-thin oxides on InGaN nanowires

    Neuderth P., Hille P., Schörmann J., Frank A., Reitz C., Martí-Sánchez S., De La Mata M., Coll M., Arbiol J., Marschall R., Eickhoff M. Journal of Materials Chemistry A; 6 (2): 565 - 573. 2018. 10.1039/c7ta08071a. IF: 9.931

    An experimental strategy for systematically assessing the influence of surface passivation layers on the photocatalytic properties of nanowire photoanodes by combining photocurrent analysis, photoluminescence spectroscopy and high resolution transmission electron microscopy with a systematic variation of sample structure and the surrounding electrolyte is demonstrated. Following this approach we can separate the impact on recombination and transport processes of photogenerated carriers. We apply this strategy to analyze the influence of ultra-thin TiO2, CeO2 and Al2O3 coatings deposited by atomic layer deposition on the photoelectrochemical performance of InxGa1-xN/GaN nanowire (NW) photoelectrodes. The passivation of surface states results in an increase of the anodic photocurrent (PC) by a factor of 2.5 for the deposition of 5 nm TiO2. In contrast, the PC is reduced for CeO2- and Al2O3-coated NWs due to enhanced defect recombination in the passivation layer or increased band discontinuities. Furthermore, photoelectrochemical oxidation of the InxGa1-xN/GaN NW photoelectrode is attenuated by the TiO2 layer and completely suppressed for a layer thickness of 7 nm or more. Due to efficient charge transfer from the InxGa1-xN NW core a stable TiO2-covered photoanode with visible light excitation is realized. © 2018 The Royal Society of Chemistry.

  • Reduction of Thermal Conductivity in Nanowires by Combined Engineering of Crystal Phase and Isotope Disorder

    Mukherjee S., Givan U., Senz S., De La Mata M., Arbiol J., Moutanabbir O. Nano Letters; 18 (5): 3066 - 3075. 2018. 10.1021/acs.nanolett.8b00612. IF: 12.080

    Nanowires are a versatile platform to investigate and harness phonon and thermal transport phenomena in nanoscale systems. With this perspective, we demonstrate herein the use of crystal phase and mass disorder as effective degrees of freedom to manipulate the behavior of phonons and control the flow of local heat in silicon nanowires. The investigated nanowires consist of isotopically pure and isotopically mixed nanowires bearing either a pure diamond cubic or a cubic-rhombohedral polytypic crystal phase. The nanowires with tailor-made isotopic compositions were grown using isotopically enriched silane precursors 28SiH4, 29SiH4, and 30SiH4 with purities better than 99.9%. The analysis of polytypic nanowires revealed ordered and modulated inclusions of lamellar rhombohedral silicon phases toward the center in otherwise diamond-cubic lattice with negligible interphase biaxial strain. Raman nanothermometry was employed to investigate the rate at which the local temperature of single suspended nanowires evolves in response to locally generated heat. Our analysis shows that the lattice thermal conductivity in nanowires can be tuned over a broad range by combining the effects of isotope disorder and the nature and degree of polytypism on phonon scattering. We found that the thermal conductivity can be reduced by up to ∼40% relative to that of isotopically pure nanowires, with the lowest value being recorded for the rhombohedral phase in isotopically mixed 28Six 30Si1-x nanowires with composition close to the highest mass disorder (x ∼ 0.5). These results shed new light on the fundamentals of nanoscale thermal transport and lay the groundwork to design innovative phononic devices. © 2018 American Chemical Society.

  • Selective-Area-Grown Semiconductor-Superconductor Hybrids: A Basis for Topological Networks

    Vaitiekenas S., Whiticar A.M., Deng M.-T., Krizek F., Sestoft J.E., Palmstrøm C.J., Marti-Sanchez S., Arbiol J., Krogstrup P., Casparis L., Marcus C.M. Physical Review Letters; 121 (14, 147701) 2018. 10.1103/PhysRevLett.121.147701. IF: 8.839

    We introduce selective area grown hybrid InAs/Al nanowires based on molecular beam epitaxy, allowing arbitrary semiconductor-superconductor networks containing loops and branches. Transport reveals a hard induced gap and unpoisoned 2e-periodic Coulomb blockade, with temperature dependent 1e features in agreement with theory. Coulomb peak spacing in parallel magnetic field displays overshoot, indicating an oscillating discrete near-zero subgap state consistent with device length. Finally, we investigate a loop network, finding strong spin-orbit coupling and a coherence length of several microns. These results demonstrate the potential of this platform for scalable topological networks among other applications. © 2018 American Physical Society.

  • SnP nanocrystals as anode materials for Na-ion batteries

    Liu J., Wang S., Kravchyk K., Ibáñez M., Krumeich F., Widmer R., Nasiou D., Meyns M., Llorca J., Arbiol J., Kovalenko M.V., Cabot A. Journal of Materials Chemistry A; 6 (23): 10958 - 10966. 2018. 10.1039/c8ta01492b. IF: 9.931

    Tin monophosphide is a layered material consisting of Sn-P-P-Sn sandwiches that are stacked on top of each other to form a three dimensional crystallographic structure. Its composition and crystal structure makes it an excellent candidate anode material for sodium-ion batteries (SIBs). However, SnP is yet to be explored for such and other applications due to its challenging synthesis. In the present work, we report the synthesis of SnP nanocrystals (NCs) from the reaction of hexamethylphosphorous triamide (HMPT) and a tin phosphonate prepared from tin oxalate and a long chain phosphonic acid. SnP NCs obtained from this reaction displayed a spherical geometry and a trigonal crystallographic phase with a superstructure attributed to ordered diphosphorus pairs. Such NCs were mixed with carbon black and used as anode materials in SIBs. SIBs based on SnP NCs and sodium(i) bis(fluorosulfonyl)imide (NaFSI) electrolyte displayed a high reversible capacity of 600 mA h g-1 at a current density of 100 mA g-1 and cycling stability for over 200 cycles. Their excellent cycling performance is associated with both the small size of the crystal domains and the particular composition and phase of SnP which prevent mechanical disintegration and major phase separation during sodiation and desodiation cycles. These results demonstrate SnP to be an attractive anode material for sodium ion batteries. © 2018 The Royal Society of Chemistry.

  • Supported Mn3O4 Nanosystems for Hydrogen Production through Ethanol Photoreforming

    Barreca D., Bigiani L., Monai M., Carraro G., Gasparotto A., Sada C., Martí-Sanchez S., Grau-Carbonell A., Arbiol J., Maccato C., Fornasiero P. Langmuir; 34 (15): 4568 - 4574. 2018. 10.1021/acs.langmuir.8b00642. IF: 3.789

    Photoreforming promoted by metal oxide nanophotocatalysts is an attractive route for clean and sustainable hydrogen generation. In the present work, we propose for the first time the use of supported Mn3O4 nanosystems, both pure and functionalized with Au nanoparticles (NPs), for hydrogen generation by photoreforming. The target oxide systems, prepared by chemical vapor deposition (CVD) and decorated with gold NPs by radio frequency (RF) sputtering, were subjected to a thorough chemico-physical characterization and utilized for a proof-of-concept H2 generation in aqueous ethanolic solutions under simulated solar illumination. Pure Mn3O4 nanosystems yielded a constant hydrogen production rate of 10 mmol h-1 m-2 even for irradiation times up to 20 h. The introduction of Au NPs yielded a significant enhancement in photocatalytic activity, which decreased as a function of irradiation time. The main phenomena causing the Au-containing photocatalyst deactivation have been investigated by morphological and compositional analysis, providing important insights for the design of Mn3O4-based photocatalysts with improved performances. © 2018 American Chemical Society.

  • Tailoring Copper Foam with Silver Dendrite Catalysts for Highly Selective Carbon Dioxide Conversion into Carbon Monoxide

    Urbain F., Tang P., Carretero N.M., Andreu T., Arbiol J., Morante J.R. ACS Applied Materials and Interfaces; 10 (50): 43650 - 43660. 2018. 10.1021/acsami.8b15379. IF: 8.097

    The present study outlines the important steps to bring electrochemical conversion of carbon dioxide (CO 2 ) closer to commercial viability by using a large-scale metallic foam electrode as a highly conductive catalyst scaffold. Because of its versatility, it was possible to specifically tailor three-dimensional copper foam through coating with silver dendrite catalysts by electrodeposition. The requirements of high-yield CO 2 conversion to carbon monoxide (CO) were met by tuning the deposition parameters toward a homogeneous coverage of the copper foam with nanosized dendrites, which additionally featured crystallographic surface orientations favoring CO production. The presented results evidence that Ag dendrites, owing a high density of planes with stepped (220) surface sites, paired with the superior active surface area of the copper foam can significantly foster the CO productivity. In a continuous flow-cell reactor setup, CO Faradaic efficiencies reaching from 85 to 96% for a wide range of low applied cathode potentials (<1.0 V RHE ) along with high CO current densities up to 27 mA/cm 2 were achieved, far outperforming other tested scaffold materials. Overall, this research provides new strategic guidelines for the fabrication of efficient and versatile cathodes for CO 2 conversion compatible with large-scale integrated prototype devices. Copyright © 2018 American Chemical Society.

  • Template-Assisted Scalable Nanowire Networks

    Friedl M., Cerveny K., Weigele P., Tütüncüoglu G., Martí-Sánchez S., Huang C., Patlatiuk T., Potts H., Sun Z., Hill M.O., Güniat L., Kim W., Zamani M., Dubrovskii V.G., Arbiol J., Lauhon L.J., Zumbühl D.M., Fontcuberta Morral A.I. Nano Letters; 18 (4): 2666 - 2671. 2018. 10.1021/acs.nanolett.8b00554. IF: 12.080

    Topological qubits based on Majorana Fermions have the potential to revolutionize the emerging field of quantum computing by making information processing significantly more robust to decoherence. Nanowires are a promising medium for hosting these kinds of qubits, though branched nanowires are needed to perform qubit manipulations. Here we report a gold-free templated growth of III-V nanowires by molecular beam epitaxy using an approach that enables patternable and highly regular branched nanowire arrays on a far greater scale than what has been reported thus far. Our approach relies on the lattice-mismatched growth of InAs on top of defect-free GaAs nanomembranes yielding laterally oriented, low-defect InAs and InGaAs nanowires whose shapes are determined by surface and strain energy minimization. By controlling nanomembrane width and growth time, we demonstrate the formation of compositionally graded nanowires with cross-sections less than 50 nm. Scaling the nanowires below 20 nm leads to the formation of homogeneous InGaAs nanowires, which exhibit phase-coherent, quasi-1D quantum transport as shown by magnetoconductance measurements. These results are an important advance toward scalable topological quantum computing. © 2018 American Chemical Society.

  • Tin Diselenide Molecular Precursor for Solution-Processable Thermoelectric Materials

    Zhang Y., Liu Y., Lim K.H., Xing C., Li M., Zhang T., Tang P., Arbiol J., Llorca J., Ng K.M., Ibáñez M., Guardia P., Prato M., Cadavid D., Cabot A. Angewandte Chemie - International Edition; 2018. 10.1002/anie.201809847. IF: 12.102

    In the present work, we detail a fast and simple solution-based method to synthesize hexagonal SnSe2 nanoplates (NPLs) and their use to produce crystallographically textured SnSe2 nanomaterials. We also demonstrate that the same strategy can be used to produce orthorhombic SnSe nanostructures and nanomaterials. NPLs are grown through a screw dislocation-driven mechanism. This mechanism typically results in pyramidal structures, but we demonstrate here that the growth from multiple dislocations results in flower-like structures. Crystallographically textured SnSe2 bulk nanomaterials obtained from the hot pressing of these SnSe2 structures display highly anisotropic charge and heat transport properties and thermoelectric (TE) figures of merit limited by relatively low electrical conductivities. To improve this parameter, SnSe2 NPLs are blended here with metal nanoparticles. The electrical conductivities of the blends are significantly improved with respect to bare SnSe2 NPLs, what translates into a three-fold increase of the TE Figure of merit, reaching unprecedented ZT values up to 0.65. © 2018 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

  • Triphenyl Phosphite as the Phosphorus Source for the Scalable and Cost-Effective Production of Transition Metal Phosphides

    Liu J., Meyns M., Zhang T., Arbiol J., Cabot A., Shavel A. Chemistry of Materials; 30 (5): 1799 - 1807. 2018. 10.1021/acs.chemmater.8b00290. IF: 9.890

    Transition metal phosphides have great potential to optimize a number of functionalities in several energy conversion and storage applications, particularly when nanostructured or in nanoparticle form. However, the synthesis of transition metal phosphide nanoparticles and its scalability is often limited by the toxicity, air sensitivity, and high cost of the reagents used. We present here a simple, scalable, and cost-effective "heating up" procedure to produce metal phosphides using inexpensive, low-toxicity, and air-stable triphenyl phosphite as source of phosphorus and chlorides as metal precursors. This procedure allows the synthesis of a variety of phosphide nanoparticles, including phosphides of Ni, Co, and Cu. The use of carbonyl metal precursors further allowed the synthesis of Fe2P and MoP nanoparticles. The fact that minor modifications in the experimental parameters allowed producing nanoparticles with different compositions and even to tune their size and shape shows the high potential and versatility of the triphenyl phosphite precursor and the presented method. We also detail here a methodology to displace organic ligands from the surface of phosphide nanoparticles, which is a key step toward their application in energy conversion and storage systems. © 2018 American Chemical Society.

  • Ultrasensitive binder-free glucose sensors based on the pyrolysis of in situ grown Cu MOF

    Zhang X., Luo J., Tang P., Morante J.R., Arbiol J., Xu C., Li Q., Fransaer J. Sensors and Actuators, B: Chemical; 254: 272 - 281. 2018. 10.1016/j.snb.2017.07.024. IF: 5.667

    A non-enzymatic glucose sensor based on carbon/Cu composite materials was developed by the in-situ growth and subsequent pyrolysis of metal-organic frameworks (MOFs) on Cu foam. After pyrolysis, SEM, HRTEM and STEM-EELS were employed to clarify the hierarchical Cu@porous carbon electrode. It is found that the Cu nanoparticles are uniformly embedded in the carbon matrix, carbon matrix in close contact with the pyrolized carbon sheets. The electrocatalytic activity of the Cu@porous carbon matrix electrode for glucose sensing was explored by cyclic voltammetry (CV) and chronoamperometry. The resulting Cu@porous carbon matrix electrode displays ultrahigh sensitivity (10.1 mA cm−2 mM−1), low detection limit (0.6 μM), short response time (less than 2 s) and good stability, indicating that the developed electrode is a promising glucose sensor. © 2017 Elsevier B.V.


  • A prototype reactor for highly selective solar-driven CO2 reduction to synthesis gas using nanosized earth-abundant catalysts and silicon photovoltaics

    Urbain F., Tang P., Carretero N.M., Andreu T., Gerling L.G., Voz C., Arbiol J., Morante J.R. Energy and Environmental Science; 10 (10): 2256 - 2266. 2017. 10.1039/c7ee01747b. IF: 29.518

    The conversion of carbon dioxide (CO2) into value-added chemicals and fuels, preferably using renewable energy and earth-abundant materials, is considered a key priority for future energy research. In this work, a bias-free reactor device for the solar-driven conversion of CO2 to synthesis gas (syngas) has been developed. The integrated fluidic device consists of a cathode made of copper foam coated with low-cost nanosized zinc flakes as catalyst to perform the CO2 reduction reaction (CO2RR) to syngas, an adapted silicon heterojunction solar cell structure as photoanode with nickel foam as catalyst to facilitate the oxygen evolution reaction (OER), and a bipolar membrane separating the respective catholyte and anolyte compartments. The membrane allows for the operation of the catholyte and anolyte at different pH values. Stable and tunable hydrogen-to-carbon monoxide (H2:CO) ratios between 5 and 0.5 along with high CO Faradaic efficiencies of up to 85% and CO current densities of 39.4 mA cm-2 have been demonstrated. Under photoelectrolysis conditions, the photovoltage of the photoanode was varied between 0.6 V and 2.4 V by connecting up to four heterojunction solar cells in series, and thus reducing the overall cell voltage solely by solar energy utilization. Bias-free operation of the integrated device has been achieved under ambient conditions with active areas for CO2RR and OER, respectively, of 10 cm2. An operation current density of 5.0 mA cm-2 was measured under 100 mW cm-2 illumination of the complete device, which corresponds to a solar-to-syngas conversion efficiency of 4.3%. © The Royal Society of Chemistry.

  • Charge Transfer Characterization of ALD-Grown TiO2 Protective Layers in Silicon Photocathodes

    Ros C., Andreu T., Hernández-Alonso M.D., Penelas-Pérez G., Arbiol J., Morante J.R. ACS Applied Materials and Interfaces; 9 (21): 17932 - 17941. 2017. 10.1021/acsami.7b02996. IF: 7.504

    A critical parameter for the implementation of standard high-efficiency photovoltaic absorber materials for photoelectrochemical water splitting is its proper protection from chemical corrosion while remaining transparent and highly conductive. Atomic layer deposited (ALD) TiO2 layers fulfill material requirements while conformally protecting the underlying photoabsorber. Nanoscale conductivity of ALD TiO2 protective layers on silicon-based photocathodes has been analyzed, proving that the conduction path is through the columnar crystalline structure of TiO2. Deposition temperature has been explored from 100 to 300 °C, and a temperature threshold is found to be mandatory for an efficient charge transfer, as a consequence of layer crystallization between 100 and 200 °C. Completely crystallized TiO2 is demonstrated to be mandatory for long-term stability, as seen in the 300 h continuous operation test. © 2017 American Chemical Society.

  • Cobalt boride modified with N-doped carbon nanotubes as a high-performance bifunctional oxygen electrocatalyst

    Elumeeva K., Masa J., Medina D., Ventosa E., Seisel S., Kayran Y.U., Genç A., Bobrowski T., Weide P., Arbiol J., Muhler M., Schuhmann W. Journal of Materials Chemistry A; 5 (40): 21122 - 21129. 2017. 10.1039/c7ta06995b. IF: 8.867

    The development of reversible oxygen electrodes, able to drive both the oxygen evolution reaction (OER) and the oxygen reduction reaction (ORR), is still a great challenge. We describe a very efficient and stable bifunctional electrocatalytic system for reversible oxygen electrodes obtained by direct CVD growth of nitrogen-doped carbon nanotubes (NCNTs) on the surface of cobalt boride (CoB) nanoparticles. A detailed investigation of the crystalline structure and elemental distribution of CoB before and after NCNT growth reveals that the NCNTs grow on small CoB nanoparticles formed in the CVD process. The resultant CoB/NCNT system exhibited outstanding activity in catalyzing both the OER and the ORR in 0.1 M KOH with an overvoltage difference of only 0.73 V between the ORR at -1 mA cm-2 and the OER at +10 mA cm-2. The proposed CoB/NCNT catalyst showed stable performance during 50 h of OER stability assessment in 0.1 M KOH. Moreover, CoB/NCNT spray-coated on a gas diffusion layer as an air-breathing electrode proved its high durability during 170 galvanostatic charge-discharge (OER/ORR) test cycles (around 30 h) at ±10 mA cm-2 in 6 M KOH, making it an excellent bifunctional catalyst for potential Zn-air battery application. © 2017 The Royal Society of Chemistry.

  • Colloidal Silicon-Germanium Nanorod Heterostructures

    Lu X., De La Mata M., Arbiol J., Korgel B.A. Chemistry of Materials; 29 (22): 9786 - 9792. 2017. 10.1021/acs.chemmater.7b03868. IF: 9.466

    Colloidal nanorods with axial Si and Ge heterojunction segments were produced by solution-liquid-solid (SLS) growth using Sn as a seed metal and trisilane and diphenylgermane as Si and Ge reactants. The low solubility of Si and Ge in Sn helps to generate abrupt Si-Ge heterojunction interfaces. To control the composition of the nanorods, it was also necessary to limit an undesired side reaction between the Ge reaction byproduct tetraphenylgermane and trisilane. High-resolution transmission electron microscopy reveals that the Si-Ge interfaces are epitaxial, which gives rise to a significant amount of bond strain resulting in interfacial misfit dislocations that nucleate stacking faults in the nanorods. © 2017 American Chemical Society.

  • Enhanced photoelectrochemical water splitting of hematite multilayer nanowire photoanodes by tuning the surface state via bottom-up interfacial engineering

    Tang P., Xie H., Ros C., Han L., Biset-Peiró M., He Y., Kramer W., Rodríguez A.P., Saucedo E., Galán-Mascarós J.R., Andreu T., Morante J.R., Arbiol J. Energy and Environmental Science; 10 (10): 2124 - 2136. 2017. 10.1039/c7ee01475a. IF: 29.518

    The optimization of multiple interfaces in hematite (α-Fe2O3) based composites for photoelectrochemical water splitting to facilitate charge transport in the bulk is of paramount importance to obtain enhanced solar-to-fuel efficiency. Herein, we report the fabrication of ITO/Fe2O3/Fe2TiO5/FeNiOOH multi-layer nanowires and a series of systematic experiments designed to elucidate the mechanism underlying the interfacial coupling effect of the quaternary hematite composite. The hierarchical ITO/Fe2O3/Fe2TiO5/FeNiOOH nanowires display photocurrents that are more than an order of magnitude greater than those of pristine Fe2O3 nanowires (from 0.205 mA cm-2 to 2.2 mA cm-2 at 1.23 V vs. RHE and 1 Sun), and higher than those of most of the recently reported state-of-the-art hematite composites. Structural, compositional and electrochemical investigations disclose that the surface states (SS) are finely regulated via the atomic addition of an Fe2TiO5 layer and FeNiOOH nanodots, while the upgrading of back contact conductivity and charge donor densities originate from the epitaxial relationship and enhanced Sn doping contributed from the ITO underlayer. We attribute the superior water oxidation performance to the interfacial coupling effect of the ITO underlayer (Sn doping and back contact conductivity promoter), the atomic level Fe2TiO5 coating (Ti doping, surface state density and energy level modulation) and the FeNiOOH nanodot electrocatalyst (regulating surface state energy level). Our work suggests an effective pathway for rational designing of highly active and cost-effective integrated photoanodes for photoelectrochemical water splitting. © The Royal Society of Chemistry.

  • Hollow metal nanostructures for enhanced plasmonics: Synthesis, local plasmonic properties and applications

    Genç A., Patarroyo J., Sancho-Parramon J., Bastús N.G., Puntes V., Arbiol J. Nanophotonics; 6 (1): 193 - 213. 2017. 10.1515/nanoph-2016-0124. IF: 4.492

    Metallic nanostructures have received great attention due to their ability to generate surface plasmon resonances, which are collective oscillations of conduction electrons of a material excited by an electromagnetic wave. Plasmonic metal nanostructures are able to localize and manipulate the light at the nanoscale and, therefore, are attractive building blocks for various emerging applications. In particular, hollow nanostructures are promising plasmonic materials as cavities are known to have better plasmonic properties than their solid counterparts thanks to the plasmon hybridization mechanism. The hybridization of the plasmons results in the enhancement of the plasmon fields along with more homogeneous distribution as well as the reduction of localized surface plasmon resonance (LSPR) quenching due to absorption. In this review, we summarize the efforts on the synthesis of hollow metal nanostructures with an emphasis on the galvanic replacement reaction. In the second part of this review, we discuss the advancements on the characterization of plasmonic properties of hollow nanostructures, covering the single nanoparticle experiments, nanoscale characterization via electron energy-loss spectroscopy and modeling and simulation studies. Examples of the applications, i.e. sensing, surface enhanced Raman spectroscopy, photothermal ablation therapy of cancer, drug delivery or catalysis among others, where hollow nanostructures perform better than their solid counterparts, are also evaluated. © 2016 Aziz Genç, Jordi Arbiol et al., published by De Gruyter.

  • Inorganic photocatalytic enhancement: Activated RhB Photodegradation by surface modification of SnO2 Nanocrystals with V2 O5-like species

    Epifani M., Kaciulis S., Mezzi A., Altamura D., Giannini C., Díaz R., Force C., Genç A., Arbiol J., Siciliano P., Comini E., Concina I. Scientific Reports; 7 ( 44763) 2017. 10.1038/srep44763. IF: 4.259

    SnO2 nanocrystals were prepared by precipitation in dodecylamine at 100 °C, then they were reacted with vanadium chloromethoxide in oleic acid at 250 °C. The resulting materials were heat-treated at various temperatures up to 650 °C for thermal stabilization, chemical purification and for studying the overall structural transformations. From the crossed use of various characterization techniques, it emerged that the as-prepared materials were constituted by cassiterite SnO2 nanocrystals with a surface modified by isolated V(IV) oxide species. After heat-treatment at 400 °C, the SnO2 nanocrystals were wrapped by layers composed of vanadium oxide (IV-V mixed oxidation state) and carbon residuals. After heating at 500 °C, only SnO2 cassiterite nanocrystals were obtained, with a mean size of 2.8 nm and wrapped by only V2 O5-like species. The samples heat-treated at 500 °C were tested as RhB photodegradation catalysts. At 10-7 M concentration, all RhB was degraded within 1 h of reaction, at a much faster rate than all pure SnO2 materials reported until now. © The Author(s) 2017.

  • Insights into the Performance of CoxNi1-xTiO3 Solid Solutions as Photocatalysts for Sun-Driven Water Oxidation

    Murcia-López S., Moschogiannaki M., Binas V., Andreu T., Tang P., Arbiol J., Jacas Biendicho J., Kiriakidis G., Morante J.R. ACS Applied Materials and Interfaces; 9 (46): 40290 - 40297. 2017. 10.1021/acsami.7b12994. IF: 7.504

    CoxNi1-xTiO3 systems evaluated as photo- and electrocatalytic materials for oxygen evolution reaction (OER) from water have been studied. These materials have shown promising properties for this half-reaction both under (unbiased) visible-light photocatalytic approach in the presence of an electron scavenger and as electrocatalysts in dark conditions in basic media. In both situations, Co0.8Ni0.2TiO3 exhibits the best performance and is proved to display high faradaic efficiency. A synergetic effect between Co and Ni is established, improving the physicochemical properties such as surface area and pore size distribution, besides affecting the donor density and the charge carrier separation. At higher Ni content, the materials exhibit behavior more similar to that of NiTiO3, which is a less suitable material for OER than CoTiO3. © 2017 American Chemical Society.

  • Low-Temperature Growth of Axial Si/Ge Nanowire Heterostructures Enabled by Trisilane

    Hui H.Y., De La Mata M., Arbiol J., Filler M.A. Chemistry of Materials; 29 (8): 3397 - 3402. 2017. 10.1021/acs.chemmater.6b03952. IF: 9.466

    Axial Si/Ge heterostructure nanowires, despite their promise in applications ranging from electronics to thermal transport, remain notoriously difficult to synthesize. Here, we grow axial Si/Ge heterostructures at low temperatures using a Au catalyst with a combination of trisilane and digermane. This approach yields, as determined with detailed electron microscopy characterization, arrays of epitaxial Si/Ge nanowires with excellent morphologies and purely axial composition profiles. Our data indicate that heterostructure formation can occur via the vapor-liquid-solid or vapor-solid-solid mechanism. These findings highlight the importance of precursor chemistry in semiconductor nanowire synthesis and open the door to Si/Ge nanowires with programmable quantum domains. © 2017 American Chemical Society.

  • Polybenzoxazine-Derived N-doped Carbon as Matrix for Powder-Based Electrocatalysts

    Barwe S., Andronescu C., Masa J., Ventosa E., Klink S., Genç A., Arbiol J., Schuhmann W. ChemSusChem; 10 (12): 2653 - 2659. 2017. 10.1002/cssc.201700593. IF: 7.226

    In addition to catalytic activity, intrinsic stability, tight immobilization on a suitable electrode surface, and sufficient electronic conductivity are fundamental prerequisites for the long-term operation of particle- and especially powder-based electrocatalysts. We present a novel approach to concurrently address these challenges by using the unique properties of polybenzoxazine (pBO) polymers, namely near-zero shrinkage and high residual-char yield even after pyrolysis at high temperatures. Pyrolysis of a nanocubic prussian blue analogue precursor (KmMnx[Co(CN)6]y⋅n H2O) embedded in a bisphenol A and aniline-based pBO led to the formation of a N-doped carbon matrix modified with MnxCoyOz nanocubes. The obtained electrocatalyst exhibits high efficiency toward the oxygen evolution reaction (OER) and more importantly a stable performance for at least 65 h. © 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

  • Probing the surface reactivity of nanocrystals by the catalytic degradation of organic dyes: The effect of size, surface chemistry and composition

    Piella J., Merkoçi F., Genç A., Arbiol J., Bastús N.G., Puntes V. Journal of Materials Chemistry A; 5 (23): 11917 - 11929. 2017. 10.1039/c7ta01328k. IF: 8.867

    We herein present a comprehensive study on how the catalytic performance and reusability of Au nanocrystals (NCs) are affected by systematic variations of crystal size, surface coating and composition. The reductions of different organic dyes (4-nitrophenol, rhodamine B and methylene blue) by borohydride ions were used as model catalytic reactions. The catalytic performance of the Au NCs ranged between 3.6 to 110 nm was found to be dependent on crystal size, indicating that Au surface atoms have a distinct size-dependent reactivity in this reaction. Similarly, the catalytic performance was found to be strongly dependent on the nature of the coating molecule, obtaining lower catalytic activities for molecules strongly bound to the Au surface. Finally, the catalytic performance was found to be dependent on the chemical composition of the NC (Au, Ag, Pt) and the model dye used as a testing system, with the highest degradation rate found for methylene blue, followed by 4-nitrophenol and rhodamine B. We believe that this study provides a better understanding of the catalytic performance of Au NCs upon controlled modifications of the structural and morphological parameters, and a working environment that can be used to facilitate the selection of the optimum NC size, coating molecule and evaluation system for a particular study of interest. © 2017 The Royal Society of Chemistry.

  • Solution-based synthesis and processing of Sn- and Bi-doped Cu3SbSe4 nanocrystals, nanomaterials and ring-shaped thermoelectric generators

    Liu Y., García G., Ortega S., Cadavid D., Palacios P., Lu J., Ibáñez M., Xi L., De Roo J., López A.M., Martí-Sánchez S., Cabezas I., Mata M.D.L., Luo Z., Dun C., Dobrozhan O., Carroll D.L., Zhang W., Martins J., Kovalenko M.V., Arbiol J., Noriega G., Song J., Wahnón P., Cabot A. Journal of Materials Chemistry A; 5 (6): 2592 - 2602. 2017. 10.1039/c6ta08467b. IF: 8.867

    Copper-based chalcogenides that comprise abundant, low-cost, and environmental friendly elements are excellent materials for a number of energy conversion applications, including photovoltaics, photocatalysis, and thermoelectrics (TE). In such applications, the use of solution-processed nanocrystals (NCs) to produce thin films or bulk nanomaterials has associated several potential advantages, such as high material yield and throughput, and composition control with unmatched spatial resolution and cost. Here we report on the production of Cu3SbSe4 (CASe) NCs with tuned amounts of Sn and Bi dopants. After proper ligand removal, as monitored by nuclear magnetic resonance and infrared spectroscopy, these NCs were used to produce dense CASe bulk nanomaterials for solid state TE energy conversion. By adjusting the amount of extrinsic dopants, dimensionless TE figures of merit (ZT) up to 1.26 at 673 K were reached. Such high ZT values are related to an optimized carrier concentration by Sn doping, a minimized lattice thermal conductivity due to efficient phonon scattering at point defects and grain boundaries, and to an increase of the Seebeck coefficient obtained by a modification of the electronic band structure with Bi doping. Nanomaterials were further employed to fabricate ring-shaped TE generators to be coupled to hot pipes, which provided 20 mV and 1 mW per TE element when exposed to a 160 °C temperature gradient. The simple design and good thermal contact associated with the ring geometry and the potential low cost of the material solution processing may allow the fabrication of TE generators with short payback times. © The Royal Society of Chemistry.

  • Solvothermal Synthesis, Gas-Sensing Properties, and Solar Cell-Aided Investigation of TiO2–MoOx Nanocrystals

    Epifani M., Kaciulis S., Mezzi A., Altamura D., Giannini C., Tang P., Morante J.R., Arbiol J., Siciliano P., Comini E., Concina I. ChemNanoMat; 3 (11): 798 - 807. 2017. 10.1002/cnma.201700160. IF: 2.937

    Titania anatase nanocrystals were prepared by sol-gel/solvothermal synthesis in oleic acid at 250 °C, and modified by co-reaction with Mo chloroalkoxide, aimed at investigating the effects on gas-sensing properties induced by tailored nanocrystals surface modification with ultra-thin layers of MoOx species. For the lowest Mo concentration, only anatase nanocrystals were obtained, surface modified by a disordered ultra-thin layer of mainly octahedral MoVI oxide species. For larger Mo concentrations, early MoO2 phase segregation occurred. Upon heat treatment up to 500 °C, the sample with the lowest Mo concentration did not feature any Mo oxide phase segregation, and the surface Mo layer was converted to dense octahedral MoVI oxide. At larger Mo concentrations all segregated MoO2 was converted to MoO3. The two different materials typologies, depending on the Mo concentration, were used for processing gas-sensing devices and tested toward acetone and carbon monoxide, which gave a greatly enhanced response, for all Mo concentrations, to acetone (two orders of magnitude) and carbon monoxide with respect to pure TiO2. For the lowest Mo concentration, dye-sensitized solar cells were also prepared to investigate the influence of anatase surface modification on the electrical transport properties, which showed that the charge transport mainly occurred in the ultra-thin MoOx surface layer. © 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

  • Surface-Guided Core-Shell ZnSe@ZnTe Nanowires as Radial p-n Heterojunctions with Photovoltaic Behavior

    Oksenberg E., Martí-Sánchez S., Popovitz-Biro R., Arbiol J., Joselevich E. ACS Nano; 11 (6): 6155 - 6166. 2017. 10.1021/acsnano.7b02199. IF: 13.942

    The organization of nanowires on surfaces remains a major obstacle toward their large-scale integration into functional devices. Surface-material interactions have been used, with different materials and substrates, to guide horizontal nanowires during their growth into well-organized assemblies, but the only guided nanowire heterostructures reported so far are axial and not radial. Here, we demonstrate the guided growth of horizontal core-shell nanowires, specifically of ZnSe@ZnTe, with control over their crystal phase and crystallographic orientations. We exploit the directional control of the guided growth for the parallel production of multiple radial p-n heterojunctions and probe their optoelectronic properties. The devices exhibit a rectifying behavior with photovoltaic characteristics upon illumination. Guided nanowire heterostructures enable the bottom-up assembly of complex semiconductor structures with controlled electronic and optoelectronic properties. © 2017 American Chemical Society.

  • Ultrathin High Surface Area Nickel Boride (NixB) Nanosheets as Highly Efficient Electrocatalyst for Oxygen Evolution

    Masa J., Sinev I., Mistry H., Ventosa E., de la Mata M., Arbiol J., Muhler M., Roldan Cuenya B., Schuhmann W. Advanced Energy Materials; 7 (17, 1700381) 2017. 10.1002/aenm.201700381. IF: 16.721

    The overriding obstacle to mass production of hydrogen from water as the premium fuel for powering our planet is the frustratingly slow kinetics of the oxygen evolution reaction (OER). Additionally, inadequate understanding of the key barriers of the OER is a hindrance to insightful design of advanced OER catalysts. This study presents ultrathin amorphous high-surface area nickel boride (NixB) nanosheets as a low-cost, very efficient and stable catalyst for the OER for electrochemical water splitting. The catalyst affords 10 mA cm−2 at 0.38 V overpotential during OER in 1.0 m KOH, reducing to only 0.28 V at 20 mA cm−2 when supported on nickel foam, which ranks it among the best reported nonprecious catalysts for oxygen evolution. Operando X-ray absorption fine-structure spectroscopy measurements reveal prevalence of NiOOH, as well as Ni-B under OER conditions, owing to a Ni-B core@nickel oxyhydroxide shell (Ni-B@NiOxH) structure, and increase in disorder of the NiOxH layer, thus revealing important insight into the transient states of the catalyst during oxygen evolution. © 2017 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

  • Unveiling the nucleation & coarsening mechanisms of solution-derived self-Assembled epitaxial Ce0.9Gd0.1O2-yNanostructures

    Queralto A., De La Mata M., Arbiol J., Hühne R., Obradors X., Puig T. Crystal Growth and Design; 17 (2): 504 - 516. 2017. 10.1021/acs.cgd.6b01358. IF: 4.055

    Self-Assembling approaches based on chemical solution deposition (CSD) are ideal methods for the cost-effective production of epitaxial nanostructures with high throughput. Therefore, an in-depth investigation of the nucleation and coarsening processes involved in the self-Assembly of nanostructures is mandatory to achieve a good control over nanostructure shape, dimensions, and orientation. Heteroepitaxial Ce0.9Gd0.1O2-y (CGO) is an ideal model system to unveil the underlying nanostructure development mechanisms in addition to their promising properties for catalysis, gas sensors, and ionic conductivity. Rapid thermal annealing furnaces have been used to study separately the thermodynamic and kinetic nucleation and coarsening mechanisms of self-Assembled CGO isotropic and anisotropic nanostructures based on strain-engineering and surface energies control. Different CGO nanoislands are obtained: isotropic (001)CGO nanodots are grown on (001)-oriented Y2O3:ZrO2(YSZ) and LaAlO3 (Lao) substrates, whereas (011)Lao substrates promote the growth of elongated (011)CGO nanowires. HRTEM and RHEED analyses are used to study the early stages of nucleation, as well as the shape and interfacial structure of CGO nanostructures. A systematic study with the heating ramp, annealing temperature and time, and strain in combination with thermally activated theoretical models provides information on the nucleation behavior, nucleation barriers, and atomic diffusion coefficients along in-plane and out-of-plane island orientations. Highly anisotropic atomic diffusion constants have been shown to be at the origin of the high aspect ratios of some of the nanostructures. Overall, our study provides a general method for the evaluation of nucleation and coarsening of multiple CSD-derived oxide nanostructures and understanding the shape development by combining thermodynamic and kinetic approaches. ©2016 American Chemical Society.


  • Co-Cu Nanoparticles: Synthesis by Galvanic Replacement and Phase Rearrangement during Catalytic Activation

    Nafria R., Genç A., Ibáñez M., Arbiol J., Ramírez De La Piscina P., Homs N., Cabot A. Langmuir; 32 (9): 2267 - 2276. 2016. 10.1021/acs.langmuir.5b04622. IF: 3.993

    The control of the phase distribution in multicomponent nanomaterials is critical to optimize their catalytic performance. In this direction, while impressive advances have been achieved in the past decade in the synthesis of multicomponent nanoparticles and nanocomposites, element rearrangement during catalyst activation has been frequently overseen. Here, we present a facile galvanic replacement-based procedure to synthesize Co@Cu nanoparticles with narrow size and composition distributions. We further characterize their phase arrangement before and after catalytic activation. When oxidized at 350 °C in air to remove organics, Co@Cu core-shell nanostructures oxidize to polycrystalline CuO-Co3O4 nanoparticles with randomly distributed CuO and Co3O4 crystallites. During a posterior reduction treatment in H2 atmosphere, Cu precipitates in a metallic core and Co migrates to the nanoparticle surface to form Cu@Co core-shell nanostructures. The catalytic behavior of such Cu@Co nanoparticles supported on mesoporous silica was further analyzed toward CO2 hydrogenation in real working conditions. © 2016 American Chemical Society.

  • Demonstrating the steady performance of iron oxide composites over 2000 cycles at fast charge-rates for Li-ion batteries

    Sun Z., Madej E., Genç A., Muhler M., Arbiol J., Schuhmann W., Ventosa E. Chemical Communications; 52 (46): 7348 - 7351. 2016. 10.1039/c6cc00168h. IF: 6.567

    The feasibility of using iron oxides as negative electrode materials for safe high-power Li-ion batteries is demonstrated by the carbon-coated FeOx/CNT composite synthesized by controlled pyrolysis of ferrocene, which delivered a specific capacity retention of 84% (445 mA h g-1) after 2000 cycles at 2000 mA g-1 (4C). © 2016 The Royal Society of Chemistry.

  • Disentangling Epitaxial Growth Mechanisms of Solution Derived Functional Oxide Thin Films

    Queraltó A., de la Mata M., Arbiol J., Obradors X., Puig T. Advanced Materials Interfaces; 3 (18, 1600392) 2016. 10.1002/admi.201600392. IF: 3.365

    This study investigates the mechanisms of epitaxial development and functional properties of oxide thin films (Ce0.9Zr0.1O2− y, LaNiO3, and Ba0.8Sr0.2TiO3) grown on single crystal substrates (Y2O3:ZrO2, LaAlO3, and SrTiO3) by the chemical solution deposition approach. Rapid thermal annealing furnaces are very powerful tools in this study providing valuable information of the early stages of nucleation, the kinetics of epitaxial film growth, and the coarsening of nanocrystalline phases. Advanced transmission electron microscopies, X-ray diffraction, and atomic force microscopy are employed to investigate the film microstructure and morphology, microstrain relaxation, and epitaxial crystallization. This study demonstrates that the isothermal evolution toward epitaxial film growth follows a self-limited process driven by atomic diffusion, and surface and interface energy minimization. All investigated oxides experience a transformation from the polycrystalline to the epitaxial phase. This study unequivocally evidences that the film thickness highly influences the epitaxial crystallization rate due to the competition between heterogeneous and homogeneous nucleation barriers and the fast coarsening of polycrystalline grains as compared to epitaxial growth. The investigated films possess good functional properties, and this study successfully confirms an improvement at long annealing times that can be correlated with grain boundary healing processes. Thick epitaxial films can be crystallized by growing sequential individual epitaxial layers. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

  • Enhanced Activity and Acid pH Stability of Prussian Blue-type Oxygen Evolution Electrocatalysts Processed by Chemical Etching

    Han L., Tang P., Reyes-Carmona A., Rodríguez-García B., Torréns M., Morante J.R., Arbiol J., Galan-Mascaros J.R. Journal of the American Chemical Society; 138 (49): 16037 - 16045. 2016. 10.1021/jacs.6b09778. IF: 13.038

    The development of upscalable oxygen evolving electrocatalysts from earth-abundant metals able to operate in neutral or acidic environments and low overpotentials remains a fundamental challenge for the realization of artificial photosynthesis. In this study, we report a highly active phase of heterobimetallic cyanide-bridged electrocatalysts able to promote water oxidation under neutral, basic (pH < 13), and acidic conditions (pH > 1). Cobalt-iron Prussian blue-type thin films, formed by chemical etching of Co(OH)1.0(CO3)0.5·nH2O nanocrystals, yield a dramatic enhancement of the catalytic performance toward oxygen production, when compared with previous reports for analogous materials. Electrochemical, spectroscopic, and structural studies confirm the excellent performance, stability, and corrosion resistance, even when compared with state-of-the-art metal oxide catalysts under moderate overpotentials and in a remarkably large pH range, including acid media where most cost-effective water oxidation catalysts are not useful. The origin of the superior electrocatalytic activity toward water oxidation appears to be in the optimized interfacial matching between catalyst and electrode surface obtained through this fabrication method. © 2016 American Chemical Society.

  • Enhanced thermoelectric performance of solution-derived bismuth telluride based nanocomposites via liquid-phase Sintering

    Zhang C., de la Mata M., Li Z., Belarre F.J., Arbiol J., Khor K.A., Poletti D., Zhu B., Yan Q., Xiong Q. Nano Energy; 30: 630 - 638. 2016. 10.1016/j.nanoen.2016.10.056. IF: 11.553

    Bismuth telluride based thermoelectric materials show great promise in electricity generation from waste heat and solid-state refrigeration, but improving their conversion efficiency with economical approaches for widespread use remains a challenge. An economical facile bottom-up approach has been developed to obtain nanostructured powders, which are used to build bulk thermoelectric materials. Using excess tellurium as sacrificial additive to enable liquid-phase sintering in the spark plasma sintering process, the lattice and bipolar contributions to the thermal conductivity are both greatly reduced without compromising too much the power factor, which leads to the achievement of high figure of merit (ZT) in both n-type and p-type bismuth telluride based nanocomposites. The ZT values are 1.59±0.16 for p-type Bi0.5Sb1.5Te3 and 0.98±0.07 for n-type Bi2Te2.7Se0.3 at 370 K, which are significantly high for bottom-up approaches. These results demonstrate that solution-chemistry approaches as facile, scalable and low-energy-intensive ways to achieve nanopowders, combined with liquid-phase sintering process, can open up great possibilities in developing high-performance low-price thermoelectric bulk nanocomposites. © 2016 Elsevier Ltd

  • Fe3O4@NiFexOy Nanoparticles with Enhanced Electrocatalytic Properties for Oxygen Evolution in Carbonate Electrolyte

    Luo Z., Martí-Sànchez S., Nafria R., Joshua G., De La Mata M., Guardia P., Flox C., Martínez-Boubeta C., Simeonidis K., Llorca J., Morante J.R., Arbiol J., Ibáñez M., Cabot A. ACS Applied Materials and Interfaces; 8 (43): 29461 - 29469. 2016. 10.1021/acsami.6b09888. IF: 7.145

    The design and engineering of earth-abundant catalysts that are both cost-effective and highly active for water splitting are crucial challenges in a number of energy conversion and storage technologies. In this direction, herein we report the synthesis of Fe3O4@NiFexOy core-shell nanoheterostructures and the characterization of their electrocatalytic performance toward the oxygen evolution reaction (OER). Such nanoparticles (NPs) were produced by a two-step synthesis procedure involving the colloidal synthesis of Fe3O4 nanocubes with a defective shell and the posterior diffusion of nickel cations within this defective shell. Fe3O4@NiFexOy NPs were subsequently spin-coated over ITO-covered glass and their electrocatalytic activity toward water oxidation in carbonate electrolyte was characterized. Fe3O4@NiFexOy catalysts reached current densities above 1 mA/cm2 with a 410 mV overpotential and Tafel slopes of 48 mV/dec, which is among the best electrocatalytic performances reported in carbonate electrolyte. © 2016 American Chemical Society.

  • High-performance thermoelectric nanocomposites from nanocrystal building blocks

    Ibáñez M., Luo Z., Genç A., Piveteau L., Ortega S., Cadavid D., Dobrozhan O., Liu Y., Nachtegaal M., Zebarjadi M., Arbiol J., Kovalenko M.V., Cabot A. Nature Communications; 7 ( 10766) 2016. 10.1038/ncomms10766. IF: 11.329

    The efficient conversion between thermal and electrical energy by means of durable, silent and scalable solid-state thermoelectric devices has been a long standing goal. While nanocrystalline materials have already led to substantially higher thermoelectric efficiencies, further improvements are expected to arise from precise chemical engineering of nanoscale building blocks and interfaces. Here we present a simple and versatile bottom-up strategy based on the assembly of colloidal nanocrystals to produce consolidated yet nanostructured thermoelectric materials. In the case study on the PbS-Ag system, Ag nanodomains not only contribute to block phonon propagation, but also provide electrons to the PbS host semiconductor and reduce the PbS intergrain energy barriers for charge transport. Thus, PbS-Ag nanocomposites exhibit reduced thermal conductivities and higher charge carrier concentrations and mobilities than PbS nanomaterial. Such improvements of the material transport properties provide thermoelectric figures of merit up to 1.7 at 850 K.

  • Mn3O4@CoMn2O4-CoxOy Nanoparticles: Partial Cation Exchange Synthesis and Electrocatalytic Properties toward the Oxygen Reduction and Evolution Reactions

    Luo Z., Irtem E., Ibánez M., Nafria R., Martĺ-Sánchez S., Genç A., De La Mata M., Liu Y., Cadavid D., Llorca J., Arbiol J., Andreu T., Morante J.R., Cabot A. ACS Applied Materials and Interfaces; 8 (27): 17435 - 17444. 2016. 10.1021/acsami.6b02786. IF: 7.145

    Mn3O4@CoMn2O4 nanoparticles (NPs) were produced at low temperature and ambient atmosphere using a one-pot two-step synthesis protocol involving the cation exchange of Mn by Co in preformed Mn3O4 NPs. Selecting the proper cobalt precursor, the nucleation of CoxOy crystallites at the Mn3O4@CoMn2O4 surface could be simultaneously promoted to form Mn3O4@CoMn2O4-CoxOy NPs. Such heterostructured NPs were investigated for oxygen reduction and evolution reactions (ORR, OER) in alkaline solution. Mn3O4@CoMn2O4-CoxOy NPs with [Co]/[Mn] = 1 showed low overpotentials of 0.31 V at -3 mA·cm-2 and a small Tafel slope of 52 mV·dec-1 for ORR, and overpotentials of 0.31 V at 10 mA·cm-2 and a Tafel slope of 81 mV·dec-1 for OER, thus outperforming commercial Pt-, IrO2-based and previously reported transition metal oxides. This cation-exchange-based synthesis protocol opens up a new approach to design novel heterostructured NPs as efficient nonprecious metal bifunctional oxygen catalysts. © 2016 American Chemical Society.

  • One-pot polyol synthesis of highly monodisperse short green silver nanorods

    Patarroyo J., Genç A., Arbiol J., Bastús N.G., Puntes V. Chemical Communications; 52 (73): 10960 - 10963. 2016. 10.1039/c6cc04796c. IF: 6.567

    Green silver nanorods (Ag NRs) of a low aspect ratio (2.8) have been produced in high yields via an optimized, simple, and robust one-pot polyol method in the presence of tannic acid, which favors the nucleation of decahedral seeds needed for the production of monodisperse Ag NRs. These Ag NRs were further used as sacrificial templates to produce Au hollow nanostructures via galvanic replacement reaction with HAuCl4 at room temperature. © 2016 The Royal Society of Chemistry.

  • Orientation symmetry breaking in self-assembled Ce1-: XGdxO2- y nanowires derived from chemical solutions

    Queraltó A., De La Mata M., Martínez L., Magén C., Gibert M., Arbiol J., Hühne R., Obradors X., Puig T. RSC Advances; 6 (99): 97226 - 97236. 2016. 10.1039/c6ra23717g. IF: 3.289

    Understanding the growth mechanisms of nanostructures obtained from chemical solutions, a high-throughput production methodology, is essential to correlate precisely the growth conditions with the nanostructures' morphology, dimensions and orientation. It is shown that self-organized (011)-oriented Ce0.9Gd0.1O2-y (CGO) nanowires having a single in-plane orientation are achieved when an anisotropic (011)-LaAlO3 (LAO) substrate is chosen. STEM and AFM images of the epitaxial nanowires reveal the (001)CGO[0-11](011)LAO[100] growth orientation, with the enlargement occurring along the [0-11]CGO direction with (111) lateral facets. The chosen substrate allowed us to study a unique case where the resulting biaxial strain is isotropic, while the dissimilar lateral surface energies are the key factor to obtain an energetically imbalanced and non-degenerated nanowire configuration. Rapid Thermal Annealing (RTA) has allowed sorting of experimental nucleation from coarsening and analysis of the kinetic phenomena of the nanowires. A thermodynamic driving force is shown to exist for a continuous elongation of the nanowires while the coarsening rates are found to be strongly temperature dependent and so kinetic effects are the key factors to control the size and density of the self-organized nanowire system. A remarkably fast nanowire growth rate (14-40 nm min-1) is observed, which we associate with a high atomic mobility probably linked to a high concentration of oxygen vacancies, as detected by XPS. These nanowires are envisaged as model systems pushing forward the study of low energetic and highly oxygen deficient {111} lateral facets useful for catalysis, gas sensors and ionic conductivity applications. © 2016 The Royal Society of Chemistry.

  • Orientationally Ordered Silicon Nanocrystal Cuboctahedra in Superlattices

    Yu Y., Lu X., Guillaussier A., Voggu V.R., Pineros W., De La Mata M., Arbiol J., Smilgies D.-M., Truskett T.M., Korgel B.A. Nano Letters; 16 (12): 7814 - 7821. 2016. 10.1021/acs.nanolett.6b04006. IF: 13.779

    Uniform silicon nanocrystals were synthesized with cuboctahedral shape and passivated with 1-dodecene capping ligands. Transmission electron microscopy, electron diffraction, and grazing incidence wide-angle and small-angle X-ray scattering show that these soft cuboctahedra assemble into face-centered cubic superlattices with orientational order. The preferred nanocrystal orientation was found to depend on the orientation of the superlattices on the substrate, indicating that the interactions with the substrate and assembly kinetics can influence the orientation of faceted nanocrystals in superlattices. © 2016 American Chemical Society.

  • Pd2Sn [010] nanorods as a highly active and stable ethanol oxidation catalyst

    Luo Z., Lu J., Flox C., Nafria R., Genç A., Arbiol J., Llorca J., Ibáñez M., Morante J.R., Cabot A. Journal of Materials Chemistry A; 4 (42): 16706 - 16713. 2016. 10.1039/c6ta06430b. IF: 8.262

    The development of highly active, low cost and stable electrocatalysts for direct alcohol fuel cells remains a critical challenge. While Pd2Sn has been reported as an excellent catalyst for the ethanol oxidation reaction (EOR), here we present DFT analysis results showing the (100) and (001) facets of orthorhombic Pd2Sn to be more favourable for the EOR than (010). Accordingly, using tri-n-octylphosphine, oleylamine (OLA) and methylamine hydrochloride as size and shape directing agents, we produced colloidal Pd2Sn nanorods (NRs) grown in the [010] direction. Such Pd2Sn NRs, supported on graphitic carbon, showed excellent performance and stability as an anode electrocatalyst for the EOR in alkaline media, exhibiting 3 times and 10 times higher EOR current densities than that of Pd2Sn and Pd nanospheres, respectively. We associate this improved performance with the favourable faceting of the NRs. © 2016 The Royal Society of Chemistry.

  • Polymer-Enhanced Stability of Inorganic Perovskite Nanocrystals and Their Application in Color Conversion LEDs

    Meyns M., Perálvarez M., Heuer-Jungemann A., Hertog W., Ibáñez M., Nafria R., Genç A., Arbiol J., Kovalenko M.V., Carreras J., Cabot A., Kanaras A.G. ACS Applied Materials and Interfaces; 8 (30): 19579 - 19586. 2016. 10.1021/acsami.6b02529. IF: 7.145

    Cesium lead halide (CsPbX3, X = Cl, Br, I) nanocrystals (NCs) offer exceptional optical properties for several potential applications but their implementation is hindered by a low chemical and structural stability and limited processability. In the present work, we developed a new method to efficiently coat CsPbX3 NCs, which resulted in their increased chemical and optical stability as well as processability. The method is based on the incorporation of poly(maleic anhydride-alt-1-octadecene) (PMA) into the synthesis of the perovskite NCs. The presence of PMA in the ligand shell stabilizes the NCs by tightening the ligand binding, limiting in this way the NC surface interaction with the surrounding media. We further show that these NCs can be embedded in self-standing silicone/glass plates as down-conversion filters for the fabrication of monochromatic green and white light emitting diodes (LEDs) with narrow bandwidths and appealing color characteristics. © 2016 American Chemical Society.

  • Quantum heterostructures based on GaAs nanomembranes for photonic applications

    Tütüncüoglu G., Friedl M., De La Mata M., Deianae D., Leran J.-B., Potts H., Matteini F., Arbiol J., Morral F.I. 2016 IEEE Photonics Society Summer Topical Meeting Series, SUM 2016; (7548759): 128 - 129. 2016. 10.1109/PHOSST.2016.7548759.

    III-V nanostructures are promising building blocks for future optoelectronics applications. In order to exploit the unique properties of the III-V nanostructures such as high carrier mobility, high spin-orbit interaction and optimum band-gap for various applications one needs to be able to grow nanostructures with high crystallinity and desired dimensions and configurations. © 2016 IEEE.

  • Scalable Heating-Up Synthesis of Monodisperse Cu2ZnSnS4 Nanocrystals

    Shavel A., Ibáñez M., Luo Z., De Roo J., Carrete A., Dimitrievska M., Gencì A., Meyns M., Pérez-Rodríguez A., Kovalenko M.V., Arbiol J., Cabot A. Chemistry of Materials; 28 (3): 720 - 726. 2016. 10.1021/acs.chemmater.5b03417. IF: 9.407

    Monodisperse Cu2ZnSnS4 (CZTS) nanocrystals (NCs), with quasi-spherical shape, were prepared by a facile, high-yield, scalable, and high-concentration heat-up procedure. The key parameters to minimize the NC size distribution were efficient mixing and heat transfer in the reaction mixture through intensive argon bubbling and improved control of the heating ramp stability. Optimized synthetic conditions allowed the production of several grams of highly monodisperse CZTS NCs per batch, with up to 5 wt % concentration in a crude solution and a yield above 90%. © 2016 American Chemical Society.

  • Surface Hydrogen Enables Subeutectic Vapor-Liquid-Solid Semiconductor Nanowire Growth

    Sivaram S.V., Hui H.Y., De La Mata M., Arbiol J., Filler M.A. Nano Letters; 16 (11): 6717 - 6723. 2016. 10.1021/acs.nanolett.6b01640. IF: 13.779

    Vapor-liquid-solid nanowire growth below the bulk metal-semiconductor eutectic temperature is known for several systems; however, the fundamental processes that govern this behavior are poorly understood. Here, we show that hydrogen atoms adsorbed on the Ge nanowire sidewall enable AuGe catalyst supercooling and control Au transport. Our approach combines in situ infrared spectroscopy to directly and quantitatively determine hydrogen atom coverage with a "regrowth" step that allows catalyst phase to be determined with ex situ electron microscopy. Maintenance of a supercooled catalyst with only hydrogen radical delivery confirms the centrality of sidewall chemistry. This work underscores the importance of the nanowire sidewall and its chemistry on catalyst state, identifies new methods to regulate catalyst composition, and provides synthetic strategies for subeutectic growth in other nanowire systems. © 2016 American Chemical Society.

  • Synergistic effects in 3D honeycomb-like hematite nanoflakes/branched polypyrrole nanoleaves heterostructures as high-performance negative electrodes for asymmetric supercapacitors

    Tang P.-Y., Han L.-J., Genç A., He Y.-M., Zhang X., Zhang L., Galán-Mascarós J.R., Morante J.R., Arbiol J. Nano Energy; 22: 189 - 201. 2016. 10.1016/j.nanoen.2016.02.019. IF: 11.553

    Rational assembly of unique branched heterostructures is one of the facile techniques to improve the electrochemical figure of merit of materials. By taking advantages of hydrogen bubbles dynamic template, hydrothermal method and electrochemical polymerization, branched polypyrrole (PPy) nanoleaves decorated honeycomb-like hematite nanoflakes (core-branch Fe2O3@PPy) are fabricated. X-ray diffraction, X-ray photoelectron spectroscopy, scanning electron microscopy, transmission electron microscopy (TEM), high-resolution TEM, and scanning transmission electron microscopy in high angle annular dark field mode with electron energy loss spectroscopy were combined to elucidate the mechanisms underlying formation and morphogenesis evolution of core-branch Fe2O3@PPy heterostructures. Benefiting from the stability of honeycomb-like hematite nanoflakes and the high conductivity of PPy nanoleaves, the resultant core-branch Fe2O3@PPy exhibits an ultrahigh capacitance of 1167.8 F g-1 at 1 A g-1 in 0.5 M Na2SO4 aqueous solution. Moreover, the assembled bi-metal oxides asymmetric supercapacitor (Fe2O3@PPy//MnO2) gives rise to a maximum energy density of 42.4 W h kg-1 and a maximum power density of 19.14 kW kg-1 with an excellent cycling performance of 97.1% retention after 3000 cycles at 3 A g-1. These performance features are superior than previous reported iron oxide/hydroxides based supercapacitors, offering an important guideline for future design of advanced next-generation supercapacitors. © 2016 Elsevier Ltd.

  • The Ethylhexanoate Route to Metal Oxide Nanocrystals: Synthesis of CoO Nanooctahedra from CoII2-Ethylhexanoate

    Epifani M., Tang P.-Y., Genç A., Morante J.R., Arbiol J., Díaz R., Wicker S. European Journal of Inorganic Chemistry; 2016 (24): 3963 - 3968. 2016. 10.1002/ejic.201600511. IF: 2.686

    CoO nanocrystals were prepared by solvothermal processing of Co 2-ethylhexanoate in oleylamine at 250 °C. The obtained products, identified as CoO by X-ray diffraction, had an octahedral shape, as seen by transmission electron microscopy, reflecting the cubic symmetry of the CoO crystallographic phase. The materials were converted into the Co3O4phase after heat treatment at 400 °C. The nanocrystal evolution was investigated by FTIR spectroscopy. It was concluded that weak oleylamine bonding to the nanocrystal surface during the synthesis step favored the exchange with 2-ethylhexanoato ligands, and that the interplay between the two ligands favored the kinetic control of the growth, resulting in the finally observed octahedral morphology. The Co3O4phase obtained from the heat treatment at 400 °C was used to process chemoresistive sensors, which were able to detect ethanol under dry and humid conditions (0 and 50 % r.h. H2O at 25 °C) at low temperatures (100 °C). © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

  • Thermoelectric properties of semiconductor-metal composites produced by particle blending

    Liu Y., Cadavid D., Ibáñez M., Ortega S., Martí-Sánchez S., Dobrozhan O., Kovalenko M.V., Arbiol J., Cabot A. APL Materials; 4 (10, 104813) 2016. 10.1063/1.4961679. IF: 4.323

    In the quest for more efficient thermoelectric material able to convert thermal to electrical energy and vice versa, composites that combine a semiconductor host having a large Seebeck coefficient with metal nanodomains that provide phonon scattering and free charge carriers are particularly appealing. Here, we present our experimental results on the thermal and electrical transport properties of PbS-metal composites produced by a versatile particle blending procedure, and where the metal work function allows injecting electrons to the intrinsic PbS host. We compare the thermoelectric performance of composites with microcrystalline or nanocrystalline structures. The electrical conductivity of the microcrystalline host can be increased several orders of magnitude with the metal inclusion, while relatively high Seebeck coefficient can be simultaneously conserved. On the other hand, in nanostructured materials, the host crystallites are not able to sustain a band bending at its interface with the metal, becoming flooded with electrons. This translates into even higher electrical conductivities than the microcrystalline material, but at the expense of lower Seebeck coefficient values. © 2016 Author(s).

  • Tuning the Plasmonic Response up: Hollow Cuboid Metal Nanostructures

    Genç A., Patarroyo J., Sancho-Parramon J., Arenal R., Duchamp M., Gonzalez E.E., Henrard L., Bastús N.G., Dunin-Borkowski R.E., Puntes V.F., Arbiol J. ACS Photonics; 3 (5): 770 - 779. 2016. 10.1021/acsphotonics.5b00667. IF: 5.404

    We report the fine-tuning of the localized surface plasmon resonances (LSPRs) from ultraviolet to near-infrared by nanoengineering the metal nanoparticle morphologies from solid Ag nanocubes to hollow AuAg nanoboxes and AuAg nanoframes. Spatially resolved mapping of plasmon resonances by electron energy loss spectroscopy (EELS) revealed a homogeneous distribution of highly intense plasmon resonances around the hollow nanostructures and the interaction, that is, hybridization, of inner and outer plasmon fields for the nanoframe. Experimental findings are accurately correlated with the boundary element method (BEM) simulations demonstrating that the homogeneous distribution of the plasmon resonances is the key factor for their improved plasmonic properties. As a proof of concept for these enhanced plasmonic properties, we show the effective label free sensing of bovine serum albumin (BSA) of single-walled AuAg nanoboxes in comparison with solid Au nanoparticles, demonstrating their excellent performance for future biomedical applications. © 2016 American Chemical Society.

  • Twin-Induced InSb Nanosails: A Convenient High Mobility Quantum System

    De La Mata M., Leturcq R., Plissard S.R., Rolland C., Magén C., Arbiol J., Caroff P. Nano Letters; 16 (2): 825 - 833. 2016. 10.1021/acs.nanolett.5b05125. IF: 13.779

    Ultra narrow bandgap III-V semiconductor nanomaterials provide a unique platform for realizing advanced nanoelectronics, thermoelectrics, infrared photodetection, and quantum transport physics. In this work we employ molecular beam epitaxy to synthesize novel nanosheet-like InSb nanostructures exhibiting superior electronic performance. Through careful morphological and crystallographic characterization we show how this unique geometry is the result of a single twinning event in an otherwise pure zinc blende structure. Four-terminal electrical measurements performed in both the Hall and van der Pauw configurations reveal a room temperature electron mobility greater than 12 000 cm2·V-1·s-1. Quantized conductance in a quantum point contact processed with a split-gate configuration is also demonstrated. We thus introduce InSb "nanosails" as a versatile and convenient platform for realizing new device and physics experiments with a strong interplay between electronic and spin degrees of freedom. © 2016 American Chemical Society.

  • Ultrafast Epitaxial Growth Kinetics in Functional Oxide Thin Films Grown by Pulsed Laser Annealing of Chemical Solutions

    Queraltó A., Pérez Del Pino A., De La Mata M., Arbiol J., Tristany M., Obradors X., Puig T. Chemistry of Materials; 28 (17): 6136 - 6145. 2016. 10.1021/acs.chemmater.6b01968. IF: 9.407

    The crystallization process and physical properties of different functional oxide thin films (Ce0.9Zr0.1O2-y, LaNiO3, Ba0.8Sr0.2TiO3, and La0.7Sr0.3MnO3) on single crystal substrates (Y2O3:ZrO2, LaAlO3, and SrTiO3) are studied by pulsed laser annealing (PLA). A Nd:YAG laser source (λ = 266 nm, 10 Hz and τ ∼3 ns) is employed to crystallize chemical solution deposited (CSD) amorphous/nanocrystalline films under atmospheric conditions. We provide new insight on the influence of photochemical and photothermal interactions on the epitaxial crystallization kinetics of oxide thin films during the transformation from amorphous/polycrystalline material (i.e., atomic diffusion, epitaxial growth rates, and activation energies of nucleation and crystallization). The epitaxial growth is investigated by varying the laser fluence and the applied number of pulses. The morphology, structure, and epitaxial evolution of films are evaluated by means of atomic force and transmission electron microscopies and X-ray diffraction. Highly epitaxial oriented films of 20-40 nm in thickness are obtained by PLA. The crystallization kinetics of laser treatments is determined to be orders of magnitude faster than thermal treatments with similar activation energies (1.5-4.1 eV), mainly due to the large temperature gradients inducing modified atomic diffusion mechanisms derived mainly from photothermal interactions, as well as a minor contribution of photochemical effects. The fast heating rates achieved by PLA also contribute to the fast epitaxial growth due to reduced coarsening of polycrystalline material. The measurement of the physical properties (electrical resistivity and magnetism) of laser processed CSD films has revealed significantly good functionalities, close to those of thermally grown films, but with much shorter processing times. © 2016 American Chemical Society.

  • UV Photosensing Characteristics of Nanowire-Based GaN/AlN Superlattices

    Lähnemann J., Den Hertog M., Hille P., De La Mata M., Fournier T., Schörmann J., Arbiol J., Eickhoff M., Monroy E. Nano Letters; 16 (5): 3260 - 3267. 2016. 10.1021/acs.nanolett.6b00806. IF: 13.779

    We have characterized the photodetection capabilities of single GaN nanowires incorporating 20 periods of AlN/GaN:Ge axial heterostructures enveloped in an AlN shell. Transmission electron microscopy confirms the absence of an additional GaN shell around the heterostructures. In the absence of a surface conduction channel, the incorporation of the heterostructure leads to a decrease of the dark current and an increase of the photosensitivity. A significant dispersion in the magnitude of dark currents for different single nanowires is attributed to the coalescence of nanowires with displaced nanodisks, reducing the effective length of the heterostructure. A larger number of active nanodisks and AlN barriers in the current path results in lower dark current and higher photosensitivity and improves the sensitivity of the nanowire to variations in the illumination intensity (improved linearity). Additionally, we observe a persistence of the photocurrent, which is attributed to a change of the resistance of the overall structure, particularly the GaN stem and cap sections. As a consequence, the time response is rather independent of the dark current. © 2016 American Chemical Society.


  • Cu2ZnSnS4-Ag2S Nanoscale p-n Heterostructures as Sensitizers for Photoelectrochemical Water Splitting

    Yu X., Liu J., Genç A., Ibáñez M., Luo Z., Shavel A., Arbiol J., Zhang G., Zhang Y., Cabot A. Langmuir; 31 (38): 10555 - 10561. 2015. 10.1021/acs.langmuir.5b02490. IF: 4.457

    A cation exchange-based route was used to produce Cu2ZnSnS4 (CZTS)-Ag2S nanoparticles with controlled composition. We report a detailed study of the formation of such CZTS-Ag2S nanoheterostructures and of their photocatalytic properties. When compared to pure CZTS, the use of nanoscale p-n heterostructures as light absorbers for photocatalytic water splitting provides superior photocurrents. We associate this experimental fact to a higher separation efficiency of the photogenerated electron-hole pairs. We believe this and other type-II nanoheterostructures will open the door to the use of CZTS, with excellent light absorption properties and made of abundant and environmental friendly elements, to the field of photocatalysis. © 2015 American Chemical Society.

  • Cu2ZnSnS4-PtM (M = Co, Ni) Nanoheterostructures for Photocatalytic Hydrogen Evolution

    Yu X., An X., Genç A., Ibáñez M., Arbiol J., Zhang Y., Cabot A. Journal of Physical Chemistry C; 119 (38): 21882 - 21888. 2015. 10.1021/acs.jpcc.5b06199. IF: 4.772

    We report the synthesis and photocatalytic and magnetic characterization of colloidal nanoheterostructures formed by combining a Pt-based magnetic metal alloy (PtCo, PtNi) with Cu2ZnSnS4 (CZTS). While CZTS is one of the main candidate materials for solar energy conversion, the introduction of a Pt-based alloy on its surface strongly influences its chemical and electronic properties, ultimately determining its functionality. In this regard, up to a 15-fold increase of the photocatalytic hydrogen evolution activity was obtained with CZTS-PtCo when compared with CZTS. Furthermore, two times higher hydrogen evolution rates were obtained for CZTS-PtCo when compared with CZTS-Pt, in spite of the lower precious metal loading of the former. Besides, the magnetic properties of the PtCo nanoparticles attached to the CZTS nanocrystals were retained in the heterostructures, which could facilitate catalyst purification and recovery for its posterior recycling and/or reutilization. © 2015 American Chemical Society.

  • Electron Bottleneck in the Charge/Discharge Mechanism of Lithium Titanates for Batteries

    Ventosa E., Skoumal M., Vazquez F.J., Flox C., Arbiol J., Morante J.R. ChemSusChem; 8 (10): 1737 - 1744. 2015. 10.1002/cssc.201500349. IF: 7.657

    The semi-solid flow battery (SSFB) is a promising storage energy technology featured by employing semi-solid fluid electrodes containing conductive additive and active Li-ion battery materials. The state of art anode material for SSFB is Li4Ti5O12 (LTO). This work shows that LTO improves drastically the performance in fluid electrode via hydrogen annealing manifesting the importance of the electrical conductivity of the active material in SSFBs. On the other hand, the properties of fluid electrodes allow the contributions of ionic and electrical resistance to be separated in operando. The asymmetric overpotential observed in Li4Ti5O12 and TiO2 is proposed to originate from the so-called electron bottleneck mechanism based on the transformation from electrically insulator to conductor upon (de-)lithiation, or vice versa, which should be considered when modelling, evaluating or designing advanced materials based on Li4Ti5O12, TiO2 or others with insulating-conducting behavior materials. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  • Enhanced reactivity of high-index surface platinum hollow nanocrystals

    González E., Merkoçi F., Arenal R., Arbiol J., Esteve J., Bastús N.G., Puntes V. Journal of Materials Chemistry A; 4 (1): 200 - 208. 2015. 10.1039/c5ta07504a. IF: 7.443

    The precise morphological control of the surface of inorganic nanocrystals (NCs) is critical for the understanding of the unique properties of the materials at the nanoscale and useful in a wide range of applications, such as catalysis, where the development of highly active and low-cost materials represents a landmark for the development of industrial technologies. Here we show how combining solid state chemistry and colloidal synthesis allows us to prepare exotic materials, in particular, PtAg@Pt single-crystal hollow NCs with high-index planes synthesized at room temperature by controlled corrosion of silver templates, which minimize Pt consumption and maximize surface reactivity. © The Royal Society of Chemistry 2016.

  • High aspect ratio gold nanorods grown with platinum seeds

    Varón M., Arbiol J., Puntes V.F. Journal of Physical Chemistry C; 119 (21): 11818 - 11825. 2015. 10.1021/acs.jpcc.5b01263. IF: 4.772

    Using Au chloride as precursor, Pt nanocrystals as seeds, ascorbic acid as a reducer, and CTAB as surfactant and complexing agent, extremely long Au nanorods have been grown. The influence of different parameters such as the composition of the seeds, the amount of Pt, or the type of Pt present in solution has been analyzed. These large Au NRs have been exhaustively characterized by (S)TEM, SEM and optical microscopy as well as UV-vis spectroscopy and their morphology correlated with the growth mechanism. © 2015 American Chemical Society.

  • High yield of gaas nanowire arrays on si mediated by the pinning and contact angle of Ga

    Russo-Averchi E., Vukajlovic Plestina J., Tütüncüoglu G., Matteini F., Dalmau-Mallorquí A., De La Mata M., Rüffer D., Potts H.A., Arbiol J., Conesa-Boj S., Fontcuberta I. Morral A. Nano Letters; 15 (5): 2869 - 2874. 2015. 10.1021/nl504437v. IF: 13.592

    GaAs nanowire arrays on silicon offer great perspectives in the optoelectronics and solar cell industry. To fulfill this potential, gold-free growth in predetermined positions should be achieved. Ga-assisted growth of GaAs nanowires in the form of array has been shown to be challenging and difficult to reproduce. In this work, we provide some of the key elements for obtaining a high yield of GaAs nanowires on patterned Si in a reproducible way: contact angle and pinning of the Ga droplet inside the apertures achieved by the modification of the surface properties of the nanoscale areas exposed to growth. As an example, an amorphous silicon layer between the crystalline substrate and the oxide mask results in a contact angle around 90°, leading to a high yield of vertical nanowires. Another example for tuning the contact angle is anticipated, native oxide with controlled thickness. This work opens new perspectives for the rational and reproducible growth of GaAs nanowire arrays on silicon. © 2015 American Chemical Society.

  • High-yield synthesis and optical properties of g-C3N4

    Yuan Y., Zhang L., Xing J., Utama M.I.B., Lu X., Du K., Li Y., Hu X., Wang S., Genc A., Dunin-Borkowski R., Arbiol J., Xiong Q. Nanoscale; 7 (29): 12343 - 12350. 2015. 10.1039/c5nr02905h. IF: 7.394

    Graphitic carbon nitride (g-C3N4), a metal-free semiconductor with a band gap of 2.7 eV, has received considerable attention owing to its fascinating photocatalytic performances under visible-light. g-C3N4 exhibits high thermal and chemical stability and non-toxicity such that it has been considered as the most promising photocatalyst for environmental improvement and energy conservation. Hence, it is of great importance to obtain high-quality g-C3N4 and gain a clear understanding of its optical properties. Herein, we report a high-yield synthesis of g-C3N4 products via heating of high vacuum-sealed melamine powder in an ampoule at temperatures between 450 and 650°C. Using transmission electron microscopy (TEM), scanning transmission electron microscopy (STEM), electron energy loss spectroscopy (EELS), thermogravimetric analysis (TGA), X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS), the chemical composition and crystallization of the as-produced g-C3N4 are demonstrated. A systematic optical study of g-C3N4 is carried out with several approaches. The optical phonon behavior of g-C3N4 is revealed by infrared and Raman spectroscopy, and the emission properties of g-C3N4 are investigated using photoluminescence (PL) spectroscopy, while the photocatalytic properties are explored by the photodegradation experiment. This journal is © The Royal Society of Chemistry.

  • Long-lived excitons in GaN/AlN nanowire heterostructures

    Beeler M., Lim C.B., Hille P., Bleuse J., Schörmann J., De La Mata M., Arbiol J., Eickhoff M., Monroy E. Physical Review B - Condensed Matter and Materials Physics; 91 (20, 205440) 2015. 10.1103/PhysRevB.91.205440. IF: 3.736

    GaN/AlN nanowire heterostructures can display photoluminescence (PL) decay times on the order of microseconds that persist up to room temperature. Doping the GaN nanodisk insertions with Ge can reduce these PL decay times by two orders of magnitude. These phenomena are explained by the three-dimensional electric field distribution within the GaN nanodisks, which has an axial component in the range of a few MV/cm associated to the spontaneous and piezoelectric polarization, and a radial piezoelectric contribution associated to the shear components of the lattice strain. At low dopant concentrations, a large electron-hole separation in both the axial and radial directions is present. The relatively weak radial electric fields, which are about one order of magnitude smaller than the axial fields, are rapidly screened by doping. This bidirectional screening leads to a radial and axial centralization of the hole underneath the electron, and consequently, to large decreases in PL decay times, in addition to luminescence blue shifts. © Published by the American Physical Society.

  • Phonon Engineering in Isotopically Disordered Silicon Nanowires

    Mukherjee S., Givan U., Senz S., Bergeron A., Francoeur S., De La Mata M., Arbiol J., Sekiguchi T., Itoh K.M., Isheim D., Seidman D.N., Moutanabbir O. Nano Letters; 15 (6): 3885 - 3893. 2015. 10.1021/acs.nanolett.5b00708. IF: 13.592

    The introduction of stable isotopes in the fabrication of semiconductor nanowires provides an additional degree of freedom to manipulate their basic properties, design an entirely new class of devices, and highlight subtle but important nanoscale and quantum phenomena. With this perspective, we report on phonon engineering in metal-catalyzed silicon nanowires with tailor-made isotopic compositions grown using isotopically enriched silane precursors 28SiH4, 29SiH4, and 30SiH4 with purity better than 99.9%. More specifically, isotopically mixed nanowires 28Six30Si1-x with a composition close to the highest mass disorder (x ∼ 0.5) were investigated. The effect of mass disorder on the phonon behavior was elucidated and compared to that in isotopically pure 29Si nanowires having a similar reduced mass. We found that the disorder-induced enhancement in phonon scattering in isotopically mixed nanowires is unexpectedly much more significant than in bulk crystals of close isotopic compositions. This effect is explained by a nonuniform distribution of 28Si and 30Si isotopes in the grown isotopically mixed nanowires with local compositions ranging from x = ∼0.25 to 0.70. Moreover, we also observed that upon heating, phonons in 28Six30Si1-x nanowires behave remarkably differently from those in 29Si nanowires suggesting a reduced thermal conductivity induced by mass disorder. Using Raman nanothermometry, we found that the thermal conductivity of isotopically mixed 28Six30Si1-x nanowires is ∼30% lower than that of isotopically pure 29Si nanowires in agreement with theoretical predictions. (Figure Presented). © 2015 American Chemical Society.

  • Position-controlled growth of GaN nanowires and nanotubes on diamond by molecular beam epitaxy

    Schuster F., Hetzl M., Weiszer S., Garrido J.A., De La Mata M., Magen C., Arbiol J., Stutzmann M. Nano Letters; 15 (3): 1773 - 1779. 2015. 10.1021/nl504446r. IF: 13.592

    In this work the position-controlled growth of GaN nanowires (NWs) on diamond by means of molecular beam epitaxy is investigated. In terms of growth, diamond can be seen as a model substrate, providing information of systematic relevance also for other substrates. Thin Ti masks are structured by electron beam lithography which allows the fabrication of perfectly homogeneous GaN NW arrays with different diameters and distances. While the wurtzite NWs are found to be Ga-polar, N-polar nucleation leads to the formation of tripod structures with a zinc-blende core which can be efficiently suppressed above a substrate temperature of 870 °C. A variation of the III/V flux ratio reveals that both axial and radial growth rates are N-limited despite the globally N-rich growth conditions, which is explained by the different diffusion behavior of Ga and N atoms. Furthermore, it is shown that the hole arrangement has no effect on the selectivity but can be used to force a transition from nanowire to nanotube growth by employing a highly competitive growth regime. © 2015 American Chemical Society.

  • Resonant tunnelling features in a suspended silicon nanowire single-hole transistor

    Llobet J., Krali E., Wang C., Arbiol J., Jones M.E., Pérez-Murano F., Durrani Z.A.K. Applied Physics Letters; 107 (22, 223501) 2015. 10.1063/1.4936757. IF: 3.302

    Suspended silicon nanowires have significant potential for a broad spectrum of device applications. A suspended p-type Si nanowire incorporating Si nanocrystal quantum dots has been used to form a single-hole transistor. Transistor fabrication uses a novel and rapid process, based on focused gallium ion beam exposure and anisotropic wet etching, generating <10 nm nanocrystals inside suspended Si nanowires. Electrical characteristics at 10 K show Coulomb diamonds with charging energy ∼27 meV, associated with a single dominant nanocrystal. Resonant tunnelling features with energy spacing ∼10 meV are observed, parallel to both diamond edges. These may be associated either with excited states or hole-acoustic phonon interactions, in the nanocrystal. In the latter case, the energy spacing corresponds well with reported Raman spectroscopy results and phonon spectra calculations. © 2015 AIP Publishing LLC.

  • Semiconductor Nanowires: Materials, Synthesis, Characterization and Applications

    Arbiol J., Xiong Q. Semiconductor Nanowires: Materials, Synthesis, Characterization and Applications; : 1 - 554. 2015. 10.1016/C2013-0-16507-5.

    Semiconductor nanowires promise to provide the building blocks for a new generation of nanoscale electronic and optoelectronic devices. Semiconductor Nanowires: Materials, Synthesis, Characterization and Applications covers advanced materials for nanowires, the growth and synthesis of semiconductor nanowires�including methods such as solution growth, MOVPE, MBE, and self-organization. Characterizing the properties of semiconductor nanowires is covered in chapters describing studies using TEM, SPM, and Raman scattering. Applications of semiconductor nanowires are discussed in chapters focusing on solar cells, battery electrodes, sensors, optoelectronics and biology. Explores a selection of advanced materials for semiconductor nanowires Outlines key techniques for the property assessment and characterization of semiconductor nanowires Covers a broad range of applications across a number of fields © 2015 Elsevier Inc. All rights reserved.

  • Size and aspect ratio control of Pd2Sn nanorods and their water denitration properties

    Luo Z., Ibáñez M., Antolín A.M., Genç A., Shavel A., Contreras S., Medina F., Arbiol J., Cabot A. Langmuir; 31 (13): 3952 - 3957. 2015. 10.1021/la504906q. IF: 4.457

    Monodisperse Pd2Sn nanorods with tuned size and aspect ratio were prepared by co-reduction of metal salts in the presence of trioctylphosphine, amine, and chloride ions. Asymmetric Pd2Sn nanostructures were achieved by the selective desorption of a surfactant mediated by chlorine ions. A preliminary evaluation of the geometry influence on catalytic properties evidenced Pd2Sn nanorods to have improved catalytic performance. In view of these results, Pd2Sn nanorods were also evaluated for water denitration. © 2015 American Chemical Society.

  • Strain-induced spatially indirect exciton recombination in zinc-blende/wurtzite CdS heterostructures

    Li D., Liu Y., de la Mata M., Magen C., Arbiol J., Feng Y., Xiong Q. Nano Research; 8 (9): 3035 - 3044. 2015. 10.1007/s12274-015-0809-8. IF: 7.010

    Strain engineering provides an effective mean of tuning the fundamental properties of semiconductors for electric and optoelectronic applications. Here we report on how the applied strain changes the emission properties of hetero-structures consisting of different crystalline phases in the same CdS nanobelts. The strained portion was found to produce an additional emission peak on the low-energy side that was blueshifted with increasing strain. Furthermore, the additional emission peak obeyed the Varshni equation with temperature and exhibited the band-filling effect at high excitation power. This new emission peak may be attributed to spatially indirect exciton recombination between different crystalline phases of CdS. First-principles calculations were performed based on the spatially indirect exciton recombination, and the calculated and experimental results agreed with one another. Strain proved to be capable of enhancing the anti-Stokes emission, suggesting that the efficiency of laser cooling may be improved by strain engineering. [Figure not available: see fulltext.] © 2015, Tsinghua University Press and Springer-Verlag Berlin Heidelberg.

  • Surface modification of TiO2 nanocrystals by WOx coating or wrapping: Solvothermal synthesis and enhanced surface chemistry

    Epifani M., Diaz R., Force C., Comini E., Manzanares M., Andreu T., Gencc A., Arbiol J., Siciliano P., Faglia G., Morante J.R. ACS Applied Materials and Interfaces; 7 (12): 6898 - 6908. 2015. 10.1021/acsami.5b00632. IF: 6.723

    TiO2 anatase nanocrystals were prepared by solvothermal processing of Ti chloroalkoxide in oleic acid, in the presence of W chloroalkoxide, with W/Ti nominal atomic concentration (Rw) ranging from 0.16 to 0.64. The as-prepared materials were heat-treated up to 500 °C for thermal stabilization and sensing device processing. For R0.16, the as-prepared materials were constituted by an anatase core surface-modified by WOx monolayers. This structure persisted up to 500 °C, without any WO3 phase segregation. For Rw up to R0.64, the anatase core was initially wrapped by an amorphous WOx gel. Upon heat treatment, the WOx phase underwent structural reorganization, remaining amorphous up to 400 °C and forming tiny WO3 nanocrystals dispersed into the TiO2 host after heating at 500 °C, when part of tungsten also migrated into the TiO2 structure, resulting in structural and electrical modification of the anatase host. The ethanol sensing properties of the various materials were tested and compared with pure TiO2 and WO3 analogously prepared. They showed that even the simple surface modification of the TiO2 host resulted in a 3 orders of magnitude response improvement with respect to pure TiO2. © 2015 American Chemical Society.

  • Towards defect-free 1-D GaAs/AlGaAs heterostructures based on GaAs nanomembranes

    Tutuncuoglu G., De La Mata M., Deiana D., Potts H., Matteini F., Arbiol J., Fontcuberta I Morral A. Nanoscale; 7 (46): 19453 - 19460. 2015. 10.1039/c5nr04821d. IF: 7.394

    We demonstrate the growth of defect-free zinc-blende GaAs nanomembranes by molecular beam epitaxy. Our growth studies indicate a strong impact of As4 re-emission and shadowing in the growth rate of the structures. The highest aspect ratio structures are obtained for pitches around 0.7-1 μm and a gallium rate of 1 Å s-1. The functionality of the membranes is further illustrated by the growth of quantum heterostructures (such as quantum wells) and the characterization of their optical properties at the nanoscale. This proves the potential of nanoscale membranes for optoelectronic applications. © 2015 The Royal Society of Chemistry.

  • What do you do, titanium? Insight into the role of titanium oxide as a water oxidation promoter in hematite-based photoanodes

    Monllor-Satoca D., Bärtsch M., Fàbrega C., Genç A., Reinhard S., Andreu T., Arbiol J., Niederberger M., Morante J.R. Energy and Environmental Science; 8 (11): 3242 - 3254. 2015. 10.1039/c5ee01679g. IF: 20.523

    Hematite (α-Fe2O3) is a promising photoanode in solar water splitting devices with a set of intrinsic limitations that lessen its maximum performance; among the methods used for improving its photoactivity, titanium doping has witnessed an intensive research during recent years. However, the origin of the Ti-induced enhancement remains elusive to date with the lack of a systematic mechanistic study. In this contribution, we prepared mesoporous hematite (host)-titania (guest) composite films by mixing the respective preformed nanoparticles obtained by a non-aqueous sol-gel route in a wide range of loading levels (0-20 mol%) up to the solid state solubility limits of both components. Voltammetric and impedance measurements were performed observing an optimum 10% doping, with a 15-fold photocurrent increase (up to 1.3 mA cm-2 at 1.23 VRHE) and a 100-fold decrease in the charge transfer resistance. The roles of surface states and charge donor (dopant) densities were also assessed, assuming a charge transfer mechanism through hole trapping at surface states and its isoenergetic transfer to water; an optimum 10-15% doping range was obtained similarly to photocurrent, where the maximum overlapping between surface and water states is prevalent. Finally, HR-TEM and EELS measurements were employed to detect the presence of pseudobrookite and titania phases (20% doping), evincing that hematite-pseudobrookite heterojunctions have a beneficial cascade of charge transfers but titania-pseudobrookite heterojunctions depict a deleterious "hole mirror" mechanism that prevents water photooxidation. Tailoring the combined effect of donor states (conductivity), phase coexistence (solubility), heterojunctions (energetics) and surface states (kinetics) in the composite paves the way for understanding the mechanism of other dopant-induced changes and could be extended to further photoactive materials. © 2015 The Royal Society of Chemistry.


  • Enabling electromechanical transduction in silicon nanowire mechanical resonators fabricated by focused ion beam implantation

    Llobet, J.; Sansa, M.; Gerbolés, M.; Mestres, N.; Arbiol, J.; Borrisé, X.; Pérez-Murano, F. Nanotechnology; 2014. 10.1088/0957-4484/25/13/135302. IF: 3.672

  • Programmed iron oxide nanoparticles disintegration in anaerobic digesters boosts biogas production

    Casals, E.; Barrena, R.; García, A.; González, E.; Delgado, L.; Busquets-Fité, M.; Font, X.; Arbiol, J.; Glatzel, P.; Kvashnina, K.; Sánchez, A.; Puntes, V. Small; 10 (14): 2801 - 2808. 2014. 10.1002/smll.201303703. IF: 7.514


  • Spontaneous formation of hollow cobalt oxide nanoparticles by the Kirkendall effect at room temperature at the water-air interface

    Varón, M.; Ojea-Jimenez, I.; Arbiol, J.; Balcells, L.; Martínez, B.; Puntes, V.F. Nanoscale; 5: 2429 - 2436. 2013. 10.1039/c2nr32657d. IF: 6.233


  • Citrate-Coated Gold Nanoparticles As Smart Scavengers for Mercury(II) Removal from Polluted Waters

    Ojea-Jiménez, I.; López, X.; Arbiol, J.; Puntes, V. ACS Nano; 6: 2253 - 2260. 2012. .

  • Synthesis of co-organosilane-Au nanocomposites via a controlled interphasic reduction

    Ojea-Jiménez, I.; Lorenzo, J.; Rebled, J.M.; Sendra, J.; Arbiol, J.; Puntes, V. Chemistry of Materials; 24: 4019 - 4027. 2012. 10.1021/cm300757j.


  • Carving at the nanoscale: Sequential galvanic exchange and Kirkendall growth at room temperature

    González, E.; Arbiol, J.; Puntes, V.F. SCIENCE; 334: 1377 - 1380. 2011. 10.1126/science.1212822.

  • Pt nanocrystal evolution in the presence of Au(iii)-salts at room temperature: Spontaneous formation of AuPt heterodimers

    Lim, S.I.; Varon, M.; Ojea-Jiménez, I.; Arbiol, J.; Puntes, V. Journal of Materials Chemistry; 21: 11518 - 11523. 2011. 10.1039/c1jm10313j.


  • Exploring the limitations of the use of competing reducers to control the morphology and composition of Pt and PtCo nanocrystals

    Lim, S.I.; Varón, M.; Ojea-Jiménez, I.; Arbiol, J.; Puntes, V. Chemistry of Materials; 22: 4495 - 4504. 2010. 10.1021/cm101436p.

  • Size-dependent passivation shell and magnetic properties in antiferromagnetic/ferrimagnetic core/shell MnO nanoparticles

    Lopez-Ortega, A.; Tobia, D.; Winkler, E.; Golosovsky, I.V.; Salazar-Alvarez, G.; Estrade, S.; Estrader, M.; Sort, J.; González, M.A.; Suriñach, S.; Arbiol, J.; Peiró, F.; Zysler, R.D.; Baro, M.D.; Nogués, J. Journal of the American Chemical Society; 132: 9398 - 9407. 2010. 10.1021/ja1021798.

  • Synthesis of platinum cubes, polypods, cuboctahedrons, and raspberries assisted by cobalt nanocrystals

    Lim, S.I.; Ojea-Jiménez, I.; Varon, M.; Casals, E.; Arbiol, J.; Puntes, V. Nano Letters; 10: 964 - 973. 2010. 10.1021/nl100032c.