Staff directory Xu Han

Publications

2022

  • 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.


  • 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.


  • Antibacterial Films Based on MOF Composites that Release Iodine Passively or Upon Triggering by Near-Infrared Light

    Han X., Boix G., Balcerzak M., Moriones O.H., Cano-Sarabia M., Cortés P., Bastús N., Puntes V., Llagostera M., Imaz I., Maspoch D. Advanced Functional Materials; 32 (19, 2112902) 2022. 10.1002/adfm.202112902. IF: 18.808

    Multidrug-resistant bacteria have become a global health problem for which new prophylactic strategies are now needed, including surface-coatings for hospital spaces and medical equipment. This work reports the preparation and functional validation of a metal-organic framework (MOF) based composite for the triggered controlled release of iodine, an antimicrobial element that does not generate resistance. It comprises beads of the iodophilic MOF UiO-66 containing encapsulated gold nanorods (AuNRs) coated with a silica shell. Irradiation of the AuNRs with near-infrared light (NIR) provokes a photothermal effect and the resultant heat actively liberates the iodine. After validating the performance of this composite, it is integrated into a polymer for the development of antibacterial films. This work assesses the adsorption of iodine into these composite films, as well as its passive long-term release and active light-triggered. Finally, this work validates the antibacterial activity of the composite films in vitro against gram-positive and gram-negative bacteria. The findings will surely inform the development of new prophylactic treatments. © 2022 Wiley-VCH GmbH.


  • 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


  • 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.


  • 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.


  • How Reproducible are Surface Areas Calculated from the BET Equation?

    Osterrieth J.W.M., Rampersad J., Madden D., Rampal N., Skoric L., Connolly B., Allendorf M.D., Stavila V., Snider J.L., Ameloot R., Marreiros J., Ania C., Azevedo D., Vilarrasa-Garcia E., Santos B.F., Bu X.-H., Chang Z., Bunzen H., Champness N.R., Griffin S.L., Chen B., Lin R.-B., Coasne B., Cohen S., Moreton J.C., Colón Y.J., Chen L., Clowes R., Coudert F.-X., Cui Y., Hou B., D'Alessandro D.M., Doheny P.W., Dincă M., Sun C., Doonan C., Huxley M.T., Evans J.D., Falcaro P., Ricco R., Farha O., Idrees K.B., Islamoglu T., Feng P., Yang H., Forgan R.S., Bara D., Furukawa S., Sanchez E., Gascon J., Telalović S., Ghosh S.K., Mukherjee S., Hill M.R., Sadiq M.M., Horcajada P., Salcedo-Abraira P., Kaneko K., Kukobat R., Kenvin J., Keskin S., Kitagawa S., Otake K.-I., Lively R.P., DeWitt S.J.A., Llewellyn P., Lotsch B.V., Emmerling S.T., Pütz A.M., Martí-Gastaldo C., Padial N.M., García-Martínez J., Linares N., Maspoch D., Suárez del Pino J.A., Moghadam P., Oktavian R., Morris R.E., Wheatley P.S., Navarro J., Petit C., Danaci D., Rosseinsky M.J., Katsoulidis A.P., Schröder M., Han X., Yang S., Serre C., Mouchaham G., Sholl D.S., Thyagarajan R., Siderius D., Snurr R.Q., Goncalves R.B., Telfer S., Advanced Materials; 34 (27, 2201502) 2022. 10.1002/adma.202201502.

    Porosity and surface area analysis play a prominent role in modern materials science. At the heart of this sits the Brunauer–Emmett–Teller (BET) theory, which has been a remarkably successful contribution to the field of materials science. The BET method was developed in the 1930s for open surfaces but is now the most widely used metric for the estimation of surface areas of micro- and mesoporous materials. Despite its widespread use, the calculation of BET surface areas causes a spread in reported areas, resulting in reproducibility problems in both academia and industry. To prove this, for this analysis, 18 already-measured raw adsorption isotherms were provided to sixty-one labs, who were asked to calculate the corresponding BET areas. This round-robin exercise resulted in a wide range of values. Here, the reproducibility of BET area determination from identical isotherms is demonstrated to be a largely ignored issue, raising critical concerns over the reliability of reported BET areas. To solve this major issue, a new computational approach to accurately and systematically determine the BET area of nanoporous materials is developed. The software, called “BET surface identification” (BETSI), expands on the well-known Rouquerol criteria and makes an unambiguous BET area assignment possible. © 2022 The Authors. Advanced Materials published by Wiley-VCH GmbH.


  • 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.


  • 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.


  • 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.


2021

  • 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. ©


  • 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. ©


  • 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.


  • Millimeter-Shaped Metal-Organic Framework/Inorganic Nanoparticle Composite as a New Adsorbent for Home Water-Purification Filters

    Boix G., Han X., Imaz I., Maspoch D. ACS Applied Materials and Interfaces; 13 (15): 17835 - 17843. 2021. 10.1021/acsami.1c02940. IF: 9.229

    Heavy-metal contamination of water is a global problem with an especially severe impact in countries with old or poorly maintained infrastructure for potable water. An increasingly popular solution for ensuring clean and safe drinking water in homes is the use of adsorption-based water filters, given their affordability, efficacy, and simplicity. Herein, we report the preparation and functional validation of a new adsorbent for home water filters, based on our metal-organic framework (MOF) composite containing UiO-66 and cerium(IV) oxide (CeO2) nanoparticles. We began by preparing CeO2@UiO-66 microbeads and then encapsulating them in porous polyethersulfone (PES) granules to obtain millimeter-scale CeO2@UiO-66@PES granules. Next, we validated these granules as an adsorbent for the removal of metals from water by substituting them for the standard adsorbent (ion-exchange resin spheres) inside a commercially available water pitcher from Brita. We assessed their performance according to the American National Standards Institute (ANSI) guideline 53-2019, "Drinking Water Treatment Units - Health Effects Standard". Remarkably, a pitcher loaded with a combination of our CeO2@UiO-66@PES granules and activated carbon at standard ratios met the target reduction thresholds set by NSF/ANSI 53-2019 for all the metals tested: As(III), As(V), Cd(II), Cr(III), Cr(VI), Cu(II), Hg(II), and Pb(II). Throughout the test, the modified pitcher proved to be robust and stable. We are confident that our findings will bring MOF-based adsorbents one step closer to real-world use. © 2021 American Chemical Society.


  • 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.


  • 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.


  • 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.


2020

  • 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.


  • 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.


  • 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


  • 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


  • 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.


2019

  • 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.