Publications
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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. ©
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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.
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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
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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.
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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.
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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
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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. ©
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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
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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.
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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.
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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.
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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
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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.
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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.
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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
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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
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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
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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.
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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
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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.
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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
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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.
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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.
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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.
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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
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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.
