Staff directory Xu Han

Xu Han

Fellowship Doctoral Student
China Scholarship Council
Universitat Autònoma de Barcelona (UAB)
xu.han(ELIMINAR)@icn2.cat
Advanced Electron Nanoscopy - Supramolecular NanoChemistry and Materials

Publications

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.


  • 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.