Staff directory Pengyi Tang



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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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


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

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

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

  • NiSn bimetallic nanoparticles as stable electrocatalysts for methanol oxidation reaction

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

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

  • Role of Tungsten Doping on the Surface States in BiVO4 Photoanodes for Water Oxidation: Tuning the Electron Trapping Process

    Shi Q., Murcia-López S., Tang P., Flox C., Morante J.R., Bian Z., Wang H., Andreu T. ACS Catalysis; 8 (4): 3331 - 3342. 2018. 10.1021/acscatal.7b04277. IF: 11.384

    The nanostructured BiVO4 photoanodes were prepared by electrospinning and were further characterized by XRD, SEM, and XPS, confirming the bulk and surface modification of the electrodes attained by W addition. The role of surface states (SS) during water oxidation for the as-prepared photoanodes was investigated by using electrochemical, photoelectrochemical, and impedance spectroscopy measurements. An optimum 2% doping is observed in voltammetric measurements with the highest photocurrent density at 1.23 VRHE under back side illumination. It has been found that a high PEC performance requires an optimum ratio of density of surface states (NSS) with respect to the charge donor density (Nd), to give both good conductivity and enough surface reactive sites. The optimum doping (2%) shows the highest Nd and SS concentration, which leads to the high film conductivity and reactive sites. The reason for SS acting as reaction sites (i-SS) is suggested to be the reversible redox process of V5+/V4+ in semiconductor bulk to form water oxidation intermediates through the electron trapping process. Otherwise, the irreversible surface reductive reaction of VO2 + to VO2+ though the electron trapping process raises the surface recombination. W doping does have an effect on the surface properties of the BiVO4 electrode. It can tune the electron trapping process to obtain a high concentration of i-SS and less surface recombination. This work gives a further understanding for the enhancement of PEC performance caused by W doping in the field of charge transfer at the semiconductor/electrolyte interface. © 2018 American Chemical Society.

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

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

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

  • Tin Diselenide Molecular Precursor for Solution-Processable Thermoelectric Materials

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

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

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

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

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


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

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

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

  • A universal strategy for metal oxide anchored and binder-free carbon matrix electrode: A supercapacitor case with superior rate performance and high mass loading

    Zhang X., Luo J., Tang P., Ye X., Peng X., Tang H., Sun S.-G., Fransaer J. Nano Energy; 31: 311 - 321. 2017. 10.1016/j.nanoen.2016.11.024. IF: 12.343

    Despite the significant advances in preparing carbon-metal oxide composite electrodes, strategies for seamless interconnecting of these two materials without using binders are still scarce. Herein we design a novel method for in situ synthesis of porous 2D-layered carbon–metal oxide composite electrode. Firstly, 2D-layered Ni-Co mixed metal-organic frameworks (MOFs) are deposited directly on nickel foam by anodic electrodeposition. Subsequent pyrolysis and activation procedure lead to the formation of carbon–metal oxides composite electrodes. Even with an ultrahigh mass loading of 13.4 mg cm−2, the as-prepared electrodes exhibit a superior rate performance of 93% (from 1 to 20 mA cm−2), high capacitance (2098 mF cm−2 at a current density of 1 mA cm−2), low resistance and excellent cycling stability, making them promising candidates for practical supercapacitor application. As a proof of concept, several MOF derived electrodes with different metal sources have also been prepared successfully via the same route, demonstrating the versatility of the proposed method for the preparation of binder-free carbon–metal oxide composite electrodes for electrochemical devices. © 2016 Elsevier Ltd

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

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

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

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

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

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

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

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

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


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

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

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