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A graded catalytic–protective layer for an efficient and stable water-splitting photocathode

Nature Energy volume 2, Article number: 16192 (2017) Cite this article

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Abstract

Achieving solar-to-hydrogen efficiencies above 15% is key for the commercial success of photoelectrochemical water-splitting devices. While tandem cells can reach those efficiencies, increasing the catalytic activity and long-term stability remains a significant challenge. Here we show that annealing a bilayer of amorphous titanium dioxide (TiOx) and molybdenum sulfide (MoSx) deposited onto GaInP2 results in a photocathode with high catalytic activity (current density of 11 mA cm−2 at 0 V versus the reversible hydrogen electrode under 1 sun illumination) and stability (retention of 80% of initial photocurrent density over a 20 h durability test) for the hydrogen evolution reaction. Microscopy and spectroscopy reveal that annealing results in a graded MoSx/MoOx/TiO2 layer that retains much of the high catalytic activity of amorphous MoSx but with stability similar to crystalline MoS2. Our findings demonstrate the potential of utilizing a hybridized, heterogeneous surface layer as a cost-effective catalytic and protective interface for solar hydrogen production.

Hydrogen, utilized in fuel cells to power electric motors or burned in internal combustion engines, is an environmentally friendly energy carrier with the potential to reduce our dependence on fossil fuels. However, the production of hydrogen by the traditional gasification of coal and oil and by steam-methane reforming produces large amounts of carbon dioxide, which has implications for climate change1,2. An alternative long-term, sustainable pathway to hydrogen production is a photoelectrochemical (PEC) cell that absorbs sunlight and converts this energy into hydrogen and oxygen via the dissociation of water molecules3,4. Oxide semiconductor materials, such as Fe2O3, WO3, SrTiO3 and TiO2, have been studied for many years for PEC water splitting5,6. However, the slow charge transport kinetics and/or large bandgaps that typically define these oxide semiconductors result in very low energy conversion efficiencies. In contrast, conventional photovoltaic semiconductors, such as GaInP2 (refs 7,8,9), offer excellent transport properties and smaller bandgaps than oxides, but are susceptible to corrosion during the water-splitting process10. To realize and commercialize future solar hydrogen concepts based on PEC devices, durability of tens of thousands of hours and a device cost of hundreds of dollars per square metre must be achieved11.

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Figure 1: Photoelectrochemical measurements of GaInP2-based photocathodes for hydrogen evolution.
Figure 2: Structural and chemical profiling of the a-MoSx/TiO2x–GaInP2 and g-MoSx/TiOx–GaInP2 electrodes.
Figure 3: Chemical profiling of the non-annealed (a-MoSx/TiOx–GaInP2) and annealed (g-MoSx/TiO2–GaInP2) electrodes.
Figure 4: XPS spectra of the MoSx/TiOx–GaInP2 electrode before and after annealing and before and after electrolysis for 20 h.

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Acknowledgements

This material is based on work supported by the US Department of Energy, Office of Science, Office of Basic Energy Sciences, Solar Photochemistry Program under contract number DEAC36-08GO28308. We gratefully acknowledge C. Antunes for ICP-MS measurement, A. Norman for the helpful discussions and plan-view TEM measurement for the PtRu–GaInP2 electrode.

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Author notes

  1. Jing Gu, Jeffery A. Aguiar, K. Xerxes Steirer & Yong Yan

    Present address: † Present addresses: San Diego State University, Department of Chemistry and Biochemistry, 5500 Campanile Drive, San Diego, California 92182-1030, USA (J.G.); Idaho National Laboratory, Fuel Design and Development, 2525 Fremont Avenue, Idaho Falls, Idaho 83401, USA (J.A.A.); Physics Department, Colorado School of Mines, 1500 Illinois Street, Golden, Colorado 80401, USA (K.X.S.); Department of Chemistry and Environmental Sciences, New Jersey Institute of Technology, 151 Tiernan Hall, University Heights, Newark, New Jersey 07102, USA (Y.Y.).,

Authors and Affiliations

  1. National Renewable Energy Laboratory, Chemistry and Nanoscience Center, Golden, Colorado 80401, USA

    Jing Gu, Jeffery A. Aguiar, Suzanne Ferrere, K. Xerxes Steirer, Yong Yan, Chuanxiao Xiao, James L. Young, Mowafak Al-Jassim, Nathan R. Neale & John A. Turner

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Contributions

J.G., J.A.A., S.F., N.R.N. and J.A.T. wrote the manuscript. J.G. and S.F. conceived the experiments. J.G. conducted the photoelectrochemical characterization. J.A.A. conducted the STEM, EDS and EELS measurements. J.A.A. and M.A.-J. analysed and interpreted the STEM, EDS and EELS data. K.X.S. conducted the XPS experiment and related analysis. Y.Y. conducted the initial testing for MoSx catalyst deposition. C.X. conducted the SEM measurements and J.L.Y. conducted the atomic layer TiO2 deposition.

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Correspondence to Jing Gu or John A. Turner.

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Supplementary Figures 1–5, Supplementary Tables 1–2 and Supplementary References. (PDF 1022 kb)

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Gu, J., Aguiar, J., Ferrere, S. et al. A graded catalytic–protective layer for an efficient and stable water-splitting photocathode. Nat Energy 2, 16192 (2017). https://doi.org/10.1038/nenergy.2016.192

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