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Water reduction by a p-GaInP2 photoelectrode stabilized by an amorphous TiO2 coating and a molecular cobalt catalyst

Abstract

Producing hydrogen through solar water splitting requires the coverage of large land areas. Abundant metal-based molecular catalysts offer scalability, but only if they match noble metal activities. We report on a highly active p-GaInP2 photocathode protected through a 35-nm TiO2 layer functionalized by a cobaloxime molecular catalyst (GaInP2–TiO2–cobaloxime). This photoelectrode mediates H2 production with a current density of 9 mA cm−2 at a potential of 0 V versus RHE under 1-sun illumination at pH 13. The calculated turnover number for the catalyst during a 20-h period is 139,000, with an average turnover frequency of 1.9 s−1. Bare GaInP2 shows a rapid current decay, whereas the GaInP2–TiO2–cobaloxime electrode shows ≤5% loss over 20 min, comparable to a GaInP2–TiO2–Pt catalyst particle-modified interface. The activity and corrosion resistance of the GaInP2–TiO2–cobaloxime photocathode in basic solution is made possible by an atomic layer-deposited TiO2 and an attached cobaloxime catalyst.

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Figure 1: Surface modification strategies for the p-GaInP2 photoelectrodes.
Figure 2: ATR-IR spectra of electrode surfaces.
Figure 3: Linear-sweep voltammetry of electrodes 1–5 at a 20-mV s−1 scan rate, with Pt foil as the counter electrode, and Ag/AgCl as the reference electrode.
Figure 4: IPCE performance of electrodes 1–5 at −1 V versus Ag/AgCl in pH 13 aqueous solution.
Figure 5: Current density–time profile of electrodes 1–5 at −1 V versus Ag/AgCl (or 0 V versus RHE) under 1-sun illumination for 20 min.

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Acknowledgements

We gratefully acknowledge H. Doscher for supplying the GaInP2 wafers, C. Xiao for AFM measurements, L. Gedvilas for ATR-IR measurements, C. Macomber for ICP-MS measurements, S. George for advice on ALD and H. Wang and T. Deutsch for useful discussions. 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 DE-AC36-08GO28308. J.L.Y. acknowledges NSF Graduate Research Fellowship Grant No. DGE 1144083.

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J.G., Y.Y., N.R.N. and J.A.T. designed the research; J.G. and Y.Y. performed the research; J.L.Y. performed the ALD deposition; and K.X.S. performed the XPS study. J.G., Y.Y., N.R.N. and J.A.T. co-wrote the paper.

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Correspondence to John A. Turner.

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Gu, J., Yan, Y., Young, J. et al. Water reduction by a p-GaInP2 photoelectrode stabilized by an amorphous TiO2 coating and a molecular cobalt catalyst. Nature Mater 15, 456–460 (2016). https://doi.org/10.1038/nmat4511

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