Abstract
High-efficiency photoelectrochemical water-splitting devices require the integration of electrocatalysts (ECs) with light-absorbing semiconductors (SCs), but the energetics and charge-transfer processes at SC/EC interfaces are poorly understood. We fabricate model EC-coated single-crystal TiO2 electrodes and directly probe SC/EC interfaces in situ using two working electrodes to independently monitor and control the potential and current at both the SC and the EC. We discover that redox-active ion-permeable ECs such as Ni(OH)2 or NiOOH yield ‘adaptive’ SC/EC junctions where the effective Schottky barrier height changes in situ with the oxidation level of the EC. In contrast, dense, ion-impermeable IrOx ECs yield constant-barrier-height ‘buried’ junctions. Conversion of dense, thermally deposited NiOx on TiO2 into ion-permeable Ni(OH)2 or NiOOH correlated with increased apparent photovoltage and fill factor. These results provide new insight into the dynamic behaviour of SC/EC interfaces to guide the design of efficient SC/EC devices. They also illustrate a new class of adaptive semiconductor junctions.
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Acknowledgements
This work was supported by the DOE Basic Energy Sciences, Grant DE-FG02-12ER16323. S.W.B. acknowledges support from the DuPont Young Professor Program. The authors thank T. J. Mills for helpful discussions and acknowledge use of equipment in the CAMCOR and SuNRISE Laboratories.
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F.L. and S.W.B. designed the study, analysed the data and wrote the manuscript. F.L. performed the experiments.
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Lin, F., Boettcher, S. Adaptive semiconductor/electrocatalyst junctions in water-splitting photoanodes. Nature Mater 13, 81–86 (2014). https://doi.org/10.1038/nmat3811
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DOI: https://doi.org/10.1038/nmat3811
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