Photoelectrochemical water splitting presents an attractive strategy to produce hydrogen gas as an alternative clean fuel in an environmentally benign and sustainable manner. The key component of a photoelectrochemical cell is a semiconductor electrode (photoelectrode) that absorbs solar light to generate, separate, and transport charge carriers to the semiconductor/electrolyte interface to participate in desired chemical reactions. The electron-hole separation and interfacial charge transfer of the photoelectrode are considerably affected by the interfacial energetics between the photoelectrode and the electrolyte and/or between the photoelectrode and the buffer, protection, or catalyst layers; hence, the interfacial properties of a photoelectrode are as important as the bulk properties of the photoelectrode. To date, strategies for altering the atomic arrangement at the photoelectrode surface that do not involve extrinsic doping have mainly involved changing the semiconductor surface facets. However, for ternary oxide photoelectrodes with a formula of AxByOz, there exist numerous ways to terminate the surface even for the same facet. For example, the surface can be terminated with A-O or B-O, and the surface A:B ratio may be different from the bulk A:B ratio. In fact, if not grown as single crystals, AxByOz photoelectrodes can have an A-rich or B-rich surface depending on the synthesis method, which can affect their photoelectrochemical properties. However, despite being important and ubiquitous, the effects of surface termination/composition on a ternary oxide photoelectrode have not been systematically studied, and the atomic origin of their effects on interfacial energetics and photoelectrochemical properties have not been elucidated. In this presentation, we will discuss the effects of surface termination/composition on the interfacial energetics and photoelectrochemical properties of photoanodes using BiVO4 as an example. We will compare epitaxially grown BiVO4 photoelectrodes with V-rich and Bi-rich (010) exposed facets and demonstrate that the surface Bi:V ratio has a considerable effect on the surface energetics and photocurrent generation of BiVO4 even for the same (010) facet.

Understanding the surface effects of ternary oxide photoelectrodes on photoelectrochemical water splitting

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