Photoelectrochemical water splitting is a promising method of generating solar fuels. However, the direct solar-to-fuel approach has several critical issues on the photoelectrodes, such as bulk recombination, sluggish surface reaction kinetics, and photocorrosion. In this study, the photoanodes were prepared using a GaN p−n junction (p−n GaN) with the decoration of nickel oxide formed by the thermally annealed nickel film on the p-GaN surface layer. The surface p−n junction enhances the charge separation of the p−n GaN photoanodes, thereby increasing the photocurrent density as well as providing a higher photovoltage. The nickel oxide catalysts placed on the pn-GaN photoanodes lowered the activation energy and provided a facile route for the photogenerated holes to participate in water oxidation. As a result, the nickel oxide-decorated p−n junction GaN photoanodes exhibit a stable photocurrent density with negligible photocorrosion during the photoelectrochemical reactions.

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