Efficient photoelectrochemical water splitting by a doping-controlled GaN photoanode coated with NiO cocatalyst

Efficient photoelectrochemical (PEC) water splitting was demonstrated by a doping-controlled GaN photoanode coated with NiO cocatalyst. Highly doped n-GaN was sandwiched between undoped GaN layers to effectively collect electrons through ohmic contact. With zero external bias, the photocurrent density of the optimized doping profile was similar to 3.5 times higher than that of the undoped GaN reference. However, the increased doping concentration degraded the photoanode stability, which was attributed to crystalline defects generated in the highly doped n-GaN. NiO cocatalyst improved the long-term stability of the photoanode because of GaN/NiO band alignment, enhancing hole transport into NiO and suppressing PEC corrosion mediated by hole crowding in GaN. This work established a design strategy for increasing the photocurrent as well as improving stability during water splitting with a GaN-based photoanode. (C) 2014 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.