Exploring the Photocorrosion Mechanism of a Photocatalyst

Photoelectrochemical (PEC) water splitting using Ta₃N₅ anodes shows a high solar-to-hydrogen (STH) efficiency approaching 10%. However, the long-term stability of gas evolution should be improved for the commercial utilization of PEC water-splitting technology. Herein, we examined the photocurrent degradation of photoanodes prepared by uniformly loading a NiFeO cocatalyst onto a Ta₃N₅ semiconductor. Although spectroscopic analysis showed that the degradation was attributable to the formation of an oxide layer, several oxide growth kinetic laws and mechanisms are known. We theoretically derived the photocurrent kinetic laws instead of the oxide growth kinetic laws by generalizing the Cabrera-Mott oxidation theory of metal oxidation in air to apply it to photocorrosion. The measured photocurrent kinetics are fully consistent with the theoretical kinetic laws. We show that ion drift due to charging of the oxide layer limits oxide growth even though uniform cocatalyst loading is designed to prevent self-oxidation of Ta₃N₅.