Exploring the Photocorrosion Mechanism of a Photocatalyst

J Phys Chem Lett. 2022 Nov 10;13(44):10356-10363. doi: 10.1021/acs.jpclett.2c02779. Epub 2022 Oct 31.

Abstract

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 NiFeOx 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.