In situ investigation of the bismuth vanadate/potassium phosphate interface reveals morphological and composition dependent light-induced surface reactions

Abstract

Bismuth vanadate (BiVO4) is an established n-type oxide semiconductor for photoelectrochemical oxygen evolution. Direct charge carrier recombination at the solid/liquid interface is a major cause of efficiency loss in BiVO4-based devices. Intrinsic and extrinsic surface states (SSs) can act as electron and hole traps that enhance the recombination rate and lower the faradaic efficiency. In this study, we investigate the BiVO4/aqueous KPi interface using two types of samples. The samples were prepared at two different deposition and annealing temperatures (450 °C and 500 °C) leading to different morphologies and stoichiometries for the two samples. Both samples exhibit SSs in the dark that are passivated under illumination. In situ ambient pressure hard x-ray photoelectron spectroscopy experiments performed under front illumination conditions reveal the formation of a bismuth phosphate (BiPO4) surface layer for the sample annealed at 450 °C, whereas the sample annealed at 500 °C exhibits band flattening without the formation of BiPO4. These results imply that the light-induced formation of BiPO4 may not be responsible for SS passivation. Our study also suggests that slight differences in the synthesis parameters lead to significant changes in the surface stoichiometry and morphology, with drastic effects on the physical-chemical properties of the BiVO4/electrolyte interface. These differences may have important consequences for device characteristics such as long-term stability.