Different Photostability of BiVO4 in Near-pH-Neutral Electrolytes

TL;DR

This study systematically examines the stability and dissolution behavior of BiVO4 photoelectrodes during water splitting in various near-neutral electrolytes, revealing electrolyte-dependent corrosion mechanisms and the importance of operando measurements.

Contribution

It provides the first detailed operando analysis of BiVO4 dissolution in different electrolytes, linking corrosion behavior to surface chemistry and morphology at the nanoscale.

Findings

Dissolution rates depend on electrolyte composition and pH.

Citrate electrolyte offers kinetic protection against corrosion.

BiVO4 stability varies significantly across different near-neutral electrolytes.

Abstract

Photoelectrochemical water splitting is a promising route to produce hydrogen from solar energy. However, corrosion of semiconducting photoelectrodes remains a fundamental challenge for their practical application. The stability of BiVO4, one of the best performing photoanode materials, is systematically examined here using an illuminated scanning flow cell to measure its dissolution operando. The dissolution rates of BiVO4 under illumination depend on the electrolyte and decrease in the order: borate (pH=9.3) > phosphate (pH=7.2) > citrate (pH=7.0). BiVO4 exhibits an inherent lack of stability during the oxygen evolution reaction (OER), while hole-scavenging citrate electrolyte offers kinetic protection. The dissolution of Bi peaks at different potentials than the dissolution of V in phosphate buffer, whereas both ions dissolve simultaneously in borate buffer. The life cycle of a 90 nm BiVO4 film is monitored during one hour of light-driven OER in borate buffer. The photocurrent and dissolution rates show independent trends with time, highlighting the importance to measure both quantities operando. Dissolution rates are correlated to the surface morphology and chemistry characterized using electron microscopy, X-ray photoelectron spectroscopy and atom probe tomography. These correlative measurements further the understanding on corrosion processes of photoelectrodes down to the nanoscopic scale to facilitate their future developments.