Modifying BiVO4 as a photocatalyst for water oxidation using constant-duration alkaline-etched post treatments

Abstract

BiVO₄ with suitable band edges and a small band gap is considered an efficient photocatalyst for the oxygen evolution reaction (OER), but short charge-transfer lengths limit its photocatalytic ability. Increasing active sites can essentially enhance oxidation reactions and photocatalytic ability. The alkaline etching technique can refine the surface properties of BiVO₄ by introducing oxygen vacancies and possibly establishing a heterojunction, but suitable alkaline etching methods are rarely discussed. In this study, three alkaline etching methods, including hydrothermal, soaking, and electrodeposition processes, are first applied for a constant duration to tailor the surface properties of BiVO₄ as a photocatalyst for the OER. Alkaline-etched BiVO₄ prepared using hydrothermal and soaking processes shows better photocatalytic abilities due to the generation of additional oxygen vacancies, while poor photocatalytic ability is found for that fabricated using electrodeposition due to the formation of less photocatalytic VO₂. The highest photocurrent density of 2.38 mA cm⁻² is obtained at 1.23 V versus a reversible hydrogen electrode in an electrolyte without a hole scavenger for the BiVO₄ etched in the hydrothermal process, while the untreated BiVO₄ presents a photocurrent density of 0.58 mA cm⁻². A photocurrent retention of 92.3% is achieved after 5000 seconds of continuous illumination. The study supplies blueprints for establishing effective alkaline etching methods for enhancing the photocatalytic ability of BiVO₄, with the exception of time costs.