In Situ Formation of Oxygen Vacancies Achieving Near‐Complete Charge Separation in Planar BiVO4 Photoanodes

Abstract Despite a suitable bandgap of bismuth vanadate (BiVO 4 ) for visible light absorption, most of the photogenerated holes in BiVO 4 photoanodes are vanished before reaching the surfaces for oxygen evolution reaction due to the poor charge separation efficiency in the bulk. Herein, a new sulfur oxidation strategy is developed to prepare planar BiVO 4 photoanodes with in situ formed oxygen vacancies, which increases the majority charge carrier density and photovoltage, leading to a record charge separation efficiency of 98.2% among the reported BiVO 4 photoanodes. Upon loading NiFeO x as an oxygen evolution cocatalyst, a stable photocurrent density of 5.54 mA cm −2 is achieved at 1.23 V versus the reversible hydrogen electrode (RHE) under AM 1.5 G illumination. Remarkably, a dual‐photoanode configuration further enhances the photocurrent density up to 6.24 mA cm −2 , achieving an excellent applied bias photon‐to‐current efficiency of 2.76%. This work demonstrates a simple thermal treatment approach to generate oxygen vacancies for the design of efficient planar photoanodes for solar hydrogen production.