New BiVO4 Dual Photoanodes with Enriched Oxygen Vacancies for Efficient Solar‐Driven Water Splitting

Abstract Bismuth vanadate (BiVO 4 ) is a promising photoanode material for photoelectrochemical (PEC) water splitting. However, owing to the short carrier diffusion length, the trade‐off between sufficient light absorption and efficient charge separation often leads to poor PEC performance. Herein, a new electrodeposition process is developed to prepare bismuth oxide precursor films, which can be converted to transparent BiVO 4 films with well‐controlled oxygen vacancies via a mild thermal treatment process. The optimized BiVO 4 film exhibits an excellent back illumination charge separation efficiency mainly due to the presence of enriched oxygen vacancies which act as shallow donors. By loading FeOOH/NiOOH as the cocatalysts, the BiVO 4 dual photoanodes exhibit a remarkable and highly stable photocurrent density of 5.87 mA cm − 2 at 1.23 V versus the reversible hydrogen electrode under AM 1.5 G illumination. An artificial leaf composed of the BiVO 4 /FeOOH/NiOOH dual photoanodes and a single sealed perovskite solar cell delivers a solar‐to‐hydrogen conversion efficiency as high as 6.5% for unbiased water splitting.