New Iron‐Cobalt Oxide Catalysts Promoting BiVO4 Films for Photoelectrochemical Water Splitting

Abstract Owing to the sluggish kinetics for water oxidation, severe surface charge recombination is a major energy loss that hinders efficient photoelectrochemical (PEC) water splitting. Herein, a simple process is developed for preparing a new type of low‐cost iron‐cobalt oxide (FeCoO x ) as an efficient co‐catalyst to suppress the surface charge recombination on bismuth vanadate (BiVO 4 ) photoanodes. The new FeCoO x /BiVO 4 photoanode exhibits a high photocurrent density of 4.82 mA cm −2 at 1.23 V versus the reversible hydrogen electrode under AM 1.5 G illumination, which corresponds to >100% increase compared to that of the pristine BiVO 4 photoanode. The photoanode also demonstrates a high charge separation efficiency of ≈90% with excellent stability of over 10 h, indicating the excellent catalytic performance of FeCoO x in the PEC process. Density functional theory calculations and experimental studies reveal that the incorporation of Fe into CoO x generates abundant oxygen vacancies and forms a p‐n heterojunction with BiVO 4 , which effectively promotes the hole transport/trapping from the BiVO 4 photocatalyst and reduces the overpotential for oxygen evolution reaction (OER), resulting in remarkably increased photocurrent densities and durability. This work demonstrates a feasible process for depositing cheap FeCoO x as an excellent OER cocatalyst on photoanodes for PEC water splitting.