New iron-cobalt oxide catalysts promoting BIVO4 films for photoelectrochemical water splitting

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 (FeCoOx) as an efficient co‐catalyst to suppress the surface charge recombination on bismuth vanadate (BiVO4) photoanodes. The new FeCoOx/BiVO4 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 BiVO4 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 FeCoOx in the PEC process. Density functional theory calculations and experimental studies reveal that the incorporation of Fe into CoOx generates abundant oxygen vacancies and forms a p‐n heterojunction with BiVO4, which effectively promotes the hole transport/trapping from the BiVO4 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 FeCoOx as an excellent OER cocatalyst on photoanodes for PEC water splitting