Unveiling the Activity and Stability Origin of BiVO₄ Photoanodes with FeNi Oxyhydroxides for Oxygen Evolution

Understanding the origin of formation and active sites of oxygen evolution reaction (OER) cocatalysts is highly required for solar photoelectrochemical (PEC) devices that generate hydrogen efficiently from water. Herein, we employed a simple pH-modulated method for in situ growth of FeNi oxyhydroxide ultrathin layers on BiVO₄ photoanodes, resulting in one of the highest currently known PEC activities of 5.8 mA cm^-2 (1.23 V_RHE , AM 1.5 G) accompanied with an excellent stability. More importantly, both comparative experiments and density functional theory (DFT) studies clearly reveal that the selective formation of Bi-O-Fe interfacial bonds mainly contributes the enhanced OER activities, while the construction of V-O-Ni interfacial bonds effectively restrains the dissolution of V⁵⁺ ions and promotes the OER stability. Thereby, the synergy between iron and nickel of FeNi oxyhydroxides significantly improved the PEC water oxidation properties of BiVO₄ photoanodes.