FeOOH Cocatalysts with Gradient Oxygen Vacancy Distribution Enabling Efficient and Stable BiVO4 Photoanodes

• First demonstration of a gradient distributed oxygen vacancies (GOV) strategy to promote hole transport within FeOOH. • Clearly monitoring and verifying the progressive upward shift of the valence band within the shallow surface of FeOOH-GOV for enhancing holes transport capability. • Setting new photoelectrochemical activity and stability benchmarks of FeOOH based-BiVO4 photoanodes. • Achieving a photocurrent density of 5.37 mA cm−2 and operational stability up to 160 h at 1.23 VRHE.