Oxygen network formation for efficient charge transport and durable BiVO4 photoanodes with ultra-thin TiO2 layer in solar water splitting

• Analysis and exploitation of oxygen vacancies in BiVO 4 photoanodes at the atomic scale. • Surface chemical reduction reaction (SCR) enables selective control of V O in BiVO 4 photoanodes. • The SCR-enhanced TiO 2 interface improves charge kinetics and photostability. • Maximizing charge kinetics in SCR-BiVO 4 /TiO 2 to optimize CoPi electrodeposition. Bismuth vanadate (BiVO 4 ) has emerged as a prominent oxide semiconductor in solar water splitting investigations owing to facile synthesis and favorable band-alignment with the water oxidation level. Oxygen and oxygen vacancies (V O ) within the BiVO 4 exhibit multifaceted roles across bulk, surface, and interface. This study presents a method for selectively regulating the surface and bulk V O in BiVO 4 through facile chemical redox reactions. A large amount of V O on the BiVO 4 surface enables the formation of a robust networking interface with oxide-based protection overlayers, whereas V O in bulk region must be effectively suppressed. A significant amount of V O can be specifically formed on the BiVO 4 surface via a controlled surface chemical reduction reaction (SCR) at the atomic level, precisely controlling the presence of O 2- and OH - ions. Here, we quantitatively and qualitatively analyze V O changes and the impact of V O on photoelectrochemical operation. As a result, The SCR process allows for the strategic control of the BiVO 4 surface into a V O -rich surface. The controlled surface enhances the charge kinetic by promoting the conformal coating of a n-TiO 2 protective layer and decreasing the charge loss in the interface junction with ensuring stability. Furthermore, the SCR-BiVO 4 /TiO 2 /CoPi photoanodes exhibit a highly stable photocurrent density of 3.9 mA cm −2 at 1.23 V RHE . Surface modification and understanding of the oxygen-end network can be broadly applied to photoelectrodes that require oxide-based overlays. A novel surface chemical reduction reaction method is proposed to selectively regulate surface and bulk V O in BiVO 4 photoanodes, enhancing charge transfer efficiency for oxygen evolution reaction.