A durable VO₂ transition layer and defect inactivation in BiVO₄via spontaneous valence-charge control

The performance of bismuth vanadate (BiVO₄) photoanodes is limited by surface defects and photo-corrosion instability. This paper proposes a revolutionary protection layer that overcomes these problems. Considering the role of V⁵⁺ ion dissolution in photo-corrosion, we propose a surface photoelectrochemical oxidation approach, artificially altering photo-corrosion to advanced photo-oxidation by strategically adding V⁵⁺ and H₂O₂ to the electrolyte. The surface phase transition thus induced creates an unprecedented vanadium oxide (VO₂) photoelectrochemical protection layer that is robust, conductive, and ultrathin, while exhibiting atomic controllability. Charge-kinetic characterization of the BiVO₄/VO₂ photoanodes revealed faster transport of interfacial charges (86%) and transfer of photogenerated carriers through the VO₂ protection layer (95%); this approach affords near-ideal performance and contributes toward high stability and extreme durability. The BiVO₄/VO₂/CoFeO_x photoanodes displayed a high photocurrent density of 6.2 mA cm⁻² and an onset potential of 0.25 V_RHE, with an applied bias photon-to-current efficiency of 2.4% at 0.62