A Study on Vanadium Dioxide Protective Layer and Defect Inactivation for Stability and Efficiency of Bismuth Vanadate Photoelectrode via Spontaneous Valence-Charge Control

Photoelectrochemical (PEC) cells for water splitting have garnered significant interest as a promising solar-to-energy conversion technology. Bismuth vanadate (BiVO₄), a key photoanode material, offers numerous advantages but suffers from surface defects and photo-corrosion instability. To address these challenges, we introduce an innovative passivation strategy. Recognizing the role of V⁵⁺ ion dissolution in photo-corrosion, we propose a surface photoelectrochemical reduction-oxidation technology that transforms detrimental photo-corrosion into beneficial photo-oxidation by strategically introducing V⁵⁺ and H₂O₂ into the photoelectrochemical deposition electrolyte. This approach induces a surface phase transition of metal, resulting in the formation of an ultrathin and atomically controllable vanadium dioxide (VO₂) photoelectrochemical protective layer that enhances conductivity.<br/>Characterization of the BiVO₄/VO₂ photoanodes reveals enhanced charge transport (86%) and efficient transfer of photogenerated carriers (95%) through the VO₂ protection layer. This advancement enables near-ideal performance, high stability, and exceptional durability. BiVO₄/VO₂/CoFeO_x photoanodes exhibit a high photocurrent density of 6.2 mA/cm², an onset potential of 0.25 V_RHE, and an applied bias photon-to-current efficiency of 2.4% at 0.62 V_RHE, maintaining vigorous active oxygen evolution over 100 hours.