A durable VO transition layer and defect inactivation in BiVO spontaneous valence-charge control

The performance of bismuth vanadate (BiVO 4 ) 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 V 5+ ion dissolution in photo-corrosion, we propose a surface photoelectrochemical oxidation approach, artificially altering photo-corrosion to advanced photo-oxidation by strategically adding V 5+ and H 2 O 2 to the electrolyte. The surface phase transition thus induced creates an unprecedented vanadium oxide (VO 2 ) photoelectrochemical protection layer that is robust, conductive, and ultrathin, while exhibiting atomic controllability. Charge-kinetic characterization of the BiVO 4 /VO 2 photoanodes revealed faster transport of interfacial charges (86%) and transfer of photogenerated carriers through the VO 2 protection layer (95%); this approach affords near-ideal performance and contributes toward high stability and extreme durability. The BiVO 4 /VO 2 /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 V RHE . Formation of a durable VO 2 transition protection layer and defect inactivation in BiVO 4 via spontaneous valence-charge control.