Increasing Charge Separation Property and Water Oxidation Activity of BiVO4 Photoanodes via a Postsynthetic Treatment

Postsynthetic treatments of BiVO4 photoanodes have recently shed light on better understanding and improving the photoanodes for water splitting. We demonstrate that a mild heat treatment of BiVO4 under O2 flow at 200 °C improves its water oxidation activity. Charge separation and charge injection efficiencies increase along with the decreased charge transfer resistances across the BiVO4/electrolyte interface. The depletion region width and the band bending have shown to increase after annealing, while charge carrier density remains unchanged. Transient photocurrent measurements further confirm the reduced charge carrier recombination as a result of enlarged band bending. The surface states decrease and the fraction of vanadium ions increases in the surface region after the heat treatment. Since the surface of the BiVO4 photoanodes is generally vanadium deficient, it is suggested that such a treatment can improve the BiVO4 photoanodes performance prepared by other methods as well.