Heterojunction BiVO4/WO3 electrodes for enhanced photoactivity of water oxidation

Abstract

Heterojunction electrodes were fabricated by layer-by-layer deposition of WO₃ and BiVO₄ on a conducting glass, and investigated for photoelectrochemical water oxidation under simulated solar light. The electrode with the optimal composition of four layers of WO₃ covered by a single layer of BiVO₄ showed enhanced photoactivity by 74% relative to bare WO₃ and 730% relative to bare BiVO₄. According to the flat band potential and optical band gap measurements, both semiconductors can absorb visible light and have band edge positions that allow the transfer of photoelectrons from BiVO₄ to WO₃. The electrochemical impedance spectroscopy revealed poor charge transfer characteristics of BiVO₄, which accounts for the low photoactivity of bare BiVO₄. The measurements of the incident photon-to-current conversion efficiency spectra showed that the heterojunction electrode utilized effectively light up to 540 nm covering absorption by both WO₃ and BiVO₄ layers. Thus, in heterojunction electrodes, the photogenerated electrons in BiVO₄ are transferred to WO₃ layers with good charge transport characteristics and contribute to the high photoactivity. They combine merits of the two semiconductors, i.e. excellent charge transport characteristics of WO₃ and good light absorption capability of BiVO₄ for enhanced photoactivity.