Conformal BiVO₄-Layer/WO₃-Nanoplate-Array Heterojunction Photoanode Modified with Cobalt Phosphate Cocatalyst for Significantly Enhanced Photoelectrochemical Performances

Constructing semiconductor heterojunctions via surface/interface engineering is an effective way to enhance the charge carrier separation/transport ability and thus the photoelectrochemical (PEC) properties of a photoelectrode. Herein, we report a conformal BiVO4-layer/WO3-nanoplate-array heterojunction photoanode modified with cobalt phosphate (Co-Pi) as oxygen evolution cocatalyst (OEC) for significant enhancement in PEC performances. The BiVO4/WO3 nanocomposite is fabricated by coating a thin conformal BiVO4 layer on the surface of presynthesized WO3 nanoplate arrays (NPAs) via stepwise spin-coating, and the decoration of Co-Pi OEC is realized by photoassisted electrodeposition method. The optimized Co-Pi@BiVO4/WO3 heterojunction photoanode shows a maximum photocurrent of 1.8 mA/cm2 at 1.23 V vs RHE in a phosphate buffer electrolyte under an AM1.5G solar simulator, which is 5 and 12 times higher than those of bare WO3 and BiVO4 photoanode, respectively. Measurements of UV–vis absorption spectra, electrochemical impedance spectra (EIS) and photoluminescence (PL) spectra reveal that the enhanced PEC performances can be attributed to the increased charge carrier separation/transport benefited from the type II nature of BiVO4/WO3 heterojunction and the promoted water oxidation kinetics and photostability owing to the decoration of Co-Pi cocatalyst.