Efficient and Stable MoO_X@Mo-BiVO₄ Photoanodes for Photoelectrochemical Water Oxidation: Optimization and Understanding

In this study, we propose a facilely dip-coated and intermediate heat-treated MoOX@Mo-BiVO4 photoanode that displays extremely efficient and stable photoelectrochemical H2 production. The formation of MoOX as an intermediate species is investigated using time of flight-secondary ion mass spectrometry (TOF-SIMS). The MoOX@2% Mo-BiVO4 photoanode exhibited a photocurrent density of approximately 1 mA cm–2 at 1.23 V versus the reversible hydrogen electrode (RHE), which was 5.5 times higher when compared with that of the BiVO4 photoelectrode because of the formation of MoOX and the induced oxygen vacancies (VOs), which are beneficial for the suppression of electron–hole recombination. The incident photon current efficiency of approximately 17.7% for the MoOX@2% Mo-BiVO4 photoanode is a noticeable improvement over the pure BiVO4 photoelectrode. The H2 and O2 productions of the MoOX@2% Mo-BiVO4 photoanode after 2 h were 32.46 and 15.85 μmol cm–2, respectively, which reached approximately 85% Faradaic efficiency, at 1.23 V versus RHE under 100 mW/cm2.