Hydrogenated Oxide as Novel Quasi-metallic Cocatalyst for Efficient Visible-Light Driven Photocatalytic Water Splitting

The frequent use of noble metals such as Pt as a cocatalyst to improve photocatalytic performance has stimulated an extensive search for cost-effective materials as alternative cocatalysts. Here we report the use of hydrogenated MoO3 (HMO) with a unique quasi-metallic property as an excellent cocatalyst for the ZnIn2S4 photocatalyst. The HMO–ZnIn2S4 composite with an optimized ratio realizes a H2 production rate of 1564 μmol h–1 g–1 under visible light (λ ≥ 420 nm) excitation. It not only significantly surpasses the performance of pristine ZnIn2S4 (327 μmol h–1 g–1), but also outperforms the 1 wt % Pt-decorated ZnIn2S4 (1308 μmol h–1 g–1). The reasons for this improvement, as disclosed by photoelectrochemical characterization, ultrafast laser spectroscopy, and density functional calculation, is that the efficient charge transfer from ZnIn2S4 to HMO facilitates electron–hole separation after photoexcitaiton, and HMO substantially lowers the overpotential of the H2 evolution reaction. This work thus demonstrates the potential of quasi-metallic hydrogenated metal oxide as an alternative to noble metal cocatalyst for photocatalytic application.