Controlling photocatalytic properties of Eosin Y-sensitized hydrogen evolution reaction of Cu2−xSe nanoparticles through surface band bending

Solar-driven water splitting for hydrogen (H₂) production and energy conversion technologies have inspired impressive attention due to energy and environmental crises, but still challenges limit commercialization. To overcome these challenges, the visible-light-responsible noble-metal-free photocatalytic H₂ production system is imperative. In this study, scalable synthesis of copper selenides which is one of promising semiconductor materials is developed and the Cu/Se compositions of the Cu_2−xSe were readily controlled from copper (II) selenide (CuSe) to copper (I) selenide (Cu₂Se). In addition, the synthesized copper selenides were applied to Eosin Y (EY)-sensitized photocatalytic H₂ production, and Cu₂Se exhibited the highest photocatalytic H₂ production rate (1017.82 μmol∙g⁻¹∙h⁻¹) which was 21.17% higher than that of the commercial P25 (TiO₂) under the same conditions. Through careful characterization and calculation, we investigated the band structures of the synthesized copper selenides with different Cu/Se molar ratio, and were able to propose the theory of enhanced surface H₂-evolution kinetics based on downward band bending at equilibrium state in the EY-sensitized system.