Enhancement of Hydrogen Productions by Accelerating Electron-Transfers of Sulfur Defects in the CuS@CuGaS2 Heterojunction Photocatalysts

Abstract

CuS and CuGaS2 heterojunction catalysts were used to improve hydrogen production performance by photo splitting of methanol aqueous solution in the visible region in this study. CuGaS2, which is a chalcogenide structure, can form structural defects to promote separation of electrons and holes and improve visible light absorbing ability. The optimum catalytic activity of CuGaS2 was investigated by varying the heterojunction ratio of CuGaS2 with CuS. Physicochemical properties of CuS, CuGaS2 and CuS@CuGaS2 nanoparticles were confirmed by X-ray diffraction, ultraviolet visible spectroscopy, high-resolution transmission electron microscopy, scanning electron microscopy and energy dispersive X-ray spectroscopy. Compared with pure CuS, the hydrogen production performance of CuGaS2 doped with Ga dopant was improved by methanol photolysis, and the photoactivity of the heterogeneous CuS@CuGaS2 catalyst was increased remarkably. Moreover, the 0.5CuS@1.5CuGaS2 catalyst produced 3250 μmol of hydrogen through photolysis of aqueous methanol solution under 10 h UV light irradiation. According to the intensity modulated photovoltage spectroscopy (IMVS) results, the high photoactivity of the CuS@CuGaS2 catalyst is attributed to the inhibition of recombination between electron-hole pairs, accelerating electron-transfer by acting as a trap site at the interface between CuGaS2 structural defects and the heterojunction.