Coupling CoS2 and CaIn2S4 for efficient electron trapping and improved surface catalysis to promote solar hydrogen evolution

Photocatalytic H2 evolution requires excellent charge separation and fast surface electron injection, whereas it is difficult to achieve with a single semiconductor catalyst. Herein, we present a simple two-step hydrothermal method for coupling metalloid CoS2 nanospheres with CaIn2S4 micro-flowers, which exhibits a 6-fold increase in the photocatalytic hydrogen evolution rate as bare CaIn2S4. This activity enhancement surpasses that of noble metal (Pt or AuCu) modified CaIn2S4. During five runs of photocatalytic tests, the composite photocatalysts maintain high photostability, without significant changes in crystal structure or morphology. The charge transfer at CoS2/CaIn2S4 interface is revealed by synchronous illumination X-ray photoelectron spectroscopy, surface photovoltage spectrum and DFT calculation. According to the mechanism study, it shows that metallic CoS2 can act as electron traps to speed up electron transfer due to the formation of intimate CoS2/CaIn2S4 heterojunctions, while at the same time CoS2 can serve as active centers to catalytic the water reduction into H2 molecules. Overall, we propose a simple route to modify a semiconductor photocatalyst that can result in multiple distinct effect including improved charge separation and injection efficiency.