Efficient photocatalytic H-2 generation over In2.77S4/NiS2/g-C3N4 S-scheme heterojunction using NiS2 as electron-bridge

Herein, In2.77S4/NiS2 heterojunction was firstly synthesized through an in-situ solvothermal method, then it was introduced to the surface of g-C3N4 to construct a ternary In2.77S4/NiS2/g-C3N4 S-scheme heterojunction via a simple physical solvent evaporation process. The investigation shows that the ternary In2.77S4/NiS2/g-C3N4 heterojunction exhibits an excellent light harvesting ability from 200 nm to 800 nm for the metallic-like NiS2 and the narrower bandgap of In2.77S4, it also has a better charge carrier separation and migration property compared to single and binary components. According to the photocatalytic tests, the photocatalytic H2 production rate over 20 wt% In2.77S4/NiS2/g-C3N4 can attain 7481.7 mu mol center dot g(-1)center dot h(-1), 52.5, 33.8 and 28.5 times higher than that of g-C3N4, In2.77S4 and In2.77S4/g-C3N4 respectively. Further investigation shows that the charge carriers transfer between g-C3N4 and In2.77S4 follows a S-scheme transfer route on the basis of the photoelectrochemical tests and density functional theory (DFT) calculations. In addition, NiS2 as an electron-bridge can further improve the charge transfer between the interface of g-C3N4 and In2.77S4, making more useful electrons and holes with strong REDOX capacity participating the surface reactions. What's more, In2.77S4/NiS2 can also induce more electro-chemical active sites, which can lead to a faster surface H-2 releasing kinetics by reducing the overpotential of H-2 evolution. This work offers an effective method for the designing novel g-C3N4-based S-scheme heterojunctions by introducing a charge-bridge to facilitate the charge carrier transfer between different photocatalysts.