Construction of a Surface Hydroxyl Group on ZnIn₂S₄ Promotes Photocatalytic CO₂ Reduction

Photocatalysis holds significant promise for the reduction of CO₂ to valued chemicals under mild conditions. However, its potential is severely limited by weak CO₂ adsorption and slow proton-coupled electron transfer (PCET) rates. In this work, ZnIn₂S₄-based catalysts with varying hydroxyl contents were synthesized via the solvothermal method. The hydroxyl group, acting as a basic site, improves CO₂ adsorption and inhibits the hydrogen evolution reaction (HER). Additionally, the hydroxyl group serves as a proton acceptor, facilitating proton transfer; the internal electric field formed by the redistribution of hydroxyl-induced charges promotes the separation of photogenerated carriers, jointly accelerating the PCET process. The hydroxyl-rich ZnIn₂S₄ catalyst exhibits superior CO₂ reduction performance, with a CO generation rate of 4.55 mmol g^-1 h^-1, 20 times that of ZnIn₂S₄ with a lower hydroxyl content. Furthermore, the CO:H₂ ratio is increased by 18. This study highlights the critical roles of PCET and effective CO₂ adsorption in the CO₂ reduction reactions.