Strong support effect induced by MXene for the synthesis of metal sulfides nanosheet arrays with sulfur vacancies towards selective CO2-to-CO photoreduction

Selective CO₂-to-CO photoreduction is under intensive research and requires photocatalysts with tuned microstructures to accelerate the reaction kinetics. Here, we report CuInS₂ nanosheet arrays with sulfur vacancies (V_S) grown on the two-dimensional (2D) support of Ti₃C₂T_x MXene for CO₂-to-CO photoreduction. Our results reveal that the use of Ti₃C₂T_x induces strong support effect, which causes the hierarchical nanosheet arrays growth of CuInS₂ and simultaneously leads to charge transfer from CuInS₂ to Ti₃C₂T_x support, resulting in V_S formed in CuInS₂. The strong support effect based on Ti₃C₂T_x is proven to be applicable to prepare a series of different metal indium sulfide arrays with V_S. CuInS₂ nanosheet arrays with V_S supported on Ti₃C₂T_x benefit the photocatalytic selective reduction of CO₂ to CO, manifesting a remarkable over 14.8-fold activity enhancement compared with pure CuInS₂. The experimental and computational investigations pinpoint that V_S of CuInS₂ resulting from the support effect of Ti₃C₂T_x lowers the barrier of the rate-limiting step of *COOH → *OH + *CO, which is the key to the photoactivity enhancement. This work demonstrates MXene support effects and offers an effective approach to regulate the atomic microstructure of metal sulfides toward enhancing photocatalytic performance.