The Role of Cu Clusters on Two-Electron CO₂ Reduction at SnS₂ Surface: A First-Principles Study

Improving the efficiency and product selectivity of CO2 reduction on catalysts is of great importance. In this work, the CO2 reduction performance on Cux@SnS2 (x = 1–6) was systematically investigated by density functional theory (DFT). Although the CO2 adsorption strength can only be slightly enhanced, the activity of the two-electron reduction can be effectively governed by the cluster size. Cux@SnS2 with x being even exhibits a lower energy barrier for the formation of both CO and HCOOH than that in the odd case. Particularly, Cu4@SnS2 has the lowest energy barrier for the formation of CO, while Cu2@SnS2 has a preference for the formation of HCOOH, showing product selectivity. This unique behavior is determined by the splitting of energy levels and orbital symmetry between the interacted frontier orbitals of Cu-dz2/xz/yz and intermediates. Our findings show that including the Cux cluster is a promising way of designing CO2 electrocatalysts with high activity and product selectivity.