Unveiling the Selectivity of CO₂ Reduction on Cu₂ZnSnS₄: The Effect of Exposed Termination

With the advantage of excellent light absorption ability and earth-abundant elements, Cu₂ZnSnS₄ (CZTS) is widely applied in the photoelectrochemical (PEC) reduction of CO₂. However, the microscopic mechanism of the CO₂ conversion on CZTS is still unclear. Here, we have theoretically investigated the electronic properties of the CZTS to reveal the special bonding properties of CO₂ under both exposed metal and sulfur terminations of the CZTS and the formation mechanisms of producing CO, HCOOH, and CH₄ from a microscopic perspective. Our study shows that when the metal is exposed to the surface, CO₂ will convert to HCOOH with a high selectivity with the limiting potential of 0.23 V (vs RHE). However, on the sulfur termination, the onset potentials of producing HCOOH, CO, and CH₄ are all lower than 0.4 V, indicating the mix formations. These findings provide theoretical insight into the PEC experiments of CO₂ reduction on CZTS.