Axial and Asymmetric Coordination Coupling Adjust the Electronic Structure of Single-Atom Zinc Sites for Efficient Electroreduction of Carbon Dioxide.

Breaking the symmetric structure of active centers to adjust their electronic structure is a promising strategy for improving the performance of single-atom catalysts (SACs) in electrocatalytic carbon dioxide (CO2) reduction (ECR). However, it remains highly challenging to achieve precise regulation and fine-tuning of single-atom sites at the atomic level. Here, by introducing S and Cl atoms, a Zn-SAC (ZnN3S1Cl/C) with coupled axial and asymmetric coordination is successfully constructed, thereby enhancing the ECR performance. In situ attenuated total reflection infrared spectroscopy demonstrates that ZnN3S1Cl/C promotes the formation of *COOH and the desorption of *CO species. Theoretical calculations show that the asymmetric coordination of S and the axial coordination of Cl can lead to the electron redistribution near the single Zn sites, increasing the overlap between the Zn (3d) and *COOH (2p) orbitals. This enhances the adsorption strength of *COOH on the Zn site and reduces the desorption energy of *CO, thus facilitating catalytic performance. Therefore, the ZnN3S1Cl/C catalyst achieves a CO faradaic efficiency of ≈100% in an H-cell, with excellent long-term stability of 240 h. This work may pave the way for the development of efficient ECR catalysts via fine manipulation of asymmetric and electronic structures of single-atom metal sites.