Asymmetric Coordination Engineering of Tin Single-Atom Catalysts Toward CO2 Electroreduction: the Crucial Role of Charge Capacity in Selectivity

Electrochemical reduction of CO2 is an efficient strategy for CO2 utilization under mild conditions. Tin (Sn) single-atom catalysts (SACs) are promising candidates due to their controllable CO/formate generation via asymmetric coordination engineering. Nevertheless, the factors that govern the selectivity remain unclear. Herein, using constant-potential first-principles calculations, the crucial role of charge capacity in affecting the catalytic selectivity is revealed. The conventional SnN4 moiety of Sn SACs exhibits a physisorbed CO2 configuration at operating potentials, thereby facilitating the generation of their energetically favorable intermediate, (OCHO)-O-*. Remarkably, oxygen doping on the SnN4 moiety breaks the uniform charge distribution and improves the charge capacity of (CO2)-C-*. This promotes CO2 adsorption with a V-shaped chemisorption configuration, which is conducive to the formation of the kinetically dominant (COOH)-C-* intermediate due to their similar configurations. Therefore, asymmetric coordination engineering not only enhances the reactivity of Sn SACs but also shifts the selectivity from formate to CO. The study provides a mechanistic understanding of CO2 reduction selectivity and offers practical guidance for the rational design of SACs.