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. Remarkably, oxygen doping on the SnN₄ moiety breaks the uniform charge distribution and improves the charge capacity of ^*CO₂. This promotes CO₂ adsorption with a V-shaped chemisorption configuration, which is conducive to the formation of the kinetically dominant ^*COOH 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.