Specific construction of asymmetric carbon-nickel-chlorine single-atom sites via carbon vacancy engineering for efficient CO2 electroreduction.

Breaking the structural symmetry of active sites in single-atom catalysts (SACs) allows efficient regulation of the electron distribution around the metal centers, holding great promise for promoting their performance in electrocatalytic carbon dioxide reduction reaction (ECO2RR). Herein, we propose a vacancy-engineering strategy for constructing asymmetric carbon-nickel-chlorine (C-Ni-Cl) sites in Ni SAC (Ni1-C/Cl). In strongly acidic media (pH=1), Ni1-C/Cl achieves Faradaic efficiency over 98% for carbon monoxide (CO) product at the operated current density of 500 mA cm-2. In situ X-ray absorption spectra reveal that during electrocatalysis, the C3-Ni-Cl sites exhibit potential-dependent structure evolutions, which can optimize their adsorption configurations for the reactive species. Theoretical calculations demonstrate that the Ni-C/Ni-Cl co-coordination induces the asymmetric electron distribution in C3-Ni-Cl sites, resulting in the regulation of the electronic properties of the Ni centers, thereby optimizing the reaction pathway of CO2-to-CO on these single-atom sites. This work extends the synthesis of SACs containing asymmetric single-atom sites, provides insights into designing industrial-oriented electrocatalysts toward other important electrocatalytic reactions.