Atomically Structural Regulations of Carbon-Based Single-Atom Catalysts for Electrochemical CO 2 Reduction.

The electrochemical carbon dioxide reduction reaction (CO 2 RR) converting CO 2 into value-added chemicals and fuels to realize carbon recycling is a solution to the problem of renewable energy shortage and environmental pollution. Among all the catalysts, the carbon-based single-atom catalysts (SACs) with isolated metal atoms immobilized on conductive carbon substrates have shown significant potential toward CO 2 RR, which intrigues researchers to explore high-performance SACs for fuel and chemical production by CO 2 RR. Especially, regulating the coordination structures of the metal centers and the microenvironments of the substrates in carbon-based SACs has emerged as an effective strategy for the tailoring of their CO 2 RR catalytic performance. In this review, the current in situ/operando study techniques and the fundamental parameters for CO 2 RR performance are first briefly presented. Furthermore, the recent advances in synthetic strategies which regulate the atomic structures of the carbon-based SACs, including heteroatom coordination, coordination numbers, diatomic metal centers, and the microenvironments of substrates are summarized. In particular, the structure-performance relationship of the SACs toward CO 2 RR is highlighted. Finally, the inevitable challenges for SACs are outlined and further research directions toward CO 2 RR are presented from the perspectives.