The peripheral environment: key to advanced single-atom catalysis for CO2 reduction.

Electrocatalytic reduction of CO2 into value-added fuels and chemicals is a crucial pathway to achieving carbon neutrality and energy regeneration. Single-atom catalysts (SACs) are considered among the most promising catalysts for CO2 electroreduction due to their high atom utilization and well-defined active site structures. However, the traditional design concept centered on the central metal atom and the first coordination shell is insufficient to fully explain the differences in activity, selectivity, and stability exhibited by catalysts under operating conditions. Here, we emphasize the role of peripheral factors, including higher coordination shells, support defects, pore confinement, and neighboring metal species. Through an "outside-in" mechanism, these factors regulate the electronic structure, adsorption behavior, and stability of single-atom sites, while their interplay with solvation, electrolytes, and interfacial electric fields under operating conditions dynamically reshapes the coordination environment and reaction energetics. We systematically summarize the experimental and theoretical progress of peripheral environment regulation for CO2 electroreduction over SACs, including construction and identification of peripheral structures through precise synthesis and operando characterization, as well as theoretical understanding using electronic structure analysis, explicit solvent dynamics, and constant-potential simulations. The remaining challenges and opportunities in unified descriptor construction, dynamic mechanism analysis, and industrial applications, are also discussed. This perspective reframes single-atom catalysis by shifting the focus from the isolated metal center to the full catalytic active domain, providing a new design paradigm for efficient, stable, and selective CO2 electroreduction.