Fundamentals of Electrochemical CO2 Reduction on Single-Metal-Atom Catalysts

Electrochemical carbon dioxide (CO2) reduction powered by renewable electricity offers a path to produce valuable products from CO2-an earth-scale human waste-and to store intermittent renewable energy in the form of chemical fuels. Recently, single metal atoms (SMAs) immobilized on a conductive substrate have been shown as effective catalysts for the electrochemical CO2 reduction, opening the door to a generation of low-cost and high-performance catalysts for fuel and chemical production. The unique physical and chemical properties of a single-atomic structure and the homogeneity of the active sites, combined with tunable coordination environments, are essential for realizing highly active and selective catalysts. In this Review, we focus on the structure-performance relationship in SMA catalysts for CO2 reduction from both theoretical and experimental aspects. We discuss why SMA catalysts exhibit a distinct catalytic performance compared to their counterpart nanoparticles. Recent strategies for improving the CO2 reduction selectivity and activity by tuning the nature and coordination environment of SMA active sites are described. Finally, we highlight potential applications of SMA catalysts in practical CO2 reduction conditions, critical challenges, and the path toward efficient electrochemical CO2 reduction catalysis based on SMAs.