Theoretical and experimental investigation of the coordination effect on photocatalytic CO₂ reduction efficiency of cobalt single atom catalyst

Visible-light-driven carbon dioxide (CO2) reduction, which converts CO2 into value-added fuels, is an intriguing strategy to simultaneously mitigate the energy crisis and achieve a carbon-neutral economy. Single-atom cat-alysts (SACs) with homogeneously dispersed definite active sites and adjustable coordination environments show great potential in catalyzing photocatalytic CO2 reduction reaction (CO2RR). According to previously reported studies, the catalytic performance of SACs applied in various fields has a great relationship with their local coordination environment of metal centers. However, in-depth investigation of the coordination effect, which has been widely explored to regulate the electronic structure of SACs, on the activity, selectivity, and stability of CO2 photoreduction has never been reported. Herein, a series of Co single atom photocatalysts with diverse N coordination number (Co-SA-N-x/C, x = 2, 3, and 4) were synthesized and their photocatalytic CO2RR perfor-mance was examined. Theoretical and experimental investigation demonstrated that the photocatalytic CO2RR activity of Co SACs can be effectively adjusted by fine-regulating the N coordination. The optimal Co-SA-N-2/C photocatalyst with two-coordinate N atoms with increased unoccupied Co 3d electronic orbitals possesses enhanced CO2 adsorption and activation as well as reduced energy barrier for *COOH intermediate generation, thus showing superior photoconversion of CO2-to-CO performance with 10110 mu mol g(-1)h(-1) CO evolution yield, 82.6 % CO selectivity, and long-term stability. This work promotes the future rationally design and synthesis of photocatalysts applied in targeted reactions at atomic scale.