Unveiling Active Sites of CO2 Reduction on Nitrogen-Coordinated and Atomically Dispersed Iron and Cobalt Catalysts

Herein, we report the exploration of understanding the reactivity and structure of atomically dispersed M-N-4 (M = Fe and Co) sites for the CO, reduction reaction (CO2RR). Nitrogen coordinated Fe or Co site atomically dispersed into carbons (M-N-C) containing bulk- and edge hosted M-N-4 coordination were prepared by using Fe-or Co doped metal-organic framework precursors, respectively, which were further studied as ideal model catalysts. Fe is intrinsically more active than Co in M-N4 for the reduction of CO2 to CO, in terms of a larger current density and a higher CO Faradaic efficiency (FE) (93% vs. 45%). First principle computations elucidated that the edge-hosted M-N2+2-C-8 moieties bridging two adjacent armchair-like graphitic layers is the active sites for the CO2RR They are much more active than previously proposed bulk-hosted M-N-4-C-10 moieties embedded compactly in a graphitic layer. During the CO2RR, when the dissociation of *COOH occurs on the M-N2+2-C-8, the metal atom is the site for the adsorption of *CO and the carbon atom with a dangling bond next to an adjacent N is the other active center to bond *OH In particular, on the Fe-N2+2-C-8 sites, the CO2RR is more favorable over the hydrogen evolution reaction, thus resulting in a remarkable FE.