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Herein, we report the exploration of understanding the reactivity and structure of atomically dispersed M–N4 (M = Fe and Co) sites for the CO2 reduction reaction (CO2RR). Nitrogen coordinated Fe or Co site atomically dispersed into carbons (M–N–C) containing bulk- and edge-hosted M–N4 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–C8 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–N4–C10 moieties embedded compactly in a graphitic layer. During the CO2RR, when the dissociation of *COOH occurs on the M–N2+2–C8, 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–C8 sites, the CO2RR is more favorable over the hydrogen evolution reaction, thus resulting in a remarkable FE.

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Development of effective nonprecious metal and nitrogen codoped carbon catalysts for the oxygen reduction reaction (ORR) requires a fundamental understanding of the mechanisms underlying their catalytic activity. In this study, we employed the first-principles density functional theory calculations to predict some key parameters (such as activation energy for O−O bond breaking and free-energy evolution as a function of electrode potential) of ORR on three FeN 4 -type active sites with different local carbon structures. We find that the FeN 4 site surrounded by eight carbon atoms and at the edge of micropores has the lowest activation energy (about 0.20 eV) for O−O bond breaking among the three FeN 4 -type active sites for promoting a direct four-electron ORR. Consequently, our computational results suggest that introduction of micropores in the nonprecious metal catalysts could enhance their catalytic activity for ORR through facilitating the formation of FeN 4 −C 8 active sites with high specific activity.

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