Intermediates-induced CO₂ Reduction Reaction Activity at Single-Atom M-N₂ (M=Fe, Co, Ni) Sites

Single-atom M-N₂ (M=Fe, Co, Ni) catalysts exhibit high activity for CO₂ reduction reaction (CO₂ RR). However, the CO₂ RR mechanism and the origin of activity at the single-atom sites remain unclear, which hinders the development of single-atom M-N₂ catalysts. Here, using density functional theory calculations, we reveal intermediates-induced CO₂ RR activity at the single-atom M-N₂ sites. At the M-N₂ sites, the asymmetric *O*CO configuration tends to split into *CO and *OH intermediates. Intermediates become part of the active moiety to form M-(CO)N₂ or M-(OH)N₂ sites, which optimizes the adsorption of intermediates on the M sites. The maximum free energy differences along the optimal CO₂ RR pathway are 0.30, 0.54, and 0.28 eV for Fe-(OH)N₂ , Co-(CO)N₂ , and Ni-(OH)N₂ sites respectively, which is lower than those of Fe-N₂ (1.03 eV), Co-N₂ (1.24 eV) and Ni-N₂ (0.73 eV) sites. The intermediate modification can shift the d-band center of the spin-up (minority) state downward by regulating the charge distribution at the M sites, leading to less charge being accepted by the intermediates from the M sites. This work provides new insights into the understanding of the activity of single-atom M-N₂ sites.