Coordination engineering of the hybrid Co-C and Co-N active sites for efficient catalyzing CO2 electroreduction

Abstract Single-atom catalysts (SACs) with well-defined active sites provide an efficient route for catalyzing CO2 reduction reaction (CO2RR). Although enormous attention has been focused on metal-Nx moieties, understanding the effect of metal-C coordination and engineering of the hybrid metal-N/C sites have rarely been reported. Herein, we fabricated Co SACs with tunable isolated Co-N5-xCx (x = 1, 2, 3) sites supported on porous carbon frameworks. Benefiting from the difference in electronegativity of the coordinated N and C atoms, the CO Faradaic efficiency (FECO) enhanced considerably from 54 % to 76 % and 92 % at −0.8 V vs. RHE for Co-N4C1, Co-N3C2, and Co-N2C3, respectively. Further density functional theory (DFT) calculations uncover that the increased ratio of Co-C coordination induced electron enrichment of Co atoms and upper-shift the d-band center to near Fermi level, and thus favorably promotes the electron-donating ability of Co centers and strengthens the adsorption of *COOH.