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

[Display omitted] • A series of Co SACs were synthesized with tunable Co-N 5- x C x (x = 1, 2, 3) sites. • Engineering the hybrid N and C coordination greatly affect the CO 2 RR performance. • FE CO boosted from 54 to 76 and 92% at −0.8 V with increased ratio of Co-C. • Co-C promotes the electron donation and strengthen binding interaction with *COOH. Single-atom catalysts (SACs) with well-defined active sites provide an efficient route for catalyzing CO 2 reduction reaction (CO 2 RR). Although enormous attention has been focused on metal-N x 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-N 5-x C x (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 (FE CO) enhanced considerably from 54% to 76% and 92% at −0.8 V vs. RHE for Co-N 4 C 1 , Co-N 3 C 2 , and Co-N 2 C 3 , 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. [ABSTRACT FROM AUTHOR]