Atomic-Level Active Sites of Efficient Imidazolate Frameworks-Derived Nickel Catalysts for CO2 Reduction
Nickel and nitrogen co-doped carbon (Ni-N-C) has emerged as a promising catalyst for CO2 reduction reaction (CO2RR); however, the chemical nature of its active sites has remained elusive. Herein, we report the exploration of the reactivity and active sites of Ni-N-C for CO2RR. Single atomic Ni coordinated with N confined in the carbon matrix was prepared through thermal activation of chemically Ni-doped zeolitic imidazolate frameworks (ZIF) and directly visualized by aberration-corrected scanning transmission electron microscopy. Electrochemical results show the enhanced intrinsic reactivity and selectivity of Ni−N sites for the reduction of CO2 to CO, delivering a maximum CO Faradaic efficiency of 96% at a low overpotential of 570 mV. Desnity functuional theory (DFT) calculations predict that the edge-located Ni-N2+2 sites with dangling bond-containing carbon atoms is the active site facilitating the dissociation of the C−O bond of *COOH intermediate, while the bulk-hosted Ni−N4 is kinetically inactive. Furthermore, the high capability of the edge-located Ni−N4 being able to thermodynamically suppress the competitive hydrogen evolution is also explained. The proposal of edge-hosed Ni−N2+2 site provides new insight in designing high-efficiency Ni-N-C for CO2 reduction.