Controllable fabrication of atomic dispersed low-coordination nickel-nitrogen sites for highly efficient electrocatalytic CO2 reduction

Single-atom catalysis has been considered as a powerful approach for CO2 reduction reaction (CO2RR) to achieve efficient resource conversion and carbon neutrality. The electrocatalytic activity of single-atom catalysts (SACs) is closely related to the local coordination environment. Herein, Ni SACs with well-defined low-coordination nickel-nitrogen sites (denoted as Ni-SA@N-3-C) have been successfully developed via a facile sacrificial template method. XAS results reveal that the coordination environment of the atomically dispersed Ni active sites can be controlled by the pyrolysis temperature. Significantly, Ni-SA@N-3-C displays remarkably excellent activity toward electrocatalytic CO2RR with CO Faradaic efficiency (FECO) of 96.0% at -0.83 V vs. RHE and remains high FECO exceeding 90% over a broad potential range from -0.63 to -0.93 V vs. RHE, outperforming those of Ni-SA@N-4-C and Ni-NP@NC. More importantly, Ni-SA@N-3-C exhibits an excellent CO selectivity of 99.2% with a considerable current density of -160 mA cm(-2) in the flow cell reactor. Density functional theory (DFT) calculations further suggest that the Ni single atoms coordinated by three N atoms possesses a suitable free energy barrier for *COOH formation and *CO desorption, thereby exhibiting the most excellent CO2RR performance. This study sheds a new light on the design of SACs with controllable coordination structures for CO2RR.