Fluorine-tuned single-atom catalysts with dense surface Ni-N4 sites on ultrathin carbon nanosheets for efficient CO2 electroreduction

A fluorine-tuned single-atom catalyst with an ultrathin nanosheet morphology (only similar to 1.25 nm) and high Ni content of 5.92 wt% was fabricated by a polymer-assisted pyrolysis approach. The synthetic approach not only controls the establishment of the ultrathin nanosheet structure for achieving high surface communication, but also incorporates F dopants to manipulate the electronic structure of the metalloporphyrin-like active sites (Ni-N-4). As a result, such catalyst with unique structural features exhibits a remarkable electrocatalytic performance for CO2-to-CO conversion with the Faradaic efficiency (FE) over 95 % in a wide potential range and an outstanding CO evolution rate of 1146 mmol g(cat)(-1) h(-1) at -0.97 V vs. RHE. The in situ attenuated total reflectioninfrared spectroscopy (ATR-IR) and theoretical calculations further demonstrate that the F-doping modulates the electron configuration of the central Ni-N-4 sites and thereby reduces the energy barrier for CO2 activation, which is favorable to the generation of the key *COOH intermediate.