Edge-Site Co–Nx Model Single-Atom Catalysts for CO2 Electroreduction

Metal–nitrogen–carbon single-atom catalysts with metal sites at the edge of the carbon layers are widely used in electrocatalytic processes such as CO2 reduction. For the single-atom catalysts prepared with pyrolysis methods, the local structure of the metal sites, including the type of the ligands and the coordination number, cannot be precisely controlled, making it difficult to investigate the relationship between the electrocatalytic properties and the local structure. In this work, Co–Nx complexes with 2–4 pyridinic ligands are prepared and anchored at the edge of carbon black with conjugated pyrazine linkers as the model edge-site Co single-atom catalysts. Only the Co–N4 catalyst shows high selectivity toward CO in CO2 electroreduction, with the turnover frequency 1 order of magnitude higher than that of Co–N2 and Co–N3 catalysts. Compared with Co–N2 and Co–N3 sites, the Co–N4 site shows stronger adsorption of COOH and CO species and weaker adsorption of H2O and the H atom due to the low-spin electron configuration, which rationalizes the high CO2 reduction activity and low hydrogen evolution activity of the Co–N4 catalyst.