An accurate "metal pre-buried" strategy for constructing Ni-N2C2 single-atom sites with high metal loadings toward electrocatalytic CO2 reduction

Although single-atom catalysts (SACs) dispersed on N-doped carbon supports with the M-N2C2 configuration have high application potential in electrocatalysis, combining this configuration with high metal loadings remains a considerable challenge. In this study, a Ni-salen polymer with a confined metal position and precise coordination mode (Ni-N2O2) serves as a precursor, which not only suppresses the aggregation of metal atoms but also promotes the creation of Ni-N2C2 centers owing to the cleavage of Ni-O bonds and formation of Ni-C bonds during high-temperature pyrolysis. A Ni-N2C2 SAC with a metal loading of 9.15 wt% exhibits excellent catalytic performance for the CO2 electroreduction to CO with a faradaic efficiency (FECO) of 98.7% at -0.82 V vs. the reversible hydrogen electrode (RHE). Theoretical calculation data have further demonstrated that the modified electronic structure of the Ni-N2C2-p model is responsible for its high intrinsic activity. This work proposes a new strategy for maintaining both the precise Ni-N2C2 structure and high metal loading.