Nickel Single Atom Density-Dependent CO₂ Efficient Electroreduction

The transition metal-nitrogen-carbon (MNC) with MNx sites has shown great potential in CO2 electroreduction (CO2RR) for producing high value-added C1 products. However, a comprehensive and profound understanding of the intrinsic relationship between the density of metal single atoms and the CO2RR performance is still lacking. Herein, a series of Ni single-atom catalysts is deliberately designed and prepared, anchored on layered N-doped graphene-like carbon (x Ni-1@NG-900, where x represents the Ni loading, 900 refers to the temperature). By modulating the precursor, the density of Ni single atoms (D-Ni) can be finely tuned from 0.01 to 1.19 atoms nm(-2). The CO2RR results demonstrate that the CO faradaic efficiency (FECO) predominantly increases from 13.4% to 96.2% as the D-Ni increased from 0 to 0.068 atoms nm(-2). Then the FECO showed a slow increase from 96.2% to 98.2% at -0.82 V versus reversible hydrogen electrode (RHE) when D-Ni increased from 0.068 to 1.19 atoms nm(-2.) The theoretical calculations are in good agreement with experimental results, indicating a trade-off relationship between D-Ni and CO2RR performance. These findings reveal the crucial role of the density of Ni single atoms in determining the CO2RR performance of MNC catalysts.