Nickel Single Atom Density-Dependent CO₂ Efficient Electroreduction

The transition metal-nitrogen-carbon (M─N─C) 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 Ni₁@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 (FE_CO) predominantly increases from 13.4% to 96.2% as the D_Ni increased from 0 to 0.068 atoms nm^-2. Then the FE_CO 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 M─N─C catalysts.