Nickel Single Atom Density-Dependent CO 2 Efficient Electroreduction.

The transition metal-nitrogen-carbon (M─N─C) with MNx sites has shown great potential in CO 2 electroreduction (CO 2 RR) for producing high value-added C 1 products. However, a comprehensive and profound understanding of the intrinsic relationship between the density of metal single atoms and the CO 2 RR 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 CO 2 RR 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 CO 2 RR performance. These findings reveal the crucial role of the density of Ni single atoms in determining the CO 2 RR performance of M─N─C catalysts.