Modulating the Coordination Environment of Atomically Dispersed Nickel for Efficient Electrocatalytic CO₂ Reduction at Low Overpotentials and Industrial Current Densities.

Abstract

Electrocatalytic CO₂-to-CO conversion with a high CO Faradaic efficiency (FE_CO) at low overpotentials and industrial-level current densities is highly desirable but a huge challenge over non-noble metal catalysts. Herein, graphitic N-rich porous carbons supporting atomically dispersed nickel (NiN₄-O sites with an axial oxygen) were synthesized (denoted as O-Ni-N_<i>x</i>-GC) and applied as the cathode catalyst in a CO₂RR flow cell. O-Ni-N_<i>x</i>-GC showed excellent selectivity with a FE_CO over 92% at low overpotentials ranging from 17 to 60 mV, and over 99% at 80 mV. The FE_CO was ∼100% at industrial-level current densities from 200 to 900 mA·cm^-2. Impressively, O-Ni-N_<i>x</i>-GC delivered a state-of-the-art FE_CO of >96% at 1 A·cm^-2 with a turnover frequency of 81.5 s^-1 in a 1 M KOH electrolyte. O-Ni-N_<i>x</i>-GC offered excellent stability during long-term operation for 140 h at 100 mA·cm^-2, maintaining a FE_CO > 99%. Mechanism studies revealed that the axial oxygen at the atomically dispersed nickel sites enhanced electron delocalization, with the graphitic N-rich porous carbon support lowering the CO₂-to-CO energy barrier and inducing a negative shift in the Ni-3d d-band center, effectively promoting the formation of the *COOH intermediate while weakening the adsorption of the *CO intermediate, thus optimizing the catalytic activity/selectivity to CO under practical conditions.