Modulating the Coordination Environment of Atomically Dispersed Nickel for Efficient Electrocatalytic CO<sub>2</sub> Reduction at Low Overpotentials and Industrial Current Densities
Yichen Sun, Xiaolu Liu, Jiazheng Tian, Zixuan Zhang, Yang Li, Yinghui Xie, Mengjie Hao, Zhongshan Chen, Hui Yang, Geoffrey I. N. Waterhouse, Shengqian Ma, Xiangke Wang
Abstract
Electrocatalytic CO 2 -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 (NiN 4 –O sites with an axial oxygen) were synthesized (denoted as O–Ni–N x –GC) and applied as the cathode catalyst in a CO 2 RR flow cell. O–Ni–N x –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 x –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 x –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 CO 2 -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.