Nitrogen imported in nickel clusters promotes carbon dioxide electrochemical reduction to carbon monoxide.

The Ni-N coordination structure has been shown to be conducive to the electrochemical CO2 reduction reaction (CO2RR) to CO, and this process has been extensively validated. However, the impact of Ni-N coordination structures within Ni-based clusters on CO2RR has received relatively limited research attention to date. In this study, catalysts containing Ni single atoms and Nin clusters (Ni-N/Nin) were synthesised, and subsequently, Nin clusters were transformed into NinNx clusters (Ni-N/NinNx) through secondary nitridation. The experimental results, as illustrated by X-ray photoelectron spectra and X-ray absorption fine structure spectra, demonstrate that the Ni-N bond in Ni-N/NinNx increased and Ni-N-Ni bonds within atomic clusters were generated, thereby confirming the transformation from Nin clusters to NinNx clusters. Density functional theory calculations show that the NinNx clusters have a lower energy barrier for the *CO2- + H+ → *COOH step compared to Nin clusters, and promote the entire reaction. Furthermore, in-situ attenuated total reflection surface-enhanced infrared absorption spectroscopy (ATR-SEIRAS) and density functional theory (DFT) calculations collectively indicate that abundant Ni-N coordination structures in clusters effectively reduce the energy barrier of CO2 + e- → *CO2- and facilitate the activation of CO2 to *CO2- across a broader potential window. Ni-N/NinNx demonstrates high Faraday efficiency of CO (FECOmax = 98.6 % at -0.4 V vs. RHE), a wider potential window (-0.3 to -0.8 V vs. RHE, FECO > 90 %) and high CO partial current density (jCO > 100 mA cm-2). In comparison with Ni-N/Nin, the maximum CO partial current density of Ni-N/NinNx is enhanced by approximately 4.6 times. These findings offer valuable insights into the structure-activity relationship of Ni-based cluster catalysts and facilitate the development of more advanced atomically cluster catalysts.