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 Ni_n clusters (Ni-N/Ni_n) were synthesised, and subsequently, Ni_n clusters were transformed into Ni_nN_x clusters (Ni-N/Ni_nN_x) 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/Ni_nN_x increased and Ni-N-Ni bonds within atomic clusters were generated, thereby confirming the transformation from Ni_n clusters to Ni_nN_x clusters. Density functional theory calculations show that the Ni_nN_x clusters have a lower energy barrier for the *CO₂^- + H⁺ → *COOH step compared to Ni_n 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/Ni_nN_x demonstrates high Faraday efficiency of CO (FE_COmax = 98.6 % at -0.4 V vs. RHE), a wider potential window (-0.3 to -0.8 V vs. RHE, FE_CO > 90 %) and high CO partial current density (j_CO > 100 mA cm^-2). In comparison with Ni-N/Ni_n, the maximum CO partial current density of Ni-N/Ni_nN_x 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.