Electronic structure engineering of nickel single-atom catalyst by phosphorous for efficient electrocatalytic CO₂ reduction reaction in a proton-rich microenvironment

The electrocatalytic carbon dioxide reduction reaction (eCO₂RR) in an acidic environment is crucial for mitigating carbonate and bicarbonate formation while enhancing CO₂ conversion efficiency. However, the hydrogen evolution reaction (HER) often outcompetes eCO₂RR in a proton-rich microenvironment, posing a significant challenge. This study introduces an in-situ phosphatizing method to alter the electronic structure of a Ni–N₄ single-atom catalyst (Ni–N₃PC), thereby suppressing HER and promoting eCO₂RR performance in acidic environments. The Ni–N₃PC catalyst achieves a CO Faradaic efficiency (FE) exceeding 90 % over a wide potential range, high carbon conversion efficiency, a CO partial current density of –357.7 mA cm⁻², and long-term stability for 100 h at –100 mA cm⁻² with a FE of 85 %. Electrochemical impedance spectroscopy and turnover frequency analysis reveal that Ni–N₃PC exhibits lower charge-transfer resistance and higher intrinsic activity, respectively. The structural characterization using X-ray absorption spectroscopy confirms the formation of Ni–P and Ni–N bonds while scanning transmission electron microscopy shows atomically dispersed Ni atoms on carbon networks. Density functional theory calculations further support the experimental results, showing that Ni–N₃PC significantly lowers the energy barrier for the key *COOH intermediate, resulting in outstanding eCO₂RR performance. This research provides valuable insights into the design of highly efficient Ni single-atom catalysts for industrial eCO₂RR applications.