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.
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