Electrochemical conversion of CO₂ (CO₂RR) into high-value fuel is identified as one of the promising approaches to achieve carbon neutrality. The synthesis of high-efficiency CO₂ reduction electrocatalysts with high C₂:C₁ selectivity remains a field of intense interest. Previous studies have shown that the presence of Cu(I) is beneficial for the reduction of CO₂ into C₂ products. However, the stable presence of Cu(I) remains controversial, especially in the negative potential window. Here we report a simple and easily scalable catalyst precursor Cu₂(OH)₃Cl/C, which automatically forms in-situ chlorine-doped Cu/Cu₂O hetero-interface during electrocatalysis. The catalyst not only exhibits a Faradaic efficiency of 33.03% but also provides a long-term stability of Cu⁺, gaining a stable electrolysis of 11 h, with an ethylene/methane ratio over 50. The experimental results and mechanistic studies confirm that the presence of Cl⁻ inhibits the reduction of Cu⁺, inducing the formation of Cu⁰/Cu⁺, and reduces the reaction energy of the intermediate *CO dimerization, thereby facilitating the formation of C₂ products. This work provides a feasible way to synthesize copper ions with long-term and stable positive charge in CO₂RR and expands a new way to synthesize ethylene industrial products in the future.