Constructing and stabilizing Cu⁰/Cu⁺ sites through dual chlorine-induced strategy for CO₂ electroreduction to C₂H₄

Cu-based catalysts with Cu⁰/Cu⁺ dual sites demonstrate unique synergistic advantages in promoting CO₂ electroreduction. To construct effective Cu⁰/Cu⁺ sites, inhibiting over-reduction of Cu⁺ species is essential while remains a critical challenge due to their inherent thermodynamic instability. Herein, we propose a dual chlorine regulation strategy involving chlorine doping within the Cu₂O matrix and chlorine supplementation in the electrolyte to enhance the stability and activity of Cu⁰/Cu⁺ sites during CO₂-to-C₂H₄ conversion. Notably, the chlorine-doped Cu₂O (Cl-Cu₂O) electrode in 0.1 M KHCO₃ + 0.2 M KCl exhibited a ∼2.5-fold improvement in ethylene Faradaic efficiency (FE_C2H4 increased from 13.0 % to 32.0 %) along with a 4-fold enhancement in operational lifetime compared to pristine Cu₂O evaluated in 0.3 M KHCO₃. The combined results of control experiments, theoretical calculations and in situ characterizations demonstrate that the strong electronic interaction between Cu⁺ and Cl^- effectively suppressed oxygen vacancy formation and retarded the reduction kinetics of Cu⁺ species in reconstructed Cu⁰/Cu⁺ active sites, which further lowered the energy barrier for adsorption of *CO intermediates and facilitated the C-C coupling. Furthermore, introducing Cl^- into the electrolyte significantly mitigated chlorine leaching from the catalyst surface, making Cu⁰/Cu⁺ active sites stably operate for C₂H₄ production. This study provided a novel insight into the stability enhancement mechanism of Cu⁰/Cu⁺ sites and offered a reference for design of Cu-based catalysts for more electrocatalytic reactions.