Mechanism of surface oxygen-containing species promoted electrocatalytic CO₂ reduction

Oxygen-containing species have been demonstrated to play a key role in facilitating electrocatalytic CO₂ reduction (CO₂RR), particularly in enhancing the selectivity towards multi-carbon (C₂₊) products. However, the underlying promotion mechanism is still under debate, which greatly limits the rational optimization of the catalytic performance of CO₂RR. Herein, taking CO₂ and O₂ co-electrolysis over Cu as the prototype, we successfully clarified how O₂ boosts CO₂RR from a new perspective by employing comprehensive theoretical simulations. Our results demonstrated that O₂ in feed gas can be rapidly reduced into *OH, leading to the partial oxidation of Cu surface under reduction conditions. Surface *OH accelerates the formation of quasi-specifically adsorbed K⁺ due to the electrostatic interaction between *OH and K⁺ ions, which significantly increases the concentration of K⁺ near the Cu surface. These quasi-specifically adsorbed K⁺ ions can not only lower the C-C coupling barriers but also promote the hydrogenation of CO₂ to improve the CO yield rate, which are responsible for the remarkably enhanced efficiency of C₂₊ products. During the whole process, O₂ co-electrolysis plays an indispensable role in stabilizing surface *OH. This mechanism can be also adopted to understand the effect of high pH of electrolyte and residual O in oxide-derived Cu (OD-Cu) on the catalytic efficiency towards C₂₊ products. Therefore, our work provides new insights into strategies for improving C₂₊ products on the Cu-based catalysts, i.e., maintaining partial oxidation of surface under reduction conditions.