Synergistic Regulation of *CO Adsorption and *CO−*CHO Coupling on Cu₂O Enables Selective CO₂ Electroreduction to C₂₊ Products

Copper-based electrocatalysts demonstrate significant potential for electrochemical CO₂ reduction toward value-added chemicals. However, achieving selective synthesis of multi-carbon (C₂₊) products on copper-based catalysts remains a substantial challenge. In this study, a Cu₂O electrocatalyst (Mg_0.1-Cu₂O-SC) doped with magnesium (Mg) and surface-modified by sodium citrate (SC) was successfully synthesized via a simple wet chemical reduction method. The Mg_0.1-Cu₂O-SC achieves a Faradaic efficiency (FE) of 77.8% and a partial current density of 357.9 mA cm⁻² for C₂₊ products, which is 1.35 times higher than the FE of unmodified Cu₂O. Mg_0.1-Cu₂O achieves an enhancement in the FE for CO, demonstrating that the Lewis-acidic Mg weakens the bond strength of Cu−*CO and enhances the local concentration of *CO by attracting electrons from Cu. In situ spectroscopic analysis reveals that the surface modification of SC facilitates the *CO to *CHO hydrogenation, which shifts the C−C coupling to a more favorable *CO−*CHO route with a lower-energy barrier and consequently improves the FE for C₂₊ products. Theoretical calculations indicate that the electron-withdrawing effect of Mg induces a downward shift in the copper d-band center. Energy barrier analyses reveal that SC effectively lowers the energy barriers for both the water dissociation reaction and the *CO−*CHO coupling reaction. This work confirms that Mg effectively modulates the adsorption behavior of key intermediates and synergistically optimizes the reaction pathway in concert with SC.