Stabilizing Cuδ+ Sites via Bidentate Coordination toward Efficient Electrochemical C-C Coupling

Copper (Cu)-based electrocatalysts can promote C-C coupling during the electrocatalytic CO2 reduction reaction (eCO2RR). However, the easily variable oxide states of Cu cause the generated *CO intermediate to either desorb as CO or undergo further coupling into a mixture of C2+ products, resulting in poor selectivity and yield toward ethanol. Herein, we stabilize Cuδ+ (0 < δ < 1) active sites with high dispersion in a polyacrylic acid immobilized Cu (PAA-Cu) electrocatalyst, where Cu atoms form strongly bidentate chelates with carboxylate (-COO-) ligands in the PAA matrix. This coordination environment precisely modulates the local electronic structure of Cu, promotes electron redistribution, and upshifts the d-band center of Cu ions. Density functional theory calculations reveal that stabilized Cuδ+ sites facilitate *CO-COH coupling to form the *OCCOH intermediate, thereby favoring the selective production of ethanol with a Faradaic efficiency of up to 61.9%, which is approximately twofold higher than that of an unmodified Cu nanoparticle electrode (31.2%) while maintaining stable operation for ∼28 h. This work demonstrates the critical role of ligand-mediated coordination engineering in regulating Cu active sites for selective eCO2RR.