Br-doped CuO promotes water dissociation and enables efficient asymmetric C-C coupling during electrochemical reduction of CO2 to ethylene

Carbon-carbon (C-C) coupling, the rate-determining step in electrocatalytic CO 2 reduction reaction (CO 2 RR) to C 2+ products, has low efficiency and poor stability. It originates from an ineffective water dissociation capability and a high energy barrier for the C-C coupling pathway on existing catalysts. Herein, an efficient and facile Br-CuO electrocatalyst was synthesized to promote water dissociation and achieve an impressive Faradic Efficiency (FE) of around 60% C 2 H 4 at a current density of up to -350 mA/cm 2 with stability of 16 h. Combinative theoretical and experimental protocols strongly evidence that the architecture of Cu 0 -Cu + sites is crucial for the enhancement in CO 2 RR activity. Cu 0 activates CO 2 and Cu + strengthens *CO adsorption to further boost C-C coupling. Furthermore, Br doping can facilitate the dissociation of water to generate *H, which promotes the protonation of *CO to *CHO, thereby enabling the low energy barrier asymmetric *CHO-*CO coupling. The in situ ATR-FTIR and Density functional theory (DFT) was analyzed to explain the reaction mechanism and pathway. This study elucidates the critical function of water dissociation and provides a promising avenue to efficient CO 2 -to-C 2 H 4 electrocatalysis.