Enriching Hydroxyl Species via Grain Boundaries to Shift CO₂ Electroreduction toward Ethylene over Methane in Neutral...

Neutral CO₂ electroreduction reaction alleviates the substantial CO₂ and energy loss from carbonate formation, but the slow C-C coupling kinetics restricts both activity and selectivity for multicarbon products. Herein, we found that the *OH_ad-enriched microenvironment at grain boundary copper sites promotes asymmetric C-C coupling with a low-energy barrier. In situ spectra combined with theoretical calculations confirmed that enriched Cu-OH species in grain boundaries not only promote Bridge *CO and high-frequency *CO_Atop species but also restructure the interfacial water layer into an ice-like configuration, which concurrently suppresses HER and accelerates the asymmetric coupling between *COH and *CO. In contrast, on the *OH_ad-deficient Cu(111) facet, the exclusive low-frequency *CO_Atop favors deep hydrogenation to methane. Consequently, the major product shifts from methane (Faradaic efficiency, FE_CH4 = 54.82%) to ethylene (FE_C2H4 = 76.67%) as the grain boundary density increases, with a high ethylene partial current density of -379.22 mA·cm^-2.