Promoting Water Activation via Molecular Engineering Enables Efficient Asymmetric C–C Coupling during CO₂ Electroreduction

Water activation plays a crucial role in CO₂ reduction, but improving the electrocatalytic performance through controlled water activation presents a significant challenge. Herein, we achieved electrochemical CO₂ reduction to ethene and ethanol with high selectivity by promoting water dissociation and asymmetric C-C coupling by engineering Cu surfaces with N-H-rich molecules. Direct spectroscopic evidence, coupled with density functional theory calculations, demonstrates that the N-H-rich molecules accelerate interfacial water dissociation via hydrogen-bond interactions, and the generated hydrogen species facilitate the conversion of *CO to *CHO. This enables the efficient asymmetric *CHO-*CO coupling to C₂ products with a faradaic efficiency (FE) ∼ 30% higher than that of the unmodified catalyst. Moreover, by adjustment of the relative *CHO/*CO coverage via Cu surface facet regulation, the selectivity can be entirely switched between C₂ products and CH₄. These mechanistic insights further guided the development of a more efficient catalyst by directly modifying Cu₂O nanocubes with the N-H-rich molecule, achieving remarkable C₂ product (mainly ethene and ethanol) FEs of 85.7% at a current density of 800 mA cm^-2 and excellent stability under nearing industrial conditions. This study advances our understanding of the CO₂ reduction mechanisms and offers an effective and general strategy for enhancing electrocatalytic performance by accelerating water dissociation.