Bidentate Piperazine Matrices Steering Interfacial Proton Flux toward Ampere-Level Ethanol Electrosynthesis in CO ₂ Electrolyzers

Ampere-level ethanol electrosynthesis via CO₂ electroreduction (CO₂ER) critically depends on the dynamic reconstruction of interfacial water networks within the electric double layer (EDL), which provides a confined space for a sustained proton supply. Conventional reconstruction strategies like electrolyte engineering, however, introduce spatial heterogeneity. This causes local variations in activity and selectivity, especially in membrane electrode assembly (MEA) electrolyzers, where scarce cathodic electrolyte worsens proton transport limitations. Here, we introduce a bidentate-N-enriched organic interlayer that strategically modulates the orientation of interfacial water molecules, thereby enhancing proton supply and optimizing hydrogenation kinetics. In situ spectroscopy and theoretical simulations reveal that the piperazine layer promotes water dissociation through interfacial reorientation, thus accelerating *CO → *CHO hydrogenation and asymmetric *CHO-*CO coupling for selective ethanol production. The piperazine-modified Cu catalyst achieves >85% C₂₊ Faradaic efficiencies (FEs) at 400-1000 mA cm^-2 and 50.5% ethanol FEs in a flow cell and maintains 40.1% ethanol FEs at 2.0 A in the MEA electrolyzer. This work provides a molecular-level design strategy to tailor electrolytic interfaces for CO₂ conversion at the electrolyzer level.