Hetero-Solvent Microenvironment for Selective CO₂ to Ethanol Electrolysis via Interfacial Water Control

Electrochemical reduction of carbon dioxide (CO₂RR) offers a route for sustainable chemical production using water as a clean proton source. However, water also promotes the competing hydrogen evolution reaction, limiting CO₂RR performance. Here we establish interfacial water as a decisive but overlooked design parameter for selective CO₂-to-ethanol electrolysis. A hetero-solvent microenvironment confining diglyme (DiG) near the Cu catalyst substantially suppresses HER under both neutral and alkaline conditions, where protons are supplied via water dissociation. In situ infrared absorption spectroscopy and theoretical calculation results reveal that DiG strengthens the hydrogen-bonding network of interfacial water, reducing free-water population prone to dissociation. Concurrently, the modulated water network effectively hinders solvent-mediated hydrogenation that favors ethylene formation, thereby promoting ethanol formation. Because this strategy modulates the microenvironment rather than the catalyst, it readily extends to Cu-Ag bimetallic catalyst. Moreover, confining hetero-solvent within microenvironment rather than in the bulk electrolyte enables high-current operation at low cell voltages, achieving an ethanol partial current density of 184.2 mA cm^-2 at 3.6 V under neutral condition.