Hybrid Hydrogen-Bond Networks Steer Proton-Coupled Pathway for Acidic CO2-To-Ethanol Electrosynthesis.

Acidic CO2 reduction prevents carbonate loss but is limited by uncontrolled interfacial proton dynamics that trigger hydrogen evolution and favor ethylene. Here, we demonstrate that an adaptive hybrid ionomer interface steers proton-coupled pathways to achieve highly selective ethanol electrosynthesis. Through surface-limited oxidative reconstruction, the interphase evolves into a robust hydrogen-bonding network paired with an intact cationic sublayer. This architecture limits solvated proton diffusion, effectively suppressing the disruptive Eley-Rideal (ER) pathway toward ethylene. Instead, it dynamically shifts the reaction toward the Langmuir-Hinshelwood (LH) mechanism, optimizing surface-bound *H availability within a fixed mildly alkaline microenvironment (pH ≈ 10.5). Consequently, our membrane electrode assembly achieves >64% ethanol Faradaic efficiency at 200 mA cm-2 with >350 h of stability in pH = 1 electrolyte. This elucidates the pivotal role of interfacial hydrogen-bond networks in dictating proton-coupling mechanisms, offering a paradigm for pathway-specific acidic electrosynthesis.