Steering Ethylene Electrosynthesis by Controlling Interfacial Water Orientation.

Controlling reaction pathway via solvent polarization dynamics remains a grand challenge in catalysis due to elusive interfacial kinetic regulation mechanisms. Here, we resolve this dilemma by establishing interfacial water orientation that directly couples H2O polarization with reaction pathway bifurcation. Using electrocatalytic CO2 reduction as a typical platform, we demonstrate that precisely engineered H-down water alignment, achieved via adaptive subsurface tuning (AST) strategy of Ga-doped Cu catalysts, dynamically regulates proton transfer directionality and intermediate stabilization. The optimized Ga/Cu catalyst achieved a Faradaic efficiency (FE) of 68.8% for ethylene at 800 mA cm-2, surpassing ethanol production by 8.2-fold, and the current density was among the highest reported for catalysts with high ethylene FE. Detailed experimental studies and theoretical calculations corroborate that H-down alignment enhanced *H availability, directing protons to selectively cleave the C─O bond of *CHCOH intermediates over hydrogenation pathways, yielding high ethylene FE and current density. These findings establish interfacial water orientation as a pivotal descriptor for steering C─C coupling selectivity in electrocatalysis, offering a rational design principle for efficient electroreduction systems.