Tailoring Hydrogenation Pathway to Redirect CO2 Electroreduction From Ethylene to Ethanol.

Electrochemical CO2 reduction to ethanol faces a fundamental challenge: competing ethylene formation through shared C2 intermediates. While previous studies focused on modifying catalyst electronic structures or increasing *CO coverage, the critical role of competitive hydrogenation pathways remains unexplored. Here, we demonstrate that the selectivity between ethanol and ethylene is governed by the balance between Langmuir-Hinshelwood (surface *H) and Eley-Rideal (solvent H) hydrogenation mechanisms. Through hierarchically assembled BPEI/PT interfaces, we dynamically modulate this balance by reconstructing interfacial hydrogen-bond networks without altering catalyst electronic properties. In situ Raman spectroscopy captures enhanced *OCHCH2/*OCHCH3 intermediates, directly correlating ethanol selectivity with suppressed ER pathway. Combined experimental and theoretical studies establish quantitative relationships between hydrogen-bond strength and pathway selectivity. This strategy achieves 38.7% ethanol Faradaic efficiency (FE) at 900 mA cm- 2 on CuO-derived catalysts (116% improvement) and 53% at 800 mA cm- 2 on CuAg systems-among the highest reported efficiencies. Our findings reveal that controlling competitive hydrogenation pathways through interfacial engineering provides an independent parameter for steering CO2 reduction selectivity.