Interfacial Dynamic Oxygen Exchange Preserves C─O Bonds for Selective CO 2 ‐to‐Ethanol Electrosynthesis

Intermediate‐valence copper (Cu + ) is essential for preserving C─O bonds during the electrochemical reduction of CO 2 to ethanol, yet its progressive over‐reduction to Cu 0 under operating potentials inevitably dictates C─O bond cleavage and shifts selectivity toward ethylene. Herein, we propose an interfacial dynamic oxygen exchange strategy to stabilize Cu + sites and steer the ethanol reaction pathway. We realize this mechanism by engineering a few‐layer ceria‐coated cuprous oxide (Cu 2 O@CeO 2 ) catalyst featuring an oxygen vacancy‐rich heterointerface (Ce−O V −Cu). Operando spectroscopic measurements and density functional theory calculations reveal that these interfacial oxygen vacancies act as core mediators; by continuously capturing and migrating oxygen species derived from CO 2 , they effectively arrest the reduction of adjacent Cu + siteversuss. Crucially, this dynamic interface dictates the asymmetric C─C coupling of *CH 2 and *CHO, successfully preserving the C−O bond during the subsequent protonation of *CH 2 CHO to *CH 3 CHO. Consequently, the optimized catalyst delivers an outstanding ethanol Faradaic efficiency of 68.5% at −1.1 V versus RHE and exhibits robust operational stability exceeding 150 h, substantially outperforming pristine Cu 2 O. This study establishes vacancy‐mediated dynamic oxygen exchange as a robust strategy for preserving key oxygen‐containing functional groups in highly selective CO 2 ‐to‐ethanol electrosynthesis.