Unlocking n-Propanol Electrosynthesis From CO2 via Constructing *CO─H2O Reaction Microregion.

Selective electroreduction of CO2 (CO2RR) to n-propanol represents a promising route for low-carbon chemical synthesis. However, achieving high selectivity at industrially relevant current densities remains challenging due to inefficient *CO utilization and strong competition from C2 products. Herein, we demonstrate that a Cu2O/CeO2 interfacial catalyst overcomes these limitations by constructing a *CO─H2O reaction microregion that facilitates selective C1─C2 coupling. Isotope-competitive in situ differential electrochemical mass spectrometry (DEMS) reveals that the CeO2-induced interfacial structure shifts protonation pathway of activated CO2 from adsorbed hydrogen to solvent hydrogen, thereby generating high local *CO flux. Under CO2RR conditions, the *CO─H2O reaction microregion arises from non-covalent interaction between high-density *CO and loosely H-bonded water molecules. Time-resolved pulsed spectroscopy and theoretical calculations confirmed that this microregion dynamically confines *CO and reduces their molecular orbital degeneracy, enhancing *CO availability for C─C coupling reaction. Site-specific kinetics isotope effect experiments further indicate the reaction microenvironment promotes *CO attack on the α carbon of *C2 intermediates, effectively steering reaction pathway toward n-propanol. As a result, the catalyst achieves n-propanol Faradaic efficiency (FE) of 26.1%. These findings underscore the significance of non-covalent interactions between intermediates and electrolyte in controlling proton-related surface reaction, offering opportunities for steering electrocatalytic pathways toward valuable products.