Strong Hydrogen-Bonded Interfacial Water Inhibiting Hydrogen Evolution Kinetics to Promote Electrochemical CO2 Reduction to C2

Interfacial water is an important participant in electrochemical CO2 reduction (CO2RR), directly affecting the kinetics of hydrogenation steps occurring in the CO2RR and competitive hydrogen evolution reaction (HER). However, its structural composition and dynamic evolution are difficult to investigate due to bulk water interference and the bias dependence. Herein, we adopt electrochemical in situ vibration spectroscopy combined with molecular dynamics simulations to probe the dynamic change of interfacial water structure on an electrified hydrophobic electrode surface and further explore the mechanism origin of suppressed HER activity and enhanced multicarbon products’ selectivity. We reveal that interfacial water near the hydrophobic electrode surface exhibits rigid intermolecular hydrogen bonding interaction, and the degree of which increases with a bias potential. The strong intermolecular hydrogen bond makes it hard for water reorientation leading to a longer metal–H distance, which inhibits water dissociation and decreases *H coverage. Moderate *H coverage not only inhibits hydrogen evolution but also ensures hydrogenation of intermediates realizing promoted C–C dimerization. A faradaic efficiency of 75.2% for CO2 reduction to multicarbon products was ultimately achieved. Our results provide insights into understanding the role of interfacial water structure in controlling reaction selectivity in CO2RR.