Promoting Electroreduction CO2 to Multi-Carbon Products by Tailoring the *H Availability With Optimized Interfacial H2O Configuration.

The electroreduction of CO2 to multi-carbon products provides a promising path for approaching carbon neutrality. H2O is generally considered a hydrogen source in CO2RR, tailoring the interfacial H2O configuration is critical yet often overlooked strategy for modulating CO2RR performance. In this work, we demonstrated that regulating the interfacial water configuration through ionomer confinement is an effective strategy for enhancing multi-carbon (C2+) product selectivity in CO2RR. The optimized catalyst 15.79% A5-Cu achieves 82% Faradaic efficiency (FE) for C2+ products at 200 mA cm-2 in 0.1 M KHCO3 and operates stably for over 100 h without salt precipitation in MEA system. In situ ATR-SEIRAS and Raman spectroscopy revealed that the confined environment tunes the proportion between K+-H2O and 4-HB-H2O configuration of interfacial H2O. This enhanced *H generation and transfer ability can improve the *H utilization efficiency. Moreover, a moderate *H availability constructed by the balanced proportion of K+-H2O and 4-HB-H2O configurations lowers the energy barrier for *CO hydrogenation and subsequently C─C coupling step at a higher *CO coverage, which was confirmed by DFT calculations. This work highlights the critical role of interfacial H2O configuration in steering C2+ product selectivity for that in addition to *H generation, the hydrogen bonding network can accurately guide *H toward *CO intermediate, thereby avoiding excessive accumulation of *H species.