Promoting Electroreduction CO ₂ to Multi‐Carbon Products by Tailoring the * H Availability With Optimized Interfacial H ₂ O Configuration

The electroreduction of CO 2 to multi‐carbon products provides a promising path for approaching carbon neutrality. H 2 O is generally considered a hydrogen source in CO 2 RR, tailoring the interfacial H 2 O configuration is critical yet often overlooked strategy for modulating CO 2 RR performance. In this work, we demonstrated that regulating the interfacial water configuration through ionomer confinement is an effective strategy for enhancing multi‐carbon (C 2+ ) product selectivity in CO 2 RR. The optimized catalyst 15.79% A5‐Cu achieves 82% Faradaic efficiency (FE) for C 2+ products at 200 mA cm −2 in 0.1 M KHCO 3 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 + ‐H 2 O and 4‐HB‐H 2 O configuration of interfacial H 2 O. 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 + ‐H 2 O and 4‐HB‐H 2 O 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 H 2 O configuration in steering C 2+ 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.