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

ABSTRACT 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.