Carbon Efficient CO2 Interfaces in Acid through Ion Management Channels.

CO2 electroreduction (CO2E) in acidic media enables high carbon utilization but is often limited by enhanced hydrogen evolution (HER). Cation-exchange ionomer coatings can suppress HER by enriching alkali cations at the catalyst surface, yet in situ SERS reveals that they also cause excessive *OH adsorption, hindering CO2 access and suppressing C-C coupling. To address this, we introduce ion management channels (IMCs), a spatially distributed ionomer architecture combining cation- and anion-exchange domains to modulate nanoscale ion transport. Applied to PTFE-Cu gas diffusion electrodes, IMCs facilitate the removal of excess *OH by restructuring interfacial water, increasing *CO coverage, and enhancing multicarbon (C2+) selectivity. IMC-functionalized electrodes achieve ∼80% Faradaic efficiency for C2+ products at 0.5 A·cm-2, with ∼90% single-pass carbon utilization sustained over 70 h of pulsed operation. This represents a 39% improvement in peak C2+ partial current density over monopolar cation-exchange ionomers and a ∼3.4-fold enhancement relative to bare Cu, highlighting the importance of ion-transport engineering for efficient CO2E.