Water‐Mediated Proton Facilitation for Stable Acidic CO 2 Electrocatalysis

ABSTRACT Electrochemical CO 2 conversion in acid can, in principle, maximize carbon efficiency but is typically undermined by facile hydrogen evolution. Moreover, operating at high current density often triggers a sharp local pH increase that propagates into the bulk electrolyte, causing an overall pH shift that erodes nominally “acidic CO 2 reduction” toward neutral/alkaline conditions. To address these limitations, we incorporated Ce species with high proton affinity into the surface of porous Cu nanosheet, constructing proton‐mitigating Cu─O─Ce active sites. Beyond conventional C─C coupling driven by local * CO accumulation, Cu─O─Ce motifs accelerate * CO formation and its protonation, thereby enabling downhill proton‐coupled electron transfer (PCET) toward and beyond * CO─ * CHO dimerization. This strategy demonstrates efficient multi‐carbon generation under retentive pH conditions minimizing the collateral deficiencies of acidic CO 2 reduction. Facilitating kinetically suppressed C─C coupling at a relatively low current density offers a strategic catalyst design that maintains a stable bulk pH compared to high current density operations, thereby maximizing the in situ generation of CO 2 within the acidic media.