Proton-Transfer Inhibition by Imine-Linked Covalent Organic Frameworks Enables Efficient C2+ Production From Acidic CO2 Electroreduction.

Acidic CO2 electroreduction offers a compelling route to mitigate carbonate formation and improve carbon efficiency, yet the high proton concentration intensifies hydrogen evolution reaction (HER), severely suppressing multi‑carbon (C2+) production. While covalent organic frameworks (COFs) are explored to modulate the reaction microenvironment, existing studies primarily focus on the confinement of alkali cations, CO2, and CO intermediates, largely overlooking the critical role of proton‑transport. Herein, we demonstrate that an imine‑linked COF (TAPB-BTCA) anchored on Cu electrocatalysts functions as a proton‑regulating interlayer. Combined experimental and molecular dynamics simulation analyses reveal that the reversible protonation of its C═N bonds retards H+ diffusion to the Cu surface, suppressing HER and preserving a locally alkaline environment conducive to C─C coupling. The Cu/TAPB-BTCA electrode achieves 74.0% Faradaic efficiency for C2+ at -250 mA cm-2, a 58% improvement over bare Cu, and outperforms previously reported COF‑based electrocatalysts under similar acidic conditions. Comparison with two other imine-linked COFs (LZU‑1 and CQN) shows that the protonation capability, dictated by the conjugated framework structure, governs proton‑blocking efficacy, local microenvironment, and consequently CO2RR performance. This work highlights proton‑transport management via rationally designed COF frameworks as a promising strategy to achieve efficient acidic CO2 electroreduction.