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

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.