Self-Accelerating Effect in a Covalent-Organic Framework with Imidazole Groups Boosts Electroreduction of CO₂ to CO

Solvent effect plays an important role in catalytic reaction, but there is little research and attention on it in electrochemical CO₂ reduction reaction (eCO₂ RR). Herein, we report a stable covalent-organic framework (denoted as PcNi-im) with imidazole groups as a new electrocatalyst for eCO₂ RR to CO. Interestingly, compared with neutral conditions, PcNi-im not only showed high Faraday efficiency of CO product (≈100 %) under acidic conditions (pH ≈ 1), but also the partial current density was increased from 258 to 320 mA cm^-2 . No obvious degradation was observed over 10 hours of continuous operation at the current density of 250 mA cm^-2 . The mechanism study shows that the imidazole group on the framework can be protonated to form an imidazole cation in acidic media, hence reducing the surface work function and charge density of the active metal center. As a result, CO poisoning effect is weakened and the key intermediate *COOH is also stabilized, thus accelerating the catalytic reaction rate.