Hydrophobic Cation-Immobilized Covalent Organic Frameworks Enable Selective and Stable Electrosynthesis of Ethylene from CO 2

The electrochemical reduction of CO 2 (CO 2 RR) offers a promising strategy for the synthesis of multicarbon fuels and chemicals. However, the highly dynamic gas/electrolyte/catalyst interface, where ions and reactant molecules exchange in a disorderly manner, restricts the electrocatalytic selectivity and stability. Herein, we immobilize quaternary ammonium cations onto covalent organic frameworks (COFs) to tailor the interface environment for boosting the electrosynthesis of ethylene. We find that the hydrophobic and microporous structures of the COFs enable fast CO 2 transport and rational H 2 O distribution, while the migration of cations is elegantly tailored through the Donnan effect. As a result, the COF-based electrode delivers a Faradaic efficiency of 46.8% and a high partial current density of 374.2 mA cm –2 for ethylene. A developed COF-based practical zero-gap membrane electrode assembly electrolyzer is further demonstrated with stable ethylene production over 89.6 h. In situ spectra and density functional theoretical calculations unveil that the cationic COFs further enhance the local electric field strength, resulting in stronger *CO adsorption and a boosted *CO dimerization rate. Our study provides a new avenue to enhance multicarbon production via tuning the cathode local mass and charge transfer.