Cationic Microenvironment Enhancing Covalent Organic Frameworks for Electrocatalytic CO₂ to CH₄ Conversion

Electrocatalytic reduction of CO₂ to CH₄ is hindered by sluggish proton-coupled electron transfer kinetics and competing reaction pathways. Herein, we introduce a cationic microenvironment strategy that integrates reactant enrichment, proton regulation, and intermediate stabilization within a single framework. A tetra-alkylammonium cation-functionalized copper porphyrin covalent organic framework (Cu-Tph-COF-N⁺) achieves a CH₄ Faradaic efficiency of 66.8% at -1.2 V versus RHE, together with markedly enhanced turnover frequency and partial current density relative to its hydroxyl-functionalized analogue. Mechanistically, the cationic framework generates a localized electrostatic field that concentrates CO₂ near active sites through charge-dipole interactions while cooperatively interacting with hydrated K⁺ ions to modulate proton transfer, thereby suppressing hydrogen evolution without compromising proton availability. The resulting electronic modulation at Cu porphyrin stabilizes key *COOH and *CHO intermediates and facilitates C-H bond formation, as supported by theoretical calculations and in situ spectroscopy. This work highlights cationic microenvironment engineering as a concise and general strategy to steer multi-step CO₂ electroreduction toward deep reduction products.