Covalent Organic Framework Ionomer Steering the CO₂ Electroreduction Pathway on Cu at Industrial-Grade Current Density

CO₂ electroreduction holds great promise for addressing global energy and sustainability challenges. Copper (Cu) shows great potential for effective conversion of CO₂ toward specific value-added and/or high-energy-density products. However, its limitation lies in relatively low product selectivity. Herein, we present that the CO₂ reduction reaction (CO₂RR) pathway on commercially available Cu can be rationally steered by modulating the microenvironment in the vicinity of the Cu surface with two-dimensional sulfonated covalent organic framework nanosheet (COF-NS)-based ionomers. Specifically, the selectivity toward methane (CH₄) can be enhanced to more than 60% with the total current density up to 500 mA cm^-2 in flow cells in both acidic (pH = 2) and alkaline (pH = 14) electrolytes. The COF-NS, characterized by abundant apertures, can promote the accumulation of CO₂ and K⁺ near the catalyst surface, alter the adsorption energy and surface coverage of *CO, facilitate the dissociation of H₂O, and finally modulate the reaction pathway for the CO₂RR. Our approach demonstrates the rational modulation of reaction interfaces for the CO₂RR utilizing porous open framework ionomers, showcasing their potential practical applications.