Conversion of CO2 to multicarbon products in strong acid by controlling the catalyst microenvironment

Electrosynthesis of multicarbon products from the reduction of CO2 in acidic electrolytes is a promising approach to overcoming CO2 reactant loss in alkaline and neutral electrolytes; however, the proton-rich environment near the catalyst surface favours the hydrogen evolution reaction, leading to low energy efficiency for multicarbon products. Here we report a heterogeneous catalyst adlayer—composed of covalent organic framework nanoparticles and cation-exchange ionomers—that suppresses hydrogen evolution and promotes CO2-to-multicarbon conversion in strong acid. The imine and carbonyl-functionalized covalent organic framework regulates the ionomer structure, creating evenly distributed cation-carrying and hydrophilic–hydrophobic nanochannels that control the catalyst microenvironment. The resulting high local alkalinity and cation-enriched environment enables C–C coupling between 100 and 400 mA cm−2. A multicarbon Faradaic efficiency of 75% is achieved at 200 mA cm−2. The system demonstrates a full-cell multicarbon energy efficiency of 25%, which is a twofold improvement over the literature benchmark acidic system for the reduction of CO2.