Tailoring Dual-Functional Ionomers for Efficient CO2 Electroreduction to Ethanol.

Alcohols production through the electrochemical CO2 reduction reaction (CO2RR) provides a sustainable route for resource utilization and energy storage. However, achieving sustained and efficient CO2-to-ethanol conversion with long-term performance remains a challenge. Here, we propose an ionomer microenvironment engineering strategy that demonstrates that the functionalized ionomer effectively boosts the performance toward ethanol conversion in the CO2RR for the first time. The poly[2-acrylamido-2-methylpropanesulfonic acid-co-(2-methyl-2-(trifluoromethylsulfonamido)propyl methacrylate)-co-(1-vinyl-3-butylimidazolium hexafluorophosphate)] ionomer (PAMV) is designed and synthesized, which contains both hydrophilic and CO2-philic structural units, thus creating a microenvironment to enhance the adsorption of both water and CO2. Using commercial copper nanoparticles as the catalyst, 57.3% ethanol faradaic efficiency (FE) and 29.3% cathodic energy efficiency (CEE) are achieved over PAMV-Cu based gas diffusion electrodes in bicarbonate electrolyte. This performance is approximately 4 times that of the commonly used commercial Nafion ionomer under the same conditions. Long-term electrolysis demonstrates its prominent ability to inhibit salt precipitation and H2 evolution. Experimental and theoretical studies reveal that the functionalized structural units in PAMV modulate the mass transfer of CO2 and H2O on the interface of the Cu catalyst, promoting the formation of *CO intermediate and enhancing the thermodynamic competitiveness of the ethanol production pathway. This work provides a novel ionomer-engineered approach for modulating electrocatalytic reactions, which offers a robust and convenient solution for the efficient conversion of CO2 to value-added products.