Efficient and stable CO2 reduction using quaternary ammonium-based high-durability polymer membrane and ionomer in zero-gap electrolyzers

Abstract

Anion exchange membranes and ionomers are key components to efficient and stable CO₂ reduction reaction (CO₂RR) in electrolyzers. However, their roles at the membrane electrode assembly (MEA) level remain underexplored despite recent advances in CO₂RR technology. This study investigated physicochemical properties of a quaternary benzyl ammonium (QBA)-based membrane and commercial membranes to identify key descriptors enhancing CO₂RR for CO production. The QBA membrane possessed high anion conductivity, low swelling ratio, and chemical/mechanical durability. In addition, the QBA ionomer formed a hydrophobic and porous catalyst layer to increase mass transfer and suppress the hydrogen evolution reaction. The MEA with a QBA-based membrane and ionomer binder showed high CO Faradaic efficiencies (FE_CO) of 90–96% over a wide cell voltage range (1.8–2.5 V) at 343 K. The CO partial current density of the QBA increased with cell voltage and reached 251.53 mA cm⁻² at 2.5 V. The QBA exhibited long-term stability at 200 mA cm⁻², FE_CO above 80% for 350 h, and FE_CO above 70% for the next 150 h while maintaining a cell voltage of 2.43 V. Moreover, QBA exhibited lower sensitivity to relative humidity than the commercial FAA membrane and ionomer, enabling stable CO₂RR under varying operating conditions. The high CO₂RR performance and long-term stability resulted from the synergistic effect of the QBA membrane and ionomer.