Synthesis Characterization and Electrochemical Evaluation of Quaternized Poly(2,6-dimethyl-1,4-phenylene oxide)/Ionic Liquid Composite Membrane for Anion Exchange Membrane Fuel Cell Application

Quaternized poly(2,6-dimethyl-1,4-phenylene oxide) (QPPO) serves as a polymer electrolyte membrane facilitating hydroxide ion conduction, whereas with limited hydroxide conductivity and certain physiochemical drawbacks. To address this, modifications are necessary to enhance its overall performance. Composite membranes of QPPO and an ionic liquid were fabricated using the solvent casting technique. The ionic liquid, which contains quaternized imidazole groups, enhances hydroxide transport pathways within the QPPO membrane. Varying weight % of the ionic liquid were incorporated into the QPPO membrane during fabrication. The role of the ionic liquid in the QPPO membrane is to increase the bound water content and develop a hydrogen bonding network with the hydroxide ion transport channels, thereby increasing the hydroxide ion conductivity. Remarkably, the optimized QIL-8% composite membrane exhibits superior hydroxide conductivity compared to the QPPO membrane, achieving 135 mS cm^-1 at 90 °C, while the QPPO membrane reached 56 mS cm^-1 at the same temperature. Additionally, the QPPO/ionic liquid composite membranes exhibit appreciable water uptake, swelling ratio, thermal, and mechanical properties. In single-cell tests, the QIL-8% composite membrane achieves a maximum power density of 328 mW cm^-2 at 60 °C, under conditions of 70% humidity on the anode side, 100% humidity on the cathode side, and an H₂/O₂ flow rate of 100/200 mL min^-1. Overall, this study illustrates the enhancement of QPPO membrane performance through the incorporation of synthesized ionic liquids.