Performance of Photo-Cross-Linked Anion Conductive Membranes with High-Density Quaternary Ammonium Copolymers for Anion Exchange Membrane Fuel Cells

A range of photo-cross-linkable poly(aryl ether) copolymers with high-density quaternary ammonium groups were synthesized. Then, the anion exchange membranes (AEMs) were fabricated through quaternization and alkalization of the copolymers, with subsequent photo-cross-linking under UV irradiation while in hydration state at room temperature. The photosensitivity, thermal stability, and surface morphology of the membranes were evaluated through UV–vis spectrum, thermogravimetric analysis (TGA), field emission scanning electron microscopy (FE-SEM), and high-resolution transmission electron microscopy (HR-TEM), respectively. The membrane properties were evaluated based on mechanical properties, ion exchange capacity (IEC), water uptake, water swelling ratio, ionic conductivity, methanol permeability, and alkaline stability. The tensile strength of membranes ranged from 19.5 to 25.6 MPa, and the photo-cross-linking significantly enhanced the tensile strength of the membranes. The IEC values of the cross-linked membranes were varied between 1.48 and 2.08 mmol g^–1 at 20 °C. The water uptake and swelling ratio of cQPPAE-x-y were varied from 4.96% to 75.36% and 0.75% to 19.31% at 20 °C, respectively. The hydroxide conductivity of the cross-linked membranes ranged from 11.57 to 29.56 mS cm^–1 at 20 °C, reaching a peak of 167.50 mS cm^–1 at 80 °C. Additionally, the copolymer membranes demonstrated outstanding methanol resistance, with a methanol permeability of 1.573 × 10^–7 cm² s^–1 at room temperature, markedly reduced compared to Nafion 117 (23.8 × 10^–7 cm² s^–1) by a factor of 15. Notably, the cross-linked membranes retained high ionic conductivity while achieving enhanced dimensional and alkaline stability.