Proton exchange membrane based on crosslinked sulfonated polyphosphazene containing pendent perfluorosulfonic acid groups with sulfonated poly(ether ether ketone)

A series of crosslinked membranes based on new sulfonated polyphosphazene bearing pendent perfluorosulfonic acid groups (PMFP-g-PS) and sulfonated poly (ether ether ketone) were prepared and evaluated as proton exchange membranes for direct methanol fuel cells (DMFCs). The structure of PMFP-g-PS was characterized by Fourier transform infrared spectroscopy, ¹H and ¹⁹F NMR spectra. In comparison with the pristine PMFP-g-PS membrane, the crosslinked membranes showed improved water uptakes and proton conductivities. The methanol permeability values of the membranes were in the range of 1.32 × 10^-7 to 3.85 × 10^-7 cm²/s, which were lower than Nafion 117 (12.1 × 10^-7 cm²/s). The selectivity of all the membranes was much higher compared with Nafion 117. Furthermore, transmission electron microscopy observation revealed that clear phase-separated structures were well dispersed and connected to each other in the membranes. These membranes displayed high water uptakes and low swelling ratios, high proton conductivities, low methanol permeability values, good thermal, and oxidative stabilities. The results indicate that these membranes are potential candidate proton exchange membrane materials for DMFCs.