Direct polymerization of a novel sulfonated poly(arylene ether ketone sulfone)/sulfonated poly(vinylalcohol) crosslinked membrane for direct methanol fuel cell applications

Sulfonated poly(arylene ether ketone sulfone) copolymers containing carboxylic acid groups (C-SPAEKS) were prepared by direct aromatic nucleophilic substitution polymerization. Novel C-SPAEKS-based crosslinked membranes containing different amounts of sulfonated poly(vinyl alcohol) (SPVA) were fabricated. The Fourier transform infrared and 1H NMR analyses showed the presence of carboxylic acid and sulfonic acid groups, as well as ester bonds in the crosslinked membranes. As expected, the crosslinked membranes exhibited enhanced thermal stability relative to the uncrosslinked membranes. Both the atomic force microscopy (AFM) and transmission electron microscopy (TEM) images clearly show the hydrophilic domains and hydrophobic polymer backbone. The methanol permeability coefficients of the crosslinked membranes with the SPVA content from 10% to 90% ranged from 10.67×10−7 cm2 s−1 to 1.05×10−7 cm2 s−1 at 25 °C, and from 22.24×10−7 cm2 s−1 to 2.41×10−7 cm2 s−1 at 60 °C, which are much lower than those of C-SPAEKS membrane (12.79×10−7 cm2 s−1 at 25 °C and 26.85×10−7 cm2 s−1 at 60 °C). The proton conductivities of all the crosslinked membranes were above 10−2 S cm−1, satisfying the requirement of fuel cells. Furthermore, the crosslinked membranes exhibited a high selectivity, further confirming that this series of crosslinked membranes are potential candidates as new polymeric electrolyte materials for direct methanol fuel cells.