Synthesis and properties of cross-linked poly(arylene ether ketone) electrolyte membranes containing hygroscopic proton conductors

• Sulfonated cross-linker was introduced to CSPAEK membrane not to reduce the proton conductivity.
• Sulfonated mesoporous benzene silica hygroscopic particles were embedded in CSPAEK membranes.
• Composite membranes showed enhanced proton conductivity at low humidity via their capillary condensation effect.
• Composite membranes exhibited high selectivity along with the reduced methanol permeability.

Sulfonated poly(arylene ether ketone) (SPAEK) fuel cell membranes were prepared in a cross-linked structure to enhance their dimensional and mechanical stability. Sulfonated mesoporous benzene-silica (SMBS) hygroscopic conductors were embedded in the membranes to lessen their dehydration in the low humid environment. Synthesis of the cross-linked SPAEK (CSPAEK) and its precursor was confirmed using 1H NMR spectroscopy and FT-IR spectroscopy. The effects of sulfonation degree (SD) and hygroscopic conductors on the membranes properties such as proton conductivity, methanol crossover, and thermal and mechanical stability were analyzed. The prepared CSPAEK membranes were thermally stable up to 250 °C without any chemical degradation. While the CSPAEK membranes containing hygroscopic proton conductors exhibited superior conductivity to that of Nafion®117, those with a sulfonation percent of less than 20% showed lower methanol permeability. Although the water uptake of the composite membranes was higher than that of the pristine membranes, no mechanical failure was observed.