PTFE-reinforced pore-filling proton exchange membranes with sulfonated poly(ether ether ketone)s and poly(aryl ether sulfone)s

It is a technical challenge to improve the dimensional and chemical stability of pore-filling proton exchange membranes (PEMs) filled with high-sulfonated poly(ether ether ketone) (SPEEK) electrolytes. To solve this issue, double-electrolyte pore-filling PTFE PEMs were prepared by co-filling sulfonated poly(aryl ether sulfone) (SPAES) and SPEEK in this work. Utilizing ethanol hydrophilic pre-treatment, the double-electrolyte can be efficiently and uniformly infused into the porous PTFE, resulting in a compact, homogeneous and defect-free membrane. The existence of low-sulfonated SPAES40 in the double-electrolyte demonstrates a quite positive effect on inhibiting the dissolution of high-sulfonated SPEEK70 at high temperatures and controlling membrane swelling. Consequently, the PTFE/SPEEK-SPAES membrane shows 103.4 % higher proton conductivity, 33.6 % and 21.5 % lower in-plane and through-plane swelling than the control PTFE/SPEEK70 membrane at 90 °C. Moreover, heat treatment further enhances the mechanical and antioxidant characteristics of the membrane by forming –SO2- crosslinking. The resulting thermally cross-linked membrane exhibits 76.5 % lower oxidation mass loss, 70.4 % and 38.2 % higher elongation at break and tensile stress than the control PTFE/SPEEK70 membrane. After 48 h fuel cell operation, the output voltage of the PTFE/SPEEK-SPAES(1:1)* membrane only decreases by 3.6 %, which is better than the control PTFE/SPEEK70 membrane (46.2 %). This proves that a double-electrolyte pore-filling membrane is an efficient and facile method to strengthen the stability of PEMs.