Proton exchange membranes modified with sulfonated silica nanoparticles for direct methanol fuel cells

Nanocomposite proton exchange membranes were prepared from sulfonated poly(phthalazinone ether ketone) (sPPEK) and various amounts of sulfonated silica nanoparticles (silica-SO3H). The use of silica-SO3H compensates for the decrease in ion exchange capacity of membranes observed when non-sulfonated nano-fillers are utilized. The strong –SO3H/–SO3H interaction between sPPEK chains and silica-SO3H particles leads to ionic cross-linking in the membrane structure, which increases both the thermal stability and methanol resistance of the membranes. The membrane with 7.5 phr of silica-SO3H (phr = g of silica-SO3H/100 g of sPPEK in membranes) exhibits low methanol crossover, high bound-water content, and a proton conductivity of 3.6 fold increase to that of the pristine sPPEK membrane.