A study on the characterization of FEP-g-PVBSA membranes as polymer electrolytes for direct methanol fuel cells

Poly(vinylbenzyl sulfonic acid)-grafted poly(tetrafluoroethylene-co-hexafluoropropylene) (FEP-g-PVBSA) electrolyte membrane was prepared by radiation-induced grafting of vinylbenzyl chloride onto FEP film with subsequent sulfonation processes. An energy dispersive X-ray analysis was used to observe the cross-sectional distribution behaviors of the hydrophilic sulfonic acid groups and hydrophobic fluorine groups. The characteristics of an ion-exchange capacity (IEC), water and methanol uptake, methanol permeability, and proton conductivity as a function of the degree of grafting were studied. The IECs and water uptakes of membranes with different degrees of grafting (36 to 102%) were measured in the range of 0.8 to 1.62 meq g−1 and 10 to 30%, respectively. The proton conductivity was higher than that of a Nafion 212 membrane (6.1 E−02 S cm−1), when the degree of grafting reached 60%. The methanol permeability and uptake of the FEP-g-PVBSA membrane was significantly lower than that of the Nafion 212 membran...