Poly(tetrafluoroethylene-co-hexafluoropropylene) (FEP) film was homogeneously and highly grafted by styrene monomer under simultaneous irradiation with an electron beam, whereas preirradiation with an electron beam was insufficient to accomplish a high degree of grafting without activation of the styrene monomer. Following its subsequent sulfonation, the styrene-grafted FEP film exhibited considerably higher values of both the IEC and IC and less methanol crossover than the Nafion membrane. The grafting of styrene onto the FEP polymer is thought to be initiated by the abstraction of F atoms from the CF3 groups in the polymeric structure. It was estimated that two sulfonic acid groups can be attached to the benzene ring of one styrene molecule. The profile of sulfur across the FEP film, which is related to the concentration profile of sulfonic acid groups inside the styrene-grafted FEP film, became more and more homogeneous over a period of several hours, due to the step by step diffusion of monomers into the film, eventually showing a high IC value of 0.25 S/cm in the case of the 125 μm thick FEP film, whereas Nafion 117 (125 μm thickness) exhibited an IC value of 0.12 S/cm.

Fuel Cell Membrane FEP Styrene Electron Beam Grafting Sulfonation IEC IC Sulfur Profile

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