Proton conduction characteristics in radiation-grafted polymer electrolyte membranes based on perfluorinated and aromatic hydrocarbon polymers

Sawada, Shinichi; Maekawa, Yasunari

In order to improve the performance of the radiation-grafted polymer electrolyte membranes (PEMs), it is important to characterize the PEMs prepared by various conditions. In this study, we investigated the proton conduction properties of grafted PEMs based on crosslinked poly(tetrafluoroethylene) (cPTFE) (perfluoropolymer) and poly(etheretherketone) (PEEK) (hydrocarbon polymer). For obtaining a deep insight, the self-diffusion coefficient of protons, D, was calculated. In the case of PEEK PEMs, the D did not depend on the ion exchange capacity (IEC). On the other hand, for cPTFE PEMs, the D prominently increased with the IEC. The small D at low IEC can be related to the high crystallinity of the base cPTFE film. Due to PTFE crystallites, poly(styrene sulfonic acid) graft chains were not homogeneously introduced. As a result, the ion-channnel network structures should not be well-connected, thereby restricting the proton mobility.