Relationship between structural and proton conductive properties of crosslinked-fluoropolymer-based electrolyte membranes; Consideration based on nanometer-to-micrometer hierarchical structures

Yamaki, Tetsuya; Motokawa, Ryuhei   ; Iwase, Hiroki*; Sawada, Shinichi; Asano, Masaharu; Koizumi, Satoshi; Maekawa, Yasunari

The nanometer-to-micrometer hierarchical structure was investigated by small-angle neutron/X-ray scattering (SANS/SAXS) analysis, a dissipative particle dynamics (DPD) simulation, and transmission electron microscopy (TEM) observation and then discussed in relation to proton conductivity. In a macroscopic scale, the grafting reaction was found to occur in a PTFE amorphous layer between rigid lamellar crystals and, however, a main reaction field was the outside of the lamellae, which would determine proton conductivity of the membranes. The microscopically-aggregated ionic clusters basically appeared smaller than that of Nafion, and the phase-separated domain including them grew large by connecting with each other toward high ion exchange capacities. This morphological change was accompanied by an increase in the self-diffusion coefficient of protons mainly representing proton conductivity.