Water diffusion in fluoropolymer-based fuel-cell electrolyte membranes investigated by radioactivated-tracer permeation technique

Sawada, Shinichi; Yamaki, Tetsuya; Asano, Masaharu; Suzuki, Akihiro*; Terai, Takayuki*; Maekawa, Yasunari

In polymer electrolyte fuel cells, the water transport properties of the polymer electrolyte membranes (PEMs) would affect the cell performance. In this study, we investigated the self-diffusion coefficient of water molecules in the PEMs by using radioactivated-tracer permeation technique. The PEMs were synthesized from crosslinked-polytetrafluoroethylene (cPTFE) by the radiation-induced grafting method. The Dw of the PEMs increased with their ion exchange capacities (IECs), and reached the maximum value of 3.710m/s at the IEC of 2.4 meq/g. interestingly, commercially-available Nafion membrane exhibited the highest Dw of 4.910m/s despite of its low IEC. The lower Dw in the cPTFE PEMs is probably attributed to the geometry of hydrophilic regions phase-separated from the surrounding hydrophobic polymers.