Water transport properties of crosslinked-PTFE based electrolyte membranes

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

We measured the self-diffusion coefficient of water, D, in proton exchange membranes (PEMs) based on crosslinked polytetrafluoroethylene (PTFE) films by a radiotracer-permeation method using tritium labeled water (HTO). When the crosslinking density of the PTFE matrix increased, the D value became smaller. This decreasing trend coincided with that of a water-content parameter, , defined as the number of water molecules per sulfonic acid (SOH) group. According to the model assumption of hydrophilic regions, the relationship between the D and indicates that the amount of free water in the crosslinked-PTFE PEMs could be lower than that in the non-crosslinked one, thereby restricting the mobility of water molecules through strong interactions between the majority of water and SOH groups.