Styrene grafted and sulfonated proton conducting membranes based on radiation-crosslinked polytetrafluoroethylene and their fuel cell applications

Yamaki, Tetsuya; Asano, Masaharu; Morita, Yosuke*; Suwa, Takeshi*; Yoshida, Masaru

Proton exchange membranes were prepared by the radiation-induced grafting of styrene into crosslinked polytetrafluoroethylene (PTFE) films and subsequent sulfonation. The degree of grafting was controlled in the range of 7-75% by the crosslinking density of the PTFE matrix as well as the grafting conditions. The films at the grafting yield of 30% were found to give the ion exchange membranes with a homogeneous distribution of sulfonic acid groups. The resulting membranes showed a large ion exchange capacity reaching 2.9 meq g, which exceeded the performance of commercially-available perfluorosulfonic acid films such as Nafion. This will encourage the use of our ion exchange membranes in polymer electrolyte fuel cells.