Preparation of sulfonated crosslinked PTFE--poly(alkyl vinyl ether) membranes for polymer electrolyte membrane fuel cells by radiation processing

放射線によるビニルエーテルグラフトPTFE電解質膜の作製

Chen, J.; 浅野 雅春; 八巻 徹也; 吉田 勝

Chen, J.; Asano, Masaharu; Yamaki, Tetsuya; Yoshida, Masaru

放射線同時照射法による新しい燃料電池用電解質膜を作製した。電子線架橋したPTFE膜に放射線同時照射法により、プロピルビニルエーテル(nPVE)及びイソプロピルビニルエーテル(iPVE)をグラフト重合させたところ、照射線量とともにグラフト率は、見かけ上直線的に増加することがわかった。また、照射温度を変化させた場合、グラフト反応はそれぞれの沸点付近において急激に進行した。一方、塩化アルミなどの触媒を共存させることにより、グラフト率は顕著に加速された。スルホン化後の電解質膜の特性を調べたところ、イオン交換容量が小さいにもかかわらずナフィオンに同等のプロトン導電性を示した。

New polymer electrolyte membranes having sulfonic acid groups for polymer electrolyte membrane fuel cell applications were prepared by simultaneous radiation-induced grafting method. The poly(tetrafluoroethylene) (PTFE) films, crosslinked by electron-beam radiation at molten temperature, were used as substrates for grafting of two alkyl vinyl ether monomers, propyl vinyl ether (nPVE) and isopropyl vinyl ether (iPVE), under controlled grafting conditions followed by sulfonation reactions. Thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), water contact angle and Fourier transform infrared (FTIR) were used to characterize the crosslinked PTFE (cPTFE) and grafted cPTFE films. The degree of grafting was found to be dependent on the grafting parameters such as irradiation temperature and Lewis acid catalyst, in which in the presence of Lewis acid catalyst or at a temperature close to the boiling point of each monomer, the grafting reaction significantly accelerated even when the relatively low dose was irradiated. Finally, the grafted cPTFE films were sulfonated in a chlorosulfonic acid solution. In spite of the lower ion-exchange capacity (0.75 mmol/g), the membrane synthesized in this study showed a proton conductivity as high as the Nafion 112.