Chemical and radiation crosslinked polymer electrolyte membranes prepared from radiation-grafted ETFE films for DMFC applications

化学及び線架橋を組合せたDMFC用電解質膜の合成

Chen, J.; 浅野 雅春; 八巻 徹也; 吉田 勝

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

放射線グラフト重合により、ビスビニルフェニルエタン(BVPE)及びジビニルベンゼン(DVB)の2成分の架橋剤とビニルトルエン(MeSt)及びt-ブチルスチレン(tBuSt)の2成分のスルホン化可能なモノマーを組合せた4元系成分電解質膜を作製した。これらの電解質膜の特性として、含水率,プロトン導電性,メタノール透過性及び耐久性について検討した。また、線架橋の導入としては、(1)グラフト重合前,(2)グラフト重合後,(3)グラフト重合・スルホン化後などのタイミングで行った。グラフト重合・スルホン化後などのタイミングで架橋した電解質膜の耐久性加速試験の結果、従来のポリスチレンスルホン酸電解質膜に比べて6倍耐久性が向上することがわかった。また、この電解質膜のメタノール透過はナフィオンの1/10まで抑制できることもわかった。

To develop a highly chemically stable polymer electrolyte membrane for application in a direct methanol fuel cell(DMFC), doubly crosslinked membranes were prepared by chemical crosslinking using bifunctional monomers, such as divinylbenzene(DVB) and bis(p, p-vinyl phenyl) ethane(BVPE), and by radiation crosslinking. The membranes were prepared by grafting of m, p-methylstyrene(MeSt) and p-tert-butylstyrene(tBuSt) into poly(ethylene-co-tetrafluoroethylene)(ETFE) films and subsequent sulfonation. The effects of the DVB and BVPE crosslinkers on the grafting kinetics and the properties of the prepared membranes, such as water uptake, proton conductivity and chemical stability were investigated. Radiation crosslinking was introduced by irradiation of the ETFE base film, the grafted film or the sulfonated membrane. The membrane crosslinked by DVB and BVPE crosslinkers and post-crosslinked by -ray irradiation of the corresponding grafted film possessed the highest chemical stability among the prepared membranes, a significantly lower methanol permeability compared to Nafion membranes, and a better DMFC performance for high methanol feed concentration. Therefore, this doubly crosslinked membrane was promising for application in a DMFC where relatively high methanol concentration could be fed.