Preparation of anion-exchange membranes for fuel cell applications by -ray pre-irradiation grafting; Effect of the structure of quaternary ammonium ions

Koshikawa, Hiroshi; Asano, Masaharu; Yamaki, Tetsuya; Yoshimura, Kimio; Maekawa, Yasunari; Yamamoto, Kazuya*; Shishitani, Hideyuki*; Asazawa, Koichiro*; Yamaguchi, Susumu*; Tanaka, Hirohisa*

We investigated the effect of a linear carbon chain length (n) in quaternary ammonium ions, on the durability of ion conductivity of anion exchange membrane. The poly(ethylene-co-tetrafluoroethylene) grafted chloromethylstyrene film was quaternized in four different tertiary amines, that is, trimethylamine (n=1), dimethylethylamine (n=2), n-butyldimethylamine (n=4) and n-hexyldimethylamine (n=6) solutions. The n dependence of ion conductivity and chemical durability, which was represented by a residual percentage of the conductivity after treatment with a Fenton solution (3% hydrogen peroxide+ 4 ppm iron sulfate) at 80 C for 2 h. When n increased from 1 to 6, the ion conductivity decreased slightly, but it still stayed 20 mS/cm for n = 6. Interestingly, the chemical durability seemed to increase eight-fold at the same time. The chemical attack by hydroxyl radicals on the quaternary ammonium ions would be controlled by hydrophobicity and steric hindrance of the alkyl group.