同位体トレーサーを用いた高分子電解質膜中の物質輸送解析; トリチウム水と重酸素水の比較

Mass transport analysis of polymer electrolyte membranes by isotope tracer technique; Comparison between tritiated water and heavy-oxygen water

八巻 徹也; 関根 敏彦; 澤田 真一; 浅野 雅春; 前川 康成; 鈴木 晶大*; 寺井 隆幸*

Yamaki, Tetsuya; Sekine, Toshihiko; Sawada, Shinichi; Asano, Masaharu; Maekawa, Yasunari; Suzuki, Akihiro*; Terai, Takayuki*

トリチウム水(HTO)と重酸素水(HO)における同位体効果に起因した拡散挙動の違いを利用して、高分子電解質膜内の水を取り巻く環境を理解できると考えた。この発想をもとに、本研究では、HTO又はHOを含む水,メタノール水溶液を用いて、ナフィオン膜とわれわれが独自の手法で合成した架橋フッ素系電解質膜における水輸送の解析を試みた。この解析では、各トレーサーの拡散係数Dを求め比較することで、スルホン酸基と水との間に働く水素結合の強さやプロトン伝導経路であるイオンクラスター構造を反映した水の状態を知ることができた。

We investigated mass transport properties in polymer electrolyte membranes by an isotope tracer technique using tritiated water (HTO) and heavy-oxygen water (HO). The materials for our diffusion analysis were a Nafion membrane and the crosslinked-fluoropolymer-based radiation-grafted membranes which we prepared by our original method. Tritium from HTO is transported not only by translational motion of water, but also by an intermolecular hydrogen-tritium exchange. The effective diffusion coefficient of HTO, D(HTO), in an water-methanol mixture was considered by correcting statistical distribution to hydroxyl groups of methanol at a concentration of 10 M. A ratio of D(HTO) or D(HTO) to D(HO) appeared to be different between the membranes probably reflecting the isotopic effect on the interaction with sulfonic acid groups. Consequently, our analysis would give the information about the physico-chemical state of water in the membrane.