Imidazolium cation based anion-conducting electrolyte membranes prepared by radiation induced grafting for direct hydrazine hydrate fuel cells
Yoshimura, Kimio; Koshikawa, Hiroshi; Yamaki, Tetsuya; Shishitani, Hideyuki*; Yamamoto, Kazuya*; Yamaguchi, Susumu*; Tanaka, Hirohisa*; Maekawa, Yasunari
Graft-type anion-conducting electrolyte membranes (AEMs) with imidazolium cations on graft polymers were synthesized through radiation-induced graft polymerization of
-vinylimidazole (NVIm) on poly(ethylene-co-tetrafluoroethylene) (ETFE) films, followed by
-propylation and ion-exchange reactions. The
-propylation proceeded quantitatively, whereas the ion-exchange reactions in 1 M KOH at 60
C were accompanied by partial
-elimination of the imidazolium cations(AEM2), which exhibited an ion-exchange capacity (IEC) of 0.85 mmol g
and ionic conductivity of 10 mS cm
. AEM2 showed alkaline stability at 60
C but it gradually degraded at 80
C for ca. 150 h. The copolymer-type AEM (AEM3) with an IEC of 1.20 mmol g
was prepared through the copolymerization of NVIm with styrene on ETFE films, followed by the same
-propylation and ion-exchange reactions. AEM3 was shown higher alkaline durability in 1 M KOH at 80
C. As a result, it exhibited higher conductivity (
10 mS cm
) for 250 h. Therefore, alkylimidazolium cations in copolymer grafts are a promising anion conducting group for alkaline-durable AEMs. A maximum power density of 75 mW cm
is obtained for AEM3 in a direct hydrazine hydrate fuel cell.