Properties of polymer electrolyte fuel-cell membranes with controlled nano-structures prepared by heavy ion irradiation

Yamaki, Tetsuya; Kozone, Yuichi; Hiroki, Akihiro; Asano, Masaharu; Kubota, Hitoshi*; Yoshida, Masaru

Fluoropolymer-based electrolyte membranes for fuel cells were prepared by use of heavy ion beams from the synchrotron accelerator of TIARA, JAEA. The preparation method for these so-called "nano-scale structure-controlled membranes" involves (1) the swift heavy ion irradiation of polyvinylidene fluoride (PVDF) films and subsequent chemical etching to obtain cylindrical pores with a diameter of 100 nm and (2) the filling of proton-conducting polymer chains into the etched pores by -ray-induced graft polymerization. The proton transport only in the thickness direction was observed for the resulting membranes with controlled ion exchange capacities, indicating the formation of one-dimensional straight proton conducting pathways parallel to the ion-beam incident axis. The membranes exhibited less water uptake and lower methanol permeability compared to commercially-available Nafion probably because of such restricted structures that they had.