Nano-structure controlled polymer electrolyte membranes for fuel cell applications prepared by ion beam irradiation

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

Fluoropolymer-based electrolyte membranes for water electrolyzers and fuel cells were prepared by using heavy ion beams from the cyclotron accelerator. The preparation method for these so-called "nano-scale structure-controlled membranes" involves (1) the swift heavy ion irradiation of polyvinylidene fluoride 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 a lower water uptake and reduced methanol permeability compared to commercially-available Nafion probably due to the restricted structures.