量子ビームを利用した燃料電池用高分子電解質膜の創製に関する研究

Abstract

This paper describes the application of quantum beam-based technology to the development of polymer electrolyte membranes for fuel-cell applications. The γ-ray or electron-beam induced radiation grafting offers a way to prepare membranes; typically, the radical-initiated polymerization of a styrene or styrene-derivative monomer on a base polymer is followed by a sulfonation step. We previously obtained novel membranes using radiation- crosslinked fluoropolymers as the base material. Interestingly, combining this radiation-crosslinking process with the well-known chemical crosslinker method enabled us to prepare the “multiply-crosslinked” membranes, in which both the main and grafted chains have covalently bridged structures leading to a high durability. The bombardment of heavy ions accelerated to MeV or higher energies produces a continuous trail of excited and ionized molecules in polymers, which is known as a latent track. The approach using this ion-track technology is based on the chemical etching and/or modification of each track with diameters of tens to hundreds of nanometers. The resulting “nano-structure controlled” membrane was found to have perfect one-dimensional proton-conductive pathways parallel to its thickness direction, while, in contrast, other existing membranes mostly exhibited proton transport in the three-dimensional random media. We revealed the hierarchical structures of the membranes, ranging from nanometers to micrometers, by small-angle scattering experiments using a cold or thermal neutron beam. The information in such a wide length scale led to an insight into mass transport dynamics in the membrane from a molecular to macroscopic level, which can provide feedback for the reconsideration and optimization of the preparation procedure. As demonstrated above in our studies, it is important to understand that every quantum beam is different, thereby making the right beam choice.