Creation of Novel Ion Conducting Membrane by Nano-Micro Structural Control

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Novel proton conducting membranes composed of proton conducting polymers and porous matrices were prepared for direct methanol fuel cells (DMFCs). As the matrix for the composite membrane, a three-dimensionally ordered macroporous (3DOM) membrane with adequate mechanical strength was successfully obtained by use of silica or polyimide. Due to mechanical suppression of polymer expansion by the matrix, the composite membrane exhibited high dimensional stability. As a result, the methanol permeability less than a few tenths of that of Nafion【○!R】 membrane and high cell performance by feeding a desired high-concentrated methanol solution (10 mol dm-3) were successfully achieved for the first time ever. The components of the composite membrane were inexpensive, so that the production cost could be also decreased less than a few tenths of that of Nafion【○!R】 membrane. The filling state of the polymer electrolyte in the composite membrane was revealed by transmission electron microscope obser … More vation, which was conducted as a joint study with Group D01. Therefore, the relationship between the nano-structure of the composite membrane and the resulting properties became clear and the membrane properties could be improved. As another type of the electrolyte membrane, the 3DOM silica matrix filled with a novel room-temperature molten salt that was synthesized by Group C01, was evaluated. The obtained composite membrane worked stably over 100 h under dry and high-temperature condition, suggesting the realization of high temperature DMFC for electric vehicles.Researches for improving cell performance were also conducted. It was appeared that the quality between the membrane and a catalyst layer greatly influenced the cell performance by A.C. impedance measurement. As one of solutions, we performed a surface modification of the 3DOM silica by sulfonic acid groups, and the cell performance was successfully enhanced. Application of electrophoretic deposition (EPD) process to fabricate a catalyst layer onto the membrane was also studied as another method. The obtained catalyst layer by the EPD process was uniform and porous compared to that prepared by an ordinary method, i.e. a decal transfer process. This structure was favorable to gas diffusion, resulting in improvement of Pt utilization up to 76%. Accordingly, the MEA prepared by the EPD process exhibited higher cell performance with half amount of Pt loadings compared to the ordinary one. The latter process has been introduced all over the world by Electrochemical Society as Technical highlight and has attracted much attention. Less