Development of Direct Methanol Thin Solid Polymer Fuel Cells by Consecutive Vapor Phase Process

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Ion-exchange films have been used in room-temperature operating fuel cells whose fuel is hydrogen or methanol. Plasma polymerization is expected to become a novel and unique preparation method for organic thin films because uniform, pinhole-free and chemically and thermally stable thin films with cross-linked structures can be obtained by this technique. However, it is not easy to introduce functional groups such as ion-exchange moieties into the polymers because the functional groups are easily decomposed by active species in the glow discharge plasma. We have studied the introduction of sulfonic acid groups into polymers, prepared thin plasma-polymerized ion-exchanger films, and shown that the selection of the starting material and plasma parameters such as W/FM (W : power, F : monomer now rate, and M : molecular weight) are important to introduce functional groups into the polymer. In order to improve the performance of these plasma-formed polymers, knowledge of the reaction, which introduces functional groups into the polymer, is necessary for proper selection of starting materials. We have used trifluoromethane sulfonic acid and hexafluoropropylene as starting materials. In order to enhance effective electrode surface area, the thin perfluorosulfonated cation exchange membranes covered Pt electrode.