The supported Pt catalysts (Pt-Cs) were prepared according to a colloidal method in the literature. 5 The PFSI solution: an experimental Flemion® solution (Asahi Glass) was poured into butyl acetate. The mixture changed immediately to a colloidal state. Then the Pt-Cs of various acetylene blacks (Denki Kagakukogyo) were mixed with the PFSI colloidal solution. As a result of cross-linking among the PFSI chains adsorbed on the carbon supports by ultrasonic treatment, the mixture was transformed to a paste. The paste was uniformly spread over the wet-proofed carbon paper (Toray) for a gas-diffusion layer. The electrodes layered with the paste were hot pressed on both sides of a PFSI membrane. The membrane thickness of Flemion A (experimental membrane, Asahi Glass) was 80 pm in a dry state, and the equivalent weight value was 900. Identical electrodes were used for an anode and a cathode. The new method for preparation of electrodes was improvement of the previous one. The PFSI solution was dropped into the mixture of Pt-C and butyl acetate while stirring. After that, the mixture was treated with ultrasonication and M&E assembly was made in the same way as the previous method. A single cell was constructed with the M&E assembly, two porous carbon plates with rib-channel patterns on one side for gas supply, two glassy carbon frames, and two copper current collectors. The cell was compressed between two stainless steel end plates. The cell temperature was held at 50 °C throughout the experiment. The geometric reaction-area of the cell was 25 cm2. The reactant gases (hydrogen/oxygen) were fed to the cell at a flow rate of 350 ml/min. The gas-outlets from the cell were opened to the atmosphere. The anode and the cathode gases were humidified by being flowed through water held at 60 °C in glass bottles under atmospheric pressure prior to being provided to the cell. Electrochemical measurements of the single cell were done galvanostatically. The current was increased stepwise every 15 minutes, and the potential was logged in the steady state. All of the denoted polarization curves contained IR resistance. The resistance of the cell was measured at 1 kHz under load by a digital ac milliohmmeter. The pore-size distribution and the specific pore volume were calculated from an intrusion curve obtained by a mercury pore sizer.

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