Application of Self-Humidifying Polymer Electrolyte Membranes for Fuel Cells

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Recently, we have proposed new self-humidifying polymer electrolyte membranes with highly dispersed nanometer-sized Pt and/or metal oxides for polymer electrolyte fuel cells (PEFCs) operated with dry H_2 and O_2. The Pt particles were expected to suppress the crossover by the catalytic recombination of H_2 and O_2, while the oxide particles (TiO_2) that have hygroscopic property were expected to adsorb the water produced at Pt particles together with that produced at the cathode reaction and to release the water once the PEM needs water. The PEFCs with these new PEMs demonstrated the superior performances and suppression of the crossover even under externally non-humidified condition, which are comparable to that of the conventional PEM fully humidified. In order to construct a practical PEFC stack, however, a mechanical strength of the PEM is an important property. Japan Gore-Tex developed a reinforced PEM with both a sufficient mechanical strength and high proton conductivity. It is desirable to prepare the self-humidifying PEM from a commercial reinforced PEM.In this research, we examined to develop a practical preparation protocol of such new PEMs and obtained the following results..1. The preparation protocol of TiO_2 nanoparticles in a commercial PEM via in-situ sol-gel reactions was developed, resulting in a transparent membrane with uniform distribution of TiO_2 among the membrane. A water adsorbability increased more than two times by dispersing only 2 wt % TiO_2 in the PEM.2. In order to get a uniform dispersion of Pt nanoparticles in the PEM, platinum-complex -cations were impregnated in the TiO2-PEM by an ion-exchanging reaction, followed by a reduction to Pt nanocrystals (0.1 mg/cm^2) with an aqueous solution containing excess neutral hydrazine. The Pt-dispersion process was optimized.3. The newly prepared Pt-TiO_2-PEM was confirmed to perform a self-humidifying operation in a PEFC with dry H_2 and O_2.