Application of Self-Humidifying Polymer Electrolyte Membranes for Fuel Cells

最近，我们提出了一种新的自湿聚合物电解质膜，该膜具有高度分散的纳米尺寸Pt和/或金属氧化物，用于干燥H_2和O_2操作的聚合物电解质燃料电池（PEFCs）。Pt粒子通过H_2和O_2的催化重组抑制交叉反应，而具有吸湿性的氧化物粒子（TiO_2）将Pt粒子产生的水与阴极反应产生的水吸附在一起，并在PEM需要水时释放水。具有这些新型PEM的pefc即使在外部未加湿的条件下也表现出与传统PEM完全加湿的性能相当的优越性能和交叉抑制。然而，为了构建一个实用的PEFC堆栈，PEM的机械强度是一个重要的特性。日本Gore-Tex开发了一种既具有足够的机械强度又具有高质子导电性的增强型PEM。期望从商业增强PEM制备自湿PEM。在本研究中，我们试图开发一种实用的制备方法，并获得了以下结果。通过原位溶胶-凝胶反应，在商品PEM上制备TiO_2纳米颗粒，制备出TiO_2均匀分布的透明膜。在pem2中只分散2wt %的TiO_2，吸水性提高了两倍以上。为了使Pt纳米粒子在PEM中均匀分散，通过离子交换反应将铂络合阳离子浸渍在TiO2-PEM中，然后用含有过量中性肼的水溶液还原成Pt纳米晶体（0.1 mg/cm^2）。对pt分散工艺进行了优化。新制备的Pt-TiO_2-PEM在干燥H_2和O_2的PEFC中进行了自湿化操作。

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.