Effect of Confinement on Structure, Water Solubility, and Water Transport in Nafion Thin Films
Effect of Confinement on Structure, Water Solubility, and Water Transport in Nafion Thin Films
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DOI：
10.1021/ma301289v
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发表时间：
2012-10-09
期刊：
影响因子：
5.5
通讯作者：
Yager, Kevin G.
中科院分区：
文献类型：
--
作者：
Eastman, Scott A.;Kim, Sangcheol;Yager, Kevin G.
基于聚合物电解质膜(PEM)的燃料电池由于其高电荷密度和低工作温度，在交通运输和固定电力生产中显示出广泛的应用前景。虽然用于燃料电池的块状质子交换膜的结构和传输已被广泛研究，但对这些材料在界面和约束下的情况知之甚少，这些条件与工作的质子交换膜燃料电池的膜电极组件高度相关。利用X射线反射率、中子反射率、掠入射小角X射线散射、石英晶体微天平和偏振调制红外反射吸收光谱，研究了222 nm以下受限聚电解质膜的结构、溶胀、水溶和水迁移动力学随相对湿度的变化。对于厚度大于约60 nm的薄膜，其平衡溶胀比、体积含水率和有效扩散系数随湿度变化相对恒定，而在厚度小于约60 nm的薄膜中，我们观察到这些特性受到了明显的抑制。这些效应在一定范围内发生，与功能性燃料电池膜电极组件(MEA)催化层中的聚电解质粘合剂中的传输(离子和水)有关。这里介绍的薄膜方法和发现提供了一个量化和验证燃料电池领域中使用的界面阻抗模型的平台，并有可能导致MEA材料、设计和优化的改进。
Fuel cells based on polymer electrolyte membranes (PEM) show promise as a means of energy conversion for a wide range of applications both in the transportation sector and for stationary power production due to their high charge density and low operating temperatures. While the structure and transport of bulk PEMs for fuel cell applications have been studied extensively, much less is known about these materials at interfaces and under confinement, conditions that are highly relevant in the membrane electrode assembly of a working PEM fuel cell. Using X-ray reflectivity, neutron reflectivity, grazing-incidence small-angle X-ray scattering, quartz crystal microbalance, and polarization-modulation infrared reflection-absorption spectroscopy, we have studied the structure, swelling, water solubility, and water transport kinetics as a function of relative humidity for confined polyelectrolyte films thinner than 222 nm. While the humidity-dependent equilibrium swelling ratio, volumetric water fraction, and effective diffusivity are relatively constant for films thicker than ca. 60 nm, we observe measurable suppressions of these properties in films less than ca. 60 nm. These effects occur at length scales that are relevant to transport (ion and water) in the polyelectrolyte binders found in the catalyst layer of the membrane-electrode assembly (MEA) of a functional fuel cell. The thin film methodology and findings presented here provide a platform to quantify and validate models of interfacial impedance used within the fuel cell community and have the potential to lead to improvements in MEA materials, design, and optimization.