Department of Materials Science and Engineering, The Pennsylvania State University, University Park, Pennsylvania 16802, USA.
ACS Appl Mater Interfaces. 2009 Nov;1(11):2573-9. doi: 10.1021/am900498u.
A series of new Nafion-based composite membranes have been prepared via an in situ sol-gel reaction of 3-(trihydroxylsilyl)propane-1-sulfonic acid and solution casting method. The morphological structure, ion-exchange capacity, water uptake, proton conductivity, and methanol permeability of the resulting composite membranes have been extensively investigated as functions of the content of sulfopropylated polysilsesquioxane filler, temperature, and relative humidity. Unlike the conventional Nafion/silica composites, the prepared membranes exhibit an increased water uptake and associated enhancement in proton conductivity compared to unmodified Nafion. In particular, considerably high proton conductivities at 80 and 120 degrees C under 30% relative humidity have been demonstrated in the composite membranes, which are over 2 times greater than that of Nafion. In addition to a remarkable improvement in proton conductivity, the composite membranes display lower methanol permeability and superior electrochemical selectivities in comparison to the pure Nafion membrane. These unique properties could be exclusively credited to the presence of pendant sulfonic acid groups in the filler, which provides fairly continuous proton-conducting pathways between filler and matrix in the composite membranes and thus facilitates the proton transport without the anticipated trade-off between conductivity and selectivity. This work opens new opportunities of tailoring the properties of Nafion-the benchmark fuel cell membrane-to obviate its limitations and enhance the conductive properties at high temperature/low humidity and in direct methanol fuel cells.
一系列新型基于 Nafion 的复合膜通过 3-(三羟基硅基)丙基-1-磺酸的原位溶胶-凝胶反应和溶液浇铸法制备而成。研究了所得复合膜的形态结构、离子交换容量、吸水率、质子电导率和甲醇渗透率随磺丙基聚倍半硅氧烷填料含量、温度和相对湿度的变化。与传统的 Nafion/二氧化硅复合材料不同，与未改性的 Nafion 相比，所制备的膜表现出更高的吸水率和相应的质子电导率增强。特别是，在 30%相对湿度下，复合膜在 80 和 120°C 下表现出超过 2 倍于 Nafion 的高质子电导率。除了质子电导率的显著提高外，与纯 Nafion 膜相比，复合膜还显示出更低的甲醇渗透率和更高的电化学选择性。这些独特的性能可以完全归因于填料中存在的侧挂磺酸基团，这在复合膜中为填料和基质之间提供了相当连续的质子传导途径，从而促进了质子传输，而不会预期在电导率和选择性之间进行权衡。这项工作为定制 Nafion（基准燃料电池膜）的性能开辟了新的机会，可以克服其局限性，并提高在高温/低湿度和直接甲醇燃料电池中的导电性能。
