Novel Design Solving the Conductivity vs Water-Uptake Trade-Off for Polymer Electrolyte Membrane by Bicontinuous Crystalline/Amorphous Morphology of Block Copolymer
Novel Design Solving the Conductivity vs Water-Uptake Trade-Off for Polymer Electrolyte Membrane by Bicontinuous Crystalline/Amorphous Morphology of Block Copolymer
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DOI：
10.1021/ma901361s
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发表时间：
2009-09
期刊：
影响因子：
5.5
通讯作者：
H. Uehara;Masaki Kakiage;M. Sekiya;T. Yamagishi;T. Yamanobe;Katsuhiko Nakajima;Toshio Watanabe;K. Nomura;Kohei Hase;Masatoshi Matsuda
中科院分区：
文献类型：
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作者：
H. Uehara;Masaki Kakiage;M. Sekiya;T. Yamagishi;T. Yamanobe;Katsuhiko Nakajima;Toshio Watanabe;K. Nomura;Kohei Hase;Masatoshi Matsuda
燃料电池具有不产生二氧化碳的巨大优势，因此有望成为世界范围内理想的电力来源。1 r3各种聚合物材料已被用作燃料电池的电解质膜。4 r7最受欢迎的是氟聚合物，如Nafion。这种含氟聚合物电解质的特征之一是它们在潮湿条件下的自组装结构。磺酸基团在分子链中的优选分布产生由在疏水基质内形成的亲水性酸基团包围的水簇通道的网络形成。6，8 r11质子可以通过扩散机制穿过这样的水簇通道。在这种情况下，有效的质子传导性必然需要约30重量%的高吸水率，因为通道宽度由水簇本身的排阻体积维持。然而，不可避免的振动会导致燃料电池中包含的液态水泄漏，特别是在汽车等运输应用中，使得难以严格控制含水量。从这些观点来看，非常希望燃料电池在甚至更低的水含量下操作。在这项研究中，我们试图设计一种新的方法来解决传统聚合物电解质膜的电导率与吸水率的限制权衡。我们专注于嵌段共聚物（BCP）的疏水性和亲水性嵌段分子链内连接，因为前矩阵预计将作为一个骨干框架，限制水的溶胀。嵌段共聚物自组装产生不同的纳米尺寸的嵌段组分的各种微相分离，这取决于嵌段组合物。13、14结晶嵌段优选作为固体骨架。几个小组已经研究了含有结晶嵌段的BCP的制备及其结晶行为。托马斯等人15的先驱研究调查了在基底上具有纳米周期相排列的聚乙烯-嵌段-聚苯乙烯（PE-b-PS）的溶液结晶。Müller等人16 r18报道了一系列具有不同嵌段组成的PE-b-PS从熔体中的常规结晶。相比之下，Hillmyer等人18、19成功合成了PE-b-聚乳酸（PLA）。Register等人20还制备了由PE和聚苯乙烯组成的双晶BCP，并报道了其独特的结晶行为。最近，Lodge等人21开发了PE-b-聚（乙烯-交替-丙烯）作为纳米多孔陶瓷材料的前体。在本研究中，选择上述结晶PE作为目标BCP的疏水基质。PE具有最简单的链结构，但具有优异的耐化学性和机械性能。选择PS作为无定形抗衡嵌段，因为其苯基基团可以通过酸处理磺化，产生亲水性聚（苯乙烯磺酸）（PSS），其作为燃料电池应用的常见电解质聚合物而众所周知。4 r6最近，我们22 r24发现可以通过选择性化学蚀刻PE-b-PS前体膜来制备纳米多孔膜。这里，使用相同的起始材料，PE嵌段的数均分子量（MW）为6.7 X IO 4，PS嵌段的数均分子量为5.4 X IO 4。在不同的晶化条件下制备了一系列薄膜。详细制备程序见支持性信息。透射电子显微镜（TEM）观察揭示了圆柱形结晶网络与从180 C的熔体在90 C等温结晶的逐渐连接（参见支持信息，图S1）。差示扫描...
Fuel cells have the great advantage of not producing carbon dioxide and thus are expected to become ideal electric power sources worldwide. 1r3 Various polymeric materials have been applied as the electrolyte membrane for fuel cells. 4r7 The most popular are fluoropolymers, such as Nafion. 8r12 One of the characteristic features of such fluoropolymer electrolytes is their self-assembling structures under wet conditions. A preferred distribution of sulfonic acid groups in the molecular chain produces a network formation of water-cluster channels surrounded by hydrophilic acid groups that develop within the hydrophobic matrix. 6, 8r11 Protons can travel through such water-cluster channels via a diffusion mechanism. 12 In this case, efficient proton conductivity necessarily requires a high water uptake of around 30 wt% because the channel width is maintained by the exclusion volume of the water cluster itself. However, the inevitable vibration causes liquid water contained in a fuel cell to leak, especially in transport applications such as automobiles, making it difficult to strictly control water content. From these viewpoints, it is highly desirable for fuel cells to operate with even lower water content. In this study, we tried to design a new approach solving the limiting trade-off of conductivity vs water uptake for conventional polymer electrolyte membranes. We focused on a block copolymer (BCP) composed of hydrophobic and hydrophilic blocks linked within a molecular chain because the former matrix is expected to function as a backbone frame that restricts the water swelling. BCP self-assembly produces various microphase separations of different block components of nanometer size, depending on the block composition. 13, 14 A crystalline block is preferable as a solid backbone. Several groups have investigated the preparation of BCPs containing crystalline blocks and their crystallization behaviors. A pioneer study by Thomas et al. 15 investigated the solution crystallization of polyethylene-block-polystyrene (PE-b-PS) with a nanoperiodic phase arrangement on the substrate. Müller et al. 16r18 reported usual crystallization from the melt for a series of PE-b-PS having different block compositions. In contrast, Hillmyer et al. 18, 19 successfully synthesized PE-b-poly (lactic acid)(PLA). Register et al. 20 also prepared the double crystalline BCP composed of PE and polynorbornene and reported its unique crystallization behavior. Recently, Lodge et al. 21 developed PE-b-poly (ethylene-alt-propylene) as a precursor of nanoporous ceramic materials. In this study, the above crystalline PE was selected as the hydrophobic matrix for the targeted BCP. PE has the simplest chain architecture but exhibits excellent chemical resistance and mechanical properties. PS was selected as the amorphous counter block, since its phenyl groups can be sulfonated by acid treatment, yielding hydrophilic poly (styrenesulfonic acid)(PSS), which is well-known as a common electrolyte polymer for fuelcell applications. 4r6 Recently, we22r24 found that nanoporous membranes can be prepared by selective chemical etching of PE-b-PS precursor films. Here, the same starting material was used, with number-average molecular weights (MWs) of 6.7 x 104 for PE and 5.4 x 104 for PS blocks. A series of films were prepared under different crystallization conditions. The detailed preparation procedure is described in the Supporting Information. Transmission electron microscopy (TEM) observation revealed the gradual connection of a cylindrical crystalline network with isothermal crystallization at 90 C from the melt at 180 C (see Supporting Information, Figure S1). Differential scanning …