Novel aromatic proton exchange membranes based on thiazolothiazole units
Novel aromatic proton exchange membranes based on thiazolothiazole units
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DOI：
10.1038/pj.2017.47
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发表时间：
2017-08
期刊：
影响因子：
2.8
通讯作者：
S. Amari;S. Ando;Takeo Yamaguchi
中科院分区：
文献类型：
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作者：
S. Amari;S. Ando;Takeo Yamaguchi
由于其高能量和低环境负荷，聚合物电解质燃料电池（PEFC）作为替代能源受到了广泛的关注。此外，由于这些电池具有薄电解质层，因此可以小型化用于汽车、家用和移动设备，并有望成为这些设备的主要能源。 1 在 PEFC 中，质子通过质子交换膜 (PEM) 从阳极传输到阴极。磺化芳香族共聚物，如聚亚苯基、2、3聚酰亚胺、4[聚（亚芳基-醚-醚-酮）]5、6和[聚（亚芳基-醚-砜）]（SPES）、7、8是新型PEM，与传统PEM（例如Nafion）相比，其成本更低，热稳定性更好。 9 聚合物中的疏水性组分会影响其相应 SPES 膜的性能和形态。 10 此外，还研究了芳香族共聚物的不同化学成分对 PEM 性能的影响。 11, 12 例如，芳香族共聚物的共面单元（例如萘）可调节溶胀行为和膜形态。 11 这些研究表明，芳香族共聚物中引入特定疏水部分会影响膜的物理性能。此外，我们最近报道了一种基于苯并噻二唑（BT）单元的质子交换膜的新颖设计概念，13 它表现出强烈的分子间相互作用并形成平面结构。 14, 15 与母体 SPES 膜相比，基于 BT 的膜表现出更低的含水量和更有效的质子传导性，这表明独特单元（如 BT 分子）的引入促进了 PEM 中有效的质子转移。本研究重点关注噻唑并噻唑 (TT) 单元，其表现出强相互作用和刚性构象。先前基于单晶结构分析的研究表明，基于 TT 单元的单体采用平面构象。 16 此外，单体的分子间距离与其范德华半径相比较短。 16 具体而言，TT 的实际（dactual）和范德华值（dv.dW）分别为 3.25 和 3.60 Å。在 BT 单元中，有 dactual 和 dv。 dW 分别为 3.19 和 3.35 Å。 15 TT单元的比率(dactual/dv.dW)小于BT单元的比率，这表明TT单元之间的相互作用比BT单元之间的相互作用更有效。这种封闭结构不仅是由平面构象引起的，而且是由原子之间由于静电偏压而产生的分子间相互作用（杂原子相互作用）引起的。因此，TT 单元可用于以与 BT 类似的方式定制分子功能材料（例如有机半导体）的形态和物理性质。 17, 18 这些结果鼓励我们研究将 TT 单元引入聚合物膜对其形态和物理性能（包括含水量和质子电导率）的影响。因此，我们设计了一种基于 TT 单元的新型芳香族共聚物（图 1）。在芳香族共聚物中引入TT单元有望实现具有独特形态和高质子电导率的聚合物。该通讯描述了基于 TT 的共聚物的简单合成以及由这些共聚物制备膜的方法。我们还评估了合成的 TT 膜的物理性质和质子电导率。
Owing to their high energy and lowenvironmental load, polymer electrolyte fuel cells (PEFCs) have received considerable attention as an alternative energy source. Moreover, because these cells possess a thin electrolyte layer, they can be miniaturized for automotive, domestic and mobile devices and are expected to become the main energy source of these devices. 1 In PEFCs, proton transport from anode to cathode occurs through proton exchange membranes (PEMs). Sulfonated aromatic copolymers, such as polyphenylenes, 2, 3 polyimide, 4 [poly (arylene–ether–ether–ketone) s] 5, 6 and [poly (arylene–ether–sulfone)](SPES), 7, 8 are novel PEMs that offer lower cost and better thermal stability than conventional PEMs (for example, Nafion). 9 The hydrophobic components in a polymer affect the properties and morphology of its corresponding SPES membrane. 10 In addition, the effects of different chemical compositions of aromatic copolymers on the performance of PEMs have been investigated. 11, 12 For example, coplanar units (such as naphthalene) of aromatic copolymers modulate the swelling behavior and membrane morphology. 11 These investigations indicate that the physical properties of a membrane are influenced by the introduction of a specific hydrophobic moiety in aromatic copolymers. Furthermore, we have recently reported a novel design concept for PEMs based on benzothiadiazole (BT) units, 13 which exhibit strong intermolecular interactions and form planar structures. 14, 15 The BT-based membranes exhibit lower water content and more effective proton conductivity compared with those of the parent SPES membranes, which indicates that the introduction of unique units, such as BT molecules, promotes effective proton transfer in PEMs.This study focused on thiazolothiazole (TT) units, which exhibit strong interactions and a rigid conformation. Previous studies based on a single-crystal structure analysis have shown that monomers based on TT units adopt a planar conformation. 16 In addition, the intermolecular distance of the monomers is short compared to its van der Waals radius. 16 Specifically, the actual (dactual) and van der Waals values (dv. dW) of TT are 3.25 and 3.60 Å, respectively. In the BT unit, the dactual and dv. dW are 3.19 and 3.35 Å, respectively. 15 The ratio (dactual/dv. dW) of the TT unit is smaller than that of the BT unit, which indicates that the interaction between TT units is effective compared with that between the BT units. This closed structure is caused not only by the planar conformation, but also by intermolecular interactions (heteroatom interactions) between the atoms owing to their electrostatic bias. Therefore, TT units may be useful for tailoring the morphology and physical properties of molecular functional materials, such as organic semiconductors, in a similar manner to BT. 17, 18 These results encouraged us to investigate the effect of introducing TT units into a polymeric membrane on its morphology and physical properties, which include its water content and proton conductivity. Consequently, we designed a new aromatic copolymer based on the TT unit (Figure 1). The introduction of TT units to aromatic copolymers is expected to realize polymers with unique morphologies and high proton conductivities. This communication describes the simple synthesis of TT-based copolymers and the preparation of membranes from these copolymers. We also evaluated the physical properties and proton conductivity of the synthesized TT-based membranes.