面向燃料电池的亲/疏水嵌段阴离子交换膜的结构调控、性能和离子传输机理

A series of novel anion conductive amphiphilic multiblock copolymers, polyethersulfone containing quaternized ammonio-substituted tetramethylbiphenyl fluorene groups, are synthesized via block copolycondensation of tetramethylbiphenyl fluorene-containing hydrophilic oligomers and biphenyl fluorene-containing hydrophobic oligomers. Anion exchange membranes (AEMs) are further prepared using the as-synthesized copolymers. Bromination reaction on the four phenylmethyls of tetramethylbiphenyl fluorene is performed to improve the ionic conductivity of the anion exchange membranes, followed by amination using various diamines such as tetramethylmethanediamine, tetramethylethylenediamine, tetramethyl-1,3-propanediamine, tetramethyl-1,4-butanediamine and tetramethyl-1,6-hexanediamine, secondary quaternization with bromoethane and ion exchange reactions. The as-synthesized copolymers are characterized to elucidate the influence factors on the molecular weight and optimize the reaction condition for achieving the products in high purity with high molecular weight and narrow weight distribution. The mechanical properties, thermal stability, chemical stability, methanol permeability, ion conductivity and stability in alkaline environment are measured. Microstructure and morphology of the AEMs are characterized to study the effect of the block structure of the copolymers on the microstructure of the AEMs. Secondary amination using various diamines and bromoethane enables us to investigate the effect of the length of alkyl chain between two charge groups on ion transporting pathway and membrane properties. The effect of bulky fluorine group on the performance and stability of the AEMs is addressed. In-plane and through-plane diffusion coefficients of water and hydroxyl ions are measured to study the microstructure of the AEMs and the diffusion mechanism of ions across the AEMs. Single cell incorporating the as-prepared AEM is tested to evaluate the performance and stability of the membranes. This work is believed to provide a guide in the preparation of AEMs with desirable performances.

采用嵌段共聚法合成一系列结构新颖的两亲性聚醚砜类嵌段共聚物，包含亲水性季铵基团的四甲基联苯芴和疏水性联苯芴。考察影响共聚物分子量大小及分布的主因，优化反应条件获得足够分子量的产物。对四甲基联苯芴苯环上四个甲基进行溴化、季铵化和碱基化处理制备一系列阴离子交换膜(AEM)。调节离子交换基团数目，获得合适的离子交换容量。表征膜的微观结构，测试膜的性能和碱性环境中稳定性。使用不同烷基链长度的二胺与溴乙烷进行二次季铵化以提高膜的电导率，研究烷基链长度对离子传输、电导率等膜性能的影响。通过调节嵌段共聚物亲/疏水嵌段比例和烷基侧链长度来调控膜的微观结构，为合成具有高离子电导率和低甲醇渗透性的AEM提供科学指导。测试膜中水和氢氧根离子面内扩散系数和贯通扩散系数，研究膜中离子传输机理。采用制备的AEM热压制备膜电极组装单电池，测试电压/电流密度等特性。研究可望对制备具有优异稳定性和高性能的AEM提供依据。

碱性燃料电池(AFC)因具有反应动力学快、可使用非贵金属催化剂、燃料渗透率低等优点而受到越来越多的关注。阴离子交换膜 (AEM) 作为AFC的关键组成部分，其性能优劣直接影响电池的能量转化速率和使用寿命等各项性能。但是，现有的AEM普遍存在离子电导率低、尺寸稳定性和耐碱性差的问题，无法满足AFC的使用要求。因此，研发综合性能优异的AEM是AFC发展的首要目标之一。.本项目通过在酚酞侧基上接枝离子功能基团制备了一系列侧链型酚酞基聚芳醚砜腈AEM(ImSPPESN-x)，考察了腈基含量对膜结构与性能的影响。结果显示，由于离子功能基团接枝于侧链上，ImSPPESN-x膜均形成了明显的微相分离结构。随着主链上腈基含量的增加，膜内形成了更显著、高效的离子传递通道。.通过对相应的遥爪端基低聚物进行偶联聚合，成功制备了两类主链相同而亲水性季胺基团处于不同片段的阴离子交换膜F-QPES和I-QPES。所制备的F-QPES膜中的亲水离子簇尺寸9.7 nm 大于I-QPES的8.8 nm，并展现出更为明显的亲/疏水微相分离形态。.构建发达的离子传递通道和控制膜的溶胀是制备高性能AEM的关键。因此，我们合成了七甲基酚酞基聚芳醚砜聚合物并用于制备交联离子簇型AEM (C-HPPES-x/y)。交联离子簇的策略一方面能够限制膜的溶胀，另一方面也可以拉近离子簇之间的距离，使之相互聚集形成连续的亲水离子域，利于膜内形成显著的亲/疏水微相分离结构以及发达的离子传递通道，从而提高膜的离子电导率。对膜的溶胀度测试和微观结构表征结果证明上述设想成立。膜的性能测试结果表明，C-HPPES-4/1膜的性能最优，其IEC为1.83 meq. g-1, OH-离子电导率在76.7−143.4 mS.cm-1之间，80 °C时的溶胀度仅为17.4%。本项目研究结果对开发高性能AEM具有积极的参考价值。

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