无水质子传递通道的仿生构建与离子液体质子传递机理研究

Due to its high energy efficiency and environmentally benign features, the proton exchange membrane (PEM) fuel cell, which converts chemical energy directly into electric energy, is believed to be the best type of fuel cell for vehicular power sources to eventually replace gasoline and diesel internal-combustion engines. At present, development of PEM with stable and high proton conductivity under operating conditions (high temperature and low humidity) is a major challenge that must be solved. Based on biological principles, a novel approach for fabricating anhydrous proton-conducting membrane is developed in this project as follows: (i) membrane with connective hydrophilic nanochannels is created by the self-assembly of sulfonated aromatic polymer during membrane fabrication; (ii) imidazole ionic liquid is then incorporated into the nanochannels to form acid-base pairs on the channel surface, which construct biomimetic proton carriers and thus allow for efficient proton transfer; (iii) the unique physicochemical properties will yield a high proton conductivity under high temperature and low humidity, as well as anhydrous conditions; and (iv) a dense nano-layer is formed and adhered tightly to membrane surface to encapsulate ionic liquid into the nanochannels, in turn enhancing the structural stability of membrane. By investigating the influence of channel structure and component upon proton transfer ability and mechanism, we attempt to establish the transfer mechanism of acid-base pairs and ionic liquid, and then to obtain controllable preparation of high-performance anhydrous proton-conducting membranes. This project has very important theoretical significance and application value, and will provide some theoretical basis and technical support for constructing high efficient proton transfer channels and intensifying proton conduction.

质子交换膜燃料电池是一种将化学能直接转化为电能的高效、低污染的新型发电装置，被认为是很有前途的绿色替代能源装置，目前制约其商业化应用的一个关键问题是开发操作条件（高温、低湿）下具有高质子传导率且稳定的质子交换膜（电池的心脏）。本研究采用仿生学思路，提出一种新颖的无水质子交换膜设计思想：通过磺化芳香高分子在成膜过程中自组装形成亲水性纳米通道；将咪唑离子液体填充到亲水性通道内，在通道表面形成酸碱对，构建仿生质子载体环境，实现质子高效传导；利用咪唑两性和离子液体物化特性实现膜在高温低湿或无水状态下的质子传导；为提高膜结构稳定性，在膜表面修饰纳米薄层将离子液体封装于通道内。通过考察通道结构、组成对质子传递能力和传递方式的影响，揭示酸碱对、离子液体质子传递机理，实现高性能无水质子交换膜的可控制备。本研究具有重要的理论意义和应用价值，有望为高效质子传递通道构建及质子传递过程强化提供理论基础和技术支持。

本研究采用仿生学思路，提出一种新颖的无水质子交换膜设计思路，以期制备高传导质子交换膜。采用后磺化法制备不同磺化度的磺化聚醚醚酮（SPEEK），后用流延法制备SPEEK基膜，考察了磺化条件（浓硫酸用量、反应时间）与磺化度间的内在关系，研究了磺化度对膜结构的影响和规律。小角X-射线衍射和质子传导率测试结果显示膜内离子簇通道尺寸和质子传导率随磺化度的增加而增大。通过溶胀法将咪唑离子液体填充到SPEEK基膜内制备复合膜，考察了填充条件对离子液体填充量的影响及规律，研究了离子液体填充量对复合膜结构和质子传导能力的影响规律，分析了通道结构、组成与质子传递能力和传递方式间的关系，初步揭示了离子液体基复合膜的质子传递机理。研究发现，通过控制超声功率、浸泡温度和浸泡时间可有效调控复合膜的离子液体填充量；咪唑型离子液体的加入可与酸性SPEEK基质形成酸碱对，从而实现高效质子传递；随离子液体填充量增加，通道连通性增强，复合膜的质子传导能力不断提高。基于聚合物刷功能化氧化石墨烯和咪唑型离子液体协同在膜中构建无水质子传递通道。功能化氧化石墨烯在膜中构建了长程连续的界面区域，离子液体在静电引力的驱动下主要富集于聚合物-填充物界面区，两者协同在膜中构建了低能垒的无水质子传递通道，复合膜的无水传导率提高了30倍。基于聚合物微囊在膜中构建离子液体“水库”，提高复合膜的离子液体储存及保持能力。聚合物微囊的囊腔如同水库，为复合膜提供大量的储存离子液体的空间；同时，聚合物微囊交联的壳层能够控制离子液体的流失，从而赋予复合膜良好的保持离子液体能力。耦合层层自组装技术与生物矿化技术，通过单宁酸和明胶在含离子液体复合膜表面形成致密、抗溶胀的表面保护层，可强化膜的稳定性和离子液体保持能力。同时，还利用杂化思想通过向碱性（如壳聚糖）或酸性（如SPEEK）高分子基质中填充酸性（如–SO3H）或碱性（如–NH2）聚合物刷或聚合物层改性的二氧化硅球、埃洛石纳米管或氧化石墨烯制备酸碱复合质子交换膜，进一步揭示了酸碱对质子传递机理及调控手段，并初步总结了高效质子传递通道构建原则与理论。