网络化和有序化离子通道在燃料电池碱性电解质膜中的设计构筑

Low ion exchange capacity (IEC) may help to maintain good stability of an anion exchange membrane (AEM) for alkaline fuel cells. However, low IEC leads to insufficient microphase separation in a quaternized block copolymer AEM, and the dense hydrophobic microphase makes it difficult for the ion clusters to form continuous ion channels via percolation. Also, the ion transport pathway is tortuous. How to achieve continuous and less tortuous ion channel is a hot and challenging topic in the field of AEM research and development. .In this project, we design and synthesize copolymers containing PIM (polymer of intrinsic microposity) block and quaterized flexible block for AEM fabrication. PIM is characterized by highly rigid and twisted chains so that the PIM block can form micropores in the hydrophobic microphase of the AEM. Such micropores will connect the ion clusters and help them to form networked, continuous ion channels by percolation of the hydrophobic microphase. Further to this, we propose chemical modification of the PIM block so that the polarity of the micropores can be tuned and optimized for ion cluster connection. We also propose incorporation of a length controlled, flexible hydrophobic segment into the block copolymer, which will work synergistically with the PIM block for fine tuning of the micropore size and porosity so that conductivity, strength and fuel-blocking property of the membrane can be well balanced. .In order to lower the tortuosity of the ion transport pathway, we propose construction of shafted-tube-like polyrotaxane ion channel, which consists of a quaternized polymer shaft densely encircled with cyclodextrins and double-end capped with PIM segments. The densely populated cyclodextrin circles will restrain the quaternized chain entanglement so that a relatively ordered ion channel can be formed. .The networked and ordered ion channels and their construction methodology proposed in this project will promote hydroxide ion transport in AEM significantly, and hopefully will achieve further improved conductivity on basis of the present level. Our proposal helps to make conductivity less dependent on IEC, and therefore, is of high theoretical and practical significance for application oriented development of AEM and alkaline fuel cel.

低离子交换容量（IEC）有利于碱性电解质膜（AEM）的稳定性，但低IEC传统嵌段AEM微相分离不充分，膜内致密的疏水相使微相分离产生的离子簇无法有效贯通，离子传递路径曲折且不连续。如何获得低IEC下的连续通道是目前的研究热点和难点。本项目拟利用非离子化自具微孔聚合物（polymer of intrinsic microporosity, PIM）的高度不规则刚性链构筑微孔疏水相，促进离子簇溶胀贯通形成网络化通道；调控PIM极性并建立刚柔链段协同的微孔调节机制，保障网络通道传导性、稳定性和阻醇性的平衡；构筑基于PIM、离子聚合物和环糊精的聚轮烷轴管式通道，借助环糊精在离子链上的紧密环绕限制链缠结，使通道呈现一定程度有序化。本项目提出的网络化与有序化离子通道及构筑策略将显著促进AEM离子传递，有望进一步降低电导率对IEC的依赖，从根本上保障膜的稳定性，对于碱性燃料电池的实用化发展具有重要意义。

本项目针对阴离子交换膜电导性与稳定性的矛盾，利用自具微孔聚合物（PIM）构筑微孔疏水相，促进离子簇溶胀贯通形成网络化通道，同时构筑基于环糊精轴管结构和金刚烷、三乙烯二胺（DABCO）、共价有机框架（COF）等刚性单元的有序化离子通道。.制备了MmPSF/MmPIM共混膜。PIM的高自由体积使共混膜SBET增加3倍，IEC从1.08 mmol g-1降低为0.77 mmol g-1，膜内出现明显的离子团簇，直径7-8 nm，30 ℃电导率升高到16.9 mS cm-1，验证了自由体积有助于网络化通道形成。进一步制备得到含PIM的嵌段AEM，80 ℃电导率52.6 mS cm-1，氢氧燃料电池80 ℃峰值功率达到270 mW cm-2。利用DABCO刚性结构在膜内构筑有序化通道，膜在25℃下表现出31 mS cm-1的电导率，燃料电池峰值功率密度达到217 mW cm-2。采用刚性β-环糊精（β-CD）对聚芳醚接枝并引入多阳离子交联剂形成有序化通道，膜在较低IEC（1.50 mmol g-1）下，80 oC电导率为112.4 mS cm-1。聚亚芳基哌啶主链接枝哌啶化柔性长链修饰的β-CD，80 oC电导率达到121.5 mS cm-1（IEC=1.29 mmol g-1）。聚芳吲哚同时接枝金刚烷和长侧链离子化β-CD，在双重刚性结构单元作用下形成有序程度更高的离子通道，膜80 oC电导率122.0 mS cm-1，1 M碱80 oC处理1008 h电导率保留90.0%，燃料电池峰值功率密度达到603 mW cm-2。.本项目创新了碱性膜离子通道构筑策略，为膜性能和电池性能的进一步提升提供了新的可能。在ACS Appl. Mater. Interf., J. Membr. Sci.等国内外期刊发表论文10篇，授权/申请发明专利5项，其中PCT专利1项。毕业博士生2名、硕士生5名。.