有机-无机纳米复合膜多尺度质子传递网络的构建及过程强化

Too low proton conductivity of proton exchange membranes under high temperature and low humidity remains one of the biggest challenges for the development of high temperature proton exchange membrane fuel cells. The current project intends to construct a three-dimensional filler network via the multi-scale filling of hybrids of modified nanotubes and nanosheets with high proton conduction capability so that continuous channels for proton conduction can be formed and proton transport can be significantly enhanced. With the modified nanosheets as the main paths and the modified nanotubes of high aspect ratios as the bridges connecting the networks, the tortuosity of proton transport paths will be much reduced, resulting in the synergistic effect on the enhanced proton conductivity. Meanwhile, the inorganic backbone formed by the filler network can effectively suppress the membrane swelling and improve the dimensional stability. The modification of nano-fillers will be conducted based on the further functionalization of catechol groups which exhibit strong adhesive forces with the filler surfaces: on the one hand, the introduction of proton conducting groups to both surfaces of one-dimensional nanotubes and two-dimensional nanosheets will greatly improved the proton transport; on the other hand, the functionalization of the inner surfaces of one-dimensional nanotubes will help the construction of “water reservoir” to boost the water retention capability. The in-depth research on the structure regulation and proton transport mechanism of nanocomposite membranes will help further illustrate the relationships between membrane structure and properties, thus providing the theoretical guidance and scientific basis for the development of novel high temperature proton exchange membranes.

质子交换膜在高温低湿度下过低的质子电导率是目前高温质子交换膜燃料电池面临的一大难题。本项目拟通过具有高质子传导能力的改性纳米管和纳米片层的多尺度混合填充形成三维的填料网络结构,构建连续的质子传递通道,以显著强化膜的质子传递特性。以改性纳米片层作为质子传递的主干道,以长径比大的改性纳米管作为连接质子传递网络的桥梁,降低质子传输路径的曲折度,产生质子传输的协同效应,提高膜质子电导率。利用填料网络形成的无机骨架有效抑制膜溶胀,提高膜尺寸稳定性。纳米填料的改性基于表面引入的具有强粘附力的儿茶酚基团的进一步功能化修饰:在纳米管的内外表面及纳米片层的上下表面均引入质子传导基团,大大提高质子传导能力;纳米管内表面的功能化修饰可帮助构建“贮水池”增强保水能力。本项目对纳米复合膜材料的结构调控和质子传输进行深入研究,有助于进一步阐述膜结构与性能的相互影响关系,为制备新型高温质子交换膜提供理论指导和科学依据。

有机-无机纳米复合膜是一类非常值得深入研究的高温质子交换膜燃料电池(PEMFC)用质子交换膜材料，但其面临的一大难题是其在高温低湿度下过低的质子电导率。纳米复合膜质子传导性能的提高迫切需要通过合理有效的结构调控来实现；此外，传统的纳米填料的改性还普遍存在着表面活性基团的数量和位置有限、直接用偶联剂化学改性效果不佳等问题。本项目通过基于在一维纳米材料表面（包括纳米管内外表面）和二维纳米片层上下表面包覆具有强粘附力的儿茶酚基团的进一步功能化修饰，成功引入了质子传导基团，建立了无机纳米填料表面功能化修饰的新方法：分别在一维埃洛石纳米管、二维氧化石墨烯的表面进行了聚多巴胺(PDA)包覆和质子传导基团的连接，借助纳米材料的高长径比降低质子传输路径的曲折度，促进连续质子传导通道的形成和质子的跳跃传导。成功构建了多尺度的强化质子传递结构：在引进大量碱性氨基基团的同时进行一维和二维填料的混合搭接并将磷钨酸(HPW)负载于杂化填料上，从而构建三维的填料网络，促进质子沿着填料网络进行传递；借助一维纳米纤维素表面包覆的PDA成功进行了二维共价有机框架的杂化，并在此基础上通过水热获得了HPW共价改性的杂化纳米填料。制备出在高温低湿度下仍具有高质子电导率的新型纳米复合质子交换膜，提高了高温低湿度下PEMFC的性能：在45% RH下，Nafion纳米复合膜的质子电导率高达Nafion重铸膜的9倍；在80oC和50% RH下，与基于Nafion重铸膜的MEA相比，Nafion纳米复合膜显着提高了燃料电池性能，峰值功率密度达到888 mW cm-2，比Nafion重铸膜(306 mW cm-2)提高了190%。这些研究成果为新型质子交换膜的制备提供了理论指导和实践基础。