高电导率、低溶胀的碱性聚电解质膜的实现策略

碱性聚电解质膜燃料电池(APEMFC)作为质子交换膜膜燃料电池的替代,由于其可以使用非贵金属催化剂、氧还原反应动力学快及成本低等众多优点,近年来获得了长足的发展.作为其中一个关键部件,碱性聚电解质(APE)膜在APEMFC中扮演着重要的角色.然而,由于OH-的淌度明显低于H+,碱性聚电解质膜的性能尤其是电导率相对较低.通过提高聚合物中离子基团的接枝度(GD),获得高的离子浓度可以在一定程度解决这个问题.但是,这种方法往往导致聚合物膜过度亲水溶胀,机械强度大幅下降.由此看来,电导率和溶胀成为了两个影响电池性能的异常重要但又相互矛盾的因素.本文综述了近些年来解决这个矛盾的一些策略,如物理手段、化学交联、离子基团在侧链上的富集以及通过亲水/疏水相分离结构构建高效的离子传输通道等.这些手段都能在一定程度上实现在低的吸水和溶胀下获得高的电导率.

Strategies for reconciling tradeoff between conductivity and swelling in alkaline polymer electrolytes membrane

Alkaline polymer electrolytes membrane fuel cells (APEMFC) have been investigated as an alternative to proton-exchange membrane fuel cells (PEMFC) because of their compatibility with nonprecious-metal catalyst, favorability toward fuel oxidation, together with the lower cost, where the charge carrier is OH^- rather than H⁺. However, the performance of APEMFC, especially the conductivity, has thus far lagged that of PEMFC because of the intrinsic lower mobility of OH^- than that of H⁺. The improvement of ion-exchange capacity (IEC) by increasing the grafting degree (GD) of cationic functional groups can, to some extent, solve this issue; however, a high IEC is always accompanied by excessive water uptake, swelling, and backbone degradation. Balancing the ionic conductivity and the dimensional stability in APEs has been a formidable scientific challenge. Here, we reviewed the research progress of the strategies for reconciling the tradeoff between conductivity and dimensional stability. These strategies include physical stratigies, such as blending and filling pores to restain the swelling, chemical cross-linking, enrichment of quaternary ammonium cation groups in the side chains and constructing efficient ionic channels by hydrophilic/hydrophobic phase segregation morphological structure like Nafion^® membranes to enhance the mobility of OH^-. The strategies mentioned above can all realize high ion conductivity and low water uptake and swelling at the same time to some extent.