Department of Chemistry and Chemical Biology, Baker Laboratory, Cornell University, Ithaca, NY 14853.
School of Applied and Engineering Physics, Cornell University, Ithaca, NY 14853.
Proc Natl Acad Sci U S A. 2019 May 14;116(20):9729-9734. doi: 10.1073/pnas.1900988116. Epub 2019 Apr 29.
Alkaline anion exchange membranes (AAEMs) are an important component of alkaline exchange membrane fuel cells (AEMFCs), which facilitate the efficient conversion of fuels to electricity using nonplatinum electrode catalysts. However, low hydroxide conductivity and poor long-term alkaline stability of AAEMs are the major limitations for the widespread application of AEMFCs. In this paper, we report the synthesis of highly conductive and chemically stable AAEMs from the living polymerization of -cyclooctenes. A -cyclooctene-fused imidazolium monomer was designed and synthesized on gram scale. Using these highly ring-strained monomers, we produced a range of block and random copolymers. Surprisingly, AAEMs made from the random copolymer exhibited much higher conductivities than their block copolymer analogs. Investigation by transmission electron microscopy showed that the block copolymers had a disordered microphase segregation which likely impeded ion conduction. A cross-linked random copolymer demonstrated a high level of hydroxide conductivity (134 mS/cm at 80 °C). More importantly, the membranes exhibited excellent chemical stability due to the incorporation of highly alkaline-stable multisubstituted imidazolium cations. No chemical degradation was detected by H NMR spectroscopy when the polymers were treated with 2 M KOH in CDOH at 80 °C for 30 d.
碱性阴离子交换膜（AAEMs）是碱性交换膜燃料电池（AEMFCs）的重要组成部分，它使用非铂电极催化剂促进燃料向电能的高效转化。然而，AAEMs 的低氢氧化物电导率和较差的长期碱性稳定性是限制 AEMFCs 广泛应用的主要因素。在本文中，我们报告了通过 -环辛烯的活性聚合来合成高导电性和化学稳定的 AAEMs。设计并合成了一种基于 -环辛烯的融合咪唑鎓单体，可在克级规模上进行制备。使用这些高度环张力的单体，我们制备了一系列嵌段和无规共聚物。令人惊讶的是，与嵌段共聚物相比，无规共聚物制成的 AAEMs 具有更高的电导率。透射电子显微镜的研究表明，嵌段共聚物具有无序的微相分离，这可能阻碍了离子传导。交联的无规共聚物表现出高的氢氧化物电导率（80°C 时为 134 mS/cm）。更重要的是，由于掺入了高碱性稳定的多取代咪唑鎓阳离子，这些膜表现出优异的化学稳定性。当聚合物在 80°C 的 CDOH 中用 2 M KOH 处理 30 天时，通过 1H NMR 光谱检测未发现任何化学降解。
