Anion exchange membrane (AEM) stability has been a long-standing challenge that limited the widespread development and adoption of AEM fuel cells (AEMFCs). The past five years have been a period of exceptional progress in the development of several alkaline-stable AEMs with remarkable both ex situ and in situ AEMFC stability. Certain cycloaliphatic quaternary ammonium (cQA) (mainly five- and six-membered) based AEMs appear to be among those having the most promising overall performance. In this review, we categorize cQAs as cage-like (such as quaternized 1,4-diazabicyclo[2.2.2]octane, (QDABCO) and quinuclidinium), non-cage-like (such as pyrrolidinium and piperidinium) and N-spirocyclic (such as 6-azonia-spiro[5.5]undecane (ASU)). The degradation mechanisms of categorized cQAs are first elucidated. Through an understanding of how the cations are attacked by strongly nucleophilic OH^–, improved structural design of incorporating alkaline-stable cations into AEMs is facilitated. Before a detailed description and comparison of the alkaline stability of cQAs and their respective AEMs, current protocols for the assessment of alkaline stability are discussed in detail. Furthermore, the initial AEMFC performance and fuel cell performance stability based on cQA AEMs are also examined. The main focus and highlight of this review are recent advances (2015–2020) of cQA-based AEMs, which exhibit both excellent cation and membrane alkaline stability. We aim to shed light on the development of alkaline-stable cQA-type AEMs, which are trending in the AEM community, and to provide insights into possible solutions for designing long-lived AEM materials.

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中文翻译：

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燃料电池中碱性稳定的阴离子交换膜：脂环族季铵基阴离子导体

阴离子交换膜 (AEM) 的稳定性一直是限制 AEM 燃料电池 (AEMFC) 广泛开发和采用的长期挑战。过去五年是开发几种碱稳定 AEM 取得非凡进展的时期，这些 AEM 具有显着的非原位和原位 AEMFC 稳定性。某些基于脂环族季铵 (cQA)（主要是五元和六元）的 AEM 似乎是具有最有希望的整体性能的 AEM 之一。在这篇综述中，我们将 cQAs 分类为笼状（如季铵化 1,4-二氮杂双环 [2.2.2] 辛烷 (QDABCO) 和奎宁环）、非笼状（如吡咯烷和哌啶）和N-螺环（例如 6-azonia-spiro[5.5]undecane (ASU)）。首先阐明了分类 cQAs 的降解机制。通过了解阳离子如何受到强亲核 OH 的攻击^-，促进了将碱性稳定的阳离子结合到 AEM 中的改进结构设计。在详细描述和比较 cQAs 及其各自 AEMs 的碱性稳定性之前, 详细讨论了目前评估碱性稳定性的协议。此外，还检查了基于 cQA AEM 的初始 AEMFC 性能和燃料电池性能稳定性。本综述的主要焦点和亮点是基于 cQA 的 AEM 的最新进展（2015-2020），它表现出优异的阳离子和膜碱性稳定性。我们的目标是阐明碱性稳定 cQA 型 AEM 的发展，这是 AEM 社区的趋势，并提供有关设计长寿命 AEM 材料的可能解决方案的见解。

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