A comparative study of anion-exchange membranes tethered with different hetero-cycloaliphatic quaternary ammonium hydroxides
A comparative study of anion-exchange membranes tethered with different hetero-cycloaliphatic quaternary ammonium hydroxides
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DOI：
10.1039/c7ta06029g
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发表时间：
2017-11-07
影响因子：
11.9
通讯作者：
Jannasch, Patric
中科院分区：
文献类型：
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作者：
Dang, Hai-Son;Jannasch, Patric
具有高碱性稳定性的季铵（QA）阳离子对于阴离子交换膜（AEM）燃料电池的长期性能至关重要。在这里，我们通过戊基间隔链将聚（苯醚）（PPO）与8种不同的杂环脂族QA阳离子连接。的热稳定性和碱性稳定性，以及氢氧离子电导率，进行了系统的评价，主要目的是确定降解反应，并建立阳离子设计原则。该研究包括用1-甲基氮杂环庚三烯、1-甲基吡咯烷鎓、1-甲基吗啉鎓、奎宁环鎓以及1-甲基-、1，4-二甲基-、1，3，5-三甲基-和1，2，6-三甲基哌啶鎓官能化的AEM，所有这些都在窄的离子交换容量（IEC）范围内。作为参考，PPO还在戊基间隔基上用三甲基铵和二丙基甲基铵阳离子官能化，并且在PPO主链上的苄基位置直接用三甲基铵和1-甲基哌啶鎓 QA官能化。发现杂环脂族QA阳离子的碱性稳定性关键取决于它们在聚合物结构中的位置、环尺寸、额外杂原子的存在和环取代模式。例如，1，2，6-三甲基哌啶鎓和1-甲基氮杂环庚烷通过霍夫曼消除降解，1-甲基吗啉鎓通过霍夫曼消除和取代反应开环降解，而在90 ℃下在1 M NaOH中16天后，通过其他阳离子的H-1 NMR光谱没有检测到降解。研究中AEM的氢氧离子电导率在80 ℃时达到64至150 mS cm（-1）之间的值，具体取决于阳离子和IEC。通过戊基间隔基与哌啶鎓和奎宁环鎓阳离子拴系的AEMs被发现显示出最好的整体性能。因此，综合结果提供的见解，可以指导阳离子基团和膜材料的选择，以提高碱性电化学能量转换和存储装置的耐久性和性能。
Quaternary ammonium (QA) cations with high alkaline stability are crucial for the long term performance of anion-exchange membrane (AEM) fuel cells. Here, we have tethered poly(phenylene oxide) (PPO) with 8 different hetero-cycloaliphatic QA cations via pentyl spacer chains. The thermal and alkaline stabilities, as well as hydroxide ion conductivity, were systematically evaluated with the primary aim to identify degradation reactions and establish cation design principles. The study included AEMs functionalized with 1-methylazepanium, 1-methylpyrrolidinium, 1-methylmorpholinium, quinuclidinium, as well as 1-methyl-, 1,4-dimethyl-, 1,3,5-trimethyl-, and 1,2,6-trimethylpiperidinium, all within a narrow ion exchange capacity (IEC) range. For reference, PPO was also functionalized with trimethylammonium and dipropylmethylammonium cations on pentyl spacers, and with trimethylammonium and 1-methylpiperidinium QAs in benzylic positions directly on the PPO backbone. The alkaline stability of hetero-cycloaliphatic QA cations was found to depend critically on their position in the polymer structure, ring size, the presence of an additional heteroatom and ring substitution pattern. For example, 1,2,6-trimethylpiperidinium and 1-methylazepanium degraded via Hofmann elimination and 1-methylmorpholinium via ring opening by both Hofmann elimination and substitution reactions, while no degradation was detected by H-1 NMR spectroscopy of other cations after 16 days in 1 M NaOH at 90 degrees C. The hydroxide ion conductivity of the AEMs in the study reached values between 64 and 150 mS cm(-1) at 80 degrees C, depending on the cation and IEC. AEMs tethered with piperidinium and quinuclidinium cations via pentyl spacers were found to show the best overall properties. Hence, the combined results provide insights that may guide the selection of cationic groups and membrane materials to improve the durability and performance of alkaline electrochemical energy conversion and storage devices.