Gjoshi Sara, Loukopoulou Paraskevi, Plevova Michaela, Hnat Jaromir, Bouzek Karel, Deimede Valadoula
Department of Chemistry, University of Patras, GR-26504 Patras, Greece.
Department of Inorganic Technology, University of Chemistry and Technology, Prague, Technická 5, 16628 Prague, Czech Republic.
Polymers (Basel). 2023 Dec 28;16(1):99. doi: 10.3390/polym16010099.
Mechanically robust anion-exchange membranes (AEMs) with high conductivity and long-term alkali resistance are needed for water electrolysis application. In this work, aryl-ether free polyaromatics containing isatin moieties were prepared via super acid-catalyzed copolymerization, followed by functionalization with alkaline stable cyclic quaternary ammonium (QA) cationic groups, to afford high performance AEMs for application in water electrolysis. The incorporation of side functional cationic groups (pyrrolidinium and piperidinium) onto a polymer backbone via a flexible alkyl spacer aimed at conductivity and alkaline stability improvement. The effect of cation structure on the properties of prepared AEMs was thoroughly studied. Pyrrolidinium- and piperidinium-based AEMs showed similar electrolyte uptakes and no obvious phase separation, as revealed by SAXS and further supported by AFM and TEM data. In addition, these AEMs displayed high conductivity values (81. 5 and 120 mS cm for pyrrolidinium- and piperidinium-based AEM, respectively, at 80 °C) and excellent alkaline stability after 1 month aging in 2M KOH at 80 °C. Especially, a pyrrolidinium-based AEM membrane preserved 87% of its initial conductivity value, while at the same time retaining its flexibility and mechanical robustness after storage in alkaline media (2M KOH) for 1 month at 80 °C. Based on H NMR data, the conductivity loss observed after the aging test is mainly related to the piperidinium degradation that took place, probably via ring-opening Hofmann elimination, alkyl spacer scission and nucleophilic substitution reactions as well. The synthesized AEMs were also tested in an alkaline water electrolysis cell. Piperidinium-based AEM showed superior performance compared to its pyrrolidinium analogue, owing to its higher conductivity as revealed by EIS data, further confirming the ex situ conductivity measurements.
水电解应用需要具有高导电性和长期耐碱性的机械坚固的阴离子交换膜（AEM）。在这项工作中，通过超酸催化共聚制备了含异吲哚酮部分的无芳基醚聚芳烃，然后用碱性稳定的环状季铵（QA）阳离子基团进行功能化，以提供用于水电解的高性能AEM。通过柔性烷基间隔基将侧链功能性阳离子基团（吡咯烷鎓和哌啶鎓）引入聚合物主链，旨在提高导电性和碱性稳定性。深入研究了阳离子结构对制备的AEM性能的影响。SAXS显示，基于吡咯烷鎓和哌啶鎓的AEM表现出相似的电解质吸收，且无明显相分离，AFM和TEM数据进一步证实了这一点。此外，这些AEM在80°C下表现出高电导率值（基于吡咯烷鎓和哌啶鎓的AEM在80°C时分别为81.5和120 mS cm），并且在80°C的2M KOH中老化1个月后具有优异的碱性稳定性。特别是，基于吡咯烷鎓的AEM膜在80°C的碱性介质（2M KOH）中储存1个月后，保留了其初始电导率值的87%，同时保持了其柔韧性和机械坚固性。基于1H NMR数据，老化试验后观察到的电导率损失主要与哌啶鎓的降解有关，这可能是通过开环霍夫曼消除、烷基间隔基断裂和亲核取代反应发生的。合成的AEM也在碱性水电解槽中进行了测试。基于哌啶鎓的AEM与其吡咯烷鎓类似物相比表现出优异的性能，EIS数据显示其具有更高的电导率，进一步证实了非原位电导率测量结果。
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