Tuffnell Joshua M, Morzy Jędrzej K, Kelly Nicola D, Tan Rui, Song Qilei, Ducati Caterina, Bennett Thomas D, Dutton Siân E
Department of Materials Science and Metallurgy, University of Cambridge, 27 Charles Babbage Rd, Cambridge, CB3 0FS, UK.
Department of Physics, University of Cambridge, JJ Thomson Ave, Cambridge, CB3 0HE, UK.
Dalton Trans. 2020 Nov 17;49(44):15914-15924. doi: 10.1039/d0dt02576c.
IL@MOF (IL: ionic liquid; MOF: metal-organic framework) materials have been proposed as a candidate for solid-state electrolytes, combining the inherent non-flammability and high thermal and chemical stability of the ionic liquid with the host-guest interactions of the MOF. In this work, we compare the structure and ionic conductivity of a sodium ion containing IL@MOF composite formed from a microcrystalline powder of the zeolitic imidazolate framework (ZIF), ZIF-8 with a hierarchically porous sample of ZIF-8 containing both micro- and mesopores from a sol-gel synthesis. Although the crystallographic structures were shown to be the same by X-ray diffraction, significant differences in particle size, packing and morphology were identified by electron microscopy techniques which highlight the origins of the hierarchical porosity. After incorporation of Na0.1EMIM0.9TFSI (abbreviated to NaIL; EMIM = 1-ethyl-3-methylimidazolium; TFSI = bis(trifluoromethylsulfonyl)imide), the hierarchically porous composite exhibited a 40% greater filling capacity than the purely microporous sample which was confirmed by elemental analysis and digestive proton NMR. Finally, the ionic conductivity properties of the composite materials were probed by electrochemical impedance spectroscopy. The results showed that despite the 40% increased loading of NaIL in the NaIL@ZIF-8micro sample, the ionic conductivities at 25 °C were 8.4 × 10-6 and 1.6 × 10-5 S cm-1 for NaIL@ZIF-8meso and NaIL@ZIF-8micro respectively. These results exemplify the importance of the long range, continuous ion pathways contributed by the microcrystalline pores, as well as the limited contribution from the discontinuous mesopores to the overall ionic conductivity.
离子液体@金属有机框架（IL@MOF，IL：离子液体；MOF：金属有机框架）材料已被提议作为固态电解质的候选材料，它将离子液体固有的不可燃性以及高热稳定性和化学稳定性与MOF的主客体相互作用结合在一起。在这项工作中，我们比较了由沸石咪唑酯骨架（ZIF）的微晶粉末ZIF-8形成的含钠离子的IL@MOF复合材料与通过溶胶-凝胶合成法制备的同时含有微孔和介孔的分级多孔ZIF-8样品的结构和离子电导率。尽管通过X射线衍射表明晶体结构相同，但通过电子显微镜技术确定了粒径、堆积和形态上的显著差异，这突出了分级孔隙率的来源。在掺入Na0.1EMIM0.9TFSI（缩写为NaIL；EMIM = 1-乙基-3-甲基咪唑鎓；TFSI = 双（三氟甲基磺酰）亚胺）后，分级多孔复合材料的填充容量比纯微孔样品高40%，这通过元素分析和消化质子核磁共振得到了证实。最后，通过电化学阻抗谱探测了复合材料的离子导电性能。结果表明，尽管NaIL@ZIF-8微样品中NaIL的负载量增加了40%，但在25℃时，NaIL@ZIF-8介孔和NaIL@ZIF-8微样品的离子电导率分别为8.4×10-6和1.6×10-5 S cm-1。这些结果例证了微晶孔隙所贡献的长程连续离子通道的重要性，以及不连续介孔对整体离子电导率的有限贡献。
