Abstract
In this work, two new redox-active ionic liquids, one based on 2,2,6,6-tetramethylpiperidine-N-oxide and the other based on 4,4′-bipyridine, are synthesized and characterized. A ferrocene-based redox-active ionic liquid is used for referencing the results. All ionic liquids are formed via salt-metathesis from halogenate to bis(trifluoromethylsulfonyl)imide. Their fundamental thermal characteristics are assessed with differential scanning calorimetry. While the imidazolium ionic liquids show no melting point, the phase transition is well observable for the viologen-based ionic liquid. The properties of the neat redox-active ionic liquids and of binary mixtures containing these ionic liquids (0.1 m) and 1-butyl-1-methyl pyrrolidinium-bis(trifluoromethylsulfonyl)imide have been investigated. Finally, the use of these binary mixtures in combination with activated carbon-based electrodes has been considered in view of the use of these redox-active electrolytes in supercapacitors.
Highlights
With the first described ionic liquid ethylammonium nitrate, which was reported as early as 1914 by Walden, ionic liquids (ILs) are a long-known class of molecules [1]
The field gained further traction after publications from Wilkes and coworkers in 1982, who reported on dialkylimidazolium chloroaluminates [2], and from Grätzel and coworkers in 1996, who reported dialkylimidazolium-based ionic liquids without any metals [3]
It seems beneficial to combine a highly polar with a very points, this cation was selected for the realization of the redox-active ionic liquids (RAILs) considered in this work
Summary
With the first described ionic liquid ethylammonium nitrate, which was reported as early as 1914 by Walden, ionic liquids (ILs) are a long-known class of molecules [1]. There was a lack of further research interest on this class of molecules by the scientific community for nearly half a century before the first reports of bimolecular mixtures with very low melting points, comprising aluminum chloride and ethylpyridinium bromide, were published [1]. The field gained further traction after publications from Wilkes and coworkers in 1982, who reported on dialkylimidazolium chloroaluminates [2], and from Grätzel and coworkers in 1996, who reported dialkylimidazolium-based ionic liquids without any metals [3]. In the early 2000s, the term “task-specific ionic liquid”. Was coined and demonstrated the tuneability of ionic liquids to serve as “designer solvents”. The subject has been reviewed many times, and the interested reader can rely on great reviews, featuring, e.g., the topic from a general point of view [6], as reaction medium [7] and from the perspective of catalysis in cross-coupling reactions [8]
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