Thiocyanate-functionalized ionic liquids (ILs) 1-butyl-3-methylimidazolium thiocyanate [BMIM][SCN], 1-ethyl-3-methylimidazolium thiocyanate [EMIM][SCN], and 3-methylimidazolium thiocyanate [MIM][SCN], with varying chain lengths, were synthesized by using metathesis followed by ion exchange under reflux conditions. These ILs were investigated for their application as electrolyte with a ZnFe2O4 nanoflake-based supercapacitor electrode; they exhibited significantly better performance than any other previously reported ILs used as electrolytes. [BMIM][SCN] showed higher specific capacitance (781 F g-1), cycle stability (95 % retention, 3000 cycle), and energy density (156 W h kg-1) than [EMIM][SCN] (590 F g-1, 86 % retention, and 78 W h kg-1) and [MIM][SCN] (250 F g-1, 80 % retention, and 50 W h kg-1). The ZnFe2O4 nanoflake electrodes were able to deliver an energy density of 156 W h kg-1 even at an extra high power density of 7.11 kW kg-1 in [BMIM][SCN] electrolyte, justifying its utility as a potential electrolyte. Furthermore, the effect of how the hydrated ions of the ILs in aqueous media influence the overall performance of the supercapacitor was studied systematically and found to be contrary to the reported trend and use of pure ILs as electrolytes.
- Ionic liquids