Selenocyanate-based ionic liquid as redox-active electrolyte for hybrid electrochemical capacitors

Abstract

This paper describes a hybrid capacitor based on identical activated carbon (AC) electrodes and the 1-ethyl-3-methylimidazolium selenocyanate, [EMIm][SeCN], liquid salt as redox-active electrolyte. [EMIm][SeCN] is a fluorine-free ionic liquid (IL) which combines good charge and mass transport properties (σ = 25 mS cm−1 and η = 17 mPa s−1), as well as redox activity originating from the pseudohalide anion. Owing to the impact of the SeCN−/(SeCN)2 redox couple, the AC/AC capacitor based on this electrolyte displays remarkable discharge (from 1.5 V) capacitance of 49 and 56 F g−1 (expressed per total active mass of electrodes) using aluminum and stainless steel (SSt) current collectors, respectively. Although higher capacitance values were displayed for the hybrid capacitor with SSt components, more advantageous E0 localization for cell hybridization was observed when using Al current collectors.