Stability and kinetics of generated superoxide ion in trifluoromethanesulfonate anion-based ionic liquids

The generation and long-term stability of superoxide ion (O₂^•-) in two trifluoromethanesulfonate [TfO]^- anion-based ionic liquids (ILs), with cations of 1-butyl-1-methylpyrrolidinium [BMPyrr]⁺ and 1-butyl-2,3-dimethylimidazolium [BDMIm]⁺ have been investigated. The electrochemical generation was carried out by reducing O² to O₂^•- in ILs and was analyzed using a cyclic voltammetry (CV) technique. The chemical generation of O₂^•- in ILs was carried out by the solvation of potassium superoxide (KO²) in the aprotic solvent, dimethyl sulfoxide, in the presence of the corresponding IL. Long-term stability of generated O₂^•- in ILs was examined using UV-visible spectrophotometery at an absorbance range of 190-400 nm. It was found that the [BMPyrr]⁺ based IL has a lower O₂^•- consumption rate than the [BDMIm]⁺ based ILs indicating that [BMPyrr][TfO] offers a promising long-term stability of O₂^•- for various reactions and applications. This work represents the first attempt for using the [TfO]^- based ILs as media for the chemical and electrochemical generation of O₂^•-.