Generation and stability of superoxide ion in tris(pentafluoroethyl)trifluorophosphate anion-based ionic liquids

Generation of the superoxide ion (O2−) in ionic liquids (ILs) media is one of the important areas which are currently being under investigation by several research groups worldwide. In this work, the superoxide ion was successfully generated and analyzed electrochemically using cyclic voltammetry (CV) and chronoamperometry (CA) techniques from O2 dissolved in 1-(2-methoxyethyl)-1-methylpiperidinium tris(pentafluoroethyl)trifluorophosphate [MOEMPip][TPTP] and trihexyl(tetradecyl)phosphonium tris(pentafluoroethyl)trifluorophosphate [P14,666][TPTP]. Furthermore, O2− was generated chemically by the addition of potassium superoxide to the studied ILs. UV/Vis spectrophotometer was used for testing the long term stability of the generated O2−. These results encourage more exploration on the use of these particular classes of ILs in various applications involving O2−. This study reports the first successful chemical generation of O2− in tris(pentafluoroethyl)trifluorophosphate anion-based ILs which opens the way for further related studies.

O2− was generated electrochemically by reduction of O2 and chemically by solvation of KO2 in [MOEMPip][TPTP] and [P14,666][TPTP]. The diffusion coefficients and solubility of O2 were determined. The long term stability of generated O2− was investigated. It was found that diffusion coefficient of O2 in [P14,666]+ based IL is higher than in [MOEMPip]+based IL while the solubility of O2 is higher in [MOEMPip]+ than in [P14,666]+. The long term stability of O2− tests showed that O2−in [MOEMPip][TPTP] is stable while in [P14,666][TPTP] was unstable.Figure optionsDownload as PowerPoint slideHighlights
► O2− was generated electrochemically and chemically in [MOEMPip][TPTP] and [P14,666][TPTP] ILs mediums.
► The long term stability tests of O2− were conducted.
► Diffusion coefficient of O2 in [P14,666]+ based IL is higher than in [MOEMPip]+ based IL.
► The solubility of O2 is higher in [MOEMPip]+ than in [P14,666]+.
► O2− in [MOEMPip][TPTP] is stable while in [P14,666][TPTP] is unstable.