Comparing the Thermal and Electrochemical Stabilities of Two Structurally Similar Ionic Liquids

Here we focus on the thermal and variable temperature electrochemical stabilities of two ionic liquids (ILs) having a common tributyloctyl phosphonium cation [P(4,4,4,8)](+) and two different orthoborate anions: bis(mandelato)borate [BMB](−) and bis(salicylato)borate [BScB](−). The thermo-gravimetric analysis data suggest that [P(4,4,4,8)][BScB] is thermally more stable than [P(4,4,4,8)][BMB] in both nitrogen atmosphere and air, while the impedance spectroscopy reveals that [P(4,4,4,8)][BScB] has higher ionic conductivity than [P(4,4,4,8)][BMB] over the whole studied temperature range. In contrast, the electrochemical studies confirm that [P(4,4,4,8)][BMB] is more stable and exhibits a wider electrochemical stability window (ESW) on a glassy carbon electrode surface as compared to [P(4,4,4,8)][BScB]. A continuous decrease in the ESWs of both ILs is observed as a function of operation temperature.