Unusual anodic behaviour of chloride ion in 1-butyl-3-methylimidazolium hexafluorophosphate

The anodic discharge of chloride ion on platinum and graphite electrodes was investigated in a typical room temperature ionic liquid, 1-butyl-3-methylimidazolium hexafluorophosphate ([BMIM]PF6) in the presence of high concentrations of 1-butyl-3-methylimidazolium chloride ([BMIM]Cl). The unusual observation is that during constant potential or current electrolysis, the oxidation of the chloride ion did not lead to chlorine gas evolution. Investigation by cyclic voltammetry and UV-Vis spectrometry revealed that the anodic products of the electrolysis, including Cl2 and Cl3-, were retained in the ionic liquid.