Formation of an organic film on an electrode via a suspension of redox-active droplets in acidic aqueous solution

[Display omitted] •Stable voltammograms were obtained in a suspension of redox-active droplets.•The formation of a liquid film of the organic phase was detected.•Part of the film stays on the electrode after transfer to an aqueous electrolyte. Previous electrochemical studies of redox emulsions have been mainly performed in the context of electro-organic synthesis. More recently, this research has been oriented towards applications of emulsions in flow batteries. Such biphasic systems seem to provide a suitable environment for reactions at the liquid–liquid interface. Taking an emulsion consisting of microdroplets of decamethylferrocene solution in a hydrophobic ionic liquid/toluene mixture in acidic aqueous solution as an example, we have demonstrated that an electrochemical redox reaction involving the hydrophobic redox probe occurs at the glassy carbon electrode|organic liquid film interface. This reaction is followed by ion exchange between liquid phases. This effect is explained by the instability of the emulsion. A portion of the organic liquid stays on the electrode surface after transfer to a purely aqueous electrolyte and remains electroactive.