Diffusion of redox active molecules in deep eutectic solvents

Classical electrochemical approaches were evaluated for investigating the basic properties of deep eutectic solvents (DES) with a special focus on the mass transport phenomena and diffusion of charged species in DES. Three classical DES were considered: Reline, Ethaline and choline chloride-lactic acid mixture. Cyclic voltammetries of the ferrocene oxidation and of the ferricyanide reduction, respectively with charge 0 and − 3, exhibit well-defined responses in these media. For all considered DES and redox molecules, diffusion processes govern the mass-transport of the redox molecules from the solution to the electrode. Derived diffusion coefficients were extracted and found to present some inconsistencies with the classical Stokes-Einstein law for homogeneous media. The diffusion coefficients were found to be almost unaffected by the charge present on the diffusing molecules contrarily to observations made for ionic liquids.