Cyclic voltammetry of iron (III) acetylacetonate in quaternary ammonium and phosphonium based deep eutectic solvents

The electrochemical behaviour of commercially sourced iron (III) acetylacetonate is investigated in six different deep eutectic solvents (DESs) formed by means of hydrogen bonding between ammonium and phosphonium salts with glycerol, ethylene glycol and tri-ethylene glycol. Cyclic voltammetry (CV) is employed to determine kinetic and mass transport properties of the electrolytes. Diffusion coefficient, D, of the iron salt in all studied DESs is found to lie between 1.06×10^-9 to 1.08×10^-8 cm² s^-1 (the salt does not dissolve in a DES prepared from choline chloride and glycerol while not producing any measurable CV peaks in a couple of others). The rate constant for electron transfer across the working electrode/DES interface is estimated to lie between 1.34 × 10^-4 and 2.08 × 10^-4 cm s^-1. From a range of criteria for electrolyte selection (peak potential separation near 59 mV for a one-electron transfer reaction, high diffusion coefficient and heterogeneous rate constant) only the ammonium based DESs prepared from choline chloride and ethylene glycol or tri-ethylene glycol appear to be worthy of further investigation.