Electrochemical behavior of Eu(III), Ce(IV) and U(VI) in 1-hexyl-3-methylimidazolium bromide

With the advent of moisture-stable room-temperature ionic liquids (RTILs), the research on these neoteric solvents grew rapidly during the past two decades. Main features of these solvents are their unique physicochemical properties, low volatility, high chemical, thermal and radiation stability, solvating ability, wide electrochemical window and good conductivity etc. These solvents can be synthesized relatively easily, following numerous combinations by altering the cationic and anionic moieties result in tunable properties. These very characteristics of the ionic liquids have led to lots of interest in their use as alternatives to conventional organic solvents in wide ranging synthetic, catalytic and electrochemical applications. Cyclic voltammetric studies involving U, Ce and Eu were carried out in C6mimBr, a hydrophilic RTIL, which has a moderately large electrochemical window of ∼2.0 V. The rate constant of the reduction reaction of the metal ions were evaluated and it was observed that the reduction of U(VI), Ce(IV) and Eu(III) is quasi reversible and the reduction kinetics follow the trend of U(VI) < Eu(III) < Ce(IV). The diffusion coefficients (D) for the metal ions and activation energies (Ea) for diffusion were also determined. It was also observed that at a particular temperature, the diffusion coefficient followed the order, DCe(IV) > DEu(III) > DU(VI) which was explained on the basis of ionic size. Reduction of the metal ions was also carried out at varying temperatures and thermodynamic parameters such as changes in Gibbs free energy, enthalpy and entropy and of the redox reactions were computed