Solvent-Solute Interactions in Ionic Liquid Media: Electrochemical Studies of the Ferricenium- Ferrocene Couple

摘要

Electrochemical studies of the ferricenium/ferrocene ([Fc]~+/[Fc]) redox couple have been carried out in ionic liquids containing the 1-butyl-3-methylimidazolium cation [C_4mim]~+ and the anions [CF_3SO_3]~-, [N(SO_2CF_3)_2]~- and [PF_6]~-. The [Fc]~+/[Fc] couple shows electrochemical reversibility in all cases, and controlled-potential electrolysis of ferrocene to the monocation is chemically reversible. The diffusion coefficients and Stokes-Einstein products of both the oxidized and the reduced species have been determined by using cyclic voltammetry, normal pulse voltammetry and rotating disk electrode voltammetry with both platinum and glassy carbon working electrodes. The solvodynamic radii of the diffusing species in each ionic liquid were estimated using the measured diffusion coefficients and a corrected version of the Stokes-Einstein equation. A dependency of the solvodynamic radii upon the anion of the ionic liquid was observed.