Electrode Kinetics of Ferrocenium/ferrocene in Room-temperature ionic Liquids

摘要

The diffusion coefficients and heterogeneous rate constants of ferrocenium/ferrocene ([Fe(Cp)_2]~+/Fe(Cp)_2) were investigated in order to elucidate the role of solvent dynamics on the electrode kinetics in hydrophobic room-temperature ionic liquids based on bis(trifluoromethylsulfonyl)imide (TFSr). The [Fe(Cp)_2]~+/Fe(Cp)_2 redox reaction was reversible from cyclic voltammetry of a platinum electrode. The diffusion coefficient of Fe(Cp)_2 was inversely proportional to the viscosity of the ionic liquid. The diffusion coefficients of [Fe(Cp)_2]~+ in the ionic liquids were smaller than those of Fe(Cp)2 because of the Coulombic interaction between charged species and the ionic liquids. The apparent heterogeneous rate constants of [Fe(Cp)_2]~+/Fe(Cp)_2 estimated by the electrochemical impedance spectroscopy in the ionic liquids were smaller than those in organic solvents. The heterogeneous rate constants correlate with the viscosity of the electrolytes probably due to the slow dynamics of the ions composing the ionic liquids.