Kinetic Study of the Ferrocene Complex in Binary Ionic Liquid Media

A binary ionic liquid (ILs)-based electrolyte with advanced physicochemical properties has been successfully prepared. The ionic conductivity (σ) values of ILs [C₄mim][PF₆] and [C₄mim][Tf₂N] were measured using electrochemical impedance spectroscopy are 2.12 and 4.75 mS/cm at 30 °C, respectively. The results of electrode kinetics measurement using cyclic voltammetry revealed a value of the diffusion coefficient (D) of ferrocene in [C₄mim][PF₆] of 3.3 x 10^-7 cm²/s and [C₄mim][Tf₂N] 1.60 x 10^-6 cm²/s. The ferrocene complex obtained has an electron transfer rate constant (k_s) of 7.9 x 10^-4 cm/s in [C₄mim][PF₆] and 1.82 x 10^-3 cm/s in [C₄mim][Tf₂N]. The addition of [C₄mim][Tf₂N] to [C₄mim][PF₆] increased ionic conductivity, diffusion coefficient, and electron transfer rate constant overall, but only to the range of pure ILs. Furthermore, changes in conductivity, diffusion coefficient, and electron transfer rate constant value are proportional to temperature changes, according to the Arrhenius equation. Based on the diffusion activation energy (Ea_D) and the slight decrease in conductivity with temperature, [C₄mim][PF₆]_0.50-[C₄mim][Tf₂N]_0.50 is a superior electrolyte candidate at low-temperature operation.