Kinetics measurements on a stationary disk electrode in a uniformly rotating fluid (SDERF). II. The electron transfer reaction in the Fe(CN)4?6/Fe(CN)3?6-system

The operation of the SDERF-cell in the study of the electron transfer kinetics of the Fe(CN)^4?₆/Fe(CN)^3?₆-system in 1 M KCl and 1 M KNO₃-solutions at a stationary Pt-disk electrode is reported. The experimental current—overpotential curves are recorded by linear sweep voltammetry and analysed by two different methods using the theoretical relationship derived for a stationary disk electrode placed in a free rotating fluid. Both methods give the same value for the experimental rate constant k*. The effects of the temperature (0° to 40°C) and of the ratio of the rotor radius (r_r) to the electrode radius (r_e)(r_r/r_e = 0.50 to 0.81) have been studied. The activation energy for the redox process in 1 M KCl and 1 M KNO₃ are: E_a = 3.4 ± 0.6 kcal/mol and E_a = 3.7 ± 0.7 kcal/mol respectively, while the k*-values at 25°C are: k* = (5.67 ± 0.41) × 10^?3 cm.s^?1 and k* = (4.53 ± 0.29) × 10^?3 cm.s^?1 respectively. The difference from the standard rate constant k₀ ? 0.100 cm.s^?1 is explained by the effect of the cell-geometry characterized by the G-factor, so that k° = Gk*, where G ? 19 for our cell.