KINETICS MEASUREMENTS ON A STATIONARY DISK ELECTRODE IN A UNIFORMLY ROTATING FLUID (SDERF) .2. 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 (rr) to the electrode radius (re)(rr/re = 0.50 to 0.81) have been studied. The activation energy for the redox process in 1 M KCl and 1 M KNO3 are: Ea = 3.4 ± 0.6 kcal/mol and Ea = 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 {reversed tilde equals} 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 {reversed tilde equals} 19 for our cell. © 1979.