Kinetics of the Fe(CN)6/Fe(CN)6 couple at passive titanium electrodes

The Fe(CN)^3-₆/Fe(CN)^4-₆ reactions have been studied by stationary and transient polarization measurements on potentiostatically well stabilized (18–20 h) passive titanium electrodes at 25°C. The reactions appear first order in reactant dependence, provided an extra inhibiting effect of Fe(CN)^4-₆ is built into the rate constants. They further depend on the electrode potential, the solution pH, the passive film thickness and the way of forming the passive film. The results support that the electron exchange mainly occurs with the metal through thin passive films (< 45 Å) and with the conduction band in the oxide of thicker films.