, vol. 27, pp. 438-443, 1996.
The electron transfer kinetics of the Fe3+/Fe2+ redox couple on the oxide covered Ti electrodes were investigated as a function of the film thickness, film stabilization, and concentration of the redox species. The oxides were formed potentiodynamically in acidic solution of pH=3 (Na2SO4+H2SO4) at a scan rate of 1 mV s−1. The cathodic and anodic Tafel lines were also measured at the same scan rate.
The logarithm of the exchange current density i0 shows an exponential decrease with the oxide film thickness. Direct tunnelling may explain the kinetics of the reaction across thin Ti02 (oxide formed at the potential region before the O2-evolution). Values of the cathodic and anodic transfer coefficients are tabulated. It was found that, the stabilization of the oxide could possibly increase its conductivity. The electron transfer reaction showed a first order dependence on the redox species concentration, independent of the conditions of oxide film formation.