Charge transfer reactions on oxide‐covered Ti Electrodes: Effect of dielectric constant variation and oxide stabilization

Abstract

The electron transfer kinetics of the Fe"/Fe'+ 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 (Na2S04 + H~SOJ) at a scan rate of 1 mV s-'. The cathodic and anodic Tafel lines were also measured at the same scan rate.The logarithm of the exchange current density io 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 02-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.