CAPACITIVE AND KINETIC CHARACTERISTICS OF RU-TI OXIDE ELECTRODES - INFLUENCE OF VARIATION IN THE RU CONTENT

A systematic investigation has been carried out of thermally formed Ru -Ti oxide electrodes of varying Ru content, correlating their voltamme tric and impedance characteristics in NaCl solutions with the kinetics of the chlorine evolution reaction. The Tafel slope increases markedl y with lower Ru content (< ca. 25 at.%), indicative either of the cont ribution of increasing oxide resistance or of a change in mechanism. T he exchange current density is linearly proportional to the Ru content down to <10 at.% Ru, below which the film appears to respond more lik e a highly resistive film material. The film resistance and capacitanc e, determined by equivalent circuit fitting in the absence of dissolve d chlorine, were used to calculate the expected impedance response of the oxide film, based on a model of an activation-controlled surface r edox reaction occurring in a porous matrix. The calculated results sho w the dominant signature of the matrix resistance at low Ru loadings, in both the phase angle impedance data and in the Tafel plots, in agre ement with the experimental observations.