Capacitive and kinetic characteristics of Ru–Ti oxide electrodes: influence of variation in the Ru content

Abstract

A systematic investigation has been carried out of thermally formed Ru–Ti oxide electrodes of varying Ru content, correlating their voltammetric and impedance characteristics in NaCl solutions with the kinetics of the chlorine evolution reaction. The Tafel slope increases markedly with lower Ru content (< ca. 25 at.%), indicative either of the contribution of increasing oxide resistance or of a change in mechanism. The exchange current density is linearly proportional to the Ru content down to <10 at.% Ru, below which the film appears to respond more like a highly resistive film material. The film resistance and capacitance, determined by equivalent circuit fitting in the absence of dissolved chlorine, were used to calculate the expected impedance response of the oxide film, based on a model of an activation-controlled surface redox reaction occurring in a porous matrix. The calculated results show the dominant signature of the matrix resistance at low Ru loadings, in both the phase angle impedance data and in the Tafel plots, in agreement with the experimental observations. Keywords: Ru oxide, Ru–Ti oxide, chlorine evolution, kinetics, capacitance, equivalent circuit, impedance, Tafel data.