Kinetic study of the chlorine electrode reaction on Ti/RuO2 through the polarisation resistance Part III:: proposal of a reaction mechanism

A kinetic mechanism for the chlorine electrode reaction (ClER) on Ti/RuO2, electrodes is proposed. The first step is the oxidation of the superficial sites, where the chloride ion is electroadsorbed giving the atomic chlorine intermediate. The later discharge of chlorine can take place either by recombination of two adsorbed intermediates or by the reaction between the intermediate and the chloride ion, being both chemical steps. The expression of the intrinsic polarisation resistance Rp(o), as a function of the activity of chloride a(Cl-)(o*) and the partial pressure of chlorine (p) over bar (Cl2) was obtained from the resolution of the kinetic mechanism and it was compared with experimental data. The correlations of the independent experimental relationships Rp(o). versus a(Cl-)(o*) and Rp(o) versus (p) over bar (cl2) were remarkably good, giving strong evidence that the ClER takes place through the proposed mechanism on the RuO2 electrodes. The kinetic constants obtained from the correlations were used for the simulation of the dependences of the current density and the surface coverages on overpotential. (C) 2002 Elsevier Science Ltd, All rights reserved.