Electrochemical impedance spectroscopy study during accelerated life test of conductive oxides:: Ti/(Ru+Ti+Ce)O2-system

Ti-supported (Ru + Ti + Ce)O-2-clectrodes were prepared at 450 degreesC and the service life, t(6V), determined recording chronopotentiometric curves at 0.75 A cm(-2) (25 +/- 1 degreesC). The results revealed a strong influence of the nominal cerium concentration, [CeO2](N), on t(6V), showing substitution of Ti by Ce causes a major decrease in t(6V). The degree of electrode instability, A, calculated from the slope of the linear segment present in the chronopotentiometric profiles, showed [CeO2](N) exerts a strong influence on A. Voltammetric curves recorded at several anodisation times, t, support final electrode deactivation is due to Ti-support passivation. The chronopotentiometric and voltammetric data permitted to present a model for the porous electrode/electrolyte interface. The electrochemical impedance spectroscopic, EIS, investigation as function of t supports the proposed model denouncing a fast growth a TiO2 interlayer at the Ti-o/oxide interface for [CeO2](N) greater than or equal to 30 mol%. The studies also support substitution of Ti by Ce leads to an increase in the coating porosity, thus favouring electrode deactivation by passivation of the Ti-substrate. The model proposed for the porous electrode/electrolyte interface combined with the results of the EIS investigation permitted to propose an equivalent circuit to describe the modifications occurring in the electrode structure during anodisation. The true electrocatalytic activity for the oxygen evolution reaction, OER, depends on t and [CeO2](N). The dependency of the inductive behaviour on t was investigated according to the model proposed for the effective inductance, L-E, in the high frequency domain. (C) 2004 Elsevier Ltd. All rights reserved.