A systematic investigation was conducted on the mechanism and electrocatalytic properties Of 02 and Cl, evolution on mixed oxide electrodes of nominal composition: Ti/[Ru(0.3)Ti(0.6)CC(0.1-x)1]O-2[Nb2O5]((x)) (0 <= x <= 0. 1). For the oxygen evolution, a 30 mV Tafel slope is obtained in the presence of CeO2, while in its absence a 40 mV coefficient is observed. The intrinsic electrocatalytic activity is mainly due to electronic factors, as result of the synergism between Ru and Cc oxides. For chlorine evolution, the Tafel slope (30 mV) is independent on oxide composition. The best global electrocatalytic activity for CIER was observed in the absence of Nb2O5 additive. Variation of the voltammetric charge throughout the experiments confirms high CeO2 content compositions are fragile, due mainly to the porosity caused by CeO2 presence. On the other hand, Nb2O5 addition decreases considerably this instability. (c) 2005 Elsevier Ltd. All rights reserved.