A systematic investigation of the mechanistic and electrocatalytic properties of O-2 evolution from acidic solutions was conducted using Ti/RuO2(x) + Co3O4(1 - x) anodes prepared by thermal decomposition (470 degreesC), with x varied between 0 and 100% mel. Kinetics were studied by current-potential curves recorded under quasi-stationary conditions and reaction order determination. At low overpotentials, a Tafel slope of about 30 mV was found for materials having a 30-80%, mol RuO2 content. A reaction mechanism has been proposed accounting for the composition dependence of the Tafel slope and the order of reaction at constant potential. It has been concluded that mixed oxides bring about an increase in the real electrocalalytic activity, which can be attributed to the synergetic or edge effect between the oxide components. A mechanism for the anodic dissolution of Co3O4 is proposed. (C) 2001 Elsevier Science Ltd. All rights reserved.