Charging processes and electrocatalytic properties of IrO2/TiO2/SnO2 oxidefilms investigated by in situ AC impedance measurements

The electrochemical characteristics of thermally prepared oxide films of no minal composition Ir0.3Ti(0.7-x)SnxO2 were examined as a function of x by a c impedance measurements. For potential values in the double layer region, the impedance behavior observed at low frequency was attributed to the doub le layer capacitance of the oxide/electrolyte interface, while at high freq uency it was attributed to a mass transport limited process occurring in di fficult-to-access oxide regions. The main source of ohmic resistance of the system is the solution resistance and low proton transport, necessary for the Ir(III)/Ir(IV) redox transitions to occur in more difficult to reach ox ide regions. The electrocatalytic properties as a function of composition, studied using the OER in 1.0 mol dm(-3) HClO4 as a model reaction, revealed ternary mixture have slightly superior real catalytic properties when comp ared to the binary mixtures. The behavior of the charging processes as a fu nction of composition was analyzed based on the double layer parameters. (C ) 1999 Elsevier Science Ltd. All rights reserved.