OXYGEN EVOLUTION IN ACID-SOLUTION ON IRO2- A STUDY BY IMPEDANCE, VOLTAMMETRY AND SEM(TIO2 CERAMIC FILMS )

Thermally prepared oxide films (2 mu m) of nominal composition Ir0.3Ti 0.7O2 were prepared at 350, 400, 450 and 500 degrees C On a Ti support . Electrochemical impedance spectroscopy (EIS) at constant potential w as used in the range 0.4 to 1.6 V (rhe). The results were fitted by th e equivalent circuit R(Omega)(R(f)C(f))(R(ct)C(dl))L. The R(Omega) val ues obtained by EIS agree with the data derived from kinetic studies. The high R(ct) value of the 350 degrees C oxide layer is attributed to the incomplete decomposition of the precursor so that some of the und erlying insulating TiO2 layer remains uncovered. This view is corrobor ated by SEM and CV studies. Oxide layers prepared at higher temperatur es are stable, the R(ct) values increasing with calcination temperatur e. This is attributed to crystallite size increasing with temperature, resulting in a lower number of active sites being exposed. For all el ectrodes, R(ct) decreases with increasing potential. C-dl depends on b oth surface area and applied potential. At T > 350 degrees C, C-dl dim inishes as temperature increases, which is due to decrease in the acti ve surface area. Analogously, C-dl is observed to increase with increa sing potential, which is associated with the heterogeneity of the elec trode surface. Copyright (C) 1996 Elsevier Science Ltd