ELECTROCHEMICAL SURFACE CHARACTERIZATION OF IRO2+SNO2 MIXED-OXIDE ELECTROCATALYSTS

Mixed oxide layers of SnO2 + IrO2 were prepared over the whole composition range by thermal decomposition of non-aqueous solutions of SnCl2 + IrCl3 on Ti at 400 degrees C. This temperature was chosen after analysing the electrochemical behaviour of 30 mol% IrO2 + 70 mol% SnO2 layers in the range of calcination temperatures 300 to 500 degrees C. The morphology of the layers was observed using a scanning electron microscope. The surface electrochemical properties were studied by cyclic voltammetry at varying potential scan rate. The surface composition, determined from the shape of the voltammetric curves, was found to agree qualitatively with data obtained by Auger electron spectroscopy. The surface layer is strongly enriched with Ir. The ''porosity'' was obtained by extrapolating the voltammetric charge as a function of the scan rate nu to nu = 0 and nu = infinity. The morphology was found not to vary with the chemical composition. The ''looseness'' of the active layer was scrutinized from the voltammetric response.