PHYSICOCHEMICAL PROPERTIES OF THERMALLY PREPARED TI-SUPPORTED IRO2+ZRO2 ELECTROCATALYSTS

Thermally prepared mixed-oxide IrO2+ZrO2 films have been studied by Ru therford backscattering spectrometry (RBS), wide-angle X-ray scatterin g (WAXS) and cyclic voltammetry. Concentration depth profiling by RBS has shown that electrode films containing less than 50 mol.% of iridiu m dioxide have layered structures where noble metal oxide and zirconiu m oxide enrichments alternate. The outermost layer is enriched with ir idium oxide. By WAXS analysis it was possible to prove the existence o f an IrO2 and a ZrO2 phase. From cell parameters, Very limited solubil ity could be ascertained, restricted at the two limits of the composit ion coordinate. In the range 0-20 mol.% of iridium dioxide, a tetragon al ZrO2 phase is formed. For samples richer in IrO2, the ZrO2 phase be comes amorphous. The microstructural features of the tetragonal IrO2-r ich phase do not change significantly with the film composition. The e ffective surface area of the samples, as determined by cyclic Voltamme try, exhibits a maximum in the composition range 50-80 mol.% IrO2. Thi s result has been interpreted on the basis of WAXS and RBS data.