Physicochemical properties of thermally prepared Ti-supported IrO2 + ZrO2 electrocatalysts

Thermally prepared mixed-oxide IrO2+ZrO2 films have been studied by Rutherford backscattering spectrometry (RBS), wide-angle X-ray scattering (WAXS) and cyclic voltammetry. Concentration depth profiling by RBS has shown that electrode films containing less than 50 mol.% of iridium dioxide have layered structures where noble metal oxide and zirconium oxide enrichments alternate. The outermost layer is enriched with iridium oxide. By WAXS analysis it was possible to prove the existence of an IrO2 and a ZrO2 phase. From cell parameters, Very limited solubility could be ascertained, restricted at the two limits of the composition coordinate. In the range 0-20 mol.% of iridium dioxide, a tetragonal ZrO2 phase is formed. For samples richer in IrO2, the ZrO2 phase becomes amorphous. The microstructural features of the tetragonal IrO2-rich phase do not change significantly with the film composition. The effective surface area of the samples, as determined by cyclic Voltammetry, exhibits a maximum in the composition range 50-80 mol.% IrO2. This result has been interpreted on the basis of WAXS and RBS data.