Preparation and Characterization of Mixed-Oxide Electrocatalysts Based on RuO₂ and IrO₂

Abstract

The formation processes of RuO₂/TiO₂, IrO₂/TiO₂ and IrO₂/ZrO₂ film electrodes have been studied by combined thermoanalytical and mass-spectrometric methods. The obtained materials have been characterized by cyclic voltammetry (CV). The precursor path leading to mixed oxides for the first two groups of matetials, consists of several stages, including solvent desorption, oxidative cracking, combustion, noble-metal chloride decomposition. Minima of the temperature of chlorine release and organic combustion have been observed for precursor salt mixtures with intermediate-low noble-metal concentrations. The microstructural investigation, carried out by wide-angle X-ray scattering (WAXS) has shown that solid solutions are formed within quite wide composition ranges for TiO₂-stabilized materials. For the IrO₂/ZrO₂ system, segregation of amorphous ZrO₂ takes place for IrO₂ concentrations ≤ 80 mol-%. For the TiO₂-stabilized samples, the characterization by cyclic voltammetry has shown that maxima of charge-storage capacity are observed for those electrodes whose composition is in the range of minimum temperature for the precursor reaction. A dependence of the faradaic voltammetric charge on the carbon content of the electrode films, as determined by nuclear reaction analysis (NRA), has been shown. The experimental results have been explained hypothesizing that minima of pyrolysis temperature involve less favorable conditions for rearrangements in the reacting films, and, consequently, larger degree of defectivity. In the case of IrO₂/ZrO₂ electrodes, the segregation of the amorphous ZrO₂ phase seems to be main reason for the maximum of charge-storage capacity observed at 80 mol-% of IrO₂.