Thermally activated ruthenium dioxide hydrate. A reproducible, stable oxygen catalyst

Abstract

A detailed investigation has been carried out into the effect of annealing RuO₂·xH₂O at different temperatures on its ability to mediate the oxidation of water, and its stability towards anodic corrosion. The percentage corrosion of the heated samples when exposed to a strong oxidant such as Ce^IV ions decreased with increasing annealing temperature, and at temperatures 140 °C no corrosion was observed, only O₂-catalytic activity. This effect was associated with a decrease in percentage H₂O content of the samples owing to a reduction in the number of defect sites present. Raising the annealing temperature of the powders from 140 to 900 °C caused a concomitant drop in catalytic activity as a result of an observed decrease in crystallite size and surface area available for catalysis measured by X-ray diffraction and transmission electron microscopy-techniques. Thus an annealing temperature of 140–150 °C for the RuO₂·xH₂O samples represented an optimum for catalytic activity where corrosion was absent. When this material was used to catalyse the oxidation of water by Ce^IV ions, it retained its activity after repeated use and was able to generate an amount of O₂ which was 16 times larger than that of the catalyst (in molar terms). In addition, this catalyst was found to mediate the oxidation of water by many other strong oxidants such as BrO^–₃, MnO^–₄, IO^–₄, PbO₂ and MnO₂(activated).