Synthesis of Ruthenium Dioxide−Titanium Dioxide Aerogels: Redistribution of Electrical Properties on the Nanoscale

High-surface area RuO 2 −TiO 2 is an important material for catalytic and power source technologies. To create this mixed oxide as a nanoscale, high-surface-area material, we have synthesized electrically conductive aerogels of Ru n Ti 1- n O x via sol−gel chemistry and supercritical drying of the resulting gel. The structural and electrical properties of these aerogels are characterized after annealing using X-ray diffraction, X-ray photoelectron spectroscopy, surface-area measurements, and impedance spectroscopy. Their properties are affected by the nature of the RuCl 3 precursor and the initial sol-gel chemistry. Whereas bulk 32 mol % RuO 2 ·TiO 2 is an electronic conductor, a dominant ionic response is measured in the impedance of Ru 0.32 Ti 0.68 O x aerogels. This impedance is ascribed to a proton conduction mechanism associated primarily with the hydrous surface of the RuO x component. The electrical conductivity of these Ru 0.32 Ti 0.68 O x aerogels at 25 °C increases from 10 -4 S cm -1 in ambient air to 10 -2 S cm -1 under an increased partial pressure of water, which is characteristic of a protonic conductor. The electronic conductivity of these aerogels improves with exposure to dry oxygen, which is consistent with the oxidation of Ru 3+ surface defects. Synthesizing RuO 2 −TiO 2 as an aerogel i.e., as high-surface-area, networked interface accentuates the surface properties of this material. The electrical (electronic + protonic) transport properties of bulk RuO 2 −TiO 2 are redistributed when synthesized as an aerogel. Whereas electronic transport dominates the characteristics of the dense form, the protonic transport of the hydrous oxide surfaces governs the electrical properties of the aerogel. Aerogels provide a useful means to isolate, study, and control the surface of metal oxides.