Physicochemical characterization of mixed RuO2-SnO2 solid solutions

Mixed SnO2-RuO2 oxides were prepared by high-energy mechanical alloying of various proportions of pure SnO2 and RuO2 powders. The physicochemical characterization of the resulting materials was conducted by X-ray diffraction (XRD), scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), and electrochemical surface analysis. It is shown through XRD analysis that a single-phase (tetragonal) (Sn-Ru)O-2 solid solution is formed over the whole composition range, in which the Sn4+ and Ru4+ ions share the same cationic sub-lattice of the rutile-like structure. The surface of the compounds was analyzed by XPS and shows a deficit of Ru atoms, with [Ru](surface) = 36 at. % for an equimolar SnO2-RuO2 concentration in the bulk of the sample. In the case of pure nanocrystalline RuO2, the total surface charge, q(T)*, the most easily accessible surface charge, q(o)*, and the less easily accessible surface charge, q(1)*, are 35.3, 29.0, and 6.3 mC cm(-2) mg(-1), respectively. These surface charges vary linearly with the Ru content at the surface of the electrode, indicating that the surface electrochemical properties of the compounds are dominated by the redox properties of the Ru4+ cation. The ratio q(o)*/q(T)* is close to 0.8 and independent of the surface composition, suggesting that all compounds have a similar morphology.