Annealing effects on the physicochemical characteristics of hydrous ruthenium and ruthenium–iridium oxides for electrochemical supercapacitors

The electrochemical (EC) properties and stability of hydrous ruthenium oxide (denoted as RuOx·nH2O) and ruthenium–iridium oxide (denoted as (Ru+Ir)Oy·mH2O) were systematically investigated in 0.5 M H2SO4 by cyclic voltammetry (CV) and chronopotentiometry (CP). The EC characteristics of RuOx·nH2O and (Ru+Ir)Oy·mH2O annealed at temperatures equal to/above 200 °C were demonstrated to be more applicable for the EC supercapacitors. The crystalline information of these oxides annealed in air for 2 h up to 300 °C was obtained from the X-ray diffraction (XRD) spectra. The morphologies of these oxide-coated electrodes were examined by a scanning electron microscope (SEM). The effect of annealing temperatures on the surface composition of (Ru+Ir)Oy·mH2O was studied by X-ray photoelectron spectroscopy (XPS).