Electrochemical characterization of hydrous ruthenium oxide thin-film electrodes for electrochemical capacitor applications

A hydrous ruthenium oxide (Ru O2 ·x H2 O), thin-film electrode with high specific capacitance and good high rate capability was prepared by electrostatic spray deposition for an electrochemical capacitor application. The X-ray diffraction measurements indicated that the as-prepared Ru O2 ·x H2 O transformed to crystalline Ru O2 when annealed at temperatures over 200°C. It was shown that the specific capacitance change during annealing is closely related to the change in the number of reaction sites. The specific capacitance of Ru O2 ·x H2 O increased from 510 Fg for the as-prepared thin film to a maximum value of 650 Fg and then decreased rapidly to 25 Fg during the annealing process as the structural water content was decreased. This pattern was explained in terms of the change in the number of reaction sites, as well as the change in the electron and proton conductivity during dehydration, on the basis of the structural model of a complex nanocomposite of rutile-like ruthenium oxide nanocrystals and structural water proposed by Dmowski [J. Phys. Chem. B, 106, 12677 (2002)].