Journal of Electroanalytical Chemistry, Vol.482, No.2, 188-201, 2000
Electrochemical properties of ruthenised electrodes in the oxide layer region
The impact of increasing the amount of electrodeposited ruthenium and of potential/time treatment of ruthenium substrates on the electrochemical properties of anodically formed ruthenium oxide films, are investigated by use of cyclic voltammetry, electrochemical quartz crystal microbalance, anodic and cathodic current transients, and electrochemical impedance spectroscopy. In addition to the specific interpretation of results obtained by each of the techniques used, general discussion in terms of the essential charge storage characteristics of ruthenium oxide films is presented. It is shown that an increase in the ruthenium loading acts beneficially on the stability of oxide films over a range of potentials, but detrimentally on the kinetics of the overall charging/discharging reaction, which becomes proton mass transfer limited. On the other hand, potential/time treatment of ruthenium substrates acts detrimentally on the stability of related oxide films, but makes the kinetics of the oxide film charging/discharging reaction more reversible. Total capacitance values of oxide films presented per gram of electrodeposited ruthenium are found to be almost independent of ruthenium loading, and slightly increased by the potential/time treatment performed. This all points to the fact that an increase in the ruthenium loading and potential/time treatment of ruthenium substrates results primarily in beneficial changes in the morphology of related oxide films. The magnitudes of the total capacitances per gram of electroplated ruthenium, however, remain strongly determined by the method of preparation of ruthenium substrates, and cannot be significantly changed by either an increase in the ruthenium loading or by the potential/time treatment of the ruthenium substrates.
Keywords:ruthenium;supercapacitors;anodic oxidation;hydrous ruthenium oxide;charge storage;impedance spectroscopy;electrochemical quartz crystal microbalance