Electrochemical properties of ruthenised electrodes in the oxide layer region

The impact of increasing the amount of electrodeposited ruthenium and of po tential/time treatment of ruthenium substrates on the electrochemical prope rties of anodically formed ruthenium oxide films, are investigated by use o f cyclic voltammetry, electrochemical quartz crystal microbalance, anodic a nd 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 st orage characteristics of ruthenium oxide films is presented. It is shown th at an increase in the ruthenium loading acts beneficially on the stability of oxide films over a range of potentials, but detrimentally on the kinetic s of the overall charging/discharging reaction, which becomes proton mass t ransfer limited. On the other hand, potential/time treatment of ruthenium s ubstrates acts detrimentally on the stability of related oxide films, but m akes the kinetics of the oxide film charging/discharging reaction more reve rsible. Total capacitance values of oxide films presented per gram of elect rodeposited ruthenium are found to be almost independent of ruthenium loadi ng, and slightly increased by the potential/time treatment performed. This all points to the fact that an increase in the ruthenium loading and potent ial/time treatment of ruthenium substrates results primarily in beneficial changes in the morphology of related oxide films. The magnitudes of the tot al capacitances per gram of electroplated ruthenium, however, remain strong ly determined by the method of preparation of ruthenium substrates, and can not be significantly changed by either an increase in the ruthenium loading or by the potential/time treatment of the ruthenium substrates. (C) 2000 E lsevier Science S.A. All rights reserved.