Electrochemical properties of hydrous ruthenium oxide films formed and measured at different potentials

An attempt is made to describe the electrochemical properties of hydrous ru thenium oxide films in the acid sulphate electrolyte solution over a broad range of polarisation potentials. The influence of the potential/time pre-t reatment of the ruthenium substrates and three different potentials of the oxide film formation on the electrochemical behaviour of the oxide films ge nerated are followed by impedance and current transient measurements. It is shown that all oxide films exhibited charge-storage/delivery properties ov er a certain range of polarisation potentials with nearly equal total (pseu do)capacitance values that indicate no influence of either the formation po tential or the ruthenium pre-treatment procedure on the quantity of active metal sites. There is, however, a significant influence of the ruthenium pr e-treatment procedure on the content of proton oxygen sites (OH-, H2O speci es) that is responsible for the degree of kinetic inhibition of the charge- storage/delivery reaction, the fraction of the capacitance that is availabl e rapidly, the stability of the films towards the total film reduction, and the formation of the maximum possible oxidation level of the oxide films, The different contents of the proton oxygen sites are related to the differ ent contents of water molecules inside the differently pre-treated rutheniu m substrates prior to anodic oxidation. The potential of formation acts pre dominantly on the average oxidation state of ruthenium inside the oxide fil ms initially formed. The electrochemical behaviour of the oxide films over a descending range of potentials is determined by the properties of the oxi de films initially formed. The electrochemical behaviour of the oxide films over the range of increased potentials is determined by the polarisation p otential and the content of available proton oxygen sites, irrespective of the formation potential. (C) 2001 Elsevier Science B.V. All rights reserved .