Physical electrochemistry of ceramic oxides

Surface Chemistry of Ruthenium Dioxide in Heterogeneous Catalysis and Electrocatalysis: From Fundamental to Applied Research

Electrochemical impedance spectroscopy was conducted on a series of hydrous ruthenium oxides, RuO(2).xH(2)O, (x = 0.5, 0.3, 0) and a layered ruthenic acid hydrate (H(0.2)RuO(2.1).nH(2)O) in order to evaluate their protonic and electronic conduction. The capacitor response frequency was observed at lower frequency for RuO(2).xH(2)O with higher water content, which was suggested to be due to electrolyte exhaustion within the film and/or utilization of hydrated interparticle micropores that have high ionic resistance. Analysis of the impedance data indicated that the charge-transfer resistance through the film is not significantly affected by the water content in RuO(2).xH(2)O, and the capacitor frequency response is dominated by the protonic conduction. The capacitor response frequency of layered H(0.2)RuO(2.1).nH(2)O was comparable to RuO(2).0.5H(2)O. The high specific capacitance at low frequency for layered H(0.2)RuO(2.1).nH(2)O is attributed to the utilization of the expandable hydrous interlayer, which accounts for the ionic conduction. The present results demonstrate the importance of hydrous regions (either interparticle or interlayer) to allow appreciable protonic conduction for high energy and high power electrochemical capacitors.

Proton and electron conductivity in hydrous ruthenium oxides evaluated by electrochemical impedance spectroscopy: the origin of large capacitance.

In the search for a DSA®-type electrode for oxygen evolution in acidic solutions, nine binary coatings with IrO2, RuO2, Pt as conducting component, and TiO2, ZrO2, Ta2O5 as inert oxides, have been deposited on titanium, examined for their microstructural properties and tested for their electrocatalytic activity and anodic stability. Electrochemical “true” surfaces of the coatings were found to be dependent on structure and morphology: the mixtures that form a solid solution (RuO2−TiO2), or allow limited miscibility (IrO2−TiO2), show the lowest dispersion of active material. Differences in service lives, were attributed to differences in wear mechanism of the electrodes. It was found that Ti/IrO2 (70 mol%)-Ta2O5 (30 mol%) is by far the best electrode.

Characterization of DSA-type oxygen evolving electrodes: choice of a coating

Ruthenium dioxide is an important electrode material for applications in electrocatalysis and power sources. High surface areas are achieved in hydrous RuO2 precipitates and in mixed ruthenium oxide−titanium oxide, (Ru−Ti)Ox, aerogels (in which nanoscale domains are networked to form a highly porous structure). The electrochemical properties of (Ru−Ti)Ox aerogels, RuO2, and hydrous RuO2 are examined by direct pressing of sub-milligram quantities of the solid onto the surface of a conductive carbon/wax composite. Voltammetric measurements in acidic electrolyte confirm a pseudocapacitive response for all the RuOx-based materials. Despite an improvement in BET surface area, as compared with other RuO2 materials, the (Ru−Ti)Ox aerogel displays a low specific capacitance, which correlates to the high degree of crystallinity of the aerogel. Nanocrystallites of rutile RuO2, formed during thermal treatment of the sol−gel Ru/Ti precursors, deleteriously affect the specific capacitance of the material; however, all...

Voltammetric Characterization of Ruthenium Oxide-Based Aerogels and Other RuO2 Solids: The Nature of Capacitance in Nanostructured Materials

Using a refined technique, thin, homogeneous RuO2 films were prepared reproducibly on highly polished Ti surfaces by thermal decomposition of ruthenium salts The produced electrodes were investigated with electrochemical techniques Chronocoulometry experiments were found to be particularly useful because they permitted a clear separation of surface and bulk processes – The oxidation state of the surface Ru atoms was found to change in the potential range between hydrogen and oxygen evolution in 1 M H2SO4 from +2 to +6 Hydrogen adsorption is proposed at potentials more cathodic than +04 V (RHE) The associated bulk diffusion processes are discussed

Electrochemical Oxidation and Reduction of the RuO2/Ti Electrode Surface

Elektroden, die durch Aufbringen (Zerstauber-System) reproduzierbarer Mengen von Ru-Salzlosungen auf polierte Ti-Oberflachen und anschliesende thermische Oxidation zu RuO2 hergestellt wurden, werden in 1M H2SO4-Losung cyclisch voltammetrisch und durch Potentialsprungexperimente untersucht.

Z. Ogumi

Papers

Electrochemical Oxidation and Reduction of the RuO2/Ti Electrode Surface

Electrochemical oxidation and reduction of the ruthenium dioxide/titanium electrode surface