Ruthenium oxide metallic conductivity

The number of studies which utilize ionic liquid electrol54e in redox capacitor system is still small, probably due to the difficulty to reproduce the pseudo-capacitive reaction in ionic liquid media. While the principle of pseudo-capacitance of conductive polymer electrodes permits to utilize ionic liquid electrolytes, high viscosity and rather inactive ions of ionic liquid may make their pseudo-capacitive reaction slow. The combination of nanostmctured conductive polymer electrode and ionic liquid electrolyte is expected to be effective [27]. It is far difficult that ionic liquids are utilized in transition metal-based redox capacitors where proton frequently participates in the reaction mechanisms. Some anions such as thiocyanate have been reported to provide pseudo-capacitance of manganese oxide [28]. The pseudo-capacitance of hydrous ruthenium oxide is based on the adsorption of proton on the electrode surface and thus requires proton in electrolyte. Therefore ionic liquids having proton have been attempted to be utilized with ruthenium oxide electrode [29]. Recent report that 1,3-substituted imidazolium cations such as EMI promote pseudo-capacitive reaction of mthenium oxide is interesting on the viewpoint of the establishment of the pseudo-capacitive system based on chemical nature of ionic liquids [30]. 

Metallic conduction is only used in inks with very low resistances. The glass-barrier effect, explained by the ofher mechanisms, allows a broad range of sheet resistivities vs. the raho volume of metal-oxide particles (Ruthenate — ruthenium compounds like Ru02 or Bi02Ru07) to the glass matrix. With 6 to 60% of ruthenate, sheet resistivities between 1 mfl/n and 10 Q/n can be achieved (Figure 9.4). 

Several metal oxides with varying phase structures and nanostructures have been developed, including manganese oxide, iron oxide, molybdenum oxide, tin oxide, and titanium oxide. The most prominent issues surrounding transition metal oxide development efforts are (1) limited electronic conductivity and low theoretical capacitance in comparison to ruthenium oxide and (2) poor cyclability due to their redox nature and electrochemical instabilities. The varying electrochemically stable potential windows for some species of metal oxides completely eliminate their potential applications in ES devices. 

The properties typically specified for metal or conductive oxide powders may include particle size and size distributions, surface area, tap and/or bulk densities, critical impurity levels, loss on ignition, and morphological characteristics. Metal powders can be utilized in various shapes, including spheres, flakes, and combinations of both. Their particle sizes can range from submicrometer to 20 /tm. In the case of conductive oxides such as ruthenium oxide used in resistor formulations, the surface areas can approach 100 mVg, which translates to a particle size of less than 10 /tm. The state of agglomeration becomes particularly important for these types of powders. 

Recently it has been shown that the oxides of the platinum metals can have a higher corrosion resistance than the metals themselves , and have sufficient conductivity to be used as coatings for anodes, e.g. with titanium cores. Anodes with a coating of ruthenium dioxide are being developed for use in mercury cells for the electrolysis of brine to produce chlorine , since they are resistant to attack if in contact with the sodium-mercury amalgam. 

A thin layer deposited between the electrode and the charge transport material can be used to modify the injection process. Some of these arc (relatively poor) conductors and should be viewed as electrode materials in their own right, for example the polymers polyaniline (PAni) [81-83] and polyethylenedioxythiophene (PEDT or PEDOT) [83, 841 heavily doped with anions to be intrinsically conducting. They have work functions of approximately 5.0 cV [75] and therefore are used as anode materials, typically on top of 1TO, which is present to provide lateral conductivity. Thin layers of transition metal oxide on ITO have also been shown [74J to have better injection properties than ITO itself. Again these materials (oxides of ruthenium, molybdenum or vanadium) have high work functions, but because of their low conductivity cannot be used alone as the electrode. 

Titanium dioxide is a catalytically inactive but rather corrosion-resistant material. Ruthenium dioxide is one of the few oxides having metal-like conductivity. It is catalytically quite active toward oygen and chlorine evolution. However, its chemical stability is limited, and it dissolves anodically at potentials of 1.50 to 1.55 V (RHE) with appreciable rates. A layer of mixed titanium and ruthenium dioxides containing 1-2 mg/cm of the precious metal has entirely unique properties in terms of its activity and selectivity toward chlorine evolution and in terms of its stability. With a working current density in chlorine evolution of 20 to 50mA/cm, the service life of such anodes is several years (up to eight years). 

Physical properties of binary or ternary Ru/Ir based mixed oxides with valve metal additions is still a field which deserves further research. The complexity of this matter has been demonstrated by Triggs [49] on (Ru,Ti)Ox who has shown, using XPS and other techniques (UPS, Mossbauer, Absorption, Conductivity), that Ru in TiOz (Ti rich phase) adopts different valence states depending on the environment. Possible donors or acceptors are compensated by Ru in the respective valence state. Trivalent donors are compensated by Ru5+, pentavalent acceptors will be compensated by Ru3+ or even Ru2+. In pure TiOz ruthenium adopts the tetravalent state. The surface composition of the titanium rich phase (2% Ru) was found to be identical to the nominal composition. 

T/6-Arene ruthenium and osmium offer specific properties for the reactivity of arene ligand. The activation toward nucleophiles or electrophiles is controlled mainly by the oxidation state of the metal (II or 0). Recently, from classic organometallic arene ruthenium and osmium chemistry has grown an area making significant contributions to the chemistry of cyclo-phanes. These compounds are potential precursors of organometallic polymers which show interesting electrical properties and conductivity. 

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