Tungsten electrodes, oxide films

Tungsten trioxide thin films activated by gold layers have also been used for NOj. detection.115 This material possesses excellent sensitivity towards nitric oxide and nitrogen dioxide. An automobile exhaust gas NO sensor that uses a gold-platinum alloy electrode has also been reported.116... 

New inorganic electrode films based on molybdenum and tungsten oxides have been introduced for aqueous solutions heteropolyanion electrodes... 

T. Lindgren, Photo Induced Oxidation of Water at Thin Film Electrodes A study of Tungsten Oxide, Herruitite, Indium Nitride and Tin Nitride, in Department of Physical Chemistry. 2001, Uppsala... 

Solarska R, Santato C, Jorand-Sartoretti C, M. Ulmann and J. Augustynski (2005) Photoelectrolytic oxidation of organic species at mesoporous tungsten trioxide film electrodes under visible light illumination. J Appl Electrochem 35 715-721... 

A general schematic for a smart window is shown in Figure 13.10. This device is, quite literally, two chemically modified electrodes sandwiched together. In this case, the films coating the electrode surfaces are electrochromic materials. A polymer electrolyte, analogous to that used in the fuel cell discussed earlier, is sandwiched between these two electrochromic material-coated electrodes. In a recent example of this concept by Habib and Maheswari of General Motors Research Laboratories [94], the cathodic electrochromic material was a tungsten oxide and the cathodic electrochromic material was the material Prussian blue, discussed in Section II of this chapter. It seems likely that electrochromic cells will soon find their way into the commercial marketplace. 

Fig. 6.17. Cyclic voltammograms of o-phenylenediamine (101 M) oxidation for W03 thermal-treated (350°C) anodic films (b) and smooth platinum electrode (c) first sweep (curves 1) and repeated sweep (curves 2) scan rate was 80 mV/cm2. The left picture shows a schematic representation of the morphology of thermal-treated anodic W03 film tungsten support, highly defective oxide (including the continuous donor clusters), moderately doped oxide (non-shaded region), poly-o-phenylenediamine deposits.

Electrochromic materials are of three basic types [i]. In a given -> electrolyte solution, type I materials are soluble in both the reduced and oxidized (redox) states, an example being l,l -di-methyl-4,4 -bipyridylium ( methyl viologen ), which, on reduction, switches from the colorless di-cation to the blue radical cation. Type II materials are soluble in one redox state, but form a solid film on the surface of an electrode following electron transfer. An example here is l,l -di-heptyl-4,4 -bipyridylium ( heptyl viologen ). In type III materials, such as -> tungsten oxide, - Prussian blue, and electroactive conjugated polymers, both... 

The electrical potential of tungsten in solutions of different acids, bases, and salts has been measured against certain standard electrodes at 25 C. The tungsten does not behave as an insoluble electrode, but sends ions into the solutions. Under certain specified conditions— for examine, with high-current densities (2 amperes per square decimetre) in aqueous alkalis, but with low-current densities in aqueous solutions of acids and salts—-the tungsten anode becomes passive. The passivity appears to be due to adherent films of hydrated oxides. The electrochemical equivalent of tungsten has been found to be 0-3178 mg. per coulomb," which is in close agreement with the theoretical value. 

The development of a sensor for ozone (O3) and NO2 with measurable responses to less than 10 ppb was reported by Wilhams (2009). The sensor is based on a film of tungsten oxide (WO3) of 90 pm thickness screen-printed on inter-digitated gold electrodes. The author reported that the sensitivity and selectivity of the sensor is strongly related to maintaining a consistent... 

With the Ru dimers, [ Ru(bpy)2 2(M-L)], ESR data indicate that these binuclear semiquinone complexes are near the borderline between anion radical complexes and metal-centered mixed-valence species/ The thermal reaction between [W(CO)6] and tetrachloro-l,2-benzoquinone in toluene produces the tris(quinone) tungsten complex/ Features of the molecule indicate that the quinones are coordinated as catecholate ligands and the tungsten ions are in a formal +6 oxidation state. Quinones trapped within a polymeric electrode film can act as electron sinks and/or sources. IJ/I and [FeCCN) ] " " have been utilized as charge-release mediators. 

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