Tungsten oxide electrodes

Fig. 10-12. Anodic photoexcited current of oxidation of water mole cules to produce oxygen gas as a function of electrode potential of an n-type tungsten oxide electrode in an acidic solution X. = wave length of photons. [From Butler, 1977.]...

Tungsten electrode (or tungsten-tungsten oxide electrode)... 

L. Monser, N. Adhoum, S. Sadok, Gas diffusion-flow injection determination of total inorganic carbon in water using tungsten oxide electrode, Talanta 62 (2004) 389-394. 

Over the years, there have been many advances in the determination of ammonia in liquids and not so many advances in the FIA determination of TVB-N in myosystems. In this connection, Dhaouadi et al. (2007) reported a potentiometric flow injection method using a gas diffusion cell for the determination of TVB-N in sardine, red mullet, mackerel, and hake. The method was based on the change of potential of a tungsten oxide electrode when volatile basic compounds, released from the fish extract sample, diffuse via a permeable membrane into a phosphate buffer acceptor stream and locally shift the pH. 

Adhoum, N., L. Monser, S. Sadok, A. El-Abed, G. Greenway, and R. Uglow. 2003. Flow injection potentiometric detection of trimethylamine in seafood using tungsten oxide electrode. Anal. Chim. Acta 478 53-58. 

We also tested a modification of the combination redox sensor described above, in which the yttria stabilized zirconia tube was replaced by a tungsten/tungsten oxide electrode. Elsewhere, we have shown that this electrode is pH sensitive and is practically insensitive to oxygen and hydrogen," at least at low subcritical temperatures (T < 300°C). In Fig. 41, we present typical data on the response of this sensor to the changes in the gas concentration... 

To exploit the energy produced in this reaction, the half reactions are separated. The oxidation reaction is carried out at a zinc electrode (Zn Zir + 2 electrons) and the reduction reaction is carried out at a copper electrode (Cu"" + 2 electrons Cu metal). Electrons flow through a metal wire from the oxidizing electrode (anode) to the reducing electrode (cathode), creating electric current that can be harnessed, for example, to light a tungsten bulb. 

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... 

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. 

On occasion tungsten-wire electrodes are used to monitor a redox reaction. These usually are oxide-covered systems that respond to the activity of the species of a redox couple however, the response seldom obeys the Nemst equation. 

K. Machido and M. Enyo, Tungsten bronze electrodes doped with platinum (methanol oxidation), J. Electrochem. Soc. 135 1955 (1988). 

It is well- known that the presence of catalytic poisons (CO for example) in hydrogen gas exerts strong influence on the effectiveness and long-term stability of the electrodes containing Pt, Pd and other noble metals as a catalyst. The modification of this catalyst by such metals as Nb, Mo, Ta and Ru increased electrode life in presence of CO [8, 9]. Utilization of tungsten oxide (WO3) jointly with Pt and Ru increase also electrode stability towards CO [28]. 

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... 

W(CN)j /W(CN)j, and Fe3"/Fe2+ in acid solutions [90,91], Simple ETR at sodium tungsten bronzes, NaxW03, with the perovskite structure are fast and are influenced by the sodium bulk content of the electrode as can be seen in Table 2. Unfortunately, the kinetic pattern is not simple because the variation of ETR rate coefficients with sodium content is not the same for each couple [91]. A qualitative interpretation of the ETR kinetic results has been attempted in terms of the density of electronic states at the Fermi level of the oxide electrode [90]. 

WO3 has been used as an electrode for CO sensors [254—260]. Figure 13.21 [254—258] shows that the outputs of CO sensors with YSZ electrolytes and WO3 electrodes decrease with increasing temperature, which, as discussed earlier, is a general tendency for nonequilibrium sensors. Tungsten oxide has also been used as an electrode for NO sensors [246, 254—259, 261-263], some examples of which are shown in Figure 13.22 [254—259, 262, 263[. 

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