Tungsten electrochromic

Members of the ion-insertion/extraction group, as inorganic or organic thin films, especially the former, have attracted the widest interest most recently. Tungsten trioxide was the eadiest exploited inorganic compound (4), even before the mechanism of its electrochromic response was understood (5). It is stiU the best known of the important ion-insertion/extraction group. 

Metal Oxides Tungsten trioxide, undoubtedly the most widely studied electrochromic material, is used in several types of commercial electrochromic devices. 

Yao, Z., et al., Aligned coaxial tungsten oxide-carbon nanotube sheet a flexible and gradient electrochromic film. Chemical Communications, 2012. 48(66) p. 8252-8254. 

Granqvist, C. G., Electrochromic tungsten oxide films Review of progress 1993-1998. Sol Energ Mater Sol C 2000, 60, 201-262. 

Granqvist, C., Progress in electrochromics Tungsten oxide revisited. Electrochim Acta 1999,... 

Figure 8.1 Beer s law-type plot of change in optical absorbance against charge density q for the cell WO3 polymer electrolyte Prussian Blue. Reprinted from Inaba, H Iwaka, M., Nakase, K., Yasukawa, H., Seo, I. and Oyama, N., Electrochromic display device of tungsten trioxide and Prussian Blue films using polymer gel electrolyte of methacrylate , Electrochim. Acta, 40, 227-232 (1995), Copyright 1995, with permission from Elsevier Science.

The author was brought up in Hastings, on England s south coast, where he attended a local comprehensive school. Despite this education, he achieved entrance to the University of Exeter to read Chemistry. Having obtained a B.Sc. degree and then a doctorate (in 1989) on the electrochemistry of the viologens, he was awarded a fellowship at the University of Aberdeen to study the electrochromism of thin films of tungsten trioxide. 

A promising EW may be obtained by combining tungsten trioxide, WO3, a well-known primary electrochromic electrode, which is coloured by the following lithium insertion-deinsertion process ... 

All inorganic electrochromes exist in the solid state in both the colourless and coloured states, e.g. Prussian Blue and tungsten trioxide. Conducting polymers such as polyanilines, polypyrroles and polythiophenes also fall into this class of electrochromes (see 1.5.3.5). 

Inorganic oxides exhibiting electrochromism include cobalt oxide, nickel oxide, molybdenum trioxide, vanadium oxide, tungsten trioxide and their mixtures. The most important of these are those based on tungsten trioxide. 

One of the big drawbacks associated with the use of many conducting polymers as electrochromic materials is their low cycle life stability. To overcome this, and other electrochromic properties, many composite materials have been studied. These composites include mixtures with other optically complementary, conducting polymers and inorganic electrochromes, such as tungsten trioxide and Prussian Blue, and colour enhancing agents or redox indicators, exemplified by the inherently electrochromic indigo carmine (1.96). °... 

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. 

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... 

Metal oxide films which change color in an electrolyte with change in applied potential [11, 115-123,127, 128, 137] have attracted a lot of attention in the past 15 years or so because of their potential application in electrochromic displays. Tungsten trioxide was the first oxide to receive significant attention in this regard [115-119] and, later, Ir oxide films [11, 120, 121, 127,... 

Figure 32 Schematic electron density-of-states diagrams for electrochromic, EC, multilayer design. The materials include ln203 Sn (ITO), nickel oxide (presiunably hydrous), tungsten oxide (also presumably hydrous) prepared so that the EC and chemically protective (PR) properties are emphasized, and an electrol)de. The Fermi energy is denoted Ep, with Epi and Ep2 pertaining to the case of an applied potential, Ucoi fiUed states are denoted by shadings. (Ref 235. Reproduced by permission of Springer Verlag)...

Volatile tungsten(IV) 0x0 alkoxide//3-diketonate complexes of structural type W(0)(/1-diketonate)(OR)3 (R = t-Pr, f-Bu /3-diketonate = acac, 32, hfac, 33) are excellent precursors for the low-pressure CVD of electrochromic tungsten oxide films, as shown by Chisholm and coworkers. While with 32b and 33b the produced films were transparent and blue, 32a and 33a led to pale yellow layers which darkened to pale green-blue when exposed to air for several days. With the exception of 33a, all other tungsten complexes formed good-quality films with respect to adhesion and surface coverage however, no surface selectivity for quartz, pyrex or ITO was observed. 

N. Leventis Y. C. Chung, Preparation And Characterization Of Tungsten Trioxide Dibenzyl Viologen Polymer Bilayer Electrochromic Films. J. Mater. Chem. 1993, 3, 833-839. 

C. G. Granquist, Electrochromic Tungsten-Oxide-Based Thin Films Properties, Chemistry, and Technology, in Physics of Thin Films (M. Francombe and C. Vossen, eds.), Vol. 17, pp. 301-370, Academic Press, San Diego (1993). 

Solid isopoly- and heteropolymetalate compounds have been synthesized. Within this group of materials, one can include the so-called metal oxide bronzes (typically tungsten bronzes). Starting from WO, electrochemical reduction processes yield intercalation materials with electrochromic properties (Grandqvist, 1999). 

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