Electrochromism inorganic oxides

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. 

Metalate anion is also incorporated in the conducting polymer as a dopant. Tungsten oxide is a typical electrochromic inorganic molecule. An electrochromic conducting polypyrrole doped with phosphotungstate ions was investigated. It showed four colour chromisms which were attributed to chromisms of both phosphotungstate and polypyrrole [12]. 

Granqvist C.G. Electrochromics and smart windows. Solid State Ion. 1993 60(1-3) 213-214 Granqvist C.G. Handbook of Inorganic Electrochromic Materials, Elsevier, Amsterdam, 1995 Granqvist C.G., Electrochromic tungsten oxide films Review of progress 1993-1998. Sol. Energy Mater. Sol. Cells 2000 60 201-262... 

Electrochromic devices can be categorized according to several principles. Following earlier work of ours, separate discussions are given for devices based on different types of electrolytes liquid, solid inorganic, and sohd organic (polymeric). Almost all of the devices incorporate an electrochromic W oxide film. 

Electrochromic materials undergo reversible and persistent changes of their optical properties under the action of voltage pulses. The phenomenon is known both in inorganic (oxidic) and organic materials only the former ones have been discussed in this article. Electrochromic... 

Inorganic oxides as well as electroactive polymers are known for their electrochromic behavior. Tungsten trioxide - has been utilized in electrochromic windows. Among electroactive polymers polyaniline - and polythiophenes have been studied most extensively as electrochromic solids. 

It has been shown that composites consisting of hydrated inorganic oxide (antimonic acid (AA), aluminium oxide, or SiO ) nanoparticles and poly(vinyl acetate)/glycerin gel are suitable for electrochromic applications since their chemical activity and hygroscopicity are lower than those for acid-based electrolytes. The electrical conductivity of the composites is S cm at room temperature, and the optical absorption is low. Zirconium phosphate (ZP), which is a well-known proton conductor, is a promising material for producing hydrated particles. The conductivity for nanocomposites of ZP as well as AA with poly(vinyl acetate)/glycerin gel were prepared and reported. 

Iridium oxide, Ir02, is used in the fabrication of thin films for stable electrochromic materials and as an electrode material. Iridium metal is used in the manufacture of fountain pen points, airplane spark plugs, and hypodermic needles, see also Inorganic Chemistry. 

In general, metal oxides are very common inorganic commodities, widely applied, and display an assortment of unique chemical and physical properties. They are accessible by different techniques including chemical vapor deposition and sol-gel methods. Their technological application extends from super- and semiconducting materials to electrochromic devices, optical filters, protective coatings and solar absorbers ... 

Other inorganic electrochromic materials stud include M0O3 ) M0O3/ WO3 VjOj , Rh02 NbjOj and iridium oxides sso.eoi.eos-eos). orga-... 

The choice of a suitable counter-electrode for a successful EW is not easy since only a few compounds fulfil the desired operational requirements which call for an uncommon combination of electrochemical and optical properties. The most promising, and, thus far, the mostly used materials are indium tin oxide, nickel oxide, iridium oxide and cobalt oxide among the inorganic ECMs, and polyaniline (PANI) among the organic ECMs. The electrochromic properties of indium tin oxide and PANI have been described in Chapter 7. Therefore, here attention will be mainly focused on transition metal oxide counter-electrodes. 

Lampert and coworkers [36] have used a modified amorphous PEO-LiCFaSOs electrolyte for the realization of WO3 laminated windows using several types of counter-electrodes, such as niobium oxide, nickel oxide and a new class of solid redox polymerization electrodes [63]. These latter electrodes have an advantage over inorganic layers in that they can be tailored to the electrochromic material and ion specifically. Figure 8.18 illustrates the optical transmittance of a EW made of WOa/modified a-PEO/ion storage polymer [63]. 

In this section we present some examples of impedance spectra, in order to illustrate the concepts introduced above. We show how the methods in Section 4.3.4.3 may be used to characterize electrochromic materials and inorganic ion conductors. Data on titanium dioxide and tantalum oxide are emphasized, because they illustrate especially well several of the concepts treated above. Of conrse, we also review the application of impedance spectroscopy to the widely nsed electrochromic materials tungsten oxide and nickel oxide. 

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