Electrochromism electrochromic cells

There is a large potential for conducting polymers as corrosion-inhibiting coatings. For instance, the corrosion protection ability of polyaniline is pH-dependent. At lower pH polyaniline-coated steel corrodes about 100 times more slowly than noncoated steel. By comparison, at a pH of about 7 the corrosion protection time is only twice for polyaniline-coated steel. Another area of application involves creation of solid state rechargeable batteries and electrochromic cells. Polyheterocycles have been cycled thousands of times with retention of over 50% of the electrochromic activity for some materials after 10,000 cycles. IR polarizers based on polyaniline have been shown to be as good as metal wire polarizers. 

Dnring the process of colouration in electrochromic cells by passing a charge in one direction, a colour can form in one or both of the electrodes or in the electrolyte adjacent to the electrodes. When the colour is formed by reduction at a negative electrode it is called cathodic coloration and, conversely, at the anode it is anodic coloration. Two different types of cells are shown schematically in Figure 1.31. ... 

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. 

Figure 6.36 Schematic of the electrochromic cell device investigated by Fitzmaurice and co-workers [17]...

Figure 6.37 Optical absorption spectra of the electrochromic cell following the application of a...

Keywords ionic liquid, redox electrolytes, sol-gel nanocomposites, hybrid electrochromic cells... 

S. Papaefthimiou G. Leetheriotis P. Yianoulis, Study of electrochromic cells incorporating WO3, M0O3, WO3-M0O3 and V2O5 coatings. Thin Solid Films 1999, 344, 183-186. 

An electrochromic cell is schematically formed by three main layers electrochromic material/ion conductor (electrolyte)/ion storage layer (counter electrode). Since the different oxides can colour either in anodic (NiO) or in cathodic (WO3) polarization, it is interesting to make the counter electrode also an active material, and to associate electrochromic materials with cathodic coloration as well as anodic coloration. In practice, there are seven successive layers, as shown in Figure 14.1(a). 

To realize thin films for use in electrochromic cells, electrochemical polymerization is a preferred technique. In the experiments of Hugot-Lc Goff et at., the electropolymerization on a metallic substrate (platinum)... 

The simplest studied electrochromic cell, realized by B. Jelle and coll., [96] was formed by PANI and WO3 deposited on indium-tin-oxice (ITO) coated glass plates, separated by 0.l mm of poly 2-acrylamido 2-methylpropanesulfonic acid, PAMPS (Figure 14.39). 

Orthorhombic crystalline vanadium pentoxide is a typical intercalation compound as a result of its layered structure, see Fig. 5.2, which finds widespread use in lithium ion intercalation applications such as electrochromic cells [17], high energy density batteries [18], supercapacitors [19], and sensors [20], since it offers the essential advantages of low cost, abundant availability, easy synthesis, and high intercalation densities [15, 16]. 

Transparent electrochromic cells consisting of a FT0/V205/LiC104- -PC/FT0 layer sequence and an Ag/AgCl wire as reference electrode were assembled by... 

Fig. 5.3 Electrochromic cell assembly, a Schematic illustration of the layered device design based on a DG-structured electrode, b Functional electrochromic nano-device with the design pattern in the chromogenic double-gyroid film showing the crest of the University of Cambridge. The thickness of the vanadia deposit was measured to be around 1.1 p.m...

For the study on the oxidation of double-gyroid metal films and the subsequent use of NiO films in electrochromic devices, templated and nontemplated metallic films of different thickness were prepared. An uniform Ni deposition thickness, which is important when using the oxidized electrodes in electrochromic cells was achieved by limiting the plating area to 1 mm using a SU-8 mask [19]. 

A notable application of electrochromic cells is in car mirrors, which can be electrically dimmed so as to cut down dazzling reflections from bright lights. These do not use LT but instead rely upon the decomposition of atmospheric water vapour to... 

Figure 9.9 Electrochromic cells (a) idea WO structure (b) incorporation of Li into the A-sites under an electric field (c) schematic of an electrochromic cell using Lh...

Given the unique structure and properties of CPs (light weight, good tensile strength and flexibility) they have been shown as promising electrode materials for a range of different applications such as supercapacitors, sensors, solar cells, batteries, electrochromic cells and actuators [70-75]. However, CPs... 

An interesting approach to the fabrication of PEDT-based electrochromic cells is a setup that combines two PEDT PSS layers [108]. This concept utilizes the nonlinear coloring behavior of PEDT PSS, and the performance of the device is based on the fact that the sum of the absorption of both layers runs through a minimum. The drawback, however, to this dual-layer PEDTrPSS device is reduced optical contrast. 

This present study covers only electrochromic devices using proton conductors. Indeed, since the proton is the smallest ion, proton conductors have been extensively studied and used in electrochromic cells either as the solid electrolyte or as the electrochromic material or counter electrode. 

Since it seems clear that it is the combination of acid functions and free water in the electrolytes that leads to the chemical instability of WO3, the use of anhydrous protonic polymers may be attractive for this kind of application. Recently, anhydrous polymers have been synthesized and studied. However, only a few studies are reported on the performances of such complete ECDs. Table 38.2 presents the values of conductivity, at room temperature, of some of these polymers. These materials are promising for an electrochromic cell with WO3 but their conductivity has to be improved to be of the order of 10" (Q.cmj Either ammonium salts or acids have been added to polymers such as poly(ethylene oxide) (PEO), polyvinylpirolydone (PVP), poly(ethylene imine) (PEI), poly(vinylalcohol) (PVA), poly(acrylic acid) (PAA), branched poly(ethyl-ene imine) (BPEI), poly(acrylamide) (Paam) to obtain anhydrous protonic conductors. 

Also required in an electrochromic cell is an ion storage layer consisting of a redox-active material. A variety of materials, including various metal oxides such as titanium-doped cerium(IV) oxide (Ce02/Ti02> have been proposed. 

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