Electrochromic device and

Progress in the development of solid electrolytes is also being achieved from advances in several other fields of technology such as fuel and electrolysis cells, thermoelectric converters, electrochromic devices, and sensors for many chemical and physical quantities. 

The discussion of Brouwer diagrams in this and the previous chapter make it clear that nonstoichiometric solids have an ionic and electronic component to the defect structure. In many solids one or the other of these dominates conductivity, so that materials can be loosely classified as insulators and ionic conductors or semiconductors with electronic conductivity. However, from a device point of view, especially for applications in fuel cells, batteries, electrochromic devices, and membranes for gas separation or hydrocarbon oxidation, there is considerable interest in materials in which the ionic and electronic contributions to the total conductivity are roughly equal. 

For choosing the right way of preparation of PCM modified electrodes, the decisive question is the intention of preparation. There are two principally different goals (1) The electrodes ought to be applied for electrocatalysis, for electrochromic devices and the like, and (2) modified electrodes are prepared to study the electrochemistry of the compounds. For the first goal, there are two principally different approaches (a) the preparation of films on electrode surfaces, and (b) the incorporation of the PCM into a matrix, for example, a mixture of graphite and a binder, leading to composite electrodes. 

Conducting polymers have been extensively investigated due to their potential applications in supercapacitors, sensors, batteries, electrochromic devices and light... 

Ionic conductors have many practical applications. For example, solid ion conductors are used as solid electrolytes and electrode materials in -> batteries, fuel cells, - electrochromic devices and - gas sensors. 

Figure 2.52. Cross-section schematic of an (a) electrochromic device and (b) suspended-particle device.

Surface chemistry, in general, is an area in which the ability to selectively modify the chemical and physical properties of an interface is highly desirable. The synthetic chemistry of surfaces is now in a developing stage, particularly with respect to the attachment of electroactive redox sites to metal or semiconductor surfaces (L-3). Single component and bilayer (4) electroactive films have been a field of intense research activity since their applications are apparent in catalysis, solar energy conversion, directed charge transfer, electrochromic devices, and trace analysis. 

PEDOT, one of the most popular jr-conjugated polymers, has been intensively studied for developing nanoscale materials as well as for application to various nanodevices such as biosensors and electrochromic devices, and for drug delivery [82-84]. However, studies on PEDOT nanomaterials and bulk films have mainly focused on their electrical and structural properties and on the various applications of the conducting form of the material (i.e., doped PEDOT systems). The light-emitting characteristics of doped and de-doped PEDOT nanomaterials were first reported by Park et al. in 2008 [43]. 

Among the conjugated polymers, polypyrrole (PPy) is the most representative one for its easy polymerization and wide application in gas sensors, electrochromic devices and batteries. Polypyrrole can be produced in the form of powders, coatings, or films. It is intrinsically conductive, stable and can be quite easily produced also continuously. The preparation of polypyrrole by oxidation of pyrrole dates back to 1888 and by electrochemical polymerization to 1957. However, this organic p>-system attracted general interest and was foimd to be electrically conductive in 1963. Polypyrrole has a high mechanical and chemical stability and can be produced continuously as flexible film (thickness 80 mm trade name Lutamer, BASF) by electrochemical techniques. Conductive polypyrrole films are obtained directly by anodic polymerization of pyrrole in aqueous or organic electrolytes. 

Functionalized PTs have been investigated in various applications, e.g., their ability to detect, transduce, and amplify various physical or chemical informations into an electrical or an optical signal has led to the development of devices capable of detecting analytes or biomolecules in the field of environment, security, and biotechnology. Currently, functionalized PTs play a key role as active materials in the development of electrochromic devices and electronic devices, such as OLEDs, OFETs, and organic solar cells. 

In this context, this section deals with functionalized PTs developed for sensors, electrochromic devices, and plastic electronic devices as well as metal-containing PTs emphasizing on the relationships between bandgap control of the PT backbone and the corresponding application. 

Polymer electrolytes are also sought for a variety of other applications such as sensors, electrochromic devices and photoelectrochemical cells. The ambient temperature operation of many of these requires conductivities of the same magnitude as for batteries. The need for high electrolytic conductivity stems from the fact that the rate at which the solid-state devices can be operated, for example, how fast energy from a Li battery can be drained or the colour of an electrochromic window can be switched, depends to a large extent on the mobility of ionic charge carriers, hence... 

Small bandgap polymers have il ax of longer than 550 nm in the neutral state and are transparent in the visible region upon doping. A transparent conductive film can be cast from solutions of these polymers. The smallest bandgap is below 0.5 eV. These polymers are not only potentially useful electrochromic devices and switching windows but will also play an important role in the development of science of synthetic metals. 

A wide range of soUd and liquid electrolytes has been tested in various electrochromic devices and the results of these studies have been extensively discussed 4). The main dectrolyte groups are aqueous acidic dectrolytes, nonaqueous lidiium dectn tes, ceramic ionic conductms (P-alumina, Nasicon etc.), polyelectrolytes, polyrnCT solid dectrolytes (complexes of polyetfaers or polyimines with alkali metal salts and proton donors) and plasticized polymor ionic conductors. 

Poly(aniline) and its derivatives have been envisioned for a number of applications such as protective coatings, electrochromic devices, and potentiometric sensors. ... 

In summary, for lithium batteries, electrochromic devices, and nickel metal hydride batteries, sol-gel processing offers new ways to prepare component materials. A sol-gel electrolyte, such as lithium silicate, can operate at modest temperatures while playing the role of a mechanical divider between the electrodes. In other cases, sol-gel processing is appropriate for large area coatings, such as tungstic oxides, where sols can be applied directly to substrates and in successive sol-gel layers. Additionally, sol-gel processing is known to lead to metastable phases, as in the case of nickel oxyhydroxides, and these metastable phases often perform better in electrochemical processes than the stable phases. 

Examples of an electrochromic device and a typical composition used for redox reaction are shown in Figures 40.4 and 40.5, respectively. 

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