Solution Electrochromes

The divalent cation methyl viologen is highly colored in reduced form and is used as an electrochromic in solution cells (Eig. 11). 

Figure 29. (a) Evolution of the absorption spectra of an electro-chromic polypyrrole as a function of the oxidation potential obtained during voltammetry between -900 and 400 mV from a 2.5 M LiCI04 aqueous solution. The voltammetry was performed at a scan rate of 20 mV s 1. (From Ref. 161). (b) Evolution of the absorption spectra of an electrochromic polypyrrole as a function of the reduction potential obtained during voltammetry between 400 and -900 mV from a 2.5 M LiCI04 aqueous solution. The voltammetry was performed at a scan rate of 20 mV s 1. (From Ref. 161). 

Adsorption processes diagrammed, 266 Adsorption spectra of electrochromic polypyrrole, 363 Affinity for metal-water, 177 Air-solution interface, Nikitas on the potential of zero charge at, 30 Albury and Mount, interpretation of the semi-circle, 584 Alloys, potential of zero charge gold and silver, 142 tin and lead, 142 Kukk and Puttsepp on, 145 metals alloys, 141... 

Electrolytic oxidation of acetonitrile solutions of monomer mixtures of dithioenopyrrole 23 and dithienothiophene 15a using tetrabutylammonium perchlorate as an electrolyte can produce poly(dithienopyrrole-dithienothiophene) copolymer which shows good electrochromic <1994EAC2159> characteristics. Similarly, films of poly(dithienopyrrole-thionapthene indole) and poly(dithienopyrrole-thionapthene indole) co-polymers can be obtained from DTT and DTP with thionapthene indole 85 (TNI) <1996SM(82)11>. 

Electrochromic materials (either as an electroactive surface film or an electroactive solute) are generally first studied at a single working electrode, under potentiostatic or galvanostatic control, using three-electrode circuitry.1 Traditional electrochemical techniques such as cyclic voltametry (CV), coulometry, and chronoamperometry, all partnered by in situ spectroscopic measurements... 

Kashiwazaki67 has fabricated a complementary ECD using plasma-polymerized ytterbium bis(phthalocyanine) (pp—Yb(Pc)2) and PB films on ITO with an aqueous solution of 4M KC1 as electrolyte. Blue-to-green electrochromicity was achieved in a two-electrode cell by complementing the green-to-blue color transition (on reduction) of the pp—Yb(Pc)2 film with the blue (PB)-to-colorless (PW) transition (oxidation) of the PB. A three-color display (blue, green, and red) was fabricated in a three-electrode cell in which a third electrode (ITO) was electrically connected to the PB electrode. A reduction reaction at the third electrode, as an additional counter electrode, provides adequate oxidation of the pp Yb(Pc)2 electrode, resulting in the red coloration of the pp—Yb(Pc)2 film. 

Doped silicon, conductivity in, 23 35 Doped/undoped electrochromic organic films, 6 580-582 Dope-dyeing, 9 197 Dope-making process, in acrylic fiber solution spinning, 11 204 Dope solids, in air gap spinning, 11 209 Doping, 23 838—839 calcium, 23 842-844 conducting polymers, 7 528-529... 

Amb, C. M. Dyer, A. L. Reynolds,. R., Navigating the color palette of solution-processable electrochromic polymers. Chem. Mater 2010, 23, 397-415. 

By combining these two equations, we can say that if a material is electrochromic and the electrolysis is performed within a constant volume of solution, then the (faradaic) charge is proportional to the optical absorbance. This relationship of Abs a 2 is illustrated in Figure 8.1, where the absorbance, Abs, of the electrochromic colour (as y ) is seen to increase linearly as the charge increases (as x ). The linearity of the graph indicates that both Q and Abs relate to the same... 

The first demonstration of a PEM with electrochromic properties was disclosed by SchlenofFand coworkers [66], using poly(butanylviologen)/ PSS films. While this film exhibited strong electrochromic response, it still required the use of an outer electrolyte solution. DeLongchamp and Hammond disclosed for the first time a solid-state device comprised of two electrochromic PEM-modified ITO electrodes separated by a 200-p,m thick poly(2-acrylamido-methane-2-propanesulfonic acid), proton-conducting PAMPS membrane (see Eigure 2.30) [196]. Both PEMs used in... 

Sonochemical methods have been used by the Cordoba de Torresi group to prepare Ni(OH)2, Co(OH)2 and mixed Ni/Co hydroxide NPs [33, 34]. For the sonochemical synthesis, the appropriate metal nitrate was mixed with ammonium hydroxide solutions and then sonochemically irradiated for various times. This produced about 5-nm diameter metal-hydroxide NPs that were then immobilized at ITO surfaces using a LbL approach with poly(allylamine) hydrochloride (PAH). In one study, the electrochromic behavior of the LbL deposits was compared with that of bulk deposits... 

PB and its derivatives are of interest for a variety of reasons, the most important of which is its electrochromism [93]. In addition, it is an electrocatalyst for several different types of substrates, notably hydrogen peroxide, as will be seen below. Synthesis of nanopartides of Prussian Blue is relatively straightforward. It relies on many of the prindples of colloid chemistry, and produces ionically stabilized colloidal solutions (Figure 4.7). As a consequence, the electrochemical behavior of PB N Ps has been examined by several groups. In this section, we discuss the behavior of P B N Ps immobilized at electrodes. 

The materials that change colour on passing a charge are called electrochromes, and these can be classified into three groups. In the first type the colouring species remain in solution in the second type the reactants are in solution but the coloured product is a solid the third type are those where all the materials are solids, e.g. in films. The first type is used in car, anti-dazzle, rear-view mirrors, the second type in larger mirrors for commercial vehicles and the third type in smart windows (see section 1.5.4.2). 

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