Electrochromic devices electrolytes

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. 

Electrolytes for Electrochromic Devices Liquids are generally used as electrolytes in electrochemical research, but they are not well suited for practical devices (such as electrochromic displays, fuel cells, etc.) because of problems with evaporation and leakage. For this reason, solid electrolytes with single-ion conductivity are commonly used (e.g., Nafion membranes with proton conductivity. In contrast to fuel cells in electrochromic devices, current densities are much lower, so for the latter application, a high conductivity value is not a necessary requirement for the electrolyte. 

Electrochromic devices work in the opposite sense to an electrochemical cell instead of harnessing the chemical reaction between the electrodes to give an electric current, an electric current is applied to the cell, causing the movement of ions through the electrolyte and creating a coloured compound in one of the electrodes. When an electric current is applied to the following device (Figure 5.23) ... 

The potential benefits of using ionic liquids as electrolytes in conducting polymer devices have been investigated by a number of authors in recent years, for applications such as actuators [8-17], supercapacitors [18-20], electrochromic devices [12, 21] and solar cells [22], with significant improvements in lifetimes and device performance reported. 

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. 

Preparation of a Gel Electrolyte for a Hybrid Electrochromic Device Application... 

All books, reviews, and entries on CPs describe the potential applications. Chandrasekhar and others ° have reviewed in comprehensive fashion the applications of CPs, including batteries sensors electro-optic and optical devices microwave- and conductivity-based technologies electrochromic devices electrochemomechanical and chemomechanical devices corrosion protection semiconductor, lithography, and electrically related applications— photovoltaics, heterojunction, and photoelectrochemical cells capacitors electrolytic and electroless metal plating CP-based molecular electronic devices catalysis and delivery of drugs and chemicals membranes and LEDs. 

Electrochromism is in principle a device property, although the optical function can sometimes be caused by a single layer. The basic design of an electrochromic device, presented in Fig. 3.24, consists of several layers. The substrate (mostly glass) is covered by a transparent, conducting film in contact with a film of the electrochromic substance. These films are followed by a layer of a fast ion conductor (electrolyte), an ion storage film, and another transparent conductor. The electrochromic and ion storage layers are conductors for ions and electrons while, the ion conductor has zero conductance for electrons. 

The development of high performance electrolytes is an important task in the production of devices for electric energy storage and delivery such as lithium ion batteries, capacitors, and electrochromic devices. Carbonate-based materials are one of the liquid electrolytes. Carbonate-based liquid electrolytes are now commonly used for the economical lithium ion batteries [31]. The solution of carbonate and lithium salts exhibits high ionic conductivity, on the order of 10-3 S cm-1 at ambient temperature. 

Other materials being investigated include ferrocene with a bipyridinium salt,234 niobium oxide,235 nickel oxo-hydroxide,236 and cobalt oxohydroxide.237 The last is pale yellow in the reduced state and dark gray in the oxidized state. A typical electrolyte is lithium perchlorate in propylene carbonate. Solid electrolytes, such as a lithium salt (perchlorate, tetrafluoroborate, or triflate), in a polyepoxide238 or in a polyvinyl chloride gel in ethylene carbonate-propylene carbonate,239 lithium iodide in polyvinyl bu-tyral,240 and Naflon H (a polymeric perfluorocarbon-sulfonic acid),241 have also been tested. Some other systems use suspended particles between two panes of glass.242 When the particles are aligned by an electric field, the window becomes transparent. Combination photo-voltaic-electrochromic devices are under study.243... 

Current developments in battery technology, electrochromic devices (see Box 22.4) and research into electrically powered vehicles make use of solid electrolytes (see Box 10.3). The sodium/sulfur battery contains a solid 3-alumina electrolyte. The name (3-alumina is misleading since it is prepared by the reaction of Na2C03, NaN03, NaOH and AI2O3 at 1770K and is a non-stoichiometric compound of approximate... 

An electrochromic device embodies a number of superimposed layers on a transparent substrate or between two transparent substrates, and optical transmittance is altered when an electrical potential is applied so that charge is shuttled between layers serving in the same way as anodes and cathodes in an electrical battery. One specific design with a five-layer construction shown in Figure 30 uses cathodically coloring WO3 and anodically coloring nickel oxide joined by an ion-conducting electrolytic laminate. A potential of a few volts, preferably supplied by solar cells, is applied between... 

The electrolyte is probably the layer in which the maximum number of difficulties can occur. The use of a solid electrolyte, either a protonic conductor, or a lithium electrolyte is compulsory for practical applications. It can be an oxide [3], such as tantalum pentoxide, or a polymer [4]. The research field about the solid electrolytes is in fast expansion, with probable repercussions on the future of electrochromic devices. 

Electrochromic devices using poly(3-octylthiophene) associated to vanadium oxide as cathodically colouring material and a solution of polyethylene oxide (PEO) mixed with lithium perchlorate as solid electrolyte were tested [12]. Bithiophene properties were also discussed... 

Electrochromism is the reversible change in optical properties that occurs when a material is electrochemically oxidized or reduced [224], This working definition includes a change in optical properties anywhere in the solar (and even in some cases the microwave) range. In addition to the active electrochromic layer, a device consists of an electrolyte and a counter electrode, which may or may not be electrochromic. The electrolyte should be a good ionic conductor and electrically insulating in order to be nonvolatile. 

The principle of electrochromic devices can be exploited in tinting ordinary window glass. Very thin polymer layers embedded in a colorless Solid electrolyte and sandwiched between two layers of glass may tint a window when an electric potential is applied. The d ee of tinting can be controlled by the size of the electric potentiaL... 

Compared with PEO electrolytes, PDVF, and PMMA electrolytes exhibited higher ionic conductivities. In particular, PMMA has attracted increasing attentions due to its low cost, high solvent retention ability, high transparency, and processibility. The first allpolymer electrochromic device was obtained based on a gel electrolyte and PEDOT-PSS [poly(styrene sulfonate)] electrochromic material (Argun et al., 2003). The fabricated device exhibited a maximum transmittance change of 51% at 540 nm. In addition, this device was fairly stable and only 5% contrast loss was observed after 32,000 cycles. 

Nguyen, C.A., Argun, A.A., Hammond, P.T., Lu, X., Lee, P.S., 2011. Layer-by-layer assembled solid polymer electrolyte for electrochromic devices. Chem. Mater. 23,2142-2149. 

Randin, J.P., 1982. Ion-containing polymers as semisolid electrolytes in WO 3-based electrochromic devices. J. Electrochem. Soc. 129,1215-1220. 

Flexible electrochromic devices (ECDs) are becoming increasing important for their promising applications in many areas, such as the portable and wearable electronic devices, including smart windows, functional supercapacitors, and flexible displays. Typically, an ECD consists of four parts of substrate, conductive electrode, electrochromic material, and electrolyte. Enormous efforts have been made to improve the flexibility of ECDs including utilizing flexible polymer substrates and conductive materials. 

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. 

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