Electrochromic, electrochromism electronic conductivities

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. 

Electronically conducting polymers also have an important role to play as electrodes in electrochromic devices. This is described in Chapter 9. 

Solid-state electrochemistry is an important and rapidly developing scientific field that integrates many aspects of classical electrochemical science and engineering, materials science, solid-state chemistry and physics, heterogeneous catalysis, and other areas of physical chemistry. This field comprises - but is not limited to - the electrochemistry of solid materials, the thermodynamics and kinetics of electrochemical reactions involving at least one solid phase, and also the transport of ions and electrons in solids and interactions between solid, liquid and/or gaseous phases, whenever these processes are essentially determined by the properties of solids and are relevant to the electrochemical reactions. The range of applications includes many types of batteries and fuel cells, a variety of sensors and analytical appliances, electrochemical pumps and compressors, ceramic membranes with ionic or mixed ionic-electronic conductivity, solid-state electrolyzers and electrocatalytic reactors, the synthesis of new materials with improved properties and corrosion protection, supercapacitors, and electrochromic and memory devices. 

Schottland, R, K. Zong, and C.L. Gaupp. 2000. Poly(3,4-alkylenedioxypyrrole)s Highly stable electronically conducting and electrochromic polymers. Macromolecules 33 7051-7061. 

A number of potential applications of conducting polymers are expected because they are organic compounds, have conjugated structure and many subordinating properties and functions, such as electronic conducting properties, electrochemically active properties (electrochemical doping-undoping), electrochromic behaviours, nonlinear optical properties, etc. 

Chromatic changes caused by electrochemical processes were originally described in the literature in 1876 for the product of the anodic deposition of aniline [271]. However, the electrochromism was defined as an electrochemically induced phenomenon in 1969, when Deb observed its occurrence in films of some transition metal oxides [272]. Electrochromism in polypyrrole was first reported by Diaz et al. in 1981 [273]. Electrochromism is defined as the persistent change of optical properties of a material induced by reversible redox processes. Electronic conducting polymers have been known and studied as electrochromic materials since the initial systematic studies of their electronic properties. 

K-Conjugated polymers and oligomers are organic materials with many interesting and useful properties [1, 2], Examples of this class of materials include polyacetylene, polythiophene, polypyrrole, poly(phenylenevinylene) and their derivatives. Electronic conductivity, luminescence and nonlinear optical behavior are all observed in these materials and these properties have been exploited in applications such as electroluminescent devices (polymer light-emitting devices or PLEDs), electrostatic coatings, electrochromic windows, chemical sensors and memory devices [3-9]. 

Secondary electrochromic polymer Electronically conductive traneparent film Glass or plastic substrate... 

In addition to conventimial applications such as electrocatalysis, electronic devices, solar cells, and electrochromic windows, conducting... 

The system consists of five functional layers, which are located between two glass or plastic substrates. Each plate is coated with a thin transparent conductive electrode (TCE), usually a doped form of tin oxide e.g., fluorine doped tin oxide (FTO Sn02 F) or Sn-doped indium oxide (ITO In203 Sn). One ofthe TCE is coated with an electrochromic coating (EC-layer), the other with a coimter electrode (CE layer). Both layer systems are separated by an ionic conductive electrolyte with very low electronic conductivity. In order to have high diffusion coefficients and fast kinetics, the ions should be small, therefore protons (H" ) or lithium (Li ) are preferred. The electrical contacts are attached at the TCE coatings. 

The high proportion of nonbridging bonds in gels produces a very high coefficient of thermal expansion [32,33] as well as providing reaction sites for chemical modification. The open structure of gels also provides exceptional ionic conductivity [34] as well as electronic conductivity and electrochromic performance much superior to crystalline ceramics [35]. 

The technique is suitable for depositing oxides of Pb, Co, Mn and Cr, and has been reported primarily for wide bandgap n-type oxide semiconductors, such as ZnO and TiOj. A number of the oxide deposits are electronically conductive and can be used as electrical contacts. Although not demonstrated, the process should also be suitable for semiconductors more commonly used in electronics. Imaging via oxidative photodeposition has also been reportedfor conductive organic polymers on ZnO and other semiconductors (37). The polymer forms on electrochemical oxidation of solutions of the monomer, e.g., pyrrole, thiophene and aniline. Since the conductive polymers are also electrochromic, the process might be... 

P Schottland, K. Zong, C. L. Gaupp, B. C. Thompson, C. A. Thomas, I. Giurgiu, R. Hickman, K. A. Abboud, and J. R. Reynolds. 2000. Poly(3,4-alkylenedioxypyrrolejs Highly stable electronically conducting and electrochromic polymers. Macromolecules 33(1) 7051-7061. 

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