Electrochromic devices liquids

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. 

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. 

Ahmad S, Singh S (2008) Electrochromic device based on carbon nanotubes functionalized poly(methyl pyrrole) synthesized in hydrophobic ionic liquid medium. Electrochem Commun 10 895-898... 

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. 

Hassab, S., Padilla, J., 2014. Use of ionic liquids in electrochromic devices. Ionic Liq. Sep. Technol., 301. 

Electrochromism is a phenomenon displayed by some materials reversibly changing colors. Various materials can be used to construct electrochromic devices, such as transition metal oxides, liquid crystals, photonic crystals, and polymers (Booth and Casey, 2009 Nicoletta et al., 2005 Arsenault et al., 2007 Gamier et al., 1983). Here, we will focus on the electrochromic materials based on polymers. There are several mechanisms to explain the color changes of polymer electrochromic materials like electro-induced oxidation-reduction and electrothermal chromatic transition and so on. 

Osterholm, A. M., Shen, D. E., Dyer, A L, and Reynolds, J. R (2013). Optimization of PEDOT films in ionic liquid supercapacitors Demonstration as a power source for polymer electrochromic devices, ACS App/. Mater. Interfaces, 5,pp. 13432-13440. 

Lu, W., A.G. Fadeev, B. Qi, and B.R. Mattes. 2004. Fabricating conducting polymer electrochromic devices using ionic liquids. J Electrochem Soc 151 H33-H39. 

Electrochromic displays are simple electrochemical cells with an electrochromic material as one of the electrodes. A potential applied between the anode and cathode, typically less than 5 V, produces the desired color change. Once switched, the current between the anode and cathode diminishes. Most electrochromic displays have a memory (stay switched even if no potential is applied as long as the electronic connection between anode and cathode is broken), many on the order of hours. Thus, they are ideal for low-power applications. Unfortunately, many printed electrochromic devices are relatively slow. Speeding up the device requires a liquid electrolyte, which is difficult to manufacture and encapsulate in an inexpensive device. 

Polymer-based, variable light transmission electrochromic devices have been fabricated with counter-electrodes that are either optically passive or electrochromic in the complementary mode. Two devices with pMeT, electrochemically grown by monomer oxidation on ITO-coated glass as the electrochromic electrode, having colourless counter-electrodes in both oxidized and reduced states, and operating in liquid electrolyte, such as PC-LiC104, have been developed [29, 30]. 

An all solid-state device configuration has a great advantage over a liquid one and is suitable for large-area devices. The remarkable development of polymer electrolytes is a very promising advance in the technology of the solid-state electrochromic device, which represents a very important, fertile field of research. 

The interest in electrochromic devices lies in the fact that they have a number of specific advantages, such as high optical contrast with continuous variation of the transmittance and no dependence on viewing angle, optical memory, UV stability, and wide operation temperature ranges. These favourable characteristics may ultimately overcome the well known deficiencies of liquid crystal displays and thus place electrochromic devices in a prominent position for the production of large visual angle panels. 

Electrochromic devices (ECDs) consist of a two-electrode electrochemical cell. They include an ion-conducting liquid or solid electfolyte medium sandwiched between two electrode surfaces coated with organic or inorganic electrochromic materials, chosen for their electrical and optical properties. Their purpose is the generation of a variable-color system that can be changed in a controllable fashion for potential applications as displays, smart windows or in other technologies. 

In addition to the previous architectures, two more alternatives are possible for the structure of an electrochromic device (1) the solution configuration, including an electrochemical cell having an electrochromic material (or two) dissolved in a liquid or gel electrolyte (Figure 20.7b), and (2) the hybrid... 

Kelly FM, et al. Evaluation of solid or liquid phase conducting polymers within a flexible textile electrochromic device. J Disp Technol 2013 9(8) 626—31. 

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