Electrolytes electrochromic displays

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 leucos 7h-o are claimed in electrolytic recording paper using a process coined electrochromic recording which is an irreversible electrooxidation of the leuco dye to regenerate Methylene Blue, not to be confused with reversible electrochromic display. The process consists of passing an electrical pulse through a substrate containing the leuco dye and... 

Figure 8.1 Beer s law-type plot of change in optical absorbance against charge density q for the cell WO3 polymer electrolyte Prussian Blue. Reprinted from Inaba, H Iwaka, M., Nakase, K., Yasukawa, H., Seo, I. and Oyama, N., Electrochromic display device of tungsten trioxide and Prussian Blue films using polymer gel electrolyte of methacrylate , Electrochim. Acta, 40, 227-232 (1995), Copyright 1995, with permission from Elsevier Science.

There is growing evidence of developing high-technology uses of pyridines, particularly as quaternary salts, as components of electrolytic capacitors, photocondnctors. rechargeable batteries, complex-coated electrodes for photosensors, electrochromic display elements and photoresist matrix resins. 

Metal oxide films which change color in an electrolyte with change in applied potential [11, 115-123,127, 128, 137] have attracted a lot of attention in the past 15 years or so because of their potential application in electrochromic displays. Tungsten trioxide was the first oxide to receive significant attention in this regard [115-119] and, later, Ir oxide films [11, 120, 121, 127,... 

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. 

FIGURE 4.2 Reflective electrochromic display structures, (a) Vertical display structure cross section, to be seen from the top. The opaque (white) electrolyte hides the counterelectrode, (b) Lateral display structure cross section. The transparent electrolyte allows the visible electrode to be seen. The counterelectrode should be placed under another printed object if it must be hidden. 

Due to its many advantageous properties (low cost, fast color change, good contrast, stability, etc.), PANI is also a favorite material for use in electrochromic display devices. Pictures of a PANI-based flexible device are shown in Fig. 7.11. The display pattern, which consists of 25 pixels and the connections that allow each pixel to be driven separately, was fabricated by depositing gold onto a plastic sheet. Another plastic sheet covers the display. The electrochemical switching is executed using a counterelectrode, which also serves as a reference electrode, and an acidic gel electrolyte is placed between the two sealed plastic sheets. 

An electrochromic display (ECD) is basically an electrochemical battery where the cyclable energy output is revealed by a colour change. Similarly to any electrochemical cell, the typical configuration of ECDs involves, in sequence, the electrochromic electrode (for instance a WO 3 film deposited on an ITO-coated glass), an electrolyte and a counter-electrode. The electrochromic electrode provides the colour changes while the electrolyte allows the ionic transport and the counter-electrode assures the electrochemical balance. 

These remarkable electrochemical properties have many potential applications, in batteries, electrochromic display devices, supercapacitors and, more recently, for the conception and production of various sensors for molecular electronics. The main problem, however, is cycling reversibility, which will determine the suitability of PPP for these applications. The electroactivity of a given PPP depends on several factors, particularly on the nature of solvent and electrolyte, and on the potential range at which it is cycled. 

Materials which change colour reversibly during the electrochemical processes of charge and discharge are called electrochromic materials. Electrochromic displays are typically assembled by combining an electrode covered with a thin layer of electrochromic material, a transparent electrolyte and a complementary electrochromic material as a counter-electrode. If the... 

By combining an electrically conductive polymer (e.g. POT) prepared by spin coating from solution with a solid polymer electrolyte and a metal oxide, a sohd state electrochromic device is constructed [713]. Substrates coated with PT can be used in electrochromic displays, in solar cells (cf Sect. 6.3), and for corrosion protection [714]. Poly(3,4-ethylenedioxythiophene-2,5-diyl), which has good electrochromic properties, (for structure cf Sect. 1.2) can used as an electrode in a solid state electrochromic cell (cf Sect. 3.4.3) [43]. PITN can be reversibly cation- and anion-doped without decomposition. This polymer, with... 

Antistatic, ESD coatings Absorption of radar frequencies Corrosion prevention EMI/RFI shielding Electrochromic displays Electrochemical actuators Lithographic resists Lightning protection Microelectronics Polymer electrolytes Photovoltaics Rechargeable batteries Smart windows Solar cells... 

A solid state electrochromic device can be constructed by combining a thin layer of an electrically conductive polymer like 3-octylPT produced by spin coating from solution with a solid polymer electrolyte and a metal oxide [175]. Substrates coated with PT have been claimed for use in electrochromic displays, in solar cells and for corrosion protection [185]. 

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