Polypyrrole-based electrochromic devices

Few reports on polypyrrole-based electrochromic devices have appeared due to air instability of the neutral undoped state of the polymer. A polypyrrole-based optical window performing in water has been proposed [423]. DePaoli et al. [424] have produced a device from electrochemically deposited polypyrrole dodecylsulfonate which results in improved properties over polypyrrole doped with perchlorate. 

Another interesting application that uses the dynamic properties of conducting polymers is electrochromic devices.44,45 46 47 An electrochromic device based on polypyrrole is shown in Figure 1.8. The polypyrrole changes from colorless to black when it is oxidized by the application of positive potentials. Similarly, polythiophene and polyaniline undergo distinct color changes when an electrical potential is applied. 

FIGURE 1.8 Example of electrochromic device based on polypyrrole-coated glass. 

Gazotti, Jr., W.A., M.-A. De Paoli, G. Casalbore-Miceli, A. Geri, and G. Zotti. 1999. A soKd-state electrochromic device based on complementary polypyrrole/polythiophene derivatives and an elastomeric electrolyte, f Appl Electrochem 20-153-131. 

Poly (thiophene)s are of particular interest as electfochromic materials owing to their chemical stability, ease of synthesis and processability. For the most part, current research has been focused on composites, blends and copolymer formations of several conjugated polyheterocyclics, polythiophene and its derivatives, especially PEIX)T. In one example, poly(3,4-ethylenedioxythiophene) (PEDOT)/poly(2-acrylamido-2-methyl-l-propanesulfonate) (PAMPS) composite films were prepared by Sonmez et al. for alternative electrochromic applications [50]. Thin composite films comprised of PEDOT/PAMPS were reported to switch rapidly between oxidized and neufial states, in less than 0.4 s, with an initial optical contrast of 76% at A.max. 615 nm. Nanostructured blends of electrochromic polymers such as polypyrrole and poly(3,4-ethylenedioxythiophene) were developed via self-assembly by Inganas etal. for application as an electrochromic window [26]. Uniir etal. developed a graft-type electrochromic copolymer of polythiophene and polytetrahydrofuran for use in elecfiochromic devices [51]. Two EDOT-based copolymers, poly[(3,4-ethylenedioxythiophene)-aZ/-(2,5-dioctyloxyphenylene)] and poly[(3,4-ethylenedioxythiophene)-aft-(9,9 -dioctylfluorene)] were developed by Aubert et al. as other candidates for electrochromic device development [52],... 

Electrochromic devices using solid electrolytes have been produced more recently. A device [425] is based on poly(3-octylthiophene) or polypyrrole films with vanadium oxide as a counter-material and poly(ethylen-oxide) as a solid electrolyte. The poor performances (maximum 100 cycles of operation) of these early devices, due to the instability of the materials and the high operating temperature, have been greatly improved by the use of poly(3,4-ethylenedioxythiophene), provided with a low oxidation potential and optimum contrast, and of a poly(ethylenoxide)-poly(phospha-zene) solid electrolyte of high room temperature conductivity [153]. This device may be operated up to 1000 cycles without losses. 

---