Electrochromic mechanism

L. M. Loew, S. Scully, L. Simpson, and A. S. Waggoner, Evidence for a charge-shift electrochromic mechanism in a probe of membrane potential, Nature 281, 497 (1979). 

Besides electricity-induced oxidation-reduction and heating mechanisms, there are other electrochromic mechanisms that give rise to the electrochromic behavior, such as electro-introduced conformational changes of conjugated polymers, reorientation of liquid crystals and change of lattice constant in opals. 

Ye C, Tamagawa T, Polla DL (1991) Experimental studies on primary and secondary pyroelectric effects in Pb(Zr, Tij x,) , PbTiOj, and ZnO thin films. J Appl Phys 70(10) 5538-5543 Zampiceni E, Comini E, Faglia G, Sberveglieri G, Kaciulis S, Pandolfi L, Viticoli S (2003) Composition influence on the properties of sputtered Sn-W-0 films. Sens Actuators B 89 225-231 Zhang J-G, Benson DK, Tracy CE, Deb SK, Czanderna AW, Bechinger C (1996) Electrochromic mechanism in a-WO films. J Electrochem Soc 24 251-259... 

From the electrochromic mechanism described above, it can be concluded that the polymer electrolyte must be employed in the ion conducting layer. However, what type of polymer electrolyte is adopted depends on which ion is used in an electrochromic device. Theoretically, all cations can be used in electrochromic devices. Actually, only a few kinds of cations, such as H+, Li", Na", OH, F" and the like, are appropriate. As a result, when H" is used, the ion conducting layer is based on PFSA and so on. If LF is used, the ion conducting layer is similar to that used in a lithium ion battery. And for OH , it is an alkaline polymer electrolyte. 

Members of the ion-insertion/extraction group, as inorganic or organic thin films, especially the former, have attracted the widest interest most recently. Tungsten trioxide was the eadiest exploited inorganic compound (4), even before the mechanism of its electrochromic response was understood (5). It is stiU the best known of the important ion-insertion/extraction group. 

Quantitative analysis of the XPS data indicates a constant O/Ir ratio of close to 3 [34] and an OH/O ratio of 2 for a potential of 0.9 V and of 1/2 at 1.25 Vsce. These results, together with electrochemical data substantiate the reaction mechanism given in Fig. 26 for the electrochromic effect and for 02 evolution. 

Quantum Mechanical-Classical Mechanical (QM-MM) Methods for Solvatochromism and Electrochromism Predictions... 

In the nonstochiometric redox state, intervalence charge transfer between adjacent WVI and Wv sites leads to the observed intense blue color. Apparently, if the ratio of WVI to Wv is increased further, the ion insertion becomes irreversible, resulting in a permanent color change to red or golden [34,35]. It should be noted that in spite of the apparent progress in explaining the electrochromism on a fundamental level, questions remain and alternate mechanisms have been proposed which suggest the involvement of other oxidation states [36]. 

Chapter 6 takes the much studied supramolecular dye-sensitized TiC>2 as an example of an operational supramolecular interfacial device. The fundamental operation of these devices are discussed, including their mechanism of operation. The application of modified semiconductor surfaces as electrochromic devices is also considered. 

For the unique properties of PBs to be exploited, PBs must be deposited properly onto a solid support. It is highly desirable to prepare mechanically robust PBs films with controlled thickness, chemical composition and crystallinity, having ion-sieving membranes and electrochromic devices in mind [6], or to create regular patterns of PB-based single molecule magnets [13],... 

Hydrous oxides films, many of them with electrochromic properties, have been grown on a number of other metals using potential cycling methods, for example Rh [126] and Ni [159] in alkaline solution. Film formation seems to occur via a similar mechanism to Ir on the various metals under potential cycling conditions. Further, the films exhibit the same type of potential-pH response [150,160] as that described above in the case of Ir. 

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