Proton conductors as electrolytes in ECD devices

In an ECD, the electrolyte is used as the reservoir of cations needed for injection into the electrochromic films for either coloration or bleaching. Such a device needs fast response, chemical and electrochemical stability, reversibility and memory properties. To achieve fast coloration kinetics with WO3, the use of protonic electrolytes is very attractive since protons have the highest mobility in the electrochromic films compared with other cations. Their use would then lead to the fastest ECD performances. However, the presence of protons is not sufficient and a conductivity of 

Most of the earlier studies on proton insertion in ECDs, have been devoted to acidic aqueous electrolytes. However, since most of the electrochromic materials are chemically unstable in acidic medium, commercially viable ECDs must use other electrolytes. Recently, the use of solid anhydrous proton electrolytes seems to be very promising. We present some of the materials which have been used in ECDs. 

The first attempt to use ion-containing polymers in ECDs was made by Randin in 1982 . He investigated polystyrene sulphonic acid (PSSA), polyethylene sulphonic acid (PESA), poly-2-acrylamide-2-methylpropane 

Since it seems clear that it is the combination of acid functions and free water in the electrolytes that leads to the chemical instability of WO3, the use of anhydrous protonic polymers may be attractive for this kind of application. Recently, anhydrous polymers have been synthesized and studied. However, only a few studies are reported on the performances of such complete ECDs. Table 38.2 presents the values of conductivity, at room temperature, of some of these polymers. These materials are promising for an electrochromic cell with WO3 but their conductivity has to be improved to be of the order of 10 (Q.cmj Either ammonium salts or acids have been added to polymers such as poly(ethylene oxide) (PEO), polyvinylpirolydone (PVP), poly(ethylene imine) (PEI), poly(vinylalcohol) (PVA), poly(acrylic acid) (PAA), branched poly(ethyl-ene imine) (BPEI), poly(acrylamide) (Paam) to obtain anhydrous protonic conductors. 

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