The advantages of applying polymeric ion conductors to electrochromic(EC) devices' were mentioned in relatively early studies of the EC research. The electrochromic devices based upon amorphous W03 in the past used the liquid protonic electrolytes such as sulfonic acid. However, the W03 films were found to be dissolved in contact with aqueous media, forming poly- tungstate. Such degradation of the W03 film in electrochromic devices was partly overcome by replacing the sulfonic acid with proton conducting polymers. In the meanwhile, reduction of underlying transparent conductive oxides were found as a result of proton attack. Thus appeared the non- aqueous electrolytes,e.g. solutions of an alkali salts in aprotic solvents.
J. Nagai, J. Nagai,
"Polymeric ion conductors", Proc. SPIE 10304, Large-Area Chromogenics: Materials and Devices for Transmittance Control, 103040O (28 March 1990); doi: 10.1117/12.2283627; https://doi.org/10.1117/12.2283627