Study of ionically conducting nanocomposites for reflective electrochromic devices

Highlights: • Ionically conducting gelatin-montmorilonite nanocomposites were studied and applied in reflective ECDs. • Gel-SCa-3-Li nanocomposites had higher reflectance values than Gel-SCa-3-Na. • The best conductivity was of 3.49 × 10⁻⁴ S cm⁻² at 25 °C for the sample of Gel-15-SCa-3-Na. • The ECD's reflectance changed from 15 (in colored state) to 8% (in discolored state) at 450 nm (blue light region). • The HYSCORE spectra of Gel showed one proton and for Gel-SCa-3-Na two proton signals. -- Abstract: New, nanocomposite, and ionically conducting membranes have been developed by using plasticized and crosslinked gelatin and clay (montmorillonite SCa-3) with concentration of 1–20 wt%. The samples were studied by FTIR, X-ray diffraction, UV-Vis (transmittance and reflectance), CW-EPR, HYSCORE, and ionic conductivity properties. The obtained results have revealed that the incorporation of clay has promoted changes in the physical properties of the samples. The transparency of theses membranes decreased, while the reflectance augmented with the rise of the clay content. The best ionic conductivity result of 3.49 × 10⁻⁴ S/cm² at 25 °C was obtained for the sample with 15 wt% of clay. CW-EPR spectra of Gel-SCa-3-Na samples doped with Cu²⁺ ions showed that SCa-3-Na had no significant impact on the Cu²⁺ local coordination surroundings and HYSCORE spectra showed one and two proton signals depending on the sample. Finally, the samples were inserted in the electrochromic devices (ECDs) composed of glass/ITO/Prussian blue/gelatin-SCa-3/CeO₂-TiO₂/ITO/glass. The best results were registered with the ECD containing 15 wt% of clay, which changed its reflectance from 15 to 8% at 450 nm. Moreover, this ECD demonstrated to be completely reversible. The obtained results confirmed the impact of the clay on the ionic conductivity, transparency, and performance of the ECDs. In summary, the nanocomposite electrolytes seem to be very interesting materials, mainly because of their possible practical use in electrochromic devices.