Agar-Based Solid Polymer Electrolyte-Containing Ionic Liquid for Sustainable Electrochromic Devices

In the scope of circular economy, in order to achieve a new generation of sustainable and environmentally friendly materials and devices, sustainable solid polymer electrolytes emerge as a requirement for applications such as electrochromic devices (ECDs). The dispersion of ionic liquids (ILs) into polymer matrices allows the development of solid polymer electrolytes with high ionic conductivity. Agar-based electrolytes have been developed containing different contents of 1-ethyl-3-methylimidazolium thiocyanate ([Emim][SCN]). The ionic conductivity of the samples varies with the IL concentration and temperature. The highest conductivity value is obtained for the sample with 40 wt % [Emim][SCN], being 2.9 × 10 –3 S cm –1 at 30 °C and 5.6 × 10 –3 S cm –1 at 90 °C. Assembled ECDs with poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonate) screen-printed electrodes show that the optical density depends on the IL content, the coloration efficiency at 90% being 2120 and 1422.8 cm 2 ·C – 1 for 20 and 40 wt % [Emim][SCN] content, respectively. Thus, the developed sustainable solid polymer electrolytes, based on natural polymers and ILs, represent suitable candidates for environmentally friendly ECDs.