Solid Polymer Electrolytes Based on Gellan Gum and Ionic Liquid for Sustainable Electrochromic Devices

[Image: see text] Materials sustainability is becoming increasingly relevant in every developed technology and, consequently, environmentally friendly solid polymer electrolytes (SPEs) based on gellan gum and different quantities of ionic liquid (IL) 1-ethyl-3-methyl-imidazolium-thiocyanate [Emim][SCN] have been prepared and applied in electrochromic devices (ECDs). The addition of the IL does not affect the crystalline phase of gellan gum, and the samples show a compact morphology, surface uniformity, no phase separation, and good distribution of the IL within the carrageenan matrix. The developed SPE are thermally stable up to ∼100 °C and show suitable mechanical properties. The most concentrated sample (39 wt % IL content) reaches a maximum ionic conductivity value of 6.0 × 10(–3) S cm(–1) and 1.8 × 10(–2) S cm(–1) at 30 and 90 °C, respectively. The electrochromic device (ECD) was fabricated with poly(3,4-ethylenedioxythiophene) polystyrenesulfonate (PEDOT:PSS) as working electrode and the developed SPE was compared with an aqueous 0.1 M KNO(3) solution. The electrochromic performance of the electrolyte was assessed in terms of spectroelectrochemistry, demonstrating a fully flexible ECD operating at voltages below 1.0 V. This novel electrolyte opens the door to the preparation of high performance sustainable ECD.