Deep Eutectic Solvent with Prussian Blue and Tungsten Oxide for Green and Low-Cost Electrochromic Devices

Deep eutectic solvents (DESs), as a class of green and sustainable solvents, are the valuable alternative media for various applications. Here choline chloride (ChCl)-urea DES was used as the electrolyte for electrochromic reactions of two inorganic electrochromic materials (Prussian blue (PB) and tungsten trioxide (WO3)). Starting from the evaluations of thermal and electrochemical properties of ChCl-urea DES, we found the DES electrolyte can be used in the electrochromic experiments at a wide temperature range (from 25 to 100 °C) and potential range (from −0.8 to 1.0 V vs Ag). And as the temperature increased, both coloring and bleaching time dramatically decreased but efficiency decreased little. A complementary electrochromic device with PB-DES-WO3 was also fabricated to demonstrate the feasibility for electrochromic applications with the combination of green and cheap DES and inorganic electrochromic materials.