Semi-solid state electrochromic device based on deep eutectic solvent gel electrolyte and transparent Au modified FTO electrode

A semi-solid state electrochromic device with deep eutectic solvent gel as the electrolyte, Ethyl-viologen as the electrochromic compound, and K 4 Fe(CN) 6 as the electron donor was reported. Four kinds of silica were simply mixed with ethaline for preparing the gel electrolyte, and the hydrophilic ones were found to be capable of being used as the gelling agent . To enhance the electron transfer at the electrode/gel interface and keep the transparency of the electrode, tiny amount of Au was electrochemically deposited on the FTO electrode. The as-prepared electrochromic device shows a coloration time of ca. 60 s at −0.7 V with the coloration efficiency of 91 cm 2 /C, and a bleaching time of ca. 150 s at 0 V with the efficiency of 194 cm 2 /C. The reversible response of the electrochromic device up to 820 cycles with Δ T max > 60% was also demonstrated.