Influence of water on the electrochemical properties of (CeO2)x(TiO2)1−x and WO3 sol–gel coatings and electrochromic devices

The paper focuses on a systematic study of the influence of water on the electrochemical and optical properties of (CeO2)x(TiO2)1−x and WO3 sol–gel coatings as well as devices made with these layers. The coatings were studied electrochemically in 1 M LiClO4 in propylene carbonate (PC) electrolyte with water content up to 3 wt.% by cyclic voltammetry (CV) and chronoamperometry (CA) up to 7000 cycles. For (CeO2)x(TiO2)1−x the exchanged charge was found to increase from 3 mC/cm2 (dry electrolyte) up to 11 mC/cm2 (3 wt.% water) so that the capacity of this counter electrode is greatly improved. For WO3 coatings, the transmittance change (Tcolored−Tbleached) is higher in wet electrolyte (1 wt.% water) than in dry electrolyte and remains constant (74%) under extended CV or CA cyclings. The electro-optical behavior of solid state electrochromic (EC) devices made with these layers with incorporation of water in the solid electrolyte is also drastically improved. They color and bleach reversibly with a constant and higher contrast and higher coloration efficiency (about 36 cm2/C) from the first cycle up to more than 50 000 CA cycles using safe applied voltages.