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

Abstract

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/cm(2) (dry electrolyte) up to 11 mC/cm(2) (3 wt.% water) so that the capacity of this counter electrode is greatly improved. For WO3 coatings, the transmittance change (T-colored - T-bleached) is higher in wet electrolyte (I wt.% water) than in dry electrolyte and remains constant (74%) under extended CV or CA cyclings. The electrooptical 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 cm(2)/C) from the first cycle up to more than 50000 CA cycles using safe applied voltages.