Influence of water on the electrochemical properties of CeO_2-TiO_2 sol-gel coatings and electrochromic devices

摘要

The paper focuses on a systematic study of the influence of water on the electrochemical and optical properties of CeO_2-TiO_2 and WO_3 sol-gel coatings as well as devices made with these layers. The coatings were studied electrochemically in 1 M LiClO_4 in propylene carbonate electrolyte with water content up to 3 wt%. The intercalated and deintercalated charge was measured during Cyclic Voltammetry (CV) and Chronoamperometric (CA) cycles up to 500 cycles (TiO_2-CeO_2) and 7000 cycles (WO_3). For CeO_2-TiO_2 it was found to increase from 3 mC/cm~2 (dry electrolyte) up to 11 mC/cm~1 (3 wt% water). This increase is important for the coloration of EC-devices because the charge capacity of this counter electrode is known to be a limiting factor for the transmission change of the EC-devices. For WO_3 coatings, the transmission change (T_(colored)-T_(bleached)) is higher in wet electrolytes (1 wt% water) than in dry electrolyte and above all remains constant (74%). These improvements are essentially due to an increase of the kinetics of the intercalation and deintercalation of Li~+ ions. The electro-optical behavior of solid state EC-devices with and without incorporation of water in the solid electrolyte measured up to 50000 CA cycles is also presented and discussed.