Influence of Metal Overlayers on Electrochromic Behavior of WO sub(3) Films

Metallic overlayers have been deposited on vapor-deposited WO sub(3) to control the kinetics of coloration and bleaching in a WO sub(3)-liquid electrolyte electrochromic cell. These overlayers, when porous, have been found to increase the rate of coloration/bleaching and the proton transfer rate at the WO sub(3)-electrolyte interface, when appropriate voltages were applied. This effect has been characterized with potentiostatic and galvanostatic measurements and compared to the coloration and bleaching of WO sub(3) (without metallic overlayers). Coloration of WO sub(3) films is influenced at short times by resistance and electric field effects, in disagreement with the general assumtion of high conductivity in vapor-deposited WO sub(3).