Electrodeposition of electrochromic V2O5 thin films.

Abstract

A uniform and adherent deposit of V2O5 thin film onto electroconductive glasses (ITO) has been obtained by electrolyzing colloidal V2O5 solution.A V2O5 sol was prepared from dilute solution of ammonium metavandate by passing the solution through an ion-exchange column (filled with Dowex 50 WX2 resin). The sol was then allowed to stand in a 40°C thermostat for 80 hrs. The viscosity of this sol increased with time, The measurement of the zeta potential of this sol indicated that the sol was negatively charged. Cathodic deposition of V2O5 is not a simple electrophoretic nature, since actually the V2O5 deposition occurred at the negative pole. We propose a following mechanism; the reduction of polyvanadic acid sol yielded a kind of vanadium bronze which coagulated onto the cathode (ITO) to form a solid film.On cathodic reduction the color of V2O5 film changes to green and on anodic oxidation it changes to light orange. The intermediate color tone has been also obtainable, therefore this system can be used as a multicolor device. The reversibility and durability for the electrochromic uses was almost comparable to a vacuum evaporated film.