An Inexpensive Device for Studying Electrochromism

Abstract

A novel procedure for the preparation of electrochromic WO3 films from readily available materials is presented. It is based on the electrochemical preparation of potassium tungstate from tungsten filaments of incandescent light bulbs in a potassium hydroxide solution. Tungstic acid is then produced by proton exchange using a super-absorbing polymer from a baby diaper. Simple air drying of the tungstic acid produces a tungsten(VI) oxide layer. On the surface of a copper foil or coupon or of a conducting glass, an electrochromic bleached (colorless)-to-colored (blue) transition of this oxide layer is easily observed by applying an external potential with a common power source in an electrochemical cell where the Cu (or the conducting glass) electrode is the cathode and a Pb electrode is the anode. This experiment can be performed in 2–3 h and is suitable for an applied inorganic chemistry or electrochemistry lab course.