Tungsten Oxide‐Prussian Blue Electrochromic System Based on a Proton‐Conducting Polymer Electrolyte

Abstract

A new solid‐state electrochromic system is presented. It is transparent and is comprised of a tungsten oxide and Prussian blue (PB) thin film couple in combination with a proton‐conducting, solid polymer electrolyte. This electrochromic system exhibits rapid and deep optical switching; characteristic of a complementary configuration, both electrochromic films color and bleach in phase. Complementary electrochromic cells with the tungsten oxide‐PB couple have previously been based on Li+ or K+‐conducting electrolytes. A repetitively cycling cell has not previously been reported with a proton‐conducting solid polymer electrolyte. The devices were operated at low applied voltages, +1.2 V to darken and −0.6 V to bleach. Repeated reduction and oxidation of the current system over 20,000 cycles has been demonstrated, indicating a large number of switchings without great degradation or irreversible side reactions. The sustained, high overall coloration efficiency of the devices suggests the insertion/extraction of protons into and out of both and PB films. The effects of cell size and operating temperature on the switching response are discussed.