Limiting concentration of hydrogen in an electrochromic tungsten trioxide film

The electrochromic phenomena in tungsten trioxide (WO 3 ) films involve the formation of H x WO 3 . The maximum value of x in H x WO 3 is found to be 0.4 from EMF measurements of the WO 3 films during electrochemical reduction. The optical absorbance of H x WO 3 increases linearly with the increase of x up to x=0.4. Further injection of cathodic charge results in the evolution of hydrogen