Electrochromic effects in solid phosphotungstic acid and phosphomolybdic acid

The electrochromic performance of all solid-state cells employing phosphotungstic acid and phosphomolybdic acid is reported. These cells employ SnO2 as the viewing electrode and graphite as the back electrode. Diffuse reflectivity changes of ∼50% are readily achieved in ∼10 msec. The cells, in the bleached state, can be made white to red, and become black in the colored state.