Electrochromic Properties of Ruthenium Compound Films Formed by Chemical Deposition

Ru II (NH3)6Cl2 was dissolved in aerated distilled water to a concentration of 3×10-2mol/L, and the solution was then aged in contact with the atmosphere for 24 hours at 25°C. ITO glass substrates were then immersed in the aged solution for 72 hours, taken out, and dried. A uniform, blue-colored thin film was obtained. Electrochemical measurements were performed in 0.01mol/L H2SO4 electrolyte, using SCE as the reference electrode. The surface morphology of the ruthenium compound film showed many granular deposits, indicating a relatively large surface area. TEM and electron diffraction observations showed that the film was composed of grains of various sizes and was amorphous. The electrochromic bohavior showed reversible color change of 104 times, being almost colorless at an applied potential of +100mV vs SCE and blue at +900mV. In the cyclic voltammograms, two redox peaks were observed, corresponding to the coloration and bleaching respectively. The main coloration reaction occurred at +300mV, and bleaching occurred at +230mV. However, the relation between the injected charge and the optical density was not proportional, because there was a two-step coloration/bleaching reaction. The coloration efficiency calculated from these data was ca. 80cm2/C, which is comparable to that of WO3.