Ageing of electrochromic WO3 coatings characterized by electrochemical impedance spectroscopy

We have developed a method for characterization of ageing of electrochromic materials by electrochemical impedance spectroscopy (EIS). Electrochromic WO3 thin films have been electrochemically cycled in propionic acid electrolyte and probed by EIS and optical measurements. A very small amount of optical degradation was observed in both the bleached and coloured states. The samples exhibited a few hundred times higher impedance in the bleached state than in the coloured state. It was observed that, in the bleached state, impedance values at low frequencies increased significantly with increasing number of cycles.