Influence of ferrocyanide on the long-term stability of poly(butyl viologen) thin film based electrochromic devices

Abstract

High bleaching/coloring electrochemical reversibility is crucial for practical applications of an electrochromic material. In this study, ferrocyanide-containing poly(butyl viologen) (PBV:fc) thin films were prepared by electropolymerization, and subsequently investigated and compared their redox properties by using the electrolyte with and without the addition of potassium ferrocyanide (K4Fe(CN)6). Electrochemical and electrochromic properties of the PBV:fc thin films were studied by using cyclic voltammetry (CV) and UV–Vis spectroscopy techniques. The mass changes of the PBV:fc thin films during their redox reactions were studied by using electrochemical quartz crystal microbalance (EQCM) technique. In addition, the scanning electrochemical microscope (SECM) studies confirmed the stable anion insertion/extraction of Fe(CN)64− within a PBV:fc thin film. The obtained results indicate that the redox reversibility of the PBV:fc thin film can be effectively improved by the addition of K4Fe(CN)6 in the electrolyte. It is deduced that the enhancement of bleaching/coloring stability of the PBV:fc thin film is affected by Fe(CN)64− charge balance during the reactions. Complementary electrochromic devices (ECDs) using the PBV:fc and Prussian blue (PB) thin films were fabricated. Finally, the ECD with the electrolyte containing K4Fe(CN)6 shows the superior transmittance modulation stability than the one without K4Fe(CN)6.