Electrochemically prepared poly(o-phenylenediamine) — Prussian blue composite film for a three-colour expressible ECD material

Abstract

Both Prussian blue (PB) and poly(o-phenylenediamine) (PoPD) were easily electrodeposited as stable films onto a transparent indium tin oxide (ITO) electrode. The voltammogram of the PB film showed a reversible sharp redox peak current at about 0.25 V. Although the colour change was caused by altering the applied potentials, no colour change was seen after about 10⁴ repetitions. The PoPD film also showed a reversible redox peak current at about −0.05 V. The redox reaction was accompanied by a readily observable colour change between nearly red (vermilion) and colourless. The PoPD film was electrodeposited onto the PB coated electrode to obtain a PB/PoPD composite film. The voltammogram of the film was comprised of the two redox waves of the individual components. The film retained the electrochromic properties of each component and there was no undesirable interference. By changing the potentials, the film exhibited a continuous variety of colours: colourless (-0.2 V), vermilion (0.1 V) and emerald green (0.6 V). The switching time of the colour change was found to be <600 ms. Compared with the PB film, the composite film lasted longer. About 60% of the colouration remained after 10⁵ repetitions since the PoPD worked as a binder which enhanced the adhesion of PB to the electrode surface.