Electrochromic response in polypyrrole sensitized by Prussian blue

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Abstract

The electrochromic response of polypyrrole (PPy)/Prussian blue (PB) composite films has been studied in different electrolytes such as KCl, LiClO4, K2SO4, KNO3, KI/I2, etc., by depositing the Prussian blue films on top of the conducting polypyrrole films, both being prepared by an electrochemical method. The results show that the use of PB on PPy not only yields high contrast but also extends the electrochromic response to a wider region of the visible spectrum, thus working as a sensitizer for improving the electrochromic contrast of the conducting polypyrrole.

Introduction

In the recent years, conducting polymers have attracted much attention because of the large number of possible applications of these materials in various electronic devices such as electrochromic displays (ECD), light emitting diodes (LED), field effect transistors (FET), chemical sensors, etc. 1, 2, 3, 4, 5. One of the extensively studied conducting polymers is polypyrrole (PPy) because of its better environmental stability and ease of synthesis 6, 7. The feasibility of the use of PPy in ECD, Schottky diodes, photovoltaic cells and chemical sensors has been demonstrated in the past 8, 9. However, it suffers a main drawback of having response characteristics limited to a narrow range of the visible spectrum. Prussian blue (PB) has been manufactured as an important inorganic pigment to be used for paints, printing inks, lacquers, etc. Also it has been known that the chemical reduction and oxidation of PB can lead to Prussian white (Everitt's salt) and Prussian green (Berlin green), respectively. Thus PB exhibits an interesting electrochromic behaviour 10, 11. However, PB films have a tendency to peal off the bare metallic substrates, especially during repeated handling and electrochemical cycling. Hence it was thought that by combining PPy with PB not only could the adhesion of PB be improved but also this combination would exhibit a wider range of electrochromic colours.

We report here the preparation and characterization of PPy films impregnated with Prussian blue and the electrochromic behaviour of the same. The resulting films show dramatic electrochromic properties, changing from blue to brown. Also, it has been seen that the use of PB yields high contrast together with extension of the electrochromic response to a wider region of the visible spectrum.

Section snippets

Experimental

The PPy/PB electrochromic composite system was fabricated by the following method. Conducting polypyrrole (PPy) films were deposited on gold-coated glass and also on transparent conducting (20 Ω/sq) indium–tin oxide (ITO) electrodes by conventional potentiostatic technique 12, 13using a single compartment electrolytic cell, with a platinum counter electrode, standard calomel reference electrode (SCE) and aqueous sulfuric acid (0.1 M) in which the pyrrole monomer (0.1 M) was thoroughly mixed.

Results and discussion

Fig. 1A depicts the cyclic voltammograms (CV) of PPy (curve a), PPy/PB composite film (curve c) and of PB by itself (curve b) all in a aqueous 0.01 M LiClO4 solution at a scan rate of 50 mV/s. It is apparent that the cyclic voltammograms of the PPy/PB composite films retain the features of both PPy and PB observed individually and the waves in the figure can be attributed to the oxidation and reduction processes as given in , as 8, 11PPyox+nePPyred,Fe3+4[Fe11(CN)6]3(Prussian blue)+neFe2+4[Fe

Summary and conclusions

The studies on the electrochromic response of the conducting polypyrrole films with Prussian blue film on top and for different electrolytes reveal that the colour change can be extended to longer wavelengths by changing the PB content in the films. The electrochromic contrast depends on the nature of the electrolyte, especially the size of the dopant ions and their electronegativity. It may be pointed here that the contrast in these films arises from the doping and undoping action due to ion

References (25)

  • D.P Amalnerkar et al.

    Solid State Commun.

    (1992)
  • J.A. Chilton, M. Goosey, Special Polymers for Electronics and Optoelectronics, Chapman & Hall, London,...
  • J.L. Bredas, W.R. Salaneck, G. Wegner, Organic Materials for Electronics, Elsevier, Amsterdam,...
  • B. Scrosati, Applications of Electroactive Polymers, Chapman & Hall, London,...
  • D Braun et al.

    Appl. Phys. Lett.

    (1991)
  • G Gustafson et al.

    Nature

    (1992)
  • L Jasne

    Encycl. Polym. Sci. Technol.

    (1988)
  • H Naarman

    J. Polym. Sci. Polym. Symp.

    (1993)
  • K Kaneko et al.

    Adv. Polym. Sci.

    (1988)
  • J.M. Bockris, in: L. Alcacer (Ed.), Conducting Polymers — Special Applications, ch. 1, Reidel, Dordrecht,...
  • K Itaya et al.

    J. Am. Chem. Soc.

    (1982)
  • K Itaya et al.

    J. Electrochem. Soc.

    (1982)
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