Electrochromic response in polypyrrole sensitized by Prussian blue
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, 11
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)
- 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,...
- et al.
Appl. Phys. Lett.
(1991) - et al.
Nature
(1992) Encycl. Polym. Sci. Technol.
(1988)J. Polym. Sci. Polym. Symp.
(1993)- et al.
Adv. Polym. Sci.
(1988) - J.M. Bockris, in: L. Alcacer (Ed.), Conducting Polymers — Special Applications, ch. 1, Reidel, Dordrecht,...
J. Am. Chem. Soc.
J. Electrochem. Soc.
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