INTRODUCTION:

The considerable interest in research of electrically conducting polymers is due to their wide range of potential applications such as electrochemical displays, smart windows, sensors, batteries, light emitting diodes and so on ^(1,2,3,4). The conducting polymers possess the electrical and optical properties of metals or semiconductors and that retain the attractive mechanical properties and processing advantages of polymers ⁽⁴⁾. The conducting polymeric materials are prepared chemically and electrochemically. In the electro chemical process polymers are formed potentiostatic (constant potential), galvenostatic (constant current) and potentiodynamic (cyclic voltammetry) means. The technique is an elegant way to obtain conducting polymers^(5,6,7,8).We reported previously electrochemical polymerization of pyrrole and aniline on some commodity metals such as Fe and Al and preparation of electrically conducting fibers by in situ electrochemical formation of polypyrrole in the solution of sulfosalicylic acid and p-toluene sulfonic acids^(9,10).In this paper we describe polymerization of pyrrole under the galvenostatic and potentiodynamic conditions in aqueous solution of oxalic acid as supporting electrolyte.

MATERIALS AND METHODS:

Material:

Pyrrole and water were fractionally distilled and middle fractions were collected. Oxalic acid was analytical reagent and used as received.

Polymerization:

The polymerization was carried out in a simple glass vial of 100 ml capacity. The anode and cathode were platinum electrodes of 0.5cm x 2.5cm. The solution was de-aerated by N₂ gas and thermo stated at 25⁰C. The amount of polymer formed on the anode was determined gravimetrically.

Cyclic voltammograms were recorded in a CV-27 BAS (Bio Analytical System, U.S.A) and the cyclic voltammetry system was equipped with a BAS X-Y recorder. The reference electrode was Ag /Agcl electrode.

RESULT AND DISCUSSION:

The polymerization of pyrrole (0.50 mole/L) in a solution of oxalic acid (0.50 mole/L) in water was carried on Pt. anode at different impressed currents as shown in Figure 1. As soon as current was switched on, a shining black mass began to deposit on the anode.

Thus the various thickness of polypyrrole films were obtained by varying the time of polymer deposition on the anode. The anolyte remained completely clear during the course of polymerization. The weight of polypyrrole formed at the anode increase linearly with the time of electrolysis at different impressed current level, as is seen from Figure 1.

Cyclic voltammograms of polypyrrole film:

The voltammetric behaviors of pyrrole in an aqueous solution of oxalic acid at the potential range of +0.50V to 1.65V vs. Ag/Agcl electrode at 150mv/s were examined as shown in Figure 2.

The experiment was repeated at different potential cycles. It was observed that the peak current regularly decreases with number of potential cycles as is seen from figure 3.

In Figure 3 top curve represents the first cycle and the bottom one the last cycle. It suggests that electro active species are not stable in an aqueous solution and their concentration decreases rapidly. In a separate run a thin film of polypyrrole was made at 1.0V on Pt microelectrode. The film was washed several times to remove the pyrrole monomer and then immersed in the solution of oxalic acid. The voltammograms of polypyrrole film in absence of the monomer were recorded at different scan rates. The redox peak current gradually increases with the scan rates as is evident from Figure 4.

It shows that the film is quite stable. The polymerization occurs via a cation radical intermediate ⁽⁹⁾. The initial oxidation of the monomer gives a monomeric radical cation that couples to form the dimer with the expulsion 2H⁺. This process is repeated with 2e^- and 2H⁺ involved in each addition step to finally yield polymers. The neutral and oxidized states of polypyrrole is shown below⁽¹¹⁾.

CONCLUSION:

In conclusion pyrrole electrochemically polymerizes on the anode in the aqueous solution of oxalic acid and polymer yields increase with increasing impressed current levels. Cyclic voltammograms show that the polymer film is stable.

REFERENCES:

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9. Bhadani Reena, Kumari M, Baranwal PP,and Bhadani SN. Electrochemical polymerization of pyrrole and aniline on some commodity metals. Journal of Polymer Materials. 19(1); 2002: 93-102.

10. Bhadani Reena, Baranwal PP, and Bhadani SN. Electrically conductive nylon fibers by in situ electrochemical formation of polypyrrole. Journal of Polymer Materials. 19(3); 2002: 259-264.

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Received on 23.12.2012 Modified on 12.01.2013

Asian J. Research Chem. 6(1): January 2013; Page 92-94