Improvement of conductivity of electrochemically synthesized polyaniline

The electrochemical polymerization of aqueous solution of aniline and HCl was carried out in a single compartment electrochemical cell. After 2 h of the polymerization reaction, polarity of the electrodes was reversed and kept for 1 h. By this process the conductivity of the polyaniline (PAni) formed was found to increase dramatically from 1.1 x 10(-4) to 3.0 x 10(-1) S/cm. The PAni samples obtained both by reversing the polarity (PANI-R) and without reversing the polarity (PANI) were characterized by the infrared spectroscopy (FT-IR), thermogravimetric analysis (TGA), ultraviolet spectroscopy (UV), Hall effect experiment, X-ray analysis (XRD) and scanning electron microscope (SEM). The results show that the increase in the conductivity of PAni through the reversion of polarity is due to the partial reduction of over oxidized sample giving more emeraldine base and hence more polaron formation with increased charge carrier density and its mobility. The degree of crystallinity and the crystallite size is decreased marginally and the d-spacing is increased marginally due to this reduction. The PAni behaves like a p-type semiconductor that means the majority current carriers are holes. A plausible reduction mechanism due to reversal of polarity during electrochemical polymerization is also proposed. (C) 2007 Wiley Periodicals, Inc.