Electrochemistry of conductive polymers XVII characterization of polythiophene electrochemically polymerized in aqueous solutions

Summary form only given. Polythiophene has been prepared in aqueous solutions containing 1.2 M HCI, 5.7 M ethyl alcohol, and 0.43 M thiophene by repeatedly cycling potentials between -0.25 V /spl tilde/ 1.75 V vs. the Ag/AgCl, saturated KCl reference electrode. The polymer films thus prepared were denser and more stable than those prepared in nonaqueous solutions. The films could be doped both anodically at 1.2 V an cathodically at -0.3 V; their cyclic voltammograms (CVs) were better defined and more reversible than those obtained in aqueous solvents for both oxidation and reduction. While the anodic CV currents at 1.2 V were not affected significantly by the pH of the medium, those at -0.3 V were markedly affected. The CV peak potentials were not very sensitive to pH, suggesting that proton transfer may not play a significant role during the electrochemiscal doping. The films were not destroyed even when they are anodized at +2.5 V in a LiCl solution. In-situ spectroelectrochemical experiments show that the polymer films have their maximum absorbances observed between 350 nm and 420 nm depending on the electrolytes used, indicating the band gaps, and therefore chain lengths, of the polymers could be significantly different in different electrolyte solutions. The conductivities of these polymers appear to be inferior to those prepared in nonaqueous solutions is shown by large resistances obtained from the ac impedance measurements.