Electronic Conduction in Polymers. II. The Electrochemical Reduction of Polypyrrole at Controlled Potential

Molecular iodine was removed from polypyrrole by electrochemical reduction of slurries at a mercury cathode. This method was found to be more effective than the treatment of rigid or packed polymer electrodes. Voltammetric plots indicated that two reductions occurred, at potentials insensitive to pH. The current passage was dependent on the iodine content, while partial reduction or solvent extraction deleted the first current peak. Complete reduction or alkali treatment removed both peaks, whereas iodide in solution increased the reduction potentials. From this evidence it is postulated that the first peak is due to iodine in solution, the second to iodine present as a charge-transfer complex of polypyrrole. By estimating the amount of iodine and iodide present in the electrolyte the reduction potential for dissolved iodine was calculated and found to agree with that observed for the first peak in the slurry reduction. Confirmation of this potential was obtained in the reduction of a blank containing the found amounts of iodine and iodide. Quantitative data were obtained for the reduction of slurries in neutral electrolytes. There was reasonable agreement between coulometric estimations and the iodine removed, after correction for iodide already present, provided that the anode reaction did not supply reducible material to the catholyte. Reduction of iodine by polypyrrole itself did not appear significant in neutral suspensions. Iodine was readily removed electrochemically from the early polymers which contained only about 2.2 m-equiv/g. A later polymer contained almost a third more iodine and required prolonged reduction times which were cut considerably by the use of a silver anode to mop up iodide ion as it was formed. The reduction products were compared for changes in acidity, resistivity, and oxygen content. I.