Electrically controlled ion transfer and pH change near a conducting polymer-coated electrode

The incorporation and release of bromide anions into and out of a conducting polypyrrole film matrix polymerized on the disk of a rotating ring-disk electrode were electrically induced in an aqueous solution containing NaBr by electrical oxidation or neutralization of the film. The amount of Br^- incorporated into the film matrix was estimated by measuring (1) the difference in the Br^- oxidation current at the ring electrode before and after oxidation of the film on the disk electrode and (2) the oxidation current of the polypyrrole film at the disk electrode upon Br^- incorporation. The discrepancy between the amount of Br^- incorporated into the film matrix and the oxidation charge of the film, indicating simultaneous doping of anions other than Br^-, was attributed to simultaneous doping of OH^- anions. This hypothesis was tested and supported by the measurement of large pH changes near the polypyrrole film-coated electrode during the Br^- incorporation process.