ON THE NATURE OF THE POTENTIOMETRIC RESPONSE OF POLYPYRROLE IN ACIDICSOLUTIONS

The potentiometric response of electrochemically coated polypyrrole la yers was studied both in hydrochloric acid and in alkali metal chlorid e solutions. The H+ ions were found to exert an influence, different f rom that of alkali metal cations, resulting in a positive slope of the open-circuit potential vs. log[H+] dependence. This was found also fo r concentrated KCl solutions, where the Donnan potential is close to z ero. Voltammetric and coulometric experiments demonstrated that this b ehaviour cannot be explained only by the acid-base properties of polyp yrrole. Additionally, redox reactions between the polymer film and sol ution components, whose equilibrium constants (and thus final open-cir cuit potential) may be pH dependent, should be taken into consideratio n. On the basis of model calculations, the influence of the concentrat ion of redox species on the potential of a polymer electrode is discus sed.