ELECTROCHEMICAL PROPERTIES OF CATION SENSITIVE POLYPYRROLE FILMS

The influence of the electrochemical pretreatment (potentiodynamic cyc ling) and previous conditioning of thick cation sensitive PPB films (3 0 mu m) doped with sulphate, naphthalene-2-sulfonate (N-2-S) and napht halene-1,5-disulfonate (N-1,5-DS) on the electrochemical properties we re studied. The changes in the chemical composition of the PPy films w ere determined by electron probe microanalysis (EPMA). The poor mobili ty of dopant anions in the film and participation of cations in the PP y film redox process is the basis of their cation sensitivity. The inf luence of potentiodynamic cycling on the properties of these PPy films is correlated with the change of several factors, such as the redox a ctivity in the potential interval of the potentiometric measurements, the redox capacity, the ionic content and the quality of contact with the substrate. The long-term conditioning of the PPy electrode in a ce rtain solution is necessary for the achievement, maintenance or re-est ablishment of the stable quasi-equilibrium state of PPy film character ized by a quasi-equilibrium potential E-r. The conditioning process of the untreated PPy\N-2-S and PPy\N-1,5-DS electrodes proceeds very slo wly. It accelerates after potentiodynamic cycling, enabling the use of the electrodes for potentiometric measurements after only 2 days of c onditioning. The potentiodynamic cycling of the PPy electrodes doped w ith big organic anions improves also their potentiometric response, ex tending considerably the linear parts of E-log a plots towards low con centrations. The nature of this effect consists in the change of a thi ck PPy film to become redox active in the potential region of the pote ntiometric measurements. (C) 1998 Elsevier Science S.A. All rights res erved.