Charge Transport at Polypyrrole Film Electrodes: Effect of the Electrolyte Concentration

From measurements of the a.c. response of polypyrrole film electrodes in KNO3 solution, we found that solvent swelling of the polymer greatly influences the kinetic behaviors of the polymer film electrodes. Electric migration in bulk film was due to background electrolyte ions which permeated through the film. Inside the film in contact with a supporting electrolyte solution, the mobility of the electrons may be much smaller than that of ions. The charge-transfer resistance of a partially oxidized film decreases along with increasing concentration of the electrolyte solution, because of a resultant increase in the activity of polarons. Such an increased activity of polarons also brings about a smaller Warburg coefficient, and thus a smaller limiting diffusion resistance (RL). The pseudocapacitance appearing at low frequencies increases along with an increase in the concentration of the electrolyte solution, which is opposed to the change in RL. These results corroborate that variations in the charge-transport parameters with the electrolyte concentration can be ascribed to an increase in the polaron activity with increasing ion concentration inside the polymer film.