Frequency Dispersion of Double Layer Capacitance of Polyaniline-Coated Electrodes Under the Conducting State

The double layer capacitance of polyaniline (PANi)-coated electrode in acidic solution exhibited little frequency dispersion under the emeraldine (electrically conducting) state, while it showed large frequency dispersion under the insulating state. The former has a possibility of working as such an ideal capacitor that it may generate neither heat in iterative charge-discharge processes nor leakage of stored charge. The frequency dispersion is generally expressed by f-l for ac-frequency f and a constant l. This power law is ascribed to orientation of solvent dipoles rather than non-uniform distribution of ions. The value of l under the conducting state was close to zero, implying the orientation to be facilitated by less interaction of solvents. The less interaction was supported indirectly with strain-stress curves of PANi by atomic force microscopy. l-Values close to zero were retained even for thick PANi films.