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

Abstract

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.

Frequency Response Analysis of a Nonstationary System: Electrochemical Transition of Polyaniline

“…Impedance values and types of impedance/frequency responses at different polarization potentials are in general agreement to those already obtained for PANI films at various oxidation states. [9,[35][36][37][38][39][40][41][42][43][44][45] Impedance due to experimental artefacts [35,37] and pure resistive impedance response which is mainly due to the uncompensated solution resistance, appeared at the highest frequencies, and are followed by PANI film impedance response at lower frequencies [32][33][34] . As expected, the impedance magnitude of PANI film is the highest for the reduced, PANI-LE state at -0.20 V and the lowest for the half-oxidized, PANI-EM state at 0.45 V vs. SCE.…”

“…Just the Nyquist type of PANI film impedance representation has been most frequently analysed in the literature. [35][36][37][38][39][40][41][42][43][44][45] Semicircle responses have usually been ascribed to double-layer interfacial capacitance coupled with charge transfer kinetics, while more or less vertical lines are due to more or less overlapped Warburg and pseudo-capacitive impedance responses. Time changes of IS are in Figure 5 denoted by arrows, suggesting either continuous decrease of circle diameters for LE-EM transition (Figure 5a), or continuous increase of circle diameters for EM-LE transition (Figure 5b).…”