Dynamic Behavior of Electric Double Layer Impedance

Abstract

Electric double layer capacitance has the time-dependence with the power law of the ac-frequency. The dependence gives rise to a resistance component at the interface when the impedance is measured dynamically. The interfacial resistance does not really exist but is inevitably involved in the measured current as a result of the time-dependent capacitance. It is infinite for dc-response, but decreases with an increase in the ac-frequency in the inversely proportional form. It cannot be discriminated against the heterogeneous kinetics. The frequency-dependence agrees with the behavior of the constant phase element. The capacitance is brought about by orientation of solvent molecules, independent of concentration of salts, kinds of salts, and applied dc-potential. The orientation is modeled by combination of the external electric field and the interaction of nearest neighboring solvent molecules. Since the former conflicts with the latter in the orientation, phases may be formed two-dimensionally with competition, which prolong the relaxation with the lower law.