AC Impedance Behavior of Electrochemical Capacitors and Other Electrochemical Systems

Abstract

It was shown in Chapter 3 how capacitance can be characterized by the response functions of current to various time-dependent changes of potential or, complementarity, changes of potential across a capacitance in response to a charging current. One of the most direct response functions that characterize the inter-facial or pseudocapacitance of an electrode is the alternating current generated in response to an alternating voltage (av) addressed to an electrode interface. This response, represented by the imaginary component, Z″, of the impedance (see Section 16.2.1, Eq. 16.25), is related to the capacitance, through that equation, as Z″ = 1/jωC. Hence the employment of alternating current (ac) impedance measurement has become one (among several) of the principal procedures for evaluating the capacitative behavior of individual electrodes and two-, or multielectrode electrochemical devices.