Randles circuit

In real electrochemical systems, impedance spectra are usually more complicated and, thus, the Randles circuit may not give appropriate results.

Figure 1 shows the equivalent circuit initially proposed by John Edward Brough Randles for modeling of interfacial electrochemical reactions in presence of semi-infinite linear diffusion of electroactive particles to flat electrodes.

A simple model for an electrode immersed in an electrolyte is simply the series combination of the ionic resistance, RS, with the double layer capacitance, Cdl.

The key assumption is that the rate of the faradaic reaction is controlled by diffusion of the reactants to the electrode surface.

Values of the charge transfer resistance and Warburg coefficient depend on physico-chemical parameters of a system under investigation.