Determination of Constant Phase Element Parameters under Cyclic Voltammetry Conditions Using a Semi-theoretical Equation

An electrical double layer typically behaves as a constant phase element (CPE) rather than a pure capacitor. To separate the non-faradaic current contributed by the electrical double layer from the total current, which is obtained from cyclic voltammetry using modeling, the CPE parameters-the CPE parameter (Y-0) and the CPE exponent (gamma)-need to be determined. In this work, a semi-theoretical equation for directly evaluating the CPE parameters from cyclic voltammetry experiments was developed by investigating cyclic voltammetry performed under a narrow potential window. The experiments were performed using a ferri/ferrocyanide solution with a cylindrical graphite electrode. The obtained parameters were quantitatively different from those obtained from electrochemical impedance spectroscopy analysis. However, the obtained parameters were in an excellent agreement with cyclic voltammograms. This suggested that to model a non-faradaic current using a CPE in cyclic voltammetry, it is important to evaluate the CPE parameters using cyclic voltammetry. An application of the CPE parameters for simulating cyclic voltammograms that contain both faradaic and non-faradaic currents is also presented. The results show that the model can satisfactorily simulate entire cyclic voltammograms. (C) The Electrochemical Society of Japan, All rights reserved.