On the use of a constant phase element (CPE) in electrochemistry

Several techniques can be used to experimentally determine the interfacial capacitance of an electrode, which is a crucial parameter used for quantifying the efficiency of supercapacitors. However, the values obtained from cyclic voltammetry can be significantly different from those extracted from electrochemical impedance spectroscopy analysis. This is particularly due to the fact that the interface does not behave like an ideal (i.e., frequency independent) capacitor, and requires the adoption of a constant phase element (CPE). In this article, we present the state of the art on this apparent difference and on the error that can result from one or the other technique using CPE analysis.