On the electrical capacitance of interfaces exhibiting constant phase element behaviour

Abstract

It is stressed that any attempt to characterise the interfacial double layer exhibiting a constant phase element (CPE) behaviour by electrical capacitance is misleading. The only possibility to obtain the value of the interfacial double layer capacitance is to ascribe to the double layer a capacitive character. Such a simplifying assumption causes a modelling error and influences all parameters of the system. The problem is analysed for several characteristic examples of an electrode system, where a simple electrode reaction takes place. The two most frequently used definitions of CPE are applied. One of them should be rejected, as intrinsically erroneous. An electrode with a double layer of CPE character can never be an `ideally polarizable electrode'. The conclusions can be qualitatively applied to all systems with an interface revealing CPE behaviour.