On the potential-step hold time when the transient-current response exhibits a Mittag-Leffler decay

Abstract We present the theoretical underpinnings for the use of a constant phase element (CPE), along with the potential-step test method (PSM), to determine the parameter values of a CPE-RP Randles-type circuit model from the transient-current response. Specifically, we analyze the potential-step hold time covering the fractional-order dynamic transition between the sufficiently short times, in which the current measured is practically due to the non-ideal interfacial capacitance, and the longer times corresponding to a current practically faradaic. An interface of biomedical interest consisting of a gold electrode immersed in a 0.9% NaCl physiological saline solution was analyzed using both PSM and impedance measurements.