The Apparent CPE Behavior of a Disk Electrode with Faradaic Reactions: A Global and Local Impedance Analysis

Abstract

Geometry-induced current and potential distributions modify both the global and local impedance response of a disk electrode subject to Faradaic reactions. The problem was treated for both linear and Tafel kinetic regimes. At frequencies above the characteristic frequency for the Faradaic reaction, the global impedance response has a quasi-CPE character, but with a CPE coefficient α that is a function of both dimensionless frequency K and dimensionless current density J. For small values of J, α approached unity; whereas, for larger values of J, α reached values near 0.78. While the calculated global impedance was purely capacitive, the local impedance has high-frequency inductive loops. The local impedance is influenced by the local Ohmic impedance, which has complex behavior near a characteristic dimensionless frequency K = 1.