A Way for Determining the Effective Three Phase Boundary Width of Solid State Electrochemical Reactions from the Primary and Secondary Current Distribution at Microelectrodes

Abstract

A way is suggested for determining the effective three phase boundary width of electrodes on solid electrolytes from the difference between the electrolyte resistance of the primary and the secondary current distribution at a circular microelectrode. It is shown by means of numerical finite element calculations how the potential distribution in the solid electrolyte depends on the frequency and how the corresponding variation of the electrolyte resistance can lead to an additional semicircle in the complex impedance plane. An equivalent circuit is introduced for analyzing such a situation and thus for determining the additional ohmic resistance due to current constriction close to the three phase boundary region of the electrode. This additional resistance is quantitatively related to the effective three phase boundary width and thus can serve as a tool to estimate the size of the electrochemically active region of electrode reactions such as oxygen reduction or hydrogen oxidation on oxide ion conducting solid electrolytes.