EIS measurements on a RDE Part I: Determination of a diffusion coefficient using the new element Winf – Application Note 66

Abstract

In this application note, the BluRev RDE is used along with a potentiostat to perform impedance measurements on a rotating disk electrode. An easy methodology to derive the diffusion constants of the reactive species using the fitting results of the impedance data is also presented. ZFit, the fitting analysis module in EC-Lab®, offers various elements to fit diffusion and convective diffusion impedances (Warburg, Wδ and Winf). The element which gives the best approximation of a convective diffusion is the newer element Winf, for which the goodness of fit is the highest. Another advantage of this element is that it directly gives the diffusion coefficient, without any further calculation as it is the case for the Warburg and Wδ element.

Introduction

Levich and Koutecký-Levich methods [1] are powerful analysis tools used to obtain kinetic electrochemical parameters such as the diffusion coefficient of a redox species in a given medium and the reaction constant. These analyses require to have potentiodynamic curves at various rotation speeds. However, fitting impedance measurements made on a redox reaction occurring at a quiescent or rotating electrode at only one rotation speed also enables the identification of the above-mentioned kinetic parameters. This first part of the application note will deal with the determination of a diffusion coefficient, while the second part of this note will deal with the determination of the redox reaction kinetic constant. The applications of these analysis tools are extremely wide: electrocatalysis, fuel cells, corrosion, sensors, electroanalytical chemistry, energy storage…

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