Electrohydrodynamical Impedance on a Rotating Disk Electrode: I . Redox System

Abstract

Analytical expressions of the response of the observable electrical quantities (current or potential) to a sinusoidal perturbation of the rotation speed of a rotating disk electrode have been derived for a redox process. These expressions hold in the limiting diffusion current conditions as well as in the intermediate kinetics and whatever the regulating mode used (potentiostatic or galvanostatic). For a galvanostatic regulation the normalized electrohydrodynamical impedance only depends on the Schmidt number and does not depend on the electrochemical kinetics. On the other hand for a potentiostatic regulation the normalized electrohydrodynamical impedance depends both on the Schmidt number and on the electrochemical kinetics. Hence the expression of this last electrohydrodynamical impedance involves the usual electrochemical impedance. The analysis of the experimental results obtained by using two fast redox systems for high values of the Schmidt number and covering a wide frequency range shows a good agreement with the theoretical derivations.