Rotating disk electrode

A rotating disk electrode (RDE) is a hydrodynamic working electrode used in a three electrode system. [Bard, A.J.; Faulkner, L.R. Electrochemical Methods: Fundamentals and Applications. New York: John Wiley & Sons, 2nd Edition, 2000.]

Structure

The electrode includes a conductive disk embedded in an inert non-conductive polymer or resin that can be attached to an electric motor that has very fine control of the electrode's rotation rate. The disk, like any working electrode, is generally made of a noble metal or glassy carbon, however any conductive material can be used based on specific needs.

Function

The disk's rotation is usually described in terms of angular velocity. As the disk turns, some of the solution described as the "hydrodynamic boundary layer" is dragged by the spinning disk and the resulting centrifugal force flings the solution away from the center of the electrode. Solution flows up, perpendicular to the electrode, from the bulk to replace the "boundary layer". The sum result is a laminar flow of solution towards and across the electrode. The rate of the solution flow can be controlled by the electrodes angular velocity and modeled mathematically. This flow can quickly achieves conditions in which the steady-state current is controlled by the solution flow rather than diffusion. This is a contrast to still and unstirred experiments such as cyclic voltammetry where the stead-state current is limited by the diffusion of substrate.

By running linear sweep voltammetry and other experiments at various rotation rates different electrochemical phenomenon can be investigated, including multi-electrons transfer, the kinetics of a slow electron transfer, adsorption/desorption steps, and electrochemical reaction mechanisms.

Limitation

Potential sweep reversals as used in cyclic voltammetry are not possible for a RDE system since the products of the potential sweep are continual swept away from the electrode. A reversal would simple produce an "i-E" curve which exactly matched the initial scan direction. Further complications arise in investigate the reactivity of these products, since they are swept away from the electrode. In contrast, the rotating ring-disk electrode is well suited to investigate this further reactivity.

ee also

* working electrode
* voltammetry
* hydrodynamic technique
* rotating ring-disk electrode

References