Rotating ring-disk electrode

A rotating ring-disk electrode (RRDE) is double working electrode used in hydrodynamic voltammetry, very similar to a rotating disk electrode (RDE). The electrode actually rotates during experiments inducing a flux of analyte to the electrode. These working electrode are used in electrochemical studies when investigating reaction mechanisms related to redox chemistry among other chemical phenomena.

The difference between a rotating ring-disk electrode and a rotating disk electrode is the addition of a second working electrode in the form of a ring around the central disk of the first working electrode. The two electrodes are separated by a non-conductive barrier and connected to the potentiostat through different leads. To operate such an electrode it is necessary to use a bipotentiostat or some potentiostat capable of controlling a four electrode system. This rotating hydrodynamic electrode motif can be extend to rotating double-ring electrodes and rotating double-ring-disk electrodes and other even more esoteric constructions as suited to a given experiment.

The RRDE takes advantage of the form of the laminar flow created during rotation. As the system is rotated the solution in contact with the electrode is driven to the side of the electrode the same as with a rotating disk electrode. As the solution flows to the side it crosses the ring electrode and back into the bulk of the solution. If the flow in the solution is laminar then the solution is brought in contact with the disk quickly followed by the ring in a very controlled manner. The resulting currents are dependent on the electrodes' respective potentials, areas, and spacing as well as the rotation rate and given substrate.

This design makes a variety of experiments possible, for example a complex could be oxidized at the disk and then reduced back to the starting material at the ring. It is easy to predict what the ring/disk current ratios is if this process is entirely controlled by the flow of solution. If it is not controlled by the flow of the solution the current will deviate. For example, if the first oxidation is followed by a chemical reaction, an EC mechanism, to form a product that can not be reduced at the ring then the magnitude of the ring current would be reduced. By varying the rate of rotation it is possible to determine the rate of the chemical reaction if its in the proper kinetic regime.

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