Rotating ring-disk electrode

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A rotating ring-disk electrode (RRDE) is double working electrode used in hydrodynamic voltammetry, very similar to a rotating disk electrode (RDE).^[1]

Contents 1 Structure 2 Function 3 Application 4 References

[edit] Structure

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.

[edit] Function

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 and back into the bulk of the solution. If the flow in the solution is laminar than 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/risk 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.

[edit] Application

The RRDE setup allows for many additional experiments well beyond the capacity of a RDE. For example while one electrode conducts linear sweep voltammetry the other can be kept at a constant potential or also swept in a controlled manner. Step experiments with each electrode acting independently can be conducted. These as well as many other extremely elegant experiments are possible, including those tailored to the needs of a given system. Such experiments are useful in studying multi-electrons processes, the kinetics of a slow electron transfer, adsorption/desorption steps, and electrochemical reaction mechanisms.

[edit] References