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Concept
Rotating ring-disk electrode
Summary
In analytical chemistry, a rotating ring-disk electrode (RRDE) is a double working electrode used in hydrodynamic voltammetry, very similar to a rotating disk electrode (RDE). The electrode rotates during experiments inducing a flux of analyte to the electrode. This system used in electrochemical studies when investigating reaction mechanisms related to redox chemistry and 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. To operate such an electrode, it is necessary to use a potentiostat, such as a bipotentiostat, capable of controlling a four-electrode system. The two electrodes are separated by a non-conductive barrier and connected to the potentiostat through different leads. This rotating hydrodynamic electrode motif can be extended to rotating double-ring electrodes, rotating double-ring-disk electrodes, and even more esoteric constructions, as suited to the experiment.
The RRDE takes advantage of the laminar flow created during rotation. As the system is rotated, the solution in contact with the electrode is driven to its side, similar to the situation of a rotating disk electrode. As the solution flows to the side, it crosses the ring electrode and flows back into the bulk solution. If the flow in the solution is laminar, the solution is brought in contact with the disk and with the ring quickly afterward, in a very controlled manner. The resulting currents depend on the potential, area, and spacing of the electrodes, as well as the rotation speed and the 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.
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