Ring-Disk Impedance Measurements

The species B leaves the disk and is transported by convective diffusion to the ring. 

The product P may be identical to A, the initial species, as in the case of a redox system, or may be different. 

The number of electrons concerned in reaction (14.29) or (14.30), i.e., n isk or nng/ is positive for an anodic and negative for a cathodic process. It can be seen that the rrde operates in three distinct processes electrochemical reaction at the disk, coupling between the disk and the ring through the convective diffusion, and collection at the ring. 

In a similar way, the collection efficiency under an ac signal at the angular frequency CO is defined by  

As the disk and the ring current are linked through three distinct steps, M co) can hence be split as the product of three transfer functions, i.e.. 

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What sort of instrumentation would be needed for electrochemical experiments A potentiometry experiment requires little more than a pH meter. A potentiostat or galvanostat can be used for the controlling potential or current in an experiment. In a coulometric procedure, a device to integrate the current (i.e., a coulometer) would also be needed. A hydrodynamic voltammetry [e.g., a rotating disk electrode (RDE)] experiment would require an electrode rotor (to spin the electrode at a precisely known rotation speed), and the rotating ring-disk or RRDE refinement (see below) would necessitate the use of a bipotentiostat so that the disk and ring potentials can be independently controlled. An ac impedance measurement involves the use of a sine-wave oscillator and... 

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