Diffusion equations, redox properties

Mention has been made previously of the possibility that the maximum electron-transfer rate observed in a series of reactions, as the driving force is increased, may be due to the onset of diffusion control, unrelated to the redox properties of the reactants. This has usually been discussed by amending the value of Z in the Marcus equation (1). Thus for uncharged reactants in water at room temperature Za 10 M s, but for like-charged reactants it may be very much less. Brunschwig and Sutin have now proposed a different formulation in which Z is a parameter independent of the encounter rate. Writing the general bimolecular electron-transfer mechanism as... 

It is known that the performance of an electrode with respect to temporal and spatial resolution and sensitivity scales inversely with the electrode radius. For an inlaid fiber electrode, the exposed end can be approximated as a disk-shaped electrode. As the electrode diameter is smaller than that of the diffusion layer thickness, electrochemical properties become fundamentally different from a conventional macroelectrode. In cyclic voltammetry (CV) measurements, the magnitude of the peak current of the redox signal is the sum of two terms linear diffusion as described in the Cottrell equation, and nonlinear radial diffusion [76] ... 

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