Other Cases of Diffusional Mass Transport

A (hemi)spherical electrode has been applied to estimation of charge transfer kinetics, effect of electric migration, and kinetics of chemical steps. Spherical diffusion takes place through an increasing area as the radial coordinate r, measured from the center of the spherical electrode, increases. The main differential equation for three-dimensional mass transport is given in Table 3.1. On substitution of c=y r, this relationship can be reduced to the one-dimensional mass transport yielding 

In contrast to the semi-infinite diffusion at a plane electrode, this diffusion equation has the steady-state solution 

Solid electrodes utilized in electrochemical investigations are often made of wire and present a small cylinder with radius Tq and height h. It is commonly assumed that symmetric diffusion flows are directed toward side surface, whereas 

The behavior of array electrodes depends on the ratio of the diameter of the individual electrode to the spacing between electrode features. High diffusion current densities conditioned by radial flows and low values of ohmic potential drop are most prominent in the case of ultramicroelectrodes [13, 14]. By replacing a single macroelectrode by an array of ultramicroelectrodes, the current density can be increased by orders of magnitude as well as the ratio of faradaic to capacitive currents. 

The so-called partially blocked electrodes containing active and passive sites can be also treated as microelectrode arrays, when the charge transfer is utterly impossible at the passive area. Simulations of their electrochemical behavior under linear potential sweep conditions showed [15] that a good agreement 

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