Classification of Models for Convective Diffusion

A significant effort has been expended to identify analytic solutions for equation (11.87). These differ primarily in the manner in which the convective contribution is approximated. The different models and their influence on the impedance response are described in this section. 

The classification of models for convective diffusion to a rotating disk electrode may be imderstood in the context of the solution to the steady-state equation (11.3). 

The current density can be expressed in terms of the gradient of dimensionless concentration at the electrode surface as  

The corrections to the current density were obtained by accounting for additiorud terms in the velocity expansion given as equation (11.77). 

Within the Nemst hypothesis, the diffusion impedance is assumed to be that for a stagnant film of effective thickness that is related to velocity by 

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