Useful concepts in the solution of mass transport equations

2 USEFUL CONCEPTS IN THE SOLUTION OF MASS TRANSPORT EQUATIONS 

Let us suppose that there is a layer of solution close to the electrode within which all concentration changes due to electrode reaction occur and that transport within this layer is entirely by diffusion. For hydro-dynamic electrodes, this approximation is reasonable since the diffusion layer is very thin owing to the effects of forced convection. Following Nernst, we assume that the concentration varies linearly within the diffusion layer such that the flux, j, at the electrode is 

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