Mass transport corrected Tafel analysis of voltammetric waves: When can it be applied?

The derivations of mass transport corrected Tafel equations are presented for a heterogeneous electron transfer. It is shown that the equations are valid for an electrode which is uniformly accessible to the electroactive species in solution. It is also shown that the equations are valid for any electrode geometry when the electron transfer is fast and reversible and the chemical species involved have equal diffusion coefficients. The microdisc and tubular flow electrodes are used as examples of non-uniformly accessible electrodes. The case is considered when the electron transfer is fast and reversible, the electrode is non-uniformly accessible and the species involved have unequal diffusion coefficients. Under these conditions it is shown by analytical solution that the Tafel equation is valid at the tubular flow electrode when axial and radial diffusion are insignificant. It is shown by numerical solution that at the same electrode the Tafel equation is not valid when axial and radial diffusion are significant.