Current—voltage curves. The general case

Pure kinetic control can only be evidenced at the foot of an irreversible wave. In all other cases and at all other parts of the irreversible wave, mass transfer has to be taken into account. 

For irreversible processes, we can neglect the contribution made by the back reaction. In the Butler—Volmer formulation of electrode kinetics, k i is given as 

Equation (120) is true at any particular point on any electrode since the diffusion layer thickness is constant for a uniformly accessible electrode, in this case we simply replace j by i. Otherwise, the equation must be integrated over the area of the electrode. 

Analysis for uniformly accessible electrodes is by plotting (1/M vs. i/k u which leads to ik and hence k. If n is unknown, then plot log i vs. log i/k D to give /u. Other plots are also possible [143]. In the particular case where n = 1 (no adsorption) 

For the rotating disc electrode, we plot i l vs. cj 1/2 we can determine ) from the slope and k from the intercept. Application of this relation has been thoroughly discussed [144] (Fig. 11). 

---