The Tafel Equation
In the case of a large cathodic current density the current as a function of overpotential h can be written
Solving for h gives
This corresponds to an early empirical equation by Tafel
Below (Figure 1) is a plot of h vs. log of anodic current with a=0.5. The linear plot is of the Tafel equation. The slope b is 2.3RT/anF. The intercept at h=0 gives the exchange current density i0. This is known as a Tafel plot. With this we can calculate a and i0.
Figure 1.