If the intermediate activities of the rds become constant in an extended potential region, the Tafel slope is then only dependent on the symmetry coefficient and the number of electrons transferred in this particular step (Eq. 17a,b). Interestingly, if any of the intermediate activities varies exponentially with overpotential, one would also find a constant Tafel slope (assuming no change in rds and 𝛼 𝑟𝑑𝑠 ), as depicted in Fig. for the varying-coverage Tafel region. In this situation, the reactant activity (free sites) increases exponentially alongside the potential, halving the required increase in potential to achieve the same current increase if the reactant activities were to stay constant.