2b) The Tafel slope The Tafel slope expresses how much overpotential (driving force) is needed to increase the current density by one decade. One can obtain a Tafel slope in both kinds of Tafel regions through applying Eq. 16a to Eq. 8b using Eq. 7a. From the derived general equation for the forward and backward Tafel slope (Eq. 16c-d) one finds that the