Insights from existing data Turning to experimental findings, the 1 st observation is that the i-V curve follows a B-V like behavior, having a linear i-η dependency at small overpotentials and exponential at higher, with a HER Tafel slope of approx. 120 to 150 mV/dec [41] , , at current densities of ca. -1 mA/cm 2 and overpotentials of ca. -0.1 V. A smaller value of the "Tafel slope" is often quoted at small overpotentials, but this is due to the increasing anodic current contribution when the condition for the Tafel region (Eq. 13) is violated. This 1 st observation dismisses the Tafel step from being the rds at intermediate overpotentials but is still not sufficient to dismiss the T-V path with a Tafel rds limiting the current density at higher overpotentials.