2) The Tafel method This method is used to explore the kinetics in the so-called It is important to realize that such analysis must only be performed at high enough overpotentials (Eq. 13), e.g. higher than at least 60 mV at 20 °C for 𝑧 𝑘 = 1 and 𝛼 𝑘 = 0.5 to introduce an error of less than 10% (in the case of ideal B-V kinetics), a condition that is frequently violated in mechanistic discussions. This is especially important when highly active catalyst layers are analyzed whose high current densities only allow a small overpotential region to be probed, where many authors determine Tafel slopes at too low overpotentials [13][14] . Additionally, even at small overpotentials, mass transport limitations cannot be neglected, as we will discuss later. For clarity, we now explore a two-step reaction for three distinct scenarios in the Tafel region (Eq. 14a, 14b).