Examining Eq. 35a more closely, one finds that in the mass-transport-controlled regime, the apparent micropolarization exchange current density must approach the limiting current differently, depending on the mass transport limited specie and its stoichiometry. In Fig. the apparent and kinetic micropolarization exchange current densities are displayed, together with the three different limiting currents associated with molecular hydrogen, proton donor, and acceptor species. At low pH, 𝑖 0,𝑚𝑖𝑐𝑟𝑜,𝑎𝑝𝑝 is about twice that of 𝑖 𝑙𝑖𝑚,𝐻 2 , at medium pH values from 3 to 10 it matches 𝑖 𝑙𝑖𝑚,𝐴 𝑃 or 𝑖 𝑙𝑖𝑚,𝐷 𝑃 , while at higher pH-values we enter the mixed-kinetic-and-mass-transport-control regime. This observation is in line with Eqs. 37a-b, which are limiting values of Eq. 36a, and confirms the qualitative description of the i-V curves provided earlier.