Therefore, the presented mechanism appears to be qualitatively correct, but is yet too simplistic to yield a quantitative description of the entire alkaline HOR/HER range. This finally brings us to the H-upd feature that we called the alkaline peak 3. Due to its more negative formal potential than of features 1 and 2, the respective binding sites are emptier during the HOR, which could be critical for the initial fixation and splitting of the hydrogen molecule, but more active during the HER. In this context, the experimentally observed, substantially and consistently decreasing micropolarization exchange current densities above pH 12 are important: As the HER currents follow the proposed model rather well, this decrease is not predicted and would expect a constant micropolarization exchange current density. This points towards the decreasing fixation and splitting of the H2 molecule as the reason for the decreasing micropolarization exchange current density at high pH. Resolving this phenomenon in combination with a detailed microkinetic model that considers the distribution of binding sites accessible from the H-upd is the key to accurately describe the HOR/HER mechanism and its associated phenomena. The role of anions for the H-upd and HOR/HER When comparing the HER Tafel slopes in pure alkali metal hydroxides with the HER Tafel slopes in supported electrolytes, one finds a stark difference (Fig. ), like what we have already shown in Fig. for the overpotential at a benchmark potential. However, in contrast to Fig. , one observes some trends: All Tafel slopes in supporting electrolytes are significantly higher than that in pure alkali metal hydroxides, suggesting an additional form of mass transport or kinetic limitation. The discrepancy shrinks at higher pH, and the Tafel slopes in supporting electrolytes approach that in pure alkali metal hydroxides. While the cation concentration stays the same, the relative proportion of hydroxyl ions increases, strongly suggesting that they play a decisive role in this phenomenon. In fact, throughout this work we did not observe any distinctive effect of cations, both in terms of concentrations and type (concerning only lithium, sodium, and potassium). This is evident from the similarity of the HOR/HER kinetics at high pH (Fig. ), the agreement of CV patterns in general (Figs. 9-10), and specifically from the similarity of the positions of the equilibrium H-upd peak potentials and rate constants (Figs. ). Instead, the anions play a more significant role: In acidic, the CV patterns are distinctive for perchlorate, chloride, and sulfate (not included in this study). In alkaline, the dominating anion becomes the hydroxyl anion, which is known to be a strong ligand so its dominating influence on the electrode interface cannot be surprising. However, the dual role of the hydroxyl anion, both as reactant and through interacting with the H-upd complicates the interpretation of its role. An indication for competing interfacial presence of hydroxyl and other anions is the emergence of the O-upd feature in chloride containing electrolytes when the pH is increased beyond the anion switch pH (Fig. ): At lower pH values the O-upd formation is strongly inhibited by the presence of chloride anions, however, past the anion switch pH, the O-upd appears, even more pronounced compared to perchlorate containing electrolytes (see Fig. ). At this pH, not all hydroxyl ions are consumed by the alkaline HOR as its rate is now M-T limited by molecular hydrogen.