A representative overview of the H-upd behavior at different pH is shown in Fig. , starting from the H-upd current at acidic conditions and pseudo-capacitance after the subtraction of the HOR/HER contribution (Fig. ). In line with the aforementioned potential step measurements, the H-upd extends further into the HER until the proton limiting current is reached. Increasing scan rate results in decreased H-upd charge (pseudo-capacitance) and small peak shifts, suggesting that the H-upd kinetics can be investigated through the relationship between peak position and scan rate. In mildly alkaline conditions (Fig. ), the hydroxyl ion limiting current makes its appearance in the anodic direction. In the forward direction the familiar H-upd pattern appears when the HOR switches from the alkaline to the acidic path being dominant, with molecular hydrogen as the limiting reactant.