The previous derivation allows us to survey the H-upd kinetics in a wide range of electrolyte conditions. Examining the CVs in Fig. one finds that the H-upd features occur in a potential region where the pH on the electrode surface is different from the bulk electrolyte due to the HOR/HER until the anion switch pH. We must take this into account when examining the H-upd kinetics due to their supposed dependency on the availability of proton acceptors and donors in the form of hydronium and hydroxyl ions. Above the anion switch pH, the H-upd features occur in the molecular hydrogen transport limited region and peak 1 and 2 appear at potentials sufficiently positive of the HOR/HER equilibrium potential, meaning that the local pH corresponds to the bulk pH. This behavior is illustrated in Fig. where the peak positions from a bulk pH of 4 to 9 are constant, sharply increase around the anion switch pH before following again Nernstian behavior in the alkaline region. We now applied Eq. 36b to determine the local pH, assuming the HOR/HER governs the local pH. Strictly speaking this assumption is only valid when the contribution to the overall current of the H-upd can be neglected as it should also produce or consume hydronium and hydroxyl ions. Due to the high scan rates, the H-upd currents are in some cases much greater than the HOR/HER currents (see Fig. ), so we will reexamine this approximation in a moment. Considering the local pH instead of the bulk pH leads to Fig. where one notices that the positions of the acidic peak 2 in the forward direction and the positions of the alkaline peak 2 in the backward direction remain constant with pH. Instead, the positions of peak 2 in the corresponding reverse direction cannot be identified in the region between local pH 4-10. To explain this, we specifically write Eqs. 47a-d for the four distinct H-upd reaction branches.