The potential at the point of zero charge (PZC, φ σ =0 ) of the cathode is the potential at which the charge density of the surface is zero and no electrical double layer is therefore present in the electrolyte solution facing the electrode. The φ σ =0 is thus a natural choice for a reference for all the potential values used in this study. PZC of a metal surface depends on the crystal facet as well as on the electrolyte solution in case specific adsorption happens on the surface . For reference, the PZC in an aqueous solution for Ag surfaces is given in the SI. The range of OHP potentials considered in our simulations correspond to surface potentials of -0.10 to -0.61 V vs PZC, which translate to -0.55 to -1.06 V vs SHE for a Ag(111) surface and -0.80 to -1.31 V vs SHE for a polcrystalline Ag surface. It should be noted that the PZC for a polycrystalline metallic surface is not a uniquely defined quantity but is in some cases estimated using the minimum of the measured differential capacitance. We assume only non-specific adsorption of solvent species on the cathode surface for our simulations.