In order to elucidate the role of the presence of alkali ions for the activity of the oxygen evolution reaction, we applied a grand-canonical scheme based on the computational hydrogen electrode to determine the most stable interface structures of β-NiOOH/water under varying pH and electrode potential for the deprotonation and alkali metal cation adsorption processes. We discussed the crucial importance of double-layer effects due to induced surface dipole moment and the explicit treatment of surficial water molecules. We found that the surface electronic properties change more significantly with the size of the adsorbed cations due to their stronger polarizability. Accounting for these effects provided an explanation on the experimentally observed alkali metal cation adsorption on the deprotonated NiOOH surfaces under OER conditions. Still, open questions remain with respect to the particular form of the cation adsorption phases which will be the focus of ongoing research efforts.