For the electrolysis of water, the oxygen evolution reaction (OER) is the limiting half-reaction, where the overpotential could not yet reach lower limits like they were achieved for the hydrogen evolution reaction. To meet the performance demands of scalable and economical electrolyser stacks for industry, there are many contributions in literature, which aim to improve the OER activity. A promising and economic materials class are transition metal oxides used in alkaline water electrolysis anodes. These oxides are studied in various morphologies, elemental compositions, and electrochemical conditions. One parameter out of many that can influence the activity of the catalysts is the composition of the electrolyte. Ions in the electrolyte have a direct impact on the electric double layer (EDL). Its understanding has a pivotal role in understanding and tailoring materials in electrocatalytic systems. At the EDL, the surface of the OER active phase is in contact with the electrolyte. The precise structure of this EDL is influenced by the detailed surface structure of the catalyst, the kind of ions including solvation shells in the electrolyte as well as adsorbed at the electrode, and the interfacial pH, which can deviate from the bulk pH. In this study, we focus on the contribution of different alkali metal cations, whose effect on the EDL has been probed in various experimental and theoretical works. In the order Li + -Na + -K + -Cs + , the cation size increases, the electronegativity decreases, the hydration energy decreases , and the Lewis acidity decreases . These properties have implications on the hydration shell of these cations in the alkaline electrolyte. Taking Cs + and Li + for comparison, the solvation shell of Li + is built from stronger non-covalent bonds. Cs + , as a softer cation, on the other hand, is less solvated and is, therefore, expected to adsorb in larger quantities on the electrode surface. Their hydration enthalpies range from 519 kJ/mol for Li + to 409, 322, and 264 kJ/mol for Na + , K + , and Cs + , respectively. The surface of the catalyst, that is in our case the surface of a NiOOH, OER active phase, varies depending on the conditions. The NiOOH phase is unstable at open circuit potential, but is created when polarizing the Ni(OH)2 phase, of which two polymorphs exist, where α-Ni(OH)2 is a hydrated, disordered form of β-Ni(OH)2. Charging of β-Ni(OH)2 first leads to an oxidation of Ni to Ni and a phase change to β-NiOOH. Upon further charging, the oxidation state of Ni increases up to Ni and a γ-NiOOH phase is formed. When starting with α-Ni(OH)2, immediately γ-NiOOH crystallizes upon polarization. In contrast to β-NiOOH, in γ-NiOOH, both H2O and ions, including alkali metal cations, are intercalated. With XAS, the intercalation of the cations was shown to be reversible when reducing the sample back to Ni(OH)2. Yet, the nuances of the phase transitions and structures are still a matter of debate. For instance, Garcia et al. have shown the formation of NiOO -at 1.7 V vs. RHE with Raman spectroscopy. The peroxo band increases when using different electrolytes from LiOH to NaOH, KOH, and finally CsOH. In the same manner, the current density increased during the OER. They propose that the NiOO --M + species acts as an intermediate of the OER. Such findings show that the surface structure of the NiOOH catalyst is complex, which complicates an evaluation whether the β-NiOOH or γ-NiOOH phase is more active towards the OER. Several studies exist claiming the β-NiOOH phase to be the optimum phase, yet several other studies challenge that view and report higher activities of the γ-NiOOH phase. In many more publications, the active phase has not been explicitly specified due to its instability under ex-situ conditions, its often low crystallinity, disorder, and resulting difficulties obtaining high quality HRTEM and XRD data. Here, we used a combination of Raman spectroscopy, performed both in-situ and ex-situ, and X-ray photoelectron spectroscopy to track changes in the NiOOH phase induced by Li + , Na + , K + , or Cs + in a purified (Fe-free) electrolyte. Furthermore, the ultra-high vacuum stabilized NiOOH phase was exposed to controlled doses of H2O, which is a quasi in-situ approach to follow the electrolyte-surface interactions. The outcome is followed with Xray and ultraviolet photoelectron spectroscopy (XPS, UPS). Our results imply that the improved OER activity in the order Cs + > K + > Na + > Li + goes along with a more γ-NiOOH like structure of the activated catalyst. These structural changes seem to be induced by an increased intercalation of the alkali cations in the same order, that is c(Cs + )>c(K + )>c(Na + )>c(Li + ) after activation. Importantly, these alterations facilitate the dissociation of water. Both in the O 1s core level spectra and in the valence band spectra, a relative increase in adsorbed OH groups is observed, which is correlating with activity of the catalyst. In many of the proposed mechanistic pathways for the alkaline OER, the dissociation of H2O is necessary for the formation of OER intermediates at the surface. Therefore, the enhanced water dissociation has a direct effect on the overpotential required for the OER reaction.