We now address the question what might cause this structural transformation. X-ray photoelectron spectroscopy allows for a quantitative analysis of the elemental surface composition of the samples, which we used to determine the amount of alkali metal cations adsorbed on the surface or intercalated in the outer layers of the films. For the stoichiometry calculations, we used the core level spectra Li 1s, Na 1s, K 2p, Cs 3d for the alkali metal cations (Figure ), Ni 2p and O 1s for the NiOOH catalyst, and C 1s to include carbon residuals, employing the relative sensitivity factors of Scofield. Figure lists the calculated values. During the activation, the respective alkali metal cations are adsorbed, where c(Cs + ) > c(Na + ) > c(Li + ). The exact concentration of Li + was not calculated as the core level spectrum hardly shows any intensity (Li also has a very low photoionization cross section). In the middle column the concentration of K + was included because it shows that some K + is left in the structure after the conditioning in 1 M KOH. It also shows that Cs + is most effective in replacing K + , since c(K + )CsOH < c(K + )NaOH < c(K + )LiOH after activation. Actually, when analysing Ni(OH)2 after conditioning, very little K + appears in XPS, with values of 0.1-0.2 at.%. The increase of K + in the XPS spectrum after activation in LiOH, NaOH, and CsOH, needs to either stem from K + traces in the respective electrolyte or from K + that was built into the bulk of the Ni(OH)2 structure during conditioning and was enriched at the surface during the activation. This is an indication that the intercalation or adsorption of alkali metal cations is quasi reversible when the NiOOH phase is reduced to Ni(OH)2 inside the electrolyte, as it was also observed with in-situ XAS by Trzesniowski et al. In a next step, we exposed the activated catalyst to controlled doses of H2O to study by XPS and UPS if the adsorption or dissociation of water is influenced by the type of cation in the electrolyte. This is a quasi in-situ approach to test any impact on the energetics of the OER mechanism. There are several possible pathways for the oxygen evolution reaction. Many of those include one step, where H2O needs to dissociate to form an OER intermediate at the catalyst surface. In the experiment, the vacuum stabilized NiOOH phase was exposed inside UHV to a dose of 15 s•10 -3 mbar H2O, measured with XPS and UPS, exposed again to H2O, but now for 15 min•10 -3 mbar, and measured again with XPS and UPS. The changes that are observed are gradual. Therefore, only the initial and the final spectra, after 15 min•10 -3 mbar, will be shown in the following plot. For easier readability, the final spectra will be denoted as "H2O exposed". The H2O exposure was done at room temperature. Water in contact with the surface will either adsorb as H2O molecule, dissociate, or not react with the surface at all. Figure shows the O 1s spectra directly after stabilization in vacuum and after exposure to H2O for each electrolyte. What they have in common is an increase of the peak at 530.5 eV and a slight shift of this peak to higher binding energies. Figure displays the difference spectra "H2O exposed"-"initial". For Figure , the O 1s was fitted with one peak at 528.8 eV for O bonded to Ni, one peak around 530.4 eV for OH bonded to Ni, and one small peak around 532.8 eV for molecular H2O. An exemplary fit is shown in Figure . The relative change of these components with H2O exposure is pictured in Figure . In all of those illustrations it is visible, that the increase of OH groups after H2O exposure scales with the electrolyte cations in the order Li + < Na + < K + < Cs + . Simultaneously, the at.% of Ni-O decreases, while there are no significant changes in the component assigned to adsorbed or intercalated H2O. To probe adsorbates on the outmost surface, ultraviolet photoelectron spectroscopy (UPS) is a suitable method with a detection depth of 20 Å at most. Figure shows the valence band, measured with monochromatic He II radiation (40.8 eV), of Ni(OH)2 and NiOOH formed in 1 M KOH. The three peaks in the valence band of Ni(OH)2 stem from a Ni 3d 8 emission, and from the 3σ and 1π orbitals of the OH groups in Ni(OH)2. In NiOOH these peaks appear as well, just shifted by 1.1 eV to lower binding energies due to a Fermi level shift. Note, that these measurements were not done in-situ and that the present valence band spectrum should not be taken as a reference for a clean and well-structured NiOOH surface. In this study, the important finding is that upon exposure to H2O, there is an intensity increase at 6-8 eV and a decrease at 2.4 eV. To interpret these changes, difference spectra have been calculated and are plotted in Figure . In this representation, it becomes visible that the intensity increase from 6-8 eV is actually composed of 2 peaks. Those can be assigned to the 3σ and 1π orbitals of OH groups adsorbed onto the surface. These add to the maximum detection depth of UPS, which is the cause for the decrease of the Ni 3d 8 emission at 2.4 eV and the decrease of the signal of the K 3p and Cs 5p core levels in the case of activation in KOH and CsOH, respectively. The adsorption of OH recognized in the valence band fits to the increase of OH groups in the O 1s core level spectra. Similarly, a cation dependence is also visible in the valence band spectra, where NiOOH activated in LiOH adsorbs the least OH groups on the surface. We have shown that structural changes and a deprotonation of the NiOOH surface upon interaction with different alkali metal cations cause an improved dissociation of H2O. A favoured dissociation also implies a modified adsorption free energy and an enhanced stability of the dissociation products on the catalyst surface. Their adsorption is part of most mechanisms to form key OER intermediates. For instance, the reaction