is the rate and potential determining step (RDS/PDS) in many calculations. Hou et al. have already calculated a higher OH adsorption energy in the presence of Cs + . In the present study, we could verify this result experimentally. What exactly causes the changes in dissociation activities of H2O and the associated improvement of the OER? Our paper and the works of others have shown that NiOOH undergoes structural transformations depending on the electrolyte cations. First, there are variations of Ni-O bond lengths. Raman results show they are elongated in CsOH, whereas XAS measurements indicate the opposite. We speculate that Cs + is attracting charge of the lattice oxygen, whereby the Ni-O bond length is increased in Raman spectroscopy. A new finding is that the peak ratios of the Eg and Ag lattice vibrations of NiOOH in the Raman spectra are also affected. The peak ratio rises from LiOH to CsOH, which signifies a structural change to a more γ-like NiOOH. This phase has a more open structure compared to β-NiOOH, as it is intercalated with H2O and ions. This result supports the calculations of Görlin et al., who calculated an increase in layer separation from Li + to Cs + . The cause is an increased cationoxygen coordination distance of the cations both with lattice oxygen and nearby water molecules. We could interpret that the intercalation is directly visible in the XPS core level spectra of the alkali metal cations, where more at.% of Cs + than of Li + have been detected in the surface near layers. Yet, here, we cannot specify how much of the signal is from intercalated or surface adsorbed cations. We expected to see the intercalation of H2O in the FTIR spectra, however, no unambiguous correlation of the spectra with the electrolyte could be found. The O 1s core level spectra show that the structural change is accompanied by more deprotonated sites after activation in CsOH. This makes sense, as Ni was found to have a higher oxidation state in γ-NiOOH. Furthermore, from the perspective of charge compensation, the presence of, e.g., Cs + on the surface can contribute to the deprotonation. As Cs + has a weaker solvation shell, it is able to interact with and adsorb on the surface more effectively than the small, harder, hence stronger solvated, Li + . The abundance of deprotonated sites could be a major factor in the enhanced dissociation of H2O. Zaffran and Toroker have calculated that the formation of the OOH intermediate, that forms with the dissociation of H2O, requires less energy on a deprotonated NiO2 surface than on a partly hydrogenated NiOOHx surface. They argue that an electrostatic repulsion of the OOH intermediate with the H atoms on the catalyst surface destabilizes the OOH group. Furthermore, the deprotonation promoted by the alkali metal cation could first increase the Ni oxidation state and then favour a charge transfer from O to Ni. Both outcomes, an elevated oxidation state of Ni or an electron deficient oxygen site, were shown to enhance the OER. We also want to reflect on the findings of Görlin et al., who correlate the increase in OER activity from LiOH to CsOH with an increase of pH of these solutions. Since we see an increased absorption of the larger cations and a correlating structural transformation of NiOOH, we believe that the cations do have their own contribution on the OER activity. However, the change in pH can very well have an additional and significant influence, especially when discussing the deprotonation of the catalyst surface. The pH of the solutions used in this study is displayed in Table .