The following electrolytes were used: 1 M LiOH (anhydrous, 99.9% trace metals basis, Sigma-Aldrich), 1 M NaOH (1 N, volumetric standard solution, Carl Roth), 1 M KOH (1 N, volumetric standard solution, Carl Roth), 1 M CsOH (caesium hydroxide monohydrate, 99.95% trace metals basis, Sigma-Aldrich). 1 M LiOH and 1 M CsOH were prepared with Millipore water and the molarity was verified by titration. All electrolytes were purified using the method by Spanos et al. , yielding Fe contents ≤ 1 ppb measured with ICP-OES. The activation consisted of chronoamperometry (CA) at 1.6 V vs. RHE for 2 x 10 min. Before and after activation, the OER activity was measured using cyclic voltammetry (CV) and chronopotentiometry (CP). The full protocol is again outlined in Figure . After the last CA step, the sample was removed from the electrolyte while the potential was still applied. The sample was rinsed with ultrapure water and transferred as quickly as possible to the ex-situ spectroscopy. A first set of samples was quickly stabilized in ultra-high vacuum (UHV) for XPS and UPS measurements. A second set was freshly prepared and activated and likewise transferred as quickly as possible the FTIR sample compartment and evacuated to p < 3 mbar, then to the Raman microscope for the ex-situ and in-situ characterization. After the vibrational spectroscopy characterization, an extended activity measurement of the samples was added. The detailed procedure is outlined in Figure . All experiments were performed at RT.