Hydrogen oxidation/evolution reactions (HOR/HER) are the main key for the hydrogen economy in the future. The control of an efficient hydrogen generation from water and of its reverse reaction, particularly in fuel cells, is still insufficient. For instance, very low Pt loadings are required for the HOR in proton exchange membrane fuel cells,1 whereas the HOR kinetics change tremendously in alkaline media and become at least two order of magnitudes slower.2 To design catalyst materials with improved HOR/HER performance in alkaline conditions, a deeper understanding about the reaction mechanism and kinetics is needed. This includes to uncover the significant role of cations during the HOR in alkaline media.3 Firstly, we have studied the effect of monovalent cations on the HOR kinetics on polycrystalline and nanosized platinum in different alkaline solutions (MOH, M = K+, Na+, Li+). Depending on the cations, we observed a significant change of the HOR activity and activation energy for the Pt. More precisely, the HOR activity of Pt increases in the order of K+ < Na+ < Li+, respectively, while the activation energy simultaneously decreases in the same order. We suggest that the catalytic properties of the Pt are strongly influenced by non-covalent interactions of the hydrated cations with the adsorbed hydrogen by the hydrogen bond formation. In the second part, various Pt-Co alloys were investigated for the HOR/HER in alkaline media using rotating disc electrode set up. Our results show that the HOR/HER performance can be tuned by variation of atomic Pt & Co arrangements like core-shell, segregation and alloy nanoparticles. We developed a multi-dimensional matrix to clarify the relationship between structural parameters and catalytic HOR activities for the Pt-Co nanoparticles. The combination of both works allows to provide a deeper understanding about the mechanism and kinetics of the HOR/HER for Pt and Pt alloys in alkaline media. References 1. H. A. Gasteiger, S. S. Kocha, B. Sompalli and F. T. Wagner, Applied Catalysis B: Environmental, 56(1-2), 9–35 (2005). 2. J. Durst, A. Siebel, C. Simon, F. Hasché, J. Herranz and H. A. Gasteiger, Energy Environ. Sci., 7(7), 2255–2260 (2014). 3. D. J. Weber, M. Janssen and M. Oezaslan, Journal of the Electrochemical Society, 166(2), F66-F73 (2019).