There is an ongoing discussion about the nature of the high hydrogen oxidation reaction (HOR) activity of bimetallic Pt-Ru catalysts in alkaline media. We provide an insight on the HOR mechanism for this type of catalyst, excluding bifunctionality as the main driving force for the oxidation of hydrogen. In order to do so, we prepared and evaluated Ru@Pt core-shell nanoparticles with sub-, mono- and multilayered Pt-shells. Rotating disk electrode (RDE) studies in 0.1 M NaOH solution of all prepared catalysts, including Pt/C as a reference show that Ru particles fully encapsulated with a Pt-shell show significantly higher activity than Ru particles that are solely covered with Pt-submonolayers. Furthermore, we found a 4-fold enhancement of Ru@Pt vs. pure Pt with respect to the surface normalized HOR activity. The Ru@Pt catalysts were characterized by COads-stripping voltammetry, as well as cyclic voltammetry (CV) in order to identify the Pt-coverage and shell thickness.