Finally, we address the relevance of our results for realistic Ru-core Pt-shell particles used as highly efficient catalysts in various reactions, as presented in the introduction. The main requirement for these catalysts is that Pt always covers the Ru substrate to prevent Ru dissolution or Pt restructuring induced by the strong interaction of OH/O species with Ru. For closed Pt layers and reactions such as the ORR, HER and HOR, a possible restructuring by an irreversible place exchange process is presumably negligible, since these reactions normally proceed at potentials well below the onset potential of restructuring, which for these systems is higher than that for pure Pt. In the presence of oxidizable species in the feed, one could expect an even higher stability since their reaction with OH/O species would decrease the steadystate coverage of these species at a given potential and thus shift the onset potential for surface restructuring to higher potentials. The detailed understanding of the layer-dependent stability of such systems is, however, still incomplete. Earlier studies indicated that Ru-core Pt-shell systems with two layers of Pt are rather stable, which is not the case for well-defined Pt layers on Ru(0001). These discrepancies are most likely due to the different structural properties of the core-shell particles as compared to the present model systems.