Using Ru(0001) electrodes covered by a monolayer and three layers of Pt, we demonstrate by DEMS measurements during the COOR and by operando SXRD measurements during the MOR, as well as by STM imaging before and after the electrocatalytic investigation, that submonolayer Pt films start to restructure for potentials more positive than 1.1 V (as shown previously), in contrast to films with three layers (and more), which are stable up to about 1.4 V during the COOR and MOR.