The results presented above for the Pt-1 and Pt-3 electrodes, as well as those for Pt-2 (Section S5), have shown that in the COOR during potential cycles up to 1.35 V, the monolayer Pt film is more stable against irreversible restructuring than bilayer islands on the monolayer film and that three to four-layer films remain almost unchanged. Bilayer Pt films also seem less stable in CO-free electrolytes, as shown in Fig. . For the Pt-3 electrode, a high stability was also shown for the MOR up to 1.4 V. In the following, we will briefly discuss possible reasons for these differences in the layer-dependent stability and draw comparisons with Pt(111).