Overall, the shape of the COOR-CVs is rather similar to those reported for Pt electrodes. Based on these studies and previous ones on Pt-modified Ru(0001) electrodes, the processes taking place in different potential regions can be qualitatively described as follows. Starting with the positive-going scan from the low-potential limit up to the onset of the COOR (0.5 V for Pt-1 and 0.6 V for Pt-3), the surface is poisoned by CO, inhibiting any surface redox processes, as has been demonstrated for pure Pt 62,66-71 and Ptmodified Ru(0001) electrodes. With the onset of OH/O formation on the surface (from water splitting) in the CO adlayer, the COOR starts, which had been described in detail for the COOR in CO-saturated electrolytes on pure Pt electrodes. Note that the increase of the current density around the onset potential changes in the first potential cycles, which is illustrated in Fig. . A similar phenomenon has been reported for Pt(111) during the COOR in CO saturated 0.1 M HClO 4 . In this potential region, up to the onset of the reaction, the MS-CV closely follows the COOR-CV.