In the negative-going scan, the COOR shows a higher activity in the potential region around the onset potential for COOR in the positivegoing scan. Such a hysteresis is commonly observed for the COOR on Pt-modified Ru and also on pure Pt electrodes. More important, the current density in the MS-CV seems to be slightly larger than that in the COOR-CV, which must be due to surface reduction processes taking place simultaneously in this potential region. This is discussed further in the next section. Once the current density decayed to zero in the COOR-CV, a reduction peak / region C1 appears at more negative potentials, which is rather broad for Pt-1 and more peak-like for Pt-3 (see insets in Figs. and and Fig. ). The appearance of this peak C1 indicates that under present conditions, part of the surface OH/O adspecies are reduced to water instead of reacting with adsorbed CO. Nevertheless, the removal via COOR is also possible, as indicated by a small current in the MS-CV in the potential region of peak C1. This also means that the observed current peak C1 is a sum of currents related to the direct removal of OH/O from Pt to form water (negative current) and OH removed by the COOR (positive current). The amount of removed, adsorbed OH/O, either by reduction to water or by reaction with CO, is presented in the redox-CVs in Figs. and. These curves indicate the reductive or reactive OH/O removal in a peak / region for potentials below about 1.0 V for both electrodes. The oscillatory behaviour of the reduction peak in the redox-CV is possibly an artefact caused by problems in the temporal correlation of the MS-CV and the COOR-CV.