For the Ag200 electrode, the expected peaks of metallic Ag, namely the 3d3/2 peak at 374.2 eV and the 3d5/2 peak at 368.2 eV, are present before and after 24 hours CPE, as illustrated in Fig. . On the other hand, no oxygen peak can be detected, as seen in Fig. ). However, after electrolysis, an intense oxygen peak at 531.4 eV is observed (Fig. ). This oxygen peak is not attributed to any oxidation products of Ag, but rather to carbonate, due to residues of the KHCO3 electrolyte deposited on the catalyst surface. For the fresh Ag200P36 electrode, the two Ag peaks at 374.2 eV and 368.2 eV are present, however, the shape of the peaks clearly changed (Fig. )) with respect to the non-plasma-treated sample. By fitting the spectra, it can be seen, that the signal includes the contribution from oxidized Ag species. The location of peaks at 367.5 eV and 373.4 eV indicates the presence of silver (I) species (Ag2O). This is in accordance with the presence of the Ag2O peak in the X-ray diffractogram in Fig. . This is also supported by the presence of O peaks (Fig. )): while the peak at 530.8 eV can be attributed to atomic oxygen at the surface , the peak at 528.9 eV is characteristic of silver (I) oxide species. However, after the long-term catalytic testing, the cationic Ag species, as well as the silver oxide peaks, cannot be detected anymore. This is caused by the reductive reaction conditions that converted all oxidic silver species back into metallic Ag, which is also in agreement with the XRD pattern of the used sample (Fig. ). The emergence of a large oxygen peak at 531.3 eV (Fig. ) is due to the deposition of KHCO3 buffer on the catalyst surface, as also seen for the non-plasma-treated electrode.