COad. — without CO

Fig. 2-26 Cyclic voltammograms of PtdlO) in 0.5 M HCIO4 with COad. (---) without CO at 50mV/s.

Figure 10.6 shows CL spectra of Pt4/7/2 for stabilized Pt-Co with and without COad- The CO adsorption induced both a shift in the Pt4/7/2 CL to higher binding energy and an increase in the full width at half maximum (FWHM). Such changes can be explained by surface core level (SCL) shifts of Pt4/7/2 by COad, whereas the bulk CL is not affected by COad- hi order to extract the change in SCL shift (ASCLS) by COad, we decomposed the Pt4/7/2 spectra into two components the bulk CL and SCL. It was found that the value of ASCLS decreased in the order pure Pt > stabilized Pt-Co > Pt-Ru. 

Compared to Fig. 2-15, the voltammogram without CO, it is notable that the oxidation potential of COad is far cathodic from the potential where most platinvun starts to be oxidized. Thus, it is not likely that Pt-OH is the oxygen source for COad oxidation. Since water is the only possible oxygen soiirce other than Pt-OH, free water or water interacted weakly with platinvun is utilized as the oxygen source ... 

Voltammograms of Ptdll) with and without COad adsorption in 0.5 M perchloric add are shown in Fig. 2-25. The voltammogram without CO was considerably different from those in sulfuric acid. The symmetric features in the range from 600 to 800 mV correspond to the anodic portion of the two split area of hydrogen adsorption-desorption in sulfuric add. Hydrogen adsorption-desorption features did not change after the oxidation peak at 1050 mV and its reduction while the further oxidation removes the feature irreversibly. Therefore the peak at 1050 mV is considered as a formation of a weak interaction with water. 

In the hydrogen region (50 - 350 mV) in the first cycle, the hydrogen adsorption-desorption ciirrents were depressed because the surface was covered with COad COad oxidized to CO2 in the anodic peak between 700 mV and 1000 mV. This peak overlapped with the platiniim oxidation whose voltammogram is shown as the dashed line. After this peak the voltammogram became identical with the voltammogram without CO. The h rdrogen adsorption-desorption peaks were fully recovered. This shows the COad completely oxidized and there was no CO in the liquid phase. 

The voltammograms are shown and compared with that of pure platinum in Fig. 4-14 and Fig. 4-15 for smooth and high area platinum electrodes, respectively. Since the COad oxidation current overlaps with the current related to tin, the net current of the COad oxidation is taken as the difference of with CO and without CO . 

Fig. 4-21 Cyclic voltanunogram of a high area Pt-Mo electrode in 3 M H2SO4 with COad at 10 mV/s. Shown anodic scan only. Compared with Pt-Mo without CO and Pt with CO. 

Then, the potential was cycled up to 1.0 V to desorb molybdates in oreder to expose the platinum surface as shown in the previous figure (Fig. 4—20) and held at 50 mV again while CO was introduced. In Fig. 4-21, the voltammogram of the COad oxidation is shown with the voltammograms for pure Ft with COad and Pt-Mo without COad (second cycle). The peak position for the oxidation of AoCOad is unaffected. Beside this peak, there are two peaks at 280 mV and 420 mV. It is hardly possible to judge whether these peaks are the results of the COad oxidation or the oxidation of molybdates because the oxidation peaks of eoCOad and adsorbed molybdates are in the same potential region. 

Both these concerns were addressed by the development of modified IR techniques. In the technique of Subtractively Normalised Fourier Transform IR Spectroscopy (SNIFTIRS) or Potential Difference IR (SPAIRS or PDIR) [37], the increased stability and sensitivity of Fourier Transform IR is exploited, allowing usable spectra to be obtained by simple subtraction and ratioing of spectra obtained at two potentials without the need for potential modulation or repeated stepping. A second technique which does not call for potential modulation, but actually modulates the polarisation direction of the incoming IR beam is termed Photo-elastically Modulated Infra-Red Reflectance Absorption Spectroscopy (PM-IRRAS) this was applied to the methanol chemisorption problem by Russell and co-workers [44], and Beden s assignments verified, including the potential-induced shift model for COads. 

The data on CO adsorption during exposure of Ru/Ti02 at different temperatures to 4.1 pmol pulses of CO under He flow are included in Fig. Id for a conqjarison. It is of interest to note that the ratio of CO adsorbed with and without the presence of hydrogen [ COjid(H2)/COad(He) ] is aroimd 2 for a catah tenq)erature of 300 K ( Figs 1 a,d ). This... 

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