High Area Platinum

From the results of Pt(lll). water can be used as an oxs gen source for COad oxidation even on a smooth single crystal surface. This path is available in a dilute add as infrared measurements show that CO2 buildup starts at very low potential like 300 mV. Probably because the niunber of the sites for this reaction is limited, so is the reaction. When the add is concentrated, this path seems only available when CO is adsorbed on spedal sites (probably defects, kinks or edges) at a low potential such as 50 mV. On high area platinum, this path is more likely to occur because the density of those sites is higher. 

Chemically and electrochemically platinized platinum electrode (180 as roiighness factors for both electrodes) were used as high area platinum electrodes. While they showed slightly different COad oxidation characteristics, their methanol oxidation characteristics were virtually the same. Therefore, the results will be shown for only chemically platinized platinum electrodes. 

The voltammograms in a more concentrated methanol electrolyte (1 M methanol, 3 M sulfuric add) is shown in Fig. 3-33. For the high area platinum, the decrease in the oxidation current in the anodic scan starts at a more anodic potential (900 mV for smooth Ft, 1010 mV for high area Ft), while it ends at the same potential with the smooth platinum. It is also notable that the oxidation current in the cathodic scan increases more suddenly at 880 mV. These differences suggest that the morphology of... 

The step functions were appUed to the high area platinum electrode. The results are shown and compared with the smooth electrode in Fig. 3-34. Although the high area platinum showed slightly large current most of the time, the difference is siuprisingly small except after 20 s for 400 mV. 

This sui ests faster COad oxidation to CO2. As it was shown in Chapter 2 that high area platinum has sites for eoCOad (Easily Oxidized COad)> those sites may play a role in the oxidation of COad formed as the resTilt of partial oxidation of methanol. 

Figs. 3-36 The ratio of the total osddation charge to the suppressed hydrogen desorption charge for smooth and high area platinum electr es. 

High area platinum electrodes were made by painting platinum powders as described earlier. The electrodes were electrochemically cleaned by scanning the potential 50 to 1500 mV for 3 h in 3 M sulfuric add. After that the electrolyte was exchanged with 3 M sulfuric acid with 1 M methanol. 

High area platinum showed different voltammetric features from smooth platinum for methanol oxidation and provided slightly higher sustained current density. These results provided evidences that the morphology of platinum affects the mechanisms and the kinetics of methanol oxidation. 

CO was introduced into the electrolste while the potential was held at 50 mV. After the full coverage was achieved, the potential was swept in the anodic direction. The voltammograms are compared with ones without ruthenium in Fig. 4-5 and Fig. 4—6 for the smooth and the high area platinum electrodes, respectively. 

In both cases, the COad oxidation peaks shifted significantly to more cathodic potentials with the Pt-Ru electrode. On high area platinum without ruthenium as discussed in Copter 2, the oxidation curve was made up of two peaks, i. e. peaks for easily oxidized COad (eoCOad) and hard-to-... 

On the high area platinum, the same phenomena seem to occur while the oxidation current is more constant over a wide potential range. 

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 . 

On the high area platinum, the oxidation peak for easily oxidized COad (eoCOad) seems shifted approximately 100 mV in the cathodic direction. As for the main oxidation peak for hard-to xidize COad (AoCOad). however, only the starting potential shifted in the more cathodic direction. 

Ruthenium was first deposited on platinum in the same condition as described in the section for Pt-Ru electrodes. For high area platinum, tin was deposited after washing the electrode with hydrogen-saturated water. For smooth platinum, before that, ruthenium was removed at 1100 mV for 30 s to obtain higher activities as described before. 

Scavenging of residual impurities in the solution may be necessary ifth e rate-potential relation betrays the effects of impurities in the solution by some kind of aberrant behavior. One introduces a large auxiliary electrode of high area platinum black and changes the potential on it slowly and cyclically over the range of potentials of the intended experiment (Bockris and Conway, 1949). A day or so of this cycling may be necessary and the platinum black sheet (which now contains deposited or adsorbed impurities) must be removed carefully with the potential still on (so that the impurities do not desorb back into the solution). 

Figure 25. Polarization curves for the O2 electrode reaction on Teflon-bonded high-area platinum in O2 saturated 0.1 Af a, log i vs. Eh 1, cathodic 2, anodic, b, i vs. t/h 1, cathodic ...

Bae IT, Scherson DA (1996) Insitu core-electron spectroscopy of carbon monoxide adsorbed on high-area platinum in an acid electrolyte. J Phys Chem 100 19215-19217... 

Despite the fact that iron has been the subject of the large majority of Mossbauer studies reported in the literature, it is rather interesting to note that the first in situ application of this technique involved tin as the active nuclide. In that work, Bowles and Cranshaw examined the emission spectra of adsorbed on a high-area platinum electrode. Although some of the conclusions made by the authors may be open to question, the results obtained clearly indicated that the tin, in whatever form was present at the interface, was bound sufficiently strongly to the host lattice to give a Mossbauer spectrum. Thus, these types of measurements were indeed feasible. 

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