Hydrogen adsorption/desorption

Figure 12.5 CO stripping voltammogram with a CO- tee 0.1 M H2SO4 electrolyte. Compare the data in Fig. 12.4 the CO oxidation region begins at V = 0.43 V. After CO stripping, hydrogen adsorption/desorption peaks and the beginning of the Pt oxidation range are shown.

Cyclic voltammetry studies of single-crystal platinum electrodes in acidic aqueous electrolytes showed that the two characteristic peaks of hydrogen adsorption/desorption on platinum (see Fig. 5.40) correspond in fact to reactions at two different crystal faces the peak at lower potential to Pt(100) and the other one to Pt(lll). 

The second most widely used noble metal for preparation of electrodes is gold. Similar to Pt, the gold electrode, contacted with aqueous electrolyte, is covered in a broad range of anodic potentials with an oxide film. On the other hand, the hydrogen adsorption/desorption peaks are absent on the cyclic voltammogram of a gold electrode in aqueous electrolytes, and the electrocatalytic activity for most charge transfer reactions is considerably lower in comparison with that of platinum. 

Hou, P.X., S.T. Xu, Z. Ying, Q.H. Yang, C. Liu, H.M. Cheng, Hydrogen adsorption/desorption behavior of multi-walled carbon nanotubes with different diameters. Carbon 41,2471-2476,2003. 

However the aore iaportant question which can be solved with such saaples is related to characterization of surface sites because each basal orientation shows well-characterized hydrogen adsorption-desorption peaks which eight be helpfully used for this purpose. 

The sharp and narrow peak at -0.15 V on the Pt(110) plane indicates on a coupling of hydrogen adsorption/desorption and HSO - and S0 2- desorption/adsorption. This will be further discussed in connection with the data for stepped surfaces. 

Chen Dong, Chen Lian, Liu Shi et al. The properties of hydrogen adsorption/desorption for Mg/MW NTs Composites, The Chinese Journal of Nonferrous Metals,13,850-53 (2003)... 

The reconstructed surface showed a polycrystalline—like hydrogen adsorption-desorption voltanunogram. Therefore, the reconstructed Pt(lll) surface cannot be regarded as PtClll) any more. 

The cyclic voitammogram for Pt (111) in 5 M sulfuric acid is shown in Fig. 2-21. Compared with that in 0.5 M sulfuric acid (Fig. 2-15), the anodic part of the two split hydrogen adsorption-desorption areas was compressed in the cathodic direction and became two sharp peaks while the cathodic part did not change its shape very much. The asymmetric peak at 700 mV shifted cathodicly and became more symmetric and sharp. The oxidation of platinum shifted about 100 mV in the anodic direction. All these changes could be attributed to the increase in specific adsorption of anions or the decrease of the activity of water as well as the pH change. 

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. 

The cyclic voltammograms for Pt(llO) and Pt(lOO) in 0.5 M perchloric acid are shown in Fig. 2-26 and Fig. 2—27 respectively. The shapes of the voltammograms for hydrogen adsorption-desorption were significantly different from those in sulfuric add. Although these anion... 

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. 

Platinum was deposited on Nafion membrane by the method described earlier. Ibe cyclic voltammogram is shown in Fig. 2-i6 using 3 M H2SO4 as the electrolyte in the solution side of the membrane. The hydrogen adsorption—desorption features are not very well-defined probably because of some impurities. 

Fie 3-16 Hydrogen adsorption-desorption features in cyclic voltammograms for polycrystalline Pt electrode in 3 M H2SO4 with 0.1 M CH3OH after holding the potential at 600 mV for various time at... 

Fig. S-40 Hydrogen adsorption-desorption features of Nafion SPE Pt and platinized Pt electrodes b ore and after 24 hour potential holding at GOOmV.

Ruthenium was electrochemically deposited on platinum foil at a potential of 50 mV for 10 s. The cyclic voitammogram of this Pt—Ru electrode in 3 M H2SO4 is shown in Fig. 4—2. The voitammogram shows the hydrogen adsorption-desorption features from 50 mV to 200 mV and the oxidation and reduction current over 300 mV. The voltanunogram seemed stable when the upper limit potential was 800 mV. When the upper limit was higher than 800 mV, the voitammogram became slowly like pure... 

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