Platinum single crystals, voltammetric profiles

FIGURE 1.10 Current intensity versus electrode potential voltammetric profile for platinum single crystals, Pt(100) (cooled in air) with blue lines, Pt(110) with black lines and Pt(lll) in red lines, in 0.5 M sulfuric acid solution run at 0.05 V s 1 at room temperature. A difference with respect to the early single crystal preparation method by Will [18] is that the ones reported here are those obtained by Clavilier early in 1980. After 50 years of the first paper by Will on the use of single crystals for the oxygen electroreduction reaction and his finding of the given preferred activities on (111) and (100) planes, the industry still uses polycrystalline surfaces. 

There is a strong difference between the voltammetric profiles of the carbon monoxide oxidative desorption on a pure platinum single crystal in the presence of an ad-metal species and the same in the absence of an ad-metal species. The carbon monoxide adsorption and oxidation are also different depending on the type of the deposited metal as shown in Figure 11.4. 

Since their first publication in 1980 (7), the voltammetric profiles of clean, ordered platinum single crystals have been a subject of controversy, especially in the case of Pt(l 11). At first, the main discussion point was related to the surface state of the sample after the flame treatment. Did the obtained voltammetric profile correspond to the clean, atomically ordered surface expected for the crystallographic basal plane or was the ordered surface obtained only after some voltammetric cycles involving oxygen adsorption (2) The answer to these questions was gotten by means of well-established Surface Science techniques, such as ex-situ LEED, either with clean samples (J) or with those prepared by I-CO replacement (4), and by in-situ STM (5). These results proved that the flame treatment and subsequent water protection led to clean, well-ordered Pt(lll) surfaces, which gave a voltammetric response never observed before 1980. 

Adsorption of acetic acid on Pt(lll) surface was studied the surface concentration data were correlated with voltammetric profiles of the Pt(lll) electrode in perchloric acid electrolyte containing 0.5 mM of CHoCOOH. It is concluded that acetic acid adsorption is associative and occurs without a significant charge transfer across the interface. Instead, the recorded currents are due to adsorption/desorption processes of hydrogen, processes which are much better resolved on Pt(lll) than on polycrystalline platinum. A classification of adsorption processes on catalytic electrodes and atmospheric methods of preparation of single crystal electrodes are discussed. 

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