Platinum single crystals, voltammetric

A voltammetric characterization of platinum single crystal surfaces produced by these three methods shows that a very similar surface order and cleanliness are obtained in each case. The features embodied by the third method which we use for the radio-electrochemistry work, are as follows ... 

A detailed comparison of the voltammetric behavior of platinum single-crystal and faceted electrodes was also given [218]. 

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. 

A detailed comparison of the voltammetric behavior of platinum single crystal and faceted electrodes was also given. A mechanistic model for the electrochemical faceting of metals with development of preferred crystallographic orientations was proposed. ... 

A voltammetric study of the behavior of glyoxylic acid on platinum single crystal electrodes in sulfuric acid medium was performed in order to get information on the effect of surface structure on the electrosorption and oxidation. The oxidation (taking place at high potentials 1.0 V RHE) has been found structure sensitive. At lower potentials the formation of poisoning intermediates is considered as the predominant process. Two kinds of stable residues were distinguished ... 

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. 

Fig. 12. Voltammetric i-U curves on the three main faces of platinum single crystals in 4 M H2SO4 at 25°C and 0.1 V/sec in the hydrogen region...

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. 

Actually, the results of a comparative study of the voltammetric behavior of NO3 ion at a platinized platinum electrode with (100) preferred orientation and at a polycrystalline one prove the higher catalytic activity of the former system over the latter one, as expected on the basis of single crystal studies. It should be mentioned that this kind of difference was not found in the reduction of CIO4. 

Size- and shape-controlled cubo-octahedral platinum(o) nanoparticles of 4nm average size stabilized by sodium polyacrylate showing 111 and 100 surfaces were used to prepare Vulcan supported electrocatalysts. Cyclic voltammetric CO oxidation studies carried out by the thin film rotating disc method show two different sites of CO oxidation (Fig. 2.19). This can be assigned to differences in the activity of the crystal surfaces and is in agreement with single crystal studies. TEM results after cyclic voltammetric characterization show a complete absence of agglomerations. 

Watson DJ, Attard GA. Surface segregation and reconstructive behaviour of the (1 0 0) and (1 1 0) surfaces of platinum-palladium bulk alloy single crystals a voltammetric and LEED/AES study. Surf Sci 2002 515 87-93. 

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