Platinum surface morphology

Kraenert, R. (2005) Ammonia Oxidation over polycrystalline platinum surface morphology... 

Platinum—Iridium. There are two distinct forms of 70/30 wt % platinum—iridium coatings. The first, prepared as prescribed in British patents (3—5), consists of platinum and iridium metal. X-ray diffraction shows shifted Pt peaks and no oxide species. The iridium [7439-88-5] is thus present in its metallic form, either as a separate phase or as a platinum—iridium intermetallic. The surface morphology of a platinum—iridium metal coating shown in Figure 2 is cracked, but not in the regular networked pattern typical of the DSA oxide materials. 

Fig. 28. Data recorded for CO oxidation on platinumfl 1 0) with an STM in a flow reactor. The upper panel shows mass spectrometer signals recorded directly from the reactor cell. The STM images show the surface morphology at different stages, corresponding to the curves in the mass spectrometer signal. High CO oxidation activity was correlated with the observation of a rough, oxidic platinum surface. With permission from Reference (163).

Fig. 26. Surface morphology of a platinum sample after 4 h of oxygen plasma treatment. The platinum surface is partially covered by faceted particles 5 pm in diameter (245).

Methanol strongly dissociatively chemisorbs on platinum surfaces, but the extent of adsorption depends critically on the surface morphology, the crystal face exposed, and the presence of other anions in solution that themselves can competitively co-adsorb. 

Physical properties of the carbon substrate, such as electronic conductivity, surface area, and surface morphology are important, since the former can contribute to resistive losses in the electrocatalyst structure and the latter may determine the sites on which the platinum electrocatalyst crystallites may be located. Both the initial deposition of the platinum crystallites on the carbon substrate and the subsequent surface area loss of the platinum crystallites under operating conditions by a surface migration mechanism can be influenced by the surface carbon structure. 

Figure 2 Changes of the surface morphology of a traditional woven platinum/rhodium gauze during use. The surface of fresh catalyst is smooth, but during use dendritic excrescences of alloy grow from the wire surface.

Fig. 15. Surface morphology of a micro electrode with a mesoporous platinum coating...

In comparison to SO2, hydrogen sulfide is reported to have an even more adverse effect on fuel cell catalysts [33,37,43,50]. H2S can strongly adsorb onto Ft and affect the catalyst layer by disrupting its morphology [43]. By occupying polyatomic sites on the catalyst, it prevents the reactants from reaching reaction sites. A mechanism proposed for the interaction of hydrogen sulfide with a platinum surface involves the formation of adsorbed... 

Carbon supports typically undergo chemical or physical activation prior to platinum impregnation. The alteration of surface groups and functionalities on the carbon support can strongly influence the carbon-metal interaction that can directly affect the metal particle size, metal particle distribution, surface morphology of the carbon, and surface impurities that may be present. These parameters have been known to influence the catalytic metal stability and activity of the resulting catalyst. Common surface modifications strategies include chemical oxidation of the carhon or thermal activation to modify the surface structures. 

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