Preparation of CO-tolerant Catalysts

The first step in the development of an anode catalyst is preparation. Several approaches have been used for the production of catalysts, both supported and unsupported. It is generally agreed that preparation has an important influence on catalyst performance [380]. Several techniques have been used to prepare the catalysts, such as colloidal chemistry methods [381-385], the impregnation method [386-390], and the reverse micelles method [391, 392]. Although the colloidal chemistry methods and the reverse micelles method produce very promising results, they are very complex compared to the impregnation method. The 

Reduetion of the metallic ions from their salts with sulfite [209], borohydride [383], formaldehyde [393], hydrazine [394], or formic acid [395] has been proposed, resulting in catalysts with such diverse physical characteristics that direct comparison of their electrochemical performances is a rather diffieult task. In the ease of bimetallic catalysts, the reduction of both metals ean be done simultaneously or one after the other, as was described for Pt-Ru/C [396] and Pt-Co/C [397]. 

Electrocatalyst XRD crystallite size, nm Calculated metal area m g PtRu CO chemisorption, metal area, m g PtRu XRD lattice parameter, nm 

Although as described above fliese alloy systems have been studied by a number of research groups, it is difficult to directly compare one system to another because of differences between sample preparation methods and experimental techniques. Such multielement comparisons do not appear routinely in the literature because flic amount of work involved in sample preparation and testing using traditional one at a time mefliods is prohibitive. Thus, a paper published by Stevens et al. [235] demonstrated flic usefijlness of composition spread preparation and analysis techniques for fuel ceU catalyst research. Furthermore, performance measurements of Pti composition were used to identify more complex ternary or quaternary composition for future studies. 

There is a considerable drive to raise the operating temperatures of the PEMFC to above 100 °C. This would raise the system efficiency and dramatically improve the CO tolerance of Pt-based electrocatalysts. If the temperature can be raised to 160 °C, studies in the phosphoric acid fuel cell (PAFC) with 1 to 2% CO indicate 

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Another approach for the preparation of CO-tolerant catalyst is to combine a highly active element for HOR with a second metal to produce the surface (ideally), which does not adsorb CO under the fuel cell operating conditions. Along this line, PdAu-black alloys have already been proposed. Indeed, much lower CO adsorption energies on different poly- and single-crystalline PdAu surfaces were found in ultrahigh vacuum (UHV) studies compared with pure Pd or pure Pt [86]1. In the oxidation measurement of Schmidt [87], which was based on an earlier study by Fishman [88], the Pd-Au/C catalyst... 

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