Platinum, limitations from corrosion

Alloys with ruthenium Additions of ruthenium have a most marked effect upon the hardness of platinum, but the limit of workability is reached at about 15% ruthenium, owing to the fact that ruthenium belongs to a crystallographic system different from that of platinum. Apart from a somewhat greater tendency to oxide formation at temperatures above 800°C, the resistance to corrosion of ruthenium-platinum alloys is comparable to that of iridium-platinum alloys of similar composition. 

It is possible to separate the cathode from the anode by putting the iron in contact with a platinum electrode, thus creating an electrochemical cell (Figure 1.6). The cathodic partial reaction (1.6) takes place more easily on the platinum, whose surface acts as a catalyst, than on the iron surface. As a result, a significant production of hydrogen is observed on the platinum, while at the hydrogen production on the iron practically stops. Simultaneously, the corrosion rate of iron increases. In this example, the anodic partial reaction takes place exclusively on the iron, whereas the cathodic partial reaction, which here limits the corrosion rate, takes place mostly on the... 

From a practical point of view, isocyanates, together with carbamates and ureas (Chapter 3), are the most important organic products discussed in this book. Their synthesis from nitroarenes has indeed been the subject of many patents. There are also limited examples of aliphatic isocyanates obtained by this route. Organic mono- and diisocyanates may be prepared in a continues liquid phase method by treating the appropriate amine with phosgene. However, the reaction is rather complex [6] and, besides the use of the dangerous phosgene, the formation of the corrosive hydrochloric acid creates several problems. Aliphatic isocyanates can also be obtained from olefins with isocyanate ion in the presence of a salt of a coordination compound of palladium or platinum [7], from olefins with isocyanic acid in the vapour phase over Pt/ALOs [8], and from formamides, by oxidation over a silver catalyst [9]. Apparently only the last reaction seems to have some potential practical applications [10]. 

This system seems to be the only alloy to date whose hydrous oxide growth behavior under potential cycling conditions has been investigated.189 190 Burke and O Sullivan189 demonstrated that with an alloy containing 10% by weight of rhodium in platinum both components corroded on cycling between certain limits (0-1.5 V) in 1.0 mol dm-3 NaOH. However, while the platinum corrosion product was found to be soluble under these conditions the rhodium one was not—in fact the hydrous film developed on the surface in this case was apparently derived almost totally from the minor component in the alloy. 

This chapter is devoted to a review of material issues for HT-PEMFC components and is built on relevant evaluation of data from literature on membrane oxidation, acid loss, platinum dissolution, and carbon corrosion. Finally, the state-of-the-art durability of PBI-based fuel cells is summarized. For certain applications, like in mobile auxiliary power units exposed to severe vibrations and road dust or to maritime saline mists, the picture becomes more complicated and knowledge today is rather limited. 

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