Platinum Alloys and Composites as Catalysts for Anodes

The catalytic problems associated with the anodic oxidation of methanol are very similar to those associated with the anodic oxidation of CO-containing technical hydrogen. At present, the standard catalyst for both reactions is a mixed Pt-Ru catalyst (with about 50 at% of each metal) obtained by their joint chemical or electrochemical deposition from solutions of simple or complex compounds on carbon black. 

It is a defect of the Pt-Ru catalysts that ruthenium partly dissolves from the alloy and leaves the catalyst with a purely platinum surface layer this will 

In a comprehensive review, Antolini and Gonzalez (2010) present an overview of the relationship between structural characteristics of Pt-Sn catalysts (catalyst composition, degree of alloying, presence of oxides) and their electrocat-alytic activity for the electrooxidation of various fuels (i.e., carbon monoxide, hydrogen-carbon monoxide, methanol) in acid media. 

Of great interest is the use of intermetallic compounds of platinum with rare-earth metals such as cerium and praseodymium for anodic methanol oxidation, known from the work of Lux and Cairns (2006). This combination is attractive inasmuch as it involves two metals that differ strongly in their own electrode potentials Pt with = -1-1.2 V and Pr with = —2.3 V(SHE), and thus in their electronic structure. However, for the same reason, traditional methods of preparing joint disperse deposits of these metals by chemical or electrochemical reduction in a solution of the corresponding salts fail in such a situation. Lux and Cairns developed a new technology for preparing disperse powders of such compounds by thermal decomposition of complex cyanide salts of these metals. The catalyst obtained had some activity in ethanol oxidation (although somewhat 

Composite platinum catalysts containing complex oxides of the perovskite type (ABO3 where A = Sr, Ce, La, etc., and B = Fe, Ni, Pt, Ru, etc.) were studied by Deshpande et al. (2006). The perovskites were prepared by combustion synthesis, where an aqueous solution of the starting components was evaporated to dryness, then the residue ignited or self-ignited, quickly heating up to temperatures above 1500°C. It was found that when platinum was introduced into the composite during the first step (i.e., was added to the aqueous solution), the properties of the catalyst were markedly better than with platinum intfoduced into the finished perovskite matrix. 

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