Praseodymium oxide electrodes

The chemistry of rare earths is often discussed only in terms of the trivalent ions and indeed, contrary to the actinides, the oxidation states encountered in lanthanide compounds in the solid state and especially in solution are few in number. Standard electrode potentials M(II-III) and M(III-IV) indicate that, besides the trivalent rare earth ions, only Eu (-0.35 V), Yb + ( — 1.15 V), Sm + ( — 1.55 V) and Ce (+1.74 V) are sufficiently stable to exist in aqueous solutions (Nugent, 1975). It has long been known that alkaline conditions and many complexing anions such as nitrate, phosphate and sulfate stabilize Ce(IV) (Jorgensen, 1979) and recently it has been shown that large complex-forming ligands such as heteropolyanions also stabilize to some extent tetravalent praseodymium and terbium (Spitsyn, 1977). 

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... 

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