Samarium

Abstract: The high platinum loadings required to compensate for the slow kinetics of the oxygen reduction reaction (ORR) impede the widespread uptake of low-temperature fuel cells in automotive vehicles. We have studied the ORR on eight platinum (Pt)–lanthanide and Pt-alkaline earth electrodes, Pt5M, where M is lanthanum, cerium, samarium, gadolinium, terbium, dysprosium, thulium, or calcium. The materials are among the most active polycrystalline Pt-based catalysts reported, presenting activity enhancement by a factor of 3 to 6 over Pt. The active phase consists of a Pt overlayer formed by acid leaching. The ORR activity versus the bulk lattice parameter follows a high peaked “volcano” relation. We demonstrate how the lanthanide contraction can be used to control strain effects and tune the activity, stability, and reactivity of these materials.

Abstract: Analyses for the rare-earth elements in sea water, in a phosphorite, and in a manganese nodule were made by neutron activation and x-ray fluorescence techniques. These marine samples showed a depletion in the heavier rareearth elements, relative to chondritic meteorites, beginning with samarium. Cerium was enriched in the manganese nodule, probably as a result of its oxidation to the 4+ valence state. The ratios of the rare-earth abundances in the two minerals to those of sea water go through a maximum in the vicinity of samarium. The europium concentration, often anomalous in terrestrial minerals, was normal relative to the other rare earths in all of the samples. The sea water showed four times the concentration of rare earths at a depth of 4000 meters as compared with surface values. (auth)