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Tuning the activity of Pt alloy electrocatalysts by means of the lanthanide contraction

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Science  01 Apr 2016:
Vol. 352, Issue 6281, pp. 73-76
DOI: 10.1126/science.aad8892

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A lanthanide boost for platinum

High loadings of precious platinum are needed for automotive fuel cells, because the kinetics of the oxygen reduction reaction (ORR) are relatively slow. Escudero-Escribano et al. studied a series of platinum alloys with lanthanides and alkaline earth elements. When the surfaces were leached to leave pure platinum, they developed compressive strain that boosted the ORR activity—up to a factor of 6 for terbium. Enthalpy effects helped to stabilize these alloys under operating conditions.

Science, this issue p. 73

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.

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