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.

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.

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

http://science.sciencemag.org/content/352/6281/73

通过镧系收缩调整铂合金电催化剂活性

为补偿氧化还原反应速度慢的动力学特征，所使用的铂合金催化剂中铂用量一般较高，但这也限制了低温燃料电池在车辆中的广泛使用。我们研究了八种铂-镧系和铂-碱土金属电极的氧化还原反应，即Pt5M，其中M是指镧、铈、钐、钆、铽、镝、铥和钙。这些催化剂是记录过的活性最高的多晶体铂合金类催化剂，催化活性是铂的三到六倍。其活化过程包含一个通过酸浸法产生的铂叠层。氧化还原反应的活性与主体催化剂晶格常数的关系类似一个有高峰值的“火山”的形状。本文中我们阐述了镧系收缩如何能被用作控制应变效应以及改善这些材料的活性、稳定性和反应性。（科研圈）