Patricia Hernandez-Fernandez

Mass-selected nanoparticles of PtxY as model catalysts for oxygen electroreduction

Low-temperature fuel cells are limited by the oxygen reduction reaction, and their widespread implementation in automotive vehicles is hindered by the cost of platinum, currently the best-known catalyst for reducing oxygen in terms of both activity and stability. One solution is to decrease the amount of platinum required, for example by alloying, but without detrimentally affecting its properties. The alloy PtxY is known to be active and stable, but its synthesis in nanoparticulate form has proved challenging, which limits its further study. Herein we demonstrate the synthesis, characterization and catalyst testing of model PtxY nanoparticles prepared through the gas-aggregation technique. The catalysts reported here are highly active, with a mass activity of up to 3.05 A mgPt(-1) at 0.9 V versus a reversible hydrogen electrode. Using a variety of characterization techniques, we show that the enhanced activity of PtxY over elemental platinum results exclusively from a compressive strain exerted on the platinum surface atoms by the alloy core.

Local composition of alloy catalysts for oxygen reduction by STEM-EDS

Fuel cell technology is a potentially clean alternative to traditional power sources, in particular for the automotive industry [1]. The widespread usability is limited by the high cost of the Pt cathode catalyst [2]. Numerous studies therefore focus on finding cheaper alternative catalysts with higher efficiency for the oxygen reduction reaction (ORR) [3]. Bimetallic catalysts are known for their enhanced ORR activity [3,4]. Pt3Y has been identified based on density functional theory calculations as being both active and stable for ORR. Recent experimental results have shown that PtxY in nanoparticulate form exhibit an unprecedented ORR activity of 3.05 A/mg at 0.9 V with respect to a reversible hydrogen electrode [5,6]. Following the same scheme but focusing on the electrochemical oxygen reduction for the production of hydrogen peroxide, Pd-Hg nanoparticles have been identified as a metal electrocatalyst exhibiting high mass activity [7,8]. In order to understand the enhanced performance of these catalysts, knowledge of how the two elements forming the bimetallic compound are distributed at the atomic level is important.