Atomically Ordered Pt5La Nanoparticles as Electrocatalysts for the Oxygen Reduction Reaction

In this study, atomically ordered intermetallic Pt5La nanoparticles (NPs) were successfully prepared using a relatively simple wet chemical process. X-ray diffraction measurements were carried out to determine the crystal structures of the prepared catalysts. The transmission electron microscopy results revealed that the Pt5La NPs with a size of 3–15 nm were distributed on the carbon surface. The crystal structure of the Pt–La alloy depended on the annealing temperature. A face-centered cubic-type (i.e., a disordered phase) structure was formed at temperatures less than 700 °C, while a CaCu5-type structure (i.e., an ordered phase) could be formed at 800 °C. The prepared Pt5La NPs exhibited oxygen reduction reaction (ORR) specific (1.39 mA cm–2) and mass (0.657 A mg–1) activities approximately 3.7 and 5.1 times higher than those of commercially available Pt NPs on carbon, respectively. Furthermore, the as-prepared NPs showed enhanced ORR durability. The enhanced ORR activity was evaluated through surface analysis using high-angle annular dark-field scanning transmission electron microscopy and X-ray photoelectron spectroscopy. The significantly enhanced ORR activity of the ordered Pt5La NPs was due to their compressive strain and rich atomic steps. The findings of this study will be helpful in the development of electrocatalysts with high electrochemical activity.