title: Strained lattice with persistent atomic order in Pt3Fe2 intermetallic core-shell nanocatalysts.
abstract: Fine-tuning nanocatalysts to enhance their catalytic activity and durability is crucial to commercialize proton exchange membrane fuel cells. The structural ordering and time evolution of ordered Pt3Fe2 intermetallic core-shell nanocatalysts for the oxygen reduction reaction that exhibit increased mass activity (228%) and an enhanced catalytic activity (155%) compared to Pt/C has been quantified using aberration-corrected scanning transmission electron microscopy. These catalysts were found to exhibit a static core-dynamic shell regime wherein, despite treating over 10,000 cycles, there is negligible decrease (9%) in catalytic activity and the ordered Pt3Fe2 core remained virtually intact while the Pt shell suffered a continuous enrichment. The existence of this regime was further confirmed by X-ray diffraction and the compositional analyses using energy-dispersive spectroscopy. With atomic-scale two-dimensional (2-D) surface relaxation mapping, we demonstrate that the Pt atoms on the surface are slightly relaxed with respect to bulk. The cycled nanocatalysts were found to exhibit a greater surface relaxation compared to noncycled catalysts. With 2-D lattice strain mapping, we show that the particle was about -3% strained with respect to pure Pt. While the observed enhancement in their activity is ascribed to such a strained lattice, our findings on the degradation kinetics establish that their extended catalytic durability is attributable to a sustained atomic order.
authors.affiliation: Department of Materials Science and Engineering, McMaster University, Hamilton, Ontario, Canada L8S 4L8.
authors.forename: Sagar
authors.initials: S
authors.lastname: Prabhudev
authors.forename: Matthieu
authors.initials: M
authors.lastname: Bugnet
authors.forename: Christina
authors.initials: C
authors.lastname: Bock
authors.forename: Gianluigi A
authors.initials: GA
authors.lastname: Botton
mesh_terms: D000497:Alloys / Q000737:chemistry; D002384:Catalysis; D055119:Elastic Modulus; D007501:Iron / Q000737:chemistry*; D008422:Materials Testing; D053768:Metal Nanoparticles / Q000737:chemistry* / Q000648:ultrastructure*; D058608:Nanopores / Q000648:ultrastructure*; D010984:Platinum / Q000737:chemistry*; D013718:Tensile Strength
chemical_list: D000497:Alloys; D010984:Platinum; D007501:Iron