Lattice contracted ordered intermetallic core-shell PtCo@Pt nanoparticles: Synthesis, structure and origin for enhanced oxygen reduction reaction

Electrocatalysts in ordered intermetallic phases are highly desirable for the oxygen reduction reaction (ORR) with enhanced activity and durability. Here, we develop carbon-supported ordered core-shell PtCo@Pt (O-PtCo@Pt/C with the Pt:Co atomic ratio of 1:1) intermetallic compound (IMC) nanoparticles with the metal loading as high as of 60 wt%, aiming to understand the effects of the ordered structure, metal loading and particle size on the ORR performance. The O-PtCo@Pt/C is synthesized by a two-step reduction method and followed by a heat-treatment. The mean particle diameter is about 4.8 nm with a narrow size distribution. The surface of the core-shell nanoparticles is enriched with about 3 layers of Pt atoms after the acid treatment. Noticeable lattice contraction in the O-PtCo@Pt/C has been observed by X-ray diffraction and high resolution transmission electron microscopy. Such a structurally ordered PtCo@Pt/C catalyst exhibits higher ORR activity and durability than the disordered PtCo/C and commercial Pt/C catalysts, which could be ascribed to the Pt-rich shell, ordered core structure, small particle size, lattice contraction, as well as strengthened d-hybridization. This research provides new insights to design an ordered intermetallic structure in the core and a Pt-rich surface with special facets for the excellent catalytic performance.