Phase conversion of Pt₃Ni₂/C from disordered alloy to ordered intermetallic with strained lattice for oxygen reduction reaction

Tuning the surface strain and atom arrangement to control the surface chemistry process is one of efficient strategies to enhance the electrocatalytic performance of nanomaterials. This research introduces an ordered Pt₃Ni₂/C intermetallic nanoparticle as a new type of the Pt-Ni system for the ORR, which is rarely reported at present. Besides, it focuses on the phase conversion of Pt₃Ni₂/C nanocatalysts from a disordered phase to an ordered phase. X-ray diffraction (XRD) and transmission electron microscopy (TEM) measurements confirm the formation of ordered face-centered cubic (fcc) type Pt₃Ni₂/C nanocatalysts with homogeneous particle distribution and average crystallite size of 6.4 nm. The ordered fcc-Pt₃Ni₂/C exhibits improved electrocatalytic activities toward the oxygen reduction reaction (ORR) in 0.1 M HClO₄ and 0.1 M KOH electrolyte when compared with Pt₃Ni₂/C disordered alloy. Besides, the robust ordered fcc-Pt₃Ni₂/C showed a smaller activity loss after durability tests in alkaline medium than acid electrolyte. The improved ORR activity and stability could be ascribed to the surface atom arrangement and reasonable surface strain originated from the ordered structure of Pt₃Ni₂/C nanoparticles relative to the disordered Pt₃Ni₂/C alloy, forcefully demonstrating that the Pt₃Ni₂/C intermetallic compound may act as highly efficient ORR electrocatalysts in energy conversion process.