Atomic-scale insights into thermal stability of Pt3Co nanoparticles: A comparison between disordered alloy and ordered intermetallics

Abstract

Pt3Co nanoparticles are promising catalyst candidates for fuel-cell applications because their catalytic performances are superior to pure Pt nanoparticles. Fundamental insights into the thermostability of Pt3Co nanoparticles are critical for their syntheses, post-treatments, and ultimate applications. In this article, the thermal stability of Pt3Co nanoparticles has been investigated by molecular dynamics simulations. Two types of structures, chemically disordered alloy and ordered intermetallic compound, are considered. Besides, two-atomic-layered Pt and Co have been introduced to coat the Pt3Co nanoparticles to form Pt3Co-Pt and Pt3Co-Co core-shell nanoparticles. The simulated results reveal that the ordered intermetallic Pt3Co nanoparticles exhibit better thermal stability than the disordered alloy ones. Pt coating is greatly superior to Co coating for improving both structural and thermal stability of Pt3Co nanoparticles. For Pt3Co and Pt coated Pt3Co nanoparticles, the overall melting simultaneously happens in both Pt and Co. However, Co-coated surface induces the two-stage melting of Pt3Co nanoparticles at large sizes; it markedly decreases the thermal stability of the nanoparticles at small sizes, resulting in the melting point even lower than pure Co ones. The remarkably lowered melting temperature is associated with the order-to-disorder transformation in the Co-coated shell and the appreciable change of particle shape before surface premelting.