Pd surface and Pt subsurface segregation in Pt1-c Pd c nanoalloys

Area of Science:

• Materials Science
• Computational Chemistry
• Nanotechnology

Background:

• Understanding the surface and subsurface chemical arrangement of bimetallic nanoparticles is crucial for catalysis and materials design.
• Platinum-palladium (Pt-Pd) nanoalloys are of significant interest due to their unique electronic and catalytic properties.

Purpose of the Study:

• To investigate the structural and chemical arrangement of Pt-Pd nanoalloys with icosahedral and face-centered cubic symmetries.
• To elucidate the factors governing the segregation behavior of Pt and Pd atoms within these nanoparticles.

Main Methods:

• Monte Carlo simulations were employed to model Pt-Pd nanoalloys.
• A tight-binding interatomic potential, fitted to density-functional theory (DFT) calculations, was utilized.

Main Results:

• Palladium (Pd) segregation to the surface and platinum (Pt) enrichment in the subsurface were predicted, irrespective of nanoparticle structure and size.
• An onion-shell chemical configuration was observed, initiated by Pd surface segregation.
• This segregation behavior was found to be stable at elevated temperatures.
• For larger nanoparticles, an oscillating segregation profile across several atomic shells was observed.

Conclusions:

• The lower cohesive energy of Pd compared to Pt drives surface segregation.
• Weak ordering tendencies contribute to Pt subsurface enrichment.
• Atomic size mismatch plays a role, with smaller Pd atoms occupying highly compressed core sites and larger Pt atoms favoring less compressed subsurface sites.