Noncrystalline-to-crystalline transformations in Pt nanoparticles

Area of Science:

• Materials Science
• Nanotechnology
• Surface Science

Background:

• Bulk platinum (Pt) typically exists in a crystalline phase.
• Small nanoparticles (NPs) may exhibit unique properties due to their size.
• Understanding phase transitions in nanomaterials is crucial for catalysis and electronics.

Purpose of the Study:

• To investigate the noncrystalline-to-crystalline transition in supported platinum nanoparticles (NPs).
• To determine the influence of particle size, support materials, and adsorbates on this transition.
• To establish a generalizable model for NP phase behavior.

Main Methods:

• High-resolution transmission electron microscopy (HRTEM) was used to observe over 3000 individual platinum nanoparticles.
• Systematic variation of NP size (subnanometer to nanometer), support type, and adsorbate (hydrogen) was employed.
• Statistical analysis was applied to correlate structural observations with experimental parameters.

Main Results:

• A stable noncrystalline phase exists for small supported platinum NPs, a deviation from bulk behavior.
• The transition from noncrystalline to crystalline is not abrupt but occurs over a size regime where both phases coexist.
• The critical size for this transition is significantly influenced by the nature of the support and the presence of adsorbates like hydrogen.
• This size-dependent, adsorbate-influenced transition is a general phenomenon for late 5d transition metals.

Conclusions:

• The noncrystalline-to-crystalline transition in supported NPs is a statistical phenomenon governed by particle size, support interactions, and adsorbate binding.
• A stable noncrystalline phase in small NPs is a general mesoscopic feature, not unique to platinum.
• The findings provide a framework for understanding and controlling the structure of supported metal nanoparticles for various applications.