Visualizing Facet-Dependent Hydrogenation Dynamics in Individual Palladium Nanoparticles.

Area of Science:

• Materials Science
• Nanotechnology
• Physical Chemistry

Background:

• Nanoparticle surface faceting significantly affects chemical reaction rates and selectivity.
• Ensemble measurements lack the spatial resolution to study reactions at the single-particle level.
• Understanding surface termination's role in nanoparticle transformations is crucial.

Purpose of the Study:

• To investigate solute intercalation in individual palladium hydride nanoparticles with distinct surface terminations ({100} cubes and {111} octahedra).
• To compare the thermodynamics and visualize the kinetics of phase transformation at the nanoscale.
• To elucidate the influence of surface faceting versus other factors on reaction pathways.

Main Methods:

• Utilized an environmental transmission electron microscope (TEM) for high-resolution imaging.
• Employed diffraction, electron energy loss spectroscopy (EELS), and dark-field contrast.
• Analyzed 40-70 nm palladium hydride nanoparticles with ~2 nm spatial resolution.

Main Results:

• Phase nucleation occurred at particle tips for both cubes and octahedra.
• Phase-front propagation differed: cubes required rotation, while octahedra allowed multi-directional propagation.
• Interface propagation was linear, limited by diffusion and lattice strain accommodation.

Conclusions:

• Low-coordination number sites and lattice strain are more critical than surface faceting in governing solute-driven reactions.
• Both particle morphologies reached equilibrium hydrogenation at similar rates and pressures.
• The study provides direct visualization of nanoscale reaction kinetics and thermodynamics.