Facets and vertices regulate hydrogen uptake and release in palladium nanocrystals

Area of Science:

• Materials Science
• Surface Chemistry
• Nanotechnology

Background:

• Crystal facets, vertices, and edges influence metal surface energy and chemical interactions.
• Palladium's hydrogen absorption/desorption properties are crucial for energy storage, catalysis, and sensing.
• In situ techniques allow tracking of palladium nanocrystal phase transitions during hydrogen absorption.

Purpose of the Study:

• To demonstrate in situ X-ray diffraction for tracking hydrogen absorption/desorption in palladium nanocrystals.
• To delineate distinct absorption/desorption mechanisms based on nanocrystal facets ((111) vs. (100)).
• To correlate nanocrystal morphology (vertices, facets) with hydrogen interaction kinetics.

Main Methods:

• In situ X-ray diffraction to monitor hydrogen absorption and desorption.
• Synthesis and characterization of palladium nanocrystals with controlled facets ((111) or (100)) and vertex density.
• Kinetic analysis of hydrogen absorption and desorption rates.

Main Results:

• Distinct hydrogen absorption and desorption mechanisms were identified for (111) and (100) faceted nanocrystals.
• Higher vertex density correlated with increased hydrogen absorption rates, linked to β-phase nucleation at strained vertices.
• Nanocrystals with (100) facets exhibited nearly tenfold faster initial hydrogen desorption rates due to efficient surface hydrogen recombination.

Conclusions:

• In situ X-ray diffraction is effective for studying hydrogen dynamics in palladium nanocrystals.
• Nanocrystal facet orientation and vertex density significantly impact hydrogen interaction kinetics.
• Tailoring nanocrystal morphology with high vertex density and (100) facets optimizes fast hydrogen uptake and release for energy applications.