Reactivity and structural evolution of urchin-like Co nanostructures under controlled environments

Area of Science:

• Materials Science
• Nanotechnology
• Catalysis

Background:

• In situ transmission electron microscopy (TEM) is crucial for understanding nanomaterial behavior under operational conditions.
• Controlled gas environments in TEM allow real-time observation of dynamic changes at high temperatures and pressures.
• Studying catalysts in their working environments is fundamental for advancing catalytic science.

Purpose of the Study:

• To investigate the thermal stability and reactivity of crystalline cobalt nanostructures.
• To observe the influence of different gaseous environments on cobalt nanostructure morphology and phase.
• To understand the role of native surface ligands in stabilizing nanostructures.

Main Methods:

• Utilized a microelectromechanical systems (MEMS)-based atmospheric gas cell for in situ TEM observations.
• Exposed cobalt nanostructures to various controlled gas environments: vacuum, inert atmosphere, oxygen, dihydrogen, carbon monoxide, and syngas.
• Analyzed morphological and structural changes at high temperatures with near-atomic resolution.

Main Results:

• Observed cobalt atom migration and template-driven carbon nanostructure formation under vacuum/inert conditions.
• Monitored void formation via the Kirkendall effect in reactive oxygen environments.
• Demonstrated reversible oxidation and reduction of cobalt nanostructures.
• Documented sintering in pure hydrogen and metal particle carburization under CO/syngas.

Conclusions:

• Cobalt nanostructure behavior is highly dependent on the surrounding gas environment.
• Native ligands play a critical role in stabilizing nanostructure morphology.
• In situ TEM with controlled gas environments provides unprecedented insights into nanomaterial dynamics and reactivity.