Revealing High-Temperature Reduction Dynamics of High-Entropy Alloy Nanoparticles via In Situ Transmission Electron...

Area of Science:

• Materials Science
• Nanotechnology
• Physical Chemistry

Background:

• High-entropy alloys (HEAs) show promise for structural, catalytic, and energy applications.
• Understanding HEA behavior in hydrogen (H₂) environments is critical for their deployment.
• Oxidized HEA nanoparticles require investigation for H₂ interactions.

Purpose of the Study:

• To investigate the reduction behavior of oxidized FeCoNiCuPt HEA nanoparticles (NPs) under atmospheric pressure H₂.
• To elucidate the structural and chemical transformations during H₂ reduction.
• To understand the diffusion mechanisms governing the reduction process.

Main Methods:

• In situ gas-cell transmission electron microscopy (TEM) was employed.
• Real-time observation of reduction reactions at the nanoscale.
• In situ chemical analysis was performed.

Main Results:

• The reduction reaction front remained at the external surface of the oxide layer.
• The oxide layer expanded and developed a porous structure during reduction.
• Oxidized copper (Cu) was fully reduced to Cu nanoparticles, while Fe, Co, and Ni remained oxidized.
• Outward diffusion of all transition metals (Fe, Co, Ni, Cu) caused the oxide layer expansion.

Conclusions:

• The H₂ reduction of oxidized HEA NPs leads to unique structural transformations.
• Understanding these transformations is key for designing HEAs for H₂ applications.
• This research aids in developing advanced alloys for H₂ storage, catalysis, and corrosion mitigation.