Hydride-Based Electride Material, LnH2 (Ln = La, Ce, or Y)

Area of Science:

• Materials Science
• Solid-State Chemistry
• Catalysis

Background:

• Hydrogen insertion into metals leads to vacancy formation and exhibits strong electron-donating properties.
• Electrides are ionic compounds where electrons occupy interstitial spaces, typically rare in anion-rich forms.
• Anion-rich electrides require cage sites free from lone pair electrons of adjacent ions.

Purpose of the Study:

• To synthesize and characterize novel hydride-based electrides.
• To investigate the electronic structure and formation mechanism of these electrides.
• To evaluate the catalytic activity of these materials in ammonia synthesis.

Main Methods:

• Synthesis of LnH2+x (Ln = La, Ce, Y) compounds with fluorite-type structures.
• Characterization of electronic properties, including electron transfer and covalent interactions.
• Hydrogen embrittlement method for synthesizing Ru-loaded LnH2+x electride powders.

Main Results:

• LnH2+x compounds were identified as the first hydride-based electrides with itinerant electrons in the cage surrounded by H(-) anions.
• Electron transfer is attributed to Ln-cage covalent interaction, creating isotopic electronic character.
• Ru-loaded LnH2+x catalysts demonstrated efficient ammonia synthesis at ambient pressure, resisting hydrogen poisoning.

Conclusions:

• Anion-rich electrides, previously rare, can be formed from hydride-based materials.
• The unique electronic structure, including low work function from Ln-H(-) covalent interaction, contributes to high catalytic activity.
• These hydride-based electrides show promise as robust catalysts for ammonia synthesis.