Structural insight into the magnesium borohydride - ethylenediamine solid-state Mg-ion electrolyte system

Area of Science:

• Materials Science
• Inorganic Chemistry
• Crystallography

Background:

• The magnesium borohydride-ethylenediamine (Mg(BH₄)₂-en) system is investigated for hydrogen storage applications.
• Understanding the complex phases and structures within this system is crucial for optimizing its properties.

Purpose of the Study:

• To elucidate the complex crystal structure of Mg₅(en)₆(BH₄)₁₀.
• To investigate the role of amorphous Mg(BH₄)₂ in the reactivity of the Mg(BH₄)₂-en system.
• To characterize a previously overlooked phase, Mg(en)₂(BH₄)₂.

Main Methods:

• Single crystal synchrotron X-ray diffraction was employed to solve the crystal structure.
• Neutron powder diffraction (NPD) on isotopically substituted samples confirmed the structure.
• Reactivity studies were performed on the Mg(BH₄)₂-en system.

Main Results:

• A complex crystal structure of stoichiometric Mg₅(en)₆(BH₄)₁₀ was successfully determined.
• The amorphous Mg(BH₄)₂ was identified as a key component influencing system reactivity.
• A previously unrecognized phase, Mg(en)₂(BH₄)₂, was characterized.

Conclusions:

• The study provides a detailed structural understanding of a complex phase in the Mg(BH₄)₂-en system.
• The findings contribute to the knowledge of magnesium-based hydrogen storage materials.
• Identification of the new phase and understanding amorphous component's role may guide future material design.