Microstructural Study of MgB₂ in the LiBH₄-MgH₂ Composite by Using TEM

Area of Science:

• Materials Science
• Chemical Engineering
• Nanotechnology

Background:

• Reactive hydride composites (RHCs) show promise for hydrogen storage but suffer from slow hydrogen release kinetics.
• Additives can enhance RHC performance, yet the underlying mechanisms remain poorly understood.
• Understanding kinetic limitations is crucial for advancing hydrogen storage technologies.

Purpose of the Study:

• To elucidate the mechanism by which additives improve the kinetics of LiBH4-MgH2 composites for hydrogen storage.
• To investigate the role of the MgB2 phase formation in the rate-limiting steps of dehydrogenation.
• To correlate additive effects with MgB2 nucleation, growth, and morphology.

Main Methods:

• Utilized versatile transmission electron microscopy (TEM) to analyze the LiBH4-MgH2 composite with 3TiCl3·AlCl3 additives.
• Focused on the formation and characteristics of the MgB2 phase, identified as the rate-limiting step.
• Examined heterogeneous nucleation of MgB2 on different centers (Mg, TiB2, AlB2) and analyzed interfacial atomic misfit.

Main Results:

• Identified heterogeneous nucleation of MgB2 on Mg, TiB2, and AlB2 as dependent on interfacial strain energy and atomic misfit.
• Observed distinct MgB2 morphologies (bars and platelets) resulting from varied nucleation and growth.
• Demonstrated that the formation of numerous MgB2 platelets significantly enhances dehydrogenation kinetics.

Conclusions:

• The formation of MgB2 platelets, facilitated by additives with small atomic misfit, is the primary driver for improved dehydrogenation kinetics in LiBH4-MgH2.
• Selecting additives that minimize atomic misfit is a key strategy for optimizing RHC performance in hydrogen storage applications.
• This study provides critical mechanistic insights for designing advanced materials for efficient hydrogen energy conversion.