Microstructural Study of MgB 2 in the LiBH 4 -MgH 2 Composite by Using TEM.

The hampered kinetics of reactive hydride composites (RHCs) in hydrogen storage and release, which limits their use for extensive applications in hydrogen storage S1and energy conversion, can be improved using additives. However, the mechanism of the kinetic restriction and the additive effect on promoting the kinetics have remained unclear. These uncertainties are addressed by utilizing versatile transmission electron microscopy (TEM) on the LiBH 4 -MgH 2 composite under the influence of the 3TiCl 3 ·AlCl 3 additives. The formation of the MgB 2 phase, as the rate-limiting step, is emphatically studied. According to the observations, the heterogeneous nucleation of MgB 2 relies on different nucleation centers (Mg or TiB 2 and AlB 2 ). The varied nucleation and growth of MgB 2 are related to the in-plane strain energy density at the interface, resulting from the atomic misfit between MgB 2 and its nucleation centers. This leads to distinct MgB 2 morphologies (bars and platelets) and different performances in the dehydrogenation kinetics of LiBH 4 -MgH 2 . It was found that the formation of numerous MgB 2 platelets is regarded as the origin of the kinetic improvement. Therefore, to promote dehydrogenation kinetics in comparable RHC systems for hydrogen storage, it is suggested to select additives delivering a small atomic misfit.