Enhancement of Hydrogen Desorption from Nanocomposite Prepared by Ball Milling MgH₂ with In Situ Aerosol Spraying LiBH₄

The prospect of LiBH₄ + MgH₂ mixtures has been limited by their sluggish kinetics despite their excellent hydrogen storage capacity theoretically. This study demonstrates that ball milling with aerosol spraying (BMAS) established in the previous study can not only tune the thermodynamics but also improve the kinetics for hydrogen release from a LiBH₄ + MgH₂ mixture. The improved thermodynamics has been evaluated from the viewpoint of the significantly heightened dissociation pressure. Nine different kinetics models have been used to analyze the solid-state dehydrogenation behavior of the BMAS powder with 50% LiBH₄ at 265 °C. The kinetics analysis reveals that the rate-limiting step of this BMAS powder is initially controlled by the nucleation/growth process but then is changed to moving-phase boundary control and finally to diffusion control as the number of dehydrogenation/rehydrogenation cycles increases. The change in the dehydrogenation kinetics with increasing cycles has been attributed to the presence of three parallel dehydrogenation reaction pathways and their different contributions to the overall H₂ release as the number of cycles increases. Thermal analysis indicates that the apparent activation energy of the BMAS powder has been reduced by 23.3 and 30.6 kJ/mol when compared to that of bulk LiBH₄ and ball-milled MgH₂ + C mixtures, respectively, revealing that BMAS is an effective method to promote hydrogen release from LiBH₄ + MgH₂ mixtures.