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

摘要

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 degrees 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 H-2 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.