Dehydriding and re-hydriding properties of high-energy ball milled LiBH4 + MgH2 mixtures

Here we report the first investigation of the dehydriding and re-hydriding properties of 2LiBH4 + MgH2 mixtures in the solid state. Such a study is made possible by high-energy ball milling of 2LiBH4 + MgH2 mixtures at liquid nitrogen temperature with the addition of graphite. The 2LiBH4 + MgH2 mixture ball milled under this condition exhibits a 5-fold increase in the released hydrogen at 265 °C when compared with ineffectively ball milled counterparts. Furthermore, both LiBH4 and MgH2 contribute to hydrogen release in the solid state. The isothermal dehydriding/re-hydriding cycles at 265 °C reveal that re-hydriding is dominated by re-hydriding of Mg. These unusual phenomena are explained based on the formation of nanocrystalline and amorphous phases, the increased defect concentration in crystalline compounds, and possible catalytic effects of Mg, MgH2 and LiBH4 on their dehydriding and re-hydriding properties.