In situ formation of Al3Ti, MgF2 and Al and their superior synergetic effects on reversible hydrogen storage of MgH2

A mixture with the composition of MgH2-10 wt% (Mg(AlH4)(2)-0.5TiF(4)) (denoted as Mg-Al-Ti-F-doped MgH2) is designed and prepared by high-energy ball milling under the hydrogen pressure of 60 bar for 12 h. During the milling, a chemical reaction occurs between Mg(AlH4)(2) and TiF4 to generate in situ Al3Ti, MgF2 and Al, which work together to induce a reduction of greater than 100 degrees C in the dehydrogenation temperature. At 275 degrees C, the Mg-Al-Ti-F-doped MgH2 rapidly releases 6.3 wt% H-2 within 10 min in an isothermal experiment, while no appreciable hydrogen release is observed for the pristine MgH2 under identical conditions. The dehydrogenated Mg-Al-Ti-F-doped sample starts to take up hydrogen at room temperature with the 6.3 wt% amount of H-2 at 150 degrees C, which is greatly superior to that of the pristine sample. A comprehensive kinetic analysis reveals that the superior functionality of the in situ formed Al3Ti, MgF2 and Al are mainly attributed to the following two factors: acting as nucleation centers and reducing the activation energy of growth.