Direct synthesis and hydrogen storage behaviors of nanocrystalline Na2LiAlH6

Nanocrystalline Na2LiAlH6 was directly synthesized by mechanical milling 2NaH/LiH/Al mixture with TiF3 catalyst under hydrogen pressure of 3.0 MPa. The synthesized Na2LiAlH6 exhibits a dehydriding capacity of 3.09 wt% in the first cycle, which is higher than that of Na3AlH6. Because of the complexity of mass transfer, the rehydrogenation process of the dehydrided Na2LiAlH6 is more intricate than that of the dehydrided sodium alanate, causing the formation of Na3AlH6 and the reduction of rehydriding capacity in the following cycles. As temperature increases from 70 to 120 °C, hydrogen absorption kinetics is extremely enhanced. The dehydrided material can reabsorb 80% of the reversible hydrogen capacity within 5 min when the temperature is above 100 °C with an initial hydrogen pressure of 4 MPa. The scanning electron microscopy and energy dispersive X-ray spectroscopy show that the as-synthesized Na2LiAlH6 along with the catalyst form a much homogeneous composite with a spherical particle size of 200 nm–2 μm.