Hydrogen storage properties and reaction mechanism of the Mg-Li-Na-Al ternary hydride system

This research uses the ball milling technique to study the preparation of the MgH2-LiAlH4-NaAlH4 with a molar ratio of 4:1:1 ternary-hydride system. The hydrogen storage behavior and reaction mechanisms have been carefully explored. The result demonstrates a reduction in the onset decomposition temperature of the 4MgH2-LiAlH4-NaAlH4 ternary composite compared to the as-milled MgH2, LiAlH4, and NaAlH4 components. Four substantial dehydrogenation processes, corresponding to the decomposition of LiAlH4, NaAlH4, and MgH2 were detected in a system with a total hydrogen capacity of 8.4 wt%. The onset decomposition temperature of LiAlH4 in this system is around 110 °C, while NaAlH4-relevant decomposition began releasing hydrogen at 153 °C, approximately 52 °C lower than the as-milled NaAlH4. Meanwhile, the destabilized system modifies the reaction route of MgH2, where MgH2-relevant decomposition begins around 270 °C, 82 °C lower than the as-milled MgH2. The apparent activation energy, Ea, for the decomposition of MgH2 in the composite was lowered to 124 kJ/mol based on the Kissinger analysis. It is believed that the enhancement of the dehydrogenation properties was attributed to the formation of intermediate compounds, including Li-Mg, Mg-Al and Li-Al alloys, upon dehydrogenation, which improved the thermodynamics properties by altering the de/rehydrogenation pathway.