Enhanced reversible hydrogen desorption properties and mechanism of Mg(BH4)2-AlH3-LiH composite

The Mg(BH 4 ) 2 -AlH 3 - x LiH ( x  = 0, 0.5, 1) novel ternary composites have been synthesized through mechanical ball milling, their favorable dehydrogenation properties and mechanism have been experimentally investigated. It can be found that during ball milling, a slight amount of Mg(BH 4 ) 2 would react with LiH and transform into LiBH 4 , while most Mg(BH 4 ) 2 remained stable after ball milling. Two major dehydrogenation steps can be detected in the Mg(BH 4 ) 2 -AlH 3 - x LiH composite, which belong to the decomposition of AlH 3 and Mg(BH 4 ) 2 , respectively. Remarkably, the onset hydrogen desorption temperature of Mg(BH 4 ) 2 -AlH 3 - x LiH composite can be reduced to 125.9 °C, with a total hydrogen desorption capacity of 10.3 wt%. It is worth emphasizing that the reversible dehydrogenation capacity is obviously improved to 3.8 wt%, compared to the Mg(BH 4 ) 2 -AlH 3 composite. This reversible capacity can be held for 3 cycles without obvious degeneration. Microstructural analysis on de/rehydrogenated composite has identified the regeneration of [BH 4 ] - in Mg(BH 4 ) 2 -AlH 3 -0.5LiH composite and revealed the role of LiH in the cycling hydrogen desorption and absorption processes. The formation of LiBH 4 and MgH 2 resulted from the rehydrogenation between MgAlB 4 and LiH could be helpful for the stability of reversible hydrogen storage performance.