Destabilization of combined Ca(BH4)2 and Mg(AlH4)2 for improved hydrogen storage properties

A reactive hydride system of Ca(BH4)2+Mg(AlH4)2 in a molar ratio of 1: 1 with improved dehydrogenation thermodynamics and kinetics compared with either initial constituent is obtained. The system shows a three-step dehydrogenation process, the temperature of which is lower than that of the main dehydrogenation of pure Ca(BH4)2. There is 8.4 wt.% H2 released when the system is heated to 330 °C, significantly higher than the corresponding value of 2.6 wt.% H2 for pure Ca(BH4)2. The rate of the main dehydrogenation of the Ca(BH4)2+Mg(AlH4)2 system isothermally maintaining at 300 °C is 0.337 wt.% H2/min, which is 10 times faster than that of pure Ca(BH4)2. The reversibility of the combined system is also improved compared with either of the starting constituents. A mechanism study reveals that the initially decomposed MgH2 and Al from Mg(AlH4)2 prefer to react with each other, forming a Al(Mg) solid solution, which reacts further with Ca(BH4)2, reducing the reaction enthalpy and activation energy of the system. Thus, the system is destabilized, resulting in improved overall hydrogen storage properties.