Several new destabilized borohydride systems were prepared by mechanochemical synthesis and characterized to determine their suitability for hydrogen storage. The mixtures included: Mg(BH 4 ) 2 /Ca(BH 4 ) 2 ; Mg(BH 4 ) 2 /CaH 2 /3NaH; and Mg(BH 4 ) 2 /CaH 2 ; systems as well as a double cation hydride MnLi(BH 4 ) 3 . Temperature programmed desorption, TPD, analyses showed that the desorption temperature of Mg(BH 4 ) 2 can be lowered by ball milling it with Ca(BH 4 ) 2 . The resulting mixture absorbed and released hydrogen with the pressure composition temperature, PCT, isotherm displaying a well-defined plateau region.
The other two systems; Mg(BH 4 ) 2 /CaH 2 and Mg(BH 4 ) 2 /CaH 2 /NaH, can also absorb and release hydrogen. The desorption enthalpies are all in the 84e88 kJ/mol range. These systems, however, are only partially reversible and lose some of their hydrogen-holding capacity after the initial desorption. A plausible explanation for this is that the mechanisms involve the formation of a (B 12 H 12 ) Γ2 -containing intermediate which has a high kinetic barrier to re-hydrogenation. TPD analysis also showed that the double cation material, MnLi(BH 4 ) 3 can release hydrogen in the range of 130 C but the process is irreversible. A Kissinger analysis of the first decomposition step in the differential thermal analysis, DTA, data showed that the activation energies for all the Mg(BH 4 ) 2 -based borohydrides range from 115 to 167 kJ/mol.