Assessment of hydrogen storage property of CaMgBH system using NMR and thermal analysis techniques

Thermal dehydrogenation of Ca(BH4)2 and Ca(BH4)22MgH2 composite has been investigated, and the results were compared. The Ca((BH4)2 dehydrogenated in two steps between 325 °C and 500 °C as per the reactions Ca(BH4)2 = CaH2 + 2B + 3H2, and Ca(BH4)2 = 1/3CaB6 + 2/3CaH2 + 10/3H2. The partial dehydrogenation of CaH2 also takes place during the second step dehydrogenation according to the reaction CaH2 + 6B = CaB6 + H2. The completion of second step dehydrogenation requires a temperature of higher than 500 °C. The activation energies corresponding to these steps were found to be 149 ± 8 kJ/mol and 162 ± 10 kJ/mol, respectively. The Ca(BH4)22MgH2 composite dehydrogenates in a single step as per the reaction: Ca(BH4)2 + 3MgH2 = CaMg2 + 2B + 7H2 + Mg. The dehydrogenation of Ca(BH4)22MgH2 started at 340 °C and completed before 450 °C. The activation energy of Ca(BH4)22MgH2 dehydrogenation was found to be 180 ± 8 kJ/mol.