Modified Magnesium Hydride and Calcium Borohydride for High-Capacity Thermal Energy Storage

MgH₂ and Ca(BH₄)₂ are potential thermal energy storage (TES) materials that possess extraordinarily high inherent thermal energy densities of up to 2 MJ/kg. However, the high desorption temperatures at atmospheric pressure [>300°C for Ca(BH₄)₂, >400°C for MgH₂] coupled with slow kinetics represent significant challenges for their use in TES. In order to address these challenges, the present work focuses on the development of new modification approaches based on nanostructuring via high-energy vibratory ball milling and catalytic enhancement using pure Ni and Ni alloys. Our work reveals that high-energy vibrating-mill technique with ball-to-powder weight ratio as low as 13:1can produce MgH₂ powders with nanocrystallites after 2h of milling. MgH₂ milled with Ni (5 wt%) and Ni₅Zr₂ (5 wt%) catalysts for 2 h showed apparent activation energies, E_A of 81 and 79 kJ/mol, respectively, corresponding to ∼50% decrease in E_A and ∼100°C decrease in the decomposition temperature (T_dec). On the other hand, the decomposition reaction of Ca(BH₄)₂ does not seem to be catalyzed by the Ni-based catalysts tested.