Agile Thermal Management STT-RX, Modified Magnesium Hydride and Calcium Borohydride for High-Capacity Thermal Energy Storage (PREPRINT)

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 deg C for Ca(BH4)2, 400 deg 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 13:1 can 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, EA of 81 and 79 kJ/mol, respectively, corresponding to 50% decrease in EA and 100% deg C decrease in the decomposition temperature (Tdec). On the other hand, the decomposition reaction of Ca(BH4)2 does not seem to be catalyzed by the Ni-based catalysts tested. Preprint article to be submitted to Proceedings of the ASME/JSME 2011 8th Thermal Engineering Joint Conference, March 13-17, 2011, Honolulu, HI, paper AJTEC2011-44133.