Development of Magnesium Boride Etherates as Hydrogen Storage Materials

Recipient University of Hawaii at Manoa/UH Manoa (PI: Godwin Severa)

Abstract Magnesium borohydride, Mg(BH4)2, is one of the few materials that has a demonstrated gravimetric hydrogen storage capacity greater than 11 wt% and thus a demonstrated potential to be utilized in a hydrogen storage system meeting US DOE hydrogen storage targets. However, due to very slow kinetics, cycling between Mg(BH4)2 and MgB2 has been accomplished only at high temperature (~400 ˚C) and under high charging pressure (900 bar). Previous work has shown, rapid kinetics at moderate temperatures for the reversible dehydrogenation of Mg(BH4)2(ether)x to Mg(B3H8)2(ether)x. These type of materials have much lower hydrogen cycling capacities as a consequence of the weight contribution of the coordinated ethers. However, they do show the plausibility of continual improvement in hydrogen cycling kinetics in the Mg(BH4)2 system. The development of modified MgB2 by either extending the dehydrogenation of magnesium borane etherates to MgB2 or by direct combination of MgB2 with sub-stoichiometric amounts of additives (e.g. ethers, reactive liquids, metals or hydrides) would result in the H2 wt % of the system potentially meeting DOE targets. If successful, the solid-state modified MgB2 would be safer and cheaper than the high pressure compressed H2 (700 bar) or liquid H2 alternative onboard storage systems on the market.