Mg-based complex hydrides are very attractive as potentially convenient hydrogen storage materials in application for fuel cells as well as materials for thermochemical thermal energy storage in heat storage systems. Among them, the hydride Mg_2CoH_5 has theoretical hydrogen capacity of about 4.5wt%, which is higher than 3.6wt% for the Mg_2NiH_4 compound. However, as opposed to the Mg_2Ni intermetallic which exists in the equilibrium Mg_2Ni system, the Mg_2Co compound only exists in its hydrided form. In this paper we present the results of our efforts to directly synthesize Mg_2CoH_5 in a nanocrystalline form by controlled reactive mechanical alloying (CRMA) in a magneto-mill Uni-Ball-Mill 5 under hydrogen atmosphere.
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