Dehydriding and rehydriding processes of well-crystallized Mg(BH4)2 accompanying with formation of intermediate compounds

Dehydriding and rehydriding properties of well-crystallized Mg(BH4)(2) were systematically investigated by thermogravimetry (TG) and pressure-composition-temperature (PCT) measurements. The dehydriding reaction of Mg(BH4)(2) starts at approximately 500 K, and about 14.4 mass% of hydrogen is desorbed according to the following multi-step reaction: Mg(BH4)(2) --> some intermediate compounds --> MgH2 + 2B + 3H(2) --> Mg + 2B + 4H(2) The apparent enthalpy change in the dehydriding reaction from Mg(BH4)2 to MgH2 is estimated to be 57 +/- 5 kJ mol(-1) H-2 based on the result of the PCT measurement. It is proved that approximately 6.1 mass% of hydrogen can be reversibly stored for the sample of Mg(BH4)(2) after the dehydriding reaction, through the formation of a possible intermediate compound such as MgB12H12. (C) 2007 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.