Dehydriding reactions of mixed complex hydrides

Dehydriding reactions of the mixtures LiBH4 + 2LiNH(2) and LiAlH4 + 2LiNH(2) were investigated. The new pathways confirmed for the dehydriding reactions were LiBH4 + 2LiNH(2) -> Li3BN2 + 4H(2) and LiAlH4 + 2LiNH(2) -> Li3AlN2 + 4H(2) in which 11.9 and 9.6 mass% of hydrogen can be desorbed theoretically. The quantities of desorbed hydrogen were deduced experimentally to be approximately 7.9-9.5 and 4.1 mass% for the mixtures of LiBH4 + 2LiNH(2) and LiAlH4 + 2LiNH(2), respectively. The dehydriding temperature of LiBH4 reduces by 150 K by mixing 2 M LiNH2. An exothermic peak was observed at a slightly higher temperature of the dehydriding reaction; however, this peak might be due to the solidification of the product after the dehydriding reaction and not due to the exothermic dehydriding reaction. Although the first-step dehydriding reaction of LiAlH4 is exothermic, the mixture of LiAlH4 + 2LiNH(2) exhibits an endothermic dehydriding reaction. These results suggest that the stability of the dehydriding reactions of complex hydrides can be controlled by introducing new pathways that are produced by mixing. Two criteria for selecting complex hydrides that are mixed together for producing new pathways were proposed from the viewpoints of both the melting/dehydriding temperatures and the products of the dehydriding reactions. (c) 2005 Elsevier B.V. All rights reserved.