Dehydriding reactions of mixed complex hydrides

摘要

Dehydriding reactions of the mixtures LiBH_4 + 2LiNH_2 and LiAlH_4 + 2LiNH_2 were investigated. The new pathways confirmed for the dehydriding reactions were LiBH_4 + 2LiNH_2 → Li_3BN_2 + 4H_2 and LiAlH_4 + 2LiNH_2 → Li_3AlN_2 + 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 LiBH_4 + 2LiNH_2 and LiAlH_4 + 2LiNH_2, respectively. The dehydriding temperature of LiBH_4 reduces by 150 K by mixing 2 M LiNH_2. 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 LiAlH_4 is exothermic, the mixture of LiAlH_4 + 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.