9-2-3 Synthesis and Characterization of NH₃BH₃-NaAlH₄ composite

Abstract

Ammonia borane (AB: NH₃BH₃) is a promising solid state hydrogen storage material because it contains >19 mass% of hydrogen. However, the thermal decomposition of AB kinetically requires high temperature, and considerable amount of harmful by-product gases emit from AB. Recently, the decomposition properties of AB have been improved by the composite with alanates (MAlH₄, M = Na, Li). It was reported that the new compound NaAl(NH₂BH₃)₄ formed during mechanical milling of 4AB-NaAlH₄. In this work, we have tried to synthesize NaAl(NH₂BH₃)₄ in THF solvent (Solution method) to obtain the single phase with high-purity. The powder X-ray diffraction pattern of the product obtained by the solution method was similar to that obtained by the solid method, suggesting that NaAl(NH₂BH₃)₄ can be synthesized by the solution method as well. However, the ²³Na-nuclear magnetic resonance (NMR) spectrum suggests that a different phases from NaAl(NH₂BH₃)₄ coexist. Thus, in order to obtain the single phase of NaAl(NH₂BH₃)₄, further optimization of reaction conditions would be necessary.