Synthesis, structural characterization, and hydrogen desorption properties of Na[Al(NH2BH3)4

Abstract

Na[Al(NH2BH3)4], a mixed-metal amidoborane, was synthesized by ball-milling (solid method) and the chemical reaction in THF (solution method). Solid method has a tendency to remain unreacted NaAlH4 and AB. In the solution method, the partial decomposition of Na[Al(NH2BH3)4] would proceed during mixing in THF. The local structural characterization of as-synthesized material was performed by MAS NMR and FT-IR. While Na[Al(NH2BH3)4] desorbed hydrogen in two steps as reported, the results of structural characterization suggested that the hydrogen desorption in the 2nd step would originate from the AlNBH phase. Effect of hydrogen pressure during ball-milling was also investigated for nNH3BH3NaAlH4 (n = 1, 4) composites. In the case of n = 4, Na[Al(NH2BH3)4] was formed under both Ar and H2 atmosphere. However, in the case of n = 1, Na[Al(NH2BH3)4] was only formed under H2 atmosphere, whereas most of H2 was desorbed during ball-milling under Ar atmosphere. Thus, the hydrogen pressure is necessary for the synthesis in the case of n = 1. Potential energy diagram of AB-NaAlH4 system was described.