Synthesis of sodium-magnesium amidoborane by sodium amide: An investigation of functional properties for hydrogen/ammonia storage

Sodium magnesium amidoborane, which can be regarded as one of the ammonia borane (NH3BH3) based materials, has superior hydrogen storage properties. In this study, we investigated the hydrogen release process and ammonia absorption phase of sodium-magnesium amidoborane. The sodium-magnesium amidoborane was prepared by ball-milling of NH3BH3, MgH2 and NaNH2 with two kinds of molar ratios (NH3BH3: MgH2: NaNH2 = 4:1:2 and 3:1:1). As a result, a single hydrogen release step from Na-2 Mg(NH2BH3)(4) was clearly observed in the molar ratio (4:1:2), and multiple hydrogen release steps were observed in the molar ratio (3:1:1). The synthesized Na2Mg(NH2BH3)(4) released hydrogen of 7.5 wt% in an endothermic reaction. Also, we found an ammonia absorption phase of Na2Mg(NH2BH3)(4) by using sodium amide as a starting material. The Na2Mg(NH2BH3)(4) absorbs 5 mol of ammonia in the form of solid as the pressure of ammonia gas reaches 100 kPa. After that, a total of 15 mol of ammonia is absorbed up to 600 kPa in the liquid phase. (C) 2019 Elsevier B.V. All rights reserved.