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

• Published in: Journal of alloys and compounds 2019-09, Vol.801, p.645-650
• Main Authors: Lee, Chung-Hyun, Nakagawa, Yuki, Isobe, Shigehito, Hashimoto, Naoyuki, Sugino, Seiki, Miyaoka, Hiroki, Ichikawa, Takayuki
• Format: Article
• Language: English
• Subjects: Absorption; Ammonia; Ammonia absorption; Ammonia borane; Ball milling; Dual-metal amidoborane; Endothermic reactions; Hydrogen; Hydrogen storage; Liquid phases; Magnesium; Magnesium hydride; Sodium; Sodium amide
• ISSN: 0925-8388; 1873-4669
• DOI: 10.1016/j.jallcom.2019.06.175

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 Na2Mg(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. •New synthesis method of sodium-magnesium amidoborane was developed.•The samples were prepared by ball-milling of NH3BH3, MgH2 and NaNH2.•The Na2Mg(NH2BH3)4 would absorb ammonia gas.•The Na2Mg(NH2BH3)4·5NH3 as a new solid phase was founded.