Reactivity of magnesium borohydride - Metal hydride composites, γ-Mg(BH4)2 -MHx, M = Li, Na, Mg, Ca

JOURNAL OF ALLOYS AND COMPOUNDS

卷:770

Article

Grube, Elisabeth¹  Jensen, Steffen R. H.¹  Nielsen, Ulla Gro²  Jensen, Torben R.¹ 

[1] Aarhus Univ, Interdisciplinary Nanosci Ctr, Dept Chem, Langelandsgade 140, DK-8000 Aarhus C, Denmark

[2] Univ Southern Denmark, Dept Phys Chem & Pharm, Campusvej 55, Odense M, Denmark

关键词: Hydrogen storage;    Magnesium borohydride;    Reactive hydride composites;    In-situ powder X-ray diffraction;    Thermal decomposition;   

DOI  :  10.1016/j.jallcom.2018.08.177

来源: Elsevier

【 摘 要 】

The reactivity and thermal decomposition of gamma-Mg(BH4)(2)-MHx, M = Li, Na, Mg, and Ca composites has been examined with the objective of studying the hydrogen storage capability of the composites. The samples were prepared by manual grinding gamma-Mg(BH4)(2) with a metal hydride to obtain homogenous mixtures. In-situ synchrotron radiation powder X-ray diffraction (SR-PXD) and simultaneous thermogravimetric analysis, differential scanning calorimetry, and mass spectrometry was performed to analyse the decomposition mechanism, whereas solid-state B-11 nuclear magnetic resonance spectroscopy and SR-PXD was used to investigate the decomposition products. Interestingly, substitution reactions take place between magnesium borohydride and lithium, sodium and calcium hydride forming the more stable metal borohydrides, M(BH4)(x), M = Li, Na or Ca. The composite gamma-Mg(BH4)(2)-LiH has a hydrogen release at T similar to 380-420 degrees C, which indicates the formation of amorphous LiBH4 during decomposition. For the composites gamma-Mg(BH4)(2)-NaH, formation of crystalline NaBH4 is observed by SR-PXD from T = 150-450 degrees C, and hydrogen release ascribed to NaBH4 is observed in MS data at T= 460-480 degrees C. gamma-Mg(BH4)(2)-MgH2 composite decomposes as the individual constituents. beta-Ca(BH4)(2) is formed at T=175-375 degrees C in the composites of gamma-Mg(BH4)(2)-CaH2. Bragg diffraction from CaB6 at T> 370 degrees C is detected by SR-PXD for gamma-Mg(BH4)(2)-CaH2 (1:0.5) but not for samples richer in CaH2. Release of diborane was not observed for any of the magnesium borohydride metal hydride composites. (C) 2018 Elsevier B.V. All rights reserved.

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