Journal Article

PUBDB-2018-04225

http://join2-wiki.gsi.de/foswiki/pub/Main/Artwork/join2_logo100x88.png Reactivity of magnesium borohydride – Metal hydride composites, $\mathrm{γ-Mg(BH_{4})_{2}-MH_{x}, M = Li, Na, Mg, Ca}$

Grube, E. ; Jensen, S. R. H.Extern* ; Nielsen, U. G. ; Jensen, T. (Corresponding author)Extern*

2019
ScienceDirect Amsterdam [u.a.]

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Please use a persistent id in citations: doi:10.1016/j.jallcom.2018.08.177

Abstract: The reactivity and thermal decomposition of γ-Mg(BH$_4$)$_2$-MH$_x$, 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 $γ$-Mg(BH$_4$)$_2$ 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 $^{11}$B 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(BH$_4$)$_x$, M = Li, Na or Ca. The composite $γ$-Mg(BH$_4$)$_2$-LiH has a hydrogen release at T ∼380–420 °C, which indicates the formation of amorphous LiBH$_4$ during decomposition. For the composites γ-Mg(BH$_4$)$_2$-NaH, formation of crystalline NaBH$_4$ is observed by SR-PXD from T = 150–450 °C, and hydrogen release ascribed to NaBH$_4$ is observed in MS data at T = 460–480 °C. $γ$-Mg(BH$_4$-MgH$_2$ composite decomposes as the individual constituents. $β$-Ca(BH$_4$ is formed at T = 175–375 °C in the composites of $γ$-Mg(BH$_4$-CaH$_2$. Bragg diffraction from CaB$_6$ at T > 370 °C is detected by SR-PXD for $γ$-Mg(BH$_4$-CaH$_2$ (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.

Note: © Elsevier B.V.; Post referee fulltext in progress; Embargo 12 months from publication

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Contributing Institute(s):

1. DOOR-User (DOOR)

Research Program(s):

1. 6G3 - PETRA III (POF3-622) (POF3-622)

Experiment(s):

1. PETRA Beamline P02.1 (PETRA III)

Appears in the scientific report 2019

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Database coverage:
; Clarivate Analytics Master Journal List ; Current Contents - Physical, Chemical and Earth Sciences ; Ebsco Academic Search ; IF < 5 ; JCR ; No Authors Fulltext ; SCOPUS ; Science Citation Index ; Science Citation Index Expanded ; Web of Science Core Collection

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