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

Elisabeth Grube, Steffen R.H. Jensen, Ulla Gro Nielsen, Torben R. Jensen*

*Kontaktforfatter for dette arbejde

Publikation: Bidrag til tidsskriftTidsskriftartikelForskningpeer review

Resumé

The reactivity and thermal decomposition of γ-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 γ-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 11B 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 γ-Mg(BH4)2-LiH has a hydrogen release at T ∼380–420 °C, which indicates the formation of amorphous LiBH4 during decomposition. For the composites γ-Mg(BH4)2-NaH, formation of crystalline NaBH4 is observed by SR-PXD from T = 150–450 °C, and hydrogen release ascribed to NaBH4 is observed in MS data at T = 460–480 °C. γ-Mg(BH4)2-MgH2 composite decomposes as the individual constituents. β-Ca(BH4)2 is formed at T = 175–375 °C in the composites of γ-Mg(BH4)2-CaH2. Bragg diffraction from CaB6 at T > 370 °C is detected by SR-PXD for γ-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.

OriginalsprogEngelsk
TidsskriftJournal of Alloys and Compounds
Vol/bind770
Udgave nummerJanuary
Sider (fra-til)1155-1163
ISSN0925-8388
DOI
StatusUdgivet - 5. jan. 2019

Fingeraftryk

Borohydrides
Hydrides
Magnesium
Metals
Synchrotron radiation
Composite materials
X ray powder diffraction
Decomposition
Hydrogen
Hydrogen storage
Nuclear magnetic resonance spectroscopy
Mass spectrometry
Thermogravimetric analysis
Differential scanning calorimetry
Calcium
Lithium
Pyrolysis
Substitution reactions
Diffraction
Sodium

Citer dette

Grube, Elisabeth ; Jensen, Steffen R.H. ; Nielsen, Ulla Gro ; Jensen, Torben R. / Reactivity of magnesium borohydride – Metal hydride composites, γ-Mg(BH4)2-MHx, M = Li, Na, Mg, Ca. I: Journal of Alloys and Compounds. 2019 ; Bind 770, Nr. January. s. 1155-1163.
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abstract = "The reactivity and thermal decomposition of γ-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 γ-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 11B 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 γ-Mg(BH4)2-LiH has a hydrogen release at T ∼380–420 °C, which indicates the formation of amorphous LiBH4 during decomposition. For the composites γ-Mg(BH4)2-NaH, formation of crystalline NaBH4 is observed by SR-PXD from T = 150–450 °C, and hydrogen release ascribed to NaBH4 is observed in MS data at T = 460–480 °C. γ-Mg(BH4)2-MgH2 composite decomposes as the individual constituents. β-Ca(BH4)2 is formed at T = 175–375 °C in the composites of γ-Mg(BH4)2-CaH2. Bragg diffraction from CaB6 at T > 370 °C is detected by SR-PXD for γ-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.",
keywords = "Hydrogen storage, In-situ powder X-ray diffraction, Magnesium borohydride, Reactive hydride composites, Thermal decomposition",
author = "Elisabeth Grube and Jensen, {Steffen R.H.} and Nielsen, {Ulla Gro} and Jensen, {Torben R.}",
year = "2019",
month = "1",
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Reactivity of magnesium borohydride – Metal hydride composites, γ-Mg(BH4)2-MHx, M = Li, Na, Mg, Ca. / Grube, Elisabeth; Jensen, Steffen R.H.; Nielsen, Ulla Gro; Jensen, Torben R.

I: Journal of Alloys and Compounds, Bind 770, Nr. January, 05.01.2019, s. 1155-1163.

Publikation: Bidrag til tidsskriftTidsskriftartikelForskningpeer review

TY - JOUR

T1 - Reactivity of magnesium borohydride – Metal hydride composites, γ-Mg(BH4)2-MHx, M = Li, Na, Mg, Ca

AU - Grube, Elisabeth

AU - Jensen, Steffen R.H.

AU - Nielsen, Ulla Gro

AU - Jensen, Torben R.

PY - 2019/1/5

Y1 - 2019/1/5

N2 - The reactivity and thermal decomposition of γ-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 γ-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 11B 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 γ-Mg(BH4)2-LiH has a hydrogen release at T ∼380–420 °C, which indicates the formation of amorphous LiBH4 during decomposition. For the composites γ-Mg(BH4)2-NaH, formation of crystalline NaBH4 is observed by SR-PXD from T = 150–450 °C, and hydrogen release ascribed to NaBH4 is observed in MS data at T = 460–480 °C. γ-Mg(BH4)2-MgH2 composite decomposes as the individual constituents. β-Ca(BH4)2 is formed at T = 175–375 °C in the composites of γ-Mg(BH4)2-CaH2. Bragg diffraction from CaB6 at T > 370 °C is detected by SR-PXD for γ-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.

AB - The reactivity and thermal decomposition of γ-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 γ-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 11B 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 γ-Mg(BH4)2-LiH has a hydrogen release at T ∼380–420 °C, which indicates the formation of amorphous LiBH4 during decomposition. For the composites γ-Mg(BH4)2-NaH, formation of crystalline NaBH4 is observed by SR-PXD from T = 150–450 °C, and hydrogen release ascribed to NaBH4 is observed in MS data at T = 460–480 °C. γ-Mg(BH4)2-MgH2 composite decomposes as the individual constituents. β-Ca(BH4)2 is formed at T = 175–375 °C in the composites of γ-Mg(BH4)2-CaH2. Bragg diffraction from CaB6 at T > 370 °C is detected by SR-PXD for γ-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.

KW - Hydrogen storage

KW - In-situ powder X-ray diffraction

KW - Magnesium borohydride

KW - Reactive hydride composites

KW - Thermal decomposition

U2 - 10.1016/j.jallcom.2018.08.177

DO - 10.1016/j.jallcom.2018.08.177

M3 - Journal article

VL - 770

SP - 1155

EP - 1163

JO - Journal of Alloys and Compounds

JF - Journal of Alloys and Compounds

SN - 0925-8388

IS - January

ER -