Structural analysis of calcium reactive hydride composite for solid state hydrogen storage

Fahim Karimi, P. Klaus Pranzas, Armin Hoell, Ulla Vainio, Edmund Welter, Vikram S. Raghuwanshi, Claudio Pistidda, Martin Dornheim, Thomas Klassen, Andreas Schreyer

Research output: Contribution to journalArticleResearchpeer-review

Abstract

Owing to a theoretical hydrogen storage capacity of 10.5 wt% H2, Ca(BH4)2+MgH2, the so-called calcium reactive hydride composite (Ca-RHC), has a great potential as a hydrogen storage material. However, its dehydrogenation temperature (∼623 K) is too high for any mobile applications. By addition of 10 mol% of NbF5 into Ca(BH4)2+MgH2, a decrease of the dehydrogenation onset temperature by ∼120 K is observed. In order to understand the reasons behind this desorption temperature decrement two sets of samples [Ca(BH4)2+MgH2 and Ca(BH4)2+MgH2+0.1NbF5] in different hydrogenation states, were prepared. The structural investigation of the above mentioned sets of samples by means of volumetric measurements, anomalous small-angle X-ray scattering (ASAXS) and X-ray absorption spectroscopy (XAS) is reported here. The XAS results show that after the milling procedure NbB2 is formed and remains stable upon further de/rehydrogenation cycling. The results of Nb ASAXS point to nanometric spherical NbB2 particles distributed in the hydride matrix, with a mean diameter of ∼10 nm. Results from Ca ASAXS indicate Ca-containing nanostructures in the Ca-RHC+0.1NbF5 samples to be ∼50% finer compared to those without additive. Thus, a higher reaction surface area and shorter diffusion paths for the constituents are concluded to be important contributions to the catalytic effect of an NbF5 additive on the hydrogen sorption kinetics of the Ca(BH4)2+MgH2 composite system.

Original languageEnglish
Pages (from-to)67-75
Number of pages9
JournalJournal of Applied Crystallography
Volume47
Issue number1
DOIs
Publication statusPublished - Feb 2014
Externally publishedYes

Keywords

  • anomalous small-angle X-ray scattering
  • hydrogen storage
  • reactive hydride composite
  • structure analysis
  • X-ray absorption spectroscopy

Cite this

Karimi, Fahim ; Pranzas, P. Klaus ; Hoell, Armin ; Vainio, Ulla ; Welter, Edmund ; Raghuwanshi, Vikram S. ; Pistidda, Claudio ; Dornheim, Martin ; Klassen, Thomas ; Schreyer, Andreas. / Structural analysis of calcium reactive hydride composite for solid state hydrogen storage. In: Journal of Applied Crystallography. 2014 ; Vol. 47, No. 1. pp. 67-75.
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title = "Structural analysis of calcium reactive hydride composite for solid state hydrogen storage",
abstract = "Owing to a theoretical hydrogen storage capacity of 10.5 wt{\%} H2, Ca(BH4)2+MgH2, the so-called calcium reactive hydride composite (Ca-RHC), has a great potential as a hydrogen storage material. However, its dehydrogenation temperature (∼623 K) is too high for any mobile applications. By addition of 10 mol{\%} of NbF5 into Ca(BH4)2+MgH2, a decrease of the dehydrogenation onset temperature by ∼120 K is observed. In order to understand the reasons behind this desorption temperature decrement two sets of samples [Ca(BH4)2+MgH2 and Ca(BH4)2+MgH2+0.1NbF5] in different hydrogenation states, were prepared. The structural investigation of the above mentioned sets of samples by means of volumetric measurements, anomalous small-angle X-ray scattering (ASAXS) and X-ray absorption spectroscopy (XAS) is reported here. The XAS results show that after the milling procedure NbB2 is formed and remains stable upon further de/rehydrogenation cycling. The results of Nb ASAXS point to nanometric spherical NbB2 particles distributed in the hydride matrix, with a mean diameter of ∼10 nm. Results from Ca ASAXS indicate Ca-containing nanostructures in the Ca-RHC+0.1NbF5 samples to be ∼50{\%} finer compared to those without additive. Thus, a higher reaction surface area and shorter diffusion paths for the constituents are concluded to be important contributions to the catalytic effect of an NbF5 additive on the hydrogen sorption kinetics of the Ca(BH4)2+MgH2 composite system.",
keywords = "anomalous small-angle X-ray scattering, hydrogen storage, reactive hydride composite, structure analysis, X-ray absorption spectroscopy",
author = "Fahim Karimi and Pranzas, {P. Klaus} and Armin Hoell and Ulla Vainio and Edmund Welter and Raghuwanshi, {Vikram S.} and Claudio Pistidda and Martin Dornheim and Thomas Klassen and Andreas Schreyer",
year = "2014",
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Karimi, F, Pranzas, PK, Hoell, A, Vainio, U, Welter, E, Raghuwanshi, VS, Pistidda, C, Dornheim, M, Klassen, T & Schreyer, A 2014, 'Structural analysis of calcium reactive hydride composite for solid state hydrogen storage' Journal of Applied Crystallography, vol. 47, no. 1, pp. 67-75. https://doi.org/10.1107/S1600576713031567

Structural analysis of calcium reactive hydride composite for solid state hydrogen storage. / Karimi, Fahim; Pranzas, P. Klaus; Hoell, Armin; Vainio, Ulla; Welter, Edmund; Raghuwanshi, Vikram S.; Pistidda, Claudio; Dornheim, Martin; Klassen, Thomas; Schreyer, Andreas.

In: Journal of Applied Crystallography, Vol. 47, No. 1, 02.2014, p. 67-75.

Research output: Contribution to journalArticleResearchpeer-review

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T1 - Structural analysis of calcium reactive hydride composite for solid state hydrogen storage

AU - Karimi, Fahim

AU - Pranzas, P. Klaus

AU - Hoell, Armin

AU - Vainio, Ulla

AU - Welter, Edmund

AU - Raghuwanshi, Vikram S.

AU - Pistidda, Claudio

AU - Dornheim, Martin

AU - Klassen, Thomas

AU - Schreyer, Andreas

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Y1 - 2014/2

N2 - Owing to a theoretical hydrogen storage capacity of 10.5 wt% H2, Ca(BH4)2+MgH2, the so-called calcium reactive hydride composite (Ca-RHC), has a great potential as a hydrogen storage material. However, its dehydrogenation temperature (∼623 K) is too high for any mobile applications. By addition of 10 mol% of NbF5 into Ca(BH4)2+MgH2, a decrease of the dehydrogenation onset temperature by ∼120 K is observed. In order to understand the reasons behind this desorption temperature decrement two sets of samples [Ca(BH4)2+MgH2 and Ca(BH4)2+MgH2+0.1NbF5] in different hydrogenation states, were prepared. The structural investigation of the above mentioned sets of samples by means of volumetric measurements, anomalous small-angle X-ray scattering (ASAXS) and X-ray absorption spectroscopy (XAS) is reported here. The XAS results show that after the milling procedure NbB2 is formed and remains stable upon further de/rehydrogenation cycling. The results of Nb ASAXS point to nanometric spherical NbB2 particles distributed in the hydride matrix, with a mean diameter of ∼10 nm. Results from Ca ASAXS indicate Ca-containing nanostructures in the Ca-RHC+0.1NbF5 samples to be ∼50% finer compared to those without additive. Thus, a higher reaction surface area and shorter diffusion paths for the constituents are concluded to be important contributions to the catalytic effect of an NbF5 additive on the hydrogen sorption kinetics of the Ca(BH4)2+MgH2 composite system.

AB - Owing to a theoretical hydrogen storage capacity of 10.5 wt% H2, Ca(BH4)2+MgH2, the so-called calcium reactive hydride composite (Ca-RHC), has a great potential as a hydrogen storage material. However, its dehydrogenation temperature (∼623 K) is too high for any mobile applications. By addition of 10 mol% of NbF5 into Ca(BH4)2+MgH2, a decrease of the dehydrogenation onset temperature by ∼120 K is observed. In order to understand the reasons behind this desorption temperature decrement two sets of samples [Ca(BH4)2+MgH2 and Ca(BH4)2+MgH2+0.1NbF5] in different hydrogenation states, were prepared. The structural investigation of the above mentioned sets of samples by means of volumetric measurements, anomalous small-angle X-ray scattering (ASAXS) and X-ray absorption spectroscopy (XAS) is reported here. The XAS results show that after the milling procedure NbB2 is formed and remains stable upon further de/rehydrogenation cycling. The results of Nb ASAXS point to nanometric spherical NbB2 particles distributed in the hydride matrix, with a mean diameter of ∼10 nm. Results from Ca ASAXS indicate Ca-containing nanostructures in the Ca-RHC+0.1NbF5 samples to be ∼50% finer compared to those without additive. Thus, a higher reaction surface area and shorter diffusion paths for the constituents are concluded to be important contributions to the catalytic effect of an NbF5 additive on the hydrogen sorption kinetics of the Ca(BH4)2+MgH2 composite system.

KW - anomalous small-angle X-ray scattering

KW - hydrogen storage

KW - reactive hydride composite

KW - structure analysis

KW - X-ray absorption spectroscopy

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