Understanding Li2B12H12Bjarne R. S. Hansena and Torben R. Jensena
a Interdisciplinary Nano Science Center, Center for Materials Crystallography and Department of Chemistry, University of Aarhus, Langelandsgade 140, DK-8000 Aarhus C, Denmark
Acknowledgements and referencesSincere acknowledgements are directed to the Interdisciplinary Nano Science Center (iNANO), Danscatt, MAX-Lab
Bor4Store (EU) and Center for Materials Crystallography (CMC)
IntroductionLight metal borohydrides, such as LiBH4, has a massive potential as hydrogen storage materials for storage applications in a wide scale. Most borohydrides require high temperatures for hydrogen release, but this can in many cases be lowered by utilizing eutectic composites, reactive hydride composites or by nanoconfinement. However, one major challenge still remains: Reversibility!
Sample preparation In situ SR-PXD
In practically all metalborohydrides M-B12H12 species are formed during decomposition which ultimately reduces the reversible hydrogen storage capacity[1]. In order to understand or avoid this more knowledge of these compounds is required. Therefore this current study investigates Li2B12H12.
β-Li2B12H12
Li2B12H12
γ-Li2B12H12-x
RT → 700 °C (5K/min), p(H2) = vac.λ = 0.9941 Å
Li2B12H12 - 4 H2O (Katchem) was heated to 240 °C under dynamic vacuum for 10 h to completelydry the sample and obtain an anhydrous, crystalline phase[2]
As the temperature increases the hump is shifting towards lower 2θ angle. The end product is ex-pected to be amorphous B. These observations agree well with thermal analysis and a previous study [4]. The fact that the sample becomes amor-phous during heating complicates characteri-zation of the decomposition reactions with PXRD. Therefore 11B MAS NMR studies are currently being conducted.
[1] B. R. S. Hansen et al., J. Phys. Chem. C 2013, 117, 7423−7432 [2] Pitt et al, J. Am. Chem. Soc. 2013, 135, 6930−6941 [3] Whang et al., J. Phys. Chem. C, 2008, 112 (9), 3164–3169 [4] Paskevicious et al, Phys. Chem. Chem. Phys. 2013, 15, 15825
Thermal analysisThe B12H12
2- ion [3]
DSC and TGA indicate three reaction steps are present, where the first step may be owing to water contamination. These steps will be fur-ther investigated using FT-IR and 11B MAS NMR.
An in situ SR-PXD experiment on Li2B12H12 was performed at Maxlab, I711. At T = 280 °C a phase transformation is obser-ved, and at T = 355 °C the sample turns amor-phous and a broad hump is observed.
[1]
