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The effect of ball-milling lithium hydride with lithium/rare-earth borohydrides: Synthesis, decomposition pathways and hydrogenation properties
Norwegian University of Science and Technology, Faculty of Natural Sciences and Technology, Department of Physics.
2013 (English)MasteroppgaveStudent thesis
Abstract [en]

Mixed-metal borohydride hydrogen storage composites (3LiBH4 + LiLn(BH4)3Cl) and reactive hydride composites (6LiBH4 + LnH(2+x) (Ln = La, Yb) have been synthesized from LiBH4 and the corresponding rare rare-earth chlorides LnCl3. The thermodynamic properties, decomposition pathways and hydrogenation properties of these composites have been studied. The synthesis was performed with high-energy ball-milling, the thermodynamic properties were studied with differential scanning calorimetry, thermogravimetry and mass spectroscopy, changes in the crystal structure during decomposition and re-hydrogenation were followed with synchrotron-radiation powder X-ray diffraction, and volumetry and IR spectroscopy were used to assess the hydrogenation properties. Synthesis of the desired composites was successful, although additional heating was required for the lanthanum composites, whereas the ytterbium composites released diborane during milling. The decomposition product of each mixed-metal borohydride is LnH(2+x) (Ln = La, Yb), which results in the decomposition of LiBH4 at approximately 300 and 366 C for Ln = La and Yb, respectively. The reactive hydride composites decomposed at 334 and 380 C for Ln = La and Yb, respectively, due to an alternative decomposition pathway involving LiBH_4 and LnH_{2+x}. Decomposition under back pressure has only the effect of increasing the decomposition temperature. Both reactive hydride composites show limited reversibility (around 2 wt% hydrogen could be re-absorbed). The ytterbium-based composites tend to release diborane during decomposition, making the lanthanum-based samples preferable as hydrogen storage materials, in particular the mixed-metal borohydride composite, which released most (5.5 wt%) hydrogen at the lowest (150 - 350 C) temperature.

Place, publisher, year, edition, pages
Institutt for fysikk , 2013. , 112 p.
URN: urn:nbn:no:ntnu:diva-21822Local ID: ntnudaim:9018OAI: diva2:644220
Available from: 2013-08-29 Created: 2013-08-29 Last updated: 2013-08-29Bibliographically approved

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