X-ray and Synchrotron FTIR Studies of Partially Decomposed Magnesium Borohydride

Rashmi Dahal, Jenny G. Vitillo, Anna C. Åsland, Christoph Frommen, Stefano Deledda and Olena Zavorotynska ()
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Rashmi Dahal: Department of Mathematics and Physics, University of Stavanger, P.O. Box 8600, NO-4036 Stavanger, Norway
Jenny G. Vitillo: Department of Science and High Technology and INSTM, Università degli Studi dell’Insubria, Via Valleggio 9, I-22100 Como, Italy
Anna C. Åsland: Department of Mathematics and Physics, University of Stavanger, P.O. Box 8600, NO-4036 Stavanger, Norway
Christoph Frommen: Department for Hydrogen Technology, Institute for Energy Technology, P.O. Box 40, NO-2027 Kjeller, Norway
Stefano Deledda: Department for Hydrogen Technology, Institute for Energy Technology, P.O. Box 40, NO-2027 Kjeller, Norway
Olena Zavorotynska: Department of Mathematics and Physics, University of Stavanger, P.O. Box 8600, NO-4036 Stavanger, Norway

Energies, 2022, vol. 15, issue 21, 1-16

Abstract: Magnesium borohydride (Mg(BH 4 ) 2 ) is an attractive compound for solid-state hydrogen storage due to its lucratively high hydrogen densities and theoretically low operational temperature. Hydrogen release from Mg(BH 4 ) 2 occurs through several steps. The reaction intermediates formed at these steps have been extensively studied for a decade. In this work, we apply spectroscopic methods that have rarely been used in such studies to provide alternative insights into the nature of the reaction intermediates. The commercially obtained sample was decomposed in argon flow during thermogravimetric analysis combined with differential scanning calorimetry (TGA-DSC) to differentiate between the H 2 -desorption reaction steps. The reaction products were analyzed by powder X-ray diffraction (PXRD), near edge soft X-ray absorption spectroscopy at boron K-edge (NEXAFS), and synchrotron infrared (IR) spectroscopy in mid- and far-IR ranges (SR-FTIR). Up to 12 wt% of H 2 desorption was observed in the gravimetric measurements. PXRD showed no crystalline decomposition products when heated at 260–280 °C, the formation of MgH 2 above 300 °C, and Mg above 320 °C. The qualitative analysis of the NEXAFS data showed the presence of boron in lower oxidation states than in (BH 4 ) − . The NEXAFS data also indicated the presence of amorphous boron at and above 340 °C. This study provides additional insights into the decomposition reaction of Mg(BH 4 ) 2 .

Keywords: hydrogen storage; magnesium borohydride; soft X-ray absorption spectroscopy; boron K-edge; synchrotron FTIR (search for similar items in EconPapers)
JEL-codes: Q Q0 Q4 Q40 Q41 Q42 Q43 Q47 Q48 Q49 (search for similar items in EconPapers)
Date: 2022
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