Combined X-ray and Raman studies on the effect of cobalt additives on the decomposition of magnesium borohydride

Olena Zavorotynska, Stefano Deledda, Jenny G. Vitillo, Ivan Saldan, Matylda N. Guzik, Marcello Baricco, John C. Walmsley, Jiri Muller, Bjørn C. Hauback

Research output: Contribution to journalArticlepeer-review

17 Scopus citations

Abstract

Magnesium borohydride (Mg(BH4)2) is one of the most promising hydrogen storage materials. Its kinetics of hydrogen desorption, reversibility, and complex reaction pathways during decomposition and rehydrogenation, however, present a challenge, which has been often addressed by using transition metal compounds as additives. In this work the decomposition of Mg(BH4)2 ball-milled with CoCl2 and CoF2 additives, was studied by means of a combination of several in-situ techniques. Synchrotron X-ray diffraction and Raman spectroscopy were used to follow the phase transitions and decomposition of Mg(BH4)2. By comparison with pure milled Mg(BH4)2, the temperature for the γ → ε phase transition in the samples with CoF2 or CoCl2 additives was reduced by 10-45 °C. In-situ Raman measurements showed the formation of a decomposition phase with vibrations at 2513, 2411 and 766 cm-1 in the sample with CoF2. Simultaneous X-ray absorption measurements at the Co K-edge revealed that the additives chemically transformed to other species. CoF2 slowly reacted upon heating till ~290 °C, whereas CoCl2 transformed drastically at ~180 °C.

Original languageEnglish (US)
Pages (from-to)9173-9190
Number of pages18
JournalEnergies
Volume8
Issue number9
DOIs
StatePublished - 2015

Bibliographical note

Publisher Copyright:
© 2015 by the authors.

Keywords

  • Cobalt additives
  • Hydrogen storage
  • In-situ
  • Magnesium borohydride (Mg(BH4)2)
  • Synchrotron X-ray diffraction
  • X-ray absorption spectroscopy (XAS)

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