A Composite of Complex and Chemical Hydrides Yields the First Al-Based Amidoborane with Improved Hydrogen Storage Properties

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  • Iurii Dovgaliuk, Université Catholique de Louvain, Louvain-la-Neuve, Belgium
  • Lars H Jepsen
  • ,
  • Damir A Safin, Université Catholique de Louvain, Louvain-la-Neuve, Belgium
  • Zbigniew Łodziana, Polish Academy of Sciences, Poland
  • Vadim Dyadkin, Swiss-Norwegian Beam Lines, European Synchrotron Radiation Facility, 38043 Grenoble, France, France
  • Torben R Jensen
  • Michel Devillers, Université Catholique de Louvain, Louvain-la-Neuve, Belgium
  • Yaroslav Filinchuk, Université Catholique de Louvain, Louvain-la-Neuve, Belgium

The first Al-based amidoborane Na[Al(NH2 BH3 )4 ] was obtained through a mechanochemical treatment of the NaAlH4 -4 AB (AB=NH3 BH3 ) composite releasing 4.5 wt % of pure hydrogen. The same amidoborane was also produced upon heating the composite at 70 °C. The crystal structure of Na[Al(NH2 BH3 )4 ], elucidated from synchrotron X-ray powder diffraction and confirmed by DFT calculations, contains the previously unknown tetrahedral ion [Al(NH2 BH3 )4 ](-) , with every NH2 BH3 (-) ligand coordinated to aluminum through nitrogen atoms. Combination of complex and chemical hydrides in the same compound was possible due to both the lower stability of the AlH bonds compared to the BH ones in borohydride, and due to the strong Lewis acidity of Al(3+) . According to the thermogravimetric analysis-differential scanning calorimetry-mass spectrometry (TGA-DSC-MS) studies, Na[Al(NH2 BH3 )4 ] releases in two steps 9 wt % of pure hydrogen. As a result of this decomposition, which was also supported by volumetric studies, the formation of NaBH4 and amorphous product(s) of the surmised composition AlN4 B3 H(0-3.6) were observed. Furthermore, volumetric experiments have also shown that the final residue can reversibly absorb about 27 % of the released hydrogen at 250 °C and p(H2 )=150 bar. Hydrogen re-absorption does not regenerate neither Na[Al(NH2 BH3 )4 ] nor starting materials, NaAlH4 and AB, but rather occurs within amorphous product(s). Detailed studies of the latter one(s) can open an avenue for a new family of reversible hydrogen storage materials. Finally, the NaAlH4 -4 AB composite might become a starting point towards a new series of aluminum-based tetraamidoboranes with improved hydrogen storage properties such as hydrogen storage density, hydrogen purity, and reversibility.

Original languageEnglish
JournalChemistry: A European Journal
Pages (from-to)14562-70
Number of pages9
Publication statusPublished - 2015

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