title: A composite of complex and chemical hydrides yields the first Al-based amidoborane with improved hydrogen storage properties.
abstract: 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.
authors: Institute of Condensed Matter and Nanosciences, Université catholique de Louvain, Place L. Pasteur 1, 1348 Louvain-la-Neuve (Belgium).
authors: Iurii
authors: I
authors: Dovgaliuk
authors: Center for Materials Crystallography, Interdisciplinary Nanoscience Center and Department of Chemistry, Aarhus University, Langelandsgade 140, 8000 Aarhus C (Denmark).
authors: Lars H
authors: LH
authors: Jepsen
authors: Institute of Condensed Matter and Nanosciences, Université catholique de Louvain, Place L. Pasteur 1, 1348 Louvain-la-Neuve (Belgium).
authors: Damir A
authors: DA
authors: Safin
authors: Department of Structural Research, INP Polish Academy of Sciences ul. Radzikowskiego 152, 31-342 Kraków (Poland).
authors: Zbigniew
authors: Z
authors: Łodziana
authors: Swiss-Norwegian Beam Lines, European Synchrotron Radiation Facility, Rue Horowitz 6, 38043 Grenoble (France).
authors: Vadim
authors: V
authors: Dyadkin
authors: Center for Materials Crystallography, Interdisciplinary Nanoscience Center and Department of Chemistry, Aarhus University, Langelandsgade 140, 8000 Aarhus C (Denmark).
authors: Torben R
authors: TR
authors: Jensen
authors: Institute of Condensed Matter and Nanosciences, Université catholique de Louvain, Place L. Pasteur 1, 1348 Louvain-la-Neuve (Belgium).
authors: Michel
authors: M
authors: Devillers
authors: Institute of Condensed Matter and Nanosciences, Université catholique de Louvain, Place L. Pasteur 1, 1348 Louvain-la-Neuve (Belgium). yaroslav.filinchuk@uclouvain.be.
authors: Yaroslav
authors: Y
authors: Filinchuk
keywords: boranes; crystal engineering; hydrides; hydrogen storage; sodium alanate