Tailoring the properties of ammine metal borohydrides for solid-state hydrogen storage.

Lars H Jepsen, Morten B Ley, Yaroslav Filinchuk, Flemming Besenbacher, Torben R Jensen

ChemSusChem 2015 Apr 24

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A series of halide-free ammine manganese borohydrides, Mn(BH4 )2 ⋅nNH3 , n=1, 2, 3, and 6, a new bimetallic compound Li2 Mn(BH4 )4 ⋅6NH3 , and the first ammine metal borohydride solid solution Mg1-x Mnx (BH4 )2 ⋅6NH3 are presented. Four new crystal structures have been determined by synchrotron radiation powder X-ray diffraction and the thermal decomposition is systematically investigated for all the new compounds. The solid-gas reaction between Mn(BH4 )2 and NH3 provides Mn(BH4 )2 ⋅6NH3 . The number of NH3 per Mn has been varied by mechanochemical treatment of Mn(BH4 )2 ⋅6NH3 -Mn(BH4 )2 mixtures giving rise to increased hydrogen purity for n/m≤1 for M(BH4 )m ⋅nNH3 . The structures of Mg(BH4 )2 ⋅3NH3 and Li2 Mg(BH4 )4 ⋅6NH3 have been revisited and new structural models are presented. Finally, we demonstrate that ammonia destabilizes metal borohydrides with low electronegativity of the metal (χp <∼1.6), while metal borohydrides with high electronegativity (χp >∼1.6) are generally stabilized. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Citation

Lars H Jepsen, Morten B Ley, Yaroslav Filinchuk, Flemming Besenbacher, Torben R Jensen. Tailoring the properties of ammine metal borohydrides for solid-state hydrogen storage. ChemSusChem. 2015 Apr 24;8(8):1452-63