Metal borohydride formation from aluminium boride and metal hydrides.

Metal borides are often decomposition products from metal borohydrides and thus play a role in the reverse reaction where hydrogen is absorbed. In this work, aluminium boride, AlB, has been investigated as a boron source for the formation of borohydrides under hydrogen pressures of p(H) = 100 or 600 bar at elevated temperatures (350 or 400 °C). The systems AlB-MH (M = Li, Na, Mg, Ca) have been investigated, producing LiBH, NaBH and Ca(BH), whereas the formation of Mg(BH) was not observed at T = 400 °C and p(H) = 600 bar. The formation of the metal borohydrides is confirmed by powder X-ray diffraction and infrared spectroscopy and the fraction of boron in AlB and M(BH) is determined quantitatively by B MAS NMR. Hydrogenation for 12 h at T = 350-400 °C and p(H) = 600 bar leads to the formation of substantial amounts of LiBH (38.6 mol%), NaBH (83.0 mol%) and Ca(BH) (43.6 mol%).