Towards room temperature, direct, solvent free synthesis of tetraborohydrides

Due to their high hydrogen content, tetraborohydrides are discussed as potential synthetic energy carriers. On the example of lithium borohydride LiBH4, we discuss current approaches of direct, solvent free synthesis based on gas solid reactions of the elements or binary hydrides and/or borides with gaseous H2 or B2H6. The direct synthesis from the elements requires high temperature and high pressure (700°C, 150bar D2). Using LiB or AlB2 as boron source reduces the required temperature by more than 300 K. Reactive milling of LiD with B2H6 leads to the formation of LiBD4 already at room temperature. The reactive milling technique can also be applied to synthesize other borohydrides from their respective metal hydrides.