Effective synthesis of magnesium borohydride via B-O to B-H bond conversion

Magnesium borohydride (Mg(BH4)2) is widely regarded as a promising hydrogen storage material due to its high capacity; however, it is still challenging to synthesize Mg(BH4)2 with low cost. Traditionally, Mg(BH4)2 has been mainly produced using other borohydride as the starting materials via exchange reactions. Herein, we report an economical method to synthesize Mg(BH4)2 by converting B-O bonds in widely available borates or boric acid to B-H. The borates or boric acid is ball-milled with MgH2 under ambient conditions to form Mg(BH4)2 with high yield (>80%). Mg(BH4)2 was also successfully generated by reacting low-cost Mg with boric acid. Compared with previous approaches, this method avoids expensive boron sources such as LiBH4, NaBH4, and B2H6, and does not require high pressure H2 gas and high temperatures, and therefore significantly reduces costs. This method could be an alternative to the current Mg(BH4)2 synthesis processes.