Economic and effective regeneration of LiBH4 from its direct hydrolytic products using Al-rich alloys

The hydrolysis of lithium borohydride (LiBH 4 ) is very promising for on-site hydrogen generation to supply hydrogen since it has appealing features such as a high hydrogen capacity (13.9 wt%, water included), fast hydrogen evolution rate, and mild reaction conditions. The large-scale application of LiBH 4 , however, is restricted by its difficult regeneration from stable hydrolytic products (LiBO 2 · x H 2 O), which requires expensive reducing agents such as MgH 2 , high energy-consuming dehydration process for LiBO 2 ·2H 2 O, and additional hydrogen input. Herein, we develop a facile method to directly regenerate LiBH 4 from LiBO 2 ·2H 2 O by ball milling with low-cost Al-rich alloys as reductants and Li 2 O as additives, balancing efficiency and economy well. Introducing Mg (or Ca) into Al to form Al-rich alloys optimizes the mechanical brittleness and chemical reducibility, which facilitate the crushing, collision, and reaction of reactants and the conversion of H + to H − . The specific mechanism study illustrates that Mg in Al 3 Mg 2 preferentially reacts and the in-situ derived Al with fresh surface and fine size is highly active for reductive regeneration of LiBH 4 . Besides, a little addition of Li 2 O suppresses the formation of “boron sink”, [B 12 H 12 ] − , further increasing the yield of LiBH 4 . This work evidences the regeneration potential of Al-based reducing agents on metal borohydrides.