Effect of Metaborate Additive Modification on Hydrolysis Performance of MgH₂

Magnesium hydride (MgH2) is one of the most promising candidates for hydrogen generation materials due to the benign byproduct Mg(OH)2. However, the low solubility of Mg(OH)2 inevitably causes sluggish hydrolysis kinetics and low hydrogen yield. Herein, a facile strategy is reported to promote the hydrolysis performance of MgH2viain situ formation of metal borohydrides (M(BH4)x). MgH2@M(BH4)x composites are synthesized by ball milling of MgH2 and cheap metaborates. Different ball-milled durations of NaBO2 metaborate and electronegativities (χp) of cation elements of metaborates (i.e., KBO2, NaBO2, LiBO2, Ca(BO2)2, and Mg(BO2)2) were compared to reveal that the MgH2-4 mol % NaBO2 composite after 6 h ball milling has the best hydrolysis performance. Specifically, it could release 1597.2 mL g-1 H2 (95% theoretical H2) in 60 min with a fast hydrolysis rate of 1216 mL g-1 min-1 H2 during the first minute of the hydrolysis at 55 °C. Our finding is expected to facilitate the application of MgH2 for on-site hydrogen generation.