Effect of Various Additives on the Hydrolysis Performance of Nanostructured MgH2 Synthesized by High-Energy Ball Milling in Hydrogen

Magnesium hydride is a promising material for hydrogen generation via hydrolysis owing to high hydrogen storage capacity, mild reaction conditions, and low cost of magnesium metal. Unfortunately, the hydrolysis reaction of MgH2 is rapidly hindered due to the formation of a passive Mg(OH)2 layer. Various additives can be used to improve the efficiency of the reaction. The present study examines the influence of 5 wt.% EDTA and TiC–2TiB2 additives on the hydrolysis of the nanostructured MgH2 and compares it with the hydrolysis performance of pure MgH2 and MgH2 + 5 wt.% AlCl3 for the first time. MgH2 was synthesized by high-energy ball milling of Mg powder in hydrogen gas, while MgH2-based nanocomposites were prepared either by mixing the obtained MgH2 with 5 wt.% of additives or by milling Mg with 5 wt.% of additive in hydrogen. The synthesized MgH2 is nanosized, containing a mixture of β-MgH2 and high-pressure γ-modification of MgH2. The hydrogen generation performance in terms of MgH2 conversion rate and hydrogen yield was determined volumetrically. It was found that the MgH2 + 5 wt.% EDTA composite displays the lowest reactivity among the tested materials, probably due to the interaction of MgH2 with EDTA during the ball milling. Pure MgH2 and MgH2 + 5 wt.% (TiC–2TiB2) composite demonstrate almost twice as better hydrolysis performance, which is, however, still quite far from application requirements. The maximum hydrogen yield of 557 mL/g MgH2 and conversion rate of 30.3% was observed for MgH2 + 5 wt.% AlCl3 composition after 10 min of hydrolysis, which can be attributed to the destabilization of the Mg(OH)2 layer by chlorine ions.