Enhanced Hydrogen Generation Properties of MgH₂-Based Hydrides by Breaking the Magnesium Hydroxide Passivation Layer

Due to its relatively low cost, high hydrogen yield, and environmentally friendly hydrolysis byproducts, magnesium hydride (MgH₂) appears to be an attractive candidate for hydrogen generation. However, the hydrolysis reaction of MgH₂ is rapidly inhibited by the formation of a magnesium hydroxide passivation layer. To improve the hydrolysis properties of MgH₂-based hydrides we investigated three different approaches: ball milling, synthesis of MgH₂-based composites, and tuning of the solution composition. We demonstrate that the formation of a composite system, such as the MgH₂/LaH₃ composite, through ball milling and<i> in situ</i> synthesis, can improve the hydrolysis properties of MgH₂ in pure water. Furthermore, the addition of Ni to the MgH₂/LaH₃ composite resulted in the synthesis of LaH₃/MgH₂/Ni composites. The LaH₃/MgH₂/Ni composites exhibited a higher hydrolysis rate—120 mL/(g·min) of H₂ in the first 5 min—than the MgH₂/LaH₃ composite— 95 mL/(g·min)—without the formation of the magnesium hydroxide passivation layer. Moreover, the yield rate was controlled by manipulation of the particle size via ball milling. The hydrolysis of MgH₂ was also improved by optimizing the solution. The MgH₂ produced 1711.2 mL/g of H₂ in 10 min at 298 K in the 27.1% ammonium chloride solution, and the hydrolytic conversion rate reached the value of 99.5%.