Effects of Fe3O4-assisted ball milling of MgH2 on characteristics of the nanocomposite, its hydrolysis and product

Hydrogen generation during hydrolysis of MgH2 is practically impeded by a passivated layer of Mg(OH)2 formed on reactant surfaces. To address this challenge, various metal oxides have been added to improve its hydrolysis performance. However, magnetite (Fe3O4), a widely available, eco-friendly and cheap metal oxide, has little been tested so far. This work explored how Fe3O4-assisted ball milling of MgH2 would affect the characteristics of the nanocomposite, its hydrolysis and products. As expected, milled nanosized MgH2-containing samples have significantly superior characteristics and hydrolysis reactivity than the unmilled MgH2. The data further show that, the introduction of Fe3O4 during MgH2 ball milling can reduce crystallite size and pore size, increase pore volume and BET surface area. These advantageous features are determined to play important roles in enhancing hydrogen generation during MgH2-Fe3O4-BM hydrolysis, though chemical effects may also be possible. Five-staged changes in hydrogen generation rate are observed, which are interpreted from the point of view of changes of reactive surface area, diffusion of water molecules and heat release during hydrolysis. The products from hydrolysis of milled samples possess distinct structures, with agglomerated particles showing interesting flower-like nanostructures. The magnetic Fe3O4 nanoparticles are almost uniformly distributed in the MgH2-Fe3O4-BM hydrolysis product, and are closely associated with the product particles. A magnetic performance test shows that these particular features benefit the separation/recovery of the hydrolysis product. This investigation shows that Fe3O4-assisted ball milling of MgH2 is a promising approach to enhancing MgH2 hydrolysis, and also enabling the easy recovery the product.