Hydrogenation properties and kinetic study of MgH₂ - x wt% AC nanocomposites prepared by ball milling

The high de-/hydrogenation temperature of magnesium hydride is still a challenge in solid-state hydrogen storage system for automobiles applications. To improve the hydrogenation properties of MgH_2, we select activated carbon/charcoal (AC) as a catalyst. A systematic investigation was performed on the hydrogen storage behaviors of MgH₂ and MgH₂ - 5 wt% AC nanocomposites, which were prepared by a high-energy planetary ball mill. These synthesized nanocomposites were characterized by X-ray diffraction (XRD), high-resolution transmission electron microscope (HRTEM) for phase identification, surface morphology and microstructural analysis. The pressure-composition-temperature (PCT) isotherm investigation shows the maximum hydrogen storage capacity ~ 6.312 wt% for MgH₂-AC nanocomposites, while 3.417 wt% for MgH₂ at 300 °C. The onset temperature for MgH₂-AC nanocomposites is shifted towards lower side than the 50 h milled MgH₂. The HRTEM study show the activated carbon helps to reduce oxygen from MgO phase in MgH₂, so that significantly improvement achieved in the absorption capacity and kinetics also for the MgH₂-AC nanocomposites. The presence of β- and γ-phases of MgH₂ in MgH₂-AC nanocomposites also supports the high hydrogenation properties and with the support of XRD data.