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 MgH2, 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.