Noticeable improvement in the desorption temperature from graphite in rehydrogenated MgH2/graphite composite

MgH2/graphite composite was fabricated by mechanically milling elemental ingredients in hydrogen using a special low-energy ball-particle shearing milling. Rehydrogenated MgH2/graphite composite exhibits a desorption temperature that is lower by about 35 °C compared with that of the as-prepared composite. X-ray diffraction (XRD), transmission electron microscopy (TEM), scanning electron microscope (SEM), differential scanning calorimeter (DSC), and Raman and IR spectroscopy were used to investigate the possible origins of the noticeable enhancement in the desorption temperature. It is found that γ-MgH2, a by-product of ball milling, does not contribute to the enhancement of the hydrogen desorption. Carbon hydrogen bonding is not detected and it seems that the formation of classical C–H bonding is not feasible with this kind of milling mode. It is believed that the structural change in hydrogenated carbon clusters and/or charge-transfer reactions upon hydrogen cycling are likely to be responsible for the enhancement in the hydrogen desorption temperature.