Hydrogenation/dehydrogenation in MgH2-activated carbon composites prepared by ball milling

A systematic investigation was performed on the hydrogen storage behaviors of ball-milled MgH2-activated carbon (AC) composites. Differential Scanning Calorimetry (DSC) measurement on the desorption temperature was carried out and indicated that the onset and peak temperatures both decreased with increasing AC adding amount, for example, the desorption peak temperature shifted from 349 °C for 1 wt% AC to 316 °C for 20 wt% AC. Furthermore, it is noted that the hydrogen absorption capacity and hydriding kinetics of the composites were also dependent on the adding amount of AC, and the optimum condition could be achieved by mechanical milling of MgH2 with 5 wt% AC. The Mg-5wt%AC composite can absorb about 6.5 wt% hydrogen within 7 min at 300 °C and 6.7 wt% within 2 h at 200 °C, respectively. It is also demonstrated that MgH2-5wt% AC exhibited good hydrogen desorption property that could release 6.5 wt% at 330 °C within 30 min. X-ray diffraction patterns (XRD) and transmission electron microscopy (TEM) observations revealed that the grain size of the synthesized composites decreased with increasing AC amount. This may contribute to the improvement of hydrogen storage in MgH2-AC composites.

► The effect of activated carbon (AC) on Mg hydrogenation is confirmed. ► The optimal hydrogen storage properties of Mg are achieved by adding 5 wt% AC. ► Both total surface area and grain size of Mg lead to the optimal AC adding amount.