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A MgH2/FeCl3/carbon nanotubes (CNTs) composite was prepared by dry ball milling, and its hydrogen storage properties were investigated. The CNT addition resulted in both a decreased desorption temperature and improved sorption kinetics compared to the undoped MgH2–FeCl3 composite. The desorption temperature of the 5 wt % CNT-added MgH2–FeCl3 composite was decreased to 230 °C compared with 275 °C for undoped MgH2–FeCl3. For the dehydrogenation kinetics, the 5 wt % CNT-added MgH2–FeCl3 sample released about 4.3 wt % hydrogen at 320 °C after 4 min of dehydrogenation, while the MgH2–FeCl3 composite released about 3.1 wt % hydrogen under the same conditions. Meanwhile, for the rehydrogenation kinetics, the 5 wt % CNT-added MgH2–FeCl3 sample absorbed about 5.21 wt % hydrogen at 300 °C after 1 min of rehydrogenation, but the MgH2–FeCl3 composite only absorbed about 4.8 wt % hydrogen. The apparent activation energy, E a, for dehydrogenation decreased from 130 kJ/mol for the MgH2–FeCl3 composite to 112 kJ/mol by the addition of 5 wt % CNTs. It is believed that the enhancement of the hydrogenation performance of the MgH2/FeCl3/CNTs composite is due to the active Fe-containing species and the function of the Cl anions, as well as the unique structure of the CNTs.

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A sample of MgH 2 and 10 wt.% Co 2 NiO was prepared by the ball milling technique. The hydrogen storage properties and reaction mechanism of the sample were examined. The temperature-programmed desorption result shows that the addition of 10 wt.% Co 2 NiO to MgH 2 exhibited a lower onset desorption temperature of 300 °C, which was decreased to 117 and 70 °C compared to as-received and as-milled MgH 2 , respectively. The de/rehydrogenation kinetics of MgH 2 + 10 wt.% Co 2 NiO showed improvement compared to un-doped MgH 2 . The results of the Kissinger plot shows that the activation energy for the hydrogen desorption of MgH 2 was reduced to about 65.0 and 15.0 kJ/mol compared to as-received and as-milled MgH 2, respectively. Meanwhile, the X-ray diffraction analysis shows the formation of a new phase of Mg-Co alloy and Co 1.29 Ni 1.71 O 4 after the dehydrogenation and rehydrogenation process. It is reasonable to conclude that the Co 2 NiO additive plays a catalytic role through the formation of active species of Mg-Co alloy and Co 1.29 Ni 1.71 O 4 during the heating process, thus improving the hydrogen storage properties of MgH 2 .

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