Improved Hydrogen Storage Properties of MgH₂ Co-Doped with FeCl₃ and Carbon Nanotubes

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, Ea, 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.