Enhancement of hydrogen storage properties in 4MgH2 Na3AlH6 composite catalyzed by TiF3

In this work, we have investigated the hydrogen release and uptake pathways storage properties of the MgH2Na3AlH6 with a molar ratio of 4:1 and doped with 10 wt% of TiF3 using a mechanical alloying method. The doped composite was found to have a significant reduction on the hydrogen release temperature compared to the un-doped composite based on the temperature-programme-desorption result. The first stage of the onset desorption temperature of MgH2Na3AlH6 was reduced from 170 °C to 140 °C with the addition of the TiF3 additive. Three dehydrogenation steps with a total of 5.3 wt% of released hydrogen were observed for the 4MgH2Na3AlH6-10 wt% TiF3 composite. The re/dehydrogenation kinetics of 4MgH2Na3AlH6 system were significantly improved with the addition of TiF3. Kissinger analyses showed that the apparent activation energy, EA, of the 4MgH2Na3AlH6 doped composite was 124 kJ/mol, 16 kJ/mol and 34 kJ/mol lower for un-doped composite and the as-milled MgH2, respectively. It was believed that the enhancements of the MgH2Na3AlH6 hydrogen storage properties with the addition of TiF3 were due to formation of the NaF, the AlF3 and the Al3Ti species. These species may played a synergetic catalytic role in improving the hydrogenation properties of the MgH2Na3AlH6 system.