Synergistic Catalytic Effects of AlH3-TiF3 Composites on the Hydrogen Storage Performance of MgH2

We report the synergistic catalytic effects of AlH3-TiF3 composites that can improve the kinetic properties of Mg based hydrogen storage materials. The resulting MgH2-AlH3-TiF3 composites (MA-F) exhibit 5.55 wt % reversible hydrogen storage capacity with a reduced activation energy of 100.85 kJ/mol H2. The X-ray diffraction (XRD) and transmission electron microscopy (TEM) measurements revealed that the in situ generated Al* reacts with TiF3 and Mg, forming Al3Ti, AlF3, and Mg17Al12 during the heating process. Al3Ti and AlF3 act as the actual catalytically active centers for the hydrogen desorption and absorption processes, accelerating the reversible conversion between Mg and MgH2. Moreover, the presence of Mg17Al12 can narrow the free energy gap between the hydrogenated and dehydrogenated states, favoring the improvement of thermodynamic properties. These discoveries demonstrate the importance of the interaction between Mg/MgH2 and transition metal composites to improve the hydrogen storage functionalities.