Hydrogen storage behaviors and microstructure of MF3 (M=Ti, Fe)-doped magnesium hydride

MgH2+10%MF3 (M=Ti, Fe) (mass fraction) composites were prepared by ball-milling in hydrogen atmosphere, and their hydrogen storage behaviors and microstructure were investigated systematically. The results show that the hydriding and dehydriding kinetics of MgH2 are markedly improved by doping TiF3 and FeF3 fluorides. At 573 K, the two composites can absorb 5.67%-6.07% (mass fraction) hydrogen within 5 min under an initial hydrogen pressure of 3.5 MPa, and desorb 5.34%-6.02% hydrogen within 6 min. Furthermore, the composites can absorb hydrogen rapidly in moderate temperature range of 313-473 K. In comparison, TiF3-doped sample has a better hydriding-dehydriding kinetics than FeF3-doped sample. The microstructure analysis shows that some active particles including MgF2, TiH2 and Fe could be formed in the hydriding-dehydriding processes of the MF3-doped composites. From the Kissinger's plot, the apparent activation energies for the hydrogen desorption of the composites are estimated to be 74.1 kJ/mol for TiF3-doped composite and 77.6 kJ/mol for FeF3-doped composite, indicating MgH2 is significantly activated due to the catalytic effect of the doping of MF3.