Abstract: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.

Key words: Mg-based composites; TiF₃; FeF₃; hydrogen storage properties; microstructure