Phase Components And Hydrogen Storage Prorerties Of Mechanically Ball-milled Mg-based Materials

Mg-based hydrogen storage alloys have attracted more attention because of their high capcities and low costs. However, their practical applications are blocked by sluggish kinetics and bad thermdynamics. Based on the review of the researchs and developments of Mg-based hydrogen storage alloys, Mg10 YNi alloy prapared by melt-spinning were selected as the subject of the present work. The hydrogen storage properties of the Mg10 YNi samples produced by ball-milling at differeent atmospheres and times were studied firstly. Then, the hydrogen storage properties of the Mg10YNi-xTiH2(x=1, 2, 9) samples prepared by ball-milling at 5 MPa H2 were studied. Finally, the hydrogen properties of NaMgH3 synthesized with Mg10 YNi and NaH were investigated in detail.(1) Although the Mg10 YNi samples ball-milled for 10 h under Ar, 0.5 MPa H2 and 5 MPa H2 atmosphere have similar activation and hydrogen desorption kinetics as compared to the unball-milled sample, they exhibit superior hydrogen absorption kinetics. The Mg10 YNi alloy can be partly hydrogenated during the ball-milling under both 0.5 MPa H2 and 5 MPa H2 for 100h. The fully de-hydrogenated products can absorb 4.8 wt.% hydrogen within 1 min at 250 °C without activation. Moreover, the re-hydrogenated samples can be fully de-hydrogenated within38 min at 250 °C. The improvement in activation and hydrogen absorption-desorption kinetics is related to the fine particles with several hundred nano-metres after ball-milling for 100 h.(2) The Mg10YNi-xTiH2(x=1, 2, 9) composites can be partly hydrogenated during ball-milling for 100 h under 5 MPa H2. The fully de-hydrogenated products can absorb 3.2wt.%, 3.4 wt.%, 1.9 wt.% hydrogen within 60 min at 300 °C, respectively. Even at 50 °C, the hydrogen absorption amounts also reach 1.65 wt.%, 1.8 wt.% and 0.85 wt.% within 60 min,respectively. Obviously, the addition of TiH2 has a positive effect on improving the hydrogen absorption-desorption kinetics of the composite systems. Unfortunately, the hydrogen absorption-desorption thermodynamic property cannot be improved by TiH2.(3) The NaMgH3 sample synthesized with Mg10 YNi and NaH can desorbed fully within 7min at 400 °C, and the total amount of hydrogen desorption is 4.6 wt.%, showing a good hydrogen desorption kinetics. The improvement of kinetics is attributed to the synergetic effect of minor Mg2NiH4 and YH3 formed in situ during the preparation of NaMgH3. In addition, thede-hydrogenated products of as-prepared NaMgH3 could form NaMgH3 again at 350 °C.However, the composite exhibit a bad cycle property owning to the volatilization of Na with low melting point in the hydrogen desorption process.