Study On Microstructure And Hydrogen Storage Properties Of LaMg₂Cu_2-xNi_x Alloys

The AB2C2–type of Rare earth–Mg–Transitional metal elements based hydrogen storage alloys showed high hydrogen storage capacity and low cost, however, they suffered from high hydrogen desorption temperature and poor hydriding kinetics. In this paper, the impact of catalystic element Ni which partly substituted for Cu on the microstructure and hydrogen storage properties of LaMg2Cu2-xNix (x = 0.2, 0.4, 0.5, 0.6, 0.8, 1.0) alloys and ball milling treatment were studied.The XRD analysis showed that the LaMg2Cu2-xNix (x = 0.2, 0.4, 0.5, 0.6, 0.8, 1.0) alloys consisted of LaMg2Ni phase, LaMg2Cu phase and LaMg3 phase. The reversible hydrogen storage capacity and D/A (denoted as the ratio of hydrogen desorption to absorption) increased firstly and then decreased with the increasing of x, when x was 0.5, The reversible hydrogen storage capacity and D/A reached the maximum of 1.07 wt.% and 47.85%, respectively. In addition, for the LaMg2Cu1.5Ni0.5 alloy, the maximum hydrogen storage capacity increased firstly from 3.22 wt.% at 538 K to 3.62 wt.% at 558 K and then descreased to 2.86 wt.% at 573 K, the D/A increased from 56.97% (538 K) to 89.70% (573 K).Amorphous LaMg2Cu1.5Ni0.5 was prepared by ball milling for 50 h and the equilibrium pressure decreased from 0.1 MPa to 0.008 MPa. The uptake time for hydrogen content to reach above 90% of the maximum storage capacity for the milled alloys was 100 s, which was higher than 87% of the alloy of as-cast in the same condition. The efficiency of ball milling treatment enhanced after the addition of TiO2 in the milling process, the hydrogen storage capacity increased by 1.25% (538 K), 5.11% (548 K) and 5.67% (558 K). The ball milled LaMg2Cu1.5Ni0.5+3 wt.%TiO2 exhibited better hydriding kinetics than that of the ball-milled LaMg2Cu1.5Ni0.5 alloy. The experimental curve of hydrogen absorption kinetics for ball-milled LaMg2Cu1.5Ni0.5 and LaMg2Cu1.5Ni0.5+3 wt.%TiO2 at 473 K can both be well fitted by JDM hydriding diffusion model, which suggested that the hydriding of ball-milled LaMg2Cu1.5Ni0.5 and LaMg2Cu1.5Ni0.5+3 wt.%TiO2 alloys were basically three-dimensional diffusion-controlled nucleation and growth processes. The hydrogen storage properties of LaMg2Cu1.5Ni0.5 alloy prepared by ball milling in different organic reagents were also investigated. The hydriding kinetics were improved further that the uptake time of hydrogen content reached above 90% of the maximum storage capacity were all within 50 s.