To improve the hydrogen storage properties of Mg-based alloys, a composite material of MgH_2 + 10wt%LaH_3 + 10wt%NbH was prepared by a mechanical milling method. The composite exhibited favorable hydrogen desorption properties, releasing 0.67wt% H2 within 20 min at 548 K, which was ascribed to the co-catalytic effect of LaH_3 and NbH upon dehydriding of MgH_2. By contrast, pure MgH_2, an MgH_2 + 20wt%LaH_3 composite, and an MgH_2 + 20wt%NbH composite only released 0.1wt%, 0.28wt%, and 0.57wt% H2, respectively, under the same conditions. Analyses by X-ray diffraction and scanning electron microscopy showed that the composite particle size was small. Energy-dispersive X-ray spectroscopic mapping demonstrated that La and Nb were distributed homogeneously in the matrix. Differential thermal analysis revealed that the dehydriding peak temperature of the MgH_2 + 10wt%LaH_3 + 10wt%NbH composite was 595.03 K, which was 94.26 K lower than that of pure MgH_2. The introduction of LaH_3 and NbH was beneficial to the hydrogen storage performance of MgH_2.
Jian-zheng SongZi-yang ZhaoXin ZhaoRui-dong FuShu-min Han
The hydrogenation/dehydrogenation kinetics and thermodynamic behaviors of the MgH2-WS2 composites were investigated. The TPD(Temperature-Programmed-Desorption) curves showed that the onset dehydrogenation temperature of the MgH2 + 20wt% WS2 composite was 615 K, 58 K lower than that of the pristine MgH2. The kinetic measurements showed that within 21 min, the MgH2 + 20wt% WS2 composite could absorb 2.818wt% at 423 K, and release 4.244 wt% of hydrogen at 623 K, while the hydriding/dehydriding capacity of MgH2 reached only 0.979wt% and 2.319wt% respectively under identical conditions. The improvement of hydrogenation/dehydrogenation performances for the composite was attributed to the cocatalytic effect between the new phases W and MgS which formed during the ball-milling process.
The phase structure and hydrogen storage properties of LaMg 3.70 Ni 1.18 alloy were investigated. The LaMg 3.70 Ni 1.18 alloy consists of main LaMg 2 Ni phase, minor La 2 Mg 17 and LaMg 3 phases. The alloy can be activated in the first hydriding/dehydriding process, and initial LaMg 2 Ni, La 2 Mg 17 , and LaMg 3 phases transfer to LaH 2.34 , Mg, and Mg 2 Ni phases after activation. The reversible hydrogen storage capacity of the LaMg 3.70 Ni 1.18 alloy is 2.47 wt.% at 558 K, which is higher than that of the LaMg 2 Ni alloy. The pressure-composition-temperature (PCT) curves display two hydriding plateaus, corresponding to the formation of MgH 2 and Mg 2 NiH 4 . However, only one dehydriding plateau is observed, owing to the synergetic effect of hydrogen desorption between MgH 2 and Mg 2 NiH 4 . The uptake time for hydrogen content to reach 99% of saturated state is less than 250 s, and 90% hydrogen can be released in 1200 s in the experimental conditions, showing fast kinetics in hydriding and dehydriding. The activation energies of the LaMg 3.70 Ni 1.18 alloy are -51.5 ± 1.1 kJ/mol and -57.0 ± 0.6 kJ/mol for hydriding and dehydriding, respectively. The hydriding/dehydriding kinetics of the LaMg 3.70 Ni 1.18 alloy is better than that of the Mg 2 Ni alloy, owing to the lower activation energy values.
LI JinhuaLIU BaozhongHAN ShuminHU LinZHAO XinWANG Mingzhi
