A Comparison Study of Hydrogen Storage Thermodynamics and Kinetics of YMg11Ni Alloy Prepared by Melt Spinning and Ball Milling

Melt spinning （MS） and ball milling （BM） were employed to fabricate YMg11Ni alloy, and their structures and hydrogen storage performances were examined. The results reveal that the as-spun and as-milled alloys both exhibit the nanocrystalline and amorphous structure. The as-milled alloy shows a larger hydrogen absorption capacity as compared with the as-spun alloy. More than that, the as-milled alloy exhibits lower onset hydrogen desorption temperature than the as-spun one, which are 549.8 and 560.9 K, respectively. Additionally, the as-milled alloy shows a superior hydrogen desorption property to the as-spun one. On the basis of the time needed by desorbing hydrogen of 3 wt% H2, for the as- milled alloy, it needs 1106, 456, 343, and 180 s corresponding to hydrogen desorption temperatures of 593, 613, 633, and 653 K. However, for the as-spun alloy, the time needed is greater than 2928, 842, 356, and 197 s corresponding to the same temperatures. Hydrogen desorption activation energies of as-milled and as-spun alloys are 98.01 and 105.49 kJ/mol, respectively, which is responsible for that the as-milled alloy possesses a much faster dehydriding rate. By means of the measurement of pressure-composition-temperature （P-C-T） curves, the dehydrogenation enthalpy change of the alloys prepared by MS （△Hoe（MS）） and BM （△Hdc（BM）） is 81.84 and 79.46 kJ/mol, respectively, viz. △Hde（MS） 〉 △Hoc（BM）.

Hydrogen storage thermodynamic and kinetic characteristics of PrMg12-type alloys synthesized by mechanical milling

To improve the hydrogen storage performance of PrMg12-type alloys, Ni was adopted to replace partially Mg in the alloys. The PrMgllNi＋x wt.% Ni （x=100, 200） alloys were prepared via mechanical milling. The phase structures and morphology of the experimental alloys were in vestigated by X-ray diffraction and transmission electron microscopy. The results show that increasing milling time and Ni content accelerate the formation of nanocrystalline and amorphous structure. The gaseous hydrogen storage properties of the experimental alloys were determined by differential scanning calorimetry （DSC） and Sievert apparatus. In addition, increasing milling time makes the hydrogenation rates of the alloys augment firstly and decline subsequently and the dehydrogenation rate always increases. The maximum capacity is 5. 572 wt. % for the x = 100 alloy and 5. 829 wt. % for the x = 200 alloy, respectively. The enthalpy change （ △H ）, entropy change （△S） and the dehydrogenation activation energy （Exde） markedly lower with increasing the milling time and the Ni content due to the generation of nanocrystalline and amorphous structure.

Structure and electrochemical performances of as-milled LaMg12-type alloy-Ni composites

LaMg11Ni+x wt.%Ni(x=100,200)alloys were prepared by ball milling and researched by various methods to study their structure and electrochemical hydrogen storage property.The outcomes reveal that increasing Ni content contributes to improving its electrochemical performance.Particularly,the discharge capacity of as-milled(40 h)alloy will be increased from 157.3 to 1053.5 mAh/g through enhancing Ni percentage from 100 to 200 wt.%when discharging at 60 mAh/g.Ball milling obviously affects the electrochemical performanee of alloys.With milling duration prolonging,the discharge capacity of x=100 alloy keeps increasing,while that of the x=200 alloy has a maximum value.Milling time also affects the cycle stability of experimental alloys.Extendi ng milli ng duration clearly decreases the cycle stability of x=100 alloy but weakens that of the x=200 alloy at first and strengthens it later.In addition,prolonging milling time makes the milling prepared x=100 and 200 alloys get the maximal values of high rate discharge ability of 81.60%and 84.52%,respectively.

A comparison study of hydrogen storage performances of SmMg_(11)Ni alloys prepared by melt spinning and ball milling

The melt spinning（MS） and ball milling（BM） technologies are thought to be efficient to prepare nanostructured Mg and Mg-based alloys for improving their hydrogen storage performances. In this paper, two technologies, viz. melt spinning and ball milling, were employed to fabricate the SmMg_（11）Ni alloy. The structure and hydrogen storage performance of these two kinds of alloys were researched in detail. The results reveal that the as-spun and milled alloys both contain nanocrystalline and amorphous structures. By means of the measurement of PCT curves, the thermodynamic parameters of the alloys prepared by MS and BM are ΔN_（Ms）（des） = 82.51 kJ/mol and ΔH_（BM）（des） = 81.68 kJ/mol, respectively, viz.ΔH_（MS）（des） 〉 ΔH_（BM）（des）. The as-milled alloy shows a larger hydrogen absorption capacity as compared with the as-spun one. The as-milled alloy exhibits lower onset hydrogen desorption temperature than the as-spun one. As to the as-milled and spun alloys, the onset hydrogen desorption temperatures are557.6 and 565.3 K, respectively. Additionally, the as-milled alloy shows a superior hydrogen desorption property than the as-spun one. On the basis of time that required by desorbing hydrogen of 3 wt% H_2, the as-milled alloy needs 1488.574,390 and 192 s corresponding to hydrogen desorption temperatures 593,613,633 and 653 K, while the as-spun alloy needs 3600,1020,778 and 306 s corresponding to the same temperatures. The dehydrogenation activation energies of the as-milled and spun alloys are 100.31 and105.56 kJ/mol, respectively, the difference of which is responsible for the much faster dehydriding rate of the as-milled alloy.