Hydrogen Storage Thermodynamics and Dynamics of Nd–Mg–NiBased Nd Mg_（12~-）Type Alloys Synthesized by Mechanical Milling

Nanocrystalline and amorphous Nd Mg_（12~-）type Nd Mg_（11）Ni＋ x wt% Ni（x=100, 200） hydrogen storage alloys were synthesized by mechanical milling. The effects of Ni content and milling time on hydrogen storage thermodynamics and dynamics of the alloys were systematically investigated. The gaseous hydrogen absorption and desorption properties were investigated by Sieverts apparatus and differential scanning calorimeter connected with a H_2 detector. Results show that increasing Ni content significantly improves hydrogen absorption and desorption kinetics of the alloys. Furthermore,varying milling time has an obvious effect on the hydrogen storage properties of the alloys. Hydrogen absorption saturation ratio（R~a_（10）; a ratio of the hydrogen absorption capacity in 10 min to the saturated hydrogen absorption capacity） of the alloys obtains the maximum value with varying milling time. Hydrogen desorption ratio（R~d_（20）, a ratio of the hydrogen desorption capacity in 20 min to the saturated hydrogen absorption capacity） of the alloys always increases with extending milling time. The improved hydrogen desorption kinetics of the alloys are considered to be ascribed to the decreased hydrogen desorption activation energy caused by increasing Ni content and milling time.