Hydrogen storage properties of mechanically milled La2Mg17-x wt.%Ni (x=0, 50, 100, 150 and 200) composites

Abstract

Melting method was used to obtain La2Mg17 alloy, and then Ni powder was added by mechanical alloying method. The kinetics of hydriding process and electrochemical properties of La2Mg17-x wt.%Ni (x=0, 50, 100, 150, 200) composites were investigated. X-ray diffraction (XRD) and scanning electron microscopy (SEM) analyses showed that the crystal structure of composite alloy gradually transformed into amorphous phase by the effect of ball milling and Ni powders. The research of hydrogen absorption properties found that La2Mg17-50 wt.%Ni reached the highest hydrogen absorption than other alloys with more addition of Ni content, reached to 5.796 wt.% at 3 MPa, and up to 5.229 wt.% merely in 2 min, which revealed that the amorphous phase reduced the H occupation of the lattice clearance, resulting in the decline of hydrogen absorption capacity. The electrochemical tests indicated that the maximum discharge capacity increased to 353.1 mAh/g at 30 °C, however, the cycle stability decreased considerably. A series of kinetic measurements demonstrated that the controlling steps of electrochemical process of La2Mg17-x wt.%Ni alloys transferred from hydrogen diffusion on alloy bulk (x=50, 100) to hydrogen diffusion on both alloy bulk and surface (x=150, 200).