Gaseous and Electrochemical Hydrogen Storage Kinetics of As–Spun Nanocrystalline Mg2Ni1−xCux(x=0–0.4) Alloys

The Mg_2Ni_(1-x)Cu_x(x=0,0.1,0.2,0.3,0.4) hydrogen storage alloys have been prepared by melt-spinning technology.The structures of the as-cast and spun alloys are characterized by XRD, SEM and TEM.The gaseous hydrogen absorption and desorption kinetics of the alloys were measured by an automatically controlled Sieverts apparatus.The electrochemical hydrogen storage kinetics of the as-spun alloys is tested by an automatic galvanostatic system.The results show that all the as-spun alloys hold an entire nanocrystalline structure and are free of amorphous phase.The substitution of Cu for Ni, instead of changing the major phase Mg_2Ni,leads to a visible refinement of the grains of the as-cast alloys. Furthermore,both the melt spinning treatment and Cu substitution significantly improve the gaseous and electrochemical hydrogen storage kinetics of the alloys.As the spinning rate increases from 0(As-cast is defined as spinning rate of 0 m/s) to 30m/s,the hydrogen absorption saturation ratio in 5 min,for the Mg_2Ni_(0.8)Cu_(0.2)alloy,increases from 56.7 to 92.7%,the hydrogen desorption ratio in 20 min from 14.9 to 40.4%,the high rate discharge ability from 38.5 to 75.5%,the hydrogen diffusion coefficient from 8.34×10~(-12) to 3.74×10~(-11)cm~2/s.