Improved Physical and Electrochemical Hydrogen Storage Kinetics of the Mg_(20)Ni_(10-x)M_x(M=Cu, Co; x=0, 4) Alloys by Melt Spinning

摘要

It has come to light that the Mg_2Ni-type alloy with a nanocrystalline/amorphous structure possesses superior hydrogen storage kinetics. The Mg_2Ni-type Mg_(20)Ni_(10-x)M_x (M=Cu, Co; x=0, 4) hydrogen storage alloys were synthesized by a melt-spinning technique. The microstructures of the as-cast and spun alloys were characterized by XRD, SEM and HRTEM. The gaseous and electrochemical hydrogen storage kinetics of the alloys was measured. The results show that whatever spinning rate the as-spun (M=Cu) alloys hold an entire nanocrystalline structure. As spinning rate approaches to 20 m/s, the as-spun (M=Co) alloys display a nanocrystalline and amorphous structure, confirming that the substitution of Co for Ni facilitates the glass formation in the Mg_2Ni-type alloy. Furthermore, such substitution results in the formation of secondary phases Mg_2Cu and MgCo_2 instead of changing the major phase of Mg_2Ni. The melt spinning markedly improves the gaseous and electrochemical hydrogen storage kinetics of the alloys. The hydrogen absorption ratio (R_5~a), hydrogen desorption ratio (R_(20)~d) and the high rate discharge ability (HRD) notably mount up with the growing of the spinning rate.