Electrochemical hydrogen storage characteristics of nanocrystalline and amorphous Mg 20Ni 10-xCo x(x=0−4) alloys prepared by melt spinning

Abstract

Nanocrystalline and amorphous Mg 2Ni-type alloys with nominal compositions of Mg 20Ni 10-xCo x (x = 0, 1, 2, 3, 4) were synthesized by melt-spinning technique. The microstructures of the as-cast and spun alloys were characterized by XRD, SEM and HRTEM. The electrochemical hydrogen storage characteristics of the as-cast and spun alloys were measured. The obtained results show that the substitution of Co for Ni does not change the major phase of Mg 2Ni, but it leads to the formation of secondary phase MgCo 2 and Mg. No amorphous phase forms in the as-spun alloy (x = 0), whereas the as-spun alloy (x = 4) holds a nanocrystalline and amorphous structure, confirming that the substitution of Co for Ni significantly heightens the glass forming ability of the Mg 2Ni-type alloy. The substitution of Co for Ni and melt spinning significantly improve the electrochemical hydrogen storage performances of the alloys. When Co content x increases from 0 to 4, the maximum discharge capacity of the as-cast alloy increases from 30.3 to 113.3 mAh/g, and from 135.5 to 402.5 mAh/g for as-spun (30 m/s) alloy. The capacity retaining rate of the as-cast alloy after 20 cycles rises from 36.71 to 37.04%, and from 27.06 to 83.35% for as-spun (30 m/s) alloy, respectively.