Enhanced electrochemical hydrogen storage characteristics of the as-spun Mg2Ni-type alloys by substituting Ni with M (M=Cu, Co)

Mg2Ni-type Mg20Ni10-xMx (M=Cu, Co; x=0, 1, 2, 3, 4) electrode alloys with nanocrystalline and amorphous structure were synthesized by melt-spinning technique. The microstructures of the as-spun alloys were characterized by XRD, SEM and HRTEM. The electrochemical hydrogen storage properties of the experimental alloys were measured. The obtained results show that the as-spun (M=Cu) alloys hold an entire nanocrystalline structure, whereas 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 Mg2Ni-type alloy. Furthermore, such substitution results in the formation of secondary phases Mg2Cu and MgCO2 instead of changing the major phase of Mg2Ni. The substitution of M (M=Cu, Co) for Ni markedly improves the electrochemical performances of the alloys, involving the discharge capacity and the cycle stability as well as the high rate discharge ability.