Electrochemical hydrogen storage characteristics of nanocrystalline and amorphous Mg_(20)Ni_(10-x)Co_x (x = 0-4) alloys prepared by melt spinning

摘要

Nanocrystalline and amorphous Mg_2Ni-type electrode alloys with nominal compositions of Mg_(20)Ni_(10-x)Co_x (x = 0, 1, 2, 3, 4) were synthesized by melt-spinning technique. The microstructures of the as-spun alloy ribbons were characterized by XRD, SEM and HRTEM. The electrochemical properties of the alloys were measured. The experimental results showed that the substitution of Co for Ni did not change the major phase of Mg_2Ni, but it led to the formation of secondary phase MgCo_2. No amorphous phase formed in the as-spun alloy (x = 0), whereas the as-spun alloy (x = 4) held a nanocrystalline and amorphous structure, confirming that the substitution of Co for Ni significantly enhances the glass forming ability of the Mg_2Ni-type alloy. The substitution of Co for Ni significantly improves the electrochemical hydrogen storage performances of the alloys, involving both the discharge capacity and the cycle stability, for which the increased glass forming ability by Co substitution is mainly responsible.