The effects of Pd and/or Zr additives on the structures and cyclic stabilities of Mg50Ni50-based electrode alloys

• Mg45Pd5Ni45Zr5 alloy was prepared for the anode of Ni-MH battery.
• The cycle stability of Mg45Pd5Ni45Zr5 is remarkably enhanced from that of Mg50Ni50.
• The composite film on Mg45Pd5Ni45Zr5 surface can effectively suppress corrosion.

The Mg50Ni50–based ternary and quaternary alloys partially substituted by Pd and/or Zr have been intensively studied on their structures and electrochemical hydrogen storage performances. The Mg45Pd5Ni50 and Mg45Pd5Ni45Zr5 alloys contained both amorphous phase and body-centered cubic phase, differing from most previously studied amorphous Mg50Ni50–based alloys. The detected lattice parameters of nano-crystalline BCC phase in Mg45Pd5Ni50 and Mg45Pd5Ni45Zr5 alloys were 0.2916 nm and 0.2933 nm, respectively. Charge-discharge tests indicated that Pd facilitates lifting the cyclic retention rate in 20 cycles (C20/Cmax) from 13.2% of Mg50Ni50 alloy to 47.3% of Mg45Pd5Ni50 alloy. The partial substitution of Zr for Ni in Mg50Ni50 alloy improved the initial capacity by 12% from that of Mg50Ni50 alloy (445 mAh g−1). Synergetic substitution of Pd and Zr in Mg50Ni50 can greatly inhibit the corrosion of Mg45Pd5Ni45Zr5 alloy. According to XPS study, the Mg, Pd, Ni and Zr on the surface of Mg45Pd5Ni45Zr5 alloy would be oxidized into MgO, PdO2, Ni2O3 and ZrO2 during charge/discharge cycles. They formed a passive composite film and therefore improved the cyclic stability.