Effect of Zr-substitution on the Electrochemical Performance of Rare Earth Based Hydrogen Storage Alloys

摘要

The effect of partial substitution of misch metal by zirconium in Ml(NiCoMn)_5 alloy on the electrochemical performance were investigated in detail. It was found that the hydrogen storage alloys containing zirconium showed higher plateau pressure and lower discharge capacity, especially at high temperatures. The addition of zirconium strongly improved the rate capability and significantly improved the electrochemical stability of the alloys in the charge and discharge processes. X-ray powder diffraction analysis indicated that the alloys containing zirconium had a second phase besides for the hexagonal CaCu_5-type structure, which was Zr(NiCo)_5. The second phase improved the electrocatalytic activity for the hydrogen electrode reaction, which might be the cause of the improvement of rate capability. The improved cycling stability might be explained by the compact oxide layer formed on the surface of the alloy, which protected the hydrogen storage alloy from pulverization and oxidation in the electrochemical cycles.