EFFECTS OF PARTIAL SUBSTITUTION AND ANODIC-OXIDATION TREATMENT OF ZR-V-NI ALLOYS ON ELECTROCHEMICAL PROPERTIES

In order to develop a high capacity hydrogen-absorbing alloy electrode based on the Zr-(V-Ni) system pseudobinary Laves phase compound, partial substitutions by titanium, cobalt, iron and manganese were attempted. It was found that substitution of manganese for 25% of the nickel increases the discharge capacity by 20% owing to a remarkable increase in absorbed hydrogen content. The Zr(V0.33Ni0.50Mn0.17)2.4 electrode exhibited a large discharge capacity of 366 mA h g-1 at a current density of 10 mA cm-2. Substitution of titanium for zirconium and substitutions of cobalt and iron for nickel improved the discharge efficiency of hydrogen owing to an increase in the partial molar enthalpy of hydrogen in the metal, and substitutions of cobalt, iron and Ti + Co also contributed to a slight increase in discharge capacity. It was also found that an anodic oxidation treatment at -0.6 V (vs. Hg-HgO) of the Zr-(V-Ni) electrode surface in an alkaline electrolyte is effective for electrode activation. Furthermore, the addition of a small amount of aluminium (1.5%-2.9%) to the alloy elements improved the durability for charge-discharge cycling.