Electrochemical properties of ZrMnNi1+x hydrogen-storage alloys

In order to improve the performance of the AB2-type hydrogen-storage alloy for nickel–metal hydride Ni–MH secondary battery, AB2-type ZrMnNi1+x hydrogen-storage alloys were prepared and their electrochemical properties were investigated. 4 Laves phase formed in all the alloys ZrMnNi1+x (x=0.0–0.4). The lattice parameters a and c, and the volumes of the unit cell for the alloys tend to decrease as the value of x increases. Among these alloys ZrMnNi1.0 was activated after three charge–discharge cycles and had the largest discharge capacity of 42 mAh/g. For all the alloys Zr was dissolved most, on the whole, into the 6 M KOH solution. For the ZrMnNi1.0 alloy Mn was dissolved much more into the 6 M KOH solution, and Ni was dissolved more, as compared with the other alloys. These may be related with the largest discharge capacity of the ZrMnNi1.0 alloy. The absorption and desorption of hydrogen in extended ranges y for ZrMnNi1.0Hy may lead to the greater dissolution of Zr, Mn and Ni. the alloys ZrMnNi1+x (x=0.0–0.4), ZrMnNi1.0 had the largest discharge capacity and a relatively good cycling performance, and it showed the easiest activation. The added or substituted Ni acted as the catalyst for the electrochemical reaction.