Electrochemical hydrogenation behavior of C15-type Zr(Mn,Ni)2 alloy electrodes

A series of Laves phase AB(2) metal hydride electrodes based on Zr(Mn,Ni), were studied. Partial substitution or addition with Ti,V, and Co was made, and most of the alloys maintained the C15-type structure. The alloy powders were coated with Ni by electroless plating for electrode application. The charge-discharge properties were examined and correlated with the gas-phase hydrogenation properties. Alloys with a large hydrogen desorption capacity, a small hysteresis, and a flat plateau pressure at around 0.1 MPa had better electrochemical performance. During the cyclic charge-discharge test, manganese was decomposed from the electrode, causing degradation of the electrode. Overcharge caused faster degradation of the electrode. Based on the compositions studied, the composition ZrMn0.6V0.2Co0.1Ni1.2 is recommended as a good electrode material. Its discharge capacity at a discharge rate 50 mA/g was similar to 350 mAh/g. It also maintained excellent discharge capacities when discharged at higher rates. (C) 2000 Elsevier Science B.V. All rights reserved.