Characteristics of the superstoichiometric C15-tyge Laves phase alloys and their hydride electrodes

Laves phase alloy hydrides have some promising properties as electrode materials in reversible metal hydride batteries. In this work, the hydrogen storage performance, crystallographic parameters, surface state and electrochemical characteristics of the superstoichiometric Zr(V-Mn-Ni-Mo)(2.4) alloys were examined. These as-cast pseudobinary alloys were found to have mainly a cubic C15-type Laves phase structure by X-ray diffraction analysis. The plateau pressure of the hydrides obtained from desorption P-C isotherms was in the range 10(-3)-0.1 MPa at 30 degrees C with [H]/[M] capacities of about 1.0. Some electrodes exhibited electrochemical capacities of about 300 mA h g(-1). Molybdenum-containing alloy hydride electrodes showed a better electrocatalytic activity by means of electrochemical impedance spectroscopy. This was attributed to both the improvement of the alloy surface state and the synergism of molybdenum and nickel in the electrocatalytic reaction. The discharge capacity and high rate capability of the alloy electrodes were correlated not only to the electrocatalytic activity of the electrodes but also to the hydrogen storage performance of the hydrides.