Electrochemical properties of Zr-V-Ni system hydrogen storage alloys

The Zr-V-Ni system multicomponent alloys were investigated by electrochemical measurements, X-ray diffraction analysis, scanning electron microscopy, and energy-dispersive spectroscopy At room temperature, the discharge capacity of ZrVxMn0.9-xNi1.1 (x = 0.1-0.8) alloys remains at a high level when x = 0.3-0.5. A C15 main phase alloy has good capacity. ZrV0.5Mn0.3T0.1Ni1.1 (T = Ni, Co, Fe, or Al) alloys exhibit lower discharge ability at room temperature because higher contents of V and Mn (i.e., (V + Mn)/AB(2) = 0.8) form more stable hydrides. Al substitution also stabilizes the hydrides effectively. All these alloys have discharge capacities of about 350 mAh g(-1) on heating to 328 K. Our further investigation showed that the substitution of Ti for Zr decreases markedly the thermodynamic stability of the hydrides and promotes a promising discharge capacity at room temperature. During cycling, the preferential anodic oxidation of some components, such as Ti and V, degrades the reversible storage ability. An electrochemical method was adopted to evaluate the PcT isotherm for Zr-based alloys. This method is suitable for all hydride electrodes as well. (C) 1999 The Electrochemical Society. S0013-4651(98)06-050-9. All rights reserved.