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

The Zr-V-Ni system multicomponent alloys were investigated by electrochemic al measurements, X-ray diffraction analysis, scanning electron microscopy, and energy-dispersive spectroscopy At room temperature, the discharge capac ity 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 temp erature because higher contents of V and Mn (i.e., (V + Mn)/AB(2) = 0.8) fo rm more stable hydrides. Al substitution also stabilizes the hydrides effec tively. All these alloys have discharge capacities of about 350 mAh g(-1) o n 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 cy cling, 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 su itable for all hydride electrodes as well. (C) 1999 The Electrochemical Soc iety. S0013-4651(98)06-050-9. All rights reserved.