Effect of partial substitution of nickel by tin, aluminum, manganese and palladium on the properties of LaNi5-type metal hydride alloys

Elki C Souza,Edson A Ticianelli

doi:10.1590/s0103-50532003000400009

Abstract

This work reports studies on the electrochemical behavior of AB5-type hydrogen storage alloys, formed by LaNi(5-x)Zx, where Z is a metallic element partially replacing Ni, which included Sn, Al, Mn, and Pd. In the case of Mn, some AB6-type structures were also considered. Substitution of a small fraction of Ni by Al, Sn, and Mn (x @ 0.3) leads to an increase of the hydrogen storage capability (HSC), while for Pd there is a decrease of this property. Generally all alloys presenting larger initial HSC exhibit lower stability. A decrease of the hydrogen equilibrium pressure as a function of Mn content is observed for the AB5 alloys and this is related to an increase of the crystalline unit cell volume. Electrochemical impedance measurements show a significant increase of the hydration/dehydration reaction kinetics due to a raise on the active area as a function of the charge/discharge cycle number. It is also seen that the alloys presenting larger HSC are those showing smaller activation energies for the hydrogen oxidation reaction.

Highlights

The use of metal-hydride (MH) alloys as negative electrode material in rechargeable alkaline batteries has grown in recent years, because of its high energy density, high rate capability, and environmental acceptability
Substitution of a small fraction of Ni by Al, Sn, and Mn leads to an increase of the hydrogen storage capability of the metal hydride alloys, while for Pd the effect is the opposite
No correlations can be established between the hydrogen storage capability (HSC) and the unit cell volumes, indicating that electronic effects of the substituents on the Ni band occupancy are more important than the changes in the cell volume to define the HSC

Summary

Introduction

The use of metal-hydride (MH) alloys as negative electrode material in rechargeable alkaline batteries has grown in recent years, because of its high energy density, high rate capability, and environmental acceptability. In this work a comparative study of the effects of Ni substitution by Sn, Al, Pd, and Mn atoms on the charge storage capacity, the cycling life, the hydrogen equilibrium pressure, and the charge-discharge reaction kinetics in AB -

Results

Conclusion