AB5-type Hydrogen Storage Alloys Research Articles

Characteristics of the Alkaline-pretreated AB5 Type Hydrogen Storage Alloys as the Negative Electrode in Ni-MH Battery.

Study of the surface structures reformed by the alkaline treatment of the rare-earth metal based AB 5 type alloys

Effects of substitution with foreign metals on the crystallographic, thermodynamic and electrochemical properties of AB 5-type hydrogen storage alloys

Effects of substitution with foreign metals on the crystallographic, thermodynamic and electrochemical properties of AB 5-type hydrogen storage alloys were investigated. The unit cell volume of MmNi 5 − x Al x ( Mm = mischmetal, 0.2 ⩽ x ⩽ 1.0) alloys and the values of enthalpy change (−ΔH) in hydride formation increased monotonously with an increase in x-value, but the discharge capacity and high-rate dischargeability had a limiting value. For the MmNi 4.2Al 0.4M 0.4 ( M = Cr, Mn, Fe, Co) alloys, both the unit cell volume and the −ΔH value increased with increasing metallic bond radius of the foreign metal. Especially, manganese improved the discharge capacity and the high-rate dischargeability.

Effect of alloy composition on hydrogen diffusion in the AB 5-type hydrogen storage alloys

Disc-type and powder-type electrodes of hydrogen storage alloys having the compositions MmNi 4.2Al 0.5M 0.3(Mm = misch metal; M  Cr, Mn, Fe, Co, Ni) were used for the evaluation of diffusion coefficients of hydrogen by the potential-step method and the electrochemical measurement of the pressure-composition isotherm respectively. The Einstein diffusion coefficient, being independent of hydrogen concentration, was measured as a function of the atomic radius of foreign metals(M). The diffusion kinetics of the hydrogen atom in the alloys was discussed based on the thermodynamic stability of the resulting hydrides and electrostatic interaction between foreign metals and hydrogen.

Low cost AB5-type hydrogen storage alloys for a nickel-metal hydride battery

The studies have been carried out on utilizing Ml(NiAl)5-based alloys as a low cost negative battery electrode. The replacement of nickel by copper improved the cycle lifetime to some extent without a decrease in capacity. Using Ml(NiAlCu)5 alloys, hydrogen storage alloys with good overall characteristics and low cost were obtained through substituting cobalt or silicon for nickel. The discharge capacity was further increased by increasing the lanthanum content in lanthanum-rich mischmetal.

Passivation behavior of AB 5-type hydrogen storage alloys for battery electrode application

In many applications, AB 5 type hydrogen storage alloys show passivation behavior, i.e. when fully discharged, metal hydride electrodes show (especially at higher temperatures) a decrease in activity and therefore a decrease in capacity at normal discharge currents for ensuing cycles. Passivation may continue to the point where activity becomes so low that the capacity is no longer accessible. Electrochemical measurements were taken of two different AB 5-type alloys, one with manganese and one without manganese (LaNi 3.4Co 1.2Al 0.4 and LaNi 3.4Co 1.2Al 0.3Mn 0.1). Both alloys showed passivation behavior after remaining in the discharged state. The alloy with manganese showed a stronger tendency to passivation which is in contradiction with earlier observations. Photoelectron spectroscopic analysis together with sputter depth profiling was used to investigate the surface composition of samples which had undergone different surface pretreatments. Surface analysis of electrodes in the passivated state shows a lower content of metallic nickel and a thicker nickel surface oxide film. We attribute the low electrochemical kinetics of the alloys after passivation to the loss of metallic nickel and/or cobalt at the electrode-electrolyte interface.

The Hydriding and Dehydriding Kinetics of Some AB5 Type Hydrogen Storage Alloys*

The Hydriding and Dehydriding Kinetics of Some AB₅ Type Hydrogen Storage Alloys*