Electrochemical impedance and deterioration behavior of metal hydride electrodes

A brief historical survey is given of how the study of coercitivity mechanisms in SmCo5 permanent-magnet materials eventually led to the discovery of the favourable hydrogen sorption properties of the compound LaNi5. It is shown how continued research by many investigators dealing with a variety of different physical and chemical properties has resulted in an advanced understanding of some of the principles that govern hydrogen absorption and which are responsible for the changes in physical properties that accompany it. The problems associated with various applications of LaNi5-based hydrogen-storage materials are also briefly discussed. A large part of this paper is devoted to the applicability of LaNi5-type materials in batteries. Research in this area has resulted in the development of a new type of rechargeable battery: the nickel-hydride cell. This battery can be charged and discharged at high rates and is relatively insensitive to overcharging and overdischarging. Special attention is given to the nature of the electrode degradation process and the effect of composition variations in LaNi5-related materials on the lifetime of the corresponding hydride electrodes when subjected to severe electrochemical charge-discharge cycles.

From permanent magnets to rechargeable hydride electrodes

Study of two-dimensional heat and mass transfer during desorption in a metal-hydrogen reactor

Electrochemical behaviour of intermetallic-based metal hydrides used in Ni/metal hydride (MH) batteries: a review

The use of metal hydrides in fuel cell applications

The electrochemical capacities and the durabilities for charge and discharge cycling of Ti1−YZrYNiX alloy hydride electrodes were examined. It was found that the zirconium-rich alloys such as Ti0.5Zr0.5Ni1.0, Ti0.2Zr0.8Ni1.35 and Ti0.2Zr0.8Ni1.25 have considerably large capacities and good durabilities. Nickel or copper plating on hydride powder was very effective in improving the durability. In addition, a coefficient was introduced to evaluate quantitatively the durability.

Capacities and durabilities of TiZrNi alloy hydride electrodes and effects of electroless plating on their performances

Electrochemical Properties of Zr–V–Ni System Hydrogen-Absorbing Alloys of Face-Centered Cubic Structure

The hydrogen-absorbing capacities, the discharging capacities and the corrosion resistance of TiNix (x = 0.5–1.0) and zirconium-substituted Ti1−yZryNix (y = 0.05–0.7) electrodes were examined. The zirconium-substituted alloy electrode generally had a larger capacity and a better corrosion resistance than the TiNix electrode. It is believed that the stable passive oxide film formed on the surface protects the underlying metal from oxidation. Zirconium substitution helps in the formation of this film, but sometimes inhibits hydrogen discharge.

Electrochemical capacities and corrosion of TiNix and its zirconium-substituted alloy hydride electrodes☆

In order to develop a high capacity hydrogen-absorbing alloy electrode based on the Zr−(V−Ni) system pseudobinary Laves phase compound, partial substitutions by titanium, cobalt, iron and manganese were attempted. It was found that substitution of manganese for 25% of the nickel increases the discharge capacity by 20% owing to a remarkable increase in absorbed hydrogen content. The Zr(V0.33Ni0.50Mn0.17)2.4 electrode exhibited a large discharge capacity of 366 mA h g−1 at a current density of 10 mA cm−2. Substitution of titanium for zirconium and substitutions of cobalt and iron for nickel improved the discharge efficiency of hydrogen owing to an increase in the partial molar enthalpy of hydrogen in the metal, and substitutions of cobalt, iron and Ti+Co also contributed to a slight increase in discharge capacity. It was also found that an anodic oxidation treatment at −0.6 V (vs Hg−HgO) of the Zr−(V−Ni) electrode surface in an alkaline electrolyte is effective for electrode activation. Furthermore, the addition of a small amount of aluminium (1.5%–2.9%) to the alloy elements improved the durability for charge-discharge cycling.

Shinjiro Wakao

Papers

Capacities and durabilities of TiZrNi alloy hydride electrodes and effects of electroless plating on their performances

Electrochemical Properties of Zr–V–Ni System Hydrogen-Absorbing Alloys of Face-Centered Cubic Structure

Electrochemical capacities and corrosion of TiNix and its zirconium-substituted alloy hydride electrodes☆

Effects of partial substitution and anodic oxidation treatment of Zr−V−Ni alloys on electrochemical properties

Effects of Oxidation Treatment of Ti — Zr — Ni Hydride Electrodes Containing Zr7Ni10 Phase on Their Electrochemical Properties*