Tatsuoki Kohno

Hydrogen storage properties of new ternary system alloys: La2MgNi9, La5Mg2Ni23, La3MgNi14

The hydrogen storage properties of the new ternary system alloys, La2MgNi9, La5Mg2Ni23, La3MgNi14, were investigated. As a result, the negative electrode of the La5Mg2Ni23 alloy (La0.7Mg0.3Ni2.8Co0.5) showed a large discharge capacity (410 mAh/g), 1.3 times larger than that of AB5 type alloys. These ternary system alloys were found to be mainly composed of stacked AB5 and AB2 structure subunits in a superstructure arrangement.

Effect of Partial Substitution on Hydrogen Storage Properties of Mg2Ni Alloy

The effect of partial substitution on the hydrogen storage properties of Mg{sub 2}Ni was investigated. It was found that as a result of substitution of Mg with a more electronegative element (Al or Mn), absorption of hydrogen easily occurs at lower temperature. The alloy powder prepared with a mechanical grinding method was also studied. This alloy powder was found to be mainly changed to an amorphous-like state by this treatment. Consequently, the negative electrode of the mechanically ground Mg{sub 2}Ni alloy shows a large discharge capacity, 750 mAh/g, which is two and one-half times that of AB{sub 5} type alloys. It was also found that the hydrogen reversibility of the mechanically ground Mg{sub 1.9}A{sub 0.1}Ni alloy electrode remarkably increased.

The Hydrogen Storage Properties of New Mg2Ni Alloy

The hydrogen storage properties of a novel Mg{sub 2}Ni alloy powder prepared with a mechanical grinding method were investigated. This alloy powder was transformed to an amorphous-like state by this treatment. As a result, an electrode of this alloy shows a large discharge capacity (750 mAh/g) which is 2.5 times higher than that of AB{sub 5}-type alloys. This significant improvement of hydrogen storage properties seems to be achieved by the increase in the crystal boundary and a heterogeneous strain in this alloy. The hydrogen equilibrium pressure of this alloy increased markedly.

Electrochemical properties of mechanically ground Mg2Ni alloy

The electrochemical properties of Mg 2 Ni type alloy powder prepared with a mechanical grinding (MG),of Mg 2 Ni and Ni or Pd powders were investigated. This alloy powder was found to be mainly changed to an amorphous-like matrix with dispersed nano-size Ni or Pd particles by the MG treatment. As a result, the negative electrode of the mechanically ground Mg 2 Ni alloy with Ni showed a large discharge capacity (830 mAh/g) which is 2.5 times larger than that of AB 5 type alloys. In the mechanically ground Mg 2 Ni alloy with Pd, the cycle life of the alloy electrode was considerably improved. The effect of partial substitution on the hydrogen storage properties of Mg 2 Ni was also investigated. It was found that the hydrogen reversibility of the mechanically ground Mg 1.9 M 0.1 Ni (M=Al, B, C, Ag) alloy electrode was remarkably improved by the substitution of Mg with more electronegative elements.

Hydrogen storage properties of La(Ni0.9M0.1)3 alloys

Abstract The hydrogen storage properties of LaNi 3 -type hydrogen storage alloys were investigated in order to increase the capacity of rechargeable nickel–metal hydride batteries. By partially substituting a foreign metal at Ni sites, the discharge capacity of La(Ni 0.9 M 0.l ) 3 (M=Al, Fe, Mn, Si, Sn, Cu) alloy electrodes could be increased at room temperature. In particular, La(Ni 0.9 Al 0.l ) 3 and La(Ni 0.9 Mn 0.l ) 3 alloy electrodes showed significantly higher hydrogen storage capacities and markedly better reversibilities than LaNi 3 .

Mixing Effect of Metal Oxides on Negative Electrode Reactions in the Nickel‐Hydride Battery

Negative electrodes for use in nickel-hydride batteries were prepared from MmNi[sub 3.6]Mn[sub 0.4]Al[sub 0.3]Co[sub 0.7] (Mm = misch metal with the composition of 24.87% La, 52.56% Ce, 5.57% Pr, 16.86% Nd, and 0.14% Sm) alloy being mixed with RuO[sub 2] or Co[sub 3]O[sub 4] powder. Then the hydrogen evolution reactions at the electrodes were investigated by measuring the potential decay immediately after the interruption of an applied cathodic current. The reactions were found to proceed by the Volmer-Tafel mechanism. The total overvoltage ([eta]) was divided into two components ([eta][sub 1] and [eta][sub 2]) corresponding to the Tafel and Volmer reactions. The exchange current densities of the elementary reactions, i[sub 0V] and i[sub 0T], were then evaluated by extrapolating the Tafel lines for [eta][sub 1] and [eta][sub 2]. The Volmer reaction is much more accelerated by surface modification with RuO[sub 2] or Co[sub 3]O[sub 4] powder than the Tafel reaction, which results in the enrichment of adsorbed hydrogen, leading to higher charging efficiency.

Structural analysis of La-Mg-Ni-based new hydrogen storage alloy

The structural analysis of new hydrogen storage alloys, La5Mg2Ni23 and La3MgNi14, was performed using HRTEM. As a result, these ternary system alloys were found to be mainly composed of stacked RNi5 (CaCu5 type) and R2Ni4 (Laves type) structure subunits in a superstructure arrangement. La5Mg2Ni23 alloy is composed of the primitive cell of three LaNi5 units and the primitive cell of two La2Mg2Ni4 units. La3MgNi14 alloy is composed of four LaNi5 and two La2Mg2Ni4 unit cells.