Keisuke Oguro

Some factors affecting the cycle lives of LaNi5-based alloy electrodes of hydrogen batteries

The electrode characteristics, the hydrogen equilibrium properties, the crystallographic and mechanical properties of simple ternary alloys of the type LaNi5−xMx(M ≡ Ni, Mn, Cu, Cr, AlandCo) were examined. The effect of substituting elements to improve the cycle life increased in the order: M ≡ Mn, Ni, Cu, Cr, AlandCo. The lower the capacity, the smaller the volume expansion ratio, the slower the pulverizing rate and the lower the Vickers hardness were, the longer the cycle life became. The alloy LaNi2.5Co2.5, which showed the highest durability as a negative electrode, satisfied all these requirements.

The influence of small amounts of added elements on various anode performance characteristics for LaNi2.5Co2.5-based alloys

The addition of small amounts of elements such as silicon, aluminium and titanium to LaNi2.5Co2.5 greatly influenced anode performance characteristics such as usable temperature range, capacity and its decay rate during repeated cycles, rate capability, low temperature dischargeability and self-discharge rate. The capacity decay was suppressed by the addition of silicon, but the rate capability decreased and the self-discharge rate increased. The alloy containing titanium exhibited a much longer cycle life, but much lower storage capacity and worse low temperature dischargeability. The addition of aluminium was very useful for improving the usable temperature range, cycle life and charge retention, and it did not cause too great a decrease in capacity and/or increase in overpotentials.

Self‐Discharge Mechanism of Nickel‐Hydrogen Batteries Using Metal Hydride Anodes

The self-discharge mechanism of nickel-hydrogen batteries using metal hydride anodes is investigated and discussed by dividing the capacity loss during the storage in open-circuit conditions into two parts, i.e., reversible and irreversible ones. The reversible capacity loss is attributed to the desorption of hydrogen from the metal hydride anode and the irreversible capacity loss to the deterioration of the hydrogen-absorbing alloy. Microencapsulation of the alloy with a thin copper layer is found to improve the self-discharge characteristics.

Preparation and properties of hydrogen storage alloy-copper microcapsules

Abstract Fine particles of hydrogen storage alloys such as LaNi5 and MmNi4.5-Mn0.5 (Mm  misch metal) were encapsulated in a thin layer of copper 1–2 μm thick by means of a special chemical plating method. This treatment prevented further disintegration of the metal and improved the thermal conductivity. The alloy-copper microcapsules, which had dimensions of less than 30 μm, were able to absorb hydrogen easily without special activation and exhibited no decrease in hydrogen storage capacity. Pellets obtained by compressing the microencapsulated powder under a pressure of 5–10 tf cm−2 did not show any visible cracks after 1000 hydrogen sorption cycles.

Study of Anode Catalysts and Fuel Concentration on Direct Hydrazine Alkaline Anion-Exchange Membrane Fuel Cells

A platinum-free fuel cell using liquid hydrazine hydrate (N 2 H 4 ·H 2 O) as the fuel and comprised of a cobalt or nickel anode and a cobalt cathode exhibits high performance. In this study, the fuel cell performances using nickel, cobalt, and platinum as anode catalysts are evaluated and compared. It is found that fuel cell performance in the case of nickel and cobalt is higher than that in the case of platinum. Further, anodic reactions are discussed by comparing the hydrazine consumption and ammonia generation when cobalt and nickel are used as anode catalyst. Cobalt exhibits a higher rate of decomposition than nickel. Nickel is found to be the most suitable anode catalyst among the above mentioned anode catalysts for this fuel cell. The influence of hydrazine hydrate and KOH concentrations in the fuel on cell performance is also discussed. Cell performance is the highest at a hydrazine hydrate concentration of 4 M and a KOH concentration of 1 M. The maximum power density of the alkaline anion-exchange membrane fuel cell, comprised of a nickel anode and a Co-PPY-C (cobalt polypyrrole carbon) cathode, is 617 mW cm -2 .

Hydrogen absorption-desorption characteristics of MmNiAlM and MmNiMnM alloys (Mm misch metal)

In order to reduce the large hysteresis effect in MmNi hydrides (Mm  misch metal) we studied the hydrogen absorption-desorption characteristics of multicomponent alloys such as MmNi5−xAl(Mn)y−zMz and MmNi5−xAl(Mn)yM2 (M = Co, Cr, Cu, Nb, Ti, V, Zr; x = 0.3 − 0.5; y = 0.3 − 0.5; z = 0.05 − 0.1). The substitution or addition of the element M eliminates the large hysteresis effect that occurs during an absorption-desorption cycle. The hysteresis factor (equal to In(PaPd)) for MmNi4.7Al0.3M0.1 hydrides decreased for additives M in the following order: Zr > Co > Cr > Ti,V > Cu. Investigations of the effects of cycling showed that spalling occurred more rapidly for MmNi4.5Mn0.5 than for MmNi4.5Mn0.5Zr0.005 and MmNi4.5Mn0.5Zr0.1.

Development of mischmetal-nickel and titanium-cobalt hydrides for hydrogen storage☆

Abstract Fundamental studies were carried out to develop hydrides of mischmetal-nickel (Mm-Ni) and Ti-Co alloys with suitable properties for use as stationary hydrogen storage materials. In order to improve the properties of MmNi5 and TiCo hydrides we studied the hydrogen absorption-desorption characteristics of ternary alloys such as Mm1−x AxNi5 (A  Ca, Ti; x = 0.1−0.75), MmNi5−yBy (B  Al, Co, Cr, Mn; y = 0.1 − 4), Ti1−xAxCo and TiCO1−x Ax (A  Cr, Cu, Fe, La, Mn, Ni, V; x = 0.05− 0.5). The hydrides of MmNi4.5Al0.5, MmNi2.5Co2.5, MmNi4.5Cr0.5, MmNi4.5Mn0.5, TiCo0.5Mn0.5 and TiCo0.5Fe0.5, judged according to an appropriate set of criteria, rank higher than or equal to those of LaNi5, MmNi5, TiFe and TiCo and have properties suitable for a stationary hydrogen storage material.

Preparation and properties of hydrogen storage alloys microencapsulated by copper

Abstract Fine particles of LaNi 5 were coated with a thin porous copper layer about 1 μm thick by a chemical plating method. The encapsulated alloy powder had a hydrogen storage capacity almost equal to that of the original alloy powder and its compacted pellet had a high thermal conductivity, leading to fast reaction kinetics. The pellet was able to withstand more than 5000 repeated hydriding-dehydriding cycles without disintegration.

Hydrogen storage properties of Ti1 + xCr2−yMny alloys

Abstract Fundamental studies were performed with the aim of developing hydrides of titanium-based alloys with suitable properties for hydrogen and energy storage applications. We investigated the hydrogen absorption-desorption characteristics of the alloy Ti1 + xCr2−yMny (0.1 ⩽ x ⩽ 0.3; 0 ⩽ y ⩽ 1). The rate of the initial activation process increased as x was increased, but the reversible hydrogen storage capacity decreased. Ti1 + xCr2−yMny reacted readily with hydrogen to form hydrides at a hydrogen pressure of 40 atm and −20 °C. The reversible hydrogen storage capacity of Ti1.2Cr2−yMny decreased with decreasing manganese content while the plateau pressure increased. The hysteresis in the absorption-desorption isotherms decreased markedly for titanium concentrations in the range 0.2 ⩽ x ⩽ 0.3 and for manganese concentrations in the range 0.5 ⩽ y ⩽ 0.8.

Hydrogen absorption-desorption characteristics of mischmetal-Ni-Cr-Mn alloys

Abstract The hydrogen absorption and desorption characteristics of mischmetal (Mm)-Ni-Cr-Mn alloys were investigated. The alloys MmNi5−yCry−zMnz (y = 0.5; z = 0-0.25) were found to have the same hexagonal structure as LaNi5 and MmNi5, and they reacted readily with hydrogen to form the hydrides MmNi4.5Cr0.5H6.3, MmNi4.5Cr0.46Mn0.04H6.3, MmNi4.5Cr0.45 Mn0.05H6.8 and MmNi4.5Cr0.25Mn0.25H6.9 (hydrogen contents (wt.%) of 1.4, 1.4, 1.5 and 1.6 respectively) under a hydrogen pressure of 25 atm at room temperature. The dissociation pressures of these hydrides were dependent on the manganese content (manganese partially substitutes for chromium) and the value of logP became lower than that for MmNi4.5Cr0.5 hydrides as z was increased. The enthalpy changes on hydride formation as determined from the dissociation isotherms for the MmNi4.5Cr0.5−zMnz-H (z = 0.04, 0.05 and 0.25) systems were − 6.7 kcal (mol H2)−1, −7.1 kcal (mol H2)−1 and −7.1 kcal (mol H2)−1 respectively; these values were smaller than that for LaNi5. The dissociation pressures of these hydrides at 20°C were 4.0 atm, 3.0 atm and 1.9 atm respectively. The desorption rate of hydrogen for MmNi4.5Cr0.46Mn0.04 was larger than those for LaNi5 and MmNi5, and a value of 7.3–7.9 kcal mol−1 was obtained for the apparent activation energy of hydrogen desorption. For MmNi4.5Cr0.46Mn0.04 and MmNi4.5Cr0.25Mn0.25 the hydrogen absorption-desorption cycles were repeated 30 times but no variation in the hydrogen absorption capacity was observed. The hydrides of MmNi4.5Cr0.46Mn0.04 MmNi4.5Cr0.45Mn0.05 and MmNi4.5Cr0.25Mn0.25 have properties which make them suitable as stationary hydrogen storage materials.