Hydrogen Absorption Desorption Characteristics Research Articles

Hydrogen sorption properties of graphite-modified magnesium nanocomposites prepared by ball-milling

The hydrogen absorption–desorption characteristics of the nanocomposites 90 wt.% Mg 2Ni–10 wt.% C (graphite) and 75 wt.% Mg–15 wt.% Mg 2Ni–10 wt.% C obtained by mechanical alloying have been investigated. Modification with graphite has been found to improve the hydriding kinetics of Mg 2Ni at a temperature of 573 K and below. The composite 75 wt.% Mg–15 wt.% Mg 2Ni–10 wt.% C has a high hydrogen absorption capacity and is characterised by very good kinetic parameters of hydriding at 473 and 423 K. Modification of the surface of this composite with graphite accelerates the desorption of hydrogen. The results obtained as well as the XPS data have confirmed the opinion expressed previously by several authors about the effect of graphite on the magnesium oxide layer present on the composite surface during hydriding. The difference observed between the dehydriding rates of the two graphite-containing composites is probably due to a difference in size of the interface formed on both magnesium systems as a result of hydrogen absorption.

Hydrogen sorption properties of the nanocomposites Mg–Mg 2Ni 1− xCo x obtained by mechanical alloying

The hydrogen absorption–desorption characteristics of magnesium composites containing 10 and 15 wt.% Mg 2Ni 1− x Co x ( x=0.1 and 0.3) obtained by mechanical alloying in an inert atmosphere have been investigated. A significant improvement of the hydriding kinetics of these composites has been established, the high absorption capacity being preserved even at temperatures below 573 K. The catalytic effect of the intermetallic additive on the hydriding of magnesium has been explained as due to the presence of Ni and Co clusters in the nanocomposites, the increase of the specific surface area during mechanical alloying and the formation of MgNi 2 and Mg 2NiH 4 phases.

Effect of Excess Vacancies on Hydrogen Absorption-Desorption Characteristics in Rapidly Solidified B2 TiCo

Effect of Excess Vacancies on Hydrogen Absorption-Desorption Characteristics in Rapidly Solidified B2 TiCo

Hydrogenation characteristics of the proton conducting oxide–hydrogen storage alloy composite

Hydrogen absorption–desorption characteristics of a proton conducting oxide, SrCe 0.95Yb 0.05O 3− δ , were investigated using an electrochemical technique for the first time. It is suggested that the oxide can electrochemically repeat hydrogen absorption and desorption like hydrogen storage alloys. Subsequently, we attempted to improve activation properties of a hydrogen storage alloy, MmNi 3.72Co 0.60Mn 0.45Al 0.32, by mixing the proton conducting oxide. As a result, the oxide–alloy composite was found to enhance the activation performance of anode in Ni–metal hydride battery. The proton conducting oxide lying on the surface corrosion layer of alloy particles plays a role as a new path for hydrogen atoms to go into the alloy.

Effects of annealing treatment on phase structures, hydrogen absorption–desorption characteristics and electrochemical properties of a V 3TiNi 0.56Hf 0.24Mn 0.15Cr 0.1 alloy

The effects of annealing treatment on the phase structures, hydrogen absorption–desorption characteristics and electrochemical properties of the V 3TiNi 0.56Hf 0.24Mn 0.15Cr 0.1 alloy have been studied. It is found that both the as-cast and annealed alloys consist of a main phase with b.c.c. structure and a C14-type secondary phase with hexagonal structure. With increasing annealing temperature, the lattice parameters of two phases decrease and the volume fraction of the main phase increases slightly. The present results indicate that annealing treatment decreases the maximum hydrogen desorption capacity, which could be attributed to a decrease in stability of alloy hydride due to the decrease in cell volume of the alloy phases. Furthermore, increasing annealing temperature decreases the high rate capability and deteriorates the durability of the alloy electrode in the alkaline electrolyte during charging–discharging cycles, which would be associated with the change in composition of the secondary phase and the grain growth of the main phase.

Hydrogen absorption–desorption characteristics, kinetics of hydrogen absorption and thermodynamics of dissolved hydrogen in Zr 0.1Tb 0.9Fe 1.5Co 1.5

The hydrogen absorption and desorption pressure–composition isotherms of the PuNi 3 type rhombohedral Zr 0.1Tb 0.9Fe 1.5Co 1.5 are investigated by using a Sieverts’ type apparatus based on pressure reduction method in the ranges 75≤ T(°C)≤150 and 0.01≤ P(bar)≤30. The hydrogen solubility properties are compared with those of Zr 0.1Tb 0.9Fe 3 to study the effect of Co substitution at the Fe site. The P–C isotherms show the α→(α+β) transition at an average hydrogen concentration ( y= n H/ n fu) of 0.2 and (α+β)→β transition at an average value of y=2.5. Further, the plateau pressure of Zr 0.1Tb 0.9Fe 1.5Co 1.5–H at any given temperature increases when compared to that of Zr 0.1Tb 0.9Fe 3–H. It is found that hysteresis is quite small in the temperature regions investigated. At a hydrogen concentration of 3.1 hydrogen atoms per formula unit, the host lattice is accompanied by an expansion of about 16% without any change in crystal structure as evidenced by powder X-ray diffraction studies of Zr 0.1Tb 0.9Fe 1.5Co 1.5H 3.1. The thermodynamical parameters viz., the relative partial molar enthalpy (Δ H H) and the relative partial molar entropy (Δ S H) of dissolved hydrogen are found to be in the ranges −(17–23) kJ(mol H) −1 and −(48–66) JK −1(mol H) −1 respectively for absorption and, +(19–23) kJ(mol H) −1 and +(46–72) JK −1(mol H) −1 for desorption. From the dependence of Δ H H on y, the different phases [α, (α+β), β] and phase boundaries [α→(α+β)], [(α+β)→β] of the alloy–hydrogen system are identified. The different phases identified by the thermodynamic studies agree well with those seen in the hydrogen absorption isotherms of the respective alloy. These phases are further confirmed through powder X-ray diffraction studies. The kinetic studies show that the rate of hydrogen absorption is relatively slow when compared with Zr 0.1Tb 0.9Fe 3–H.

Effect of annealing treatment on electrochemical properties of Mm-based hydrogen storage alloys for Ni/MH batteries

Several multi-component Mm-based hydrogen storage alloys with cobalt content from 0.8–1.0 have been prepared. The hydrogen absorption–desorption characteristics in gas–solid reactions and the electrochemical properties as MH electrodes have been investigated. The addition of small amounts of Al effectively lowers the hydrogen equilibrium pressure and improves the cycling stability of the alloys. Electrochemical measurements show that the MmNi 3.4Co 1.0Mn 0.5Al 0.1 alloy exhibits a maximum electrochemical capacity of ∼322 mA h g −1 with a capacity decay of about 19.5% after 100 cycles. Annealing treatments flatten the plateau region and lower the hydrogen equilibrium pressure, which results in an increase of hydrogen uptake below 1 atm. The increasing trend of hydrogen storage capacity from the as-cast sample to the annealed sample in the gas–solid reactions is in good agreement with the electrochemical results. The electrochemical discharge capacity of the MmNi 3.4Co 1.0Mn 0.5Al 0.1 alloy increases to 334 mA h g −1 and 340 mA h g −1 after annealing for 3 h and 28 h, respectively, from 322 mA h g −1 in the as-cast condition. The electrochemical cycling stability of the annealed samples was also greatly improved. The capacity decay for both annealed samples is about 8.3% and 6.8%, respectively, after 100 charge–discharge cycles. It was suggested that annealing treatments enhance the compositional homogeneity and cause the secondary phase (separated phase) to dissolve in main phase, which result in the improvement of electrochemical cycling stability of the alloy electrodes.

バナジウムまたはジルコニウムとチタン‐コバルト‐マンガン系およびチタン‐コバルト‐鉄系四元合金の水素吸蔵，放出特性

中温域(100～150℃)の熱を有効利用する金属水素化物ヒートポンプに利用するチタン系合金め特性改善を目的として,TiCo0.5Mn0.5M'0.05およびTiCo0.5Fe0.5・M'0.05 (M'= V, Zr)の水素吸蔵,放出特性について検討した。これらの合金は水素と容易に反応し,TiCo0.5 Mn0.5 V 0,05H1.4,TiCo0.5Mn0.5 Zr0.05H1.6,TiCo0.5Fe0.5V0.05H1.4およびTiCo0.5Fe0.5V0.05H1.4(水H1 素含有量:1.3,1.4,1.3および1.3wt%)の水素化物を120℃,4MPaで生成した。TiCo0.5Mn0.5V0.05-H,TiC0.5Fe0.5Zr0.05-HおよびTiCo0.5Fe0.5Zr0.05-H系の120。Cの解離圧は,0.2,0.15,0.41および0.28MPaで,圧力-組成等温線から求めたエンタルピー変化は,-41.8,-46.0,-41.8および-46.0kJ/mol H2であった。TiCo0.5Fe0.5Zr0.05の圧力-組成等温線のプラトーは明瞭でほぼ水平に近い。この合金はヒートポンプシステムの熱貯蔵材としての利用に適した特性を示した。

Hydrogen absorption-desorption characteristics of MmNiAlM and MmNiMnM 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 MmNi 5− x Al(Mn) y−zM z and MmNi 5− x Al(Mn) y M 2 (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( P a P d )) for MmNi 4.7Al 0.3M 0.1 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 MmNi 4.5Mn 0.5 than for MmNi 4.5Mn 0.5Zr 0.005 and MmNi 4.5Mn 0.5Zr 0.1.

Hydrogen storage properties of Ti 1 + xCr 2− yMn y alloys

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 Ti 1 + x Cr 2− y Mn y (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. Ti 1 + x Cr 2− y Mn y reacted readily with hydrogen to form hydrides at a hydrogen pressure of 40 atm and −20 °C. The reversible hydrogen storage capacity of Ti 1.2Cr 2−yMn y 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.

Structure and properties of amorphous metal hydrides

Current progress in investigations of the structure and properties of amorphous metal hydrides, including hydrogen absorption-desorption characteristics, hydrogen-induced surface segregation, the static and dynamic environments around hydrogen atoms, the electronic density of states, positron annihilation and normal and superconducting properties, is reviewed.

Hydrogen absorption-desorption characteristics of Ti-Co-Fe Alloys

The hydrogen absorption and desorption characteristics of Ti-Co-Fe alloys were investigated. Alloys of composition TiCo 1− x Fe x ( x = 0.05 − 0.5) were found to have the same cubic structure as TiCo and they reacted readily with hydrogen to form the hydrides TiCo 0.95Fe 0.05H 1.2, TiCo 0.7Fe 0.3H 1.2 and TiCo 0.5Fe 0.5H 1.2 (hydrogen contents, 1.1 wt.%) under a hydrogen pressure of 30 atm at room temperature. The dissociation pressures of these hydrides are dependent on the iron content x (the iron partially substitutes for the cobalt) and the value of log P H 2 increases gradually with increasing x. The enthalpy change on hydride formation, determined from the dissociation isotherms for the TiCo 0.5Fe 0.5-H system, is −10.1 kcal (mol H 2) −1; this value is smaller than those (−13.8 kcal (mol H 2) −1 and −11.2 kcal (mol H 2) −1 respectively) of the TiCo-H and TiCo 0.5Mn 0.5-H systems. The temperature required to produce a dissociation pressure of 1 atm is 70 °C, which is lower than the temperatures required for TiCo (130 °C) or TiCo 0.5Mn 0.5 (90 °C). A value of 6.2 kcal mol −1 was obtained for the apparent activation energy of hydrogen desorption. For TiCo 0.5Fe 0.5, only two cycles under mild conditions are needed for the activation treatment so the alloy can easily be activated. The hydrogen absorption-desorption cycles were repeated 30 times but no variation in the hydrogen absorption-desorption capacity was observed. The hydride of TiCo 0.5Fe 0.5 proved to be suitable for use as a hydrogen storage material.

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

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 MmNi 5 and TiCo hydrides we studied the hydrogen absorption-desorption characteristics of ternary alloys such as Mm 1− x A x Ni 5 (A  Ca, Ti; x = 0.1−0.75), MmNi 5− y B y (B  Al, Co, Cr, Mn; y = 0.1 − 4), Ti 1− x A x Co and TiCO 1− x A x (A  Cr, Cu, Fe, La, Mn, Ni, V; x = 0.05− 0.5). The hydrides of MmNi 4.5Al 0.5, MmNi 2.5Co 2.5, MmNi 4.5Cr 0.5, MmNi 4.5Mn 0.5, TiCo 0.5Mn 0.5 and TiCo 0.5Fe 0.5, judged according to an appropriate set of criteria, rank higher than or equal to those of LaNi 5, MmNi 5, TiFe and TiCo and have properties suitable for a stationary hydrogen storage material.

Hydrogen absorption-desorption characteristics of titanium-cobalt-manganese alloys

The hydrogen absorption and desorption characteristics of Ti-Co-Mn alloys were investigated. Alloys of composition TiCo 1− x Mn x ( x = 0.05 – 0.5) were found to have the same cubic structure as TiCo and they reacted readily with hydrogen to form the hydrides TiCo 0.95Mn 0.05H 1.4, TiCo 0.9Mn 0.1H 1.4, TiCo 0.8Mn 0.2H 1.6 and TiCo 0.5Mn 0.5H 1.7 (hydrogen content 1.3, 1.3, 1.4 and 1.6 wt.% respectively) under a hydrogen pressure of 30 atm at room temperature. The dissociation pressures of these hydrides are dependent on the manganese content x (the manganese partially substitutes for the cobalt) and the value of log P increases gradually with increasing x. In addition, with increasing x, the width of the plateau in the isotherms becomes greater than that of TiCo hydride and the hydrogen content increases. The enthalpy change on hydride formation determined from the dissociation isotherms for the TiCo 0.5Mn 0.5−H system is −11.2 kcal (mol H 2) −1; this value is smaller than that of the TiCo-H system. The temperature required to produce a dissociation pressure of 1 atm is 90 °C, which is lower than the temperature required for TiCo (130 °C). The desorption rate of hydrogen for TiCo 0.5Mn 0.5 is greater than that for TiCo, and a value of 9.9–11.4 kcal mol −1 was obtained for the apparent activation energy of hydrogen desorption. For TiCo 0.5Mn 0.5, only two cycles under mild conditions are needed for the activation treatment so the alloy can be easily activated. The hydrogen absorption-desorption cycles were repeated 30 times but no variation in the hydrogen absorption-desorption capacity was observed. The hydride of TiCo 0.5Mn 0.5 proved to be suitable for use as a hydrogen storage material.