Absorption Plateau Pressure Research Articles

Hydrogen storage properties of AB2 type Ti–Zr–Cr–Mn–Fe based alloys

This investigation explores the solid-state hydrogen storage properties of two series of hydrogen storage alloys: (Ti0.85Zr0.15)xMn0.8CrFe0.2 (x = 1.00∼1.10) and (Ti0.85Zr0.15)1.02MnyCr1.8-yFe0.2 (y = 1.00∼0.40) alloys. These alloys exhibit a single C14-Laves phase structure and demonstrate promising capabilities for solid-state hydrogen storage. The (Ti0.85Zr0.15)xMn0.8CrFe0.2 (x = 1.00∼1.10) alloys display an increased hydrogen absorption capacity and a reduced plateau pressure at higher super-stoichiometric ratios of x. When x = 1.10, the alloy achieves a maximum capacity of 1.86 wt%. The hydrogen storage capacity of the (Ti0.85Zr0.15)1.02MnyCr1.8-yFe0.2 (y = 1.00∼0.40) alloys diminishes as the value of y decreases. Furthermore, the hydrogen absorption plateau pressure and hysteresis factor of the alloys increase with an escalating Mn/Cr ratio. The analysis of cyclic stability reveals that the primary factor contributing to poor cycling stability of the (Ti0.85Zr0.15)1.02Mn0.4Cr1.4Fe0.2 alloy is the compositional decomposition, rather than pulverization or alterations in the phase structure.In summary, this investigation enhances our understanding of the solid-state hydrogen storage properties of these alloys. It establishes a foundation for further research and development in this pivotal field of hydrogen storage.

Experimental study of the microstructures and hydrogen storage properties of the LaNi4Mn0·5Co0.5 alloys

In the present study, the absorption and desorption kinetics of hydrogen and the isotherm (P–C-T)) of the LaNi4Mn0·5Co0.5 alloy were measured at values of 283 K, 303 K, and 313 K. The morphological states of this sample were examined using characterization techniques, including X-ray diffraction and scanning electron microscopy. The thermodynamic functions for the absorption-desorption of hydrogen by hydrides, such as enthalpy (H) and entropy (S), were calculated from the experimental data or by using a model that exists in the literature and is premised on the adjustment of isotherm curves at various temperatures. This model is based on an integrated form of the Van't Hoff equation and a simultaneous examination of the isotherms. According to the experimental results, the amount of hydrogen absorbed or desorbed by the sample is significantly affected by the partial substitution of the nickel atom by the elements Mn and Co. However, this substitution increased the absorption or de-sorption plateau pressure.

Effect of Mn substitution on plateau pressure regulation of the Ti0.92Zr0.1Cr1.6−xMnxFe0.4 alloys for primary hydrogen compressor

The Ti0.92Zr0.1Cr1.6−xMnxFe0.4 (x = 0.15, 0.3, 0.45, 0.6 at%) alloys were synthesized by vacuum electric arc furnace. The effect of Mn substitution on plateau pressure regulation of these alloys was investigated for the primary hydrogen compressor. With increasing Mn content, the hydrogen absorption/desorption plateau pressures of the Ti0.92Zr0.1Cr1.6−xMnxFe0.4 (x = 0.15, 0.3,0.45,0.6 at%) alloys increased, the plateau slope factor decreased, meanwhile, both enthalpy and entropy change values decreased. The Ti0.92Zr0.1Cr1.0Mn0.6Fe0.4 alloy had the best comprehensive performance. Based on the pressure composition isotherms measurement, the plateau pressure and hydrogen storage capacity were obtained at 298–363 K. The hydrogen absorption/desorption curves of the Ti0.92Zr0.1Cr1.0Mn0.6Fe0.4 alloy at 353 and 363 K were firstly tested by experiment method. At 298 K, the hydrogen absorption plateau pressure and maximum capacity were 7.82 MPa and 1.79 wt%. At 363 K, the hydrogen desorption plateau pressure and maximum capacity were 27.21 MPa and 1.54 wt%. Hydrogen pressure from 8 MPa to 25 MPa was successfully obtained at 298–363 K, satisfying operating temperature and pressure requirements for the primary hydrogen compression materials.

Enhanced hydrogen storage properties of Ti–Cr–Nb alloys by melt-spin and Mo-doping

Ti–Cr–Nb hydrogen storage alloys with a body centered cubic (BCC) structure have been successfully prepared by melt-spin and Mo-doping. The crystalline structure, solidification microstructural evolution, and hydrogen storage properties of the corresponding alloys were characterized in details. The results showed that the hydrogen storage capacity of Ti–Cr–Nb ingot alloys increased from 2.2 wt% up to around 3.5 wt% under the treatment of melt-spin and Mo-doping. It is ascribed that the single BCC phase of Ti–Cr–Nb alloys was stabilized after melt-spin and Mo-doping, which has a higher theoretical hydrogen storage site than the Laves phase. Furthermore, the melt-spin alloy after Mo doping can further effectively increase the de-/absorption plateau pressure. The hydrogen desorption enthalpy change ΔH of the melt-spin alloy decreased from 48.94 kJ/mol to 43.93 kJ/mol after Mo-doping. The short terms cycling test also manifests that Mo-doping was effective in improving the cycle durability of the Ti–Cr–Nb alloys. And the BCC phase of the Ti–Cr–Nb alloys could form body centered tetragonal (BCT) or face center cubic (FCC) hydride phase after hydrogen absorption and transform to the original BCC phase after desorption process. This study might provide reference for developing reversible metal hydrides with favorable cost and acceptable hydrogen storage characteristics.

Improvement of hydrogenation sorption properties of Ti0.90V0.30Mn1.00Ni0.80 for ultra-high pressure metal-hydride compressor

Metal-hydride compressors are considered as an alternative to mechanical compressors in Hydrogen Refueling Stations. In this paper, several Ti-based AB2 compounds were synthesized and their hydrogen sorption properties were evaluated under ultra-high pressure up to 40 MPa. All the studied compounds exhibit absorption plateau pressure close to or higher than 10 MPa at 30 °C. The substitution by a small amount of Al was shown to drastically decrease the hysteresis. All the compounds herein studied follow the trend ln(P)∝−V0, except for the Nb-containing compound. This compound has a different behavior towards hydrogenation and exhibits sorption pressure much higher than expected from the above-mentioned relationship. It was confirmed that the Al and Nb substitution in AB2 compounds plays a great role on reducing hysteresis and increasing the sorption pressure, respectively.

Hydrogen storage properties of Pr-Mg-Ni- based alloys prepared by vacuum induction melting

Pr5Mg95-xNix(x = 5,10,15) alloys were melted in a vacuum induction furnace. The phase composition, microstructure and storage properties of gaseous hydrogen were investigated using X-ray diffractometry (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The hydrogen storage properties of the alloy were systematically studied, including activation property, hydrogen absorption capacity, comminution property and plateau pressure. The results show that PrMg12 and Mg2Ni are the main and secondary phases of the alloys, respectively. As the Ni content increases, the activation ability is improved, and the hydrogen uptake ability reaches the best level at the first activation. The hydrogenation process leads to many cracks and fractures in the alloy, which reduces the grain size. PCT test results show that the alloy has two plateaus caused by the reversible processes of Mg ⇄ MgH2 and Mg2Ni⇄Mg2NiH4 during the hydrogenation cycle. The change of Ni content has a significant effect on the hysteresis effect during hydrogen cycling. PrH2.93 has poor thermal stability and can be easily decomposed into PrH2.

Microstructural characterization and hydrogenation performance of ZrxV5Fe(x=3-9) alloys

ZrxV5Fe(x = 3, 5, 7, 8, 9) alloys were designed to investigate the influence of Zr addition on hydrogenation performance. The alloys were prepared by arc melting and then annealed at 1273K for 168 h. The results showed that the alloys were composed of α-Zr and C15–ZrV2 phases. The cell volume of C15–ZrV2 phase firstly increased and then decreased as the content of Zr increased, while the reversed trend was found for the cell volume of α-Zr phase, which was related to the stoichiometric ratio of elements. α-Zr phase distributed in C15–ZrV2 phase matrix in ZrxV5Fe(x = 5, 7, 8, 9) alloys, among which Zr7V5Fe alloy showed the best distribution. The PCT curves of the alloys under 623 K, 673 K and 723 K showed that the hydrogen absorption plateau pressure of the phases in different alloys decreased gradually with the increasing content of Zr. However C15–ZrV2 phase in Zr7V5Fe alloy had the lowest hydrogen absorption plateau pressure at room temperature, which was consistent with the change tendency of the corresponding cell volume. Moreover, the kinetic curves of hydrogen absorption at 623 K revealed that Zr7V5Fe alloy with the smallest average particle size and the largest phase boundary area showed the fastest hydrogen absorption kinetics. Compared with other four alloys(including St707 alloy), Zr7V5Fe alloy is more suitable for the use of getter.

High‐pressure hydrogen storage properties of Ti x Cr 1 − y Fe y Mn 1.0 alloys

TixCr1 − yFeyMn1.0 (x = 1.02, 1.05, 1.1, 0.05 ≤ y ≤ 0.25) alloys were prepared by plasma arc melting and annealing at 1273 K for 2 hours. The XRD results show that the main phase of all alloys is the C14 type Laves phase, and a little secondary phase exists in a mixture of the binary alloy phase. The lattice parameters increase with Ti super-stoichiometry ratio increasing, whereas smaller lattice parameters emerge with increasing Fe stoichiometry content. Additionally, as the Ti super-stoichiometry ratio decreases, the pressure-composition-temperature measurements indicated that hydrogen absorption and desorption plateau pressures of TixCr0.9Fe0.1Mn1.0 (x = 1.1, 1.05, 1.02) alloys increase from 3.15, 0.67, to 5.94, 1.13 MPa at 233 K, respectively. On the other hand, with the Fe content increasing in Ti1.05Cr1 − yFeyMn1.0 (0.1 ≤ y ≤ 0.25) alloys from 0.1 to 0.25, the hydrogen desorption plateau pressures increased from 1.41 to 2.46 MPa at 243 K. The hydrogen desorption plateau slopes reduce to 0.2 with Ti super-stoichiometry ratio decreasing to 1.02, but the alloys are very difficult to activate for hydrogen absorption and cannot activate when the Fe substituting for Cr exceeds 0.2. The maximum hydrogen storage capacities were more than 1.85 wt% at 201 K. The reversible hydrogen storage capacities can remain more than 1.55 wt% at 271 K. The enthalpy and entropy for all hydride dehydrogenation are in the range of 21.0 to 25.5 kJ/mol H2 and 116 to 122 J mol−1 K−1, respectively. Our results suggest that Ti1.05Cr0.75Fe0.25Mn1.0 alloy with low enthalpy holds great promise for a high hydrogen pressure hybrid tank in a hydrogen refueling station (45 MPa at 333 K), and the other alloys of low cost may be used for a potable hybrid tank due to high dissociation pressure at 243 K and high volumetric density exceeding 40 kg/m3.

Study on the hydrogen storage property of (TiZr0.1)xCr1.7-yFeyMn0.3 (1.05

The hydrogen storage of (TiZr0.1)xCr1.7-yFeyMn0.3 (1.05 <x < 1.2, 0.2 <y < 0.6) alloys, prepared by Ar plasma arc melting, were investigated by X-ray diffraction, pressure-composition- temperature (PCT). The results indicated that all (TiZr0.1)xCr1.7-yFeyMn0.3 (1.05 ≤x ≤ 1.2, 0.2 ≤y ≤ 0.6) alloys were determined as C14-type Laves phase, the cell parameters a, c and unit cell volume of (TiZr0.1)xCr1.1Fe0.6Mn0.3 (1.05 ≤x ≤ 1.2) alloys increased with increasing the (TiZr) super-stoichiometry from 1.05 to 1.2, and the value of a/c almost unchanged. The hydrogen absorption and desorption plateau pressure decreased from 5.6, 4.4–2.6, 2.2 MPa with the increase of (TiZr) super-stoichiometry from 1.05 to1.2 at 274 K respectively, and the hydrogen desorption plateau pressure decline was not obvious when the (TiZr) super-stoichiometry exceeded 1.15. The (TiZr0.1)1.1Cr1.1Fe0.6Mn0.3 alloy had the best comprehensive properties about the maximum and reversible hydrogen storage capacity was 1.79 and 1.45 wt% respectively. The cell parameters a, c and unit cell volume of (TiZr0.1)1.1Cr1.7-yFeyMn0.3(0.2 ≤y ≤ 0.6) alloys increased as the ratio of Fe/Cr content decreased. The hydrogenation and dehydrogenation plateau pressure decreased from 4.5, 3.4–1.0, 0.9 MPa respectively and the maximum hydrogen storage capacity increased from 1.79 to 2.0 wt% as the Fe content reduced from 0.6 to 0.2 at 274 K. The maximum and the reversible hydrogen storage capacity were about 2.0 and 1.65 wt% as the ratio of Fe/Cr was 0.13 (ie, (TiZr0.1)1.1Cr1.5Fe0.2Mn0.3 alloy), its relative molar enthalpy of dissociation hydrogen was 24.30 kJ/mol H2.

Hydrogen storage properties of (Ti0.85Zr0.15)1.05Mn1.2Cr0.6V0.1M0.1 (M=Ni, Fe, Cu) alloys easily activated at room temperature

The (Ti0.85Zr0.15)1.05Mn1.2Cr0.6V0.1M0.1 (M=Ni, Fe, Cu) alloys with a single C14-type Laves phase have been fabricated by arc melting. They are able to be easily activated by one hydrogen absorption and desorption cycle under 4MPa hydrogen pressure and vacuum at room temperature. Partial substitution of M for Mn results in the increase of hydrogenation and dehydrogenation capacities in an order of Ni < Fe < Cu. M elements increase the absorption and desorption plateau pressure in an order of (Ti0.85Zr0.15)1.05Mn1.2Cr0.6V0.1Cu0.1 < (Ti0.85Zr0.15)1.05Mn1.2Cr0.6V0.1Fe0.1 < (Ti0.85Zr0.15)1.05Mn1.2Cr0.6V0.1Ni0.1. The (Ti0.85Zr0.15)1.05Mn1.2Cr0.6V0.1Cu0.1 alloy has reversible hydrogen capacities of 1.81wt% at 273 K and 1.58wt% at 318K with formation enthalpy (ΔHab) of −20.66kJmol−1 and decomposition enthalpy (ΔHde) of 27.37kJmol−1. The differences in the hydrogen storage properties can be attributed to the increase of the interstitial size for hydrogen accommodation caused by the increase of unit cell volumes in the order of (Ti0.85Zr0.15)1.05Mn1.2Cr0.6V0.1Ni0.1 < (Ti0.85Zr0.15)1.05Mn1.2Cr0.6V0.1Fe0.1 < (Ti0.85Zr0.15)1.05Mn1.2Cr0.6V0.1Cu0.1.

Hydrogenation improvement of TiFe by adding ZrMn2

In this paper, we report the microstructure and hydrogen storage properties of TiFe + x wt.%ZrMn2 (x = 2, 4, 8, 12) alloys prepared by arc melting. Each alloy was made of two phases: a TiFe phase with very small amount of zirconium and manganese, and a second phase which has a higher proportion of zirconium and manganese. We found that the first hydrogenation kinetics increase with x. This is most likely due to the presence of zirconium-rich secondary phase that acts as a gateway for hydrogen to enter the main TiFe phase. Pressure-composition isotherms also show that increasing x decreases the absorption plateau pressure. Moreover, for x = 12, air exposure had a minimal impact on hydrogen absorption behaviour. Finally, we found that cold rolling has minimal effect on the activation kinetics of TiFe + x wt.%ZrMn2 (x = 4) alloy.

Delaminated MoS2 as a structural and functional modifier for MgH2 – Better hydrogen desorption kinetics through induced worm-like morphologies

Magnesium hydride (MgH2) nanoparticles have been synthesized in the presence of MoS2 via a simple hydrogenolysis route, involving the decomposition of di-n-butylmagnesium. Remarkably using delaminated MoS2 instead of bulk MoS2 led to the formation of magnesium worm-like structures, which collapsed and recrystallized to some extent upon hydrogen cycling. Hydrogen release from these structures occurred at a relatively low temperature (300 °C), and MoS2 was found to effectively improve the hydrogen desorption kinetics of nanosized MgH2. It took less than 150 min to fully release hydrogen from MgH2 catalyzed by delaminated MoS2. In comparison, uncatalysed nanosized MgH2 particles required more than 300 min. Furthermore, MoS2 was found to significantly influence the thermodynamic properties of the Mg/MgH2 reaction, via the destabilization of the Mg–H bond. Compared to ball-milled MgH2, the MoS2 modified materials showed significantly higher hydrogen absorption plateau pressures (∼0.15 MPa). This demonstrates that pathways enabling the tuning of the hydrogen storage properties of nanosized MgH2 toward lower temperatures and fast kinetics may exist.

Structural and Hydriding Properties of the LaZr2Mn4Ni5-AB3 Type Based Alloy Prepared by Mechanical Alloying from the LaNi5 and ZrMn2 Binary Compounds

In this study, we report on the synthesis of a new AB3-type compound LaZr2Mn4Ni5 (with a content of 40 wt %) at room temperature during 5h of mechanical alloying. This compound was synthesized from the two binary compounds LaNi5 (CaCu5-type structure, P6/mmm space group) and ZrMn2-Laves phase (MgZn2-type structure, P63/mmc space group) in order to take advantage of the hydrogen absorption properties of these two types of intermetallic compounds. Structural properties were investigated using X-ray diffraction (XRD). The surface morphology of the cycled electrode was observed by a scanning electron microscope (SEM). The electrochemical properties of the LaZr2Mn4Ni5–based alloy were determined using the chrono-potentiometry method. The experimental results indicate that the discharge capacity reaches a maximum value of 300 mAh/g. Solid-gaz reaction shows that this compound is able to form the LaZr2Mn4Ni5H13 hydride at room temperature at an absorption plateau pressure of about 7 bar.

Hydrogen storage properties of in-situ stabilised magnesium nanoparticles generated by electroless reduction with alkali metals

As strong reducing agents, alkali metals including Li, Na and K enable the electroless synthesis of magnesium nanoparticles. In this investigation, we determined the effects of such alkali metals on the properties of magnesium at the nanoscale. The magnesium nanoparticles were successfully synthesised by directly reducing di-n-butylmagnesium with an excess amount of alkali-metal naphthalenide in order to coat individual magnesium nanoparticles within an alkali matrix. Upon heat treatment under hydrogen pressure a perovskite structure MMgH3 was formed on Na- and K-coated magnesium nanoparticles under mild conditions but was absent on the Li-coated materials leading to LiH only. These perovskite structures were found to have no significant influence on the thermodynamics of magnesium. Compared to ball-milled MgH2, these materials showed lower hydrogen absorption plateau pressure (∼0.05 MPa). However, the magnesium particles generated with potassium had fast hydrogen kinetics and low reaction enthalpy due to their small size. More remarkably these coated magnesium nanoparticles remained stable upon cycling which provides a new route to stabilise magnesium nanoparticles.

Influence of annealing treatment on the microstructure and hydrogen storage performance of Ti1.02Cr1.1Mn0.3Fe0.6 alloy for hybrid hydrogen storage application

The as-cast Ti1.02Cr1.1Mn0.3Fe0.6 alloy for hybrid hydrogen storage vessel application was annealed at different temperatures (873K, 973K, 1123K, 1173K) for 2h, and annealed at 1123K for different time (2, 5, 8h) respectively, and their microstructure and hydrogen storage properties were investigated systematically. The results show that the as-cast alloy has a single C14 Laves phase, and all annealed alloys consist of a C14 Laves main phase and a secondary phase. After annealing at different temperatures for 2h, the hydrogen absorption pressure at 298K decreases, however, the maximum hydrogen storage capacity and desorption pressures at 318K decrease slightly too. As the annealing time extends, the hydrogen absorption plateau pressure at 298K and hydrogen desorption plateau pressure at 318K increase, and the hydrogen desorption capacity increases first and then decreases, which reaches the highest desorption capacity of 1.721wt.% at the annealing time of 5h. Among the studied alloys, the alloy annealed at 1123K for 5h has the best overall properties for hybrid hydrogen storage application, its hydrogen absorption plateau at 298K is 29.09MPa, its hydrogen desorption plateau pressure at 318K is 45.12MPa, its hydrogen storage capacity is 1.721wt.% and its dissociation enthalpy (ΔHd) is 17.78kJ/mol H2.

Hydrogen storage performance of TiFe after processing by ball milling

Activation of TiFe for hydrogen storage by severe plastic deformation (SPD) through ball milling technique and the effect of microstructure on this activation have been investigated. TiFe becomes activated after the ball milling and is not deactivated after exposure to air, similar to TiFe activated by high-pressure torsion (HPT). The hydrogenation capacity reaches 1.3–1.5wt.% at 303K for the first to third cycles and the hydrogen absorption plateau pressure decreases to ∼1MPa for any hydrogenation cycles. Observation of the microstructure after ball milling shows that the average grain size and crystallite size are as small as ∼7 and ∼11nm, respectively (smaller than that after HPT or rolling), but few dislocations are detected within the detection limit of high-resolution transmission electron microscopy. This study shows clearly that there is a strong relation between the grain size of TiFe and its activation for hydrogen absorption: the activation is easier and the hydrogen pressure for activation is smaller, when the grain size is smaller.

Crystal structures and hydrogenation–dehydrogenation characteristics of Er(Ni1−xMnx)2

Abstract The crystal structures and hydrogenation–dehydrogenation characteristics of Er(Ni 1− x Mn x ) 2 compounds are investigated in this work. It is found that either annealing or hydrogenation leads to ordering transition of ErNi 2 from MgCu 2 -type structure to TmNi 2 -type superstructure. As Mn content is within x = 0.2–0.8 and 0.9–1, Er(Ni 1 − x Mn x ) 2 compounds have C15 and C14 structures, respectively. The hydrogen absorption content of the C15-type Er(Ni 1 − x Mn x ) 2 increases with raising Mn content x , however, the absorption plateau pressure decreases gradually and hydrogen desorption becomes difficult. ErMn 2 can absorb hydrogen to form irreversible ErMn 2 H 3.4 and reversible ErMn 2 H 4.8 at 3.5 × 10 −5 and 1.5 × 10 −1 MPa, respectively. Nevertheless, the C14-type Er(Ni 0.1 Mn 0.9 ) 2 compound is subjected to decomposition into ErMn 2 H z and ErNi 2 H y during hydrogen absorption.

Improving the Cyclic Stability of V&amp;ndash;Ti&amp;ndash;Mn bcc Alloys Using Interstitial Elements

The effect of nitrogen interstitial atoms on the cyclic stability of V0.37Ti0.33Mn0.3 was investigated. V0.37Ti0.33Mn0.3 with and without nitrogen were hydrogenated and dehydrogenated for 100 times. During hydrogen cycling, the hydrogen absorption plateau pressure of both samples decreased significantly but the desorption plateau pressure stayed the same resulting in smaller hysteresis at higher cycle. Their reversible hydrogen storage capacity progressively diminished with increasing cycle number. At the first cycle, V0.37Ti0.33Mn0.3 without nitrogen absorbed more hydrogen than V0.37Ti0.33Mn0.3 with nitrogen but at the 100th cycle the situation was reversed; V0.37Ti0.33Mn0.3 with nitrogen showed a higher reversible hydrogen storage capacity. This result strongly suggests that nitrogen interstitial atoms somehow retard the degradation of the hydrogen storage capacity of V0.37Ti0.33Mn0.3.

Development of Ti–Cr–Mn–Fe based alloys with high hydrogen desorption pressures for hybrid hydrogen storage vessel application

Three series of Ti–Cr–Mn–Fe based alloys with high hydrogen desorption plateau pressures for hybrid hydrogen storage vessel application were prepared by induction levitation melting, as well as their crystallographic characteristics and hydrogen storage properties were investigated. The results show that all of the alloys were determined as a single phase of C14-type Laves structure. As the Fe content in the TiCr1.9−xMn0.1Fex (x = 0.4–0.6) alloys increases, the hydrogen absorption and desorption plateau pressures increase, and the hydrogen storage capacity and plateau slope factor decrease respectively. The same trends are observed when increasing the Mn content in the TiCr1.4−yMnyFe0.6 (y = 0.1–0.3) alloys, except for the plateau slope factor. Compared with the stoichiometric TiCr1.1Mn0.3Fe0.6 alloy, the titanium super-stoichiometric Ti1+zCr1.1Mn0.3Fe0.6 (z = 0.02, 0.04) alloys have larger hydrogen storage capacities and lower hydrogen desorption plateau pressures. Among the studied alloys, Ti1.02Cr1.1Mn0.3Fe0.6 has the best overall properties for hybrid hydrogen storage application. Its hydrogen desorption pressure at 318 K is 41.28 MPa, its hydrogen storage capacity is 1.78 wt.% and its dissociation enthalpy (ΔHd) is 16.24 kJ/mol H2.

Hydrogen isotherms for annealed, un-activated LaNi5 (273–333 K)

Hydrogen absorption isotherms (273–333K) have been measured for closely stoichiometric, annealed, un-activated LaNi5, i.e., a virgin un-activated LaNi5 sample was employed at each temperature. This is the first time that such isotherms have been measured for annealed, un-activated LaNi5 at such low temperatures ⩽298K. After measurement of the initial absorption isotherms, the second absorption and desorption isotherms have been measured at each temperature. Van’t Hoff plots have been made from these absorption and desorption plateau pressure data and, from these, ΔHplat values have been obtained for the initial and subsequent absorption and desorption reactions. The ∣ΔHplat∣ determined from the van’t Hoff plot is smaller for the initial isotherm for the annealed, un-activated form of LaNi5 than it is for activated LaNi5.