Hydrogen Absorbing Properties Research Articles

Enhancing hydrogen storage performance via optimizing Y and Ni element in magnesium alloy

Magnesium-based hydrogen storage materials are considered as one of the most promising candidates for solid state hydrogen storage due to their advantages of high hydrogen capacity, excellent reversibility and low cost. In this paper, Mg91.4Ni7Y1.6 and Mg92.8Ni2.4Y4.8 alloys were prepared by melting and ball milling. Their microstructures and phases were characterized by X-ray diffraction, scanning electron microscope and transmission electron microscope, and hydrogen absorbing and desorbing properties were tested by the high pressure gas adsorption apparatus and differential scanning calorimetry (DSC). In order to estimate the activation energy and growth mechanism of alloy hydride, the JMAK, Arrhenius and Kissinger methods were applied for calculation. The hydrogen absorption content of Mg92.8Ni2.4Y4.8 alloy reaches 3.84 wt.% within 5 min under 350 ℃, 3 MPa, and the maximum hydrogen capacity of the alloy is 4.89 wt.% in same condition. However, the hydrogen absorption of Mg91.4Ni7Y1.6 alloy reaches 5.78 wt.% within 5 min, and the maximum hydrogen absorption of the alloy is 6.44 wt.% at 350 ℃ and 3 MPa. The hydrogenation activation energy of Mg91.4Ni7Y1.6 alloy is 25.4 kJ/mol H2, and the enthalpy and entropy of hydrogen absorption are -60.6 kJ/mol H2 and 105.5 J/K/mol H2, separately. The alloy begins to dehydrogenate at 210 ℃, with the dehydrogenation activation energy of 87.7 kJ/mol H2. By altering the addition amount of Ni and Y elements, the 14H-LPSO phase with smaller size and ternary eutectic areas with high volume fraction are obtained, which provides more phase boundaries and catalysts with better dispersion, and there are a lot of fine particles in the alloy, these structures are beneficial to enhance the hydrogen storage performance of the alloys.

Resistivity Testing of Palladium Dilution Limits in CoPd Alloys for Hydrogen Storage.

Palladium satisfies most of the requirements for an effective hydrogen storage material with two major drawbacks: it has a relatively low gravimetric hydrogen density and is prohibitively expensive for large scale applications. Pd-based alloys should be considered as possible alternatives to a pure Pd. The question is how much one can dilute the Pd concentration in a variety of candidate materials while preserving the hydrogen absorption capability. We demonstrate that the resistivity measurements of thin film alloy samples can be used for a qualitative high-throughput screening and study of the hydrogen absorbing properties over the entire range of palladium concentrations. Contrary to palladium-rich alloys where additional hydrogen scattering indicates a degree of hydrogen content, the diluted alloy films respond by a decrease in resistance due to their thickness expansion. Evidence of significant hydrogen absorption was found in thin CoPd films diluted to just 20% of Pd.

Experimental studies of hydrogen-absorbing properties of intermetallic compound LaNi4.4Fe0.3Al0. 3 for hydrogen purification

Hydrogen/methane mixtures draw attention due to the idea of the injection of hydrogen into natural gas networks and biological production of biohythane by one- and two-step anaerobic fermentation/digestion methods. It is hard to extract hydrogen from dilute mixtures with methane by traditional separation processes, since hydrogen is the minor component with low partial pressure. Metal hydrides selectively absorb hydrogen and offer an opportunity to overcome the limitations of traditional separation methods. Intermetallic alloy of lowered pressure LaNi4.4Fe0.3Al0.3 was made (obtained) to use it in the extraction of hydrogen out of a mixture of gases. Hydrogen absorption properties of alloy were investigated. PCT isotherms between 313K and 353K, porosity, average particle size, specific surface area and permeability of metal hydride bed were measured, X-ray diffraction (XRD) and SEM investigation of bed structure were implemented. Experimental study of processes during the extraction of hydrogen out of binary mixture H2-CH4 (10% vol.-90% vol.) were carried out by means of continuous-flow metal hydride reactor RSP-8, filled with 1 kg of LaNi4.4Fe0.3Al0.3. Recover ratio with the mixture pressure of 1.0 MPa stood at 70%.

Gaseous hydrogen storage properties of Mg-Y-Ni-Cu alloys prepared by melt spinning

For purpose of promoting the hydrogen absorption and desorption thermodynamics and kinetics properties of MgNi-based alloys, partially substituting Y and Cu for Mg and Ni respectively and melt spinning technique were applied for getting Mg25–xYxNi9Cu (x = 0–7) alloys. Their microstructures and phases were characterized with the help of X-ray diffraction and transmission electron microscopy. Their hydrogen absorbing and desorbing properties were tested by a Sievert apparatus, DSC, and TGA, which were connected with a H2 detector. In order to estimate the dehydrogenation activation energy of alloy hydride, both Arrhenius and Kissinger methods were applied for calculation. It is found that their hydriding kinetics notably declines, however, their hydrogen desorption kinetics conspicuously improves, with spinning rate and Y content increasing. Their hydrogen desorption activation energy markedly decreases under the same constraint, and it is found that melt spinning and Y substituting Mg improve the real driving force for dehydrogenation. As for the tendency of hydrogen absorption capacity, it presents an elevation firstly and soon after a decline with the rising of spinning rate, however, it always lowers with Y content growing. With Y content and spinning rate increasing, their thermodynamic parameters (ΔH and ΔS absolute values) visibly decrease, and the starting hydrogen desorption temperatures of alloy hydrides obviously lower.

Synthesis of TiFe Hydrogen Absorbing Alloys Prepared by Mechanical Alloying and SPS Treatment

This study aims to clarify the influence of the Spark Plasma Sintering (SPS) method on structural morphology, mechanical properties and also functional characteristics, such as hydrogen absorbing properties, for titanium-iron intermetallic compounds. We could synthesize B2-TiFe phase using mechanical alloying (MA) during 3 h and SPS treatment of 5 min at 500–1000 °C, which was confirmed by XRD and Electron Probe Microanalyzer (EPMA) measurements. In addition, the synthesized TiFe intermetallic compound has been found to absorb hydrogen with high kinetics in both high pressure Differential Scanning Calorimetry (DSC) and Pressure-Composition-Temperature (PCT) measurements. Therefore, we have successfully developed TiFe alloy in bulk form from initial raw powders by using a combination of short period mechanical alloying and SPS heat treatment. This combined route enhances the potential of the SPS method to synthesize new materials.

Preparation of nickel modified activated carbon/AB5 alloy composite and its electrochemical hydrogen absorbing properties

Due to the good catalysis of metal nickel for the electrochemical reduction/oxidation reactions between H2O and H in alkaline electrolyte, it is separately introduced into activated carbon (AC) by ball milling (named AC-1), liquid phase reduction (AC-2) and hydrothermal (AC-3) methods. The results of scanning electron microscopy (SEM) show that different to the aggregation of metal nickel in AC-1 and the coating of metal nickel on the surface of AC-2, metal nickel introduced by the hydrothermal method is uniformly dispersed among the AC-3 particles. The AC-3/AB5 alloy (90 wt%) composite shows the best electrochemical hydrogen absorbing activity. Its capacity at a 0.2 C rate reaches to 318 mA h/g. Compared to the AB5 alloy electrode, its discharge capacity separately increases 16% at a 1 C rate and 59% at a 3 C rate, which is particularly suitable for the high-power nickel metal-hydride (Ni–MH) battery.

Structure and hydrogen absorbing properties of ScCrMn alloy

The crystal structures of ScCrMn alloy and its hydride are determined by XRD Rietveld analysis and TEM examination. The ScCrMn alloy exhibits a rarely ideal close-packed C14 type hexagonal Laves phase structure with lattice parameters a = 5.064(1), c = 8.263(2) Å, deviating from the ANOE dependent rule on Laves phase structure. The hydrogenation of the alloy to ScCrMnH 3.9 results in significant lattice expansion of 27%, but does not alter the matrix lattice structure. The XRD pattern of the hydride also shows close-packed structure with little line broadening, comparable to that of the alloy, indicating a high degree of crystallinity, where the hydrogen atoms are homogeneously distributed in evenly distributed interstitials with minimal defects. The alloy demonstrates extremely easy activation property. The alloy can be activated at a low pressure of 0.46 kPa and exhibit very fast absorption rate at sub-atmosphere at room temperature. The hydrogenation thermodynamics of the alloy are evaluated by P– C– T measurements at different temperatures. At hydrogen concentration H/M = 0.66 corresponding to a defined room temperature plateau pressure, the relative partial molar enthalpy Δ H and entropy Δ S derived by Van’t Hoff equation are −63 kJ/mol and −111 J/mol K, respectively. These results manifest that the hydride stability of the ScCrMn alloy is comparable to those of the hydrogen isotope storage alloys of ZrCo and ZrTi 0.2V 1.8, and would be superior on relevant applications. The DSC–TG measurements of the hydride reveal that the total release of hydrogen can basically be achieved at 653 K, accompanied by an oxidation reaction with residual oxygen to form water vapor. The results indicate that the alloy is an effective catalyst for the dissociation of hydrogen and combination of oxygen.

Anomalous hydrogen absorption on non-stoichiometric iron-carbon compound

On the synthesis of nano-structural hydrogenated graphite by ball-milling under H 2 atmosphere, iron contamination was mingled from steel balls during ball-milling. It is clarified by spectroscopic measurements that the mingled iron formed a non-stoichiometric iron–carbon (Fe–C) compound. The Fe–C phase was transformed to a well-ordered phase with H 2 desorption at 450 °C, suggesting that the hydrogen atoms were anomalously trapped at the Fe–C phase. With respect to hydrogen absorbing properties, the mingled iron enhanced the hydrogen capacity by about 50% compared with iron free hydrogenated graphite, where H/Fe was about 13 mass%. Therefore, if the hydrogen absorption site originated in the Fe–C phase could be synthesized independently, it should be recognized as a promising hydrogen storage system.

Mg/Ti multilayers: Structural and hydrogen absorption properties

Mg-Ti alloys have uncommon optical and hydrogen absorbing properties, originating from a ``spinodal-like'' microstructure with a small degree of chemical short-range order in the atomic distribution. In the present study we artificially engineer short-range order by depositing Pd-capped Mg/Ti multilayers with different periodicities. Notwithstanding the large lattice mismatch between Mg and Ti, the as-deposited metallic multilayers show good structural coherence. On exposure to ${\text{H}}_{2}$ gas a two-step hydrogenation process occurs with the Ti layers forming the hydride before Mg. From in situ measurements of the bilayer thickness $\ensuremath{\Lambda}$ at different hydrogen pressures, we observe large out-of-plane expansions of Mg and Ti layers on hydrogenation, indicating strong plastic deformations in the films and a consequent shortening of the coherence length. On unloading at room temperature in air, hydrogen atoms remain trapped in the Ti layers due to kinetic constraints. Such loading/unloading sequence can be explained in terms of the different thermodynamic properties of hydrogen in Mg and Ti, as shown by diffusion calculations on a model multilayered systems. Absorption isotherms measured by hydrogenography can be interpreted as a result of the elastic clamping arising from strongly bonded Mg/Pd and broken Mg/Ti interfaces.

Influence of the Ti/Zr ratio and the synthesis route on hydrogen absorbing properties of (Ti1−xZrx)Mn1.5V0.5 alloys

The hydrogenation properties of two pseudo-binary Ti 1− x Zr x Mn 1.5 V 0.5 alloys with x =0.15 and 0.5 obtained by arc melting and mechanical alloying have been studied. All alloys crystallize in the hexagonal C14 Laves phase. Arc-melted alloys are microcrystralline and exhibit local variations of Ti and Zr contents which are not overcome by annealing treatments. As for milled alloys, agglomerated nanocrystallites (∼9 nm in diameter) are obtained after subsequent thermal annealing at 800 °C. For high Zr-contents, a better chemical homogeneity is obtained by the milling route. Whatever the synthesis route is, the hydrogen equilibrium pressure decreases with increasing Zr content due to cell-volume increase of the intermetallic compound. As concerns kinetics, very fast hydrogenation rates of few seconds are obtained at room temperature, particularly for milled alloys.

Composition dependence of hydrogen absorbing properties in melt quenched and annealed TiMn2 based alloys

We have investigated the hydrogen absorbing properties of binary TiMn2 based alloys with the compositions ranging from Ti–56.4 to 66.8at.% Mn, which were prepared by melt quenching and subsequent annealing, as well as arc melting and subsequent annealing for comparison. All the alloys are composed of TiMn2 and TiMn phases, where the volume fraction of the TiMn2 Laves phase increases with increasing Mn content. In the annealed alloys with Ti–56.4 to 59.4at.% Mn, the Mn content of the TiMn2 phase is about 60at.%; whereas in the alloys beyond 59.4at.%, it increases with increasing the Mn content of the alloys. Correspondingly, the hydrogen absorbing capacity of the alloys increases with increasing the Mn content up to 59.4at.%, but rapidly decreases with a further increase of the Mn content. These observations suggest that the alloy composition exhibiting the maximum hydrogen absorbing capacity is determined by a compromise of a high volume fraction and a low Mn content of the TiMn2 phase. In addition, we found that rapidly solidified alloys exhibited poor hydrogenation behavior. Therefore, it is concluded that the hydrogen absorbing capacity of the TiMn2 based alloys is mainly governed by the composition of alloy and probably by the atomic arrangement of excess Ti atoms within the TiMn2 phase.

Hydrogen absorbing properties and structures of Ti–Cr–Mo alloys

Ti–Cr–Mo alloys show different hydrogenation properties to Ti–Cr–V and Ti–Mn–V hydrogen absorbing alloys with b.c.c. structure. Ti–Cr–Mo alloys have a smaller solid solution range (<0.5 wt.%) than Ti–Cr–V (<1.3 wt.%). In order to understand this difference, crystal structure and hydrogenation behaviors were investigated by X-ray diffraction and pressure–composition isotherms (P–C–T) measurements. Most of the alloys investigated were single bcc phase. The relation of the plateau pressure vs. lattice volume of Ti–Cr–Mo alloys was opposite to Ti–Cr–V and many of conventional intermetallic alloys. The new parameter, the radius of tetrahedral hydrogen site, is introduced. This new parameter gives a linear relationship with the plateau pressure for both Ti–Cr–Mo and Ti–Cr–V alloys. Hydrogen capacity of Ti–Cr–Mo and Ti–Cr–V are the same in a hydrogen to metal ratio basis. Slight addition of V to Ti–Cr–Mo alloys leads to dramatic increase of solid solution range.

Effect of composition on hydrogen absorbing properties in binary TiMn 2 based alloys

The hydrogen absorbing properties of binary TiMn 2 based alloys have been investigated as a function of composition in the range between Ti–56.4 and –66.8 at% Mn. The volume fraction of TiMn 2 phase increases with increasing Mn content. The Mn content of TiMn 2 phase is almost constant at compositions between Ti–56.4 and –59.4 at% Mn, while it increases with increasing Mn content at compositions between Ti–59.4 and –66.8 at% Mn. Ti–59.4 at% Mn containing TiMn 2 phase with 60 at% Mn exhibits the superior hydrogen absorption capacity and the least degradation of capacity during repeated hydrogen absorption and desorption. It is concluded that both hydrogen absorbing capacity and cyclic property in binary TiMn 2 based alloy are improved by increasing the volume fraction of TiMn 2 phase with keeping Mn content as low as possible.

レビテーション溶解したＴｉ‐Ｃｒ‐Ｖ系合金の水素吸蔵特性

Recently, hydrogen absorbing alloys are used as the negative electrode of nickel-metal hydride secondary batteries, hydrogen storage of the polymer electrolyte fuel cells, and so on. An improvement of hydrogen-absorbing properties is required, because hydrogen storage capacity of the alloy is thought to be insufficient for the hydrogen storage use. In addition, the alloy is required to show small hysteresis factor and plain plateau slope in P-C-T curve for practical use. Levitation melting, which is well-known for preparing way to obtain high purity alloys, is a promising method for the production of high performance hydrogen absorbing alloy, since the impurity such as the oxygen brings a deterioration of hydrogen absorbing properties. In this study, we have first tried the levitation melting method to prepare the hydrogen absorbing alloy. Ti-Cr-V alloys were successfully prepared by levitation melting method with special structural water-cooled cooper crucible. The characteristics of these alloys were investigated and the following results were obtained: (1) Microstructure of the Ti-Cr-V alloy by levitation melting was more homogeneous than that prepared by arc-melting. (2) The Ti-Cr-V alloys prepared by levitation melting contained lower impurity than those prepared with refractory crucible. (3) The effective hydrogen storage capacity of Ti6.5Cr13V79Mn1.5 alloy by levitation melting was more than 2.1 mass%. Furthermore the plateau slope in P-C-T curve was very flat (0.16 Np/mass%), and hysteresis factor was very small (0.49 Np). From the above results, the levitation melting method is thought to be suitable for the production method for hydrogen absorbing alloys with high performance.

Role of intermetallics in hydrogen storage materials

Many intermetallics such as AB 5, AB 2, A 2B show the excellent hydrogen absorbing properties. Specially, LaNi 5 compound has been extensively studied for the negative electrode of Ni–MH batteries. In today's use for the negative electrode of Ni–MH batteries, alloys must be single phase. But it is well known that it is difficult to make non-stoichiometric LaNi 5 alloys as single phase because of its limited solid-solution range. The present study describes the rapid quenching effects on the solid-solution range of La(Ni, M) x ( x=3–5) alloys prepared by melt spinning in discussing their hydrogen absorption properties. It is found that the single phase with CaCu 5 crystal structure extends to LaNi 4.65 compositional alloys. For fuel cell automobile, the alloys with high content of hydrogen must be developed. Strong candidates for this will be Vanadium based BCC alloys, which would be hard to be activated. Since it is well known that the Laves phases undergo easy activation treatment, it may be possible that the BCC phases will be easily activated if the alloys contain such Laves phases. The present study also found that Zr addition is effective on forming Laves phase as grain boundary phases in BCC phases in V–Ti–Zr–Ni alloys, and on improving the hydrogen absorbing properties. The study will be also extended to future hydrogen absorbing alloys with high capacity.

Hydrogenation properties and crystal structures of Ti−Mn-V BCC solid solution alloys

We have proposed new hydrogen absorbing alloys of the ‘Laves phase related BCC solid solution alloy’, the hydrogen capacity of which reaches almost double that of conventional rare-earth based AB5 alloys. We have reported the hydrogen absorbing properties of Ti−V−Mn, Ti−V−Cr and T−V−Mn−Cr alloys. It has been accepted that the crystal structural change of BCC hydrogen absorbing alloys is the same as that of V metal. The mono-hydride (H/M=1) of V metal has a BCT structure and the di-hydride (H/M=2) has an FCC structure. However, we recently found that the Ti−V−Mn alloy shows different behaviors in phase transformation with hydrogenation to V metal. We found three hydride phases with a BCC, a deformed FCC and an FCC structure in the Ti−V−Mn solid solution alloy-H2 system. The deformed FCC hydride phase has not yet to our knowledge been reported. The lattice constant of the deformed FCC was 0.407 nm, one axis of which is reduced by about 4%. Its single-phase region appeared at a hydrogen content between 0.8 H/M and 1.0 H/M in absorption at 298 K. The lower plateau observed due to formation of the deformed FCC hydride phase gives an increase of effective hydrogen capacity by decreasing hydrogen remaining in the alloy in the desorption process.

ガス噴霧したＴｉ‐Ｖ‐Ｃｒ系水素吸蔵合金の水素吸蔵特性

Recently, hydrogen absorbing alloys are of great need in applications to nickel-metal hydride secondary batteries and the polymer electrolyte fuel cells etc. In particular, Ti-V-Cr hydrogen absorbing alloy has large capacity for hydrogen storage. To increase hydrogen absorbing capacity, the authors investigated the properties of rapidly quenched powder made by gas atomization. It was discovered that the layer of high oxygen content existed on the surface of the gas atomization powder from the result measured by Auger electron spectroscopy. The small hydrogen absorbing capacity in the P-C-T curve was due to the high concentration of oxygen in the alloy. It was thought that the CaO crucible for melting the alloy caused high oxygen concentration. We also studied the relationship between the hydrogen absorbing properties and the oxygen concentration of the alloy by arc melting. As a result, the existence of oxygen had bad influences on hydrogen absorbing capacity, plateau slope and adjustment of plateau pressure.

Improved rapidly-quenched hydrogen-absorbing alloys for development of improved-capacity nickel metal hydride batteries

The effects of annealing a rapidly-quenched hydrogen-absorbing alloy with a stoichiometric ratio of 4.76 were investigated concerning its hydrogen-absorbing properties, crystal structure and electrochemical characteristics. Annealing at 1073 K homogenized the alloy microstructure and flattened its plateau slope in the P–C isotherms. However, annealing at 1273 K segregated a second phase rich in rare earth elements, increased the hydrogen-absorbing pressure and decreased the hydrogen-absorbing capacity. As the number of charge–discharge cycles increases, the particle size distribution of the rapidly-quenched alloy became broad due to partial pulverization. However, particle size distribution of the rapidly-quenched, annealed, alloy was sharp, since the annealing homogenized the microstructure, thereby improving the cycle characteristics. A high-capacity rectangular nickel metal hydride battery using a rapidly-quenched, annealed, surface-treated alloy for the negative electrode and an active material coated with cobalt compound containing sodium for the positive electrode was developed. The capacity of the resulting battery was 30% greater than that of a conventional battery.

Hydrogen absorbing and desorbing properties of Nd–Fe–B and Nd–Co–B amorphous alloys

Hydrogen absorbing and desorbing rates are measured for melt-spun Nd–Fe(or Co)–B amorphous alloys containing 5–30% Nd and 0–15% B. The hydrogen capacity changes with the Nd concentration roughly as ∼3.0 H/Nd, although it is also affected by the B concentration. In alloys where Nd concentration does not exceed 20%, most of the absorbed hydrogen is desorbed from the amorphous phase. X-ray structure analysis shows that the short-range order of the amorphous alloy is maintained before and after the hydrogenation.

Crystal Structure and Hydrogen Absorption Properties of La(Ni, M)&lt;SUB&gt;x&lt;/SUB&gt; (M=Al, Co, Mn, Si. x=3&amp;sim;7) Melt-Spun Ribbons

The present study describes the appeared phases and hydrogen absorbing properties of the non-stoichiometric LaNi X and LaNi x-1 M (M=Al, Co, Mn, Si) melt-spun ribbons. A new metastable phase with TbCu 7 -type structure is observed in LaNi X (x>5) melt-spun ribbons. A high melt-spinning rate is able to form the single phase of the TbCu 7 structure. It is found that the Mn or Si addition stabilizes the CaCu 5 structure in wide compositional range of LaNi X-1 Mn (X=5∼6.5), or LaNi X-1 Si (X=5∼8) melt-spun ribbons. But the amount of absorbed hydrogen decreases with increasing Ni content.