Hydrogen Absorption Desorption Properties Research Articles

A new methodology for extra enhancement of hydrogen storage capacity of Mg–Ni based alloys: The role of gaseous O2/H2 mixture

In the present study, Mg–5Ni and Mg–15Ni alloys are prepared, and their (de)hydrogenation properties are investigated by thermal desorption spectroscopy (TDS). A new hydrogenation condition is developed to improve the hydrogen uptake properties of the Mg–Ni alloy. It is found that the hydrogen absorption and thermal desorption properties of both alloys are extremely sensitive to the presence of 3% O2 in the hydrogenation environment. Although O₂ accelerates hydrogen absorption, it lowers the desorption temperature and reduces the hydrogen storage capacity of the Mg–Ni alloy by consuming Mg₂Ni if it is added in every cycle. The hydrogen storage capacity of Mg–Ni alloys can be significantly increased by adding oxygen only in the second cycle instead of in all cycles. In the early stages of hydrogenation, only two TDS peaks are observed, while in later cycles a new peak appears at higher temperatures. These peaks correspond to the decomposition of Mg₂NiH₄ (peak 1), MgH₂ (peak 2), and the release of hydrogen from the bulk material (peak 3). It is also evident that the Mg–15Ni sample has a better hydrogen storage capacity than the Mg–5Ni sample.

Structural Evolution and Hydrogen Sorption Properties of YxNi2−yMny (0.825 ≤ x ≤ 0.95, 0.1 ≤ y ≤ 0.3) Laves Phase Compounds

The YxNi2−yMny system was investigated in the region 0.825 ≤ x ≤ 0.95, 0.1 ≤ y ≤ 0.3. The alloys were synthesized by induction melting and corresponding annealing. The substitution of Mn for Ni (y = 0.1) favors the formation of a C15 structure with disordered Y vacancies against the superstructure of Y0.95Ni2. For y = 0.2 and 0.3, Mn can substitute in both Y and Ni sites. Single-phase compounds with a C15 structure can be formed by adjusting both the Y and Mn contents. Their hydrogen absorption–desorption properties were measured by pressure–composition isotherm (PCI) measurements at 150 °C, and the hydrides were characterized at room temperature by X-ray diffraction and TG–DSC experiments. The PCIs show two plateaus corresponding to the formation of crystalline and amorphous hydrides. The heating of the amorphous hydrides leads to an endothermic desorption at first and then a recrystallization into Y(Ni, Mn)3 and YHx phases. At higher temperatures, the Y hydride desorbs, and a recombination into a Y(Ni, Mn)2 Laves phase compound is observed. For y = 0.1, vacancy formation in the Y site and partial Mn substitution in the Ni site enhance the structural stability and suppress the hydrogen-induced amorphization (HIA). However, for a larger Mn content (y ≥ 0.2), Mn substitutes also in the Y sites at the expense of Y vacancies. This yields worse structural stability upon hydrogenation than for y = 0.1, as the mean ratio r(Y, Mn)/r(Ni/Mn) becomes larger than for y = 0.1 r(Y, ☐)/r(Ni/Mn).

Crystal structure of intermetallic compound Y5Co19 and its hydride phases

Y–Co intermetallic compounds and their hydrides were investigated as magnetic materials, but the hydrogenation of these alloys was not observed. We established the existence of Y5Co19 in the phase diagrams of the Y–Co system. Y5Co19, an intermetallic compound, was synthesized and its crystal structure was determined by the Rietveld refinement of X-ray diffraction (XRD) data. The structural model of Y5Co19 is a Ce5Co19-type model with lattice parameters a = 0.4994 (1) nm and c = 4.800 (1) nm. The crystal structure of the original alloy and its hydride phase is closely related to the hydrogen absorption–desorption property. The hydrogen capacity of Y5Co19 was 0.63 H/M, while two plateaus were observed in the P–C isotherm. We discovered two hydride phases: Y5Co19H3.8 (phase I) and Y5Co19H14.9 (phase II), and the structural model of these phases (I and II) was Ce5Co19-type, which was the same as the original alloy. The unit cell of phase I showed an expansion of 3.9% only along the c-axis from the original alloy, whereas that of phase II indicated an expansion along the a- and c-axes. Additionally, a close isotropic expansion was observed in phase II.

Synergetic effect of multiple phases on hydrogen desorption kinetics and cycle durability in ball milled MgH2–PrF3–Al–Ni composite

A new MgH2–PrF3–Al–Ni composite was prepared by ball milling under hydrogen atmosphere. After initial dehydrogenation and rehydrogenation, Pr3Al11, MgF2, PrH3 and Mg2NiH4 nanoparticles formed accompanying the main phase MgH2. The hydrogen absorption-desorption properties were measured by using a Sieverts-type apparatus. The results showed that the MgH2–PrF3–Al–Ni composite improved cycle stability and enhanced hydrogen desorption kinetics. The improvement of hydrogen absorption-desorption properties is ascribed to the synergetic effect of the in situ formed Pr3Al11, MgF2, PrH3 and Mg2NiH4 nanoparticles. This work provides an important inspiration for the improvement of hydrogen storage properties in Mg-based materials.

Study of hydrogen storage and electrochemical properties of AB2-type Ti0.15Zr0.85La0.03Ni1.2Mn0.7V0.12Fe0.12 alloy

A C15 AB2 Laves-type Ti0.15Zr0.85La0.03Ni1.2Mn0.7V0.12Fe0.12 alloy was prepared by arc melting and annealing. Phase-structural composition, microstructure, hydrogen absorption-desorption properties, thermodynamic and electrochemical performances were characterized by X-ray diffraction, scanning electron microscopy, hydrogen absorption-desorption measurements and electrochemical characterization and were related to the use of the alloys as metal hydride battery anodes.The alloy contains a C15 FCC intermetallic compound as the main phase and a LaNi secondary phase as the minor constituent (∼1 wt%).During the electrochemical tests, the anode electrodes quickly, after just a few activation cycles, reached a maximum discharge capacity. This was related to the catalytic effect of the La-rich secondary phase which acted as a catalyst of hydrogen absorption-desorption.Annealing resulted in increase of the maximum discharge capacity from 345 mAh/g for the as cast alloy to 370 mAh/g. Furthermore, the annealed alloy showed a better high rate dischargeability and a higher cyclic stability. After 100 cycles with 100% DOD at discharge current density of 1C, the discharge capacity of the annealed alloy was very high, at a level of 90% of the initial capacity.The rates of hydrogen diffusion have been characterized by Potentiostatic Intermittent Titration Technique and Electrochemical Impedance Spectroscopy. With increasing an extent of transformation into the hydride, the H diffusion rate in the bulk of the alloy particles decreased. The maximum value of DH measured by PITT for the annealed alloy was observed for the nearly fully discharged electrode, (SOC 2%).

Scale-up of milling in a 100 L device for processing of TiFeMn alloy for hydrogen storage applications: Procedure and characterization

In this work, the mechanical milling of a FeTiMn alloy for hydrogen storage purposes was performed in an industrial milling device. The TiFe hydride is interesting from the technological standpoint because of the abundance and the low cost of its constituent elements Ti and Fe, as well as its high volumetric hydrogen capacity. However, TiFe is difficult to activate, usually requiring a thermal treatment above 400 °C. A TiFeMn alloy milled for just 10 min in a 100 L industrial milling device showed excellent hydrogen storage properties without any thermal treatment. The as-milled TiFeMn alloy did not need any activation procedure and showed fast kinetic behavior and good cycling stability. Microstructural and morphological characterization of the as-received and as-milled TiFeMn alloys revealed that the material presents reduced particle and crystallite sizes, even after such short time of milling. The refined microstructure of the as-milled TiFeMn is deemed to account for the improved hydrogen absorption-desorption properties.

Electrochemical Features and Hydrogen Absorption-Desorption Properties of A2B7-type Pr–Mg–Ni-Based Alloys

To explore the electrochemical characteristic of 2H- and 3R-type superlattice structure isomerides which are consisted of [REMgNi4] and [RENi5] subunits, we prepare A2B7-type Pr-Mg-Ni-based alloys composed of different amounts of 2H and 3R phases and mainly study the effects on properties including the charging/discharging and absorption/desorption process. The volume change of [PrMgNi4] and [PrNi5] subunits before and after hydrogenation/dehydrogenation is calculated. The results show that the expansion and shrinkage rates of the two subunits in 2H- and 3R-type phases are close, which may be the leading cause that the alloy exhibits single platform in P–C–T curve. While electrochemical measurement shows that the cycling stability of the alloy electrodes improves with the increase of 2H-type phase and the high rate dischargeability at 1500 mA g−1 shows opposite trend. It is found that the exchange current density gradually increases from 499.8 to 653.8 mA g−1 and the hydrogen diffusion coefficient of the alloys increases from 7.6 × 10−9 to 8.8 × 10−9 cm2 s−1 when the 3R phase abundance increases from 38.5 wt% to 59.3 wt%, indicating that the 3R-type phase is beneficial to the charge transfer rate and hydrogen diffusion of the alloy.

Solid State Hydrogen Storage in Alanates and Alanate-Based Compounds: A Review

The safest way to store hydrogen is in solid form, physically entrapped in molecular form in highly porous materials, or chemically bound in atomic form in hydrides. Among the different families of these compounds, alkaline and alkaline earth metals alumino-hydrides (alanates) have been regarded as promising storing media and have been extensively studied since 1997, when Bogdanovic and Schwickardi reported that Ti-doped sodium alanate could be reversibly dehydrogenated under moderate conditions. In this review, the preparative methods; the crystal structure; the physico-chemical and hydrogen absorption-desorption properties of the alanates of Li, Na, K, Ca, Mg, Y, Eu, and Sr; and of some of the most interesting multi-cation alanates will be summarized and discussed. The most promising alanate-based reactive hydride composite (RHC) systems developed in the last few years will also be described and commented on concerning their hydrogen absorption and desorption performance.

Tailoring the hydrogen absorption desorption's dynamics of Mg[sbnd]MgH2 system by titanium suboxide doping

Titanium suboxide (TiO) is one of the best catalysts which improved the hydrogen absorption-desorption property of MgH2 Mg system. The TiO catalyzed Mg MgH2 have shown a remarkably reduced apparent activation energy and enhanced the hydrogen absorption-desorption kinetics. The X-ray photoelectron spectroscopy (XPS) analysis has indicated that the oxidation state of Ti in TiO remains unchanged during ball milling and hydrogen absorption-desorption of TiO-doped-MgH2. The X-ray diffraction (XRD) analysis further confirms the XPS result. The TiO has shown the excellent catalytic effect on the MgMgH2 system which remarkably reduced the hydrogen absorption-desorption temperatures.

Effects of cerium on the hydrogen absorption-desorption properties of rare earth-Mg-Ni hydrogen-absorbing alloys

Abstract The influence of Ce addition on the phase constitution, microstructure, hydrogen absorption/desorption properties and battery performances of newly developed rare earth (RE)-Mg-Ni hydrogen-absorbing superlattice alloys for negative electrode materials in Ni-metal hydride (MH) batteries were investigated. The partial substitution of RE (La and Nd) with Ce results in a higher discharge performance and a lower cycle life in the battery. The Ce addition greatly affects the phase constitution, which is mainly characterized by increased formation of the AB2 phase (A = RE or Mg and B = Ni or Al). The existence of the AB2 phase is found to accelerate alloy pulverization and oxidation when the alloys are used as negative electrode materials in Ni-MH model cells. The accelerated pulverization and oxidation are considered to be responsible for the observed higher discharge performance and lower cycle life in the batteries, respectively.

Synthesis of PuNi3-type PrCo3 and its hydrogen absorption–desorption property

We synthesized the intermetallic compound PrCo3 with the PuNi3-type structure. The structural parameters were refined by the Rietveld method. The refined lattice parameters were a = 0.5076(1) nm and c = 2.4831(6) nm. The pressure-composition (PC) isotherm of PrCo3 was measured at 413 K. The maximum hydrogen capacity reached 0.95 H/M. Two plateaus were observed in the absorption–desorption process. The hydrogenation properties were reversible. The structure change of the hydride phase was investigated by X-ray diffraction. The space group of the full hydride phase (PrCo3H3.8) was determined to be R32; the metal sublattice of the original alloy (space group R-3m) transformed to R32 during the hydrogen absorption process. The volume expansions of the unit cell, and the CaCu5-type and MgZn2-type cells of the full hydride phase from the original alloy were 25.0%, 18.4%, and 22.7%, respectively. The structural change was accompanied by anisotropic lattice expansion.

Mg-(TiFe<sub>0.8</sub>Mn<sub>0.2</sub>)-Graphite 複合体の水素吸蔵・放出特性評価

This study deals with the assessment of the hydrogen absorption-desorption properties of Mg-based composites containing TiFe0.8Mn0.2, Fe, and graphite (Mg-10Gr, Mg-10TFM-10Fe, Mg-10TFM-10Gr, Mg-10Fe-10Gr, and Mg-5TFM-5Fe-10Gr) that were gotten with ball milling under Ar atmosphere. The TiFe0.8Mn0.2 and Fe were used as catalysts for improving hydrogen absorption-desorption properties of Mg and the graphite to prevent them from oxidizing. We conducted hydrogenation, X-ray diffraction (XRD) analyses, differential scanning calorimetries (DSC), and Pressure-Composition-Temperature (PCT) measurements for the samples. MgH2 was observed in Mg-10TFM-10Gr, Mg-10Fe-10Gr, and Mg-5TFM-5Fe-10Gr with XRD analyses after hydrogenation at 200℃ under hydrogen pressure of 2.5–2.6 MPa. It might be that the added graphite prevented from oxidizing from the samples and consequently enhanced the catalytic effects of TiFe0.8Mn0.2 and Fe. These samples desorbed hydrogen around 275–350℃ in DSC processes. Mg-10TFM-10Gr, Mg-10Fe-10Gr, and Mg-5TFM-5Fe-10Gr stored hydrogen up to 2.5 wt.%, 3.5 wt.%, and 4.0 wt.%, respectively at 200℃ under hydrogen pressure of 2.6 MPa on PCT measurements without any activation process, and Mg-5TFM-5Fe-10Gr stored hydrogen up to 4.1 wt.% at 200℃ and 4.8wt.% at 280℃ under hydrogen pressure of 2.6 MPa after activation.

Comparative Investigations on Hydrogen Absorption–Desorption Properties of Sm–Mg–Ni Compounds: The Effect of [SmNi5]/[SmMgNi4] Unit Ratio

To understand the effect of [RNi5]/[RMgNi4] unit ratio on hydrogen storage properties of layered R–Mg–Ni compounds, the hydrogen absorption–desorption characteristics of Sm–Mg–Ni compounds have been investigated comparatively in this work. As the [SmNi5]/[SmMgNi4] unit ratio increases, the parameters of [SmNi5] and [SmMgNi4] units in layered Sm2MgNi9, Sm3MgNi14, and Sm4MgNi19 compounds decrease gradually, leading to the elevation of equilibrium pressure, enlargement of slope, and reduction of hysteresis of their P–C isotherms as well as the decline of enthalpy change for hydrogen absorption–desorption. The hydrogen capacities of the layered Sm–Mg–Ni compounds at 298 K are higher than those of SmMgNi4 and SmNi5, and the cycle stability can be improved by the increase of [SmNi5]/[SmMgNi4] unit ratio.

Improvement on the hydrogen storage properties of ZrFe2 Laves phase alloy by vanadium substitution

In this paper, ZrFe2−xVx (x = 0.2, 0.4, 0.6, 0.8) alloys have been studied to see the effects of V substitution for Fe. The structure and hydrogen absorption desorption properties of V doped ZrFe2 system has been considered during the study. Though the stable structure of ZrFe2 is C15 cubic phase, certain amount of V substitution leads to the stabilization of C14 hexagonal phase. The hydrogen absorption desorption measurements have been done at different temperatures for all the alloys using Sievert's type set up. From the results the enthalpies of formation of the hydrides have been calculated. The study reveals that by V substitution for Fe, there is a great increase in the hydrogen storage capacity, with significant increase in the stability of the hydrides. The results are correlated well with the temperature programmed desorption data. The alloy ZrFe1.2V0.8 is found to absorb 3.78 H/formula unit with an enthalpy of formation value of −41.8 KJ/mol.

Crystal Structure and Cyclic Hydrogenation Property of Pr4MgNi19

The hydrogen absorption-desorption property and the crystal structure of Pr4MgNi19 was investigated by pressure-composition isotherm measurement and X-ray diffraction (XRD). Pr4MgNi19 consisted of two phases: 52.9% Ce5Co19-type structure (3R) and 47.0% Gd2Co7-type structure (3R). Sm5Co19-type structure (2H) and Ce2Ni7-type structure (2H) were not observed in the XRD profile. The Mg atoms substituted at the Pr sites in a MgZn2-type cell. The maximum hydrogen capacity reached 1.14 H/M (1.6 mass%) at 2 MPa. The hysteresis factor, Hf = ln(Pabs/Pdes), was 1.50. The cyclic hydrogenation property of Pr4MgNi19 was investigated up to 1000 absorption-desorption cycles. After 250, 500, 750, and 1000 cycles, the retention rates of hydrogen were reduced to 94%, 92%, 91%, and 90%, respectively. These properties were superior to those of Pr2MgNi9 and Pr3MgNi14.

Hydrogen storage properties of Ti2−xCrVMx (M = Fe, Co, Ni) alloys

In this work, quaternary alloys having compositions Ti1.9CrVM0.1 and Ti1.8CrVM0.2 (M = Fe, Co and Ni) have been studied in detail for their structural aspects and hydrogen absorption–desorption properties. All the alloys form bcc phase solid solutions and after hydrogen absorption the structures change to fcc. The pressure composition isotherms, hydrogen storage capacities and hydrogen absorption kinetics were studied using Sievert's type of volumetric setup. The Ti1.9CrVFe0.1, Ti1.9CrVCo0.1 and Ti1.9CrVNi0.1 alloys are found to absorb maximum 3.80, 3.68 and 3.91 wt.% of hydrogen respectively; whereas, Ti1.8CrVCo0.2 and Ti1.8CrVNi0.2 alloys show 3.52 and 3.67 wt.% of hydrogen at room temperature. All the alloys show fast hydrogen absorption kinetics at the room temperature. From differential scanning calorimetric measurements, it has been found that Fe, Ni and Co substitution in place of Ti decreased the hydrogen desorption temperature drastically compared to the parent alloy.

Crystal structure and cyclic properties of hydrogen absorption–desorption in Pr2MgNi9

We investigated the crystal structure and cyclic hydrogen absorption–desorption properties of Pr2MgNi9. The structural model is based on the PuNi3-type structure; the Mg atom is assumed to substitute for the Pr site in an MgZn2-type cell. The refined lattice parameters were determined from X-ray diffraction. A wide plateau region was observed in the P–C (pressure composition) isotherm at 298 K. The maximum hydrogen capacity reached 1.12 H/M (1.62 mass%) under a hydrogen pressure of 2.0 MPa. After 1000 hydrogen absorption–desorption cycles, the hydrogen capacity was superior to that of LaNi5 (82%). Anisotropic lattice strain occurred in the hydriding process. The anisotropic peak-broadening vector was determined to be <001>. The calculated anisotropic lattice strains of the initial cycle and after 1000 cycles were far smaller than those of LaNi5.

Crystal structure of GdNi3 with superlattice alloy and its hydrogen absorption–desorption property

We synthesized the intermetallic compound GdNi3, which has a PuNi3-type structure (space group R-3m), and investigated its P–C isotherm. The refined lattice parameters were a = 0.4993(1) nm and c = 2.4536(4) nm. In the first absorption process, two plateaus were observed, and the maximum hydrogen capacity reached 1.07 H/M. In the first desorption process, a narrow and sloping plateau was observed at approximately 0.02 MPa. After the first full desorption, 0.6 H/M of hydrogen remained in the sample. This sample showed severe peak broadening in the XRD pattern, indicating that the metal sublattice deformed from the original alloy. No plateau region was observed in the second absorption–desorption cycle.

Nanostructured rapidly solidified LaMg11Ni alloy: Microstructure, crystal structure and hydrogenation properties

In our earlier publication (Poletaev et al., J Alloys Compd., 509S (2011) S633) we reported a drastic variation of the structural and hydrogenation properties of LaMg∼12 intermetallic alloy caused by Rapid Solidification (RS). In present work we have probed the effect of nickel during the chemical modification of LaMg12, in combination with RS, on the structure, microstructure and hydrogen absorption–desorption properties of the alloys.RS was performed at three solidification rates, 300–2000 rpm. Ni was found to form a solid solution replacing both La and Mg to yield La1.7Mg16.7Ni0.6 intermetallic. With increasing RS cooling rates, the very fine, almost amorphous microstructures were formed. The LaMg11Ni alloy solidified at the highest cooling rate exhibited the fastest hydrogenation kinetics, reaching maximum hydrogenation capacity of 5.02 wt. % H. Studies of the hydrogenated RS ribbons showed the formation of the nano-scale embryos of MgH2, growing to form polyhedral grains of magnesium dihydride.

ChemInform Abstract: Synthesis and Crystal Structure of a Pr5Ni19 Superlattice Alloy and Its Hydrogen Absorption—Desorption Property.

AbstractThe title compound is synthesized by arc melting of Pr and Ni metals under Ar followed by annealing at 1403 K and quenching in ice water.