Hydrogen Absorption Desorption Characteristics Research Articles

Hydrogen absorption–desorption characteristics of R3MgNi14(R = Nd, Gd and Er) alloys

Hydrogen absorption–desorption characteristics of R3MgNi14(R = Nd, Gd and Er) alloys

Hydrogen occupation in Ti4M2Oy compounds (M = Fe, Co, Ni, Cu, and y = 0, 1) and their hydrogen storage characteristics

The hydrogen sorption properties of Ti4M2Oy compounds (M = Fe, Co, Ni, Cu or their mixture and y = 0, 1) were studied to assess their utility as room-temperature hydrogen storage materials. The main parameter controlling the hydrogen sorption property is the energy of hydrogen incorporation into the compounds, which was evaluated by density functional theory total-energy calculations. Energetics provides basic information on the sequence of hydrogen filling into the available interstitial sites, and when the minimum H–H distance is also considered, a more sensible prediction of the site occupation becomes possible. The calculation results suggested that between Ti4Fe2O and Ti4Ni2O, Ti4Ni2O was a better candidate for room-temperature hydrogen storage. An almost-single-phase Ti4Ni2O compound was successfully synthesized starting from TiO2, Ti, and Ni using the arc-melting method. Ti4Ni2O stored 1.3 wt% of hydrogen under 7 MPa of H2 pressure at 30 °C. The storage properties of Ti4Ni2O were modified by the partial substitution of Fe, Co, and Cu for Ni. The partial substitution did not improve the usable capacity, but the hydrogen absorption–desorption characteristics demonstrated that the equilibrium hydrogen pressure could be precisely controlled via composition change.

Comparative investigation on the hydrogen absorption-desorption characteristics of R2MgNi9 (R = Nd, Gd and Er) compounds

To understand the effect of rare earth atomic radius on hydrogen storage properties of layered R-Mg-Ni compounds, the hydrogen absorption-desorption characteristics of R2MgNi9 (R = Nd, Gd and Er) compounds have been investigated in this work. As the radii of rare earth atoms decrease from Nd to Gd and Er, the lattice parameters (a and c) decrease gradually, leading to the decreases in dehydriding enthalpies and hydrogen capacities. Additionally, the cycle stabilities also decrease from Nd2MgNi9 to Gd2MgNi9 and Er2MgNi9 because their lattice strains increase after 50 cycles.

Effect of Ti-based nanosized additives on the hydrogen storage properties of MgH2

MgH2-based nanocomposites were synthesized by high-energy reactive ball milling (RBM) of Mg powder with 0.5–5 mol% of various catalytic additives (nano-Ti, nano-TiO2, and Ti4Fe2Ox suboxide powders) in hydrogen. The additives were shown to facilitate hydrogenation of magnesium during RBM and substantially improve its hydrogen absorption-desorption kinetics. X-ray diffraction analysis showed the formation of nanocrystalline MgH2 and hydrogenation of nano-Ti and Ti4Fe2Ox. The possible reduction of TiO2 during RBM in hydrogen was not observed, which is in agreement with lower hydrogenation capacity of the corresponding composite, 5.7 wt% for Mg + 5 mol% nano-TiO2 compared to 6.5 wt% for Mg + 5 mol% nano-Ti. Hydrogen desorption from the as-prepared composites was studied by Thermal Desorption Spectroscopy (TDS) in vacuum. A significant lowering of the hydrogen desorption temperature of MgH2 by 30–90 °C in the presence of the additives is associated with lowering activation energy from 146 kJ/mol for nanosized MgH2 down to 74 and 67 kJ/mol for MgH2 modified with nano-TiO2 and Ti4Fe2O0.3 additives, respectively. After hydrogen desorption at 300–350 °C, these materials are able to absorb hydrogen even at room temperature. It is shown that nano-structuring and addition of Ti-based catalysts do not decrease thermodynamic stability of MgH2. The thermodynamic parameters, obtained from hydrogen desorption isotherms for the Mg–Ti4Fe2O0.3 nanocomposite, ΔHdes = 76 kJ/mol H2 and ΔSdes = 138 J/K·mol H2, correspond to the reported literature values for pure polycrystalline MgH2. Hydrogen absorption-desorption characteristics of the composites with nano-Ti remain stable during at least 25 cycles, while a gradual decay of the reversible hydrogen capacity occurred in the case of TiO2 and Ti4Fe2Ox additives. Cycling stability of Mg/Ti4Fe2Ox was substantially improved by introduction of 3 wt% graphite into the composite.

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.

Development of hydrogen absorption–desorption experimental test bench for hydrogen storage material

A volumetric experimental set-up used for measuring hydrogen absorption–desorption characteristics of hydrogen storage material will be presented. Although the experimental set-up is mainly employed to do hydrogen absorption–desorption cycling (including pressure cycling and thermal cycling) measurement automatically, it also can incidentally provide general measurements such as pressure-composition-temperature (P–C–T) curves and kinetics measurements in manual way in the ranges of 0.004–12 MPa and 213–773 K. The experimental set-up can be used to investigate the influence of hydrogen absorption–desorption cycles to hydrogen storage properties of material. The leakage rate of the whole experimental set-up was evaluated systemically. The usability and reliability of the experimental set-up were checked with LaNi5 and Pd/K (kieselguhr).

Hydrogen absorption characteristics and structural transformation during the hydrogenation process of Er3Ni

The X-ray diffraction (XRD) patterns of the corresponding hydrides with different hydrogen content and the pressure–composition–temperature (p–c–T) relations for hydrogen absorption of Er3Ni at different temperatures (293 K, 363 K and 563 K) are measured to explore the hydrogenation process and the hydrogen absorption–desorption characteristics of Er3Ni. The influence of the hydrogenation temperature on the structures of hydrides (with the same hydrogen content) and the hydrogenation process is analyzed. The experimental results show that the hydrogenation of Er3Ni can be characterized by an irreversible reaction process (from Er3Ni phase to hydride I phase) and a reversible reaction process (from hydride I phase to hydride II phase). The structure of Er3Ni hydride behaves continuous transformation as the hydrogen content rises. The p–c–T relations demonstrate the extremely low equilibrium hydrogen pressure, the hydrogenation enthalpy change ΔH (verified by additional measurement by differential scanning calorimeter) and the entropy change ΔS, indicating that the Er3Ni hydrides are relatively stable in a hydrogen gas atmosphere.

Study on the structure and hydrogen absorption–desorption characteristics of as-cast and annealed La 0.78Mg 0.22Ni 3.48Co 0.22Cu 0.12 alloys

La 0.78Mg 0.22Ni 3.48Co 0.22Cu 0.12 alloy is one kind of nonstoichiometric AB 3.5 type hydrogen storage alloy with low cost and high capacity. In this paper, the effect of annealing treatment on the structure and hydrogen absorption–desorption characteristics of the alloy is discussed. The annealing temperature is determined by using thermogravimetry–differential scanning calorimetry (TG–DSC) tests. The structure of as-cast and annealed alloys is examined by X-ray diffraction (XRD) and scanning electron microscopy (SEM). XRD results show that the crystal cell volume decreases after annealing treatment. SEM tests reveal that the structure of the annealed alloys is more regular than that of the as-cast alloy. Influences of annealing treatment on maximum and reversible hydrogen storage capacity, hysteresis factor ( H f) between hydrogen absorption and desorption, sloping factor ( S f), enthalpy changes (Δ H) and entropy changes (Δ S) of hydrogen absorption are discussed in detail.

Improvement of hydrogen storage properties of TiCrV alloy by Zr substitution for Ti

Abstract The effects of Zr substitution for Ti on the hydrogen absorption–desorption characteristics of Ti 1− x Zr x CrV alloys ( x = 0, 0.05, 0.1 and 1.0) have been investigated. The crystal structure, maximum hydrogen absorption capacity, kinetics and hydrogen desorption properties have been studied in detail. While TiCrV crystallizes in body centered cubic (BCC) structure, ZrCrV is a C15 cubic Laves phase compound and the intermediate compositions with 5 and 10 at% Zr substitutions for Ti ( x = 0.05 and 0.1) show the presence of a small amount of ZrCr 2 Laves phase along with the main BCC phase. The pressure–composition isotherms have been studied at room temperature. TiCrV shows separation of TiH 2 phase on cycling. A small amount of Zr substitution for Ti is found to have advantageous effects on the hydrogen absorption properties of TiCrV as it suppresses TiH 2 phase separation and decreases hysteresis. It is found that the hydrogen absorption capacity of Ti 1− x Zr x CrV decreases as the Zr content increases due to the increased fraction of Laves phase. Temperature-programmed desorption studies have been carried out on the saturated hydrides in order to find the relative desorption temperatures.

Hydrogen sorption characteristics of the composites 90 wt.% Mg (MgH2)–10 wt.% V0.855Ti0.095Fe0.05

The hydrogen absorption–desorption characteristics of composites containing 90 wt.% Mg or MgH2 and 10 wt.% of the intermetallic compound V0.855Ti0.095Fe0.05 obtained by mechanical alloying for 1 and 5 h in an inert medium were investigated. Absorption measurements were performed under a hydrogen pressure P = 1 MPa at temperatures of 623, 573, 523, and 473 K. Dehydriding was studied at 623 and 573 K and a pressure of 0.15 MPa. It was established that the presence of the additive improved significantly the hydriding kinetics of magnesium while the effect of the duration of mechanical alloying was less pronounced. Due to the small difference in specific surface areas and crystallite sizes, both composites investigated showed no substantial difference in behavior during absorption and desorption of hydrogen. The best absorption–desorption properties were found with the composite 90 wt.% Mg–10 wt.% V0.855Ti0.095Fe0.05 mechanically activated for 5 h.

Effects of the addition of Pd on the hydrogen absorption–desorption characteristics of Ti33V33Cr34 alloys

Abstract The hydrogen absorption–desorption performance of the body-centered-cubic (bcc) Ti–V–Cr–Pd alloys have been investigated. Ti 33 V 33 Cr 34 ingots with 0, 0.05, 0.5 at.% Pd were prepared by arc melting. X-ray diffraction (XRD) revealed that all of these alloys were homogeneous bcc solid solutions. Pd-containing (0.05, 0.5 at.% Pd) Ti–V–Cr alloys have better initial activation properties than those without Pd, and the desorption plateau pressure of the (Ti 33 V 33 Cr 34 ) 99.5 Pd 0.5 alloy was substantially higher than that of the alloy without Pd. It is also found that the hysteresis difference is smaller in these alloys and degradation of hydrogen absorption capacity becomes steady after the 25th cycling test. (Ti 33 V 33 Cr 34 ) 99.5 Pd 0.5 alloy exhibits large hydrogen absorption and desorption capacity of up to 3.42 and 2.07 mass% at 353 K, respectively.

Cyclic hydrogen absorption–desorption characteristics of TiCrV and [formula omitted] alloys

The cyclic hydrogen absorption–desorption characteristics of TiCrV and Ti 0.8 Cr 1.2 V alloys are investigated. Experimental results show that the cyclic hydrogen capacity increases with increasing hydrogen-desorption temperature for both TiCrV and Ti 0.8 Cr 1.2 V alloys. The Ti 0.8 Cr 1.2 V and TiCrV alloys can maintain steady cyclic hydrogen capacities of about 2.5 wt% and 2.0 wt%, respectively, even after 15 cycles with hydrogen absorption at 25 ∘ C and hydrogen desorption at 400 ∘ C . The hydrogenation for both TiCrV and Ti 0.8 Cr 1.2 V alloys includes the processes of first saturated solid-solution and then forming TiCr 1.8 H 5.3 and TiH 2 hydrides. The TiCr 1.8 H 5.3 hydride has better reversibility than TiH 2 hydride during the hydrogen absorption–desorption.

Hydriding Properties of MgH2-Mg2Ni0.8Co0.2 Composites Obtained by Ball Milling

Abstract The hydrogen absorption-desorption characteristics of composites consisting of 90 wt.% MgH2- 10 wt.% Mg2Ni0.8Co0.2 prepared by ball milling for 30 and 180 min under argon have been investigated. The results obtained have been compared with those for the 90 wt.% Mg-10 wt.% Mg2Ni0.8Co0.2 composite synthesized in the same medium after 30 min of milling. The presence of the Mg2Ni0.8Co0.2 phase has been found to improve the hydriding kinetics of magnesium, the absorption capacity remaining high at temperatures below 573 K. The use of magnesium hydride instead of magnesium has proved to have a favorable effect on the properties of the composites after prolonged activation in an inert medium. It has been established that the absorption-desorption characteristics of the composite 90 wt.% MgH2-10 wt.% Mg2Ni0.8Co0.2 activated mechanically for 180 min are comparable with those of the composite 90 wt.% Mg-10 wt.% Mg2Ni0.8Co0.2 after mechanical activation for only 30 min. The favorable absorption-desorption characteristics of the composites have been explained with the catalytic effect of the additive, the presence of magnesium hydride and the duration of ball milling.

Structure, morphology and hydrogen storage properties of composites prepared by ball milling [formula omitted] with La–Mg-based alloy

Hydrogen storage alloy composites Ti 0.9 Zr 0.2 Mn 1.5 Cr 0.3 V 0.3 - x wt % La 0.7 Mg 0.25 Zr 0.05 ( Ni 0.85 Co 0.15 ) 3.5 ( x = 0 , 5 , 10 ) were prepared by ball milling method. Their structures, morphologies and the hydrogen storage characteristics were intensively studied in the present work. It was found that the bulk of composites maintained the hexagonal C14 Laves phase structure after ball milling with additional La–Mg-based alloy for two hours. Scanning electron microscopy (SEM) observations revealed that the average size of Ti 0.9 Zr 0.2 Mn 1.5 Cr 0.3 V 0.3 and La 0.7 Mg 0.25 Zr 0.05 ( Ni 0.85 Co 0.15 ) 3.5 particles were reduced to several hundred nanometers after ball milling process. Energy dispersive X-ray spectrometer (EDS) patterns of the composites showed that the La 0.7 Mg 0.25 Zr 0.05 ( Ni 0.85 Co 0.15 ) 3.5 phase was uniformly distributed on the surface of Ti 0.9 Zr 0.2 Mn 1.5 Cr 0.3 V 0.3 . The hydrogen absorption–desorption characteristics of the composites were improved with increasing dispersivity of the La 0.7 Mg 0.25 Zr 0.05 ( Ni 0.85 Co 0.15 ) 3.5 alloy particles. Pressure–composition–temperature (PCT) measurements revealed that the pressure plateau and the hysteresis decreased with increasing x. Among these composites, the sample of x = 10 exhibited more significant hydrogen storage performances. Its hydrogen absorption and desorption plateau pressure were 0.547 and 0.302 MPa, respectively, which were much lower than those of the Ti 0.9 Zr 0.2 Mn 1.5 Cr 0.3 V 0.3 alloy. Moreover, it took only 200 and 2500 s to reach the constant pressure for the hydrogen absorption and desorption reaction. These improvements can be attributed to the preferable dispersivity of La–Mg-based alloy particles and also the formation of micro-crack after ball milling. Both factors synergetically facilitate the diffusion of hydrogen atoms in the composites and accelerate the dissociation of hydrogen molecules and recombination of hydrogen atoms on the surface of composites during the hydrogen absorption–desorption process.

Effect of NiCo 2O 4 additives on the hydriding properties of magnesium

The effect of NiCo 2O 4 additives on the hydrogen absorption–desorption characteristics of 85 wt% Mg–15 wt% NiCo 2O 4 and 95 wt% Mg–5 wt% NiCo 2O 4 composites prepared by mechanical alloying in an inert atmosphere was investigated. The absorption of hydrogen was measured at temperatures of 573, 473, 423 and 373 K and pressures of 1, 0.4 and 0.2 MPa while the desorption studies proceeded at 573 K under a pressure of 0.15 MPa. The addition of NiCo 2O 4 was found to exercise a positive effect on the hydriding kinetics of pure magnesium, the absorption capacity remaining high at temperatures below 573 K and pressures lower than 1 MPa. A three-fold decrease of the additive content (from 15 to 5 wt%) did not deteriorate the hydriding kinetics of the composite. After 85 absorption–desorption cycles the composite 95 wt% Mg–5 wt% NiCo 2O 4 showed no drastic drop in absorption capacity. The favourable absorption–desorption characteristics found for the composites investigated were supposed, on the basis of XPS data, to be due to the catalytic effect of the nickel and cobalt species obtained during hydriding of NiCo 2O 4 on the sample surface.

Influence of Ni or Mn on hydrogen absorption–desorption performance of V–Ti–Cr–Fe alloys

The hydrogen desorption performance of the BCC alloys V 55− x Ti 20.5Cr 18.1Fe 6.4Ni x ( x = 0.1, 0.3, 0.5 and 1) and V 55− y Ti 20.5Cr 18.1Fe 6.4Mn y ( y = 0.3, 0.7 and 1) were evaluated by pressure-composition-temperature tests. Their hydrogen absorption kinetic properties were studied through hydrogen absorption curves. The crystallographic structures of these alloys before hydrogen absorption and after hydrogen desorption PCT test were identified by X-ray diffraction (XRD). The mechanism affecting their hydrogen absorption–desorption characteristics by Ni or Mn were discussed.

Influence of Fe addition on hydrogen storage characteristics of Ti–V-based alloy

In order to improve the hydrogen storage properties and reduce the cost of Ti–V-based BCC alloys, the effect of Fe substitution for part V on hydrogen absorption–desorption characteristics of Ti–10Cr–18Mn–32V alloy was investigated. It was found that proper amount of Fe addition was effective in improving the activation performance, enhancing the hydrogen absorption–desorption plateau pressure, reducing the hysteresis of hydrogen absorption–desorption plateau, increasing the hydrogen desorption capacity and decreasing the alloy's cost, while it depressed the hydrogen absorption capacity. X-ray diffraction (XRD) patterns and back scattering electron (BSE) images display that the single BCC phase of Fe-free alloy transformed into two phases of, BCC and C14 Laves, of Fe-containing alloy. Three phase transformations happened in the two alloys during the hydrogen release process, which resulted from the formation of three different hydride phases in the two hydrided alloys.

Hydrogen absorption–desorption characteristics of Ti (0.22 + X) Cr (0.28 + 1.5 X) V (0.5 − 2.5 X) (0 ≤ X ≤ 0.12) alloys

The hydrogen absorption–desorption characteristics of Ti (0.22 + X) Cr (0.28 + 1.5 X) V (0.5 − 2.5 X) ( X = 0, 0.04, 0.08, 0.10, 0.12) bcc alloys have been investigated at 303 K. The compositions of alloys were chosen for alloys to have equal lattice parameters of about 3.03 Å by a linear combination of each element. The alloys of about 20 g each were arc-melted into button shaped ingots under argon atmosphere and re-melted five times to improve their homogeneities. The XRD analysis showed that all of the samples prepared had bcc single phases and their lattice parameters were nearly the same regardless of their chemical compositions. The P C isotherms of the alloys revealed that the hydrogen storage capacities of the alloys exceeded 3 mass% owing to the control of the lattice parameters and only the second plateau was reversible at room temperature. A reversible structural transition from fcc to bcc occurred with dehydrogenation of the second plateau. Some hydrogen remained unreleased even at a considerable low pressure corresponds to the bcc hydride and needed thermal activation energy for desorption. The hydrogen absorption rate of the Ti 0.32Cr 0.43V 0.25 alloy was considerably fast and more than 95% of the hydrogen was absorbed within the first 10 min.

Addition of 3d-metals with formation of nanocomposites as a way to improve the hydrogenation characteristics of Mg 2Ni

The hydrogen absorption–desorption characteristics of a composite material containing 85 wt.% Mg 2Ni, 10 wt.% V and 5 wt.% Ti, obtained by mechanical alloying in a planetary mill under argon have been investigated. The experimental data on the kinetics of hydriding and dehydriding and the absorption capacity values established at various temperatures and hydrogen pressures have been compared with those of a previously studied composite obtained by the same method but containing no titanium. It has been shown that the presence in the composite of a second hydride-forming 3d-metal leads to an enhanced absorption capacity and improved hydriding and dehydriding kinetics. The 85 wt.% Mg 2Ni–10 wt.% V–5 wt.% Ti composite has shown a significant hydrogen absorption at room temperature. The improved characteristics of the Ti-containing composite are attributed to the formation, along with Mg 2NiH 4 and VH x , of a third hydride, TiH x , which increases the interface and facilitates both nucleation and back diffusion of hydrogen from the sample.

Hydrogen absorption–desorption characteristics of the LaNi 5Sn intermetallic compound

The pressure–composition–temperature (P–C–T) relations in the LaNi 5Sn–H system were measured volumetrically at temperatures between 258 and 423 K. Two hydride phases, β-LaNi 5SnH 2 and γ-LaNi 5SnH 3 are formed in this system in addition to the α-solid solution with a limiting H content of 0.3 H atoms per formula unit. The calculated work loss due to hysteresis is rather small, 112 J (mol H) −1 at 298 K. The partial molar enthalpy and entropy calculated for the formation of the β-LaNi 5SnH 2 are −18.5±0.8 kJ (mol H) −1 and −53.7±2.3 J (K mol H) −1, respectively. An advanced van der Waals lattice gas model was applied to fit the isotherms. The critical temperature of the LaNi 5SnH 2 equals T C=421±17 K.