Hydriding Dehydriding Research Articles

Influence of Titanium and Iron Additives to Magnesium on Hydrogen-Sorption Properties, Thermal Stability, and Kinetics of Hydrogen Desorption from MgH2 Phase of Mechanical Alloy

We report on studies of the process of cyclic hydriding–dehydriding (eight cycles) of a mechanical alloy synthesized in a ball mill by grinding powder mixture Mg + 10 wt.% TiH2 + 10 wt.% Fe in argon medium. Hydrogen-sorption properties and thermal stability of the mechanical alloy are studied employing thermodesorption spectroscopy at hydrogen pressure of 0.1 MPa. Hydrogen capacity of the mechanical alloy is determined to be 4.9 wt.%, and onset temperature of hydrogen desorption from the alloy under this study equals 220°C. Kinetics of the process of hydrogen desorption from the hydride phases of the mechanical alloy is examined. The present studies have revealed that mechanical treatment of the magnesium powder in Ar medium with both Fe and Ti additives causes a greater effect on improving the kinetics of hydrogen desorption from hydride phase MgH2 of the alloy and decreasing its thermal stability in comparison with that caused by mechanical treatment of the same powder with either Fe or Ti additives in hydrogen medium.

Significantly improved dehydrogenation of ball-milled MgH2 doped with CoFe2O4 nanoparticles

CoFe2O4 nanoparticles are added to magnesium hydride (MgH2) by high-energy ball milling in order to improve its hydriding properties. The hydrogen storage properties and catalytic mechanism are investigated by pressure-composition-temperature (PCT), differential thermal analysis (DTA), X-ray diffraction (XRD), field-emission scanning electron microscopy (FESEM) and transmission electron microscopy (TEM). The nonisothermal desorption results show that the onset desorption temperature of the MgH2 + 7 mol% CoFe2O4 is 160 °C, which is 200 °C lower than of the as-received MgH2. The dehydrogenation process of the MgH2 doped with the CoFe2O4 nanoparticles includes two steps. DTA curves and XRD patterns reveal that a chemical reaction happens between MgH2 and CoFe2O4, forming the final products of the ternary combination, corresponding to Co3Fe7, MgO and Co. The onset desorption temperature of the ball-milled MgH2 doped with Co3Fe7, MgO and Co is about 260 °C, approximately 100 °C lower than the un-doped MgH2, demonstrating that the ternary combination (Co3Fe7, MgO, and Co) also has a great catalytic effect on the MgH2 hydrogen storage properties. It is also confirmed that the various methods of adding the ternary combination have different effects on the MgH2 hydriding–dehydriding process.

NUMERICAL TRANSIENT HEAT TRANSFER ANALYSIS OF REACTOR FOR MAGNESIUM BASED ALLOY FOR HYDROGEN STORAGE APPLICATION

Metal hydrides are potential hydrogen storage media. They release hydrogen at moderate temperatures and pressures. Magnesium hydride is a promising approach for stationary power system application, due to high hydrogen storage capacity by weight. Magnesium hydride based reactor design is more complex due to high thermal energy release and absorption during hydriding reaction and dehydriding reaction, respectively. In this study, results of a numerical modeling study are presented for a 1.5 kg Magnesium alloy based hydriding reactor. Temperature profile in the reactor is computed by FEM analysis using ANSYS software for hydriding and dehydriding reaction. FEM analysis indicates that the reactor temperature is raised from 200 C to 422 ºC in 20 minutes during the hydriding process. Hence, a “cooling system” is required for maintaining temperature during the hydriding process. During the dehydriding process, maximum temperature drop occurs from 350 C to 189 ºC in 20 minutes. Therefore, an external heat source of 2 kW is required for maintaining the temperature during dehydriding. Details are presented.

Enhanced hydriding–dehydriding performance of a 2LiH–MgB2 composite by the catalytic effects of Ni–B nanoparticles

A system of 2LiH–MgB2 and its hydrogenated 2LiBH4–MgH2 is an attractive candidate for hydrogen storage. However, its hydriding–dehydriding kinetics have to be further improved for practical application. In the present work, three kinds of Ni–B nanoparticles with different crystalline states and particle sizes were prepared by wet-chemical reduction and mechanochemical methods, and then introduced into a 2LiH–MgB2 composite for catalytic enhancement. The catalytic roles of Ni–B nanoparticles on the hydriding–dehydriding properties were investigated systematically. The results show that all of the Ni–B nanoparticles can significantly enhance the hydriding–dehydriding kinetics of the 2LiH–MgB2 composite, resulting in no incubation period for the formation of MgB2 during dehydrogenation. The more disordered the amorphous structure and the smaller sized the Ni–B particles are, the better the catalytic effect that is obtained. Microstructure analyses clearly reveal the formation of the MgNi3B2 phase in the dehydriding process, which acts as the nucleation agent for MgB2 formation determined by an edge-to-edge model. Directly doping with Ni–B nanoparticles in the 2LiH–MgB2 system shows a higher hydrogen desorption capacity of 9.4 wt% and obtains a better catalytic efficiency than doping with NiCl2.

Hydriding–dehydriding cycling behavior of magnesium–nickel–iron oxide alloy

By measuring the absorbed hydrogen quantity as a function of number of cycles, cycling characteristics of the Mg–15wt%Ni–5wt%Fe2O3 alloy was investigated. The sample was hydriding–dehydriding cycled 150 times. The absorbed hydrogen quantity decreased as the number of cycles increased from the second to the 150th cycle. The Ha value varied almost linearly with the number of cycles. The degradation rate from n=1 to n=100 is 0.01201wt%/cycle for the hydriding reaction time of 10min, and 0.00860wt%/cycle for the hydriding reaction time of 60min. After the 150th hydriding–dehydriding cycle, Mg, Mg2Ni, Mg(OH)2, MgO, and Fe were observed. The phases were analyzed by Rietveld analysis from the XRD patterns of the Mg–15Ni–5Fe2O3 alloy after 150th hydriding–dehydriding cycles. The crystallite size and strain of Mg were then estimated by Williamson–Hall technique.

Enhanced hydriding–dehydriding performance of 2LiBH4–MgH2 composite by the catalytic effects of transition metal chlorides

2LiBH4–MgH2 is an attractive system for hydrogen storage. However, its dehydriding and rehydriding kinetics have to be further improved for practical applications. To solve these problems, three transition metal chlorides (FeCl2, CoCl2 and NiCl2) were introduced into the 2LiBH4–MgH2 system and their catalytic roles in the dehydrogenation–rehydrogenation properties were investigated systematically. The results show that all three chlorides can significantly enhance the dehydriding and rehydriding kinetics of the 2LiBH4–MgH2 system with/without hydrogen back pressure, and NiCl2 is the best modifier among them. The NiCl2-doped sample exhibits no incubation period for generating MgB2 during dehydrogenation. X-Ray diffraction and scanning electron microscopy analyses clearly reveal the phase formation of MgNi3B2, which may act as the nucleation site for MgB2 formation, and thus the incubation period shrinks. A highly homogeneous distribution of the in situ formed MgNi3B2 nanoclusters can significantly improve the dehydriding–rehydriding kinetics. Single-phase MgNi3B2 was successfully synthesized and a similar catalytic effect is obtained by directly doping identical MgNi3B2 into the 2LiBH4–MgH2 system, which results in a higher hydrogen storage capacity of 9.4 wt%.

Producing nanocrystalline bulk Mg–3Al–Zn alloy by powder metallurgy assisted hydriding–dehydriding

Nanocrystalline bulk Mg–3Al–Zn alloy with an average grain size of 48 nm has been prepared by powder metallurgy assisted hydriding–dehydriding. Evolutions of nanograined structure powders and bulk alloy have been investigated by TEM, SEM and XRD, respectively. The results showed that by milling in hydrogen for 60 h, as-hydriding powder possessed an average grain size of 5.9 nm. After a subsequent process of desorption-recombination treatment (at 350 °C) and consolidation process (extruded at 200 °C) resulted in bulk samples with an average crystallite size of 48 nm and MgH 2 was fully turned into Mg. The consolidated samples of 60 h milled powder had a final density of 1.77663 ± 0.006 g/cm 3, which corresponded to 97.57 ± 0.3% of theoretical density. The highest microhardness of the nanocrystalline bulk alloy reached about 872.5 MPa, which is about three times higher than that of the coarse-grained AZ31.

Hydrogen-storage property characterization of Mg–15 wt%Ni–5 wt%Fe 2O 3 prepared by reactive mechanical grinding

Mg–15 wt%Ni–5 wt%Fe 2O 3 (Mg155) was prepared by reactive mechanical grinding (RMG). Mg155 exhibited high hydriding and dehydriding rates even at the first cycle, and its activation was completed after only two hydriding–dehydriding cycles. The activated Mg155 absorbed 5.06 and 5.38 wt% of hydrogen, respectively, for 5 and 60 min at 573 K under 12 bar H 2. It desorbed 1.50 and 5.28 wt% of hydrogen, respectively, for 5 and 60 min at 573 K under 1.0 bar H 2. The initial hydrogen absorption rate decreased, but the hydrogen desorption rate increased rapidly with an increase in temperature from 563 K to 603 K. The rate-controlling step for the dehydriding reaction in a range from F ≃ 0.20 to F ≃ 0.75 is considered to be the chemical reaction at the Mg hydride/α-solid solution interface. The absorption and desorption PCT curves exhibited two plateaus at 573 K. The hydrogen-storage capacity of the activated Mg155 was about 6.43 wt% at 573 K.

Transformation mismatch plasticity in Pd induced by cyclic hydrogen charging

Transformation mismatch plasticity is achieved in swaged palladium wires by cyclical hydriding–dehydriding. Upon multiple cycles at ambient temperature, a total strain of ∼40% is accumulated under a constant tensile stress. This value is much higher than the tensile ductility for swaged Pd subjected to monotonic deformation without transformation (<2% for this wire). Strain increments after a single cycle are proportional to the applied stress, in agreement with the Greenwood–Johnson equation for transformation mismatch plasticity. The yield stress of hydrogen-cycled Pd calculated from this equation is 760 MPa, which is much higher than the value of the original wire and about 50% higher than previous values reported for Pd that was hydrogen cycled at 100 °C without an applied stress.

Enhancement of the hydrogen storage characteristics of Mg by reactive mechanical grinding with Ni, Fe and Ti

Mg-10wt%Ni-5wt%Fe-5wt%Ti powder was prepared by reactive mechanical grinding using a planetary ball mill. The Mg-10wt%Ni-5wt%Fe-5wt%Ti powder exhibited high hydriding and dehydriding rates even at the first cycle, and its activation was completed after two hydriding–dehydriding cycles. After the reactive mechanical grinding, the particle size of the powder was reduced, as compared with those of the starting materials. The hydrogen storage properties were measured at temperatures of 473 K, 573 K and 623 K. The activated Mg-10wt%Ni-5wt%Fe-5wt%Ti powder absorbed 5.31 wt% and 5.51 wt% of hydrogen for 5 min and 1 h, respectively, at 573 K under 12 bar H 2. It desorbed 5.18 wt% of hydrogen at 573 K under 1.0 bar H 2 for 1 h. The initial hydrogen absorption rate increased when passing from 473 K to 573 K, but decreased at 623 K. The hydrogen desorption rate increased rapidly with increasing temperature from 473 K to 623 K. The hydrogen storage capacity was about 6.72 wt% at 573 K.

Microstructure nanocrystallization of a Mg–3 wt.%Al–1 wt.%Zn alloy by mechanically assisted hydriding–dehydriding

In order to develop nanocrystalline microstructure in Mg alloy powders, the mechanically assisted hydriding–dehydriding process was proposed, and a pioneering experimental study was performed on a Mg–3 wt.%Al–1 wt.%Zn (AZ31 Mg) alloy. Firstly, the as-cast alloy was hydrided by room-temperature ball milling in hydrogen. Then, a thermal dehydriding treatment was carried out under vacuum. The microstructure change due to hydriding/dehydriding was examined by XRD and TEM, respectively. The results show that the alloy can be mechanically hydrided at ambient temperature, with the polycrystalline Mg phase transformed into nano-structured MgH 2. After a subsequent thermal dehydriding at 350 °C, the MgH 2 is turned into Mg again, and nanocrystalline alloy powders are thus obtained.

Development of Mg-oxide–Ni hydrogen-storage alloys by reactive mechanical grinding

Mg-oxide and Mg-oxide–Ni hydrogen storage alloys were prepared by mechanical grinding under H 2 (reactive mechanical grinding). Among these alloys, Mg – ( 7.5 wt % Fe 2 O 3 , 7.5 wt%Ni) prepared by grinding for 4 h with nano-structured Fe 2 O 3 particles and Ni showed the best hydrogen storage properties. The as-milled sample absorbed 4.75 wt% H at 593 K under 12 bar H 2 for 60 min. Its activation was accomplished after two hydriding–dehydriding cycles. The activated sample absorbed 4.36 wt% H at 593 K under 12 bar H 2 for 60 min and desorbed 4.26 wt% H at 593 K under 1.0 bar H 2 for 60 min. After hydriding–dehydriding cycling, Mg 2 Ni , Fe and MgO are formed. The large bar-like hydrided particles have round and expanding surfaces, suggesting that they expanded during the hydriding reaction, while the dehydrided particles exhibit contracted surfaces with wrinkles.

Structural and hydriding–dehydriding properties of Ho 1− xTi xCo 2 alloys

The influence of Ti on the structural and hydrogen absorption–desorption properties of Laves phase Ho 1− x Ti x Co 2 ( x = 0–0.6) alloys have been studied using X-ray diffraction (XRD), pressure–composition (PC) isotherms, differential scanning calorimetry (DSC) and thermogravimetry (TG). The crystalline nature and lattice expansion of hydrogenated alloys at different hydrogen concentrations have been reported. In addition, the coexistence of two hydride phases at intermediate hydrogen concentrations has been identified from the XRD. The changes in plateau pressure and hydrogen absorption–desorption capacity upon increasing Ti content have been discussed. The preferential occupation of different types of interstitial sites has been identified from the DSC studies of hydrides. The complete desorption temperature of hydrogen has been obtained from the TG studies of hydrides.

Hydrogen-storage properties of a Mg-based mixture prepared by reactive mechanical grinding with ultrafine Fe 2O 3 particles and Ni

The sample Mg-10 wt.% (Fe 2O 3, Ni) was prepared by grinding Mg mechanically under H 2 (reactive mechanical grinding) with ultrafine Fe 2O 3 particles and Ni particles. The sample Mg-10 wt.% (Fe 2O 3, Ni) as milled absorbed 4.24 wt.% hydrogen at 593 K under 12 bar H 2 for 60 min. Its activation was accomplished only by one hydriding–dehydriding cycle. The activated sample absorbed 4.05 wt.% hydrogen at 593K, 12 bar H 2 for 60 min and desorbed 3.05 wt.% hydrogen at 593 K, 1.0 bar H 2 for 60 min. After hydriding–dehydriding cycling, Fe 2O 3 was reduced, Mg 2Ni was formed by the reaction of Mg with Ni, and a small fraction of Mg was oxidized.

Hydrogenation and degradation of Mg–10 wt% Ni alloy after cyclic hydriding–dehydriding

Hydrogenation and degradation properties of Mg–10 wt% Ni hydrogen storage alloys were investigated by cyclic hydriding–dehydriding tests. Mg–10 wt% Ni alloy was synthesized by rotation-cylinder method (RCM) under 0.3% HFC-134a/air atmosphere and their hydrogenation and degradation properties were evaluated by pressure-composition-isotherm (PCI) measurement. Hydrogen storage capacities gradually increased following 160 hydriding–dehydriding cycles and thereafter started to decrease. Measured maximum hydrogen capacity of Mg–10 wt% Ni alloy is 6.97 wt% at 623 K. Hydriding and dehydriding plateau pressure were kept constant for whole cycles. Reversible hydrogen capacity started to descend after 280 hydriding–dehydriding cycles. The lamellar eutectic structure of Mg–Ni alloy consists of Mg-rich α -phase and β - Mg 2 Ni . It is assumed that the lamellar eutectic structure enhances hydrogenation properties.

Amelioration of the hydriding and dehydriding kinetics of Mg by pulverization and the formation of Mg 2Ni hydride

The addition of an oxide Fe 2O 3 is considered to increase the hydriding rate of Mg by pulverization, and the addition of Ni to increase the hydriding and dehydriding rates by the formation of Mg 2Ni hydride. The sample Mg–10 wt.% (Fe 2O 3, Ni) was prepared by grinding Mg mechanically under H 2 (reactive mechanical grinding) with nano-structured Fe 2O 3 particles and Ni. The as-milled sample absorbed 4.24 wt.% hydrogen at 593 K under 12 bar H 2 for 60 min. Its activation was accomplished after two hydriding–dehydriding cycles. The activated sample absorbed 4.05 wt.% hydrogen at 593 K, 12 bar H 2 for 60 min and desorbed 3.05 wt.% hydrogen at 593 K, 1.0 bar H 2 for 60 min. After hydriding–dehydriding cycling, Mg 2Ni is formed by the reaction of Mg with Ni, Fe 2O 3 is reduced, and a small fraction of Mg is oxidized.

The influence of tetrahydrofuran treatment on hydrogen storage properties of the magnesium

The hydriding and dehydriding properties of the tetrahydrofuran (THF) treated magnesium, along with its electronic energy states, crystalline structure and micro morphology have been investigated. The THF treated magnesium absorbs 6.3 wt% hydrogen at 723 K and 3.5 MPa. After hydrogenation, in addition to the expected hydride MgH2, a new less-stable hydride phase appears at 673 K, but not at a lower temperature. Desorption produces 5.5 wt% hydrogen at 723 K against a back-pressure of 1.3 Pa after 20 cycles of hydriding–dehydriding. The THF treatment improves the kinetics of hydrogen absorption and desorption. The THF treated Mg exhibited reasonable reaction rates with hydrogen at 623 K. XPS (X-ray Photo-electron Spectroscopy) studies show that THF treatment causes the electronic energy state of the magnesium atoms to shift, but the XRD (X-Ray Diffractometer) studies show the crystal structure remains unchanged. It is believed that the chemical state of magnesium surface is activated by THF treatment in favor of hydrogen absorption and desorption. Metallographic observation of the magnesium hydrides reveals some interesting features during hydrogenation.

Improvement of hydrogen-sorption characteristics of Mg by reactive mechanical grinding with [formula omitted] prepared by spray conversion

Nano-structured Cr 2 O 3 powder could be produced by spray conversion (spray drying of an aqueous of Cr nitrate, oxidation and milling). The samples Mg—10 wt% Cr 2 O 3 using nano-structured Cr 2 O 3 synthesized by spray conversion were prepared by mechanical grinding under H 2 (reactive mechanical grinding) under the optimum conditions, previously studied, for the preparation of the sample Mg—10 wt% Fe 2 O 3 using purchased Fe 2 O 3 . The sample Mg—10 wt% Cr 2 O 3 as milled absorbed 4.48 wt% H 2 at 593 K under 12 bar H 2 for 60 min. Its activation was accomplished after two hydriding–dehydriding cycles. The activated sample absorbed 5.48 wt% H 2 for 10 min and 5.93 wt% H 2 for 60 min at 593 K, 12 bar H 2 , and desorbed 3.65 wt% H 2 at 603 K, 1.0 bar H 2 for 60 min. H 2 -storage capacity was 6.38 wt% under 12 bar H 2 at 593 K (from P–C-T curve). Reactive mechanical grinding of Mg with Cr 2 O 3 by spray conversion increased the hydriding rate effectively but increased a little the dehydriding rate, compared with reactive mechanical grinding of Mg with Fe 2 O 3 purchased, Fe 2 O 3 by spray conversion, MnO and SiO 2 by spray conversion.

Hydrogen-storage properties of Mg–10 wt.% (Fe 2O 3, Ni, MnO) alloy prepared by reactive mechanical grinding

The samples Mg–10 wt.% (Fe 2O 3, Ni, MnO) was prepared by mechanical grinding under H 2 (reactive mechanical grinding) under the optimum conditions, studied previously, for the preparation of the sample Mg–10 wt.% Fe 2O 3 using purchased Fe 2O 3. The sample Mg–10 wt.% (Fe 2O 3, Ni, MnO) as milled absorbed 4.15 wt.% hydrogen at 593 K under 12 bar H 2 for 60 min. Its activation was accomplished after two hydriding–dehydriding cycles. The activated sample absorbed 4.02 wt.% hydrogen at 593 K, 12 bar H 2 for 60 min desorbed 3.03 wt.% hydrogen at 603 K, 1.0 bar H 2. Hydrogen-storage capacity was 5.34 wt.% under 12 bar at 593 K (from P– C– T curve). The equilibrium plateau pressure is about 1.5 bar H 2. Mg–10 wt.% (Fe 2O 3, Ni, MnO) has lower hydriding rate than Mg–10 wt.% Fe 2O 3 by spray conversion, but it has higher dehydriding rate than Mg–10 wt.% MnO and Mg–10 wt.% Fe 2O 3 by spray conversion.

Preparation of hydrogen-storage alloy Mg–10 wt% [formula omitted] under various milling conditions

We tried to improve the H 2-sorption properties of Mg by mechanical grinding under H 2 (reactive mechanical grinding) at various weight ratios of sample to ball (1/9, 1/27 and 1/45) with 10 wt% Fe 2O 3. The revolution speed was 250 rpm and the milling time was 2 h. The sample Mg–10 wt% Fe 2O 3, prepared by milling at the weight ratio of sample to ball 1/45, has the best hydrogen-storage properties. It absorbs 5.56 wt% hydrogen at the first cycle at 593 K under 12 bar H 2 for 60 min. Its activation is accomplished after two hydriding–dehydriding cycles. The activated sample absorbs 4.26 wt% hydrogen at 593 K, 12 bar H 2 for 10 min. The reactive grinding of Mg with Fe 2O 3 increases the H 2-sorption rates by facilitating nucleation (by creating defects on the surface of the Mg particles and by the additive), by making cracks on the surface of Mg particles and reducing the particle size of Mg and thus by shortening the diffusion distances of hydrogen atoms. Hydriding–dehydriding cycling also increases the H 2-sorption rates by creating defects on the surface of the Mg particles, and by making cracks on the surface of Mg particles and reducing the particle size of Mg.