Hydrogen Desorption Temperature Research Articles

G0400604 圧延Mg箔にFeが積層されたフィルムの水素吸蔵放出特性評価

Hydrogen storage alloy is expected as one of the promising storage system and it has the advantages that are higher safety and hydrogen storage density per volume than other storage systems. There are several kinds of the materials and the Mg based alloy is an attractive one for hydrogen storage one. Because of the density up to 7.6 wt.% in the reversible Mg hydride, the light weight and the reasonable price. In this research, they were prepared that the cold rolling Mg-foil, the Mg-foil deposited with Fe and Pd, and the Mg film deposited on a substrate and then deposited with Fe and Pd. Each hydrogenated films was examined with the X-ray diffraction (XRD) and the films which had formed hydride were carried out the differential scanning calorimetry (DSC) to characterize the hydrogen desorption temperature. From the results, we examined the thickness effect of Mg layer in hydrogen storage properties.

Improvement on Hydrogen Desorption Performance of Calcium Borohydride Diammoniate Doped with Transition Metal Chlorides

Calcium borohydride diammoniate with a molecular formula of Ca(BH4)(2).2NH(3) is a novel complex hydride for hydrogen storage. However, it suffers from high temperature and sluggish kinetics for hydrogen desorption. In this work, the temperature and kinetics for hydrogen desorption of calcium borohydride diammoniate were effectively improved through doping transition metal chlorides (such as CoCl2, NiCl2, and FeCl3) in a closed vessel. Three additives could effectively decrease the temperature for hydrogen desorption of Ca(BH4)(2).2NH3. Among them, CoCl2-doped Ca(BH4)(2).2NH3 could desorb hydrogen even at a low temperature of 170 degrees C, and at 200 degrees C, 7.6 wt % hydrogen with high purity is released, which shows superior performance for hydrogen desorption than that of pristine Ca(BH4)(2).2NH(3.) For CoCl2-doped Ca(BH4)(2).2NH(3), X-ray absorption fine structure (XAFS) revealed that the improvements could be ascribed to the catalytic function of well-dispersed cobalt particles, which results in a much lower activation energy (86.1 kJ/mol) for hydrogen desorption of calcium borohydride diammoniate.

Enhanced hydrogen desorption property of MgH2 with the addition of cerium fluorides

Hydrogen desorption property of MgH2 doped with cerium fluorides with different valences prepared using ball milling has been studied. CeF4 is catalytically active for hydrogen desorption of MgH2. Hydrogen desorption temperature and apparent activation energy of MgH2 are significantly reduced with dopant of 2mol% of CeF4, which might be attributed to the formation of a new Ce–F–Mg specie at the CeF4/MgH2 interface and the easy electron transfer induced from the high valence Ce-cation. The apparent activation energy of hydrogen desorption of MgH2 is reduced from ∼160kJ/mol to ∼110kJ/mol with the dopant of CeF4.

Hydrogen Behavior in Chromium-Coated Zirconium Alloy E-110 During Deposition in a Gas Discharge

The regularities and mechanisms of the processes characterizing the behavior of hydrogen in the zirconium alloy E-110 with a chromium coating were studied at different stages of the experiment: during irradiation of the substrate by ions from argon plasma and in the process of coating deposition. After ion bombardment of the zirconium, the hydrogen was retained in the interior and in the defects of the surface layer of the zirconium, and hydrogen trapping decreased with increasing residual gas pressure during irradiation in the range 1.3–30 mPa. The hydrogen atoms trapped during deposition of the chromium coating were retained primarily in the zirconium. As the pressure of the deuterium added to the residual gas during coating deposition increased, the trapping of deuterium atoms increased in the zirconium and remained unchanged in the chromium coating. Hydrogen atoms were observed to transition from the interior of the zirconium to the trapping centers in the oxide layer, which was accompanied by a reduction of the hydrogen desorption temperature and observed during ion irradiation of the substrate and coating deposition in a low vacuum.

Preparation and hydrogen sorption properties of a Ni decorated Mg based Mg@Ni nano-composite

For the first time, a nano Ni decorated Mg ultrafine powder, Mg@Ni nano-composite powder, was prepared through arc plasma evaporation of pure Mg followed by the electroless plating of Ni on the Mg ultrafine particles in a NiCl2 solution. The phase components, microstructure and hydrogen sorption properties of the Mg@Ni composite powder were carefully investigated. It is observed that the composite is mainly composed of ultrafine Mg particles decorated by nano Ni grains introduced during electroless plating. Based on the Pressure-Composition-Temperature measurements, the hydrogenation enthalpy of the Mg@Ni composite is determined to be −73.6 kJ/mol H2, close to that of pure Mg. Meantime, the hydrogen absorption kinetics can be improved and the hydrogen desorption temperature of the hydrogenated Mg@Ni nano-composite can be reduced as compared to those of the pure Mg ultrafine powder. The improved hydrogen sorption properties can be mainly attributed to the gateway effects from the Mg2Ni/Mg2NiH4 phases formed on Mg/MgH2 ultrafine particles after re-/dehydrogenation cycles. The results showed that through arc plasma method followed by electroless plating of transition metals, the hydrogen storage properties of Mg ultrafine powders can be effectively improved.

In situ μ+SR measurements on the hydrogen desorption reaction of magnesium hydride

In order to clarify the reason why the hydrogen desorption temperature (Td) of MgH2 is lowered by milling, we have studied the change in a local nuclear magnetic field with temperature by means of μ+SR. We have found a very clear oscillation in the ZF-spectrum at 2 K for the "milled" and "milled with Nb2O5" samples, while such oscillation is weaker for the "as prepared" MgH2. It was also found that the oscillation signal is stable up to 250 K and is assigned mainly due to the formation of a H-μ-H system. At temperatures above ambient T, we also found that the ZF-μ+SR spectrum exhibits a static Kubo-Toyabe behavior due to the nuclear magnetic field of 1H. Furthermore, it was clarified that rapid H diffusion starts well below Td only in the milled samples, leading to the conclusion that the consequent enhanced diffusion rate in MgH2 is essential to accelerate the desorption reaction and to decrease Td.

Evaluation of the enthalpy change due to hydrogen desorption for M–N–H (M = Li, Mg, Ca) systems by differential scanning calorimetry

The enthalpy changes (ΔH) corresponding to the hydrogen desorption reactions LiNH2 + LiH → Li2NH + H2, 3 Mg(NH2)2 + 8LiH → Mg3N2 + 4Li2NH + 8H2, Ca(NH2)2 + 2LiH → CaNH + Li2NH + 2H2, and 2LiNH2 + CaH2 → CaNH + Li2NH + 2H2 were evaluated using differential scanning calorimetry (DSC) and were estimated to be 66.5, 47.1, 47.7, and 48.0 kJ/mol H2, respectively. To obtain accurate and precise values of ΔH, the cell constant of the DSC apparatus was determined using a reference sample, which has a similar hydrogen desorption temperature to those of the above systems. Furthermore, the accurate sample amount corresponding to the hydrogen desorption was estimated from the weight loss obtained by thermogravimetry (TG). It is clear from the experimental results that evaluation using DSC and TG measurements is a useful technique to obtain accurate ΔH values for the hydrogen desorption systems with complicated reaction processes. In addition, the required experimental time is shorter than those of conventional techniques using a volumetric method.

Hydrogen Absorption and Desorption during Heat Treatment of AISI 4140 Steel

Hydrogen plays an important role in the formation of quench cracks of structural steels. To clarify hydrogen absorption and desorption during heat treatment of AISI 4140 steel, thermal desorption spectrometry (TDS) analysis was carried out for the specimens in the as-rolled, as-quenched, and quenched and tempered conditions. Results show that hydrogen content increased from 0.127×10−6 in the as-rolled specimen to 0.316×10−6 in the as-oil-quenched specimen. After tempering at 200 °C, the hydrogen content in the oil-quenched specimen decreased to 0.155×10−6, and the peak temperature of hydrogen desorption increased from 200 to 360 °C. From the dependence of hydrogen content in the as-quenched specimens on austenitizing time, it can be deduced that hydrogen absorption occurs during austenitizing. The simulation of hydrogen absorption contributes to a better understanding on the distribution of hydrogen during the heat treatment in structural steels.

New insights into the thermal desorption of the 2LiNH2 + KBH4 + LiH mixture

In situ two-dimensional synchrotron X-ray powder diffraction investigation combined with Rietveld method data analysis were performed in order to yield a complete and quantitative phases structure evolution of the polycrystalline mixture 2LiNH2 + KBH4 + LiH during H2 desorption. While a first-principles, purely thermodynamics approach of the system predicted a single dehydrogenation step reaction at relatively low temperatures, it is assessed experimentally that the reaction occurs in two steps with first the formation of Li2NH at ca. 230 °C due to the reaction between LiNH2 and LiH plus hydrogen and ammonia evolution, followed by an additional reaction of the resulting phases with KBH4 at 360 °C, which releases hydrogen and leads to the formation of the monoclinic and tetragonal Li3BN2 polymorphs. Besides pointing out possible limits of a purely thermodynamics approach inevitably relying exact knowledge of experimental quantities, it is concluded that before assuming it viable for on-board vehicle use, additional stoichiometries may be worth of investigation in order to assess any existence of lower hydrogen desorption temperature of such system.

Magnesium Composites with Additions of Oxygen-Stabilized η-Zr4Fe2O0.5 for Effective Hydrogen Accumulation

The advantages of reactive ball grinding for preparation of new efficient Mg-based hydrogen storage materials are discussed. Magnesium-based nanocomposites were synthesized with additions of η-Zr4Fe2O0.5 intermetallic compound, which is characterized by enhanced resistance to disproportionation in hydrogen and can prolong the cyclic life of materials. The improvement of hydrogen absorption parameters for Mg–intermetallic composites was observed. It was shown that fourfold increase in the reaction rate during mechanochemical synthesis of MgH2 and decrease in hydrogen desorption temperature by 80°C were induced by catalytic additions.

Ab-initio calculations of the elastic and finite-temperature thermodynamic properties of niobium- and magnesium hydrides

Density Functional Theory (DFT) calculations have been used for calculating the elastic and thermodynamic properties of Mg, Nb, and their hydrides. The study is motivated by a previous work that showed constraints arising from Mg/Nb layer interfaces de-stabilized the magnesium hydride and resulted in decomposition temperatures much lower than in the bulk state. The calculated mechanical properties and the difference in the volume expansion of Mg- and Nb-hydrides support the ideas of large, de-stabilizing mechanical stresses arising from significant volume expansion incompatibilities in Mg/Nb multilayers. The stress and corresponding formation of metastable phases result in significant destabilization of MgH2 and provide ultra-low hydrogen desorption temperature in Mg/Nb multilayers.

Structural Characterization of Mg2CoH5-based Nanocomposites for Hydrogen Storage

Hydrogen is considered the ideal energy carrier, mainly due to its heating power, the highest among all chemical fuels, and to possibility of using it in fuel cells, therefore with efficiency and producing only water as by-product. However, the development of safe and effective hydrogen storage solutions remains as a challenge of applied research. MgH2, Mg2FeH6 and Mg2CoH5complex hydrides are promising materials for hydrogen storage, avoiding the inconvenient of gaseous or liquid storage alternatives. The main attractives of these phases are their volumetric and gravimetric hydrogen capacities, their reversibility during absorption/desorption cycles and the relatively low cost. Recently, we have achieved an important control of the synthesis of Mg-based complex hydrides with nanocrystalline structure, using reactive milling (RM) under hydrogen atmosphere as processing route [1, 2]. In this study, we present new results concerning the synthesis, hydrogen storage properties and structural characterization of MgH2–Mg2CoH5nanocomposites prepared by RM. The nanocomposites were produced by milling different Mg-Co starting compositions (2:1, 3:1, 5:1, 7:1, 1:0) for 12 h in a planetary mill under 3 MPa of H2. All samples were fully hydrogenated during milling, generating different MgH2–Mg2CoH5hydride mixtures. Mg presents the tendency of agglomerate during milling, so the sample that presents more MgH2shows larger agglomerates. This behavior causes a slight increase in the temperature of hydrogen desorption and the presence of two peaks, showed by DSC analysis for those samples which presents MgH2and Mg2CoH5. Using in-situ XRD and XANES during hydrogen desorption revealed that Mg and Co tend to remain coupled forming intermetallics after the complex hydride decomposition, differently from that was observed for Mg2FeH6. This effect is correlated to the high-reversibility exhibited by the Mg2CoH5phase. Furthermore, the nanocomposites of MgH2+Mg2CoH5showed better H-absorption/desorption kinetics than the Mg2CoH5or MgH2alone, as shown by volumetric measurements. The combination of MgH2and Mg2CoH5is therefore a promising strategy to produce hydrogen storage materials, matching the good reversibility and high capacity of magnesium hydride with the lower thermal stability.

Symbiotic CeH2.73/CeO2 catalyst: A novel hydrogen pump

Using additives/catalysts to destabilize hydrides of high hydrogen storage density, e.g. MgH2 with 7.6wt%-H and desorption temperature as high as 300–400°C, is one of the most important strategies to overcome the hurdle of applying hydrogen storage materials in technologies related to hydrogen energy. Despite tremendous efforts, to develop additives/catalysts with high catalytic activity and easy doping remains a great challenge. Here, we report a simple method to induce a novel symbiotic CeH2.73/CeO2 catalyst in Mg-based hydrides, which is capable of massive fabrication. More importantly, we reveal a spontaneous hydrogen release effect at the CeH2.73/CeO2 interface, which leads to dramatic increase of catalysis than either sole CeH2.73 or CeO2 catalyst. Maximum hydrogen desorption temperature reduction of MgH2 could reach down to ~210°C as molar ratio of CeH2.73 to CeO2 was 1:1. The dynamic boundary evolution during hydrogen desorption was observed in the symbiotic CeH2.73/CeO2 at atomic resolution using in situ High-Resolution Transmission Electron Microscope (HRTEM). Combining the ab-initio calculations, which show significant reduction of the formation energy of VH (hydrogen vacancy) in the CeH2.73/CeO2 boundary region in comparison to those in the bulk MgH2 and CeH2.73, we demonstrate that the outstanding catalytic activity can be attributed to the spontaneous hydrogen release effect at the CeH2.73/CeO2 interface.

An Investigation into the Hydrogen Storage Characteristics of Ca(BH4)2/LiNH2 and Ca(BH4)2/NaNH2: Evidence of Intramolecular Destabilization

We report a study of the hydrogen storage properties of materials that result from ball milling Ca(BH4)2 and MNH2 (M = Li or Na) in a 1:1 molar ratio. The reaction products were examined experimentally by powder X-ray diffraction, thermogravimetric analysis and differential scanning calorimetry (TGA/DSC), simultaneous thermogravimetric modulated beam mass spectrometry (STMBMS), and temperature-programmed desorption (TPD). The Ca(BH4)/LiNH2 system produces a single crystalline compound assigned to LiCa(BH4)2(NH2). In contrast, ball milling of the Ca(BH4)/NaNH2 system leads to a mixture of NaBH4 and Ca(NH2)2 produced by a metathesis reaction and another phase we assign to NaCa(BH4)2(NH2). Hydrogen desorption from the LiCa(BH4)2(NH2) compound starts around 150 °C, which is more than 160 °C lower than that from pure Ca(BH4)2. Hydrogen is the major gaseous species released from these materials; however various amounts of ammonia form as well. A comparison of the TGA/DSC, STMBMS, and TPD data suggests that the amount of NH3 released is lower when the desorption reaction is performed in a closed vessel. There is no evidence for diborane (B2H6) release from LiCa(BH4)2(NH2), but traces of other volatile boron–nitrogen species (B2N2H4 and BN3H3) are observed at 0.3 mol % of hydrogen released. Theoretical investigations of the possible crystal structures and detailed phase diagrams of the Li–Ca–B–N–H system were conducted using the prototype electrostatic ground state (PEGS) method and multiple gas canonical linear programming (MGCLP) approaches. The theory is in qualitative agreement with the experiments and explains how ammonia desorption in a closed volume can be suppressed. The reduced hydrogen desorption temperature of LiCa(BH4)2(NH2) relative to Ca(BH4)2 is believed to originate from intramolecular destabilization.

Influence of aluminum location on hydrogen sorption kinetics of magnesium-based materials

Hydrogen storage materials from Mg – Al alloy and Mg + Al mixture were prepared by reactive milling under H 2 atmosphere with carbonized anthracite as milling aid. The crystal structure of the materials and influence of Al location on hydrogen absorption/desorption kinetics were investigated. Results show that Mg partly got hydrided into β- MgH 2 and γ- MgH 2 during reactive milling. The average crystallite sizes of β- MgH 2 in the as-milled Mg – Al alloy and Mg + Al mixture were calculated by Scherrer equation to be 10 nm and 17 nm, respectively. In the process of hydrogen desorption, the catalytic ability of Al in Mg crystal lattice was not as effective as that on particle surface. The apparent activation energies for hydrogen desorption of the two materials were estimated by Kissinger equation to be 112.2 kJ/mol and 63.7 kJ/mol, respectively. Mg 17 Al 12 reacted with H 2 to convert into MgH 2 and elemental Al during static hydrogenation at 300°C. For the hydrogenated Mg + Al mixture, the obvious increase of crystallite size resulted in a low rate of hydrogen absorption and a high temperature for hydrogen desorption.

Hydrogen Sorption Efficiency of Titanium-Functionalized Mg–BN Framework

Hydrogen is considered as a potential candidate for future energy source in automobile industry. Hydrogen storage is the major problem in achieving this goal. In this study, metal–organic framework (MOF) with organic linker is replaced with BN linker namely borazocine (B4N4H8) and is functionalized with Ti, enhancing the stability and storage capacity of the framework. A first-principles electronic structure calculation using spin polarized generalized gradient approximation with Perdew–Burke–Ernzerhof functional, structural optimization and molecular dynamics (MD) simulations have been performed for hydrogen sorption efficiency of the Ti-functionalized Mg4O–BN framework (MBF). Low adsorption and desorption energies suggest the high hydrogen reversibility of the system. BN ring coordinates strongly with the Ti metal by Dewar interaction while each Ti metal adsorbs 4 H2 molecules by Kubas interaction. In MD simulations, 75% of the physisorbed H2 molecules are desorbed at 300 K while at 373 K chemisorbed hydrogen also began to desorb with the MBF framework remaining structurally stable. The average hydrogen desorption temperature using van’t Hoff equation is predicted to be 323 K with hydrogen storage capacity of 7.8 wt %. For the first time, the H2 sorption efficiency of the Ti-functionalized metal–BN framework has been studied and is found to be better than MOF or metal-functionalized MOF with respect to storage capacity, stability, and reversibility, making it a potential hydrogen storage material.

The Size Dependence of Hydrogen Mobility and Sorption Kinetics for Carbon‐Supported MgH2 Particles

MgH2 is a promising material for reversible solid‐state hydrogen storage. It is known that particle size can have a strong impact on hydrogen dynamics and sorption characteristics, but more detailed insight has been hampered by the great challenge to prepare small and well‐defined particles and study their hydrogen storage properties upon cycling. The preparation of MgH2 nanoparticles supported on high surface area carbon aerogels with pore sizes varying from 6–20 nm is reported. Two distinctly different MgH2 particle populations are observed: X‐ray diffraction invisible nanoparticles with sizes below 20 nm, and larger, crystalline, MgH2 particles. They release hydrogen at temperatures 140 °C lower than bulk MgH2. The size‐dependent hydrogen kinetics is for the first time corroborated by intrinsic hydrogen dynamics data obtained by solid state 1H NMR. Fast cycling is possible (80% of the capacity absorbed within 15 min at 18 bar and 300 °C), without a change in the hydrogen sorption properties, showing that the growth of the nanoparticles is effectively prevented by the carbon support. A clear correlation is found between the hydrogen desorption temperature and the size of the MgH2 nanoparticles. This illustrates the potential of the use of supported nanoparticles for fast, reversible, and stable hydrogen cycling.

Hydrogen Adsorption Structures and Energetics on Iron Surfaces at High Coverage

Hydrogen adsorption structures and energetics on the (100), (110), (111), (210), (211), (310), and (321) iron surfaces up to saturation have been computed using spin-polarized density functional theory and ab initio thermodynamics. The computed hydrogen desorption temperatures and energies on the (100), (110), (111), and (211) surfaces as well as the Fe–H binding energies on the (110) and (111) surfaces agree well with the available experimental data. At typical hydrogen reduction temperature (675 K), the mainly exposed (110) and (310) facets represent the active surfaces, as supported by the transmission electron microscopy study. Our results offer an example of investigating and understanding surface structures and active facets of heterogeneous catalysts under experimental conditions.

Deuterium adsorption on (and desorption from) SiC(0 0 0 1)-(3 × 3), R30°, R30° and quasi-free-standing graphene obtained by hydrogen intercalation

We present a comparative high-resolution electron energy-loss spectroscopy study on the interaction of atomic hydrogen and deuterium with various reconstructions of SiC(0 0 0 1). We first show that on both the (3 × 3) and reconstructions, deuterium atoms only bind to silicon atoms, thereby confirming the silicon-rich appellation of these reconstructions. Deuterium passivation of the (3 × 3) is only reversible when exposed to atomic deuterium at a surface temperature of 700 K since tri- and dideuterides, necessary precursors for silicon etching, are not stable. On the other hand, we show that the deuteration of the is always reversible because precursors to silicon etching are scarce on the surface. Then, we demonstrate that hydrogen (deuterium) adsorption at 300 K on both the (buffer-layer) and the quasi-free-standing graphene occurs on carbon atoms justifying their carbon-rich appellation. Comparison of the deuterium binding in the intercalation layer of quasi-free-standing graphene with the deuterated surface provides some indication on the bonding structure at the substrate intercalation layer. Finally, by measuring C–H (C–D) vibrational frequencies and hydrogen (deuterium) desorption temperatures we suggest that partial sp2-to-sp3 rehybridization occurs for the carbon atoms of the buffer-layer because of the corrugation related to covalent bonding to the SiC substrate. In contrast, on quasi-free-standing graphene hydrogen (deuterium) atoms adsorb similarly to what is observed on graphite, i.e. without preferential sticking related to the underlying SiC substrate.

Hydrogen Storage Properties of LiNH<sub>2</sub>/MgH<sub>2</sub> Complex Materials with Ti Catalyst by Mechanical Alloying

A LiNH2/MgH2 (1:1) complex was prepared by mechanical alloying and the effects of Ti and TiF3 on the characteristics of hydrogen storage were investigated. It was found that LiMgN and Li2NH phases exist as the main phases in the LiNH2/MgH2 (1:1) complex and that Mg (NH2)2 and NH4HF2 phases appear when TiF3 is added. The onset temperature of hydrogen desorption was reduced with increasing mill time, and the hydrogen saturation absorption temperature for the LiNH2/MgH2 complex decreased about 30°C with the addition of Ti and TiF3. Ti and TiF3 as catalysts are favorable for reducing the dehydrogenation temperature. The addition of TiF3 can also facilitate the increase of hydrogen desorption for the LiNH2/MgH2 (1:1) complex.