Hydrogen Sorption-desorption Research Articles

A statistical physics approach to hydrogen sorption-desorption isotherms in LaNi4.3Fe0.7

This study explores experimental hydrogen sorption and desorption isotherms on LaNi4.3Fe0.7 at four temperatures, employing different statistical physics models based on the grand canonical ensemble. The choice of the most appropriate model considered statistical parameters and physical analysis of the estimated parameters, culminating in selecting the monolayer model with two types of energies. The detailed analysis of these parameters provides an improved understanding of the process, highlighting the presence of hysteresis in the H2sorption and desorption in the metallic alloy. The sorption and desorption energies determined for this model vary between 82 and 109 kJmol−1, indicating a predominant chemical mechanism. Calculations of thermodynamic potentials suggest that the processes are exothermic and spontaneous. When comparing with other alloys of the same base, we observed that adding Fe presents similar trends in the model parameters, contributing to subtle improvements in the process.

The phase transitions behavior and defect structure evolution in magnesium hydride/single-walled carbon nanotubes composite at hydrogen sorption-desorption processes

The development of hydrogen storage methods is one of the important areas of research in the field of hydrogen energy, while metal hydrides and composites based on them are the most preferred candidates for this. In this paper, one of the composite hydrogen storage materials based on magnesium hydride and single-walled carbon nanotubes was considered. The hydrogen sorption and desorption behavior in composite have been investigated for temperatures and pressures ranges (593−653) K and (0−3) MPa, respectively. Using scanning electron microscopy, it was shown that carbon nanotubes are homogeneously distributed on the surface of MgH2 particles and some of nanotubes are partially embedded in the bulk of MgH2. According to pressure-composition-temperature curves and Van’t Hoff plots it was determined that the enthalpy value of hydrogen absorption process was 69 KJ/mol H2 and 62 KJ/mol H2 for milled MgH2 and MgH2 with 5 wt% single-walled carbon nanotubes, respectively. The main regularities of phase transition in the magnesium-hydrogen system for composite and magnesium hydride during dehydrogenation have been researched for temperatures in the range of 298–750 K. The in situ analysis of the phase transitions during dehydrogenation of MgH2 and composite based on MgH2 and 5 wt% of single-walled carbon nanotubes in argon atmosphere indicates pronounced catalytic effect of carbon nanotubes on the hydrogen desorption. The thermally stimulated desorption curves showed that hydrogen begins to release from the composite where the MgH2 decomposition is minimal. An in situ Doppler broadening spectroscopy study revealed that this is caused by a significant changes magnesium defect structure as a result of the carbon nanotubes/nanoparticles embedding, and the low-temperature hydrogen release follows from the decomposition of associated defects (dislocation-hydrogen or vacancy-hydrogen complexes) as well as its effective diffusion to the surface.

Positron Annihilation Spectroscopy Complex for Structural Defect Analysis in Metal-Hydrogen Systems.

The current work is devoted to developing a system for the complex research of metal–hydrogen systems, including in an in situ mode. The system consists of a controlled gas reactor with a unique reaction chamber, a radioisotope positron source, and a positron annihilation spectroscopy complex. The use of the system enables in situ investigation of the defect structure of solids in hydrogen sorption–desorption processes at temperatures up to 900 °C and pressures up to 50 bar. Experimental investigations of magnesium and magnesium hydride during thermal annealing were carried out to approve the possibilities of the developed complex. It was shown that one cycle of magnesium hydrogenation–dehydrogenation resulted in the accumulation of irreversible hydrogen-induced defects. The defect structure investigation of the magnesium–hydrogen system by positron annihilation techniques was supplemented with a comprehensive study by scanning electron microscopy, X-ray diffraction analysis, and hydrogen sorption–desorption studies.

SYNTHESIS AND ELECTROCHEMICAL HYDROGENATION OF Tb2Co17-х-ySbxLiy AND Tb2Co17-х-yAlxMgy PHASES

Metal hydride batteries have a high sorption ability to the reverse hydrogen absorption, moderate pressure and temperature of the processes of hydrogen sorption-desorption and stability to cycling. We synthesized doped derivatives of binary intermetallic compound consisting terbium with cobalt to establish electrochemical properties when using them as anode materials in prototypes of nickel metal hydride batteries. The samples were made of high purity metals in an electric arc furnace in an argon atmosphere. Phase analysis was performed using X-ray diffraction data obtained on the DRON-2.0M powder diffractometer (Fe Kα-radiation). Scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDX) and X-ray fluorescence spectroscopy (XRF) were used to determine the quantitative and qualitative composition of the alloys. Electrochemical hydrogenation was performed in Swagelok cell two-electrode prototypes of chemical sources of electric current on a two-channel MTech G410-2 galvanostat in galvanostatic mode at a current density of 1.0 mA/cm2. The elemental composition of the Tb2Co16.5Sb0.2Li0.3 and Tb2Co16Al0.5Mg0.5 samples before and after hydrogenation was determined by the XRF method, a slight decrease in the content of terbium on the surface was found. Phase analysis of diffractograms of both samples before and after electrochemical hydrogenation showed that they contain hexagonal phases with a stoichiometry of 2:17. Only a phase with a structure of the Th2Ni17 type was found in the Tb2Co16.5Sb0.2Li0.3 alloy. In the Tb2Co16Al0.5Mg0.5 sample, in addition to the main phase with Th2Ni17 structure, the existence of another hexagonal phase with a similar crystal structure (TbCo5-x-yMgxAly) was detected. The results of X-ray diffraction of the Tb2Co16Al0.5Mg0.5 sample are fully consistent with the results of EDX analysis. The Tb2Co16.5Sb0.2Li0.3-based electrode undergoes significant amorphization due to the active hydrogenation/dehydrogenation process, but the hydrogen absorption properties remain acceptable. The cell parameters after hydrogenation increase, which indicates the inclusion of hydrogen atoms into the structure. The amount of deintercalated Hydrogen under experimental conditions is approximately 0.40 H/f.u. The Coulomb efficiency on the 10th cycle is equal to 81.3%, and on the 20th cycle is 90.2%. The Ni-MH battery prototype with the Tb2Co16Al0.5Mg0.5-based electrode demonstrates good reproducibility and Coulomb efficiency. The amount of deintercalated Hydrogen under experimental conditions is approximately 0.44 H/f.u. The Coulomb efficiency on the 10th cycle is 95.5%, and on the 20th is equal to 93.4%. Due to the amorphization processes as the number of cycles increases, the charging plateau voltage increases and a small decrease in the capacitive parameter τ is observed similarly to the Li,Sb-containing electrode. As electrode materials both alloys showed corrosion resistance in the electrolyte solution. Keywords: terbium; cobalt; solid solutions; crystal structure; electrochemical hydrogenation; anode materials.

Influence of the Substitution of Chromium for Manganese on the Structure and Hydrogen-Sorption Properties of Ti47.5Zr30Mn22.5 Eutectic Alloy

We study the influence of alloying with chromium on the structure and phase composition of the Ti47.5Zr30Mn22.5 eutectic alloy and its hydrogen sorption-desorption. It is shown that the addition of chromium to the alloy changes the type of crystal lattice of the Laves phase from the C14 hexagonal phase to the C15 cubic, which does not affect the hydrogen-sorption properties. It is demonstrated that hydrides obtained on the basis of the C14 and C15 Laves phases have different thermal stabilities.

Dependence of hydrogen sorption-desorption on the structure of amorphous and amorphous-crystalline Fe62.7Nd33.7B1.1Cu1.5Ti1.0 alloys

Dependence of hydrogen sorption-desorption on the structure of amorphous and amorphous-crystalline Fe62.7Nd33.7B1.1Cu1.5Ti1.0 alloys

Investigation of Hydrogen Sorption-Desorption Processes at Gas-Phase Hydrogenation and Defects Formation in Titanium by Means of Electron-Positron Annihilation Techniques

The results of hydrogen sorption and desorption processes investigation at commercially pure titanium alloy during hydrogenation at gas atmosphere are shown in this article. Titanium alloy hydrogenation at temperatures 350, 450 и 550 °С leads to δ-hydrides formation in samples’ volume. Hydrogen sorption rates were calculated on the linear parts of sorption curves and equal to 0.15·10-4 wt%/s at 350 °C, 0.86·10-4 wt%/s at 450 °C, 1.55·10-4 wt%/s at 550 °C. Phase transition in titanium-hydrogen system during thermally stimulated hydrogen desorption investigation by the means of short-wave diffraction of synchrotron radiation shows hydrides dissociation until 520-530 °C. Then α→β transition takes place until 690-720 °C and at this temperatures the phase transformation ends and additional hydrogen desorption peak appears in thermally stimulated hydrogen desorption curve. Defect structure at different hydrogen concentration investigation by the means of electron-positron annihilation techniques shows that hydrogen penetration into titanium leads to crystal lattice expansion. It initiates vacancy-type defects formation which reacts with hydrogen and forms defect-hydrogen complexes.

Strategy for the enhancement of H2 uptake in porous materials containing TiO2

The good affinity of TiO2 surface for hydrogen sorption has prompted in the past the synthesis of high specific surface area, Ti-doped mesoporous silicas. Since most TiO2 is buried in the pore walls of the silicas, such materials did not express their full potential H2 uptake. In order to overcome this limitation, different amounts of titania were deposited on the pore surface of a pre-formed SBA-15 of 704 m2/g, and the resulting oxides were calcined at 300 or 500 °C. The hydrogen sorption–desorption isotherms of the materials prepared in this study, at 77.4 K and up to 100 kPa, reveal that a small amount of titania doubles the hydrogen storage capacity of SBA-15, provided that the materials are calcined at least at 300 °C. Reproducible H2 uptakes up to 1.4 wt.% at 77.4 K and 100 kPa have been measured. The optimal amount of TiO2 is 4.5% in moles, leading to a uniform dispersion in the mesopores. A higher loading (7.3%) brings about the formation of large titania particles that tend to block the lumen of the mesopores, with no gain in the H2 sorption capacity.

Investigation of Hydrogen Sorption-Desorption Processes and Hydrides Formation and Dissolution in Zirconium by Using Sievert Apparatus and Short-Wave Diffraction of Synchrotron Radiation

Hydrogen sorption-desorption processes by zirconium alloy Zr-1Nb was investigated in this article. Sievert apparatus was used for investigation of hydrogen interaction with material. It was shown that hydrogenation at gas atmosphere at 350, 450 and 550 °C temperatures leads to the δ-hydride formation in all material volume. Hydrogen sorption rates were calculated on the linear parts of sorption curves and equal to 0.5·10-4 wt%/s at 350 °C, 9.5·10-4 wt%/s at 450 °C and 23.1·10-4 wt%/s at 550 °C. Short-wave diffraction of synchrotron radiation was used for investigation of hydrides dissociation during heating. Hydrides dissociation formed after hydrogenation at gas atmosphere occurs at temperature 522-540 °C. Further temperature increasing leads to β-phase appearance which indicates α to β phase transition at zirconium.

The Evolution of Defects in Zirconium in the Process of Hydrogen Sorption and Desorption

The influence of hydrogen sorption-desorption cycles on defect structure of Zr-1Nb alloy was investigated. Specimens were hydroganated from gas atmosphere at temperature 500 °C and pressure 2 atm up to the hydrogen concentration equal to 0.05 wt.% for each cycle. The hydrogen concentration during saturation was determinate by the volumetric method. Then samples were annealed at temperature 900 °C with the heating rate of 4 °C/s. The lattice defects were studied by means of positron lifetime spectroscopy (PLS) and doppler broadening spectroscopy (DBS). New experimental data about the evolution of the average positron lifetieme τavg, as well as the relative changes in the parameters S, W depending treatment stage in Zr-1Nb alloy during thermo hydrogen proccessing was obtained.

Effect of γ-ray irradiation on the sorption of hydrogen by nanoporous carbon materials

The effects of radiation exposure in a hydrogen atmosphere on hydrogen sorption by a synthetic porous carbon nanosorbent, SCN (spherical carbonite saturated). The exposure was created by γ-rays from cobalt-60 (photon energy 1.2 MeV, irradiation dose 4.8 × 107 rad) in a normal hydrogen atmosphere at a pressure of 1 atm and a temperature of 300 K. The processes of hydrogen sorption-desorption by SCN samples before and after irradiation were studied in a temperature interval of 15–1173 K. It was found that the irradiation of SCN in a hydrogen atmosphere significantly increased the amount hydrogen sorbed in the sample. We conducted a comparison with the results of earlier studies investigating the influence of irradiation on the sorption of hydrogen by single-walled carbon nanotubes. The amount of physically sorbed hydrogen in the synthetic SCN sorbent that was irradiated in the hydrogen atmosphere, is four times greater than the amount of hydrogen that was physically sorbed by the single-walled carbon nanotubes that were irradiated under similar conditions. At a temperature below 25 K, the hydrogen diffusion in the SCN was almost temperature independent for the porous subsystem with the highest diffusion coefficients, which is typical for cases when the tunnel diffusion mechanism dominates the thermodynamic mechanism.

Investigation of Defects Accumulation in the Process of Hydrogen Sorption and Desorption

This paper is devoted to the defect structure study of commercially pure titanium after hydrogen sorption-desorption cycles by means of positron lifetime (PL) and Doppler broadening spectrometry. Material was loaded with hydrogen from the gas phase till the concentration of hydrogen reached the value of 0.05 wt.% for each cycle. The essential changes in the positron annihilation characteristics of the sample are occurred after the each stage of treatment.

Hydrogen sorption–desorption studies on ZrCo–hydrogen system

The ZrCo–H2 system was investigated in this study owing to its importance as a suitable candidate material for storage, supply, and recovery of hydrogen isotopes. Desorption hydrogen pressure-composition isotherms were generated at six different temperatures in the range of 524–624 K. A van’t Hoff plot was constructed using the plateau pressure data of each pressure-composition isotherms and the thermodynamic parameters were calculated for the hydrogen desorption reaction of ZrCo hydride. The enthalpy and entropy change for the desorption of hydrogen were found to be 83.7 ± 3.9 kJ mol−1 H2 and 122 ± 4 J mol−1 H2 K−1, respectively. Hydrogen absorption kinetics of ZrCo–H2 system was studied at four different temperatures in the range of 544–603 K and the activation energy for the absorption of hydrogen by ZrCo was found to be 120 ± 5 kJ mol−1 H2 by fitting kinetic data into suitable kinetic model equation.

Hydrogen Storage in Irradiated Low-Dimensional Structures

Experimentally, two types of samples (carbon nanotube – CNT, NbSe2) were tested and both irradiated by γ-rays and nonirradiated at two temperature levels — room temperature (293 K) and liquid nitrogen temperature (78 K). The irradiated samples were tested concerning the hydrogen absorption capability, and comparative analysis was done. It has been showed that CNT, NbSe2 are sustainable for irradiation. The increasing (∼15%) of hydrogen sorption-desorption capability for carbon nanotubes after irradiation treatment was demonstrated. Low temperature procedure of hydrogen storing showed the 2.9–3.5 mass% of hydrogen. The increasing of hydrogen storing in NbSe2 has not been observed.

Physicomechanical properties of the hydrogen-accumulating intermetallics LaNi5 and TiFe and a LaNi5-Al composite

Some physicomechanical properties of the hydrogen-accumulating intermetallics LaNi5 and TiFe and a LaNi5-20 wt % Al composite are determined by kinetic microindentation. Indentation diagrams are obtained in the load P-indentation depth h-time t coordinates. The following main dependences and properties of the materials are calculated using these indentation diagrams: the dependence of the hardness on the indentation depth, the influence of the strain rate on the hardness, the activation volume, Young’s modulus, and the hysteresis losses during cyclic loading. The parameters characterizing the resistance of the material to disintegration during cycling under hydrogen sorption-desorption conditions are determined.

Ti/C and Ti/B Nanocomposites: Comparison of Sorption-Desorption Properties

Hydrogen sorption-desorption properties of Ti/B and Ti/C nanocomposites prepared under ball-milling of the corresponding powders in H2 flow were studied using kinetic, microscopic and spectroscopic techniques. Amorphous boron was found to be more effective in spurring Ti – H2 interaction than carbon because of the following properties: (1) significant fragmentation of Ti powder by preventing agglomeration of the particles; (2) unhindered hydrogen access to the surface of Ti nanoparticles through the boron matrix; (3) appearance of new occupation sites available for H atoms, which are characterized by low H2 desorption temperature. The dynamics of the formation of these sites and the H2 distribution between different occupation sites in dependence on phase composition and morphology were studied for the Ti/B system.

Stimulating Effect of Graphite Admixture on Hydrogen Sorption−Desorption Properties of Mechanically Activated Titanium Powder

The effect of graphite admixture on hydrogen sorption-desorption properties of mechanically activated electron microscopy, temperature-programmed reaction, and temperature-programmed desorption techniques. The major effect of graphite addition was found to be the formation of microporous carbon matrix particles containing randomly distributed titanium particles only several nanometers in diameter. This powder architecture enhances hydrogen transport to the titanium surface without hindrances and promotes titanium-hydrogen interaction by modifying the titanium surface and subsurface layers with interstitial carbon atoms.

Synthesis and characterization of Fe and composite Fe–TiN nanoparticles by dc arc-plasma

Fe and composite Fe–TiN nanoparticles were prepared by an active plasma–metal reaction method. The structure and morphology were examined by X-ray diffraction, transmission electron microscopic observation and Mössbauer experiment. The morphology of Fe is spherical and that of the composite Fe–TiN nanoparticle is dumbbell-like. The surface oxide of the nanoparticles exposed to air was characterized and the reduction characteristics in a hydrogen atmosphere were examined. The thermal stability of the nanocomposite particle is vastly superior to that of the metal particle. The hydrogen sorption–desorption characteristics of the nanoparticles were examined by temperature-programmed desorption measurements. Hydrogen desorption at above 450 K was observed for the composite Fe–TiN nanoparticles. The effect of CO coadsorption on the hydrogen desorption was also examined and a large amount of hydrogen desorption was observed.

Electrochemical behavior of metal hydrides

Metal hydride electrodes are of particular interest owing to their potential and practical application in batteries. A large number of hydrogen storage materials has been characterized so far. This paper deals with the effect of the chemical nature and stoichiometry of specific alloy families (AB5, A2B, AB/AB2 and AB2) on the hydride stability, hydrogen storage capacity and kinetics of hydrogen sorption-desorption in the solid phase/gas and solid phase/electrolyte solution systems. Special attention has been paid towards the electrochemical properties of metal hydrides in terms of their performance in Ni-MH rechargeable alkaline cells.

Morphology and hydrogen desorption characteristic of Ni-TiN nanocomposite particle prepared by RF plasma

Abstract Ni-TiN nanocomposite particles are prepared by RF plasma. Dumbbell-like and dice-like morphologies are seen. Hydrogen sorption-desorption characteristics of the nanocomposite particles were examined by temperature-programmed desorption measurements. Hydrogen desorption at 500–700 K is observed, which implies that a new adsorption state of hydrogen exists. Hydrogen desorption characteristics are not so influenced by coadsorption of CO. The results are compared with the previously reported ones that were produced by a DC plasma reaction method.