Hydrogen Pressure-composition Isotherms Research Articles

An investigation into the multi-parameter identification and model optimization strategy of the PCT curves of hydrogen storage alloys by multiple intelligent algorithms

A multi-parameter sensitivity analysis method was proposed based on Latin hypercube sampling and the rank correlation method. The general genetic algorithm was improved by incorporating a niche parallel algorithm, suspicious peak point judgment, and a local search strategy, and both the improved genetic algorithm and multi-parameter sensitivity analysis method were implemented through C++ programming. The hydrogen pressure-composition isotherm (PCT curve) was found to play an important role in the study of hydrogen storage properties of metallic materials, and its reaction enthalpy change term was widely replaced by a power series form of smoothing. Based on the improved multi-parameter sensitivity analysis method, the effects of the range of parameter values and the number of samples on sensitivity were investigated, where the sensitivity ranking of the 10 parameters in the classical model was obtained. In addition, the equilibrium hydrogen pressure expression models of the highest order i of the power series from 3 to 9 were developed. The influence of the highest order on the optimization of multi-parameter identification was compared using an improved genetic algorithm, and we concluded that the eighth order polynomial model had the optimal convergence and fitting effect. Based on the inspiration of the function trend shape, two innovative forms of the PCT model power series were proposed in this work. Combined with typical examples, three high-order models were fully evolved, and a better power series form was obtained compared to the traditional model.

Shape-dependent hydrogen-storage properties in Pd nanocrystals: which does hydrogen prefer, octahedron (111) or cube (100)?

Pd octahedrons and cubes enclosed by {111} and {100} facets, respectively, have been synthesized for investigation of the shape effect on hydrogen-absorption properties. Hydrogen-storage properties were investigated using in situ powder X-ray diffraction, in situ solid-state (2)H NMR and hydrogen pressure-composition isotherm measurements. With these measurements, it was found that the exposed facets do not affect hydrogen-storage capacity; however, they significantly affect the absorption speed, with octahedral nanocrystals showing the faster response. The heat of adsorption of hydrogen and the hydrogen diffusion pathway were suggested to be dominant factors for hydrogen-absorption speed. Furthermore, in situ solid-state (2)H NMR detected for the first time the state of (2)H in a solid-solution (Pd + H) phase of Pd nanocrystals at rt.

Hydrogen storage in Pd nanocrystals covered with a metal-organic framework.

Hydrogen is an essential component in many industrial processes. As a result of the recent increase in the development of shale gas, steam reforming of shale gas has received considerable attention as a major source of H2, and the more efficient use of hydrogen is strongly demanded. Palladium is well known as a hydrogen-storage metal and an effective catalyst for reactions related to hydrogen in a variety of industrial processes. Here, we present remarkably enhanced capacity and speed of hydrogen storage in Pd nanocrystals covered with the metal-organic framework (MOF) HKUST-1 (copper(II) 1,3,5-benzenetricarboxylate). The Pd nanocrystals covered with the MOF have twice the storage capacity of the bare Pd nanocrystals. The significantly enhanced hydrogen storage capacity was confirmed by hydrogen pressure-composition isotherms and solid-state deuterium nuclear magnetic resonance measurements. The speed of hydrogen absorption in the Pd nanocrystals is also enhanced by the MOF coating.

Hydrogen uptake of reduced graphene oxide and graphene sheets decorated with Fe nanoclusters

Graphene oxide (GO) has been prepared by employing modified Staudenmaier's method through thermal exfoliation of graphite oxide. High pressure hydrogen sorption isotherms up to 50 bar of GO, reduced by thermal reduction (TR-GO), chemical reduction (CR-GO) and graphene sheets decorated with Fe nanoclusters (Fe-GS) have been investigated. Thermal reduction of GO at 623 K under high vacuum yields TR-GO. Chemical reduction of GO using hydrazine forms CR-GO. Fe-GS was synthesized through arc-discharge between the ends of two graphite rods with one rod carrying Fe nanoparticles. The surface areas of these graphene samples were determined from the nitrogen adsorption isotherm employing Brunauer, Emmett and Teller (BET) method. Kelvin's equation was used to determine the pore size distribution of all graphene based samples. Hydrogen pressure-composition isotherms (PCI) were determined at 300 K and at 77 K, between 0.1 and 50 bar. Further, in this paper, we present a comparative adsorption isotherm analysis of hydrogen and helium on TR-GO. This reveals that the volume of hydrogen and helium adsorbed by TR-GO is nearly equal. The similar uptake volume determined for both hydrogen and helium indicates the possibility of monolayer adsorption of hydrogen and also nearly similar binding energy between TR-GO and H2/He.

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.

Finding Hydrogen-Storage Capability in Iridium Induced by the Nanosize Effect

We report nanosize-induced hydrogen storage in Ir, which does not absorb hydrogen in its bulk form. The mean diameter of the obtained Ir nanoparticles was estimated as 1.5 ± 0.5 nm by transmission electron microscopy. Hydrogen storage was confirmed by solid-state (2)H NMR and hydrogen pressure-composition isotherm measurements.

Lattice defects introduced into LaNi 5-based alloys during hydrogen absorption/desorption cycling

LaNi 5-based intermetallic compounds before and after hydrogen absorption/desorption cycling were observed by transmission electron microscopy. Both a-type and c-type dislocations, which had respective Burgers vectors of 1 / 3 < 1 1 2 ¯ 0 > and <0 0 0 1> in the { 0 1 1 ¯ 0 } slip plane, were introduced into LaNi 5, LaNi 4.5Cu 0.5 and LaNi 4.5Fe 0.5 after the first absorption/desorption cycle. These alloys exhibited large difference in the equilibrium pressure between the first absorption and first desorption. Dislocations were introduced during hydrogenation in order to accommodate lattice mismatch between the metal-hydrogen solid solution and the metal hydride; furthermore, the interface between the solid solution and hydride was suggested to be the { 0 1 1 ¯ 0 } plane. In contrast, neither dislocations nor stacking faults were observed in LaNi 4.5Si 0.5, LaNi 4.5Al 0.5 and LaNi 4.75Sn 0.75, which showed little or no hysteresis in the hydrogen pressure–composition isotherms. Excess pressure was needed in the absorption process for the formation of misfit dislocations.

Hydrogen insertion in Pd core/Pt shell cubo-octahedral nanoparticles

We report a theoretical density functional theory study of the absorption and adsorption of hydrogen in Pd core/Pt shell cubo-octahedral nanoparticles of 55 and 147 atoms. We have explored all the possible sites available for hydrogen loading. The relative stability of H in the different sites is calculated and discussed in terms of the local geometrical and chemical environments. As a general trend, the most stable absorption sites are pyramidal interstices at the interface offering a volume for H around 2 × 2.60 A3, with a moderate atomic rearrangement upon H insertion and in which the H atom maximizes the number of Pd neighbors. Our theoretical findings give support to the recent hydrogen pressure-composition isotherms and NMR measurements carried out in this type of bimetallic nanoparticle [Kobayashi et al., J. Am. Chem. Soc. 130, 1818 (2008)].

リチウムアミドの融解によるリチウム-窒素系水素貯蔵材料の熱力学的特性変化

In this study, we used the Sieverts' method to measure the hydrogen pressure-composition isotherms of LiH and LiNH2 mixed in a molar ratio of 2:1 in order to obtain the standard reaction enthalpy and entropy of the hydrogenation reaction. The amounts of hydrogen absorbed and desorbed by the mixture were equal to the theoretical value at temperatures ranging from 653 K to 873 K (which were higher than the melting temperature of the mixture), where the standard reaction enthalpy and entropy were −32±3 kJ•(mol H2)−1 and −68±4 J•K−1•(mol H2)−1, respectively. On the other hand, the amounts were less than the theoretical value at 553 K and 623 K (which were lower than the melting temperature) due to the incomplete reaction, indicating that these isotherms would not afford reliable estimates of the standard reaction enthalpy and entropy. Hence, we instead calculated the standard enthalpy and entropy below the melting temperature using the values above the melting temperature and the standard enthalpy and entropy of fusion of the mixture. The values thus obtained, −49±3 kJ•(mol H2)−1 and −95±5 J•K−1•(mol H2)−1, respectively, are significantly different from those previously reported. Here, the differences are discussed from the standpoint of the difficulty in measuring the hydrogen pressure-composition isotherms at lower temperatures as well as the validity of the method.

Hydrogen-Storage Properties of Solid-Solution Alloys of Immiscible Neighboring Elements with Pd

Rh and Ag are the elements neighboring Pd, which is well known as a hydrogen-storage metal. Although Rh and Ag do not possess hydrogen-storage properties, can Ag-Rh alloys actually store hydrogen? Ag-Rh solid-solution alloys have not been explored in the past because they do not mix with each other at the atomic level, even in the liquid phase. We have used the chemical reduction method to obtain such Ag-Rh alloys, and XRD and STEM-EDX give clear evidence that the alloys mixed at the atomic level. From the measurements of hydrogen pressure-composition isotherms and solid-state (2)H NMR, we have revealed that Ag-Rh solid-solution alloys absorb hydrogen, and the total amount of hydrogen absorbed reached a maximum at the ratio of Ag:Rh = 50:50, where the electronic structure is expected to be similar to that of Pd.

Atomic-Level Pd−Pt Alloying and Largely Enhanced Hydrogen-Storage Capacity in Bimetallic Nanoparticles Reconstructed from Core/Shell Structure by a Process of Hydrogen Absorption/Desorption

We have achieved the creation of a solid-solution alloy where Pd and Pt are homogeneously mixed at the atomic level, by a process of hydrogen absorption/desorption as a trigger for core (Pd)/shell (Pt) nanoparticles. The structural change from core/shell to solid solution has been confirmed by in situ powder X-ray diffraction, energy dispersive spectra, solid-state (2)H NMR measurement, and hydrogen pressure-composition isotherms. The successfully obtained Pd-Pt solid-solution nanoparticles with a Pt content of 8-21 atom % had a higher hydrogen-storage capacity than Pd nanoparticles. Moreover, the hydrogen-storage capacity of Pd-Pt solid-solution nanoparticles can be tuned by changing the composition of Pd and Pt.

Inhomogeneous Phase Transition upon Hydrogenation of Nanocluster Pd Films

Phased out: A combination of electrochemical and optical techniques is used to study the interaction of hydrogen with palladium nanoclusters. Hydrogen pressure-composition isotherms reveal the reduced presence of the beta phase in palladium nanoclusters. Hydrogen extraction transients relate the reduced miscibility gap to a core-shell phase transformation in the palladium nanoclusters (see picture).

Atomic-level Pd–Au alloying and controllable hydrogen-absorption properties in size-controlled nanoparticles synthesized by hydrogen reduction

Size-controlled atomic-level Pd-Au alloy nanoparticles have been synthesized with a wide range of atomic ratios by a facile method using H2 gas, and their controllable hydrogen-absorption properties have been studied from hydrogen pressure-composition isotherms and solid-state 2H NMR spectra.

Nanosize Effects on Hydrogen Storage in Palladium

The size dependencies of the hydrogen-storage properties in polymer-coated Pd nanoparticles with diameters of 2.6 ± 0.4 and 7.0 ± 0.9 nm were investigated by a measurement of hydrogen pressure-composition isotherms. Their storage capacities per constituent Pd atom in the particles decreased with decreasing particle size, whereas the hydrogen concentrations in the two kinds of nanoparticles were almost the same and 1.2 times as much, respectively, as that in bulk palladium after counting zero hydrogen occupancy on the atoms in the first surface layer of the particles. Furthermore, apparent changes in hydrogen absorption behavior with decreasing particle size were observed, that is, a narrowing of the two-phase regions of solid-solution and hydride phases, the lowering of the equilibrium hydrogen pressure, and a decrease in the critical temperature of the two-phase state. By analyzing the isotherms, we quantitatively determined the heat of formation (ΔHα→β) and the entropy change (ΔSα→β) in the hydride form...

Effect of microstructure on hydrogen absorption in LaMg 2Ni

Hydrogen absorption properties in LaMg 2Ni compound are presented. Nanostructured phases have been obtained by crystallisation of an amorphous alloy, in order to study the influence of the microstructure on the absorption/desorption properties. In order to improve absorption kinetic, chemical etching has been also performed. The structural and hydriding properties were examined by X-ray diffraction, thermal analysis and hydrogen pressure-composition. An amorphous phase has been obtained from the LaMg 2Ni phase by means of melt spinning technique. Crystallisation occurs in two stages at 500 K and 530 K. After crystallisation, a nanostructured phase has been obtained. Hydrogenation at 443 K leads to the formation of LaMg 2NiH 7, but at higher temperatures (523 K) LaH X is produced. Hydrogen pressure-composition isotherm of LaMg 2Ni at 443 K is presented. The enthalpy of LaMg 2Ni hydride formation was measured to be −47 kJ mol H −1 by thermal analysis.

Hydrogen absorption of the polymer-coated Pd nanoparticle

Mono-dispersed palladium nanoparticles, which were coated with polymer, were prepared and their hydrogen absorption properties were investigated. The averaged diameter of the prepared particles was estimated to be 2.6 ± 0.4 nm from a TEM photograph. By measurement of hydrogen pressure-composition isotherms, the hydrogen solubility of the Pd particles was determined to be 0.5 H per Pd. In the isotherms, plateau-like region was observed in the temperature rang of 303 to 393 K, indicating the coexistence of solid solution and hydride phases in the Pd nanoparticles in this temperature range.

Hydrogen Pressure-Composition Isotherms for Ti&lt;SUB&gt;45&lt;/SUB&gt;Zr&lt;SUB&gt;38&lt;/SUB&gt;Ni&lt;SUB&gt;17&lt;/SUB&gt; Amorphous and Quasicrystal Powders Produced by Mechanical Alloying

Pressure-composition isotherms (PCTs) for amorphous and icosahedral (i) quasicrystal powders produced by mechanical alloying of Ti45Zr38Ni17 powder mixtures were measured at temperatures of 473 K and 523 K at low-hydrogen pressures, lower than 0.1 MPa. Sloping plateau-like features on PCTs were observed at equilibrium hydrogen pressures lower than 1 kPa, below an H/M (hydrogen to metal atom ratio)≈1.2 and ≈1 for the amorphous and i-phase powders respectively. The plateau-like region for the i-phase powder was steeper and narrower than that for the amorphous powder, implying some small differences between the local structures of the i-phase and the amorphous phase. After the PCT measurements, an increase in the nearest-neighbor atom spacing and an expansion of the quasilattice were observed for the amorphous and i-phase powders respectively. Impurities from some unsynthesized elemental material and a Ti2Ni type phase were also present. These also absorbed hydrogen, shown by an expansion of their crystal lattices. However, no crystal hydride formation was observed in any of the powders.

The effect of absorbed hydrogen on the magnetic properties of DyFe 11Ti

The effect of absorbed hydrogen on the structural and magnetic properties of DyFe 11Ti has been investigated. The compound DyFe 11Ti was hydrogenated to the composition DyFe 11TiH x , where x ranges from 0 to 1.5. The absorption hydrogen pressure-composition isotherms of the hydrides indicate solid solution behavior. Hydrogen absorption does not change the tetragonal structure of the host compound but is accompanied by an expansion in unit cell volume. Magnetic characteristics of the host material and its hydrides (measured in situ in a hydrogen atmosphere) were investigated over the temperature range 77–700 K and at applied fields up to 12 kOe. Upon hydrogenation the magnetic ordering temperature T c as well as the spin-reorientation temperatures T sr are observed to increase. Moreover, the incorporation of hydrogen leads to an expansion of the temperature range in which the magnetic anisotropy of the rare-earth sublattice dominates over that of the iron sublattice.

還元拡散法によるニッケル‐ミッシュメタル系化合物の直接製造に関する研究 （第２報） ＲｍＮｉ５化合物の水素吸・脱蔵特性について

Aiming at the development of less energy-consumptive process for producing hydrogen storage materials, an experimental study was carried out on absorption-desorption characteristics of hydrogen for the RmNi5 compounds which were produced from various mischmetal oxides (Rm2O3) by the reduction-diffusion (R-D) method. In the R-D process, a mischmetal oxide was reduced by metallic calcium in the presence of nickel particles and the reduced mischmetal elements diffused into the nickel particles to directly form a RmNi5 compound.The hydrogen pressure-composition isotherms (PCT) were determined by a Sievert's apparatus for hydrides of (a) lanthanum-base RmNi5, (b) cerium-base RmNi5, (c) cerium-base RmNi4.5 Coos, RmNi4.5 Al0.3 and RmNi4.5 Mn0.5, and (d) cerium-base RmNi3.55 Co0.75 Mn0.5 Al0.3. The hydride of the lanthanum-base RmNi5 presented a plateau region extending up to nH (=H/M) of about 1, where the equilibrium PH2 in the desorption isotherm was 4.5 atm at 20°C. On the other hand, a small hydrogen absorbability was shown for the cerium-base RmNi5 and no plateau region was observed in the PCT diagram. The hydrogen absorbability increased significantly by replacing some nickel sites of lattice of the cerium-base RmNi5 by cobalt, aluminium or manganese and forming RmNi4.5 Co0.5, RmNi4.5 Al0.5 or RmNi4.5 Mn0.5. The cerium-base RmNi3.5 5 Co0.75 Mn0.4 Al0.3 cornpound also showed favourable characteristics amenable to the use for a hydrogen storage material. It absorbed hydrogen at ambient temperatures so fast that there seemed to be no need of an activation procedure for the hydrogen absorption.

Thermodynamic studies of hydrides of R 6Fe 23 (R ≡ Y, Er, Ho, Lu) and R 6Mn 23 (R ≡ Gd, Dy, Er, Ho)

The results of a thermodynamic study of the dehydrogenation of R 6Mn 23 (R ≡ Gd, Dy, Ho, Er) are reported and correlated with earlier work on R 6Fe 23 hydrides (R ≡ Y, Er, Ho, Lu). The enthalpy and entropy changes ( ΔH, ΔS) associated with the desorption of hydrogen from particular hydride phases have been calculated from hydrogen pressure-composition isotherms and the van't Hoff expression. The thermodynamic work indicates four hydride phases for the iron-containing systems and three for the manganese-containing systems. A Lundin-type plot of the free energy of hydrogen desorption vs. the interstitial hole radius for the R 6Fe 23H x system illustrates the dependence of hydride stability on the lattice dimensions. The relative stabilities of the different hydrogen sites that are occupied for these R 6T 23-H systems were established by correlating thermodynamic and published structural information. In general, the affinity of an interstitial hole for hydrogen was found to follow R 6 > R 3 T > RT 3, where T ≡ Fe or Mn (spatially defined by R x T y ). Attention is drawn to the importance of H-H nearest-neighbor interactions in regard to the structures of these materials. Isotope effects are observed for the Ho 6Fe 23-H(D) systems.