Pressure-composition Isotherms Research Articles

Thermodynamic assessment of the Ce[sbnd]H and CeNi5[sbnd]H system

Interstitial metal hydrides (MHs) have attracted considerable attention in the field of hydrogen technology, particularly in the context of storage and compression applications. Because of their minor hysteresis effects, good cyclability, activation simplicity, and high volumetric storage density, LaNi5-based alloys are recognized as prominent candidates for hydrogen storage application. Additionally, the system’s thermodynamic and electrochemical properties can be modified to suit the requirements of a particular application by alloying specific substituents. To ascertain the thermodynamic effects of Ce addition within LaNi5, in this work the CeH and CeNi5H systems have been modeled with the CALPHAD method. For this reason, in this work, two different thermodynamic models have been developed and assessed using the same pressure-composition isotherms (PCIs) datasets obtained from literature and theoretical formation energies newly calculated employing periodic density functional theory (DFT). Direct comparison of the models against each other in terms of accuracy and physical plausibility revealed that extrapolation of thermodynamic properties to data-scarce regions is more reasonable with fewer model parameters and in agreement with other similar systems within the rare-earth (RE) metal-hydride class. In addition, the CeNi5H system was investigated by assessing the (Ce)(Ni)5(V a,H)7 phase model, which could accurately predict hydrogen storage properties while being compatible with previously developed LaNi5H models. Ultimately, the models developed in this study may be employed and extended to describe multi-component REH systems and allow for thermodynamic computations that are highly desirable for accurate predictions of hydrogen absorption/desorption properties and degradation characteristics within the (La,Ce)Ni5H metal hydride family.

Structural Evolution and Hydrogen Sorption Properties of YxNi2−yMny (0.825 ≤ x ≤ 0.95, 0.1 ≤ y ≤ 0.3) Laves Phase Compounds

The YxNi2−yMny system was investigated in the region 0.825 ≤ x ≤ 0.95, 0.1 ≤ y ≤ 0.3. The alloys were synthesized by induction melting and corresponding annealing. The substitution of Mn for Ni (y = 0.1) favors the formation of a C15 structure with disordered Y vacancies against the superstructure of Y0.95Ni2. For y = 0.2 and 0.3, Mn can substitute in both Y and Ni sites. Single-phase compounds with a C15 structure can be formed by adjusting both the Y and Mn contents. Their hydrogen absorption–desorption properties were measured by pressure–composition isotherm (PCI) measurements at 150 °C, and the hydrides were characterized at room temperature by X-ray diffraction and TG–DSC experiments. The PCIs show two plateaus corresponding to the formation of crystalline and amorphous hydrides. The heating of the amorphous hydrides leads to an endothermic desorption at first and then a recrystallization into Y(Ni, Mn)3 and YHx phases. At higher temperatures, the Y hydride desorbs, and a recombination into a Y(Ni, Mn)2 Laves phase compound is observed. For y = 0.1, vacancy formation in the Y site and partial Mn substitution in the Ni site enhance the structural stability and suppress the hydrogen-induced amorphization (HIA). However, for a larger Mn content (y ≥ 0.2), Mn substitutes also in the Y sites at the expense of Y vacancies. This yields worse structural stability upon hydrogenation than for y = 0.1, as the mean ratio r(Y, Mn)/r(Ni/Mn) becomes larger than for y = 0.1 r(Y, ☐)/r(Ni/Mn).

Machine Learning for Quantitative Structural Information from Infrared Spectra: The Case of Palladium Hydride.

Infrared spectroscopy (IR) is a widely used technique enabling to identify specific functional groups in the molecule of interest based on their characteristic vibrational modes or the presence of a specific adsorption site based on the characteristic vibrational mode of an adsorbed probe molecule. The interpretation of an IR spectrum is generally carried out within a fingerprint paradigm by comparing the observed spectral features with the features of known references or theoretical calculations. This work demonstrates a method for extracting quantitative structural information beyond this approach by application of machine learning (ML) algorithms. Taking palladium hydride formation as an example, Pd-H pressure-composition isotherms are reconstructed using IR data collected in situ in diffuse reflectance using CO molecule as a probe. To the best of the knowledge, this is the first example of the determination of continuous structural descriptors (such as interatomic distance and stoichiometric coefficient) from the fine structure of vibrational spectra, which opens new possibilities of using IR spectra for structural analysis.

Microstructure and hydrogen storage properties of the Mg2−xYxNi0.9Co0.1 (x = 0, 0.2, 0.3, and 0.4) alloys

Rare earth elements have excellent catalytic effects on improving hydrogen storage properties of the Mg2Ni-based alloys. This study used a small amount of Y to substitute Mg partially in Mg2Ni0.9Co0.1 and characterized and discussed the effects of Y on the solidification and de-/hydrogenation behaviors. The Mg2−xYxNi0.9Co0.1 (x = 0, 0.2, 0.3, and 0.4) hydrogen storage alloys were prepared using a metallurgy method. The phase composition of the alloys was studied using X-ray diffraction (XRD). Additionally, their microstructure and chemical composition were studied using scanning electron microscopy and energy-dispersive X-ray spectroscopy, respectively. The hydrogen absorption and desorption properties of the alloys were studied using pressure-composition isotherms and differential scanning calorimetric (DSC) measurements. The structure of the as-cast Mg2Ni0.9Co0.1 alloy was composed of the peritectic Mg2Ni, eutectic Mg–Mg2Ni, and a small amount of pre-precipitated Mg–Ni–Co ternary phases, and was converted into the Mg2NiH4, Mg2Ni0.9Co0.1H4, and MgH2 phases after hydrogen absorption. Furthermore, the XRD patterns of the alloys showed the MgYNi4 phase and a trace amount of the Y2O3 phase along with the Mg and Mg2Ni phases after the addition of Y. After hydrogen absorption, the phase of the alloys was composed of the Mg2NiH4, MgH2, MgYNi4, YH3, Y2O3, and Mg2NiH0.3 phases. With the increase of Y addition, the area ratios of the peritectic Mg2Ni matrix phase in the Mg2−xYxNi0.9Co0.1 (x = 0, 0.2, 0.3, and 0.4) alloys gradually decreased until they disappeared. However, the eutectic structure gradually increased, and the microstructures of the alloys were obviously refined. The addition of Y improves the activation performance of the alloys. The alloy only needed one cycle of de-/hydrogenation to complete the activation for x = 0.4. The DSC curves showed that the initial dehydrogenation temperatures of Mg2Ni0.9Co0.1 and Mg1.8Y0.2Ni0.9Co0.1 were 200 and 156 °C, respectively. The desorption activation energies of the hydrides of the Mg2Ni0.9Co0.1 and Mg1.8Y0.2Ni0.9Co0.1 alloys calculated using the Kissinger method were 94.7 and 56.5 kJ/mol, respectively. Moreover, the addition of Y reduced the initial desorption temperature of the alloys and improved their kinetic properties.

Tuning Hydrogen Storage Properties in La1−xYxNi4.5Cu0.5 (x = 0.1; 0.2; 0.3; 0.4, 0.5) Alloys

Metal hydrides of AB5 compositions have been investigated over the years as they offer extraordinary volumetric hydrogen densities with high cycling stability and purity of released hydrogen. Moreover, by doping with different elements, the sorption properties of alloys can be significantly changed according to their foreseen applications. In this contribution, we report the synthesis routes and hydrogenation characteristics of La1−xYxNi4.5Cu0.5. The synthesized alloys exhibit excellent structural purity with all reflections indexed by the hexagonal P6/mmm structure. It was found that the Y content can easily tune (raise) the equilibrium pressures of the pressure–composition isotherms, while overall gravimetric density remains at a level exceeding 1.5 wt.% up to x = 0.3 then strongly decreases. The pressure range for desorption can be tuned from 1.5 to 5 bars at room temperature. Some alloys (x = 0; 0.2) exhibit very good stability during 1000 cycles of hydrogen loading and unloading. Furthermore, activation of the alloys is prompt, making them good candidates for stationary hydrogen storage, non-mechanical hydrogen compressors, or soft actuators.

Stoichiometry and annealing condition on hydrogen capacity of TiCr2-x AB2 alloys

This study presents the effect of stoichiometry and annealing condition on Ti–Cr AB2-type hydrogen storage alloys. Prior to annealing the majority phase of the as-cast alloys was the C14 Laves phase, with separate Ti and Cr phases. Annealing treatment (1273 K/14 d) led to a transition from C14 to C15 Laves phase structure. Both C14 (as-cast) and C15 (annealed) cell size increased with Ti content, up to a ratio (Cr/Ti) of 1.6, due to B-site Ti substitution in the lattice up to a limit. Pressure composition isotherm (PCI) measurements demonstrated alloys containing a greater Ti content had a better maximum hydrogen storage capacity (1.5 vs. 1.03 wt%) and lower plateau pressure (9.4 vs. 15.8 bar) at 253 K. Annealing resulted in a lower storage capacity (1.05 vs. 1.49 wt%), greater plateau pressure (ca. 30 bar) and flatter plateau slope (25 % reduction in plateau slope). Reduction in hydrogen storage capacity of annealed alloys could be due to diffusion of residual Cr in the alloy into the C15 Laves phase during the annealing process, thereby changing the local composition as confirmed through X-ray diffraction (XRD).

Exploring the Hydrogen Storage Performance of MgH2 Catalyzed by Two Transition Metals Ni and Co by In‐situ Calorimetry and Density Functional Theory Calculations

AbstractAddressing the drawbacks of magnesium‐based hydrogen storage materials with high thermal stability and slow kinetics of hydrogen absorption and discharge remains a current research challenge. In this paper, MgH2 catalyzed by Ni and Co has been prepared by ball milling. The hydrogen storage performance of the 90MgH2+5Ni+5Co composite has been investigated using common techniques, such as differential scanning calorimetry (DSC) and pressure‐composition‐isothermal (PCI) method. Furthermore, the main focus of the study was to investigate the changes in dehydrogenation enthalpy of MgH2 upon addition of Ni and Co, and the bonding mode during the dehydrogenation process of MgH2 and the dissociation energy barrier of hydrogen molecules on the surface of Mg were calculated using density functional theory. The results showed that the dehydrogenation activation energy of 90MgH2+5Ni+5Co decreased by 55.9 kJ/mol compared with that of MgH2. The dehydrogenation enthalpies of as‐milled MgH2 and 90MgH2+5Ni+5Co were 64.8 kJ/mol H2 and 63.4 kJ/mol H2, respectively. Thus the co‐doping of Ni and Co contributed significantly to decrease the thermodynamic stability and improve the hydrogen sorption kinetic properties of MgH2.

High entropy alloys containing immiscible Mg and refractory elements: Synthesis, structure, and hydrogen storage properties

In this work, the influence of Mg incorporation on the structural properties of the Mgx(TiVCrNb)100−x (x = 0, 10, and 20) hydrides was investigated and correlated with the hydrogen sorption properties. For material’s synthesis, the TiVCrNb pre-alloy was prepared by arc melting and subsequently, Mg was introduced via reactive high-energy ball milling (RBM) under H2 pressure. The hydrogen uptake of as-prepared hydrides strongly depends on the Mg content, as revealed by thermogravimetric analysis: 1.05, 1.28, and 1.62 H/M for the samples with x = 0, 10, and 20, respectively. The desorbed materials reabsorb hydrogen at 25 °C with fast kinetics, achieving capacities of 0.98, 1.23, and 1.49 H/M for x = 0, 10 and 20, respectively. The Pressure-Composition-Isotherm (PCI) curves present a flattening of the plateau pressure with increasing Mg content, which could explain better uptake for Mg-rich materials. Remarkably, Mg content significantly impacts the overall crystallinity of the RBM hydrides. Synchrotron XRD and related pair distribution function analysis (PDF) demonstrate that increasing Mg amount prevents the loss of long-range ordering during the ball milling process. Positron annihilation spectroscopy (PAS) shows that the as-prepared hydrides have a significant concentration of vacancies and dislocations usually introduced by ball milling. Coincidence Doppler broadening spectroscopy (CDB) hints that Mg atoms are preferentially located in the vicinity of vacancies, which may help relaxing the structure. In summary, this study highlights the potential benefit of adding Mg to refractory high entropy alloys produced by RBM, as Mg enhances crystallinity and subsequently improves the hydrogen storage properties.

Semi-empirical degradation rate estimation of TiFe1-xMnx alloy for thermochemical hydrogen compression durability tests

The substitution effects of Fe by Mn in TiFe1-xMnx (x = 0.1–0.5) alloys on the cyclic durability for thermochemical hydrogen compressors were investigated. In the substitution ratio range of 0.1–0.5, TiFe1-xMnx alloy shows a single CsCl phase structure, and thus is further used for a thermochemical hydrogen compressor at 500 °C. The compression tests are performed for 26 cycles in temperature range from 25 °C to 500 °C. The variation of hydrogen storage capacity during pressure composition isotherm test and structural identification by x-ray diffraction measurements are conducted to investigate the cyclic durability of TiFe1-xMnx alloy at the above compression conditions. The Mn substitution increased the cyclic durability of TiFe for the thermochemical hydrogen compressor, and 30% of Mn (TiFe0.7Mn0.3) is the optimum ratio for the reduction rate of hydrogen storage capacity and achieved maximum pressure. In addition, TiFe0.5Mn0.5, as the respective sample with the maximum capacity loss, was evaluated by the acceleration test to estimate the lifetime of the alloys. The reaction kinetics v0 [(H/M)/s] of the capacity loss of TiFe0.5Mn0.5 is defined as ln v0 = 1.68 ln (PH2/P0) − (2.39 × 1000)/T − 18.967. Therefore, it is possible to predict the durability of TiFe1-xMnx alloy at different pressure and temperature conditions by the presented acceleration test.

Thermodynamic improvement of lithium hydrides for hydrogen absorption and desorption by incorporation of porous silicon

Lithium is a popular lightweight material in the field of energy storage because of its hydrogen-binding properties and electrochemical advantages. The high hydrogen uptake capacity (∼12.6 wt%) of lithium hydride (LiH) is limited by the major thermodynamic constraint of requiring a higher temperature (∼700 °C) for desorption at 0.1 MPa. Incorporating a third element that creates Li phases during LiH dehydrogenation can help overcome thermodynamic constraints. This study involves modifying the hydrogen storage properties and thermodynamic characteristics of LiH through mechanical alloying with porous silicon (PS). Pressure composition isotherms measure the reversible hydrogen storage capacity (∼3.39 wt%) of LiH-PS alloy at different temperatures. The energy of hydrogen interaction is quantified by isosteric heat of absorption, which provides the enthalpy change in the reaction system. Hydrogen absorption and desorption enthalpies of 94.5 kJ (mol H2)−1 and 114.9 kJ (mol H2)−1 demonstrate the lowest energy demand among previously reported LiH alloys. The energy of hydrogen interaction is quantified by isosteric heat of absorption, which provides the enthalpy change in the reaction system. The hydride decomposition of the alloy indicates the possible range of hydrogen desorption.

Endergonic Hydrogenation at Ambient Conditions Using an Electrochemical Membrane Reactor.

Here, we determine how the hydrogen loading (x) of an electrochemical palladium membrane reactor (ePMR) varies with electrochemical conditions (e.g., applied current density, electrolyte concentration). We detail how x influences the thermodynamic driving force of an ePMR. These studies are accomplished by measuring the fugacity (P) of hydrogen desorbing from the palladium-hydrogen membrane and subsequently relating P to pressure-composition isotherms to determine x. We find that x increases with both applied current density and electrolyte concentration, but plateaus at a loading of x ≅ 0.92 in 1.0 M H2SO4 at -200 mA·cm-2. The validity of the fugacity measurements is supported experimentally and computationally by: (a) electrochemical hydrogen permeation studies; and (b) a palladium-hydrogen porous flow finite element analysis (FEA) model. Both (a) and (b) agree with the fugacity measurements on the following x-dependent properties of the palladium-hydrogen system during electrolysis: (i) the onset for spontaneous hydrogen desorption; (ii) the point of steady-state hydrogen loading; and (iii) the function describing hydrogen desorption between (i) and (ii). We proceed to detail how x defines the free energy of palladium-hydrogen alloy formation (ΔG(x)PdH), which is a descriptor for the thermodynamic driving force of hydrogenation at the PdHx surface of an ePMR. A maximum value ΔGPdH of 11 kJ·mol-1 is observed, suggesting that an ePMR is capable of driving endergonic hydrogenation reactions. We empirically demonstrate this capability by reducing carbon dioxide to formate (ΔGCO2/HCO2H = 3.4 kJ·mol-1) at ambient conditions and neutral pH.

The Role of Bulk Stiffening in Reducing the Critical Temperature of the Metal-to-Hydride Phase Transition and the Hydride Stability: The Case of Zr(MoxFe1−x)2-H2

This study aims to shed light on the unusual trend in the stabilities of Zr(MoxFe1−x)2, 0 ≤ x ≤ 1, hydrides. Both the rule of reversed stability and the crystal volume criterion correlate with the increased hydride stabilities from x = 0 to x = 0.5, but are in contrast with the destabilization of the end member ZrMo2 hydride. The pressure-composition isotherms of ZrMo2-H2 exhibit very wide solid solubility regions, which may be associated with diminished H–H elastic interaction, uelas. In order to discern this possibility, we measured the elastic moduli of Zr(MoxFe1−x)2, x = 0, 0.5, 1. The shear modulus, G, shows a moderate variation in this composition range, while the bulk modulus, B, increases significantly and monotonically from 148.2 GPa in ZrFe2 to 200.4 GPa in ZrMo2. The H–H elastic interaction is proportional to B and therefore its increase cannot directly account for a decrease in uelas. Therefore, we turn our attention to the volume of the hydrogen atom, vH, which usually varies in a limited range. Two coexisting phases, a Laves cubic (a = 7.826 Å) and a tetragonal (a = 5.603 Å, c = 8.081 Å) hydride phase are identified in ZrMo2H3.5, obtained by cooling to liquid nitrogen temperature at about 50 atm. The volume of the hydrogen atom in these two hydrides is estimated to be 2.2 Å3/(H atom). Some very low vH values, have been reported by other investigators. The low vH values, as well as the one derived in this work, significantly reduce uelas for ZrMo2-H2, and thus reduce the corresponding critical temperature for the metal-to-hydride phase transition, and the heat of hydride formation. We suggest that the bulk stiffening in ZrMo2 confines the corresponding hydride expansion and thus reduces the H-H elastic interaction.

Microstructure and hydrogen storage properties of Zr-based AB2-type high entropy alloys

This paper reports the partial substitution of Fe, Co, Ni and Cu for Mn in ZrMnCr0.5V0.5 alloy with to obtain ZrMn0.5Cr0.5V0.5M0.5 (M = Fe, Co, Ni and Cu) high entropy alloys. These alloy samples are prepared by electric arc melting, and their microstructure and hydrogen storage properties are investigated in detail. Structural analysis results show that all the five alloys consist of C14 type Laves primary phase. Metastable cubic phase can be observed in ZrMnCr0.5V0.5 and Fe-, Co-substituted alloys, while ZrNi, Cu10Zr7 and Cu8Zr3 phase secondary phases exist in Ni- and Cu-substituted alloys. Hydrogen storage testing results show that elemental substitution greatly improves the first activation properties of the alloys. All the five alloys can absorb hydrogen rapidly when the temperature is above 100 ℃, while the elemental substitution significantly affects the hydrogen absorption kinetics at lower temperatures. Compared with other four alloys, the Cu-substituted alloy has two kinds of Cu-Zr secondary phases, resulting in a poorer hydrogen absorption performance. Pressure-composition isotherms (P-C-T) test results show that all these alloys have very sloping absorption and desorption plateaus. It is also found that all the alloy particles are pulverized spontaneously during hydrogenation cycles, but there is no clearly change on phase structure of C14 type Laves phase, and the alloys show a good cycling performance. Among these alloys, the ZrMn0.5Cr0.5V0.5Fe0.5 alloy has the best hydrogen storage performance because it has the shortest activation time and fast hydrogen absorption at room temperatures.

Crucial role of Ce particles during initial hydrogen absorption of AB-type hydrogen storage alloys

The hydrogen storage behavior and the microstructural features of AB-type Ti50Fe48V2 hydrogen storage alloys containing a small amount of cerium (Ce) were investigated to understand the effect of Ce addition during initial hydrogen absorption. The initial hydrogen absorption kinetics of the alloys improved significantly at room temperature with Ce addition, which exhibited no significant influence on the pressure-composition isotherms for hydrogen absorption and desorption. Fine spherical particles containing Ce, which were determined to be γ-Ce mixed with cerium oxide, were dispersed in the ordered body-centered cubic TiFe matrix. During the early stage of hydrogen absorption, small cracks were initiated around the Ce particles, likely caused by the volume expansion owing to the formation of ε-CeH2. Subsequently, many large cracks, believed to have formed owing to the hydrogenation of the TiFe matrix, propagated during further hydrogen absorption. Therefore, these Ce particles appear to play a crucial role by providing starting points for the initial hydrogenation, with this mechanism explaining the significant increase in the primary hydrogen absorption kinetics after Ce addition. Notably, some small pits were observed after partial hydrogen absorption, possibly attributed to the hydrogenation of Ce particles underneath the alloy surfaces.

Exploring the Hydrogen Sorption Capabilities of a Novel Ti-V-Mn-Zr-Nb High-Entropy Alloy

Hydrogen is considered as a clean energy carrier able to achieve the decarbonization of the economy, but its compact, safe, and efficient storage represents an important challenge. Among many materials forming hydrides, this work reports the study of hydrogen sorption properties of a novel bcc high-entropy alloy, Ti0.30V0.25Mn0.10Zr0.10Nb0.25, synthesized by arc melting. In less than 60 s, the alloy fully absorbs hydrogen at room temperature, reaching a capacity of 2.0 H/M (2.98 wt.%). A two-step reaction with hydrogen is confirmed by pressure-composition isotherms, synchrotron X-ray and neutron diffraction: bcc solid solution ↔ bcc monohydride ↔ fcc dihydride. For the second step transformation, the calculated thermodynamic values indicate the formation of a very stable dihydride, with ΔHabs = −97 kJ/molH2. Moreover, the pair distribution function analysis of high-energy synchrotron X-ray scattering data validates a completely random distribution of metal atoms in the fcc dihydride phase, without noticeable lattice strain nor elemental segregation. In situ synchrotron X-ray and neutron diffraction, performed during hydrogen desorption by heating under vacuum, demonstrated full reversibility of the reaction with hydrogen. On the basis of these results, tuning the chemical composition of high-entropy alloys may have great implications in terms of hydrogen sorption properties.

Hydrogen Compression Materials with Output Hydrogen Pressure in a Wide Range of Pressures Using a Low-Potential Heat-Transfer Agent

In order to meet the demand of metal hydride–hydrogen compressors (MHHC) and their hydrogen compression materials for high-pressure hydrogen filling in a hydrogen energy field, four kinds of hydrogen storage alloys with low-grade heat source (<373 K) heating outputs and different hydrogen pressures (up to 80 MPa) were developed as hydrogen compression materials. The preliminary compositions of the hydrogen storage alloys were determined by using a statistical model and research experience. The rare earth series AB5 and Ti/Zr base AB2 hydrogen storage alloys were prepared using a high-temperature melting method. The composition, structure, and hydrogenation/dehydrogenation plateau characteristics of the alloys were tested by an inductively coupled plasma mass spectrometer (ICP-MAS), X-ray diffractometer (XRD), and pressure–composition isothermal (PCT) tester. The median output pressures of the four-stage hydrogen storage alloys at 363 K were 8.90 MPa, 25.04 MPa, 42.97 MPa, and 84.73 MPa, respectively, which met the requirements of the 20 MPa, 35 MPa, and 70 MPa high-pressure hydrogen injections for the MHHCs. In fact, due to the tilted pressure plateau of the PCT curve, the synergy between the adjacent two alloys still needed to be adjusted.

Phase formation behavior and hydrogen sorption characteristics of TiFe0.8Mn0.2 powders prepared by gas atomization

In this article we have investigated the phase formation behavior and hydrogen storage characteristics of TiFe0.8Mn0.2 samples produced by electrode induction melting gas atomization (EIGA) as well as conventional vacuum arc-melting (VAM). TiFe (46Ti–46Fe–8Mn (wt%) with cubic, CsCl-type structure) and C14 Laves (37Ti–51Fe–12Mn (wt%) with hexagonal, MgZn2-type structure) phases were detected in both atomized powders and crushed ingots, the latter possessing a lower fraction of Laves phase. Microstructural characterization included electron probe micro-analysis (EPMA) and transmission electron microscopy (TEM), which evidenced the existence of a non-equilibrium Ti2Fe phase in the atomized powders. The formation of this additional secondary phase was attributed to the rapid cooling rate during powder manufacturing, based on earlier findings and phase formation thermodynamic calculations combined with Scheil solidification simulations. In addition, kinetics and pressure-composition isotherms (PCIs) were acquired to determine both absorption and desorption enthalpy/entropy, as well as to study the influence of the synthesis route (and hence the resulting microstructure) on kinetics, thermodynamics and reaction mechanisms of the TiFe0.8Mn0.2 alloy.

Effect of Mn substitution on plateau pressure regulation of the Ti0.92Zr0.1Cr1.6−xMnxFe0.4 alloys for primary hydrogen compressor

The Ti0.92Zr0.1Cr1.6−xMnxFe0.4 (x = 0.15, 0.3, 0.45, 0.6 at%) alloys were synthesized by vacuum electric arc furnace. The effect of Mn substitution on plateau pressure regulation of these alloys was investigated for the primary hydrogen compressor. With increasing Mn content, the hydrogen absorption/desorption plateau pressures of the Ti0.92Zr0.1Cr1.6−xMnxFe0.4 (x = 0.15, 0.3,0.45,0.6 at%) alloys increased, the plateau slope factor decreased, meanwhile, both enthalpy and entropy change values decreased. The Ti0.92Zr0.1Cr1.0Mn0.6Fe0.4 alloy had the best comprehensive performance. Based on the pressure composition isotherms measurement, the plateau pressure and hydrogen storage capacity were obtained at 298–363 K. The hydrogen absorption/desorption curves of the Ti0.92Zr0.1Cr1.0Mn0.6Fe0.4 alloy at 353 and 363 K were firstly tested by experiment method. At 298 K, the hydrogen absorption plateau pressure and maximum capacity were 7.82 MPa and 1.79 wt%. At 363 K, the hydrogen desorption plateau pressure and maximum capacity were 27.21 MPa and 1.54 wt%. Hydrogen pressure from 8 MPa to 25 MPa was successfully obtained at 298–363 K, satisfying operating temperature and pressure requirements for the primary hydrogen compression materials.

Impact of yttrium hydride formation on multi-isotopic hydrogen retention by a getter trap for the DONES lithium loop

Compliance with imposed hydrogen concentration limits in the lithium loop of the DEMO-Oriented Neutron Source (DONES) requires the installation of an yttrium-based hydrogen trap. To determine an appropriate H-trap design, it is essential to have access to a numerical tool capable of simulating hydrogen transport in the DONES lithium loop connected to an yttrium pebble-bed. In the past, a simplified model was created that allows such calculations when hydrogen concentrations in the lithium are low. However, in certain DONES operating phases, the concentration in the lithium is high and in a range where yttrium dihydride (YH2) formation is likely. Due to the anticipated great impact of YH2 formation on the H-trap performance a new model is developed that includes the mechanism of hydride formation. It is based on a mathematical reproduction of complete pressure-composition isotherms of the Li–H and Y–H systems. Thus, the conditions that trigger YH2 formation are determined and the variation of hydrogen solubility in different yttrium hydride phases is deduced. An approximate concentration-dependent relationship of hydrogen diffusivity in yttrium is derived and incorporated into the model. Simulations are performed to analyze the dynamics of the concentration decrease during purification of the lithium circuit prior to the experimental DONES phase by varying design parameters of the trap. It is found that hydride formation greatly increases the hydrogen gettering capacity of the H-trap and limits the maximum concentration in the lithium. Indeed, YH2 formation may be purposefully triggered to exploit its beneficial properties for DONES. Simulations of the hydrogen purification process during the experimental phase of DONES show that the H-trap must be replaced at least every 28 days to meet tritium limits. This work sets the conditions for the required pebble-bed mass of the H-trap at a given temperature to comply with the DONES safety requirements. Finally, the model is validated by numerical reproduction of experimental results.

A novel method towards improving the hydrogen storage properties of hypoeutectic Mg-Ni alloy via ultrasonic treatment

Ultrasonic treatment has great contributions on modifying the morphology, dimension and distribution of constituent phases during solidification, which serve as dominate factors influencing the hydrogen storage performance of Mg-based alloys. In this research, ultrasonic treatment is utilized as a novel method to enhance the de-/hydriding properties of Mg-2Ni (at.%) alloy. Due to ultrasonic treatment, the microstructure of as-cast alloy is significantly refined and homogenized. Ascribing to the increased eutectic boundaries and shortened distance inside α-Mg for hydrogen atoms diffusion, the hydrogen uptake capacities and isothermal de-/hydriding rates improve effectively, especially at lower temperature. The peak desorption temperature reduces from 392.99 °C to 345.56 °C, and the dehydriding activation energy decreases from 101.93 kJ mol−1 to 88.65 kJ mol−1. Weakened hysteresis of plateau pressures and slightly optimized thermodynamics are determined from the pressure-composition isotherms. Owing to the refined primary Mg, a larger amount of hydrogen with the higher hydriding proportion is absorbed in the first stage when hydrides nucleate in eutectic region and grow on primary Mg periphery subsequently before MgH2 colonies impinging, resulting in the enhancement of hydrogenation rates and capacities.