Hydride Decomposition Research Articles

Ignition and Combustion of Aluminum Hydride Dust Aerosols

ABSTRACT The results of comparative experimental studies of aluminum hydride AlH3 and aluminum Al particle aerosols, in particular, of the critical conditions for auto-ignition and the features of the flame propagation in low-volume (V ≈ 5.1·10−3 m3) and large clouds (volume is varied from 40 to 60 m3) are presented in this article. Experiments have shown that for aerosols of AlH3 particles, the auto-ignition temperature is much lower than for aluminum particles. This is due to the thermal decomposition of aluminum hydride into hydrogen and active aluminum. The laminar flame was studied in low-volume clouds. A two-frontal form of a laminar flame wave in AlH3 aerosol was found. Moreover, the visible flame propagation speeds for AlH3 correspond to those for finely dispersed Al and are two times higher compared to coarse Al. The turbulent flame in the large free clouds of aluminum hydride dusts has flame propagation speeds several times higher than those in the aluminum clouds and is characterized by the formation of a toroid vortex with a complex internal structure.

Alloying and Segregation in PdRe/Al2O3 Bimetallic Catalysts for Selective Hydrogenation of Furfural

X-ray absorption fine structure (XAFS) spectroscopy, temperature-programmed reduction (TPR), and temperature-programmed hydride decomposition (TPHD) were employed to elucidate the structures of a series of PdRe/Al2O3 bimetallic catalysts for the selective hydrogenation of furfural. TPR evidenced low-temperature Re reduction in the bimetallic catalysts consistent of the migration of [ReO4]− (perrhenate) species to hydrogen-covered Pd nanoparticles on highly hydroxylated γ-Al2O3. TPHD revealed a strong suppression of β-PdHx formation in the reduced catalysts prepared by (i) co-impregnation and (ii) [HReO4] impregnation of the reduced Pd/Al2O3, indicating the formation of Pd-rich alloy nanoparticles; however, reduced catalysts prepared by (iii) [Pd(NH3)4]2+ impregnation of calcined Re/Al2O3 and subsequent re-calcination did not. Re LIII X-ray absorption edge shifts were used to determine the average Re oxidation states after reduction at 400 °C. XAFS spectroscopy and high-angle annular dark field (HAADF)-scanning transmission electron microscopy (STEM) revealed that a reduced 5 wt.% Re/Al2O3 catalyst contained small Re clusters and nanoparticles comprising Re atoms in low positive oxidation states (~1.5+) and incompletely reduced Re species (primarily Re4+). XAFS spectroscopy of the bimetallic catalysts evidenced Pd-Re bonding consistent with Pd-rich alloy formation. The Pd and Re total first-shell coordination numbers suggest that either Re is segregated to the surface (and Pd to the core) of alloy nanoparticles and/or segregated Pd nanoparticles are larger than Re nanoparticles (or clusters). The Cowley short-range order parameters are strongly positive indicating a high degree of heterogeneity (clustering or segregation of metal atoms) in these bimetallic catalysts. Catalysts prepared using the Pd(NH3)4[ReO4]2 double complex salt (DCS) exhibit greater Pd-Re intermixing but remain heterogeneous on the atomic scale.

The influence of hydrogen content on the Zr-4 alloy diffusion bonding joint: From experiments to molecular dynamics simulations

Bonding the Zr-4 alloy in the high temperature can lead to many problems, for example grain coarsening and large welding deformation resulting from high residual stresses. Hydrogenation is an effective approach to decrease the bonding temperature. In the present research, the influence of hydrogen contents on the microstructure evolution and shear strength of Zr-4 alloy joints were studied. The number of interface voids markedly decreased with increasing hydrogen content at 650 °C. A sound joint was obtained at the hydrogen content of 0.2 wt% hydrogen. This achieved joint had a shear strength of 244 MPa, and the fracture mode of the joint presented the brittle/ductile mixed mode. With the increase of hydrogen content, the flow stress of the hydrogenated Zr-4 alloy decreased due to the decomposition of zirconium hydrides. The plasticity of the joint enhanced with increasing hydrogen content in the view of electron backscatter diffraction (EBSD) results, and the kernel average misorientation increased from 0.11° to 0.77°. In addition, the diffusion behavior and diffusion coefficient of the Zr atoms were investigated by molecular dynamics simulation. The calculation results showed that hydrogen enhanced the diffusivity of the Zr atoms, and the diffusion coefficient of the Zr atoms accordingly increased by four orders of magnitude. The addition of hydrogen influenced the directly diffusion bonding process through two aspects: improvement of plasticity and enhancement of diffusion ability.

In-situ EBSD analysis of hydride phase transformation and its effect on micromechanical behavior in Zircaloy-4 under uniaxial tensile loading

In this work, hydrogen charged Zircaloy-4 has been investigated under an in-situ electron backscatter diffraction during tensile loading. Aim were, first, to distinguish the hydride phase type and its spatial distribution, second to determine hydride phase transformation (HPT) and orientation relationship (OR) subjected to uniaxial tensile condition, and third to correlate the hydrides evolution and their effect on the micromechanical behavior, such as slip mode activation and lattice rotation, of Zircaloy-4. Apart from the applied stress, the analysis reveals that hydride reorientation is strongly related to temperature and loading mode. We noted that deformation induced δ-ZrH1.5 transformed to γ-ZrH and ε-ZrH2, and the former follows the confirmed OR {0001}α//{111}δ/γ with <11 2‾ 0>α//<110>δ/γ, while the latter's OR changed to {10 1‾ 0}α//{121}ε with <11 2‾ 0>α//<100>ε after HPT. The coexistence of δ-ZrH1.5 and γ-ZrH or ε-ZrH2 is observed, and the main corresponding OR is {111}δ//{111}γ with <121>δ//<121>γ, and {100}δ//{110}ε with <110>δ//<100>ε, respectively. The characterized microstructure and the measured lattice rotation results indicate that HPT delayed cracking in hydride and promoted deformation in parent grains. As the strain increases, the maintenance of hydride-matrix (H-M) coherent interfaces restricts further lattice rotation. HPT accelerates the hydride decomposition ascribed to the intensification of hydrogen diffusion under stress, and the hydride and the H-M interfaces act as priority sites for initiating microcracks. The sequence of HPT depends on the possibility of activated slip mode among grains. These findings contribute to developing the understanding of the HPT and hydrogen embrittlement.

Reconstructing brittle hydrides using pulsed electric current to restore the degraded performance of zirconium alloys

When zirconium alloy undergoes water corrosion reaction during the service process, it absorbs hydrogen to form brittle hydrides, which is one of the main reasons for the deterioration of the mechanical properties of zirconium alloy. There is an urgent need to find an effective method to regulate brittle hydrides to restore the properties of hydrogen-containing zirconium alloys. This study conducted electropulsing treatment on the hydrogen-charged nuclear grade Zr-4 alloy, and the results showed that the electropulsing process caused the hydrides to transform from large-sized brittle stripe-shaped δ-phase to the small-sized ζ-phase. The hydrogen content in the alloy is significantly reduced, which basically restores the mechanical properties of the alloy. However, in the comparative experiment of isothermal heat treatment at 400 °C, brittle hydrides did not dissolve and their mechanical properties did not recover. A mathematical model was established for the characteristics and morphological changes of strip hydrides, and the current density distribution and introduced free energy during the microstructure evolution process were calculated and analyzed. The calculation results indicate that the pulsed current promotes the decomposition of hydrides through the introduction of free energy, reduces the activation energy of hydrogen atom diffusion, accelerates the diffusion and desorption of hydrogen atoms, and realizes the repair of mechanical properties of hydrogen-charged zirconium alloy.

Determination of change in enthalpy and entropy for hydride formation and decomposition of palladium using in-situ electrical resistance measurement with various hydrogen pressures

Detection of hydride formation and decomposition of palladium is performed on pure palladium in the hydrogen gas atmosphere up to 0.5 MPa between room temperature and 673 K using an in-situ electrical resistance measurement system. Introduction of hydrogen gas increases the electrical resistance about 1.1 time higher than that in vacuum. Electrical ratio-temperature plot gives a peak during heating and cooling with the temperature changing ration of 0.067 K/s under hydrogen gas, which are associated with the hydride composition and decomposition. Change in enthalpy ΔH and entropy ΔS are determined using van't Hoff plot, and the values were comparable to the reported ones obtained by pressure-composition-temperature measurements. Those for hydride decomposition are 45.6±2.6 (kJ/mol) and 104.8±5.3 (J/mol), respectively, and those for hydride formation are -29.4±2.1 (kJ/mol) and 73.8±4.6 (J/mol), respectively. Furthermore, the measurement method is relatively simple and easy compared with pressure-composition-temperature measurements.

In-situ precipitation of ultrafine Mg2Ni particles in Mg-Ni-Ag metal fibers and their hydrogen storage properties

The intermetallic compound Mg2Ni shows improved hydrogen de-/absorption kinetics and a lower desorption temperature compared to pure Mg. However, the coarse Mg2Ni phase and its limited hydrogenation capacity restrict the application of the Mg2Ni alloy. In this study, an attempt was made to prepare Mg-Ni alloy fibers with a higher Mg content and a well-distributed Mg2Ni catalytic phase using the melt extraction (ME) method, and a unique metallic glass fiber was formed. With pre-annealing at 350 °C in a vacuum, uniformly dispersed Mg2Ni nanoparticles are in-situ formed, the phase transition is revealed to be metallic glass → Mg6Ni → Mg2Ni + Mg. About 1.5 wt% of hydrogen can be absorbed by the Mg-Ni fibers at 50 °C, and it is completely released in 8.8 min at 225 °C. Both the JMA and Kissinger models were utilized to accurately characterize the dehydrogenation activation energy, and the values of 90.4 and 95.8 kJ/mol were obtained, respectively. The hydrogen desorption process involves two distinct processes, the decomposition of Mg2NiH4 nanoparticles and MgH2 hydride in sequence, with dehydrogenation enthalpy changes of 64.5 and 78.2 kJ/mol, respectively. After hydrogen absorption and desorption cycles, a loose structure forms around the Mg2Ni nanoparticles. This structure serves as an efficient nucleation site for hydrides and provides diffusion paths for H atoms.

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.

Palladium-Rhenium Catalysts for Selective Hydrogenation of Furfural: Influence of Catalyst Preparation on Structure and Performance

PdRe/Al2O3 catalysts are highly selective for hydrogenation of furfural to furfuryl alcohol (FAL). Moreover, the synergy between the metals can result in greater specific activity (higher turnover frequency, TOF) than exhibited by either metal alone. Bimetallic catalyst structure depends strongly on the metal precursors employed and their addition sequence to the support. In this work, PdRe/Al2O3 catalysts were prepared by: (i) co-impregnation (CI) and sequential impregnation (SI) of γ-Al2O3 using HReO4 and Pd(NO3)2, (ii) SI using NH4ReO4 and [Pd(NH3)4(NO3)2], (iii) HReO4 addition to a reduced and passivated Pd/Al2O3 catalyst, and (iv) impregnation with the double complex salt (DCS), [Pd(NH3)4(ReO4)2]. Raman spectroscopy and temperature-programmed reduction (TPR) evidence larger supported PdO crystallites in catalysts prepared using Pd(NO3)2 than [Pd(NH3)4(NO3)2]. Surface [ReO4]− species detected by Raman exhibit TPR peak temperatures from ranging 85 to 260 °C (versus 375 °C for Re/Al2O3). After H2 reduction at 400 °C, the catalysts were characterized by chemisorption, temperature-programmed hydride decomposition (TPHD), CO diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS), and scanning transmission electron microscopy (STEM) with energy-dispersive x-ray (EDX) spectroscopy. The CI catalyst containing supported Pd–Re alloy crystallites had a TOF similar to Pd/Al2O3 but higher (61%) FAL selectivity. In contrast, catalysts prepared by methods (ii–iv) containing supported Pd-Re nanoparticles exhibit higher TOFs and up to 78% FAL selectivity.

Simple Ways to Obtain Activation Energy for Hydride Decomposition by Applying Data from a Volumetric Method to the Kissinger Equation

Thermal analysis methods - such as TGA, DSC analysis, DTA, and TDS analysis - have been used in many reports to determine the activation energy for hydride decomposition. In our preceding work, we showed that the dehydriding rate of Mg-5Ni samples obeyed the first-order law and the Kissinger equation could thus be used to determine the activation energy. In the present work, we used the Mg-5Ni samples after activation. We obtained Tm at different heating rates by finding the temperature at which the ratio of the desorbed hydrogen quantity Hd change to T change, dHd/dT, was the highest from the desorbed hydrogen quantity Hd versus temperature T curves. Tm’s at different heating rates were also obtained from points of inflection (Φ = dT/dt = 0) in temperature T versus time t curves. The activation energy for hydride decomposition was then calculated by applying Tm’s at different heating rates to the Kissinger equation.

Growth mode and characterizations of electrodeposited Re thick films from aqueous solutions with additives on Cu (110) + (311) substrates

Rhenium (Re) thick films were electrodeposited on copper (Cu) substrates with (110) + (311) texture from aqueous solutions with additives of 2 g l−1 gelatin, 1 mM sodium lauryl sulfate, and 1 mM vanillin. The microstructure and morphology of the films with different thickness values were characterized by scanning electron microscopy and atomic force microcopy. The chemical composition and the crystallographic structure of the films were identified by energy dispersive spectroscopy and x-ray diffraction, respectively. Re thick films were obtained due to the synergistic effect of additives. The additives had a significant influence on electrodeposition of the films. The microstructure and growth mode of Re films were influenced by surface topography and orientation texture of the substrate. The deposition rate was about 0.064 mg min−1. Re thin films adhered well to the substrate with no evidence of delamination and cracking. However, the Re thick film was not stable, fine microcracks were present, and even delamination occurred in vacuum condition due to large residual stress in the deposits or the shrinkage from decomposition of Re hydrides in the vacuum environment. Re films consisted of an amorphous phase structure. The Re film had a high hardness of 349 ± 15 VHN and exhibited a Stranski–Krastanov growth mode.

Effects of magnesium hydride on the thermal decomposition and combustion properties of DAP-4

Ammonium perchlorate-based molecular perovskites (DAP-4) have garnered immense interest due to their exceptional burst performance and good thermal stability. Similarly, metallic hydrides are widely acknowledged as an exceedingly promising material class for implementation in energetic systems, given their exceptional hydrogen storage density. Therefore, it is crucial to investigate the impact of hydrogen storage material MgH2 on the thermal decomposition and combustion characteristics of molecular perovskite materials ((H2dabco)[NH4(ClO4)3],DAP-4). In this study, DAP-4/MgH2 composites were synthesized and characterized for their morphology, structure, elemental distribution, thermal decomposition properties, and combustion properties. The findings indicated that the inclusion of MgH2 reduce the thermal decomposition temperature of DAP-4. Moreover, when MgH2 was added at a mass ratio of 5 wt%, the apparent activation energy (Ea) decreased to 212.0 kJ/mol, while the peak combustion pressure and boosting rate increased with more intense flames. A plausible thermal decomposition and combustion mechanism of DAP-4/MgH2 composites was postulated. This study enhances our understanding of the thermal decomposition and combustion properties of DAP-4 and magnesium hydride in energy-containing systems.

Mechanical synthesis of Mg6Pd1-xAgx alloys and their hydrogen absorption capability

In the present paper, we report the result of interactions between mechanically alloyed Mg6Pd1−xAgx alloys and hydrogen. Five Mg6Pd1−xAgx (x = 0, 0.1, 0.3, 0.5, and 0.7) alloys were selected to determine the possibility of substituting palladium with silver and determining the ability of such alloys to interact with hydrogen. Their structures were studied with an X-ray diffraction (XRD) analysis. The XRD analysis confirmed the existence of a single Mg6Pd – type phase for samples with silver concentrations reaching x = 0.5. A higher silver content resulted in a two-phase mixture with a dominating ε Mg25.04Ag7.96 phase. The kinetics of the hydrogenation process were determined with a Sievert-type sorption analyzer. A partial substitution of palladium with silver in the Mg6Pd1−xAgx alloys made the hydrogen sorption kinetics slightly better than those of a pure Mg6Pd intermetallic phase and pure magnesium; however, the hydrogen content was lower. The hydride decomposition temperature and the synthesized hydride kinetic properties were investigated by differential scanning calorimetry (DSC) with thermogravimetric analysis (TGA). The influence of silver on the decomposition kinetics was noticeable.

Excellent activity and selectivity of Pd/ZSM-5 catalyst in the selective catalytic reduction of NOx by H2

Superior de-NOx activity and N2 selectivity of the Pd/ZSM-5 catalyst was observed at low temperature (<200 °C) for the selective catalytic reduction of NOx by H2 (H2-SCR). Various Pd/ZSM-5 catalysts were prepared by calcinating at different temperatures (e.g., 500 °C, 650 °C, 750 °C, and 850 °C) and treated at reductive conditions before the H2-SCR reaction was performed. Among the prepared catalysts, the one prepared at the calcination temperature at 750 °C resulted in 96.7% NOx conversion and 96.8% N2 selectivity at 150 °C. Based on the H2–O2 reaction, the higher activity of the Pd/ZSM-5 catalyst calcined at 750 °C was attributed to its superior H2 activation ability for the H2-SCR reaction. The combined X-ray diffraction (XRD), temperature-programmed hydride decomposition (TPHD), and transmission electron microscopy (TEM) results revealed that highly dispersed Pd particles were generated on the catalyst calcined at 750 °C, while large Pd agglomerates were formed on the one calcined at 500 °C. It can be concluded that the catalytic activity of Pd/ZSM-5 improves by optimizing the calcination temperature, resulting in high Pd dispersion. Moreover, the Pd catalyst calcined at 750 °C showed high resistance to CO, maintaining >94% NOx conversion at 175 °C under 1000 ppm CO in the feed gas. Therefore, the catalyst calcined at 750 °C can be potentially used for industrial applications because of its simple preparation method and high resistance to CO.

Crying Wulff on vapor–solid distributions of crystallogen chemical vapor deposition via p-block element hydride thermal decomposition

Chemical vapor deposition is key in silicon device manufacturing. Surprisingly, crystallogen thin film deposition is executed without adequate knowledge of vapor–solid distributions. To address the issue, classical thermodynamics is applied to the determination of vapor–solid distributions for Si1-xCx, Si1-xGex and Ge1-xSnx depositions via a hydride route. The enthalpy of formation is substituted with a X – H bond dissociation energy which stands for the surface energy. Theory and experiments are in reasonable agreements. Indeed, the surface energy drives the solid growth, in line with Wulff’s principle. And the thermal decomposition of a covalent hydride is a quasistatic process. Chemical vapor deposition and thermal decomposition are unified with thermodynamics. Growth Rate, partial reaction order n = 1/2 and activation energy E fingerprint an interface chemistry consistently across covalent precursors. E is often found equal to a fraction of either X – H or H – H bond dissociation energy, i. e., E = n BDE, where n is a partial reaction order, and 1/n an integer matching the molecular hydrogen stoichiometric coefficient. Thus, p-Block elemental deposition mechanism is elucidated. Three sequential deposition mechanisms are identified. In the first mechanism, the growth rate is controlled by the dissociation of a X – H bond. In the second mechanism, a H – H bond dissociation is controlling the growth rate. The H – H path is triggered by a near complete surface hydrogenation. Finally, in the third mechanism, the deposition turns out amorphous from the lack of vacant lattice sites, as the H – H breaking energy is exhausted, and once more complete surface hydrogenation is achieved.

Three Methods for Application of Data from a Volumetric Method to the Kissinger Equation to Obtain Activation Energy.

Thermal analysis methods have been used in many reports to determine the activation energy for hydride decomposition (dehydrogenation). In our preceding work, we showed that the dehydrogenation rate of Mg-5Ni samples obeyed the first-order law, and the Kissinger equation could thus be used to determine the activation energy. In the present work, we obtained the activation energy for dehydrogenation by applying data from a volumetric method to the Kissinger equation. The quantity of hydrogen released from hydrogenated Mg-5Ni samples and the temperature of the reactor were measured as a function of time at different heating rates (Φ) in a Sieverts-type volumetric apparatus. The values of dHd/dt, the dehydrogenation rate, were calculated as time elapsed and the temperature (Tm) with the highest dHd/dt was obtained. The values of dHd/dT, the rate of increase in released hydrogen quantity (Hd) to temperature (T) increase, were calculated according to time, and the temperature (Tm) with the highest dHd/dT was also obtained. In addition, the values of dT/dt, the rate of increase in temperature to time (t) increase, were calculated according to time, and the temperature (Tm) with the highest dHd/dt was obtained. Φ and Tm were then applied to the Kissinger equation to determine the activation energy for dehydrogenation of Mg-5Ni samples.

Quantification of Hydride Coverage on Cu(111) by Electrochemical Mass Spectrometry.

Electrochemical mass spectrometry (EC-MS) is combined with chronoamperometry to quantify H coverage associated with the surface hydride phase on Cu(111) in 0.1 mol/L H2SO4. A two-step potential pulse program is used to examine anion desorption and hydride formation, and the inverse, by tracking the 2 atomic mass unit (amu) signal for H2 production in comparison to the charge passed. On the negative potential step, the reduction current is partitioned between anion desorption, hydride formation, and the hydrogen evolution reaction (HER). For modest overpotentials, variations in partial processes are evident as inflections in the chronoamperometry and EC-MS signal. On the return step to positive potentials, hydride decomposition by H recombination to H2 occurs in parallel with sulfate adsorption. The challenge associated with the inherent diffusional delay in the EC-MS response is mitigated by total H2 collection and steady-state analysis facilitated by the thin-layer EC-MS cell geometry as demonstrated for the HER on a non-hydride forming Ag electrode. Analysis of the respective transients and steady-state response on Cu(111) reveals a saturated hydride fractional coverage of 0.67 at negative potentials with an upper bound charge of 106 μC/cm2 (average electrosorption valency of ≈1.76) associated with adsorption of the () mixed sulfate-water adlayer at positive potentials.

Anion Influenced Hydride Formation on Cu(111) during Electrocatalysis

In aqueous systems several environmentally relevant proton-coupled electron transfer reactions such as the reduction of O2, NO3, CO or CO2 are known to proceed on Cu surfaces in combination with proton and/or water reduction. Among these, the electrochemical reduction of CO2 receives the most attention because of Cu’s unique ability to produce varying degrees of hydrogenated multicarbon products. Despite intense experimental and theoretical studies, understanding of Cu’s facet specific selectivity is still limited especially regarding the role of H in hydrogenation steps. Using operando electrochemical mass spectrometry (ECMS) and shell-isolated nanoparticle enhanced Raman spectroscopy (SHINERS) this work identifies the existence of surface hydride on Cu(111) (Figure 1a) under conditions relevant for the aforementioned reduction reactions. The identified surface hydride is significantly impacted to changes in electrolyte composition, such as the cation, anion or dissolved gas species and likely has significant impact over electrocatalytic performance. ECMS plots (Figure 1b) of hydride formation and decomposition show that the stronger the binding affinity of the anion to the Cu(111) surface the larger the overpotential required for hydride formation (e.g. Cl- vs ClO4 -). Likewise, decomposition occurs at more negative potentials. Peak areas of respective vibrational modes (Figure 1 c-d) corroborate the ECMS data, also demonstrating that in the presence of Cl- (vs SO4 2-) both hydride formation and decomposition shifts negatively by nearly 100 mV. These dynamics among other more quantitative analysis of hydride coverage and kinetics will be presented within this talk. Figure 1

Synthesis, characterization and first hydrogen absorption/desorption of the Mg35Al15Ti25V10Zn15 high entropy alloy

In this work, a novel Mg-containing high entropy alloy (HEA), namely Mg35Al15Ti25V10Zn15, was synthesized, characterized, and the phases formed after synthesis and after first hydrogen absorption/desorption were analyzed. The alloy composition was conceptualized aiming at increasing the atomic fraction of lightweight elements (35 at.% Mg and 15 at.% Al) to increase its gravimetric hydrogen storage capacity. Ti and V were selected to increase the hydrogen affinity of the alloy. Finally, Zn was selected as an alloying element because of its negative enthalpy of mixing with Mg, which could favor the formation of solid solution and avoid Mg segregation. The Mg35Al15Ti25V10Zn15 HEA was synthesized by high-energy ball milling (HEBM) in two different routes: under argon atmosphere (mechanical alloying – MA) and under hydrogen pressure (reactive milling – RM). The sample produced by MA was composed of a body-centered cubic (BCC) phase with an amount of unmixed Mg. When hydrogenated at 375 °C and under 4.0 MPa of H2, the MA sample absorbed about 2.5 wt% of H2 by forming a mixture of MgH2, a face-centered cubic (FCC) hydride, a body-centered tetragonal (BCT) phase and MgZn2. The desorption sequence upon heating was investigated and it was shown that the MgH2 is the first to desorb. The sequence of desorption is completed by the decomposition of the FCC hydride and BCT phase leading to the formation of the BCC phase. On the other hand, the alloy produced by RM was composed of a mixture of an FCC hydride and MgH2. During desorption upon heating, the MgH2 is also the first to desorb. At lower temperatures (below 350 °C), the FCC hydride decomposes partially forming the BCT phase. At higher temperatures, both FCC hydride and BCT phase decomposes forming the BCC phase. The desorption capacity of the RM sample was 2.75 wt% H2.

Experiments on a novel metal hydride cartridge for hydrogen storage and low temperature thermal storage

Even though metal hydrides have been mainly studied for hydrogen storage, their applications can be extended to thermal energy storage by utilizing the exothermic and endothermic reactions during the hydride formation and decomposition processes, respectively. In this paper, a low temperature hydride, La0.75Ce0.25Ni5 is experimentally investigated for hydrogen storage and thermal energy storage applications. Heat and mass transfer characteristics of a novel scalable cartridge type reactor is studied at various heat transfer fluid temperatures and hydrogen supply pressures. Maximum hydrogen storage capacity of 1.38 wt% and a gravimetric thermal energy storage capacity of 127.01 kJ.kgMH-1 at about 70% efficiency were achieved. The energy storage capacity achieved during experiments is compared with the theoretically possible output by defining a performance index, namely, the energy storage effectiveness, and its maximum value was found to be 0.67 at 20 °C and 20 bar.