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While the overwhelming number of papers on multi-principal-element alloys (MPEAs) focus on the mechanical and microstructural properties, there has been growing interest in these alloys as solid-state hydrogen stores. We report here the synthesis optimization, the physicochemical and the hydrogen sorption properties of Ti0.325V0.275Zr0.125Nb0.275. This alloy was prepared by two methods, high temperature arc melting and ball milling under Ar, and crystallizes into a single-phase bcc structure. This MPEA shows a single transition from the initial bcc phase to a final bct dihydride and a maximum uptake of 1.7 H/M (2.5 wt%). Interestingly, the bct dihydride phase can be directly obtained by reactive ball milling under hydrogen pressure. The hydrogen desorption properties of the hydrides obtained by hydrogenation of the alloy prepared by arc melting or ball milling and by reactive ball milling have been compared. The best hydrogen sorption properties are shown by the material prepared by reactive ball milling. Despite a fading of the capacity for the first cycles, the reversible capacity of the latter material stabilizes around 2 wt%. To complement the experimental approach, a theoretical investigation combining a random distribution technique and first principle calculation was done to estimate the stability of the hydride.

A large number of metallic alloys are currently under investigation in the field of hydrogen storage and hydrogen separation membranes. For such applications, the knowledge of the hydrogen diffusion coefficient in the given alloy is of great importance even if its direct measurement is not always easy to perform. In this view, the aim of this work is to describe an innovative procedure able to provide the lower limit of the hydrogen diffusion coefficient by performing hydrogen absorption kinetic experiments. Two different tools are presented: The first is a numerical code which solves the diffusion problem inside metals according to the general theory of the transport phenomena, and the second is a dimensional analysis that describes the dependence of the hydrogen diffusion coefficient from a few governing parameters. Starting from the results of several hydrogen absorption kinetic experiments performed on a Pd−Ag sample under different experimental conditions, the hydrogen diffusion coefficients were assessed by using both the described tools. A good agreement among the results obtained by means of the two procedures was observed.

Pd-Au nanoalloys confined in mesoporous carbonaceous materials were synthesized by a rapid one-pot microwave assisted approach. Green polymer resins based on phloroglucinol/glyoxylic acid or glyoxal were co-assembled in the presence of a template and metallic salts followed by microwave treatment between 40 and 80 °C and subsequent thermal annealing, allowing simultaneous formation of mesoporous carbonaceous materials with in-situ confined Pd-Au nanoparticles. Several Pd-Au compositions were prepared (Pd x Au 100−x , where x = 90; 80; 70 and 50) and their impact on the alloy structure and particle size/distribution evaluated. For Pd 90 Au 10 , homogeneously dispersed nanoalloy particles (∼8 nm) are obtained in the carbonaceous framework. The increase in the Au content in the alloy gradually induces an increase in the particle size and agglomeration of the particles along with the formation of multiphased alloys, i.e., segregated Pd- and Au-rich nanoparticles. The particle agglomeration was avoided by decreasing the thermal annealing time. The homogeneity of the alloy structure was found to strongly depend by two parameters, the chelating/cross-linker agents and the microwave temperature, i.e., the chelating/cross-linker agents containing carboxylic groups and the higher temperatures inducing more heterogeneous structures. The hydrogen absorption in Pd 90 Au 10 particles with different homogeneity degree was studied at room temperature up to 1 bar. Generally, hydrogen absorbs in Pd-rich nanoalloys forming a hydride phase whereas Au-rich phases do not absorb hydrogen under the present conditions. [ABSTRACT FROM AUTHOR]

Hydrogen was inserted into 2024 aluminum alloy by cathodic polarization in sulfuric acid at 25 °C. Scanning Kelvin Probe Force Microscopy (SKPFM) measurements performed perpendicularly to the charging side revealed a potential gradient and confirmed the insertion of hydrogen over hundreds of microns. A hydrogen diffusion coefficient of 1.7 × 10 −9 cm 2 s −1 was calculated from SKPFM measurements of H-charged samples for different durations. The evolution of the potential gradient during desorption of hydrogen in air, at room temperature and at 130 °C was investigated. Additional experiments performed at a corrosion defect showed that SKPFM could detect both reversibly and irreversibly bounded hydrogen. These results show that SKPFM is a cutting-edge technique for hydrogen detection and localization at a local scale. [ABSTRACT FROM AUTHOR]

A safe and efficient method for storing hydrogen is solid state storage through a chemical reaction in metal hydrides. A good amount of research has been conducted on hydrogenation properties of metal hydrides and possible methods to improve them. Background research shows that heat transfer is one of the reaction rate controlling parameters in a metal hydride hydrogen storage system. Considering that some very well-known hydrides like lanthanum nickel (LaNi5) and magnesium hydride (MgH2) are paramagnetic materials, the effect of an external magnetic field on heat conduction and reaction kinetics in a metal hydride storage system with such materials needs to be studied. In the current paper, hydrogenation properties of lanthanum nickel under magnetism were studied. The properties which were under consideration include reaction kinetics, hydrogen absorption capacity, and hydrogenation time. Experimentation has proven the positive effect of applying magnetic fields on the heat conduction, reaction kinetics, and hydrogenation time of a lanthanum nickel bed. However, magnetism did not increase the hydrogenation capacity of lanthanum nickel, which is evidence to prove that elevated hydrogenation characteristics result from enhanced heat transfer in the bed. [ABSTRACT FROM AUTHOR]

Comprehensive understanding of the hydrogen gas interaction with metal nanoparticles is crucial for the development of multifunctional materials. The hydrogen absorption properties of well-dispersed Pd-Ir nanoalloys on a mesoporous carbon are reported here. The average size of nanoalloys depends on the composition and is comprised between 2.7 and 3.5 nm with decreasing Ir content. Structural analysis evidences a single phase FCC structure for all nanoparticles and a linear variation of the lattice parameter with composition confirming the formation of nanoalloys in this bulk-immiscible system. The hydrogen absorption properties can be tuned by the chemical composition: Pd-rich nanoparticles form hydride phases, whereas Ir-rich phases do not absorb hydrogen under ambient temperature and pressure conditions. The thermodynamic properties of hydride formation in Pd-rich phases are altered relative to the bulk counterparts. Moreover, the hydrogen absorption capacity in Pd-rich nanoalloys is larger as compared to bulk alloys. This might be explained by an important finite size effect that increases the hydrogen absorption capability of Pd-Ir alloys at nanoscale. [ABSTRACT FROM AUTHOR]

A two-dimensional axisymmetric model is developed to study the hydrogen absorption reaction and resultant mass and heat transport phenomena inside a metal hydride canister. The model is compared against published literature and experimental data. Experimental tests are performed on an in-house fabricated setup using different cooling scenarios. An extensive study on the effects of the metal properties on charging performance is carried out through non-destructive testing (NDT). Results show that the properties that most influence the charging performance are: absorption rate constant ( C a ), activation energy ( E a ) and thermal conductivity ( k m ). A Higher porosity ( ε ) reduces charging time and amount of hydrogen stored while a higher cooling level produces a faster charging process. These results can be used to select metal hydride materials but also to estimate the metal hydride internal state and the process can be used for future evaluation of metal hydride degradation. [ABSTRACT FROM AUTHOR]

Measurements using an alternating current scanning electrochemical microscope (AC-SECM) were performed on a 2024 aluminum alloy pre-charged with hydrogen. A gradient in AC current magnitude was observed over several hundreds of microns on the side perpendicular to the charging side. After heat treatment at 130 °C for 2 h, the current gradient disappeared. Comparison with scanning Kelvin probe force microscopy (SKPFM) measurements confirmed that the increase in AC current magnitude observed with AC-SECM was due to the presence of hydrogen in the material. Fitting of localized impedance spectra with a suitable equivalent circuit showed the influence of H on the corrosion rate. AC-SECM is thus a powerful new method to detect hydrogen and study its effect on corrosion at the micrometer scale. [ABSTRACT FROM AUTHOR]

The atomic-scale structural evolution and crystallization mechanism of Ti-Zr-Ni-Cr amorphous ribbons subjected to hydrogen absorption have been studied. The atomic degree of order and amount of one-dimensional (1D), two-dimensional (2D) or three-dimensional (3D) ordered atomic packing structure of Ti-Zr-Ni-Cr amorphous ribbons were found to increase in the process of hydrogen absorption, resulting in excellent mechanical and hydrogen absorption properties. When the hydrogen absorption capacity reached 22.4 mL/g, crystallization occurred on the basis of 1D, 2D or 3D ordered atomic packing structure. Hydrogen atom induced Ti-Zr-Ni-Cr amorphous ribbons to crystallize into ZrH, TiH hydride and (ZrTi)Ni phases during the process of hydrogen absorption. When the samples absorbed hydrogen for a long time, formation of crystalline phases of ZrH, TiH hydride and (ZrTi)Ni led to degraded mechanical properties. [ABSTRACT FROM AUTHOR]

A non-stoichiometric Zr-based alloy with the composition of Zr 0.8 Ti 0.5 V 1.7 is designed to investigate the hydrogen absorption properties against gaseous impurities at different temperatures. The alloy has been synthesized by arc melting and annealing treatment. Microstructure, hydrogen absorption properties in presence of air impurities, hydrides and dehydrogenation behavior of the annealed Zr 0.8 Ti 0.5 V 1.7 have been investigated in this work. The results reveal that 0.1 mol.% air impurities in hydrogen decrease the initial absorption rate but preserve no significant effect on the hydrogen storage capacity of the experimental alloy at 25 °C. 1 mol.% air impurities evidently deteriorate the hydrogen absorption ability of alloy at temperature below 180 °C and the poisoning effect declines with the increase of temperature. Gaseous impurities have little impact to the absorption behavior of fully activated alloy at temperature above 340 °C. The above results indicate that the poisoning effect of gaseous impurities on hydrogenation properties of alloy depends on the concentration and temperature, and the tolerance of alloy to gases poisoning can be improved after one saturated hydrogen absorption/desorption cycle. DSC curve reveals the multi-stage dehydrogenation behavior of alloy. [ABSTRACT FROM AUTHOR]

The effect of high-pressure gaseous H 2 on the fracture behavior of pipeline steel X70 and austenitic stainless steel type 304L and 316L was investigated by means of notched-tensile tests at 10 MPa H 2 gas and various test speed. The notch tensile strength of pipeline X70 steel and austenitic stainless steels were degraded by gaseous H 2 , and the deterioration was accompanied by noticeable changes in fracture morphology. The loss of notch tensile strength of type 316L and X70 steels was comparable, but type 304L was more susceptible to hydrogen embrittlement than the others. In the X70 steel, hydrogen embrittlement increased as test speed decreased until the test speed reached 1.2 × 10 −3 mm/s, but the effect of test speed was not significant in 304L and 316L steels. [ABSTRACT FROM AUTHOR]

Mg–Ni alloys are among the most promising candidates for solid-state hydrogen storage systems. This paper reveals the effect of Na doping in accelerating initial hydrogen uptake in Mg–Ni alloys using in-situ Synchrotron X-ray powder diffraction. A minimum concentration of approximately 0.2 wt.% Na must be achieved for the alloys to show reasonably fast hydriding kinetics. Surface analysis shows that a Na-modified Mg–Ni surface facilitates the chemisorption and dissociation of hydrogen molecules in the early stage of hydriding as evidenced by a rapid formation of the saturated hydrogen solid solution Mg2NiH0.3 from the original Mg2Ni. The subsequent hydrogen absorption is based on a mechanism of nucleation and growth of MgH2 where a high density of dislocations develops ahead of the growing hydride-metal interface. [ABSTRACT FROM AUTHOR]

Hydrogen exposure of Tb 2 Pd 2 Mg crystallizing in the tetragonal Mo 2 FeB 2 structure results in the absorption 8 ± 1 H/f.u. The absorption is not reversible and leads to a structure transition yielding a new structure type (Pearson symbol oI 40, space group Fmmm ). Tb 2 Pd 2 Mg is an antiferromagnet with T N ≈ 60 K showing 2 metamagnetic transitions. Upon hydrogenation the susceptibility cusp related to AF ordering disappears and the susceptibility increases monotonously with decreasing temperature. Magnetic remanence, which starts to develop below 20–25 K, can be attributed to a randomness in H sites occupancy. [ABSTRACT FROM AUTHOR]

The effects of the volumetric expansion of uranium due to hydride formation during hydrogen absorption are examined numerically. To assess the effects of the volume changes, a three-dimensional transient metal hydride model is applied to multiple computational domains, i.e., generated as a function of the H/M atomic ratio during hydrogen absorption. The numerical simulations are carried out with or without considering the volume change effect. The simulation results clearly show that a higher temperature rise and slower hydrogen absorption reaction are predicted when the volumetric expansion of uranium hydride is taken into consideration in the model simulations. The comparison results highlight that neglecting the volumetric expansion of metal hydride during hydrogen absorption can lead to an overestimation of the hydrogen charging performance. [ABSTRACT FROM AUTHOR]

The pseudo-potential Density Functional Theory (DFT) method using the Generalized Gradient Approximation (GGA) was applied to investigate hydrogen absorption trends in the cubic C15-ZrFe 2 Laves phase in the presence of several ternary additions. The effect of the ternary addition on the stability of the Laves phase was investigated. The relative stability of atomic hydrogen at various interstitial sites was determined taking into account the type of ternary addition for different H contents in the hydrides. The results were analyzed and particular attention was given to the formation and binding energies of hydrogen. It was found that hydrogen prefers the 96g site in the clean C15-Fe 2 Zr, and its absorption leads to decrease the heat of formation of the formed hydrides with occurrence of phase separation around 6H/ fu. This effect was enhanced by the presence of ternary additions. Moreover, alloys with Be, V, Cr, Mn, Y and Tc elements at the Fe sites were found to absorb hydrogen up to 6H/ fu. More interestingly, the cohesion of hydrogen atoms was found to be very sensitive to the third element nature. The hydrides with V, Y, and more particularly Tc and Ru have exhibited interesting energetics which would be very attractive for practical applications. [ABSTRACT FROM AUTHOR]

The hydrogen storage and hydrogen generation of CaMg 2 and CaMg 1.9 Ni 0.1 alloys were investigated by X-ray diffraction (XRD) and pressure-composition-isotherm (PCI) measurements. The results confirmed that the CaMg 2 alloy cannot absorb hydrogen at room temperature. While the addition of Ni to the CaMg 2 -based alloys resulted in room-temperature hydrogen absorption without an activation process, and a maximum hydrogen-absorption capacity of 5.65 wt%. The hydrolysis performance of hydrogenated CaMg 2 and hydrogenated CaMg 1.9 Ni 0.1 (abbreviated as H-CaMg 2 and H-CaMg 1.9 Ni 0.1 hereafter) was also evaluated. The hydrolysis reaction of H-CaMg 2 occurred rapidly in water and resulted in a hydrogen yield of 800 mL/g. Furthermore, the hydrolysis properties of H-CaMg 1.9 Ni 0.1 were significantly enhanced with the addition of Ni, as evidenced by a hydrogen yield of 1053 mL/g in 12 min, this yield is 94.7% of the theoretical hydrogen yield of H-CaMg 1.9 Ni 0.1 . [ABSTRACT FROM AUTHOR]

Carbon supported Pd–Ni nanoalloys with well controlled composition and particle size distribution were synthesized by incipient wetness impregnation method. The Pd-rich nanoalloys (10 and 20 Ni at.%) form a hydride phase at atmospheric pressure and ambient temperature whereas, no hydride formation is observed for higher Ni content (30 at%), as determined by Pressure-Composition-Isotherms and in situ X-ray diffraction. Significant thermodynamic changes for hydride forming Pd–Ni nanoalloys are noticed as compared to pure Pd, in agreement with the bulk counterparts: the enthalpy of the hydride formation of Pd–Ni nanoalloys decreases by increasing the Ni content. These thermodynamic changes are not related to downsizing of particles but rather to an alloying effect. The solely effects of particle downsizing are the sloping and the shortening of the plateau observed in the PCI curves. [ABSTRACT FROM AUTHOR]

First-principles calculations were carried out to compare hydrogen absorption in pristine metallic and semiconductor carbon nanotubes (CNTs) with the situation in their Ge- and GeO 2 -doped counterparts. We found out that the pristine carbon nanotubes have low absorption efficiency (−1.53 eV in the metallic, and −2.06 eV in the semiconductor carbon nanotube). When Ge was doped into both carbon nanotubes, the hydrogen absorption was enhanced to −5.29 eV in the metallic and −3.99 eV in the semiconductor carbon nanotubes. Investigating the Partial density of states proved that there was considerable overlap between Ge 4p and hydrogen 1s orbitals in both CNTs. When CNTs were doped with GeO 2 , hydrogen atoms were bound to oxygen atoms, due to high electronegativity of oxygen atom. The hydrogen absorption was found to be increased remarkably in the metallic carbon nanotube (−6.59 eV). In order to compare the binding energy of Ge and GeO 2 doped metallic and semiconductor carbon nanotubes, the partial density of states and the magnetization of the samples were studied. [ABSTRACT FROM AUTHOR]

Pd/Y bilayers and Pd/Ti/Y trilayers were prepared in a UHV chamber by DC/RF magnetron sputtering. The characterization of the Pd-Y and Ti-Y interfaces was performed immediately after the deposition using in-situ X-ray photoelectron spectroscopy (XPS). The results indicated significant interface mixing for the Pd/Y bilayers. Further studies showed that the additional Ti layer deposited between the palladium and yttrium layers can significantly reduce the mixing of the Pd-Y layers during the deposition process at room temperature, leading to the formation of a sharp Ti-Y interface. The structure of the obtained layers before and after the hydrogenation was examined by the standard X-ray diffraction method. The hydrogenation kinetics was studied in-situ at room temperature and pressure up to 1 bar using simultaneous measurements of resistivity and optical transmittance. It was found that for a thickness of Ti equal to 5 nm, the shortest transition time to the YH 3 phase was obtained while maintaining a short switching time. • Interface mixing for the Pd/Y bilayers and Pd/Ti/Y trilayers was studied in-situ by X-ray Photoelectron Spectroscopy. • Hydrogen absorption was monitored in-situ by simultaneous resistivity and optical transmittance measurements. • The Pd/Ti/Y trilayers showed a significantly shorter transition time from YH 2 to YH 3 phase. [ABSTRACT FROM AUTHOR]

Manganese-doped intermetallic TiFe x Mn (1−x) nanoparticles (NPs) were synthesized by a molten-salt synthesis method using TiO 2 , FeSO 4 •7H 2 O, and Mn(NO 3) 2 •6H 2 O as the raw materials. The Ti–Fe–Mn oxide precursors prepared from the raw materials were efficiently reduced at temperatures as low as 600 °C in molten LiCl in the presence of CaH 2 as the reducing agent. This resulted in the formation of TiFe x Mn (1−x) NPs exhibiting few impurities (e.g., TiFe 2 or/and TiFe 39). Increase in the Mn content led to peak shifts in the X-ray diffraction (XRD) patterns, indicating good incorporation of Mn into the cubic CsCl-type structure of intermetallic TiFe to form a solid solution. Nano-sized particles of< 100 nm were clearly observed in the obtained powders by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Moreover, homogeneous distribution of the constituent elements (i.e., Ti, Fe, and Mn) was confirmed by energy dispersive X-ray (EDX) spectroscopy. Finally, the hydrogen absorption properties of the prepared TiFe 0.7 Mn 0.3 NPs were analyzed. Notably, with the exception of micron-sized TiFe 0.7 Mn 0.3 prepared by common arc melting, the generated NPs exhibited almost no hydrogen absorption. The results obtained herein demonstrated the importance of particle size in activating TiFe-based hydrogen absorption materials. • TiFe x Mn (1−x) NPs were prepared by a non-electrical molten-salt method at 600 °C. • The synthesized TiFe x Mn (1−x) NPs (20–32 nm) exhibit high purity. • Effects of particle size of TiFe x Mn (1−x) on hydrogen absorption were analyzed. [ABSTRACT FROM AUTHOR]

In order to study the effect of titanium ion implantation and deposition on hydrogenation behavior of Zr–1Nb alloy, the samples were subjected to plasma immersion implantation and deposition (PIII&D) of titanium ions at the bias voltage of 0.5–1.5 kV using a filtered metal vapor vacuum arc source. The crystalline structure, surface morphology and depth distributions of elements in the surface layer of the samples were analyzed by X-ray diffraction (XRD), scanning electron microscopy (SEM) and glow-discharge optical emission spectroscopy (GD-OES), respectively. Hydrogen saturation was performed from hydrogen atmosphere at 673 K temperature and 2 atm. pressure. It was found that hydrogen absorption rate by Zr–1Nb alloy decreased after PIII&D. The modified layers contained a mixing zone of titanium and zirconium, which decreases with increasing bias voltage. Hydrogenation causes the formation of titanium hydrides and lattice distortions of α–Zr at the low bias voltage that does not occur at higher bias voltages. The hydrogenation behavior of modified zirconium alloy was discussed. [ABSTRACT FROM AUTHOR]

To improve the poisoning resistance of ZrCo alloy, Pd membranes have been prepared over the surface of the alloy substrates by using electroless plating method. The characteristics of Pd membranes have been examined by XRD, SEM, EDS and EPMA technologies. From SEM images, the uniform and compact thin Pd film was revealed. The effect of this Pd film was evaluated by comparing the hydrogen absorption properties of bare and Pd-coated ZrCo specimens in contaminated hydrogen gas. The degradation of hydrogen absorption of Pd-coated ZrCo induced by poisoning was less than that of bare ZrCo sample obviously, meaning that the Pd membranes over the surface of substrates appeared to be effective in improving the poisoning resistance of ZrCo alloy. Furthermore, the effect became more significant with the increasing of impurity contents in the experimental gas and the operation temperatures. [ABSTRACT FROM AUTHOR]

The hydrogen absorption and desorption of Ti53Zr27Ni20 icosahedral quasicrystal (ICQ) and Ti50Ni50 shape memory alloy (SMA) melt-spun ribbons was studied. Samples were exposed to hydrogen gas at 623 K and 4 MPa for 1000 minutes. The total capacity of hydrogen obtained for Ti53Zr27Ni20 and Ti50Ni50 was 3.2 and 2.4 wt. % respectively. The Thermal Desorption Spectrometry (TDS) of the hydrogenated alloys shows that both alloys start to desorb hydrogen around 750 K. X-ray diffraction (XRD) patterns, performed after hydrogenation, indicate a complete amorphization of the Ti53Zr27Ni20 i-phase alloy, while the Ti50Ni50 alloy remained crystalline after hydride formation.