Stability Of Hydrides Research Articles

Interface Induced Fast Ion Conduction in Complex Hydride/Oxide Nanocomposites: Interplay between Hydride and Oxide Properties

Solid-state electrolytes are crucial for next generation batteries with high energy density, long lasting and improved safety. The compatibility of most solid electrolytes with metallic anodes such as Li and Na metals, and cathodes such as sulfur, makes them suitable for high-capacity batteries (e.g., Li-S). They also address the safety concerns of current batteries by eliminating the flammable organic solvents in liquid electrolytes and by preventing/limiting dendrite formation. The lithium and sodium containing complex metal hydrides (e.g., LiBH4, NaBH4, LiCB11H12) have recently gained attention as solid-state electrolyte. They show high ionic conductivities but only at elevated temperatures (typically above 110 °C). Extending the high ionic conductivities to ambient temperatures is pivotal to the application of this fascinating class of solid electrolytes [1]. In this contribution, we will use LiBH4 and NaBH4 as examples to show that the ionic conductivities of complex hydrides can be greatly enhanced through interface effects resulting from the formation of nanocomposites with metal oxides. This strategy can lead to several orders of magnitude increase in the room temperature ionic conductivity [2]. Using DSC, DRIFT, solid-state NMR, and XRS (Xray Raman scattering), I will discuss how nanocomposite formation and presence of interfaces modifies either the phase stability, the defect concentration and/or leads to the formation of tertiary phase, and thereby increase profoundly the ion mobility of the complex hydrides. Systematic studies with different oxide nanoscaffolds and surface modified metal oxides, reveal that these effects can be optimized by tuning/engineering the nanostructure and interfaces in the nanocomposites. [3-4]. We will show that the effects also depend on a complex interplay between the stability of the metal hydride and surface properties of the metal oxide. Finally, the performance of some of the nanocomposite electrolytes in all-solid-state batteries, will be highlighted [5] References [1] L.M de Kort, P. Ngene et al. J. Journal of Alloys and Compounds 901 (2022) 163474[2] D. Blanchard et al., Advanced Functional Material. 25 (2015), 182.[3] P. Ngene et al. Physical Chemistry Chemical Physics 21 (40), 22456-22466[4] L.M de Kort, P. Ngene et al. Journal of Materials Chemistry A 8.39 (2020): 20687-20697[5] D. Blanchard et al, J. Electrochem. Soc. (2016).

Stability of hydrides in sub-Neptune exoplanets with thick hydrogen-rich atmospheres.

Many sub-Neptune exoplanets have been believed to be composed of a thick hydrogen-dominated atmosphere and a high-temperature heavier-element-dominant core. From an assumption that there is no chemical reaction between hydrogen and silicates/metals at the atmosphere-interior boundary, the cores of sub-Neptunes have been modeled with molten silicates and metals (magma) in previous studies. In large sub-Neptunes, pressure at the atmosphere-magma boundary can reach tens of gigapascals where hydrogen is a dense liquid. A recent experiment showed that hydrogen can induce the reduction of Fe[Formula: see text] in (Mg,Fe)O to Fe[Formula: see text] metal at the pressure-temperature conditions relevant to the atmosphere-interior boundary. However, it is unclear whether Mg, one of the abundant heavy elements in the planetary interiors, remains oxidized or can be reduced by H. Our experiments in the laser-heated diamond-anvil cell found that heating of MgO + Fe to 3,500 to 4,900 K (close to or above their melting temperatures) in an H medium leads to the formation of Mg[Formula: see text]FeH[Formula: see text] and H[Formula: see text]O at 8 to 13 GPa. At 26 to 29 GPa, the behavior of the system changes, and Mg-H in an H fluid and H[Formula: see text]O were detected with separate FeH[Formula: see text]. The observations indicate the dissociation of the Mg-O bond by H and subsequent production of hydride and water. Therefore, the atmosphere-magma interaction can lead to a fundamentally different mineralogy for sub-Neptune exoplanets compared with rocky planets. The change in the chemical reaction at the higher pressures can also affect the size demographics (i.e., "radius cliff") and the atmosphere chemistry of sub-Neptune exoplanets.

First-principles calculations on structural stability and electronic properties of nitrogen-doped lutetium hydrides under pressure

First-principles calculations on structural stability and electronic properties of nitrogen-doped lutetium hydrides under pressure

Superconducting ternary hydrides: progress and challenges.

Since the discovery of the high-temperature superconductors H3S and LaH10 under high pressure, compressed hydrides have received extensive attention as promising candidates for room-temperature superconductors. As a result of current high-pressure theoretical and experimental studies, it is now known that almost all the binary hydrides with a high superconducting transition temperature (T c) require extremely high pressure to remain stable, hindering any practical application. In order to further lower the stable pressure and improve superconductivity, researchers have started exploring ternary hydrides and had many achievements in recent years. Here, we discuss recent progress in ternary hydrides, aiming to deepen the understanding of the key factors regulating the structural stability and superconductivity of ternary hydrides, such as structural motifs, bonding features, electronic structures, electron-phonon coupling, etc. Furthermore, the current issues and challenges of superconducting ternary hydrides are presented, together with the prospects and opportunities for future research.

Effect of Ti0.9Zr0.1Mn1.5V0.3 alloy catalyst on hydrogen storage kinetics and cycling stability of magnesium hydride

As a high-capacity hydrogen storage material, MgH2 still has the problem of high operating temperature and slow reaction kinetics. In this work, an TiMn2-based Laves phase alloy (Ti0.9Zr0.1Mn1.5V0.3, denoted as Ti–Mn) was first synthesized by arc melting and then employed to regulate the hydrogen storage properties of MgH2, with the carbon nanotubes (CNTs) as an aid agent to facilitate the hydrogen diffusion and heat transfer. It was shown that the introduction of Ti–Mn/CNTs can remarkably improve the hydrogen storage properties of MgH2. The MgH2 + 10 wt% Ti–Mn + 1 wt% CNTs composite has an initial dehydrogenation temperature of 195 °C and can absorb hydrogen at room temperature. As for the kinetics, it can release 6.1 wt% H2 in 5 min at 300 °C, and absorb 4.8 wt% H2 in 10 min at 150 °C. It still has a reversible capacity of 6.2 wt% after 100 cycles. Combination of Ti–Mn alloy and CNTs is more effective than Ti–Mn alloy or CNTs alone for regulating MgH2. Ti–Mn/CNTs does not alter the overall thermodynamics of MgH2. However, local destabilization of Mg–H bonds induced by the MgH2/Ti–Mn interfaces was observed experimentally and confirmed theoretically, which partially contributes to the enhanced hydrogen storage of MgH2. In addition, the active transition metals contained in the alloy was believed to accelerate the hydrogen dissociation and delivery during the hydrogen storage process. This work not only achieves the synergistic improvement of hydrogen storage of MgH2 by combination of Ti–Mn alloy and CNTs, but also presents the local destabilization mechanism to explain the improved hydrogen storage of MgH2 by Ti–Mn alloy experimentally and theoretically.

Promising materials based on Ti–Al for hydrogen energy produced by “Hydride Technologyˮ

The connection of Ti–H by ATAT, USPEX codes with QE and VASP interfaces is investigated in the work. Predictive estimates revealed a number of stable and geometrically optimized hydrides with different atomic compositions: Ti6H2, Ti5H3, Ti5H2, Ti4H3, Ti3H5 of a simple triclinic group and highly symmetrical TiH2, Ti2H2, Ti6H2, Ti3H5 alloys. The stability of hydrides was evaluated by first principles calculations and by the convex hull method. Model estimates of mechanical characteristics have shown that hydrides with low mass density are high-strength compounds. The detected hydrides can be included in the reference database of Ti–H compounds. The possibility of obtaining alloys based on Ti–Al with additions of Sc, Y, Dy, Ho by “Hydride technologyˮ is considered. The formation of a lamellar structure upon the introduction of 2 at.% Sc, Y into Ti–50Al (at.%) was found. When 2 at.% Dy, Ho is added to Ti–50Al (at.%), isotype compounds Y6Ti4Al43, Dy6Ti4Al43, Ho6Ti4Al43 are formed. The values of microhardness and electrical resistance are given.

The synergistic effect of Ni and C14 Laves phase on the hydrogen storage properties of TiVZrNbNi high entropy hydrogen storage alloy

As a hydrogen storage alloy, the body-centered cubic (BCC) structure has been well studied due to its large hydrogen storage capacity. On this basis, the introduction of catalytic elements and an appropriate amount of C14 Laves phase can further improve the comprehensive hydrogen storage properties of hydrogen storage alloys. Based on this theory, (Ti32.5V27.5Zr7.5Nb32.5) 1-xNix (x = 0.03, 0.06, 0.09) high entropy hydrogen storage alloys with an appropriate amount of catalytic element Ni are prepared in this study. The raise in Ni content is accompanied by grain refinement of the dendritic structure, an increase in the number of grains and grain boundaries, and a gradual increase in the proportion of C14 Laves phase. The introduction of catalytic element Ni reduces the dissociation energy of hydrogen molecules. The increasing grain and grain boundaries increase more hydrogen absorption sites with lower activation energy. The diffusion channel provided by the appropriate amount of C14 Laves phase makes it easier for hydrogen atoms to diffuse into the main phase BCC phase with strong hydrogen absorption capacity, and the hydrogen atoms are trapped by vacancy defects with large hydrogen binding energy. The synergistic effect of the three factors ensures the improvement of hydrogen absorption performance of high entropy hydrogen storage alloys. (Ti32.5V27.5Zr7.5Nb32.5) 0.94Ni0.09 high entropy hydrogen storage alloy achieves excellent saturated hydrogen storage capacity of 2.78 wt % and 2.99 wt % at room temperature and 150 °C under 3 MPa hydrogen pressure, respectively. In addition, the introduction of Ni element reduces the thermal stability of metal hydrides, thereby improving the dehydrogenation performance of high entropy hydrogen storage alloys. The reversible phase transition occurs during the whole hydrogen absorption and desorption cycle.

Environment-dependent phase stabilities of titanium hydrides: First-principles prediction

Various phases of TiHx (x=1−2) were constructed, with all possible H-atom configurations being considered. The first-principles energetics calculations were performed to evaluate their formation preference and mechanical and thermodynamic stabilities. All the results were then combined to construct the stable and metastable phase stability diagrams of TiHx. It is suggested that many stable and metastable TiHx phases have very comparable formation energies and thus are likely to co-exist. Their relative stabilities are strongly depended on temperature (T) and the partial pressure of hydrogen (p(H2)). Over the entire T and p(H2) range of interest, γ-TiH and γ-TiH2 are the only two stable phases. ɛ-TiH, γ-TiH1.5, ɛ- and δ-TiH1.75, and ɛ-TiH2 can possibly present as metastable phases. These metastable phases are all mechanically stable, and have a thermodynamic tendency to continuously absorb or release H until reaching the equilibrium phases of γ-TiH2 or γ-TiH.

Formation of eutectic structure and de/ hydriding kinetics properties: A novel Ti-Hf-V-Mn multi-principal element alloy

The novel Ti23-xV40Mn37Hfx (x = 8 and 10 at%) multi-principal element alloys (MPEAs) were prepared using vacuum non-consumable electrode arc-melting furnace. An analysis of the hydrogen sorption process unveiled a thought-provoking discovery, shedding light on the microstructure and performance of the alloys. The MPEAs exhibited a higher abundance of the C14 Laves phase in comparison to the Ti23V40Mn37 alloy. The C14 Laves phase underwent a transformation into columnar dendrites, resulting in the formation of a finely textured eutectic structure within the MPEAs. This distinctive microstructure endowed the MPEAs with superior activity and faster hydrogen absorption kinetics compared to the Ti23V40Mn37 alloy. The initial hydrogen absorption process followed a nucleation and crystal growth mechanism. In addition, the Ti13V40Mn37Hf10 alloy exhibited an impressive maximum hydrogen desorption capacity of 1.96 wt%, representing a significant 38% increase when compared to the Ti23V40Mn37 alloy. This enhanced hydrogen desorption capacity can be attributed to the presence of numerous diffusion channels for hydrogen atoms, as well as shorter diffusion distances within the MPEAs. Furthermore, the values of ΔH increased to 30.38 and 32.76 kJ/mol H2, respectively, for the MPEAs. This indicates a higher stability of hydrides within the MPEAs.

Identification, classification and characterisation of hydrides in Zr alloys

Hydride precipitation in zirconium alloys leads to embrittlement, making it essential to understand their prevalence and stability in the microstructure. Dictionary indexing of Kikuchi patterns, along with orientation relationship analysis and x-ray diffraction, confirmed the presence of both delta and gamma hydride phases in Zircaloy-4. Both phases were found to be stable in recrystallised zirconium, with the gamma phase exhibiting a distinct orientation relationship with the matrix. Delta hydride morphology and orientation were influenced by local stresses, resulting in a change in orientation during precipitation. By analysing the orientation relationships, the evolution of hydride phases could be visualised, providing insights into the room temperature stability of both delta and gamma hydrides.

Effect of C14 Laves/BCC on microstructure and hydrogen storage properties of (Ti32.5V27.5Zr7.5Nb32.5) 1-xFex (x = 0.03, 0.06, 0.09) high entropy hydrogen storage alloys

In order to explore the effect of C14 Laves/BCC on the hydrogen storage properties of high entropy hydrogen storage alloys, (Ti32.5V27.5Zr7.5Nb32.5) 1-xFex (x = 0.03, 0.06, 0.09) high entropy hydrogen storage alloys are prepared. The C14 Laves/BCC rises with the increase of Fe content. The C14 Laves phase provides a path for the diffusion of hydrogen atoms, so that defects with higher hydrogen binding energy capture more hydrogen atoms to ensure the increase of initial hydrogen absorption content in the activation process. The appropriate ratio of C14 Laves/BCC ensures that the main hydrogen absorbing phase BCC phase of high entropy hydrogen storage alloy plays a full role. The (Ti32.5V27.5Zr7.5Nb32.5) 0.94Fe0.06 high entropy hydrogen storage alloy possesses the best hydrogen absorption capacity of 3.19 wt% at 150 °C under 3 MPa hydrogen pressure. The gradual increase of Fe content makes the VEC value of C14 Laves phase rise, so that the hydrogen binding energy decreases. The factor reduces the thermal stability of metal hydrides. The reversible phase transition of BCC phase + metal C14 Laves phase → FCC phase + metal hydride C14 Laves phase → BCC phase + metal C14 Laves phase occurs in the whole cycle.

Machine learning-based high-throughput screening of Mg-containing alloys for hydrogen storage and energy conversion applications

The development of novel materials for hydrogen storage and conversion applications is expected to facilitate the transition to clean energy. In particular, near-ambient hydrogen storage, thermal energy storage, and lithium conversion electrodes are selected in this study as the applications for which the development of novel Mg-containing materials is of great importance. We utilize a machine learning model, based on the graph neural network, developed for predicting hydride formation enthalpy in intermetallic compounds, to perform high-throughput screening based on the atomic composition and crystal structure of the starting intermetallic compounds. Trends and structure-property relations are discussed, as well as the possibilities for tailoring the stability of Mg-containing hydrides by alloying. For 636 compounds identified as stable by DFT calculations, we predict hydride formation enthalpy and equilibrium potential of metal hydride conversion electrode for Li-ion batteries. Based on the predicted enthalpy of hydride formation, 32 intermetallics are identified as suitable for near-ambient hydrogen storage applications. Among them, MgBe13, seen as a promising material to achieve a high gravimetric density of hydrogen, is additionally studied using DFT. Further investigation of the Na-Mg-Al alloys is proposed as a good route in the search for new thermal energy storage materials. Binary Mg-containing intermetallics are discussed as conversion-type negative electrodes in Li-ion batteries.

Structure, stability, and superconductivity of N-doped lutetium hydrides at kbar pressures

Structure, stability, and superconductivity of N-doped lutetium hydrides at kbar pressures

Hydrogen storage properties of Mg0.10Ti0.30V0.25Zr0.10Nb0.25 lightweight high entropy alloy: A theoretical study

In the past several years, Mg-based high entropy alloys (HEAs) have attracted great attention in high gravimetric hydrogen storage capacity. In this work, the hydrogen storage properties of Mg0.10Ti0.30V0.25Zr0.10Nb0.25 HEA are investigated by first-principles calculations. With increasing hydrogen concentration, the structural stability of BCC and FCC hydrides decreases and increases, respectively. By comparing the lattice constants, number of hydrogenation-induced abnormal short hydrogen-hydrogen bonds and radial distribution functions of BCC and FCC hydrides, it is found that the hydrogen accommodation ability of BCC phase is weaker than that of FCC phase, and a BCC to FCC phase transformation occurs during hydrogenation process. Further total energy calculations suggest that the threshold hydrogen content of phase transformation for Mg0.10Ti0.30V0.25Zr0.10Nb0.25 is around H/M = 1.16. By phonon spectra calculation, the maximum gravimetric hydrogen storage capacity of Mg0.10Ti0.30V0.25Zr0.10Nb0.25 is predicated to be as high as 3.16 wt%, demonstrating that Mg0.10Ti0.30V0.25Zr0.10Nb0.25 HEA is a potential hydrogen storage material.

Effect of reaction path on high-pressure synthesis and stability of ruthenium hydrides

This study explores the behavior of ruthenium hydrides under high-pressure conditions through three thermodynamical paths using laser-heated diamond anvil cells. The synthesis of RuH0.9 occurs gradually exceeding the pressure of 23.5 GPa in the ambient temperature path, while RuH is successfully synthesized at pressures above 20 GPa and a temperature of 1500 K. High-temperature conditions are found to reduce the pressure required for synthesis. The results demonstrate that the hydrogen occupancy of octahedral interstitial sites in the ruthenium hydrides is found to reach saturation with complete hydrogen absorption in the high-temperature path. Moreover, the crystallinity of the ruthenium hydride samples improves at higher temperatures, with the grain size increasing from 10 nm in the ambient temperature path to submicron in the high-temperature path. However, the predicted RuH6 and RuH3 were not observed in the present work.

First-principles calculations of the crystal structure, electronic structure, and thermodynamic stability of Si-doped Mg2Ni and Mg2NiH4

Mg2Ni is considered as one of the promising candidates of hydrogen storage materials because of its reasonable (de)hydrogenation kinetics and low costs. In view of the high operating temperature for hydrogen release due to the high thermodynamic stability of hydride, Mg2NiH4 is a serious obstacle to overcome for application usage. In this work, the crystal structure, electronic structure and thermodynamic stability of Si doped Mg2Ni and Mg2NiH4 are studied by first-principles calculations based on density functional theory. It is shown that the hydrogen desorption enthalpy can be reduced from 63.3 to 48.2 and 46.2 kJ/mol H2 with one in sixteen Mg and one in eight Ni atoms is replaced by Si, respectively. The crystal structure and electron properties of Si doped Mg2Ni and Mg2NiH4 are clarified. It is found that the weakened covalent interaction of H–Ni bonding contributes dominantly to the deteriorative thermodynamic stability of hydrides.

Tuning the hydride stability of the TiVNb-based alloys by equimolar Cr/Al addition

Body-centered multi-principal element alloys (BCC-MPEAs) based only on hydride-forming elements have low equilibrium plateau pressures during reaction with hydrogen and, consequently, high decomposition temperatures due to the high thermodynamic stability of related hydrides. In this work, we present a strategy to decrease the stability of the final hydrides formed in the BCC TiVNb alloy by simultaneous addition of two non-hydride forming elements, Cr and Al. The (TiVNb)100-x(CrAl)x alloys with x = 10, 20, 30, and 40 at.% crystallize as major BCC solid solutions with dendritic microstructures. Pressure-Composition-Temperature diagrams revealed that the combined addition of Cr and Al thermodynamically destabilizes the dihydride formation for x = 10 and 20 at.%. For higher Cr/Al contents the destabilization is too large to form stable hydrides under maximum 100 bar pressure. The absorption/desorption plateau pressure at room temperature for (TiVNb)80(CrAl)20 alloy are 9 and 0.6 bar, respectively, enabling a reversible capacity of about 0.8 H/M (1.4 wt%) at ambient conditions. The present results provide important insights into the effects of simultaneous Cr and Al additions in BCC-MPEAs and shed light on the design of new alloys with hydrogen absorption and desorption ability at ambient conditions.

Enhanced Stability of Hydride in Ceria/Copper Composite Catalysts

A composite material, as a combination of two or more components, may provide better properties than any single part. Here, we performed the density functional theory calculations to study the hydride formation on inverse CeOx/Cu(111) catalysts and found that these composite catalysts can give rise to more abundant active hydride species than CeO2 or Cu alone. Such property is largely attributed to the efficient combination of the unique structural feature of CeOx islands and the electronic promotion from Cu. Moreover, by further modifying the Cu(111) surface with pyridine molecules, both thermo- and dynamical stabilities of the hydride species can be enhanced.

Formation of Zr-rich BCC phase and its relation on the hydrogen storage properties of TiVNbZr high entropy alloy

Due to the large difference in atomic size between Zr and Nb, TiVNbZr high entropy alloy possesses greater lattice distortion. The change of Zr content can affect the stability of hydrides, which can have an important impact on the hydrogen storage performance. In order to explore the effect of Zr/Nb on hydrogen storage properties, Ti32.5V27.5Nb40-xZrx (x = 7.5, 10, 12.5, 15) high entropy alloys composed of BCC phase are designed. It is found that with the increase of Zr/Nb, the dendritic microstructures first disappear and then gradually become coarse. The Zr-rich BCC phase and the Nb-rich BCC phase appear in the interdendritic and dendritic regions, respectively. Ti32.5V27.5Nb25Zr15 shows excellent activation performance, which is related to the Zr-rich BCC phase with the most catalytic phase on the surface. The hydrogen storage performance of low Zr/Nb composition is better at low temperature, and that of high Zr/Nb composition becomes better after rising to high temperature. This is because with the change of Zr/Nb, low temperature can promote the hydrogen absorption reaction and high temperature can increase the diffusion rate of hydrogen atoms in the interstitial positions of the alloy. Ti32.5V27.5Nb32.5Zr7.5 achieves the best hydrogen absorption capacity of 1.71 wt % at 150 °C. All components undergo a transition from the BCC phase to the FCC phase during the hydrogen absorption process, and then change to a single-phase BCC structure after dehydrogenation. With the increase of Zr content, the first step desorption temperature raises in turn, owing to the stronger thermal stability of hydride.

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.