Hydride Alloys Research Articles

Performance analysis of metal hydride heat pump system with CFD modelling development and actual reactor designs

Hydrogen and metal hydride reactions in a decarbonized heat pump system with low-grade waste heat recovery offer a promising path for sustainable energy storage and conversion. Based on actual metal hydride reactor designs, this study developed a 2D transient Computational Fluid Dynamics (CFD) model for such a heat pump system working with hydrogen and a metal hydride alloy pair of Zr0.9Ti0.1Cr0.6Fe1.4 and LaNi4.25Al0.75. The effects of operating temperatures on the coefficient of performance (COP) and specific heat power (SHP) of the system have been presented and analyzed. Subsequently, raising the medium-temperature heat sink (TM) from 358.15 K to 373.15 K, and low-temperature heat source (TL) from 308.15 K to 323.15 K, results in a decrease in the COP by 25.57%, and an increase in the COP by 38.2%, respectively. An optimum value of high-temperature heat source (TH) exists at 493.15 K for a maximum COP. In addition, the higher thermal conductivity increases the absorption and desorption capacity of hydrogen.

The role of hydrogen in the synthesis of High-entropy alloys and their hydrides

The aim of this work is to present the new technique processes of formation of stable hydrides of High-entropy alloys (HEAs) with high hydrogen content. The essence of the proposed method is the sequential use of self-propagating high-temperature synthesis (SHS) method for producing the metal hydrides, followed by the formation of alloys in the hydride cycle (HC) method. Preliminary, the hydrides of three compositions of metal mixtures were synthesized in SHS: 0.2TiH2+0.2ZrH2+0.2HfH2+0.2VH2+0.2NbH2, 0.3TiH2+0.15ZrH2+0.15HfH2+0.2VH2+0.2NbH2 and 0.3TiH2+0.1ZrH2+0.1HfH2+0.2VH2+0.2NbH2+0.1MgH2. From the synthesized mixtures of metal hydrides, the HEAs were produced in HC. The resultant hard alloys Ti0.2Zr0.2Hf0.2V0.2Nb0.2, Ti0.3Zr0.15Hf0.15V0.2Nb0.2 and Ti0.3Zr0.15Hf0.15V0.2Nb0.2Mg0.1 without crushing combusted in Н2 at РH2 = 5–30 atm. in SHS mode. As a result, the hydrides of HEAs (Ti0.2Zr0.2Hf0.2V0.2Nb0.2)Н2.05, (Ti0.3Zr0.15Hf0.15V0.2Nb0.2)H2.05 and (Ti0.3Zr0.1Hf0.1V0.2Nb0.2 Mg0.1)H182 were synthesized with H2 content between 2.17 and 2.42 wt% and H/Me = 1.82–2.05. The repeating the hydrogenation-dehydrogenation processes for 1–3 times confirmed the exceptional cyclic stability of hydrides and the reversible high hydrogen storage capacity of the alloys. The regularities and the mechanism of formation of HEAs and their hydrides were elucidated. The applicability of combination of SHS and HC methods for synthesis of solid solutions of BCC structure HEAs and of their hydrogen-rich hydrides was demonstrated. The remarkable advantages of the developed efficient, low-energy consuming, waste-free and safe method for the synthesis of HEAs and their hydrides can be of commercial interest and attractive to industry, given the current needs for the development of renewable energy, in particular, the solid hydrogen storage facilities.

Fretting corrosion behavior and microstructure evolution of hydrided zirconium alloy under gross slip regime in high temperature high pressure water environment

Fretting corrosion behavior and microstructure evolution of hydrided zirconium alloy under gross slip regime in high temperature high pressure water environment

Computational insights of double perovskite Na2CaCdH6 hydride alloy for hydrogen storage applications: a DFT investigation

Prospective use of perovskite hydride materials in H storage a crucial element of clean energy systems has drawn a lot of attention. The structural, electrical, mechanical, thermodynamic, and H storage qualities of Na2CaCdH6 hydride alloys were examined in this work using DFT. According to the structural properties, Na2CaCdH6 has space group 225 (Fm3m), and optimized lattice parameters and volume of Na2CaCdH6 are 3.3485 Å and 593.764 Å3. The measured gravimetric H storage capacity of Na2CaCdH6 hydrides is 2.956 wt%. The hydrides under research are semiconductors, as indicated by the computed electronic characteristics. Elastic constants, Pugh’s ratio, modulus, Poisson’s ratio, anisotropic, and microhardness of Na2CaCdH6 are calculated under mechanical properties. The hydrides are dynamically stable, as indicated by the phonon dispersion curves, but mechanically stable according to the Born criterion for elastic constant (Cij). The Cauchy’s pressure (C″ = 7.836) revealed the ductile behavior. The electronic and mechanical characteristics imply that Na2CaCdH6 hydride can conduct electricity and is also mechanically stable. Our findings shed light on the possibilities of Na2CaCdH6 perovskite hydride material for H storage utilization.

Metal Hydride Storage Systems: Approaches to Improve Their Performances

AbstractMetal hydrides provide a safe and efficient way to store hydrogen. However, current metal hydride storage systems, i.e., hydrides incorporated within a storage tank, are far from efficient. Depending on the design, (dis)charging rates may be very long. However, this can be significantly improved by implementing strategies tackling the issue of heat management at the level of: i) the metal hydride bed, and ii) the overall storage system design. This review summarises recent progress in tackling heat management of hydride systems. In this respect, modeling has emerged as a powerful tool. In particular, simulation results show that the compaction of hydride powders with binders and the use of metal foams are both effective in lifting the poor thermal conductivity of hydride beds. For tank designs, cylindrical shapes remain the preferred choice because of the flexibility and ease of supplementing heat management with fins and tubular heat exchangers. The addition of phase change materials to the hydride tank can lead to further heat storage, but any add‐on to simple hydride tanks can only lead to cumbersome systems. It is still a fine art to tune the thermal conductivity of hydride beds while selecting a suitable metal hydride alloy composition.

A parametric study on hydrogen storage in AB5 hydride alloys: Heat and mass transfer, thermodynamics, and design

The design of heat exchangers plays an important role in the performance of solid-state hydrogen storage devices. In this study, three different designs of hydrogen storage devices were investigated, incorporating phase change material (PCM), specifically, RT25HC into their walls in various shapes. A mathematical model, validated using previous experimental data, was employed to calculate heat and mass transfer and determine the reaction time period. The calculations were conducted using ANSYS Fluent, with a constant hydrogen supply pressure of 10 bars and a temperature of 295 K. The absorption properties of the storage reactor were investigated through various parameters such as liquid fraction, hydrogen concentration, and natural convection heat transfer coefficients. Results showed that the geometric structure and PCM distribution significantly impacted the performance of the hydrogen storage devices. Design 1, with a centralized PCM distribution, demonstrated moderate heat transfer rates and a longer reaction time. Design 2, featuring a more distributed PCM layout, improved heat transfer rates and reduced hydrogen kinetics time by 40%. Design 3, which optimized the geometric structure with advanced PCM shapes, achieved the highest heat transfer rates and improved hydrogen kinetics time by 50%. This design also enabled the storage of thermal energy at a high density, ranging from 10.2 J/g to approximately 190.5 J/g. The study provides critical information on the design of efficient solid hydrogen storage processes. The findings suggest significant potential for improved performance in industrial applications such as electric vehicles and domestic energy supply. The high efficiency of the large-scale reactor is due to its well-designed system, which effectively converts chemical energy into thermal energy. Optimizing the reactor geometry and PCM distribution is crucial for achieving superior hydrogen storage and retrieval performance.

Effects of Mg and Al doping on the desorption energetics and electronic structure of a Ti-V-Zr-Nb alloy hydride

Refractory high-entropy alloys (HEAs) show promise for novel hydrogen storage technology, but addressing their limited gravimetric hydrogen storage capacity necessitates exploration of light alloying elements including Mg and Al. Here, we employ density-functional theory to investigate the hydrogen desorption energetics of Ti0.325V0.275Zr0.125Nb0.275 alloy and the impact of doping with Mg and Al. Our analysis reveals that Mg and Al addition thermodynamically destabilize the Ti0.325V0.275Zr0.125Nb0.275-hydride and lower its storage capacity. The observed destabilization is attributed to reduced chemical contributions to the desorption enthalpy in the Mg and Al-doped hydrides. Detailed examination of the electronic density of states, electron localization function, and crystal orbital Hamilton population analysis unveils fundamental features of chemical bonding in these hydrides. Notably, H-H antibonding states occur for hydrogen atoms located in the nearest-neighbor interstices of Mg and Al atoms. Charge transfer facilitates formation of these antibonding states. This comprehensive analysis enhances our understanding of the intricate interplay between electronic structure, hydrogen desorption energetics, and chemical bonding in HEA hydrides, offering valuable insights for the design and optimization of advanced hydrogen storage materials.

Catalytic mechanism of Nb2O5 and Ni on hydrogen storage properties of CeMg12-type alloy for automatic weather station emergency fuel cell

In this paper, CeMg12/Ni/Nb2O5 was prepared by mechanical ball milling technology for the sake of probing into the impact of Ni and Nb2O5 on microstructure and hydrogen sorption properties of alloys. The microstructure research results indicate that adding Nb2O5 can promote the formation of nanocrystal structure; through ball milling the Nb2O5 dispersed on the surface of alloy particles uniformly enhances the surface activity of the alloy and improves the hydrogen absorption and releasing kinetics of the alloy. The research on hydrogen absorption performance shows that the addition of Nb2O5 can significantly increase the hydrogen release platform pressure of the alloy hydride, the enthalpy value of hydrogen releasing process drops from 74.82 kJ/mol to 71.07 kJ/mol when the content of Nb2O5 is increased from 0 wt% to 9 wt%, the above qualitative and quantitative discussion further proves that Nb2O5 is beneficial for amending the thermodynamic stability of alloy hydride. Besides, adding Nb2O5 can remarkably reduce the hydrogen dissociation activation energy of experimental alloy hydride, ameliorating the dynamic performances of hydrogen release. The alloy with 9 wt% Nb2O5 has the smallest activation energy and the best performances of hydrogen release.

The influence of hydrogen on the synthesis of biocompatible alloy Ti-6Al-7 Nb by a new Hydride Cycle method

The Hydride Cycle (HC) method is proposed as a new approach for synthesis of biocompatible alloy Ti-6Al-7 Nb. In this approach, preliminary, (Ti-7 Nb)H3.81 hydride is synthesised by Self-propagating High-temperature Synthesis (SHS) method. The heating of a mixture of this hydride with aluminum, (Ti-7 Nb)H3.81+6Al, at 1000°C for 30 minutes in the HC device results in the synthesis of Ti-6Al-7 Nb alloy containing the α- and β-phases of Ti, 92 wt% and 8 wt%, respectively. The alloy interacted with hydrogen in the combustion mode (SHS) forming the hydride (Ti-6Al-7 Nb)H3.17 with hydrogen content 3.07 wt%. This amount of hydrogen ensures the brittleness of the hydride and its grinding for 30–40 minutes to the agglomerates down to submicron or nano sizes. The presence of hydrogen in the crystal lattice enhances the plasticity of the hydride facilitating its compaction. The compaction of the (Ti-6Al-7 Nb)H3.17 alloy hydride and dehydrogenation under T=1000°C results in the reaction-activated sintering and the formation of practically porous less Ti-6Al-7 Nb alloy. The HC synthesis of the biocompatible alloy Ti-6Al-7 Nb compiled with SHS mode of the hydride synthesis is provided with the several advantages over the traditional methods. It is a low temperature, short duration, waste less process, proceeding by solid-state mechanism without melting of components, being an energy-saving in total. The proposed HC approach for synthesis of Ti-6Al-7 Nb alloy in combination with the high-technology SHS process for the hydrides formation can be used in manufacturing the biocompatible alloys. The hydrogenation-sintering of the alloy hydride (Ti-6Al-7 Nb)H3.17 can be used for producing of items of any designed complex form, particularly of implants.

Structural alterations on copper cages containing hydrides coordinated to the central Pd(0)

A crucial component of nanocluster (NC) chemistry is the design and control of complex molecular architectures with atomic precision. Herein, we report the synthesis and structure of [PdH2Cu11{S2P(OiPr)2}6(CCPh)3] (PdH2Cu11), confirmed by single-crystal X-ray diffraction (SC-XRD), NMR spectroscopy, elemental analysis, and electrospray ionization mass spectrometry (ESI-MS). PdH2Cu11 is obtained from the reaction of a parent cluster [PdH2Cu14{S2P(OiPr)2}6(CCPh)6] (PdH2Cu14) with trifluoroacetic acid (TFA). Importantly the addition of TFA does not result in the loss of the hydride atoms located at the kernel, and H-Pd-H motif is retained. The molecular structure of PdH2Cu11 consists of a distorted 3,3,4,4,4-pentacapped trigonal prism Cu11 cage encapsulating a quasi-linear H-Pd-H unit, stabilized by dithiophosphate and alkynyl ligands. DFT calculations suggest an ionic inclusion complex of the type [{PdH2}2−]@[{Cu11{S2P(OiPr)2}6(CCPh)3}2+] and confirm the hydride positions. A non-covalent inter-cluster interaction results in the unique formation of a unique honeycomb crystal lattice. Overall, this work broadens and deepens the understanding of Pd-Cu hydride alloy nanoclusters.

Tribological and corrosion behavior of hydrided zirconium alloy

Zirconium alloys (Zr-alloys) are used for the core components of nuclear reactors due to their exceptional properties, which make them suitable for the given applications such as low neutron absorption cross-section, good corrosion resistance, good wear resistance, good mechanical stability at high temperatures etc. The coolant water that flows inside the pressure tube contains LiOH to control the pH value of the coolant water, which can cause corrosion. The flow of coolant water produces low amplitude vibration, which can cause fretting wear of the components. Further, the coolant water at high temperature causes the hydride formation in the material, degrading the properties of zirconium alloys. The safe working of nuclear reactors is the prime objective, and the corrosion and wear behavior of the core components must be explored to prevent possible failure. Fretting wear or tribo-corrosion experiments were conducted on Zr‐2.5Nb alloy against SS-410 for varied fretting duration to understand the tribological response. Electrochemical corrosion experiments were performed under the aqueous solution of LiOH (10.4 pH) using Electrochemical Impedance Spectroscopy (EIS) and potentiodynamic polarization technique. The comparison was made between the tribological and corrosion response of unhydrided‐Zr‐2.5Nb alloy (Zr‐2.5Nb) and hydrided- Zr‐2.5Nb alloy (Zr‐2.5Nb‐H). The hydride formation causes the reduction in corrosion resistance of Zr‐2.5Nb alloy. The oxide layer is formed during the wear and corrosion process which protects the material from further wear and corrosion respectively.

Zirconium-Modified Medium-Entropy Alloy (TiVNb)85Cr15 for Hydrogen Storage.

In this study, we investigate the effect of small amounts of zirconium alloying the medium-entropy alloy (TiVNb)85Cr15, a promising material for hydrogen storage. Alloys with 1, 4, and 7 at.% of Zr were prepared by arc melting and found to be multiphase, comprising at least three phases, indicating that Zr addition does not stabilize a single-phase solid solution. The dominant BCC phase (HEA1) is the primary hydrogen absorber, while the minor phases HEA2 and HEA3 play a crucial role in hydrogen absorption/desorption. Among the studied alloys, Zr4 (TiVNb)81Cr15Zr4 shows the highest hydrogen storage capacity, ease of activation, and reversibly retrievable hydrogen. This alloy can absorb hydrogen at room temperature without additional processing, with a reversible capacity of up to 0.74 wt.%, corresponding to hydrogen-to-metal ratio H/M = 0.46. The study emphasizes the significant role of minor elemental additions in alloy properties, stressing the importance of tailored compositions for hydrogen storage applications. It suggests a direction for further research in metal hydride alloys for effective and safe hydrogen storage.

Novel NLi4-BGra/MgH2-based heterojunctions for efficient hydrogen storage and modulation of hydrogen-desorption temperature ranges

In this study, a novel superalkali NLi4 decorated Boron doped graphene/magnesium hydride heterojunction NLi4-BGra/MgH2 was designed using density functional theory (DFT). Molecular dynamics (MD) confirmed that this material can release H2 adsorbed near NLi4 and H stored within MgH2 at a fixed hydrogen-desorption temperature (Td) of 298 K and 570 K, respectively. Subsequently, 132 magnesium alloy hydrides Mg1-XMeXH2 with various hydrogen-storage capacities and hydrogen-desorption temperatures were predicted by DFT combined with machine learning (ML). Among them, Mg0.875Li0.125H2 (Td = 400K) and Mg0.875Be0.125H2 (Td = 500K) were selected to form NLi4-BGra/Mg0.875Me0.125H2 (Me = Li, Be). The successful validation of Root Mean Square Deviation, diffusion coefficient and hydrogen-desorption trajectories to qualify the hydrogen-desorption capability of NLi4-BGra/Mg0.875Me0.125H2 (Me = Li, Be) (Td = 400, 500K) confirms that the strategy of using Mg1-XMeXH2 to substitute MgH2 in NLi4-BGra/MgH2 enables the effective modulation of the hydrogen-desorption temperature ranges of NLi4-BGra/MgH2-based heterojunctions. In particular, partial density of state, electron localization function, and charge density difference were comprehensively analyzed to understand the hydrogen-storage mechanism and the nature of the hydrogen-desorption temperature variation.

Investigation of hydrolysis properties of MgH2 in different anionic/cationic salt solutions

MgH2 is a promising metal hydride for high-density hydrogen storage, offering advantages such as operational safety, high hydrogen yield, and cost-effectiveness in hydrolysis-based hydrogen generation. However, challenges persist in this field, including reaction interruption caused by the formation of passivating layers and sluggish kinetics. In this study, MgH2 hydrolysis experiments were conducted, utilizing various solutions including 1 M AlCl3, Al2(SO4)3, Al(NO3)3, NiCl2, NiSO4, Ni(NO3)2, FeCl3, Fe2(SO4)3, and Fe(NO3)3 at different temperatures. The resulting hydrolysis products were analyzed using X-ray diffraction and scanning electron microscopy to examine their phases and morphology. Through comprehensive analysis of the hydrolysis mechanism and kinetics, chloride ion solutions were identified as highly efficient, demonstrating excellent rates and yields. Notably, AlCl3, NiCl2, and FeCl3 outperformed other solutions, exhibiting kinetic performance with hydrolysis activation energies of 17.3 ± 1.7, 24.2 ± 1.3, and 14.7 ± 1.7 kJ/mol, respectively. Furthermore, we extended our investigation to compare the hydrolysis effects of different cations, incorporating MnCl2, CoCl2, and CuCl2. Mechanistic analysis pinpointed Al3+ and Fe3+ as catalysts with exceptional hydrolysis performance and remarkable kinetic properties. The aforementioned remarkable MgH2 hydrolysis properties are of significant interest for investigating the corresponding Mg-based alloy hydrides, which are worthwhile to consider.

Numerical study of polymer embedded metal hydride-based self-sensing actuator

Metal hydride actuators have amassed increasing attention over the past decade owing to their desirable operational characteristics, such as a high power-to-weight ratio, noiseless and vibration-less operation, lightweight, safety and environmental friendliness. Essentially, there are two ways in which we can attain actuation using hydrides. Primarily, actuation force is generated by the hydrogen gas pressure changes associated with charge–discharge process. Alternatively, the incompressible volumetric changes in the hydride bed during sorption can also result in actuation. However the studies reported on this type of actuators are rare and mostly deal with bimorph actuators. The present study investigates the effect of soft silicone rubber composited metal hydride bed within a hollow stainless steel spring for its potential use as a self-sensing actuator element. LaNi5 is used as the metal hydride alloy. For an equivalent quantity of hydride by mass, the estimated actuation stroke and force for the composite bed actuator are better than their powder bed counterpart (12 mm and 100 N, respectively, in contrast to 5.84 mm and 60 N), due to improved heat transfer. Bed thickness, coil pitch and coil diameter are important geometric parameters which control the performance of the device. As previously reported, hydrogen supply pressure and heat transfer coefficient are found to be important operating parameters controlling the force –stroke characteristics of the actuating element. The simulation study has been executed using COMSOL Multiphysics™ commercial code.

Graph Neural Network-Accelerated Multitasking Genetic Algorithm for Optimizing PdxTi1-xHy Surfaces under Various CO2 Reduction Reaction Conditions.

Palladium (Pd) hydride-based catalysts have been reported to have excellent performance in the CO2 reduction reaction (CO2RR) and hydrogen evolution reaction (HER). Our previous work on doped PdH and Pd alloy hydrides showed that Ti-doped and Ti-alloyed Pd hydrides could improve the performance of the CO2 reduction reaction compared with pure Pd hydride. Compositions and chemical orderings of the surfaces with only one adsorbate under certain reaction conditions are linked to their stability, activity, and selectivity toward the CO2RR and HER, as shown in our previous work. In fact, various coverages, types, and mixtures of the adsorbates, as well as state variables such as temperature, pressure, applied potential, and chemical potential, could impact their stability, activity, and selectivity. However, these factors are usually fixed at common values to reduce the complexity of the structures and the complexity of the reaction conditions in most theoretical work. To address the complexities above and the huge search space, we apply a deep learning-assisted multitasking genetic algorithm to screen for PdxTi1-xHy surfaces containing multiple adsorbates for CO2RR under different reaction conditions. The ensemble deep learning model can greatly speed up the structure relaxations and retain a high accuracy and low uncertainty of the energy and forces. The multitasking genetic algorithm simultaneously finds globally stable surface structures under each reaction condition. Finally, 23 stable structures are screened out under different reaction conditions. Among these, Pd0.56Ti0.44H1.06 + 25%CO, Pd0.31Ti0.69H1.25 + 50%CO, Pd0.31Ti0.69H1.25 + 25%CO, and Pd0.88Ti0.12H1.06 + 25%CO are found to be very active for CO2RR and suitable to generate syngas consisting of CO and H2.

Synthesis and superconductivity in yttrium-cerium hydrides at high pressures

Further increasing the critical temperature and/or decreasing the stabilized pressure are the general hopes for the hydride superconductors. Inspired by the low stabilized pressure associated with Ce 4f electrons in superconducting cerium superhydride and the high critical temperature in yttrium superhydride, we carry out seven independent runs to synthesize yttrium-cerium alloy hydrides. The synthetic process is examined by the Raman scattering and X-ray diffraction measurements. The superconductivity is obtained from the observed zero-resistance state with the detected onset critical temperatures in the range of 97-141 K. The upper critical field towards 0 K at pressure of 124 GPa is determined to be between 56 and 78 T by extrapolation of the results of the electrical transport measurements at applied magnetic fields. The analysis of the structural data and theoretical calculations suggest that the phase of Y0.5Ce0.5H9 in hexagonal structure with the space group of P63/mmc is stable in the studied pressure range. These results indicate that alloying superhydrides indeed can maintain relatively high critical temperature at relatively modest pressures accessible by laboratory conditions.

Phase-field simulations of the effect of temperature and interface for zirconium δ-hydrides

Hydride precipitation in zirconium cladding materials can damage their integrity and durability. Service temperature and material defects have a significant effect on the dynamic growth of hydrides. In this study, we have developed a phase-field model based on the assumption of elastic behaviour within a specific temperature range (613 K–653 K). This model allows us to study the influence of temperature and interfacial effects on the morphology, stress, and average growth rate of zirconium hydride. The results suggest that changes in temperature and interfacial energy influence the length-to-thickness ratio and average growth rate of the hydride morphology. The ultimate determinant of hydride orientation is the loss of interfacial coherency, primarily induced by interfacial dislocation defects and quantifiable by the mismatch degree q. An escalation in interfacial coherency loss leads to a transition of hydride growth from horizontal to vertical, accompanied by the onset of redirection behaviour. Interestingly, redirection occurs at a critical mismatch level, denoted as q c, and remains unaffected by variations in temperature and interfacial energy. However, this redirection leads to an increase in the maximum stress, which may influence the direction of hydride crack propagation. This research highlights the importance of interfacial coherency and provides valuable insights into the morphology and growth kinetics of hydrides in zirconium alloys.

High-throughput Compositional Screening of PdxTi1-xHy and PdxNb1-xHy Hydrides for CO2 Reduction.

Electrochemical experiments and theoretical calculations have shown that Pd-based metal hydrides can perform well for the CO2 reduction reaction (CO2RR). Our previous work on doped-PdH showed that doping Ti and Nb into PdH can improve the CO2RR activity, suggesting that the Pd alloy hydrides with better performance are likely to be found in the PdxTi1-xHy and PdxNb1-xHy phase space. However, the vast compositional and structural space with different alloy hydride compositions and surface adsorbates, makes it intractable to screen out the stable and active PdxM1-xHy catalysts using density functional theory calculations. Herein, an active learning cluster expansion (ALCE) surrogate model equipped with Monte Carlo simulated annealing (MCSA), a CO* binding energy filter and a kinetic model are used to identify promising PdxTi1-xHy and PdxNb1-xHy catalysts with high stability and superior activity. Using our approach, we identify 24 stable and active candidates of PdxTi1-xHy and 5 active candidates of PdxNb1-xHy. Among these candidates, the Pd0.23Ti0.77H, Pd0.19Ti0.81H0.94, and Pd0.17Nb0.83H0.25 are predicted to display current densities of approximately 5.1, 5.1 and 4.6 μA cm-2 at -0.5 V overpotential, respectively, which are significantly higher than that of PdH at 3.7 μA cm-2.

Thermal conductivity switching for a Y–Mg alloy hydride thin film due to hydrogenation/dehydrogenation reactions using dilute H2 gas

Thermal switching requires a significant contrast in thermal conductivity between the on and off states. We focus on thermal conductivity switching performance and mechanism for switchable mirror materials, which changes reversible metallic and semiconductor states due to hydrogenation and dehydrogenation. A thin film of yttrium–magnesium (Y–Mg) alloy hydride covered with a Pd catalyst layer was fabricated on quartz glass substrates by dc magnetron sputtering using a 60 at. % Y and 40 at. % Mg alloy target and a mixture of 50% Ar and 50% H2 gases. The crystal structure, electrical conductivity, and thermal conductivity in each state were measured using in situ x-ray diffraction analysis, Hall effect measurement, and thermoreflectance apparatus, respectively. The Y–Mg alloy hydride film was hydrogenated and dehydrogenated on exposure to a mixture of 3% H2 in N2 gas and air, respectively. The structural change in Y hydrides due to hydrogenation and dehydrogenation was clarified, whereas Mg or Mg hydride in the film showed no apparent crystallization. The thermal conductivity of the on-state was 4.5 times larger than that of the off-state. The thermal conductivity change from hydrogenated to dehydrogenated state was ∼5.4 W m−1 K−1, and ∼2.5 W m−1 K−1 of thermal conductivity change could be attributed to electron contribution based on the estimation using Wiedemann–Franz law. The thermal conductivity changes of Y–Mg alloy hydrides due to hydrogenation/dehydrogenation resulted from both electrons and phonons.