Hydrogen Storage Applications Research Articles

A DFT study of structural, electronic, mechanical, phonon, thermodynamic, and H2 storage properties of lead-free perovskite hydride MgXH3(X=Cr, Fe, Mn)

Perovskite hydride materials have gained significant attention for their potential in hydrogen storage, a key component of renewable energy systems. In this study, we used density functional theory (DFT) to investigate the structural, vibrational, electronic, mechanical, thermodynamic, and hydrogen storage properties of MgXH3 (X = Cr, Fe, Mn) hydrides. The energy volume curves were used to determine optimized lattice parameters of MgCrH3(3.4590 Å), MgFeH3(3.0284 Å), and MgMnH3(3.3485 Å). The Born criteria for elastic constant (Cij) showed that the hydrides are mechanically stable, whereas the phonon dispersion curves showed their dynamic stability. The calculated electronic properties revealed the metallic nature of hydrides under investigation. The Cauchy pressure (Cp) revealed the brittle and ductile behavior. The calculated gravimetric hydrogen storage capacity of MgCrH3, MgFeH3, and MgMnH3 hydrides was 3.771, 3.606, and 3.643 wt% respectively. The electronic and thermodynamic properties suggest that MgXH3 hydrides can conduct electrical as well as thermal energy. Our results provide insight into the potential of MgXH3(X = Cr, Fe, Mn) perovskite hydride material for hydrogen storage application.

Carbonous nanocomposites of Mn2Mo3O8/MnO as active materials for studying lithium and hydrogen storage application

High conductivity of carbon-based materials makes them capable of offering the ideal conditions for energy storage via electrochemistry. Along with metal oxide complexes, nanoscale carbon materials with active sites can play a function in the lithium or hydrogen storage process. The active materials of Mn2Mo3O8/MnO were synthesized via solvothermal method in the presence of diverse carbonous compounds such as graphene oxide (GO), multiwall carbon nanotubes (MWCNTs) and activated charcoal (AC). The resultant samples analyzed as electrode materials for using in the hydrogen storage and lithium-ion battery. Both electrochemical devices assemble in the specific medium for investigating the capacity and performance in order to energy storage ability. The synthesized sample in the presence of MWCNTs show better results in terms of capacity and cycle life in the lithium-ion battery system and hydrogen storage application. Also, data collected from XRD patterns were used to characterize the microstrain and crystal size for the obtained samples. FE-SEM, HR-TEM, and BET-BJH techniques were used to examine the morphology and porosity of the samples.

Li-decorated bilayer borophene as a potential hydrogen storage material: A DFT study

Two-dimensional (2D) materials have recently attracted much attention in the field of hydrogen storage, owing to their beneficial properties such as high surface-to-volume ratio and light weight. Motivated by recent experimental developments of bilayer borophene (BL) sheets, we investigate the suitability of hydrogen storage on Li-decorated BL via density functional theory (DFT) calculations. The H2 molecules are adsorbed on BL sheet via weak physisorption. By decorating BL with Li atoms, its hydrogen storage performance has been improved. We find that Li atoms can firmly adsorb on the substrate without forming clusters. Meanwhile, the Li-decorated structure exhibits good stability, verified by molecular dynamics calculations. Remarkably, in the fully loaded case, the compound obtains a 6.08 wt% H2 content and 0.13 eV/H2 average adsorption energy, which is promising for onboard hydrogen storage. Furthermore, electronic structure analysis reveals the electrostatic nature of interactions between the H2 molecules and the protruding Li atoms on BL sheets, which originates from polarization and orbital hybridization. Overall, our results suggest that Li-decorated BL is a promising candidate for potential hydrogen storage applications, and contribute to a better understanding of bilayer materials for hydrogen storage.

Sol-gel synthesis, characterization, and electrochemical evaluation of magnesium aluminate spinel nanoparticles for high-capacity hydrogen storage

In this research, we successfully synthesized magnesium aluminate (MgAl2O4) spinel nanoparticles using a sol-gel process, with stearic acid serving as a capping agent. The synthesis process involved calcination at 900 °C for 4 h, resulting in the formation of nanoparticles with an average crystallite size of approximately 12 nm, as determined through Debye–Scherrer analysis and X-ray diffraction (XRD) data. The optical band gap was measured as 2.84 eV using Diffuse Reflectance Spectroscopy (DRS) analysis. Additionally, we found the mean pore size of the nanoparticles to be 20.2 nm through Brunauer–Emmett–Teller (BET) analysis. We characterized the resulting powders using various techniques, including Fourier Transform Infrared (FTIR) spectroscopy, Field Emission Scanning Electron Microscopy (FESEM), Energy-Dispersive X-ray Spectroscopy (EDS), and Vibrating Sample Magnetometry (VSM). We conducted electrochemical investigations utilizing the Chronopotentiometry (CP) technique. The electrochemical analysis demonstrated that MgAl2O4 spinel nanoparticles exhibit a noteworthy hydrogen storage capacity of 4000 mAh/g, highlighting their potential as promising candidates for hydrogen storage applications. This comprehensive study underscores the successful synthesis, thorough characterization, and exceptional electrochemical performance of MgAl2O4 spinel nanoparticles, firmly positioning them as valuable materials for advancing hydrogen storage technologies.Graphical

Intrinsic kinetics of benzyltoluene hydrogenation over a supported Ni catalyst for green hydrogen storage

Liquid organic hydrogen carrier technology is a promising alternative for hydrogen storage and transportation. Benzyltoluene (BT) is a high-performance hydrogen storage carrier, but the hydrogenation kinetic parameters that are important to guide reactor and catalyst design are not clear. Here, we systematically investigated the kinetics of BT hydrogenation over a supported Ni catalyst for its potential application in hydrogen storage. Our results suggest that BT hydrogenation reaction follows a two-step series reaction from BT to 12H-BT with 6H-BT as the intermediate. The reaction order is 0 and 1 with respect to BT and 6H-BT concentration, respectively, whereas that with respect to H2 pressure is approximately equal (1.0 and 1.1 for BT and 6H-BT hydrogenation, respectively). Calculated activation energy suggests that 6H-BT hydrogenation is the rate-determining step in the whole process. Moreover, both kinetic and DFT results indicate that the presence of BT would inhibit the further 6H-BT hydrogenation to 12H-BT. This study is expected to provide a new understanding of BT hydrogenation reactions and a useful guideline for reactor and catalyst design.

DFT insights on structural, electronic, optical and mechanical properties of double perovskites X2FeH6 (X = Ca and Sr) for hydrogen-storage applications

Hydrogen has been delivered as a magnificent alternative clean energy source to alleviate the growing energy dilemma and the harmful consequences of traditional energy sources on the environment and the population. This one-of-a-kind energy-efficient technique involves storing hydrogen in solid-state compounds and then releasing it as needed for utilization in possible energy applications. Metal hydrides have shown to be highly effective hydrogen storage mechanisms in this setting. To improve the efficiency of hydrogen storage and release at standard temperatures and pressures, however, the use of metal hydrides with high gravimetric, poor thermodynamic stability and high kinetics is required. X2FeH6 (X = Ca and Sr) has promising promise for hydrogen-storage applications, with gravimetric hydrogen densities of 4.28 wt% and 2.54 wt% weight, respectively. We used the DFT technique inside the GGA + PBE framework to undertake the first comprehensive study of the structural, electronic, optical and mechanical properties of X2FeH6 (X = Ca and Sr). Structural properties indicate that both the compounds are thermodynamically stable. The Ca2FeH6 and Sr2FeH6 are semiconductors with an estimated indirect band gap of 1.67 eV and 1.37 eV, respectively. Dielectric constants, absorption, reflectivity, energy loss functions and refractive indices are among the optical characteristics determined by the calculations. The results of mechanical properties suggest that both of these hydrides fall within the category of brittle materials. These findings are crucial for the future development of metal hydrogen storage materials.

Enhancing the hydrogen storage properties of (Ti, M)C1−x materials (M = W, Mg, Ni, and Al) depends on the carbon vacancies: Potential for the recycling of scraps

New energy storage systems and recycling schemes are required to solve the increasing environmental and energy problems. Owing to the increasing cost of raw materials, scraps need to be recycled. Carbides can be used as hydrogen storage materials; however, their mechanical properties remain unclear. To fabricate high-quality carbides from scraps as potential candidates for hydrogen storage materials, it is necessary to understand the mechanical properties of the carbides when absorbing hydrogen atoms. In this study, we evaluated the thermodynamic stabilities, mechanical properties, and electronic structures of (Ti, M)C1-x materials (M = W, Mg, Ni, and Al, x=0–1. The effects of the carbon vacancies were examined using density functional theory calculations. Based on the results, the TiC0.625 composition was stable at ambient temperature and pressure. Titanium carbides have shown potential for use in hydrogen storage applications at 0≤x≤0.375, as the hardness decreases rapidly when x≥0.375. In addition, the results indicate that (Ti, Al)C should mainly be used in the target hydrogen storage materials at a composition below x=0.25. These findings support the design of hydrogen storage materials based on recycled carbides.

Compositional tuning of A2B7-type La0.7–xYxMg0.3Ni3.5 alloys for gaseous hydrogen storage

Rare earth-based superlattice alloys have great potential for gaseous hydrogen storage, as well as successful application as nickel-metal hydride batteries anodes. In this work, Y substitution was carried out to adjust the gaseous hydrogen storage properties of A2B7-type La0.7Mg0.3Ni3.5 alloys. The results indicate a multiphase structure in the alloys comprised of the main rhombohedral Gd2Co7 and PuNi3 phases, with a small amount of CaCu5 phase. Moreover, the Y substitution results in higher abundance of the Gd2Co7 phase. The alloy La0.42Y0.28Mg0.3Ni3.5 exhibits a hydrogen storage capacity of 1.55 wt% at 298 K and a desorption plateau pressure of 0.244 MPa. In addition, this alloy demonstrates a stable cycle life by a capacity retention of 94.2% after 50 cycles, with the main capacity degradation occurring during the initial 20 cycles. This work accentuates the potential of the La–Y–Mg–Ni-based superlattice alloys for applications in solid-state hydrogen storage.

Improvement of the thermodynamic properties of lithium borohydride LiBH4 by mechanical treatment for hydrogen storage applications: A DFT investigation

In the present work, single, double and triaxial (tensile/compression) strains were applied to lithium borohydride LiBH4 using Density Functional Theory (DFT) based on Perdew-Burke-Ernzerhor for solids (PBEsol) approach. The results show that the structural properties change with the deformation amplitude. The total density of state (TDOS) and partial density of state (PDOS) studies show that the LiBH4 complex hydride is an insulator with an energy band gap of 6.73 eV and the width of the valence and conduction bands vary with the change of the strain amplitude. The deformation energy shows that triaxial deformation on LiBH4 complex hydride requires more energy than single and double strains. Hence, these deformations are found responsible for the decrease of the thermodynamic properties of LiBH4 hydride. Specifically, under a maximum uni/bi/triaxial compressive strain of ε = −9%, the enthalpy of formation and decomposition temperature decrease by 3.25 %, 7.59 %, and 36.54 %, respectively. While, under a maximum uni/bi/triaxial tensile strain of ε = +9 %, the enthalpy of formation and decomposition temperature decrease by 3.85 %, 11.83 %, and 26.44 %, respectively, compared to unstrained hydride. Consequently, the findings are in excellent agreement with the standards of the U.S. Department of Energy (DOE) (ΔHf = −40 Kj/mol.H2 and Td = 289–393 K) for hydrogen storage in the solid state.

An analytical review of recent advancements on solid-state hydrogen storage

As global energy consumption is rapidly climbing to maximum, fossil fuel resources face depletion on a global scale. The rapid depletion and higher energy demand consequences an escalation of energy prices originating from conventional sources as well as the release of greenhouse gases into the environment. Hydrogen as an alternative energy source merged as an ideal candidate, distinguished by its remarkable attributes and manifold advantages. It has an exceptional energy density of 120 MJ/kg and encompasses non-toxicity, sustainability, and a favorable environmental profile. Renewable and non-renewable sources can produce hydrogen and have versatile applications in transportation, power generation via fuel cells, and other industrial processes. Beyond having these advantages hydrogen has the benefits of energy security and can be produced locally. Nevertheless, commercial hydrogen has exceptionally low volumetric density under standard conditions which is the major obstacle in the way of its development. To cater this issue and to enhance its economic feasibility, two well-established methodologies are used by alterations in temperature and/or pressure conditions which facilitate the storage of hydrogen either in a pressurized gas or a cryogenic liquid. However, both methods incur energy consumption and pose safety concerns and complexity in the system, which raises the question of having other storage solutions. An emerging technology based on Solid-state hydrogen storage systems has recently gained substantial attention because of its high storage capacity and relatively mild temperature and pressure requirements. However, this technology is not yet mature enough because it doesn't fulfil the requirements to be implemented for industrial applications. But, intensive research in this field is underway to develop novel materials with enhanced performance at both the material and the system level. The current review report is focused on a comprehensive and in-depth comparative analysis of various hydrogen storage methods, with a major focus on the enhancement of the performance of the material which is suitable for solid-state hydrogen storage applications.

Synthesis of Ni and Mg MOF-derived carbons for potential hydrogen storage applications

The synthesis of a Ni-trimesic acid (Ni-BTC) metal–organic framework (MOF) under ambient conditions followed by pyrolysis yields a porous MOF-derived carbon (MDC) doped with elemental Ni, appropriate for hydrogen storage applications. The same methods cannot be used for the synthesis of Mg-BTC MOF and its MDC as the reactivity of Mg towards BTC is not sufficient to prevent competing reactions, and Mg is oxidized to MgO during pyrolysis, preventing hydrogen storage via the formation of MgH2.

Hydrogen storage of high entropy alloy NbTiVZr and its effect on mechanical properties: A first-principles study

In recent years, high entropy alloys (HEAs) have demonstrated remarkable potential for hydrogen storage applications. Although extensive experimental studies have been conducted, a detailed understanding of the hydrogenation process at the atomic level is still lacking. In this study, first-principles calculations were employed to explore the microstructural evolution during hydrogen absorption in NbTiVZr as well as the mechanical characteristics of hydrides. The results indicate that a phase transition from BCC to FCC occurs in the hydride when the hydrogen content reaches 0.05 wt%. Hydrogen tends to occupy the octahedral interstitial sites in the BCC hydrides, while the preferred hydrogen sites in FCC hydrides undergo a transition from octahedral sites → tetrahedral + octahedra sites → tetrahedral sites as the hydrogen content increases. The highest hydrogen storage capacity of NbTiVZr was predicted by the phonon spectra of hydrides to be 2.94 wt%. Vanadium (V) is discovered to play a crucial role in hydrogen absorption capacity by causing significant lattice distortion and forming stronger bonds with hydrogen. Additionally, all hydrides exhibit great mechanical properties and thermal stability. Our research reveals that NbTiVZr has an excellent capacity for storing hydrogen and has the potential for applications in hydrogen storage materials.

Multi-objective optimisation of ionic liquid parameters for hydrogen compressors by Taguchi and grey relational analysis methods

The ionic liquid compressor developed in recent decades possesses a prospective application for hydrogen storage. The design of this new compressor considering multiple design parameters and objectives is critical for product development. This study investigated the percentage contribution of four design parameters of the ionic liquid to compressor performance by Taguchi and ANOVA. A two-objective optimisation was conducted to identify the near-optimal setting of ionic liquid parameters combining the Taguchi and grey relational analysis (GRA) methods considering both the liquid mass taken off and the specific energy consumption. It was found that the liquid height was the most influential parameter with percentage contributions of 84.65 % and 90.08 % to the liquid mass taken off and specific energy consumption, respectively. The optimal setting is obtained as the liquid height of 15 mm, liquid density of 1600 kg/m3, liquid viscosity of 50 mPa∙s and surface tension of 0.052 N/m.

Utilizing Nanostructured Materials for Hydrogen Generation, Storage, and Diverse Applications.

The rapid advancement of refined nanostructures and nanotechnologies offers significant potential to boost research activities in hydrogen storage. Recent innovations in hydrogen storage have centered on nanostructured materials, highlighting their effectiveness in molecular hydrogen storage, chemical storage, and as nanoconfined hydride supports. Emphasizing the importance of exploring ultra-high-surface-area nanoporous materials and metals, we advocate for their mechanical stability, rigidity, and high hydride loading capacities to enhance hydrogen storage efficiency. Despite the evident benefits of nanostructured materials in hydrogen storage, we also address the existing challenges and future research directions in this domain. Recent progress in creating intricate nanostructures has had a notable positive impact on the field of hydrogen storage, particularly in the realm of storing molecular hydrogen, where these nanostructured materials are primarily utilized.

Sustainable stationary hydrogen storage application selection with interval-valued intuitionistic fuzzy AHP

The transition to a hydrogen-based economy necessitates a comprehensive evaluation of different hydrogen storage options, considering their sustainability performance. This study innovatively applies the Interval-Valued Intuitionistic Fuzzy Analytic Hierarchy Process (IVIF-AHP) to evaluate and compare four hydrogen storage options: Compressed Hydrogen Gas (CHG), Cryogenic Liquid Hydrogen (CLH), Metal Hydride (MH), and Underground Hydrogen (UH). The evaluation criteria are derived from four dimensions of sustainability: economic, environmental, social, and technical performance, each further decomposed into sub-criteria. The study's novelty lies in using a novel intuitionistic fuzzy AHP, offering a more nuanced and robust understanding of the trade-offs between the various options and effectively capturing the vagueness and subjectivity inherent in human decision-making. Through this methodology, CHG emerged as the most promising option with a preference score of 0.487, closely followed by UH with a score of 0.453. The lowest preference score was accorded to MH, with a score of 0.301. These quantitative insights underscore the relative sustainability performance of each technology under the defined criteria. The findings contribute to the growing body of literature on sustainable hydrogen storage, providing policymakers and practitioners with a multicriteria decision-making tool that captures the complexity of sustainability considerations. This study underlines the critical role of holistic, multicriteria evaluations in advancing sustainable hydrogen storage. It encourages further exploration and validation of its approach in different contexts and with updated technological advancements.

Computational study of effects of doping Ni and Pd on CoAl for hydrogen storage capacity, elastic and electronic properties

Intermetallic compounds in B2 structure which have low density, fracture, and high strength have important applications in different engineering applications. For energy storage apparatus, the researchers have investigated new materials to improve effective efficiency in energy storage devices such as batteries and green energy technologies. The investigation of transition metal–aluminide alloys has increased due to their attractive elastic features. Like many hydrogen storage alloys, B2-type hydrogen storage alloys such as ZrCo utilize the systems of hydrogen storage in atomic gaps. If hydrogen atoms settle in the interstitial spaces, lattice expansion forms due to lattice distortion. Since plastic and elastic deformations change pressure and temperature, they are important for the material during hydrogen desorption and absorption. According to the literature, element doping effects boost hydrogen storage sufficiency. The effects of Ni- and Pd-substituted dopants on hydrogen storage, electronic and elastic features of a Cobalt-Aluminum alloy were performed using the first-principles calculations with and without spin-polarized configurations. Obtained lattice parameters for Co8Al8 are good agreement with literature values. Interstitial H doping has changed the crystal structure from cubic (BCC) to tetragonal. It is concluded that all investigated CoAl alloys included H doping has negative formation energies showing thermodynamically stabilities. All investigated alloys are stable mechanically and dynamically. Doping of H2 atoms to CoAl changes from a brittle to ductile nature. Also, Ni contributions improve ductility behavior to improve the cycle performance of the Co7NiAl8 and Co8Al7Ni alloy. It can be concluded from electronic band structure that they exhibite metallic behavior. Our obtained gravimetric and volumetric capacities which are comparable with B2 hydrogen storage material such as ZrCo, FeAl, indicate that CoAl alloys may be suitable for hydrogen storage applications.

Ab initio insight into the physical properties of MgXH3 (X = Co, Cu, Ni) lead-free perovskite for hydrogen storage application.

Renewable energy systems are vital for a sustainable future, where solid-state hydrogen storage can play a crucial role. Perovskite hydride materials have attracted the scientific community for hydrogen storage applications. The current work focuses on the theoretical study using density functional theory (DFT) to evaluate the characteristics of MgXH3 (X = Co, Cu, Ni) hydrides. The structural, vibrational, electronic, mechanical, thermodynamic, and hydrogen storage properties of these hydrides were investigated. The equilibrium lattice parameters were calculated using the Birch-Murnaghan equation of state-to-energy volume curves. The elastic constants (Cij) and relevant parameters, such as Born criteria, were calculated to confirm the mechanical stability of the hydrides. The Cauchy pressure (Cp) revealed brittle or ductile behavior. The outcomes of the Pugh ratio, Poisson ratio, and anisotropy were also calculated and discussed. The absence of negative lattice vibrational frequencies in phonon dispersion confirmed the lattice's dynamic stability. The heat capacity curves of thermodynamic properties revealed that hydrides can conduct thermal energy. The metallic character and ample interatomic distances of hydrides were confirmed by the band structure and population analysis, which confirmed that hydrides can conduct electrical energy and adsorb hydrogen. The density of state (DOS) and partial DOS unveiled the role of specific atoms in the DOS of the crystal. The calculated gravimetric hydrogen storage capacity of MgCoH3, MgCuH3, and MgNiH3 hydrides was 3.64, 3.32, and 3.49wt%, respectively. Our results provide a deeper understanding of its potential for hydrogen storage applications through a detailed analysis of MgXH3 (X = Co, Cu, Ni) perovskite hydride material.

Enhancement of hydrogen storage using functionalized MoSe2/Graphene monolayer and bilayer systems: DFT study

Utilizing the spin-polarized density-functional theory (DFT), we present an investigation of the adsorption properties of hydrogen-gas molecules on ten different substrates, which are based upon defected and TM-doped MoSe2 monolayer (ML) and MoSe2/graphene bilayer (BL) systems (TM = Ni, Cu). Particularly, Ni, and Cu substitutional doping at Se site showed distinct high H2 uptake capacity and thus to be good candidates for H2 storage. On these latter catalysts, H2 molecule exhibited physisorption with moderate respective energies Eads = −0.307 and −0.362 eV, attributed to the enhancement in electric dipole moment and spin splitting (magnetism) induced in the substrate. The desorption processes of the H2 molecule are found to cost energies of about 0.46 and 0.44 eV, respectively. Moreover, the H2 molecule can move parallel to the substrate after crossing potential barriers of 0.56 and 0.65 eV, respectively. Furthermore, the gravimetric uptake density can further be improved by increasing the dopants concentrations. For instance, by increasing the number of Ni dopants from one to two atoms in the computational sample 4 × 4 PCs of MoSe2 ML, the gravimetric density raises from 1.28 wt% to 3.6 wt% (almost triple). This should corroborate the candidacy of TM-doped @Se MoSe2 for hydrogen storage applications. PAC Numbers31.15.E; 68.43.-h; 68.43.Mn; 68.65.Pq; 73.43.Cd; 75.70.Rf.

Hydrogen storage mechanism of metal–organic framework materials based on metal centers and organic ligands

AbstractThe effective storage and utilization of hydrogen energy is expected to solve the problems of energy shortage and environmental pollution currently faced by human society. Metal–organic framework materials (MOFs) have been shown by scientists to be very potential hydrogen storage materials. However, the current design methods and strategies for MOFs are still generally in the trial‐and‐error stage, and the research works are at the overall level. To solve the problems of directional design and rational construction of new MOFs, this work uses the principles and methods of coordination chemistry and crystal engineering to carry out the theoretical design and mechanism research of new MOFs for high‐efficiency hydrogen storage application scenarios. In this study, the structures selected for theoretical calculation were divided into two types: different ligands for the same metal (IRMOFs, MOF‐205, and DUT‐23‐Zn) and different metals for the same ligand (DUT‐23‐M [(M = Co, Ni, Cu, and Zn]). The model construction process, hydrogen loading with temperature, specific surface area, hydrogen adsorption energy, charge density and hydrogen storage mechanism of the above structures were analyzed, and the key indicators that may affect the hydrogen storage performance of MOFs were summarized: type and quantity of coordination metals, temperature, pressure, adsorption site and specific surface area.

Exploring the structural, elastic, phonon, optoelectronics, and thermoelectric properties of tetragonal complex metal hydride X2MgH4 (X=K, Rb, and Cs) compounds for hydrogen storage applications

Hydrogen storage is of great interest to researchers due to its renewable and clean energy properties. Therefore, there is a continuous search for innovative compounds that can provide hydrogen storage conditions. A first-principles study of X2MgH4 (X = K, Rb, and Cs) compounds has been carried out to investigate their physical properties using the Generalized Gradient Approximation (GGA) with the SIESTA package. The elastic, optical, structural, electronic, phonon, and thermoelectric properties of X2MgH4 (X = K, Rb, and Cs) compounds with tetragonal crystal structures have been investigated. The electronic properties of X2MgH4 (X = K, Rb, and Cs) compounds are insulators. All three compounds fulfil the Born stability condition. The gravimetric hydrogen storage capacities of X2MgH4 (X = K, Rb, and Cs) compounds are 3.8, 2.02, and 1.37 wt%, respectively. X2MgH4 (X = K, Rb, and Cs) crystals are dynamically stable. The thermoelectric and optical properties of X2MgH4 (X = K, Rb, and Cs) compounds are also discussed.