Potential Hydrogen Storage Material Research Articles

First-principles calculations of phase stability, electronic structure, mechanical properties and thermal conductivities of TMH2 (TM=V, Nb, Ta) metal hydrides

TMH2 (TM = V, Nb, Ta) metal hydrides can be used as potential hydrogen storage materials. However, there have been no available data on the mechanical and thermodynamic properties of these hydrides, especially TaH2. Herein, based on first-principles calculations, the phase stability, electronic structure, mechanical properties and thermal conductivities of TMH2 (TM = V, Nb, Ta) hydrides are investigated. The results show that VH2, NbH2, and TaH2 are thermodynamically and dynamically stable. The calculated electronic structures show that these three hydrides possess electron orbital hybridization among atoms and strong chemical bonding. The chemical bonds in TMH2 are mainly ionic and partially covalent. According to the calculated Poisson's ratios, Pugh’s ratio and Cauchy pressures, VH2, NbH2, and TaH2 are ductile. Moreover, these three hydrides have elastic anisotropy and good damage tolerance. Finally, the predicted thermodynamic properties indicate that TMH2 can be used as potential thermal insulating materials.

Fabrication of V2O3-TiO2-rGO ternary heterojunction composite to enhance the hydrogen storage performance of MgH2

The application prospects of MgH2 as a potential solid hydrogen storage material are limited by its stable thermodynamic properties and slow hydrogenation/dehydrogenation kinetics. In this study, a ternary heterogeneous composite material V2O3-TiO2-rGO (V-T-rGO) was synthesized using the ultrasonic hydrothermal method and doped into MgH2 through ball milling to improve its hydrogen storage performance. The experimental results demonstrated that the MgH2 + V-T-rGO samples exhibit superior hydrogen storage properties compared with single-doped V2O3, TiO2, rGO or V-T materials. Specifically, it can uptake hydrogen at room temperature, and adsorbs 5.00 wt% H2 in just 4 min at 150 °C, and releases 5.87 wt% H2 within 6 min at 325 °C, demonstrating a faster reaction rate and successful hydrogen absorption. Additionally, the hydrogenation/dehydrogenation activation energies of MgH2 + V-T-rGO samples are measured at 27.1/72.3 kJ·mol−1, representing a reduction of 51.2/59.2 kJ·mol−1 compared to MgH2 alone. Mechanistic analysis revealed that the multiphase composite system produced synergistic catalytic effects, providing abundant active sites and hydrogen diffusion channels to enhance the hydrogen storage performance of MgH2. This study presents an innovative approach for constructing transition metal oxide heterostructured materials and holds significant reference value for applications in the field of hydrogen storage.

WO2–N co-doped 2D Carbon nanosheets as multifunctional additives for enhancing the electrochemical hydrogen storage performance of Co2B

Co2B, with its high theoretical hydrogen storage capacity, is a potential solid-state hydrogen storage material. However, its poor cycling life limits its practical application. In this work, in order to improve the cycling stability and reversibility of hydrogen absorption and desorption of Co2B, we propose to use WO2–N–C nanosheets as dopants to mix with Co2B, thereby enhancing its practical performance. Two-dimensional tungsten oxide-nitrogen-carbon (WO2–N–C) nanosheets was syntheized via a liquid-phase approach, using a tungstenate-polydopamine precursor followed by thermal treatment. Subsequently, these WO2–N–C nanosheets were compounded with cobalt boride (Co2B) particles through ball milling at various ratios of 1%, 3%, and 5%, which were confirmed by XRD (X-ray diffraction) and SEM (Scanning Electron Microscope) methods. Employing a comprehensive suite of electrochemical analyses, including corrosion potential measurements, polarization curves, step voltammetry, and electrochemical impedance spectroscopy (EIS), we found that the incorporation of WO2–N–C significantly enhances the corrosion resistance and electrochemical activity of Co2B. Furthermore, cyclic life tests revealed that the WO2–N–C-doped Co2B composites exhibit superior discharge capacities and capacity retention rates compared to pristine Co2B. Notably, the 3% WO2–N–C-doped Co2B composite demonstrated the optimal electrochemical performance, achieving a maximum discharge specific capacity of 555 mAh g−1 and maintaining 82% of its initial capacity after 50 cycles. Our findings underscore the dual role of WO2–N–C in not only augmenting the surface electrochemical activity of Co2B but also providing a protective surface layer, thereby enhancing its overall electrochemical performance.

Al–Cu–Fe–Ni–Ti high entropy alloy nanoparticles as new catalyst for hydrogen sorption in MgH2

The earth's abundance of magnesium hydride (MgH2), along with its favorable qualities like high capacity, excellent reversibility, and cost-effectiveness under mild hydrogenation conditions, make it a potential material for hydrogen storage. Its practical applicability is limited by unfavorable thermodynamics and kinetics, despite these advantages. In this work, we investigate the use of a leached form of the mechanically alloyed high entropy alloy (HEA) Al–Cu–Fe–Ni–Ti as a catalyst to improve the hydrogen storage capabilities of MgH2. The onset desorption temperature of MgH2 is significantly reduced from 360 °C (for as-received MgH2) to 200 °C when catalyzed by the previously stated HEA catalyst. In addition, the catalyst exhibits enhanced kinetics, as it can absorb around 6.2 wt. % in just 2.3 min. at 300 °C and 15 atm of hydrogen pressure, and desorb approximately 5.8 wt. % in 3.8 min. When compared to other known catalysts, these results show some of the lowest desorption temperatures for MgH2. Furthermore, MgH2 catalyzed by the leached form of Al–Cu–Fe–Ni–Ti HEA exhibits good cyclic stability for up to 21 cycles, with just a small variation of about ∼0.02 wt. %. A thorough analysis using X-ray diffraction, transmission electron microscopy, scanning electron microscopy, and X-ray photoelectron spectroscopy have been carried out. We suggest a workable catalytic mechanism for the high entropy alloy Al–Cu–Fe–Ni–Ti on MgH2 based on these findings.

Effect of rotation speed on hydrogen storage properties of Ti45Zr38Ni17 alloy ribbons produced by melt spinning

Abstract Ti/Zr-based icosahedral (i) quasicrystals are believed to have a Bergman-type cluster with a large number of tetrahedral interstitials, making them attractive as potential hydrogen storage materials. In this study, Ti45Zr38Ni17 alloy ribbons were prepared by melt spinning at different rotation speeds, and the effect of the rotation speed on the microstructures and hydrogen storage capacities was investigated. The i-phase with a small amount of Ti2Ni phase and/or some minor crystal phase was identified after melt spinning, but the amount of amorphous phase increased and the Ti2Ni and the other crystal phases decreased with increasing rotation speed. After gaseous hydrogen loading at 573 K and a pressure of 3 MPa, a hydride phase was observed in the samples with more amorphous phase, suggesting that the amorphous phase turned into the hydride phase. The maximum gaseous hydrogen capacity (H/M), 1.31, was obtained for the sample with more i-phase. After electrochemical hydrogen loading, a slightly higher maximum discharge capacity was observed in a less-quality quasicrystal sample at the first loading, that decreased drastically after the second cycle, but gradually increased with increasing cycling up to 20 cycles. The maximum hydrogen discharge capacity obtained in sample with more i-phase, reached about 10 mAh/g, while the less-amount one 4 mAh/g, suggesting the i-phase has higher hydrogen capacity than the crystal and the amorphous phases.

First-principles calculations to investigate Mg3XH8 (X = Ca, Sc, Ti, V, Cr, Mn) materials for hydrogen storage

An ideal hydrogen storage material is a key topic in efficient hydrogen energy utilization. We have explored several potential hydrogen storage materials Mg3XH8 (X = Ca, Sc, Ti, V, Cr, Mn) by first-principles calculations. The studied materials all belong to lightweight hydrogen storage materials. The normal phonon dispersion spectrum indicates, without regard to other materials, at least Mg3TiH8 and Mg3VH8 are completely stable in dynamics, which is also demonstrated by elastic stability criteria. The elastic properties show that they are all ductile materials with the applicable potential in flexible fields. Besides, they are gapless and metallic in band structures. With the correction of Hubbard values, all transition metal based Mg3XH8 materials are magnetic materials with magnetic moments of 0.34 μB for Mg3ScH8, and 2.14 μB for Mg3TiH8, 1.29 μB for Mg3TiH8, 2.65 μB for Mg3TiH8 and 4.86 μB for Mg3MnH8, respectively. Whereas Mg3CrH8 and Mg3MnH8 exhibit highly light active in infrared and visible region. Considering overall structural stability, excellent mechanical properties, high gravimetric hydrogen density (6.21% and 6.07%) and moderate hydrogen desorption temperature (∼350 K), Mg3TiH8 and Mg3VH8 are considered as the candidates for promising hydrogen storage materials. Besides, Due to half-metallic nature, they are also potential in spin electronic devices.

Fabrication and design of four-component Bi2S3/CuFe2O4/CuO/Cu2O nanocomposite as new active materials for high performance electrochemical hydrogen storage application

Considering the growth of the population and the demand for clean and renewable energy systems such as hydrogen, the development and optimization of the active materials for advanced electrochemical hydrogen storage require considerable effort. The goal of this research was to synthesize a four-component Bi2S3/CuFe2O4/CuO/Cu2O nanocomposite through a series of multiple steps. In order to examine the physicochemical characteristics of the sample, a variety of techniques were employed, including field-emission scanning electron microscopy (FE-SEM), energy dispersive X-ray spectroscopy (EDS), high-resolution transmission electron microscopy (HR-TEM), X-ray powder diffraction (XRD), Brunauer- Emmett–Teller (BET), Fourier-transform infrared (FT-IR) and vibrating sample magnetometer (VSM). Among these features are the morphological characteristics, structure properties, porosity, and the magnetic properties of the Bi2S3/CuFe2O4/CuO/Cu2O nanocomposite. In addition, as-synthesized materials were investigated for electrochemical performance as potential electrochemical hydrogen storage materials. A chronopotentiometer (ChP), cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS) and linear polarization method were used to study the hydrogen storage efficiency of as-schemed materials. A hydrogen storage capacity of approximately 225 mAhg−1 was determined for the Bi2S3/CuFe2O4/CuO/Cu2O nanocomposite after one cycle at a constant current of 1 mA, while this value was calculated for the Bi2S3, CuFe2O4 and Bi2S3/CuFe2O4 samples at 292 mAhg−1, 433 mAhg−1, and 276 mAhg−1, respectively. A quadruple Bi2S3/CuFe2O4/CuO/Cu2O nanocomposite showed excellent discharge capacity after 15 cycles in comparison with other samples. According to our calculations, this value is 1200 mAhg−1, while Bi2S3, CuFe2O4 and Bi2S3/CuFe2O4 nanostructures have capacities of 750 mAhg−1, 800 mAhg-1 and 1000 mAhg-1, respectively. In view of the demonstrated superior electrochemical properties of the Bi2S3/CuFe2O4/CuO/Cu2O nanocomposite, it has a very promising future for electrochemical hydrogen storage.

Hydrogen production from chemical hydrogen storage materials over copper‐based catalysts

AbstractHydrogen, as a clean and efficient energy source, is one of the important energy carriers in the future. However, the safe storage and delivery of hydrogen is still a bottleneck in its practical applications. Chemical hydrides (such as NaBH4, NH3BH3, N2H4·H2O, N2H4BH3, and HCOOH) are considered as potential chemical hydrogen storage materials that can achieve rapid on‐site hydrogen production. At present, the most critical issue for them is to develop economic catalysts to achieve efficient hydrogen production from chemical hydrides. Copper (Cu) is considered as a promising catalyst that is one of the most reactive metals among the first‐row transition metals and economically cheap. In this review, we outline the recent advancements of Cu‐based catalysts in catalyzing hydrogen production from chemical hydrides. Moreover, the synthesis methods, characterization techniques, and hydrogen production catalytic activity of Cu‐based catalysts were also introduced. Finally, a brief conclusion and outlook are given for the application of Cu‐based catalysts in the dehydrogenation of chemical hydrides. We hope that this review will stimulate interest in the promising research area of Cu‐based catalysts for the dehydrogenation of chemical hydrides.

Evaluating hydrogen storage potential of NaNbO3-xHx: DFT-based approach

Alternative energy carrier materials are needed since non-renewable energy resources are diminishing at a fast rate. Increasingly, hydrogen storage has gained popularity as a clean energy source. For the first time, NaNbO3-xHx has been explored computationally as a potential material for hydrogen storage using the GGA-PBE approach as implemented in the CASTEP code. Structural, elastic, mechanical, electronic, and optical characteristics have been investigated to evaluate the suitability of the proposed material for hydrogen storage applications. All H-incorporated concentrations are thermodynamical and energetically stable and can be synthesized. Structural parameters vary with varying hydrogen concentrations; however, against each hydrogen concentration, the material maintains cubical geometry. The NaNbO2.7H0.3 show the highest (742.92 GPa) bulk modulus, while NaNbH3 stands with the lowest (52.48 GPa) among all. Standardizing the Poisson ratio reveals a brittle nature except for the X=0.3 composition. With increasing H-incorporation in the structure, the band gap increases (1.624 eV » 2.505 eV) and also causes electronic nature shifting (p-type → n-type); however, the band gap remains indirect over different symmetry points in BZ. Hence, have the potential for numerous optoelectronic applications. Furthermore, optical parameters, dielectric constant, refractive index, extinction coefficient, reflectivity, absorption coefficients, and loss functions are analyzed, which reveal the potential for numerous optoelectronic applications. Hydrogen storage capacity achieved up to 2.48 %, allowing this material to be utilized in energy storage systems.

Stable hydrogen storage of lithium borohydrides via the catalytic effect of Ni2B induced by thermodynamic destabilization reaction

Lithium borohydride (LiBH4) is regarded as a potential hydrogen storage material due to its high gravimetric and volumetric capacity, but its practical application suffers from high operating temperature and poor reversibility. Herein, porous hollow carbon microspheres composed of carbon-coated Ni nanoparticles with high content (denoted as Ni/C) are rationally designed as functional support, which not only induces effective nanoconfinement of LiBH4 but also promotes efficiently homogeneous destabilization reaction between LiBH4 and Ni nanoparticles. The introduction of Ni nanoparticles leads to the decrease of the Gibbs free energy change for H2 desorption of LiBH4 based on the formation of Ni2B down to −0.95 eV while this value reaches 1.19 eV for bulk LiBH4, validating the effective role of Ni in thermodynamically destabilizing H2 desorption. Impressively, the average B–H bond length of LiBH4 on Ni2B reaches 1.291 Å and thus the corresponding dissociation energy of removing one H atom from LiBH4 is lowered to 1.00 eV, much lower than bulk LiBH4 (4.22 eV) and even LiBH4 on Ni (1.27 eV), which verifies superior role of Ni2B than Ni in catalytically enhancing H2 desorption. Therefore, a capacity of 8.86 wt.% is obtained for LiBH4 confined into Ni/C at 320 °C after 10 cycles.

The first principles insights of aluminum-based hydrides for hydrogen storage application

Hydrogen storage is an urgent issue for mobile applications, to overcome this issue solid materials have a potential role for hydrogen storage applications. Moreover, the perovskite hydride materials have been extensively investigated for improvement in the field of hydrogen storage. However, this work is focused on the computational study of XAlH3 (X: Na, Mg) perovskite-type hydrides for different physical properties and hydrogen storage applications. Both materials were found thermodynamically, and mechanically stable from the negative formation energy and elastic properties. They exhibited cubic phases with computed lattice constants are 3.827 Å and 3.752 Å, respectively. The electronic properties indicated that both compounds have a metallic nature, and found the high contribution of Al-p state, and H-1s state near the Fermi level. However, the Hirshfeld net charge analysis detected, that charge transfer from Al and X (Na, Mg) atoms to H atoms. Furthermore, the metallic hydrides have promised candidates for hydrogen storage applications. Both compounds have observed non-magnetic behavior with zero magnetic moments. Elastic constants were calculated to determine the mechanical stability of the compounds, it was found that MgAlH3 is harder than NaAlH3, and it exhibited that higher Bulk, Shear, and Young's modulus. The Poisson's, and Pugh's (G/B) ratios suggested that ionic boning of the atoms, additionally, Pugh's ratio (B/G) and Cauchy pressure (Cp) confirmed that NaAlH3 ductile and MgAlH3 is brittle behavior. Besides this, Optical properties were determined for both compounds including the dielectric function, conductivity, refractive index, absorption, and loss function. It is found that the MgAlH3 compound optical more suitable than NaAlH3 due to calculated optical factors promised and both compounds are undertaken for solar cells, optoelectronics, and energy storage applications. Finally, the computed hydrogen storage capacity for NaAlH3 and MgAlH3 compounds are 6.01 wt%, and 5.56 wt% respectively. These results revealed that both have the potential materials for hydrogen storage, but NaAlH3 unique material to fulfill the US-DOE criteria of 2020.

CdAl4O7/CdO nanocomposites: green tea extract-mediated sol-gel auto-combustion synthesis, characterization, and study as a potential hydrogen storage material.

In this article, we present the synthesis of binary CdAl4O7/CdO nanocomposites using green tea extracts and green chemistry methods for high-performance hydrogen storage. The green tea extract contains bioactive compounds (polyphenols) that act as reducing agents, which facilitate the reaction between metal ions and water. By examining the structural and morphological characteristics of the obtained substrates using scanning electron microscopy (SEM), X-ray diffraction (XRD), transmission electron microscopy (TEM), and Fourier transform infrared spectroscopy (FT-IR), it was demonstrated that the nanocomposites were successfully synthesized. We evaluated the electrochemical performance of the synthesized CdAl4O7/CdO nanocomposites using a three-electrode chronopotentiometry system. According to the results, the synthesized nanocomposites are capable of storing 1750 mAh/g of hydrogen at a constant current of 1 Amp. By using green tea extract as a natural structure-directing agent, the CdAl4O7/CdO nanocomposite can be developed more sustainably as high-performance hydrogen storage materials. Ultimately, this work contributes to the advancement of sustainable energy storage through the synthesis of a promising new material.

Enhanced hydrogen storage of alkaline earth metal-decorated Bn (n = 3-14) nanoclusters: a DFT study.

Boron-based nanostructures hold significant promise for revolutionizing hydrogen storage technologies due to their exceptional properties and potential in efficiently accommodating and interacting with hydrogen molecules. In this paper, boron-based Bn (n = 3-14) nanoclusters decorated with alkaline earth metals (AEM = Ca and Be) were investigated for hydrogen storage applications based on density function theory (DFT) calculations. To evaluate H2 adsorption capability, the adsorption energies, frontier molecular orbitals (FMOs), natural bond orbital (NBO), and quantum theory of atoms in molecule (QTAIM) analysis are performed. The primary aim of this research work is to achieve targeted value of 5.5 wt% set by the US Department of Energy (DOE) for the year 2025. The results revealed that B5Ca2, B6Ca2, and B10Ca2 structures have the ability to hold up to 12H2 molecules with gravimetric capacities of 15.20, 14.21, and 8.60 wt%, respectively, when compared to other boron structures decorated with calcium. Similarly, for Be-decorated structure, B3Be2 structure can accommodate 3H2 molecules with gravimetric capacity of 10.59 wt%. The result of this study indicates that AEM-decorated Bn nanoclusters hold great promise as potential materials for hydrogen storage. Density functional theory (DFT) approach at ωB97XD/6-311++G(d,p) level of theory is employed to investigate the possibility of storing H2 molecules on alkaline earth metal (AEM = Ca and Be)-decorated Bn (n = 3-14) nanoclusters. All DFT computations were performed using Gaussian 09 software. To calculate frontier molecular orbitals (FMOs) and quantum theory of atoms in molecule (QTAIM) analysis, we have used GaussView and Multiwfn software, respectively.

Density Functional Theory Investigation of Cu, Ni, and Ag Inclusion in ZSM-5 to Study Dihydrogen Binding for Cryogenic Molecular Sieve Bed Adsorber in Nuclear Fusion Systems

A computational investigation of Cu-, Ni-, and Ag-introduced ZSM-5 as potential hydrogen storage materials for nuclear fusion energy systems is performed. Among the 24 distinct tetrahedral sites of the monoclinic phase of ZSM-5, systematic periodic density functional theory (DFT) computations have been carried out on 15 experimentally identified T sites that show clear Al site preference and stability in high Si ZSM-5. Adsorption energies estimated from DFT studies have revealed that the T sites in the sinusoidal channels T4 and T10 are the most stable for including all three metal ions. Hence, these should also be considered as potential active sites for dihydrogen binding investigations in addition to the common T12 site in the intersection. The average hydrogen binding energies at these representative T sites were −79 to −45 kJ/mol, which correlates well with both the metal-H2 distance and H-H bond elongation distance. The computed hydrogen bond stretching frequency values were in the 3300 to 3755 cm−1 range upon adsorption of H2 onto the Ni, Cu, and Ag, indicating Kubas-type dihydrogen complex formation. The evidence for dihydrogen binding was also obtained from investigating the σ donation and back donation between the metal ion valence orbitals and the H2σ, H2σ* orbitals through projected density of states and natural bond order analysis. Our analysis indicates that Ni is better stabilized in the framework sites and is considered a potential candidate for dihydrogen binding.

Computational evaluation of comprehensive properties of MgX3H8 (X = Sc, Ti and Zr) as effective solid state hydrogen storage materials

In this study, structural, mechanical, electronic, dynamic, thermodynamic and hydrogen storage properties of MgX3H8 (X = Sc, Ti, Zr) were investigated by means of density functional theory which was not studied/reported experimentally or theoretically in the previous literature. This is the first thorough study about various properties of these materials. These materials were considered as promising potential host materials for solid state hydrogen storage. The evaluation of computed formation enthalpies of MgX3H8 (X = Sc, Ti, Zr), elastic constants, and phonon dispersion graphs revealed that MgX3H8 (X = Sc, Ti, Zr) is thermodynamically, mechanically, and dynamically stable and synthesizable. The analysis of B/G ratio, Cp and Poisson's ratio showed that MgSc3H8 is a brittle material whereas MgTi3H8 and MgZr3H8 are ductile materials. Moreover, anisotropy factor, machinability index, hardness, melting and Debye temperature of the materials were obtained and analysed in depth. The electronic band structures of MgX3H8 (X = Sc, Ti, Zr) illustrated metallic character since the bands (valence and conduction) intersect the Fermi level along the main symmetry directions. The phonon dispersion curves, and the partial state densities of the materials have positive frequencies, therefore, materials are dynamically stable in the cubic structure. The gravimetric hydrogen densities were calculated as 4.60 wt% for MgSc3H8, 4.38 wt% for MgTi3H8 and 2.56 wt% for MgZr3H8. The hydrogen desorption temperatures were computed as 239.54 K for MgSc3H8, 241.76 K for MgTi3H8 and 303.87 K for MgZr3H8. The mechanical properties of the materials suggest that they can be promising host materials for hydrogen storage.

Pressure mediated phase transition and dihydrogen bonding formation in trimethylamine borane

Trimethylamine borane as a potential hydrogen storage material was investigated at high pressures up to 35 GPa where its structural stability, phase transformation, bonding and electronic properties were elucidated.

Hydrogen generation from NaBH4 for portable proton exchange membrane fuel cell

Sodium borohydride (NaBH4) is considered as the most potential hydrogen storage material for portable proton exchange membrane fuel cells (PEMFC) because of its high theoretical hydrogen capacity. However, the slow and poor kinetic stability of hydrogen generation from NaBH4 hydrolysis limits its application. There are two main factors influencing the kinetics stability of hydrogen generation from NaBH4. One factor is that the alkaline by-products (NaBO2) of the hydrolysis reaction can increase the pH of the solution, thus inhibiting the reaction process. It mainly happens in the NaBH4 solution hydrolysis system. Another factor is that the monotonous increase in reaction temperature leads to uncontrollable and unpredictable hydrolysis rates in the solid NaBH4 hydrolysis system. This is due to the excess heat generated from this exothermic reaction in the initial reaction of NaBH4 hydrolysis. In this perspective, we summarize the latest research progress in hydrogen generation from NaBH4 and emphasize the design principles of catalysts for hydrogen generation from NaBH4 solution and solid state NaBH4. The importance of carbon as catalyst support material for NaBH4 hydrolysis is also highlighted.

Diffusion quantum Monte Carlo study on magnesium clusters as large as nanoparticles

Nanoscale magnesium clusters are important potential hydrogen storage materials, and density functional theory (DFT) is mainly used for their theoretical investigation. The results of the coupled-cluster theory at the singles and doubles level with a perturbative treatment of triples [CCSD(T)] were employed previously to choose proper exchange–correlation (XC) functionals in DFT calculations for magnesium clusters, but it is too expensive to be applied to Mgn with n > 7. The diffusion Monte Carlo (DMC) method is employed in this work to study magnesium clusters up to nanosize. The error of atomization energies with DMC using single-determinant-Jastrow (SDJ) trial wavefunctions has been shown to be somewhat larger than that of CCSD(T) for many molecules. However, cohesive energies with DMC using SDJ for Mgn with n ≤ 7 are in excellent agreement with those of CCSD(T) using the aug-cc-pVQZ basis set, with a difference of less than 1 kcal/mol. DMC results are employed to investigate the performance of different XC functionals on magnesium clusters. Our results indicate that the PBE0 functional is the best XC functional for determining the lowest-energy isomer when compared with DMC results, while the RPBE functional is the best XC functional for calculating cohesive energies per atom of these magnesium clusters with a mean absolute error of 0.5 kcal/mol. These XC functionals are expected to provide reasonable results for even larger magnesium clusters.

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.

Solid state hydrogen storage: Decoding the path through machine learning

We present a machine learning (ML) framework HEART (HydrogEn storAge propeRty predicTor) for identifying suitable families of metal alloys for hydrogen storage under ambient conditions. Our framework includes two ML models that predict the hydrogen storage capacity (HYST) and the enthalpy of hydride formation (THOR) of multi-component metal alloys. We demonstrate that a chemically diverse set of features effectively describes the hydrogen storage properties of the alloys. In HYST, we use absorption temperature as a feature which improved H2wt% prediction significantly. For out-of-the-bag samples, HYST predicted H2wt% with R2 score of 0.81 and mean absolute error (MAE) of 0.45 wt% whereas R2 score is 0.89 and MAE is 4.53 kJ/molH2 for THOR. These models are further employed to predict H2wt% and ΔH for ∼ 6.4 million multi-component metal alloys. We have identified 6480 compositions with superior storage properties (H2wt% > 2.5 at room temperature and ΔH < 60 kJ/molH2). We have also discussed in detail the interesting trends picked up by these models like temperature dependent variation in the rate of hydrogenation and alloying effect on H2wt% and ΔH in different families of alloys. Importantly certain elements like Al, Si, Sc, Cr, and Mn when mixed in small fractions with hydriding elements like Mg, Ti, V etc. systematically reduce ΔH without significantly compromising the storage capacity. Further upon increasing the number of elements in the alloy i.e from binary to ternary to quaternary, the number of compositions with lower enthalpies also increases. From the 6.4 million compositions, we have reported new alloy families having potential for hydrogen storage at room temperature. Finally, we demonstrate that HEART has the potential to scan vast chemical spaces by narrowing down potential materials for hydrogen storage.