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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 Mg 0.10 Ti 0.30 V 0.25 Zr 0.10 Nb 0.25 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 Mg 0.10 Ti 0.30 V 0.25 Zr 0.10 Nb 0.25 is around H/M = 1.16. By phonon spectra calculation, the maximum gravimetric hydrogen storage capacity of Mg 0.10 Ti 0.30 V 0.25 Zr 0.10 Nb 0.25 is predicated to be as high as 3.16 wt%, demonstrating that Mg 0.10 Ti 0.30 V 0.25 Zr 0.10 Nb 0.25 HEA is a potential hydrogen storage material. • Mg 0.10 Ti 0.30 V 0.25 Zr 0.10 Nb 0.25 has a maximum hydrogen storage capacity of 3.16 wt%. • A BCC to FCC phase transition occurs as the hydrogen content reaches H/M = 1.16. • The FCC phase presents stronger ability to accommodate hydrogen than BCC phase. • The structure of HEA hydrides becomes more ordered after phase transition. [ABSTRACT FROM AUTHOR]

Doping can modify the properties of metal hydrogen storage materials significantly. Currently, the metal doping is a frequent strategy, while the non-metal cation doping has not been examined extensively so far. In this study, the effects of NH 4 + doping on the hydrogen storage properties of different metal hydrides, including TiH 2 , Ti 0·25 V 0·25 Nb 0·25 Zr 0·25 H 2 , Ti 0·5 V 0·5 H 2 and VH 2 , are investigated by first-principles calculations. It is found that the NH 4 + presents a good affinity for metal hydrides and the NH 4 + incorporation leads to charge redistribution and formation of dihydrogen bond. Furthermore, the NH 4 + doping in metal hydrides is favorable for enhancing the hydrogen storage capacity and decreasing the thermal stability simultaneously. The possible reason for the NH 4 + doping induced destabilization in metal hydrides is the relatively weak interaction between NH 4 + and hydrogen atoms. [Display omitted] • The NH 4 + is first proposed to dope metal hydrides. • All the investigated metal hydrides are still dynamically stable after NH 4 + doping. • The NH 4 + doping enhances the hydrogen storage capacity of metal hydrides. • The thermal stability of metal hydride decreases with increasing NH 4 + content. [ABSTRACT FROM AUTHOR]

Hybrid energy storage systems (HESSs) play a crucial role in enhancing the performance of electric vehicles (EVs). However, existing energy management optimization strategies (EMOS) have limitations in terms of ensuring an accurate and timely power supply from HESSs to EVs, leading to increased power loss and shortened battery lifespan. To ensure an accurate and timely power supply from HESSs to EVs, this paper proposes a dual-layer multi-mode (DLMM) EMOS. This strategy comprises two layers. The upper layer is a backpropagation neural network (BPNN) model enhanced by the particle swarm optimization (PSO) algorithm. It is used for real-time HESS power demand prediction. In the lower layer, a HESS operational mode determination process is formulated, and an objective optimization function is established based on HESS power loss. Under constraints designed according to the HESS state parameters, the PSO algorithm is utilized to search for the optimal power allocation ratio of the HESS in real time. The proposed DLMM-EMOS strategy is capable of providing optimal power reference values for the batteries and ultracapacitors of the HESS. The DLMM-EMOS is tested on an electrical experimental platform using US06, NEDC, and WLTP driving cycles. Results indicate that the DLMM-EMOS effectively reduces the HESS power loss while enhancing the driving range of the battery. [ABSTRACT FROM AUTHOR]

Metal hydrogen storage materials have been the focus of intensive research in the field of hydrogen-based economy. An outstanding question is that the number of hydrogen atoms accommodated in metal hydrides is generally much below the number of interstices, which limits their hydrogen storage capacities. Unlike traditional FCC metal hydrides where hydrogen can only occupy tetrahedral interstices, this study demonstrates that hydrogen can also occupy octahedral interstices in FCC high entropy alloy (HEA) hydrides, which leads to the violation of the Switendick criterion. For Ti25V25Nb25Ta25 and Ti25V25Nb25Zr25 HEAs, nearly 20% and 17.5% of octahedral interstices can be occupied by hydrogen, respectively. The anomalous hydrogen occupation mainly originates from the intrinsic electron delocalization between hydrogen atoms in HEA hydrides, which presents a sharp contrast to traditional metal hydrides. Such electron delocalization decreases repulsive interactions between hydrogens and promotes the electron localization at octahedral interstices. Additionally, this study reveals that hydrogen occupation at octahedral interstices enhances the structural disordering and decreases the thermal stability of HEA hydrides, which will be beneficial to reduce the dehydrogenation temperature. The presented results may provide a new strategy for the design of high-density storage materials. [ABSTRACT FROM AUTHOR]

In recent years, U3Si2 has been proposed as an alternative nuclear fuel material to uranium dioxide (UO2) because of its intrinsically high uranium density and thermal conductivity. However, the operation environment in the nuclear reactor is complex and extreme, such as in-pile neutron irradiation, and thus it is necessary to explore the radiation response behavior of U3Si2 and the physical properties of its damaged states. In the present study, first-principles calculations based on density functional theory were carried out to investigate the mechanical and electronic properties of defective U3Si2. Our results showed that the defect stability in U3Si2, except its interstitial defects, is dependent on its chemical environment. When vacancy, antisite or interstitial defects are introduced into U3Si2, its elastic modulus are decreased and its ductility is enhanced. Although the presence of defects in U3Si2 does not change its metallic nature and the electron distribution in its Fermi level, their effect on the partial chemical bonding interaction is significant. This study suggests that under a radiation environment, the created defects in U3Si2 remarkably affect its mechanical and electronic properties. [ABSTRACT FROM AUTHOR]

In this study, density functional theory calculations have been carried out to study the hydrogen storage properties of high entropy alloy (HEA) TiZrVMoNb. It reveals that a BCC→FCC phase transformation occurs when the hydrogen content reaches 1.5 wt% during hydrogenation process, and octahedral and tetrahedral interstitial sites are preferable for hydrogen occupation before and after phase transformation, respectively. Further energetic analyses show that different hydrogen occupations in HEAs play an important role in the thermal stability of hydrides. The maximum hydrogen storage capacity for TiZrVMoNb is predicted to be 2.65 wt%, which is comparable to the largest value of 2.7 wt% for TiZrVHfNb and larger than that of other reported HEA hydrogen storage materials reported in the literature. As compared with the previously reported HEA TiZrHfMoNb with the change of only one principal element, the TiZrVMoNb not only has much higher hydrogen storage capacity, but also has more moderate hydrogen desorption temperature. The difference in hydrogen storage properties between these two HEAs is mainly attributed to the atomic weight, site occupation, lattice distortion and chemical effect of metal elements. The present study thus suggests that the TiZrVMoNb HEA has great potential as hydrogen storage materials and proposes a strategy to enhance the hydrogen storage properties of HEAs. [Display omitted] • HEA TiZrVMoNb has a maximum hydrogen storage capacity of 2.65 wt%. • A BCC to FCC phase transition occurs when the hydrogen content reaches to 1.5 wt%. • The thermal stability of HEA hydrides can be influenced by hydrogen occupation. • The hydrogen storage property of HEA TiZrVMoNb is superior to HEA TiZrHfMoNb. [ABSTRACT FROM AUTHOR]

The desorption behaviors of hydrogen from high entropy alloy TiZrVMoNb hydride surface have been investigated using the density functional theory. The (110) surface has been determined to be the most preferable surface for hydrogen desorption from TiZrVMoNb hydride. Due to the high lattice distortion and heterogeneous chemical environment in HEA hydride, hydrogen desorption from the HEA hydride surface is found to be complex. A comparison of molecular and atomic hydrogen desorption reveals that hydrogen prefers to desorb in atomic states from TiZrVMoNb hydride (110) surface rather than molecular states during the hydrogen desorption process. To combine as H2 molecules, the hydrogen atoms need to overcome attractive interaction from TiZrVMoNb hydride (110) surface. These results suggest that the hydrogen desorption on TiZrVMoNb hydride (110) surface is a chemical process. The presented results provide fundamental insights into the underlying mechanism for hydrogen desorption from HEA hydride surface and may open up more possibilities for designing HEAs with excellent hydrogen desorption ability. [ABSTRACT FROM AUTHOR]

High entropy alloys (HEAs) are composed of multiple main metal elements and have attracted wide attention in various fields. In this study, a novel Ti0.20Zr0.20Hf0.20Nb0.40 HEA was synthesized and its hydrogenation properties were studied, including sorption thermodynamics and hydrogen absorption/desorption kinetics. The maximum hydrogen absorption capacity was 1.5 H/atom at 573 K. X-ray diffraction (XRD) analysis indicated that the crystal structure of Ti0.20Zr0.20Hf0.20Nb0.40 HEA transformed from body-centered cubic (BCC) to body-centered tetragonal (BCT) with increasing hydrogen content, and to face-centered cubic (FCC) after hydrogen absorption to saturation. As a multi-principal element alloy, the Ti0.20Zr0.20Hf0.20Nb0.40 HEA possesses unique hydrogen absorption characteristics. The hydrogen absorption platform pressure rises gradually with the increase of the hydrogen absorption amount, which is caused by multiple kinds of BCT intermediate hydrides with consecutively increasing c/a. The full hydrogen absorption of the Ti0.20Zr0.20Hf0.20Nb0.40 HEA was completed in almost 50 s, which is faster than that of the reported hydrogen storage alloys in the literature. The experimental results demonstrate that the Ti0.20Zr0.20Hf0.20Nb0.40 HEA has excellent kinetic properties, unique thermodynamic hydrogen absorption performance, as well as a low plateau pressure at room temperature. [ABSTRACT FROM AUTHOR]

In recent years, high-entropy alloys have been proposed as potential hydrogen storage materials. Despite a number of experimental efforts, there is a lack of theoretical understanding regarding the hydrogen absorption behavior of high-entropy alloys. In this work, the hydrogen storage properties of a new TiZrHfScMo high-entropy alloy are investigated. This material is synthesized successfully, and its structure is characterized as body-centered cubic. Based on density functional theory, the lattice constant, formation enthalpy, binding energy, and electronic properties of hydrogenated TiZrHfScMo are all calculated. The calculations reveal that the process of hydrogenation is an exothermic process, and the bonding between the hydrogen and metal elements are of covalent character. In the hydrogenated TiZrHfScMo, the Ti and Sc atoms lose electrons and Mo atoms gain electrons. As the H content increases, the bonding is weakened, and the and bonding are strengthened. Our calculations demonstrate that the TiZrHfScMo high-entropy alloy is a promising hydrogen storage material, and different alloy elements play different roles in the hydrogen absorption process. [ABSTRACT FROM AUTHOR]

An equiatomic TiZrHfMoNb high-entropy alloy (HEA) was developed as a solar thermal energy storage material due to its outstanding performance of hydrogen absorption. The TiZrHfMoNb alloy transforms from a body-centered cubic (BCC) structure to a face-centered cubic (FCC) structure during hydrogen absorption and can reversibly transform back to the BCC structure after hydrogen desorption. The theoretical calculations demonstrated that before hydrogenation, the BCC structure for the alloy has more stable energy than the FCC structure while the FCC structure is preferred after hydrogenation. The outstanding hydrogen absorption of the reversible single-phase transformation during the hydrogen absorption–desorption cycle improves the hydrogen recycling rate and the energy efficiency, which indicates that the TiZrHfMoNb alloy could be an excellent candidate for solar thermal energy storage. [ABSTRACT FROM AUTHOR]

A body-centered cubic equiatomic TiZrTaNbAl multi-principal element alloy (MPEA) with elemental fluctuations was investigated to further understand the relationship between the microstructure and hydrogen distribution. In this study, a composition dependence of the hydrogen distribution was observed in the TiZrTaNbAl MPEA. An inhomogeneous electron density distribution of the MPEA was revealed by advanced differential phase-contrast scanning electron microscopy (DPC-STEM) for the first time. The results showed that the electron density has a significant effect on the hydrogen distribution in TiZrTaNbAl MPEAs. This work provides new insight into the design of materials with high hydrogen storage capacity and high hydrogen embrittlement resistance. [ABSTRACT FROM AUTHOR]

In the past decades, uranium silicide (U 3 Si 2 ) as a promising accident tolerant fuel (ATF) has drawn considerable attention in the field of nuclear physics. In comparison with traditional nuclear fuel (UO 2 ), the U 3 Si 2 has higher thermal conductivity and uranium density, thereby resulting in lower centerline temperatures and better fuel economy. However, during the nuclear fission reaction, some unexpected fission products, such as Xe and Cs, are released and form the defective states. In this study, we explore the influence of Xe and Cs on the thermal conductivity of the U 3 Si 2 lattice from 200 to 1500 K using density functional theory calculations combined with Boltzmann transport equation. Our results reveal that the lattice and electronic thermal conductivities of defective U 3 Si 2 are reduced at a constant temperature, as compared with that of ideal system, thus resulting in a decrease of the total thermal conductivity. In the case of Cs occupation at U1 site, the total thermal conductivity (4.42 W mK -1 ) is decreased by ∼56% at 300 K, as compared with the value of 9.99 W mK -1 for ideal system. With U1 and Si sites being occupied by Xe, the total thermal conductivities (4.45 and 6.52 W mK -1 ) are decreased by ∼55% and 35% at 300 K, respectively. The presented results suggest that the U 3 Si 2 has potential as a promising ATF at high temperatures., (© 2023 IOP Publishing Ltd.)

In the past several years, the U 3 Si has been suggested as an alternative nuclear fuel for light water reactors due to its high uranium density and outstanding thermal conductivity. In order to gain fundamental insights into the behavior of fission products in U 3 Si, the trapping and migration behaviors of the fission products Xe and Cs in U 3 Si are investigated using density functional theory calculations in this work. Under U -rich and Si-rich conditions, both the Xe and Cs atoms prefer to substitute for Si and U atoms, respectively. Besides, both Xe and Cs tend to migrate through the vacancy-mechanism. It is noticeable that Xe diffuses faster and forms Xe bubbles more easily than Cs, which is mainly caused by the weaker interaction between Xe and its surrounding atoms., (© 2022 IOP Publishing Ltd.)

In the past several decades, the U 3 Si 2 has received much attention for the development of accident tolerant fuel in light water reactors because of its superior thermal conductivity and higher uranium density. In this study, density functional theory calculations have been carried out to study the occupation and diffusion behaviors of fission products Xe and Cs in U 3 Si 2 . It is revealed that the occupation sites of Xe and Cs depend on the chemical environment, and both of Xe and Cs are favorable to substitute for U or Si sites. The diffusions of Xe and Cs in U 3 Si 2 are predicted to be via the vacancy mechanism and both of Xe and Cs form cluster easily. As compared with Cs, the Xe exhibits a smaller solubility, faster diffusion as well as stronger clustering tendency, which may cause larger bubble size for Xe than Cs under the same conditions in U 3 Si 2 . The differences in the diffusion behaviors between Xe and Cs mainly result from their different valence electronic configurations and different atomic radii., (© 2022 IOP Publishing Ltd.)

In recent years, U 3 Si 2 has been proposed as an alternative nuclear fuel material to uranium dioxide (UO 2 ) because of its intrinsically high uranium density and thermal conductivity. However, the operation environment in the nuclear reactor is complex and extreme, such as in-pile neutron irradiation, and thus it is necessary to explore the radiation response behavior of U 3 Si 2 and the physical properties of its damaged states. In the present study, first-principles calculations based on density functional theory were carried out to investigate the mechanical and electronic properties of defective U 3 Si 2 . Our results showed that the defect stability in U 3 Si 2 , except its interstitial defects, is dependent on its chemical environment. When vacancy, antisite or interstitial defects are introduced into U 3 Si 2 , its elastic modulus are decreased and its ductility is enhanced. Although the presence of defects in U 3 Si 2 does not change its metallic nature and the electron distribution in its Fermi level, their effect on the partial chemical bonding interaction is significant. This study suggests that under a radiation environment, the created defects in U 3 Si 2 remarkably affect its mechanical and electronic properties.