Method for evaluating hydrogen storage performance of magnesium-based high-entropy alloy

Abstract

This invention discloses a method for evaluating the hydrogen storage performance of magnesium-based high-entropy alloys. First, a model of the magnesium-based high-entropy alloy and its hydrides is established using a randomization method. Then, the structure of the material is optimized using first-principles methods, selecting the geometric structure model with the lowest energy for the magnesium-based high-entropy alloy and its hydrides. Next, the ground-state total energy, binding energy, and violation of the "the" principle are calculated for the magnesium-based high-entropy alloy hydrides. The stability of hydrides with different phase structures is evaluated by the number of hydrogen-hydrogen bonds in the "rule"; the evolution of the system's microstructure during the phase transition is then determined by the radial distribution function; finally, based on the assessment of the hydride's energy stability, the maximum hydrogen storage capacity of the magnesium-based high-entropy alloy is predicted by calculating the phonon spectrum. The first-principles calculation method used in this invention can relatively accurately evaluate the hydrogen storage performance of magnesium-based high-entropy alloys.

Description

Evaluation Methods for Hydrogen Storage Performance of Magnesium-Based High-Entropy Alloys Technical Field

[0001] This invention belongs to the field of high-entropy alloy hydrogen storage technology in solid-state hydrogen storage, and particularly relates to a method for evaluating the hydrogen storage performance of magnesium-based high-entropy alloys. Background Technology

[0002] Due to the rapid depletion of fossil fuels, the world is experiencing an increasingly severe energy crisis, making more efficient and cleaner energy sources urgently needed. Hydrogen, one of the most abundant elements on Earth, possesses high energy density and can serve as a carrier of renewable clean energy. Developing hydrogen energy is key to entering the hydrogen energy economy era. The development of the hydrogen energy economy includes hydrogen production, storage, and application. Regarding hydrogen production, the hydrogen produced from various renewable energy sources is sufficient to meet the supply and demand. However, hydrogen exists in a gaseous form at normal temperature and pressure, exhibiting characteristics such as flammability, explosiveness, and easy diffusion. Therefore, developing efficient, safe, and low-cost hydrogen storage methods is a significant challenge for realizing the practical application of hydrogen energy.

[0003] Currently, typical hydrogen storage technologies mainly include gaseous, liquid, and solid-state hydrogen storage. However, gaseous and liquid hydrogen storage methods are unsafe and costly, making them uneconomical and unsuitable for large-scale application in daily production and daily life. In recent years, researchers have been studying a new type of solid-state hydrogen storage alloy—high-entropy alloys, also known as multi-principal element alloys. These are single-phase solid solutions composed of five or more principal elements in equimolar ratios or with atomic concentrations ranging from 5 to 35 at.%. Studies have shown that high-entropy alloys with good hydrogen storage performance are all composed of transition metal elements, limiting their gravimetric hydrogen storage capacity and failing to meet the needs of practical applications. Therefore, researchers have proposed the concept of lightweight high-entropy alloys, which involve adding lightweight metal elements such as lithium, magnesium, and aluminum to high-entropy alloys to reduce their overall molar mass ratio. Currently, there are few experimental and theoretical studies on the hydrogen storage performance of magnesium-based high-entropy alloys, a significant reason being the lack of effective evaluation methods for their hydrogen storage performance. Therefore, the purpose of this invention is to provide a low-cost, safe, and efficient method for evaluating the hydrogen storage performance of magnesium-based high-entropy alloys. Summary of the Invention

[0004] To address the problems existing in the prior art, this invention, combining first-principles calculations, provides a method for evaluating the hydrogen storage performance of magnesium-based high-entropy alloys. The specific technical solution includes:

[0005] Step 1: Use randomization methods to establish geometric structure models of magnesium-based high-entropy alloys with different metal atom arrangements;

[0006] Step 2: Optimize the geometric structure models of various magnesium-based high-entropy alloys obtained in Step 1 to obtain the configuration with the lowest energy, i.e. the most stable geometric structure.

[0007] Step 3: Establish geometric structure models of magnesium-based high-entropy alloy hydrides with different hydrogen concentrations, optimize the structure of multiple hydride configurations for each hydrogen concentration, and select the most stable structure.

[0008] Step 4: Calculate the binding energy and violation energy of two magnesium-based high-entropy alloy hydride systems with different phase structures under the same hydrogen concentration. The number of hydrogen-hydrogen bonds is used to determine whether a structural phase transition will occur during hydrogenation.

[0009] Step 5: If it was determined in Step 4 that the system will undergo a phase transition, calculate the total energy difference of the ground state for different phase structures to obtain the hydrogen concentration threshold corresponding to the phase transition.

[0010] Step 6: By analyzing the radial distribution function between atoms in the system, the evolution trend of the microstructure of the system during the phase transition is studied;

[0011] Step 7: Based on the analysis of hydride binding energy and the number of hydrogen-hydrogen short bonds in Step 4, the maximum hydrogen storage capacity of magnesium-based high-entropy alloys is predicted by calculating the phonon spectrum.

[0012] Furthermore, the step one, which uses a randomization method to establish geometrical models of magnesium-based high-entropy alloys with different metal atom arrangements, includes:

[0013] (1) The possible phase structure of single-phase magnesium-based high-entropy alloys was determined through literature review;

[0014] (2) Determine the proportion of metal atoms in the single-phase magnesium-based high-entropy alloy under study and establish a unit cell model;

[0015] (3) Expand the unit cell obtained in (2) appropriately, and determine the appropriate supercell size based on the computational accuracy and efficiency. Generally, the supercell needs to have more than 20 metal atoms, and the larger the supercell, the more accurate the calculation results;

[0016] (4) Since high-entropy alloys are disordered solid solutions, atoms are randomly distributed in different positions of the crystal lattice and are indistinguishable. To ensure that the atomic distribution environment after cell expansion is sufficiently disordered, a program was designed using Python based on the supercell obtained in (3) to randomly arrange the atomic coordinates. Specifically, the supercell structure obtained in (3) is converted into an atomic coordinate information file using VESTA, and the program randomly rearranges the file line by line, and then outputs the rearranged coordinate information file. The program was used multiple times to randomly generate various magnesium-based high-entropy alloy configurations with different atomic distributions.

[0017] Furthermore, in step two, the geometrical models of various magnesium-based high-entropy alloys obtained in step one are structurally optimized to obtain the configuration with the lowest energy, i.e., the most stable geometrical structure, including:

[0018] (1) Select appropriate exchange-correlation functionals and pseudopotentials. It is recommended to use the PBE functional under the generalized gradient approximation to describe the exchange-correlation interaction between electrons, and the projected plane wave pseudopotential to describe the interaction between the atomic nucleus and electrons.

[0019] (2) Determine the calculation parameter K-point and cutoff energy ENCUT through convergence test;

[0020] (3) Use VASP software to optimize the structure of the various random configurations obtained in step one. Set IBRION=2 and PREC=Medium in INCAR and select the configuration with the lowest energy as the structure of the magnesium-based high-entropy alloy.

[0021] Furthermore, in step three, geometrical models of magnesium-based high-entropy alloy hydrides with different hydrogen concentrations are established. Structural optimization is performed on multiple hydride configurations for each hydrogen concentration, and the most stable structures are selected, including:

[0022] (1) Since reversible structural phase transitions are common in high-entropy alloys during hydrogen absorption and dehydrogenation, it is necessary to first determine whether the material will undergo a phase transition during hydrogenation. Therefore, two different phase structure models need to be established for each hydrogen concentration of hydride;

[0023] (2) Based on the periodicity characteristics of the structural phase and combined with VESTA software, determine the coordinates of all tetrahedral and octahedral interstitial positions in the supercell of magnesium-based high-entropy alloy.

[0024] (3) First, determine the hydrogen atom concentration in the hydride, that is, the ratio of the number of hydrogen atoms to the number of metal atoms (H / M). Then, add the hydrogen atom position coordinates to the structure file of the lowest energy magnesium-based high-entropy alloy configuration obtained in step three. Use the same random method as in step one to generate multiple hydrides with different hydrogen atom distributions. Then, use the same structure optimization parameters as in step two to take the lowest energy configuration for each hydride structure with hydrogen concentration.

[0025] Furthermore, in step four, the binding energy and violation energy of two magnesium-based high-entropy alloy hydride systems with different phase structures are calculated under the same hydrogen concentration. The number of hydrogen-hydrogen bonds is used to determine whether a structural phase transition will occur during hydrogenation, including:

[0026] (1) Based on the lowest energy configuration of the magnesium-based high-entropy alloy and its hydride obtained in steps two and three, the calculation accuracy is further improved by using the ENCUT value obtained by the test to perform structural optimization again to obtain the ground state total energy; at the same time, the lattice constant is also obtained and compared with the experimental value.

[0027] (2) The binding energy of magnesium-based high-entropy alloy hydrides is calculated using the following formula:

[0028]

[0029] Where E tot (M) is the total energy of the magnesium-based high-entropy alloy; E(H2) is the total energy of a single H2 molecule; E tot (MH n ) is the total energy of a magnesium-based high-entropy alloy hydride containing n hydrogen atoms; the more positive the binding energy, the stronger the interaction between hydrogen atoms and the magnesium-based high-entropy alloy, and thus the higher the structural stability of the hydride.

[0030] (3) Based on the binding energy calculated in (2), plot and compare the binding energies of magnesium-based high-entropy alloy hydrides with the same hydrogen concentration, and obtain the trend of the stability of the two phase structures hydrides as the hydrogen concentration increases.

[0031] (4) Using LOBSTER software, set "cohpGenerator from 0 to 2type H type H" in the lobsterin file to calculate the hydrogen-hydrogen distance in magnesium-based high-entropy alloy hydrides. The number of hydrogen-hydrogen bonds; proposed by Switchick This indicates that the hydrogen-hydrogen distance in metal hydrides is less than [the specified value]. The more numerous the elements, the more unstable the system becomes;

[0032] (5) Based on the calculations in (4), plots were drawn to compare the hydrogen-hydrogen distances in the magnesium-based high-entropy alloy hydrides with the same hydrogen concentration, which are less than [the required distance]. The number of hydrogen-hydrogen bonds was determined to show the trend of stability changes of the two phase structures of hydrides with increasing hydrogen concentration.

[0033] Furthermore, in step five, if it is determined in step four that a structural phase transition will occur in the system, then the total energy difference of the ground state for different phase structures is calculated to obtain the hydrogen concentration threshold corresponding to the phase transition, including:

[0034] (1) Calculate the total energy difference of the ground state of hydrides with two phase structures under the same hydrogen concentration, using the following formula:

[0035] ΔE=E phase1 -E p h ase2 .

[0036] Where E ph ase1 It is the ground-state total energy of the structure after the phase transformation of magnesium-based high-entropy alloys; E ph ase2 It is the ground-state total energy of the magnesium-based high-entropy alloy structure before phase transformation; when the value of ΔE is negative, the structure after phase transformation is more stable.

[0037] (2) Based on the ΔE calculated in (1), plot ΔE as the vertical axis and hydrogen concentration as the horizontal axis. When ΔE = 0, the corresponding horizontal axis is the hydrogen concentration threshold corresponding to the structural phase transition.

[0038] Furthermore, in step six, the evolution trend of the microstructure of the system during the phase transition is studied by analyzing the radial distribution function between atoms, including:

[0039] (1) Select two hydrogen concentrations near the phase transition threshold for hydride analysis, and use OVITO software to analyze their interatomic radial distribution function. For comparison, the interatomic radial distribution function of the magnesium-based high-entropy alloy before hydrogenation also needs to be plotted.

[0040] (2) Use OVITO software to plot the interatomic radial distribution functions between metals and between hydrogens for further analysis.

[0041] Furthermore, in step seven, based on the analysis of hydride binding energy and the number of hydrogen-hydrogen short bonds in step four, the prediction of the maximum hydrogen storage capacity of the magnesium-based high-entropy alloy by calculating the phonon spectrum includes:

[0042] (1) Using the binding energy of magnesium-based high-entropy alloys with low hydrogen concentration as a reference, select hydrides with a binding energy difference of about 0.03 eV, and the number of hydrogen-hydrogen short bonds in the hydride should not be too many.

[0043] (2) Calculate the phonon spectrum of the hydride. If the phonon spectrum has imaginary frequencies, reduce the hydrogen concentration and make an initial guess on the range of hydrogen concentrations with the maximum hydrogen storage capacity. Narrow the range by calculating the phonon spectrum until the maximum hydrogen storage capacity of the magnesium-based high-entropy alloy is found. If the phonon spectrum has no imaginary frequencies or only has tiny imaginary frequencies (less than 10 wavenumbers), the hydrogen concentration needs to be further increased and the phonon spectrum needs to be calculated until the maximum hydrogen storage capacity is obtained.

[0044] Based on the above technical solutions and the technical problems they solve, the advantages of this technical solution and its positive effects are as follows:

[0045] (1) By using first-principles calculations, the present invention successfully established a reasonable model of magnesium-based high-entropy alloys and their hydrides, thereby reducing time and material costs;

[0046] (2) By using first-principles calculations, this invention investigated the relationship between the stability of magnesium-based high-entropy alloy hydrides and hydrogen concentration, and found that excessively short hydrogen-hydrogen distances within the lattice also affect hydride stability. These findings are of great significance for assessing the maximum hydrogen storage capacity of materials;

[0047] (3) By using first-principles calculations, the present invention can predict the hydrogen concentration threshold corresponding to the material during the phase transition, and thus can simulate the evolution of the microstructure of magnesium-based high-entropy alloys during the phase transition caused by hydrogenation.

[0048] (4) By using first-principles calculations, the present invention can predict the theoretical value of the maximum hydrogen storage capacity of the material relatively accurately;

[0049] (5) The technical solution provided by this invention is simple to operate, highly repeatable, and has significant effects. This solution can relatively accurately evaluate the hydrogen storage performance of magnesium-based high-entropy alloys, providing certain guidance and reference value for experiments, and greatly reducing experimental costs. Attached Figure Description

[0050] Figure 1 shows the Mg provided in the embodiment of the present invention. 0.10 Ti 0.30 V 0.25 Zr 0.10 Nb 0.25 Flowchart of a method for evaluating the hydrogen storage performance of high-entropy alloys;

[0051] Figure 2 shows the optimized (a) BCC phase Mg provided in the embodiment of the present invention. 0.10 Ti 0.30 V 0.25 Zr 0.10 Nb 0.25 and its hydrogenated (b) BCC phase Mg 0.10 Ti 0.30 V 0.25 Zr 0.10 Nb 0.25 H2 and (c)FCC phase Mg 0.10 Ti 0.30 V 0.25 Zr 0.10 Nb 0.25 Geometric structure diagram of H2 hydride;

[0052] Figure 3 shows the BCC and FCC phase Mg provided in the embodiments of the present invention. 0.10 Ti 0.30 V 0.25 Zr 0.10 Nb 0.25 The (a) binding energy and (b) hydrogen-hydrogen distance of hydrides are less than A schematic diagram showing how the number of hydrogen-hydrogen short bonds changes with hydrogen concentration;

[0053] Figure 4 shows the Mg phases of FCC and BCC provided in the embodiment of the present invention. 0.10 Ti 0.30 V 0.25 Zr 0.10 Nb 0.25 Schematic diagram showing how the energy difference of the total ground-state energy of hydrides changes with hydrogen concentration;

[0054] Figure 5 shows the BCC and FCC phase Mg provided in the embodiments of the present invention. 0.10 Ti 0.30 V 0.25 Zr 0.10 Nb 0.25 A schematic diagram of the interatomic radial distribution function of the hydride system near the hydrogen concentration threshold during phase transition;

[0055] Figure 6 shows the FCC phase (a) Mg provided in the embodiment of the present invention. 0.10 Ti 0.30 V 0.25 Zr 0.10 Nb 0.25 H 1.7 (b)Mg 0.10 Ti 0.30 V 0.25 Zr 0.10 Nb 0.25 Schematic diagram of the phonon spectrum of H2 hydride. Detailed Implementation

[0056] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to embodiments. It should be noted that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention.

[0057] As shown in Figure 1, the magnesium-based high-entropy alloy Mg provided in this embodiment of the invention... 0.10 Ti 0.30 V 0.25 Zr 0.10 Nb 0.25 The method for evaluating hydrogen storage performance includes the following steps:

[0058] S101, Mg with the lowest energy is selected. 0.10 Ti 0.30 V 0.25 Zr 0.10 Nb 0.25 Geometric structure model;

[0059] S102, Mg obtained in S101 0.10 Ti 0.30 V0.25 Zr 0.10 Nb 0.25 Based on the lowest energy configuration, hydrogen atoms are added to the interstitial positions of the crystal lattice, and the lowest energy configuration is selected for each hydrogen concentration of hydride.

[0060] S103 improves calculation accuracy by further refining the Mg obtained from S101. 0.10 Ti 0.30 V 0.25 Zr 0.10 Nb 0.25 The lowest energy configuration and the lowest energy configuration of the hydride obtained from S102 were structurally optimized to obtain the total ground state energy.

[0061] S104, calculate Mg 0.10 Ti 0.30 V 0.25 Zr 0.10 Nb 0.25 Binding energy and violation of hydride The number of hydrogen-hydrogen bonds;

[0062] S105, If it is determined in S104 that the system will undergo a structural phase transition, then the total ground state energy of the two phase structures under the same hydrogen concentration is compared to obtain the hydrogen concentration threshold corresponding to the phase transition.

[0063] S106, based on the phase transition hydrogen concentration threshold obtained from S105, uses the radial distribution function to determine the evolution trend of the system's microstructure during the phase transition;

[0064] S107, Mg in S104 0.10 Ti 0.30 V 0.25 Zr 0.10 Nb 0.25 Based on calculations of hydride binding energy and the number of hydrogen-hydrogen short bonds, the maximum hydrogen storage capacity of this magnesium-based high-entropy alloy is predicted by calculating the phonon spectrum.

[0065] In step S101 provided in this embodiment of the invention, Mg with the lowest energy is selected. 0.10 Ti 0.30 V 0.25 Zr 0.10 Nb 0.25 The geometric structure model includes the following steps:

[0066] Step 1.1, through literature review, Mg 0.10 Ti 0.30 V 0.25 Zr 0.10 Nb 0.25 Magnesium-based high-entropy alloys have a body-centered cubic (BCC) structure.

[0067] Step 1.2, determine the Mg under study 0.10 Ti 0.30 V 0.25 Zr 0.10 Nb 0.25 The ratio of metal atoms was 2:6:5:2:5, and a single-cell model (containing 20 atoms) was established, which was then expanded to 60 metal atoms.

[0068] Step 1.3: Using a program written in Python, 20 configurations are randomly generated for the supercell model obtained in Step 1.2. The metal atoms in these configurations have different distributions in the crystal lattice.

[0069] Step 1.4: The exchange correlation between electrons is described by the PBE functional under the generalized gradient approximation, and the interaction between the atomic nucleus and electrons is described by the projected fused plane wave pseudopotential.

[0070] Step 1.5: Test the calculation parameters K-point and kinetic energy cutoff value ENCUT to determine the K-point and ENCUT required in the structural optimization process. Finally, the K-point is determined to be 2×2×2 and the ENCUT is 450eV.

[0071] Step 1.6: Use VASP software to optimize the structure of the 20 random configurations obtained in Step 1.3. Set IBRION=2 and PREC=Medium in INCAR, and select the configuration with the lowest energy as Mg. 0.10 Ti 0.30 V 0.25 Zr 0.10 Nb 0.25 The initial structure is shown in Figure 2(a).

[0072] In step S102 provided in this embodiment of the invention, the Mg obtained in S101... 0.10 Ti 0.30 V 0.25 Zr 0.10 Nb 0.25 Based on the lowest energy configuration, hydrogen atoms are added to the interstitial positions of the crystal lattice. For each hydrogen concentration of hydride, the lowest energy configuration is selected, including the following steps:

[0073] Step 1.1, through literature review, Mg 0.10 Ti 0.30 V 0.25 Zr 0.10 Nb 0.25 When the hydrogen absorption concentration of magnesium-based high-entropy alloys reaches a certain level, the structural phase transformation occurs to face-centered cubic (FCC) phase.

[0074] Step 1.2: First, determine the hydrogen atom concentration in the hydride as H / M = 0.33, 0.58, 1, 1.25, 1.5, 1.7, and 2. Then, add the corresponding hydrogen atom position coordinates to S101. Step 1.6: Obtain the BCC phase Mg. 0.10 Ti 0.30 V 0.25 Zr 0.10 Nb 0.25 From the structure file, hydride structures with H / M = 0.33, 0.58, 1, 1.25, 1.5, 1.7 and 2 can be obtained; for each hydrogen concentration H / M, a program written in Python randomly generates 20 configurations, and the hydrogen atoms in the 20 configurations corresponding to each hydrogen concentration have different distributions in the crystal lattice;

[0075] Step 1.3, because Mg 0.10 Ti 0.30 V 0.25 Zr 0.10 Nb 0.25 Magnesium-based high-entropy alloys undergo a structural phase transition from BCC to FCC when the hydrogen absorption reaches a certain concentration. Therefore, for comparison, an FCC phase Mg with the same hydrogen concentration as in step 1.2 was also established. 0.10 Ti 0.30 V 0.25 Zr 0.10 Nb 0.25 Hydride configurations: For each hydrogen concentration H / M, a program written in Python randomly generates 20 configurations, and the hydrogen atoms in the 20 configurations corresponding to each hydrogen concentration have different distributions in the crystal lattice.

[0076] Step 1.4: The exchange correlation between electrons is described by the PBE functional under the generalized gradient approximation, and the interaction between the atomic nucleus and electrons is described by the projected fused plane wave pseudopotential.

[0077] Step 1.5, the calculation of parameter K point and cutoff energy ENCUT is consistent with step 1.5 in S101;

[0078] Step 1.6: Using VASP software, the structures of multiple hydrides obtained in steps 1.2 and 1.3 are optimized according to their respective configurations. The calculation parameters are consistent with those in step 1.6 of S101. BCC and FCC phases with H / M values ​​of 0.33, 0.58, 1, 1.25, 1.5, 1.7, and 2 are selected. 0.10 Ti 0.30 V 0.25 Zr 0.10 Nb 0.25The configurations with the lowest hydride energy are shown in Figures 2(b) and (c), which are schematic diagrams of BCC and FCC hydrides with H / M = 2, respectively. In the BCC phase, hydrogen atoms occupy octahedral interstitial positions, while in the FCC phase, hydrogen atoms occupy tetrahedral interstitial positions.

[0079] In step S103 of the present invention embodiment, the calculation accuracy is improved by further refining the Mg obtained in S101. 0.10 Ti 0.30 V 0.25 Zr 0.10 Nb 0.25 The optimization of the lowest energy configuration and the lowest energy configuration of the hydride obtained from S102 to obtain the total ground-state energy includes the following steps:

[0080] Step 1.1, use VASP software to process the BCC Mg obtained in step 1.6 of S101. 0.10 Ti 0.30 V 0.25 Zr 0.10 Nb 0.25 The lowest energy configuration was used for structural optimization. The K-point was set to 2×2×2, and the INCAR file was configured with IBRION = 2, ISIF = 2, ENCUT = 450 eV, and ISPIN = 2. One structural optimization was performed. Then, ISIF = 7, and another structural optimization was performed. This process of changing the ISIF value was repeated until the energy difference was less than 1 meV / atom, at which point the total ground-state energy of the system was obtained, along with the lattice constant. Its relationship with experimental values The match is very good, indicating that the calculation parameters are set reasonably;

[0081] Step 1.2, similarly using VASP software, analyze the BCC and FCC phases of Mg obtained in step 1.6 of S102. 0.10 Ti 0.30 V 0.25 Zr 0.10 Nb 0.25 For structural optimization of the lowest energy configuration of the hydride, the calculation parameters must be consistent with those in step 1.1. The total ground-state energies of the hydrides at different hydrogen concentrations are shown in Table 1.

[0082] Table 1 Mg 0.10 Ti 0.30 V 0.25 Zr 0.10 Nb 0.25 Total ground state energy of hydrides

[0083]

[0084] In step S104 of the embodiment of the present invention, Mg is calculated.0.10 Ti 0.30 V 0.25 Zr 0.10 Nb 0.25 Binding energy and violation of hydride The number of hydrogen-hydrogen bonds is determined by the following steps:

[0085] Step 1.1: Calculate the Mg phases of BCC and FCC for H / M = 0.33, 0.58, 1, 1.25, 1.5, 1.7, and 2 respectively, using the hydride binding energy calculation formula. 0.10 Ti 0.30 V 0.25 Zr 0.10 Nb 0.25 Binding energy of hydrides. The results are shown in Figure 3(a). With increasing hydrogen concentration, the stability of BCC hydride decreases, while the stability of FCC hydride increases.

[0086] Step 1.2: Using LOBSTER software, set "cohpGenerator from 0 to 2type H type H" in the lobsterin file to calculate BCC and FCC Mg for each hydrogen concentration. 0.10 Ti 0.30 V 0.25 Zr 0.10 Nb 0.25 The distance between hydrogen atoms in a hydride is less than The number of hydrogen-hydrogen short bonds. As shown in Figure 3(b), with the increase of hydrogen concentration, the number of hydrogen-hydrogen short bonds in the BCC phase hydride lattice increases with the increase of hydrogen concentration, while the number of hydrogen-hydrogen short bonds in the FCC phase hydride does not increase significantly; according to the calculation results of binding energy and the number of hydrogen-hydrogen short bonds, it can be seen that with the increase of hydrogen concentration, the stability of the BCC phase is lower than that of the FCC phase, and it can be inferred that the system will undergo a structural phase transition, which is consistent with the experimental results.

[0087] In step S105 of this embodiment of the invention, if it is determined in S104 that a structural phase transition will occur in the system, then the total ground state energy of the two phase structures at the same hydrogen concentration is compared to obtain the hydrogen concentration threshold corresponding to the phase transition, including the following steps:

[0088] Step 1.1, according to the formula ΔE=E FCC -E BCC Calculate the Mg content in BCC and FCC phases with hydrogen concentrations of H / M = 0.33–1.7. 0.10 Ti 0.30 V 0.25 Zr 0.10 Nb 0.25 Total energy difference in the ground state of hydrides;

[0089] Step 1.2: Plot a graph with the total energy difference of the ground state obtained in Step 1.1 as the vertical axis and the hydrogen concentration H / M as the horizontal axis, as shown in Figure 4. When ΔE = 0, the corresponding horizontal axis H / M = 1.16, which is the hydrogen concentration threshold for phase transition.

[0090] In step S106 of this embodiment of the invention, based on the phase transition hydrogen concentration threshold obtained in S105, the evolution trend of the system's microstructure during the phase transition is determined by the radial distribution function, including the following steps:

[0091] Step 1.1: Select the two nearest hydrogen concentration values ​​H / M = 1 and 1.25 before and after H / M = 1.16, and analyze the radial distribution function of the corresponding hydride;

[0092] Step 1.2: Use OVITO software to analyze BCC and FCCmg at H / M = 1 and 1.25. 0.10 Ti 0.30 V 0.25 Zr 0.10 Nb 0.25 Interatomic radial distribution function of the hydride. For comparison, the BCCMG before hydride treatment is also plotted. 0.10 Ti 0.30 V 0.25 Zr 0.10 Nb 0.25 The interatomic radial distribution function is shown in Figure 5(a). It can be seen that the BCCMG before hydrogenation... 0.10 Ti 0.30 V 0.25 Zr 0.10 Nb 0.25 The geometry is ordered in both the short and long ranges. After hydrogenation, the long-range disorder of both BCC and FCC hydrides with H / M = 1 and 1.25 increases. Furthermore, the atomic arrangement of the FCC hydride with H / M = 1.25 is more ordered than that with H / M = 1, indicating stable Mg. 0.10 Ti 0.30 V 0.25 Zr 0.10 Nb 0.25 The geometry of hydrides tends to be more ordered after the phase transition;

[0093] Step 1.3: Further use OVITO software to draw the BCC and FCCMG for H / M = 1 and 1.25. 0.10 Ti 0.30 V 0.25 Zr 0.10 Nb 0.25The interatomic radial distribution functions between metals and between hydrogen atoms in the hydride are shown in Figures 5(b) and (c). It can be seen that after the phase transition, the distribution of hydrogen and metal atoms in the FCC hydride is more ordered.

[0094] In step S107 provided in this embodiment of the invention, Mg is in S104 0.10 Ti 0.30 V 0.25 Zr 0.10 Nb 0.25 Based on calculations of hydride binding energy and the number of hydrogen-hydrogen short bonds, the maximum hydrogen storage capacity of this magnesium-based high-entropy alloy is predicted by calculating the phonon spectrum, including the following steps:

[0095] Step 1.1, using a low concentration (H / M = 0.33) of BCC Mg 0.10 Ti 0.30 V 0.25 Zr 0.10 Nb 0.25 H 0.33 Using the binding energy of the hydride (0.539 eV) as a reference, the hydride with a binding energy difference of approximately 0.03 eV is FCC Mg. 0.10 Ti 0.30 V 0.25 Zr 0.10 Nb0. 25 H 1.7 (0.568 eV). Additionally, it has fewer than 15 hydrogen-hydrogen short bonds;

[0096] Step 1.2: Using VASP software, calculate the phonon spectrum of the FCC hydride when H / M = 1.7, where hydrogen atoms occupy interstitial positions in the FCC tetrahedrons. In the INCAR file, set IBRION = 6, NSW = 1, EDIFF = 0.1E-06, and EDIFFG = -0.1E-06 to calculate the Mg phase of the FCC. 0.10 Ti 0.30 V 0.25 Zr 0.10 Nb 0.25 H 1.7 The phonon spectrum. As shown in Figure 6(a), the phonon spectrum has no obvious imaginary frequencies, indicating that the hydride is stable from the perspective of lattice dynamics;

[0097] Step 1.3 further ensures that all hydrogen atoms occupy the interstitial positions of the FCC tetrahedron, at which point H / M = 2. Using the same calculation parameters as in Step 1.2, calculate the FCC Mg. 0.10 Ti 0.30 V 0.25 Zr 0.10 Nb 0.25The phonon spectrum of H2, as shown in Figure 6(b), shows no obvious imaginary frequencies, indicating that the hydride is stable from a lattice dynamics perspective. At this point, Mg can be theoretically determined. 0.10 Ti 0.30 V 0.25 Zr 0.10 Nb 0.25 The material's maximum hydrogen storage capacity is at least H / M = 2, corresponding to a hydrogen storage capacity of 3.16 wt%, exceeding the hydrogen storage capacity of most reported high-entropy alloys. Therefore, the hydrogen storage capacity of Mg can be evaluated. 0.10 Ti 0.30 V 0.25 Zr 0.10 Nb 0.25 It has good hydrogen storage performance and is of synthetic value.

[0098] Compared with the prior art, the technical solution of the present invention has the following technical advantages:

[0099] This invention evaluates the hydrogen storage performance of magnesium-based high-entropy alloys using first-principles calculations, which helps reduce the manpower and financial resources required to test the hydrogen storage performance of materials. The method is simple, easy to implement, and highly effective, with significant theoretical and experimental implications, and will contribute to the development of the field of alloy hydrogen storage.

[0100] The above description is merely a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any modifications, equivalent substitutions, and improvements made by those skilled in the art within the scope of the technology disclosed in the present invention, and within the spirit and principles of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A method for evaluating the hydrogen storage performance of magnesium-based high-entropy alloys, characterized in that, Includes the following steps: Step 1: Establish geometrical models of magnesium-based high-entropy alloys with different metal atom arrangements using a randomization method. Step 2: Optimize the structures of the various magnesium-based high-entropy alloy geometrical models obtained in Step 1 to obtain the configuration with the lowest energy, i.e., the most stable geometrical structure. Step 3: Establish geometrical models of magnesium-based high-entropy alloy hydrides with different hydrogen concentrations, optimize the structures of multiple hydride configurations for each hydrogen concentration, and select the most stable structure. Step 4: Calculate the binding energy and violation of the 2-Å principle for two magnesium-based high-entropy alloy hydride systems with different phase structures under the same hydrogen concentration. The number of hydrogen-hydrogen bonds in the "rule" is used to determine whether the system will undergo a structural phase transition during hydrogenation; Step 5: If the system is determined to undergo a structural phase transition in Step 4, the ground state total energy difference of different phase structures is calculated to obtain the hydrogen concentration threshold corresponding to the phase transition; Step 6: By analyzing the radial distribution function between atoms in the system, the evolution trend of the microstructure of the system during the phase transition is studied; Step 7: Based on the analysis of hydride binding energy and the number of hydrogen-hydrogen short bonds in Step 4, the maximum hydrogen storage capacity of magnesium-based high-entropy alloy is predicted by calculating the phonon spectrum; Step 4 includes: (1) Further improve the calculation accuracy, use the ENCUT value obtained by the test to perform another structural optimization on magnesium-based high-entropy alloy and its hydride to obtain the ground state total energy; (2) Calculate the binding energy of magnesium-based high-entropy alloy hydride; (3) Use LOBSTER software, set "cohpGenerator from 0 to 2 type Htype H" in the lobsterin file, and calculate the distance between hydrogen and hydrogen in magnesium-based high-entropy alloy hydride that is less than 2 The number of hydrogen-hydrogen bonds in Å; step five includes: calculating the total energy difference of the ground state of hydrides of the two phase structures at the same hydrogen concentration, when When the x-axis corresponds to the hydrogen concentration threshold during the phase transition, the x-axis represents the threshold value of the hydrogen concentration during the phase transition.

2. The method for evaluating the hydrogen storage performance of magnesium-based high-entropy alloys as described in claim 1, characterized in that, Step one includes: establishing a unit cell model based on the proportion of metal atoms in the magnesium-based high-entropy alloy, selecting criteria for the supercell size, and designing a program for random arrangement of atomic coordinates using Python.

3. The method for evaluating the hydrogen storage performance of magnesium-based high-entropy alloys as described in claim 1, characterized in that, The selection criteria include more than 20 metal atoms within the cell.

4. The method for evaluating the hydrogen storage performance of magnesium-based high-entropy alloys as described in claim 1, characterized in that, Step two uses first-principles calculations, including the selection of the PBE functional and projected fused plane wave pseudopotential under the generalized gradient approximation, the K-point and cutoff energy ENCUT convergence test, setting the key parameter IBRION=2 in the INCAR file, replacing the ENCUT value with PREC=Medium, and optimizing the structure of magnesium-based high-entropy alloy supercells with different atomic distributions obtained in step one, taking the configuration with the lowest energy as its final structure.

5. The method for evaluating the hydrogen storage performance of magnesium-based high-entropy alloys as described in claim 1, characterized in that, Step three includes: determining the coordinates of all tetrahedral and octahedral interstitial positions of the magnesium-based high-entropy alloy supercell based on the periodicity characteristics of the structural phase and in conjunction with VESTA software; and establishing the most stable structure for each hydrogen concentration of the magnesium-based high-entropy alloy hydride using randomization and first-principles calculation methods.

6. The method for evaluating the hydrogen storage performance of magnesium-based high-entropy alloys as described in claim 1, characterized in that, Step six includes: using OVITO software to analyze the total atomic, metal-metal, and hydrogen-hydrogen radial distribution functions of hydrides at two hydrogen concentrations before and after the phase transition threshold.

7. The method for evaluating the hydrogen storage performance of magnesium-based high-entropy alloys as described in claim 1, characterized in that, Step seven includes: using the obtained binding energy and the number of hydrogen-hydrogen short bonds to preliminarily determine the maximum hydrogen storage capacity of the alloy material, and further narrowing down the range of the maximum hydrogen storage capacity of the alloy material by calculating the phonon spectrum.

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