Double-layer double-vacancy graphene hydrogen storage material, construction method and adsorption energy calculation method

Abstract

The application discloses a metal atom modified double-layer double-vacancy graphene hydrogen storage material construction method, and obtains 5555-6-7777 vacancy graphene through rotation of a vacancy bond, obtains a stable double-layer structure after B atom doping, and uses Ti atoms with large mass and many charges to modify an inner layer and uses Li atoms with small mass and few charges to modify an outer layer. The application also discloses a metal atom modified double-layer double-vacancy graphene hydrogen storage material, which is constructed by the construction method. The application further discloses a calculation method of interlayer adsorption energy of the metal atom modified double-layer double-vacancy graphene hydrogen storage material, and the interlayer adsorption energy formula is updated by calculating interlayer electrostatic force calculation parameters, and it is also found that the inner and outer layers of the hydrogen storage system as a whole have a maximum hydrogen storage threshold.

Description

Technical Field

[0001] This invention belongs to the field of quantum mechanical calculation technology, and relates to metal atom-modified bilayer double-vacancy graphene hydrogen storage materials, as well as the construction method of metal atom-modified bilayer double-vacancy graphene hydrogen storage materials, and the calculation method of inner layer composite adsorption energy of metal atom-modified bilayer double-vacancy graphene hydrogen storage materials. Background Technology

[0002] Hydrogen, as a sustainable energy source that does not produce any greenhouse gases, is considered the most promising energy source to replace fossil fuels and change the existing energy structure due to its wide availability, safety, controllability, high efficiency, flexibility, low carbon footprint, and environmental friendliness. However, the high density and safe storage of hydrogen are the main challenges for its large-scale application. Currently, there are three main hydrogen storage technologies: high-pressure gaseous hydrogen storage, organic liquid hydrogen storage, and solid-state hydrogen storage. However, considering the limitations of safety risks, huge energy consumption, and high costs, solid-state hydrogen storage will become the key technology for large-scale commercial hydrogen storage and transportation in the future. Graphene, due to its high specific surface area, is considered a potential hydrogen storage material. Adding non-metallic elements such as boron to graphene can enhance the stability of metal atoms on the graphene surface. Since the experimentally synthesized graphene is mostly layered, the adsorption mechanism and adsorption mode of hydrogen molecules between layers are the focus of research.

[0003] Over the past few decades, first-principles calculations (DFT) have provided powerful tools for predicting and understanding materials properties. Among them, the Vienna Ab-initio Simulation Package (VASP), a commonly used first-principles calculation software, has played a significant role in materials research. Based on density functional theory, VASP can accurately calculate the structure, band structure, electronic structure, and response properties of hydrogen storage materials, providing strong support for hydrogen storage material research. Therefore, it is both advantageous and necessary to use theoretical research to analyze and explain the inner layer adsorption mechanism of single-metal atom modified bilayer graphene, replacing experimental methods. Summary of the Invention

[0004] The purpose of this invention is to provide a method for constructing bilayer, double-vacancy graphene materials, thereby enabling two-dimensional graphene materials to be applied in three-dimensional hydrogen storage.

[0005] The purpose of this invention is to provide a double-layer, double-vacancy graphene hydrogen storage material modified and doped with metal atoms and non-metal atoms, which improves the stability and hydrogen storage capacity of existing graphene hydrogen storage materials.

[0006] The purpose of this invention is to provide a method for calculating the interlayer adsorption energy of metal atom-modified bilayer double-vacancy graphene hydrogen storage materials, which solves the problem of calculating the adsorption energy of the inner layer of layered graphene in the existing formula for calculating the adsorption energy of hydrogen molecules.

[0007] The first technical solution adopted in this invention is a method for constructing a metal atom-modified bilayer double-vacancy graphene hydrogen storage material, which is implemented according to the following steps:

[0008] Step 1: Expand the original graphene unit cell to 5×6 graphene, and remove two adjacent carbon atoms on the graphene to construct double-vacancy graphene.

[0009] Step 2: Export the dual-vacancy graphene .cif file, and then export a .vasp type POSCAR file from this file and load it to the server. Set the calculation parameters required for INCAR, generate a K-point mesh using the Monkhorst-pack method, and optimize the dual-vacancy graphene structure using VASP and exchange correlation energy.

[0010] Step 3: Generate a pseudopotential file for double-vacancy graphene using VASPKit, and optimize the constructed structure to obtain the lowest energy, i.e., the most stable structure, 5-8-5 vacancy graphene.

[0011] Step 4: Convert the obtained 5-8-5 vacancy graphene from VESTA to a .cif file and input it into MS. Rotate the rightmost bond of the vacancy in the graphene by 90 degrees and perform structural optimization according to Step 2 and Step 3 to obtain 555-777 vacancy graphene.

[0012] Step 5: Convert the obtained 555-777 vacancy graphene from VESTA to a .cif file and input it into MS. Rotate the bottom side bond of the vacancy graphene by 90 degrees and perform structural optimization according to Step 2 and Step 3 to obtain 5555-6-7777 vacancy graphene.

[0013] Step 6: Convert the 5555-6-7777 vacancy graphene obtained by structural optimization from VESTA into a .cif file and input it into MS. Construct a bilayer double vacancy graphene by combining two 5555-6-7777 monolayers in a heterojunction manner. Optimize the structure of the bilayer double vacancy graphene material.

[0014] The first technical solution of the present invention is further characterized in that,

[0015] Step 2 involves setting the required calculation parameters for INCAR, including setting the convergence of the forces acting on the atoms to... Set the energy convergence criterion to 1×10. -5 eV / atom, set the kinetic energy cutoff value to 500eV.

[0016] The second technical solution adopted in this invention is to construct the hydrogen storage material by means of the method of constructing a metal atom-modified double-layer double-vacancy graphene.

[0017] The third technical solution adopted in this invention is a method for calculating the adsorption energy of metal atom-modified bilayer double-vacancy graphene hydrogen storage material. This method is used to calculate the adsorption energy of the inner and outer layers of the metal atom-modified bilayer double-vacancy graphene hydrogen storage material of this invention, and is implemented according to the following steps:

[0018] Step 1: To store hydrogen in a bilayer double-vacancy graphene hydrogen storage material modified with metal atoms, hydrogen molecules are added around the outer Li atoms. Each time a hydrogen molecule is added around a Li atom, the structure is optimized. The maximum hydrogen storage capacity of the outer layer is obtained through continuous adsorption. The hydrogen storage capacity of the outer layer of the material is calculated by correcting van der Waals interactions using the Grimme-DFT-D3 exchange-correlation function.

[0019] Step 2: Each time a hydrogen molecule is adsorbed in the inner layer, the interlayer electrostatic force energy generated by this adsorption is calculated. The interlayer electrostatic force energy is calculated by the difference in total energy of the upper and lower single layers before and after the adsorption of hydrogen molecules and the difference in energy of the double layers before and after the adsorption of hydrogen molecules.

[0020] Step 3: Update the adsorption energy formula by interlayer electrostatic force energy. The updated adsorption energy calculation formula is applied to the calculation of the adsorption energy of inner layer hydrogen molecules. The overall hydrogen storage threshold of the system is calculated by structural relaxation.

[0021] Step 4: After obtaining the maximum hydrogen storage capacity of the outer layer, perform the inner layer hydrogen molecule adsorption calculation. Use the inner layer hydrogen storage adsorption energy calculation formula updated in Step 3 to perform the calculation. Add 1 hydrogen molecule near the inner layer Ti atom each time until the maximum hydrogen storage threshold of the entire system is reached.

[0022] The third technical solution of the present invention is further characterized in that,

[0023] The formula for calculating the interlayer electrostatic energy in step 2 is as follows:

[0024] E j =(E ud2 -E ud1 )-[(E u2 -E u1 )+(E d2 -E d1 (1)

[0025] In equation (1): E j It is the energy of interlayer electrostatic force; E ud2 E is the energy of the bilayer structure after the structural change caused by the adsorption of hydrogen molecules; ud1 It is the energy of the pre-adsorption hydrogen molecule bilayer structure; E u2 E is the energy of the upper structure after the structural change caused by the adsorption of hydrogen molecules;u1 It is the energy of the upper structure before the adsorption of hydrogen molecules; E d2 E is the energy of the lower structure after the structural change caused by the adsorption of hydrogen molecules; d1 It is the energy of the lower structure before the adsorption of hydrogen molecules.

[0026] The adsorption energy of inner-layer hydrogen molecules in step 3 is calculated as follows:

[0027] E a[H2] =(E all+(H2)*n +E j -E all -E (H2)*n ) / n (2)

[0028] In equation (2): E a[H2] E is the average adsorption energy of H2 molecules. all+(H2)*n It is the total energy of the system after H2 molecules are adsorbed in the inner layer of the structure, E j It is the energy of the interlayer electrostatic interaction generated by the H2 adsorption molecules, E all The energy of the system where the inner layer of the structure does not adsorb H2 molecules, E (H2)*n It is the energy of adsorbing n H2 molecules in the inner layer, where n is the number of adsorbed H2 molecules.

[0029] The beneficial effects of this invention are:

[0030] The present invention provides a simple and clear method for constructing a novel bilayer graphene hydrogen storage material modified with metal atoms. This method produces a novel bilayer graphene hydrogen storage material that is closer to practical applications, has low research and development costs, avoids experimentation, and does not cause environmental pollution, thus conforming to the concept of green and environmentally friendly development.

[0031] The present invention relates to a metal atom-modified bilayer double-vacancy graphene hydrogen storage material, which has a stable structure with a large central mass and a small external mass, and a hydrogen storage weight ratio as high as 5.1 wt%. Furthermore, the stability was verified by molecular dynamics (AIMD) simulation, and the simulation results at 300K for 3000 fs showed that it has high stability.

[0032] This invention presents a method for calculating the adsorption energy of metal atom-modified bilayer double-vacancy graphene hydrogen storage materials. It proposes an interlayer electrostatic force energy parameter and updates the formula for calculating the inner layer hydrogen storage adsorption energy based on this energy calculation. The adsorption energy calculated by this formula is in perfect agreement with the bond length of the adsorbed hydrogen molecules. It also reveals that there is a maximum hydrogen storage threshold in both the inner and outer layers of the hydrogen storage system. The entire process is implemented through server calculations and can be applied to the calculation of the inner layer adsorption energy of similar materials, demonstrating strong generalization. Attached Figure Description

[0033] Figure 1 This is the structure diagram of 5555-6-7777 after geometric optimization with B atoms modified;

[0034] Figure 2 This is a diagram of the inner layer structure of Ti-modified bilayer double-vacancy graphene;

[0035] Figure 3 This is a diagram of the inner and outer structure of a double-layered, double-vacancy graphene modified with metal atoms Ti and Li;

[0036] Figure 4 This is a flowchart of hydrogen adsorption in a double-layer, double-vacancy graphene structure.

[0037] Figure 5 This is a diagram showing the hydrogen adsorption of a double-layer, double-vacancy graphene structure.

[0038] Figure 6 This is a simulation diagram of AIMD molecular dynamics at 3000 fs. Detailed Implementation

[0039] The present invention will now be described in detail with reference to the accompanying drawings and specific embodiments.

[0040] Example 1

[0041] This embodiment provides a method for constructing a metal atom-modified bilayer double-vacancy graphene hydrogen storage material, which is implemented according to the following steps:

[0042] Step 1: Using the materials simulation software Material Studio (MS), expand the original graphene unit cell to 5×6 graphene, and remove two adjacent carbon atoms on the graphene to construct double-vacancy graphene.

[0043] Step 2: Export the dual-vacancy graphene .cif file from MS, and then export the .vasp type POSCAR file from the file and load it to the server. Set the calculation parameters required for INCAR, and generate a 3×3×1 K-point grid with a precision of 0.03 using the Monkhorst-pack method. Use VASP and exchange correlation energy to optimize the dual-vacancy graphene structure.

[0044] Step 2 involves setting the required calculation parameters for INCAR, including setting the convergence of the forces acting on the atoms to... Set the energy convergence criterion to 1×10. -5 eV / atom, set the kinetic energy cutoff value to 500eV;

[0045] Step 3: Automatically generate a pseudopotential file for double-vacancy graphene using VASPKit, and optimize the constructed structure to obtain the lowest energy, i.e., the most stable 5-8-5 vacancy graphene structure. During the structure optimization process, all atoms can be relaxed, the lattice constants in the X and Y directions of the unit cell can change, and the lattice constant of the Z axis is fixed.

[0046] When performing structural optimization, the cutoff energy should be set to 1 to 1.3 times the NEMAX parameter in the POTCAR file. Vaspkit generates pseudopotentials and selects Monkhorst-Pack Scheme for K-points, with an accuracy of 0.03. It generates pseudopotential POTCAR and mesh KPOINTS files. After setting the parameters, the optimization step count NSW is set to 500 to perform structural optimization until the required energy and force convergence accuracy is achieved.

[0047] Step 4: Convert the obtained 5-8-5 vacancy graphene into a .cif file using VESTA and input it into MS. Rotate the rightmost bond of the vacancy in the graphene by 90 degrees and use VASP to optimize the structure to obtain 555-777 vacancy graphene.

[0048] Step 5: Convert the obtained 555-777 vacancy graphene from VESTA to a .cif file and input it into MS. Rotate the bottommost side bond of the graphene vacancy by 90 degrees, and perform structural optimization according to steps 2 and 3 to obtain the following... Figure 1 The graphene with 5555-6-7777 vacancy shown is optimized using the same settings as in steps 2 and 3.

[0049] Step 6: Convert the 5555-6-7777 vacancy graphene obtained from the structure optimization into a .cif file from VESTA and input it into MS. Use Build Layers to construct a bilayer double vacancy graphene from two 5555-6-7777 monolayers. Then, perform structure optimization according to Step 2 and Step 3 to obtain a metal atom modified bilayer double vacancy graphene hydrogen storage material. The settings during structure optimization are the same as in Step 2 and Step 3.

[0050] As can be seen from the above embodiments, the method for constructing a metal atom-modified bilayer double-vacancy graphene hydrogen storage material of the present invention obtains 5555-6-7777(Banhart F, Kotakoski J, Krasheninnikov AV. Structural defects in graphene[J].ACS nano,2011,5(1):26-41.) vacancy graphene through vacancy bond rotation. After B atom doping, a stable bilayer structure is obtained. The inner layer is modified with Ti atoms with large mass and high charge, and the outer layer is modified with Li atoms with small mass and low charge, which provides strong support for the research of hydrogen storage materials.

[0051] Example 2

[0052] This embodiment provides a metal atom-modified bilayer double-vacancy graphene hydrogen storage material, which is constructed using the method described in Example 1 for constructing a metal atom-modified bilayer double-vacancy graphene hydrogen storage material. Figure 2 The image shows the inner layer structure of Ti-modified bilayer double-vacancy graphene, as shown. Figure 3 The diagram shows the structure of Ti and Li modified bilayer double-vacancy graphene.

[0053] Example 3

[0054] This embodiment provides a method for calculating the adsorption energy of a metal atom-modified bilayer double-vacancy graphene hydrogen storage material, used for calculating the adsorption energy of the inner and outer layers of the metal atom-modified bilayer double-vacancy graphene hydrogen storage material in Example 2. The method is implemented according to the following steps:

[0055] Step 1: Modify the bilayer double-vacancy graphene hydrogen storage material with metal atoms to store hydrogen. In MaterialsStudio, hydrogen molecules are added around the outer Li atoms. Each time a hydrogen molecule is added around a Li atom, the structure is optimized. The maximum hydrogen storage capacity of the outer layer is obtained through continuous adsorption. The hydrogen storage capacity of the outer layer of the material is calculated by correcting van der Waals interactions using Grimme-DFT-D3 exchange-correlation function.

[0056] Step 2: Each time a hydrogen molecule is adsorbed in the inner layer, the interlayer electrostatic energy generated by this adsorption is calculated. The interlayer electrostatic energy is calculated by the difference in total energy of the upper and lower single layers before and after the adsorption of hydrogen molecules and the difference in energy of the double layers before and after the adsorption of hydrogen molecules. The interlayer electrostatic energy calculation process is as follows:

[0057] The formula for calculating the energy of interlayer electrostatic force is as follows:

[0058] E j =(E ud2 -E ud1 )-[(E u2 -E u1 )+(E d2 -E d1 (1)

[0059] In equation (1): E j It is the energy of interlayer electrostatic force; E ud2 E is the energy of the bilayer structure after the structural change caused by the adsorption of hydrogen molecules; ud1 It is the energy of the pre-adsorption hydrogen molecule bilayer structure; E u2 E is the energy of the upper structure after the structural change caused by the adsorption of hydrogen molecules; u1 It is the energy of the upper structure before the adsorption of hydrogen molecules; E d2 E is the energy of the lower structure after the structural change caused by the adsorption of hydrogen molecules; d1 It is the energy of the lower structure before the adsorption of hydrogen molecules;

[0060] Step 3: Update the adsorption energy formula by interlayer electrostatic force energy. The updated adsorption energy calculation formula is applied to the calculation of the adsorption energy of inner layer hydrogen molecules. The overall hydrogen storage threshold of the system is calculated by structural relaxation.

[0061] The adsorption energy of inner-layer hydrogen molecules is calculated as follows:

[0062] E a[H2] =(E all+(H2)*n +E j -E all -E (H2)*n ) / n (2)

[0063] In equation (2): E a[H2] E is the average adsorption energy of H2 molecules. all+(H2)*n It is the total energy of the system after H2 molecules are adsorbed in the inner layer of the structure, E j It is the energy of the interlayer electrostatic interaction generated by the H2 adsorption molecules, E all The energy of the system where the inner layer of the structure does not adsorb H2 molecules, E (H2)*n It is the energy of adsorbing n H2 molecules in the inner layer, where n is the number of adsorbed H2 molecules;

[0064] Step 4: After obtaining the maximum hydrogen storage capacity of the outer layer, perform the adsorption calculation of the inner layer hydrogen molecules. Use the updated formula for calculating the adsorption energy of the inner layer hydrogen storage, i.e., formula (2), to perform the calculation. Add one hydrogen molecule near the Ti atom in the inner layer each time until the maximum hydrogen storage threshold of the entire system is reached.

[0065] like Figure 4 The diagram shows the hydrogen adsorption process of a bilayer, double-vacancy graphene structure. The hydrogen storage effect of the bilayer, double-vacancy graphene material is as follows: Figure 5 As shown, the inner layer can store 11 hydrogen molecules and the outer layer can store 32 hydrogen molecules, for a total of 43 hydrogen molecules, with a hydrogen storage weight ratio of 5.1 wt%.

[0066] according to Figure 6 As shown in the AIMD molecular dynamics 3000fs simulation, the metal atom modified bilayer double-vacancy graphene hydrogen storage material of this invention has high stability at 300K and very small energy fluctuations.

[0067] As can be seen from the above, the adsorption energy calculation method of the metal atom modified bilayer double-vacancy graphene hydrogen storage material of the present invention solves the problem of calculating the adsorption energy of the inner layer of layered graphene in the existing hydrogen molecule adsorption energy calculation formula. By calculating the interlayer electrostatic force calculation parameters, the inner layer adsorption energy formula is updated. The energy calculated by the updated adsorption energy formula not only matches the bond length of the hydrogen molecule after adsorption, but also matches the overall charge transfer and hydrogen storage threshold of the system.

Claims

1. A method for calculating the adsorption energy of a metal atom-modified bilayer double-vacancy graphene hydrogen storage material, characterized in that, The material is prepared through the following steps: Step 1: Expand the original graphene unit cell to 5×6 graphene, and remove two adjacent carbon atoms on the graphene to construct double-vacancy graphene. Step 2: Export the dual-vacancy graphene .cif file, and then export a .vasp type POSCAR file from this file and load it to the server. Set the calculation parameters required for INCAR, generate a K-point mesh using the Monkhorst-pack method, and optimize the dual-vacancy graphene structure using VASP and exchange correlation energy. Step 3: Generate a pseudopotential file for double-vacancy graphene using VASPKit, and optimize the constructed structure to obtain the lowest energy, i.e., the most stable structure, 5-8-5 vacancy graphene. Step 4: Convert the obtained 5-8-5 vacancy graphene from VESTA to a .cif file and input it into MS. Rotate the rightmost bond of the vacancy in the graphene by 90 degrees and perform structural optimization according to Step 2 and Step 3 to obtain 555-777 vacancy graphene. Step 5: Convert the obtained 555-777 vacancy graphene from VESTA to a .cif file and input it into MS. Rotate the bottom side bond of the vacancy graphene by 90 degrees and perform structural optimization according to Step 2 and Step 3 to obtain 5555-6-7777 vacancy graphene. Step 6: Convert the 5555-6-7777 vacancy graphene obtained by structural optimization into a .cif file from VESTA and input it into MS. Construct two 5555-6-7777 monolayers into a bilayer double vacancy graphene. Through structural optimization, obtain a metal atom modified bilayer double vacancy graphene hydrogen storage material. Step 2 involves setting the required calculation parameters for INCAR, including setting the force convergence on the atoms to 0.02 eV / Å and the energy convergence criterion to 1 × 10⁻⁶. -5 eV / atom, set the kinetic energy cutoff value to 500eV; The specific method for calculating the adsorption energy of the hydrogen storage material constructed in the above steps is as follows: Step 1: To store hydrogen in a bilayer double-vacancy graphene hydrogen storage material modified with metal atoms, hydrogen molecules are added around the outer Li atoms. Each time a hydrogen molecule is added around a Li atom, the structure is optimized. The maximum hydrogen storage capacity of the outer layer is obtained through continuous adsorption. The hydrogen storage capacity of the outer layer of the material is calculated by correcting van der Waals interactions using the Grimme-DFT-D3 exchange-correlation function. Step 2: Each time a hydrogen molecule is adsorbed in the inner layer, the interlayer electrostatic force energy generated by this adsorption is calculated. The interlayer electrostatic force energy is calculated by the difference in total energy of the upper and lower single layers before and after the adsorption of hydrogen molecules and the difference in energy of the double layers before and after the adsorption of hydrogen molecules. Step 3: Update the adsorption energy formula by interlayer electrostatic force energy. The updated adsorption energy calculation formula is applied to the calculation of the adsorption energy of inner layer hydrogen molecules. The overall hydrogen storage threshold of the system is calculated by structural relaxation. Step 4: After obtaining the maximum hydrogen storage capacity of the outer layer, perform the inner layer hydrogen molecule adsorption calculation. Use the inner layer hydrogen storage adsorption energy calculation formula updated in Step 3 to perform the calculation. Add one hydrogen molecule near the inner Ti atom each time until the maximum hydrogen storage threshold of the entire system is reached. The formula for calculating the interlayer electrostatic energy in step 2 is as follows: AND j =(And ud2 -AND ud1 )-[(AND u2 -AND u1 )+(E d2 -AND d1 )](1) In equation (1): E j It is the energy of interlayer electrostatic force; E ud2 E is the energy of the bilayer structure after the structural change caused by the adsorption of hydrogen molecules; ud1 It is the energy of the pre-adsorption hydrogen molecule bilayer structure; E u2 E is the energy of the upper structure after the structural change caused by the adsorption of hydrogen molecules; u1 It is the energy of the upper structure before the adsorption of hydrogen molecules; E d2 E is the energy of the lower structure after the structural change caused by the adsorption of hydrogen molecules; d1 It is the energy of the lower structure before the adsorption of hydrogen molecules; The adsorption energy of inner-layer hydrogen molecules in step 3 is calculated as follows: AND a[H2] =(And all+(H2) n +E j -AND all -AND (H2) n ) / n (2) In equation (2): E a[H2] E is the average adsorption energy of H2 molecules. all+(H2) n It is the total energy of the system after H2 molecules are adsorbed in the inner layer of the structure, E j It is the energy of the interlayer electrostatic interaction generated by the H2 adsorption molecules, E all The energy of the system where the inner layer of the structure does not adsorb H2 molecules, E (H2) n It is the energy required for the inner layer to adsorb n H2 molecules. n This represents the number of H2 molecules adsorbed.

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