Method for regulating coordination environment of bimetallic supported graphene based on first-principle calculation

Abstract

The application discloses a method for regulating and controlling a coordination environment of a double-metal-loaded graphene based on first-principle calculation, wherein formation energy of different coordination environments in a first coordination environment of a double metal is obtained by using first-principle calculation, and overpotential of oxygen reduction reaction of the different coordination environments is calculated to obtain catalyst performance of the first coordination environment of the double-metal-loaded graphene, and after a catalyst with better performance is calculated, a second coordination environment is regulated and controlled. The application is suitable for fuel cell cathode material design, is used for replacing a traditional Pt / C catalyst, reduces use of a noble metal catalyst, and achieves the purpose of reducing cost.

Description

Technical Field

[0001] This invention belongs to the field of electrochemical energy technology and relates to a method for regulating the coordination environment of bimetallic-loaded graphene based on first-principles calculations. Background Technology

[0002] With societal development, energy demand continues to rise, and fossil fuels remain one of the primary energy sources. However, the use of fossil fuels has also brought environmental problems, such as climate change and air pollution. To address these issues, new strategies for utilizing renewable energy are needed to reduce dependence on fossil fuels and promote sustainable development. These strategies may include developing renewable energy sources such as solar, wind, and hydropower, as well as promoting energy conservation and efficiency improvements. The implementation of these measures will help reduce fossil fuel consumption, decrease environmental pollution and carbon emissions, and improve energy security and sustainability. Hydrogen, as a renewable energy source, has attracted considerable attention. To achieve efficient utilization, it is necessary to accelerate the development of novel catalysts to increase the rate of the oxygen reduction reaction (ORR).

[0003] The oxygen reduction reaction (ORR) is a crucial electrochemical process involving the reduction of oxygen molecules to water molecules on an electrode surface. ORR is a key step in generating electricity in devices such as fuel cells, metal-air batteries, and lithium-air batteries. Therefore, improving the catalytic activity and stability of ORR is essential for enhancing the performance and reliability of these devices. Currently, researchers are working to develop ORR catalysts with high catalytic activity, good stability, and low cost. Common ORR catalysts include metals such as platinum, copper, and nickel, and their alloys, as well as non-precious metal materials such as carbon-based materials, nitrides, and sulfides. The choice of these catalysts depends on their catalytic activity, durability, and cost-effectiveness in the ORR reaction.

[0004] Meanwhile, to further improve the catalytic efficiency of ORR, researchers are exploring novel catalyst construction methods. For example, they are utilizing nanotechnology, surface modification, and heterostructures to enhance catalyst activity and selectivity. Furthermore, some researchers are integrating knowledge from multiple disciplines such as biology, chemistry, and physics, using biomimetic and multi-scale modeling methods to design novel ORR catalysts.

[0005] In conclusion, accelerating the development of novel ORR catalysts and improving their performance is of great significance for promoting the efficient utilization of renewable energy sources such as hydrogen. Continuous research and innovation can further advance the development of ORR catalysts, facilitating energy transition and sustainable development.

[0006] In the current context, transition metal-nitrogen-carbon (MNC, M = Fe, Co, Ni, etc.) catalysts exhibit comparable catalytic activity to Pt-based catalysts under acidic conditions, and these metals have the advantage of high abundance on the Earth's surface. However, exploring different coordination environments to screen for better structures is challenging. These non-noble metals, by regulating active sites, show potential to replace platinum-supported graphene-based catalysts. Therefore, improving the activity and stability of non-noble metals is of great significance for the widespread application of fuel cell cathode materials. The team of Limin Dai and Zhenhai Xia achieved high-potential ORR activity by using non-metals (B, N, P, and S) as doping atoms to dope graphene. Adjusting the local coordination environment of the main group metal-nitrogen-carbon catalyst can enhance the oxygen reduction reaction. The results show that as the number of O atoms in the coordination environment increases, the p-band position of Mg deviates from the Fermi level, and the highest occupied energy level of O is also lower. Li Li's team used non-metallic elements (B, N, P and S) to dope graphene to achieve thermodynamic and kinetic control of active sites (ortho-C). Chen Chen's team proved, based on experiments and density functional theory, that the use of N and S co-doping to modify Fe / Co / Ni-N4 can achieve better ORR results. Summary of the Invention

[0007] The purpose of this invention is to provide a method for regulating the coordination environment of bimetallic supported graphene based on first-principles calculations, which can replace traditional Pt / C catalysts, reduce the use of precious metal catalysts, and is suitable for fuel cell cathode material design.

[0008] The technical solution adopted in this invention is a method for controlling the coordination environment of bimetallic supported graphene based on first-principles calculations. The formation energy of different coordination environments in the first coordination environment of the bimetal is calculated using first-principles calculations, and the overpotential of the oxygen reduction reaction in different coordination environments is calculated to obtain the catalyst performance of the first coordination environment of the graphene-supported bimetal. After calculating the catalyst with better performance, the second coordination environment is then controlled.

[0009] The invention is further characterized in that,

[0010] The specific steps are as follows:

[0011] Step 1: Construct a graphene-supported bimetallic crystal model, export the model in .cif format, and then convert the .cif data to .vasp format when exporting.

[0012] Step 2: Rename the .vasp format data to POSCAR, input the optimized INCAR, perform geometric optimization and electronic structure calculations, generate the required files POTCAR and KPOINT, perform simulation calculations on the POSCAR data, and output the file CONTCAR after reaching convergence accuracy. Obtain the energy in the last step of the optimized file OSZICAR, select the transition metal atom Fe as the reactive site, and the coordination environment B atoms as C, N, O, P, S, and calculate the formation energy.

[0013] Step 3: Rename the optimized CONTCAR to POSCAR. Adsorb O*, OH*, and OOH* at the Fe sites. Then, use the initial geometric optimization parameters to re-optimize the new adsorbed oxygen-containing intermediate structure data. After the calculation converges, extract the energy from the last step in OSZICAR. Modify the model after extraction, fix all atoms except for the oxygen-containing intermediates O*, OH*, and OOH*, calculate the frequency, correct the frequency calculation, subtract the corrected energy from the optimized energy, and calculate the overpotential of the structure.

[0014] Step 4: Change the transition metal atom A and the different coordination environments B atoms, repeat the above steps, calculate and analyze the most stable structure in the first coordination environment, that is, the structure corresponding to the minimum negative formation energy in the first coordination environment, and regulate the doping of the most stable site B atom in the second coordination environment. The most stable site in the second coordination environment is the site corresponding to the minimum negative formation energy in the second coordination environment. Regulate the doping of different element B atoms at its symmetric sites, thereby changing the catalyst stability and catalytic performance by changing the two transition metals and their coordination environments.

[0015] The formula for calculating the formation energy in step 2 is as follows:

[0016]

[0017] In formula (1), A represents transition metal atoms of Fe, Co, Ni, Cu, and Zn, and B represents the coordination environment of nonmetallic atoms of C, N, O, P, and S. c and μ Fe μ represents the chemical potential of C and Fe, respectively. A Represents the chemical potentials of Fe, Co, Ni, Cu, and Zn, where n represents the number of C defects, and μ represents the chemical potentials of Fe, Co, Ni, Cu, and Zn. B Represents C, N, O, P, and S, e represents the number of C, N, O, P, and S doped or modified, E FeAN2B4 E represents the total energy of the bimetallic compound. gra This represents the total energy of the defective graphene.

[0018] In step 2, when performing geometric optimization and electronic calculations, the initial magnetic moment was set to 5.

[0019] The reciprocal space lattice was automatically generated using the Monkhorst-Pack method. The Brillouin zone K point was set to 2×2×1. During the geometric optimization and electronic structure calculations, the cutoff energy was set to 500 eV.

[0020] DFT-D3 was used to correct for weak van der Waals interactions between layers, and the vacuum layer was set to... Geometry optimization is set to 1×10 -5 eV, energy convergence criterion for frequency calculation 1×10⁻⁶ -7 In the self-consistent calculation, the broadening factor was set to 0.05, and the force convergence criterion for each atom in the optimized unit cell was set to eV.

[0021] In step 3, the correction energy is calculated as follows:

[0022] ΔG=ΔE+ΔZPE-TΔS+ΔG PH +ΔG U (2)

[0023] In equation (2), ΔG represents the change in adsorption free energy of the oxygen-containing intermediate, ΔE is the adsorption energy difference between the initial and final states, ΔZPE and ΔS represent the changes in zero-point energy and entropy of the adsorbed species, respectively. ΔZPE and ΔS are obtained by fixing the bottom atoms of the catalyst and calculating the vibrational frequency of the oxygen-containing intermediate. The energy convergence criterion is set to 10. -7 eV.

[0024] The beneficial effects of this invention are:

[0025] This invention relates to a method for calculating and controlling the coordination environment of bimetallic supported graphene based on first-principles calculations. By using calculations to control the coordination environment, a catalyst with both formation energy and catalytic performance meeting the requirements can be obtained. Its oxygen reduction reaction overpotential is lower than that of traditional platinum-supported graphene catalysts, which is significant for improving the reaction rate and durability of fuel cell cathode catalysts. Attached Figure Description

[0026] Figure 1 This is a schematic diagram of the method for calculating and controlling the coordination environment of bimetallic-loaded graphene based on first-principles calculations according to the present invention.

[0027] Figure 2 This is a diagram of non-metallic doping sites;

[0028] Figure 3 This is the formation energy diagram of a single nonmetallic dopant with Fe as the active site;

[0029] Figure 4 It involves renumbering stable sites;

[0030] Figure 5 This is a formation energy diagram of stable sites for multiple nonmetallic dopants with Fe as the active site;

[0031] Figure 6 It is an overpotential map of a single site;

[0032] Figure 7 It is the optimal overpotential diagram for multiple doping sites;

[0033] Figure 8 This is the initial doping pattern;

[0034] Figure 9 It is the optimal structure among the data from multiple non-metallic atom doping calculations.

[0035] Figure 10 This is a structural diagram showing the lowest overpotential when B is modified at the most stable site in the second coordination environment. Detailed Implementation

[0036] The present invention will now be described in detail with reference to the accompanying drawings and specific embodiments.

[0037] Example 1

[0038] This embodiment provides a method for controlling the coordination environment of bimetallic supported graphene based on first-principles calculations. The formation energy of different coordination environments in the first coordination environment of the bimetal is calculated using first-principles calculations, and the overpotential of the oxygen reduction reaction in different coordination environments is calculated to obtain the catalyst performance of the first coordination environment of the graphene-supported bimetal. After calculating the catalyst with better performance, the second coordination environment is then controlled.

[0039] Example 2

[0040] This embodiment provides a method for controlling the coordination environment of bimetallic-loaded graphene based on first-principles calculations. Based on Embodiment 1, it is implemented according to the following steps:

[0041] Step 1: Use Materials Studio software to build a graphene-supported bimetallic crystal model, export the model in .cif format, and then use VESTA software to convert the .cif format data to .vasp format when exporting.

[0042] Step 2: Rename the .vasp format data to POSCAR, input the optimized INCAR, perform geometric optimization and electronic structure calculations, and generate the required files POTCAR and KPOINT. Use VASP to simulate the POSCAR data. After reaching convergence accuracy, output the file CONTCAR. Obtain the energy in the last step of the optimized file OSZICAR. Select the transition metal atom Fe as the reactive site. The input bimetallic data are: Fe-Fe, Fe-Co, Fe-Ni, Fe-Cu, Fe-Zn. Adjust its coordination environment. The coordination environment B atom is C, N, O, P, S. Calculate the formation energy.

[0043] In step 2, when performing geometric optimization and electronic calculations, the initial magnetic moment was set to 5.

[0044] The reciprocal space lattice was automatically generated using the Monkhorst-Pack method. The Brillouin zone K point was set to 2×2×1. During the geometric optimization and electronic structure calculations, the cutoff energy was set to 500 eV.

[0045] The time-range modified density functional DFT-D3 was used to decorrect the weak van der Waals interactions between layers, and the vacuum layer was set as Geometry optimization is set to 1×10 -5 eV, energy convergence criterion for frequency calculation 1×10⁻⁶ -7 In the self-consistent calculation, the broadening factor was set to 0.05, and the force convergence criterion for each atom in the optimized unit cell was set to eV.

[0046] Step 3: Rename the optimized CONTCAR to POSCAR. Adsorb O*, OH*, and OOH* at the Fe sites. Then, use the initial geometric optimization parameters to re-optimize the new adsorbed oxygen-containing intermediate structure data. After the calculation converges, extract the energy from the last step in OSZICAR. Modify the model after extraction, fix all atoms except for the oxygen-containing intermediates O*, OH*, and OOH*, calculate the frequency, correct the frequency calculation, subtract the corrected energy from the optimized energy, and calculate the overpotential of the structure.

[0047] Step 4: Change the transition metal atom A and the different coordination environments B atoms, repeat the above steps, calculate and analyze the most stable structure in the first coordination environment, that is, the structure corresponding to the minimum negative value of the formation energy in the first coordination environment, and dop the most stable site in the second coordination environment with B atoms. The most stable site in the second coordination environment is the site corresponding to the minimum negative value of the formation energy in the second coordination environment. Dop the symmetric sites with different element B atoms, thereby changing the stability and catalytic performance of the catalyst by changing the two transition metals and their coordination environments.

[0048] Example 3

[0049] This embodiment provides a method for regulating the coordination environment of bimetallic-supported graphene based on first-principles calculations. Building upon Example 2, step 2 uses Fe as the reactive site, and the formula for calculating the formation energy is as follows:

[0050]

[0051] In formula (1), A represents transition metal atoms of Fe, Co, Ni, Cu, and Zn, and B represents the coordination environment of nonmetallic atoms of C, N, O, P, and S. c and μ Fe μ represents the chemical potential of C and Fe, respectively. A Represents the chemical potentials of Fe, Co, Ni, Cu, and Zn, where n represents the number of C defects, and μ represents the chemical potentials of Fe, Co, Ni, Cu, and Zn. B Represents C, N, O, P, and S, e represents the number of C, N, O, P, and S doped or modified, E FeAN2B4 E represents the total energy of the bimetallic compound. gra This represents the total energy of the defective graphene.

[0052] E FeAN2B4 The formation energy at each site is as follows Figure 2 and Figure 3 As shown, the results indicate that the formation energies of different nonmetallic A dopants are all negative, suggesting that their thermodynamic properties are stable. A stability pattern can be observed among different nonmetallic atom dopants, and the stability also exhibits certain variations with C, N, O, P, and S doping.

[0053] In step 3, the correction energy is calculated as follows:

[0054] ΔG=ΔE+ΔZPE-TΔS+ΔG PH +ΔG U (2)

[0055] In equation (2), ΔG represents the change in adsorption free energy of the oxygen-containing intermediate, ΔE is the adsorption energy difference between the initial and final states, ΔZPE and ΔS represent the changes in zero-point energy and entropy of the adsorbed species, respectively. ΔZPE and ΔS are obtained by fixing the bottom atoms of the catalyst and calculating the vibrational frequency of the oxygen-containing intermediate. The energy convergence criterion is set to 10. -7 eV.

[0056] In Examples 2 and 3, the N in the first coordination environment was adjusted starting from FeCoN6. Figure 8 The overall flowchart is as follows Figure 1 With element sites such as Figure 1 (Doping with one type) can form energy such as Figure 3The most stable sites 1 and 2 were identified, and therefore, multi-element doping was performed on sites 1 and 2, with the doping sites as follows: Figure 4 The formation energy of the various types of sites (multiple doping) is shown in Figure (5); the catalyst free energy transformation with the change of elemental sites is as follows: Figure 6 The free energy changes of FeFeCNON (CNON represents atoms at four sites in multiple elements) are shown in the calculations, reflecting the optimal structure. Figure 7 The updated calculation data reveals the catalytic performance variation patterns, enabling catalyst design. The study explores the changes in stable sites outside the first coordination environment with doping or modification of B atoms, and calculates the optimal catalyst in the first coordination environment, FeFeCNON, such as... Figure 9 As shown, its overpotential is 0.31V (under acidic conditions). The most stable site in the second coordination environment is controlled according to the pattern observed in the first coordination environment, and its symmetric sites are also controlled. Specifically, in the first coordination environment, the overpotential increases with increasing atomic number when doped with (B:C, N, O, P, S). In the second coordination environment, only the most stable doped structure is considered, which involves doping B atoms at site 4 and (symmetric site 6). As the atomic number of C, N, and O increases, their overpotentials increase, but the overpotentials of P and S decrease with increasing atomic number, and the rate-determining step is altered. Therefore, the catalyst is designed to dope the two most stable sites in the second coordination environment with different elements. The optimal catalyst structure is... Figure 10 Its overpotential is 0.268V (under acidic conditions), therefore, it is feasible to modify its catalytic performance by using a non-metallic catalyst.

[0057] As can be seen from the above, 1) the present invention is based on the first principle calculation method to regulate the coordination environment of bimetallic supported graphene, which reveals the internal catalytic mechanism of bimetallic materials, clarifies the law of influence of different coordination environments on the bimetallic formation energy and catalytic performance, and can obtain the desired catalytic performance characteristics and the desired material formation energy by regulating the coordination environment.

[0058] 2) By doping bimetallic atoms and their coordination environment atoms, the formation energy and catalytic performance can be obtained. Through calculation, the shortcomings of insufficient understanding of the basic physical properties of materials during the application process can be made up for, and better catalysts can be designed.

[0059] 3) It overcomes the shortcomings of the traditional experimental method of "trial and error", and the process is easier to control, saves experimental resources, and plays a guiding role in the experiment.

Claims

1. A method for controlling the coordination environment of bimetallic-supported graphene based on first-principles calculations, characterized in that, The formation energies of different coordination environments in the first coordination environment of bimetallic materials were calculated using first-principles calculations, and the overpotentials of the oxygen reduction reaction in different coordination environments were calculated. The performance of the graphene-supported bimetallic catalyst in the first coordination environment was obtained. After calculating the catalyst with better performance, the second coordination environment was then adjusted. The specific steps are as follows: Step 1: Construct a graphene-supported bimetallic crystal model, export the model in .cif format, and then convert the .cif data to .vasp format when exporting. Step 2: Rename the .vasp format data to POSCAR, input the optimized INCAR, perform geometric optimization and electronic structure calculations, generate the required files POTCAR and KPOINT, perform simulation calculations on the POSCAR data, and output the file CONTCAR after reaching convergence accuracy. Obtain the energy in the last step of the optimized file OSZICAR, select the transition metal atom Fe as the reactive site, and the coordination environment B atoms as C, N, O, P, S, and calculate the formation energy. Step 3: Rename the optimized CONTCAR to POSCAR and apply it to the Fe sites for O adsorption. OH OOH Then, the initial geometric optimization parameters are used to re-optimize the new adsorbed oxygen-containing intermediate structure data. After convergence, the final step energy in OSZICAR is extracted. After extraction, the model is modified to remove the oxygen-containing intermediate O. OH OOH All atoms except those in the structure are fixed. The frequency is calculated, the frequency calculation is corrected, the corrected energy is subtracted from the optimized energy, the data is obtained, and the overpotential of the structure is calculated. Step 4: Change the transition metal atom A and the different coordination environments B atoms, repeat the above steps, calculate and analyze the most stable structure in the first coordination environment, that is, the structure corresponding to the minimum negative energy in the first coordination environment, and regulate the doping of the most stable site B atom in the second coordination environment. The most stable site in the second coordination environment is the site corresponding to the minimum negative energy in the second coordination environment. Regulate the doping of different element B atoms at its symmetric site, thereby changing the catalyst stability and catalytic performance by changing the two transition metals and their coordination environments. The formula for calculating the formation energy in step 2 is as follows: （1） In formula (1), A represents transition metal atoms of Fe, Co, Ni, Cu, and Zn, and B represents the coordination environment of nonmetallic atoms of C, N, O, P, and S. μ c and μ Fe The other represents the chemical potential of C and Fe. μ A The chemical potentials of Fe, Co, Ni, Cu, and Zn are represented by n, where n represents the number of C defects. μ B Represents C, N, O, P, and S, e represents the number of C, N, O, P, and S doped or modified, E FeAN2B4 E represents the total energy of the bimetallic compound. gra This represents the total energy of the defective graphene.

2. The method for controlling the coordination environment of bimetallic-loaded graphene based on first-principles calculations according to claim 1, characterized in that, In step 2, when performing geometric optimization and electronic calculations, the initial magnetic moment is set to 5. The reciprocal space lattice was automatically generated using the Monkhorst-Pack method. The Brillouin zone K-point was set to 2×2×1. During the geometric optimization and electronic structure calculations, the cutoff energy was set to 500 eV. DFT-D3 was used to correct for weak van der Waals interactions between layers, with the vacuum layer set to 20 Å and the geometry optimization set to 1. 10 -5 eV, energy convergence criterion 1 for frequency calculation 10 -7 In the self-consistent calculation, the broadening factor was set to 0.05, and the force convergence criterion for each atom in the optimized unit cell was set to 0.02 eV / Å.

3. The method for controlling the coordination environment of bimetallic-supported graphene based on first-principles calculations according to claim 1, characterized in that, In step 3, the correction energy is calculated as follows: （2） In equation (2), The change in adsorption free energy represents the oxygen-containing intermediate. It is the difference in adsorption energy between the initial state and the final state. and These represent the changes in zero-point energy and entropy of the adsorbed species, respectively. and The energy convergence criterion was set to 10-1 by calculating the vibrational frequencies of the oxygen-containing intermediates after fixing the bottom atoms of the catalyst. -7 eV.

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