A prediction method for the electrocatalytic ammonia synthesis performance of magnetically regulated Cr2C-MXene materials
By regulating the magnetism of Cr2C-MXene materials, the unknown impact of magnetic properties in existing electrocatalysts is solved, and the theoretical basis for efficient electrocatalytic synthesis of ammonia under normal temperature and pressure is realized, laying the foundation for catalyst research and development.
Patent Information
- Application Number
- CN202211591503.1
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- Filing Date
- 2022-12-12
- Publication Date
- 2025-09-02
- Estimated Expiration
- 2042-12-12
AI Technical Summary
The electrocatalysts for synthesizing ammonia in the prior art lack investigation on the magnetic properties of the materials, resulting in high overpotential and low Faraday efficiency, making it difficult to achieve efficient electrocatalytic synthesis of ammonia under normal temperature and pressure.
The magnetic properties of Cr2C-MXene materials are calculated and regulated through density functional theory, and the impact of different magnetic configurations on the properties of electrocatalytic synthesis is analyzed, including structural optimization, magnetic regulation and performance prediction.
It provides a theoretical basis for the research and development of electrocatalytic nitrogen reduction catalysts, explains the mechanism of action of magnetism in electrocatalytic nitrogen reduction, and improves the selectivity and reaction efficiency of the catalyst.
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Figure CN115810402B_ABST
Abstract
Description
Technical Field
[0001] The present invention relates to the field of computational chemistry, and in particular to a method for predicting the performance of ammonia electrocatalytic synthesis using a magnetically regulated Cr2C-MXene material. Background Art
[0002] Developing an efficient ammonia synthesis process is crucial for increasing modern agricultural yields, addressing global energy shortages, and addressing environmental sustainability. Current industrial ammonia production relies primarily on the Haber reaction, which requires temperatures of 200 atmospheres and 500 degrees Celsius. These harsh reaction conditions not only consume significant amounts of fossil energy but also result in significant CO2 emissions. Electrocatalytic methods are considered an important alternative to the energy-intensive and environmentally polluting Haber process for industrial ammonia synthesis. However, identifying a satisfactory electrocatalytic eNRR process with low overpotential and high Faradaic efficiency (FE) remains challenging. Precious metal catalysts, such as Au and Pb, remain commonly used for electrocatalytic nitrogen reduction, but their widespread application is severely hampered by their scarcity and high cost. Therefore, it is urgent to design efficient, highly selective, and low-cost electrocatalysts for ammonia synthesis and to develop new theories and methods for regulating the performance of electrocatalytic ammonia synthesis under ambient temperature and pressure conditions.
[0003] Research on electrocatalytic nitrogen reduction (eNRR) catalysts has been widely reported. It's not hard to see that previous work on NRR electrocatalyst design has primarily focused on regulating charge properties. However, spin, one of the two intrinsic properties of electrons, is also crucial for catalytic performance. The macroscopic manifestation of spin properties is magnetism, and exploring the influence of magnetism on the eNRR reaction is particularly important. In recent years, research has been gaining momentum on the relationship between catalyst magnetism and electrochemical reactions such as the oxygen evolution reaction (OER), the carbon dioxide reduction reaction (CO2RR), and the nitrogen reduction reaction (NRR). Researcher Yang Haitao from the Institute of Physics, Chinese Academy of Sciences, in collaboration with Professor Xu Zhiliang from Nanyang Technological University, Singapore, discovered that the local spin configuration of NixFe1-xOOH is strongly correlated with the redox reaction of water. Professor Xu Ping and others from Harbin Institute of Technology have identified the mechanisms by which charge transfer and magnetoresistance effects influence the OER process in nickel-based catalysts under an external magnetic field. However, the mechanism by which magnetism influences the product selectivity and reaction efficiency of the eNRR reaction remains unclear. Therefore, studying the relationship between magnetism and the eNRR reaction is crucial. Summary of the Invention
[0004] The purpose of the present invention is to provide a method for regulating the magnetic properties of Cr2C-MXene materials based on first-principles calculations of density functional theory and exploring the effect of magnetism on the performance of electrocatalytic ammonia synthesis, in response to the lack of research on the influence of material magnetism on catalytic performance in the existing technology of electrocatalysts for ammonia synthesis.
[0005] MXenes, as a new type of two-dimensional material, have an intrinsic atomic-level layered structure that gives them a huge specific surface area. The large number of functional groups on the surface give them excellent surface structure and performance adjustability. At the same time, MXenes contain transition metal atoms, and the spin-orbit-charge-lattice properties of their strongly correlated electrons and the easy controllability of their coupling give them great potential in the field of spin-regulated electrochemistry.
[0006] To solve the above problems, the present invention provides a method for predicting the performance of Cr2C-MXene material electrocatalytic ammonia synthesis by magnetic regulation, comprising the following steps:
[0007] S1. Obtain the crystal structure information of the Cr2C primitive package and perform structural optimization to obtain a stable Cr2C primitive cell;
[0008] S2. Loading O functional groups on the surface of the stable Cr2C unit cell and optimizing its structure to obtain a stable Cr2CO2-MXene structure;
[0009] S3. Magnetic manipulation of the stable structure of Cr2CO2-MXene to obtain Cr2CO2-MXene with different magnetic configurations;
[0010] S4. Adsorption of nitrogen on Cr2CO2-MXene surfaces with different magnetic configurations and calculation of the full-path Gibbs free energy, differential charge density, density of states, and band structure.
[0011] S5. Analyze the effects of different magnetic configurations of Cr2CO2-MXene on N2 catalysis based on the calculation results.
[0012] Preferably, in step S1, the structure of the Cr2C primitive cell is optimized and relaxed using VASP software to obtain a stable Cr2C primitive cell.
[0013] Preferably, in step S2, O functional groups are loaded above C and / or above Cr on the upper and lower sides of the surface of the Cr2C unit cell in the stable state.
[0014] Preferably, in step S2, the structure of the Cr2C unit cell loaded with O functional groups is optimized and relaxed using VASP software to obtain Cr2CO2-MXene with a stable structure.
[0015] Preferably, before magnetic regulation of the Cr2CO2-MXene with a stable structure in step S3, the Cr2CO2-MXene with a stable structure is adjusted to a 001 crystal plane and expanded into a 3×3×1 supercell structure.
[0016] Preferably, in step S3, the Build-Cleave Surfaces function in the Materials Studio software is used to cut the Cr2CO2-MXene with a stable structure to obtain a 001 crystal plane.
[0017] Preferably, in step S3, the magnetic properties of Cr2CO2-MXene are controlled by adjusting the parameters of the VASP input file INCAR.
[0018] Preferably, the Cr2CO2-MXene with different magnetic configurations in step S3 are Cr2CO2-MXene in four states: non-magnetic, ferromagnetic, interlayer antiferromagnetic and intralayer antiferromagnetic.
[0019] Preferably, the calculation formula of the full path Gibbs free energy in step S4 is:
[0020] G(T)=EDFT+EZPE+U(T)–TS+ΔG pH
[0021] Where T = 298.15K, EDFT and EZPE are the energy and zero-point vibration energy output after VASP calculation, U and S are the internal energy and entropy of the system, respectively, ΔG pH It is H + The free energy correction value of .
[0022] Preferably, the differential charge density in step S4 is obtained by post-processing the VASP output file CHGCAR with VESTA, and the state density and band structure are derived by the VASPKIT post-processing program.
[0023] The beneficial effects of the present invention are:
[0024] Based on the first-principles calculations of density functional theory, this paper regulates the magnetism of Cr2C-MXene materials and explores the influence of magnetism on the performance of electrocatalytic ammonia synthesis. Compared with the existing technology, the advantages of this paper are: considering the action mechanism of charge, orbital and spin order in electrocatalytic nitrogen reduction, it can lay a theoretical foundation for the research and development of electrocatalytic nitrogen reduction catalysts; using a series of analytical methods such as state density, differential charge, energy band, etc., to explain the activation mechanism of nitrogen-nitrogen triple bond from the three perspectives of charge, orbital and spin, providing a reference for the interpretation of charge, orbital and spin in electrocatalytic nitrogen reduction. BRIEF DESCRIPTION OF THE DRAWINGS
[0025] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings of the embodiments are briefly introduced below.
[0026] Figure 1These are two O functional group loading sites, hcp-Site1 and fcc-Site2, on the surface of the exposed Cr2C-MXene in the embodiment of the present invention;
[0027] Figure 2 Four different magnetic configurations of Cr2CO2-MXene, from left to right: non-magnetic, ferromagnetic, interlayer antiferromagnetic, and intralayer antiferromagnetic;
[0028] Figure 3 The six-electron reaction mechanism for the production of 2 mol of ammonia from 1 mol of nitrogen;
[0029] Figure 4 is the eNRR Gibbs free energy barrier on the Cr2CO2-MXene surface with different magnetic configurations;
[0030] Figure 5 is the density of states of different O adsorption sites on Cr2CO2-MXene;
[0031] Figure 6 Orbital and charge transfer of nitrogen molecules on the surface of Cr2CO2-MXene with different magnetic configurations;
[0032] Figure 7 The band structures of Cr2CO2-MXene with different magnetic configurations. DETAILED DESCRIPTION
[0033] The following will be combined with the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the embodiments described are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.
[0034] This embodiment provides a method for predicting the performance of ammonia electrocatalysis by magnetically regulated Cr2C-MXene materials, comprising the following steps:
[0035] S1: The cif file of the Cr2C unit cell obtained from the crystal database website Materials Project was converted into a standard VASP input structure file with the suffix .vasp using VESTA software. The Cr2C unit cell was then structurally optimized and relaxed using VASP software to obtain the stable state of the Cr2C unit cell, that is, the crystal structure with the lowest energy.
[0036] In the calculations involving VASP software, the interaction between the ionic core and the valence electrons was described using the plane wave augmentation (PAW) method, and the exchange-correlation interaction of the electrons was treated using the PBE functional in the generalized gradient approximation (GGA). The entire calculation process was performed under spin conditions. The plane wave cutoff energy was set to 450 eV, and the energy convergence criterion during the structure optimization process was selected as 10 -5 eV, the convergence criterion for the force is Grimme's DFT-D3 method was used to effectively correct the van der Waals forces in the calculated structures. The Brillouin zone was sampled using the Gamma method, with a 3×3×1 K-point pattern used during structure optimization and a 5×5×1 K-point pattern used for static calculations.
[0037] S2: If Figure 1 As shown in the figure, according to the different coordination environments of the O functional group loading sites on the Cr2C surface, they are divided into hcp-Site1 and fcc-Site2. O functional groups are loaded on the upper and lower sides of the Cr2C surface, and the structure is optimized and relaxed using VASP software to obtain Cr2CO2-MXene with a stable structure. Among them, based on the existing experimental conclusions, the Cr2C-MXene with exposed surface cannot exist stably, and the surface is usually passivated by the O functional group. The passivation site of the O functional group, Site1, is located above C, and Site2 is located above Cr.
[0038] S3: Use the Build-Cleave Surfaces function of Materials Studio software to cut the stable structure of Cr2CO2-MXene to obtain the 001 surface that can be adsorbed on the surface, and set it in the Z-axis direction. It is expanded to a 3×3×1 supercell structure to avoid the influence of the periodic structure on the catalytic results.
[0039] S4: By adjusting the parameters in the VASP input file INCAR, the different magnetic properties of Cr2CO2-MXene can be controlled;
[0040] Among them, the adjustment of the parameters in the VASP input file INCAR refers to setting the initial MAGMOM value of the Cr atom of Cr2CO2-MXene to achieve the purpose of controlling the magnetic configuration of Cr2CO2-MXene. In this embodiment, the initial MAGMOM value of C and O is set to 0, the initial MAGMOM value of Cr in the non-magnetic state is 0, and the initial MAGMOM values of spin-up and spin-down are +2 and -2, respectively. Figure 2 As shown, the structures of four states are obtained, namely, non-magnetic, ferromagnetic, interlayer antiferromagnetic and intralayer antiferromagnetic.
[0041] S5: The full-path Gibbs free energy of the Cr2CO2-MXene surface with different magnetic configurations is calculated through the typical six-electron reaction from N2 to NH3. The calculation formula of the full-path Gibbs free energy of the Cr2CO2-MXene surface with different magnetic configurations is:
[0042] G(T)=EDFT+EZPE+U(T)–TS+ΔG pH .
[0043] Where T = 298.15K, EDFT and EZPE are the energies directly read from the output file OSZICAR after VASP calculation and the zero-point vibrational energy calculated by the VASPKIT post-processing program 501 function, respectively. U and S are the internal energy and entropy of the system, respectively. pH It is H + The free energy correction value can be determined by the following formula:
[0044] ΔG pH =kBT×pH×ln 10.
[0045] S6: The differential charge density is obtained by post-processing the VASP output file CHGCAR with VESTA. This output file is obtained by performing a self-consistent calculation on the stable structure file obtained in step S5. During this self-consistent calculation, the IBRION parameter in the VASP input file INCAR is set to -1. The density of states and band structure are obtained by processing the VASP standard output file from the self-consistent calculation using the VASPKIT post-processor to generate the TDOS.dat and PBAND.dat files, which are then mapped using Origin.
[0046] S7: Analyze the N2 molecules adsorbed on the surface of Cr2CO2-MXene to explore the influence mechanism of Cr2CO2-MXene with different magnetic configurations on N2 catalysis.
[0047] The process from the capture of nitrogen by the catalyst to the release of ammonia is a six-electron reaction. Figure 3 As shown in the figure, depending on the protonation site at each step, the NRR reaction has three mechanisms: distal, alternating, and enzymatic. In both the distal and alternating mechanisms, nitrogen is adsorbed on the catalytic site in a vertical configuration. The difference between the two mechanisms is that in the distal mechanism, three hydrogen protons continuously attack the distal nitrogen atom until ammonia is released, and then attack the proximal nitrogen atom; in the alternating mechanism, hydrogen protons alternately attack two nitrogen atoms, and the release of ammonia is continuous. In the enzymatic mechanism, nitrogen is adsorbed on the catalytic site in a horizontal configuration. The protonation process is similar to the alternating mechanism, with hydrogen protons alternating between the two nitrogen atoms, and finally two ammonia atoms are released continuously.
[0048] from Figure 4 The eNRR Gibbs free energy barriers on the surface of Cr2CO2-MXene with different magnetic configurations show that, except for the enzymatic mechanism in the ferromagnetic state, the rate-determining steps of all other reactions are N2-NNH. The interlayer antiferromagnetic Cr2CO2-MXene catalyst exhibits excellent reaction activity under the enzymatic mechanism, and the rate-determining step barrier is only 0.18 eV.
[0049] from Figure 5 The intermediate state density shows that when C-Cr-O forms triangular prism coordination and hexahedral coordination, there are completely different orbital splitting situations. When C-Cr-O forms hexahedral coordination, the d orbital of the Cr atom is completely split, unlike the merger situation when forming triangular prism coordination.
[0050] Figure 6 It can be seen that the molecular orbital of N2 shows the most obvious splitting on the surface of Cr2CO2-MXene with interlayer antiferromagnetic configuration, indicating that the nitrogen-nitrogen triple bond is fully activated at this time, which explains the excellent catalytic performance of Cr2CO2-MXene with interlayer antiferromagnetic configuration.
[0051] Figure 7 The band structures of different magnetic configurations show that Cr2CO2-MXene catalysts with different magnetic configurations have different band structures. Among them, compared with the non-magnetic configuration, the bands at the Fermi level of ferromagnetism, interlayer antiferromagnetism and intralayer antiferromagnetism are denser, have better conductivity, and are more conducive to catalysis.
[0052] In summary, the present invention regulates the magnetic properties of Cr2C-MXene materials through first-principles calculations based on density functional theory. By analyzing the full-path Gibbs free energy of the typical six-electron reaction from N2 to NH3 on the surface of Cr2CO2-MXene with different magnetic configurations, the influence of Cr2CO2-MXene with different magnetic configurations on the electrocatalytic nitrogen fixation performance is obtained. By analyzing the N2 molecules adsorbed on the surface of Cr2CO2-MXene through differential charge density, density of states, energy band diagram and other analytical methods, the influence mechanism of Cr2CO2-MXene with different magnetic configurations on N2 catalysis is explored, and the important role of magnetism in electrocatalytic nitrogen reduction is given, laying a theoretical foundation for the research and development of electrocatalytic nitrogen reduction catalysts.
[0053] It should be noted that the above embodiments all belong to the same inventive concept, and the description of each embodiment has its own focus. For any details not described in individual embodiments, reference may be made to the description in other embodiments.
[0054] The above-described embodiments merely illustrate the implementation methods of the present invention. While the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the patent. It should be noted that a person skilled in the art would be able to make various modifications and improvements without departing from the spirit of the present invention, all of which fall within the scope of protection of the present invention. Therefore, the scope of protection of the patent for this invention shall be determined by the appended claims.
Claims
1. A method for predicting the performance of Cr2C-MXene material electrocatalytic ammonia synthesis by magnetic regulation, characterized in that: The steps include: S1. Obtain the crystal structure information of the Cr2C primitive package and perform structural optimization to obtain a stable Cr2C primitive cell; S2. Loading O functional groups on the surface of the stable Cr2C unit cell and optimizing its structure to obtain a stable Cr2CO2-MXene structure; S3. Magnetic manipulation of the stable Cr2CO2-MXene structure to obtain Cr2CO2-MXene with different magnetic configurations, including: using the Build-Cleave Surfaces function in Materials Studio software to cut the stable Cr2CO2-MXene structure to obtain a 001 surface capable of surface adsorption, and setting a 25Å Z-axis angle to expand it into a 3×3×1 supercell structure; and adjusting parameters in the VASP input file INCAR to achieve different magnetic control of the Cr2CO2-MXene. Adjusting the parameters in the VASP input file INCAR refers to setting the initial MAGMOM value of the Cr atoms in the Cr2CO2-MXene. S4. Adsorption of nitrogen on Cr2CO2-MXene surfaces with different magnetic configurations and calculation of the full-path Gibbs free energy, differential charge density, density of states, and band structure. S5. Analyze the effects of different magnetic configurations of Cr2CO2-MXene on N2 catalysis based on the calculation results.
2. The method for predicting the performance of electrocatalytic ammonia synthesis of magnetically regulated Cr2C-MXene materials according to claim 1, characterized in that: In step S1, the structure of the Cr2C primitive cell is optimized and relaxed using VASP software to obtain a stable Cr2C primitive cell.
3. The method for predicting the performance of electrocatalytic ammonia synthesis of magnetically regulated Cr2C-MXene materials according to claim 1, characterized in that: In step S2, O functional groups are loaded above C and / or above Cr on the upper and lower sides of the surface of the Cr2C unit cell in the stable state.
4. The method for predicting the performance of electrocatalytic ammonia synthesis of magnetically regulated Cr2C-MXene materials according to claim 1, characterized in that: In step S2, the VASP software is used to perform structural optimization and relaxation on the Cr2C unit cell loaded with O functional groups to obtain Cr2CO2-MXene with a stable structure.
5. The method for predicting the performance of electrocatalytic ammonia synthesis of magnetically regulated Cr2C-MXene materials according to claim 1, characterized in that: The Cr2CO2-MXene with different magnetic configurations in step S3 are Cr2CO2-MXene in four states: non-magnetic, ferromagnetic, interlayer antiferromagnetic and intralayer antiferromagnetic.
6. The method for predicting the performance of electrocatalytic ammonia synthesis of magnetically regulated Cr2C-MXene materials according to claim 1, characterized in that: The calculation formula of the full path Gibbs free energy in step S4 is: G(T) = EDFT + EZPE + U(T)–TS +ΔG pH Where T = 298.15K, EDFT and EZPE are the energy and zero-point vibration energy output after VASP calculation, U and S are the internal energy and entropy of the system, respectively, and ΔG pH It is H + The free energy correction value of .
7. The method for predicting the performance of electrocatalytic ammonia synthesis of magnetically regulated Cr2C-MXene materials according to claim 1, characterized in that: In step S4, the differential charge density is obtained by post-processing the VASP output file CHGCAR with VESTA, and the state density and band structure are derived by the VASPKIT post-processing program.