阅读说明：本技术 一种金属-氮-碳固氮电催化剂的设计方法 (Design method of metal-nitrogen-carbon nitrogen fixation electrocatalyst ) 是由 刘杨 郑晓楠 姚远 吴晓宏 秦伟 卢松涛 李杨 康红军 洪杨 于 2021-07-30 设计创作，主要内容包括：本发明公开了一种金属-氮-碳固氮电催化剂的设计方法,属于化学和材料领域。本发明解决了由于实验条件和成本的约束,目前过渡金属氮掺杂碳材料的催化性能研究多以先设计制备、再表征性能的方式,使得催化剂的设计缺乏指导、制备缺乏定向、性能无法预判。本发明方法：通过金属负载类型和不同的氮配位构建金属-氮掺杂碳材料的模型；进行优化；计算金属-氮掺杂碳材料的结合能；判断稳定性；固氮金属-氮掺杂碳材料的筛选。本发明提供了一种基于第一性原理筛选固氮金属-氮-碳催化剂的方法和流程,为实验研究提供直接的理论指导,避免大量试错实验造成的时间和成本损失。(The invention discloses a design method of a metal-nitrogen-carbon nitrogen fixing electrocatalyst, belonging to the field of chemistry and materials. The invention solves the problems that due to the constraint of experimental conditions and cost, the current research on the catalytic performance of the transition metal nitrogen-doped carbon material mostly adopts a mode of firstly designing and preparing and then characterizing the performance, so that the design of the catalyst is lack of guidance, the preparation is lack of orientation, and the performance cannot be predicted. The method comprises the following steps: constructing a model of the metal-nitrogen-doped carbon material through metal loading types and different nitrogen coordination; optimizing; calculating the binding energy of the metal-nitrogen doped carbon material; judging the stability; screening nitrogen-fixing metal-nitrogen-doped carbon materials. The invention provides a method and a process for screening a nitrogen-fixing metal-nitrogen-carbon catalyst based on a first principle, which provide direct theoretical guidance for experimental research and avoid time and cost loss caused by a large number of trial and error experiments.)

1. A design method of a metal-nitrogen-carbon nitrogen fixing electrocatalyst is characterized by comprising the following steps: the design method is realized by the following steps:

step 1, constructing a model of a metal-nitrogen-doped carbon material through metal loading types and different nitrogen coordination;

step 2, optimizing the model constructed in the step 1;

step 3, calculating the binding energy of the metal-nitrogen doped carbon material;

step 4, judging the stability of the metal-nitrogen doped carbon material according to the calculated binding energy in the step 3, and if the stability is stable, executing the step 5, and if the stability is not stable, executing the step 13;

step 5, calculating Gibbs free energy when nitrogen adsorbs different active sites on the surface of the metal-nitrogen doped carbon material;

step 6, judging the nitrogen adsorption capacity according to the Gibbs free energy calculated in the step 5, executing the step 6 when the Gibbs free energy is less than 0, and executing the step 13 when the Gibbs free energy is more than 0;

step 7, calculating Gibbs free energy of hydrogen atoms adsorbed on the surface of the metal-nitrogen doped carbon material;

step 8, if the Gibbs free energy of the step 5 is less than the Gibbs free energy of the step 7, executing the step 9, otherwise executing the step 13;

step 9, calculating the first hydrogenation step (N) of the metal-nitrogen doped carbon material₂+H⁺+e^-→*N₂H) And generating the last oneNH₃Molecular step (. NH)₂+H⁺+e^-→*NH₃) Gibbs free energy change value of;

step 10, if the Gibbs free energy change value of the first hydrogenation step and the production of the last NH₃If the Gibbs free energy change value of the molecular step is less than 1.0, executing step 11, otherwise executing step 13;

step 11, constructing and optimizing each intermediate adsorption state according to a nitrogen fixation reaction mechanism, and calculating a Gibbs free energy change value of each step of the nitrogen fixation reaction mechanism, wherein in the step that all Gibbs free energy change values are positive values, the step with the maximum Gibbs free energy change value is the speed determining step of the whole nitrogen fixation reaction;

step 12, if the Gibbs free energy change value of the metal-nitrogen-carbon material speed-determining step is less than 0.5eV, the catalyst is a nitrogen reduction catalyst with excellent performance, and if the Gibbs free energy change value of the speed-determining step is more than or equal to 0.5eV, the step 13 is executed;

and step 13, abandoning.

2. The design method according to claim 1, wherein in step 1, a metal-nitrogen doped carbon material model is constructed by using a structure library of Materials Studio software through metal loading types and different nitrogen coordination, and a corresponding CIF file is obtained, and then the CIF file is converted into a POSCAR file required by VASP software for calculation by combining with VESTA software.

3. The design method according to claim 1, wherein in step 2, the POSCAR file in step 1 is utilized, and the INCAR and KPOINTS files required by the setting calculation are combined, the geometric structure of the metal-nitrogen doped carbon material is optimized to obtain a corresponding CONTCAR file, and the VESTA software is utilized to obtain the information of key bond length, bond angle and energy of the structure.

4. The design method according to claim 1, wherein the step 3 is performed by calculating the binding energy E of the metal-nitrogen doped carbon material according to the energy information obtained in the step 2 by using the formula (1)_b：

E_b＝E(MN₄-MN₄/C)–E(NC)–E(M_{General assembly}) (1)

Wherein, E (MN)₄-MN₄[ C ] is the energy of the entire metal-nitrogen-doped carbon material, [ E (NC) ] is the energy of the nitrogen-doped carbon material containing no metal atom, and [ E (M) ]_{General assembly}) Is the sum of the energies of all metal monoatomic atoms, M_{General assembly}Represents all metal single atoms.

5. The method according to claim 1, wherein the Gibbs free energy of nitrogen gas adsorbing different active sites on the surface of the metal-nitrogen doped carbon material is calculated according to the formula (2) in the step 5

Wherein, represents a metal-nitrogen doped carbon material, N₂Represents N₂Adsorbed on the surface of metal-nitrogen doped carbon material, and the Gibbs free energy of each structure is G ═ E + E_ZPE-TS, E is the electron energy of the structure, E_ZPEZero energy, S entropy and temperature T298.15K.

6. The method according to claim 1, wherein the Gibbs free energy of adsorption Δ G of hydrogen atoms on the surface of the metal-nitrogen doped carbon material is calculated according to the formula (3) in step 7_*H：

Wherein, H represents H atom adsorbed on the surface of the metal-nitrogen doped carbon material, the energy sum of proton and electron is equal to 1/2 hydrogen, and Gibbs free energy of each structure is G ═ E + E_ZPE-TS, E is the electron energy of the structure, E_ZPEZero energy, S entropy and temperature T298.15K.

7. The design method according to claim 1, wherein the first hydrogenation step (/ N) is calculated in step 9 using equation (4)₂+H⁺+e^-→*N₂H) Change in Gibbs free energy of Δ G (. about.N)₂+H⁺+e^-→*N₂H)：

The last NH generated is calculated using equation (5)₃Molecular step (. NH)₂+H⁺+e^-→*NH₃) Change in Gibbs free energy of Δ G (. about.NH)₂+H⁺+e^-→*NH₃)：

Wherein, represents a metal-nitrogen doped carbon material, N₂H and NH₃Each represents N₂H and NH₃The energy sum of protons and electrons is equal to 1/2 hydrogen energy when the metal-nitrogen doped carbon material is adsorbed on the surface, and the Gibbs free energy of each structure is G ═ E + E_ZPE-TS, E is the electron energy of the structure, E_ZPEZero energy, S entropy and temperature T298.15K.

8. The method according to claim 1, wherein the mechanism of the nitrogen fixation reaction in step 11 is a remote, alternating, continuous or enzymatic mechanism.

Technical Field

The invention relates to the field of chemistry and materials, in particular to a design method of a graphene-based electrocatalyst with catalytic nitrogen reduction reaction activity based on a first principle.

Background

Ammonia is an important chemical raw material and an energy carrier, and is widely applied to the fields of agriculture, chemical industry, energy, medicine and the like. At present, the traditional Haber-Bosch method is still adopted for industrial ammonia synthesis, and the method needs to be carried out under the conditions of high temperature and high pressure under the action of an iron-based catalyst, so that the energy consumption is high, a large amount of carbon dioxide is generated, and the emission is high. The method for synthesizing ammonia by catalyzing nitrogen reduction reaction under environmental conditions by using an electrochemical method has the advantages of low energy consumption, cleanness, greenness and the like, and becomes one of potential methods for industrially synthesizing ammonia by replacing a Haber-Bosch method. However, the conventional electrocatalysts are limited by their own performance and influenced by competitive hydrogen evolution reaction when catalyzing nitrogen reduction reaction, and have the problems of low yield, poor faraday efficiency and the like, and the demand of industrial synthesis of ammonia cannot be met. Therefore, the development of a nitrogen reduction electrocatalyst having high activity, high stability, and high selectivity has been a hot research topic in recent years.

The transition metal has rich d electronic structure, low price and rich reserves, and shows higher electrocatalytic nitrogen fixation potential. But some transition metals have low conductivity. The nitrogen-doped carbon has higher conductivity, stronger stability and larger specific surface area, and has important application in the field of electrocatalysis. Transition metal atoms are uniformly dispersed on the surface of the nitrogen-doped carbon through the anchoring effect of nitrogen atoms, so that various types of catalysts such as single atoms, double atoms or single clusters can be formed. These catalysts have exposed active sites, tunable electronic structures, and are one of the ideal electrocatalytic nitrogen fixation catalysts. However, these catalysts lack theoretical guidance in design, are not highly targeted, have certain difficulties in preparation, require a large number of trial and error experiments, and result in high cost and low efficiency. Therefore, there is a need to develop transition metal embedded nitrogen doped carbon materials with efficient electrochemical nitrogen fixation activity.

Disclosure of Invention

Under the constraint of experimental conditions and cost, the current research on the catalytic performance of the transition metal nitrogen-doped carbon material mostly adopts a mode of firstly designing and preparing and then characterizing the performance, so that the design of the catalyst is lack of guidance, the preparation is lack of orientation, and the performance cannot be predicted.

The invention develops a method for screening metal-nitrogen-doped carbon materials with nitrogen reduction performance based on a first principle simulation method, provides necessary theoretical guidance for later experimental preparation, accelerates the research progress of a novel catalyst, and further discloses the mechanism of catalytic reaction.

The design method of the metal-nitrogen-carbon nitrogen fixing electrocatalyst is realized by the following steps:

step 1, constructing a model of a metal-nitrogen doped carbon material through metal loading types and different nitrogen coordination (as shown in figure 1);

step 2, optimizing the model constructed in the step 1;

step 3, calculating the binding energy of the metal-nitrogen doped carbon material;

step 4, judging the stability of the metal-nitrogen doped carbon material according to the calculated binding energy in the step 3, and if the stability is stable, executing the step 5, and if the stability is not stable, executing the step 13;

step 5, calculating Gibbs free energy when nitrogen adsorbs different active sites on the surface of the metal-nitrogen doped carbon material;

step 6, judging the nitrogen adsorption capacity according to the Gibbs free energy calculated in the step 5, executing the step 6 when the Gibbs free energy is less than 0, and executing the step 13 when the Gibbs free energy is more than 0;

step 7, calculating Gibbs free energy of hydrogen atoms adsorbed on the surface of the metal-nitrogen doped carbon material;

step 8, if the Gibbs free energy of the step 5 is less than the Gibbs free energy of the step 7, executing the step 9, otherwise executing the step 13;

step 9, calculating the first hydrogenation step (N) of the metal-nitrogen doped carbon material₂+H⁺+e^-→*N₂H) And generating the last NH₃Molecular step (. NH)₂+H⁺+e^-→*NH₃) Gibbs free energy change value of;

step 10, if the Gibbs free energy change value of the first hydrogenation step and the production of the last NH₃If the Gibbs free energy change value of the molecular step is less than 1.0, executing step 11, otherwise executing step 13;

step 11, constructing and optimizing each intermediate adsorption state according to a nitrogen fixation reaction mechanism, and calculating a Gibbs free energy change value of each step of the nitrogen fixation reaction mechanism, wherein in the step that all Gibbs free energy change values are positive values, the step with the maximum Gibbs free energy change value is the speed determining step of the whole nitrogen fixation reaction;

step 12, if the Gibbs free energy change value of the metal-nitrogen-carbon material speed-determining step is less than 0.5eV, the catalyst is a nitrogen reduction catalyst with excellent performance, and if the Gibbs free energy change value of the speed-determining step is more than or equal to 0.5eV, the step 13 is executed;

and step 13, abandoning.

Further limiting, in the step 1, a metal-nitrogen doped carbon material model is constructed by utilizing a structural library of Materials Studio software through metal loading types and different nitrogen coordination, a corresponding CIF file is obtained, and then the CIF file is converted into a POSCAR file required by VASP software calculation by combining VESTA software.

And further limiting, optimizing the geometric structure of the metal-nitrogen doped carbon material by using the POSCAR file in the step 1 in the step 2 and combining an INCAR file and a KPOINTS file required by setting calculation to obtain a corresponding CONTCAR file, and obtaining the information of key bond length, bond angle and energy of the structure by using VESTA software. The key length and key angle information can help to understand the structure of the material.

Further defined, the binding energy E of the metal-nitrogen doped carbon material is calculated by using the formula (1) according to the energy information obtained in the step 2 in the step 3_b: all energies are in eV:

E_b＝E(MN₄-MN₄/C)–E(NC)–E(M_{general assembly}) (1)

Wherein, E (MN)₄-MN₄[ C ] is the energy of the entire metal-nitrogen-doped carbon material, [ E (NC) ] is the energy of the nitrogen-doped carbon material containing no metal atom, and [ E (M) ]_{General assembly}) Is the sum of the energies of all metal monoatomic atoms, M_{General assembly}Represents all metal single atoms.

Further defined, in step 5, the Gibbs free energy of nitrogen gas adsorbing different active sites on the surface of the metal-nitrogen doped carbon material is calculated according to the formula (2)

Wherein, represents a metal-nitrogen doped carbon material, N₂Represents N₂Adsorbed on the surface of metal-nitrogen doped carbon material, and the Gibbs free energy of each structure is G ═ E + E_ZPE-TS, E is the electron energy of the structure, E_ZPEZero energy, S entropy and temperature T298.15K.

The nitrogen gas adsorption on the metal-nitrogen-carbon material has two main configurations, namely a vertical mode and a horizontal mode, and is shown in a figure 3; when the nitrogen is vertically adsorbed on the surface, one N atom is connected with the surface; when nitrogen is adsorbed horizontally on the surface, two N atoms are attached to the surface.

Further limiting, in step 7, calculating adsorption gibbs of hydrogen atoms on the surface of the metal-nitrogen doped carbon material according to the formula (3)sLeave energy Δ G_*H：

Wherein, H represents H atom adsorbed on the surface of the metal-nitrogen doped carbon material, the energy sum of proton and electron is equal to 1/2 hydrogen, and Gibbs free energy of each structure is G ═ E + E_ZPE-TS, E is the electron energy of the structure, E_ZPEZero energy, S entropy and temperature T298.15K.

Further defined, the first hydrogenation step (× N) is calculated in step 9 using equation (4)₂+H⁺+e^-→*N₂H) Change in Gibbs free energy of Δ G (. about.N)₂+H⁺+e^-→*N₂H)：

The last NH generated is calculated using equation (5)₃Molecular step (. NH)₂+H⁺+e^-→*NH₃) Change in Gibbs free energy of Δ G (. about.NH)₂+H⁺+e^-→*NH₃)：

Wherein, represents a metal-nitrogen doped carbon material, N₂H and NH₃Each represents N₂H and NH₃The energy sum of protons and electrons is equal to 1/2 hydrogen energy when the metal-nitrogen doped carbon material is adsorbed on the surface, and the Gibbs free energy of each structure is G ═ E + E_ZPE-TS, E is the electron energy of the structure, E_ZPEZero energy, S entropy and temperature T298.15K.

Further defined, the mechanism of the nitrogen fixation reaction in step 11 is a remote, alternating, continuous and enzymatic mechanism.

High stability is the basis for all properties. Transition metal and nitrogen-doped carbon materials are various in types and structures, and the coordination mode of metal and nitrogen atoms directly influences the stability of the materials. Designing metal-nitrogen doped carbon materials with different compositions, structures and coordination modes, calculating by combining a first principle, and screening the metal-nitrogen doped carbon material with high stability by taking the binding energy of the metal-nitrogen doped carbon material as a judgment basis.

The electrocatalytic nitrogen fixation performance of the metal-nitrogen doped carbon material with high stability is researched by utilizing a first principle calculation method, and a catalyst with weak competitive hydrogen evolution capacity and strong nitrogen fixation performance is screened out.

The invention provides a method and a process for screening a nitrogen-fixing metal-nitrogen-carbon catalyst based on a first principle, which provide direct theoretical guidance for experimental research and avoid time and cost loss caused by a large number of trial and error experiments.

Drawings

FIG. 1 is a flow diagram of a nitrogen-fixing metal-nitrogen-carbon catalyst of the present invention;

FIG. 2 is a metal-nitrogen doped carbon material model;

FIG. 3 is an adsorption configuration of nitrogen at different active sites; (a) (c) a vertical adsorption configuration, (b), (d) a horizontal adsorption configuration;

FIG. 4 is a diagram of the four mechanisms of the nitrogen fixation reaction (remote, alternate, continuous and enzymatic mechanisms)

FIG. 5 is CrN₄-MnN₄Structure diagram of the remote mechanism and the alternate mechanism of the/C material.

Detailed Description

Example 1 a design method of a metal-nitrogen-carbon nitrogen fixation electrocatalyst in this implementation is achieved by the following steps:

step 1, constructing a metal-nitrogen doped carbon material model by utilizing a structure library of Materials Studio software through metal load types and different nitrogen coordination, obtaining a corresponding CIF file, and then converting the CIF file into a POSCAR file required by VASP software calculation by combining VESTA software;

step 2, optimizing the model constructed in the step 1: optimizing the geometric structure of the metal-nitrogen doped carbon material by using the POSCAR file in the step 1 and combining an INCAR file and a KPOINTS file required by setting calculation to obtain a corresponding CONTCAR file, and obtaining key bond length, bond angle and energy information of the structure by using VESTA software; see table 1.

TABLE 1MN₄-M’N₄Key bond length of/C MaterialAnd binding energy (eV)

Step 3, calculating the binding energy of the metal-nitrogen doped carbon material: calculating the binding energy E of the metal-nitrogen doped carbon material by using a formula (1) according to the energy information obtained in the step 2_b：

E_b＝E(MN₄-MN₄/C)–E(NC)–E(M)–E(M’) (1)

Wherein, E (MN)₄-MN₄Energy of the metal-nitrogen-doped carbon material as a whole, E (NC) energy of the nitrogen-doped carbon material containing no metal atom, E (M) energy of the metal monoatomic atom M, E (M ') energy of the metal monoatomic atom M ', and M ' may represent the same metal monoatomic atom or different metal atoms;

step 4, judging the stability according to the binding energy calculated in the step 3, if the stability is stable, executing the step 5, and if the stability is not stable, executing the step 13;

step 5, calculating Gibbs free energy when nitrogen adsorbs different active sites on the surface of the metal-nitrogen doped carbon material according to the formula (2)

Wherein, represents a metal-nitrogen doped carbon material, N₂Represents N₂Adsorbed on the surface of metal-nitrogen doped carbon material, and the Gibbs free energy of each structure is G ═ E + E_ZPE-TS, E is the electron energy of the structure, E_ZPEZero energy, S entropy and temperature T298.15K.

Step 6, judging the nitrogen adsorption capacity according to the Gibbs free energy calculated in the step 5, executing the step 6 when the Gibbs free energy is less than 0, and executing the step 13 when the Gibbs free energy is more than 0;

step 7, calculating the Gibbs free energy delta G of hydrogen atoms adsorbed on the surface of the metal-nitrogen doped carbon material according to the formula (3)_*H：

Wherein, H represents H atom adsorbed on the surface of the metal-nitrogen doped carbon material, the energy sum of proton and electron is equal to 1/2 hydrogen, and Gibbs free energy of each structure is G ═ E + E_ZPE-TS, E is the electron energy of the structure, E_ZPEZero energy, S entropy and temperature T298.15K;

step 8, if Δ G_*N2<ΔG_*HExecuting step 9, otherwise executing step 13;

step 9, calculating the first hydrogenation step (/ N) using equation (4)₂+H⁺+e^-→*N₂H) Change in Gibbs free energy of Δ G (. about.N)₂+H⁺+e^-→*N₂H)：

The last NH generated is calculated using equation (5)₃Molecular step (. NH)₂+H⁺+e^-→*NH₃) Change in Gibbs free energy of Δ G (. about.NH)₂+H⁺+e^-→*NH₃)：

Wherein, represents a metal-nitrogen doped carbon material, N₂H and NH₃Each represents N₂H and NH₃The energy sum of protons and electrons is equal to 1/2 hydrogen energy when the metal-nitrogen doped carbon material is adsorbed on the surface, and the Gibbs free energy of each structure is G ═ E + E_ZPE-TS, E is the electron energy of the structure, E_ZPEZero energy, S entropy and temperature T298.15K;

TABLE 2MN₄-M’N₄Nitrogen adsorption site and configuration, nitrogen and hydrogen atom adsorption free energy (eV) of/C material

Step 10, if Δ G (. about.N)₂→*N₂H)<1.0 simultaneously satisfies Δ G (. about.NH)₂→*NH₃)<1.0, executing step 11, otherwise executing step 13;

step 11, constructing and optimizing each intermediate adsorption state according to a nitrogen fixation reaction mechanism, calculating a Gibbs free energy change value of each step of the nitrogen fixation reaction mechanism, wherein in the step that all Gibbs free energy change values are positive values, the step with the maximum Gibbs free energy change value is the speed determining step delta G of the whole nitrogen fixation reaction_max；

Wherein, the Gibbs free energy change value is calculated according to a specific reaction selection formula (2), a formula (3), a formula (4) and a formula (5) which are carried out in each step of the reaction mechanism.

TABLE 3 Gibbs free energy values (. DELTA.G/eV) for each step of the catalyst in the different mechanisms

Step 12, if Gibbs free energy change value delta G of the metal-nitrogen-carbon material speed-determining step_maxIf the amount is less than 0.5eV, the catalyst is excellent in performance as a nitrogen-reducing catalyst, and if the change in Gibbs free energy in the rate-dependent step is Δ G_maxStep 13 is executed at 0.5eV or more;

wherein the speed-dependent step Δ G is shown in Table 3_maxIf the concentration is less than 0.5eV, the catalyst is a nitrogen reduction catalyst with excellent performance;

and step 13, abandoning.