Calculation method for property of Bi surface electrocatalytic reduction nitrate in acid solution environment

Abstract

The invention provides a method for calculating the property of Bi surface electrocatalytic reduction nitrate in an acid solution environment, which comprises the following steps of: obtaining the result of the property of Bi (012) surface electrocatalytic reduction nitrate in the acid solution environment by using vasp software based on a density functional theory, and analyzing the surface charge distribution of Bi (012) after each reaction intermediate is adsorbed in the acid solution environment. Support can be provided for regulating and controlling an electronic structure on the surface of the catalyst; the adsorption energy of different adsorption intermediates is analyzed, the adsorption strength of the adsorption intermediates is effectively obtained, and the reaction mechanism can be further elaborated by combining in-situ infrared and other experimental methods; the reaction energy barrier and reaction energy of the element reaction are analyzed, free energy is drawn by utilizing origin software, so that the reaction speed steps can be intuitively observed, a reaction key intermediate is more reasonably determined, and an efficient catalyst is designed according to the guidance.

Description

Technical Field

[0001] The invention belongs to the technical field of catalysts, and in particular relates to a method for calculating the properties of electrocatalytic reduction of nitrates on a Bi surface in an acidic solution environment. Background Art

[0002] Over the past century, anthropogenic emissions of nitrogen-containing pollutants have increased rapidly, leading to a serious imbalance in the global nitrogen cycle and causing many ecological and environmental problems. The accumulation of nitrates in groundwater can cause eutrophication of water bodies, while excessive nitrate content in surface water and drinking water can pose a threat to human health. Among many nitrate removal technologies, electrocatalytic nitrate removal is a very promising solution, and is expected to become a powerful means to meet the growing demand for nitrates and restore the global nitrogen balance. As a commonly used and efficient nitrate electroreduction catalyst, the study of Bi-based catalysts' catalytic properties will help understand the catalytic mechanism and provide guidance for the design of more efficient catalysts. Traditional electrocatalytic property research often uses computational hydrogen electrode models, which pay more attention to the free energy changes of elementary reactions. The performance of catalysts designed based solely on free energy changes needs to be further improved. Summary of the invention

[0003] The purpose of the present invention is to provide a method for calculating the properties of the electrocatalytic reduction of nitrates on the Bi surface in an acidic solution environment. The calculation method in the present invention simultaneously considers the solution environment in the electrocatalytic reaction and the reaction energy barrier of the elementary reaction, more reasonably determines the key intermediates in the reaction, and guides the design of efficient catalysts.

[0004] The present invention provides a method for calculating the properties of electrocatalytic reduction of nitrates on Bi surface in an acidic solution environment, comprising the following steps:

[0005] A) Using Materials Studio software to construct a Bi reaction surface supercell, water molecules and hydronium ions are placed above the supercell to obtain an initial model;

[0006] B) using vasp software to select PBE pseudopotential for the initial model in step A), using GGA to describe the exchange-correlation interaction, first performing molecular dynamics simulation, obtaining a structure at regular intervals, then performing structural optimization on the obtained n structures, calculating and comparing the energies of different structures, and the structure with the lowest energy is the most stable model;

[0007] C) adding different reaction intermediates to the most stable model in step B) to obtain multiple reaction models;

[0008] D) For the multiple reaction models in step C), PBE pseudopotentials are selected using vasp software, exchange-correlation interactions are described using GGA, and the structure of the adsorption configuration is optimized for each reaction model. After the optimal adsorption configuration of each reaction model is obtained, vaspkit software is used to calculate and obtain the charge distribution, adsorption energy, elementary reaction energy barrier and elementary reaction free energy corresponding to the added reaction intermediates, and the adsorption strength of the reaction intermediates is obtained, and the most critical reaction intermediates are further determined.

[0009] Preferably, in step A), the Bi(012) surface supercell is constructed, and the specific steps are as follows:

[0010] Cut the metal Bi primitive cell along the 012 plane to create two layers of Bi atoms, each layer has 3×4, a total of 12 Bi atoms, and add Vacuum layer, preferably A vacuum layer is formed to form a three-dimensional surface structure, and the side of the Bi atomic layer far from the vacuum layer is fixed to simulate the Bi metal solid part, and the side close to the vacuum layer is allowed to relax to study the surface characteristics.

[0011] Preferably, in step A), above the supercell Water molecules and hydronium ions are arranged to simulate the double electric layer in an acidic environment, and the number ratio of the water molecules to the hydronium ions is preferably 29:1.

[0012] Preferably, during the molecular dynamics simulation in step B), the convergence accuracy of the energy and self-consistent field used in the iterative process is 10 -–5 eV, the maximum force acting on each atom is The plane wave cutoff energy is set to 400 eV, the Brillouin zone k point is 1×1×1, the simulation time is set to 8 to 12 ps, preferably 10 to 11 ps, the simulation step is 0.4 to 0.6 fs, preferably 0.5 fs, and a structure is obtained every 1 to 2 ps, preferably every 1.5 ps; n is preferably any integer between 4 and 12;

[0013] In the structural optimization process in step B), the convergence accuracy of energy and self-consistent field used is 10 -–5 eV, the maximum force acting on each atom is The plane wave cutoff energy is set to 400 eV, and the Brillouin zone k-point is 3 × 3 × 1.

[0014] Preferably, the reaction intermediate in step C) comprises *NO3, *NO3H, *NO2, *NO2H, *NO, *NHO, *NHOH, *NH2OH or *NH2.

[0015] In the present invention, for the structural optimization of the adsorption configuration of different reaction models, the present invention preferably adds the same reaction intermediate at different positions of the most stable model to form different adsorption configurations of the reaction intermediate, and structurally optimizes multiple different adsorption configurations of the reaction intermediate to obtain the optimal adsorption configuration of the reaction model, and so on, to obtain the optimal adsorption configurations of multiple reaction models.

[0016] Specifically, in the embodiment of the present invention, the present invention preferably adds reaction intermediate molecules into the gap between the water molecules and the Bi atomic layer.

[0017] Preferably, in the structural optimization process in step D), the convergence accuracy of the energy and self-consistent field used is 10 -–5 eV, the maximum force acting on each atom is The plane wave cutoff energy is set to 400 eV, and the Brillouin zone k-point is 3 × 3 × 1.

[0018] In the present invention, on the basis of the reaction model with good structural optimization, the charge distribution, adsorption energy, reaction energy barrier and reaction free energy, and their corresponding accuracies are selected, and the properties of each reaction intermediate result are analyzed using VASPkit software to obtain the charge distribution, adsorption energy, and corresponding reaction energy barrier and reaction free energy of different reaction species, and draw a free energy diagram to determine the most critical reaction intermediate and evaluate the reaction selectivity.

[0019] Preferably, in the step D), the charge distribution is obtained by a bader charge analysis program.

[0020] Preferably, in step D), the adsorption energy of the reaction intermediate E ads According to formula I, we can calculate:

[0021] E ads =G ads -G slab -G gas Formula I;

[0022] In Formula I, G ads is the adsorption energy of the reaction intermediate, G slab is the total energy without the introduction of reaction intermediates, G gas is the energy of the gaseous unadsorbed reaction intermediate.

[0023] Preferably, in step D), the elementary reaction energy barrier G of the reaction intermediate is a According to formula II, we can get:

[0024] G a =ΔEDFT(TS-IS)+ΔEZPE(TS-IS)+TΔS(TS-IS) Formula II;

[0025] In formula II, ΔEDFT(TS-IS) is the first-principles calculated energy difference between the reaction transition state and the reaction initial state, ΔE ZPE (TS-IS) is the zero-point energy difference between the reaction transition state and the reaction initial state, T is the simulation temperature, which is generally considered to be room temperature, ΔS(TS-IS) is the entropy difference between the reaction transition state and the reaction initial state, calculated by vaspkit software; the transition state is calculated by vasp software using the CI-NEB method.

[0026] Preferably, in step D), the elementary reaction free energy ΔG of the reaction intermediate is calculated according to formula III:

[0027] ΔG=ΔE DFT (FS-IS)+ΔE ZPE (FS-IS)+TΔS(FS-IS) Formula III;

[0028] In formula III, ΔEDFT (=FS-IS) is the first principles energy difference between the final state and the initial state of the reaction, ΔE ZPE (FS-IS) is the zero-point energy difference between the final state and the initial state of the reaction, T is the simulation temperature, generally considered to be room temperature, ΔS(FS-IS) is the entropy difference between the final state and the initial state of the reaction, calculated by vaspkit software. Then, the intermediates under the same reaction path are drawn into a free energy diagram using origin software.

[0029] The invention provides a method for calculating the properties of electrocatalytic reduction of nitrates on a Bi surface in an acidic solution environment. The invention uses vasp software based on density functional theory to obtain the results of the properties of electrocatalytic reduction of nitrates on a Bi (012) surface in an acidic solution environment, analyzes the charge distribution on the Bi (012) surface after the adsorption of various reaction intermediates in the acidic solution environment, and can provide support for regulating the electronic structure of the catalyst surface; analyzes the adsorption energy of different adsorbed intermediates, effectively obtains the adsorption strength of the adsorbed intermediates, and can further explain the reaction mechanism by combining experimental methods such as in-situ infrared; analyzes the reaction energy barrier and reaction energy of elementary reactions, and uses origin software to draw free energy, so as to intuitively observe the rate-determining step of the reaction, more reasonably determine the key intermediates of the reaction, and guide the design of an efficient catalyst based on the above.

[0030] The implementation of the method of the present invention has the following beneficial effects:

[0031] 1. The present invention provides a method for calculating the properties of electrocatalytic reduction of nitrate on the Bi(012) surface in an acidic solution environment, which solves the problem that most catalyst mechanism studies ignore the solution environment in the electrocatalytic reaction and do not consider the reaction energy barrier of the elementary reaction. It can provide theoretical support for related experiments, and provide certain value for the practical application of Bi-based catalysts for electrocatalytic nitrate reduction, and guide the design of more efficient catalysts.

[0032] 2. The method of the present invention has the advantages of low cost and no pollution, saving manpower and material resources, and has strong portability. The Bi(012) surface in the model can be replaced by various modified Bi surface catalysts. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on the provided drawings without paying creative work.

[0034] Figure 1 It is a flow chart of a method for calculating the properties of electrocatalytic reduction of nitrates on Bi surface in an acidic solution environment of the present invention;

[0035] Figure 2 The metal Bi unit cell used in the initial model building has the following lattice parameters: α=β=90°, γ=120°;

[0036] Figure 3 In order to introduce 29 water molecules and one hydronium ion to simulate the optimal model of Bi-based surface in acidic environment;

[0037] Figure 4 This is a model diagram of the *NO adsorption intermediate in Example 1;

[0038] Figure 5 This is the charge analysis diagram of the *NO adsorption intermediate in Example 1;

[0039] Figure 6 is the adsorption energy diagram of various adsorption intermediates in Example 2;

[0040] Figure 7 This is a free energy change diagram of the reaction path in Example 2. DETAILED DESCRIPTION

[0041] In order to further illustrate the present invention, a method for calculating the properties of electrocatalytic reduction of nitrate on Bi surface in an acidic solution environment provided by the present invention is described in detail below in combination with examples, but it should not be construed as limiting the scope of protection of the present invention.

[0042] Example 1 Obtaining the Charge Distribution of NO Adsorption Intermediates in Acidic Environment

[0043] Bismuth metal (Bi) belongs to the triclinic system, with a space group of R3-m and a lattice parameter of α=β=90°,γ=120°,Bi crystal model containing 6 Bi atoms (such as Figure 2 As shown), cut along its 012 plane, build 2 layers of Bi atoms, each layer has 3×4, a total of 12 Bi atoms, and add The vacuum layer forms a three-dimensional surface structure. The side away from the vacuum layer is fixed to simulate the bulk material, and the side close to the vacuum layer is allowed to relax to study the surface properties. 29 water molecules and one H3O are introduced + ions to simulate the double electric layer in an acidic environment, thus completing the construction of the initial model.

[0044] Then, the PBE pseudopotential was selected using vasp software, and the exchange-correlation interaction was described using GGA. The convergence accuracy of the energy and self-consistent field used in the molecular dynamics simulation was 10 -–5 eV, the maximum force acting on each atom is The plane wave cutoff energy was set to 400 eV, the Brillouin zone k-point was 1×1×1, the simulation time was set to 10 ps, ​​the simulation step was 0.5 fs, and a structure was obtained every 1.5 ps. The six structures obtained were optimized separately. During the structural optimization process, the convergence accuracy of the energy and self-consistent field used was 10 -–5 eV, the maximum force acting on each atom is The plane wave cutoff energy was set to 400 eV, the Brillouin zone k-point was 3 × 3 × 1, and the first-principles molecular dynamics calculations and analyses were performed on the six structurally optimized models. The structural energies were compared and the structure with the lowest energy was determined to be the most stable model (e.g. Figure 3 shown).

[0045] *NO molecules were added to the gap between water molecules and the Bi(012) surface to obtain a preliminary *NO model. *NO molecules were then added to different positions of the model to form multiple *NO models with different adsorption configurations. VASP software was used to select PBE pseudopotential and GGA to describe the exchange-correlation interaction. The convergence accuracy of the energy and self-consistent field used in the iteration process was 10 -–5 eV, the maximum force acting on each atom is The plane wave cutoff energy is set to 400 eV, the Brillouin zone k point is 3×3×1, and the structures of multiple *NO models are optimized and the total energy of each model is calculated. The model with the minimum energy and consistent with chemical common sense is the optimal model. Figure 4 As shown, the charge distribution is analyzed using Bader charge and visualized using Vesta software (see Figure 5 shown).

[0046] Example 2 Calculate the adsorption energy of key intermediates and the reaction energy barrier and reaction energy of the corresponding elementary reaction and draw a free energy diagram

[0047] According to the method of Example 1, the optimal models of 9 reaction intermediates such as *NO3, *NO3H, *NO2, *NO2H, *NO, *NHO, *NHOH, *NH2OH, *NH2 were constructed respectively, and their corresponding gaseous energies were calculated using the formula E ads =G ads -G slab -G gas (G ads is the energy of the reaction intermediate, G slab is the total energy without the introduction of reaction intermediates, G gas is the energy of the gaseous unadsorbed reaction intermediate) to calculate the adsorption energy of each species, such as Figure 6 Then, according to the relationship between the adsorbed species and the corresponding elementary reaction (as shown in Table 1), the final state of the elementary reaction is calculated, and then the transition state is obtained using the CI-NEB method using vasp software. The elementary reaction energy barrier and reaction free energy are calculated according to the following two formulas:

[0048] G a =ΔE DFT (TS-IS)+ΔE ZPE (TS-IS)+TΔS(TS-IS) Formula II;

[0049] ΔG=ΔE DFT (FS-IS)+ΔE ZPE (FS-IS)+TΔS(FS-IS) Formula III.

[0050] Table 1 Relationship between adsorbed species and corresponding elementary reactions

[0051]

[0052] Use origin software to draw a reaction free energy diagram, such as Figure 7 As shown. From the free energy diagram, we can analyze that *NO3+H + +e -→*NO3H has the highest reaction energy barrier, so this step is the rate-determining step of the reaction. Reasonable design of catalyst to reduce the reaction energy barrier of this step can effectively reduce the overall overpotential of the reaction. For the products nitric oxide (NO) and hydroxylamine (NH2OH), reasonable regulation of their adsorption energy is conducive to improving their single selectivity.

[0053] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principle of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A method for calculating the properties of Bi surface electrocatalytic reduction of nitrate in an acidic solution environment, comprising the following steps: A) Using Materials Studio software to construct a Bi reaction surface supercell, water molecules and hydronium ions are placed above the supercell to obtain an initial model; B) using vasp software to select PBE pseudopotential for the initial model in step A), using GGA to describe the exchange-correlation interaction, first performing molecular dynamics simulation, obtaining a structure at regular intervals, then performing structural optimization on the obtained n structures, calculating and comparing the energies of different structures, and the structure with the lowest energy is the most stable model; C) adding different reaction intermediates to the most stable model in step B) to obtain multiple reaction models; D) For the multiple reaction models in step C), PBE pseudopotentials are selected using vasp software, exchange-correlation interactions are described using GGA, and the structure of the adsorption configuration is optimized for each reaction model. After the optimal adsorption configuration of each reaction model is obtained, vaspkit software is used to calculate and obtain the charge distribution, adsorption energy, elementary reaction energy barrier and elementary reaction free energy corresponding to the added reaction intermediates, and the adsorption strength of multiple reaction intermediates is obtained, and the most critical reaction intermediate is further determined.

2. The method for calculating the properties of Bi surface electrocatalytic reduction of nitrate in an acidic solution environment according to claim 1, characterized in that: In the step A), a Bi(012) surface supercell is constructed, and the specific steps are as follows: Cut the metal Bi primitive cell along the 012 plane, build two Bi atomic layers, each with 12 Bi atoms, and add A vacuum layer is formed to form a three-dimensional surface structure, and the side of the Bi atomic layer far from the vacuum layer is fixed to simulate the Bi metal solid part, and the side close to the vacuum layer is allowed to relax to study the surface characteristics.

3. The method for calculating the properties of electrocatalytic reduction of nitrate on Bi surface in an acidic solution environment according to claim 1, characterized in that: In the step A), above the supercell Water molecules and hydronium ions are set at the positions.

4. The method for calculating the properties of Bi surface electrocatalytic reduction of nitrate in an acidic solution environment according to claim 1, characterized in that: In the molecular dynamics simulation in step B), the convergence accuracy of energy and self-consistent field used is 10 -–5 eV, the maximum force acting on each atom is The plane wave cutoff energy was set to 400 eV, the Brillouin zone k-point was 1 × 1 × 1, the simulation time was set to 8–12 ps, the simulation step was 0.4–0.6 fs, and a structure was acquired every 1–2 ps; In the structural optimization process in step B), the convergence accuracy of energy and self-consistent field used is 10 -–5 eV, the maximum force acting on each atom is The plane wave cutoff energy is set to 400 eV, and the Brillouin zone k-point is 3 × 3 × 1.

5. The method for calculating the properties of electrocatalytic reduction of nitrate by Bi surface in an acidic solution environment according to claim 1, characterized in that: The reaction intermediate in step C) includes *NO3, *NO3H, *NO2, *NO2H, *NO, *NHO, *NHOH, *NH2OH or *NH2.

6. The method for calculating the properties of electrocatalytic reduction of nitrate by Bi surface in an acidic solution environment according to claim 1, characterized in that: In the structural optimization process in step D), the convergence accuracy of energy and self-consistent field used is 10 -–5 eV, the maximum force acting on each atom is The plane wave cutoff energy is set to 400 eV, and the Brillouin zone k-point is 3 × 3 × 1.

7. The method for calculating the properties of Bi surface electrocatalytic reduction of nitrate in an acidic solution environment according to claim 1, characterized in that: In the step D), the adsorption energy E ads According to formula I, we can calculate: E ads = G ads - G slab - G gas Formula I; In Formula I, G ads is the adsorption energy of the reaction intermediate, G slab is the total energy without the introduction of reaction intermediates, G gas is the energy of the gaseous unadsorbed reaction intermediate.

8. The method for calculating the properties of electrocatalytic reduction of nitrate by Bi surface in an acidic solution environment according to claim 1, characterized in that: In the step D), the elementary reaction energy barrier G of the reaction intermediate a According to formula II, we can calculate: G a = ΔEDFT(TS - IS) + ΔEZPE(TS - IS) + TΔS(TS - IS); Equation II In formula II, ΔEDFT(TS-IS) is the first-principles calculated energy difference between the reaction transition state and the reaction initial state, ΔE ZPE (TS-IS) is the zero-point energy difference between the reaction transition state and the reaction initial state, T is the simulation temperature, and ΔS(TS-IS) is the entropy difference between the reaction transition state and the reaction initial state.

9. The method for calculating the properties of electrocatalytic reduction of nitrate on Bi surface in an acidic solution environment according to claim 1, characterized in that: In the step D), the elementary reaction free energy ΔG of the reaction intermediate is calculated according to formula III: ΔG = ΔE DFT (FS-IS) + ΔE ZPE (FS-IS) + TΔS(FS-IS), Equation III In formula III, ΔEDFT (=FS-IS) is the first principles energy difference between the final state and the initial state of the reaction, ΔE ZPE (FS-IS) is the zero-point energy difference between the final state and the initial state of the reaction, T is the simulation temperature, and ΔS(FS-IS) is the entropy difference between the final state and the initial state of the reaction.

10. The method for calculating the properties of electrocatalytic reduction of nitrate on Bi surface in an acidic solution environment according to claim 1, characterized in that: In the step D), the charge distribution is obtained by the bader charge analysis program.

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