A Design Method for a Single-Atom Alloy Electrocatalyst for Carbon Dioxide Reduction

Abstract

The present invention discloses a design method for a single-atom alloy electrocatalyst for reducing carbon dioxide, belonging to the fields of chemistry and materials. The present invention aims to solve the problem that a large number of trial-and-error experiments will result in high time and cost. The present invention combines first-principles calculations, uses the formation energy as the basis for judging the thermodynamic stability of materials, and the dissolution potential as the basis for judging the electrochemical environmental stability, and screens out single-atom alloy materials with high stability. Then, the first-principles calculation method is used to study the electrocatalytic reduction performance of single-atom alloy materials that meet the stability criteria, and catalysts with high selectivity for carbon dioxide reduction and inhibition of hydrogen evolution reaction are screened out. The present invention provides direct theoretical guidance for experimental research. Compared with manual experiments, it improves the screening speed and avoids the energy, time and cost losses caused by a large number of trial-and-error experiments.

Description

Technical Field

[0001] The present invention belongs to the fields of chemistry and materials, and more specifically, relates to a design method of a single-atom alloy electrocatalyst with catalytic activity for carbon dioxide reduction reaction based on first principles. Background Art

[0002] Methane is an important fuel and industrial raw material, widely used in fields such as medicine, chemical industry, energy, and military industry. At present, industrial synthesis of methane still uses the method of coal-based syngas methanation, which is carried out in a vaporizer, requires high process requirements, consumes too much in terms of economic and time costs, and it is difficult to reveal the reaction characteristics. Using an electrochemical method to catalytically reduce carbon dioxide to synthesize methane in an electrochemical environment has the advantages of being green, clean, low energy consumption, and easy to control, and has become one of the potential industrial preparation methods to replace the coal-based methane synthesis method. However, when existing electrocatalysts catalytically reduce carbon dioxide, due to the limitations of the inherent properties of the catalyst material and the influence of competitive side reactions, there are problems such as low selectivity, high cost of noble metal materials, and low Faraday efficiency, and it still cannot meet the requirements of industrial methane production. Therefore, the development of electrocatalysts for carbon dioxide reduction reaction with high stability and high selectivity has been a research hotspot in recent years.

[0003] Single-atom catalysts take into account the high selectivity of the main component material and the high activity of the secondary component material, showing unique properties different from traditional alloys, having high selectivity, high atomic utilization rate, and adjustable high activity, and showing high potential for electrocatalytic reduction of carbon dioxide. Transition metals with rich d electrons have high electrical conductivity and high selectivity for carbon dioxide products, and play a role in electrocatalytic reduction of carbon dioxide. By bonding two metals, another transition metal atom can be anchored on the surface of the host metal to form a series of electrocatalysts with isolated metal atoms and an inert metal surface. These bimetallic single-atom catalysts have specific exposed active sites and are one of the promising materials for electrocatalytic reduction of carbon dioxide. However, it is difficult to determine the reaction conditions during the synthesis and characterization of these catalysts, lacking theoretical guidance, and the catalytic systems are not consistent. A large number of trial-and-error experiments will cause large time and cost costs, bringing certain obstacles in terms of prediction and design. Therefore, it is necessary to develop a single-atom alloy material with efficient electrochemical reduction of carbon dioxide. Summary of the Invention

[0004] Constrained by experimental conditions and costs, the catalytic performance of single-atom alloys mostly follows the scheme of design and preparation → characterization and verification of performance at present, which leads to the lack of systematic theoretical guidance for catalyst design and the inability to predict performance.

[0005] Based on the first-principles simulation method, the present invention develops a method for screening single-atom alloy materials with carbon dioxide reduction performance, providing necessary theoretical guidance for experimental preparation and verification, promoting the research progress of new catalysts, and revealing the catalytic reaction mechanism at the same time.

[0006] Regarding electrocatalytic materials, their stability can reflect the stable cyclicity of catalytic materials. Design single-atom alloy materials with different compositions, and combine first-principles calculations to form a basis for judging the thermodynamic stability of materials and use the dissolution potential as a basis for judging the stability of the electrochemical environment, so as to screen out single-atom alloy materials with high stability. Then, use the first-principles calculation method to study the electrocatalytic carbon dioxide reduction performance of single-atom alloy (SAA) materials that meet the stability criteria, and screen out catalysts that inhibit the hydrogen evolution reaction and have high selectivity for carbon dioxide reduction performance.

[0007] In order to solve the above technical problems, the present invention adopts the following technical solutions:

[0008] The purpose of the present invention is to provide a design method for a single-atom alloy electrocatalyst for reducing carbon dioxide, and the design method is realized through the following steps:

[0009] Construct a single-atom alloy material model, and the model includes various metal types and different embedding sites;

[0010] Optimize the constructed model to obtain structural and energy information;

[0011] Calculate the stability of the single-atom alloy material according to the energy information, specifically including calculating the formation energy ΔE f (α) and the dissolution potential U diss ;

[0012] When U diss >0 and ΔE f (α)<0, calculate the Gibbs free energies ΔG *CO and ΔG *H of carbon monoxide and hydrogen atoms adsorbed on the active sites of the single-atom alloy material, and the active sites are obtained through the structural information;

[0013] When ΔG *CO <0 and ΔG *CO <ΔG *H , calculate the energy E abs of the single-atom alloy material adsorbed with carbon monoxide;

[0014] Select single-atom alloy materials with E abs between -0.8 eV and -0.4 eV for calculating the reaction activity of the single-atom alloy material;

[0015] According to the protonation reaction, construct the intermediate and optimize the calculation of Gibbs free energy of each step to determine the potential-determining step;

[0016] The low potential of the decisive step is selected as a single atom alloy catalyst for the reduction of carbon dioxide.

[0017] To further define, Materials Studio software was used to import the Materials project structure library to build a single-atom alloy material model, which contained a variety of metal types and different embedding sites, and the corresponding CIF files were exported. The CIF files were then converted into the POSCAR files required for calculations using VASP software.

[0018] Further definition, set the input files required for the calculation, and then optimize the geometric structures of various single-atom alloy materials to obtain the corresponding CONTCAR and OUTCAR files, and then use VESTA and VASP software to obtain the structure and energy information.

[0019] It is further defined that the input file includes POSCAR, INCAR, KPOINTS, POTCAR and script at the same time.

[0020] Further, the formation energy ΔE is calculated based on the energy information using the following formula: f (α):

[0021] ΔE f (α) = E M’@M-slab –E M-slab +n M E M –n M’ E M’

[0022] Among them, E M’@M-slab : The energy of the single-atom alloy material as a whole, E M-slab : Energy of undoped pure metal material, E M and E M’ : The energy of each metal atom in the bulk, all energies are in eV, potential units are V, M: original surface metal atom, M': doped single atom M', ΔE f α in (α): doping atom M'.

[0023] If ΔE f (α)<0, the metal single atom alloy material is stable, ΔE f (α)>0 indicates that atomic doping is difficult and the possibility of forming such a material is low thermodynamically.

[0024] Further defined, according to the energy information, the dissolution potential U is calculated using the following formula: diss :

[0025]

[0026] Among them, The standard electrode potential of the doped atom, E f : The formation energy of the single-atom alloy material, and the unit of all energies is eV, the unit of potential is V, M: metal single atom, ne: the number of electrons transferred during the dissolution process.

[0027] If U diss > 0 indicates that the single-atom alloy material is stable in the electrochemical environment. Conversely, U diss < 0 indicates that the single-atom alloy is unstable in the electrochemical environment.

[0028] Furthermore, it is defined that ΔG *CO = ΔE + ΔE ZPE – TΔS, where ΔE: the energy difference of carbon monoxide adsorption, ΔE ZPE : the zero-point energy difference, T: the temperature 298.15K.

[0029] Furthermore, it is defined that ΔG *H = ΔE + ΔE ZPE – TΔS, where ΔE: the energy difference of hydrogen atom adsorption, ΔE ZPE : the zero-point energy difference, T: the temperature 298.15K.

[0030] ΔG *CO > 0 or ΔG *CO > ΔG *H , then the single-atom alloy material is abandoned; ΔG *CO < 0 and ΔG *CO < ΔG *H , then carbon monoxide can be chemically adsorbed on the single-atom material and has a high selectivity for carbon monoxide adsorption.

[0031] Furthermore, it is defined that E abs = E CO-slab - E CO - E slab where E CO-slab : the energy of the single-atom alloy material adsorbing carbon monoxide, E CO : the energy of carbon monoxide, E slab : the energy of the single-atom alloy material.

[0032] If E abs < -0.8eV, the single-atom alloy material has too strong an adsorption ability for carbon monoxide, which will cause the material to be poisoned; if E abs > -0.4eV, it means that the single-atom alloy material is difficult to capture carbon monoxide and cannot react further. Select E absPerform the next analysis on the single-atom alloy material between -0.8 eV and -0.4 eV.

[0033] Furthermore, it is defined that the protonation reaction process that overcomes the low Gibbs free energy is the mechanism of the carbon monoxide reduction reaction. Optimize the adsorption states of each intermediate at the doping sites, and calculate the Gibbs free energy change of each step. The step with the largest Gibbs free energy value in all hydrogenation steps is the potential-determining step of this mechanism, and the corresponding one is the determining potential.

[0034] Compared with the prior art, the present invention has the following beneficial effects:

[0035] The present invention provides direct theoretical guidance for experimental research. Compared with manual experiments, it improves the screening speed and avoids the loss of energy, time, and cost caused by a large number of trial-and-error experiments. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] Figure 1 is the design flow chart of the single-atom alloy electrocatalyst for reducing carbon dioxide of the present invention;

[0037] Figure 2 are various single-atom alloy material models;

[0038] Figure 3 is the structural diagram of the mechanism for reducing Zn-based single-atom alloy material to methane. DETAILED DESCRIPTION OF THE INVENTION

[0039] The following further elaborates the present invention in conjunction with specific embodiments. It should be understood that these embodiments are only used to illustrate the present invention and not to limit the scope of the present invention.

[0040] Example 1: The design method of the single-atom zinc alloy electrocatalyst for reducing carbon dioxide in this example is achieved through the following steps:

[0041] ① Construction of the single-atom zinc alloy model

[0042] Use Materials Studio software to import the Materials project structure library to construct a single-atom alloy material model. Cut the primitive cell through the Cleave Surfaces section, click Symmetry-Supercell to expand the cell to obtain the (101) crystal plane containing 80 zinc atoms. Set the Vacuum thickness option in Crystals-BuildVacuum Slab Crystal to 15, and click Build to obtain the vacuum layer model. In the initial structure model, α = β = 90° and γ = 104°. Replace the surface atoms with the target M' atoms, and the single-atom substitution ratio is 0.0125. See the modelFigure 2 , which contains multiple metal species and different embedding sites, export the corresponding CIF file, and combine with the VASP software to convert the CIF file into the POSCAR file required for calculation.

[0043] The M metal is Zn, and the M' metals include Fe, Ru, Os, Co, Rh, Ir, Ni, Pd, Pt, Cu, Ag, Au, V, Mo, Ti, Cr.

[0044] ② Structural optimization of single-atom alloy materials

[0045] Set up the input files required for calculation (the input files contain POSCAR, INCAR, KPOINTS, POTCAR, and scripts at the same time). POTCAR is implemented through the vaspkit-103 section; KPOINTS: Select the K-space grid points in the Gamma grid method to calculate the integral in the Brillouin zone, and the K points are set to 3×3×1. INCAR: The electron-electron interaction is described by the PBE functional under the generalized gradient approximation, the valence band electron wave function uses the projector augmented wave pseudopotential basis set, and the energy convergence criterion is 1×10 -5 eV, and the force convergence does not exceed The cutoff energy is 450 eV, and other parameters are default values. Optimize the geometric structures of various single-atom alloy materials. After the calculation, the corresponding CONTCAR and OUTCAR files are obtained. Use VESTA to import the CONTCAR file to visualize the structure and obtain the structural information, and extract the energy information from the OUTCAR file through VASP calculation.

[0046] Input files, run.sh is the script:

[0047]

[0048]

[0049] Save the structural information:

[0050] $szCONTCAR

[0051] ③ Calculate the stability of single-atom alloy materials

[0052] According to the energy results calculated in step ②, use the following formula to calculate the stability of various single-atom alloy materials. The unit of all energies is eV, and the unit of electric potential is V:

[0053] a. Formation energy: ΔE f (α) = E M’@M-slab –E M-slab +n M E M –n M’ EM’

[0054] E M’@M-slab : The energy of the overall single-atom alloy material

[0055] E M-slab : The energy of the undoped pure metal material

[0056] E M and E M’ : The energy of each metal single atom in the bulk

[0057] If ΔE f (α) < 0, the single-atom alloy material is stable, and ΔE f (α) > 0 indicates that atomic doping is difficult and the possibility of forming this material is small thermodynamically.

[0058] b. Dissolution potential:

[0059] The standard electrode potential of the doped atom

[0060] E f : The formation energy of the single-atom alloy material

[0061] If U diss > 0 indicates that the single-atom alloy material is stable in the electrochemical environment, and conversely U diss < 0 indicates that the single-atom alloy is unstable in the electrochemical environment.

[0062] Table 1 Formation energy (eV) and dissolution potential (V) of single-atom alloy materials

[0063]

[0064]

[0065] From the data in Table 1, U diss > 0 and ΔE f (α) < 0, and Rh@Zn-slab, Ir@Zn-slab, Pd@Zn-slab, Pt@Zn-slab, Cu@Zn-slab, Ag@Zn-slab, Au@Zn-slab have good stability.

[0066] ④ Screening of single-atom alloy materials

[0067] The two constituent materials of the single-atom alloy need to have an adsorption difference for carbon monoxide, and it is known that the host material is conducive to the initial reduction reaction of carbon dioxide to generate carbon monoxide, and the carbon monoxide generated by the host material is captured by the doped atom and further reduced to obtain methane.

[0068] a. Calculate the adsorption Gibbs free energy of carbon monoxide on the surface of the single-atom alloy material. Perform zero-point correction on the optimized adsorption structure, only relax the surface adsorbed substances, set the force convergence to 1×10 -7 eV, and set the ionic step size to Use the finite difference method to calculate the second derivative of the total energy with respect to the ionic positions. After the calculation, perform zero-point correction through the 501 section in vaspkit to obtain the zero-point energy correction value, that is, E ZPE and TΔS. The CONTCAR file visualizes the optimized structure through the VESTA software. The atomic species and position information can be obtained by selecting the atoms through the Select(s) option on the left side of the interface. Carbon monoxide is adsorbed mainly at the top of the carbon atom on the single-atom alloy material. The Gibbs free energy of carbon monoxide and hydrogen atom adsorption at the active site is calculated according to the following formula for the energy values obtained in VASP:

[0069]

[0070] b. The carbon adsorption ability is moderate. Calculate the carbon monoxide adsorption energy of the single-atom alloy material screened in the previous step according to the following formula:

[0071] E abs =E CO-slab -E CO -E slab

[0072] E CO-slab : The energy of the single-atom alloy material adsorbing carbon monoxide

[0073] E CO : The energy of carbon monoxide

[0074] E slab : The energy of the single-atom alloy material

[0075] If E abs <-0.8 eV, the single-atom alloy material has too strong an adsorption ability for carbon monoxide, which will cause the material to be poisoned; if E abs >-0.4 eV, it means that the single-atom alloy material is difficult to capture carbon monoxide and cannot react further. Select the single-atom alloy material with E abs between -0.8 eV and -0.4 eV for the next analysis.

[0076] Table 2 Carbon monoxide adsorption energy, carbon monoxide and hydrogen atom adsorption free energy (eV) of the single-atom alloy material

[0077]

[0078] From the data in Table 2, ΔG *CO <0 and ΔG *CO<ΔG *H ,E abs is between -0.8 eV and -0.4 eV, and Pd@Zn-slab, Pt@Zn-slab, and Cu@Zn-slab have high reaction selectivity and good activity.

[0079] c. According to the mechanism of the carbon monoxide reduction reaction, H is added as a proton-electron coupling for protonation reaction during model construction, and the adsorption states of each intermediate at the doping site are constructed and optimized. The generation of POSCAR and POTCAR and the parameter settings of INCAR and KPOINTS are the same as those in steps ② and ④. The optimized structure is viewed and exported through VESTA to intuitively observe the mechanism path of the CO reduction reaction. The Gibbs free energy change of each step is calculated from the energy calculated by VASP. The step with the largest Gibbs free energy value in all hydrogenation steps is the potential-determining step of this mechanism, and the corresponding is the determining potential. The reaction mechanism and the electrochemical determining potential of this single-atom alloy material provide guidance for experiments.

[0080] Table 3 Gibbs free energy values (ΔG / eV) of each step of the catalyst in different protonation steps

[0081]

[0082]

[0083] ⑤ The structure diagram of the mechanism for the reduction of Zn-based single-atom alloy material to methane is determined, as Figure 3 shown.

Claims

1. A design method for a single-atom alloy electrocatalyst for carbon dioxide reduction, characterized in that, The described design method is achieved through the following steps: Construct a single-atom alloy material model, which includes various metal species and different embedding sites; Optimize the constructed model to obtain structural and energy information; Calculating the stability of single-atom alloy materials based on energy information, specifically including calculating the formation energy ΔE f (α) and the dissolution potential U diss ; When U diss > 0 and ΔE f (α) < 0, calculate the Gibbs free energies ΔG *CO and ΔG *H of carbon monoxide and hydrogen atoms adsorbed on the active sites of the single-atom alloy material, where the active sites are obtained from the structural information; When ΔG *CO < 0 and ΔG *CO < ΔG *H The energy E of the single-atom alloy material adsorbed with carbon monoxide abs ; Select E abs Perform reactivity calculations on single-atom alloy materials within the range of -0.8 eV to -0.4 eV; According to the protonation reaction, construct intermediates and optimize and calculate the Gibbs free energy of each step to determine the potential-determining step; Select the one with a lower potential of the determining step as the single-atom alloy catalyst for carbon dioxide reduction; Set the input files required for the calculation, then optimize the geometric structures of various single-atom alloy materials to obtain the corresponding CONTCAR and OUTCAR files, and then use VESTA and VASP software to obtain structural and energy information; Calculate the formation energy ΔE using the following formula based on the energy information f (α): ΔE f (α) = E M’ @M-slab – E M-slab + n M E M – n M’ E M’ Among them, E M’ @M-slab : The energy of the entire single-atom alloy material, E M-slab : The energy of the undoped pure metal material, E M and E M’ : The energy of each metal single atom in the bulk. The unit of all energies is eV, the unit of electric potential is V. M: The original surface metal single atom, M’: Represents the doped single atom, ΔE f In (α), α: The doped atom M’; The M metal is Zn, and the M' metal is selected from Fe, Ru, Os, Co, Rh, Ir, Ni, Pd, Pt, Cu, Ag, Au, V, Mo, Ti, Cr; Dissolution potential U is calculated according to the energy information using the following formula diss :[[-END]] U diss = U – E f / | ne | Among them, U: the standard electrode potential of the doped atom, E f : the formation energy of the single-atom alloy material, and the unit of all energies is eV, the unit of potential is V, M: metal single atom, ne: the number of transferred electrons during the dissolution process; Overcome the protonation reaction process with low Gibbs free energy as the mechanism of the carbon monoxide reduction reaction, construct and optimize the adsorption states of each intermediate at the doping sites, and calculate the change in Gibbs free energy of each step. The step with the largest Gibbs free energy value in all hydrogenation steps is the potential-determining step of this mechanism, and the corresponding one is the determining potential.

2. The design method according to claim 1, characterized in that, Use Materials Studio software to import the Materials project structure library to construct a single-atom alloy material model, which contains various metal species and different embedding sites, export the corresponding CIF file, and combine with VASP software to convert the CIF file into the POSCAR file required for the calculation.

3. The design method according to claim 1, wherein The described input file contains POSCAR, INCAR, KPOINTS, POTCAR, and scripts at the same time.

4. The design method according to claim 1, characterized in that, ΔG *CO = ΔE + ΔE ZPE – TΔS, where ΔE is the energy difference of carbon monoxide adsorption, and ΔE ZPE : is the zero-point energy difference, and T: is the temperature 298.15 K.

5. The design method according to claim 1, characterized in that ΔG *H = ΔE + ΔE ZPE – TΔS, where ΔE: energy difference of hydrogen atom adsorption, ΔE ZPE : zero-point energy difference, T: temperature 298.15 K.

6. The design method according to claim 1, characterized in that E abs = E CO-slab -E CO -E slab , where E CO-slab : the energy of the single-atom alloy material adsorbing carbon monoxide, E CO : the energy of carbon monoxide, E slab : the energy of the single-atom alloy material.

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