A method for screening a high-stability double-layer FeNC graphene ORR catalyst

Abstract

The present application belongs to the field of electrochemical oxygen reduction (ORR) catalysis technology, and provides a method for screening high-stability double-layer FeNC graphene ORR catalysts, and the main idea is to solve the problems of poor stability and activity decay of single-layer FeNC catalysts in the oxygen reduction reaction, and the main scheme comprises the following steps: constructing a series of double-layer FeNC graphene catalysts bridged by non-metallic X; according to density functional theory (DFT) calculation, the influence of the bridging non-metallic element X in the fifth coordination environment on the thermodynamic stability and ORR catalytic activity of the FeNC-X-FeNC catalyst is explored; the electrochemical stability of the active site of the FeNC-X-FeNC catalyst in the ORR catalysis process is analyzed; finally, the FeNC-X-FeNC catalyst with the highest electrochemical stability and activity is screened out. The present application can provide a theoretical basis for designing and synthesizing high-stability carbon-based ORR catalysts with accurate atomic structure, greatly save practical resources, and improve the design efficiency of the catalyst.

Description

Technical Field

[0001] This invention belongs to the field of electrochemical oxygen reduction catalysis technology, specifically, it relates to a method for screening highly stable bilayer FeNC graphene ORR catalysts. Background Technology

[0002] Non-precious metal-doped carbon-based materials are considered the most promising non-precious metal catalysts for ORR (Organic Reduction) due to their low cost, good conductivity, and high specific surface area. With further research, the initial ORR activity of carbon-based catalysts, represented by monolayer FeNC, has approached that of Pt. However, under operating conditions, compared to Pt, the activity of doped carbon-based catalysts declines sharply within the first 20 hours, with an activity reduction exceeding 50%. Therefore, the stability and durability of carbon-based catalysts under operating conditions hinder their further application in fuel cells.

[0003] The stability issues of monolayer FeNC catalysts mainly include: resistive losses generated in the catalyst layer, micropore blockage or flooding; carbon oxidation corrosion, demetallization, and protonation of N groups in the catalyst substrate and active sites. However, the main and key underlying causes of their deactivation are not yet unified; stability adjustment measures for this type of catalyst remain in the trial-and-error stage. Given the challenges of cumbersome procedures, long experimental cycles, and high manpower and material consumption in experimental catalyst synthesis, phase characterization, and electrochemical catalytic performance testing, it is essential to invent an efficient, rapid, and comprehensive method for screening highly stable FeNC catalysts.

[0004] Density functional theory, after years of development, has become an important tool and method for low-cost theoretical prediction and efficient screening, and has been widely used in the field of electrochemical oxygen reduction catalysis. Based on this theoretical foundation, this invention proposes a method for screening highly stable bilayer FeNC graphene ORR catalysts, providing a theoretical basis for designing and synthesizing highly stable carbon-based ORR catalysts with precise atomic structures, significantly saving practical resources and improving catalyst design efficiency. Summary of the Invention

[0005] This scheme aims to screen out highly stable bilayer FeNC graphene ORR catalysts through density functional theory calculations and electrochemical stability assessments, thereby solving the problems of poor stability and activity decay of monolayer FeNC catalysts in the oxygen reduction reaction and providing more efficient catalysts for fuel cells.

[0006] To achieve the above objectives, the present invention employs the following technical means:

[0007] The present invention relates to a method for screening highly stable bilayer FeNC graphene ORR catalysts, comprising the following steps:

[0008] S1. Establish a series of non-metallic X-bridged bilayer FeNC graphene catalysts FeNC-X-FeNC;

[0009] Furthermore, step 1 includes the following steps:

[0010] S1.1 The constructed bilayer FeNC graphene periodic plate model, with a vacuum layer thickness of [value missing], is shown.

[0011] S1.2. Using non-metallic single atoms X from the second and third periods, where X is any one of B, C, N, O, F, P, S, or Cl, occupying the fifth coordination of Fe and acting as an intermediate bridging atom, eight FeNC-X-FeNC models are obtained.

[0012] S2. Based on density functional theory, optimize eight FeNC-X-FeNC models and calculate their binding energy E. binding and formation energy E fonmtion Energy histograms of the two catalysts were plotted to evaluate the thermodynamic stability of the FeNC-X-FeNC catalyst.

[0013] Furthermore, step 2 includes the following steps:

[0014] S2.1 Density functional theory calculations were performed using the VASP (Vienna Ab initio Simulation Package) software package, with PAW used to describe the interaction between the ion nucleus and valence electrons, and GGA-PBE used to calculate the exchange correlation energy between electrons; the DFT+U method was used to describe the d-electron correlation of Fe; structural optimization, energy, and electronic structure calculations were performed, with the force and energy values ​​converging to... and 10 -5 eV; the Monkhorst-Pack K-point grid is set to 2×2×1, the cutoff energy is set to 500 eV, and all atoms remain relaxed during structure optimization. Considering the effects of solvation and weak intermolecular interactions during intermediate adsorption, the implicit solvation model is simulated using VASP sol, and dispersion correction is performed using the DFT-D3 method.

[0015] S2.2 Calculations are performed using the above parameters, based on the binding energy E. binding and formation energy E formation The calculation formula is used to calculate E for all pre-screened models. binding and E formtion The thermodynamic stability is assessed using the following formula:

[0016] E formation =E FeNC-X-FeNC -lμ Fe-mμ N -nμ C -μ X

[0017] E binding =E FeNC-X-FeNC -E FeNC-FeNC -E X

[0018] Where E FeNC-X-FeNC The total energy of the nonmetallic X-bridged bilayer FeNC graphene (FeNC-X-FeNC); μ Fe μ N μ C μ X , respectively, represent the chemical potentials of Fe, N, C, and X atoms, obtained from the bulk phases of their most stable elements; l, m, and n represent the number of Fe, N, and C atoms, respectively; E FeNC-FeNC E represents the total energy of the bilayer FeNC graphene (FeNC-FeNC). X This represents the energy of a nonmetallic single atom.

[0019] According to E binding <0eV and E formation <0 eV was used to assess the stability of the FeNC-X-FeNC catalyst.

[0020] S3. Based on the ORR 4e- combined mechanism, calculate the Gibbs free energy and theoretical overpotential of ORR catalyzed by Fe sites on the FeNC-X-FeNC catalyst surface. The specific formulas are as follows:

[0021] ΔG=ΔE-TΔS+ΔE ZPE

[0022] Where ΔE is the adsorption energy of the group or molecule on the structure; T is the temperature; ΔS is the entropy change before and after the reaction; and ΔE ZPE This represents the difference in zero-point energy before and after the reaction.

[0023] Based on the calculated ΔG value, ORR free energy diagrams of different FeNC-X-FeNC catalysts at a potential of U = 1.23V were plotted to obtain the corresponding theoretical overpotentials, evaluate their ORR catalytic activity, and screen out the three FeNC-X-FeNC catalysts with the most catalytic activity.

[0024] S4. Based on the three selected FeNC-X-FeNC catalysts, calculate the tradeoff potential for the ORR process catalyzed by Fe active sites.

[0025] Furthermore, step 4 includes the following steps:

[0026] S4.1 Comparing the ORR 4e- combination mechanism and the Fe active site oxidation (FeOR) mechanism, it was found that the key intermediate species *OH in ORR can directly serve as the key intermediate in the competitive relationship between ORR and FeOR.

[0027] S4.2 Gibbs free energy change ΔG of the competing ORR and FeOR steps ORR and ΔG FeOR That is, when At this time, a tradeoff potential can be obtained. value, To assess the antioxidant capacity of Fe active sites, the FeNC-X-FeNC catalyst with the highest electrochemical stability was screened.

[0028] In summary, the progressive screening in steps S2-S4 narrows down the range of research samples, quickly and accurately identifies the required model, and obtains a highly stable FeNC model for the ORR catalyst, providing theoretical guidance for the experimental design.

[0029] Because the present invention employs the above-mentioned technical means, it has the following beneficial effects:

[0030] I. Current technology can only synthesize bilayer FeNC-O-FeNC structures. This invention overcomes the technical problem of synthesizing other FeNC-X-FeNC structures due to experimental reagents and conditions by using theoretical simulation. As a result, a series of FeNC-X-FeNC structures doped with other heteroatoms were obtained. Density functional theory calculations were used to screen the stability and activity of the structures, which greatly reduces the time and resources required for subsequent catalyst preparation and practical research screening.

[0031] II. This invention simulates the ORR process of electrocatalysis with different structures, explores the competitive relationship between the electrochemical catalytic activity and stability of FeNC-X-FeNC catalysts in this process, and proposes that the potential can be used to balance the process. This is a method to further determine the electrochemical stability of the catalyst. Among them, The introduction of this concept provides a simpler and faster theoretical guide for screening the electrocatalytic stability of similar catalysts, further saving practical costs.

[0032] Third, compared with existing single-layer FeNC, the bilayer FeNC catalyst structure constructed in this invention can not only improve the ORR catalytic activity of FeNC materials, but also further improve their electrochemical stability. Attached Figure Description

[0033] Figure 1 This is a flowchart of the present invention.

[0034] Figure 2The diagrams show the eight constructed FeNC-X-FeNC structures (top is a side view, bottom is a top view). Gray, dark blue, and purple represent C, N, and Fe atoms, respectively; pink, red, light blue, light purple, yellow, and light green represent B, O, F, P, S, and Cl atoms, respectively.

[0035] Figure 3 The graph shows the calculated thermodynamic stability data for eight FeNC-X-FeNC structures.

[0036] Figure 4 The free energy diagrams are for the ORR 4e- process catalyzed by eight FeNC-X-FeNC catalysts under the condition of U = 1.23 V.

[0037] Figure 5 In the table, (a) represents the tradeoff potential of FeNC-B-FeNC; and (b) represents the Gibbs free energy of the ORR mechanism and the FeOR mechanism under the condition of U = 0.90 V.

[0038] Figure 6 In the table, (a) represents the tradeoff potential of FeNC-C-FeNC; and (b) represents the Gibbs free energy of the ORR mechanism and the FeOR mechanism under the condition of U = 0.90 V.

[0039] Figure 7 In the table, (a) represents the tradeoff potential of FeNC-O-FeNC; and (b) represents the Gibbs free energy of the ORR mechanism and the FeOR mechanism under the condition that U = 0.90V. Detailed Implementation

[0040] The embodiments of the present invention will be described in detail below. Although the present invention will be described and illustrated in conjunction with some specific embodiments, it should be noted that the present invention is not limited to these embodiments. On the contrary, any modifications or equivalent substitutions made to the present invention should be covered within the scope of the claims of the present invention.

[0041] Furthermore, to better illustrate the present invention, numerous specific details are set forth in the following detailed embodiments. Those skilled in the art will understand that the present invention can be practiced without these specific details.

[0042] The purpose of this invention is to address the problems of poor stability in monolayer FeNC catalysts and the time-consuming and laborious process of experimentally adjusting the stability of FeNC catalysts due to a lack of theoretical guidance. Based on this, this invention explores the influence of dopant species X on the stability and ORR catalytic activity of FeNC-X-FeNC catalysts, evaluates and predicts the electrochemical stability of Fe active sites in FeNC-X-FeNC catalysts with different X elements during the ORR catalytic process, and screens out the FeNC-X-FeNC catalyst with the highest electrochemical stability and activity. This provides theoretical guidance for subsequent experimental research and saves practical costs.

[0043] The present invention will now be described in further detail with reference to the accompanying drawings and specific embodiments:

[0044] Please see Figure 1 , Figure 1 This is a schematic flowchart of a method for screening highly stable bilayer FeNC graphene ORR catalysts provided by an embodiment of the present invention: First, eight non-metallic X (B, C, N, O, F, P, S, Cl) bridged bilayer FeNC graphene catalysts are established; second, the thermodynamic stability of the FeNC-X-FeNC catalysts is investigated; next, the three catalysts with the most oxygen reduction catalytic activity are screened; finally, by investigating the competition mechanism between ORR and FeOR at the Fe active sites of the FeNC-X-FeNC catalyst, a tradeoff potential is used. To further screen for catalysts with the best electrochemical stability and activity.

[0045] All calculations related to the FeNC-X-FeNC catalysts in the embodiments of this invention were simulated using density functional theory.

[0046] First, a 6×6 bilayer FeNC graphene periodic slab model was constructed. By utilizing the non-metallic single atoms X in the second and third periods occupying the fifth coordination position of Fe and acting as intermediate bridging atoms, bilayer FeNC graphene with FeNC-X active units was obtained. Figure 2 As shown, the catalyst is represented as FeNC-X-FeNC, where X is any one of B, C, N, O, F, P, S, and Cl, and the vacuum layer is... In order to eliminate the effects of mirroring.

[0047] To assess the thermodynamic stability of the catalyst, the binding energy formula E was used. binding =E FeNC-X-FeNC -E FeNC-FeNC -E X And the formula for calculating the formation energy E formation =E FeNC-X-FeNC -lμ Fe -mμ N -nμ C-μ X E binding and E formation Value. Plot as follows Figure 3 The comparison diagram shows the E values ​​of nonmetallic elements in all configurations. binding All values ​​are negative (-2.71 to -7.08 eV), indicating that thermodynamically, all eight FeNC-X-FeNC catalyst structures are thermodynamically stable, primarily due to the fact that the radii of all non-metallic atoms are smaller than the interlayer spacing of the FeNC bilayer. Furthermore, the E values ​​of the second-period non-metallic (C, N, O, F) bridging FeNC-X-FeNC are also negative. binding The values ​​are all approximately -2.0 eV lower than those of third-period nonmetals (P, S, Cl), indicating that the bridging stability of second-period nonmetals is stronger than that of third-period nonmetals. This may be due to the fact that atoms in the same group of second-period atoms have smaller atomic radii and greater electronegativity than atoms in the third-period atoms, which is more conducive to enhancing the interaction between X and Fe active sites. Compare E fotmation The data shows that the formation energies of C, O, F, and Cl are less than -1 eV, indicating that they can be easily prepared even when the most stable element is used as the nonmetal source. Other nonmetals, such as B, N, P, and S, require the selection of substances with higher chemical potentials as nonmetal sources for easy preparation.

[0048] Secondly, to evaluate the ORR catalytic activity of the eight FeNC-X-FeNC catalysts, a plot was drawn with the intermediate species (*+O2→*OOH→*O→*OH→*+OH) in the ORR 4e- combination mechanism as the x-axis and the reaction energy of each elementary reaction as the y-axis. Figure 4 ORR 4e shown - The combined mechanistic free energy diagram is shown, along with the theoretical overpotential values ​​for each catalyst. ORR 4e⁻ of FeNC-C-FeNC is also presented. - The rate-determining step in the combined mechanism is the formation of OOH, with a theoretical overpotential η of 0.43 V. For the other FeNC-X-FeNC configurations, the rate-determining step is the desorption of OH, with theoretical overpotentials η ranging from 0.30 to 1.41 V. Among these, FeNC-S-FeNC exhibits the worst ORR 4e- activity, with a theoretical overpotential of 1.41 V. FeNC-B-FeNC shows the best ORR activity, with a theoretical overpotential as low as 0.3 V. Compared to FeNC monolayer graphene (η = 1.06 V), the activity of FeNC-S-FeNC is reduced, and the FeNC-X-FeNC (X = F, Cl, P) catalyst has a relatively small modulatory effect on ORR activity. Only in the FeNC-X-FeNC (X = B, C, N, O) catalyst does the Fe active site weaken the adsorption strength of the intermediate oxygen species in ORR, lowering its theoretical overpotential and enhancing ORR activity. Compared with the theoretical overpotential of 0.45V for Pt, the activity of FeNC-X-FeNC (X = B, C, O) is close to or even better than that of Pt.

[0049] Therefore, based on the catalyst's thermodynamic stability and theoretical activity, FeNC-X-FeNC (X = B, C, O) was preliminarily screened and found to not only have good thermodynamic structural stability but also superior ORR theoretical catalytic activity.

[0050] To evaluate the electrochemical stability of the FeNC-X-FeNC (X = B, C, O) catalyst, we first calculated the trade-off potential for the ORR process catalyzed by the Fe active sites. Figure 5 a, Figure 6 a, Figure 7 Figure a shows the three catalysts. The values ​​were 1.68V, 2.17V, and 1.48V, respectively, all higher than the ORR equilibrium potential of 1.23V. This indicates that in the ORR potential range, the ORR process mainly occurs, and the oxidation and occupation of Fe active sites are difficult to occur. The increasing order of O, B, and C indicates that the Fe active sites in the FeNC-C-FeNC catalyst are the most difficult to oxidize, exhibiting the best electrochemical stability. This conclusion can serve as a simple descriptor to guide experimental research, synthesize stable catalysts, and improve the stability of FeNC carbon-based catalysts.

[0051] To further investigate the electrochemical stability mechanism of the three catalysts, a plot was created with the reaction energy of each elementary reaction as the ordinate and the intermediate species of each reaction as the abscissa, as shown below. Figure 5 b, Figure 6 b and Figure 7 As shown in Figure b, the ORR half-wave potential U RHE Gibbs free energy diagrams for the ORR and Fe oxidation (FeOR) reaction mechanisms at 0.90V. The optimized configurations of the intermediate species in the ORR and FeOR processes can be seen in the diagram.

[0052] Taking the FeNC-C-FeNC catalyst with the best antioxidant performance as an example, such as Figure 6 As shown in Figure b, the formation of Fe*OOH from the Fe active site in ORR faces three branching paths: ① ORR 4e - The path involves the breaking of OO bonds to form stable Fe*OH; ②ORR 2e - The pathway involves protonation to generate H2O2; ③ Excessive asymmetric oxidation of Fe active sites, with *OOH rearrangement to generate Fe*O(*OH). Comparing the energy changes of each reaction reveals that the Gibbs free energy change of excessive asymmetric oxidation of Fe active sites is as high as 1.83 eV, meaning it cannot occur at this reaction potential; ORR 2e - The Gibbs free energy for the formation of H₂O₂ becomes 0.31 eV; ORR₄e -The formation of Fe*OH during the process results in a Gibbs free energy of -0.77 eV, indicating a preference for the ORR 4e - The process is spontaneous. After the *OH is adsorbed and stabilized at the Fe active sites, it also faces the desorption of *OH and further excessive asymmetric adsorption and oxidation to form Fe(*OH)2. This process has a Gibbs free energy of approximately 2.31 eV, which is thermodynamically difficult to occur. Therefore, *OH will spontaneously desorb and release Fe active sites, which is beneficial to ORR 4e - The process continues.

[0053] Furthermore, the electrochemical stability mechanism of FeNC-B-FeNC catalysts, Figure 5 As shown in b, ORR 4e - All elementary steps in the process have Gibbs free energy changes less than 0, indicating they are all spontaneous processes; the Gibbs free energy change for the ORR 2e- process is 0.54 eV; however, in the excessive asymmetric oxidation of Fe active sites, the Fe*O(*OH) structure cannot exist stably, and the Gibbs free energy change for the formation of Fe*(OH)2 is still as high as 1.52 eV. Therefore, it can be concluded that the FeNC-B-FeNC catalyst can promote the ORR 4e- process. - Simultaneously, it inhibits excessive asymmetric oxidation of Fe active sites.

[0054] Electrochemical stability mechanism of FeNC-O-FeNC catalyst Figure 7 As shown in Figure b, although the elementary steps of ORR 4e- remain the most likely pathway, the Gibbs free energy change for *OOH rearrangement to generate Fe*O(*OH) is only 0.12 eV. Simultaneously, the Fe active sites in the Fe*O(*OH) and *Fe(OH)2 configurations undergo bond breaking with the bridging O. This indicates that the FeNC-O-FeNC catalyst has poor stability, leading to unavoidable excessive asymmetric oxidation of the Fe active sites.

[0055] In summary, considering the trade-off potential The values ​​and the competitive reaction mechanism between ORR and FeOR confirm that FeNC-C-FeNC can maximally avoid excessive asymmetric oxidation of Fe active sites, inhibit the occupation and dissolution of Fe active sites, while still exhibiting high catalytic ORR 4e - Activity. This conclusion can serve as direct evidence to guide experimental research, synthesize stable bilayer graphene catalysts, and improve the stability of FeNC carbon-based catalysts.

[0056] Furthermore, the tradeoff potential used in this invention to describe the electrocatalytic stability of the ORR catalyst It can be applied to other metal nitrogen-carbon materials besides the doped catalysts studied in this invention, by... Numerical prediction of electrocatalytic stability saves time required to simulate the entire competitive process of ORR and FeOR, allows for faster screening of suitable catalysts, provides theoretical guidance for experimental research, avoids waste of materials and time costs in the experimental process, and helps improve scientific research efficiency.

Claims

1. A method for screening highly stable bilayer FeNC graphene ORR catalysts, characterized in that, Includes the following steps: Step S1: Construct a series of non-metallic X-bridged bilayer FeNC graphene catalysts FeNC-X-FeNC, wherein X is any one of B, C, N, O, F, P, S, and Cl; Step S2: Based on density functional theory, optimize eight FeNC-X-FeNC models and calculate their binding energy E. binding and formation energy E formation To evaluate the thermodynamic stability of FeNC-X-FeNC catalysts; Step S3, based on ORR 4e - By combining the mechanism, the Gibbs free energy and theoretical overpotential of the Fe sites on the surface of the FeNC-X-FeNC catalyst for ORR were calculated, the ORR catalytic activity of different FeNC-X-FeNC catalysts was evaluated, and the three FeNC-X-FeNC catalysts with the most catalytic activity were screened. Step S4: Based on the three selected FeNC-X-FeNC catalysts, the tradeoff potential of the ORR process catalyzed by Fe active sites is calculated. The FeNC-X-FeNC catalyst with the best electrochemical stability was screened, and finally, the FeNC-X-FeNC catalyst with the best electrochemical stability and activity was obtained. Calculate the tradeoff potential for the Fe-active-site catalytic ORR process The specific steps include: According to ORR 4e - By combining the combined mechanism and the Fe active site oxidation mechanism, the key intermediate species *OH in ORR was found to directly act as a key intermediate in the competitive relationship between ORR and FeOR. Combined ORR 4e - Gibbs free energy change in the competing steps with FeOR and That is, when At that time, the tradeoff potential is obtained. value, V was used to evaluate the antioxidant capacity of Fe active sites and screen for the most electrochemically stable FeNC-X-FeNC catalyst.

2. The method for screening highly stable bilayer FeNC graphene ORR catalysts as described in claim 1, characterized in that, A 6×6 bilayer FeNC graphene periodic plate model was constructed, with a vacuum layer thickness of 18 Å. Using non-metallic single atoms X from the second and third periods (X can be any one of B, C, N, O, F, P, S, or Cl), which occupy the fifth coordination of Fe and act as intermediate bridging atoms, eight FeNC-X-FeNC models were obtained.

3. The method for screening highly stable bilayer FeNC graphene ORR catalysts as described in claim 1, characterized in that, The density functional theory described in step S2 was performed in the VASP software package, and PAW was used to describe the interaction between the ion nucleus and the valence electrons, and GGA-PBE was used to calculate the exchange correlation energy between electrons. The key parameters are as follows: The d-electron correlation of Fe is described using the DFT+U method; structural optimization, energy, and electronic structure calculations are performed, with the force and energy converging to 0.02 eV / Å and 10 eV / Å, respectively. -5 eV; the Monkhorst-Pack K-point grid was set to 2×2×1, the cutoff energy was set to 500 eV, and all atoms remained relaxed during structure optimization; VASPsol was used to simulate implicit solvation during calculation, and the DFT-D3 method was used for dispersion correction. Using the above calculation parameters, based on the binding energy E binding and formation energy E formation The calculation formula is used to calculate E for all pre-screened models. binding and E formation The thermodynamic stability is assessed using the following formula: in The total energy of the nonmetallic X-bridged bilayer FeNC graphene FeNC-X-FeNC; The chemical potentials of Fe, N, C, and X atoms are obtained from the bulk phases of their respective most stable elements; These represent the number of Fe, N, and C atoms, respectively. The total energy of the bilayer FeNC graphene FeNC-FeNC; Energy representing a nonmetallic single atom; According to E binding < 0 eV and E formation < 0 eV was used to assess the thermodynamic stability of the FeNC-X-FeNC catalyst.

4. The method for screening highly stable bilayer FeNC graphene ORR catalysts as described in claim 1, characterized in that, Based on ORR 4e - The combined mechanism was used to calculate the Gibbs free energy ΔG and theoretical overpotential of ORR catalyzed by Fe sites on the FeNC-X-FeNC catalyst surface. The specific steps included: ΔG=ΔE-TΔS+ΔE ZPE Where ΔE is the adsorption energy of the group or molecule on the structure; T is the temperature; ΔS is the entropy change before and after the reaction; and ΔE ZPE This represents the difference in zero-point energy before and after the reaction; Based on the calculated ΔG value, ORR free energy diagrams of different FeNC-X-FeNC catalysts at a potential of U=1.23 V were plotted to obtain the corresponding theoretical overpotentials, and the three FeNC-X-FeNC catalysts with the most catalytic activity were screened out.

Images