CN115966710A

CN115966710A - High-stability iron atom catalyst and preparation method and application thereof

Info

Publication number: CN115966710A
Application number: CN202211336682.4A
Authority: CN
Inventors: 何庭; 张翼; 陈阳
Original assignee: Central South University
Current assignee: Central South University
Priority date: 2022-10-28
Filing date: 2022-10-28
Publication date: 2023-04-14

Abstract

The invention provides a high-stability iron atom catalyst and a preparation method and application thereof, the catalyst is a three-dimensional honeycomb network structure formed by a nitrogen-doped carbon skeleton, the three-dimensional honeycomb network structure also comprises iron monoatomic groups and iron nanoclusters, the iron nanoclusters are loaded in nanopores of the three-dimensional honeycomb network structure, the iron monoatomic groups are combined on the nitrogen-doped carbon skeleton around the iron nanoclusters, gelatin hydrogel is used as a precursor and a template during preparation, and the Fe nanoclusters (NCA/Fe) are loaded near Fe monoatomic sites in the N-doped carbon aerogel through a simple two-step pyrolysis method _SA+NC ). The high-stability iron atom catalyst prepared by the invention has better electrocatalytic activity and stability, NCA/Fe _SA+NC The flexible zinc-air battery assembled with the aerogel as a cathode catalyst shows higher OCV and power density at both room temperature and low temperature, as well as excellent durability.

Description

High-stability iron atom catalyst and preparation method and application thereof

Technical Field

The invention belongs to the technical field of energy storage and conversion, and particularly relates to a high-stability iron atom catalyst, and a preparation method and application thereof.

Background

The electrocatalytic Oxygen Reduction Reaction (ORR) is the cornerstone of renewable energy conversion and storage devices for metal-air batteries, fuel cells, and the like. Although platinum (Pt) -based catalysts exhibit significant ORR performance, the development of non-noble metal catalysts is still imperative for cost and sustainability reasons. Transition metal-nitrogen-carbon (M-N-C) composites are viable alternatives due to their high activity and low cost. Among them, (metal) monoatomic catalysts (SACs) have received a wide attention. For SACs, the electrocatalytic activity of the SACs can be optimized by regulating and controlling the coordination environment of the atomic dispersion level metal sites. In particular, by embedding FeN _x Site-porous carbon derived Fe SACs exhibiting ORR activity and half-wave potential (E) comparable to commercial Pt/C catalysts in basic and acidic media _1/2 ). However, it is well known that carbon-based SACs show significant degradation in long-term electrode reactions, with demetallization, carbon oxidation and carbon corrosion resulting in poor stability, which has been a major obstacle to their practical application.

To alleviate these problems, research has focused primarily on two strategies, increasing graphitization of carbon scaffolds and stabilizing metal active sites. For example, carbon corrosion can be mitigated by incorporating metal sites into graphene or carbon nanotubes. In addition, a second metal atom may be introduced into the Fe SACs to prevent detrimental Fenton reactions. However, while these strategies do improve stability, disadvantages are also evident, such as increased graphitization leading to a reduction in carbon defects, thereby reducing activity; the structural engineering of the metal sites requires tedious operations. Therefore, it is of great importance for practical applications to develop a simple and effective strategy to enhance the stability of SACs while maintaining high activity.

Disclosure of Invention

In order to overcome the technical problem that the activity and the stability of iron monatomic catalysts (Fe SACs) cannot be considered in the prior art, the invention provides a high-stability iron atom catalyst, a preparation method and application thereof.

In order to solve the technical problems, the technical scheme provided by the invention is as follows:

the invention provides a high-stability iron atom catalyst, which is a three-dimensional honeycomb network structure formed by a nitrogen-doped carbon skeleton, wherein the three-dimensional honeycomb network structure also comprises iron monatomic and iron nanoclusters, the iron nanoclusters are loaded in nano holes of the three-dimensional honeycomb network structure, and the iron monatomic is combined on the nitrogen-doped carbon skeleton around the iron nanoclusters.

The high-stability iron atom catalyst has rich pores, and is beneficial to inhibiting metal atoms from excessively aggregating into large nano particles in a high-temperature process.

As an alternative embodiment, the present invention provides a high-stability iron atom catalyst, wherein the diameter of the iron nanocluster is less than 10nm, and the distance between the iron nanocluster and the iron monoatomic atom is less than 2nm.

According to the invention, the diameter of the iron nanocluster is set to be less than 10nm, the size standard of the nanocluster is met, the distance between the iron nanocluster and the iron monoatomic atom is set to be less than 2nm, the effect of the nanocluster is reduced due to the fact that the distance is too large, and the distance between the iron nanocluster and the iron monoatomic atom is calculated according to the distance between the outermost atom of the nanocluster and the iron monoatomic atom.

The second aspect of the present invention provides a method for preparing a high-stability iron atom catalyst, comprising the steps of:

s1, uniformly mixing a carbon source, a pore-foaming agent, an iron salt, a nitrogen source and water according to a mass ratio, and performing low-temperature self-assembly on the mixture after water bath at the temperature of between 55 and 65 ℃ to form hydrogel;

s2, placing the hydrogel prepared in the step S1 in Ar or N ₂ Heating to 400-500 ℃ under the atmosphere for pyrolysis, and etching to remove the pore-forming agent to prepare a semi-finished product;

s3, mixing the semi-finished product prepared in the step S2 with 97% Ar +3% H ₂ Heating to 900-950 ℃ for pyrolysis in the mixed atmosphere to obtain the high-stability iron atom catalyst.

The temperature in step S1 of the present invention is set to 55 to 65 ℃ to facilitate gel formation, and if it is outside this range, no gel can be formed. The pyrolysis in the step S2 at the temperature of 400-500 ℃ and the pyrolysis in the step S3 at the temperature of 900-950 ℃ are both beneficial to carbonization.

As an alternative embodiment, the invention provides a preparation method, wherein the carbon source in step S1 is one of gelatin, chitosan, starch or agar.

As an alternative embodiment, in the preparation method provided by the present invention, the nitrogen source is one of Phenanthroline (PM) or melamine.

As an optional embodiment, in the preparation method provided by the present invention, in step S1, the mass ratio of the carbon source, the pore-forming agent, the iron salt, the nitrogen source, and the water is (15 to 30): (5-12.5): (1-4): (2.97 to 11.9): (0.625-1.25).

As an optional implementation manner, in the preparation method provided by the present invention, the porogen is one of silicon dioxide or aluminum oxide.

As an optional implementation manner, in the preparation method provided by the present invention, the particle size of the silica is 10 to 30nm.

When the particle size of silica is set to more than 30nm, the particle size increases, so that the specific surface area decreases and the number of active sites decreases.

As an optional implementation manner, in the preparation method provided by the present invention, the alumina has a particle size of 10 to 50nm.

As an optional embodiment, in the preparation method provided by the present invention, the iron salt is FeCl ₂ Or Fe (NO) ₃ ) ₂ 。

As an alternative embodiment, the present invention provides the manufacturing method, wherein the temperature rise rate in step S2 and step S3 is 5 to 10 ℃ per minute.

As an optional embodiment, in the preparation method provided by the present invention, the pyrolysis time in step S2 and step S3 is 2 to 3 hours.

As an optional implementation manner, in the preparation method provided by the present invention, in step S2, 0.5 to 1.0M alkali solution is used to etch and remove the porogen at 75 to 85 ℃.

The third aspect of the invention provides the application of the high-stability iron atom catalyst in a flexible zinc-air battery as an air cathode catalyst.

As an alternative embodiment, the invention provides an application that the high-stability iron atom catalyst is used at room temperature or 0 to-40 ℃ when being used as an air cathode catalyst in a flexible zinc-air battery.

Fe-N-C nanocomposites typically contain both durable and non-durable FeN _x A site. In the former, the metal center maintains the valence state of Fe (II) during the electrode reaction; in the latter case, the oxidation state of the metal center is switched between Fe (III) and Fe (II), and is readily converted to iron oxide. This indicates that FeN can be enhanced by preventing the oxidation of Fe (II) to Fe (III) _x Stability of the site. Theoretically, ortho-position electron-rich metal nanoparticles can inhibit FeN through electron transfer _x Oxidation of the site. This electron transfer must be relatively weak in order not to impair ORR activity. Therefore, the invention can improve FeN by introducing adjacent small-size metal nano-clusters _x Stability of (2). Meanwhile, the metal nano cluster has good Oxygen Evolution Reaction (OER) performance, can endow the nano composite material with dual-functional oxygen catalytic activity, and is also a key characteristic of the rechargeable metal-air battery.

Compared with the prior art, the invention has the beneficial effects that:

(1) Aiming at the defect that the activity and the stability of iron single-atom catalysts (Fe SACs) cannot be considered at the same time in the prior art, the invention provides a high-stability iron atom catalyst, which is characterized in that iron nanoclusters are introduced into FeN in N-doped carbon aerogel _x Near the site, high stable iron atom catalyst NCA/Fe is obtained _SA+NC Electrochemical analysis shows that it has good ORR activity and half-wave potential (E) _1/2 ) The temperature is up to +0.92V, and compared with the single-iron-atom catalyst without the iron nanocluster, the stability is obviously improved.

(2) The invention can introduce the iron nano cluster into N doping by a simple two-step pyrolysis methodFeN in carbon aerogel _x Near the site, firstly pyrolyzing the hydrogel at about 500 ℃ for 2-3h to obtain nitrogen-doped carbon aerogel, and then pyrolyzing for 2-3h at about 900 ℃ for the second time to ensure that part of iron atoms which are weakly bonded with the carbon skeleton are in FeN _x The nano clusters are gathered near the sites, and the preparation method is simple and quick.

(3) In the invention, the high-stability iron atom catalyst is used as the cathode catalyst, and the assembled flexible zinc-air battery shows high power density and remarkable durability at room temperature and low temperature (as low as-40 ℃). The invention provides a new idea for the electrocatalytic activity and stability of the M-N-C composite material, and is beneficial to promoting the further development of the electrochemical energy technology.

Drawings

In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below, and it is obvious that the drawings in the following description are some embodiments of the present invention, and for those skilled in the art, other drawings can be obtained according to these drawings without creative efforts.

FIG. 1 is NCA/Fe prepared in example 1 _SA+NC A preparation schematic diagram;

FIG. 2 is the lyophilized G-Si/FePM hydrogel, NCA/Fe prepared in example 1 _SA+NC And NCA/Fe _SA SEM image of (a);

FIG. 3 is the NCA/Fe prepared in example 1 _SA+NC The HAADF-STEM image and the HRTEM image of (A);

FIG. 4 is NCA/Fe prepared in comparative example 1 _SA TEM and HAADF-STEM images of (a);

FIG. 5 is NCA/Fe _SA And NCA/Fe _SA+NC N of (2) ₂ Adsorption-desorption isotherms and pore size distribution, XRD and raman spectroscopy results;

FIG. 6 is NCA/Fe _SA And NCA/Fe _SA+NC The XPS spectrum of (1), fe 3P electron spectrum (Fe (0) 3P, respectively, in the direction of the arrow _3/2 、Fe(Ⅱ)3P _3/2 、Fe(Ⅲ)3P _3/2 Satellite peak, fe (0) 3P _1/2 、Fe(Ⅱ)3P _1/2 、Fe(Ⅲ)3P _1/2 ) And N1s electron spectra (pyridine N, metal N, pyrrole N, graphite N, and N oxide, respectively, in the direction of the arrows);

FIG. 7 is NCA/Fe _SA+NC 、NCA/Fe _SA Normalized Fe k-edge XANES spectra (inset is enlarged absorption edge), fourier transform k for Fe foil and FePc ³ Weighted Fe k-edge EXAFS spectra, NCA/Fe _SA+NC And the EXAFS fitted curve of NCA/FeSA and NCA/Fe _SA+NC And (f) NCA/Fe _SA K-space curves and corresponding fitted curves of (a);

FIG. 8 is NCA/Fe _SA And NCA/Fe _SA+NC Is/are as follows ⁵⁷ Fe

Spectrum and NCA/Fe _SA+NC And NCA/Fe _SA An EPR spectrum of (a); />

FIG. 9 is a simulated optimized constellation diagram for S1, S2 and S3 sites, and a free energy diagram at 0.90V for S1, S2, S3 and S0 sites, a free energy diagram at a limiting potential, and magnetic moments at S1, S2, S3 and S0 sites;

FIG. 10 is a schematic diagram showing the reaction pathway of ORR at the S0 site in FIG. 9;

FIG. 11 is a schematic diagram showing the reaction pathway of ORR at the S1 site in FIG. 9;

FIG. 12 is a schematic diagram showing the reaction pathway of ORR at the S2 site in FIG. 9;

FIG. 13 is a schematic diagram showing the reaction pathway of ORR at the S3 site in FIG. 9;

FIG. 14 is the S2 site of FIG. 9 and its Fe3d (in FeN) ₄ Middle) orbital DOS, DOS of Fe3d electrons at the S1, S2 and S3 sites and DOS of 5 Fe3d orbitals at the S2 position;

FIG. 15 shows the S1, S3 and S0 sites in FIG. 9 and their Fe3d (in FeN) ₄ Middle) DOS of the track; DOS of 5 Fe3d orbitals at S1, S2 and S3 sites;

FIG. 16 is NCA/Fe _SA+NC ，NCA/Fe _SA And ORR polarization curve of commercial Pt/C catalyst at 1600rpm, E _onset 、E _1/2 And J _k Comparative graph of (A), NCA/Fe _SA+NC And NCA/Fe _SA The insets are correspondingEquivalent circuit diagram and NCA/Fe _SA+NC 、NCA/Fe _SA And Tafel curve of Pt/C;

FIG. 17 is at O ₂ Saturated 0.1M KOH, pt/C at different spin rates, (b) NCA/Fe _SA And (C) NCA/Fe _SA+NC The LSV plot of (a);

FIG. 18 is a graph at O ₂ LSV curves at different spin rates in saturated 0.1M KOH and calculated electron transfer number and H ₂ O ₂ Yield results chart;

FIG. 19 is NCA/Fe _SA+NC TEM image and NCA/Fe after acid etching _SA+NC ORR polarization curves before and after acid etching;

FIG. 20 is NCA/Fe _SA+NC And NCA/Fe _SA A graph of the durability test results of (1);

FIG. 21 is NCA/Fe _SA And NCA/Fe _SA+NC Fe 2p XPS spectra before and after the endurance test;

FIG. 22 is NCA/Fe subjected to durability test _SA+NC And NCA/Fe _SA The HRTEM image of (1);

FIG. 23 is NCA/Fe in 1.0M KOH _SA+NC And NCA/Fe _SA The insert shows the Δ E of the two aerogels, b is the Tafel curve, c is NCA/Fe _SA+NC OER polarization curves before and after acid etching (1.0M KOH);

FIG. 24 shows Zn// NCA/Fe _SA+NC ，Zn//NCA/Fe _SA And Zn// Pt/C-RuO ₂ The OCV, power density and constant current discharge curve of the quasi-solid battery and a performance comparison result graph of the flexible zinc-air battery are shown;

FIG. 25 shows Zn// NCA/Fe _SA+NC And Zn// NCA/Fe _SA The current density of the battery is 5mA cm ^-2 Constant current charging and discharging curve of time, zn// NCA/Fe _SA+NC The compression results, repeated bending results and repeated compression experiment results of the battery;

FIG. 26 shows Zn// NCA/Fe _SA+NC OCV of quasi-solid battery at low temperature, power density, constant current discharge curve, low-temperature performance comparison of flexible zinc-air battery and current density of 5mA cm ^-2 A time constant current charging and discharging curve result chart;

FIG. 27 shows two Zn// NCA/Fe cascades _SA+NC The battery drives a picture of the LED at different temperatures.

Detailed Description

In order to facilitate an understanding of the invention, reference will now be made in detail to the present preferred embodiments of the invention, examples of which are illustrated in the accompanying drawings, and the scope of the invention is not limited to the following specific embodiments.

Unless otherwise defined, all terms of art used hereinafter have the same meaning as commonly understood by one of ordinary skill in the art. The terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the scope of the present invention.

Unless otherwise specifically indicated, various raw materials, reagents, instruments, equipment and the like used in the present invention are commercially available or can be prepared by existing methods.

1. High stability iron atom catalyst (NCA/Fe) _SA+NC ) The preparation of (1).

Example 1:

(1) Preparation of G-Si/FePM: taking 180.0mg of gelatin and SiO ₂ 90.0mg、FeCl ₂ ·4H ₂ O23.9 mg and PM 71.4mg were added to 7.5mL of ultrapure water, and water bath was carried out at 60 ℃ for 20min to form a blood red dispersion. The resulting mixture self-assembles into a hydrogel in a freezer at-4 ℃ and is referred to as G-Si/FePM.

(2) Preparation of NCA/Fe-500: placing G-Si/FePM freeze-dried hydrogel in Ar mixed atmosphere at 5 ℃ for min ^-1 The temperature is raised to 500 ℃ at the speed of the thermal decomposition for 2 hours; etching with 0.5M NaOH at 80 deg.C to remove SiO ₂ And is marked as NCA/Fe-500.

(3)NCA/Fe _SA+NC The preparation of (1): NCA/Fe-500 at 97% Ar +3% H ₂ Under a mixed atmosphere of (2), at 5 ℃ for min ^-1 Heating to 900 ℃, and pyrolyzing for 3h to obtain NCA/Fe _SA+NC 。

The preparation scheme is shown in figure 1.

Example 2

(1) Collecting chitosan 180.0mg and Al ₂ O ₃ 90.0mg、Fe(NO ₃ ) ₂ Adding 23.9mg and 71.4mg of melamine into 7.5mL of ultrapure water, and heating in a water bath at 55 deg.C for 20min to obtain a mixtureAnd (3) forming a dispersion. The resulting mixture self-assembles into a hydrogel in a freezer at-4 ℃.

(2) Preparation of NCA/Fe-500: placing the above lyophilized hydrogel in Ar mixed atmosphere at 5 deg.C for min ^-1 Heating to 500 ℃ at the speed of (1), and pyrolyzing for 3h; etching with 0.5M NaOH at 80 deg.C to remove Al ₂ O ₃ And is recorded as NCA/Fe-500.

(3)NCA/Fe _SA+NC The preparation of (1): NCA/Fe-500 at 97% Ar +3% H ₂ At 5 ℃ for min in a mixed atmosphere of ^-1 The temperature is increased to 900 ℃, and the NCA/Fe is obtained after 2 hours of pyrolysis _SA+NC 。

Comparative example 1

And preparing the iron monatomic catalyst without the iron nanocluster.

(1) Preparation of G-Si/FePM: taking 180.0mg of gelatin and SiO ₂ 90.0mg、FeCl ₂ ·4H ₂ O23.9 mg and PM 71.4mg were added to 7.5mL of ultrapure water, and water bath was carried out at 60 ℃ for 20min to form a blood red dispersion. The resulting mixture was self-assembled into a hydrogel in a refrigerator at-4 ℃ and was referred to as G-Si/FePM.

(2)NCA/Fe _SA The preparation of (1): the G-Si/FePM freeze-dried hydrogel is placed in 97% Ar +3% H ₂ At 5 ℃ for min in a mixed atmosphere of ^-1 The temperature is increased to 900 ℃ at the speed of the thermal decomposition for 3 hours. SiO was then removed with 4% HF ₂ The template was dried under vacuum at 60 ℃ for 1h.

2. Assembly of flexible zinc-air cells

Synthesis of polyacrylic acid (PAA) hydrogel electrolyte: 4.2mL of acrylic acid was dissolved in 9mL of ultrapure water, 6.0mg of methylenebisacrylamide and 60.0mg of potassium persulfate were added under strong magnetic stirring, magnetic stirring was carried out for 20min, and the resulting solution was poured into a bar-shaped mold and placed in an oven at 60 ℃ overnight. Finally, the prepared PAA hydrogel was removed from the mold, allowed to dry, and immersed in a solution containing 6M KOH and 0.2M Zn (AC) ₂ ·2H ₂ Solution of O for 72h.

Synthesis of Polyacrylamide (PAM) hydrogel electrolytes: dissolving 4g acrylamide and 8mL dimethyl sulfoxide in 8mL ultrapure water, adding 4.0mg methylenebisacrylamide and 10.0mg potassium persulfate under strong magnetic stirring, stirring for 20min,the resulting solution was poured into a strip mold and placed in an oven at 60 ℃ overnight. Finally, the prepared PAM hydrogel was soaked in 6M KOH and 0.2M Zn (AC) ₂ ·2H ₂ And O for 72 hours.

Quasi-solid state zinc-air cells employ a typical sandwich structure. The prepared air electrode and zinc plate are respectively placed on two sides of the PAA hydrogel electrolyte. The air electrode is composed of a catalyst layer, a gas diffusion layer and a foam nickel layer. The catalyst, acetylene black and PTFE were mixed in a ratio of 6:1:3, fully mixing, wetting by ethanol, grinding, rolling into tablets, and preparing the catalyst layer. Then, the catalyst layer, the nickel foam and the gas diffusion layer were laminated in this order to obtain an air electrode, which was dried in vacuum at 60 ℃ for 3 hours and cut into sheets of 1.0cm × 1.0cm for use.

For comparison, commercial Pt/C-RuO was used ₂ For comparison, a cathode catalyst was prepared in the same manner.

The assembly method of the low temperature zinc-air battery is the same except that the PAM hydrogel electrolyte is used instead of the PAA hydrogel electrolyte. The low-temperature measurements of the zinc-air cells were carried out in a low-temperature test chamber (Haier, DW-60W151EU 1).

3. Performance testing of high stability iron monatomic catalysts

1. Morphology and structure of high-stability iron monatomic catalyst

The highly stable iron monatomic catalyst (NCA/Fe) prepared in example 1 was used _SA+NC ) For example, N-doped carbon aerogel (NCA/Fe) prepared in comparative example 1 in which only Fe single atoms are embedded and no iron nanocluster is included _SA ) For comparison.

The morphology and structure of the carbon aerogel composite was first studied by Scanning Electron Microscopy (SEM) and Transmission Electron Microscopy (TEM), and the results are shown in fig. 2. As can be seen from the SEM images of fig. 2b and 2c, the carbon aerogel retains a 3D structure with abundant porosity, helping to inhibit excessive aggregation of metal atoms into large nanoparticles during high temperature. The TEM image of FIG. 3a shows that NCA/Fe _SA+NC The sample did not have larger metal nanoparticles. Measured in a high angle annular dark field scanning transmission electron microscope (HAADF-STEM), the results are shown in FIG. 3b, and can be obtainedThe discovery of NCA/Fe _SA+NC The composite material contains both metal nanoclusters (about 2nm in diameter) and metal monoatomic atoms, and many metal monoatomic atoms are located around the nanoclusters. As shown in FIG. 3c, the lattice fringes of the nanoclusters are clearly visible, where the pitch is

Corresponds to the (100) crystal plane of metallic Fe (PDF # 34-0529). An Element Distribution (EDS) map based on energy dispersive X-ray spectroscopy, as shown in fig. 3d, also confirms that the carbon aerogel contains both metallic Fe nanoclusters and monoatomic atoms. In contrast, NCA/Fe prepared by one-step pyrolysis _SA Only metal monoatomic sites, but no metal nanoclusters, were contained, and the results are shown in fig. 4.

2、N ₂ Adsorption-desorption measurement experiment

At N ₂ NCA/Fe in adsorption-desorption measurements _SA+NC And NCA/Fe _SA The composite materials all show IV type isotherms, which show that a complex porous network with mesopores as the main in the range of 5-15 nm is formed, and the result is shown in figure 5a, NCA/Fe _SA Has a specific surface area of about 899m ² g ^-1 ，NCA/Fe _SA+NC Is reduced to 579m ² g ^-1 This is probably due to NCA/Fe _SA Is caused by the blockage of the metal nanoclusters. In XRD measurements, NCA/Fe was seen due to the (002) diffraction of graphitic carbon (PDF # 65-6212) _SA+NC And NCA/Fe _SA All showed broad diffraction peaks at 2 ≈ 25 °, indicating that the hydrogel precursor is effectively graphitized into carbon aerogel, and the result is shown in fig. 5b, which is comparable to NCA/Fe _SA In contrast, NCA/Fe _SA+NC Two diffraction peaks at 42.5 ° and 50.1 ° could be detected, due to the (100) and (101) planes of hexagonal Fe nanocrystals (PDF # 34-0529), respectively, consistent with the results of HRTEM measurements above. In Raman spectroscopy, NCA/Fe _SA+NC And NCA/Fe _SA Are all at 1348cm ^-1 Appears in the D band at 1590cm ^-1 At the G band, the peak intensity ratio (I) of the former _D /I _G ) Slightly lower than the latter (0.89vs. 0.92), the results are shown in FIG. 5c, indicating that the former is more graphitizedThe electron transfer in the electrocatalytic reaction process can be effectively promoted, so that the catalytic activity is improved.

3. Elemental composition and corresponding valence state analysis of carbon aerogels

X-ray photoelectron spectroscopy (XPS) can be used to determine the elemental composition and corresponding valence state of carbon aerogels. At NCA/Fe _SA+NC And NCA/Fe _SA In the XPS spectrum of the carbon aerogel, as shown in fig. 6a, signal peaks at 284, 400, 530 and 710eV correspond to C, N, O and Fe element, respectively. Wherein the Fe contents are 1.8 and 1.0wt%, respectively, which are consistent with the measurement results of inductively coupled plasma emission spectroscopy (ICP-OES), and the results are shown in Table 1. From the HRXPS plot of the Fe 2p electron, NCA/Fe can be seen _SA+NC Contains three pairs of peaks, the results are shown in FIG. 6b, located at 708.0/721.2eV, 709.8/723.2eV and 713.9/727.3eV respectively, assigned to Fe (0), fe (II) and Fe (III); NCA/Fe _SA Only two substances of Fe (II) and Fe (III) are detected in the sample, which shows that the former contains Fe nano-cluster and Fe single atom at the same time, and the latter contains Fe single atom. Notably, NCA/Fe _SA+NC Fe (II) and Fe (III) binding energy ratio NCA/Fe _SA The result is shown in table 2, indicating that there is electron transfer of the Fe nanoclusters to the Fe monatomic site. Further NCA/Fe _SA+NC The percentage of Fe (II) and Fe (III) in the catalyst is obviously higher than that of NCA/Fe _SA (1.5 vs.1.1), indicating NCA/Fe _SA+NC The antioxidant stability of the composition is relatively enhanced. The O1s spectra of both carbon aerogel samples were able to detect C = O and C-O/O-H functional groups at 531.8eV and 532.0eV, respectively, with the results shown in fig. 6a and 6 b; but the corresponding metal-O (M-O) peak at 530eV was not detected in both samples. Fitting of the N1s spectra shows that the samples contained 5N species, pyridine N (398 eV), metal-N (M-N) (399 eV), pyrrole N (400 eV), graphite N (401 eV), and oxidized N (403 eV), respectively, with the results shown in FIG. 6c. The N1s spectrum result shows that Fe monoatomic atoms in the carbon aerogel are combined with N atoms to form FeN _x A site. Notably, with NCA/Fe _SA In contrast, NCA/Fe _SA+NC The binding energy of Fe-N species in the medium shows a negative shift of 0.4eV, and the result is shown in Table 3, which shows that FeN in the former is ₄ The electron cloud density of the site is greater, whichProbably due to electron transfer from neighboring Fe nanoclusters, consistent with Fe 2p XPS results.

Table 1: element content (at%) measured by XPS method and ICP-OES method

Table 2: XPS method for determining iron content

Table 3: XPS method for measuring N content (%)

4、FeN _x Analysis of coordination configuration of sites

FeN was further studied by X-ray Spectroscopy (XAS) measurements _x Coordination configuration of the sites. FIG. 7a and inset depict the Fe k-edge X-ray absorption near-edge structure (XANES) spectra of the samples, with the white line intensity sequenced as Fe foil<NCA/Fe _SA+NC ≈FePc<NCA/Fe _SA With NCA/Fe _SA+NC Contains Fe nano-cluster and Fe single atom, while NCA/Fe _SA The result is consistent with only one atom of Fe in the alloy. The corresponding trend is also reflected in the absorption edge energy, as shown in fig. 7 c. The corresponding fourier transform extended X-ray fine structure (EXAFS) curve is shown in fig. 7 b. FePc, NCA/Fe _SA+NC And NCA/Fe _SA Are all at about

A main peak is present and is classified as Fe-N bond (as can be seen from the above XPS measurement, fe-O bond is not formed); NCA/Fe _SA+NC Occurs in about +>

With Fe-Fe peak phase in Fe foilCorrespondingly, it is proved that the sample contains Fe nanoclusters. The Coordination Numbers (CN) and bond lengths of Fe-N and Fe-Fe were then further determined by EXAFS data fitting, and the results are shown in FIGS. 7 c-7 f. Specific values are shown in Table 4, and it can be seen from Table 4 that NCA/Fe _SA+NC Has a corresponding bond length of ^ 5>

Consistent with the bond length of Fe foil, CN is significantly lower (2vs.8) due to the smaller size of the metal clusters and the larger proportion of surface unsaturated coordinated metal atoms. For the Fe-N pathway, NCA/Fe _SA+NC Has a CN of 3.6 and a bond length of->

Slightly less than NCA/Fe _SA (4.2 and +>

) This is probably due to NCA/Fe _SA+NC Middle FeN ₄ There are Fe clusters near the sites. These results show that NCA/Fe _SA+NC The medium Fe is mainly composed of FeN ₄ Sites and adjacent Fe clusters, while NCA/Fe _SA In the middle of FeN ₄ 。

Table 4: EXAFS fitting results

5、 ⁵⁷ Fe

Spectroscopic and Electron Paramagnetic Resonance (EPR) analysis

⁵⁷ Fe

Spectroscopy and Electron Paramagnetic Resonance (EPR) can be used to probe the spin state of Fe. For containing FeN _x C _y Radical carbon composite material, process for producing the same, and process for producing the same ⁵⁷ Fe/>

The spectrum contains at least two distinct pairs of peaks, D1 and D2, respectively assigned to high spin Fe (III) and medium/low spin Fe (II), both having a similar isomer shift (delta) of 0.30-0.45mm s ^-1 Different quadrupole splitting energy (Δ E) _QS ) Are 1.0 and 2.5mm s, respectively ^-1 The results are shown in FIGS. 8a and 8b at NCA/Fe _SA+NC And NCA/Fe _SA Both D1 and D2 were detectable in the samples. In addition, NCA/Fe _SA+NC There is one additional peak, D3, δ = -0.06mm s ^-1 The peak can be assigned to a Fe nanocluster. Table 5 lists the percentages of D1 and D2 in the two carbon aerogels. It can be seen that D2 is at NCA/Fe _SA 50.7% in the case of NCA/Fe _SA+NC Is 58.1%, which shows that effective chemical interaction exists between the Fe monoatomic atom and the Fe nanocluster and is consistent with the XPS measurement result. According to literature reports, the D2 group shows better ORR stability than D1. From this, it was concluded that _SA In contrast, NCA/Fe _SA+NC Higher D2 ratios in the middle are expected to lead to higher stability. EPR measurement result and ⁵⁷ Fe/>

the results of the spectra were in agreement, and as shown in FIG. 8c, NCA/Fe was observed in the magnetic field strength range of 2000 to 5000G _SA+NC And NCA/Fe _SA All showed 3500G-centered signal peaks, but the former had significantly weaker amplitudes than the latter, further confirming NCA/Fe _SA+NC FeN reduction by mesoproximal Fe nanoclusters ₄ The spin state of (c).

Table 5: ⁵⁷ Fe

ratio of D1 to D2 in the test results

4. Theoretical simulation

The invention has the advantages ofTheoretical calculations investigated the interaction between Fe monatomic sites and adjacent Fe nanoclusters. As shown in fig. 9a, we discuss four configurations: feN, respectively on graphitic carbon ₄ (S ₀ Site), feN ₄ And Fe nanoclusters are separated by about

(S1 locus), (+) binding domain>

(S2 locus), (+)>

(S3 site) of FeN ₄ -Fe ₁₃ Configuration. The ORR reaction process for the four configurations is shown in FIGS. 10-13. As shown in fig. 9b, from the free energy step diagram of ORR, it can be found that at the potential of +0.9V, the first and second electron transfer steps on S1, S2, S3 and S0 are exothermic reactions, while the third and fourth electron transfer steps are endothermic reactions, and the last step, desorption of-OH is a Rate Determining Step (RDS). -OH (Δ G) _OH* ) The desorption energy at the S0 site was 0.36eV, and the desorption energy at the S1, S2, and S3 sites were slightly lower, 0.33eV, 0.30eV, and 0.34eV, respectively. This suggests that adjacent Fe nanoclusters may enhance FeN ₄ ORR activity of the site. In this series, the S2 site has the lowest energy barrier (0.30V) and the highest limiting potential (0.60V), and therefore is thermodynamically and kinetically favored to catalyze ORR, as shown in fig. 9 c.

The research finds the electron spin state and FeN of the metal active site _x The activity and/or stability of the catalyst is closely related. Therefore, the present inventors calculated the magnetic moment of Fe monoatomic sites at these sites using the Density Functional Theory (DFT) to further investigate the interaction between the Fe nanoclusters and the Fe monoatomic sites, and as a result, as shown in FIG. 9d, the 1.94. Mu.B sites for S0, and the 1.75, 1.68, and 1.65. Mu.B for S1, S2, and S3, respectively, and the above description ⁵⁷ Fe

The measurement results are consistent. This indicates the electricity of adjacent Fe nanoclusters to the Fe monoatomic atomThe seed has a significant regulatory effect and increases with decreasing distance. The electron regulation effect can be further understood through the analysis of density of states (DOS). As can be seen from FIG. 14a, for the S2 site, the Fe3d electron contributes primarily to DOS near the Fermi level (marked by black arrows), indicating that FeN ₄ The Fe atom in (1) is the main active site. Similar results can be obtained in DOS plots for the S0, S1 and S3 sites, with the results shown in FIGS. 15 a-15 c. FIG. 14b compares the DOS of the Fe3d electrons at the S1, S2 and S3 sites. As nanoclusters get closer to FeN ₄ The marker state is shifted negatively, which indicates that FeN ₄ The Fe center in (b) readily accepts electrons from neighboring Fe nanoclusters and the labeled state of S2 is closest to the fermi level, consistent with the results of the free energy step plot.

FIGS. 14c, 15d and 15e show DOS of the five Fe3d orbitals of the S1, S2 and S3 sites, where the marker states near the Fermi level are predominantly associated with d _xz The tracks are related. Whereas the labeling states near the Fermi level of the S0 site are predominantly and d _xy The tracks are correlated and the result is shown in figure 15 f. As the distance between the Fe nanocluster and the Fe monoatomic atom decreases (from S3 to S1), electrons from the nanoclusters are in FeN ₄ In which a full fill d is formed _xy Track and partially filled d _xz A track. This indicates that the electron configuration and magnetic moment change significantly from S0 to S1, S2 and S3 due to electron transfer of the Fe nanoclusters to the Fe atom. This evolution of electronic structure can lead to changes in catalytic activity, see below electrochemical measurements of ORR activity and stability.

5. ORR catalytic performance of high-stability Fe monatomic catalyst

1. Rotating Disk Electrode (RDE) evaluation of ORR Activity of catalysts

The ORR activity of two carbon aerogels at 0.1M KOH was evaluated using a Rotating Disk Electrode (RDE) at 1600rpm and compared to commercial Pt/C. The results are shown below, and it can be seen from FIGS. 16a and 16b that NCA/Fe _SA+NC Shows good ORR performance, initial potential (E) _onset ) Is +1.05V, half-wave potential (E) _1/2 ) At +0.92V, it is superior to NCA/Fe _SA (+ 1.01 and + 0.90V) and commercial Pt/C catalysisAgents (+ 0.98 and + 0.86V). The results of Electrochemical Impedance Spectroscopy (EIS) measurements showed NCA/Fe _SA+NC Charge transfer resistance (R) of _ct ) 65.9 omega, which is significantly lower than NCA/Fe _SA (89.9. Omega.) and the results are shown in FIG. 16 c. According to the polarization curves at different rotation speeds, as shown in FIG. 17, the kinetic current density (J) at a certain potential can be calculated by using the kouteckey-levich equation _k ) And a Tafel slope. As shown in FIG. 16b, NCA/Fe _SA+NC J at +0.85V _k Up to 18.7mA cm ^-2 Is about NCA/Fe _SA And 2 times Pt/C (10.8vs.9.5mA cm ^-2 )。NCA/Fe _SA+NC Tafel slope of 60mV dec ^-1 Close to NCA/Fe _SA Tafel slope of (58 mV dec) ^-1 ) But lower Tafel slope (70 mV dec) than Pt/C ^-1 ) Indicating a rapid ORR reaction kinetics, the results are shown in figure 16d. Measurement of the Rotating Ring Disk Electrode (RRDE) shows NCA/Fe _SA+NC And NCA/Fe _SA The ORR reaction occurs following a high efficiency of 4e ^- Route, similar to Pt/C. In contrast, NCA/Fe _SA+NC Exhibits the lowest average H in a potential range of +0.2V to +0.9V ₂ O ₂ The yield (2.65%) and the highest average electron transfer number (3.96) are shown in fig. 18. NCA/Fe _SA+NC Can be attributed to the electronic regulation of the Fe Shan Yuan sub-position by the adjacent Fe nanoclusters.

2. Contribution of ORR Activity of iron nanoclusters and iron monoatomic atoms

In order to distinguish the contribution of Fe clusters and single atoms to ORR electrocatalysis, the invention uses acid etching to treat NCA/Fe _SA+NC . As can be seen from the TEM image, the intensity of the field intensity is 0.5M H ₂ SO ₄ After medium etching, fe clusters disappeared with distinct nanopores appearing, and the result is shown in fig. 19 a. Electrochemical test results show that removal of Fe clusters results in E _1/2 Negative shift 20mV to +0.90V, which is comparable to NCA/Fe _SA The half-wave potential of (2) is the same, and the result is shown in FIG. 19 b. NCA/Fe _SA+NC The ORR activity of the catalyst comes from Fe single atom sites, and the existence of Fe nano-clusters has a certain promotion effect on the catalytic activity. In addition, NCA/Fe was evaluated by Cyclic Voltammetry (CV) in a potential range of +0.2 to +1.2V _SA+NC And NCA/Fe _SA Electrocatalytic stability of (c). After 8000 successive potential cycles, the ORR peak potential of the former was shifted negatively by 5mV, with the results shown in FIG. 20a, but less than one tenth of the latter (54 mV, FIG. 20 b), confirming that the presence of Fe nanoclusters significantly improves the stability of the catalyst. NCA/Fe even after 15000 consecutive cycles _SA+NC The peak potential was shifted only 14mV negatively, and the result is shown in fig. 20 a.

3. XPS measurement compares structural changes of two carbon aerogels before and after long-term cycle test

The invention compares the structural changes of two carbon aerogels before and after long-term cyclic test by XPS measurement. Comparing the Fe 2p spectra before and after 8000 CV cycles, NCA/Fe _SA+NC The main peak of the sample only shows a positive displacement of 0.1eV, which is significantly lower than NCA/Fe _SA (0.9 eV), as shown in fig. 21a and 21 b. Indicating that the antioxidant capacity of Fe species in the former is obviously enhanced. Note that: additives used during electrode preparation, such as Nafion and carbon black, make it difficult to fit the Fe 2p peak, so we compare with the shift of the main peak. HRXPS of the O1s spectrum further revealed the difference in oxidation resistance of the two catalysts. As shown in Table 6, NCA/Fe after durability test _SA+NC Only 0.03% of metal-O species (M-O) was detected in the samples, much lower than NCA/Fe _SA (0.19%) indicating NCA/Fe _SA+NC The Fe species in (1) has stronger oxidation resistance and stability. Table 7 lists the percentage of N species in the carbon aerogel before and after the durability test. It can be seen that the difference between the two is mainly reflected in the percentage change of M-N. NCA/Fe _SA The change in the percentage of M-N in the range of 0.45% to 0.11% was found to be the main cause of the decrease in electrocatalytic activity. And NCA/Fe _SA+NC The percentage of M-N of (a) is only slightly reduced (0.55% to 0.45%), indicating that a higher catalytic activity can be maintained.

FeN, as described above _x The decay in ORR performance of composite materials is largely due to the oxidation of Fe sites and aggregation into metal oxide nanoparticles. Therefore, we used TEM to explore NCA/Fe after stability testing _SA And NCA/Fe _SA+NC The microstructure of (a). As can be seen from FIG. 22 and the inset, although NCA/Fe _SA And NCA/Fe _SA+NC All can detect monoclinic Fe ₂ O ₃ Nanocrystals, but NCA/Fe _SA+NC The number of the medium nano particles is obviously lower than that of NCA/Fe _SA . This confirmed that NCA/Fe _SA+NC The oxidation resistance was more excellent, consistent with the XPS results.

Table 6: XPS method for determining content (%)% of O species in carbon aerogel before and after stability test

Table 7: XPS method for measuring N content (%)% in carbon aerogel before and after stability test

6. Application of high-stability Fe monatomic catalyst in low-temperature zinc-air battery

The above studies indicate that FeN ₄ Both the sites and the Fe nanoclusters may have catalytic activity for OER. Accordingly, the present invention discusses the OER activity of these carbon aerogels and their use as bifunctional catalysts in rechargeable zinc-air batteries. FIGS. 23a and 24b show the OER polarization curve and Tafel curve of carbon aerogels under 1.0M KOH conditions. NCA/Fe _SA+NC OER current density of 10mA cm ^-2 Corresponding overpotential (E) _OER，10 ) Is +1.57V and the Tafel slope is 71.5mV dec ^-1 Both of which are lower than NCA/Fe _SA (+ 1.61V and 97.1mV dec ^-1 ). This indicates NCA/Fe _SA+NC Has obvious advantages in the aspect of OER electrocatalysis. The acid leaching experiment suggests that NCA/Fe _SA+NC The OER activity of (a) is from Fe single atoms, with Fe nanoclusters acting as an auxiliary enhancement, as shown in fig. 23 c. As shown in the inset of FIG. 23a, NCA/Fe _SA+NC Over potential difference between ORR and OER (Δ E = E) _OER，10 -E _1/2 ) Is only 0.65V, lower than NCA/Fe _SA 60mV, superior to most dual-function oxygen electrocatalysts in the prior art.

1. Application of room temperature chargeable zinc-air battery

To explore the practical application of carbon aerogel in rechargeable zinc-air battery, NCA/Fe was used _SA+NC Or NCA/Fe _SA Is an air cathode catalyst, a high-purity zinc plate is an anode, and the PAA hydrogel is a flexible electrolyte to assemble a flexible zinc-air battery. By using commercial Pt/C and RuO ₂ The mixture of catalysts assembled a comparative cell. The results are shown in FIG. 24a, zn// NCA/Fe _SA+NC The Open Circuit Voltage (OCV) of the cell was 1.50V, the ratio Zn// NCA/Fe _SA And Zn// Pt/C-RuO ₂ The cell height was 30 and 120mV. Zn// NCA/Fe _SA+NC The maximum power density of the battery is 236mW cm ^-2 The results are shown in FIG. 24b, which is much higher than Zn// NCA/Fe _SA Battery (170 mW cm) ^-2 ) And Zn// Pt/C-RuO ₂ Battery (119 mW cm) ^-2 ). In fact, zn// NCA/Fe _SA+NC The cell is at 5 to 50mA cm ^-2 Shows a higher discharge voltage in the current density range of (a), and the result is shown in fig. 24c. Notably, this flexible Zn// NCA/Fe _SA+NC The performance of the cell was superior to most flexible zinc-air cells and even to the corresponding liquid cells in terms of OCV and maximum power density, the results are shown in fig. 24d. FIG. 25a shows a current density of 5mA cm ^-2 Constant current charge and discharge curve. Zn// NCA/Fe _SA After 770 times of continuous charging and discharging, the voltage gap is 0.90V, and the round-trip efficiency reaches 54.1%. In sharp contrast, zn// NCA/Fe _SA+NC The cell voltage gap was narrower, only 0.79V, and the round-trip efficiency was as high as 59.3% even after 1800 cycles, indicating a significant improvement in activity and durability. Notably, the Zn// NCA/Fe when the PAA layers were compressed 30% and 60% _SA+NC The cell still maintained maximum power densities of 95% and 92%, and the results are shown in fig. 25b. At 120 ° to 180 ° bend, the discharge-charge voltage hardly changed, and the result is shown in fig. 25c. After 1000 times of repeated compression, zn// NCA/Fe _SA+NC The drop in the discharge voltage of the battery was negligible and the result was shown in fig. 25d. These show Zn// NCA/Fe _SA+NC The battery has good mechanical flexibility.

2. Application in zinc-air battery at low temperature

The low-temperature zinc-air battery has great application potential in special environments such as polar exploration, space exploration and the like. However, at low temperatures the kinetics of the electrode reaction and the ionic conductivity are significantly slowed down. Thus, the operation of the device requires an effective electrode catalyst that functions even at such low temperatures. We use NCA/Fe _SA+NC The low-temperature zinc-air battery is assembled by taking a high-purity zinc plate as an anode and taking PAM hydrogel containing dimethyl sulfoxide as electrolyte for air cathode catalysis. The results are shown in FIGS. 26a and 26b, zn// NCA/Fe after assembly _SA+NC The voltage of the battery at-20 ℃ is 1.49V, and the maximum power density is 97.0mW cm ^-2 (ii) a At-40 deg.C, the voltage and maximum power density are 1.47V and 49.0mW cm ^-2 。Zn//NCA/Fe _SA+NC The battery is 0.2-5.0 mA cm ^-2 Also shows a stable discharge voltage in a current density range of 1.0mA cm at-20 ℃ and-40 DEG C ^-2 The discharge voltage was 1.36V and 1.31V, respectively, and the result is shown in fig. 26c. FIG. 26d compares the recently reported performance of related low temperature zinc-air cells, and it can be seen that Zn// NCA/Fe _SA+NC The performance of the battery is significantly better than that of most batteries. As shown in FIG. 26d, at-40 ℃ and 1.0mA cm ^-2 Then, after 2300 continuous constant current charge-discharge cycles, the Zn// NCA/Fe _SA+NC The battery keeps a stable discharge platform, the round-trip efficiency is as high as 81.4%, and the voltage gap is only 0.32V, so that the synthesized carbon aerogel catalyst has great practical application advantages at ultralow temperature. As shown in FIG. 27, even at-40 ℃ there were only two Zn// NCA/Fe _SA+NC The batteries are connected in series to drive the LED with the rated voltage of 3.0V. These results confirm that the NCA/Fe designed by the present invention _SA+NC The catalyst has good application prospect in high-efficiency and freeze-resistant zinc-air batteries.

In conclusion, the invention takes the gelatin hydrogel as the precursor and the template, and the Fe nano-cluster (NCA/Fe) is loaded near the Fe single atom site in the N-doped carbon aerogel through a simple two-step pyrolysis method _SA+NC ). The spectral characterization, the first principle calculation and the electrochemical test result show that the Fe nano-cluster has an electron-donating effect on the surrounding Fe single atoms, so that the magnetic moment is reduced,can effectively promote the electrocatalytic activity and stability of the catalyst. NCA/Fe _SA+NC The flexible zinc-air battery assembled by using the aerogel as a cathode catalyst shows higher OCV and power density at room temperature and low temperature (-40 ℃), and excellent durability. The research result provides a new paradigm for optimizing the stability and activity of the M-N-C nanocomposite catalyst in the electrochemical energy technology.

The foregoing is a further detailed description of the invention in connection with specific preferred embodiments and is not intended to limit the invention to the specific embodiments described. For those skilled in the art to which the invention pertains, several simple deductions or substitutions can be made without departing from the spirit of the invention, and all shall be considered as belonging to the protection scope of the invention.

Claims

1. The high-stability iron atom catalyst is a three-dimensional honeycomb network structure formed by a nitrogen-doped carbon skeleton, and the three-dimensional honeycomb network structure also comprises iron monatomic and iron nanoclusters, wherein the iron nanoclusters are loaded in nano holes of the three-dimensional honeycomb network structure, and the iron monatomic is combined on the nitrogen-doped carbon skeleton around the iron nanoclusters.

2. The highly stable iron atom catalyst as claimed in claim 1, wherein the diameter of the iron nanoclusters is less than 10nm and the distance between the iron nanoclusters and the iron monoatomic is less than 2nm.

3. The method for preparing a highly stable iron atom catalyst as set forth in claim 1 or 2, characterized by comprising the steps of:

s1, uniformly mixing a carbon source, a pore-foaming agent, an iron salt, a nitrogen source and water according to a mass ratio, and performing low-temperature self-assembly to form hydrogel after water bath at the temperature of 55-65 ℃;

s3, adding 9 the semi-finished product prepared in the step S27％Ar+3％H ₂ Heating to 900-950 ℃ for pyrolysis in the mixed atmosphere to obtain the high-stability iron atom catalyst.

4. The method for preparing a highly stable iron atom catalyst according to claim 3, wherein in step S1, the carbon source is one of gelatin, chitosan, starch or agar, and the nitrogen source is one of phenanthroline or melamine.

5. The method for preparing the high-stability iron atom catalyst according to claim 3, wherein the pore-forming agent is one of silicon dioxide or aluminum oxide, the particle size of the silicon dioxide is 10-30 nm, and the particle size of the aluminum oxide is 10-50 nm.

6. The method for preparing the high-stability iron atom catalyst according to claim 5, wherein the mass ratio of the carbon source, the pore-foaming agent, the iron salt, the nitrogen source and the water in step S1 is (15-30): (5-12.5): (1-4): (2.97 to 11.9): (0.625-1.25).

7. The method for preparing a highly stable iron atom catalyst as claimed in claim 3, wherein the temperature rise rate in step S2 and step S3 is 5 to 10 ℃ per minute and the pyrolysis time is 2 to 3 hours.

8. The method for preparing the high-stability iron atom catalyst according to claim 3, wherein the pore-forming agent is removed by etching with 0.5-1.0M strong alkali solution at 75-85 ℃ in step S2.

9. Use of the highly stable iron atom catalyst as claimed in claim 1 or 2 as an air cathode catalyst in a flexible zinc-air cell.

10. The use according to claim 9, wherein the highly stable iron atom catalyst is used at room temperature or at 0 to-40 ℃ when used as an air cathode catalyst in a flexible zinc-air battery.