Iron-nickel diatomic fiber catalyst with precise and adjustable local structure as well as preparation method and application of iron-nickel diatomic fiber catalyst

Abstract

The invention discloses an iron-nickel diatomic fiber catalyst with a precise and adjustable local structure and a preparation method and application thereof.The method is based on an organic small molecule coordination strategy and comprises the steps that ferric nitrate, nickel nitrate and dicyandiamide are dissolved in DMF according to a certain molar ratio, and a solution A is obtained; dispersing ZIF-8 nanoparticles in DMF (Dimethyl Formamide), and adding polyacrylonitrile to obtain a solution B; the solution A and the solution B are mixed to obtain a spinning solution, and a nanofiber membrane is obtained through electrostatic spinning; and carrying out pre-oxidation and high-temperature carbonization treatment on the nanofiber membrane to obtain the carbon nanofiber catalyst loaded with iron-nickel bimetallic atoms (metal diatoms, heterojunctions and alloys in which the metal diatoms and clusters coexist). The problem that the metal active site local structure of a metal diatom catalyst is difficult to accurately regulate and control is solved, and the prepared metal diatom heterojunction shows excellent ORR and OER bifunctional catalytic performance and cycling stability as a zinc-air battery positive electrode catalyst.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of electrocatalytic materials, and particularly relates to a Fe-Ni bimetallic atomic fiber catalyst with precise adjustable local structure, a preparation method thereof based on a differential coordination strategy of organic small molecules, and application of the Fe-Ni bimetallic atomic fiber catalyst in the field of zinc-air batteries (ZABs). BACKGROUND

[0002] Commercial application of zinc-air batteries is limited by the slow kinetics of oxygen evolution reaction (OER) and oxygen reduction reaction (ORR) during charging and discharging of the air cathode. Platinum-based catalysts (Pt / C, etc.) and iridium / ruthenium-based catalysts (Ir / C, RuO2, etc.) are the most effective ORR and OER catalysts currently used in commercial applications, but these noble metals are expensive, scarce in resources, and have poor dual-function catalytic activity. Therefore, there is an urgent need to develop a dual-function oxygen catalyst that is low in cost and highly efficient and stable, to promote the development of zinc-air batteries.

[0003] Atomically dispersed TM-N-C (TM, transition metal) catalysts have become a research hotspot in the field of electrocatalysis such as ORR / OER due to their unique local structure and high atom utilization. Among them, Fe-N-C and Ni-based single-atom catalysts exhibit excellent ORR and OER performance, respectively, but single-metal active site single-atom catalysts are difficult to simultaneously achieve high activity for both ORR and OER. Anchoring Fe and Ni single atoms in the same carbon matrix can construct bimetallic atomic catalysts, which are expected to achieve efficient dual-function oxygen catalysis. High-temperature carbonization of metal-organic framework compounds or polymers loaded with metal ions is the most commonly used strategy for constructing carbon-based bimetallic atomic catalysts.

[0004] However, during high-temperature carbonization, the organic molecules are cracked and polycondensed, and the metal atoms have high mobility due to intense thermal motion, which leads to easy agglomeration of metal atoms to form nanoparticles, making it difficult to precisely control the dispersion form and local structure of the two metal atoms. Therefore, the structure-activity relationship between the local structure of the bimetallic atoms and their catalytic performance is difficult to determine, which seriously restricts the optimization of the dual-function oxygen catalytic performance of Ni, Fe-based bimetallic atomic catalysts and their application in zinc-air batteries. Therefore, it is crucial to develop a synthesis strategy that can precisely regulate the local structure of bimetallic atomic catalysts. SUMMARY

[0005] To address the problems existing in the prior art, this invention provides a precisely tunable iron-nickel diatomic fiber catalyst with localized structure, its preparation method, and its application. This method utilizes dicyandiamide (DCD) for differentiated coordination of iron-nickel metal ions, combined with electrospinning and high-temperature carbonization strategies, to prepare iron-nickel diatomic fiber catalysts with precisely tunable atomic dispersion and localized structure. This enables the controllable construction of FeN4-NiN4 metal diatomic catalysts (Fe,Ni-DACs@BCF), FeN4-NiN4 metal diatomic catalysts coexisting with Fe4 clusters heterojunctions (Fe4 / Fe,Ni-DACs@BCF), and FeNi alloys (FeNi-NPs@BCF). The Fe4 / Fe,Ni-DACs@BCF fiber catalyst exhibits both high ORR / OER catalytic activity and stability, which is beneficial for promoting the development of high-efficiency energy storage devices such as flexible zinc-air batteries.

[0006] To solve the above-mentioned technical problems and achieve the above-mentioned technical effects, the present invention is implemented through the following technical solution: A method for preparing a locally tunable iron-nickel diatomic fiber catalyst, based on a differentiated coordination strategy of small organic molecules, includes the following steps: Step 1) Dissolve nickel-iron metal salts Fe(NO3)3·9H2O, Ni(NO3)2·6H2O and dicyandiamide in DMF solvent in a certain molar ratio. After magnetic stirring at room temperature and constant temperature ultrasonic treatment, a homogeneous mixed solution A is obtained. Step 2) Add the methanol solution containing 2-methylimidazole to the methanol solution containing Zn(NO3)2·6H2O, stir magnetically at room temperature, wash with methanol, and then centrifuge and vacuum dry to obtain ZIF-8 nanoparticles. Step 3) After magnetic stirring at room temperature and constant temperature ultrasonic treatment, ZIF-8 nanoparticles are uniformly dispersed in DMF solvent, then polyacrylonitrile polymer is added, and after magnetic stirring, solution B is obtained. Step 4) Add solution A to solution B, and after magnetic stirring at room temperature, a uniformly mixed spinning solution is obtained. Then, a porous nanofiber membrane with a beaded structure is obtained by electrospinning technology. Step 5) The porous nanofiber membrane is subjected to pre-oxidation and high-temperature carbonization treatment in sequence to finally obtain a carbon nanofiber OER / ORR bifunctional oxygen catalyst loaded with Fe and Ni bimetallic atoms.

[0007] Furthermore, in step 1, the molar ratio of Fe(NO3)3·9H2O, Ni(NO3)2·6H2O and dicyandiamide is 1:1:(0~20).

[0008] Furthermore, in step 1, the room temperature magnetic stirring time after Fe(NO3)3·9H2O, Ni(NO3)2·6H2O and dicyandiamide are dissolved together in DMF solvent is 5 min, the temperature of isothermal ultrasonic treatment is 20℃, the power of isothermal ultrasonic treatment is 1800W, and the time of isothermal ultrasonic treatment is 15 min.

[0009] Furthermore, in step 2, the mass ratio of 2-methylimidazole to Zn(NO3)2·6H2O is 3:(1~3).

[0010] Furthermore, in step 2, the methanol solution containing 2-methylimidazole is added to the methanol solution containing Zn(NO3)2·6H2O and then magnetically stirred at room temperature for 24 hours. The methanol washing is performed 3 times. The centrifugation speed is 7000 rpm, the centrifugation temperature is 15℃, and the centrifugation time is 10 minutes. The vacuum pressure for drying is ≥0.09 MPa, the drying temperature is 70℃, and the drying time is 12 hours.

[0011] Furthermore, in step 3, the mass ratio of polyacrylonitrile polymer to ZIF-8 nanoparticles is 1:(1.2~3).

[0012] Furthermore, in step 3, the ZIF-8 nanoparticles were magnetically stirred at room temperature for 30 min, the temperature of the isothermal ultrasonic treatment was 20℃, the power of the isothermal ultrasonic treatment was 1800W, the isothermal ultrasonic treatment time was 3 h, and the magnetic stirring time after dispersing the ZIF-8 nanoparticles in DMF solvent and adding polyacrylonitrile polymer was 12 h.

[0013] Furthermore, in step 4, the magnetic stirring time at room temperature after adding solution A to solution B is 2 hours. Furthermore, in step 4, the concentration of Fe(NO3)3·9H2O in the spinning solution is 0~0.03M, the concentration of Ni(NO3)2·6H2O is 0~0.03M, and the concentration of dicyandiamide is 0~0.6M.

[0014] Furthermore, in step 4, the conditions for the electrospinning technology are: voltage of 35kV; solution flow rate of 1.2mL / h; distance from needle to receiving device of 18cm; and ambient humidity of 50±5%.

[0015] Furthermore, in step 5, the specific steps of the pre-oxidation and high-temperature carbonization treatment are as follows: The porous nanofiber membrane was placed in a tube furnace and pre-oxidized by heating it to 280°C at a rate of 2°C / min and holding it for 2 hours under an argon (Ar) atmosphere. Then, it was heated to 950°C at a rate of 5°C / min and held for 3 hours for high-temperature carbonization. After natural cooling to room temperature, a bifunctional oxygen catalyst with Fe and Ni metal sites was obtained.

[0016] A locally tunable iron-nickel diatomic fiber catalyst is prepared using the aforementioned method for preparing locally tunable iron-nickel diatomic fiber catalysts.

[0017] Application of a precisely tunable local structure of an iron-nickel diatomic fiber catalyst in energy catalytic reactions.

[0018] Furthermore, the iron-nickel diatomic fiber catalyst with precisely tunable local structure can be used as a positive electrode catalyst for zinc-air batteries, and can be used in the preparation of zinc-air batteries.

[0019] The beneficial effects of this invention are as follows: The method for preparing iron-nickel bimetallic fiber catalysts with precisely tunable local structures based on a differentiated coordination strategy proposed in this invention utilizes DCD for Ni 2+ and Fe 3+ The differentiated coordination ability of this invention enables precise control over the dispersion state of bimetallic materials (single atoms, nanoclusters, alloy particles), effectively solving the common problem of difficulty in precisely controlling the local structure of metal active sites in metal diatomic catalysts. The micro / nanofibers prepared by electrospinning in this invention possess a multi-level porous structure and a large specific surface area. In the Fe4 / Fe,Ni-DACs@BCF catalyst prepared in this invention, the Fe4 clusters and FeN4 and NiN4 diatomic sites exhibit a synergistic effect, demonstrating excellent ORR and OER bifunctional catalytic activity, superior to commercial noble metal Pt / C and RuO2 catalysts, respectively. The Fe4 / Fe,Ni-DACs@BCF catalyst prepared in this invention demonstrates outstanding cycle stability in its application as an air cathode catalyst in zinc-air batteries, which is of great significance for promoting the development of high-efficiency energy storage devices such as flexible zinc-air batteries. The synthesis strategy of this invention is universal and can provide new ideas for the atomic-level preparation of other multimetal catalysts, showing broad application prospects in the field of energy conversion and storage.

[0020] The above description is merely an overview of the technical solution of the present invention. In order to better understand the technical means of the invention and to implement it according to the contents of the specification, the preferred embodiments of the present invention are described in detail below with reference to the accompanying drawings. Specific embodiments of the present invention are given in detail below with reference to the accompanying drawings. Attached Figure Description

[0021] The accompanying drawings, which are included to provide a further understanding of the invention and form part of this application, illustrate exemplary embodiments of the invention and, together with their description, serve to explain the invention and do not constitute an undue limitation thereof. In the drawings: Figure 1 These are scanning electron microscope (SEM) images of the iron-nickel bimetallic fiber catalysts with customized structures prepared in Examples 1-3 of this invention, wherein... Figure 1 In this context, 'a' corresponds to the SEM image in Example 1; Figure 1 In this context, 'b' corresponds to the SEM image in Example 2; Figure 1 c in the figure corresponds to the SEM image in Example 3.

[0022] Figure 2 The images shown are transmission electron microscope (TEM) images and corresponding elemental distribution (EDS-mapping) images of the customized iron-nickel bimetallic fiber catalyst prepared in Example 1 of this invention, and adaptive field emission high-angle annular dark-field scanning transmission electron microscope (ACHAADF-STEM) images of the customized iron-nickel bimetallic fiber catalyst prepared in Examples 1-3 of this invention. Figure 2 In this context, 'a' corresponds to the TEM image and EDS-mapping image of Example 1. Figure 2 b in the diagram corresponds to the AC HAADF-STEM diagram of Example 1; Figure 2 c in the diagram corresponds to the AC HAADF-STEM diagram in Example 2; Figure 2 In the diagram, d corresponds to the AC HAADF-STEM diagram of Example 3.

[0023] Figure 3 The images shown are transmission electron microscope (TEM) images and corresponding elemental distribution (EDS-mapping) images of the iron-nickel bimetallic fiber catalysts with customized structures prepared in Examples 2 and 3 of this invention. Figure 3 In the figure, 'a' corresponds to the TEM image and EDS-mapping image of Example 2; Figure 3 In the figure, b corresponds to the TEM image and EDS-mapping image of Example 3.

[0024] Figure 4 This is a flexible illustration of the iron-nickel bimetallic fiber catalyst with a customized structure prepared in Example 1 of the present invention.

[0025] Figure 5 The graphs show the Fe and Ni metal element content obtained by inductively coupled plasma (ICP) testing of the customized iron-nickel bimetallic fiber catalysts prepared in Examples 1-3 of this invention. Figure 5 The 'a' in the figure corresponds to the content diagram of Example 1; Figure 5 The value of 'b' in the figure corresponds to the content in Example 2. Figure 5The 'c' in the figure corresponds to the content diagram of Example 3.

[0026] Figure 6 The images show the X-ray diffraction (XRD) patterns of the iron-nickel bimetallic fiber catalysts with customized structures prepared in Examples 1-3 of this invention. Figure 6 Line a in the diagram corresponds to the XRD pattern of Example 1; Figure 6 Line b in the diagram corresponds to the XRD pattern in Example 2. Figure 6 The c-line in the diagram corresponds to the XRD pattern in Example 3.

[0027] Figure 7 The above are X-ray electron spectra (XPS) of the iron-nickel bimetallic fiber catalysts with customized structures prepared in Examples 1-3 of this invention. Figure 7 In this context, 'a' represents the full XPS spectrum. Figure 7 In the image, b represents the fine spectrum of Fe 2p. Figure 7 c in the figure represents the fine spectrum of Ni 2p.

[0028] Figure 8 The synchrotron radiation X-ray absorption spectra of the iron-nickel bimetallic fiber catalysts with customized structures prepared in Examples 1 and 3 of this invention are shown below. Figure 8 In this context, 'a' represents the fine structure of X-ray absorption on the Fe K-side. Figure 8 In the diagram, b represents the fine structure of the X-ray absorption on the NiK-edge.

[0029] Figure 9 The figures show the cyclic voltammetry (CV) curves of the ORR of the customized iron-nickel bimetallic fiber catalysts prepared in Examples 1-3 of this invention in 0.1 MKOH electrolyte. Figure 9 In this context, 'a' corresponds to the CV diagram of Example 1; Figure 9 In this context, 'b' corresponds to the CV diagram in Example 2; Figure 9 c in the figure corresponds to the CV diagram in Example 3.

[0030] Figure 10 The left image shows the linear sweep voltammetry (LSV) curves (left) and the corresponding KL curves (right) of the ORR of the customized iron-nickel bimetallic fiber catalysts prepared in Examples 1-3 of this invention in 0.1 MKOH electrolyte at different rotation speeds. Figure 10 In this context, 'a' corresponds to the LSV curve and KL curve in Example 1. Figure 10 In this context, 'b' corresponds to the LSV curve and KL curve in Example 2. Figure 10 The 'c' in the figure corresponds to the LSV curve and KL curve in Example 3.

[0031] Figure 11The graph shows the electron transfer number and hydrogen peroxide yield of the customized iron-nickel bimetallic fiber catalysts prepared in Examples 1-3 of this invention in 0.1 MKOH electrolyte at a rotation speed of 1600 rpm. Figure 11 The a-line in the figure corresponds to the electron transfer number in Example 1. Figure 11 The d-line in the figure corresponds to the hydrogen peroxide yield in Example 1; Figure 11 The b-line in the figure corresponds to the electron transfer number in Example 2. Figure 11 The e-line in the figure corresponds to the hydrogen peroxide yield in Example 2; Figure 11 The c-line in the figure corresponds to the electron transfer number in Example 3. Figure 11 The f-line in the figure corresponds to the hydrogen peroxide yield in Example 3.

[0032] Figure 12 The LSV curves of the customized iron-nickel bimetallic fiber catalysts prepared in Examples 1-3 of this invention at 1600 rpm in 0.1 MKOH electrolyte are shown. Figure 12 In this context, 'a' corresponds to the LSV curve in Example 1; Figure 12 In this context, 'b' corresponds to the LSV curve in Example 2; Figure 12 The 'c' in the figure corresponds to the LSV curve in Example 3.

[0033] Figure 13 The above are Tafel slope diagrams corresponding to the ORR of the customized iron-nickel bimetallic fiber catalysts prepared in Examples 1-3 of this invention in 0.1 MKOH electrolyte. Figure 13 Line a in the figure corresponds to the Tafel slope in Example 1; Figure 13 The b-line in the figure corresponds to the Tafel slope in Example 2; Figure 13 The c-line in the figure corresponds to the Tafel slope in Example 3.

[0034] Figure 14 The above are Tafel slope diagrams corresponding to the OER of the customized iron-nickel bimetallic fiber catalysts prepared in Examples 1-3 of this invention in 0.1 MKOH electrolyte. Figure 14 Line a in the figure corresponds to the Tafel slope in Example 1; Figure 14 The b-line in the figure corresponds to the Tafel slope in Example 2; Figure 14 The c-line in the figure corresponds to the Tafel slope in Example 3.

[0035] Figure 15 The graph shows the ORR stability test results of the customized iron-nickel bimetallic fiber catalyst prepared in Example 1 of this invention and the commercial Pt / C catalyst in 0.1M KOH electrolyte.

[0036] Figure 16The customized iron-nickel bimetallic fiber catalyst prepared in Example 1 of this invention and the commercial Pt / C+RuO2 catalyst are used as the air cathode of a zinc-air battery, and the corresponding charge-discharge cycle diagrams of the zinc-air battery are shown.

[0037] Figure 17 These are SEM images of the single-metal fiber catalysts prepared in Comparative Examples 1-3 of this invention, which are metal-free, iron-only, and nickel-only. Figure 17 Line a in the diagram corresponds to the SEM image at scale 1. Figure 17 Line b in the diagram corresponds to the SEM image at scale 2. Figure 17 The c-line in the diagram corresponds to the SEM image at scale 3.

[0038] Figure 18 The images show the XRD patterns of the single-metal fiber catalysts prepared in Comparative Examples 1-3 of this invention, which are metal-free, iron-only, and nickel-only supported. Figure 18 Line a in the diagram corresponds to the XRD pattern at scale 1. Figure 18 Line b in the diagram corresponds to the XRD pattern at scale 2. Figure 18 The c-line in the diagram corresponds to the XRD plot at scale 3.

[0039] Figure 19 The graphs show the ORR (Oriented Return Rate) and LSV (Less Per Variable Value) of the metal-free / iron-only / nickel-only single-metal fiber catalysts prepared in Comparative Examples 1-3 of this invention, as well as the commercial Pt / C catalyst, in 0.1 M KOH electrolyte at 1600 rpm. Figure 19 Line a in the graph corresponds to the LSV curve at scale 1; Figure 19 Line b in the graph corresponds to the LSV curve at scale 2. Figure 19 The c-line in the graph corresponds to the LSV curve at scale 3. Figure 19 The d-line in the graph corresponds to the LSV curve of a commercial Pt / C catalyst.

[0040] Figure 20 This is a Tafel slope diagram of the ORR corresponding to the metal-free / iron-only / nickel-only single-metal fiber catalysts prepared in Comparative Examples 1-3 of this invention and the commercial Pt / C catalyst in 0.1M KOH electrolyte. Figure 20 The a-line in the figure corresponds to the Tafel slope of proportional 1; Figure 20 The b-line in the figure corresponds to the Tafel slope of scale 2; Figure 20 The c-line in the figure corresponds to the Tafel slope of scale 3; Figure 20 The d-line in the figure corresponds to the Tafel slope of a commercial Pt / C catalyst.

[0041] Figure 21The figures show the LSV curves of the OER at 1600 rpm for the metal-free / iron-only / nickel-only single-metal fiber catalysts prepared in Comparative Examples 1-3 of this invention and the commercial RuO2 catalyst in 0.1 M KOH electrolyte. Figure 21 Line a in the figure corresponds to the LSV curve with a scale of 1; Figure 21 Line b in the figure corresponds to the LSV curve of scale 2. Figure 21 The c-line in the figure corresponds to the LSV curve of scale 3; Figure 21 The d-line in the figure corresponds to the LSV curve of a commercial RuO2 catalyst.

[0042] Figure 22 This is a Tafel slope diagram of the OER corresponding to the metal-free / iron-only / nickel-only single-metal fiber catalysts prepared in Comparative Examples 1-3 of this invention and the commercial RuO2 catalyst in 0.1M KOH electrolyte. Figure 22 The a-line in the figure corresponds to the Tafel slope of proportional 1; Figure 22 The b-line in the figure corresponds to the Tafel slope of scale 2; Figure 22 The c-line in the figure corresponds to the Tafel slope of scale 3; Figure 22 The d-line in the figure corresponds to the Tafel slope of a commercial RuO2 catalyst. Detailed Implementation

[0043] The preferred embodiments of the present invention will be described in detail below with reference to the accompanying drawings to provide a clearer understanding of the invention's purpose, features, and advantages. It should be understood that the embodiments shown in the drawings are not intended to limit the scope of the invention, but are merely illustrative of the essential spirit of the invention's technical solution.

[0044] In the following description, certain specific details are set forth for the purpose of illustrating various disclosed embodiments in order to provide a thorough understanding of the various disclosed embodiments. However, those skilled in the art will recognize that embodiments may be practiced without one or more of these specific details. In other instances, well-known apparatuses, structures, and techniques associated with this application may not have been shown or described in detail to avoid unnecessarily obscuring the description of the embodiments.

[0045] Unless the context requires otherwise, throughout the specification and claims, the word “comprising” and its variations, such as “including” and “having”, shall be understood to have an open, inclusive meaning, that is, to be interpreted as “including, but not limited to”.

[0046] Throughout this specification, references to "an embodiment" or "an embodiment" indicate that a particular feature, structure, or characteristic described in connection with the embodiment is included in at least one embodiment. Therefore, the appearance of "in an embodiment" or "an embodiment" in various places throughout the specification does not necessarily refer to the same embodiment. Furthermore, a particular feature, structure, or characteristic may be combined in any manner in one or more embodiments.

[0047] The singular forms “a” and “the” used in this specification and the appended claims include plural references unless otherwise expressly stated herein. It should be noted that the term “or” is generally used to mean “and / or” unless otherwise expressly stated herein.

[0048] Furthermore, the technical features involved in the different embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0049] Example 1 1. This embodiment demonstrates a method for preparing a customized iron-nickel bimetallic atomic fiber catalyst (Fe4 / Fe,Ni-DACs@BCF) according to the following steps: S1. Synthesis of pre-coordination compounds: 0.0336 g of Fe(NO3)3·9H2O, 0.0247 g of Ni(NO3)2·6H2O, and 0.028 g of dicyandiamide were dissolved in 1.3 mL of DMF solvent. The mixture was magnetically stirred at room temperature for 5 min and then sonicated at a constant temperature for 15 min (ultrasonic conditions: temperature 20℃, power 1800W) to obtain a solution of DMF, H2O, and dicyandiamide molecules in coordination, hereinafter referred to as solution A.

[0050] S2. Preparation of polymer spinning solution: 200 mL of a methanol solution containing 20 g of 2-methylimidazole was added to 200 mL of a methanol solution containing 10 g of Zn(NO3)2·6H2O, and the mixture was magnetically stirred at room temperature for 24 h. The mixture was then washed three times with methanol and centrifuged (centrifugation parameters: 7000 rpm, 15 °C, 10 min). The collected precipitate was dried in a vacuum oven for 12 h (drying conditions: vacuum pressure ≥0.09 MPa, temperature 70 °C) to obtain ZIF-8 nanoparticles (NPs).

[0051] Subsequently, 0.504 g of ZIF-8 nanoparticles were dispersed in 2.8 mL of DMF solvent, magnetically stirred at room temperature for 30 min, and then sonicated at a constant temperature for 3 h (ultrasonic conditions: temperature 20℃, power 1800W). 0.336 g of PAN was then added to the above solution, and magnetically stirred at room temperature for 12 h to obtain a mixed solution of nanoparticles and polymer, hereinafter referred to as solution B, which includes a ZIF-8 nanoparticle to PAN mass ratio of 1.5:1.

[0052] S3. Preparation of beaded nanofiber membranes: Solution A obtained in step S1 was added to solution B obtained in step S2, and the mixture was magnetically stirred at room temperature for 2 hours to obtain a homogeneous spinning solution. The resulting spinning solution was then used to fabricate a porous micro / nanofiber membrane with a beaded structure using electrospinning technology. The final spinning solution contained 0.02 M Fe salt, 0.02 M Ni salt, and 0.08 M dicyandiamide. The electrospinning voltage was 35 kV; the solution flow rate was 1.2 mL / h; the distance from the needle to the receiving device was 18 cm; and the ambient humidity was 50 ± 5%.

[0053] S4. Preparation of iron-nickel bimetallic fiber catalysts (Fe4 / Fe,Ni-DACs@BCF) with metal diatomic / cluster heterostructures: The porous nanofiber membrane prepared in step S3 was placed in a tube furnace and pre-oxidized in an argon (Ar) environment by heating to 280°C at a rate of 2°C / min and holding for 2 hours. Then, the temperature was increased to 950°C at a rate of 5°C / min and held for 3 hours. After natural cooling to room temperature, Fe4 / Fe,Ni-DACs@BCF was obtained.

[0054] 2. The structural properties of Fe4 / Fe,Ni-DACs@BCF obtained by the above preparation method and process parameters are as follows: 1) Morphological structure: See Figure 1 As shown in a, through Figure 1 The SEM image of 'a' shows that Fe4 / Fe,Ni-DACs@BCF has a multi-level micro-nano structure; ZIF-8 derived carbon nanocages are randomly and uniformly distributed and loaded on carbon nanofibers with a diameter of less than 200 nm, forming a beaded structure; through local magnified inset, it can be further clearly observed that curled carbon nanotubes are grown on the surface of the Fe4 / Fe,Ni-DACs@BCF sample.

[0055] See Figure 2 As shown in a, through Figure 2The TEM image of a shows that Fe4 / Fe,Ni-DACs@BCF has a highly porous morphological structure, and C, N, O, Fe and Ni are uniformly dispersed on porous carbon fibers and carbon nanotubes. No metal agglomeration or uneven distribution was observed. See Figure 2 As shown in b, through Figure 2 The AC HAADF-STEM image of b in the figure shows that in Fe4 / Fe,Ni-DACs@BCF, metal atoms exist in the form of diatomic and cluster coexisting, with the size of the clusters being <3nm.

[0056] See Figure 4 As shown, the sample can still maintain good integrity after being bent and folded multiple times, indicating that Fe4 / Fe,Ni-DACs@BCF has good mechanical flexibility.

[0057] 2) Composition and fine structure: See Figure 5 As shown in a, the ICP test results show that the Fe metal content in Fe4 / Fe,Ni-DACs@BCF is 1.34wt%, the Ni metal content is 1.40wt%, and the molar ratio of Fe to Ni is close to 1:1.

[0058] See Figure 6 As shown, through Figure 6 The XRD pattern shows that the a-line representing Fe4 / Fe,Ni-DACs@BCF exhibits a characteristic peak at approximately 24° belonging to the graphitic carbon (002) crystal plane, indicating the absence of obvious metal particles and their derivatives.

[0059] See Figure 7 As shown in a, through Figure 7 The XPS elemental spectrum of a in Fe4 / Fe,Ni-DACs@BCF shows that it contains C, N, Fe, and Ni elements; see also Figure 7 As shown in b, through Figure 7 The XPS Fe 2p fine spectrum of b in the image shows that Fe atoms in both +2 and +3 valence states exist in Fe4 / Fe,Ni-DACs@BCF; see also Figure 7 As shown in c, through Figure 7 The XPS Ni 2p fine spectrum of c in Fe4 / Fe,Ni-DACs@BCF shows that there are Ni atoms in both +2 and +3 valence states, indicating that there is no elemental Ni metal.

[0060] See Figure 8 As shown in a, Figure 8The fine X-ray absorption spectrum of Fe K-edge a in the figure shows a main characteristic peak of ≈1.47 Å and a secondary coordination peak of ≈2.12 Å in Fe4 / Fe,Ni-DACs@BCF, indicating the presence of Fe-N coordination and Fe-Fe coordination; see also Figure 8 As shown in b, Figure 8 The fine X-ray absorption spectrum of the Ni K-side of b in the study shows that Fe4 / Fe,Ni-DACs@BCF has a main characteristic peak of ≈1.44 Å consistent with NiPC, indicating that only Ni-N coordination exists on it.

[0061] 3) Catalytic performance: 5 mg of Fe⁴⁺ / Fe,Ni-DACs@BCF catalyst powder was dispersed in 1.025 mL of a mixed solution containing 1 mL of ethanol / water (1:1, v / v) and 25 µL of Nafion (5 wt.%). The solution was sonicated at 5 °C for 30 min to form a homogeneous catalyst ink. 20 µL of this ink was dropped onto the surface of a glassy carbon electrode and dried to obtain the working electrode. A stone-ground rod was used as the counter electrode, and Ag / AgCl was used as the reference electrode. The performance was tested using a standard three-electrode system in 0.1 M KOH solution. A rotating disk electrode (RDE) was used at 50 mV / s. -1 CV curves were obtained at a scan rate of 5 mVs. -1 ORR-LSV curves were obtained at scan rates of 400, 625, 900, 1225, and 1600 rpm. Using a rotating ring-disc electrode (RRDE), 30 µL was dropped onto the center of a circular region on the surface of a glassy carbon electrode. After drying, the working electrode was obtained, and the results were obtained at 5 mV / s. -1 The LSV curves were obtained at a scan rate of 1600 rpm and a loop voltage of 1.195 V. The OER-LSV curves were measured in 0.1 M KOH solution at a scan rate of 1600 rpm.

[0062] See Figure 9 As shown in a, the CV curve of Fe4 / Fe,Ni-DACs@BCF shows a distinct oxygen reduction peak at 0.814 V.

[0063] See Figure 10 As shown in Figure a, the ORR half-wave potential (E) of Fe4 / Fe,Ni-DACs@BCF in alkaline medium. 1 / 2 The V value is 0.877, which is better than that of commercial Pt / C catalysts (0.849 V). According to the KL equation, it undergoes ORR via a four-electron transfer pathway.

[0064] See Figure 11As shown by lines a and d in the figure, Fe4 / Fe,Ni-DACs@BCF exhibits a high electron transfer number of n=3.93~3.99 and a very low hydrogen peroxide (H2O2) yield (<3.6%) in the potential range of 0.2~0.9V, indicating that it has high catalytic selectivity.

[0065] See Figure 12 As shown in a, at 10 mAcm -2 OER potential (E) of Fe4 / Fe,Ni-DACs@BCF j=10 The voltage is 1.546V, which is significantly better than that of commercial RuO2 catalysts (1.577V).

[0066] See Figure 13 As shown by line a in the figure, the ORR Tafel slope of Fe4 / Fe,Ni-DACs@BCF is 75.89 mVdec. -1 Less than Pt / C catalyst (93.92 mVdec) -1 This indicates that its ORR reaction kinetics are faster.

[0067] See Figure 14 As shown by line a in the figure, the OER Tafel slope of Fe4 / Fe,Ni-DACs@BCF is 77.44 mVdec. -1 It is less than the 102.66 mVdec of commercial RuO2 catalysts. -1 This indicates that it has a faster OER kinetic reaction rate.

[0068] See Figure 15 As shown, after 10 hours of continuous stability testing at a potential of 0.7V, the current retention rate of Fe4 / Fe,Ni-DACs@BCF was 95.64%, which was higher than that of the Pt / C catalyst (88.48%), indicating that the catalyst has better stability.

[0069] 4) Application in Zinc-Air Batteries (ZAB): 5 mg of Fe⁴⁺ / Fe,Ni-DACs@BCF catalyst powder was dispersed in 1.05 mL of a mixed solution containing 1 mL of ethanol / water (1:1, v / v) and 50 µL of Nafion (5 wt.%). The solution was then sonicated at 5 °C for 30 min to form a homogeneous catalyst ink. Subsequently, 825 µL of the ink was dropped onto a 0.785 cm⁻¹ solution. -2 ZAB positive electrode was obtained on a circular carbon paper. ZAB was assembled using 6M KOH + 0.2M Zn(Ac)2 as electrolyte and Zn metal sheet as negative electrode, and then tested.

[0070] See Figure 16As shown, ZAB with Fe4 / Fe,Ni-DACs@BCF as the air cathode, at 2mAcm -2 At a current density of 1000 rpm, it can cycle stably for 3300 h without significant decay of charging and discharging voltage, which is significantly longer than ZAB with commercial Pt / C+RuO2 mixed catalyst as air cathode, indicating that this catalyst has excellent cycle stability.

[0071] The test results above show that the iron-nickel bimetallic fiber catalyst (Fe4 / Fe,Ni-DACs@BCF) has a heterostructure in which Fe4 clusters and FeN4 and NiN4 bimetallic atoms coexist. The Fe4 / Fe,Ni-DACs@BCF catalyst has excellent ORR and OER catalytic activity and stability, which are superior to commercial noble metal Pt / C and RuO2 catalysts, respectively. Moreover, this catalyst shows long-term cycling stability in ZAB applications, which is significantly better than ZAB assembled based on noble metal catalysts, and shows great application potential in high energy density energy storage systems.

[0072] Example 2 1. This embodiment demonstrates a method for preparing a customized iron-nickel bimetallic fiber catalyst (Fe,Ni-NPs@BCF) according to the following steps, which is basically the same as that in Example 1, except that dicyandiamide is not added in step S1, so that Ni 2+ and Fe 3+ The coordination sites are completely occupied by DMF and H2O molecules.

[0073] 2. The structural properties of Fe,Ni-NPs@BCF obtained through the above preparation method and process parameters are as follows: 1) Morphological structure: See Figure 1 As shown in b, through Figure 1 The SEM image of b shows that Fe,Ni-NPs@BCF has a multi-level micro-nano structure; ZIF-8 derived carbon nanocages are randomly and uniformly distributed and loaded on carbon nanofibers with a diameter of less than 200 nm to form a beaded structure.

[0074] See Figure 2 As shown in c, obvious metal particles were observed in the AC HAADF-STEM image of Fe,Ni-NPs@BCF.

[0075] See Figure 3 As shown in a, through Figure 3 The TEM image of a also shows that Fe,Ni-NPs@BCF has obvious nanoparticles of about 100 nm loaded on it, and the EDS image shows that the nanoparticles are composed of Fe and Ni.

[0076] 2) Composition and fine structure: See Figure 5 As shown in b, the ICP test results show that the Fe metal content in Fe,Ni-NPs@BCF is 1.39wt% and the Ni metal content is 1.44wt%, and the molar ratio of Fe and Ni metal is close to 1:1. However, the content of both metals is slightly higher than that in Example 1. This is because metal nanoparticles are usually easier to dissolve than single atoms in the ICP pretreatment of carbon-based catalysts.

[0077] See Figure 6 As shown, through Figure 6 The XRD pattern shows that the b-line representing Fe,Ni-NPs@BCF has characteristic peaks of different intensities at approximately 30.32°, 35.78°, 43.44° and 66°.

[0078] See Figure 7 As shown in a, through Figure 7 The XPS elemental spectrum of a in Fe,Ni-NPs@BCF shows that it contains C, N, Fe, and Ni elements; see also Figure 7 As shown in b, through Figure 7 The XPS Fe 2p fine spectrum of b in Fe,Ni-NPs@BCF shows the presence of Fe atoms in three valence states: +0, +2, and +3, indicating the presence of Fe-Fe species; see also Figure 7 As shown in c, through Figure 7 The XPS Ni 2p fine spectrum of c in Fe,Ni-NPs@BCF shows the presence of Ni atoms in three valence states: 0, +2, and +3, indicating the existence of Ni-Ni species.

[0079] 3) Catalytic performance: 5 mg of Fe,Ni-NPs@BCF catalyst powder was dispersed in 1.025 mL of a mixed solution containing 1 mL of ethanol / water (1:1, v / v) and 25 µL of Nafion (5 wt.%). The solution was sonicated at 5 °C for 30 min to form a homogeneous catalyst ink. 20 µL of this ink was dropped onto the surface of a glassy carbon electrode and dried to obtain the working electrode. A stone-ground rod was used as the counter electrode, and Ag / AgCl as the reference electrode. The performance was tested using a standard three-electrode system in 0.1 M KOH solution. A rotating disk electrode (RDE) was used at 50 mV / s. -1 CV curves were obtained at a scan rate of 5 mVs. -1 ORR-LSV curves were obtained at scan rates of 400, 625, 900, 1225, and 1600 rpm. Using a rotating ring-disc electrode (RRDE), 30 µL was dropped onto the center of a circular region on the surface of a glassy carbon electrode. After drying, the working electrode was obtained, and the results were obtained at 5 mV / s. -1The LSV curves were obtained at a scan rate of 1600 rpm and a loop voltage of 0.23 V. The OER-LSV curves were measured in 0.1 M KOH solution at a scan rate of 1600 rpm.

[0080] See Figure 9 As shown in b, the CV curve of Fe,Ni-NPs@BCF shows a distinct oxygen reduction peak at 0.779V.

[0081] See Figure 10 As shown in b, the ORR half-wave potential (E) of Fe,Ni-NPs@BCF in alkaline medium. 1 / 2 The value is 0.836V, and calculations based on the corresponding KL equation show that ORR is mainly performed via a four-electron transfer path.

[0082] See Figure 11 As shown by lines b and e in the figure, Fe,Ni-NPs@BCF exhibits an electron transfer number of n=3.71~3.98 and a low hydrogen peroxide (H2O2) yield (<14.65%) in the potential range of 0.2~0.9V.

[0083] See Figure 12 As shown in b, at 10mAcm -2 The OER overpotential (Ej=10) of Fe,Ni-NPs@BCF is 1.648V.

[0084] See Figure 13 As shown by line b in the figure, the ORR Tafel slope of Fe,Ni-NPs@BCF is 85.31 mVdec. -1 Less than Pt / C catalyst (93.92 mVdec) -1 This indicates that its ORR reaction kinetics are faster.

[0085] See Figure 14 As shown by line b in the figure, the OER Tafel slope of Fe,Ni-NPs@BCF is 103.89 mVdec- 1 .

[0086] The test results above show that the customized iron-nickel bimetallic fiber catalyst (Fe,Ni-NPs@BCF) has a specific structure in which iron oxide and FeNi alloy nanoparticles coexist. The Fe,Ni-NPs@BCF catalyst with this structure has certain ORR and OER catalytic activities, but is slightly inferior to commercial Pt / C and RuO2 catalysts.

[0087] Example 3 1. This embodiment demonstrates a method for preparing a customized iron-nickel bimetallic fiber catalyst (Fe,Ni-DACs@BCF) according to the following steps, which is basically the same as that in Example 1, except that: in step S1, 0.028g of dicyandiamide is replaced with 0.084g of dicyandiamide to ensure sufficient dicyandiamide ligands in the solution, which can simultaneously satisfy Ni 2+ and Fe 3+ The coordination requirements.

[0088] 2. The structural properties of Fe,Ni-DACs@BCF obtained through the above preparation method and process parameters are as follows: 1) Morphological structure: See Figure 1 As shown in c, through Figure 1 The SEM image of c shows that Fe,Ni-DACs@BCF has a multi-level micro-nano structure; ZIF-8 derived carbon nanocages are randomly and uniformly distributed and loaded on carbon nanofibers with a diameter of less than 200 nm to form a beaded structure.

[0089] See Figure 2 As shown in d, through Figure 2 The AC HAADF-STEM image of d shows that in Fe,Ni-DACs@BCF, all metal atoms exist in the form of single atoms.

[0090] See Figure 3 As shown in b, through Figure 3 The TEM image of b in the figure shows that Fe,Ni-DACs@BCF has a highly porous morphology, and C, N, Fe and Ni are uniformly dispersed on porous carbon fibers and carbon nanotubes. No metal agglomeration or uneven distribution was observed.

[0091] 2) Composition and fine structure: See Figure 5 As shown in c, the ICP test results show that the Fe metal content in Fe,Ni-DACs@BCF is 1.30 wt% and the Ni metal content is 1.37 wt%. The molar ratio of Fe to Ni is closer to 1:1 compared with Example 1 and Example 2, but the Fe and Ni metal contents are slightly lower than those in Example 1 and Example 2. This is because metal single atoms are usually more difficult to dissolve in the ICP pretreatment of carbon-based catalysts.

[0092] See Figure 6 As shown, through Figure 6 The XRD pattern shows that the c-line representing Fe,Ni-DACs@BCF exhibits a characteristic peak at approximately 24° belonging to the graphitic carbon (002) crystal plane, indicating that there is no obvious formation of metal and its derivative particles.

[0093] SeeFigure 7 As shown in a, through Figure 7 The XPS elemental spectrum of a in Fe,Ni-DACs@BCF shows that it contains C, N, Fe, and Ni elements; see also Figure 7 As shown in b, through Figure 7 The XPS Fe 2p fine spectrum of b in the image shows that only Fe atoms in the +2 and +3 valence states exist in Fe4 / Fe,Ni-DACs@BCF, indicating the absence of Fe-Fe species; see also Figure 7 As shown in c, through Figure 7 The XPS Ni 2p fine spectrum of c in Fe,Ni-DACs@BCF shows that there are Ni atoms in both +2 and +3 valence states, indicating that there is no Ni-Ni species.

[0094] See Figure 8 As shown in a, Figure 8 The fine X-ray absorption spectrum of Fe K-edge a in the figure shows that Fe,Ni-DACs@BCF have only a main characteristic peak of ≈1.44 Å, indicating that only Fe-N species exist thereon; see also Figure 8 As shown in b, Figure 8 The fine X-ray absorption spectrum of the NiK-edge of b in the study shows that Fe,Ni-DACs@BCF has a main characteristic peak of ≈1.44 Å consistent with NiPC, indicating the presence of Ni-N species on it.

[0095] 3) Catalytic performance: 5 mg of Fe,Ni-DACs@BCF catalyst powder was dispersed in 1.025 mL of a mixed solution containing 1 mL of ethanol / water (1:1, v / v) and 25 µL of Nafion (5 wt.%). The solution was sonicated at 5 °C for 30 min to form a homogeneous catalyst ink. 20 µL of this ink was dropped onto the surface of a glassy carbon electrode and dried to obtain the working electrode. A stone-ground rod was used as the counter electrode, and Ag / AgCl was used as the reference electrode. The performance was tested using a standard three-electrode system in 0.1 M KOH solution. A rotating disk electrode (RDE) was used at 50 mV / s. -1 CV curves were obtained at a scan rate of 5 mVs. -1 ORR-LSV curves were obtained at scan rates of 400, 625, 900, 1225, and 1600 rpm. Using a rotating ring-disc electrode (RRDE), 30 µL was dropped onto the center of a circular region on the surface of a glassy carbon electrode. After drying, the working electrode was obtained, and the results were obtained at 5 mV / s. -1 The LSV curves were obtained at a scan rate of 1600 rpm and a loop voltage of 0.23 V. The OER-LSV curves were measured in 0.1 M KOH solution at a scan rate of 1600 rpm.

[0096] See Figure 9 As shown in c, the CV curve of Fe,Ni-DACs@BCF shows a distinct oxygen reduction peak at 0.804 V.

[0097] See Figure 10 As shown in c, the ORR half-wave potential (E) of Fe,Ni-DACs@BCF in alkaline medium. 1 / 2 The V value is 0.873, which is better than that of commercial Pt / C catalysts (0.849 V). According to the corresponding KL equation calculation, it performs ORR via a four-electron transfer pathway.

[0098] See Figure 11 As shown by the c and f lines, Fe,Ni-DACs@BCF exhibits a high electron transfer number of n=3.82~3.98 and a very low hydrogen peroxide (H2O2) yield (<9.14%) in the potential range of 0.2~0.9V, indicating that it has high catalytic selectivity.

[0099] See Figure 12 As shown in c, at 10 mAcm -2 The OER overpotential (Ej=10) of Fe,Ni-DACs@BCF is 1.566V, which is lower than that of commercial RuO2 catalyst (1.577V).

[0100] See Figure 13 As shown by line c in the figure, the ORR Tafel slope of Fe,Ni-DACs@BCF is 77.75 mVdec. -1 Less than Pt / C catalyst (93.92 mVdec) -1 This indicates that its ORR reaction kinetics are faster.

[0101] like Figure 14 As shown by line c in the figure, the OER Tafel slope of Fe,Ni-DACs@BCF is 94.11 mVdec. -1 It is less than the 102.66 mVdec of commercial RuO2 catalysts. -1 This indicates that it has a faster OER kinetic reaction rate.

[0102] The test results above show that the customized iron-nickel bimetallic fiber catalyst (Fe,Ni-DACs@BCF) has a specific structure in which Fe-N4 and Ni-N4 coexist. The Fe,Ni-DACs@BCF catalyst with this structure has excellent ORR and OER catalytic activity, which is better than commercial Pt / C and RuO2 catalysts, but slightly worse than Fe4 / Fe,Ni-DACs@BCF catalyst with Fe4 atomic clusters and Fe-N4 and Ni-N4 coexistence.

[0103] Comparative Example 1 1. This comparative example demonstrates a method for preparing a metal-free supported fiber catalyst (BCF) according to the following steps, which is basically the same as that in Example 1, except that Fe(NO3)3·9H2O and Ni(NO3)2·6H2O are not added in step S1, and only dicyandiamide is introduced.

[0104] 2. The structural performance test results of BCF obtained by the above preparation method and process parameters are as follows: See Figure 17 As shown in a, through Figure 17 The SEM image of a shows that BCF has a multi-level micro-nano structure; ZIF-8 derived carbon nanocages are randomly and uniformly distributed and loaded on carbon nanofibers with a diameter of less than 200 nm to form a beaded structure.

[0105] See Figure 18 As shown, through Figure 18 The XRD pattern shows that the a-line representing BCF exhibits a characteristic peak at approximately 24° that belongs to the (002) crystal plane of graphitic carbon.

[0106] See Figure 19 As shown by line a, the ORR half-wave potential (E) of BCF in alkaline medium 1 / 2 The value is 0.769V.

[0107] See Figure 20 As shown by line a in the figure, the slope of the ORR Tafel for BCF is 91.75mVdec. -1 .

[0108] See Figure 21 As shown by line a in the figure, at 10 mA cm -2 The OER overpotential (Ej=10) of BCF was 1.831V, which is relatively low.

[0109] See Figure 22 As shown by line a in the figure, the OER Tafel slope of BCF is 156.82mVdec. -1 .

[0110] The test results above show that the catalytic activity of the metal-free fiber catalyst (BCF) is significantly lower in both ORR and OER. This is because although the few defect sites on the metal-free catalyst have certain oxygen catalytic activity, the intrinsic catalytic activity of these sites is extremely low.

[0111] Comparative Example 2 1. This embodiment demonstrates a method for preparing an iron-loaded single-atom fiber catalyst (Fe-SACs@BCF) according to the following steps, which is basically the same as that in Example 1, except that Ni(NO3)2·6H2O is not added in step S1, but only Fe(NO3)3·9H2O and dicyandiamide are introduced.

[0112] 2. The structural properties of Fe-SACs@BCF obtained through the above preparation method and process parameters are as follows: See Figure 17 As shown in b, through Figure 17 The SEM image of b shows that Fe-SACs@BCF has a multi-level micro-nano structure; ZIF-8 derived carbon nanocages are randomly and uniformly distributed and loaded on carbon nanofibers with a diameter of less than 200 nm to form a beaded structure.

[0113] See Figure 18 As shown, through Figure 18 The XRD pattern shows that the b-line representing Fe-SACs@BCF exhibits a characteristic peak at approximately 24° belonging to the (002) crystal plane of graphitic carbon, with no obvious Fe and its derivative particles.

[0114] See Figure 19 As shown by line b, the ORR half-wave potential (E) of Fe-SACs@BCF in alkaline medium 1 / 2 The value was 0.867 V, which is better than that of commercial Pt / C catalysts (0.849 V), indicating that the ORR activity of iron single atoms is higher than that reported in the literature.

[0115] See Figure 20 As shown by line b in the figure, the ORR Tafel slope of Fe-SACs@BCF is 80.12 mVdec. -1 Less than Pt / C catalyst (93.92 mVdec) -1 This indicates that its ORR reaction kinetics are faster.

[0116] See Figure 21 As shown by line b in the figure, at 10 mA cm -2 The OER overpotential (Ej=10) of Fe-SACs@BCF was 1.744V, which is relatively low. This indicates that the results reported in the literature are consistent with the poor OER activity of metallic iron.

[0117] See Figure 22 As shown by line b in the figure, the OER Tafel slope of Fe-SACs@BCF is 128.47 mVdec. -1 This is higher than the 102.66 mVdec of commercial RuO2 catalysts. -1This indicates that its OER kinetic reaction rate is relatively high.

[0118] The test results above show that an iron-supported single-atom fiber catalyst (Fe-SACs@BCF) exhibits high ORR activity, but poor OER activity, making it difficult to achieve bifunctional catalysis of ORR and OER, consistent with literature reports. Furthermore, the ORR and OER activities of Fe-SACs@BCF are significantly lower than those of Example 1 (E... 1 / 2 =0.877V, Ej=10=1.546V) and Example 3 (E 1 / 2 =0.873V, Ej=10=1.566V), indicating that the introduction of Ni metal not only compensates for the lack of OER activity in Fe-SACs@BCF, but also plays a synergistic role in promoting the ORR catalytic activity of Fe atoms. Meanwhile, the Ej of Fe-SACs@BCF is... 1 / 2 It is also significantly higher than that of Example 2 (E) 1 / 2 =0.836V). The above results collectively indicate that not only does the type of metal atoms supported on the catalyst affect its ORR and OER catalytic performance, but the local structure of the supported metal atoms is also crucial to its catalytic performance.

[0119] Comparative Example 3 1. This embodiment demonstrates a method for preparing a nickel-supported single-atom fiber catalyst (Ni-SACs@BCF) according to the following steps, which is basically the same as that in Example 1, except that Fe(NO3)3·9H2O is not added in step S1, but only Ni(NO3)2·6H2O and dicyandiamide are introduced.

[0120] 2. The structural performance test results of Ni-SACs@BCF obtained by the above preparation method and process parameters are as follows: See Figure 17 As shown in c, through Figure 17 The SEM image of c shows that Ni-SACs@BCF has a multi-level micro-nano structure; ZIF-8 derived carbon nanocages are randomly and uniformly distributed and loaded on carbon nanofibers with a diameter of less than 200 nm to form a beaded structure.

[0121] See Figure 18 As shown, through Figure 18 The XRD pattern shows that the c-line representing Ni-SACs@BCF exhibits a characteristic peak at approximately 24° belonging to the graphitic carbon (002) crystal plane, with no obvious Ni and its derivative particles forming.

[0122] See Figure 19 As shown by line c, the ORR half-wave potential (E) of Ni-SACs@BCF in alkaline medium 1 / 2The value was 0.772V, lower than that of commercial Pt / C catalysts (0.849V), indicating that, consistent with the results reported in the literature, nickel single atoms have essentially no ORR activity.

[0123] See Figure 20 As shown by line c in the figure, the ORR Tafel slope of Ni-SACs@BCF is 101.27 mVdec. -1 Greater than Pt / C catalyst (93.92 mVdec) -1 This indicates that its ORR reaction kinetics are slower.

[0124] See Figure 21 As shown by line c in the figure, at 10 mA cm -2 The OER overpotential (Ej=10) of Ni-SACs@BCF was 1.725V, which is relatively low. This is consistent with the results reported in the literature, and the OER activity of Ni single atoms is usually poor.

[0125] See Figure 22 As shown by line c in the figure, the OER Tafel slope of Ni-SACs@BCF is 183.63 mVdec. -1 .

[0126] The test results above show that the ORR and OER performance of the iron-supported single-atom fiber catalyst (Ni-SACs@BCF) are both poor, indicating that single Ni metal lacks bifunctional activity in ORR and OER.

[0127] The test results of Examples 1-3 and Comparative Examples 1-3 show that the preparation method of the present invention achieves precise control of the localized structure of metal diatomic atoms through a differentiated coordination strategy of small organic molecules (controllable construction of three structures: FeNi diatomic, FeNi diatomic / Fe cluster, and FeNi alloy). The constructed FeNi diatomic / Fe cluster diatomic fiber catalyst exhibits excellent ORR and OER bifunctional catalytic performance, which is superior to commercially available (Pt / C and RuO2). In addition, the zinc-air battery constructed based on the FeNi diatomic / Fe cluster diatomic fiber catalyst exhibits stable charge-discharge performance exceeding 3000 h, and the zinc-air battery can stably cycle for 3300 h (cycles) with the carbon fiber bifunctional oxygen catalyst. Therefore, the FeNi diatomic / Fe cluster diatomic fiber catalyst prepared by the present invention is expected to be applied in the field of energy catalysis, specifically as a positive electrode catalyst for zinc-air batteries, and used in the production of high-efficiency energy storage devices such as zinc-air batteries.

[0128] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for preparing a locally tunable iron-nickel diatomic fiber catalyst, characterized in that, Based on the differential coordination strategy of small organic molecules, the following steps are included: Step 1) Fe(NO3)3·9H2O, Ni(NO3)2·6H2O and dicyandiamide in a certain molar ratio are dissolved together in DMF solvent, and after magnetic stirring at room temperature and constant temperature ultrasonic treatment, a homogeneous mixed solution A is obtained. Step 2) Add the methanol solution containing 2-methylimidazole to the methanol solution containing Zn(NO3)2·6H2O, stir magnetically at room temperature, wash with methanol, and then centrifuge and vacuum dry to obtain ZIF-8 nanoparticles. Step 3) After magnetic stirring at room temperature and constant temperature ultrasonic treatment, ZIF-8 nanoparticles are uniformly dispersed in DMF solvent, then polyacrylonitrile polymer is added, and after magnetic stirring, solution B is obtained. Step 4) Add solution A to solution B, and after magnetic stirring at room temperature, a uniformly mixed spinning solution is obtained. Then, a porous nanofiber membrane with a beaded structure is obtained by electrospinning technology. Step 5) The porous nanofiber membrane is subjected to pre-oxidation and high-temperature carbonization treatment in sequence to finally obtain a carbon nanofiber OER / ORR bifunctional oxygen catalyst loaded with Fe and Ni bimetallic atoms.

2. The method for preparing the iron-nickel diatomic fiber catalyst with precisely tunable local structure according to claim 1, characterized in that, In step 1, the molar ratio of Fe(NO3)3·9H2O, Ni(NO3)2·6H2O and dicyandiamide is 1:1:(0~20). The room temperature magnetic stirring time after Fe(NO3)3·9H2O, Ni(NO3)2·6H2O and dicyandiamide are dissolved together in DMF solvent is 5 min. The temperature of the isothermal ultrasonic treatment is 20℃, the power of the isothermal ultrasonic treatment is 1800W, and the time of the isothermal ultrasonic treatment is 15 min.

3. The method for preparing the iron-nickel diatomic fiber catalyst with precisely tunable local structure according to claim 1, characterized in that, In step 2, the mass ratio of 2-methylimidazole to Zn(NO3)2·6H2O is 3:(1~3). The methanol solution containing 2-methylimidazole is added to the methanol solution containing Zn(NO3)2·6H2O and the stirring time at room temperature is 24h. The methanol washing is performed 3 times. The centrifugation speed is 7000rpm, the centrifugation temperature is 15℃, and the centrifugation time is 10min. The vacuum pressure of the drying process is ≥0.09MPa, the drying temperature is 70℃, and the drying time is 12h.

4. The method for preparing the iron-nickel diatomic fiber catalyst with precisely tunable local structure according to claim 1, characterized in that, In step 3, the mass ratio of polyacrylonitrile polymer to ZIF-8 nanoparticles is 1:(1.2~3), the room temperature magnetic stirring time of ZIF-8 nanoparticles is 30 min, the temperature of isothermal ultrasonic treatment is 20℃, the power of isothermal ultrasonic treatment is 1800W, the isothermal ultrasonic treatment time is 3 h, and the magnetic stirring time after dispersing ZIF-8 nanoparticles in DMF solvent and adding polyacrylonitrile polymer is 12 h.

5. The method for preparing the iron-nickel diatomic fiber catalyst with precisely tunable local structure according to claim 1, characterized in that, In step 4, the room temperature magnetic stirring time after adding solution A to solution B is 2 hours, and the concentration of Fe(NO3)3·9H2O in the spinning solution is 0~0.03M, the concentration of Ni(NO3)2·6H2O is 0~0.03M, and the concentration of dicyandiamide is 0~0.6M.

6. The method for preparing the iron-nickel diatomic fiber catalyst with precisely tunable local structure according to claim 1, characterized in that, In step 4, the conditions for the electrospinning technology are as follows: The voltage is 35kV; The solution flow rate is 1.2 mL / h; The distance from the needle tip to the receiving device is 18cm; The ambient humidity is 50±5%.

7. The method for preparing the iron-nickel diatomic fiber catalyst with precisely tunable local structure according to claim 1, characterized in that, In step 5, the specific steps of the pre-oxidation and high-temperature carbonization treatment are as follows: The porous nanofiber membrane was placed in a tube furnace and heated to 280°C at a rate of 2°C / min under an argon atmosphere and held for 2 hours for pre-oxidation. Then, the temperature is increased to 950℃ at a rate of 5℃ / min and held for 3 hours for high-temperature carbonization. After natural cooling to room temperature, a bifunctional oxygen catalyst with Fe and Ni bimetallic sites was obtained from carbon nanofibers.

8. A locally tunable iron-nickel diatomic fiber catalyst, characterized in that, It is prepared using the method for preparing iron-nickel diatomic fiber catalysts with precisely tunable local structures as described in any one of claims 1 to 7.

9. The application of a locally tunable iron-nickel diatomic fiber catalyst as described in claim 8 in energy catalytic reactions.

10. The application according to claim 9, characterized in that, The iron-nickel diatomic fiber catalyst with precisely tunable local structure is used as the positive electrode catalyst for zinc-air batteries and is used in the preparation of zinc-air batteries.

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