Difunctional oxygen electrocatalyst and preparation and application thereof

Abstract

The invention relates to the technical field of difunctional oxygen electrocatalysts and rechargeable zinc air batteries, in particular to a difunctional oxygen electrocatalyst and preparation and application thereof.The preparation method of the difunctional oxygen electrocatalyst comprises the following steps that 1, iron phthalocyanine (II) and nickel phthalocyanine (II) are mixed to obtain iron-nickel mixed powder, then a carbon nanomaterial is added, then ultrasonic treatment is conducted in an organic solvent, and the carbon nanomaterial is obtained; then centrifugally separating the mixed powder and the solvent; (2) drying the separated mixed powder, and grinding; and (3) putting the ground powder into a tubular furnace, and heating for 1 hour in an argon atmosphere at 800 DEG C to obtain the difunctional oxygen electrocatalyst FeNi-coated NC-CNM with a core-shell structure. The difunctional oxygen electrocatalyst prepared by the invention has good performance in the aspects of OER and ORR, the application test in a zinc-air battery shows that the open-circuit voltage of a rechargeable battery reaches 1.43 V and is far higher than that of a commercial Pt / C + RuO2 electrode (1.36 V), and meanwhile, the difunctional oxygen electrocatalyst has high power density (192 mW / cm < 2 >) and long service life (stable operation for 400 hours).

Description

Technical Field

[0001] The present invention relates to the technical fields of bifunctional oxygen electrocatalysts and rechargeable zinc-air batteries, and particularly relates to a bifunctional oxygen electrocatalyst and its preparation and application. Background Art

[0002] Although lithium-ion batteries have received the most attention from researchers and have been popularized in various fields at present. However, the low energy density and safety problems of currently available lithium-ion batteries (LIBs) severely limit their development. To solve these problems, many researchers have studied next-generation battery systems with higher energy density, greater safety, and lower cost. Metal-air batteries (MABs) have received extensive attention from researchers due to their higher theoretical energy density and renewable fuel resources. Among them, zinc-air batteries are relatively good metal-air batteries due to their safe, non-toxic, and low-cost properties. Currently, regarding the development of zinc-air batteries, the key obstacle lies in their air cathodes. Rechargeable zinc-air batteries (RZAB) involve oxygen reduction reaction (ORR) during discharge and oxygen evolution reaction (OER) during charging. Therefore, it is necessary to design an efficient bifunctional electrocatalyst.

[0003] Most of the commonly used bifunctional oxygen electrocatalysts on the market are noble metal catalysts such as Pt and Pd. However, noble metal catalysts have high costs and insufficient stability. Therefore, how to provide a non-noble metal efficient and stable bifunctional electrocatalyst to replace them is a technical problem that those skilled in the art urgently need to solve. Summary of the Invention

[0004] In view of the above problems, the core design idea of this research is to construct an efficient, stable, and cost-controllable bifunctional oxygen electrocatalyst to improve the performance of RZABs. To this end, an FeNi alloy is selected as the active metal center, and the nanoparticles are coated with a graphitized carbon shell layer, and combined with a carbon nanostructure as a carrier to improve the dispersibility, stability, and electrocatalytic activity of the catalyst.

[0005] To achieve the above object, the present invention adopts the following technical solutions:

[0006] A preparation method of a bifunctional oxygen electrocatalyst, comprising the following steps:

[0007] (1) Mix iron(II) phthalocyanine FePc and nickel(II) phthalocyanine NiPc to obtain an iron-nickel mixed powder, then add a carbon nanomaterial, and then perform ultrasonic treatment in an organic solvent, and then centrifuge to separate the mixed powder and the solvent;

[0008] (2) Dry and grind the separated mixed powder, and mix evenly;

[0009] (3) The ground powder is placed in a tubular furnace and heated in an argon atmosphere at 600-900 °C for 0.5-2 hours to obtain a core-shell structured bifunctional oxygen electrocatalyst FeNi@NC-CNM.

[0010] In the present invention, two metal phthalocyanines, iron phthalocyanine and nickel phthalocyanine, are selected as catalyst precursors. Metal phthalocyanines will undergo pyrolysis at high temperatures to form metal nanoparticles and amorphous carbon. During this process, the transition metal nanoparticles of Fe and Ni will catalyze the surrounding carbon to form a carbon nanoshell and wrap it around the metal (FeNi@NC-None). Since phthalocyanines of two metals are used, they will also form an alloy structure of FeNi during the pyrolysis process, which can effectively adjust the electronic structure of the core metal. Compared with the single Fe metal, the d-band center of the overall alloy moves downward, moderately adjusting the adsorption energy of the intermediates in the electrocatalytic reaction process, thereby optimizing the electrochemical reaction path.

[0011] In the molecular structure of metal phthalocyanines, there are four benzene ring-like structures, and the carbon atoms among them have undergone sp 2 hybridization, which enables the unhybridized pz orbitals to form a large π bond, the same as the carbon atoms in carbon nanomaterials (MWCNT, SWCNT, Graphene) and the carbon nanoshell formed after the pyrolysis of phthalocyanines. Therefore, non-covalent π-π interactions can occur between them and they can adsorb together.

[0012] The present invention adopts a method of precursor adsorption + one-step pyrolysis, that is, FePc and NiPc are uniformly adsorbed on the carbon support (FeNi@NC-CNM) through π-π interaction, and one-step carbonization is carried out in a high-temperature argon atmosphere.

[0013] Preferably, the carbon nanomaterial is one or more of multi-walled carbon nanotubes (Multi-walled Carbon Nanotube, MWCNT), single-walled carbon nanotubes (Single-walled Carbon Nanotube, SWCNT), and graphene (Graphene, G).

[0014] Preferably, the mass ratio of iron(II) phthalocyanine to nickel(II) phthalocyanine is 1:2 - 2:1, and the mass ratio of the added carbon nanomaterial to the iron-nickel mixed powder is 1:3 - 3:1.

[0015] Preferably, the organic solvent is anhydrous ethanol, isopropanol, propanol or acetone.

[0016] Preferably, in step (2), the separated mixed powder is dried in a vacuum drying oven at a temperature of 40 °C - 100 °C for 12 - 48 hours.

[0017] The present invention also discloses the application of the bifunctional oxygen electrocatalyst prepared by the above-mentioned preparation method in a rechargeable zinc-air battery.

[0018] Furthermore, the application of the bifunctional oxygen electrocatalyst in the air cathode of a rechargeable zinc-air battery.

[0019] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0020] In the present invention, the introduction of the bimetallic FeNi alloy has a synergistic effect. Among them, Fe mainly enhances the ORR activity, while Ni improves the OER performance, enabling the catalyst to exhibit excellent performance in bifunctional catalysis. However, the bare FeNi particles are prone to corrosion in a strong alkaline electrolyte, and the metal particles are likely to agglomerate during the high-temperature pyrolysis process, resulting in a decrease in specific surface area and a reduction in active sites. To solve these problems, the present invention adopts a strategy of coating with a graphitized carbon shell layer, which protects the metal core of this core-shell structure and prevents its oxidation during the reaction. In addition, the carbon shell layer can optimize the adsorption ability of the material to oxygen intermediates through the electronic effect with transition metals, thereby improving the electrocatalytic activity.

[0021] To further optimize the dispersibility and electron transfer ability of the catalyst, the present invention introduces carbon nanostructure carriers (such as MWCNT, SWCNT, Graphene) during the synthesis of FeNi nanoparticles. The addition of the carbon carrier can effectively regulate the number of shell layers of the core-shell structure, strengthen the electron transfer effect between carbon and metal, and solve the problem of the thick carbon nano shell synthesized by many researchers through the one-step pyrolysis method of the precursor. In addition, the introduction of the carbon nano carrier also inhibits the sintering and agglomeration of FeNi particles during the high-temperature pyrolysis process, maintaining their small size and uniform distribution, thereby exposing more active sites. Moreover, these carbon carriers themselves have excellent electronic conductivity, which can significantly improve the electron transfer rate of the catalyst, thus accelerating the reaction kinetics.

[0022] The present invention also uses nitrogen doping (N-doping) to further enhance the catalytic performance. The nitrogen element mainly comes from the FePc and NiPc precursors and can be incorporated into the carbon skeleton during the high-temperature pyrolysis process to form different types of nitrogen species such as pyridinic N, metal-nitrogen coordination (M-Nx), and graphitic N. Among them, the M-Nx structure can serve as an efficient active center to improve the adsorption and charge transfer ability of oxygen; pyridinic nitrogen regulates the electron density on the carbon surface and improves the kinetics of the ORR reaction; while graphitic nitrogen can enhance the conductivity of the carbon carrier and further enhance the overall catalytic activity.

[0023] The FeNi-based transition metal bifunctional oxygen electrocatalyst encapsulated by a graphite shell prepared in this invention is verified to have good performance in both OER and ORR through a series of characterization methods (TEM (In situ), EDS, XRD, Raman, XPS) and electrochemical tests. In addition, the application test of this catalyst in a zinc-air battery shows that the open-circuit voltage of its rechargeable battery reaches 1.43 V, which is much higher than that of a commercial Pt / C+RuO2 electrode (1.36 V). Meanwhile, it has a high power density (192 mW / cm 2 ) and a long lifespan (stable operation for 400 hours), demonstrating good performance. Description of the Drawings

[0024] Attachment Figure 1 is the material synthesis roadmap for Example 1 and Comparative Example 1;

[0025] Attachment Figure 2 is the characterization diagram of the samples prepared in Example 1 and Comparative Example 1; among them, a-d are the morphology (a), high-resolution images with different resolutions (b, c), and EDX characterization diagram (d) of FeNi@NC-None, and e-j are the morphology diagrams (e, f, g) and high-resolution images (h, i, j) of the samples after loading MWCNT, SWCNT, and Graphene respectively. The insets in the upper right corners of all morphology diagrams are the particle size distribution statistical diagrams of the corresponding samples.

[0026] Attachment Figure 3 is the XRD, Raman, and XPS characterization diagrams of the samples prepared in Example 1 and Comparative Example 1; among them, a is the XRD diagram, b is the Raman characterization, c is the ratio comparison diagram of the intensities of the D peak and G peak in Raman, d is the total spectrum of XPS, e is the high-resolution N1s diagram of XPS, and f is the proportion diagram of various N elements.

[0027] Attachment Figure 4 is the in-situ study during the synthesis process of the FeNi@NC-MWCNT sample (a-i) prepared in Example 1 and the FeNi@NC-None sample (j-l) prepared in Comparative Example 1.

[0028] Attachment Figure 5 is the OER and ORR electrochemical performance test of the samples in Example 1 and Comparative Example 1; among them, a is the LSV scanning curve of OER in an alkaline environment, b is the tafel slope calculated from Figure a, c is the double-layer capacitance test diagram, d is the sample impedance diagram, e is the LSV scanning curve of ORR in an alkaline environment, and f is the electron transfer number and H2O2 yield during the ORR process measured by the RRDE electrode for FeNi@NC-G.

[0029] Attachment Figure 6RZAB performance tests were conducted on the samples prepared in Example 1 and Comparative Example 1 and Pt / C + RuO2. Among them, a is a physical diagram of the test battery, b is an open-circuit voltage test diagram, c is a polarization current density curve during charge and discharge, d is a power density curve, e is a constant current discharge test curve of RZAB when FeNi@NC-G and Pt / C + RuO2 are used as cathode catalysts, and f is a constant current charge and discharge test curve of the battery when the two catalysts described in e are applied to RZAB. Detailed implementation mode

[0030] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0031] Example 1

[0032] A preparation method of a bifunctional oxygen electrocatalyst includes the following steps:

[0033] Mix FePc and NiPc in a mass ratio of 1:1, and then introduce MWCNT, SWCNT, and Graphene with the same mass ratio as the mixed phthalocyanine powder as carriers respectively. Ultrasonic the mixed powder in an absolute ethanol solvent for 1 hour, and then centrifuge and separate the powder and the solvent at a speed of 10,000 rpm. Then dry the separated powder in a vacuum drying oven at a temperature of 60 °C for 24 hours. Finally, grind the dried powder with a mortar and put it into a tubular furnace, and heat it in an argon atmosphere at 800 °C and 300 sccm for 1 hour to obtain the final core-shell structure powder samples, named FeNi@NC-MWCNT, FeNi@NC-SWCNT, and FeNi@NC-G respectively.

[0034] Comparative Example 1

[0035] Mix FePc and NiPc in a mass ratio of 1:1, ultrasonic the mixed powder in an absolute ethanol solvent for 1 hour, and then centrifuge and separate the powder and the solvent at a speed of 10,000 rpm. Then dry the separated powder in a vacuum drying oven at a temperature of 60 °C for 24 hours. Finally, grind the dried powder with a mortar and put it into a tubular furnace, and heat it in an argon atmosphere at 800 °C and 300 sccm for 1 hour to obtain the final core-shell structure powder sample FeNi@NC-None.

[0036] Figure 1Shows the synthesis routes of the samples in Example 1 and Comparative Example 1. By directly pyrolyzing FePc and NiPc, a graphite-encapsulated transition metal structure similar to that synthesized by most current researchers through pyrolysis of MOFs in the market can be directly synthesized. To improve the sample structure, carbon nanocarriers (MWCNT, SWCNT, Graphene) were introduced. The carriers and the two metal phthalocyanines were first ultrasonically mixed in absolute ethanol and then pyrolyzed at high temperature, which can form a control group with the samples prepared by direct pyrolysis (Comparative Example 1).

[0037] Figure 2 TEM was used to characterize the morphology and high resolution of the four samples prepared in Example 1 and Comparative Example 1. It can be found that for the samples with carriers introduced (FeNi@NC-MWCNT / SWCNT / G), compared with the samples without carriers, not only the average grain size becomes smaller, but also the number of carbon shells outside the metal decreases significantly. In addition, the introduced carbon nanocarriers do not decompose after heating, which enables more active sites to be exposed per unit mass of the sample, enhances the electron interaction between the metal core and the outermost carbon shell, and improves the conductivity of the sample under the action of the carbon nanocarriers.

[0038] Figure 3 The composition, structure and chemical state of the four catalysts prepared in Example 1 and Comparative Example 1 were analyzed by characterization methods such as XRD, Raman and XPS. Among them, XRD( Figure 3 a) shows that all samples have similar diffraction characteristics. The peaks at 43.74° and 50.91° correspond to the (111) and (200) crystal planes of the face-centered cubic (fcc) structure of FeNi(1:1), indicating that a nanoalloy structure can be formed by pyrolyzing the mixed phthalocyanines. In addition, the broad peak at 26° is attributed to C(002), indicating the formation of graphene-like carbon. With the introduction of carbon nanomaterials, the C(002) peak is enhanced, reflecting the graphitized structure of the carbon carrier.

[0039] In the Raman analysis Figure 3 b mainly shows the D-band and G-band peaks at 1350 cm -1 and 1583 cm -1 . Among them, the G-band reflects the graphitization degree of the carbon material, and the D-band reflects the structural defects in the carbon material. With the introduction of carbon nanocarriers, Figure 3 c shows the ID / IG ratios of the four samples (FeNi@NC-None: 1.03; FeNi@NC-MWCNT: 0.93; FeNi@NC-SWCNT: 1.00; FeNi@NC-G: 0.97). The decrease in the ID / IG ratio indicates an increase in the crystallinity of the material, and a higher graphitization degree helps to improve the conductivity.

[0040] XPS analysisFigure 3 It is shown in d that the catalyst surface is mainly composed of Fe, Ni, N, C, and O elements. Among them, due to the low content and high dispersion of Fe and Ni, their signals in the carbon support are weak. High-resolution N 1s spectrum ( Figure 3 e) resolves five nitrogen species: nitrogen oxide (405.42 eV), graphitic nitrogen (402.10 eV), pyrrolic nitrogen (401.02 eV), metal-coordinated nitrogen (M-Nx, 400.10 eV), and pyridinic nitrogen (398.90 eV). With the introduction of the support, the contents of metal-coordinated nitrogen and other nitrogen species increase ( Figure 3 f), indicating that the carbon support affects the chemical environment of the metal catalyst. Among them, pyridinic nitrogen can regulate the charge distribution and spin density of carbon atoms, metal-coordinated nitrogen is generally considered as the active site for ORR, and graphitic nitrogen can promote electron transport, improve the electrical conductivity of the catalyst, and thus enhance the catalytic activity.

[0041] Figure 4 The in-situ transmission electron microscopy (in-situ TEM) technique was used to characterize its growth process.

[0042] In the case of (FeNi@NC-MWCNT) supported on MWCNT ( Figure 4 a-i):

[0043] Using MWCNT as the support, FePc and NiPc mixed phthalocyanine were dispersed on the surface of the support (the principle of this support is that the sp 2 hybrid carbon atoms in the metal phthalocyanine molecule form π bonds, and π-π non-covalent interactions occur with the π bonds in the support and adsorb on the support), and heating observation was carried out at 800 °C. The study found that the phthalocyanine molecules first decomposed into amorphous carbon and small metal particles. After about 20 minutes, these particles gradually evolved into a clearer particle structure. Due to the catalytic effect of the formed metal particles, the amorphous carbon became its carbon nanoshell layer, and this shell layer was also adsorbed on the carbon tube wall through π-π interactions, making it remain relatively stable. Experiments show that the particles basically stop moving after 20 minutes of formation, and only the size increases slightly.

[0044] In the case of no support (FeNi@NC-None) ( Figure 4 j-l):

[0045] Due to the absence of carbon nanotubes as a support, the particles formed after heating FePc and NiPc mixed phthalocyanine are larger, and the amorphous carbon formed by decomposition is randomly distributed in the whole area. Due to the lack of the confinement effect of the support and the influence of the concentration gradient of surrounding carbon atoms, the metal particles move rapidly and are extremely prone to sintering during the movement, resulting in a significant increase in the final particle size and a significant increase in the number of shell layers.

[0046] Figure 5 The OER polarization curves of the four samples prepared in Example 1 and Comparative Example 1 were measured in 1 M KOH using linear sweep voltammetry (LSV, scan rate 2 mV / s). Figure 5 a The results show that the overpotential (296 - 323 mV) of the catalyst - loaded sample at 10 mA / cm 2 is much lower than that of the catalyst - free sample (335 mV). The Tafel slope ( Figure 5 b) shows that the catalyst - loaded samples have faster reaction kinetics, and FeNi@NC - G performs the best (44.1 mV / dec). The electrochemical double - layer capacitance (Cdl) test ( Figure 5 c - d) indicates that the FeNi@NC - G has the largest Cdl value (2.28 mF / cm 2 ), higher than that of FeNi@NC - MWCNT (1.65 mF / cm 2 ), FeNi@NC - SWCNT (1.61 mF / cm 2 ), and FeNi@NC - None (1.55 mF / cm 2 ), indicating its larger active surface area. The electrochemical impedance spectroscopy (EIS) results show that FeNi@NC - G has the smallest electron - transfer resistance, indicating its best electron - transport performance.

[0047] In addition, the ORR performance test was also carried out in 0.1 M KOH under oxygen - saturated conditions at 1600 rpm. It can be concluded that the onset potential of the catalyst - loaded samples is more positive (0.932 - 0.935 V) ( Figure 5 e), much higher than that of the catalyst - free sample (0.834 V), indicating a significant improvement in catalytic performance; the half - wave potential of the catalyst - loaded samples (0.824 - 0.837 V) is much higher than that of the catalyst - free sample (0.568 V), reflecting better oxygen - reduction activity. This improvement is attributed to the thinner carbon - nanoshell layer, higher dispersion, and better conductivity of the catalyst - loaded samples. In addition, since FeNi@NC - G showed the best performance in previous tests, in order to calculate the number of transferred electrons during its reaction process, LSV tests were carried out on it in a rotating ring - disk electrode (RRDE) ( Figure 5 f), showing that the number of transferred electrons is higher than 3.8 and the hydrogen - peroxide generation rate is lower than 10%, indicating its high ORR selectivity and dominant 4 - electron transfer mechanism.

[0048] Figure 6 The performance evaluation of rechargeable zinc - air batteries (RZABs) based on FeNiC catalysts was demonstrated. The practical application performance of the four catalysts prepared in Example 1 and Comparative Example 1 in rechargeable zinc - air batteries (RZABs) was tested and compared with commercial Pt / C + IrO2.

[0049] Figure 6 a shows the battery structure used in the test. A 0.5-mm-thick Zn metal sheet was selected as the anode, four catalysts prepared in Example 1 and Comparative Example 1 or Pt / C+IrO2 (1:1 mixture) were respectively loaded on the air cathode, and 6M KOH+0.2M zinc acetate (Zn(OAc)2) was used as the electrolyte. In addition, to eliminate the concentration gradient of the electrolyte, a small circulation pump was used to improve the stability of the battery. Figure 6 b measured the open-circuit voltage of the zinc-air battery composed of four samples. Among them, the open-circuit voltage of the FeNi@NC-G-based RZAB was the most prominent, reaching 1.43 V, higher than that of commercial Pt / C+RuO2 (1.36 V) and the unloaded FeNi@NC-None catalyst, indicating its better electrochemical activity. By testing their charge-discharge polarization curves ( Figure 6 c), it was found that the voltage gap of the battery loaded with the catalyst was smaller than that of the battery without the catalyst and the noble metal catalyst battery, meaning better charge-discharge reversibility and better cycling performance. The maximum power density ( Figure 6 d) showed that the peak power density of the battery loaded with the catalyst reached 188-192 mW / cm 2 , much higher than that of Pt / C+RuO2 (101 mW / cm 2 ) and the unloaded catalyst (32 mW / cm 2 ), demonstrating better catalytic activity. Figure 6 e tested the specific capacity and zinc utilization rate of FeNi@NC-G and noble metal catalysts. The results showed that the specific capacity of the FeNi@NC-G-based battery was 793 mAh / g and the zinc utilization rate was 96.7% (10 mA / cm 2 ), higher than that of Pt / C+RuO2 (specific capacity 745 mAh / g, zinc utilization rate 90.85%), showing higher energy conversion efficiency. Finally, to measure the stability of the catalyst, constant current charge-discharge tests ( Figure 6 f) were carried out using FeNi@NC-G and noble metal catalysts. The tests were carried out under the condition of a current density of 10 mA / cm 2 and each charge-discharge cycle of 30 minutes (15 minutes of discharge + 15 minutes of charge). The results showed that the RZAB using FeNi@NC-G as the cathode catalyst still worked stably after more than 700 cycles, showing excellent durability. The RZAB of the commercial Pt / C+IrO2 catalyst showed a significant charge-discharge voltage decay after only 14 cycles, indicating its poor durability.

[0050] The foregoing description of the disclosed embodiments enables those skilled in the art to implement or use the present invention. Various modifications to these embodiments will be apparent to those skilled in the art, and the general principles defined herein can be implemented in other embodiments without departing from the spirit or scope of the present invention. Thus, the present invention is not intended to be limited to the embodiments shown herein but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A preparation method of a bifunctional oxygen electrocatalyst, characterized in that, It includes the following steps: (1) Mix ferrous phthalocyanine (II) and nickel phthalocyanine (II) to obtain an iron-nickel mixed powder, then add carbon nanomaterials, then perform ultrasonic treatment in an organic solvent, and then centrifuge to separate the mixed powder and the solvent; (2) Dry the separated mixed powder and then grind it; (3) Put the ground powder into a tubular furnace and heat it in an argon atmosphere at 600-900 °C for 0.5-2 hours to obtain a core-shell structured bifunctional oxygen electrocatalyst FeNi@NC-CNM.

2. The preparation method of a bifunctional oxygen electrocatalyst according to claim 1, characterized in that, The carbon nanomaterials are one or more of multi-walled carbon nanotubes, single-walled carbon nanotubes, and graphene.

3. The preparation method of a bifunctional oxygen electrocatalyst according to claim 1, characterized in that, The mass ratio of ferrous phthalocyanine (II) to nickel phthalocyanine (II) is 1:2 to 2:1, and the mass ratio of the added carbon nanomaterials to the iron-nickel mixed powder is 1:3 to 3:

1.

4. The preparation method of a bifunctional oxygen electrocatalyst according to claim 1, characterized in that, The organic solvent is anhydrous ethanol, isopropanol, propanol or acetone.

5. The preparation method of a bifunctional oxygen electrocatalyst according to claim 1, characterized in that, In step (2), the separated mixed powder is dried in a vacuum drying oven at a temperature of 40 °C to 100 °C for 12 to 48 hours and ground to be uniformly mixed.

6. A bifunctional oxygen electrocatalyst prepared by the preparation method according to any one of claims 1-5.

7. Application of the bifunctional oxygen electrocatalyst according to claim 5 in a rechargeable zinc-air battery.

8. Application of the bifunctional oxygen electrocatalyst according to claim 5 in an air cathode of a rechargeable zinc-air battery.

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