A bifunctional catalyst, its preparation method and application

Abstract

This invention discloses a bifunctional catalyst, its preparation method, and its application, comprising the following steps: first, ZIF-8 is subjected to pyrolysis treatment; then, it is impregnated with a loaded iron source followed by carbothermal shock treatment; finally, it is impregnated with a loaded soluble metal salt followed by carbothermal shock treatment. This invention combines the advantages of high-entropy alloys and single-atom catalysts, utilizing thermal shock pyrolysis to obtain a bifunctional catalyst with uniform catalytic distribution, good catalytic activity, high stability, a simple preparation method, good catalyst performance, and ease of widespread application.

Description

Technical Field

[0001] This invention belongs to the field of battery material preparation technology, specifically relating to a bifunctional catalyst, its preparation method, and its application. Background Technology

[0002] In recent decades, the extensive development and application of fossil fuels have led to a sharp decline in their reserves; simultaneously, the large-scale use of fuels such as coal and oil has exacerbated environmental pollution. Therefore, finding new technologies for storing and converting energy is a current research hotspot. Rechargeable zinc-air batteries (RZABs) are green, safe, and high-power energy supply devices that can significantly reduce our dependence on fossil fuels and address today's environmental problems. The oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) occur at the air electrode of the battery device. Bifunctional oxygen electrocatalysts are one of the core factors determining the efficiency and performance of RZABs, and nanomaterials with highly efficient catalytic activity show promising application prospects in RZABs.

[0003] For a long time, Pt-based and Ru-based catalysts have been the most relied-upon materials for ORR / OER because these two types of noble metal catalysts have moderate adsorption and desorption strengths for oxygen-containing intermediates, thus becoming the benchmark catalysts for ORR and OER. However, these two noble metals are extremely rare in nature, expensive, and have poor durability and resistance to poisoning, which severely limits their widespread application. Among many non-noble metal catalysts, atomically dispersed transition metal-nitrogen-carbon (MNC, M=Ni, Fe, Co, etc.) materials have attracted widespread attention due to their noble metal-like catalytic activity. Compared with traditional oxygen electrocatalysts, atomically dispersed catalysts have almost 100% utilization of active sites, which significantly reduces the cost of catalyst preparation and use; by precisely controlling the microstructure and atomic site distribution of the material, the stability and catalytic activity of nanomaterials can be greatly improved.

[0004] There are currently many reports on single-atom catalysts. Chinese patent application number 202010564117.8 discloses a single-atom cobalt-supported nitrogen-doped graphite-carbon cathode catalyst for metal-air batteries. This method prepares a single-atom cobalt-supported graphite-carbon material, and the catalyst's current density can reach 290 mA·cm² at 0.5V. -2Chinese patent application number 202310580148.6 discloses a composite catalyst in which metal nanoparticles and single atoms coexist. Although its catalytic performance is good, its atom utilization rate is limited. In addition, there are reports on the use of high-entropy alloy catalysts in zinc-air batteries. Besides high configurational entropy, high-entropy alloy nanoparticles also exhibit lattice distortion, hysteretic diffusion, and the cocktail effect. These effects work together to give high-entropy alloy nanoparticles good multifunctional catalytic potential. For example, Chinese patent application number 202410299244.8 discloses a high-entropy alloy composite material, its Joule heating preparation method, and its application in zinc-air batteries. However, when high-entropy alloys are used for catalysis, most atoms are located inside the alloy and cannot participate in the catalytic reaction.

[0005] In summary, single-atom catalysts limit the efficiency of multi-step reactions due to the single type of active center. While high-entropy alloy catalysts have a rich variety of active sites, they have a smaller specific surface area and lower active site utilization compared to single-atom catalysts. Therefore, this invention is proposed. Summary of the Invention

[0006] To address the shortcomings of existing technologies, the present invention aims to provide a bifunctional catalyst, its preparation method, and its application. Combining the advantages of high-entropy alloys and single-atom catalysts, a bifunctional catalyst with uniform distribution, good catalytic activity, and high stability is obtained by thermal shock pyrolysis.

[0007] To achieve the above objectives, the present invention adopts the following technical solution:

[0008] In a first aspect, the present invention provides a method for preparing a bifunctional catalyst, wherein ZIF-8 is first subjected to pyrolysis treatment, then impregnated with a loaded iron source and subjected to carbothermal shock treatment, and finally impregnated with a loaded soluble metal salt and subjected to carbothermal shock treatment.

[0009] In the above technical solution, the applicant proposes a strategy of loading high-entropy alloys onto single atoms to solve the trade-off between the two. The high-entropy alloy, as a carrier, can effectively anchor single atoms and prevent agglomeration and loss. At the same time, the composition of the high-entropy alloy is adjustable, enabling fine control of performance. The combination of the two has a synergistic catalytic effect. Single atoms provide precise active sites, while high-entropy alloys provide diverse local environments, which can achieve efficient synergy in single-step and multi-step reactions.

[0010] Furthermore, the preparation method provided by this invention utilizes carbothermal shock to achieve the rapid formation and uniform distribution of high-entropy alloys on single atoms. A bifunctional catalyst with a uniformly distributed high-entropy alloy@carbon matrix is ​​obtained through short-time, precise thermal shock pyrolysis of a spatially confined precursor (e.g., a multi-element metal-organic framework, MOF). Rapid heating and cooling help prevent elemental segregation and promote uniform distribution. Simultaneously, rapid pyrolysis can inherit the multi-scale porous structure of precursors such as MOFs, forming unique porous single-atom structures connected by a three-dimensional carbon framework. This facilitates the exposure of more active sites and electrolyte permeation. Moreover, the anchoring of the single atom to the subsequent high-entropy alloy (HEA) is crucial to improving the bifunctional activity and stability of the catalyst.

[0011] Specifically, the above preparation method includes the following steps:

[0012] (1) Preparation of ZIF-8;

[0013] (2) Preparation of NC: The ZIF-8 obtained in step (1) is subjected to pyrolysis to obtain NC material;

[0014] (3) The iron source solution is impregnated and dripped onto the NC material obtained in step (2), and after grinding and drying, it is subjected to carbon thermal shock treatment to obtain FeNC single-atom material;

[0015] (4) The soluble metal salt solution is impregnated and dropped onto the FeNC single-atom material obtained in step (3), and after grinding and drying, it is subjected to carbon thermal shock treatment to obtain the bifunctional catalyst.

[0016] In the above technical solution, the preparation of ZIF-8 in step (1) can be achieved using existing preparation methods. For example, it can be prepared using a method including the following steps:

[0017] A zinc source was added to methanol, and the solution was ultrasonically treated to obtain solution A.

[0018] The organic ligand was added to methanol and ultrasonically treated to obtain solution B;

[0019] Solution A and solution B are mixed and then subjected to sonication while being stirred to obtain solution C;

[0020] After washing, centrifuging and drying solution C, ZIF-8 is obtained.

[0021] As a preferred embodiment of the present invention, in the preparation process of ZIF-8 provided above, the zinc source is Zn(NO3)2·6H2O, and the concentration of solution A is 0.1-0.4 mol / L. It is understood that the concentration of solution A can be any value among 0.1 mol / L, 0.15 mol / L, 0.2 mol / L, 0.25 mol / L, 0.3 mol / L, 0.35 mol / L, and 0.4 mol / L, or any value within the above range, and those skilled in the art can flexibly choose the appropriate value.

[0022] The organic ligand is selected from one or more of imidazole, dimethylimidazolium, imidazole-2-carboxaldehyde, benzimidazole, 5-methylbenzimidazole, and 2-aminobenzimidazole, and the concentration of solution B is 0.4–1.6 mol / L. It is understood that the organic ligand can be selected as needed, and preferably, dimethylimidazolium is selected as the organic ligand. The concentration of solution B can be any value from 0.4 mol / L, 0.5 mol / L, 0.6 mol / L, 0.7 mol / L, 0.8 mol / L, 0.9 mol / L, 1 mol / L, 1.1 mol / L, 1.2 mol / L, 1.3 mol / L, 1.4 mol / L, 1.5 mol / L, and 1.6 mol / L, or any value within the above range; those skilled in the art can flexibly choose the appropriate value.

[0023] The stirring speed is 800–1500 rpm, and the stirring time is 6–48 h; magnetic stirring is preferred. It is understood that the stirring speed can be any value from 800 rpm, 900 rpm, 1000 rpm, 1100 rpm, 1200 rpm, 1300 rpm, 1400 rpm, 1500 rpm, or any value within the above range, and the stirring time can be any value from 6 h, 8 h, 10 h, 12 h, 14 h, 16 h, 18 h, 20 h, 22 h, 24 h, 26 h, 28 h, 30 h, 32 h, 34 h, 36 h, 38 h, 40 h, 42 h, 44 h, 46 h, 48 h, or any value within the above range; those skilled in the art can flexibly choose the appropriate value.

[0024] Centrifugation speed is 5000–10000 rpm, and centrifugation time is 1–5 min. This means the centrifugation speed can be 5000 rpm, 5100 rpm, 5200 rpm, 5300 rpm, 5400 rpm, 5500 rpm, 5600 rpm, 5700 rpm, 5800 rpm, 5900 rpm, 6000 rpm, 6100 rpm, 6200 rpm, 6300 rpm, 6400 rpm, 6500 rpm, 6600 rpm, 6700 rpm, 6800 rpm, 6900 rpm, 7000 rpm, 7100 rpm, 7200 rpm, 7300 rpm, 7400 rpm, 7500 rpm, 7600 rpm, 7700 rpm, 7800 rpm, 7900 rpm. The centrifugation speed can be any value selected from 0 rpm, 8000 rpm, 8100 rpm, 8200 rpm, 8300 rpm, 8400 rpm, 8500 rpm, 8600 rpm, 8700 rpm, 8800 rpm, 8900 rpm, 9000 rpm, 9100 rpm, 9200 rpm, 9300 rpm, 9400 rpm, 9500 rpm, 9600 rpm, 9700 rpm, 9800 rpm, and 9900 rpm, or any value within the above range. The centrifugation time can be any value selected from 1 min, 2 min, 3 min, 4 min, and 5 min, or any value within the above range. Those skilled in the art can choose flexibly. It should be noted that washing solution C is to remove impurities such as uncoordinated ligands, and the washing agent can be at least one of methanol, ethanol, isopropanol, and N,N-dimethylformamide.

[0025] As a preferred embodiment of the present invention, the pyrolysis treatment temperature of ZIF-8 is 900–1100℃, the heating rate is 5–10℃ / min, and the holding time is 30–60min. It is understood that the pyrolysis treatment temperature can be any value from 900℃, 910℃, 920℃, 930℃, 940℃, 950℃, 960℃, 970℃, 980℃, 990℃, 1000℃, 1010℃, 1020℃, 1030℃, 1040℃, 1050℃, 1060℃, 1070℃, 1080℃, 1090℃, and 1100℃, or any value within the aforementioned range. The heating rate can be any value from 5℃ / min, 6℃ / min, 7℃ / min, 8℃ / min, 9℃ / min, and 10℃ / min, or any value within the aforementioned range. Those skilled in the art can flexibly choose the appropriate rate. It is particularly important to emphasize that the above pyrolysis process can be carried out under an atmosphere, which can be either N2 or Ar.

[0026] As a preferred embodiment of the present invention, the iron source solution is obtained by dissolving FeCl3·6H2O in ethanol, with a molar concentration of iron atoms of 0.1–0.3 mol / L and an impregnation loading of 0.01–5 wt%.

[0027] As a preferred embodiment of the technical solution of the present invention, the carbon thermal shock conditions in step (3) are: pulse heating treatment under nitrogen or argon protection, with a current of 10-60A and a treatment time of 10ms-1s. It should be particularly emphasized that pulse heating treatment is an existing technical means and can be carried out with reference to patent document CN114361634A. Specifically, a pulse power supply can be selected as the heating power supply, the pulse current waveform is a square wave, the voltage is 20-60V, the pulse time is adjusted by a relay, the pulse frequency is 0.1-1HZ, the heating time accounts for 1-5%, and the number of pulses is 1-5.

[0028] As a preferred embodiment of the present invention, the metals in the soluble metal salt solution are selected from at least five of Fe, Co, Ni, Mn, Cr, Mo, Zn, Sn, and W, with a total concentration of 0.02–0.5 mol / L and an impregnation loading of 0.01–5 wt%. Preferably, the atomic ratios of the metal salts in the soluble metal salt solution are the same.

[0029] As a preferred embodiment of the technical solution of the present invention, the carbon thermal shock conditions in step (3) are: pulse heating treatment under nitrogen or argon protection, with a current of 10-60A and a treatment time of 10ms-1s. Similarly, pulse heating treatment is an existing technical means and can be performed with reference to patent document CN114361634A. Specifically, a pulse power supply can be selected as the heating power supply, the pulse current waveform is a square wave, the voltage is 20-60V, the pulse time is adjusted by a relay, the pulse frequency is 0.1-1HZ, the heating time accounts for 1-5%, and the number of pulses is 1-5.

[0030] Secondly, the present invention aims to protect the bifunctional catalysts prepared by the above method.

[0031] Thirdly, this invention aims to protect the application of the above-mentioned bifunctional catalyst in the preparation of OER / ORR electrocatalysts and the application of the above-mentioned catalyst in the preparation of zinc-air batteries.

[0032] Compared with the prior art, the present invention has the following beneficial effects:

[0033] (1) The bifunctional catalyst provided by this invention proposes a strategy of loading high-entropy alloys onto single atoms to solve the trade-off between the two. The high-entropy alloy as a support can effectively anchor single atoms and prevent agglomeration and loss. At the same time, the composition of the high-entropy alloy is adjustable, which can achieve fine control of performance. The combination of the two has a synergistic catalytic effect. Single atoms provide precise active sites, and high-entropy alloys provide diverse local environments, which can achieve efficient synergy of single-step and multi-step reactions, making full use of the advantages of high-entropy alloys and single-atom catalysts.

[0034] (2) The method for preparing the bifunctional catalyst provided by this invention utilizes rapid pyrolysis via carbothermal shock to enable the carbon support to inherit the multi-scale porous structure of MOF, forming a unique porous and layered single-atom supported HEA connected by a three-dimensional carbon framework. Compared with common bifunctional catalysts, the HEA@FeNC bifunctional catalyst prepared by this invention not only has tunable HEA composition but also increases the specific surface area of ​​the carbon support, thereby exposing more catalytic active sites, increasing the adsorption and activation efficiency of reactants, and thus enhancing catalytic activity.

[0035] (3) The bifunctional catalyst provided by the present invention improves the stability of FeNC catalyst by introducing HEA, thereby significantly enhancing the stability of the bifunctional catalyst.

[0036] (4) The bifunctional catalyst provided by the present invention improves the OER performance of FeNC catalyst by introducing HEA, and improves the bifunctional activity by utilizing the synergistic effect of HEA+FeNC.

[0037] (5) The HEA@FeNC bifunctional catalyst provided by this invention exhibits high activity in OER / ORR electrocatalysts, with a half-wave potential of 0.9V in ORR and 10mA / cm² in OER. -2 The overpotential is 280mV, ΔE(E J＝10 - E 1 / 2 The voltage is 0.61V.

[0038] (6) The preparation method of the bifunctional catalyst provided by the present invention is simple, the preparation time is fast, the composition is controllable, the process is stable and highly repeatable, and the cost is low. Attached Figure Description

[0039] Figure 1 The images show the surface morphology of the ZIF-8 and NC materials of this invention.

[0040] Figure 2 X-ray diffraction patterns of HEA@FeNC were prepared for Examples 1, 1 Comparative Example, and 2 of this invention.

[0041] Figure 3The image shows the surface morphology of the HEA@FeNC bifunctional catalyst prepared in Example 1 of this invention.

[0042] Figure 4 The elemental distribution diagram is shown for the HEA@FeNC bifunctional catalyst prepared in Example 1.

[0043] Figure 5 Figure 1 shows the LSV curves of different bifunctional catalyst materials of the present invention; wherein, Figure (a) shows the OER performance test and Figure (b) shows the ORR performance test.

[0044] Figure 6 This is a stability curve of the bifunctional catalyst material in Example 1 of the present invention after 20K cycles.

[0045] Figure 7 The graph shows the cyclic charge-discharge stability of the bifunctional catalyst in Example 1 of this invention with a commercial Pt / C+IrO2 zinc-air battery. Detailed Implementation

[0046] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0047] It should be noted that the metal salt in the HEA precursor can be at least five of the following: Fe, Co, Ni, Mn, Cr, Mo, Zn, Sn, W, etc. Therefore, the HEA@FeNC bifunctional catalyst prepared by the carbothermal shock method in this invention has universality and can be used to prepare various combinations of HEA@single-atom catalysts. It can also be used to prepare quaternary, ternary, and binary alloy@single-atom catalysts.

[0048] Example 1

[0049] A method for synthesizing a HEA@FeNC bifunctional catalyst includes the following steps:

[0050] (1) Preparation of ZIF-8: 6.78g Zn(NO3)2·6H2O was dissolved in 300mL methanol solution, and 7.88g dimethylimidazole was dissolved in 300mL methanol solution. The solutions were ultrasonicated for 15min each until they were completely dissolved in the methanol solution. The dimethylimidazole methanol solution was then poured into zinc nitrate methanol solution and ultrasonicated for another 15min. The mixture was then placed on a magnetic stirrer and stirred at 1200rpm for 12h to obtain a milky white suspension. The suspension was centrifuged and washed three times, and then dried in a vacuum dryer at 60℃ for 360min to obtain ZIF-8.

[0051] (2) Preparation of NC: 300 mg ZIF-8 was placed in a magnetic boat and annealed at 1000 °C under an argon atmosphere for 30 min, and then naturally cooled to room temperature to obtain nitrogen-doped carbon with MOF morphology.

[0052] (3) Preparation of FeNC: 267 μL of 0.2 mol / L FeCl3·6H2O ethanol solution was impregnated onto 100 mg of nitrogen-doped carbon obtained in step (2), and the carbon was manually ground in a mortar until the ethanol was completely evaporated. The FeNC precursor was collected. The FeNC precursor was placed on a 1.5 cm * 4 cm carbon cloth, and the carbon cloth was clamped between the two ends of a pulse power supply and subjected to a carbon thermal shock at 1800 °C for 100 ms in an argon atmosphere to obtain the FeNC single-atom catalyst.

[0053] (4) Preparation of HEA@FeNC: 25 μL of 0.2 mol / L Fe, Co, Ni, Mo and Zn ethanol salt solution (with the same atomic ratio of each metal element) was impregnated onto 100 mg of FeNC single-atom catalyst obtained in step (3), and the mixture was manually ground in a mortar until the ethanol was completely evaporated. The HEA@FeNC precursor was collected. Similarly, the HEA@FeNC precursor was subjected to the same carbothermal shock as in step (3), but the temperature was changed to 1300 °C to obtain the HEA@FeNC bifunctional catalyst.

[0054] Example 2

[0055] A method for synthesizing a HEA@FeNC bifunctional catalyst includes the following steps:

[0056] (1) Preparation of ZIF-8: 6.78g Zn(NO3)2·6H2O was dissolved in 300mL methanol solution, and 7.88g dimethylimidazole was dissolved in 300mL methanol solution. The solutions were ultrasonicated for 15min each until they were completely dissolved in the methanol solution. The dimethylimidazole methanol solution was then poured into zinc nitrate methanol solution and ultrasonicated for another 15min. The mixture was then placed on a magnetic stirrer and stirred at 1200rpm for 12h to obtain a milky white suspension. The suspension was centrifuged and washed three times, and then dried in a vacuum dryer at 60℃ for 360min to obtain ZIF-8.

[0057] (2) Preparation of NC: 300 mg ZIF-8 was placed in a magnetic boat and annealed at 1000 °C under an argon atmosphere for 30 min, and then naturally cooled to room temperature to obtain nitrogen-doped carbon with MOF morphology.

[0058] (3) Preparation of FeNC: 267 μL of 0.2 mol / L FeCl3·6H2O ethanol solution was impregnated onto 100 mg of nitrogen-doped carbon obtained in step (2) of Example 1. The carbon was then manually ground in a mortar until the ethanol was completely evaporated, and the FeNC precursor was collected. The FeNC precursor was placed on a 1.5 cm * 4 cm carbon cloth, which was held between the two ends of a pulse power supply and subjected to a carbon thermal shock at 1300 °C for 300 ms in an argon atmosphere to obtain the FeNC single-atom catalyst.

[0059] (4) Preparation of HEA@FeNC: 25 μL of a 0.2 mol / L solution of Fe, Co, Ni, Mn, and Cr ethanol salts (with the same atomic ratio of each metal element) was impregnated onto 100 mg of the FeNC single-atom catalyst obtained in step (3). The mixture was then manually ground in a mortar until the ethanol was completely evaporated, and collected as the HEA@FeNC precursor. Similarly, the HEA@FeNC precursor was subjected to the same carbothermal shock as in step (3) at a temperature of 1300 °C and a pyrolysis time of 200 ms to obtain the HEA@FeNC bifunctional catalyst.

[0060] Example 3

[0061] A method for synthesizing a HEA@FeNC bifunctional catalyst includes the following steps:

[0062] (1) Preparation of ZIF-8: 6.78g Zn(NO3)2·6H2O was dissolved in 300mL methanol solution, and 7.88g dimethylimidazole was dissolved in 300mL methanol solution. The solutions were ultrasonicated for 15min each until they were completely dissolved in the methanol solution. The dimethylimidazole methanol solution was then poured into zinc nitrate methanol solution and ultrasonicated for another 15min. The mixture was then placed on a magnetic stirrer and stirred at 1200rpm for 12h to obtain a milky white suspension. The suspension was centrifuged and washed three times, and then dried in a vacuum dryer at 60℃ for 360min to obtain ZIF-8.

[0063] (2) Preparation of NC: 300 mg ZIF-8 was placed in a magnetic boat and annealed at 1000 °C under an argon atmosphere for 30 min, and then naturally cooled to room temperature to obtain nitrogen-doped carbon with MOF morphology.

[0064] (3) Preparation of FeNC: 267 μL of 0.2 mol / L FeCl3·6H2O ethanol solution was impregnated onto 100 mg of nitrogen-doped carbon obtained in step (2), and the carbon was manually ground in a mortar until the ethanol was completely evaporated. The FeNC precursor was collected. The FeNC precursor was placed on a 1.5 cm * 4 cm carbon cloth, and the carbon cloth was clamped between the two ends of a pulse power supply and subjected to a carbon thermal shock at 1800 °C for 100 ms in an argon atmosphere to obtain the FeNC single-atom catalyst.

[0065] (4) Preparation of HEA@FeNC: 100 μL of 0.2 mol / L Fe, Co, Ni, Mo, Zn ethanol salt solution (with the same atomic ratio of each metal element) was impregnated onto 100 mg of FeNC single-atom catalyst. The solution was then manually ground in a mortar until the ethanol was completely evaporated. The HEA@FeNC precursor was collected. The HEA@FeNC precursor was placed on a 1.5 cm * 4 cm carbon cloth, which was then held between the two ends of a pulse power supply and subjected to a carbon thermal shock at 1300 °C for 100 ms in an argon atmosphere to obtain the HEA@FeNC bifunctional catalyst.

[0066] Comparative Example 1

[0067] The catalyst provided in Comparative Example 1 does not anchor HEA to FeNC, but uses carbon black. Specifically, the HEA@C catalyst using carbon black includes the following steps;

[0068] 25 μL of a 0.2 mol / L solution of Fe, Co, Ni, Mo, and Zn ethoxides (with the same atomic ratio of each metal element) was impregnated onto 100 mg of carbon black. The mixture was then manually ground in a mortar until the ethanol was completely evaporated, and the HEA@C precursor was collected. The HEA@C precursor was placed on a 1.5 cm * 4 cm carbon cloth, which was then held between the two ends of a pulsed power supply and subjected to a carbothermic shock at 1300 °C for 100 ms in an argon atmosphere to obtain the HEA@C catalyst.

[0069] Comparative Example 2

[0070] In Comparative Example 2, no carbothermal shock treatment of the HEA was used. Specifically, the preparation of a catalyst included the following steps:

[0071] (1) Preparation of ZIF-8: 6.78g Zn(NO3)2·6H2O was dissolved in 300mL methanol solution, and 7.88g dimethylimidazole was dissolved in 300mL methanol solution. The solutions were ultrasonicated for 15min each until they were completely dissolved in the methanol solution. The dimethylimidazole methanol solution was then poured into zinc nitrate methanol solution and ultrasonicated for another 15min. The mixture was then placed on a magnetic stirrer and stirred at 1200rpm for 12h to obtain a milky white suspension. The suspension was centrifuged and washed three times, and then dried in a vacuum dryer at 60℃ for 360min to obtain ZIF-8.

[0072] (2) Preparation of NC: 300 mg ZIF-8 was placed in a magnetic boat and annealed at 1000 °C under an argon atmosphere for 30 min, and then naturally cooled to room temperature to obtain nitrogen-doped carbon with MOF morphology.

[0073] (3) Preparation of FeNC: 267 μL of 0.2 mol / L FeCl3·6H2O ethanol solution was impregnated onto 100 mg of nitrogen-doped carbon obtained in step (2), and the carbon was manually ground in a mortar until the ethanol was completely evaporated. The FeNC precursor was collected. The FeNC precursor was placed on a 1.5 cm * 4 cm carbon cloth, and the carbon cloth was clamped between the two ends of a pulse power supply and subjected to a carbon thermal shock at 1800 °C for 100 ms in an argon atmosphere to obtain the FeNC single-atom catalyst.

[0074] (4) Preparation of catalyst: 25 μL of 0.2 mol / L Fe, Co, Ni, Mo and Zn ethanol salt solution (with the same atomic ratio of each metal element) was impregnated and loaded onto 100 mg FeNC, and then manually ground in a mortar until the ethanol was completely evaporated. The precursor was collected. The precursor was placed in a magnetic boat and placed in a tube furnace. Under an argon atmosphere, the temperature was increased at a rate of 10 °C / min until it reached 1300 °C and held for 1 h. Then it was naturally cooled to room temperature to obtain the catalyst.

[0075] Relevant performance tests were conducted on the embodiments and comparative examples, and the results are shown in [the table below]. Figures 1-4 .

[0076] Figure 1 The images show the surface morphology of nitrogen-doped carbon obtained after ZIF-8 pyrolysis. As can be seen from the images, the nitrogen-doped carbon retains its original morphology, which is attributed to the relatively mild pyrolysis conditions of the tube furnace.

[0077] Figure 2 Bifunctional X-ray diffraction (XRD) patterns were prepared for Example 1, Comparative Example 1, and Comparative Example 2. XRD revealed the presence of two main phases, Co and Mo₂C, corresponding to standard cards Co 15-0806 and Mo₂C 72-1683. Example 1 showed the simplest and clearest diffraction peaks, indicating a relatively simple phase structure and good crystallinity. In contrast, Comparative Examples 1 and 2 showed more complex peak shapes and additional diffraction peaks, indicating greater phase separation. From the design philosophy of high-entropy alloys, the formation of simple solid solution phases should be pursued; therefore, the synthesis of Example 1 was the most successful. Furthermore, the smooth background and clear peak shapes of Example 1 indicate good single-atom dispersion of Fe-NC.

[0078] Figure 3 The image shows the surface morphology of the HEA@FeNC bifunctional catalyst synthesized in Example 1. The catalyst retains the MOF structure, attributed to the rapid heating and cooling process within milliseconds. Simultaneously, partial graphitization occurs on the carbon support, thus the carbon thermal shock not only maintains a high specific surface area but also increases conductivity.

[0079] Figure 4The figure shows the elemental distribution of the HEA@FeNC bifunctional catalyst prepared in Example 1. As can be seen from the figure, the FeCoNiMoZn@FeNC multi-level high-entropy alloy catalyst was successfully prepared on FeNC by the carbothermal shock method.

[0080] To evaluate the bifunctional performance of the catalysts in Example 1 and Comparative Examples 1 and 2, OER / ORR catalytic performance tests were conducted. The catalysts from Example 1 and Comparative Examples 1 and 2 were then assembled into zinc-air batteries for zinc-air battery performance testing. The specific test steps and results are as follows:

[0081] (1) OER performance test: 5 mg of catalyst from Example 1, Comparative Example 1, and Comparative Example 2 were mixed with 500 μL isopropanol, 500 μL deionized water, and 20 μL Nafion, respectively, and then sonicated for 20 min until the catalyst was uniformly dispersed to 1 μL. 50 μL of 1 μL was evenly dropped onto 0.5*1 cm carbon paper, dried completely, and then clamped onto the electrode holder as the working electrode. Hg / HgO was used as the reference electrode, Pt sheet as the counter electrode, and 1M KOH as the electrolyte for electrochemical testing. The potential range was set to 0-1 V, and the scan rate was 10 mV / s. LSV performance testing was performed, and the performance curves are shown below. Figure 5 As shown in (a), it can be seen from the figure that, compared with Comparative Examples 1-2, the HEA@Fe-NC bifunctional catalyst prepared in Example 1 has the best OER activity, 10 mA / cm². -2 The overpotential is 280mV.

[0082] (2) ORR performance test: 5 mg of catalysts from Examples 1, 1, and 2 were mixed with 500 μL isopropanol, 500 μL deionized water, and 20 μL Nafion, respectively. The mixture was then sonicated for 20 min until the catalyst was uniformly dispersed to a concentration of 1 μL. 10 μL of 1 μL was evenly dropped onto a clean glassy carbon electrode tip. After complete drying, this was used as the working electrode. Hg / HgO was used as the reference electrode, and a Pt sheet was used as the counter electrode. Electrochemical tests were conducted using 0.1 M KOH as the electrolyte. Before the test, high-purity O2 was continuously bubbled into the electrolyte for 30 min, followed by CV (cyclic voltammetry) activation. The scan rate was controlled at 100 Mv / s. -1 The scanning rotation was 30 revolutions. After CV activation, LSV (linear cyclic voltammetry) was performed for testing, with the scan speed controlled at 5 mV / s. -1 The IR compensation is 90%, and the disk electrode rotation speed is 1600 rpm. Figure 5 (b) The scan rate for Examples 1, Comparative Example 1, and Comparative Example 2 in O2-saturated 0.1M KOH solution was 5 mV / s. -1The LSV curves under 90% IR compensation conditions and a disk electrode rotation speed of 1600 rpm show that, compared to Comparative Examples 1 and 2, the HEA@FeNC bifunctional catalyst prepared in Example 1 exhibits the best ORR activity, with a half-wave potential of 0.9 vs. RHE. The durability of Example 1 was evaluated using an accelerated durability test (ADT) in O2-saturated 0.1 M KOH electrolyte, and the catalyst demonstrated significant stability. 1 / 2 It decays by only 5mV after 20,000 cycles (see...) Figure 6 ).

[0083] (3) Zinc-air battery test: 5 mg of catalyst from Example 1, Comparative Example 1, and Comparative Example 2 were mixed with 500 μL of isopropanol, 500 μL of deionized water, and 20 μL of Nafion, respectively, and then sonicated for 20 min until the catalyst was uniformly dispersed as Ink. Ink was dropped onto 2*2 cm conductive carbon paper with a loading of 1 mg / cm. -2 The carbon paper was dried; then the prepared HEA@FeNC was assembled into a zinc-air battery, specifically using a zinc sheet as the negative electrode, HEA@FeNC as the positive electrode catalyst, and 6M KOH containing 0.2M Zn(OAc)2 as the electrolyte; the current density was set to 5 mA / cm². 2 The charging time is 15 minutes, and the discharging time is 15 minutes. This battery exhibits long-term charge-discharge cycle stability, such as... Figure 7 As shown, Example 1 was able to run stably for 1640 cycles in 820 hours; however, commercial Pt / C+IrO2 completely failed after 170 hours of operation.

[0084] The present invention has been illustrated through the above embodiments, but the present invention is not limited to the above embodiments, that is, it does not mean that the present invention must rely on the above embodiments to be implemented. Those skilled in the art should understand that any improvements to the present invention, equivalent substitutions of individual raw materials in the product of the present invention, addition of auxiliary components, selection of specific methods, etc., all fall within the protection scope and disclosure scope of the present invention.

Claims

1. A method for preparing a bifunctional catalyst for catalyzing OER and ORR, characterized in that, The ZIF-8 is pyrolyzed, then impregnated with an iron source and carbon thermal shock treated, and finally impregnated with a soluble metal salt solution and carbon thermal shock treated. The pyrolysis temperature of the ZIF-8 is 900-1100℃, the heating rate is 5-10℃ / min, and the holding time is 30-60min. The loading amount of the iron source is 0.01-5wt%. The metal in the soluble metal salt solution is selected from at least 5 of Fe, Co, Ni, Mn, Cr, Mo, Zn, Sn, and W, and the loading amount is 0.01-5wt%.

2. The method for preparing a bifunctional catalyst for catalyzing OER and ORR according to claim 1, characterized in that, The method comprises the following steps: (1) Preparation of ZIF-8; (2) Preparation of nitrogen-doped carbon NC: the ZIF-8 prepared in step (1) is pyrolyzed to obtain a nitrogen-doped carbon NC material; (3) FeNC single-atom material: an iron source solution is impregnated and added dropwise to the NC material obtained in step (2), and then grinded, dried, and carbon thermal shock treated to obtain a FeNC single-atom material; (4) The soluble metal salt solution is impregnated and added dropwise to the FeNC single-atom material obtained in step (3), and then grinded, dried, and carbon thermal shock treated to obtain the bifunctional catalyst.

3. The method of claim 1 or 2, wherein the method is characterized by, The preparation of ZIF-8 comprises the following steps: A zinc source is added to methanol, and after ultrasonic treatment, a solution A is obtained; An organic ligand is added to methanol, and after ultrasonic treatment, a solution B is obtained; The solution A and the solution B are mixed and continuously ultrasonic treated, and stirring is maintained to obtain a solution C; After washing, centrifuging, and drying treatment of the solution C, the ZIF-8 is obtained.

4. The production method according to claim 3, characterized by, The zinc source is Zn(NO3)2·6H2O, and the concentration of the solution A is 0.1-0.4 mol / L; The organic ligand is selected from one or more of imidazole, dimethyl imidazole, imidazole-2-formaldehyde, benzimidazole, 5-methyl benzimidazole, and 2-amino benzimidazole, and the concentration of the solution B is 0.4-1.6 mol / L; The stirring speed is 800-1500 rpm, and the stirring time is 6-48h; The centrifuging speed is 5000-10000 rpm, and the centrifuging time is 1-5min.

5. The method for preparing a bifunctional catalyst for catalyzing OER and ORR according to claim 2, characterized in that, The iron source solution is obtained by dissolving FeCl3·6H2O in ethanol, and the molar concentration of the iron atom is 0.1-0.3 mol / L.

6. The method for preparing a bifunctional catalyst for catalyzing OER and ORR according to claim 5, characterized in that, The carbon thermal shock condition in step (3) is pulse heating treatment under nitrogen or argon protection, the current is 10-60A, and the treatment time is 10ms-1s.

7. The method for preparing a bifunctional catalyst for catalyzing OER and ORR according to claim 2, characterized in that, The total concentration of the soluble metal salt solution is 0.02-0.5 mol / L.

8. The method for preparing a bifunctional catalyst for catalyzing OER and ORR according to claim 7, characterized in that, The carbon thermal shock condition in step (3) is pulse heating treatment under nitrogen or argon protection, the current is 10-60A, and the treatment time is 10ms-1s.

9. The bifunctional catalyst prepared by the method of any one of claims 1-8.

10. The bifunctional catalyst of claim 9 for use in the preparation of a zinc-air battery.

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