A FeCo@NSC composite material, its preparation method and application

Abstract

This invention discloses a FeCo@NSC composite material, its preparation method, and its application. The preparation method includes the following steps: grinding and mixing nut shell powder, melamine, NaCl, and ZnCl2; pyrolyzing and cooling to room temperature to obtain the pyrolysis product; washing and drying to obtain NC; dissolving FeSO4·7H2O and CoSO4·7H2O in deionized water and bipyridine in ethanol, mixing uniformly to obtain a mixed solution; adding NC to the mixed solution, stirring, filtering, washing, and vacuum drying; heating the obtained powder to 800~1000 ℃ in nitrogen and holding at that temperature, then cooling. The FeCo@NSC composite material is a sheet-like, three-dimensionally interconnected porous network structure. This invention constructs Fe-Co bimetallic / alloy active sites and a hierarchical porous structure, increasing the specific surface area and exposing catalytic active centers, resulting in lower polarization and higher power output during battery charging and discharging.

Description

Technical Field

[0001] This invention pertains to composite catalytic materials, their preparation methods, and applications, specifically an FeCo@NSC composite material, its preparation method, and its applications. Background Technology

[0002] With the global energy structure transitioning towards green and low-carbon technologies and the booming development of wearable electronic devices, the market has placed stringent demands on energy storage systems, requiring high energy density, high safety, and mechanical flexibility. Against this backdrop, zinc-air batteries, with their extremely high theoretical energy density, environmental friendliness, and low cost, are considered an ideal choice for next-generation flexible energy storage technology. However, current zinc-air batteries still face three major challenges in practical applications: first, traditional high-performance electrodes are heavily reliant on precious metal catalysts such as platinum (Pt) and ruthenium (Ru), leading to resource constraints and high costs; second, the kinetics of the oxygen reduction (ORR) and oxygen evolution (OER) processes at the positive electrode are sluggish, resulting in low energy conversion efficiency; and third, traditional liquid electrolytes pose a risk of leakage, and their rigid structure cannot adapt to the complex deformations caused by human activity.

[0003] Traditional ORR / OER catalysts mainly rely on precious metals such as platinum (Pt) and ruthenium (Ru). These materials are not only expensive but also have limited reserves, severely restricting the large-scale commercial application of zinc-air batteries. Existing FeCo@NC materials suffer from drawbacks such as high dependence on high-purity synthetic chemical reagents as carbon and nitrogen sources, the generation of large amounts of polluting waste during preparation, and the need to improve catalytic activity. Furthermore, they do not fully utilize biomass waste, and their power density needs further improvement. Summary of the Invention

[0004] Purpose of the invention: In order to overcome the shortcomings of the existing technology, the purpose of this invention is to provide a simple and convenient method for preparing FeCo@NSC composite material. Another purpose of this invention is to provide a FeCo@NSC composite material with high power output, good stability and long cycle life. Yet another purpose of this invention is to provide an application of FeCo@NSC composite material in zinc-air batteries.

[0005] Technical solution: The preparation method of FeCo@NSC composite material according to the present invention includes the following steps:

[0006] Step 1: Grind and mix the nut shell powder, melamine, NaCl, and ZnCl2.

[0007] Step 2: Pyrolyze the product obtained in Step 1 under a nitrogen atmosphere and cool it to room temperature to obtain the pyrolysis product;

[0008] Step 3: After washing and drying the pyrolysis products, nitrogen-doped biochar powder is obtained.

[0009] Step 4: Dissolve FeSO4·7H2O and CoSO4·7H2O in deionized water, dissolve bipyridine in ethanol, and mix them evenly to obtain a mixed solution of a specific complex; add biochar powder NC to the mixed solution, stir, filter, wash, and vacuum dry;

[0010] Step 5: Heat the powder obtained in Step 4 to 800~1000 ℃ in a nitrogen atmosphere and keep it at that temperature. After cooling, FeCo@NSC composite material is obtained.

[0011] Furthermore, in step one, the nut shell powder is obtained by washing, drying, and crushing nut shells into powder using deionized water. The nut shells are waste walnut shells or macadamia nut shells.

[0012] Furthermore, in step one, the mass ratio of nut shell powder, melamine, NaCl, and ZnCl2 is 1:2:2~3.5:2~3.5.

[0013] Furthermore, in step two, the pyrolysis is first heated to 490-500℃ at a rate of 1-5℃ / min and held for 1-2 hours, then heated to 800-810℃ at a rate of 1-5℃ / min and held for 2-3 hours, and then cooled to room temperature.

[0014] Furthermore, in step three, the washing process involves first stirring and washing in a 1M HCl solution, followed by repeated rinsing with deionized water until neutral.

[0015] Furthermore, in step three, the drying temperature is 50~60℃ and the time is 24~30 hours.

[0016] Furthermore, in step four, the mass-to-volume ratio of FeSO4·7H2O, CoSO4·7H2O, and deionized water is 0.1g:0.1g:20~30mL, and the mass-to-volume ratio of bipyridine and ethanol is 0.4g:20~30mL.

[0017] Furthermore, in step four, the temperature for stirring and vacuum drying is 50~60℃.

[0018] The FeCo@NSC composite material obtained by the above preparation method is a sheet-like, three-dimensionally interconnected porous network structure, which includes micron-sized macropores and micropores and mesopores distributed on the pore walls.

[0019] FeCo@NSC utilizes the Earth's abundant iron (Fe) and cobalt (Co) as active centers, anchoring them on a carbon matrix with high specific surface area and excellent conductivity. This achieves an effective substitution of precious metals, significantly reducing catalyst costs and laying an economic foundation for the widespread adoption of zinc-air batteries. As transition metals, Fe and Co, with the synergistic effect of heteroatoms such as nitrogen and sulfur, can form unique active sites (such as Fe-N). x Co-N x Fe-Co-N x These sites (such as FeCo, etc.) exhibit excellent catalytic activity for both ORR and OER. Compared with monometallic catalysts, the synergistic effect of FeCo bimetals can optimize the adsorption energy barrier of intermediates, promote reaction kinetics, and achieve bifunctional catalytic activity comparable to or even surpassing that of noble metals. Simultaneously, the introduction of the carbon-based NSC not only provides high conductivity but also effectively disperses the metal active sites, preventing their aggregation, thereby significantly improving the catalyst's stability and cycle life. With the rise of wearable electronic devices, the demand for flexible, bendable, and stretchable energy storage devices is increasing. FeCo@NSC is typically combined with flexible substrates (such as carbon cloth, graphene films, etc.) or constructed through all-solid-state flexible battery structures, effectively solving problems such as leakage and corrosion of traditional liquid electrolytes. It also endows the battery with excellent mechanical flexibility and resistance to deformation, enabling it to adapt to complex scenarios such as human movement, providing an ideal power source for smart wearable devices.

[0020] This invention provides an application of FeCo@NSC composite material in zinc-air batteries.

[0021] Preparation Principle: The preparation of FeCo@NSC catalyst is mainly based on three principles: salt template pore formation, coordination anchoring, and high-temperature pyrolysis reconstruction. First, in the preparation stage of bio-carbon substrate NSC, NaCl acts as a physical pore-forming agent, while ZnCl2 acts as both an activator and a chemical pore-forming agent. At a high temperature of 800~810℃, it undergoes vaporization or reacts with the carbon skeleton to etch a rich microporous structure. At the same time, melamine decomposes at 490~500℃ to provide a nitrogen source, realizing the self-doping of the carbon skeleton, and finally forming nitrogen-doped porous bio-carbon with a high specific surface area.

[0022] Secondly, in the metal loading stage, bipyridine is used as an organic ligand to react with Fe in the solution. 2+ and Co 2+ A coordination reaction occurs, forming a stable [Fe(bpy)3] group. 2+ and [Co(bpy)3] 2+ Complexes. Due to the abundant porosity and nitrogen-containing functional groups of the NSC support, these metal complexes can be uniformly and firmly anchored on the carbon support surface through physical adsorption and chemical action under stirring at 60°C, effectively avoiding metal aggregation.

[0023] Finally, during the high-temperature pyrolysis stage at 800–1000 °C, the bipyridine ligand undergoes carbonization and decomposition, leading to in-situ reduction and structural reorganization of the metal complex. Fe and Co atoms bind to active nitrogen sites such as pyridine nitrogen in the NSC support at high temperatures, reconstructing a highly dispersed Fe-N complex. x and Co-N x The coordinated active structure (which may contain two atomic sites) is ultimately encapsulated in a nitrogen-doped carbon network to obtain an FeCo@NSC catalyst with excellent catalytic potential.

[0024] Beneficial effects: Compared with the prior art, the present invention has the following significant features:

[0025] 1. A Fe-Co bimetallic / alloy active site with high activity and high stability and a hierarchical porous structure were constructed, which greatly increased the specific surface area and exposed a large number of catalytic active centers, significantly improving the slow kinetics problem in the reaction, and enabling the battery to have lower polarization and higher power output during charging and discharging.

[0026] 2. Water or grinding solid-phase reaction is used in the preparation process. No toxic organic solvents or expensive ligands such as methanol or 2-methylimidazole are used. The post-treatment only requires ordinary water washing or dilute hydrochloric acid cleaning. It is non-toxic and harmless. The raw materials are agricultural waste such as nut shells, which realizes true green chemistry and extremely low cost.

[0027] 3. Utilizing bipyridine and Fe 2+ Co 2+ A stable complex is formed, and the bimetal is atomically uniformly dispersed on a nitrogen-doped porous carbon substrate through a coordination anchoring strategy. After high-temperature pyrolysis and reconstruction, a high-density Fe-N complex is formed. x Co-N x and Fe-Co-N x Bimetallic coordination active sites effectively inhibit metal aggregation and significantly improve the active site density and intrinsic catalytic activity per unit mass of catalyst. Attached Figure Description

[0028] Figure 1 This is a SEM image of FeCo@NSC of the present invention;

[0029] Figure 2 This is a comparison chart of open-circuit voltage tests of liquid zinc-air batteries using the FeCo@NSC catalyst of this invention;

[0030] Figure 3 This is a comparison chart of the power density test results of liquid zinc-air batteries using the FeCo@NSC catalyst of this invention;

[0031] Figure 4This is a comparison chart of the energy density test results of liquid zinc-air batteries using the FeCo@NSC catalyst of this invention;

[0032] Figure 5 This is a comparison chart of the rate performance of liquid zinc-air batteries using the FeCo@NSC catalyst of this invention;

[0033] Figure 6 This is a comparison chart of the bending charge-discharge test of a liquid zinc-air battery using the FeCo@NSC catalyst of this invention. Detailed Implementation

[0034] Unless otherwise specified, all materials and reagents used in the following examples are commercially available. Experimental methods not specifically described in the examples are generally performed under standard conditions or as recommended by the manufacturer. Nut shells are commercially available waste walnut shells or macadamia nut shells; melamine, sodium chloride, zinc chloride, ferrous sulfate, cobalt sulfate, 2,2'-bipyridine, and other reagents used are all of analytical grade.

[0035] Example 1

[0036] A method for preparing FeCo@NSC composite material includes the following steps:

[0037] (1) Wash the nut shells with deionized water, dry them at 60°C for 24 hours, and crush them into uniform powder using a crusher. The nut shells are macadamia nut shells.

[0038] (2) Weigh 1g of nut shell powder, 2g of melamine, 2g of NaCl and 2g of ZnCl2, grind and mix them thoroughly in a mortar, and transfer them to a corundum boat.

[0039] (3) Place the corundum boat in a tube furnace and heat it to 500°C at a rate of 5°C / min under a nitrogen atmosphere and hold it for 1 hour. Then, continue to heat it to 810°C at a rate of 1°C / min and hold it at 810°C for 2 hours. Allow it to cool naturally to room temperature.

[0040] (4) The pyrolysis product was stirred and washed in 1M HCl solution, then rinsed repeatedly with deionized water until neutral, and dried at 60°C for 24 hours to obtain biocarbon base powder NSC.

[0041] (5) Dissolve 0.1g of FeSO4·7H2O and 0.1g of CoSO4·7H2O in 20mL of deionized water, and dissolve 0.4g of bipyridine in 20mL of ethanol. Mix the two solutions to form a complex solution. Add 0.1g of NSC powder to the above solution and stir continuously at 60℃ for 24 hours.

[0042] (6) Filter and collect the loaded powder, and vacuum dry it at 60°C for 12 hours. Then place it in a tube furnace under a nitrogen atmosphere, heat it to 1000°C at a rate of 10°C / min and hold it for 1 hour. After natural cooling, the final product FeCo@NSC is obtained.

[0043] like Figure 1 The FeCo@NSC sample is a sheet-like, three-dimensionally interconnected porous network structure. After etching, its carbon matrix forms a rich hierarchical pore structure, including micron-sized macropores and micropores and mesopores distributed on the pore walls.

[0044] Example 2

[0045] A method for preparing FeCo@NSC composite material includes the following steps:

[0046] (1) Wash the nut shells with deionized water, dry them at 60°C for 24 hours, and crush them into uniform powder using a crusher. The nut shells are macadamia nut shells.

[0047] (2) Weigh 1g of nut shell powder, 2g of melamine, 2g of NaCl and 2g of ZnCl2, grind and mix them thoroughly in a mortar, and transfer them to a corundum boat.

[0048] (3) Place the corundum boat in a tube furnace and heat it to 500°C at a rate of 5°C / min under a nitrogen atmosphere and hold it for 1 hour. Then, continue to heat it to 810°C at a rate of 1°C / min and hold it at 810°C for 2 hours. Allow it to cool naturally to room temperature.

[0049] (4) The pyrolysis product was stirred and washed in 1M HCl solution, then rinsed repeatedly with deionized water until neutral, and dried at 60°C for 24 hours to obtain biocarbon base powder NSC.

[0050] (5) Dissolve 0.1g of FeSO4·7H2O and 0.1g of CoSO4·7H2O in 20mL of deionized water, and dissolve 0.4g of bipyridine in 20mL of ethanol. Mix the two solutions to form a complex solution. Add 0.1g of NSC powder to the above solution and stir continuously at 60℃ for 24 hours.

[0051] (6) Filter and collect the loaded powder, and vacuum dry it at 60°C for 12 hours. Then place it in a tube furnace under a nitrogen atmosphere, heat it to 800°C at a rate of 10°C / min and hold it for 1 hour. After natural cooling, the final product FeCo@NSC is obtained.

[0052] Example 3

[0053] A method for preparing FeCo@NSC composite material includes the following steps:

[0054] (1) Wash the nut shells with deionized water, dry them at 60°C for 24 hours, and crush them into uniform powder using a crusher. The nut shells are macadamia nut shells.

[0055] (2) Weigh 1g of nut shell powder, 2g of melamine, 2g of NaCl and 2g of ZnCl2, grind and mix them thoroughly in a mortar, and transfer them to a corundum boat.

[0056] (3) Place the corundum boat in a tube furnace and heat it to 500°C at a rate of 5°C / min under a nitrogen atmosphere and hold it for 1 hour. Then continue to heat it to 810°C at a rate of 5°C / min and hold it at 810°C for 2 hours. Allow it to cool naturally to room temperature.

[0057] (4) The pyrolysis product was stirred and washed in 1M HCl solution, then rinsed repeatedly with deionized water until neutral, and dried at 60°C for 24 hours to obtain biocarbon base powder NSC.

[0058] (5) Dissolve 0.1g of FeSO4·7H2O and 0.1g of CoSO4·7H2O in 20mL of deionized water, and dissolve 0.4g of bipyridine in 20mL of ethanol. Mix the two solutions to form a complex solution. Add 0.1g of NSC powder to the above solution and stir continuously at 60℃ for 24 hours.

[0059] (6) Filter and collect the loaded powder, and vacuum dry it at 60°C for 12 hours. Then place it in a tube furnace under a nitrogen atmosphere, heat it to 1000°C at a rate of 10°C / min and hold it for 1 hour. After natural cooling, the final product FeCo@NSC is obtained.

[0060] Example 4

[0061] A method for preparing FeCo@NSC composite material includes the following steps:

[0062] (1) Wash the nut shells with deionized water, dry them at 60°C for 24 hours, and crush them into uniform powder using a crusher. The nut shells are macadamia nut shells.

[0063] (2) Weigh 1g of nut shell powder, 2g of melamine, 3.5g of NaCl and 3.5g of ZnCl2, grind and mix them thoroughly in a mortar, and transfer them to a corundum boat.

[0064] (3) Place the corundum boat in a tube furnace and heat it to 500°C at a rate of 5°C / min under a nitrogen atmosphere and hold it for 1 hour. Then, continue to heat it to 810°C at a rate of 1°C / min and hold it at 810°C for 2 hours. Allow it to cool naturally to room temperature.

[0065] (4) The pyrolysis product was stirred and washed in 1M HCl solution, then rinsed repeatedly with deionized water until neutral, and dried at 60°C for 24 hours to obtain biocarbon base powder NSC.

[0066] (5) Dissolve 0.1 g of FeSO4·7H2O and 0.1 g of CoSO4·7H2O in 20 mL of deionized water, and dissolve 0.4 g of bipyridine in 20 mL of ethanol. Mix the two solutions to form a complex solution. Add 0.1 g of NSC powder to the above solution and stir continuously at 60 °C for 24 hours.

[0067] (6) Filter and collect the loaded powder, and vacuum dry it at 60°C for 12 hours. Then place it in a tube furnace under a nitrogen atmosphere, heat it to 1000°C at a rate of 10°C / min and hold it for 1 hour. After natural cooling, the final product FeCo@NSC is obtained.

[0068] Example 5

[0069] A method for preparing FeCo@NSC composite material includes the following steps:

[0070] (1) Wash the nut shells with deionized water, dry them at 60°C for 24 hours, and crush them into uniform powder using a crusher. The nut shells are commercially available waste walnut shells.

[0071] (2) Weigh 1g of nut shell powder, 2g of melamine, 3g of NaCl and 3g of ZnCl2, grind and mix them thoroughly in a mortar, and transfer them to a corundum boat.

[0072] (3) Place the corundum boat in a tube furnace and heat it to 490°C at a rate of 1°C / min under a nitrogen atmosphere and hold it for 1 hour. Then heat it to 800°C at a rate of 3°C / min and hold it at 800°C for 2.5 hours. Allow it to cool naturally to room temperature.

[0073] (4) The pyrolysis product was stirred and washed in 1M HCl solution, then rinsed repeatedly with deionized water until neutral, and dried at 50°C for 30 hours to obtain biocarbon base powder NSC.

[0074] (5) Dissolve 0.1 g of FeSO4·7H2O and 0.1 g of CoSO4·7H2O in 30 mL of deionized water, and dissolve 0.4 g of bipyridine in 30 mL of ethanol. Mix the two solutions to form a complex solution. Add 0.1 g of NSC powder to the above solution and stir continuously at 50 °C for 24 hours.

[0075] (6) Filter and collect the loaded powder, and vacuum dry it at 50°C for 12 hours. Then place it in a tube furnace under a nitrogen atmosphere, heat it to 1000°C at a rate of 10°C / min and hold it for 1 hour. After natural cooling, the final product FeCo@NSC is obtained.

[0076] Example 6

[0077] A method for preparing FeCo@NSC composite material includes the following steps:

[0078] (1) Wash the nut shells with deionized water, dry them at 60°C for 24 hours, and crush them into uniform powder using a crusher. The nut shells are macadamia nut shells.

[0079] (2) Weigh 1g of nut shell powder, 2g of melamine, 2.5g of NaCl and 2.5g of ZnCl2, grind and mix them thoroughly in a mortar, and transfer them to a corundum boat.

[0080] (3) Place the corundum boat in a tube furnace and heat it to 495°C at a rate of 2°C / min under a nitrogen atmosphere and hold it for 1 hour. Then heat it to 805°C at a rate of 4°C / min and hold it at 805°C for 3 hours. Allow it to cool naturally to room temperature.

[0081] (4) The pyrolysis product was stirred and washed in 1M HCl solution, then rinsed repeatedly with deionized water until neutral, and dried at 55°C for 27 hours to obtain biocarbon base powder NSC.

[0082] (5) Dissolve 0.1 g of FeSO4·7H2O and 0.1 g of CoSO4·7H2O in 25 mL of deionized water, and dissolve 0.4 g of bipyridine in 25 mL of ethanol. Mix the two solutions to form a complex solution. Add 0.1 g of NSC powder to the above solution and stir continuously at 55 °C for 24 hours.

[0083] (6) Filter and collect the loaded powder, and vacuum dry it at 55°C for 12 hours. Then place it in a tube furnace under a nitrogen atmosphere, heat it to 1000°C at a rate of 10°C / min and hold it for 1 hour. After natural cooling, the final product FeCo@NSC is obtained.

[0084] Application Example 1

[0085] The FeCo@NSC composite material prepared in Example 1 was used as a bifunctional catalyst for oxygen reduction (ORR) and oxygen evolution (OER) in a liquid zinc-air battery. The specific steps included: weighing 4 mg of the FeCo@NSC catalyst powder obtained in Example 1, adding 690 μL of anhydrous ethanol, 290 μL of deionized water, and 20 μL of 5% (w / w) Nafion dispersion. The mixture was ultrasonically treated for 30 min to obtain a uniform catalyst slurry. This slurry was then uniformly coated onto a 1 cm² surface. 2 On hydrophobic carbon paper, it serves as the active layer for the air cathode, with a loading of approximately 2.0 mg / cm². 2 A single-cell liquid zinc-air battery was assembled using a polished zinc sheet (0.2 mm thick) as the negative electrode and a mixed solution of 6.0 M KOH + 0.2 M Zn(CH3COO)2 as the electrolyte, through a Teflon mold.

[0086] The obtained liquid zinc-air battery was tested using an electrochemical workstation, and the open-circuit voltage (OCV) of the battery remained stable between 1.45V and 1.495V. In discharge performance testing, the battery's polarization curve showed extremely small overpotentials, with a peak power density as high as 158–160 mW / cm², significantly superior to Comparative Example 2 (single-metal Fe-NC) and a commercial noble metal combination with the same loading (Pt / C+RuO₂). Constant current charge-discharge cycle testing at a current density of 10 mA / cm² demonstrated excellent cycle stability; the charge-discharge voltage difference (ΔE) remained essentially constant after 100 hours of cycling, proving the chemical stability of the Fe-Co bimetallic active sites in a strongly alkaline environment.

[0087] Application Example 2

[0088] The FeCo@NSC catalyst obtained in Example 1 was applied to an all-solid-state flexible zinc-air battery to verify its application potential in wearable electronic devices. The specific steps are as follows: Polyacrylic acid (PAA) polymer gel was used as the electrolyte matrix and immersed in the above-mentioned 6.0M KOH + 0.2M (CH3COO)2Zn solution for 24 hours to allow it to fully swell and absorb electrolyte ions. A carbon cloth loaded with FeCo@NSC was used as the positive electrode, a thin zinc sheet as the negative electrode, and the above-mentioned PAA gel electrolyte was sandwiched in between. A flexible thermoplastic film was used for sandwich encapsulation.

[0089] The obtained solid-state flexible zinc-air battery was used for application scenario simulation and testing. In the drive performance test, a power system consisting of three flexible batteries connected in series successfully drove an LED light panel with a rated voltage of 2.0V to work normally. The flexible battery was fixed on a bending table and repeatedly bent at different angles of 0°, 90°, and 180°. The test showed that the discharge curve of the battery under extreme bending conditions had a voltage fluctuation of less than 0.02V compared to the flat state, and the performance did not significantly decrease after 50 cycles of bending (see appendix). Figure 6 Due to the hierarchical porous structure of the carbon derived from the nut shell, FeCo@NSC forms a good interfacial contact with the solid gel electrolyte, effectively reducing the interfacial mass transfer resistance, proving that this battery is very suitable as a power source for flexible smart wearable devices.

[0090] The obtained liquid zinc-air battery was tested using an electrochemical workstation, and the open-circuit voltage (OCV) of the battery remained stable between 1.45V and 1.495V (see appendix). Figure 2 In discharge performance testing, the battery's polarization curve showed extremely small overpotentials, with a peak power density as high as 158~160 mW / cm². 2 It is significantly superior to Comparative Example 2 (single metal Fe-NC) and commercial noble metal combinations with the same loading (Pt / C + RuO2) (see Appendix). Figure 3 At 10 mA / cm 2 Constant current charge-discharge cycle tests were conducted at a current density, and the battery exhibited excellent cycle stability, with the charge-discharge voltage difference (ΔE) remaining essentially constant after 100 hours of cycling (see Appendix). Figure 4 This demonstrates the chemical stability of the Fe-Co bimetallic active sites under strongly alkaline conditions. A comparison of the multi-stage potentiostatic tests of FeCo@NSC-based and Pt / C+RuO2-based liquid zinc-air batteries (Figure 5) shows that the FeCo@NSC battery exhibits significantly lower operating potentials and smaller charge-discharge voltage differences at various current densities, demonstrating superior bifunctional oxygen catalytic activity.

[0091] Comparative Example 1

[0092] This comparative example uses the commercially available catalyst combination, currently recognized as the gold standard in the zinc-air battery field, as a control group. Specifically, commercially available Pt / C and RuO2 powders were directly selected and mixed at a mass ratio of 1:1 without any additional heat treatment or modification.

[0093] Application Comparative Example 1

[0094] The mixed precious metal powder was used in the assembly and testing of liquid and flexible solid-state zinc-air batteries, which were exactly the same as in Application Example 1. To ensure a fair comparison, the total loading of the electrode catalyst was also controlled at 2.0 mg / cm², and the electrolyte, negative electrode, and encapsulation processes were strictly consistent with Application Example 1.

[0095] Application Comparative Example 2

[0096] The mixed precious metal powder was used in the assembly and testing of an all-solid-state flexible zinc-air battery that was exactly the same as in Application Example 2.

[0097] Results show that in the liquid zinc-air battery test (compared to application example 1), although commercial Pt / C+RuO2 exhibited a better initial open-circuit voltage (approximately 1.43V) (see Appendix). Figure 2 However, its peak power density is only 120~125 mW / cm² (lower than 158~160 mW / cm² in Example 1). In rate performance tests over any given time period, its rate performance is consistently lower than that of the FeCo@NSC catalyst of this invention (see Appendix). Figure 5 In the constant current charge-discharge cycle test at 10 mA / cm², due to the tendency of noble metals to agglomerate and detach in alkaline electrolyte, the charge-discharge voltage difference increases rapidly with cycle time, and the voltage polarization after 100 hours is much greater than that of the FeCo@NSC catalyst of this invention.

[0098] In the all-solid-state flexible zinc-air battery test (comparative application example 2), the disadvantages of commercial precious metal catalysts were further amplified. When the flexible battery was subjected to an extreme 180° bend, commercial Pt / C relied solely on physical adhesion to the surface of carbon paper / carbon cloth, lacking the "hierarchical porous structure anchoring effect" of the FeCo@NSC in this invention. This resulted in severe catalyst pulverization and detachment under mechanical stress, leading to drastic fluctuations in discharge voltage (voltage drop >0.08 V). After 50 repeated bending cycles, the power output of the battery equipped with Pt / C+RuO2 decreased by more than 20%, completely failing to meet the mechanical stability requirements of flexible wearable devices. Furthermore, this comparative example used a large amount of expensive platinum and ruthenium, with material costs dozens of times higher than the FeCo@NSC catalyst of this invention, greatly limiting its commercial application prospects.

[0099] Comparative Example 2

[0100] This comparative example demonstrates the application of SA-FeCNS-800, a catalyst derived from wood biomass and supported on Fe3O4, in a flexible zinc-air battery. The specific preparation steps are as follows:

[0101] Cellulose was mixed with varying amounts of aqueous graphene oxide (GO), and the mixture was hydrothermally carbonized at 200°C for 10 hours to obtain hydrochar nanosheets (HS). The HS was then washed and dried. Subsequent steps used HS with a GO to cellulose ratio of 1:200 as a precursor. 1.0 g of HS was dispersed in deionized water containing 0.5 g of ferric chloride hexahydrate (FeCl3·6H2O), and the mixture was dried at 80°C to obtain an iron-loaded Fe@HS composite material. The obtained Fe@HS was uniformly ground and mixed with 20.0 g of ammonium chloride (NH4Cl), and the mixture was pyrolyzed (carbonized) at 800°C for 2 hours under a nitrogen atmosphere. During this process, ammonium chloride decomposed to produce nitrogen species for doping and to form a porous structure; iron species were transformed into Fe3O4 nanoparticles and single-atom iron sites. The black solid after pyrolysis was washed with 1.0 M hydrochloric acid (HCl) solution to remove unstable metal species and impurities. After washing, the catalyst was dried overnight at 80°C to obtain a catalyst named SA-FeCNS-800. This catalyst has a nitrogen-doped carbon nanosheet structure supported on Fe3O4 nanoparticles and single-atom iron.

[0102] The prepared SA-FeCNS-800 catalyst was coated onto carbon cloth. A polished flexible zinc foil was used as the anode, and a polyvinyl alcohol (PVA) hydrogel functionalized with sodium lignosulfonate was used as the electrolyte to assemble a complete flexible zinc-air battery, which was then tested using an electrochemical workstation. As shown in the attached figure, the open-circuit voltage (OCV) of the resulting battery stabilized at approximately 1.48V. Figure 2 As shown, at the same current density, the output voltage of FeCo@NSC is significantly higher than that of SA-FeCNS-800, indicating that the oxygen reduction reaction (ORR) catalyzed by FeCo@NSC has faster kinetics and lower voltage loss. The peak power density of SA-FeCNS-800 is approximately 100 mW / cm². 2 (See attached) Figure 3 (), far lower than FeCo@NSC's 165mW / cm 2 This indicates that the zinc-air battery using FeCo@NSC as a catalyst has a stronger peak discharge capability.

[0103] In the performance comparison, the FeCo@NSC catalyst demonstrated superior electrochemical performance, significantly outperforming the Fe3O4-supported catalyst in both maintaining high operating voltage and providing high power output.

[0104] Comparative Example 3

[0105] This comparative example provides a disordered, defect-rich carbon shell-coated iron-cobalt alloy nanoparticle / porous carbon composite material (named FeCo@NC-g catalyst) prepared using existing techniques. The specific preparation steps are as follows:

[0106] Potassium citrate was placed in a tube furnace and calcined at 800°C for 1 hour under an argon atmosphere. The resulting black solid residue was thoroughly washed with 0.5M H2SO4 solution and deionized water, and then vacuum dried at 60°C to obtain black porous carbon as a substrate support. 0.5 mmol of cobalt acetate (Co(CH3COO)2·4H2O), 0.25 mmol of ferric sodium ethylenediaminetetraacetate ([CH2N(CH2COO)2]2FeNa·3H2O), and 1.2 g of glucose were dissolved in 5... mL of water was added, followed by the addition of 30 mg of the porous carbon support prepared above. The dispersion was ultrasonically treated for 30 minutes to obtain a precursor slurry. After centrifugation and drying at 60°C, the precursor powder was obtained. The obtained precursor powder was thoroughly ground and mixed with melamine at a mass ratio of 1:5. The mixture was then placed in a quartz tube and heated to 800°C at a heating rate of 5°C / min under an argon flow. The mixture was then subjected to isothermal pyrolysis and carbonization at this temperature for 1 hour. After cooling to room temperature, the comparative catalyst FeCo@NC-g was obtained.

[0107] Application Comparative Example 3

[0108] Circular carbon paper (1 cm in diameter, 2 mg / cm² catalyst loading) loaded with FeCo@NC-g catalyst. 2 The effective contact area is 0.785 cm². 2 A liquid zinc-air battery was assembled using an air positive electrode, a 0.5 mm thick smooth zinc sheet as the negative electrode, and a mixed solution of 6 M KOH + 0.2 M ZnCl2 as the electrolyte. Its charge-discharge and cycle performance were tested at room temperature.

[0109] Application Comparative Example 4

[0110] The FeCo@NC-g catalyst prepared in Comparative Example 3 was formulated into a uniform slurry and coated onto a flexible carbon cloth (with a loading of 2.0 mg / cm³). 2A flexible air cathode was constructed using a zinc foil (0.1 mm thick) as the surface of the zinc foil anode and a thin zinc foil (0.1 mm thick) as the flexible anode. A polyvinyl alcohol (PVA) solid gel electrolyte film was cut to a suitable size and sandwiched between the air cathode and the zinc foil anode. After compaction, the edges were sealed with insulating and waterproof tape to obtain a fully solid-state flexible zinc-air battery. Under normal temperature air atmosphere, the open-circuit voltage, discharge polarization curve, and constant current discharge performance of the fully solid-state battery were tested using an electrochemical workstation. At the same time, the fully solid-state flexible battery was placed at different mechanical bending angles (0°, 90°, 180°) or subjected to multiple repeated mechanical bending cycles to dynamically monitor the stability of its discharge voltage output and charge-discharge polarization behavior.

[0111] A comprehensive performance comparison was made between the FeCo@NSC catalyst prepared in Example 1 of this invention (Application Example 1, Application Example 2) and the FeCo@NC-g catalyst reported in the literature prepared in Comparative Example 3 (Comparative Application Example 3, Comparative Application Example 4). The catalyst of this invention exhibits extremely significant technical advantages:

[0112] According to publicly available data, the FeCo@NC-g catalyst in Comparative Example 3 exhibited an initial open-circuit voltage of approximately 1.456 V and a voltage of 190.2 mW / cm² in a liquid zinc-air battery. 2 The peak power density is high, but its constant current charge-discharge cycle stability test is conducted at an extremely low current density (5 mA / cm²). 2 The test was conducted at a low current density. Furthermore, only 120 cycles (a total of only 20 hours) were performed at this low current density, and the charge-discharge voltage difference (ΔE) significantly increased by 0.14V (from the initial 0.65V to 0.79V), showing a significant polarization degradation trend. In contrast, the FeCo@NSC catalyst prepared in Example 1 of this invention, under a much more stringent current density of 10 mA / cm², showed significantly better performance. 2 Constant current charge-discharge cycle tests at high current densities showed stable operation for over 100 hours, with minimal increase in charge-discharge voltage polarization over time, demonstrating long-cycle stability far exceeding that of catalysts in the literature. This proves that the present invention, through an innovative preparation process, successfully achieved highly efficient sulfur and nitrogen co-doping (NSC) in a carbon network, synergistically optimizing the electronic structure around the metal active centers. This not only significantly improves electron conduction under high current but also effectively prevents the aggregation, oxidation, and loss of metal nanoparticles under high potential and strongly alkaline oxidative polarization conditions, endowing the battery with an excellent long-term industrial application lifespan.

[0113] In extreme mechanical stress tests of all-solid-state flexible zinc-air batteries, the performance gap between the two was further amplified. Comparative Example 3 (FeCo@NC-g), prepared using the literature method, is mainly based on a common sheet-like porous carbon substrate, with only weak physical adhesion between the catalyst particles and the support, and between the catalyst layer and the conductive current collector (carbon cloth / carbon paper). Therefore, when the flexible battery is subjected to an extreme 180° bend or undergoes repeated bending cycles, under intense mechanical shear stress, the catalyst in Comparative Example 3 is prone to severe pulverization, localized agglomeration, and large-area detachment from the substrate surface, leading to drastic fluctuations in the battery's discharge voltage and an irreversible drop in power output. In contrast, this invention benefits from the unique "hierarchical porous structure anchoring effect" of the FeCo@NSC composite material. The in-situ constructed, mutually cross-linked, hierarchical porous three-dimensional network can form a strong mechanical and chemical dual anchoring with the flexible substrate. Under extreme bending of 180° and repeated bending cycles of more than 50 times, the catalyst layer of this invention exhibits excellent flexibility and adhesion, with no catalyst pulverization or detachment, and the discharge voltage remains stable with almost no power output attenuation. This demonstrates that the catalyst of this invention possesses practical mechanical stability and structural safety advantages in next-generation flexible wearable energy storage devices that are completely absent in catalysts reported in the literature.

Claims

1. A method for preparing FeCo@NSC composite material, characterized in that, Includes the following steps: Step 1: Grind and mix the nut shell powder, melamine, NaCl, and ZnCl2. Step 2: Pyrolyze the product obtained in Step 1 under a nitrogen atmosphere and cool it to room temperature to obtain the pyrolysis product; Step 3: After washing and drying the pyrolysis products, nitrogen-doped biochar powder is obtained. Step 4: Dissolve FeSO4·7H2O and CoSO4·7H2O in deionized water, dissolve bipyridine in ethanol, and mix them evenly to obtain a mixed solution of a specific complex; add nitrogen-doped biochar powder to the mixed solution, stir, filter, wash, and vacuum dry; Step 5: Heat the powder obtained in Step 4 to 800~1000℃ in a nitrogen atmosphere and keep it at that temperature. After cooling, the FeCo@NSC composite material is obtained.

2. The method for preparing a FeCo@NSC composite material according to claim 1, characterized in that: In step one, the nut shell powder is obtained by washing, drying, and crushing nut shells into powder using deionized water.

3. The method for preparing a FeCo@NSC composite material according to claim 1, characterized in that: In step one, the mass ratio of nut shell powder, melamine, NaCl and ZnCl2 is 1:2:2~3.5:2~3.

5.

4. The method for preparing a FeCo@NSC composite material according to claim 1, characterized in that: In step two, the pyrolysis is performed by first heating the temperature to 490-500°C at a rate of 1-5°C / min and holding it at that temperature for 1-2 hours, then continuing to heat the temperature to 800-810°C at a rate of 1-5°C / min and holding it at that temperature for 2-3 hours, and then cooling it to room temperature.

5. The method for preparing a FeCo@NSC composite material according to claim 1, characterized in that: In step three, the washing process involves first stirring and washing in a 1M HCl solution, followed by repeated rinsing with deionized water until neutral.

6. The method for preparing a FeCo@NSC composite material according to claim 1, characterized in that: In step three, the drying temperature is 50~60℃ and the drying time is 24~30 hours.

7. The method for preparing a FeCo@NSC composite material according to claim 1, characterized in that: In step four, the mass-to-volume ratio of FeSO4·7H2O, CoSO4·7H2O, and deionized water is 0.1g:0.1g:20~30mL, and the mass-to-volume ratio of bipyridine and ethanol is 0.4g:20~30mL.

8. The method for preparing a FeCo@NSC composite material according to claim 1, characterized in that: In step four, the temperature for stirring and vacuum drying is 50~60℃.

9. A FeCo@NSC composite material obtained by the preparation method according to any one of claims 1 to 8, characterized in that: It is a sheet-like, three-dimensionally interconnected porous network structure, which includes micron-sized macropores and micropores and mesopores distributed on the pore walls.

10. The application of the FeCo@NSC composite material according to claim 9 in zinc-air batteries.

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