A waste-based iron-nitrogen-doped carbon-based catalytic material and a preparation method and application thereof

Abstract

The application discloses a kind of iron nitrogen-doped carbon-based catalytic materials based on waste and its preparation method and application, belong to zinc bromine flow battery technical field;The method is first to waste biomass carbon and waste iron slag is systematized pretreatment, including water washing ash removal, acid leaching purification and the like steps, then using temperature programmed pyrolysis technology, pretreated raw materials are mixed with nitrogen-containing reagent and pore-forming agent, high-temperature pyrolysis is carried out under protective atmosphere, and iron nitrogen-doped carbon-based catalytic material with rich Fe-N-C active site and high specific surface area is obtained;The catalytic material is made into slurry with conductive agent and binder, coated on the positive side surface of zinc bromine flow battery carbon plastic bipolar plate, and dried and solidified to form a catalytic layer.The catalytic layer can effectively promote the redox reaction kinetics of bromine / bromide electrode pair, improve the rate performance and cycle stability of the battery.The application realizes the high-value utilization of waste resources, reduces the production cost of catalyst, and has good economic benefit and environmental benefit.

Description

Technical Field

[0001] This invention belongs to the field of zinc-bromine flow battery technology, and relates to an iron-nitrogen-doped carbon-based catalytic material based on waste, its preparation method and application. Background Technology

[0002] In the global transition towards a cleaner and lower-carbon energy structure, large-scale energy storage technology is crucial for addressing the intermittency and volatility of renewable energy generation and ensuring stable grid operation. Flow batteries, particularly zinc-bromine flow batteries, are considered a promising large-scale electrochemical energy storage technology due to their relatively high energy density, low electrolyte cost, adjustable theoretical energy density, and flexible site selection. The positive electrode side of a zinc-bromine flow battery relies on the redox reaction of a bromine / bromine (Br2 / Br-) redox couple to store and release electrical energy. However, this reaction is kineticly slow on conventional carbon material electrode surfaces (such as graphite felt and carbon-plastic bipolar plates), leading to high charge transfer impedance and electrochemical polarization. Especially under high-rate charge-discharge conditions, this slow reaction kinetics results in a significant decrease in battery output voltage and a sharp decline in coulombic and energy efficiency, severely limiting the power output capacity and economic viability of zinc-bromine flow batteries. To improve the power performance and cycle life of batteries, effectively accelerating the redox reaction kinetics of the bromide / bromine redox couple and reducing its reaction overpotential has become one of the core challenges in the development of zinc-bromine flow battery technology.

[0003] To address the aforementioned issues, existing technologies typically require the introduction of highly catalytically active materials into the positive electrode side of the battery. While noble metals (such as platinum, ruthenium, and their alloys) exhibit excellent catalytic performance, their scarcity and high cost make them unsuitable for the stringent cost control requirements of large-scale energy storage applications. In recent years, non-noble metal catalysts, particularly transition metals (such as iron and cobalt) co-doped with nitrogen (MNC-type catalysts), have attracted widespread attention due to their high catalytic activity and good stability in areas such as oxygen reduction reactions. These catalysts hold promise as alternatives to noble metals for catalyzing bromine / bromide conversion reactions. However, currently common MNC catalysts are usually prepared from commercial chemicals (such as metal salts, nitrogen-containing organic compounds, and commercial carbon black) through multi-step synthesis processes (such as coordination polymerization, high-temperature pyrolysis, and acid washing). Although this synthesis route is feasible, it still faces two main challenges: firstly, the cost of raw materials, especially high-purity chemicals, is high, and the production process may involve environmentally unfriendly reagents or steps, requiring improvement in overall cost-effectiveness and environmental benefits.

[0004] On the other hand, with the continuous industrial production and agricultural activities, a large amount of waste biomass (such as straw, fruit shells, fruit tree branches, and Chinese medicine residue) and industrial iron-containing waste slag (such as iron smelting slag, machining iron filings, and recycled waste battery materials) are generated every year. If these wastes are not disposed of properly, they will not only occupy land resources but may also cause environmental pollution. However, these wastes contain abundant carbon sources and metallic iron. Waste biomass itself is a natural porous carbon precursor with a unique structure; while industrial iron slag provides a cheap source of iron. If these wastes can be co-processed and transformed into high-value-added functional materials, it will not only achieve "waste treatment of waste" and turn waste into treasure, but also significantly reduce the preparation cost of functional materials.

[0005] Therefore, how to combine the above two needs and develop a simple, low-cost, widely available and environmentally friendly preparation method to synthesize Fe-NC-based catalytic materials with high catalytic activity and high stability using waste biomass and industrial iron slag, and successfully apply them to the positive electrode of zinc-bromine flow batteries to solve the problem of slow bromine reaction kinetics in batteries, while realizing the high-value utilization of waste resources, has become an urgent problem to be solved in this field. Summary of the Invention

[0006] The purpose of this invention is to provide an iron-nitrogen-doped carbon-based catalytic material based on waste, its preparation method and application, in order to solve the technical problem that existing technologies mainly rely on high-cost precious metals or commercial chemical catalysts and have difficulty in effectively solving the slow kinetics of bromine reaction in zinc-bromine flow batteries.

[0007] To achieve the above objectives, the present invention employs the following technical solution: In a first aspect, the present invention provides a method for preparing an iron-nitrogen-doped carbon-based catalytic material based on waste, comprising the following steps: Waste biomass and waste iron slag are washed, dried, crushed and sieved to obtain fine powder. The fine powder is then purified to obtain waste biochar powder and waste iron slag powder. Waste biochar powder and waste iron slag powder are mixed to obtain a mixed substrate; A mixed solution is prepared by dissolving a nitrogen-containing reagent and a pore-forming agent in a solvent. The mixed substrate is then immersed in the mixed solution, and after stirring, ultrasonic treatment, and drying, a precursor is obtained. The precursor was subjected to programmed temperature pyrolysis under a protective atmosphere, and after pyrolysis was completed, it was cooled to room temperature to obtain the pyrolysis product. The pyrolysis product was acid-washed and water-washed until neutral, dried, ground and sieved to obtain an iron-nitrogen-doped carbon-based catalytic material.

[0008] Furthermore, the purification process of the waste biomass includes: soaking in hot water at 60℃-80℃ for 2-4 hours, then treating in 0.1M-0.5M hydrochloric acid for 2-4 hours, then washing with deionized water until neutral, drying, and then pyrolyzing at 800℃ under a nitrogen atmosphere to obtain waste biochar powder. The purification process of the waste iron slag includes: treating it in a 1M-1.5M hydrochloric acid solution at 60℃-70℃ for 0.5 hours to 1 hour, then washing it with water until neutral and drying it to obtain waste iron slag powder.

[0009] Furthermore, the waste biomass includes at least one of straw, corn cob, fruit shell, fruit tree branches, and medicinal residue; the waste iron slag includes at least one of iron and steel smelting waste slag, machining iron filings, and waste iron-based catalysts.

[0010] Furthermore, the mass ratio of waste biochar powder to waste iron slag powder in the mixed substrate is (5~20):1.

[0011] Further, the nitrogen-containing reagent is at least one of urea, melamine, dicyandiamide, and hexamethylenetetramine, and the amount of nitrogen-containing reagent added is 0.1 to 0.3 times the mass ratio of carbon in the mixed substrate; the pore-forming agent is at least one of zinc chloride, potassium carbonate, potassium ferrate, and ammonium carbonate, and the amount of pore-forming agent added is 0.5 to 1.5 times the mass ratio of carbon in the mixed substrate; the solvent is water or ethanol.

[0012] Furthermore, in the step of immersing the mixed substrate in the mixed solution, and then stirring, ultrasonically treating and drying to obtain the precursor, the stirring time is 2 hours to 4 hours, the ultrasonic treatment time is 30 minutes to 60 minutes, and the drying process is carried out at 80℃ to 100℃ for 6 hours to 12 hours.

[0013] Further, the protective atmosphere is nitrogen or argon, with a flow rate of 100-500 mL / min; the programmed temperature pyrolysis process is as follows: the temperature is increased from room temperature to 500-600℃ at a rate of 5℃ / min to 8℃ / min, and held for 30-90 minutes; then the temperature is increased from 500-600℃ to 700-800℃ at a rate of 2℃ / min to 5℃ / min, and held for 60-90 minutes; the acid used for pickling is dilute hydrochloric acid or dilute sulfuric acid with a concentration of 0.1mol / L to 1mol / L, the pickling temperature is 60℃-80℃, and the pickling time is 1-3 hours.

[0014] Secondly, the present invention provides an iron-nitrogen-doped carbon-based catalytic material based on waste, which is prepared according to the preparation method of the aforementioned iron-nitrogen-doped carbon-based catalytic material based on waste.

[0015] Secondly, the present invention provides an application of the aforementioned waste-based iron-nitrogen-doped carbon-based catalytic material in the preparation process of the positive electrode catalytic layer of a zinc-bromine flow battery bipolar plate, comprising the following steps: Iron-nitrogen doped carbon-based catalyst, conductive agent and binder are mixed in a mass ratio of (80~90):(5~10):(5~10), and solvent is added to prepare a slurry; The slurry is coated onto the positive electrode side surface of a carbon-plastic bipolar plate for zinc-bromine flow batteries; The coated bipolar plates are then dried and heat-treated sequentially to solidify the catalyst layer onto the surface of the bipolar plates.

[0016] Further, the conductive agent is at least one of carbon black, acetylene black, superP, carbon nanotubes, and graphene; the binder is at least one of polyvinylidene fluoride, polytetrafluoroethylene, and sodium carboxymethyl cellulose; the coating process adopts a blade coating method with a coating load of 0.5 mg / cm² to 2.0 mg / cm²; the heat treatment process is carried out in a vacuum or inert atmosphere at 100°C to 200°C for 1 to 2 hours.

[0017] Compared with the prior art, the present invention has the following beneficial effects: This invention discloses a method for preparing iron-nitrogen-doped carbon-based catalytic materials based on waste. First, a stepwise purification process effectively removes impurities from the raw materials, laying the foundation for the construction of active sites. By introducing a nitrogen-containing reagent and a pore-forming agent, uniform nitrogen doping and precise control of the multi-level pore structure are achieved during pyrolysis, significantly increasing the specific surface area and the exposure of active sites. Most importantly, this method promotes the formation of a stable Fe-NC coordination structure between iron, nitrogen, and carbon atoms during high-temperature pyrolysis. This structure has been proven to be a highly efficient active center for catalyzing bromine / bromine redox reactions. Experiments show that the catalytic material prepared in this way, when used as the cathode in a zinc-bromine flow battery, can significantly reduce the overpotential of the bromine couple and improve the battery's power density and energy efficiency. Overall, this method not only achieves the green preparation of high-performance catalytic materials at extremely low cost but also realizes the high-value resource utilization of solid waste, demonstrating significant economic and environmental benefits.

[0018] This invention discloses an iron-nitrogen-doped carbon-based catalytic material based on waste materials. The material itself possesses a high specific surface area and abundant Fe-NC active sites, exhibiting high activity and stability in catalyzing bromine / bromine redox reactions. Secondly, the material uses waste biochar and industrial iron slag as its main raw materials, which are widely available and extremely low in cost, aligning with the concept of a green circular economy. Its carbon coating and graphitized structure help protect the iron active sites, slowing down dissolution and deactivation in strongly acidic and oxidizing bromine environments, and extending the service life of the catalytic layer.

[0019] This invention discloses the application of a waste-derived iron-nitrogen-doped carbon-based catalytic material in the preparation of the positive electrode catalytic layer of a zinc-bromine flow battery bipolar plate. The catalytic material is firmly attached to the surface of the carbon-plastic bipolar plate, constructing a three-dimensional reaction interface within the battery that combines highly catalytically active sites (from Fe-NC), an excellent electron transport network (from the catalytic material and conductive agent), and a stable mechanical structure. This significantly promotes the rapid redox reaction of the bromine / bromine couple. Performance is significantly improved; the bipolar plate prepared in this way effectively reduces the polarization of the battery's positive electrode reaction, improving the battery's coulombic efficiency and energy efficiency, especially under high-rate charge-discharge conditions, where battery performance degradation is significantly suppressed. The specific application method and coating process require conventional equipment, are simple in procedure, and are easy to implement in large-scale production. Attached Figure Description

[0020] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings used in the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of the present invention and should not be regarded as a limitation on the scope. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort.

[0021] Figure 1 This is a schematic diagram illustrating the preparation and application process of the catalytic material according to an embodiment of the present invention; Figure 2 This is a SEM image of the catalyst material in Example 3 of the present invention; Figure 3 The image shows the XRD pattern of the catalyst material in Example 3 of this invention. Detailed Implementation

[0022] To enable those skilled in the art to understand the features and effects of the present invention, the terms and expressions used in the specification and claims are explained and defined in general below. Unless otherwise specified, all technical and scientific terms used herein have the ordinary meaning understood by those skilled in the art regarding the present invention, and in case of conflict, the definitions in this specification shall prevail.

[0023] The theories or mechanisms described and disclosed herein, whether right or wrong, should not in any way limit the scope of the invention, that is, the contents of the invention can be implemented without being limited by any particular theory or mechanism.

[0024] In this document, all features defined by numerical ranges or percentage ranges, such as numerical values, quantities, contents, and concentrations, are for the sake of brevity and convenience only. Accordingly, descriptions of numerical ranges or percentage ranges should be considered as covering and specifically disclosing all possible sub-ranges and individual numerical values ​​(including integers and fractions) within those ranges.

[0025] In this article, unless otherwise specified, “contains,” “includes,” “containing,” “has,” or similar terms cover the meanings of “composed of” and “mainly composed of,” for example, “A contains a” covers the meanings of “A contains a and others” and “A contains only a.”

[0026] For the sake of brevity, not all possible combinations of the technical features in each implementation scheme or embodiment are described herein. Therefore, as long as there is no contradiction in the combination of these technical features, the technical features in each implementation scheme or embodiment can be combined arbitrarily, and all possible combinations should be considered within the scope of this specification.

[0027] The present invention will now be described in further detail with reference to the accompanying drawings: See Figure 1 This invention discloses a method for preparing an iron-nitrogen-doped carbon-based catalytic material based on waste, comprising the following steps: S1. Waste biomass and waste iron slag are washed, dried, crushed and sieved to obtain fine powder. The fine powder is then purified to obtain waste biochar powder and waste iron slag powder. Waste biomass and waste iron slag are washed and dried separately, then crushed and passed through a 200-mesh sieve to obtain fine powder. The waste biomass fine powder is soaked in hot water at 60-80℃ for 2-4 hours, treated with 0.1-0.5M hydrochloric acid for 2-4 hours, finally washed with deionized water until neutral, dried, and then pyrolyzed at 800℃ under a nitrogen atmosphere at a rate of 5℃ / min to obtain biochar powder. The waste iron slag fine powder is treated in 1-1.5M hydrochloric acid solution at 60-70℃ for 0.5-1 hour, washed with water until neutral, and dried to obtain treated iron powder. The drying process is performed at 100℃ for 12 hours.

[0028] Preferably, the waste biomass is selected from at least one of straw, corn cob, fruit shell, fruit tree branch, and medicinal residue; the waste iron slag is selected from at least one of iron and steel smelting waste slag, machining iron scrap, or waste iron-based catalyst.

[0029] S2, mix waste biochar powder and waste iron slag powder to obtain a mixed substrate; The treated waste biochar powder and waste iron slag powder are mixed evenly at a mass ratio of (5~20):1 to obtain a mixed substrate. This ratio ensures that the carbon carrier can sufficiently load iron species and form a good conductive network.

[0030] S3, a mixed solution is prepared by dissolving a nitrogen-containing reagent and a pore-forming agent in a solvent, the mixed substrate is immersed in the mixed solution, and after stirring, ultrasonic treatment and drying, a precursor is obtained; A nitrogen-containing reagent and a pore-forming agent are dissolved in a solvent in a certain proportion to prepare a mixed solution. The mixed substrate is then immersed in the mixed solution, stirred for 2-4 hours, and subjected to ultrasonic treatment (30-60 minutes) to ensure full wetting. Finally, it is dried at 80-100 °C for 6-12 hours to obtain the precursor.

[0031] Preferably, the nitrogen-containing reagent is selected from at least one of urea, melamine, dicyandiamide, and hexamethylenetetramine, and the addition ratio is between 0.1 and 0.3 by mass of nitrogen-containing reagent / carbon; the pore-forming agent is selected from at least one of zinc chloride, potassium carbonate, potassium ferrate, and ammonium carbonate, and the addition ratio is between 0.5 and 1.5 by mass of pore-forming agent / carbon; the solvent is selected from water or ethanol.

[0032] S4, the precursor is subjected to programmed temperature pyrolysis under a protective atmosphere, and after pyrolysis is completed, it is cooled to room temperature to obtain the pyrolysis product; The dried precursor was placed in a tube furnace and subjected to programmed pyrolysis under a protective atmosphere (such as high-purity nitrogen or argon, flow rate 100-500 mL / min). After pyrolysis, it was allowed to cool naturally to room temperature. During pyrolysis, iron species were reduced and coordinated with nitrogen and carbon atoms to form active sites such as Fe-NC, while the carbon framework was further graphitized, improving electrical conductivity.

[0033] Specifically, the programmed temperature rise is as follows: the temperature rises from room temperature to 500-600 ℃ at a rate of 5-8 ℃ / min, and is held for 30-90 min; then the temperature rises to 700-800 ℃ at a rate of 2-5 ℃ / min, and is held for 60-90 min.

[0034] S5. The pyrolysis product is acid-washed and water-washed until neutral, dried, ground and sieved to obtain iron-nitrogen-doped carbon-based catalytic material.

[0035] The product is washed with 0.1-1 mol / L dilute hydrochloric acid or dilute sulfuric acid at 60-80 °C for 1-3 hours to remove unstable inorganic salts and potentially larger metal particles. It is then washed with deionized water until neutral. Finally, it is dried in a vacuum oven at 80 °C for 12 hours, ground, and passed through a 300-mesh sieve to obtain the final iron-nitrogen-doped carbon-based catalyst.

[0036] This invention discloses an iron-nitrogen-doped carbon-based catalytic material based on waste materials, prepared using the aforementioned method. This invention uses waste biochar and industrial iron slag as main raw materials, which are widely available, extremely low in cost, and align with the concept of a green circular economy. By optimizing the pyrolysis process and nitrogen doping, abundant Fe-NC active sites and a high specific surface area were successfully constructed in the carbon matrix. These active sites can effectively adsorb bromine molecules and catalyze their rapid conversion, reducing the reaction activation energy.

[0037] This invention discloses the application of a waste-based iron-nitrogen-doped carbon-based catalytic material in the preparation of the positive electrode catalytic layer of a zinc-bromine flow battery bipolar plate, including the following steps: A. Slurry preparation: Mix the iron-nitrogen-doped carbon-based catalyst, conductive agent, and binder according to the mass ratio. Add an appropriate amount of solvent and mix thoroughly in a planetary mixer to form a slurry of suitable viscosity.

[0038] Preferably, the conductive agent is selected from at least one of carbon black, acetylene black, super P, carbon nanotubes, and graphene; the binder is selected from at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), or sodium carboxymethyl cellulose (CMC); the solvent is N-methylpyrrolidone (NMP) or water; and the mass ratio of the catalytic material, conductive agent, and binder is (80~90):(5~10):(5~10). B. Coating: The slurry is uniformly coated onto the positive electrode side surface of the pretreated carbon-plastic bipolar plate using a scraping method. The catalyst loading (typically 0.5-2.0 mg / cm²) is controlled by adjusting the scraper thickness and the number of coating passes. 2 ).

[0039] C. Drying and Curing: The coated plates are first pre-dried in an 80 ℃ forced-air drying oven for 4 hours to remove most of the solvent. Then, they are transferred to a vacuum oven or heat-treated at 100-200 ℃ for 1-2 hours under an inert atmosphere to fully cure the binder and ensure a strong bond between the catalyst layer and the bipolar plate substrate.

[0040] The carbon coating and graphitized structure of iron-nitrogen-doped carbon-based catalysts help protect iron active sites, slow down dissolution and deactivation in strongly acidic and oxidizing bromine environments, and extend the lifespan of the catalyst layer. Furthermore, high-temperature pyrolysis forms a highly graphitized carbon network, which, in synergy with the conductive agent, ensures good electronic conductivity of the catalyst layer and reduces battery internal resistance. The application method and coating process in this embodiment require conventional equipment, have simple steps, and are suitable for large-scale production.

[0041] The present invention will be further illustrated below with reference to specific embodiments. It should be understood that these embodiments are for illustrative purposes only and are not intended to limit the scope of the invention. Furthermore, it should be understood that after reading the teachings of this invention, those skilled in the art can make various alterations or modifications to the invention, and these equivalent forms also fall within the scope defined by the appended claims.

[0042] The following examples use instruments and equipment conventional in the art. Experimental methods in the following examples, unless otherwise specified, are generally performed under conventional conditions or as recommended by the manufacturer. All raw materials used in the following examples are conventional commercially available products with specifications conventional in the art. In this specification and the following examples, unless otherwise specified, "%" refers to weight percentage, "parts" refers to parts by weight, and "ratio" refers to weight proportion.

[0043] Example 1 1. Waste straw and waste processing iron filings were washed with water, dried at 100 ℃ for 12 hours, then crushed and passed through a 200-mesh sieve to obtain fine powder. The straw fine powder was soaked in 60 ℃ hot water for 2 hours, treated with 0.5M hydrochloric acid for 2 hours, and finally washed with deionized water until neutral. After drying, it was pyrolyzed at 800 ℃ under a nitrogen atmosphere at a rate of 5 ℃ / min to obtain biochar powder. The waste processing iron filings fine powder was treated in 1.5M hydrochloric acid solution at 60 ℃ for 0.5 hours, washed with water until neutral, and dried to obtain the treated powder.

[0044] 2. Mix 5.0 g of the treated waste biochar powder with 1.0 g of waste iron slag powder evenly.

[0045] 3. Dissolve 1.0 g of urea and 5.0 g of potassium carbonate in water, immerse the above mixed powder in the solution, stir for 2 hours and then sonicate for 30 minutes to ensure full immersion, and finally dry at 100 °C for 6 hours to obtain the precursor.

[0046] 4. Place the dried precursor in a tube furnace and, under a nitrogen atmosphere, raise the temperature from room temperature to 500 ℃ at a rate of 5 ℃ / min and hold for 30 min. Then, raise the temperature to 700 ℃ at a rate of 2 ℃ / min and hold for 90 min.

[0047] 5. Wash the product with 0.1 mol / L dilute hydrochloric acid at 60 °C for 3 hours to remove unstable inorganic salts and potentially large metal particles, then wash with deionized water until neutral. Finally, dry in a vacuum drying oven at 80 °C for 12 hours, grind, and pass through a 300-mesh sieve to obtain the final iron-nitrogen-doped carbon-based catalyst.

[0048] Example 2 1. The medicinal residue and waste processing iron filings were washed with water and dried at 100 °C for 12 hours, then pulverized and passed through a 200-mesh sieve to obtain fine powder. The fine powder of the medicinal residue was soaked in hot water at 70 °C for 2 hours, treated with 0.1M hydrochloric acid for 4 hours, and finally washed with deionized water until neutral. After drying, it was pyrolyzed at 800 °C under a nitrogen atmosphere at a rate of 5 °C / min to obtain biochar powder. The fine powder of waste processing iron filings was treated in 1M hydrochloric acid solution at 70 °C for 0.5 hours, washed with water until neutral, and dried to obtain the treated powder.

[0049] 2. Mix 10.0 g of the treated waste biochar powder with 0.5 g of waste iron slag powder evenly.

[0050] 3. Dissolve 1.0 g of melamine and 5.0 g of ammonium carbonate in water, immerse the above mixed powder in the solution, stir for 3 hours and then sonicate for 60 minutes to ensure full immersion, and finally dry at 80 °C for 12 hours to obtain the precursor; 4. Place the dried precursor in a tube furnace and, under a nitrogen atmosphere, raise the temperature from room temperature to 550 ℃ at a rate of 6 ℃ / min at a flow rate of 200 mL / min, hold for 60 min, raise the temperature to 750 ℃ ​​at a rate of 4 ℃ / min, and hold for 80 min. 5. Wash the product with 1.0 mol / L dilute hydrochloric acid at 60 °C for 3 hours to remove unstable inorganic salts and potentially large metal particles, then wash with deionized water until neutral. Finally, dry in a vacuum drying oven at 80 °C for 12 hours, grind, and pass through a 300-mesh sieve to obtain the final iron-nitrogen-doped carbon-based catalyst.

[0051] Example 3 1. Fruit shells and steel smelting waste slag were washed with water and dried at 100 ℃ for 12 hours, then crushed and passed through a 200-mesh sieve to obtain fine powder. The fruit shell fine powder was soaked in 80 ℃ hot water for 3 hours, treated with 0.4M hydrochloric acid for 3 hours, and finally washed with deionized water until neutral. After drying, it was pyrolyzed at 800 ℃ under a nitrogen atmosphere at a rate of 5 ℃ / min to obtain biochar powder. The steel smelting waste slag fine powder was treated in 1M hydrochloric acid solution at 65 ℃ for 1 hour, washed with water until neutral, and dried to obtain the treated powder.

[0052] 2. Mix 5.0 g of the treated waste biochar powder with 0.5 g of waste iron slag powder evenly.

[0053] 3. Dissolve 3.0 g of urea and 15.0 g of potassium carbonate in ethanol, immerse the above mixed powder in the solution, stir for 3 hours and then sonicate for 40 minutes to ensure full immersion, and finally dry at 90 °C for 4 hours to obtain the precursor; 4. Place the dried precursor in a tube furnace and, under a nitrogen atmosphere, raise the temperature from room temperature to 600 ℃ at a rate of 7 ℃ / min at a flow rate of 400 mL / min, hold for 80 min, raise the temperature to 800 ℃ at a rate of 5 ℃ / min, and hold for 60 min. 5. Wash the product with 1.0 mol / L dilute hydrochloric acid at 70 °C for 2 hours to remove unstable inorganic salts and potentially larger metal particles, then wash with deionized water until neutral. Finally, dry in a vacuum drying oven at 80 °C for 12 hours, grind, and pass through a 300-mesh sieve to obtain the final iron-nitrogen-doped carbon-based catalyst. SEM images are shown below. Figure 2 As shown, the XRD pattern is as follows Figure 3 As shown.

[0054] Example 4 1. Corn cobs and steel smelting waste slag were washed with water and dried at 100 ℃ for 12 hours, then crushed and passed through a 200-mesh sieve to obtain fine powder. The corn cob fine powder was soaked in 70 ℃ hot water for 2 hours, treated with 0.5M hydrochloric acid for 2 hours, and finally washed with deionized water until neutral. After drying, it was pyrolyzed at 800 ℃ under a nitrogen atmosphere at a rate of 5 ℃ / min to obtain biochar powder. The steel smelting waste slag fine powder was treated in 1.2M hydrochloric acid solution at 60 ℃ for 1 hour, washed with water until neutral, and dried to obtain the treated powder.

[0055] 2. Mix 10.0 g of the treated waste biochar powder with 0.5 g of waste iron slag powder evenly.

[0056] 3. Dissolve 3.0 g of dicyandiamide and 5.0 g of potassium ferrate in ethanol, immerse the above mixed powder in the solution, stir for 2 hours and then sonicate for 60 minutes to ensure full immersion, and finally dry at 100 °C for 6 hours to obtain the precursor; 4. Place the dried precursor in a tube furnace and, under a nitrogen atmosphere, raise the temperature from room temperature to 600 ℃ at a rate of 8 ℃ / min at a flow rate of 500 mL / min, hold for 60 min, raise the temperature to 800 ℃ at a rate of 5 ℃ / min, and hold for 60 min. 5. Wash the product with 1.0 mol / L dilute hydrochloric acid at 80 °C for 1 hour to remove unstable inorganic salts and potentially large metal particles, then wash with deionized water until neutral. Finally, dry in a vacuum drying oven at 80 °C for 12 hours, grind, and pass through a 300-mesh sieve to obtain the final iron-nitrogen-doped carbon-based catalyst.

[0057] Example 5 1. Fruit wood and waste iron-based catalyst were washed with water and dried at 100 °C for 12 hours, then pulverized and passed through a 200-mesh sieve to obtain fine powder. The fruit wood fine powder was soaked in hot water at 70 °C for 2 hours, treated with 0.1M hydrochloric acid for 4 hours, and finally washed with deionized water until neutral. After drying, it was pyrolyzed at 800 °C under a nitrogen atmosphere at a rate of 5 °C / min to obtain biochar powder. The waste iron-based catalyst fine powder was treated in 1.5M hydrochloric acid solution at 70 °C for 0.5 hours, washed with water until neutral, and dried to obtain the treated powder.

[0058] 2. Mix 10.0 g of the treated waste biochar powder with 0.5 g of waste iron slag powder evenly.

[0059] 3. Dissolve 1.0 g hexamethylenetetramine and 5.0 g zinc chloride in water, immerse the above mixed powder in the solution, stir for 2 hours and then sonicate for 50 minutes to ensure full immersion, and finally dry at 100 °C for 6 hours to obtain the precursor; 4. Place the dried precursor in a tube furnace and, under a nitrogen atmosphere, raise the temperature from room temperature to 600 ℃ at a rate of 8 ℃ / min at a flow rate of 500 mL / min, hold for 30 min, raise the temperature to 800 ℃ at a rate of 2 ℃ / min, and hold for 90 min. 5. Wash the product with 1.0 mol / L dilute hydrochloric acid at 80 °C for 1 hour to remove unstable inorganic salts and potentially large metal particles, then wash with deionized water until neutral. Finally, dry in a vacuum drying oven at 80 °C for 12 hours, grind, and pass through a 300-mesh sieve to obtain the final iron-nitrogen-doped carbon-based catalyst.

[0060] Application Example 1 1. The catalyst material prepared in Example 1, carbon black, and PVDF were mixed with an appropriate amount of NMP in a mass ratio of 90:5:5, and the mixture was thoroughly stirred and mixed evenly in a planetary mixer to form a slurry with a suitable viscosity.

[0061] 2. The slurry was uniformly coated onto the positive electrode side surface of the pretreated carbon-plastic bipolar plate using a scraping method. The loading of the catalyst layer was controlled to be 0.5 mg / cm² by controlling the thickness of the scraper.

[0062] 3. The coated plates are first pre-dried in an 80 ℃ forced-air drying oven for 4 hours to remove most of the solvent. Then they are transferred to a vacuum oven and heat-treated at 100 ℃ for 2 hours to fully cure the binder and ensure a firm bond between the catalyst layer and the bipolar plate substrate.

[0063] 4. Using the above bipolar plate as the positive terminal of a zinc-bromine flow battery, and 2M ZnBr2 + 3M KCl + 0.4M MEP as the electrolyte, assemble a single flow battery cell (active area 9 cm²).2 At 20, 40, and 80 mA / cm 2 Constant current charge-discharge test was performed at current density.

[0064] Application Example 2 1. The catalyst material prepared in Example 2, super P, and PVDF were added to an appropriate amount of NMP in a mass ratio of 85:8:8, and the mixture was thoroughly stirred and mixed in a planetary mixer to form a slurry with a suitable viscosity.

[0065] 2. The slurry was uniformly coated onto the positive electrode side surface of the pretreated carbon-plastic bipolar plate using a scraping method. The loading of the catalyst layer was controlled to be 1.0 mg / cm² by controlling the thickness of the scraper.

[0066] 3. The coated plates are first pre-dried in an 80 ℃ forced-air drying oven for 4 hours to remove most of the solvent. Then they are transferred to a vacuum oven and heat-treated at 150 ℃ for 2 hours to fully cure the binder and ensure a firm bond between the catalyst layer and the bipolar plate substrate.

[0067] 4. Using the above bipolar plate as the positive terminal of a zinc-bromine flow battery, and 2M ZnBr2 + 3M KCl + 0.4M MEP as the electrolyte, assemble a single flow battery cell (active area 9 cm²). 2 At 20, 40, and 80 mA / cm 2 Constant current charge-discharge test was performed at current density.

[0068] Application Example 3 1. The catalyst material prepared in Example 3, graphene, and PTFE were added to an appropriate amount of NMP in a mass ratio of 80:10:10, and the mixture was thoroughly stirred and mixed in a planetary mixer to form a slurry with a suitable viscosity.

[0069] 2. The slurry was uniformly coated onto the positive electrode side surface of the pretreated carbon-plastic bipolar plate using a scraping method. The loading of the catalyst layer was controlled to be 2.0 mg / cm² by controlling the thickness of the scraper.

[0070] 3. The coated plates are first pre-dried in an 80 ℃ forced-air drying oven for 4 hours to remove most of the solvent. Then they are transferred to a vacuum oven and heat-treated at 100 ℃ for 4 hours to fully cure the binder and ensure a firm bond between the catalyst layer and the bipolar plate substrate.

[0071] 4. Using the above bipolar plate as the positive terminal of a zinc-bromine flow battery, and 2M ZnBr2 + 3M KCl + 0.4M MEP as the electrolyte, assemble a single flow battery cell (active area 9 cm²). 2 At 20, 40, and 80 mA / cm 2 Constant current charge-discharge test was performed at current density.

[0072] Application Example 4 1. The catalyst material prepared in Example 4, acetylene black, and CMC were added to an appropriate amount of water at a mass ratio of 80:10:10. The mixture was thoroughly stirred and mixed in a planetary mixer to form a slurry with a suitable viscosity.

[0073] 2. The slurry was uniformly coated onto the positive electrode side surface of the pretreated carbon-plastic bipolar plate using a scraping method. The loading of the catalyst layer was controlled to be 1.0 mg / cm² by controlling the thickness of the scraper.

[0074] 3. The coated plates are first pre-dried in an 80 ℃ forced-air drying oven for 4 hours to remove most of the solvent. Then they are transferred to a vacuum oven and heat-treated at 200 ℃ for 3 hours to fully cure the binder and ensure a firm bond between the catalyst layer and the bipolar plate substrate.

[0075] 4. Using the above bipolar plate as the positive terminal of a zinc-bromine flow battery, and 2M ZnBr2 + 3M KCl + 0.4M MEP as the electrolyte, assemble a single flow battery cell (active area 9 cm²). 2 At 20, 40, and 80 mA / cm 2 Constant current charge-discharge test was performed at current density.

[0076] Application Example 5 1. The catalyst material, carbon nanotubes, and PVDF prepared in Example 5 were mixed with an appropriate amount of water at a mass ratio of 90:5:5 and thoroughly stirred in a planetary mixer to form a slurry with a suitable viscosity.

[0077] 2. The slurry was uniformly coated onto the positive electrode side surface of the pretreated carbon-plastic bipolar plate using a scraping method. The loading of the catalyst layer was controlled to be 1.0 mg / cm² by controlling the thickness of the scraper.

[0078] 3. The coated plates are first pre-dried in an 80 ℃ forced-air drying oven for 4 hours to remove most of the solvent. Then they are transferred to a vacuum oven and heat-treated at 200 ℃ for 2 hours to fully cure the binder and ensure that the catalyst layer is firmly bonded to the bipolar plate substrate.

[0079] 4. Using the above bipolar plate as the positive terminal of a zinc-bromine flow battery, and 2M ZnBr2 + 3M KCl + 0.4M MEP as the electrolyte, assemble a single flow battery cell (active area 9 cm²). 2 At 20, 40, and 80 mA / cm 2 Constant current charge-discharge test was performed at current density.

[0080] Comparative Example 1 An uncoated bipolar plate was used as the positive terminal of a zinc-bromine flow battery, with 2M ZnBr2 + 3M KCl + 0.4M MEP as the electrolyte. A single flow battery cell was assembled (active area 9 cm²). 2 At 20, 40, and 80 mA / cm 2 Constant current charge-discharge test was performed at current density.

[0081] Comparative Example 2 A commercially available bipolar plate with a nitrogen-doped activated carbon catalyst layer was used as the positive terminal of a zinc-bromine flow battery, with 2M ZnBr2 + 3M KCl + 0.4M MEP as the electrolyte, to assemble a single flow battery cell (active area 9 cm²). 2 At 20, 40, and 80 mA / cm 2 Constant current charge-discharge test was performed at current density.

[0082] The products of Examples 1 to 5 are compared in Table 1 below.

[0083] Table 1 Comparison of products from different embodiments

[0084] As shown in Table 1, potassium carbonate is a strong chemical activator, capable of etching the carbon skeleton at high temperatures to form abundant micropores / mesopores, resulting in a significantly higher specific surface area than ammonium carbonate, zinc chloride, and potassium ferrate. The lignocellulose structure of the nutshell is more compact, easily forming a hierarchical porous structure after pyrolysis. The nitrogen doping efficiency of dicyandiamide (66.7% nitrogen content) and melamine (66.7% nitrogen content) is far higher than that of urea (46.7% nitrogen content) and hexamethylenetetramine (40% nitrogen content). Furthermore, although ammonium carbonate has weak activation, it causes less damage to nitrogen atoms; therefore, the nitrogen content of melamine + ammonium carbonate in Example 2 is higher than that of urea + potassium carbonate in Example 1.

[0085] The electrochemical performance of Application Examples 1 to 5 and Comparative Examples 1 to 2 is compared in Table 2 below.

[0086] Table 2 Comparison of electrochemical performance in different application examples

[0087] As shown in Table 2, in Application Examples 1-5, the catalytic layer reduces bromine volatilization and interfacial side reactions while promoting rapid redox reactions of bromine. The coulombic efficiency is consistently between 97% and 98%, and the energy efficiency is between 83% and 89%, which is significantly higher than that of Comparative Example 1 and Comparative Example 2. Furthermore, the high coulombic efficiency and energy efficiency are maintained even with increased current density, indicating excellent kinetics.

[0088] The above are merely preferred embodiments of the present invention and are not intended to limit the present invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for preparing an iron-nitrogen-doped carbon-based catalytic material based on waste, characterized in that, Includes the following steps: Waste biomass and waste iron slag are washed, dried, crushed and sieved to obtain fine powder. The fine powder is then purified to obtain waste biochar powder and waste iron slag powder. Waste biochar powder and waste iron slag powder are mixed to obtain a mixed substrate; A mixed solution is prepared by dissolving a nitrogen-containing reagent and a pore-forming agent in a solvent. The mixed substrate is then immersed in the mixed solution, and after stirring, ultrasonic treatment, and drying, a precursor is obtained. The precursor was subjected to programmed temperature pyrolysis under a protective atmosphere, and after pyrolysis was completed, it was cooled to room temperature to obtain the pyrolysis product. The pyrolysis product was acid-washed and water-washed until neutral, dried, ground and sieved to obtain an iron-nitrogen-doped carbon-based catalytic material.

2. The method for preparing an iron-nitrogen-doped carbon-based catalytic material based on waste according to claim 1, characterized in that, The purification process of the waste biomass includes: soaking in hot water at 60℃-80℃ for 2-4 hours, then treating in 0.1M-0.5M hydrochloric acid for 2-4 hours, then washing with deionized water until neutral, drying, and then pyrolyzing at 800℃ under a nitrogen atmosphere to obtain waste biochar powder. The purification process of the waste iron slag includes: treating it in a 1M-1.5M hydrochloric acid solution at 60℃-70℃ for 0.5 hours to 1 hour, then washing it with water until neutral and drying it to obtain waste iron slag powder.

3. The method for preparing an iron-nitrogen-doped carbon-based catalytic material based on waste according to claim 1, characterized in that, The waste biomass includes at least one of straw, corn cob, fruit shell, fruit tree branches and medicinal residue; the waste iron slag includes at least one of iron and steel smelting waste slag, machining iron filings and waste iron-based catalysts.

4. The method for preparing an iron-nitrogen-doped carbon-based catalytic material based on waste according to claim 1, characterized in that, The mass ratio of waste biochar powder to waste iron slag powder in the mixed substrate is (5~20):

1.

5. The method for preparing an iron-nitrogen-doped carbon-based catalytic material based on waste according to claim 1, characterized in that, The nitrogen-containing reagent is at least one of urea, melamine, dicyandiamide, and hexamethylenetetramine, and the amount of nitrogen-containing reagent added is 0.1 to 0.3 times the mass ratio of carbon in the mixed substrate; the pore-forming agent is at least one of zinc chloride, potassium carbonate, potassium ferrate, and ammonium carbonate, and the amount of pore-forming agent added is 0.5 to 1.5 times the mass ratio of carbon in the mixed substrate; the solvent is water or ethanol.

6. The method for preparing an iron-nitrogen-doped carbon-based catalytic material based on waste according to claim 1, characterized in that, In the step of immersing the mixed substrate in the mixed solution, and then stirring, ultrasonically treating and drying to obtain the precursor, the stirring time is 2-4 hours, the ultrasonic treatment time is 30-60 minutes, and the drying process is carried out at 80℃-100℃ for 6-12 hours.

7. The method for preparing an iron-nitrogen-doped carbon-based catalytic material based on waste according to claim 1, characterized in that, The protective atmosphere is nitrogen or argon, with a flow rate of 100-500 mL / min; the programmed temperature pyrolysis process is as follows: the temperature is increased from room temperature to 500-600℃ at a rate of 5℃ / min to 8℃ / min, and held for 30-90 min; then the temperature is increased from 500-600℃ to 700-800℃ at a rate of 2℃ / min to 5℃ / min, and held for 60-90 min; the acid used for pickling is dilute hydrochloric acid or dilute sulfuric acid with a concentration of 0.1mol / L to 1mol / L, the pickling temperature is 60℃-80℃, and the pickling time is 1-3 hours.

8. A carbon-based catalytic material doped with iron and nitrogen based on waste, characterized in that, The iron-nitrogen-doped carbon-based catalytic material based on waste is prepared according to any one of claims 1 to 7.

9. The application of the waste-based iron-nitrogen-doped carbon-based catalytic material as described in claim 8 in the preparation process of the positive electrode catalytic layer of a zinc-bromine flow battery bipolar plate, characterized in that, Includes the following steps: Iron-nitrogen doped carbon-based catalyst, conductive agent and binder are mixed in a mass ratio of (80~90):(5~10):(5~10), and solvent is added to prepare a slurry; The slurry is coated onto the positive electrode side surface of a carbon-plastic bipolar plate for zinc-bromine flow batteries; The coated bipolar plates are then dried and heat-treated sequentially to solidify the catalyst layer onto the surface of the bipolar plates.

10. The application of the waste-based iron-nitrogen-doped carbon-based catalytic material according to claim 9 in the preparation process of the positive electrode catalytic layer of a zinc-bromine flow battery bipolar plate, characterized in that, The conductive agent is at least one selected from carbon black, acetylene black, SuperP, carbon nanotubes, and graphene; the binder is at least one selected from polyvinylidene fluoride, polytetrafluoroethylene, and sodium carboxymethyl cellulose; the coating process employs a blade coating method with a coating load of 0.5 mg / cm². 2 ~2.0 mg / cm 2 The heat treatment process is carried out in a vacuum or inert atmosphere at 100℃~200℃ for 1 to 2 hours.

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