Preparation and application of Fe2O3 anchored porous carbon material

Abstract

The invention discloses preparation and application of a Fe2O3 anchored porous carbon material, and belongs to the technical field of battery catalysts. The method comprises the following steps: cooking a biomass material by adopting an alkaline sulfite method, filtering and separating to obtain black liquor, adjusting the pH value of the black liquor to 6-8, carrying out centrifugal separation to obtain supernate, mixing the supernate with ferric salt, and sequentially carrying out freeze drying, grinding, carbonization treatment, water washing, suction filtration water washing and drying to obtain a carbon precursor; and mixing the carbon precursor with a nitrogen-containing compound, grinding, and calcining under the protection of an inert atmosphere to obtain the Fe2O3 anchored porous carbon material. The Fe2O3 anchored porous carbon material has the advantages of high specific surface area, hierarchical pore structure, good oxygen reduction activity, high catalytic activity, and good application in the field of catalysis. The method is simple, and the used raw materials are biomass materials which are cheap, easy to obtain and renewable.

Description

Technical Field

[0001] The present invention belongs to the technical field of battery catalysts, and particularly relates to the preparation and application of an Fe2O3-anchored porous carbon material. Background Art

[0002] With the rapid progress of global technology and economic expansion, as well as the significant growth in the population, the human dependence on fossil energy has increased day by day, which has triggered environmental problems such as the intensification of the greenhouse effect and energy shortages. Against this background, the development of green energy technologies has become particularly urgent, and they play a core role in solving these challenges. In particular, carbon-based materials using sustainable resources such as biomass as raw materials are becoming key components of energy conversion and storage devices due to their unique physical and chemical properties.

[0003] Traditional methods for preparing porous carbon have defects such as high raw material prices, complex processes, and the use of strong acids and bases for etching. Summary of the Invention

[0004] The present invention provides a preparation method and application of an Fe2O3-anchored porous carbon material. The present invention uses lignosulfonate and sugars in cooking black liquor to prepare a porous activated carbon matrix, combines it with ammonium chloride to multi-anchor Fe ions, and prepares a porous carbon catalyst with an Fe2O3 structure. This catalyst acts as a cathode catalyst in a zinc-air battery to promote the electrocatalytic cathode oxygen reduction reaction.

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

[0006] One of the objects of the present invention is to provide a preparation method of an Fe2O3-anchored porous carbon material, including the following steps: cooking a biomass material by an alkaline sulfite method, filtering and separating to obtain black liquor, adjusting the pH of the black liquor to 6-8, centrifuging to separate to obtain a supernatant, mixing the supernatant with an iron salt, and successively performing freeze-drying, grinding, carbonization treatment, water washing, suction filtration and water washing, and drying to obtain a carbon precursor;

[0007] Mixing the carbon precursor with a nitrogen-containing compound, grinding, and calcining under the protection of an inert atmosphere to obtain an Fe2O3-anchored porous carbon material.

[0008] The present invention uses a porous activated carbon matrix prepared from lignosulfonate and sugars in cooking black liquor and combines it with ammonium chloride to effectively fix iron ions and promote the formation of iron oxide (Fe2O3). The prepared Fe2O3-anchored porous carbon catalyst not only has a hierarchical pore structure and a high porosity, but also exhibits excellent catalytic activity in the electrocatalytic oxygen reduction reaction.

[0009] Further, the dosage ratio of the biomass material to the alkaline sulfite is 1 g∶(3 - 7) mL.

[0010] Still further, the biomass material is eucalyptus wood and / or poplar wood;

[0011] The alkaline sulfite is a mixed solution of 2.5 M NaOH and 0.4 M Na2SO3;

[0012] The conditions for cooking are: cooking at 171 °C for 2 h.

[0013] Further, the reagent used for adjusting the pH is 7 - 10 M hydrochloric acid.

[0014] Further, the dosage ratio of the supernatant to the iron salt is 1 mL∶(0.01 - 0.015) g. The iron salt is ferric chloride hexahydrate.

[0015] Further, the mass ratio of the carbon precursor to the nitrogen - containing compound is 1∶(15 - 30);

[0016] The nitrogen - containing compound is one of ammonium chloride, ammonium phosphate, urea, thiourea, and ammonium dihydrogen phosphate.

[0017] Further, the conditions for carbonization treatment are: temperature 700 - 1000 °C, time 1 - 3 h, heating rate 2 - 5 °C / min.

[0018] Further, the conditions for calcination are: temperature 700 - 1000 °C, time 1 - 3 h, heating rate 2 - 5 °C / min.

[0019] Further, the temperature for water washing is 60 - 100 °C, and the temperature for drying is 65 - 100 °C.

[0020] The second object of the present invention is to provide a Fe2O3 - anchored porous carbon material prepared by the above - mentioned preparation method.

[0021] The third object of the present invention is to provide an application of the Fe2O3 - anchored porous carbon material in the preparation of battery catalysts.

[0022] Further, the battery is selected from metal - air batteries, hydrogen - oxygen fuel cells, methanol fuel cells; the metal - air battery is a zinc - air battery.

[0023] Compared with the prior art, the present invention has the following advantages and technical effects:

[0024] (1) The raw materials used in the present invention are biomass materials, which are cheap, easily available, and renewable. The renewable biomass resources are fully utilized, and it is a green approach for preparing Fe2O3-anchored hierarchical porous carbon materials. The method of the present invention is simple and easy to implement;

[0025] (2) The Fe2O3-anchored hierarchical porous carbon material of the present invention can also be used as a substrate in various catalytic fields;

[0026] (3) The Fe2O3-anchored hierarchical porous carbon material of the present invention has a high specific surface area, a hierarchical pore structure, and good activities for oxygen reduction and oxygen evolution, with high catalytic activity.

[0027] (4) The preparation method of the present invention is simple, highly practical, and easy to promote. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] The drawings constituting a part of the present invention are used to provide a further understanding of the present invention. The schematic embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute an improper limitation to the present invention. In the drawings:

[0029] Figure 1 It is the morphology diagram of the Fe2O3-anchored porous carbon material - 900 prepared in Example 1; wherein a is the SEM diagram and b is the TEM diagram;

[0030] Figure 2 It is the nitrogen adsorption-desorption isotherms of the porous carbon materials prepared in Examples 1-3 and Comparative Examples 1-3;

[0031] Figure 3 It is the Raman spectra (a) and XRD patterns (b) of the porous carbon materials prepared in Examples 1-3 and Comparative Examples 1-3;

[0032] Figure 4 It is the XPS analysis spectrum of the Fe2O3-anchored porous carbon material - 900 prepared in Example 1;

[0033] Figure 5 It is the oxygen reduction activity curves of the porous carbon materials prepared in Examples 1-3, Comparative Examples 1-3, and commercial platinum-carbon; wherein a is the cyclic voltammetry curve; b is the oxygen reduction polarization curve; c is the time-current curve (methanol is added around 500 seconds); d is the time-current curve;

[0034] Figure 6 It is the performance test curves of the zinc-air battery when the Fe2O3-anchored porous carbon material - 900 prepared in Example 1 is used as the electrode catalytic material of the zinc-air battery; a is the polarization and energy density curves of the zinc-air battery; b is the charge-discharge polarization curve; c is the constant current charge-discharge cycle curve. DETAILED DESCRIPTION OF THE INVENTION

[0035] The various exemplary embodiments of the present invention will be described in detail below. This detailed description should not be construed as a limitation on the present invention, but rather as a more detailed description of certain aspects, features, and implementation schemes of the present invention.

[0036] It should be understood that the terms used in the present invention are only for describing specific embodiments and are not intended to limit the present invention. Additionally, for the numerical ranges in the present invention, it should be understood that each intermediate value between the upper and lower limits of the range is also specifically disclosed. Each intermediate value within any stated value or stated range, as well as each smaller range between any other stated value or intermediate value within the stated range, is also included in the present invention. The upper and lower limits of these smaller ranges may be independently included or excluded from the range.

[0037] Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by those of ordinary skill in the art to which the present invention pertains. Although the present invention only describes preferred methods and materials, any methods and materials similar or equivalent to those described herein can also be used in the implementation or testing of the present invention. All documents mentioned in this specification are incorporated by reference to disclose and describe the methods and / or materials related to the said documents. In case of conflict with any incorporated document, the content of this specification shall prevail.

[0038] Without departing from the scope or spirit of the present invention, various improvements and changes can be made to the specific embodiments of the present invention specification, which are obvious to those skilled in the art. Other embodiments obtained from the specification of the present invention are obvious to those skilled in the art. The specification and examples of the present invention are merely exemplary.

[0039] Regarding the use of "comprising", "including", "having", "containing", etc. in this article, they are all open-ended terms, meaning including but not limited to.

[0040] Compared with other carbon-based materials, the present invention uses cooking black liquor as the carbon-based material, which not only effectively realizes the self-doping of elements and improves the activity of the catalyst, but also solves the environmental pollution problem of cooking black liquor. And it forms a hierarchical porous structure during the carbonization process, optimizing the ion transport path and electron transfer network, which can effectively improve the overall performance of the material. It not only provides an efficient carbon material for energy conversion applications, but also achieves the dual goals of resource recycling and environmental protection.

[0041] The method of the present invention conforms to the concept of green and sustainable development, is simple and easy to implement, and has a low cost, and has important application prospects in the catalytic field. The Fe2O3-anchored porous carbon catalyst prepared by the present invention has a hierarchical pore structure and a high porosity, and has high catalytic activity in the electrocatalytic oxygen reduction reaction.

[0042] An embodiment of the present invention provides a method for preparing an Fe2O3-anchored porous carbon material, comprising the following steps:

[0043] (1) Cook the biomass material by the alkaline sulfite method, filter and separate to obtain black liquor, adjust the pH of the black liquor to 6-8, and centrifuge to separate the supernatant;

[0044] (2) Mix the supernatant with an iron salt, and successively perform freeze-drying, grinding, carbonization treatment, water washing, suction filtration and water washing, and drying to obtain a carbon precursor;

[0045] (3) Mix the carbon precursor with a nitrogen-containing compound, grind, and calcine under the protection of an inert atmosphere to obtain an Fe2O3-anchored porous carbon material.

[0046] In some feasible embodiments, the dosage ratio of the biomass material to the alkaline sulfite is 1 g∶(3-7) mL. As a typical but non-limiting example, in the following preferred embodiments of the present invention, the dosage ratio of the biomass material to the alkaline sulfite method can be selected as 1 g∶5 mL.

[0047] In some feasible embodiments, the biomass material is eucalyptus wood and / or poplar wood. As a typical but non-limiting example, in the following preferred embodiments of the present invention, the biomass material can be selected as eucalyptus wood for effect verification.

[0048] In the following embodiments of the present invention, the alkaline sulfite is 2.5M NaOH / 0.4M Na2SO3. " / " means "and", that is, the alkaline sulfite is a mixed solution of 2.5M NaOH and 0.4M Na2SO3.

[0049] In the following embodiments of the present invention, the conditions for cooking are: cooking at 171°C for 2 h.

[0050] In some embodiments, the reagent used to adjust the pH is 7-10M hydrochloric acid. As a typical but non-limiting example, in the following preferred embodiments of the present invention, the reagent used to adjust the pH is selected as 9M hydrochloric acid.

[0051] In some feasible embodiments, the dosage ratio of the supernatant to the iron salt is 1 mL∶(0.01-0.015) g. As a typical but non-limiting example, in the following preferred embodiments of the present invention, the dosage ratio of the supernatant to the iron salt can be selected as 1 mL∶0.012 g.

[0052] In the following embodiments of the present invention, the iron salt is ferric chloride, preferably ferric chloride hexahydrate.

[0053] In some feasible embodiments, the mass ratio of the carbon precursor to the nitrogen-containing compound is 1∶(15 - 30); as a typical but non-limiting example, in the following preferred embodiments of the present invention, the mass ratio of the carbon precursor to the nitrogen-containing compound can be selected as 1∶20.

[0054] In some feasible embodiments, the nitrogen-containing compound is one of ammonium chloride, ammonium phosphate, urea, thiourea, and ammonium dihydrogen phosphate. As a typical but non-limiting example, in the following preferred embodiments of the present invention, the nitrogen-containing compound can be selected as ammonium chloride.

[0055] In some feasible embodiments, the conditions for the carbonization treatment are: temperature 700 - 1000 °C, time 1 - 3 h, heating rate 2 - 5 °C / min. As a typical but non-limiting example, in the following preferred embodiments of the present invention, the temperature of the carbonization treatment can be selected as 700 °C, the time of the carbonization treatment can be selected as 2 h, and the heating rate of the carbonization treatment can be selected as 5 °C / min.

[0056] In some feasible embodiments, the conditions for the calcination are: temperature 700 - 1000 °C, time 1 - 3 h, heating rate 2 - 5 °C / min. As a typical but non-limiting example, in the following preferred embodiments of the present invention, the temperature of the calcination can be selected as 800 °C, 900 °C, or 1000 °C, the time of the calcination can be selected as 2 h, and the heating rate of the calcination can be selected as 5 °C / min.

[0057] In some feasible embodiments, the temperature of the water washing is 60 - 100 °C, and the drying temperature is 65 - 100 °C. As a typical but non-limiting example, in the following preferred embodiments of the present invention, the temperature of the water washing can be selected as 80 °C.

[0058] The embodiments of the present invention also provide a porous carbon material anchored with Fe2O3 prepared by using the above preparation method.

[0059] The embodiments of the present invention also provide an application of the porous carbon material anchored with Fe2O3 in the preparation of battery catalysts. The battery is selected from metal-air batteries, hydrogen-oxygen fuel cells, and methanol fuel cells; the metal-air battery is a zinc-air battery. As a typical but non-limiting example, in the following preferred embodiments of the present invention, the effect verification is carried out taking the zinc-air battery as an example.

[0060] Exemplarily, the preparation method of the porous carbon material anchored with Fe2O3 includes the following steps:

[0061] (1) Cooking eucalyptus wood chips by the alkaline sulfite method, filtering and separating to obtain black liquor, and adjusting the pH value with hydrochloric acid and centrifuging to separate to obtain the supernatant;

[0062] (2) Mix the obtained supernatant with iron salt and then perform freeze-drying treatment. After grinding, calcine it under the protection of an inert atmosphere to initially anchor Fe ions in the carbon matrix and simultaneously form more active sites on the carbon matrix, thus obtaining a carbon precursor.

[0063] (3) Mix the obtained carbon precursor with ammonium chloride, grind it, and then calcine it under the protection of an inert atmosphere. Further chelate the Fe ions through the ammonia gas generated by the thermal decomposition of ammonium chloride to enhance its stability on the carbon support and form a porous carbon catalyst with Fe2O3 anchored.

[0064] In the embodiments of the present invention, unless otherwise specified, "room temperature" refers to 20 - 30 °C.

[0065] In the embodiments of the present invention, there are no particularly strict requirements for the size and shape regularity of the eucalyptus wood chips. Cutting them into the shape of wood chips is to increase the specific surface area during the cooking process and is also easy to separate. The size of the eucalyptus wood chips should be appropriate for the cooking container to accommodate.

[0066] All raw materials used in the present invention are obtained by purchasing on the market.

[0067] The technical solution of the present invention is further described below through examples.

[0068] Example 1

[0069] A technology for preparing a porous carbon catalyst with an Fe2O3 structure by using lignosulfonate and sugars in cooking black liquor to prepare a porous activated carbon matrix and multiple anchoring of Fe ions with ammonium chloride, including the following steps:

[0070] (1) Mix eucalyptus wood chips with an alkaline sulfite cooking liquor (2.5M NaOH / 0.4M Na2SO3) at a mass-volume ratio of 1 g∶5 mL, maintain the mixed solution at 171 °C for cooking for 2 h, filter and separate to obtain black liquor; adjust the pH of the obtained black liquor to 7.5 with 9M hydrochloric acid, and centrifuge to obtain a supernatant;

[0071] (2) Take 50 mL of the supernatant, add 0.6 g of FeCl3·6H2O, disperse it evenly by ultrasonic wave, then freeze it at -80 °C for 24 h, freeze-dry it at -50 °C and a vacuum degree of 10 Torr for 48 h, then grind it for 30 min to reach a uniform and delicate powder state, and then calcine it in a nitrogen atmosphere at 700 °C for 2 h with a heating rate of 5 °C / min. Then wash it with deionized water at 80 °C for 24 h, and then perform suction filtration and water washing on the carbon powder sample with continuously flowing distilled water. This process is repeated continuously until no chloride ions are detected in the filtrate, and it is tested by dropping silver nitrate into the filtrate without the generation of a white precipitate to check the complete removal of sodium chloride, and then dry it to obtain a carbon precursor;

[0072] (3) Mix the obtained carbon precursor with ammonium chloride at a mass ratio of 1:20 and grind for 30 min to obtain a uniform and delicate powdery state. Then, calcine it in a nitrogen atmosphere at 900 °C for 2 h with a heating rate of 5 °C / min. By the combined action of lignosulfonate, saccharides, and ammonium chloride, multiple anchoring of Fe ions is achieved, and thus an iron, nitrogen, and sulfur co-doped porous carbon material (i.e., Fe2O3-anchored hierarchical porous carbon material, denoted as: Fe2O3-anchored porous carbon material - 900) is prepared.

[0073] Example 2

[0074] (1) Mix eucalyptus wood chips with an alkaline sulfite cooking liquor (2.5 M NaOH / 0.4 M Na2SO3) at a mass-to-volume ratio of 1 g:5 mL, and maintain the mixed solution at 171 °C for 2 h. Then, filter and separate to obtain black liquor. Adjust the pH of the obtained black liquor to 7.5 with 9 M hydrochloric acid, and centrifuge to obtain the supernatant.

[0075] (2) Take 50 mL of the supernatant, add 0.6 g of FeCl3·6H2O, and disperse it evenly by ultrasonic treatment. Then, freeze it at -80 °C for 24 h, and freeze-dry it at -50 °C and a vacuum degree of 10 Torr for 48 h. Grind for 30 min to obtain a uniform and delicate powdery state. Then, calcine it in a nitrogen atmosphere at 700 °C for 2 h with a heating rate of 5 °C / min. Then, wash it with deionized water at 80 °C for 24 h, and continuously filter and wash the carbon powder sample with flowing distilled water. This process is repeated continuously until no chloride ions are detected in the filtrate, and the complete removal of sodium chloride is verified by dropping silver nitrate into the filtrate without the formation of a white precipitate. Dry it to obtain the carbon precursor.

[0076] (3) Mix the obtained carbon precursor with ammonium chloride at a mass ratio of 1:20 and grind. Grind for 30 min to obtain a uniform and delicate powdery state. Then, calcine it in a nitrogen atmosphere at 800 °C for 2 h with a heating rate of 5 °C / min. By the combined action of lignosulfonate, saccharides, and ammonium chloride, multiple anchoring of Fe ions is achieved, and thus an iron, nitrogen, and sulfur co-doped porous carbon material (i.e., Fe / N / S-doped hierarchical porous carbon material, denoted as: Fe / N / S-doped porous carbon material - 800) is prepared.

[0077] Example 3

[0078] (1) Mix eucalyptus wood chips with an alkaline sulfite cooking liquor (2.5 M NaOH / 0.4 M Na2SO3) at a mass-to-volume ratio of 1 g:5 mL, and maintain the mixed solution at 171 °C for 2 h. Then, filter and separate to obtain black liquor. Adjust the pH of the obtained black liquor to 7.5 with 9 M hydrochloric acid, and centrifuge to obtain the supernatant.

[0079] (2) Take 50 mL of the supernatant, add 0.6 g of FeCl3·6H2O, and disperse it evenly by ultrasonic treatment. After freezing at -80 °C for 24 h, freeze-dry it at -50 °C and a vacuum degree of 10 Torr for 48 h. Grind it for 30 min to obtain a uniform and delicate powder. Then, calcine it in a nitrogen atmosphere at 700 °C for 2 h with a heating rate of 5 °C / min. Wash it with deionized water at 80 °C for 24 h, and then perform suction filtration and washing on the carbon powder sample with continuously flowing distilled water. Repeat this process until no chloride ions are detected in the filtrate, and check the complete removal of sodium chloride by dropping silver nitrate into the filtrate without the formation of a white precipitate. Dry it to obtain the carbon precursor;

[0080] (3) Mix the obtained carbon precursor with ammonium chloride at a mass ratio of 1:20 and grind it for 30 min to obtain a uniform and delicate powder. Then, calcine it in a nitrogen atmosphere at 1000 °C for 2 h with a heating rate of 5 °C / min. Utilize the combined action of lignosulfonate, saccharides, and ammonium chloride to achieve multiple anchoring of Fe ions, and then prepare an iron, nitrogen, and sulfur co-doped porous carbon material (i.e., a Fe / N / S-doped hierarchical porous carbon material, denoted as: Fe / N / S-doped porous carbon material - 1000).

[0081] Comparative Example 1

[0082] A technique for preparing a Fe / S-doped porous carbon catalyst by multi-anchoring iron elements on a porous activated carbon matrix prepared from lignosulfonate and saccharides in cooking black liquor, comprising the following steps:

[0083] (1) Mix eucalyptus wood chips with an alkaline sulfite cooking liquor (2.5 M NaOH / 0.4 M Na2SO3) at a mass-to-volume ratio of 1 g:5 mL, and maintain the mixed solution at 171 °C for 2 h. Filter and separate to obtain black liquor; adjust the pH of the obtained black liquor to 7.5 with 9 M hydrochloric acid, and centrifuge to obtain the supernatant;

[0084] (2) Take 50 mL of the supernatant, add 0.6 g of FeCl3·6H2O, and disperse it evenly by ultrasonic treatment. Then, perform freeze-drying treatment, grind it, and then calcine it in a nitrogen atmosphere at 700 °C for 2 h with a heating rate of 5 °C / min. Wash it with deionized water at 80 °C, and then perform suction filtration and washing on the carbon powder sample with continuously flowing distilled water. Repeat this process until no chloride ions are detected in the filtrate, and check the complete removal of sodium chloride by dropping silver nitrate into the filtrate without the formation of a white precipitate. Dry it to obtain the carbon precursor;

[0085] (3) The obtained carbon precursor was calcined in a nitrogen atmosphere at 900 °C for 2 h with a heating rate of 5 °C / min. Through the combined action of lignosulfonate and saccharides, multiple anchoring of Fe ions was achieved, and then an iron and sulfur co-doped porous carbon material (i.e., a hierarchically porous carbon material doped with Fe / S, denoted as: Fe / S-doped porous carbon material - 900) was prepared.

[0086] Comparative Example 2

[0087] A technology for preparing an N / S-doped porous carbon catalyst by using lignosulfonate and saccharides in cooking black liquor to prepare a porous activated carbon matrix and combining with ammonium chloride includes the following steps:

[0088] (1) Eucalyptus wood chips were mixed with an alkaline sulfite cooking liquor (2.5 M NaOH / 0.4 M Na2SO3) at a mass-to-volume ratio of 1 g∶5 mL, and the mixed solution was maintained at 171 °C for 2 h, followed by filtration and separation to obtain the cooking liquor; the obtained cooking liquor was adjusted to pH 7.5 with 9 M HCl, and centrifuged to obtain the supernatant;

[0089] (2) 50 mL of the supernatant was frozen at -80 °C for 24 h, then freeze-dried at -50 °C and a vacuum of 10 Torr for 48 h, ground for 30 min to reach a uniform and delicate powdery state, then calcined in a nitrogen atmosphere at 700 °C for 2 h with a heating rate of 5 °C / min, washed with deionized water at 80 °C for 24 h, and then the carbon powder sample was filtered and washed with continuously flowing distilled water. This process was repeated continuously until no chloride ions were detected in the filtrate, and the complete removal of sodium chloride was verified by the absence of white precipitate when silver nitrate was added dropwise to the filtrate; dried to obtain the carbon precursor;

[0090] (3) The obtained carbon precursor was mixed with ammonium chloride at a mass ratio of 1∶20 and ground for 30 min to reach a uniform and delicate powdery state, then calcined in a nitrogen atmosphere at 900 °C for 2 h with a heating rate of 5 °C / min. Through the co-doping of lignosulfonate, saccharides, and ammonium chloride, a nitrogen and sulfur co-doped porous carbon material (i.e., a hierarchically porous carbon material doped with N / S, N / S-doped porous carbon material - 900) was prepared.

[0091] Comparative Example 3

[0092] A technology for preparing a porous activated carbon matrix using lignosulfonate and saccharides in cooking black liquor and preparing an S self-doped porous carbon catalyst includes the following steps:

[0093] (1) Mix eucalyptus wood chips with an alkaline sulfite cooking liquor (2.5M NaOH / 0.4M Na2SO3) at a mass-to-volume ratio of 1g∶5mL, maintain the mixed solution at 171 °C for 2 h of cooking, filter and separate to obtain the cooking liquor; adjust the pH of the obtained cooking liquor to 7.5 with 9M HCl, and centrifuge to obtain the supernatant;

[0094] (2) Take 50 mL of the supernatant, freeze it at -80 °C for 24 h, then lyophilize it at -50 °C and 10 Torr vacuum for 48 h, grind it for 30 min to reach a uniform and delicate powder, and then calcine it in a nitrogen atmosphere at 700 °C for 2 h with a heating rate of 5 °C / min. Then wash it with deionized water at 80 °C for 24 h, and then perform suction filtration and water washing on the carbon powder sample with continuously flowing distilled water. This process is repeated continuously until no chloride ions are detected in the filtrate, and the complete removal of sodium chloride is tested by dropping silver nitrate into the filtrate without white precipitate formation; dry it to obtain the carbon precursor;

[0095] (3) Calcinate the obtained carbon precursor in a nitrogen atmosphere at 900 °C for 2 h with a heating rate of 5 °C / min to prepare a sulfur self-doped porous carbon material (i.e., S-doped hierarchical porous carbon material, S-doped porous carbon material - 900).

[0096] Structure characterization and performance testing:

[0097] Figure 1 Figure for the morphology of the Fe2O3-anchored porous carbon material - 900 prepared in Example 1; where a is the SEM image and b is the TEM image. From the SEM morphology image in Figure a, it can be seen that the SEM image of the Fe2O3-anchored porous carbon material - 900 obtained in Example 1 presents a rich porous structure. This is because a large amount of pore-forming self-template sodium chloride is removed in the one-step carbonization and water washing step to form a ring-shaped porous structure. After further carbonization with mixed ammonium chloride, NH3 and HCl are released during the high-temperature pyrolysis of ammonium chloride to etch the carbon, resulting in the prepared nitrogen-doped carbon material retaining the ring structure and forming nanopores. At the same time, ammonium chloride and ferric chloride hexahydrate as activators can introduce a porous structure with abundant micropores and mesopores. From the analysis of the TEM image of the Fe2O3-anchored porous carbon material - 900 in Figure b, it can be seen that the Fe2O3 particles prepared by multiple anchoring of Fe ions with lignosulfonate, sugars, and ammonium chloride are evenly distributed in the lignin-based porous carbon material.

[0098] Figure 2 Figure for the nitrogen adsorption and desorption curves of the porous carbon materials prepared in Examples 1-3 and Comparative Examples 1-3; From Figure 2From the nitrogen adsorption and desorption experiments, it can be seen that the Fe₂O₃-anchored porous carbon material - 900 prepared by the multiple anchoring of lignosulfonate, sugars, and ammonium chloride in Example 1 has the highest adsorption capacity under carbonization at 900 °C, indicating that it has the largest specific surface area. A larger specific surface area can provide more catalytic active sites; it can also be seen that the calcination temperature has a significant impact on the adsorption performance of the porous carbon material. The samples carbonized at 900 °C in the examples exhibit the best adsorption characteristics, while the samples at 800 °C and 1000 °C are relatively poor. This is because a lower temperature is not sufficient to form an adequate pore structure, and too high a temperature will cause the collapse or sintering of the pore structure, thus reducing the specific surface area. Moreover, the shape of the nitrogen adsorption and desorption curve reflects that the Fe₂O₃-anchored porous carbon material - 900 carbonized at 900 °C has a more uniform pore size distribution and a higher pore volume, which helps to improve the catalytic and adsorption efficiency. In addition, the comparative diagram further emphasizes that through the multiple anchoring effect of lignosulfonate, sugars, and ammonium chloride under the carbonization condition of 900 °C, Fe ions can be effectively chelated, that is, the Fe₂O₃-anchored porous carbon material - 900 is superior to other samples in terms of adsorption capacity, specific surface area, and pore structure.

[0099] Figure 3 Raman spectra (a) and XRD patterns (b) of the porous carbon materials prepared in Examples 1 - 3 and Comparative Examples 1 - 3; from Figure 3 Analysis of the structure shows that the obtained carbon materials have similar ID / IG values and similar crystalline structures.

[0100] Figure 4 XPS analysis spectrum of the Fe₂O₃-anchored porous carbon material - 900 prepared in Example 1; from Figure 4 Peak deconvolution of the N spectrum shows that at 398.3, 399.5, 400.4, and 400.9, they correspond to pyridine nitrogen, Fe - N x , pyrrole nitrogen, and graphitic nitrogen respectively.

[0101] The oxygen reduction activity of the porous carbon materials prepared in Examples 1 - 3, Comparative Examples 1 - 3, and commercial platinum carbon was tested. The method for electrochemical performance testing using a three - electrode system is as follows: The electrolyte is 0.1 M KOH solution saturated with N₂ or O₂, the platinum foil is used as the counter electrode, and the Ag / AgCl electrode is used as the reference electrode. All potential values are provided relative to the reversible hydrogen electrode (RHE).

[0102] The preparation method of the working electrode is as follows: Mix 5 mg of the catalyst with 1 ml of 2.0 vol% Nafion / ethanol solution, and mix and ultrasonicate for 30 min to prepare a uniform ink. Then uniformly coat 10 μL of the ink on a glassy carbon electrode with a diameter of 5 mm, and the catalyst loading is about 0.255 mg cm -2 .

[0103] For the electrochemistry test, the electrochemistry performance test was carried out in 0.1 M KOH solution saturated with N2 or O2. The cyclic voltammetry (CV) was obtained on a rotating ring-disk (RRDE) electrode at a scan rate of 50 mV s -1 The linear sweep voltammetry (LSV) was collected on a rotating ring-disk (RRDE) electrode at a scan rate of 10 mV s in 0.1 M KOH solution saturated with O2 at rotational speeds of 400, 625, 900, 1225, 1600, and 2025 rpm respectively. Among them, the stability of the catalyst was tested at 0.4 V vs. RHE in 0.1 M KOH solution saturated with O2 at 900 rpm. During the test, 1 M CH3OH was added to the 0.1 M KOH solution saturated with O2 after 500 s to evaluate the methanol tolerance of the catalyst. -1 Fig. 10 is the oxygen reduction activity curve diagram of the porous carbon materials prepared in Examples 1-3 and Comparative Examples 1-3 and commercial platinum-carbon; where a is the cyclic voltammogram; b is the oxygen reduction polarization curve; c is the time-current curve (methanol was added around 500 s); d is the time-current curve. As can be seen from Fig. a, the Fe2O3-anchored porous carbon material - 900 obtained at 900 °C has an oxygen reduction peak superior to that of platinum-carbon. It can also be seen from a that all samples exhibit obvious ORR characteristic peaks in the oxygen-saturated electrolyte, and the peak position of the Fe2O3-anchored porous carbon material - 900 is more shifted to the right, indicating its ability to reduce oxygen and good ORR performance. As can be seen from Fig. b, the onset potential and half-wave potential of the Fe2O3-anchored porous carbon material - 900 obtained at 900 °C are superior to those of commercial platinum-carbon, indicating that the Fe2O3-anchored porous carbon material - 900 obtained in Example 1 at 900 °C has good oxygen reduction activity, higher catalytic efficiency and faster kinetic response in the oxygen reduction reaction. In contrast, the samples at other temperatures and the comparative example samples are inferior to the best sample at 900 °C in terms of oxygen reduction performance, which highlights the effectiveness of the multiple anchoring Fe ion strategy of lignosulfonate, sugar and ammonium chloride in enhancing electrocatalytic activity. Fig. c shows that when 1 M methanol is added to the Fe2O3-anchored porous carbon material - 900, the change in the corresponding oxygen reduction current is negligible. Fig. d shows that the stability of the Fe2O3-anchored porous carbon material - 900 was tested and found to be superior to that of commercial platinum-carbon.

[0104] Figure 5 Application Example 1

[0105] Application Example 1

[0106] The Fe2O3-anchored porous carbon material-900 prepared in Example 1 was used as the electrode catalytic material for the zinc-air battery, and the performance of the zinc-air battery was tested. The specific method was as follows: The preparation method of the positive membrane electrode in the zinc-air battery was as follows: 20 mg of the Fe-N / S co-doped porous carbon material-1000 catalyst prepared in Example 3 was dispersed in 4 mL of 2.0 vol% naphthol ethanol solution and ultrasonically dispersed for 30 min to obtain a catalyst slurry. Subsequently, the slurry was drop-coated on carbon cloth, and the loading amount of the catalyst was 2 mg cm -2 , obtaining a membrane electrode. Assembly of the zinc-air battery: The membrane electrode was used as the air cathode, the zinc foil was used as the anode, and the electrolyte solution was 6 M potassium hydroxide + 0.2 M zinc acetate.

[0107] Figure 6 Figure for the performance test curve of the zinc-air battery when the Fe2O3-anchored porous carbon material-900 prepared in Example 1 was used as the electrode catalytic material for the zinc-air battery; a is the polarization and energy density curve of the zinc-air battery; b is the charge-discharge polarization curve; c is the constant current charge-discharge cycle curve. As can be seen from Figures a and b, for the zinc-air battery assembled with the Fe2O3 / Fe3O4-anchored porous carbon material-900 as the cathode catalyst, the voltage difference between battery charge and discharge was very small, indicating that the Fe2O3-anchored porous carbon material-900 had excellent charge-discharge ability and had a relatively large energy density of 191 mW cm -2 ; its cycle stability was tested, and it was found that when charging and discharging cycles were carried out at a current density of 5 mA cm -2 , it still had good charge-discharge efficiency after 930 h of cycling.

[0108] The above is only a preferred specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Any changes or substitutions that can be easily thought of by those skilled in the art within the technical scope disclosed by the present invention should be covered within the protection scope of the present invention. Therefore, the protection scope of the present invention should be subject to the protection scope of the claims.

Claims

1. A preparation method of Fe2O3-anchored porous carbon material, characterized in that, It includes the following steps: Cook the biomass material by the alkaline sulfite method, filter and separate to obtain black liquor, adjust the pH of the black liquor to 6 - 8, centrifuge to separate to obtain the supernatant, mix the supernatant with iron salt, and successively carry out freeze-drying, grinding, carbonization treatment, water washing, suction filtration and water washing, and drying to obtain a carbon precursor; Mix the carbon precursor with a nitrogen-containing compound, grind, and calcine under the protection of an inert atmosphere to obtain an Fe₂O₃-anchored porous carbon material.

2. The preparation method of the Fe2O3-anchored porous carbon material according to claim 1, characterized in that, The dosage ratio of the biomass material to the alkaline sulfite cooking liquor is 1 g∶(3 - 7) mL.

3. The preparation method of the Fe₂O₃-anchored porous carbon material according to claim 2, characterized in that The biomass material is eucalyptus wood and / or poplar wood; The alkaline sulfite is a mixed solution of 2.5 M NaOH and 0.4 M Na₂SO₃; The conditions for the cooking are: cook at 171 °C for 2 h.

4. The preparation method of the Fe₂O₃-anchored porous carbon material according to claim 1, characterized in that The dosage ratio of the supernatant to the iron salt is 1 mL∶(0.01 - 0.015) g; The iron salt is hydrated ferric chloride.

5. The preparation method of the Fe₂O₃-anchored porous carbon material according to claim 1, characterized in that The mass ratio of the carbon precursor to the nitrogen-containing compound is 1∶(15 - 30); The nitrogen-containing compound is one of ammonium chloride, ammonium phosphate, urea, thiourea and ammonium dihydrogen phosphate.

6. The preparation method of the Fe2O3-anchored porous carbon material according to claim 1, wherein The conditions for the carbonization treatment are: the temperature is 700 - 1000 °C, the time is 1 - 3 h, and the heating rate is 2 - 5 °C / min.

7. The preparation method of the Fe2O3-anchored porous carbon material according to claim 1, characterized in that, The conditions for the calcination are: the temperature is 700 - 1000 °C, the time is 1 - 3 h, and the heating rate is 2 - 5 °C / min.

8. The preparation method of the Fe2O3-anchored porous carbon material according to claim 1, characterized in that, The temperature for the water washing is 60 - 100 °C; the temperature for the drying is 65 - 100 °C.

9. An Fe₂O₃-anchored porous carbon material prepared by using the preparation method according to any one of claims 1 - 7.

10. An application of the Fe₂O₃-anchored porous carbon material according to claim 9 in the preparation of a battery catalyst.

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