Preparation method of supercapacitor activated carbon

Abstract

The application discloses a preparation method of supercapacitor activated carbon and belongs to the technical field of biomass porous material preparation. Sargassum thunbergii is used as a carbon source, and after acid pickling, a carbon precursor is prepared through a hydrothermal reaction with the assistance of polyvinylpyrrolidone and calcium chloride and is carbonized; subsequently, the carbonized microspheres are wetly immersed with KOH, NaCl and KCl, high-temperature molten salt limited activation, washing and drying are performed, and finally, the target product is prepared. The supercapacitor activated carbon prepared by the preparation method of the supercapacitor activated carbon has high-temperature melting limited environment constructed by the NaCl / KCl system and cooperates with KOH activation, effectively reduces the excessive etching of strong alkali to the structure of the activated carbon microspheres while the pores are formed, and significantly improves the morphology maintaining capacity of the carbon microspheres. The method has wide raw material sources and clear process path, and provides a new way for the high-value preparation of marine biomass porous carbon.

Description

Technical Field

[0001] This invention relates to the field of biomass porous material preparation technology, and in particular to a method for preparing supercapacitor activated carbon. Background Technology

[0002] With the increasing demand for green and low-carbon development and the high-value utilization of renewable resources, the preparation of functional carbon materials using biomass as a precursor has become an important research direction. Compared with traditional fossil carbon sources, biomass has advantages such as wide availability, renewability, and lower cost, providing a new raw material basis for the green preparation of porous carbon materials.

[0003] Sargassum is a large, abundant marine brown algae rich in polysaccharides and organic carbon components, possessing excellent potential for carbon material conversion. However, its natural composition is complex, with a high inorganic salt content, and direct pyrolysis easily leads to uneven morphology and difficult-to-control structure of the resulting carbon materials. Therefore, directionally converting Sargassum into regularly shaped carbon microspheres is beneficial for improving its resource utilization value and providing a stable carbon framework for subsequent pore structure control.

[0004] Hydrothermal carbonization can promote hydrolysis, dehydration, condensation, and polymerization reactions in Sargassum under relatively mild conditions, making it an effective method for preparing biomass carbon microspheres. By regulating the reaction system and adding auxiliary components, the nucleation and growth of carbonaceous particles can be promoted. However, the carbon microspheres obtained through hydrothermal processing usually have insufficiently developed pore structures and require further carbonization and activation treatment.

[0005] KOH activation has a strong pore-forming ability, but under high temperature conditions, it is easy to over-etch the carbon skeleton, causing surface damage, structural collapse, or even particle breakage of carbon microspheres, making it difficult to balance pore development and spherical structure maintenance.

[0006] Therefore, it is necessary to develop an activation method that can regulate the KOH activation process while taking into account both pore structure construction and carbon microsphere morphology preservation. Summary of the Invention

[0007] The purpose of this invention is to provide a method for preparing activated carbon for supercapacitors, which solves the problems of excessive etching of the carbon skeleton and destruction of the microsphere structure during the traditional direct activation of Sargassum-based carbon microspheres with KOH.

[0008] To achieve the above objectives, the present invention provides a method for preparing supercapacitor activated carbon, comprising the following steps: S1. Preparation of Sargassum-based carbon microsphere precursors; S2. The carbon microsphere precursor obtained in S1 is carbonized under an inert atmosphere to obtain carbonized Sargassum-based carbon microspheres. S3. The carbonized Sargassum-based carbon microspheres obtained in S2 are mixed with KOH, NaCl and KCl, and deionized water is added for wet impregnation. After impregnation, the mixture is dried and ground to obtain the mixture. S4. The mixture obtained in S3 is heated under an inert atmosphere to carry out high-temperature molten salt confinement activation treatment, so that sodium chloride and potassium chloride form a molten salt environment, and the carbon microspheres are activated under the action of potassium hydroxide to obtain the activated product. S5. The activated product obtained in S4 is acid-washed, then washed with deionized water until neutral, dried and ground to obtain supercapacitor activated carbon.

[0009] Preferably, in S1, the preparation method of the Sargassum-based carbon microsphere precursor is as follows: (1) The Sargassum fusiforme was pretreated by acid washing, then washed, dried, crushed and sieved to obtain pretreated Sargassum fusiforme powder; (2) Pretreated Sargassum powder, PVP and CaCl2 were mixed in deionized water, and after thorough stirring and ultrasonic dispersion, a hydrothermal reaction was carried out. After washing, drying and grinding, Sargassum-based microsphere precursors were obtained.

[0010] Preferably, in (1), the pickling is performed using 500 mL of 1 mol / L hydrochloric acid at 80 °C for 3 h.

[0011] Preferably, in (2), the mass ratio of Sargassum to PVP is 6:1, and the CaCl2 concentration is 0.05 mol·L⁻¹. -1 The solid-liquid ratio of Sargassum to deionized water is 1g:25mL.

[0012] Preferably, in (2), the hydrothermal reaction temperature is 180℃-210℃ and the reaction time is 12h.

[0013] Preferably, in step S2, the carbonization treatment is carried out under a N2 atmosphere, the carbonization temperature is 600℃, the carbonization time is 2 hours, and the heating rate is 5℃·min. -1 .

[0014] Preferably, in S3, the mass ratio of carbonized Sargassum-based carbon microspheres to KOH is 1:(1-4), and the mass ratio of carbonized Sargassum-based carbon microspheres to NaCl and KCl is 1:1.8:2.2.

[0015] Preferably, in S4, the temperature of the high-temperature molten salt confinement activation treatment is 700℃-800℃, the activation time is 2h, and the heating rate is 5℃·min. -1 .

[0016] Preferably, in S5, the pickling process uses 1 mol / L hydrochloric acid.

[0017] Therefore, the present invention employs the above-mentioned method for preparing supercapacitor activated carbon, which has the following beneficial effects: (1) This invention combines a NaCl / KCl binary molten salt system with KOH activation. By constructing a high-temperature molten salt confinement environment, the reaction environment of KOH directly acting on carbon microspheres is changed. NaCl / KCl forms a molten salt phase at high temperature and forms a continuous salt film on the surface of carbon microspheres and in the interparticle gaps through wetting and capillary action, thus separating adjacent carbon microspheres at the microscale. At the same time, the activator needs to diffuse to the carbon surface through the molten salt layer, so that the activation reaction is confined to the vicinity of the carbon microsphere-molten salt interface, thereby achieving microscopic confinement and suppressing local over-etching and structural collapse.

[0018] (2) The present invention uses Sargassum hydrothermal carbon with a spherical structure as an activation precursor and combines hydrothermal spheroidization, carbonization and molten salt confinement activation, which is beneficial to maintain the overall structure of carbon microspheres while developing the porous structure.

[0019] (3) The present invention uses NaCl, KCl and KOH as the main activation system. The raw materials used are common and the process is simple. The residual inorganic components after activation can be treated by acid washing and water washing, which provides a new technical approach for the high-value utilization of marine biomass such as Sargassum.

[0020] The technical solution of the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. Attached Figure Description

[0021] Figure 1 This is a process flow diagram of a method for preparing supercapacitor activated carbon according to the present invention; Figure 2 This is a SEM image (2µm) of the supercapacitor activated carbon from Example 1 of the present invention. Figure 3 This is a SEM image (2µm) of the supercapacitor activated carbon from Example 2 of the present invention. Figure 4 This is a SEM image (2µm) of the supercapacitor activated carbon from Example 3 of the present invention. Figure 5 This is a SEM image (2µm) of the supercapacitor activated carbon from Example 4 of the present invention. Figure 6 This is a SEM image (2µm) of the supercapacitor activated carbon of Comparative Example 1 of the present invention. Figure 7 This is a SEM image (10µm) of the supercapacitor activated carbon of Comparative Example 2 of this invention. Detailed Implementation

[0022] The technical solution of the present invention will be further described below with reference to the accompanying drawings and embodiments. It should be understood that these embodiments are for illustrative purposes only and are not intended to limit the scope of the invention. Any changes, modifications, substitutions, combinations, or simplifications made without departing from the spirit and principle of the present invention should be considered equivalent substitutions and are included within the protection scope of the present invention. Furthermore, it should be understood that after reading the contents 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 and are all within the protection scope of the present invention.

[0023] In this document, the term "embodiment" means that a specific feature, structure, or characteristic described in connection with an embodiment may be included in at least one embodiment of this application. The term "embodiment" appearing in various places throughout the specification does not necessarily refer to the same embodiment, nor does it specifically limit its independence or connection with other embodiments. In principle, in this application, as long as there are no technical contradictions or conflicts, the technical features mentioned in each embodiment can be combined in any way to form corresponding implementable technical solutions.

[0024] Unless otherwise defined, the technical terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application pertains; the use of related terms herein is merely for the purpose of describing particular embodiments and is not intended to limit this application.

[0025] In this invention, unless otherwise specified, all other test materials and instruments are conventional test materials in the field and can be purchased through commercial channels.

[0026] The preparation method of carbonized Sargassum-based carbon microsphere precursor includes the following steps: (1) Add 20g of Sargassum to 500mL of a solution with a concentration of 1mol·L⁻¹ -1 The Sargassum was treated in an HCl solution at 80°C for 3 hours to remove some inorganic impurities from the Sargassum.

[0027] (2) After acid washing, the Sargassum was repeatedly washed with deionized water until neutral and dried at 60°C for 12 hours. The dried Sargassum was then pulverized and passed through an 80-mesh sieve to obtain pretreated Sargassum powder.

[0028] (3) Take 25 mL of deionized water, add PVP and dissolve it completely. The PVP used is K16-18 with an average molecular weight of about 8000. Then add anhydrous CaCl2 to make the CaCl2 concentration in the system 0.05 mol·L. -1 .

[0029] (4) Add 1g of pretreated Sargassum powder, wherein the mass ratio of Sargassum to PVP is 6:1, that is, the amount of PVP added is approximately 0.167g; 0.05mol·L -1 The amount of anhydrous CaCl2 added to the CaCl2 system is approximately 0.139 g.

[0030] (5) Stir the obtained system magnetically for 4 hours, then ultrasonically disperse for 10 minutes, and then transfer it to a 50 mL polytetrafluoroethylene-lined reactor.

[0031] (6) Place the reactor in a constant temperature device and carry out a hydrothermal reaction at 200°C for 12 hours. After the reaction is completed, allow it to cool naturally to room temperature.

[0032] (7) The obtained hydrothermal product was washed once with ethanol, then repeatedly washed with deionized water, dried at 60°C for 12 hours and then ground to obtain the Sargassum-based carbon microsphere precursor.

[0033] (8) Place the obtained Sargassum-based carbon microsphere precursor in an alumina crucible and then place it in a tube furnace.

[0034] (9) Introduce N2 into the tubular furnace at a flow rate of 0.6 L·min -1 , at 5℃·min -1 The temperature was increased to 600℃ at a certain rate and held for 2 hours.

[0035] (10) After carbonization, the sample was naturally cooled to room temperature under N2 protection and the carbonized Sargassum-based carbon microspheres were obtained for subsequent activation experiments.

[0036] Example 1 like Figure 1 As shown, this invention provides a method for preparing activated carbon for supercapacitors, comprising the following steps: Weigh 1g of carbonized Sargassum-based carbon microspheres, 1g of KOH, 1.8g of NaCl, and 2.2g of KCl, add an appropriate amount of deionized water, perform wet mixing, and continuously stir and impregnate for 2 hours to ensure that KOH, NaCl, and KCl are fully in contact with the carbon microspheres to obtain the impregnated mixture.

[0037] The impregnated mixture was dried at 60°C for 12 hours, and then ground to obtain the activated precursor. The activated precursor was placed in an alumina crucible and then placed in a tube furnace, and heated at 5°C / min under N2 protection. -1 Heat to 800℃ and hold for 2 hours for molten salt confinement activation.

[0038] After activation, allow the mixture to cool naturally to room temperature, and then apply the resulting product using a 1 mol·L⁻¹ solution. -1The sample was acid-washed with HCl, and then repeatedly washed with deionized water until neutral. The washed sample was dried at 60℃ for 12 hours and then ground to obtain supercapacitor activated carbon.

[0039] Example 2 The only difference between this embodiment and Example 1 is that the amount of KOH added is 2g, that is, the mass ratio of the carbonized Sargassum-based carbon microspheres to KOH is 1:2; the amount of NaCl added is 1.8g, and the amount of KCl added is 2.2g, and all other conditions are the same.

[0040] Example 3 The only difference between this embodiment and Example 1 is that the amount of KOH added is 3g, that is, the mass ratio of the carbonized Sargassum-based carbon microspheres to KOH is 1:3; the amount of NaCl added is 1.8g, and the amount of KCl added is 2.2g, and all other conditions are the same.

[0041] Example 4 The only difference between this embodiment and Example 1 is that the amount of KOH added is 4g, that is, the mass ratio of the carbonized Sargassum-based carbon microspheres to KOH is 1:4; the amount of NaCl added is 1.8g, and the amount of KCl added is 2.2g, and all other conditions are the same.

[0042] Comparative Example 1 In this comparative example, 1 g of uncarbonized Sargassum-based carbon microspheres (i.e., Sargassum-based carbon microsphere precursor) and 2 g of KOH were weighed out, meaning the mass ratio of uncarbonized Sargassum-based carbon microspheres to KOH was 1:2. No NaCl or KCl was added. An appropriate amount of deionized water was added, and the mixture was stirred and soaked for 2 hours. After drying at 60℃ for 12 hours, it was ground.

[0043] The resulting mixture was placed in a tube furnace and heated under N2 protection at 5 °C / min. -1 The temperature was raised to 800℃ and held for 2 hours for KOH activation. After activation, 1 mol·L⁻¹ KOH was used. -1 The mixture was acid-washed with HCl, then repeatedly washed with deionized water until neutral, dried at 60°C for 12 hours, and then ground.

[0044] Comparative Example 2 In this comparative example, 1 g of carbonized Sargassum-based carbon microspheres and 2 g of KOH were weighed out, i.e., the mass ratio of carbonized Sargassum-based carbon microspheres to KOH was 1:2. No NaCl or KCl was added. An appropriate amount of deionized water was added, and the mixture was stirred and soaked for 2 hours. After drying at 60℃ for 12 hours, it was ground.

[0045] The resulting mixture was placed in a tube furnace and heated under N2 protection at 5 °C / min. -1 Heat to 800℃ and hold for 2 hours to activate with KOH.

[0046] After activation, use 1 mol·L -1 The mixture was acid-washed with HCl, then repeatedly washed with deionized water until neutral, dried at 60°C for 12 hours, and then ground.

[0047] The products prepared in Examples 1-4 and Comparative Examples 1-2 were structurally characterized, and the results are as follows: Figures 2-7 As shown.

[0048] Depend on Figures 2-7 SEM images show that different amounts of KOH and activation methods significantly affect the morphology of Sargassum-based carbon microspheres. Examples 1-4 all used NaCl / KCl molten salt confinement to assist KOH activation. When the mass ratio of carbon microspheres to KOH was 1:2, Example 2 produced a larger number of carbon microspheres with clear spherical outlines and an intact overall structure, exhibiting good morphology retention. When the KOH ratio was further increased to 1:3 and 1:4, the etching of the carbon framework intensified, and some microspheres showed surface roughness, breakage, and irregular carbon fragments. In Comparative Example 1, the hydrothermal carbon microspheres, without pre-carbonization, underwent direct KOH activation, resulting in significant damage to their original spherical structure. Comparative Example 2, even after pre-carbonization without the addition of NaCl / KCl molten salt, still showed numerous broken and irregular carbon structures, indicating that both pre-carbonization and molten salt confinement are beneficial for improving the structural stability of carbon microspheres during high-temperature KOH activation.

[0049] Further N2 adsorption-desorption tests were conducted on Example 2, and its BET specific surface area reached 2480.3 m². 2 ·g -1 The specific surface area of ​​the micropores is 2397.3 m². 2 ·g -1 The mesoporous specific surface area is 83.0 m². 2 ·g -1 The total pore volume is 1.2094 cm³. 3 ·g -1 The micropore volume is 1.0656 cm³. 3 ·g -1 The average pore size is 1.9504 nm.

[0050] The results show that Example 2 formed a well-developed porous system dominated by micropores and possessing a certain mesoporous structure. Combined with SEM results, it can be seen that when the mass ratio of carbon microspheres to KOH is 1:2, the confinement of NaCl / KCl molten salt and activation by KOH can effectively balance the preservation of carbon microsphere morphology and the construction of pore structure.

[0051] Therefore, the present invention adopts the above-mentioned method for preparing supercapacitor activated carbon. The supercapacitor activated carbon prepared utilizes a high-temperature molten confined environment constructed by the NaCl / KCl system in conjunction with KOH activation. While creating pores, it effectively reduces the excessive etching of the microsphere structure by strong alkali, and significantly improves the morphology retention ability of carbon microspheres. The method has a wide range of raw material sources and a clear process route, providing a new approach for the high-value preparation of porous carbon from marine biomass.

[0052] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit them. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can still be made to the technical solutions of the present invention, and these modifications or equivalent substitutions cannot cause the modified technical solutions to deviate from the spirit and scope of the technical solutions of the present invention.

Claims

1. A method for preparing supercapacitor activated carbon, characterized in that: Includes the following steps: S1. Preparation of Sargassum-based carbon microsphere precursors; S2. The carbon microsphere precursor obtained in S1 is carbonized under an inert atmosphere to obtain carbonized Sargassum-based carbon microspheres. S3. The carbonized Sargassum-based carbon microspheres obtained in S2 are mixed with KOH, NaCl and KCl, and deionized water is added for wet impregnation. After impregnation, the mixture is dried and ground to obtain the mixture. S4. The mixture obtained in S3 is heated under an inert atmosphere to carry out high-temperature molten salt confinement activation treatment, so that sodium chloride and potassium chloride form a molten salt environment, and the carbon microspheres are activated under the action of potassium hydroxide to obtain the activated product. S5. The activated product obtained in S4 is acid-washed, then washed with deionized water until neutral, dried and ground to obtain supercapacitor activated carbon.

2. The method for preparing supercapacitor activated carbon according to claim 1, characterized in that: In S1, the preparation method of the Sargassum-based carbon microsphere precursor is as follows: (1) The Sargassum fusiforme was pretreated by acid washing, then washed, dried, crushed and sieved to obtain pretreated Sargassum fusiforme powder; (2) Pretreated Sargassum powder, PVP and CaCl2 were mixed in deionized water, and after thorough stirring and ultrasonic dispersion, a hydrothermal reaction was carried out. After washing, drying and grinding, Sargassum-based microsphere precursors were obtained.

3. The method for preparing supercapacitor activated carbon according to claim 1, characterized in that: (1) In the pickling, 500 mL of 1 mol / L hydrochloric acid was used and the solution was treated at 80 °C for 3 h.

4. The method for preparing supercapacitor activated carbon according to claim 1, characterized in that: In (2), the mass ratio of Sargassum to PVP is 6:1, and the CaCl2 concentration is 0.05 mol·L⁻¹. -1 The solid-liquid ratio of Sargassum to deionized water is 1g:25mL.

5. The method for preparing supercapacitor activated carbon according to claim 1, characterized in that: (2) The hydrothermal reaction temperature is 180℃-210℃ and the reaction time is 12h.

6. The method for preparing supercapacitor activated carbon according to claim 1, characterized in that: In S2, the carbonization process is carried out under a nitrogen atmosphere at a carbonization temperature of 600℃ for 2 hours, with a heating rate of 5℃·min. -1 .

7. The method for preparing supercapacitor activated carbon according to claim 1, characterized in that: In S3, the mass ratio of carbonized Sargassum-based carbon microspheres to KOH is 1:(1-4), and the mass ratio of carbonized Sargassum-based carbon microspheres to NaCl and KCl is 1:1.8:2.

2.

8. The method for preparing supercapacitor activated carbon according to claim 1, characterized in that: In S4, the high-temperature molten salt confinement activation treatment was carried out at a temperature of 700℃-800℃ for 2 hours, with a heating rate of 5℃·min. -1 .

9. The method for preparing supercapacitor activated carbon according to claim 1, characterized in that: In S5, pickling is performed using 1 mol / L hydrochloric acid.

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