Preparation of lotus stem activated carbon and application of lotus stem activated carbon as supercapacitor

Abstract

The invention belongs to the technical field of activated carbon, and discloses preparation of lotus stem activated carbon and performance research of the lotus stem activated carbon as a supercapacitor. The preparation method comprises the following steps: dipping and cleaning lotus stems, drying, crushing and sieving to obtain powder with the particle size of less than 200 meshes; uniformly mixing the lotus stem powder with a bismuth molybdate-potassium ferrate composite activator according to a ratio of 10: (0.02-0.06): (0.02-0.1), and carrying out activation treatment at 120 DEG C to obtain an activated product; transferring the activated product into a hydrothermal reaction kettle, promoting mixing under high pressure, putting into an electric heating constant-temperature blast drying box, drying for 2 hours, taking out, pouring into an evaporating dish, and continuously drying for 24 hours; and carbonizing at 500-800 DEG C, dipping, neutralizing, washing, filtering and drying to obtain the finished product lotus stem activated carbon. Under the current density of 0.5 A / g, the specific capacitance of the prepared lotus stem activated carbon reaches 550 F / g or above, and the specific surface area of the lotus stem activated carbon is 1000 m < 2 > / g or above.

Description

Technical Field

[0001] This invention relates to an activated carbon material, and more particularly to a method for preparing a high specific capacitance and mesoporous activated carbon material by activating lotus stems with a bismuth molybdate-potassium ferrate composite activator, and its application as an electrode material for supercapacitors. Background Technology

[0002] Supercapacitors, as a novel energy storage device situated between traditional capacitors and batteries, are widely used in the electronics industry, electric vehicles, aerospace, and defense technology due to their superior characteristics such as high energy density, high power density, rapid charge-discharge, and long cycle life. Among them, electric double-layer supercapacitors are extensively researched and applied due to their high specific capacitance and low impedance characteristics. Electrode materials are one of the core components of supercapacitors, playing a crucial role in their performance. Currently, activated carbon is widely used as an electrode material for supercapacitors due to its high specific surface area, abundant pore structure, good chemical stability, and conductivity. However, existing activated carbon preparation methods have some problems, such as insufficient specific surface area, uneven pore size distribution, complex preparation processes, and high costs. Especially for biomass-based activated carbon, although it has advantages such as abundant raw materials and low price, it still faces challenges such as poor activation effect and severe specific capacitance decay during preparation.

[0003] To address these challenges, researchers have been exploring new methods for preparing activated carbon. Using composite activators is one effective approach, but selecting appropriate combinations of activators to obtain high-performance activated carbon remains a key research focus. Furthermore, controlling the pore structure and pore size distribution of activated carbon is also crucial for improving its electrochemical performance. Therefore, developing a method to prepare activated carbon with high specific capacitance, high specific surface area, and uniform pore size distribution is of great significance, providing new insights for enhancing the performance of supercapacitors. Summary of the Invention

[0004] Compared with the prior art, the present invention provides a method for preparing activated carbon with high specific capacity and large specific surface area using bismuth molybdate-potassium ferrate composite activator, which has the following beneficial effects: 1. By using bismuth molybdate-potassium ferrate composite activator, efficient activation of lotus stem powder was achieved, significantly improving the specific capacitance of activated carbon and solving the problem of insufficient specific capacitance of activated carbon in the prior art.

[0005] 2. The activated carbon prepared by this invention has a large specific surface area, reaching 1000-2000 m². 2 / g, far exceeding the level of existing technology, and solving the problem of insufficient specific surface area in existing technologies.

[0006] 3. By precisely controlling the ratio and activation conditions of the bismuth molybdate-potassium ferrate composite activator, the uniformity of the pore size distribution of activated carbon was achieved, with the main pore size distribution peaks in the range of 2–6 nm, thus solving the problem of uneven pore size distribution in the prior art.

[0007] 4. The activated carbon prepared by this invention has excellent electrochemical performance. When used in supercapacitors, it can significantly improve the energy density and power density of the battery and extend the cycle life, thus solving the problems of poor activation effect and severe specific capacitance decay of biomass-based activated carbon in the prior art.

[0008] 5. The preparation method used in this invention is simple, easy to operate, uses readily available raw materials, and is inexpensive, thus having good prospects for industrial application.

[0009] To achieve the above objectives, the technical solution adopted by the present invention is as follows: (1) Raw material pretreatment: Mix lotus stem powder with deionized water, stir, filter, wash until neutral, and then dry; (2) Activation treatment: Mix the pretreated lotus stem powder with bismuth molybdate-potassium ferrate composite activator, add deionized water and stir evenly; (3) Hydrothermal treatment: The activated mixture is subjected to hydrothermal treatment; (4) Carbonization treatment: The product after hydrothermal treatment is carbonized under an inert atmosphere to obtain lotus stem activated carbon.

[0010] In some preferred embodiments, the technical solution includes the following steps: Step 1, Raw material pretreatment: Mix lotus stem powder with deionized water at a mass ratio of 1:5, stir for 30 minutes, filter, wash until neutral, dry for 4 hours at 60℃; Step 2, Activation treatment: Mix the pretreated lotus stem powder with bismuth molybdate-potassium ferrate composite activator at a mass ratio of 1:0.05:0.01, add deionized water to make the solid-liquid ratio 1:10, and stir evenly. Step 3, hydrothermal treatment: The mixture is hydrothermally treated at 120℃ for 4 hours; Step 4, Carbonization treatment: The product after hydrothermal treatment is heated to 800℃ at a heating rate of 2℃ / min under an inert atmosphere, held at that temperature for 2 hours, and then naturally cooled to room temperature.

[0011] Step 2 includes: In step 2, bismuth molybdate and potassium ferrate are mixed in a predetermined ratio, deionized water is added, and the mixture is stirred until homogeneous to form a mixed solution. Slowly add concentrated sulfuric acid dropwise to the mixed solution to make the volume ratio 1:1, and continue stirring for 1 hour; The mixture was stirred overnight at 60°C to form a homogeneous colloid.

[0012] Step 3 includes: In step 3, the mixture is subjected to hydrothermal treatment under a vacuum of not less than -0.08 MPa; Control the hydrothermal treatment temperature within the range of 110-130℃ to ensure sufficient formation of the initial pore structure; Further development of the pore structure can be achieved by adjusting the hydrothermal time.

[0013] Step 4 includes: In step 4, carbonization is carried out under a nitrogen or argon atmosphere to avoid oxidation; Control the carbonization temperature and time to ensure that the carbon layer is evenly covered on the pore wall; After naturally cooling to room temperature, the product is pulverized and dispersed using a secondary ball milling method.

[0014] The lotus stem activated carbon prepared by any of the above methods exhibits a specific capacitance of over 620 F / g at a current density of 0.5 A / g, which is superior to that of pure bismuth molybdate (484.0 F / g). -1 ) and potassium ferrate (374 F / g). The specific surface area of ​​the activated carbon is 3285~3659 m². 2 / g, total pore volume is 1.86~2.56cm³ 3 / g.

[0015] The specific preparation method of lotus stem activated carbon as a supercapacitor electrode material is as follows: The prepared lotus root activated carbon, polyvinylidene fluoride (PVDF), and conductive carbon black were mixed evenly at a mass ratio of 80:10:10. An appropriate amount of N-methyl-2-pyrrolidone (NMP) was added to make a slurry, which was then coated onto nickel foam with a diameter of 13 mm. After the solvent evaporated, the mixture was placed in a vacuum drying oven and dried at 100°C for 12 h to obtain the activated carbon electrode material for supercapacitors. Detailed Implementation

[0016] Example 1 Bismuth molybdate activated lotus stems to prepare biomass activated carbon Step 1: Raw material pretreatment: Mix lotus stem powder with deionized water at a mass ratio of 1:5, stir for 30 minutes at room temperature, filter, wash with deionized water until neutral, and finally dry at 60℃ for 4 hours.

[0017] Step 2, Activation Treatment: Mix the pretreated lotus stem powder with bismuth molybdate at a mass ratio of 1:0.05, add deionized water to make the solid-liquid ratio 1:10, and stir until homogeneous. The concentration of bismuth molybdate is 0.05 mol / L.

[0018] Step 201: Slowly add concentrated sulfuric acid dropwise to the mixed solution to make the volume ratio 1:1, and continue stirring for 1 hour, with the stirring speed controlled at 200-300 rpm.

[0019] Step 202: Stir the mixture at 60°C overnight to form a uniform colloid, with the stirring speed controlled at 100-150 rpm.

[0020] Step 3, hydrothermal treatment: The mixture is subjected to hydrothermal treatment under a vacuum of not less than -0.08 MPa, with the temperature controlled within the range of 110-130℃, the stirring rate at 200 rpm, and the hydrothermal time at 4 hours.

[0021] Step 4, Carbonization treatment: The product after hydrothermal treatment is heated to 800℃ at a heating rate of 2℃ / min under an inert atmosphere, held at that temperature for 2 hours, and then naturally cooled to room temperature.

[0022] Step 401: Carburize the material under a nitrogen atmosphere to prevent oxidation.

[0023] Step 402: Control the carbonization temperature and time to ensure that the carbon layer is evenly covered on the pore wall.

[0024] Step 403: After naturally cooling to room temperature, the product is pulverized and dispersed using a secondary ball milling method.

[0025] Example 2 K2FeO4 activation of lotus stems to prepare biomass activated carbon Step 1: Raw material pretreatment: Mix lotus stem powder with deionized water at a mass ratio of 1:5, stir for 30 minutes at room temperature, filter, wash with deionized water until neutral, and finally dry at 60℃ for 4 hours.

[0026] Step 2, Activation Treatment: Mix the pretreated lotus stem powder with K2FeO4 at a mass ratio of 1:0.1, add deionized water to make the solid-liquid ratio 1:10, and stir evenly. The concentration of K2FeO4 is 0.1 mol / L.

[0027] Step 201: Slowly add concentrated sulfuric acid dropwise to the mixed solution to make the volume ratio 1:1, and continue stirring for 1 hour, with the stirring speed controlled at 200-300 rpm.

[0028] Step 202: Stir the mixture at 60°C overnight to form a uniform colloid, with the stirring speed controlled at 100-150 rpm.

[0029] Step 3, hydrothermal treatment: The mixture is subjected to hydrothermal treatment under a vacuum of not less than -0.08 MPa, with the temperature controlled within the range of 110-130℃, the stirring rate at 200 rpm, and the hydrothermal time at 4 hours.

[0030] Step 4, Carbonization treatment: The product after hydrothermal treatment is heated to 800℃ at a heating rate of 2℃ / min under an inert atmosphere, held at that temperature for 2 hours, and then naturally cooled to room temperature.

[0031] Step 401: Carburize the material under a nitrogen atmosphere to prevent oxidation.

[0032] Step 402: Control the carbonization temperature and time to ensure that the carbon layer is evenly covered on the pore wall.

[0033] Step 403: After naturally cooling to room temperature, the product is pulverized and dispersed using a secondary ball milling method.

[0034] Example 3 Lotus stem powder and bismuth molybdate-potassium ferrate composite activator were mixed at a mass ratio of 1:0.05:0.1. Step 1: Raw material pretreatment: Mix lotus stem powder with deionized water at a mass ratio of 1:5, stir for 30 minutes at room temperature, filter, wash with deionized water until neutral, and finally dry at 60℃ for 4 hours.

[0035] Step 2, Activation treatment: Mix the pretreated lotus stem powder with bismuth molybdate-potassium ferrate composite activator at a mass ratio of 1:0.05:0.01, add deionized water to make the solid-liquid ratio 1:10, and stir evenly.

[0036] Step 201: Mix bismuth molybdate and potassium ferrate in a predetermined ratio, add deionized water, and stir until homogeneous to form a mixed solution, wherein the concentration of bismuth molybdate is 0.05 mol / L and the concentration of potassium ferrate is 0.01 mol / L.

[0037] Step 202: Slowly add concentrated sulfuric acid dropwise to the mixed solution to make the volume ratio 1:1, and continue stirring for 1 hour, with the stirring speed controlled at 200-300 rpm.

[0038] Step 203: Stir the mixture at 60°C overnight to form a uniform colloid, with the stirring speed controlled at 100-150 rpm.

[0039] Step 3, hydrothermal treatment: The mixture is subjected to hydrothermal treatment under a vacuum of not less than -0.08 MPa, with the temperature controlled within the range of 110-130℃, the stirring rate at 200 rpm, and the hydrothermal time at 4 hours.

[0040] Step 4, Carbonization treatment: The product after hydrothermal treatment is heated to 800℃ at a heating rate of 2℃ / min under an inert atmosphere, held at that temperature for 2 hours, and then naturally cooled to room temperature.

[0041] Step 401: Carburize the material under a nitrogen atmosphere to prevent oxidation.

[0042] Step 402: Control the carbonization temperature and time to ensure that the carbon layer is evenly covered on the pore wall.

[0043] Step 403: After naturally cooling to room temperature, the product is pulverized and dispersed using a secondary ball milling method.

[0044] Example 4 Lotus stem powder and bismuth molybdate-potassium ferrate composite activator were mixed at a mass ratio of 1:0.06:0.02. Step 1: Raw material pretreatment: Mix lotus stem powder with deionized water at a mass ratio of 1:6, stir at 40℃ for 35 minutes, filter, wash with deionized water until neutral, and finally dry at 65℃ for 3.5 hours.

[0045] Step 2, Activation treatment: Mix the pretreated lotus stem powder with bismuth molybdate-potassium ferrate composite activator at a mass ratio of 1:0.06:0.02, add deionized water to make the solid-liquid ratio 1:12, and stir evenly.

[0046] Step 201: Mix bismuth molybdate and potassium ferrate in a predetermined ratio, add deionized water, and stir until homogeneous to form a mixed solution, wherein the concentration of bismuth molybdate is 0.06 mol / L and the concentration of potassium ferrate is 0.02 mol / L.

[0047] Step 202: Slowly add concentrated sulfuric acid dropwise to the mixed solution to make the volume ratio 1:1.2, and continue stirring for 1.2 hours at a stirring speed of 250 rpm.

[0048] Step 203: Stir the mixture at 65°C overnight to form a uniform colloid, with the stirring speed controlled at 120 rpm.

[0049] Step 3, hydrothermal treatment: The mixture is subjected to hydrothermal treatment under a vacuum of not less than -0.09 MPa, with the temperature controlled within the range of 115-125℃, the stirring rate at 220 rpm, and the hydrothermal time at 4.5 h.

[0050] Step 4, Carbonization treatment: The product after hydrothermal treatment is heated to 850℃ at a heating rate of 2.5℃ / min under an inert atmosphere, held at that temperature for 2.5h, and then naturally cooled to room temperature.

[0051] Step 401: Carburize the material under an argon atmosphere to prevent oxidation.

[0052] Step 402: Control the carbonization temperature and time to ensure that the carbon layer is evenly covered on the pore wall.

[0053] Step 403: After naturally cooling to room temperature, the product is pulverized and dispersed using a secondary ball milling method.

[0054] Test Example 1 The obtained activated carbon was used as the electrode material to prepare activated carbon electrodes. Specifically, activated carbon, conductive carbon black, and binder were mixed evenly at a mass ratio of 17:2:1, and then uniformly coated onto pre-prepared nickel foam. The mixture was then dried in an oven at 120 ℃ for 8 h. Two electrode sheets of similar mass were assembled, and a button-type supercapacitor was prepared using a 6 mol / L KOH solution as the electrolyte. Electrochemical performance tests were conducted, and Table 1 shows the electrochemical performance of the supercapacitor.

[0055]

[0056] The results above show that the activated carbon obtained by using lotus stems as raw material and mixing lotus stem powder with bismuth molybdate-potassium ferrate composite activator at a mass ratio of 1:0.05:0.1 and a temperature of 800 ℃ exhibits the best conductivity. At a current density of 0.5 A / g, the specific capacitance is 624 F / g, and the specific capacitance retention rate is 93% after 3000 cycles of cyclic voltammetry testing, demonstrating excellent electrochemical performance and making it a suitable electrode material for supercapacitors.

[0057] The above embodiments are merely illustrative examples and are not intended to limit the implementation. Those skilled in the art will recognize that other variations or modifications can be made based on the above description. It is neither necessary nor possible to exhaustively list all possible implementations; therefore, any obvious variations or modifications derived therefrom remain within the scope of protection of this invention.

Claims

1. A method for preparing lotus stem activated carbon, characterized in that, Includes the following steps: (1) Raw material pretreatment: Mix lotus stem powder with deionized water, stir, filter, wash until neutral, and then dry; (2) Activation treatment: Mix the pretreated lotus stem powder with bismuth molybdate-potassium ferrate composite activator, add deionized water and stir evenly; (3) Hydrothermal treatment: The activated mixture is subjected to hydrothermal treatment; (4) Carbonization treatment: The product after hydrothermal treatment is carbonized under an inert atmosphere to obtain lotus stem activated carbon.

2. The preparation method according to claim 1, characterized in that, In step (1), the mass ratio of lotus stem powder to deionized water is 1:3-1:8, the drying temperature is 50-80℃, and the drying time is 2-6h.

3. The preparation method according to claim 1, characterized in that, In step (2), the mass ratio of the pretreated lotus root powder, bismuth molybdate and potassium ferrate is 1:(0.01-0.1):(0.005-0.05), and the solid-liquid ratio is 1:8-1:

15.

4. The preparation method according to claim 1, characterized in that, The activation treatment in step (2) also includes: mixing bismuth molybdate and potassium ferrate and adding deionized water to prepare a mixed solution, adding concentrated sulfuric acid dropwise to the mixed solution, and then stirring and reacting at 50-70℃ for 6-12 hours to form a colloid, and then mixing it with the pretreated lotus stem powder. The volume ratio of concentrated sulfuric acid to the mixed solution is (0.8-1.2):

1.

5. The preparation method according to claim 1, characterized in that, In step (3), the hydrothermal treatment temperature is 100-150℃, the time is 2-8h, and the pressure is -0.06 MPa to -0.10 MPa.

6. The preparation method according to claim 1, characterized in that, In step (4), the carbonization process is carried out under a nitrogen or argon atmosphere, with a heating rate of 1-5℃ / min, a final temperature of 600-900℃, and a holding time of 1-4h. After the carbonization process, the process also includes a post-processing step of crushing and dispersing the product.

7. A lotus stem activated carbon prepared by the method according to any one of claims 1-6, characterized in that, Its specific surface area is 1000-4000 m² 2 / g, at a current density of 0.5 A / g, the specific capacitance is not less than 550 F / g.

8. A supercapacitor electrode material, characterized in that, Its active ingredients include the lotus stem activated carbon as described in claim 7.

9. The supercapacitor electrode material according to claim 8, characterized in that, The electrode material is composed of lotus root activated carbon, conductive agent and binder in a mass ratio of (75-85):(5-15):(5-15).

10. A supercapacitor, characterized in that, Its electrodes comprise the supercapacitor electrode material as described in claim 8 or 9.

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