A biochar / graphene composite material, its preparation method and application

Abstract

The present invention discloses a biochar / graphene composite material, a preparation method thereof and an application thereof. The method comprises impregnating a biomass raw material with a copper salt solution to obtain a precursor; pyrolyzing the precursor to obtain a biochar material modified with copper oxide, and then, under a reducing atmosphere and high temperature conditions, using carbon dioxide as a carbon source to in-situ generate graphene on the biochar material modified with copper oxide to obtain a biochar / graphene / copper composite material, and the biochar / graphene / copper composite material is obtained by leaching copper treatment. The composite material has excellent electrochemical properties, and when used for preparing a capacitor, has excellent rate performance, capacitance and good cycle service life. The preparation method is simple, low in cost and suitable for industrial production.

Description

Technical Field

[0001] The present invention relates to a graphene composite material, specifically to a biochar / graphene composite material, and also relates to its preparation method and application, belonging to the technical field of capacitor materials. Background Art

[0002] With the rapid development of the new energy industry, supercapacitors, as energy storage devices with high power density, fast charge and discharge capabilities, and long cycle life, have shown irreplaceable advantages in the fields of new energy transportation, smart grids, portable electronic devices, etc. Graphene has become the main research object of supercapacitor electrode materials due to its unique two-dimensional honeycomb structure, ultra-high specific surface area, and excellent electrical conductivity.

[0003] In recent years, graphene-like materials derived from biomass have attracted extensive attention from researchers. Through processes such as pyrolysis and activation, natural biomass can be transformed into graphene analogs with a hierarchical porous structure, which can not only effectively inhibit interlayer stacking but also accelerate the penetration of electrolytes and the rapid transfer of ions, thereby improving the performance of electrode materials. Chinese invention patents CN 110937596 B, CN 111517306 B, etc. are all based on this idea. In addition, researchers have adopted multiple strategies using graphene composite materials as active electrode materials to improve their specific capacitance performance. For example, researchers have proposed a composite strategy of graphene and carbon materials to optimize the overall electrochemical performance. Chinese invention patents CN 111017908 B, CN104495815 B, etc. are all based on this idea. However, in the prior art, the synthesis of carbon / graphene composite materials mostly uses a two-step method or even a multi-step method, the preparation process is relatively complex, and the graphene used all comes from natural minerals such as graphite, coal, and asphalt, which limits its application.

[0004] Therefore, it is of great significance to develop a simple and low-cost preparation method to prepare biochar and graphene composite materials with excellent material properties. Summary of the Invention

[0005] Aiming at the deficiencies of the prior art, the purpose of the present invention is to provide a biochar / graphene composite material. This composite material has excellent electrochemical properties and can be used for the preparation of capacitor electrode materials.

[0006] The second purpose of the present invention is to provide a preparation method of a biochar / graphene composite material. This method is simple, easy to operate, has a wide range of raw materials, low production cost, and small environmental pollution.

[0007] The third object of the present invention is to provide an application of a biochar / graphene composite material. When the biochar / graphene composite material is used as a capacitor electrode material, it has excellent rate performance and good cycle service life, effectively improving the capacitor capacity.

[0008] To achieve the above object, the present invention provides a preparation method of a biochar / graphene composite material. The method is to impregnate a biomass raw material with a copper salt solution to obtain a precursor; the precursor is pyrolyzed to obtain a copper oxide-modified biochar material, and then under a reducing atmosphere and high temperature conditions, using carbon dioxide as a carbon source, graphene is in-situ generated on the copper oxide-modified biochar material to obtain a biochar / graphene / copper composite material, and the biochar / graphene / copper composite material is obtained by leaching copper treatment.

[0009] The copper oxide-modified biochar material in the present invention can be used as a catalyst to catalyze the reduction of CO2 to graphene under a reducing atmosphere. Specifically, under the action of a reducing gas, the copper oxide on the biochar is reduced to copper metal, and catalytic active centers are formed on the biochar, catalyzing the reduction of carbon dioxide to in-situ generate aggregated multi-layer graphene on the biochar matrix. At the same time, the overflow of trace water vapor generated by the reaction will damage the composite material structure and enrich the pore structure. After the graphene layer is generated, the biochar / graphene composite material can be obtained by leaching copper from the composite material. In addition, the characteristics of natural doping of heteroatoms such as oxygen, nitrogen, and sulfur rich in biomass can further introduce redox active sites, increase the specific capacitance through pseudocapacitance reaction, and improve the electrochemical performance. The presence of biochar can effectively reduce the aggregation between graphene sheets, increase the effective specific surface area, further improve the electron transfer efficiency. By leaching copper treatment, copper and its compounds can be effectively removed, and at the same time, the pore structure of biochar can be improved, which is beneficial to charge storage and enhances the electrochemical performance.

[0010] As a preferred scheme, the mass molar ratio of the biomass raw material to the copper salt is 1-10 g:0.01-0.1 mol.

[0011] As a preferred scheme, the biomass raw material includes at least one of camellia shell, bamboo, crop straw, coconut shell, fruit peel, wood, and animal bone. A further preferred biomass raw material is camellia shell. Since the camellia shell itself contains rich nitrogen-containing and oxygen-containing functional groups, and after using the camellia shell to prepare the biochar / graphene composite material, the specific surface area of the composite material can be increased, and a rich microporous / mesoporous structure can be provided, effectively enhancing the electrochemical performance of the composite material.

[0012] As a preferred scheme, the particle size of the biomass raw material is -200 mesh. That is, the particle size ≤ 150 μm.

[0013] As a preferred embodiment, the molar concentration of the copper salt solution is 0.1 to 1 mol / L.

[0014] As a preferred embodiment, the solid-liquid ratio of the biomass raw material to the copper salt solution is 1 to 10 g / 100 ml. More preferably, the solid-liquid ratio of the biomass raw material to the copper salt solution is 6 g / 100 ml.

[0015] As a preferred embodiment, the copper salt includes at least one of copper sulfate, copper nitrate, and copper chloride. More preferably, the copper salt is copper sulfate.

[0016] As a preferred embodiment, the impregnation process is: stirring at 50 to 80 °C for 3 to 5 h.

[0017] As a preferred embodiment, the pyrolysis conditions are: the atmosphere is a protective atmosphere, the temperature is 700 to 1100 °C, and the time is 2 to 4 h.

[0018] As a preferred embodiment, the protective atmosphere is an inert gas atmosphere. The inert gas includes nitrogen, argon, etc.

[0019] As a preferred embodiment, the reducing atmosphere is hydrogen, and the gas flow rate is 80 to 100 ml / min.

[0020] As a preferred embodiment, the flow rate of carbon dioxide is 30 to 50 ml / min.

[0021] As a preferred embodiment, the high-temperature conditions are: the temperature is 600 to 900 °C, and the time is 4 to 6 h.

[0022] As a preferred embodiment, the method for leaching copper is to soak with a strong acid solution.

[0023] As a preferred embodiment, the strong acid solution is one of nitric acid, sulfuric acid-nitric acid mixture, and nitric acid-phosphoric acid mixture. More preferably, the strong acid solution is sulfuric acid-nitric acid mixture.

[0024] As a preferred embodiment, after the copper leaching treatment, washing and freeze-drying treatments are carried out in sequence.

[0025] The present invention also provides a biochar / graphene composite material, which is prepared by the above method. This material has excellent electrochemical properties.

[0026] The present invention also provides an application of the biochar / graphene composite material as a capacitor electrode material. The capacitor prepared with this composite material has excellent rate performance, capacity, and cycle service life.

[0027] Compared with the prior art, the beneficial technical effects brought by the technical solution of the present invention are:

[0028] (1) In the present invention, a biochar material modified with copper oxide is used as a catalyst to catalytically generate graphene in situ on the biochar, and then through leaching treatment of copper, a biochar / graphene composite material is obtained. Among them, the characteristics of heteroatom doping such as oxygen, nitrogen, and sulfur naturally rich in biomass can further introduce redox active sites, increase the specific capacity through pseudocapacitive reactions, and improve the electrochemical performance. The presence of biochar can effectively reduce the aggregation between graphene sheets, increase the effective specific surface area, and further improve the electron transfer efficiency. The leaching treatment of copper can improve the pore structure of biochar, which is beneficial to charge storage and enhance the electrochemical performance;

[0029] (2) When the biochar / graphene composite material prepared by the present invention is used for the preparation of a capacitor, it can effectively improve the rate performance, capacity, and cycle service life of the capacitor;

[0030] (3) The preparation method is simple, the raw materials are cheap and easy to obtain, the production cost is low, the environmental pollution is small, and it is suitable for industrial scale production. Description of the Drawings

[0031] Figure 1 It is the X-ray diffraction pattern of the copper oxide modified biochar material during the preparation process of Example 1.

[0032] Figure 2 It is the X-ray photoelectron spectroscopy of the biochar / graphene / copper composite material during the preparation process of Example 1.

[0033] Figure 3 It is the transmission electron microscope image of the biochar / graphene composite material prepared in Example 1.

[0034] Figure 4 It is the curve of the specific capacity of the biochar / graphene composite material prepared in Example 1 changing with the current density.

[0035] Figure 5 It is the cycle life curve of the biochar / graphene composite material prepared in Example 1. Detailed Embodiments

[0036] The technical solutions of the present invention will be further described below in conjunction with specific embodiments of the present invention. It should be noted that the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments; these embodiments are only for better understanding of the present invention, rather than limiting the scope protected by the present invention.

[0037] Unless otherwise specified, various reagents and raw materials used in the present invention are all products that can be purchased from the market or can be obtained by known methods.

[0038] The room temperature of the present invention is 25 °C.

[0039] Example 1

[0040] This example provides a preparation method of a biochar / graphene composite material, which specifically includes the following preparation steps:

[0041] 1) Accurately weigh 6 g of camellia shell powder, mix it evenly with 100 ml of 0.5 mol / L copper sulfate solution, stir at 60 °C for 4 h to obtain a precursor (when there is too much reaction product liquid after the stirring reaction ends, it can be removed by suction filtration);

[0042] 2) Place the precursor in a tubular furnace, pyrolyze it under a N2 atmosphere, the pyrolysis temperature is 900 °C, and the holding time is 3 h. After pyrolysis, a biochar material modified with copper oxide is obtained;

[0043] 3) When the temperature drops to 800 °C, slowly introduce H2 into the original reaction device at a flow rate of 85 ml / min, and then introduce CO2 at a flow rate of 40 ml / min for in-situ graphene generation for 5 h to obtain a biochar / graphene / copper composite material;

[0044] 4) Immerse the biochar / graphene / copper composite material in a sulfuric acid-nitric acid mixed solution (100 ml, 3:1, v / v). After all metal copper compounds are leached out (the copper ion content is detected by ICP), wash it to neutrality, filter, and freeze-dry to obtain a biochar / graphene composite material.

[0045] The crystal structure of the biochar material modified with copper oxide was observed by XRD, as Figure 1 shown. It can be found that in this material, the main existing forms of copper are CuO and Cu2O; the valence state distribution of Cu element in the biochar / graphene / copper composite material was observed by XPS, as Figure 2 shown. The results show that the main existing forms of Cu are Cu 0 、Cu + and Cu 2+ these three forms, among which Cu 0 is the reduction product of Cu x O when catalyzing the generation of graphene from CO2; the morphology of the prepared biochar / graphene composite material was observed by electron microscopy, as Figure 3 shown. It can be seen from the figure that its lattice spacing is about 0.35 nm, indicating that multilayer graphene has been successfully prepared in the composite material of the present invention.

[0046] The prepared biochar / graphene composite material was used as the electrode material of the supercapacitor for electrochemical performance testing. In a three-electrode system, the prepared material was used as the working electrode, a platinum sheet as the counter electrode, mercury / mercuric chloride as the reference electrode, and 6 mol / L KOH solution as the electrolyte. Electrochemical performance testing was carried out in the voltage range of -1 to 0 V.

[0047] It can be seen from Figure 4 that at a current density of 1 A / g, its specific capacitance can reach 437.5 F / g. When the current density increases to 100 A / g, the specific capacitance of this electrode material can still reach 358.3 F / g, maintaining 81.9% of the initial capacitance, showing excellent rate performance. As Figure 5 shown, after cycling 15,500 times at a current density of 20 A / g, its capacitance retention rate is 97%, indicating that this material has good cycle life.

[0048] Example 2

[0049] This example provides a preparation method of a biochar / graphene composite material, which specifically includes the following preparation steps:

[0050] 1) Accurately weigh 5 g of banana peel powder, mix it evenly with 100 ml of 0.3 mol / L copper sulfate solution, and stir at 60 °C for 4 h to obtain a precursor;

[0051] 2) Place the precursor in a tube furnace and pyrolyze it under a N2 atmosphere. The pyrolysis temperature is 800 °C and the holding time is 3 h. After pyrolysis, a copper oxide-modified biochar material is obtained;

[0052] 3) Keep the temperature at 800 °C unchanged, slowly introduce H2 into the original reaction device at a flow rate of 80 ml / min, and then introduce CO2 at a flow rate of 40 ml / min for in-situ graphene generation for 4 h to obtain a biochar / graphene / copper composite material;

[0053] 4) Immerse the copper-modified biochar / graphene / copper composite material in a sulfuric acid-nitric acid mixed solution (100 ml, 3:1, v / v). After all metal copper compounds are leached out (the copper ion content is detected by ICP), wash it to neutrality, filter, and freeze-dry to obtain the product.

[0054] The electrochemical performance of the biochar / graphene composite obtained in Example 2 was tested (the electrochemical test method was the same as that in Example 1): at a current density of 1 A / g, its specific capacitance could reach 418.4 F / g. When the current density increased to 100 A / g, the specific capacitance of this electrode material could still reach 331.7 F / g, maintaining 79.3% of the initial capacitance. After cycling 15,500 times at a current density of 20 A / g, its capacitance retention rate was 96.4%.

[0055] Example 3

[0056] This example provides a preparation method of a biochar / graphene composite, which specifically includes the following preparation steps:

[0057] 1) Accurately weigh 8 g of pepper straw powder, mix it evenly with 100 ml of 0.8 mol / L copper sulfate solution, and stir at 60 °C for 3 h to obtain a precursor;

[0058] 2) Place the precursor in a tube furnace and pyrolyze it under a N2 atmosphere. The pyrolysis temperature is 1000 °C and the holding time is 2.5 h. After pyrolysis, a copper oxide-modified biochar material is obtained;

[0059] 3) When the temperature drops to 700 °C, slowly introduce H2 into the original reaction device at a flow rate of 90 ml / min, and then introduce CO2 at a flow rate of 45 ml / min for in-situ graphene generation for 4 h to obtain a biochar / graphene / copper composite;

[0060] 4) Immerse the biochar / graphene / copper composite in a nitric acid solution (100 ml, 80%). After all metal copper compounds are leached out (the copper ion content is detected by ICP), wash it to neutrality, filter, and freeze-dry to obtain the product.

[0061] The electrochemical performance of the biochar / graphene composite obtained in Example 3 was tested (the electrochemical test method was the same as that in Example 1): at a current density of 1 A / g, its specific capacitance could reach 421.3 F / g. When the current density increased to 100 A / g, the specific capacitance of this electrode material could still reach 336.8 F / g, maintaining 79.9% of the initial capacitance. After cycling 15,500 times at a current density of 20 A / g, its capacitance retention rate was 97.2%.

[0062] Example 4

[0063] This example provides a preparation method of a biochar / graphene composite, which specifically includes the following preparation steps:

[0064] 1) Accurately weigh 10 g of rice straw powder, mix it evenly with 100 ml of 0.3 mol / L copper sulfate solution, and stir for 5 h at 55 °C to obtain a precursor;

[0065] 2) Place the precursor in a tubular furnace and pyrolyze it under a N2 atmosphere. The pyrolysis temperature is 700 °C and the holding time is 4 h. After pyrolysis, a biochar material modified with copper oxide is obtained;

[0066] 3) Keep the temperature at 900 °C unchanged, slowly introduce H2 into the original reaction device at a flow rate of 90 ml / min, and then introduce CO2 at a flow rate of 35 ml / min to carry out in-situ graphene generation for 5 h to obtain a biochar / graphene / copper composite material;

[0067] 4) Immerse the biochar / graphene / copper composite material in a nitric acid solution (100 ml, 80%). After all metal copper compounds are leached out (detect the copper ion content by ICP), wash it to neutrality, filter it, and freeze-dry it to obtain the product.

[0068] The electrochemical performance of the biochar / graphene composite material obtained in Example 4 was tested (the electrochemical test method was the same as that in Example 1): at a current density of 1 A / g, its specific capacitance can reach 414.6 F / g. When the current density increases to 100 A / g, the specific capacitance of this electrode material can still reach 312.9 F / g, maintaining 75.5% of the initial capacitance. After cycling 15,500 times at a current density of 20 A / g, its capacity retention rate is 95.8%.

[0069] Example 5

[0070] This example provides a preparation method of a biochar / graphene composite material, which specifically includes the following preparation steps:

[0071] 1) Accurately weigh 3 g of fish bone powder, mix it evenly with 100 ml of 0.2 mol / L copper sulfate solution, and stir for 4 h at 70 °C to obtain a precursor;

[0072] 2) Place the precursor in a tubular furnace and pyrolyze it under a N2 atmosphere. The pyrolysis temperature is 1100 °C and the holding time is 2 h. After pyrolysis, a biochar material modified with copper oxide is obtained;

[0073] 3) When the temperature drops to 900 °C, slowly introduce H2 into the original reaction device at a flow rate of 100 ml / min, and then introduce CO2 at a flow rate of 50 ml / min to carry out in-situ graphene generation for 6 h to obtain a biochar / graphene / copper composite material;

[0074] 4) Immerse the biochar / graphene / copper composite material in a mixed solution of nitric acid and phosphoric acid (2:3, v / v). After all the metal copper compounds are leached out (detect the copper ion content by ICP), wash it to neutrality, then filter and freeze-dry to obtain the product.

[0075] Perform electrochemical performance testing on the composite material obtained in Example 5 (the electrochemical testing method is the same as that in Example 1): at a current density of 1 A / g, its specific capacitance can reach 411.3 F / g. When the current density increases to 100 A / g, the specific capacitance of this electrode material can still reach 327.4 F / g, maintaining 79.6% of the initial capacitance. After cycling 15,500 times at a current density of 20 A / g, its capacitance retention rate is 95.8%.

[0076] Comparative Example 1

[0077] The difference between this comparative example and Example 1 is only that: the copper sulfate solution in step 1) is replaced with ultrapure water.

[0078] Perform electrochemical performance testing on the composite material obtained in Comparative Example 1 (the electrochemical testing method is the same as that in Example 1): at a current density of 1 A / g, its specific capacitance is only 96.3 F / g. In the absence of copper-based catalytic reaction centers, graphene cannot be generated, resulting in a significant decrease in its electrochemical performance.

[0079] Comparative Example 2

[0080] The difference between this comparative example and Example 1 is only that: the pyrolysis temperature in step 2) is controlled at 400 °C.

[0081] Perform electrochemical performance testing on the biochar-like / graphene composite material obtained in Comparative Example 2 (the electrochemical testing method is the same as that in Example 1): at a current density of 1 A / g, its specific capacitance is only 238.2 F / g. The relatively low pyrolysis temperature leads to a significant reduction in the degree of defects, pore structure, and specific surface area of the biochar itself, thereby reducing charge storage and the electron transfer rate.

[0082] Comparative Example 3

[0083] The difference between this comparative example and Example 1 is only that: the reaction temperature in step 3) is controlled at 400 °C.

[0084] Perform electrochemical performance testing on the composite material obtained in Comparative Example 3 (the electrochemical testing method is the same as that in Example 1): at a current density of 1 A / g, its specific capacitance is only 176.4 F / g. The too low catalytic reaction temperature is not conducive to the generation of graphene, resulting in a decrease in electrochemical performance.

[0085] Comparative Example 4

[0086] This comparative example is different from Example 1 only in that: the reaction temperature in step 3) is controlled at 1300 °C.

[0087] The composite material obtained in Comparative Example 4 was subjected to electrochemical performance testing (the electrochemical testing method was the same as that in Example 1): at a current density of 1 A / g, its specific capacitance was only 82.8 F / g. The excessively high catalytic reaction temperature caused the copper in the composite material to melt, which was not conducive to the formation of graphene. Moreover, the excessively high temperature would cause the structure of the biochar itself to collapse, generating macropores while reducing the effective specific surface area, resulting in a significant decrease in its specific capacitance.

[0088] Comparative Example 5

[0089] This comparative example is different from Example 1 only in that: in step 3), only H2 is introduced, and CO2 is not introduced.

[0090] The material obtained in Comparative Example 5 was subjected to electrochemical performance testing (the electrochemical testing method was the same as that in Example 1): at a current density of 1 A / g, its specific capacitance was only 102.6 F / g. This was because the lack of carbon dioxide prevented the formation of graphene layers, resulting in poor performance of the obtained material.

[0091] Comparative Example 6

[0092] This comparative example is different from Example 1 only in that: the sulfuric acid-nitric acid mixed solution is replaced with acetic acid.

[0093] The composite material obtained in Comparative Example 6 was subjected to electrochemical performance testing (the electrochemical testing method was the same as that in Example 1): at a current density of 1 A / g, its specific capacitance was only 351.7 F / g. After catalytically generating graphene, part of the Cu + and Cu 2+ was reduced to Cu 0 (elemental copper), which was not easily leached under weak acid conditions, resulting in a reduction in the effective specific surface area of the composite material and thus a decrease in electrochemical performance.

[0094] Comparative Example 7

[0095] This comparative example is different from Example 1 only in that the concentration of the copper sulfate solution is changed to 0.01 mol / L, and other preparation steps and conditions are the same as those in Example 1.

[0096] The composite material obtained in Comparative Example 7 was subjected to electrochemical performance testing (the electrochemical testing method was the same as that in Example 1): at a current density of 1 A / g, its specific capacitance was only 168.4 F / g. The too low ratio of copper to biochar was not conducive to the normal growth of graphene, resulting in poor electrochemical performance of the obtained composite material.

[0097] Comparative Example 8

[0098] This comparative example is different from Example 1 only in that the concentration of the copper sulfate solution is changed to 3 mol / L, and other preparation steps and conditions are the same as those in Example 1.

[0099] The electrochemical performance of the composite material obtained in Comparative Example 8 was tested (the electrochemical test method was the same as that in Example 1): at a current density of 1 A / g, its specific capacitance was only 325.1 F / g. An excessively high ratio of copper to biochar will result in a too thick and easily aggregated graphene layer, which is not conducive to the formation of the biochar-graphene composite material, leading to a decline in its electrochemical performance, and causing waste of raw materials and an increase in costs.

[0100] The above examples are only used to illustrate the technical solutions of the present invention, rather than to limit it: Although the present invention has been described in detail with reference to the foregoing examples, those of ordinary skill in the art should understand that they can still modify the technical solutions described in the foregoing examples, or perform equivalent replacements for some of the technical features; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the spirit and scope of the technical solutions of the various embodiments of the present invention.

Claims

1. A preparation method of a biochar / graphene composite material, characterized in that: After impregnating the biomass raw material with a copper salt solution, a precursor is obtained; the precursor is pyrolyzed to obtain a biochar material modified with copper oxide, and then under a reducing atmosphere and high temperature conditions, using carbon dioxide as a carbon source, graphene is in-situ generated on the biochar material modified with copper oxide to obtain a biochar / graphene / copper composite material, and the biochar / graphene / copper composite material is obtained by leaching copper treatment.

2. The preparation method of a biochar / graphene composite material according to claim 1, wherein: The mass molar ratio of the biomass raw material to the copper salt is 1-10 g: 0.01-0.1 mol.

3. The preparation method of a biochar / graphene composite material according to claim 2, characterized in that: The molar concentration of the copper salt solution is 0.1-1 mol / L.

4. The preparation method of a biochar / graphene composite material according to claim 1, 2 or 3, characterized in that: The copper salt includes at least one of copper sulfate, copper nitrate, and copper chloride.

5. The preparation method of a biochar / graphene composite material according to claim 1, characterized in that: The impregnation process is: stirring at 50-80 °C for 3-5 h.

6. The preparation method of a biochar / graphene composite material according to claim 1, characterized in that: The pyrolysis conditions are: the atmosphere is a protective atmosphere, the temperature is 700-1100 °C, and the time is 2-4 h.

7. According to the preparation method of a biochar / graphene composite material described in claim 1, wherein: The reducing atmosphere is hydrogen, and the gas flow rate is 80-100 ml / min; The flow rate of carbon dioxide is 30-50 ml / min; The high temperature conditions are: the temperature is 600-900 °C, and the time is 4-6 h.

8. The preparation method of a biochar / graphene composite material according to claim 1, characterized in that: The leaching copper treatment method is to soak with a strong acid solution.

9. A biochar / graphene composite material, characterized in that: Prepared by any one of the methods of claims 1-8.

10. Use of a biochar / graphene composite material according to claim 9, characterized in that: As a capacitor electrode material.

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