A self-supporting carbon electrode based on wood and bamboo materials, its preparation method and application

Abstract

The present invention discloses a self-supporting carbon electrode based on wood-bamboo materials, a preparation method thereof, and an application thereof in fabricating a supercapacitor electrode. The preparation method includes the steps of: (1) fully carbonizing wood-bamboo slices with permeable pores in an inert atmosphere to obtain wood-bamboo carbon slices; (2) soaking nickel foam in a solution containing cobalt acetate and nickel acetate, then taking it out and drying it, wrapping the wood-bamboo carbon slices, and extruding the nickel foam under a pressure of 5-15 kN / m<supgt;2< / supgt; to make it fully contact with all surfaces of the wood-bamboo carbon slices; (3) fixing the wood-bamboo carbon slices wrapped with nickel foam obtained in step (2) on a first conductive support as a working electrode, and electrolyzing it together with a counter electrode and a reference electrode in a molten salt electrolyte under an inert atmosphere. A voltage of -2.1 to -2.3 V is applied to the working electrode, and electrolysis is carried out for 8-12 hours to achieve pore formation and graphitization. After electrolysis, the wood-bamboo carbon slice sample is taken out from the nickel foam, washed and dried to obtain the self-supporting carbon electrode.

Description

Technical Field

[0001] The present invention relates to the technical field of electrodes, and particularly relates to a self-supporting carbon electrode based on wood and bamboo materials, a preparation method thereof, and an application thereof. Background Art

[0002] Supercapacitors, with their high power density, long cycle life, and fast charge and discharge capabilities, have shown great application potential in fields such as electric vehicles, smart grids, and portable electronic devices. Among them, the performance of the electrode directly determines the overall performance of the supercapacitor. Therefore, the development of high-performance, low-cost, and environmentally friendly electrode materials has become the research focus in this field.

[0003] Currently, carbon materials such as activated carbon, graphene, and carbon nanotubes are widely used in the preparation of supercapacitor electrodes. However, these materials are usually used in powder form, and non-active components such as binders, conductive agents, and additional current collectors need to be introduced during the electrode manufacturing process, thereby reducing the specific capacitance performance of the complete electrode.

[0004] In contrast, self-supporting carbon electrodes, due to integrating the current collector and the active material, without the need for additional conductive agents and binders, can maximize the use of all components of the electrode for electrical energy storage, and are considered to be representatives of the next-generation high-performance supercapacitor electrodes.

[0005] Existing methods for fabricating self-supporting carbon electrodes include in-situ activation of carbon cloth and graphitized fiber paper, self-assembly of graphene sheets into films, assembly of carbon nanotube arrays into films, and spinning of carbon nanotubes into fibers. Although these methods can prepare electrodes with high specific surface area and good conductivity, they often involve complex strong corrosion high-temperature chemical reactions, or are limited by material sources and costs, making it difficult to achieve large-scale production.

[0006] In recent years, biomass materials, due to their renewable nature, low cost, and rich resources, have become a new direction in the research of electrode materials. Wood chips and bamboo chips, as common biomass resources, show great potential as precursors for electrode materials due to their natural porous structure and rich carbon content. However, the preparation of self-supporting carbon electrodes based on wood and bamboo materials still faces challenges.

[0007] Although the traditional carbonization-gas activation method can increase the specific surface area of the electrode, it is difficult for the gas activator to come into full contact with the precursor in advance, and long-time high-temperature activation is required, resulting in high energy consumption, low efficiency, and possible damage to the self-supporting structure.

[0008] The carbonization-chemical activation method can prepare wood and bamboo-based porous carbon electrodes with high specific surface area in a shorter time and at a lower temperature, but the strong corrosive chemical reagents will severely etch the wood and bamboo carbon skeleton, damaging its structural integrity.

[0009] In addition, the low degree of graphitization of wood and bamboo materials after carbonization and activation limits their rate performance and cycle stability.

[0010] Therefore, developing a new method that does not require the use of highly corrosive chemical reagents, is simple to operate, and can prepare a high-graphitization, high-performance self-supporting carbon electrode has become a key issue that needs to be urgently addressed in the current supercapacitor field. Summary of the invention

[0011] In view of the above technical problems and the shortcomings in the art, the present invention provides a self-supporting carbon electrode based on wood and bamboo materials and a preparation method and application thereof. The preparation method provided by the present invention has a simple process, renewable raw materials and low cost, and is easy to achieve large-scale production.

[0012] The present invention proposes an innovative method for preparing a self-supporting carbon electrode based on wood and bamboo materials. Through the synchronous graphitization process of nickel foam encapsulation catalysis loaded with cobalt-nickel alloy particles and high-temperature molten salt electrolysis activation, it effectively overcomes the limitations of the existing technology and provides a new way for the large-scale production of high-performance supercapacitor electrodes.

[0013] [1] A method for preparing a self-supporting carbon electrode based on wood and bamboo materials, comprising the steps of:

[0014] (1) fully carbonizing a wood-bamboo sheet having transparent pores in an inert atmosphere to obtain a wood-bamboo carbon sheet;

[0015] (2) The nickel foam is immersed in a solution containing cobalt acetate and nickel acetate, then taken out and dried, wrapped with wood and bamboo carbon sheets, and subjected to a load of 5 to 15 kN / m 2 (e.g. 10kN / m 2 The nickel foam is squeezed under the pressure of the carbon fiber, so that it is in full contact with all surfaces of the wood and bamboo carbon sheet;

[0016] (3) The wood and bamboo carbon sheet wrapped with nickel foam obtained in step (2) is fixed on a first conductive support as a working electrode, and placed together with a counter electrode and a reference electrode in a molten salt electrolyte under an inert atmosphere for electrolysis, a voltage of -2.1 to -2.3 V (e.g., -2.15 V, -2.2 V, etc.) is applied to the working electrode, and electrolysis is performed for 8 to 12 hours (e.g., 10 hours, etc.) to achieve pore formation and graphitization. After the electrolysis is completed, the wood and bamboo carbon sheet sample is taken out from the nickel foam, washed, and dried to obtain a self-supporting carbon electrode.

[0017] In step (1), the method for preparing the wood-bamboo sheet having transparent pores may include:

[0018] Cut the peeled wood bamboo (e.g., along the vertical growth direction) into wood bamboo slices. After sanding them flat, soak them in an aqueous mixed solution of formic acid - hydrochloric acid - ethanol to thoroughly wash out the extracts and inorganic salts in the wood bamboo pipes. Then take them out, wash and dry to obtain the wood bamboo slices with permeable pores.

[0019] In the preparation method of the wood bamboo slices with permeable pores, the size of the cut wood bamboo slices can be: width 2 cm, length 3 cm, thickness 0.3 cm.

[0020] In the preparation method of the wood bamboo slices with permeable pores, 400 - mesh sandpaper can be used to perform the sanding under a pressure of 30 kN / m 2 of pressure.

[0021] In the preparation method of the wood bamboo slices with permeable pores, the aqueous mixed solution of formic acid - hydrochloric acid - ethanol can be obtained by mixing an aqueous formic acid solution, an aqueous hydrochloric acid solution and ethanol.

[0022] In the aqueous mixed solution of formic acid - hydrochloric acid - ethanol in the preparation method of the wood bamboo slices with permeable pores, the total concentration of formic acid, hydrochloric acid and ethanol can be 0.8 - 1.5 mol / L, such as 1 mol / L, etc. The molar ratio of formic acid to hydrochloric acid can be 0.05 - 0.2:1, and the molar ratio of ethanol to hydrochloric acid can be 0.08 - 0.12:1, such as 0.1:1, etc.

[0023] In the preparation method of the wood bamboo slices with permeable pores, deionized water and ethanol can be used for washing until the pH of the wood bamboo slices is 7.

[0024] In the preparation method of the wood bamboo slices with permeable pores, the drying can be carried out by vacuum drying, and the drying temperature can be 50 °C.

[0025] In step (1), the wood bamboo slices can include one or more of pine wood slices, moso bamboo slices, Chinese fir wood slices, etc.

[0026] In the present invention, an inert atmosphere refers to a gas atmosphere that does not participate in the reaction.

[0027] In step (1), the inert atmosphere can be a nitrogen atmosphere.

[0028] In step (1), the temperature of the carbonization can be 800 - 1000 °C (such as 900 °C, etc.), the heating rate can be 3 - 5 °C / min, and the time of the carbonization can be 1 - 2 hours.

[0029] In step (1), after carbonization, it can be cooled to 500 °C at a rate of 3 - 5 °C / min, and then naturally cooled to room temperature.

[0030] In step (1), the product obtained by carbonization is sanded flat, washed and dried to obtain wood bamboo carbon slices.

[0031] In step (1), the product obtained by carbonization can be polished using 220-mesh sandpaper.

[0032] In step (1), the product obtained by carbonization can be polished to obtain a cuboid with a width of 1 cm, a length of 2 cm, and a thickness of 0.1 cm.

[0033] In step (1), after the product obtained by carbonization is polished smoothly, it can be washed with deionized water and ethanol.

[0034] In step (1), after the product obtained by carbonization is polished smoothly and washed, the drying can be carried out by vacuum drying, and the drying temperature can be 60 °C.

[0035] In step (2), the thickness of the nickel foam can be 1 - 2 mm, the porosity can be 95% - 98%, and the pore diameter can be 0.2 - 0.5 mm, such as 0.3 mm, etc.

[0036] In step (2), in the solution containing cobalt acetate and nickel acetate, the total concentration of cobalt acetate and nickel acetate can be 5 - 10 mmol / L (such as 7 mmol / L, etc.), and the molar ratio of cobalt acetate to nickel acetate can be 1 - 3:1, such as 2:1, etc.

[0037] In step (2), the solvent in the solution containing cobalt acetate and nickel acetate can be ethanol.

[0038] In step (2), the time for the nickel foam to be immersed in the solution containing cobalt acetate and nickel acetate can be 5 - 15 minutes, such as 10 minutes, etc.

[0039] In step (3), 304 stainless steel wire can be used to fix the bamboo charcoal sheet wrapped with the nickel foam on the first conductive support as the working electrode.

[0040] In step (3), the first conductive support can be a stainless steel conductive support.

[0041] In step (3), the nickel-chromium alloy rod fixed on the second conductive support can be used as the counter electrode and the reference electrode.

[0042] In step (3), the second conductive support can be a stainless steel conductive support.

[0043] In step (3), the inert atmosphere can be an argon atmosphere.

[0044] In step (3), the temperature of the molten salt electrolyte can be 850 - 950 °C, such as 900 °C, etc.

[0045] In step (3), the molten salt electrolyte can be a mixed molten salt of sodium carbonate and potassium carbonate.

[0046] In step (3), in the molten salt electrolyte, based on the total molar amount of sodium carbonate and potassium carbonate being 100%, the molar proportion of sodium carbonate can be 55% - 65%, such as 59%, etc.

[0047] In step (3), hydrochloric acid and deionized water can be sequentially used for the washing. Hydrochloric acid is used to wash away the residual salts, and deionized water is used to wash the wood - bamboo carbon sheet sample until the pH reaches neutral.

[0048] In step (3), the drying can be carried out by vacuum drying, and the drying temperature can be 60 °C.

[0049] [2] The self - supported carbon electrode prepared by the preparation method according to [1].

[0050] The self - supported carbon electrode of the present invention has self - supporting ability, a high specific surface area (which can exceed 1000 m 2 / g) and excellent graphitization degree.

[0051] [3] The application of the self - supported carbon electrode according to [2] in fabricating a supercapacitor electrode. The self - supported carbon electrode of the present invention can be directly used as an electrode of a supercapacitor without additional current collectors, binders, and conductive agents. Further, the supercapacitor can be a zinc - ion supercapacitor or a lithium - ion supercapacitor. This self - supported carbon electrode exhibits excellent electrochemical performance in zinc - ion and lithium - ion supercapacitors and is a potential candidate for electrode materials.

[0052] The self - supported carbon electrode of the present invention uses wood - bamboo sheet materials as raw materials, is encapsulated and catalyzed by nickel foam loaded with cobalt - nickel alloy particles, and undergoes high - temperature molten salt electrolysis treatment to achieve key transformation. The carbon sheet material prepared by this process not only has self - supporting ability, but also has a high specific surface area and excellent graphitization degree. Particularly importantly, this carbon sheet can integrate the functions of current collector and active substance, and can be directly used as an electrode of a supercapacitor, thereby simplifying the electrode structure and improving the performance.

[0053] The core steps of the preparation method of the present invention are as follows: First, the wood - bamboo material is precisely cut to obtain sheet materials of the required size; then, these sheet materials are subjected to soaking and cleaning treatment. Next, carbonization treatment is carried out in an inert atmosphere environment to obtain wood - bamboo carbon sheet materials. Thereafter, using nickel foam pre - adsorbed with cobalt acetate and nickel acetate, the wood - bamboo carbon sheets are wrapped and encapsulated under a constant pressure. After encapsulation, the entire encapsulated body is used as a working electrode and placed in a high - temperature molten salt environment under an inert atmosphere for constant - voltage electrolysis, and finally a self - supported carbon electrode based on wood - bamboo materials is prepared.

[0054] The significant advantage of the preparation method of the present invention is that there is no need to use strong corrosive alkali for pore formation throughout the process, the operation process is simple, and the selected raw materials are renewable, low-cost and easy to obtain, so it has great potential for large-scale production. By using nickel foam with cobalt acetate and nickel acetate adsorbed on its surface for wrapping and encapsulation, the cobalt-nickel alloy particles formed by the pyrolysis of cobalt acetate and nickel acetate at high temperature can be effectively loaded on the nickel foam, and then catalyze the graphitization process on the surface of the wood-bamboo carbon sheet. In addition, by applying appropriate pressure for wrapping and encapsulation, not only is the close contact between the nickel foam and the surface of the wood-bamboo carbon sheet ensured, which is beneficial to electron transfer and electrolysis reaction, but also the full contact between the catalyst and the carbon substrate is promoted, improving the catalytic effect, while avoiding the damage of the self-supporting structure of the carbon sheet caused by excessive pressure.

[0055] The present invention also cleverly utilizes high-temperature molten salt for electrolysis. This step not only realizes pore formation through the direct chemical reaction between the molten salt and the carbon substrate, increasing the specific surface area and pore volume, but also creates a favorable environment for the deoxidation of the carbon material and the graphitization of carbon atom rearrangement, thus significantly improving the overall electrical conductivity of the material. The self-supporting carbon electrode prepared by the method of the present invention can be directly used as an electrode without additional current collector, binder and conductive agent. At the same time, due to its high specific surface area and highly graphitized characteristics, it exhibits excellent performance in supercapacitor applications.

[0056] The preparation method of the present invention has the following characteristics:

[0057] a) Nickel foam with cobalt acetate and nickel acetate adsorbed on its surface after air drying is used to wrap and encapsulate the wood-bamboo carbon sheet. The cleverness of this approach lies in that cobalt-nickel alloy particles will be formed after the pyrolysis of cobalt acetate and nickel acetate and loaded on the nickel foam, which is extremely beneficial for catalyzing the graphitization process on the surface of the wood-bamboo carbon sheet. Without the wrapping of nickel foam, the surface graphitization of the wood-bamboo carbon sheet will show significant non-uniformity, resulting in a substantial decline in its electrochemical performance. In addition, if cobalt acetate and nickel acetate are not adsorbed on the surface of the nickel foam, the graphitization degree and depth of the wood-bamboo carbon sheet will be limited, and its due electrochemical performance cannot be fully demonstrated.

[0058] b) The pressure for extruding the nickel foam is strictly controlled to ensure that it is within the range of 5 - 15 kN / m 2 This control measure has double significance: on the one hand, it can ensure the formation of close contact between the nickel foam and the surface of the wood-bamboo carbon sheet, which is beneficial to electron transfer and electrolysis reaction; at the same time, it can also ensure full contact between the catalyst and the carbon substrate, thus exerting the best catalytic effect. On the other hand, by avoiding applying excessive pressure, we can effectively protect the self-supporting ability of the carbon sheet and prevent it from being damaged due to excessive pressure.

[0059] c) During the electrolysis process, we also precisely controlled the voltage applied to the working electrode and the electrolysis time. Specifically, we selected a voltage range of -2.1V to -2.3V and set an electrolysis time of 8 to 12 hours. This selection was based on the following considerations: If the absolute voltage is too low or the electrolysis time is too short, the carbon sheet will not be able to complete sufficient graphitization and sufficient pore formation processes; while if the absolute voltage is too high or the electrolysis time is too long, the carbon sheet will decompose due to excessive graphitization and excessive pore formation, and thus lose its self-supporting ability. Therefore, through strict voltage and time control, we can ensure the preparation of wood-bamboo carbon sheets with excellent performance.

[0060] The core technical highlights of the present invention include the following points:

[0061] 1) The wood-bamboo carbon sheet is carefully wrapped and encapsulated with nickel foam pre-adsorbed with cobalt acetate and nickel acetate on its surface. During this process, the cobalt-nickel alloy particles formed after the pyrolysis of cobalt acetate and nickel acetate will be firmly loaded on the nickel foam, and this characteristic greatly promotes the graphitization process on the surface of the wood-bamboo carbon sheet.

[0062] 2) During the encapsulation process, we applied precisely controlled pressure, which is in a range that can ensure a tight contact between the nickel foam and the surface of the wood-bamboo carbon sheet, facilitating the efficient transfer of electrons and the smooth progress of the electrolysis reaction, while also ensuring sufficient contact between the catalyst and the carbon substrate, thereby exerting the best catalytic effect. In addition, this pressure control also cleverly avoids damaging the self-supporting ability of the carbon sheet due to excessive pressure.

[0063] 3) The present invention also adopts the high-temperature molten salt electrolysis technology. This step not only utilizes the direct chemical reaction between the high-temperature molten salt and the carbon substrate to effectively increase the specific surface area and pore volume of the material, but also creates a favorable environment for the deoxidation of the carbon material and the rearrangement and graphitization of carbon atoms, thereby significantly improving the overall conductivity of the material.

[0064] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0065] 1. In the preparation process of the present invention, the use of strongly corrosive alkali for pore formation is completely avoided, which not only simplifies the operation steps but also reduces the requirements for the operation environment. At the same time, the selected raw materials are renewable, low-cost and easy to obtain. Notably, the molten salt used in the electrolysis process can be recycled, further reducing the production cost and providing strong support for large-scale production.

[0066] 2. The present invention uniquely uses nickel foam pre-adsorbed with cobalt acetate and nickel acetate on its surface to wrap and encapsulate wood-bamboo carbon sheets. This innovative technology enables the cobalt-nickel alloy particles formed after pyrolysis of cobalt acetate and nickel acetate to be firmly loaded on the nickel foam, thereby effectively catalyzing the surface graphitization of wood-bamboo carbon sheets under molten salt electrolysis conditions. This discovery provides new ideas for research in related fields and has not been reported yet.

[0067] 3. The present invention has successfully achieved for the first time the efficient preparation of self-supporting carbon electrodes using wood-bamboo materials as raw materials by molten salt electrolysis. This breakthrough progress has opened up a new way for the efficient utilization of wood-bamboo materials.

[0068] 4. The self-supporting carbon electrode prepared by the method of the present invention can be directly used as an electrode without additional current collectors, binders, and conductive agents, greatly simplifying the electrode preparation process. At the same time, the electrode has a high specific surface area and degree of graphitization, enabling it to exhibit excellent application performance in supercapacitors and providing new possibilities for improving the performance of supercapacitors. Brief Description of the Drawings

[0069] Figure 1 Physical optical photograph of the self-supporting carbon electrode prepared in Example 1.

[0070] Figure 2 、 Figure 3 Scanning electron microscope photographs of the self-supporting carbon electrode prepared in Example 1 at different angles.

[0071] Figure 4 X-ray diffraction (XRD) comparison chart of the self-supporting carbon electrode (after electrolysis) and the wood carbon precursor (before electrolysis) prepared in Example 1.

[0072] Figure 5 Nitrogen adsorption-desorption curves, specific surface area, and pore volume comparison chart of the self-supporting carbon electrode (after electrolysis) and the wood carbon precursor (before electrolysis) prepared in Example 1. Detailed Description of the Invention

[0073] The present invention will be further described below in conjunction with the accompanying drawings and specific embodiments. It should be understood that these embodiments are only used to illustrate the present invention and not to limit the scope of the present invention.

[0074] Example 1

[0075] (I) Preparation of self-supporting carbon electrode

[0076] Step 1: Preparation of pine wood slices

[0077] Use a precision panel saw to precisely cut the peeled pine wood along the vertical growth direction into pine wood slices with dimensions of 2 cm × 3 cm × 0.3 cm.

[0078] Under a pressure of 30 kN / m 2 , use 400-mesh sandpaper to carefully polish both surfaces of the pine wood chips to remove surface powder and ensure that the surfaces of the pine wood chips are flat and clean.

[0079] Step 2: Treatment and cleaning of pine wood chips

[0080] Soak the flat pine wood chips in an aqueous solution of formic acid - hydrochloric acid - ethanol with a total concentration of 1 mol / L (molar ratio 0.1:1:0.1) for 10 hours at room temperature to thoroughly clean the extracts and inorganic salts in the pine wood channels.

[0081] Subsequently, soak the pine wood chips in deionized water for 2 hours at room temperature and wash repeatedly until the pH value is close to 7.0.

[0082] Rinse once more with 95% ethanol to ensure thorough cleaning.

[0083] Place the cleaned pine wood chips in a vacuum oven at 50 °C and dry for 24 hours to obtain pine wood chips with permeable pores.

[0084] Step 3: Carbonization treatment of pine wood chips

[0085] Put the pine wood chips with permeable pores into a tubular furnace. Under nitrogen protection, slowly heat to 1000 °C at a heating rate of 3 °C / min and hold for 1 hour to fully carbonize the pine wood chips.

[0086] After carbonization, cool to 500 °C at a rate of 5 °C / min, and then cool naturally to room temperature.

[0087] Take out the pine wood carbon chips and use 220-mesh sandpaper to polish the collapsed or protruding parts on the surface until they are finally polished into a cuboid with dimensions of 1 cm × 2 cm × 0.1 cm.

[0088] After alternately rinsing clean with deionized water and 95% ethanol, dry in a vacuum oven at 60 °C for 12 hours to obtain pine wood carbon chips with uniform specifications, certain electrical conductivity, flat surfaces, and permeable pores.

[0089] Step 4: Treatment of nickel foam and molten salt electrolysis of pine wood carbon chips

[0090] Take clean nickel foam (1 mm thick, purity 99.9%, porosity 95%, pore diameter 0.2 mm), and soak it in an ethanol mixed solution of cobalt acetate and nickel acetate with a total concentration of 5 mmol / L (molar ratio 1.0) for 10 minutes.

[0091] Take out the nickel foam, lay it flat in a glass container, and let it dry naturally at room temperature.

[0092] Wrap the cuboid pine charcoal sheet with permeable pores using air-dried nickel foam, and squeeze the nickel foam under a pressure of 10 kN / m 2 to ensure full contact with all surfaces of the pine charcoal sheet.

[0093] Use 304 stainless steel wire to fix the nickel foam-wrapped pine charcoal sheet on a stainless steel conductive support as the working electrode.

[0094] Place this working electrode together with a nickel-chromium alloy rod (used as the counter electrode and reference electrode) fixed on a stainless steel conductive support in an 850 °C molten salt electrolyte (Na 2 CO 3 / K 2 CO 3 with a molar ratio of 59:41) under an argon atmosphere for electrolysis.

[0095] Apply a voltage of -2.15 V to the working electrode and electrolyze for 10 hours.

[0096] After electrolysis, cool to room temperature, take out the sample from the nickel foam, and soak it in 1 M hydrochloric acid to remove residual carbonates.

[0097] Rinse the sample with deionized water until the pH reaches neutral, and dry it in vacuum at 60 °C for 12 hours to obtain a self-supporting carbon electrode.

[0098] Figure 1 Presents the actual optical image of the self-supporting carbon electrode prepared in this example, clearly showing its excellent self-supporting characteristics. Figure 2 And Figure 3 respectively show the scanning electron microscope images of the self-supporting carbon electrode from different observation angles, revealing the rich channel structure inside the electrode, which makes it very suitable for application in the field of supercapacitors. Figure 4 Further shows that after the molten salt electrolysis reaction, the graphitization degree of the self-supporting electrode has been significantly improved compared with that before electrolysis. Figure 5 Shows that after the molten salt electrolysis reaction, the specific surface area and pore volume of the self-supporting electrode have been greatly improved compared with those before electrolysis.

[0099] (II) Application performance test of the self-supporting carbon electrode

[0100] This time, test its application in a zinc-ion supercapacitor. Use the self-supporting carbon electrode as the working electrode and the zinc foil electrode as the counter electrode and reference electrode. Through a two-electrode system, in a 2 M ZnSO 4 electrolyte at room temperature, use a battery charge and discharge device (CT2001A, Wuhan Blue Electronic Co., Ltd.) to conduct a constant current charge and discharge test on the prepared electrode (charge and discharge voltage range 0.2 - 1.8 V).

[0101] According to the formula C = I×△t / M, the specific capacity C corresponding to the prepared sample at different charge-discharge current densities can be calculated based on the charge-discharge curve. Where △t (h) represents the discharge time, I (mA) represents the discharge current, and M (g) represents the mass of the entire self-supporting electrode material.

[0102] The results show that at a current density of 2.0 mA / cm 2 the mass specific capacity of the prepared self-supporting carbon electrode can reach 67 mAh / g, indicating that the self-supporting carbon electrode prepared by the method of the present invention has excellent electrochemical performance and is a potential candidate for zinc-ion supercapacitor electrodes.

[0103] Example 2

[0104] (I) Preparation of self-supporting carbon electrode

[0105] Step 1: Preparation of bamboo slices

[0106] Use a precision panel saw to precisely cut the peeled bamboo culm wall into bamboo slices with dimensions of 2 cm × 3 cm × 0.3 cm.

[0107] Under a pressure of 30 kN / m 2 use 400-mesh sandpaper to carefully polish the two surfaces of the bamboo slices to remove surface powder and ensure that the surfaces of the bamboo slices are flat and clean.

[0108] Step 2: Treatment and cleaning of bamboo slices

[0109] Soak the flat bamboo slices in an aqueous solution of formic acid - hydrochloric acid - ethanol with a total concentration of 1 mol / L (molar ratio of 0.2:1:0.1) and keep them at room temperature for 10 hours to thoroughly clean the extracts and inorganic salts in the bamboo pipes.

[0110] Subsequently, soak the bamboo slices in deionized water at room temperature for 2 hours and wash them repeatedly until the pH value is close to 7.0.

[0111] Rinse once with 95% ethanol to ensure thorough cleaning.

[0112] Place the cleaned bamboo slices in a vacuum oven at 50 °C and dry them for 24 hours to obtain bamboo slices with permeable pores.

[0113] Step 3: Carbonization treatment of bamboo slices

[0114] Put the bamboo slices with permeable pores into a tubular furnace, and under nitrogen protection, slowly heat them to 900 °C at a heating rate of 5 °C / min and keep them at this temperature for 1 hour to fully carbonize the bamboo slices.

[0115] After carbonization, the temperature was decreased to 500 °C at a rate of 5 °C / min, and then it was naturally cooled to room temperature.

[0116] The bamboo charcoal slices were taken out, and the collapsed or protruding parts on the surface were polished flat with 220-mesh sandpaper, and finally polished into a cuboid with dimensions of 1 cm × 2 cm × 0.1 cm.

[0117] After being alternately rinsed clean with deionized water and 95% ethanol, it was dried in a vacuum oven at 60 °C for 12 hours to obtain bamboo charcoal slices with uniform specifications, certain conductivity, a flat surface, and permeable pores.

[0118] Step 4: Treatment of nickel foam and molten salt electrolysis of bamboo charcoal slices

[0119] Take clean nickel foam (2 mm thick, purity 99.9%, porosity 98%, pore diameter 0.5 mm), and immerse it in an ethanol mixed solution of cobalt acetate and nickel acetate (molar ratio 2.0) with a total concentration of 7 mmol / L for 15 minutes.

[0120] The nickel foam was taken out, laid flat in a glass container, and naturally dried at room temperature.

[0121] Use the dried nickel foam to wrap the cuboid bamboo charcoal slices with permeable pores, and squeeze the nickel foam under a pressure of 5 kN / m 2 to ensure full contact with all surfaces of the bamboo charcoal slices.

[0122] Use 304 stainless steel wire to fix the bamboo charcoal slices wrapped with nickel foam on a stainless steel conductive support as the working electrode.

[0123] Place this working electrode together with a nickel-chromium alloy rod (serving as the counter electrode and reference electrode) fixed on a stainless steel conductive support in a 900 °C molten salt electrolyte (Na 2 CO 3 / K 2 CO 3 molar ratio 59:41) under an argon atmosphere for electrolysis.

[0124] Apply a voltage of -2.2 V to the working electrode and electrolyze for 8 hours.

[0125] After electrolysis, it was cooled to room temperature, the sample was taken out from the nickel foam, and immersed in 1 M hydrochloric acid to remove the residual carbonate.

[0126] The sample was rinsed with deionized water until the pH reached neutral, and vacuum dried at 60 °C for 12 hours to obtain a self-supporting carbon material.

[0127] (II) Application performance test of the self-supporting carbon electrode

[0128] This test focuses on its application in lithium-ion supercapacitors. A self-supported carbon electrode is used as the working electrode, and a commercial graphite electrode is used as the counter electrode and reference electrode. Through a two-electrode system, at room temperature and in a 1M LiPF 6 electrolyte, a battery charge-discharge device (CT2001A, Wuhan Blue Electronic Co., Ltd.) is used to perform a constant current charge-discharge test on the prepared electrode (the charge-discharge voltage range is 1.0 - 4.0V).

[0129] According to the formula C = I×△t / M, the specific capacitance C corresponding to the prepared sample at different charge-discharge current densities can be calculated based on the charge-discharge curve. Here, △t (h) represents the discharge time, I (mA) represents the discharge current, and M (g) represents the mass of the entire self-supported electrode material.

[0130] The results show that at a current density of 100 mA / g, the mass specific capacitance of the prepared self-supported carbon electrode can reach 35 mAh / g, indicating that the self-supported carbon electrode prepared by the method of the present invention has excellent electrochemical performance and is a potential candidate for lithium-ion supercapacitor electrodes.

[0131] Example 3

[0132] (I) Preparation of self-supported carbon electrode

[0133] Step 1: Preparation of Chinese fir slices

[0134] The peeled Chinese fir is precisely cut into Chinese fir slices with dimensions of 2 cm × 3 cm × 0.3 cm along the vertical growth direction using a precision panel saw.

[0135] Under a pressure of 30 kN / m 2 , the two surfaces of the Chinese fir slices are carefully polished with 400-mesh sandpaper to remove the surface powder and ensure that the surfaces of the Chinese fir slices are flat and clean.

[0136] Step 2: Treatment and cleaning of Chinese fir slices

[0137] The flat Chinese fir slices are immersed in a mixed aqueous solution of formic acid - hydrochloric acid - ethanol with a total concentration of 1.5 mol / L (molar ratio 0.05:1:0.1) and kept at room temperature for 10 hours to thoroughly clean the extracts and inorganic salts in the Chinese fir ducts.

[0138] Subsequently, the Chinese fir slices are soaked in deionized water at room temperature for 2 hours and repeatedly washed until the pH value is close to 7.0.

[0139] Then, they are rinsed once with 95% ethanol to ensure thorough cleaning.

[0140] The cleaned Chinese fir slices are placed in a vacuum oven at 50°C and dried for 24 hours to obtain Chinese fir slices with permeable pores.

[0141] Step 3: Carbonization treatment of Chinese fir chips

[0142] Put the Chinese fir chips with permeable pores into a tube furnace. Under nitrogen protection, slowly heat them to 800 °C at a heating rate of 5 °C / min and hold for 2 hours to fully carbonize the Chinese fir chips.

[0143] After carbonization, cool down to 500 °C at a rate of 5 °C / min, and then cool down to room temperature naturally.

[0144] Take out the Chinese fir carbon chips and polish the collapsed or protruding parts on the surface with 220-mesh sandpaper, and finally polish them into a cuboid with dimensions of 1 cm × 2 cm × 0.1 cm.

[0145] After alternately rinsing with deionized water and 95% ethanol and drying in a vacuum oven at 60 °C for 12 hours, Chinese fir carbon chips with uniform specifications, certain conductivity, flat surface and permeable pores are obtained.

[0146] Step 4: Treatment of nickel foam and molten salt electrolysis of Chinese fir carbon chips

[0147] Take clean nickel foam (1 mm thick, purity 99.9%, porosity 98%, pore diameter 0.3 mm), and immerse it in an ethanol mixed solution of cobalt acetate and nickel acetate with a total concentration of 10 mmol / L (molar ratio 3.0) for 10 minutes.

[0148] Take out the nickel foam, lay it flat in a glass container, and let it dry naturally at room temperature.

[0149] Use the dried nickel foam to wrap the cuboid Chinese fir carbon chips with permeable pores, and squeeze the nickel foam under a pressure of 15 kN / m 2 to ensure full contact with all surfaces of the Chinese fir carbon chips.

[0150] Use 304 stainless steel wire to fix the Chinese fir carbon chips wrapped with nickel foam on a stainless steel conductive bracket as the working electrode.

[0151] Place this working electrode together with a nickel-chromium alloy rod (used as the counter electrode and reference electrode) fixed on a stainless steel conductive bracket in a 950 °C molten salt electrolyte (Na 2 CO 3 / K 2 CO 3 molar ratio 59:41) under an argon atmosphere for electrolysis.

[0152] Apply a voltage of -2.1 V to the working electrode and electrolyze for 12 hours.

[0153] After electrolysis, cool down to room temperature, take out the sample from the nickel foam, and soak it in 1 M hydrochloric acid to remove the residual carbonates.

[0154] The sample was rinsed with deionized water until the pH reached neutrality and then vacuum-dried at 60 °C for 12 hours to obtain a self-supporting carbon material.

[0155] (II) Application performance test of the self-supporting carbon electrode

[0156] In this test, its application in a zinc-ion supercapacitor was investigated. The self-supporting carbon electrode was used as the working electrode, and the zinc foil electrode was used as the counter electrode and reference electrode. Through a two-electrode system, at room temperature and in a 2 M ZnSO 4 electrolyte solution, a constant current charge-discharge test (charge-discharge voltage range 0.2 - 1.8 V) was performed on the prepared electrode using a battery charge-discharge device (CT2001A, Wuhan Blue Electronic Co., Ltd.).

[0157] According to the formula C = I×△t / M, the specific capacitance C corresponding to the prepared sample at different charge-discharge current densities can be calculated based on the charge-discharge curve. Here, △t (h) represents the discharge time, I (mA) represents the discharge current, and M (g) represents the mass of the entire self-supporting electrode material.

[0158] The results showed that at a current density of 2.0 mA / cm 2 the mass specific capacitance of the prepared self-supporting carbon electrode could reach 63 mAh / g, indicating that the self-supporting carbon electrode prepared by the method of the present invention has excellent electrochemical performance and is a potential candidate for the zinc-ion supercapacitor electrode.

[0159] Comparative example

[0160] The total concentration of the cobalt acetate and nickel acetate (molar ratio 1.0) ethanol mixed solution in step four of Example 1 was adjusted from 5 mmol / L to 0 mmol / L, and a self-supporting carbon material could be fabricated using a similar process. The application performance test method of Example 1 was used to test the application of the fabricated carbon material in a zinc-ion supercapacitor. The results showed that at a current density of 2.0 mA / cm 2 the mass specific capacitance of the prepared self-supporting carbon electrode was only 45 mAh / g, and this performance was significantly lower than the specific capacitance of 67 mAh / g of the self-supporting carbon electrode fabricated when the total concentration of the cobalt acetate and nickel acetate (molar ratio 1.0) ethanol mixed solution was 5 mmol / L. This shows that the present invention's unique use of nickel foam pre-adsorbed with cobalt acetate and nickel acetate to wrap and encapsulate bamboo charcoal flakes for molten salt electrolysis helps to improve the electrochemical performance of the fabricated self-supporting carbon electrode.

[0161] In addition, it should be understood that after reading the above description of the present invention, those skilled in the art can make various changes or modifications to the present invention, and these equivalent forms also fall within the scope defined by the appended claims of this application.

Claims

1. A method for preparing a self-supporting carbon electrode based on wood and bamboo materials, characterized in that: Includes steps: (1) fully carbonizing a wood-bamboo sheet having transparent pores in an inert atmosphere to obtain a wood-bamboo carbon sheet; (2) The nickel foam is immersed in a solution containing cobalt acetate and nickel acetate, then taken out and dried, wrapped with wood and bamboo carbon sheets, and subjected to a load of 5 to 15 kN / m 2 The nickel foam is squeezed under the pressure to make it fully contact with all surfaces of the wood and bamboo carbon sheet; (3) The wood and bamboo carbon sheet wrapped with nickel foam obtained in step (2) is fixed on a first conductive support as a working electrode, and placed together with a counter electrode and a reference electrode in a molten salt electrolyte under an inert atmosphere for electrolysis, a voltage of -2.1 to -2.3 V is applied to the working electrode, and the electrolysis is performed for 8 to 12 hours to achieve pore formation and graphitization. After the electrolysis is completed, the wood and bamboo carbon sheet sample is taken out from the nickel foam, washed, and dried to obtain a self-supporting carbon electrode.

2. The preparation method according to claim 1, characterized in that: In step (1), the method for preparing the wood-bamboo slices having transparent pores comprises: The peeled bamboo is cut into bamboo slices, polished and then soaked in a mixed aqueous solution of formic acid-hydrochloric acid-ethanol to thoroughly clean the extract and inorganic salt in the bamboo pipes, then taken out, washed and dried to obtain the bamboo slices with transparent pores.

3. The preparation method according to claim 2, characterized in that: In the method for preparing the wood-bamboo sheet with transparent pores: The size of the cut wood and bamboo pieces is: 2 cm wide, 3 cm long, and 0.3 cm thick; Use 400 grit sandpaper at 30 kN / m 2 The grinding is performed under a pressure of The mixed aqueous solution of formic acid-hydrochloric acid-ethanol is obtained by mixing a formic acid aqueous solution, a hydrochloric acid aqueous solution and ethanol; In the mixed aqueous solution of formic acid-hydrochloric acid-ethanol, the total concentration of formic acid, hydrochloric acid and ethanol is 0.8-1.5 mol / L, the molar ratio of formic acid to hydrochloric acid is 0.05-0.2:1, and the molar ratio of ethanol to hydrochloric acid is 0.08-0.12:1; Wash with deionized water and ethanol until the pH of the wood and bamboo chips is 7; The drying is performed by vacuum drying at a drying temperature of 50°C.

4. The preparation method according to claim 1, characterized in that: In step (1): The wood and bamboo chips include one or more of pine chips, bamboo chips, and fir chips; The inert atmosphere is a nitrogen atmosphere; The carbonization temperature is 800-1000°C, the heating rate is 3-5°C / min, and the carbonization time is 1-2 hours; After carbonization, the temperature was lowered to 500°C at a rate of 3-5°C / min, and then naturally cooled to room temperature; The carbonized product is polished, cleaned and dried to obtain a wood-bamboo carbon sheet; Use 220-grit sandpaper to grind to obtain a cuboid with a width of 1 cm, a length of 2 cm, and a thickness of 0.1 cm; Wash with deionized water and ethanol; The drying is performed by vacuum drying at a drying temperature of 60°C.

5. The preparation method according to claim 1, characterized in that: In step (2): The thickness of the nickel foam is 1-2 mm, the porosity is 95%-98%, and the pore size is 0.2-0.5 mm; In the solution containing cobalt acetate and nickel acetate, the total concentration of cobalt acetate and nickel acetate is 5-10 mmol / L, and the molar ratio of cobalt acetate to nickel acetate is 1-3:1; The solvent in the solution containing cobalt acetate and nickel acetate is ethanol; The foamed nickel is immersed in the solution containing cobalt acetate and nickel acetate for 5 to 15 minutes.

6. The preparation method according to claim 1, characterized in that: In step (3): The wood-bamboo carbon sheet wrapped with nickel foam is fixed on a first conductive support using 304 stainless steel wire as a working electrode; The first conductive bracket is a stainless steel conductive bracket; A nickel-chromium alloy rod fixed on a second conductive support is used as a counter electrode and a reference electrode; The second conductive bracket is a stainless steel conductive bracket; The inert atmosphere is an argon atmosphere; The temperature of the molten salt electrolyte is 850-950°C; The molten salt electrolyte is a mixed molten salt of sodium carbonate and potassium carbonate; In the molten salt electrolyte, the molar proportion of sodium carbonate is 55% to 65%, based on the total molar number of sodium carbonate and potassium carbonate being 100%; The washing is performed sequentially using hydrochloric acid and deionized water, wherein the hydrochloric acid is used to wash away the residual salt, and the deionized water is used to wash the wood and bamboo carbon sheet sample until the pH reaches neutral; The drying is performed by vacuum drying at a drying temperature of 60°C.

7. A self-supporting carbon electrode prepared according to the preparation method according to any one of claims 1 to 6.

8. Use of the self-supporting carbon electrode according to claim 7 in preparing a supercapacitor electrode.

9. The use according to claim 8, characterized in that: The supercapacitor is a zinc ion supercapacitor or a lithium ion supercapacitor.

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