A method for growing bcn nanotubes inside wood-derived carbon pores and applications

Abstract

The application discloses a method for growing BCN nanotubes inside wood-derived carbon pores, and belongs to the technical field of supercapacitor materials. The steps of the application are as follows: wood chips are ultrasonically cleaned and dried; the wood chips are subjected to low-temperature pre-oxidation and high-temperature carbonization, and then are polished; the carbonized wood is immersed in a mixed solution of boric acid, polyethylene glycol and urea, so that the mixed solution is impregnated into the pores of the carbonized wood to obtain sample A; sample A is high-temperature calcined to obtain BCN nanotube / wood-derived carbon material; and the BCN nanotube / wood-derived hierarchical porous carbon is obtained by physically activating the BCN nanotube / wood-derived carbon material. The material prepared by the method of the application does not need to add additional binders, conductive agents and catalysts. The unique structure of the metal-free BCN nanotube and the existence of B and N make the electrode material have good conductivity, high specific capacitance and excellent cycle stability, which is beneficial to the application in supercapacitor electrode materials.

Description

Technical Field

[0001] This invention belongs to the field of supercapacitor electrode material technology, specifically relating to a method and application of growing BCN nanotubes inside wood-derived carbon channels. Background Technology

[0002] Energy storage, a crucial link in energy development, has always been considered a key challenge. With the current boom in renewable energy, efficient energy storage technologies are becoming increasingly important. The development of energy storage technologies directly impacts energy utilization efficiency, the stable operation of power systems, and the advancement of sustainable development. Among various energy storage technologies, supercapacitors have attracted considerable attention due to their high output power, long lifespan, and excellent energy storage performance. Electrode materials, as the core component of supercapacitors, directly determine key performance characteristics such as stability, energy density, and cycle life. However, current electrode materials still have some shortcomings, such as low specific surface area, poor conductivity, and slow ion transport. Therefore, finding efficient and sustainable electrode materials is of great significance for promoting the development of energy storage technologies.

[0003] Wood, as a renewable resource, possesses a naturally hierarchical porous structure, providing a large specific surface area that is beneficial for charge storage and transport. Furthermore, carbonized wood can serve as a self-supporting electrode, directly loading active materials without the need for additional conductive agents and binders. However, carbonized wood also has some drawbacks; structural changes may occur during prolonged charge-discharge cycles, leading to a decline in electrode performance.

[0004] Nanotubes, as important nanomaterials, possess many unique advantages, such as excellent electrical conductivity, high specific surface area, and good electrochemical stability. Among them, BCN nanotubes, as a novel nanomaterial, have attracted widespread attention. The presence of boron and nitrogen atoms accelerates the free transport of electrons, giving BCN nanotubes excellent electron transport performance. This high-speed electron transport can improve the conductivity of electrode materials, thereby enhancing their rate performance. Due to the excellent conductivity and high specific surface area of ​​BCN nanotubes, loading them into the pores of wood-derived carbon can increase the specific surface area and active sites of electrode materials. Furthermore, the good electron and ion transport properties of BCN nanotubes can improve the electrochemical performance of supercapacitors.

[0005] Therefore, providing a method for growing BCN nanotubes inside wood-derived carbon channels is a technical problem that urgently needs to be solved by those skilled in the art. Summary of the Invention

[0006] In view of this, the present invention provides a method for growing BCN nanotubes within the pores of wood-derived carbon. The present invention prepares BCN nanotubes / wood-derived hierarchical porous carbon with excellent electrochemical performance through a simple calcination method. The product prepared by the present invention can effectively alleviate the structural damage caused by prolonged charge-discharge cycles, thereby improving cycle stability.

[0007] To achieve the above objectives, the present invention adopts the following technical solution:

[0008] A method for growing BCN nanotubes inside wood-derived carbon channels includes the following steps:

[0009] (1) The wood chips were ultrasonically cleaned and dried after being treated with a mixture of anhydrous ethanol and water to complete the pretreatment of the wood chips.

[0010] (2) The pretreated wood chips are subjected to low-temperature pre-oxidation and then high-temperature carbonization to obtain carbonized wood;

[0011] (3) Sand the carbonized wood to a thickness of 0.5-3mm;

[0012] (4) The sanded carbonized wood was immersed in a mixed solution of boric acid, polyethylene glycol and urea. The mixed solution was then impregnated into the pores of the carbonized wood by vacuum pressure. The surface of the carbonized wood was then rinsed with water and dried to obtain sample A.

[0013] (5) Sample A was calcined at high temperature under protective gas to obtain BCN nanotubes / wood-derived carbon materials.

[0014] (6) Physically activate BCN nanotube / wood-derived carbon materials to obtain BCN nanotube / wood-derived hierarchical porous carbon.

[0015] Furthermore, the wood chips mentioned in step (1) include, but are not limited to, wood chips made of poplar, linden, pine, fir, etc.

[0016] Furthermore, in step (1), the volume ratio of anhydrous ethanol to water in the mixture of anhydrous ethanol and water is 1:1.

[0017] Furthermore, the specific parameters of the ultrasound in step (1) are: ultrasound power of 300-400W, frequency of 40KHz, and time of 2-4h.

[0018] Furthermore, the drying in step (1) is freeze drying, and the specific drying method is as follows: freeze drying for 24 hours at a vacuum degree of 10-30 Pa and a condensation temperature of ≤50℃.

[0019] Furthermore, the low-temperature pre-oxidation method described in step (2) is to perform low-temperature pre-oxidation at 150–250°C for 4–8 hours;

[0020] The high-temperature carbonization is carried out under a nitrogen atmosphere at 800–1000°C for 4–8 hours, with a gas flow rate of 40–80 cm³. 3 min-1.

[0021] Furthermore, in step (3), sanding is performed using sandpaper with a grit of 180 to 2000.

[0022] Furthermore, in step (4), the mass ratio of urea, polyethylene glycol and boric acid in the mixed solution of urea, polyethylene glycol and boric acid is 3-18:0.3-1.8:0.15, and the above raw materials are added to 10 mL of water in sequence; wherein, boric acid, urea and polyethylene glycol are boron source, nitrogen source and carbon source, respectively.

[0023] Furthermore, the molecular weight of the polyethylene glycol is 1000 to 8000.

[0024] The beneficial effects of adopting the above-mentioned further scheme are that: the present invention dops nitrogen (N) and boron (B) heteroatoms into the carbon framework, which can further improve the stability and energy density of carbon materials.

[0025] Furthermore, the vacuum pressurization method described in step (4) is as follows: a rotary vane vacuum pump is used to pressurize multiple times, each time to -0.1 MPa, for 30 minutes, and after holding the pressure for 20 minutes, it is maintained at atmospheric pressure for 10 minutes. This process is repeated three times and then maintained in a vacuum state for 4 to 12 hours.

[0026] Furthermore, the protective gas mentioned in step (5) is nitrogen, and the high-temperature calcination method is calcination at 2℃ for 1 minute. -1 The temperature is increased to 800–1000℃ at a heating rate, and then held for 4–8 hours.

[0027] Furthermore, the physical activation temperature in step (6) is 700–900°C, and the treatment time is 8–12 h.

[0028] The beneficial effects of this invention are as follows:

[0029] This invention preserves the natural porous carbon skeleton structure of wood after carbonization. A mixed solution of BCN precursors is filled into the pores of carbonized wood using vacuum pressurization technology. Then, BCN nanotubes / wood-derived carbon materials are prepared by high-temperature calcination under the protection of inert gas. Finally, the materials are physically activated to obtain BCN nanotubes / wood-derived hierarchical porous carbon materials.

[0030] In the present invention, the filling of nanotubes can not only increase the specific surface area of ​​wood-derived carbon, but also provide more active sites for chemical reactions and charge storage. Furthermore, doping the carbon framework with nitrogen (N) and boron (B) heteroatoms can improve the stability and energy density of carbon materials.

[0031] The method of the present invention is simple to operate and does not require conductive agents or binders.

[0032] This invention also claims protection for the application of the prepared BCN nanotubes / wood-derived hierarchical porous carbon in supercapacitors, wherein the application is at a current density of 5 mA cm⁻¹. -2 At that time, the areal specific capacities of BCN nanotube / wood-derived carbon and BCN nanotube / wood-derived hierarchical porous carbon reached as high as 3427 mF cm⁻¹. -2 and 5000mF cm -2 Even if the current density increases to 200 mA cm -2 At that time, its specific capacitance per unit area can still reach 2200 mF cm⁻¹. -2 and 3629mF cm -2 . Attached Figure Description

[0033] Figure 1 SEM image of carbonized wood prepared according to Comparative Example 1 of the present invention;

[0034] Figure 2 SEM image of BCN nanotubes / wood-derived hierarchical porous carbon prepared according to Example 1 of the present invention;

[0035] Figure 3 XPS image of BCN nanotubes / wood-derived hierarchical porous carbon prepared according to Example 1 of the present invention;

[0036] Figure 4 BCN nanotube / wood-derived hierarchical porous carbon, carbonized wood, and BCN nanotube / wood-derived carbon were prepared for Examples 1 and Comparative Examples 1 and 2 of the present invention at 100 mV s. -1 Cyclic voltammetry curves at scan rate;

[0037] Figure 5 For Examples 1 and Comparative Examples 1 and 2 of the present invention, BCN nanotube / wood-derived hierarchical porous carbon, carbonized wood, and BCN nanotube / wood-derived carbon were prepared at 50 mA cm⁻¹. -2 Constant current charge-discharge curves at current density;

[0038] Figure 6 Ratio curves of BCN nanotube / wood-derived hierarchical porous carbon, carbonized wood, and BCN nanotube / wood-derived carbon prepared for Examples 1 and Comparative Examples 1 and 2 of the present invention. Detailed Implementation

[0039] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0040] Example 1

[0041] A method for growing BCN nanotubes inside wood-derived carbon channels:

[0042] (1) Cut natural poplar wood into thin slices of 30mm×30mm×2mm. Clean the wood slices with a mixture of anhydrous ethanol and water (volume ratio of 1:1) using ultrasonic cleaning at a power of 360W, a frequency of 40KHz, and a time of 3h. Then place them in a refrigerator for 12h and freeze-dry them at 30pa for 24h to obtain pretreated poplar wood slices, thus completing the pretreatment of the wood slices.

[0043] (2) The pretreated wood chips were pre-oxidized at 250℃ for 6 hours, and then oxidized at 5℃ for 5 minutes in a nitrogen atmosphere. -1 The temperature was increased to 1000℃ at a heating rate and then held for 6 hours to obtain carbonized wood.

[0044] (3) Sand the carbonized wood to 1mm with 180-grit sandpaper;

[0045] (4) Add 0.15g boric acid, 5g urea and 0.5g polyethylene glycol (molecular weight 2000) to 10mL of water to form a mixed solution. Immerse the polished carbonized wood in the mixed solution and impregnate the mixed solution into the pores of the carbonized wood by vacuum pressurization. The vacuum pressurization method is to use a rotary vane vacuum pump to pressurize multiple times, pressurize to -0.1Mpa each time, pressurize for 30min, hold pressure for 20min, and then maintain atmospheric pressure for 10min. Repeat this three times and then keep it under vacuum for 8h. Then rinse the surface of the carbonized wood with water and freeze dry to obtain sample A.

[0046] (5) Sample A was placed under a nitrogen atmosphere at 2℃ for 2 min. -1 The temperature was increased to 950℃ at a heating rate and held for 6 hours to obtain BCN nanotubes / wood-derived carbon materials.

[0047] (6) The BCN nanotube / wood-derived carbon material was physically activated in a CO2 atmosphere at an activation temperature of 800℃ for 10h to obtain BCN nanotube / wood-derived hierarchical porous carbon.

[0048] Example 2

[0049] The difference between this embodiment and embodiment 1 is that step (4) is: the carbonized wood is laid flat in the porcelain boat, the porcelain boat is placed on a constant temperature heating platform at 100°C, the mixed solution is added drop by drop to the carbonized wood, and then placed in an oven at 120°C for 12 hours. Other operations are the same as in embodiment 1.

[0050] Example 3

[0051] The difference between this embodiment and embodiment 1 is that step (4) is: immersing the carbonized wood in a transparent mixed solution, and then using a method of applying pressure and heating simultaneously in a vacuum oven (pressure is -0.6 MPa, temperature is 80°C) to impregnate the transparent mixed solution into the pores of the carbonized wood; the rest is the same as in embodiment 1.

[0052] Example 4

[0053] The difference between this embodiment and embodiment 1 is that step (1) is: removing most of the lignin from natural poplar wood chips under the action of a mixed solution of sodium chlorite and glacial acetic acid, washing with water, and freeze-drying to obtain pretreated poplar wood chips. The rest is the same as in embodiment 1.

[0054] Comparative Example 1

[0055] Carbonized wood was prepared using steps (1) and (2) of Example 1. A scanning electron microscope image of the carbonized wood obtained in the comparative example is shown below. Figure 1 As shown.

[0056] Comparative Example 2

[0057] BCN nanotubes / wood-derived carbon materials were prepared using the method described in Example 1.

[0058] Scanning electron microscope image of the BCN nanotube / wood-derived hierarchical porous carbon material obtained in Example 1 is shown below. Figure 2 As shown;

[0059] XPS image of the BCN nanotube / wood-derived hierarchical porous carbon material obtained in Example 1 is shown below. Figure 3 As shown;

[0060] The products of Example 1, Comparative Example 1, and Comparative Example 2 were subjected to electrochemical performance testing in a three-electrode alkaline system, using the prepared material as the working electrode, a platinum sheet as the counter electrode, and mercury / mercury oxide as the reference electrode, at a concentration of 6 mol / L. -1 Using potassium hydroxide as the electrolyte, tests were conducted within a voltage range of -1 to 0V. Cyclic voltammetry curves at different scan rates, constant current charge-discharge curves at different current densities, and rate curves are shown below. Figure 4 , 5 As shown in Figure 6.

[0061] from Figure 6As can be seen from this, at a current density of 5 mA cm⁻¹ -2 At that time, the areal specific capacities of carbonized wood, BCN nanotube / wood-derived carbon materials, and BCN nanotube / wood-derived hierarchical porous carbon materials were 2410 mF cm⁻¹. -2 3427.6mF cm -2 and 5000.3mF cm -2 Even at 200mA cm -2 At high current densities, the areal specific capacitance is 670 mF / cm². -2 2200mF cm -2 and 3629mF cm -2 The capacity retention rates were 27.8%, 64.2%, and 72.5%, respectively, indicating that the BCN nanotube / wood-derived hierarchical porous carbon material has excellent rate performance.

[0062] Although embodiments of the present invention have been shown and described above, it is understood that the above embodiments are exemplary and should not be construed as limiting the present invention. Those skilled in the art can make changes, modifications, substitutions and variations to the above embodiments within the scope of the present invention.

Claims

1. A method for growing BCN nanotubes inside wood-derived carbon pores, characterized by, The method comprises the following steps: (1) performing ultrasonic cleaning on wood chips with a mixture of anhydrous ethanol and water, and then drying the wood chips to complete pretreatment of the wood chips; (2) performing low-temperature pre-oxidation on the pretreated wood chips, and then performing high-temperature carbonization to obtain carbonized wood; The low-temperature pre-oxidation method is pre-oxidation at 150-250 °C for 4-8 h; the high-temperature carbonization is carbonization at 800-1000 °C under a nitrogen atmosphere for 4-8 h, and the gas flow rate in the high-temperature carbonization is 40-80 cm 3 min -1 ​ (3) grinding the carbonized wood to a thickness of 0.5-3 mm; (4) immersing the ground carbonized wood in a mixed solution of boric acid, polyethylene glycol and urea, impregnating the mixed solution into the internal pores of the carbonized wood by vacuum pressing, then washing the surface of the carbonized wood with water, and drying to obtain sample A; the mass ratio of urea, polyethylene glycol and boric acid in the mixed solution of boric acid, polyethylene glycol and urea is 3-18:0.3-1.8:0.15; the vacuum pressing method is: using a rotary vane vacuum pump to press multiple times, each time to-0.1 MPa, the pressing time is 30 min, the pressure maintaining time is 20 min, then maintaining at normal pressure for 10 min, repeating three times, and then maintaining at vacuum for 4-12 h; (5) performing high-temperature calcination on sample A under the protection of a protective gas to obtain BCN nanotube / wood-derived carbon material; (6) performing physical activation on the BCN nanotube / wood-derived carbon material to obtain BCN nanotube / wood-derived hierarchical porous carbon.

2. The method of claim 1, wherein the BCN nanotubes are grown inside the pores of the wood-derived carbon. The specific parameters of the ultrasonic in step (1) are: ultrasonic power of 300-400 W, frequency of 40 kHz, and time of 2-4 h; The drying in step (1) is freeze-drying, and the specific drying method is: freeze-drying under a vacuum degree of 10-30 Pa and a condensation temperature of ≤50℃ for 24 h.

3. The method of growing BCN nanotubes inside wood-derived carbon pores according to claim 1, wherein, The molecular weight of the polyethylene glycol is 1000-8000.

4. The method of claim 1, wherein the BCN nanotubes are grown inside the pores of the wood-derived carbon. The protective gas in step (5) is nitrogen, and the high-temperature calcination method is to heat to 800~1000 ℃ at a heating rate of 2 ℃ min -1 and then keep for 4~8 h.

5. The method of growing BCN nanotubes inside wood-derived carbon pores according to claim 1, wherein, The physical activation temperature in step (6) is 700-900℃, and the treatment time is 8-12 h.

6. A BCN nanotube / wood-derived hierarchically porous carbon, characterized in that, The BCN nanotube / wood-derived hierarchical porous carbon is prepared by the method for growing BCN nanotubes in the internal pores of wood-derived carbon according to any one of claims 1-5.

7. Application of the BCN nanotube / wood-derived hierarchical porous carbon according to claim 6 in supercapacitors.

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