Three-dimensional carbon tube grid membrane with micro-nano hierarchical pore structure and preparation method and application thereof

Abstract

The present invention relates to the field of carbon nanomaterials, and specifically to a three-dimensional carbon tube grid membrane with a micro-nano graded pore structure, and a preparation method and application thereof. The present invention uses three-dimensional porous alumina as a template to confine and deposit a carbon layer, and obtains a three-dimensional interconnected carbon tube grid membrane after removing the template. The surface of the carbon tube grid membrane is orderly ablated by laser ablation, and micron-scale pits and nanopores within the thickness range of the surface layer near the pits are formed in the irradiated area, so as to obtain a three-dimensional interconnected carbon tube grid membrane based on a micron-scale pit array. The preparation method is simple to operate and has good repeatability. The graded pore structure increases the specific surface area of ​​the material. When the membrane material is used as an electrode, the area specific capacitance can be improved while obtaining frequency response performance, and it is used for AC filter capacitors and fast-response electrochemical energy storage devices, which solves the problems of low load, small area specific capacitance, poor frequency response capability, and difficulty in meeting the requirements of high-power energy storage devices when the existing carbon nanotube array is used as an electrochemical capacitor electrode.

Description

Technical Field

[0001] The invention relates to the technical field of carbon nanomaterials, and in particular to a three-dimensional carbon tube grid film with a micro-nano graded pore structure and a preparation method and application thereof. Background Art

[0002] Three-dimensional structural carbon materials have broad application potential in the fields of electrochemical energy storage and environmental governance due to their large specific surface area and excellent electrical conductivity. Carbon nanomaterials (such as carbon nanotubes and graphene) have been widely used in many fields such as supercapacitors, lithium-ion batteries, and catalyst carriers due to their excellent electrical conductivity, chemical stability, and structural diversity. Among them, carbon nanotube arrays are considered to be ideal electrode materials for energy storage devices due to their unique nanoscale structure and good ion transport capacity. However, there are still many problems in the preparation and application of carbon nanotube arrays in the existing technology, such as the limitation of aspect ratio: carbon nanotube arrays are subject to their high aspect ratio structural characteristics, and agglomeration often occurs at the top, affecting the structural stability of the array. In addition, this carbon nanotube agglomeration significantly reduces its electrical conductivity. The carbon nanotube arrays prepared by current technology are generally less than 10 microns. When these carbon nanotube arrays are used as electrochemical capacitor electrodes, they have low load, small area specific capacity, and poor frequency response, which makes it difficult to meet the needs of high-power energy storage devices.

[0003] In view of the above problems, designing and preparing carbon materials with stable structure, high load and efficient ion transport channels has become an important direction of current research. The three-dimensional carbon tube structure needs to overcome the high aspect ratio limitation, so as to show better performance in electrochemical energy storage devices. The Chinese patent document "Three-dimensional mesh carbon nanotubes and their preparation method and use" with publication number CN108217628A prepares a three-dimensional interconnected porous alumina template by anodizing aluminum sheets in phosphoric acid electrolyte and combining selective corrosion method, and then uses the geometric morphology of the template to induce chemical vapor deposition to construct a three-dimensional interconnected carbon tube grid membrane in which upright carbon nanotubes are connected by lateral carbon nanotubes. This three-dimensional interconnected structure alleviates the problem of upright carbon tube agglomeration to a certain extent, and improves the material load and the structural stability of the electrode. However, this patented technology still has certain shortcomings: when the three-dimensional carbon tube grid membrane is thicker, the lateral carbon tube has a significant hindering effect on ion migration, resulting in low ion transmission efficiency and reduced frequency response performance. In addition, the large pore size of the carbon tube element (pore diameter is 200-240 nanometers) is not conducive to improving the specific surface area, which limits the specific capacity of the electrode. Summary of the invention

[0004] In order to solve the above problems existing in the prior art, one of the purposes of the present invention is to provide a method for preparing a three-dimensional carbon tube grid membrane with a micro-nano graded pore structure. The size and distribution of the micron-scale pit array on the three-dimensional carbon tube grid membrane prepared by this method are adjustable, and nanopores penetrating the carbon tube wall are formed on the carbon tube grid membrane near the pits. The micron-scale pit array can ensure the rapid transmission of ions in the three-dimensional carbon tube grid membrane with a large thickness (20-30 microns), and the nanopores on the top of the carbon tube can effectively increase the specific surface area, thereby improving the area specific capacity. When the three-dimensional carbon tube grid membrane is used as an electrode material for an electrochemical capacitor, the area specific capacitance can be improved while obtaining frequency response performance, making it expected to be used in fields such as AC filtering and high power output.

[0005] To achieve the above object, the present invention adopts the following technical solution: a method for preparing a three-dimensional carbon tube grid membrane with a micro-nano hierarchical pore structure, comprising the following steps:

[0006] Step 1, using a three-dimensional porous alumina with interconnected pores as a template, and uniformly depositing a carbon layer on the inner wall surface of the pores of the porous alumina template by chemical vapor deposition, wherein the thickness of the carbon layer is less than the pore radius, to obtain a porous alumina with three-dimensional interconnected carbon tubes attached to the inner wall of the pores, which is recorded as an intermediate product;

[0007] Step 2, removing the aluminum oxide template in the intermediate product by chemical etching to obtain a three-dimensional interconnected carbon tube grid film;

[0008] Step 3, lay the three-dimensional interconnected carbon tube grid film flat on the platform of the CO2 laser generator, adjust the parameters and spot size of the laser generator so that the laser spot is irradiated vertically, and micron-scale pits are formed in the area after the laser spot is irradiated, and nanopores penetrating the carbon tube wall are formed within a thickness of 1-4 microns on the carbon tube grid film near the pit wall and the bottom of the micron-scale pit; the laser spot travels along the set path, and the adjacent micron-scale pits formed are separated from each other, so as to obtain a three-dimensional carbon tube grid film with a micro-nano graded pore structure.

[0009] Further improvement of the preparation method of three-dimensional carbon tube grid membrane as micro-nano hierarchical pore structure:

[0010] Preferably, the preparation method of the three-dimensional porous alumina template in step 1 is as follows: using a phosphoric acid solution with a concentration of 0.25-0.35 mol / L and containing 8-12 wt% ethanol as an electrolyte, an aluminum sheet containing trace impurities as a positive electrode, and graphite as a negative electrode, anodizing for 10-15 h at a temperature of 4-6 ° C and a DC constant voltage of 180-200 V; then placing the anodized aluminum sheet in a saturated tin tetrachloride solution to remove the remaining aluminum that has not undergone anodization to obtain anodized aluminum; then soaking the anodized aluminum in a 4-6 wt% phosphoric acid solution at a temperature of 36-44 ° C for 20-30 min to obtain a three-dimensional porous alumina template with a thickness of 20-30 microns.

[0011] Preferably, the aluminum content in the aluminum sheet containing trace impurities is 99.5-99.8 wt %, and the impurities contained include iron, silicon, and copper, and the total impurity content is ≤0.5 wt %.

[0012] Preferably, the specific steps of the chemical vapor deposition in step 1 are: placing the three-dimensional porous alumina template in a high-temperature tube furnace, evacuating the interior, introducing argon gas at a rate of 75-125 ml / min to normal pressure, heating to 600-700 ° C, and then introducing the reaction gas source acetylene C2H4 at a rate of 5-15 ml / min, and continuously introducing it for 80-100 min for chemical vapor deposition, and the thickness of the deposited carbon layer is 10-30 nanometers. After the deposition is completed, it is cooled to room temperature, and the sample surface is plasma cleaned for 8-12 min to obtain porous alumina with three-dimensional interconnected carbon tubes attached to the inner wall of the pores.

[0013] Preferably, in step 2, the aluminum oxide template inside the intermediate product is removed by chemical etching, and the etching solution used in the chemical etching is a 2-4 mol / L sodium hydroxide solution. After the etching is completed, the intermediate product is taken out and surface plasma cleaning is performed for 8-12 minutes.

[0014] Preferably, the parameters of the CO2 laser generator in step 3 are set as follows: the power is 15-25% of the maximum power, the scanning speed is 300-500 mm / s, the number of scanning steps is 50-300 steps, the interval between each step is 4-12 seconds, the wavelength is 10.64 microns, and the maximum power is 20 W.

[0015] Preferably, the model of the CO2 laser generator in step 3 is SK-MARKER, and the focal length of the laser is 13.9 cm.

[0016] Preferably, the adjacent micron-sized pits are arranged in a hexagonal pattern, the center spacing between adjacent pits is 250-500 microns, the opening diameter of the pit is 100-300 microns, the depth of the pit center is 5-30 microns, and the diameter of the nanopore is less than 50 nanometers.

[0017] The second object of the present invention is to provide a three-dimensional carbon tube grid membrane with a micro-nano hierarchical pore structure obtained by using any one of the above-mentioned methods for preparing a three-dimensional carbon tube grid membrane with a micro-nano hierarchical pore structure.

[0018] The third purpose of the present invention is to provide an application of the above-mentioned three-dimensional carbon tube grid film with micro-nano hierarchical pore structure in an electrochemical capacitor. The prepared three-dimensional carbon tube grid film with micro-nano hierarchical pore structure is cut into two pieces of the same size, which are used as positive and negative electrode materials respectively, and a platinum sheet is used as a current collector. It is assembled together with a NKK-MPF30AC-100 diaphragm and an electrolyte, and then packaged with a PET film to obtain an electrochemical capacitor. The electrolyte is one of a sulfuric acid solution, a phosphoric acid solution, a sodium hydroxide solution, and a sodium sulfate solution, and the concentration is 0.9-1.1 mol / L.

[0019] Compared with the prior art, the present invention has the following beneficial effects:

[0020] 1) The present invention provides a three-dimensional carbon tube grid membrane with a micro-nano hierarchical pore structure, and the specific steps are as follows:

[0021] First, porous anodized aluminum with three-dimensional interconnected pores is used as a template (including vertical large pores arranged in an array and horizontal small pores connecting adjacent large pores, one end of the vertical large pore is closed and the depth is close to the thick layer of anodized aluminum). Based on the spatial geometric morphology confinement induction of the template pores, a chemical vapor deposition process is used to uniformly deposit a carbon layer on the inner wall surface of the pores;

[0022] Secondly, the aluminum oxide template is removed to obtain a three-dimensional interconnected carbon tube grid film. The three-dimensional carbon tube array is the basis for the next step of preparing an ordered array of micro-nano hierarchical pores.

[0023] Finally, CO2 laser ablation technology is used to ablate a micron-scale pit array on the surface of the three-dimensional carbon tube grid membrane. Micron-scale pits are formed in the area after laser spot irradiation, and nanopores penetrating the carbon tube walls are formed on the carbon tube grid membrane near the pit walls and bottom of the micron-scale pits; the laser spot travels along the set path, and the adjacent micron-scale pits formed are separated from each other and arranged in a pattern, thereby obtaining a three-dimensional carbon tube grid membrane with a micro-nano graded pore structure.

[0024] 2) When preparing a three-dimensional carbon tube grid membrane with a micro-nano graded pore structure, the hole spacing of the micron-scale pit array can be controlled by changing the lattice spacing of the lattice array in the CO2 laser, the aperture of the micron-scale pit can be controlled by the laser power, and the hole depth of the micron-scale pit is controlled by the number of laser writing steps. Small-sized nanopores are evenly distributed in the area where the micron-scale pits are located, with high repeatability. On the premise of ensuring that the micron-scale pit array is not destroyed, the specific surface area of ​​the material is increased, thereby increasing the area specific capacity. The preparation method is simple to operate, and the thickness and load of the prepared sample are adjustable. The graded hole array has good uniformity and high repeatability. The aperture size and hole depth of the micron-scale pits change approximately linearly with the number of scanning steps. The spacing between the holes matches the spacing of the laser lattice array, and the opening diameter and hole depth of the micron-scale pit array are adjustable, thereby obtaining an orderly and adjustable micron-scale pit array based on the three-dimensional carbon tube grid membrane, and providing a template for the composite of other nanostructures and microstructures with similar morphology and arrangement, broadening the structure of the three-dimensional carbon tube grid membrane. The thickness of the three-dimensional carbon tube grid film and the diameter of the carbon tube can be artificially controlled by changing the anodizing time and the electrolyte composition, thereby realizing the construction of a micron-scale pit array with a depth matching the thickness of the carbon film. The arrangement and combination of the micron-scale pit array can be artificially controlled by designing the dot array pattern and changing the scanning steps to construct micron-scale pit arrays with different morphologies and arrangements.

[0025] 3) The three-dimensional carbon tube mesh membrane with micro-nano graded pore structure prepared by the present invention has a large thickness (up to 20-30 microns). This orderly arranged graded pore structure can not only ensure the rapid transmission of ions in the thick three-dimensional carbon tube mesh membrane, but also increase the specific surface area, thereby improving the area specific capacity. Therefore, when the three-dimensional carbon tube mesh membrane is used as an electrode material for an electrochemical capacitor, the frequency response performance can be obtained while improving the area specific capacitance. After assembling a double-layer capacitor with the above-mentioned carbon tube mesh membrane as an electrode, the surface capacitance at 120 Hz reaches 2.03, 2.52, and 3.23 mF cm, respectively. -2 , the phase angles are about -81.1 degrees, -80.9 degrees, and -80.1 degrees, respectively; when the thickness of the carbon tube film is 23 microns, the pore spacing is 350 microns, and the hole depth is 15 microns, the capacitor assembled by it has an area specific capacitance of up to 3.23 mFcm at a frequency of 120 Hz -2 , the phase angle is -80.1 degrees. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 The present invention is a schematic diagram of the process of preparing a three-dimensional carbon tube grid membrane with a micro-nano graded pore structure.

[0027] Figure 2Schematic diagram of the distribution of the three-dimensional carbon tube grid membrane with micro-nano hierarchical pore structure prepared in Example 1.

[0028] Figure 3 The electron microscope image of the three-dimensional carbon tube grid membrane with micro-nano hierarchical pore structure prepared in Example 1; (a) and (b) are scanning electron microscope (SEM) images of micron-scale pits and nanopores on the surface of the three-dimensional carbon tube grid membrane with micro-nano hierarchical pore structure, respectively, and (b) is an image of the micron-scale pits in (a) after being magnified 500 times; Figure 3 (c) and (d) are scanning electron microscope (SEM) images of the cross section of the three-dimensional carbon tube grid film with micro-nano hierarchical pore structure, and (d) is a 20-fold magnified carbon tube image below the micron-scale pit in (c); Figure 3 (e) and (f) are transmission electron microscopy (TEM) images of nanopores at different positions in the three-dimensional carbon tube grid membrane with micro-nano hierarchical pore structure.

[0029] Figure 4 The test results of the electrochemical performance test of the electrochemical capacitor prepared in Example 2 are shown in Figure 2; (a) and (b) are cyclic voltammetry (CV) curves, and (c) and (d) are constant current charge and discharge (GCD) curves.

[0030] Figure 5 The test results of the electrochemical capacitance performance test of the electrochemical capacitors prepared in Examples 1-4 and Comparative Example 1 are compared; wherein (a) is a Bode plot obtained by electrochemical impedance spectroscopy (EIS), (b) is a Nyquist curve, (c) is a curve showing the relationship between area specific capacitance and frequency, and (d) is a curve showing the relationship between frequency and imaginary capacitance of the electrochemical capacitor prepared in Example 2. DETAILED DESCRIPTION

[0031] In order to make the purpose, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in the field without making creative work are within the scope of protection of the present invention.

[0032] Preparation Example 1

[0033] This embodiment provides a method for preparing three-dimensional porous alumina, which specifically includes the following steps:

[0034] 1) Take an aluminum sheet with a thickness of 100 microns and containing trace impurities, the aluminum content in the aluminum sheet is 99.8 wt%, and the impurities contained include iron, silicon, and copper, and the total impurity content is ≤0.2 wt%;

[0035] A 0.3 mol / L phosphoric acid solution containing 10 wt% ethanol was used as the electrolyte, an aluminum sheet containing trace impurities was used as the positive electrode, and graphite was used as the negative electrode. Anodization was performed at a temperature of 5 °C and a DC constant voltage of 190 V for 11 h to obtain an anodized aluminum sheet.

[0036] 2) Place the anodized aluminum sheet in a saturated tin tetrachloride solution to remove the remaining aluminum that has not undergone anodization to obtain anodized aluminum;

[0037] 3) Then, the anodized aluminum is immersed in a 5 wt% phosphoric acid solution at 40°C for 25 min to obtain a three-dimensional porous aluminum oxide; the three-dimensional porous aluminum oxide has a thickness of 23 microns, and is internally distributed with arrayed vertical large channels and horizontal small channels connecting adjacent large channels. One end of the vertical large channel is closed, the depth is close to and lower than 23 microns, the opening diameter is about 220 nanometers, and the diameter of the horizontal small channel is about 90 nanometers.

[0038] Referring to the above preparation steps, aluminum sheets of the same thickness were used and the anodizing time was adjusted to obtain a three-dimensional porous alumina with a thickness of 20 microns. The interior of the three-dimensional porous alumina was distributed with arrayed vertical large channels and horizontal small channels connecting adjacent large channels. One end of the vertical large channel was closed, the depth was close to and less than 20 microns, the opening diameter was about 220 nanometers, and the diameter of the horizontal small channel was about 90 nanometers.

[0039] Referring to the above preparation steps, aluminum sheets of the same thickness were used and the anodizing time was adjusted to obtain a three-dimensional porous alumina with a thickness of 30 microns. The interior of the three-dimensional porous alumina was distributed with arrayed vertical large channels and horizontal small channels connecting adjacent large channels. One end of the vertical large channel was closed, the depth was close to and less than 30 microns, the opening diameter was about 220 nanometers, and the diameter of the horizontal small channel was about 90 nanometers.

[0040] Example 1

[0041] This embodiment provides a method for preparing a three-dimensional carbon tube grid membrane with a micro-nano hierarchical pore structure. The preparation process is as follows: Figure 1 As shown, the specific steps include:

[0042] S1. Take the three-dimensional porous alumina prepared in Preparation Example 1 as a template (thickness 23 μm), place it in a high-temperature tube furnace, evacuate the interior, introduce argon gas at a rate of 100 ml / min to normal pressure, raise the temperature to 650 °C, then introduce acetylene C2H4 as a reaction gas source at a rate of 10 ml / min, and continue to introduce it for 90 min for chemical vapor deposition. The thickness of the deposited carbon layer is 25 nanometers. After the deposition is completed, cool it to room temperature, plasma clean the sample surface for 10 min, and obtain porous alumina with three-dimensional interconnected carbon tubes attached to the inner wall of the pores, which is recorded as intermediate product 1;

[0043] S2, removing the aluminum oxide template in the intermediate product by chemical etching, using a 3 mol / L sodium hydroxide solution as the etching solution, taking it out after the chemical etching, and performing surface plasma cleaning for 10 min to obtain a three-dimensional interconnected carbon tube grid film 1;

[0044] S3, lay the three-dimensional interconnected carbon tube grid film flat on the platform of the CO2 laser generator, the model of the CO2 laser generator is SK-MARKER, and the focal distance from the laser is 13.9 cm; adjust the parameters and spot size of the laser generator so that the laser spot is irradiated vertically; the parameters are set as follows: the power is 20% of the maximum power (4W), the scanning speed is 400 mm / s, the number of scanning steps is 200 steps, the interval between each step is 8 seconds, the wavelength is 10.64 microns, and the maximum power is 20 W;

[0045] A micron-sized pit is formed in the area irradiated by the laser spot, and a nano-hole penetrating the carbon tube wall is formed within a certain thickness range on the carbon tube grid film near the pit wall and the bottom of the micron-sized pit; the opening diameter of the micron-sized pit is 220 microns, the depth of the pit center is 15 microns, the diameter of the nano-hole is less than 50 nanometers, and the thickness of the carbon tube forming the nano-hole is 2 microns;

[0046] The laser spot travels along the set path, the distance between the centers of adjacent laser spots is 250 microns, the adjacent micron-sized pits are separated from each other and arranged in a hexagonal pattern, and the center distance between adjacent micron-sized pits is 250 microns, thus obtaining a three-dimensional carbon tube grid film with a micro-nano graded pore structure.

[0047] Figure 1The invention discloses a preparation flow chart of a three-dimensional carbon tube grid membrane with a micron-scale hierarchical pore structure in which micron-scale pits and nanopores are orderly arranged. The specific process is as follows: placing a three-dimensional porous alumina template in a high-temperature tube furnace, performing carbon deposition in an inert gas atmosphere, and uniformly depositing a carbon layer on the inner wall surface of the pores of the porous alumina template; after cooling, performing surface plasma cleaning on the sample to obtain a porous alumina with three-dimensional interconnected carbon tubes attached to the inner wall of the pores; removing the alumina template therein by chemical corrosion, and cleaning the surface of the carbon film to obtain a three-dimensional interconnected carbon tube grid membrane; then laying the three-dimensional interconnected carbon tube grid membrane on a laser processing platform, forming a micron-scale pit array on the surface of the three-dimensional carbon tube grid membrane by laser ablation, and at the same time, in-situ reconstruction occurs within a certain thickness range on the carbon tube grid membrane close to the pit wall and bottom of the micron-scale pits to form nanopores penetrating the carbon tube wall, and finally obtaining a three-dimensional carbon tube grid membrane with a micron-scale hierarchical pore structure.

[0048] Figure 2 Schematic diagram of the distribution of the three-dimensional carbon tube grid membrane with micro-nano hierarchical pore structure prepared in Example 1. Figure 3 (a) is a scanning electron microscope (SEM) image of micron-scale pits and nanopores on the surface of the three-dimensional carbon tube grid membrane with micro-nano hierarchical pore structure prepared in Example 1, and (b) is an image of the micron-scale pits in (a) after being magnified 500 times. Figure 3 (a) and (b) show that the micron-sized pits are arranged in a hexagonal manner, the opening diameter of the micron-sized pits is 220 microns, and the center distance between adjacent micron-sized pits is 250 microns. Nanopores penetrating the carbon tube wall are formed within a certain thickness range on the carbon tube grid film near the pit wall and the bottom of the micron-sized pits, which has a unique micro-nano hierarchical pore structure. Figure 3 (c) is a scanning electron microscope (SEM) image of a cross section of a three-dimensional carbon tube grid film with a micro-nano hierarchical pore structure prepared in Example 1, and (d) is a 20-fold magnified image of the carbon tube below the micron-sized pit in (c); Figure 3 (c) and (d) show that the depth of the center of the micron-scale pit is 15 microns, the carbon tubes are well connected laterally, and the carbon tube array is composed of carbon tubes with a diameter of 220 nanometers, which indicates that the prepared three-dimensional carbon tube grid film with micro-nano hierarchical pore structure has good mechanical stability and is not prone to collapse; Figure 3 (e) and (f) are transmission electron microscopy (TEM) images of nanopores at different positions in the three-dimensional carbon tube grid membrane with micro-nano hierarchical pore structure; Figure 3 (e) and (f) show that the nanopores formed by ablation are mostly within 50 nanometers in size, which can provide a higher specific surface area.

[0049] Comparative Example 1

[0050] This comparative example 1 provides a method for preparing a three-dimensional interconnected carbon tube grid film, and the specific steps are referred to in Example 1, except that the operation of step S3 is not performed. Finally, a three-dimensional interconnected carbon tube grid film 1 is prepared.

[0051] Example 2

[0052] This embodiment provides a method for preparing a three-dimensional carbon tube grid membrane with a micron-scale hierarchical pore structure in which micron-scale pits and nanopores are orderly arranged. The specific steps are referred to in Example 1, except that the lattice spacing in step S3 is 350 microns. Finally, a three-dimensional carbon tube grid membrane with a micron-scale hierarchical pore structure is obtained.

[0053] Scanning the three-dimensional carbon tube grid film with micro-nano hierarchical pore structure prepared in Example 2 with an electron microscope shows that the center spacing of the micron-scale pit array is 350 microns, the opening diameter of the pit is 220 microns, and the depth of the pit center is 15 microns.

[0054] Example 3

[0055] This embodiment provides a method for preparing a three-dimensional carbon tube grid membrane with a micro-nano hierarchical pore structure in which micron-sized pits and nanopores are orderly arranged. The specific steps are referred to in Example 1, except that the lattice spacing in step S3 is 400 microns. Finally, a three-dimensional carbon tube grid membrane with a micro-nano hierarchical pore structure is obtained.

[0056] Scanning the three-dimensional carbon tube grid film with micro-nano hierarchical pore structure prepared in Example 3 with an electron microscope shows that the center spacing of the micron-scale pit array is 400 microns, the opening diameter of the pit is 220 microns, and the depth of the pit center is 15 microns.

[0057] Example 4

[0058] This embodiment provides a method for preparing a three-dimensional carbon tube grid membrane with a micro-nano hierarchical pore structure in which micron-sized pits and nanopores are orderly arranged. The specific steps are referred to in Example 1, except that the lattice spacing in step S3 is 500 microns. Finally, a three-dimensional carbon tube grid membrane with a micro-nano hierarchical pore structure is obtained.

[0059] Scanning the three-dimensional carbon tube grid film with micro-nano hierarchical pore structure prepared in Example 4 with an electron microscope shows that the center spacing of the micron-scale pit array is 500 microns, the opening diameter of the pit is 220 microns, and the depth of the pit center is 15 microns.

[0060] Example 5

[0061] This embodiment provides a method for preparing a three-dimensional carbon tube grid membrane with a micron-scale hierarchical pore structure in which micron-scale pits and nanopores are orderly arranged. The specific steps are referred to in Example 1, except that the number of scanning steps of the laser in step S3 is 100. Finally, a three-dimensional carbon tube grid membrane with a micron-scale hierarchical pore structure is obtained.

[0062] Scanning the three-dimensional carbon tube grid film with micro-nano hierarchical pore structure prepared in Example 5 with an electron microscope shows that the center spacing of the micron-scale pit array is 250 microns, the opening diameter of the pit is 130 microns, and the depth of the pit center is 8 microns.

[0063] By comparing the electron microscope images of the three-dimensional carbon tube grid films with micro-nano graded pore structures obtained in Examples 1, 2, 3, 4, and 5, it can be seen that the center spacing of the micron-scale pit array can be adjusted by adjusting the spacing between the centers of adjacent laser spots during CO2 laser irradiation; the opening diameter and depth of the micron-scale pits can also be adjusted by adjusting the number of laser scanning steps during CO2 laser irradiation.

[0064] Example 6

[0065] This embodiment provides a method for preparing a three-dimensional carbon tube grid membrane with a micro-nano hierarchical pore structure. The preparation process is as follows: Figure 1 As shown, the specific steps include:

[0066] S1. Take the three-dimensional porous alumina (thickness 20 μm) prepared in Preparation Example 1 as a template, place it in a high-temperature tube furnace, evacuate the interior, introduce argon gas at a rate of 75 ml / min to normal pressure, raise the temperature to 600 °C, then introduce acetylene C2H4 as a reaction gas source at a rate of 5 ml / min for 80 min for chemical vapor deposition, and the thickness of the deposited carbon layer is 10 nanometers. After the deposition is completed, cool it to room temperature, plasma clean the sample surface for 8 min, and obtain porous alumina with three-dimensional interconnected carbon tubes attached to the inner wall of the pores, which is recorded as intermediate product 2;

[0067] S2, removing the aluminum oxide template in the intermediate product by chemical etching, using a 2 mol / L sodium hydroxide solution as the etching solution, taking it out after the chemical etching, and performing surface plasma cleaning for 8 min to obtain a three-dimensional interconnected carbon tube grid film 2;

[0068] S3, lay the three-dimensional interconnected carbon tube grid film flat on the platform of the CO2 laser generator, the model of the CO2 laser generator is SK-MARKER, and the focal distance from the laser is 13.9 cm; adjust the parameters and spot size of the laser generator so that the laser spot is irradiated vertically; the parameters are set as follows: the power is 15% of the maximum power (3 W), the scanning speed is 300 mm / s, the number of scanning steps is 50 steps, the interval between each step is 4 seconds, the wavelength is 10.64 microns, and the maximum power is 20 W;

[0069] A micron-sized pit is formed in the area irradiated by the laser spot, and a nano-hole penetrating the carbon tube wall is formed on the carbon tube grid film near the pit wall and the bottom of the micron-sized pit; the opening diameter of the pit is 100 microns, the depth of the pit center is 5 microns, the diameter of the nano-hole is less than 50 nanometers, and the thickness of the carbon tube forming the nano-hole is 1 micron;

[0070] The laser spot travels along the set path, the distance between the centers of adjacent laser spots is 250 microns, the adjacent micron-sized pits are separated from each other and arranged in a hexagonal pattern, and the center distance between adjacent micron-sized pits is 250 microns, thus obtaining a three-dimensional carbon tube grid film with a micro-nano graded pore structure.

[0071] Example 7

[0072] This embodiment provides a method for preparing a three-dimensional carbon tube grid membrane with a micro-nano hierarchical pore structure. The preparation process is as follows: Figure 1 As shown, the specific steps include:

[0073] S1. Take the three-dimensional porous alumina (thickness 30 μm) prepared in Preparation Example 1 as a template, place it in a high-temperature tube furnace, evacuate the interior, introduce argon gas at a rate of 125 ml / min to normal pressure, raise the temperature to 700 °C, then introduce acetylene C2H4 as a reaction gas source at a rate of 15 ml / min for 100 min for chemical vapor deposition, and the thickness of the deposited carbon layer is 30 nanometers. After the deposition is completed, cool to room temperature, plasma clean the sample surface for 12 min, and obtain porous alumina with three-dimensional interconnected carbon tubes attached to the inner wall of the pores, which is recorded as intermediate product 3;

[0074] S2, removing the aluminum oxide template in the intermediate product by chemical etching, using a 4 mol / L sodium hydroxide solution as the etching solution, taking it out after the chemical etching, and performing surface plasma cleaning for 12 min to obtain a three-dimensional interconnected carbon tube grid film 3;

[0075] S3, lay the three-dimensional interconnected carbon tube grid film flat on the platform of the CO2 laser generator, the model of the CO2 laser generator is SK-MARKER, and the focal distance from the laser is 13.9 cm; adjust the parameters and spot size of the laser generator so that the laser spot is irradiated vertically; the parameters are set as follows: the power is 25% of the maximum power (5 W), the scanning speed is 500 mm / s, the number of scanning steps is 300 steps, the interval between each step is 12 seconds, the wavelength is 10.64 microns, and the maximum power is 20 W;

[0076] A micron-sized pit is formed in the area irradiated by the laser spot, and a nano-hole penetrating the carbon tube wall is formed on the carbon tube grid film near the pit wall and the bottom of the micron-sized pit; the opening diameter of the pit is 300 microns, the depth of the pit center is 30 microns, the diameter of the nano-hole is less than 50 nanometers, and the thickness of the carbon tube forming the nano-hole is 4 microns;

[0077] The laser spot travels along the set path, the spacing between the centers of adjacent laser spots is 500 microns, the adjacent micron-sized pits formed are separated from each other and arranged in a hexagonal pattern, and the center spacing between adjacent micron-sized pits is 500 microns, thus obtaining a three-dimensional carbon tube grid film with a micro-nano graded pore structure.

[0078] Electrochemical performance test

[0079] The three-dimensional interconnected carbon tube grid film prepared in Comparative Example 1 and the three-dimensional carbon tube grid film with micro-nano hierarchical pore structure prepared in Examples 1 to 8 were cut into two squares with a side length of 3 mm, respectively used as positive and negative electrode materials of electrochemical capacitors, with platinum sheets as current collectors and 1 mol / L sulfuric acid as electrolyte. They were first assembled with Japanese NKK-MPF30AC-100 diaphragms and then packaged with PET films to prepare electrochemical capacitors, which were named ordinary electrochemical capacitors, electrochemical capacitors 1, electrochemical capacitors 2, electrochemical capacitors 3, electrochemical capacitors 4, electrochemical capacitors 5, electrochemical capacitors 6, electrochemical capacitors 7 and electrochemical capacitors 8. The electrochemical performance of the above electrochemical capacitors was tested, and the test results are as follows:

[0080] 1) Figure 4 The test results of the electrochemical performance test of the electrochemical capacitor 2 are shown in FIG. Figure 4 (a) and (b) are cyclic voltammetry (CV) curves of the electrochemical capacitor in Example 2 at a scan rate of 100 mV / s to 1000 V / s; Figure 4 (c) and (d) are constant current charge and discharge (GCD) curves. Figure 4 It can be seen that: at scan rates from 100 mV / s to 1000 V / s, the shape of the CV curve is close to a rectangle, and the constant current charge and discharge test results are ideal isosceles triangles. The prepared capacitor exhibits nearly ideal double-layer capacitor characteristics; and at a high scan rate of 1000 V / s, it can still maintain a nearly rectangular shape, which indicates that the prepared three-dimensional carbon tube grid film with a micro-nano hierarchical pore structure has good power performance when used in electrochemical capacitor electrodes.

[0081] 2) The electrochemical performance of ordinary electrochemical capacitors and electrochemical capacitors 1-5 was tested. The results are as follows Figure 5 shown.

[0082] Figure 5(a) is the Bode plot obtained from electrochemical impedance spectroscopy (EIS), (b) is the Nyquist curve, and (c) is the area specific capacitance and frequency relationship curve. Figure 5 (a), (b), and (c) show that the imaginary resistance of the electrochemical capacitor prepared in Example 2 is close to perpendicular to the real axis in the Nyquist diagram, showing ideal capacitance characteristics and a small equivalent series resistance (0.53Ω). In the Bode diagram reflecting the relationship between the phase angle and the frequency, the phase angle in the low-frequency region is close to -90°, which also shows the characteristics of an ideal capacitor. The phase angle reaches -80.1° at a frequency of 120 Hz, showing good fast frequency response capability. The area specific capacitance at a frequency of 120 Hz can reach a very high 3.23 mF cm -2 , much higher than 1.03 mF cm in Comparative Example 1 -2 The capacitor of Example 4 has a phase angle of -81.1° at 120 Hz, showing good frequency response performance; the area specific capacitance at 120 Hz can reach 2.03 mF cm -2 , with higher energy density.

[0083] The relationship curve between the frequency and the real capacitance and the imaginary capacitance of the electrochemical capacitor 2 is tested, such as Figure 5 (d) as shown. Figure 5 The relationship curve of (d) shows that the characteristic frequency when the imaginary capacitance reaches the maximum value is 845.47 Hz, with a short relaxation time (1.18 ms), indicating efficient ion transport and electron conduction in the electrode. It can be seen that the three-dimensional carbon tube grid membrane composed of micron-sized pits and nanopores prepared in Example 2 has a higher area specific capacitance and good rapid response performance. This is because: compared with the three-dimensional carbon tube grid membrane prepared in Comparative Example 1, the three-dimensional carbon tube grid membrane composed of micron-sized pits and nanopore hierarchical structure in Example 2 has a higher material load, which can provide a larger electrochemically active specific surface area of ​​the electrode material, thereby improving the energy density of the double-layer electrochemical capacitor constructed therefrom. At the same time, the micron-sized pits can provide fast ion transport channels and electrolyte storage areas, which can improve the frequency response performance of the capacitor assembled therefrom.

[0084] 3) The electrochemical performance of electrochemical capacitors 2-7 was tested, and the test results are as follows:

[0085] ;

[0086] The test results show that the three-dimensional carbon tube mesh membrane with micro-nano hierarchical pore structure prepared in Examples 2 and 3 has the advantages of high area specific capacitance and fast frequency response performance. The area specific capacitance of the three-dimensional carbon tube mesh membrane with micro-nano hierarchical pore structure prepared in Examples 2, 3 and 4 is 3.23 mF cm -2 , 2.52 mF cm -2 , 2.03 mF cm -2 When the three-dimensional carbon tube grid films with micro-nano hierarchical pore structures prepared in Examples 2-7 are used as electrode materials for electrochemical capacitors, they can meet the frequency response performance requirements of AC filter capacitors.

[0087] Those skilled in the art should understand that the above are only some specific embodiments of the present invention, rather than all embodiments. It should be noted that for those of ordinary skill in the art, many modifications and improvements can be made, and all modifications or improvements that do not exceed the scope of protection of the present invention should be regarded as the scope of protection of the present invention.

Claims

1. A method for preparing a three-dimensional carbon tube grid membrane with a micro-nano hierarchical pore structure, characterized in that: The steps include: Step 1, using a three-dimensional porous alumina with interconnected pores as a template, and uniformly depositing a carbon layer on the inner wall surface of the pores of the porous alumina template by chemical vapor deposition, wherein the thickness of the carbon layer is less than the pore radius, to obtain a porous alumina with three-dimensional interconnected carbon tubes attached to the inner wall of the pores, which is recorded as an intermediate product; Step 2, removing the aluminum oxide template in the intermediate product by chemical etching to obtain a three-dimensional interconnected carbon tube grid film; Step 3, lay the three-dimensional interconnected carbon tube grid film flat on the platform of the CO2 laser generator, adjust the parameters and spot size of the laser generator so that the laser spot is irradiated vertically, and micron-scale pits are formed in the area after the laser spot is irradiated, and nanopores penetrating the carbon tube wall are formed within a thickness of 1-4 microns on the carbon tube grid film near the pit wall and the bottom of the micron-scale pit; the laser spot travels along the set path, and the adjacent micron-scale pits formed are separated from each other, so as to obtain a three-dimensional carbon tube grid film with a micro-nano graded pore structure.

2. The method for preparing the three-dimensional carbon tube grid membrane with micro-nano hierarchical pore structure according to claim 1, characterized in that: The preparation method of the three-dimensional porous alumina template in step 1 is as follows: using a phosphoric acid solution with a concentration of 0.25-0.35 mol / L and containing 8-12 wt% ethanol as an electrolyte, an aluminum sheet containing trace impurities as a positive electrode, and graphite as a negative electrode, anodizing for 10-15 h at a temperature of 4-6 ° C and a DC constant voltage of 180-200V; then placing the anodized aluminum sheet in a saturated tin tetrachloride solution to remove the remaining aluminum that has not undergone anodization to obtain anodized aluminum; then soaking the anodized aluminum in a phosphoric acid solution with a temperature of 36-44 ° C and a concentration of 4-6 wt% for 20-30 min to obtain a three-dimensional porous alumina template with a thickness of 20-30 microns.

3. The method for preparing the three-dimensional carbon tube grid membrane with micro-nano hierarchical pore structure according to claim 2, characterized in that: The aluminum sheet containing trace impurities has an aluminum content of 99.5-99.8 wt %, and the impurities contained include iron, silicon, and copper, and the total impurity content is ≤0.5 wt %.

4. The method for preparing the three-dimensional carbon tube grid membrane with micro-nano hierarchical pore structure according to claim 1, characterized in that: The specific steps of the chemical vapor deposition described in step 1 are: placing the three-dimensional porous alumina template in a high-temperature tube furnace, evacuating the interior, introducing argon gas at a rate of 75-125 ml / min to normal pressure, and heating to 600-700 ° C; then introducing the reaction gas source acetylene C2H4 at a rate of 5-15 ml / min, and continuously introducing it for 80-100 min for chemical vapor deposition, and the thickness of the deposited carbon layer is 10-30 nanometers. After the deposition is completed, it is cooled to room temperature, and the sample surface is plasma cleaned for 8-12 minutes to obtain porous alumina with three-dimensional interconnected carbon tubes attached to the inner wall of the pores.

5. The method for preparing the three-dimensional carbon tube grid membrane with micro-nano hierarchical pore structure according to claim 1, characterized in that: In step 2, the aluminum oxide template in the intermediate product is removed by chemical etching. The etching solution used for chemical etching is a 2-4 mol / L sodium hydroxide solution. After the etching is completed, the product is taken out and surface plasma cleaning is performed for 8-12 minutes.

6. The method for preparing the three-dimensional carbon tube grid membrane with micro-nano hierarchical pore structure according to claim 1, characterized in that: In step 3, the parameters of the CO2 laser generator are set as follows: power is 15-25% of the maximum power, scanning speed is 300-500 mm / s, scanning steps are 50-300 steps, each step interval is 4-12 seconds, wavelength is 10.64 μm, and maximum power is 20 W.

7. The method for preparing the three-dimensional carbon tube grid membrane with micro-nano hierarchical pore structure according to claim 6, characterized in that: The model of the CO2 laser generator described in step 3 is SK-MARKER, and the focal distance from the laser is 13.9 cm.

8. The method for preparing the three-dimensional carbon tube grid membrane with micro-nano hierarchical pore structure according to claim 6, characterized in that: The adjacent micron-sized pits are arranged in a hexagonal pattern, the center spacing between adjacent pits is 250-500 microns, the opening diameter of the pit is 100-300 microns, the depth of the pit center is 5-30 microns, and the diameter of the nanopore is less than 50 nanometers.

9. A three-dimensional carbon tube grid membrane with a micro-nano hierarchical pore structure obtained by the method for preparing a three-dimensional carbon tube grid membrane with a micro-nano hierarchical pore structure according to any one of claims 1 to 8.

10. An application of the three-dimensional carbon tube grid film with micro-nano hierarchical pore structure as claimed in claim 9 in an electrochemical capacitor, characterized in that: The prepared three-dimensional carbon tube grid film with micro-nano hierarchical pore structure is cut into two pieces of the same size, which are used as positive and negative electrode materials respectively. A platinum sheet is used as a current collector, and they are assembled together with a NKK-MPF30AC-100 separator and an electrolyte, and then packaged with a PET film to obtain an electrochemical capacitor. The electrolyte is one of a sulfuric acid solution, a phosphoric acid solution, a sodium hydroxide solution, and a sodium sulfate solution, and the concentration is 0.9-1.1 mol / L.

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