Bifunctional layered carbon aerogel, preparation method and application

Abstract

This invention relates to a method for preparing bifunctional layered carbon aerogels and their applications, comprising the following steps: S1, preparing a mixed solution of nanocellulose, chitosan and graphene oxide hydrogel precursors, zinc chloride activator and glutaraldehyde crosslinking agent; fixing the shape of the hydrogel using a cubic mold, and forming the hydrogel through thermal crosslinking; S2, placing the hydrogel prepared in step S1 at a right angle of an L-shaped copper plate, and applying liquid nitrogen to the bottom of the copper plate to induce rapid directional growth of ice crystals inside the hydrogel; S3, performing vacuum freeze-drying on the frozen hydrogel prepared in step S2 to obtain a layered aerogel; S4, placing the layered aerogel prepared in step S3 in a tube furnace for carbonization to obtain a layered carbon aerogel. This invention provides an effective strategy for synthesizing bifunctional carbon aerogels, which has broad application value in energy storage devices and wearable electronic devices.

Description

Technical Field

[0001] This invention belongs to the field of aerogels, specifically relating to a bifunctional layered carbon aerogel, its preparation method, and its application. Background Technology

[0002] With the rapid development of IoT and AI technologies, the demand for green, multifunctional supercapacitors and sensor materials is becoming increasingly urgent in fields such as human-computer interaction, electronic skin, and health monitoring. Carbon aerogels, due to their excellent conductivity and large specific surface area, are considered a highly promising candidate material.

[0003] However, traditional carbon aerogel preparation processes often rely on chemical raw materials such as phenolic resins and resorcinol. Although these raw materials can endow carbon aerogels with good crosslinking properties, their production processes are relatively cumbersome and pose serious environmental pollution problems. In addition, the high cost of raw materials and the poor mechanical properties caused by the disordered gel structure have, to some extent, limited the widespread application of carbon aerogels in the field of flexible electronic devices.

[0004] Against this backdrop, seeking green, sustainable, low-cost, and non-toxic precursor systems for the preparation of carbon aerogels is particularly important. This not only helps reduce production costs but also effectively reduces environmental pollution, achieving sustainable development. Meanwhile, exploring carbon aerogels with simple production processes and tunable microstructures is also a current research hotspot.

[0005] In recent years, scientists have begun to explore the use of biomass resources, such as biomass waste and biomass oils, as precursors to prepare carbon aerogels. These biomass resources are not only widely available and inexpensive, but also possess good biocompatibility and environmental friendliness. By optimizing the preparation process, precise control over the microstructure of carbon aerogels can be achieved, thereby improving their mechanical properties and expanding their applications in flexible electronic devices.

[0006] For example, using agricultural waste such as rice straw and corn stalks as carbon sources, carbon aerogels with excellent conductivity and high specific surface area can be prepared through a simple carbonization process. These carbon aerogels show promising application prospects in the fields of supercapacitors and sensors. Furthermore, by introducing nanofillers and constructing composite structures, the performance of carbon aerogels can be further improved to meet the needs of more fields.

[0007] In conclusion, with the growing acceptance of green and sustainable development concepts, the development of green and multifunctional carbon aerogel materials has become an urgent priority. Exploring green and sustainable precursor systems, optimizing production processes, and controlling microstructure hold promise for opening new avenues for the application of carbon aerogels in flexible electronic devices and providing strong support for the development of IoT and AI technologies. Summary of the Invention

[0008] This invention addresses the shortcomings of existing technologies by providing a bifunctional layered carbon aerogel, its preparation method, and its applications.

[0009] To achieve the above objectives, the present invention adopts the following technical solution:

[0010] On one hand, the present invention provides a method for preparing bifunctional layered carbon aerogel, comprising the following steps:

[0011] S1. Prepare a precursor solution of nanocellulose, chitosan, graphene oxide, activator and crosslinking agent, then pour the precursor solution into a mold and prepare a hydrogel by thermal crosslinking.

[0012] S2. Place an L-shaped copper plate at the bottom of the mold containing hydrogel in S1. One side of the L-shaped copper plate is attached to the bottom of the mold, and the other side is in contact with the side of the mold. The height of the copper plate on this side is located at 1 / 3 to 2 / 3 of the height of the side of the mold. Apply liquid nitrogen to the side of the copper plate that is attached to the bottom of the mold, so that ice crystals grow in a directional manner both inside and on the side of the hydrogel.

[0013] S3. The hydrogel frozen in step S2 is freeze-dried under vacuum to prepare a layered aerogel.

[0014] S4. Place the layered aerogel prepared in step S3 into a tube furnace for carbonization to obtain layered carbon aerogel.

[0015] Further, in step S1, the mass ratio of the nanocellulose, chitosan, and graphene oxide is 1:1:1.

[0016] Further, in step S1, the activator is zinc chloride, and its amount is used in a mass ratio of 1:1 with that of nanocellulose.

[0017] Further, in step S1, the crosslinking agent is glutaraldehyde, and its amount is used in a mass ratio of 1:5 with that of nanocellulose.

[0018] Further, in step S1, the thermal crosslinking involves placing the mold containing the precursor solution in a vacuum oven and heating it in a vacuum environment at 50-60°C for 1-2 hours.

[0019] Furthermore, in step S3, the freeze-drying conditions are -60℃, freezing for 72 hours, and a vacuum degree of 1 Pa.

[0020] Furthermore, in step S4, the carbonization temperature is 900℃, the heating rate is 3℃ / min, the holding time is 2h, and the protective atmosphere is argon.

[0021] On the other hand, the present invention provides a bifunctional layered carbon aerogel obtained by the above preparation method.

[0022] In another aspect, the present invention provides the application of the above-mentioned bifunctional layered carbon aerogel in the preparation of supercapacitors and pressure sensors.

[0023] The beneficial effects of this invention are as follows: This invention designs a low-energy bidirectional freezing method, using natural renewable cellulose nanofibers (CNF) and chitosan (CS) as biomatrix and graphene oxide (GO) as conductive filler, successfully preparing high-performance multifunctional carbon aerogels. Compared to unidirectional and isotropic freezing, bidirectional freeze-drying technology can more effectively control the pore structure and pore size distribution of aerogels when preparing aerogel supercapacitors. This method, by freezing the material from two directions, promotes the uniform growth of ice crystals within the material, thereby forming a more uniform and interconnected pore network during the drying process. Such a pore structure helps reduce the transport paths of ions in the electrolyte, improving ion transport efficiency, thus enhancing the charge storage capacity and power density of the supercapacitor. Simultaneously, bidirectional freezing can also improve the mechanical strength and structural stability of the material, making it more stable and reliable in long-term use.

[0024] Experimental results show that carbon aerogel has a large specific surface area (622.79 m²). 2 The carbon aerogel electrode material exhibits high specific capacitance (299 F / g at 1 A / g) in a three-electrode system and can withstand 80% high-pressure strain. Assembled symmetric solid-state supercapacitors were tested in a two-electrode system, which demonstrated excellent areal specific capacitance (1.8 mA / cm²). 2 The value was 381.8 mF / cm 2 The carbon aerogel exhibits good cyclic stability (91.8% capacitance retention after 5000 cycles). Furthermore, it possesses a capacitance of 25.2 kPa. -1 Its excellent linear sensitivity allows it to be assembled into pressure sensors for real-time monitoring of biosignals from the fingers, wrists, throat, and other parts of the body. These superior properties enable carbon aerogels to be used in energy storage devices and wearable electronics. Attached Figure Description

[0025] Figure 1 This is a schematic diagram of the preparation process of layered carbon aerogel;

[0026] Figure 2 This is a macroscopic morphology diagram of layered carbon aerogel;

[0027] Figure 3 The image shows the microstructure of layered carbon aerogel.

[0028] Figure 4In the figure, (a) is the nitrogen adsorption-desorption isotherm of carbon aerogel, and (b) is the pore size distribution diagram;

[0029] Figure 5 In the figure, (a) is the compression cycle curve of carbon aerogel under 20-80% strain, and (b) is the curve of 500 cycles under 40% strain.

[0030] Figure 6 In the figure, (a) is the cyclic voltammetry curve of carbon aerogel at a scan rate of 5-100 mV / s, (b) is the charge-discharge curve at a current density of 1-5 A / g, and (c) is the electrochemical impedance spectroscopy.

[0031] Figure 7 In the figure, (a) is a schematic diagram of the assembly of a solid supercapacitor, (b) is the cyclic voltammetry curve of the supercapacitor at 5 to 100 mV / s, (c) is the charge-discharge curve of the supercapacitor at 1.8 to 8 mA / cm2, (d) is the areal capacitance of the supercapacitor, (e) is the Ragone plot of the supercapacitor, and (f) is the cyclic stability of the supercapacitor.

[0032] Figure 8 In the figure, (a) the cyclic voltammetry curve of the electrode sample with the side height of the copper plate at 2 / 5 of the mold at 1 A / g, and (b) the EIS plot;

[0033] Figure 9 In the figure, (a) the cyclic voltammetry curve of the electrode sample with the copper plate side height at 4 / 5 of the mold at 1 A / g, and (b) the EIS plot;

[0034] Figure 10 In the diagram, (a) shows the brightness variation of the LED lights connected in series with the carbon aerogel, (b) shows the current signal variation at 20–80% strain, (c) shows the current signal variation at different compression rates, and (d) shows the current signal variation of the carbon aerogel at 0–12.5 kPa. -1 Linear sensitivity within the pressure range, (e) is the response and recovery time of the carbon aerogel, and (f) is the current response over 2000 cycles.

[0035] Figure 11 In the diagram, (a) is a schematic diagram of the carbon aerogel-based sensor assembly, (b) is a finger pressing, (c) is a finger bending, (d) is a wrist bending, (e) is a change in current signal caused by knee bending, (f) is a change in current signal caused by continuous swallowing while drinking water, (g) and (h) are changes in current signal caused by saying the English words Yes and No, and (i) to (l) are current signals generated by tracing the letters N, J, F and U with the fingers, respectively. Detailed Implementation

[0036] In one embodiment, such as Figure 1As shown, a method for preparing a bifunctional layered carbon aerogel specifically includes the following steps:

[0037] S1. Add 0.05g of chitosan to 10mL of 1% acetic acid solution, and then stir in a 50℃ water bath for 40min to obtain a chitosan solution (5mg / mL). Take the same mass of nanocellulose suspension (5mg / mL), chitosan solution (5mg / mL) and graphene oxide suspension (5mg / mL), mix and stir, and sonicate for 1h to obtain a mixed solution; then take 0.1g of zinc chloride and 50uL of 50% glutaraldehyde solution and add them to the above solution in sequence and stir for 20min; then pour the obtained solution into a polytetrafluoroethylene cube mold and transfer it to a vacuum drying oven, and perform thermal crosslinking treatment at 60℃ for 1h to obtain a mixed hydrogel;

[0038] S2. Place an L-shaped copper plate at the bottom of the mold containing hydrogel in S1. One side of the L-shaped copper plate is attached to the bottom of the mold, and the other side is in contact with the side of the mold. The height of the copper plate on this side is located at 1 / 3 to 2 / 3 of the height of the side of the mold. Apply liquid nitrogen to the side of the copper plate that is attached to the bottom of the mold, so that ice crystals grow in a directional manner both inside and on the side of the hydrogel.

[0039] S3. The hydrogel obtained by bidirectional freezing in step S2 is freeze-dried in a freeze dryer at -60°C and 1Pa for 72 hours to obtain a layered aerogel.

[0040] S4. The layered aerogel prepared above is carbonized in a tube furnace at a temperature of 900°C under argon atmosphere and a heating rate of 3°C / min to obtain layered carbon aerogel.

[0041] In another embodiment, a bifunctional layered carbon aerogel is obtained by the above preparation method. Figure 2 The image shows the macroscopic morphology of carbon aerogel. It can be placed on a bamboo leaf without bending the leaf, indicating that carbon aerogel is lightweight and has a low density. Figure 3 The image shows a scanning electron microscope (SEM) image of the prepared carbon aerogel. It can be seen that the carbon aerogel has a dense, parallel layer structure with an interlayer spacing of approximately 100 μm. This orderly arrangement of layers not only allows the carbon aerogel to maintain its original height well after compression but also facilitates stress transfer. Figure 4 These are the N2 adsorption / desorption isotherms and pore size distribution curves of carbon aerogel. From Figure 4 As shown in (a), the N2 adsorption / desorption isotherms of the carbon aerogel belong to Type I in the IUPAC classification. The isotherms increase sharply in the low-pressure region and tend to plateau in the high-pressure region, indicating the presence of a large number of microporous structures. Additionally, an H4-type hysteresis loop was observed, corresponding to the presence of some mesopores. The results indicate that the specific surface area of ​​the carbon aerogel is 622.79 m². 2 / g. For example... Figure 4 As shown in (b), the pore size of the carbon aerogel is mainly concentrated around 2 nm, and it is mainly composed of micropores and mesopores. Micropores are beneficial for charge storage and the diffusion of electrolyte ions, while mesopores can obtain more reaction sites. Figure 5 (a) The stress-strain curve of the carbon aerogel steepens with increasing strain, indicating that it can withstand at least 80% strain, demonstrating good compressive properties. At 80% strain, the stress is 11.4 kPa. Figure 5 (b) The carbon aerogel exhibits excellent compression cycle performance with only a 7% decrease in stress after 500 cycles at 40% strain.

[0042] In another embodiment, a supercapacitor was fabricated using layered carbon aerogel. The carbon aerogel was used directly as the working electrode in a 3M potassium chloride electrolyte without the addition of any additional conductive agents or binders. The electrochemical performance of the carbon aerogel was measured using a three-electrode system. Figure 6 (a) The cyclic voltammetry curves of the carbon aerogel electrode at different scan rates of 5-100 mV / s maintain an approximately rectangular shape, indicating that the electrode exists in the form of an electric double layer capacitor. Figure 6 (b) shows the charge-discharge curves of the carbon aerogel electrode at different current densities. The curve profiles are symmetrical triangles, exhibiting ideal capacitance characteristics. The specific capacitance of the electrode was calculated according to the formula C=IΔt / mΔV. At a current density of 1A / g, the specific capacitance is 299F / g, and at 5A / g, the specific capacitance is 192F / g. Figure 6 (c) shows the Nyquist impedance plot of the electrode in the frequency range of 0.01 Hz to 100 kHz. The curve consists of a semicircle in the high-frequency region and an approximately perpendicular straight line in the low-frequency region. This indicates that the carbon aerogel electrode has low charge transfer resistance and fast ion diffusion capability.

[0043] To evaluate the feasibility of carbon aerogel as an electrode, a sandwich-type symmetrical supercapacitor was assembled using two carbon aerogels of equal mass, a polyvinyl alcohol / sulfuric acid gel electrolyte, and a cellulose nonwoven membrane. Figure 7 a) The electrochemical performance of a symmetrical supercapacitor was investigated in a two-electrode system. For example... Figure 7 (b) The cyclic voltammetry curves of the carbon aerogel solid-state supercapacitor exhibit an approximately rectangular shape, which is well maintained even at a high scan rate of 100 mV / s, indicating its good rate performance. At different current densities, the charge-discharge curves of the supercapacitor show an approximately symmetrical triangular shape, which also indicates its good electrochemical reversibility. Figure 7 c). Calculated using the formula C=IΔt / SΔV, at 1.8mA / cm 2 At a current density of 381.8 mF / cm, the supercapacitor exhibits a current density of 381.8 mF / cm. 2High area ratio capacitor ( Figure 7 d). The energy density of a supercapacitor is given by the formula E = CΔV. 2 The power density is calculated using the formula P = E × 3600 / Δt, with a power density of 727.9 μW / cm². 2 It exhibits an extraordinary energy density of 33.9 μWh / cm³. 2 ( Figure 7 e). Furthermore, the supercapacitor exhibits excellent cycle stability, retaining 91.8% of its capacitance value after 5000 charge-discharge cycles. Figure 7 f). The excellent electrochemical properties of supercapacitors can be attributed to the unique, ordered layered structure of carbon aerogel, which provides abundant active sites and promotes the transfer of electrolyte ions.

[0044] For comparison, the side height of the L-shaped copper plate at 1 / 5 of the mold was also prepared and measured. Figure 8 ) and 4 / 5 of the places ( Figure 9 Electrode samples. Figure 8 In the middle, the electrode has a specific capacitance of 231.8 F / g at 1 A / g. Figure 9 In the experiment, the electrode exhibited a specific capacitance of 205.3 F / g at 1 A / g. This is likely attributed to the fact that bidirectional freeze-drying technology, compared to unidirectional and isotropic freeze-drying, allows for more effective control of the pore structure and pore size distribution of the aerogel during the fabrication of the aerogel supercapacitor. This method, by freezing the material from two directions, promotes the uniform growth of ice crystals within the material, thereby forming a more uniform and interconnected pore network during the drying process. Such a pore structure helps reduce the transport paths of ions in the electrolyte, improving ion transport efficiency and thus enhancing the charge storage capacity and power density of the supercapacitor.

[0045] The excellent compression cycle performance of carbon aerogel is a key element for its use as a pressure sensor; therefore, a series of pressure-current relationship tests were conducted to explore its sensing performance. In a closed-loop circuit, an LED light was connected in series with the carbon aerogel. It was observed that the LED light gradually brightens as the pressure increases, and dims after the pressure is released. Figure 10 a) This reflects the gradual decrease in resistance of carbon aerogel during compression, leading to a continuous increase in current. For example... Figure 10 As shown in (b), the real-time current response of the carbon aerogel under different compressive strains was measured. The current rises rapidly during compression, falls rapidly during release, and increases with increasing strain. Even at 80% strain, the curve maintains a symmetrical shape, indicating that the carbon aerogel can operate over a wide strain range. Furthermore, the current signal response of the carbon aerogel remains essentially consistent and symmetrical under the same strain but different compression rates. This demonstrates the excellent stability of the carbon aerogel, which is of great significance for its practical applications. Figure 10 c). Meanwhile, carbon aerogel sensing materials exhibit outstanding sensitivity and linear response over a wide pressure range. Figure 10 d). The sensitivity is calculated using the formula S=(ΔI / I0) / ΔP. Within the pressure range of 0-12.5kPa, the sensitivity is 25.2kPa. -1 The high sensitivity of carbon aerogels can be attributed to: (1) the ordered and stable structure of carbon aerogels ensures effective stress transmission; (2) good compressibility allows them to work over a wide strain range; and (3) under external force, the distance between carbon layers decreases, resulting in a continuous increase in contact area, leading to a proportional decrease in resistance and a significant increase in current signal. Carbon aerogels not only possess excellent linear sensitivity but also exhibit rapid signal response. Figure 10 As shown in (e), the response time of the carbon aerogel is 91 ms, and the recovery time is 109 ms. To verify the durability of the prepared carbon aerogel as a sensor material, it was subjected to 2000 consecutive compression-release cycles at 30% strain. Figure 10 As observed in (f), after 2000 cycles, the current signal of the sensor decayed very little and remained almost unchanged, indicating that carbon aerogel has excellent fatigue resistance and stability.

[0046] In yet another embodiment, the sensor is fabricated using layered carbon aerogel. The carbon aerogel is arranged according to… Figure 11 (a) A simple sensor device was assembled and successfully captured biosignals of human movement. Pressing the carbon aerogel sensor with a finger showed regular signal changes. Figure 11 (b) Meanwhile, the carbon aerogel sensor exhibits good repeatability and stability for different movements of the fingers, wrists, and knees. By wearing the sensor on the finger, fluctuating current signals generated by finger flexion can be easily monitored. The current signal output significantly increases with increasing finger flexion. Figure 11 c). Regular changes in electrical signals can also be detected during continuous flexion of the wrist and knee. Figure 11 (d, e) When bent, the carbon aerogel is compressed, reducing resistance and increasing current, but the current returns to its original state when the wrist and knee are straightened. Surprisingly, the sensor can detect minute motion signals. Attaching the carbon aerogel sensor to the throat allows for the clear capture of its slight vibrations, such as successfully monitoring changes in the current signal caused by continuous swallowing while drinking water. Figure 11 f). For example Figure 11As shown in (g, h), the carbon aerogel sensor can also clearly distinguish the pronunciation of different words. For example, when saying "Yes" and "No," the output current signal shows a significant difference, but the current signal for the same word pronunciation cycle is almost the same. These results indicate that the carbon aerogel sensor has high sensitivity and good stability. Furthermore, in addition to monitoring human joint movements and minute movements, the carbon aerogel sensor can also monitor complex movements. For example, by attaching the carbon aerogel sensor to a finger, it can trace the letter "N" appearing on a computer screen in space. Figure 11 i), "J" Figure 11 j), "F" Figure 11 k) and "U" Figure 11 (l) As can be seen from the figure, the current signal curves output by different letters are different. This is because the differences in letter structure cause specific deformations in the carbon aerogel sensor, resulting in different current signals. Furthermore, when repeatedly depicting the same letter, the current signal shows a similar trend, indicating that the sensor has good repeatability. In summary, the carbon aerogel pressure sensor can perform accurate pressure monitoring and can be practically applied in wearable electronic devices.

Claims

1. A method for preparing a bifunctional layered carbon aerogel, characterized in that, Includes the following steps: S1. Prepare a precursor solution of nanocellulose, chitosan, graphene oxide, activator and crosslinking agent, then pour the precursor solution into a mold and prepare a hydrogel by thermal crosslinking. The mass ratio of the nanocellulose, chitosan, and graphene oxide is 1:1:1; The activator is zinc chloride, and its mass ratio to nanocellulose is 1:

1. The crosslinking agent is glutaraldehyde, and its dosage is 1:5 with the mass ratio of nanocellulose. The thermal crosslinking involves placing a mold containing the precursor solution in a vacuum oven and heating it in a vacuum environment at 50-60°C for 1-2 hours. S2. Place an L-shaped copper plate at the bottom of the mold containing hydrogel in S1. One side of the L-shaped copper plate is attached to the bottom of the mold, and the other side is in contact with the side of the mold. The height of the copper plate on this side is located at 1 / 3 to 2 / 3 of the height of the side of the mold. Apply liquid nitrogen to the side of the copper plate that is attached to the bottom of the mold, so that ice crystals grow in a directional manner both inside and on the side of the hydrogel. S3. The hydrogel frozen in step S2 is freeze-dried under vacuum to prepare a layered aerogel. The freeze-drying conditions were -60℃, freezing for 72 hours, and a vacuum degree of 1 Pa. S4. The layered aerogel prepared in step S3 is placed in a tube furnace for carbonization to obtain a layered carbon aerogel. The carbonization temperature is 900℃, the heating rate is 3℃ / min, the holding time is 2h, and the protective atmosphere is argon.

2. The bifunctional layered carbon aerogel obtained by the preparation method according to claim 1.

3. The application of the bifunctional layered carbon aerogel as described in claim 2 in the preparation of supercapacitors and pressure sensors.

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