Wood-based piezoelectric / friction / pyroelectric composite monolithic integrated nano generator and preparation method thereof

Abstract

The invention provides a wood-based piezoelectric / friction / pyroelectric composite monolithic integrated nano-generator and a preparation method thereof, which are characterized in that chemically treated wood is used as a triboelectric positive material, silica gel is used as a triboelectric negative material, a large amount of hemicelluloses and lignin are removed from the cell wall of the wood through simple chemical treatment, and the piezoelectric / friction / pyroelectric composite monolithic integrated nano-generator is prepared. The natural rigid wood becomes more porous, meanwhile, the structure of the cellulose is well reserved, and due to the unique structure, the functional material can permeate into a cavity of the guide pipe to form conductive wood or piezoelectric wood, so that the high-performance wood-based piezoelectric / friction / pyroelectric composite monolithic integrated nano generator is realized. The high-performance wood-based composite nano generator is simple in structure and low in cost, and has wide application prospects in wearable electronic products and sustainable energy sources.

Description

Technical Field

[0001] The present invention relates to the technical field of triboelectric nanogenerators, and particularly to a wood-based piezoelectric / triboelectric / pyroelectric composite monolithic integrated nanogenerator and a preparation method thereof. Background Art

[0002] With the rapid development of the Internet of Things, revolutionary changes have taken place in a wide range of application fields such as smart home, medical care, environmental protection, and public safety. The field of energy harvesting has also been greatly affected by technological progress and has entered the digital age. Currently, wearable electronic products are usually powered in traditional ways, such as batteries. Considering environmental problems, high replacement or charging costs, and limited service life, it is highly desirable to develop sustainable energy harvesting technologies.

[0003] One way to solve the above problems is to harvest energy from the surrounding environment. There are usually five technologies for environmental energy harvesting: photovoltaic effect, thermoelectric effect, electromagnetic effect, piezoelectric effect, and triboelectric effect. Among them, triboelectric nanogenerators that utilize the coupling of triboelectric effect and electrostatic induction have been proven to be effective candidates for harvesting micro-nano energy. Currently, most of the materials used in triboelectric nanogenerators are non-degradable synthetic polymers, such as PTFE, PVDF, and PDMS. However, most of these materials are not biodegradable and will cause environmental pollution. In this case, natural materials represent a new type of triboelectric layer material and show great potential in this field.

[0004] As a renewable, sustainable, and biodegradable material, natural wood has been given a new identity in the field of electronic science. Especially in the field of energy harvesting, wood is now mostly used as the raw material for triboelectric nanogenerators, piezoelectric nanogenerators, and energy storage electrodes. However, the triboelectric series of natural wood itself is relatively neutral and it is not easy to generate high charge separation, resulting in a low output power of the triboelectric nanogenerator. Its piezoelectricity is weak and it does not have conductivity, which limits its application in electronic devices. Summary of the Invention

[0005] In view of the above problems, the present invention proposes a wood-based piezoelectric / frictional / pyroelectric composite monolithic integrated nanogenerator and a preparation method thereof. By filling polyvinylidene fluoride and silver nanowires into wood, more excellent performance can be achieved. Polyvinylidene fluoride has high polarization characteristics and is a typical negative triboelectric material. After being filled into wood, it can enhance the triboelectric charge separation ability and improve the output. When the temperature changes, the polarization intensity of polyvinylidene fluoride changes, generating pyroelectric output. After filling into the wood pores, excellent conductive materials can effectively reduce the resistance and improve the electron transport ability as electrodes. Through the strategy of filling polyvinylidene fluoride + silver nanowires, wood has triboelectric, piezoelectric and pyroelectric characteristics, providing a new idea for the development of efficient, low-cost and environmentally friendly wood-based piezoelectric / frictional / pyroelectric composite nanogenerators.

[0006] A preparation method of a wood-based piezoelectric / frictional / pyroelectric composite monolithic integrated nanogenerator, the method comprising:

[0007] Step S1: Prepare chemically treated wood. First, wash the wood chip samples with ethanol and dry them in a vacuum drying oven at 50°C - 80°C for 1 h to remove moisture. Then, prepare a mixed solution A of NaOH and Na2SO3, place the mixed solution A on a heating table at 120°C - 150°C and heat it to boiling, and then soak the moisture-removed wood in the mixed solution A for 6 h. Then, wash it 3 times with a mixed solution of deionized water and ethanol, and obtain chemically treated wood after vacuum freeze-drying;

[0008] Step S2: Prepare wood with piezoelectric / pyroelectric composite characteristics on the front side. First, prepare a mixed solution B of polyvinylidene fluoride and dimethylformamide, soak the front side of the chemically treated wood in the mixed solution B for 1 h, and perform vacuum treatment. Then, take out the wood with the front side soaked in the mixed solution B, fix it on a glass substrate, and place it in an oven at 50°C - 80°C to dry for 6 h. Finally, attach 1.5 cm × 1.5 cm copper tapes to the upper and lower surfaces of the dried wood, apply a voltage of 10 kV at one end and ground the other end at 90°C, and perform polarization treatment for 90 min to obtain wood with piezoelectric / pyroelectric composite characteristics;

[0009] Step S3: Prepare wood with conductive characteristics on the back side. First, configure an ethanol dispersion liquid C of 10 mL silver nanowires, remove the copper tapes on both sides of the wood with piezoelectric / pyroelectric composite characteristics obtained above, then soak the back side in the mixed solution C for 1 h, and perform vacuum treatment. Then, take out the wood with the back side soaked in the mixed solution C, fix it on a glass substrate, and place it in an oven at 50°C - 80°C to dry for 6 h to obtain wood with conductive characteristics.

[0010] Further, the concentration of the NaOH solution is 2.5 mol / L, and the concentration of the Na2SO3 solution is 0.4 mol / L.

[0011] Further, the mass ratio of the mixed solution of polyvinylidene fluoride and dimethylformamide is 0.9 - 1.1:18.9 - 19.1.

[0012] Further, the concentration of the ethanol dispersion of silver nanowires is 2 mg / mL.

[0013] Further, the size of the wood chip sample is 1.5 cm × 1.5 cm × 1 mm.

[0014] The wood-based piezoelectric / frictional / pyroelectric composite monolithic integrated nanogenerator prepared by the above method uses wood doped with polyvinylidene fluoride with piezoelectric / pyroelectric composite characteristics as the triboelectric positive material. An electrode is provided on the back of the triboelectric positive material, and the electrode material is wood with conductive characteristics. The triboelectric positive material and the electrode material are integrated on the front and back of a single piece of wood.

[0015] The nanogenerator includes a piezoelectric / frictional / pyroelectric composite layer and a lower electrode layer stacked on top of each other from top to bottom. The piezoelectric / frictional / pyroelectric composite layer includes dispersed particles of polyvinylidene fluoride and chemically treated wood. The lower electrode layer includes silver nanowires and chemically treated wood. The lower electrode layer and the triboelectric positive wood with piezoelectric / pyroelectric composite characteristics are an integrated structure.

[0016] The working principle of the above wood-based high-performance piezoelectric / frictional / pyroelectric composite monolithic integrated nanogenerator device is as follows:

[0017] The conductive wood electrode using the electron conduction mechanism and the piezoelectric / pyroelectric wood are on the front and back of the same piece of wood. Connect a copper wire to the edge of the wood electrode, and then fix the entire device to a glass substrate. The combination of the piezoelectric / pyroelectric wood and the conductive wood aims to form a composite monolithic integrated nanogenerator with piezoelectricity, triboelectricity, and pyroelectricity, thereby improving the output performance. Use silicone as another contact pair, i.e., the triboelectric negative material, of the piezoelectric / frictional / pyroelectric composite single-electrode nanogenerator. The triboelectric part of this hybrid nanogenerator depends on the different electron gain and loss abilities of silicone and wood. Since PVDF exists on the surface, it has a similar ability to lose or attract electrons.

[0018] In a cycle, the silicone first approaches the wood, which means the distance between the two materials starts to decrease. When the distance decreases to zero, the silicone contacts the wood, and negative charges are transferred to the silicone because it has a stronger ability to capture electrons, while the wood loses electrons and thus exhibits a positive electrical property. Once the silicone starts to leave the wood, the contact mode ends, and the electrons lost by the wood are compensated through an external circuit. The external circuit refers to the conductive path connecting the wood and the silicone for electron transfer to balance the uneven charge distribution caused by the triboelectric effect. It includes the wire connecting the electrodes and an external load (which can be a resistor or a small electronic device, etc.). At this time, the potential difference between the two surfaces increases. At the end of a cycle, the distance between the two materials reaches the maximum value and starts to decrease again. Therefore, through simple contact separation, the device can output an alternating current signal.

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

[0020] The present invention is a single-electrode-structured piezoelectric / triboelectric / pyroelectric composite nanogenerator, with a simple structure. Compared with the traditional double-electrode contact-separation structure, it is easier to fabricate and integrate. The generator is composed of only one piece of wood. The front side is the wood with piezoelectric / pyroelectric characteristics, and the back side is the wood with conductive characteristics. The whole device realizes monolithic integration, reducing the complexity of manufacturing and assembly, which helps to improve production efficiency and reduce manufacturing costs;

[0021] The wood-based piezoelectric / triboelectric / pyroelectric composite monolithic integrated nanogenerator of the present invention uses wood as the base material. Wood is a renewable and environmentally friendly resource. Compared with using chemically synthesized materials, this choice helps to reduce the dependence on harmful chemicals and non-renewable resources and reduce the negative impact on the environment. Wood exhibits biocompatibility in many aspects. Therefore, the single-electrode-structured wood-based piezoelectric / triboelectric / pyroelectric composite nanogenerator may be more suitable for contact with organisms, such as for medical devices or wearable devices, which can reduce the adverse interactions with the human body or biological tissues. Moreover, since wood is a renewable resource and the production process is relatively simple, this type of generator has the potential to play a role in the field of sustainable energy;

[0022] Wood has an inherently porous microstructure, that is, it can be modified by filling functional materials inward. Moreover, the porous structure of wood means that it has a relatively large specific surface area, that is, a large surface area per unit volume, which enables wood to accommodate more functional materials, such as conductive materials, piezoelectric materials, pyroelectric materials, etc., thereby endowing wood with different properties. Further, the pore distribution of wood is usually relatively uniform, which can evenly disperse and load functional materials, which helps to ensure the uniform distribution of functional materials throughout the wood structure, thereby improving the consistency and reliability of performance. In addition, the pore structure of wood can be regulated by chemical treatment methods. For example, a mixed solution of NaOH and Na2SO3 can remove most of the lignin and hemicellulose on the wood cell wall, thereby increasing the pore diameter to load more functional materials. Brief Description of the Drawings

[0023] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required for the description of the embodiments or the prior art. Obviously, the drawings in the following description are some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can also be obtained based on these drawings.

[0024] Figure 1 It is a schematic structural diagram of a wood-based piezoelectric / frictional / pyroelectric composite monolithic integrated nanogenerator provided by an embodiment of the present invention;

[0025] Figure 2 It is a schematic diagram of the working mechanism of a wood-based piezoelectric / frictional / pyroelectric composite monolithic integrated nanogenerator provided by an embodiment of the present invention, where a is the mechanism of the piezoelectric effect and b is the mechanism of the triboelectric effect;

[0026] Figure 3 It is an SEM image of a wood-based piezoelectric / frictional / pyroelectric composite monolithic integrated nanogenerator provided by an embodiment of the present invention, where a is the front SEM image and b is the back SEM image;

[0027] Figure 4 It is an output voltage curve graph of a composite nanogenerator based on the piezoelectric effect, pyroelectric effect, and triboelectric effect provided by an embodiment of the present invention;

[0028] Figure 5 It is an output current curve graph of a composite nanogenerator based on the piezoelectric effect, pyroelectric effect, and triboelectric effect provided by an embodiment of the present invention;

[0029] Figure 6 It is a graph showing the relationship between the peak power of a composite nanogenerator based on the piezoelectric effect, pyroelectric effect, and triboelectric effect provided by an embodiment of the present invention and the external load;

[0030] Figure 7 It is the output voltage curve graph of the application of the composite nanogenerator based on piezoelectric effect, pyroelectric effect and triboelectric effect provided by the embodiment of the present invention to human gait detection.

[0031] Explanation of reference numerals: 10 - piezoelectric / triboelectric / pyroelectric composite layer, 11 - dispersed particles of polyvinylidene fluoride, 12 - chemically treated wood, 20 - lower electrode layer, 21 - silver nanowires, 3 - silica gel. Specific embodiments

[0032] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present invention.

[0033] As Figure 1 shown, a wood-based high-performance piezoelectric / triboelectric / pyroelectric composite monolithic integrated nanogenerator provided by the present invention includes a piezoelectric / triboelectric / pyroelectric composite layer 10 and a lower electrode layer 20 stacked in sequence from top to bottom. The piezoelectric / triboelectric / pyroelectric composite layer 10 is a triboelectric positive wood with piezoelectric / pyroelectric composite characteristics, and the lower electrode layer 20 and the triboelectric positive wood with piezoelectric / pyroelectric composite characteristics are the front and back sides of the same piece of wood.

[0034] The combination of the dispersed particles 11 of polyvinylidene fluoride and the chemically treated wood 12 realizes the piezoelectric / triboelectric / pyroelectric composite layer 10, and the combination of the silver nanowires 21 and the chemically treated wood 12 realizes the lower electrode layer 20.

[0035] The specific preparation process of a wood-based high-performance piezoelectric / triboelectric / pyroelectric composite monolithic integrated nanogenerator is as follows:

[0036] The wood chip samples are cleaned with ethanol and dried in a vacuum drying oven at 50 °C for 1 h to remove moisture;

[0037] A mixed solution A is prepared by mixing a NaOH solution with a concentration of 2.5 mol / L and a Na2SO3 solution with a concentration of 0.4 mol / L. The mixed solution A is placed on a heating table at 120 °C and heated to boiling. Then, the moisture-removed wood is immersed in the mixed solution A for 6 h, and then washed 3 times with a mixed solution of deionized water and ethanol, and vacuum freeze-dried to obtain the chemically treated wood;

[0038] Put the front side of the chemically treated wood into the mixed solution B of polyvinylidene fluoride and dimethylformamide for 1 h, and perform vacuum treatment. Then dry it in an oven at 50 °C for 6 h. Then attach copper tapes of 1.5 cm × 1.5 cm to the upper and lower surfaces of the dried wood. Apply a voltage of 10 kV at one end and ground the other end at 90 °C for 90 min for polarization treatment to obtain wood with piezoelectric / pyroelectric composite properties. The mass ratio of the mixed solution of polyvinylidene fluoride and dimethylformamide is 1:19;

[0039] Prepare 10 mL of the ethanol dispersion C of silver nanowires. Remove the copper tapes on both sides of the wood with piezoelectric / pyroelectric composite properties obtained above. Then soak the reverse side in the mixed solution C for 1 h and perform vacuum treatment. Finally, place it in an oven at 50 °C for 6 h to obtain wood with conductive properties. The concentration of the ethanol dispersion of silver nanowires is 2 mg / mL;

[0040] Cut the overall size to 1.5 cm × 1.5 cm × 1 mm to obtain a wood-based high-performance piezoelectric / friction / pyroelectric composite monolithic integrated nanogenerator device.

[0041] The working mechanism of the piezoelectric / friction / pyroelectric composite monolithic integrated nanogenerator is as Figure 2As shown in the figure, a layer of silicone 3 is used as the triboelectric negative material. Figure a shows the mechanism of the piezoelectric effect. Polyvinylidene fluoride particles with piezoelectric / pyroelectric composite properties are filled into the pores of chemically treated wood. When there is no external pressure, the whole is electrically neutral. When mechanical stress (such as tensile, compressive or shear force) is applied to the device, the positive and negative charges of the internal dipoles are separated, resulting in the accumulation of charges at both ends of the material, forming a piezoelectric potential. When the temperature changes, the polarization intensity of the material changes, and charges will also be generated on the surface of the material, that is, polyvinylidene fluoride has both piezoelectric and pyroelectric properties. Figure b shows the mechanism of the triboelectric effect. In one cycle, silicone 3 first approaches the wood, which means that the distance between the two materials begins to decrease. When the distance decreases to zero, silicone 3 contacts the wood piezoelectric / triboelectric / pyroelectric composite layer 10, and negative charges transfer to silicone 3 because it has a stronger ability to capture electrons, while the wood piezoelectric / triboelectric / pyroelectric composite layer 10 loses electrons, thus showing a positive electrical property. Once silicone 3 begins to leave the wood piezoelectric / triboelectric / pyroelectric composite layer 10, the contact mode ends, and the electrons lost by the wood piezoelectric / triboelectric / pyroelectric composite layer 10 are compensated through an external circuit. The external circuit refers to the conductive path connecting the wood and silicone 3 for electron transmission to balance the uneven charge distribution caused by the triboelectric effect, including the wire connecting the electrodes and the external load (which can be a resistor or a small electronic device, etc.). At this time, the potential difference between the two surfaces increases. At the end of one cycle, the distance between the two materials reaches the maximum value and begins to decrease again. Therefore, through simple contact separation, the device can output an alternating current signal.

[0042] The front and back surfaces of the wood-based piezoelectric / triboelectric / pyroelectric composite monolithic integrated nanogenerator device were observed microscopically using a scanning electron microscope, and the SEM photos shown in Figure 3 were obtained. Among them, Figure 3 a in the figure is the front SEM photo of the wood-based piezoelectric / triboelectric / pyroelectric composite monolithic integrated nanogenerator, Figure 3 and b in the figure is the back SEM photo of the wood-based piezoelectric / triboelectric / pyroelectric composite monolithic integrated nanogenerator.

[0043] The output voltage of the fabricated piezoelectric / triboelectric / pyroelectric composite single-electrode nanogenerator device was tested using an oscilloscope. At room temperature, the device to be measured was placed on the test platform, and the signal frequency and amplitude were set through a signal generator. The vibration table connected to it applied a certain pressure regularly to the device under test. A layer of silicone 3 was covered at the bottom of the vibration mass of the vibration table as the triboelectric negative material, which repeatedly contacted and separated from the device under external force. Then, the real-time voltage output change of the composite single-electrode nanogenerator could be observed on the oscilloscope. During the reciprocating movement of the vibration table, the triboelectric positive material and the triboelectric negative material repeatedly contacted and separated, and the results were as followsFigure 4 The output voltage shown

[0044] An oscilloscope and a current amplifier were used to test the output current of the fabricated piezoelectric / triboelectric / pyroelectric composite single-electrode nanogenerator device. Under room temperature conditions, the device to be measured was placed on the above-mentioned vibration test platform. A layer of silica gel 3 was covered at the bottom of the vibration mass of the vibration table as the triboelectric negative material, which repeatedly contacted and separated from the device under an external force. Through the establishment of the current amplifier and oscilloscope system, the real-time current output change of the composite single-electrode nanogenerator could be observed on the oscilloscope. During the reciprocating movement of the vibration table, the triboelectric positive material and the triboelectric negative material repeatedly contacted and separated, and the output current shown as Figure 5 was obtained.

[0045] An oscilloscope was used to conduct a matching load test on the fabricated piezoelectric / triboelectric / pyroelectric composite single-electrode nanogenerator device. Under room temperature conditions, the device to be measured was placed on the above-mentioned vibration test platform. At the same time, resistors with different resistance values were connected in series at the output end of the generator. When the resistance value of the external resistor was changed, the voltage across the external resistor measured by the oscilloscope changed accordingly. The peak voltage was recorded as V, and the output peak power of the generator was calculated through the formula which is Figure 6 the corresponding relationship diagram between the peak power of the composite nanogenerator and the external load.

[0046] It can be seen from Figures 4 - 6 that the piezoelectric / triboelectric / pyroelectric composite single-electrode nanogenerator has excellent output performance. Compared with other nanogenerators, the present invention simplifies the processing technology without reducing the output performance.

[0047] The fabricated piezoelectric / triboelectric / pyroelectric composite single-electrode nanogenerator device was fixed on the sole of a shoe to detect the gait pattern during walking. Figure 7 shows the changes in the output voltage of the device when a person walks slowly and quickly.

[0048] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that they can still modify the technical solutions described in the foregoing embodiments, or perform equivalent replacements on some or all of the technical features; and these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A preparation method of a wood-based piezoelectric / frictional / pyroelectric composite monolithic integrated nanogenerator, characterized in that The method comprises the following steps: Step S1: Prepare chemically treated wood. First, wash the wood chip sample with ethanol and dry it at 50°C - 80°C in a vacuum drying oven for 1 h to remove moisture. Then, prepare a mixed solution A of NaOH and Na2SO3, place the mixed solution A on a heating table at 120°C - 150°C and heat it to boiling, and then immerse the moisture-removed wood in the mixed solution A for 6 h. Next, wash it 3 times with a mixed solution of deionized water and ethanol, and obtain the chemically treated wood after vacuum freeze-drying. Step S2: Prepare wood with piezoelectric / pyroelectric composite characteristics on the front side. First, prepare a mixed solution B of polyvinylidene fluoride and dimethylformamide, immerse the front side of the chemically treated wood in the mixed solution B for 1 h, and perform vacuum treatment. Then, take out the wood with the front side immersed in the mixed solution B, fix it on a glass substrate, and place it in an oven at 50°C - 80°C to dry for 6 h. Finally, attach 1.5 cm × 1.5 cm copper tapes to the upper and lower surfaces of the dried wood, apply a voltage of 10 kV at one end and ground the other end under the condition of 90°C, and perform polarization treatment for 90 min to obtain wood with piezoelectric / pyroelectric composite characteristics. Step S3: Prepare wood with conductive characteristics on the back side. First, prepare a 10 mL ethanol dispersion C of silver nanowires, remove the copper tapes on both sides of the wood with piezoelectric / pyroelectric composite characteristics obtained above, then immerse the back side in the mixed solution C for 1 h, and perform vacuum treatment. Then, take out the wood with the back side immersed in the mixed solution C, fix it on a glass substrate, and place it in an oven at 50°C - 80°C to dry for 6 h to obtain wood with conductive characteristics.

2. The preparation method according to claim 1, characterized in that, The concentration of the NaOH solution is 2.5 mol / L, and the concentration of the Na2SO3 solution is 0.4 mol / L.

3. The preparation method according to claim 1, characterized in that, The mass ratio of the mixed solution of polyvinylidene fluoride and dimethylformamide is 0.9 - 1.1:18.9 - 19.

1.

4. The preparation method according to claim 1, wherein The concentration of the ethanol dispersion of silver nanowires is 2 mg / mL.

5. The preparation method according to claim 1, characterized in that, The size of the wood chip sample is 1.5 cm × 1.5 cm × 1 mm.

6. A wood-based piezoelectric / frictional / pyroelectric composite monolithic integrated nanogenerator prepared by the preparation method according to any one of claims 1 to 5, characterized in that, The nanogenerator uses wood with piezoelectric / pyroelectric composite characteristics doped with polyvinylidene fluoride as the triboelectric positive material, and an electrode is provided on the back of the triboelectric positive material. The electrode material is wood with conductive characteristics, and the triboelectric positive material and the electrode material are integrated on the front and back sides of a single piece of wood.

7. The nanogenerator according to claim 6, characterized in that, The nanogenerator includes a piezoelectric / friction / pyroelectric composite layer and a lower electrode layer stacked sequentially from top to bottom. The piezoelectric / friction / pyroelectric composite layer includes dispersed particles of polyvinylidene fluoride and chemically treated wood, and the lower electrode layer includes silver nanowires and chemically treated wood. The lower electrode layer and the triboelectric positive wood with piezoelectric / pyroelectric composite characteristics are an integrated structure.

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