Self-powered flexible humidity sensor based on cellulose derivative as well as preparation method and application of self-powered flexible humidity sensor

Abstract

The invention provides a self-powered flexible humidity sensor based on a cellulose derivative and a preparation method and application thereof, and belongs to the technical field of sensors. The self-powered flexible humidity sensor based on the cellulose derivative comprises a flexible substrate, a bottom electrode, a porous composite functional layer and a top electrode which are sequentially arranged from bottom to top, the porous composite functional layer is a porous composite material formed by cellulose derivatives, polyvinyl alcohol and potassium hydroxide. The self-powered flexible humidity sensor based on the cellulose derivative is simple in structure and high in flexibility, and can be tightly attached to any surface; meanwhile, the porous carbon has a large specific surface area and porosity, adsorption and dissociation of the sensor to moisture are enhanced, the moisture absorption and dissociation speed of the device can be increased to a greater extent, the output voltage / current, the sensitivity and the response / recovery time of the device are effectively improved, and the sensing performance and the power supply performance of the device are comprehensively improved.

Description

Technical Field

[0001] This invention relates to the field of sensor technology, and in particular to a self-powered flexible humidity sensor based on cellulose derivatives, its preparation method, and its application. Background Technology

[0002] With the development of science and technology and industrial technology, humidity detection is becoming increasingly important in many fields such as industrial production, food preservation, agricultural management, environmental monitoring, and daily life. Currently, humidity sensors are the key means of humidity detection. With the development of information technology, humidity detection scenarios are becoming increasingly diverse, placing higher demands on the sensitivity, stability, energy efficiency, environmental friendliness, and portability of sensors. Traditional humidity sensors are mainly capacitive and resistive humidity sensors fabricated on rigid substrates. These traditional humidity sensors have the following drawbacks: First, rigid humidity sensors are poorly suited to the increasingly diverse humidity detection scenarios; therefore, flexible humidity sensors need to be developed to adapt to these scenarios. Second, traditional humidity sensors require external power, limiting their application. Therefore, developing a self-powered flexible humidity sensor has broad prospects.

[0003] Currently, based on the humidity response characteristics of hydrophilic polymer materials, flexible humidity sensors with self-powered capabilities can be fabricated using carboxymethyl cellulose composite films containing abundant hydrophilic groups (such as hydroxyl and carboxyl groups) as the functional layer of the device. This sensor utilizes the potential difference generated by ion migration driven by ambient humidity, exhibiting stable energy conversion and sensing performance in high-humidity environments. However, traditional single carboxymethyl cellulose films suffer from low humidity response sensitivity and weak electrical performance output due to insufficient hydrophilic group density and limited ion transport paths. This makes it difficult to meet the practical requirements of precise sensing and self-powered systems, limiting its further development and application in the sensing field. Summary of the Invention

[0004] The purpose of this invention is to provide a self-powered flexible humidity sensor based on cellulose derivatives with excellent sensing and power supply performance, as well as its preparation method and application.

[0005] To achieve the above-mentioned objectives, the present invention provides the following technical solution: This invention provides a self-powered flexible humidity sensor based on cellulose derivatives, comprising a flexible substrate, a bottom electrode, a porous composite functional layer, and a top electrode arranged sequentially from bottom to top; the porous composite functional layer is a porous composite material formed from cellulose derivatives, polyvinyl alcohol, and potassium hydroxide.

[0006] Preferably, the cellulose derivative includes one or more of sodium carboxymethyl cellulose, hydroxyethyl cellulose, hydroxypropyl cellulose, methyl cellulose, and hydroxypropyl methyl cellulose.

[0007] Preferably, the mass ratio of cellulose derivative, polyvinyl alcohol and potassium hydroxide in the porous composite functional layer is 75:(0~150):150.

[0008] Preferably, the thickness of the porous composite functional layer is 200 nm to 5 μm.

[0009] Preferably, the flexible substrate is a polymer film; the polymer film is made of one of polyimide, polydimethylsiloxane, and polyethylene terephthalate.

[0010] Preferably, the thickness of the flexible substrate is 1 μm to 1 mm.

[0011] Preferably, the bottom electrode is made of one of ITO, graphene, carbon nanotubes, and silver nanowires.

[0012] This invention also provides a method for preparing the self-powered flexible humidity sensor based on cellulose derivatives as described in the above technical solution, comprising the following steps: A bottom electrode is fabricated on one side surface of a flexible substrate; A cellulose derivative, polyvinyl alcohol, potassium hydroxide, and water are mixed to obtain a blend solution; the blend solution is coated on the surface of the bottom electrode and then freeze-dried to obtain a porous composite functional layer. A top electrode is fabricated on the surface of the porous composite functional layer to obtain a self-powered flexible humidity sensor based on cellulose derivatives.

[0013] Preferably, the freeze-drying temperature is -20 to -90°C; the freeze-drying time is 6 to 24 hours.

[0014] This invention also provides applications of the self-powered flexible humidity sensor based on cellulose derivatives described in the above technical solutions, or the self-powered flexible humidity sensor based on cellulose derivatives prepared by the preparation method described in the above technical solutions, in real-time monitoring of human body moisture status, dynamic monitoring of environmental moisture, monitoring of moisture processes in industrial production, precise monitoring of agricultural moisture, and moisture safety monitoring of electronic devices.

[0015] This invention provides a self-powered flexible humidity sensor based on cellulose derivatives, comprising a flexible substrate, a bottom electrode, a porous composite functional layer, and a top electrode arranged sequentially from bottom to top. The porous composite functional layer is a porous composite material formed from cellulose derivatives, polyvinyl alcohol, and potassium hydroxide. This invention utilizes a porous composite material formed from cellulose derivatives, polyvinyl alcohol, and potassium hydroxide as the porous composite functional layer. Polyvinyl alcohol in the porous composite functional layer has good adsorption and desorption properties for water molecules and can be used as a power generation material. The porous composite functional layer has a similar through-pore structure, which can enhance the transport capacity of ions or water. Potassium hydroxide in the porous composite functional layer has an adsorption effect on water molecules, allowing for the adsorption of more water molecules. The cellulose derivative has a fibrous nanocrystalline structure, enabling the transport of ions or water along the nanocrystalline structure, further enhancing the transmission capability of the self-powered flexible humidity sensor based on cellulose derivatives. Furthermore, the cellulose derivative has good biocompatibility. The self-powered flexible humidity sensor based on cellulose derivatives provided by this invention has a simple and flexible structure that can fit tightly to any surface. It also has a large specific surface area and porosity, which enhances the adsorption and dissociation of moisture by the sensor. This can greatly improve the absorption and dissociation speed of moisture by the device, effectively improve the output voltage / current, sensitivity, and response / recovery time of the device, and comprehensively improve the sensing performance and power supply performance of the device. Attached Figure Description

[0016] Figure 1 A schematic diagram of the structure of the self-powered flexible humidity sensor based on cellulose derivatives provided by the present invention; Figure 2 The electrical performance diagram of the self-powered flexible humidity sensor based on cellulose derivatives provided in Embodiment 1 of the present invention is shown. Figure 3 The electrical performance diagram of the self-powered flexible humidity sensor based on cellulose derivatives provided in Comparative Example 1 of the present invention is shown. Figure 4 The electrical performance diagram of the self-powered flexible humidity sensor based on cellulose derivatives provided in Comparative Example 2 of the present invention is shown. Figure 5 The images show the porous composite functional layers of the self-powered flexible humidity sensor based on cellulose derivatives in Embodiment 1 and Comparative Example 1 of the present invention. Detailed Implementation

[0017] This invention provides a self-powered flexible humidity sensor based on cellulose derivatives, comprising a flexible substrate, a bottom electrode, a porous composite functional layer, and a top electrode arranged sequentially from bottom to top; the porous composite functional layer is a porous composite material formed from cellulose derivatives, polyvinyl alcohol, and potassium hydroxide.

[0018] The self-powered flexible humidity sensor based on cellulose derivatives provided by the present invention includes a flexible substrate.

[0019] In this invention, the flexible substrate is preferably a polymer film. The polymer film is preferably made of one of polyimide, polydimethylsiloxane (PDMS), and polyethylene terephthalate (PET). The polymer film used in this invention exhibits excellent flexibility and mechanical properties.

[0020] In this invention, the thickness of the flexible substrate is preferably 1 μm to 1 mm, and more preferably 10 μm to 200 μm.

[0021] The self-powered flexible humidity sensor based on cellulose derivatives provided by the present invention includes a bottom electrode disposed on the flexible substrate.

[0022] In this invention, the bottom electrode is preferably made of one of the following materials: ITO, graphene, carbon nanotubes, and silver nanowires (AgNWs). The bottom electrode made of the above materials exhibits excellent conductivity and flexibility.

[0023] In this invention, the thickness of the bottom electrode is preferably 10nm~100nm, more preferably 30nm~60nm.

[0024] The self-powered flexible humidity sensor based on cellulose derivatives provided by the present invention includes a porous composite functional layer disposed on the bottom electrode.

[0025] In this invention, the porous composite functional layer is a porous composite material formed from cellulose derivatives, polyvinyl alcohol, and potassium hydroxide. This invention utilizes a porous composite material formed from cellulose derivatives, polyvinyl alcohol, and potassium hydroxide as the porous composite functional layer. Polyvinyl alcohol has good adsorption and desorption properties for water molecules and can be used as a power generation material. The porous composite functional layer has a similar through-pore structure, which can enhance the transport capacity of ions or water. The potassium hydroxide in the porous composite functional layer has an adsorption effect on water molecules, allowing for the adsorption of more water molecules. The cellulose derivative has a fibrous nanocrystalline structure, enabling the transport of ions or water along the nanocrystalline structure, further enhancing the transmission capability of the self-powered flexible humidity sensor based on the cellulose derivative. Furthermore, the cellulose derivative has good biocompatibility.

[0026] In this invention, the cellulose derivative preferably includes one or more of sodium carboxymethyl cellulose, hydroxyethyl cellulose, hydroxypropyl cellulose, methyl cellulose, and hydroxypropyl methyl cellulose, more preferably sodium carboxymethyl cellulose. This invention utilizes the above-mentioned cellulose derivative, which has a fibrous nanocrystalline structure, enabling the transport of ions or water along the nanocrystalline structure, further enhancing the transmission capability of the self-powered flexible humidity sensor based on the cellulose derivative.

[0027] In this invention, the preferred mass ratio of cellulose derivative, polyvinyl alcohol, and potassium hydroxide in the porous composite functional layer is 75:(0~150):150, more preferably 75:(90~120):150. By controlling the mass ratio of cellulose derivative, polyvinyl alcohol, and potassium hydroxide in the porous composite functional layer within the above range, this invention can form a porous composite functional layer with a large specific surface area.

[0028] In this invention, the thickness of the porous composite functional layer is preferably 200 nm to 5 μm, more preferably 500 nm to 2 μm. By controlling the thickness of the porous composite functional layer within the above range, this invention enables the porous composite functional layer to have a large specific surface area while also maintaining excellent mechanical properties.

[0029] The self-powered flexible humidity sensor based on cellulose derivatives provided by the present invention includes a top electrode disposed on the porous composite functional layer.

[0030] In this invention, the top electrode is preferably a metal sheet. The metal sheet is preferably made of zinc, aluminum, or copper. The thickness of the top electrode is preferably 0.01 mm.

[0031] A preferred structural schematic diagram of the self-powered flexible humidity sensor based on cellulose derivatives provided by this invention is shown below. Figure 1 As shown. In Figure 1 The structure, from top to bottom, consists of a top electrode, a porous composite functional layer (CMC functional layer), a bottom electrode, and a flexible substrate. The working principle of the self-powered flexible humidity sensor based on cellulose derivatives provided by this invention is as follows: Due to the hydrophilicity of the porous composite functional layer, it can spontaneously adsorb water molecules from the surrounding environment. The abundant oxygen-containing groups (such as -OH, -COOH, etc.) inside the porous composite functional layer dissociate under the action of water molecules, generating many hydrogen ions. Due to the presence of the bottom substrate, the top surface of the functional layer captures more water molecules than the bottom surface, resulting in a much higher concentration of hydrogen ions dissociated from the upper surface than from the lower surface, forming a hydrogen ion concentration gradient. Driven by this hydrogen ion concentration gradient, hydrogen ions move directionally from high concentration to low concentration. This directional movement of hydrogen ions creates a potential difference, causing the external circuit to generate a voltage output. When the external humidity is higher, the functional layer of the device adsorbs more water molecules, resulting in a larger hydrogen ion concentration gradient and a higher voltage output. When the device is placed in a low-humidity environment, the number of water molecules that the device can adsorb decreases, and the hydrogen ion concentration gradient dissociated from the upper and lower surfaces of the functional layer decreases. As the hydrogen ion concentration gradient decreases, the voltage of the external circuit decreases until it returns to its original state.

[0032] This invention also provides a method for preparing the self-powered flexible humidity sensor based on cellulose derivatives as described in the above technical solution, comprising the following steps: A bottom electrode is fabricated on one side surface of a flexible substrate; A cellulose derivative, polyvinyl alcohol, potassium hydroxide, and water are mixed to obtain a blend solution; the blend solution is coated on the surface of the bottom electrode and then freeze-dried to obtain a porous composite functional layer. A top electrode is fabricated on the surface of the porous composite functional layer to obtain a self-powered flexible humidity sensor based on cellulose derivatives.

[0033] The present invention prepares a bottom electrode on one side surface of a flexible substrate.

[0034] This invention does not impose any particular limitation on the preparation method of the flexible substrate; any conventional preparation method capable of forming a flexible substrate of the required thickness is acceptable. In this invention, the preferred preparation method for the flexible substrate is PI double-sided adhesive tape fixing or coating.

[0035] In an embodiment of the present invention, the coating method may be: coating a solution of a flexible substrate onto a rigid substrate, and then drying it to obtain a flexible substrate.

[0036] In this invention, the rigid substrate is preferably cleaned and surface-treated sequentially before the flexible substrate is fabricated. The cleaning method is not particularly limited; any conventional cleaning method that can adequately remove impurities from the surface of the rigid substrate is acceptable.

[0037] The present invention does not impose any particular limitations on the concentration of the solution and the coating thickness of the flexible substrate. These can be adjusted as needed to ensure that the thickness of the flexible substrate obtained after drying reaches the required range.

[0038] In this invention, the method for preparing the bottom electrode preferably includes sputtering or spin coating. This invention does not specifically limit the specific operation method of sputtering or spin coating, as long as it can form a bottom electrode of the required thickness range on a flexible substrate.

[0039] After obtaining the bottom electrode, the present invention mixes cellulose derivative, polyvinyl alcohol, potassium hydroxide and water to obtain a blend solution; the blend solution is coated on the surface of the bottom electrode and freeze-dried to obtain a porous composite functional layer.

[0040] In this invention, the preferred volume ratio of the cellulose derivative, polyvinyl alcohol, potassium hydroxide, and water is 75 mg:(0~150) mg:150 mg:1 mL, more preferably 75 mg:(30~120) mg:(90~150) mg:1 mL. By controlling the volume ratio of the cellulose derivative, polyvinyl alcohol, potassium hydroxide, and water within the above range, this invention facilitates better control of the flowability of the blended solution, resulting in a uniformly thick coating on the bottom electrode surface.

[0041] Preferably, the bottom electrode is first subjected to plasma treatment before the blended solution is coated onto its surface. In an embodiment of the invention, the plasma treatment method may be as follows: the bottom electrode is placed in a plasma etching machine with an RF power set to 15W and subjected to plasma treatment in an argon atmosphere for 10 minutes. The invention removes contaminants from the bottom electrode surface through plasma treatment, while simultaneously increasing the hydrophilicity of the bottom electrode surface.

[0042] The present invention does not specifically limit the coating method, as long as it can form a coating of uniform thickness on the surface of the bottom electrode. In the present invention, the coating method is preferably spin coating or blade coating.

[0043] In this invention, the freeze-drying temperature is preferably -20 to -90°C, more preferably -50 to -90°C; the freeze-drying time is preferably 6 to 24 hours, more preferably 12 to 24 hours. This invention, through freeze-drying, can remove the solvent from the blended solution while simultaneously giving the porous composite functional layer a rich pore structure.

[0044] After obtaining the porous composite functional layer, the present invention prepares a top electrode on the surface of the porous composite functional layer to obtain a self-powered flexible humidity sensor based on cellulose derivatives.

[0045] The present invention does not specifically limit the method for preparing the top electrode, as long as the top electrode can be fixed on the porous composite functional layer. In the embodiments of the present invention, the method for preparing the top electrode is preferably PI tape fixation.

[0046] The present invention preferably involves removing the rigid substrate after fabricating the top electrode to obtain a self-powered flexible humidity sensor based on cellulose derivatives.

[0047] The preparation method provided by this invention is simple and easy to operate, and can produce a self-powered flexible humidity sensor based on cellulose derivatives with excellent sensing and power supply performance.

[0048] This invention also provides the application of the self-powered flexible humidity sensor based on cellulose derivatives described in the above technical solution, or the self-powered flexible humidity sensor based on cellulose derivatives prepared by the preparation method described in the above technical solution, in the field of real-time moisture information monitoring.

[0049] The present invention does not impose any special limitations on the application method of the self-powered flexible humidity sensor based on cellulose derivatives in the field of real-time moisture information monitoring; the application method of conventional sensors can be used.

[0050] The self-powered flexible humidity sensor based on cellulose derivatives prepared in this invention has a simple and flexible structure that can fit tightly to any surface. It also has a large specific surface area and porosity, which enhances the adsorption and dissociation of moisture by the sensor. This can greatly improve the absorption and dissociation speed of moisture by the device, effectively improve the output voltage / current, sensitivity, and response / recovery time of the device, and comprehensively improve the sensing performance and power supply performance of the device. Therefore, it can be applied to the field of real-time moisture information monitoring.

[0051] The technical solutions of this invention will be clearly and completely described below with reference to the embodiments thereof. Obviously, the described embodiments are only a part of the embodiments of this invention, and not all of them. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without creative effort are within the scope of protection of this invention.

[0052] Example 1 A self-powered flexible humidity sensor based on cellulose derivatives comprises, from bottom to top, a flexible substrate (PET), a bottom electrode (ITO), a porous composite functional layer, and a top electrode (Zn metal sheet); the porous composite functional layer is a porous composite material formed by sodium carboxymethyl cellulose, polyvinyl alcohol, and potassium hydroxide; the mass ratio of sodium carboxymethyl cellulose, polyvinyl alcohol, and potassium hydroxide is 75 mg: 90 mg: 150 mg. The flexible substrate has a thickness of 175 μm; the bottom electrode has a thickness of 60 nm; the porous composite functional layer has a thickness of 1 μm; and the top electrode has a thickness of 10 μm. The method for preparing the self-powered flexible humidity sensor based on cellulose derivatives is as follows: (1) Using a rigid substrate, a flexible thin film morphology flexible substrate is prepared on the rigid substrate. The process is as follows: Glass is used as the rigid substrate, and the size of the rigid substrate is 2.5cm×2.5cm; PET was used as a flexible substrate. Commercial PET flexible substrates were cut into 2.5cm×2.5cm pieces and fixed to a rigid substrate using PI double-sided tape. A bottom electrode is obtained by sputtering a transparent ITO conductive film onto a PET substrate material; Then the PET / ITO substrate (bottom electrode) was placed in a plasma etching machine with an RF power set to 15W and surface treated for 10 minutes in an argon atmosphere; (2) Prepare CMC solution, KOH solution and PVA solution respectively, mix the three and coat them on the bottom electrode to prepare a porous composite functional layer. The process is as follows: Weigh 75 mg of CMC powder using an electronic balance and place it in a 10 mL glass bottle A. Add 3 mL of deionized water to the bottle using a pipette and place a PTFE (polytetrafluoroethylene) magnetic stir bar inside. Place glass bottle A on a heated stirring table and stir at 60°C for 5 hours until the solute is completely dissolved to obtain a CMC solution. Allow the solution to cool before use. Separately, take 300 mg of PVA powder and place it in a 10 mL glass bottle B. Add 5 mL of deionized water to the bottle using a pipette and place a PTFE magnetic stir bar inside. Place glass bottle B on a heated stirring table and stir at 90°C for 4 hours until the solute is completely dissolved to obtain a 60 mg / mL PVA solution. Allow the solution to cool. Use a pipette to add 1.5 mL of the prepared 60 mg / mL PVA solution from glass bottle B dropwise into glass bottle A. Place the bottle on a heated stirring table and stir for 0.5 hours until the solutions are completely mixed. Next, weigh 600 mg of KOH powder and place it in a 10 mL glass bottle C. Use a pipette to add 2 mL of deionized water to the bottle, gently shaking until the KOH is completely dissolved in the deionized water, obtaining a 300 mg / mL KOH solution. After the CMC / PVA mixed solution cools to room temperature, use a pipette to slowly and evenly add 0.5 mL of the prepared 300 mg / mL KOH solution dropwise to the CMC / PVA mixed solution. Turn on the magnetic stirrer and set an appropriate stirring speed to ensure that the CMC / PVA mixed solution is constantly stirred at a uniform speed during the dropwise addition process, allowing the CMC / PVA mixed solution to quickly and thoroughly mix with the KOH solution, obtaining a CMC / PVA / KOH mixed solution with a mass ratio of 75 mg:90 mg:150 mg, i.e., a blended solution.

[0053] 0.5 mL of CMC / PVA / KOH blend solution was dropped onto the pretreated ITO surface and spin-coated at 600 r / min for 60 s (acceleration 300 r / s). The film was then quickly placed in a -80℃ freezer for 8 h. The completely frozen film was then placed in a freeze dryer and dried for 24 h (-90℃) to obtain a porous composite functional layer. (3) Fix the Zn electrode onto the porous composite functional layer with polyimide tape, peel the flexible substrate off the rigid substrate, and obtain a self-powered flexible humidity sensor based on cellulose derivative.

[0054] Example 2 A self-powered flexible humidity sensor based on cellulose derivatives comprises, from bottom to top, a flexible substrate (PDMS), a bottom electrode (Ag NWs), a porous composite functional layer, and a top electrode (Al metal sheet); the porous composite functional layer is a porous composite material formed by sodium carboxymethyl cellulose, polyvinyl alcohol, and potassium hydroxide; the mass ratio of sodium carboxymethyl cellulose, polyvinyl alcohol, and potassium hydroxide is 75 mg: 90 mg: 150 mg. The thickness of the flexible substrate is 1 mm; the thickness of the bottom electrode is 60 nm; the thickness of the porous composite functional layer is ~1 μm; and the thickness of the top electrode is 10 μm. The method for preparing the self-powered flexible humidity sensor based on cellulose derivatives is as follows: (1) A flexible substrate in the form of a flexible thin film was prepared on a rigid substrate. The process is as follows: Glass was used as the rigid substrate, and the size of the rigid substrate was 2.5cm × 2.5cm. The PDMS stock solution and crosslinking agent were mixed and stirred evenly at a mass ratio of 10:1. Vacuum was drawn to remove air bubbles, and the mixture was left to stand for later use. Then, a solution of flexible substrate material was coated onto the rigid substrate using a spin coating process. The prepared PDMS film was placed in a vacuum chamber and annealed at 80°C for 24h to obtain a flexible substrate. The prepared flexible substrate was placed in a 15W plasma etching machine and plasma treated for 10min in an argon atmosphere. Subsequently, a 5mg / mL Ag NWs solution was spin-coated onto the plasma-treated flexible substrate PDMS and annealed at 115°C for 5min to obtain the bottom electrode. (2) Prepare CMC solution, KOH solution and PVA solution respectively, mix the three and coat them on the bottom electrode to prepare a porous composite functional layer. The process is the same as in Example 1. A porous composite functional layer is obtained. (3) Fix the Al electrode onto the porous composite functional layer film with polyimide tape, peel the flexible substrate off the rigid substrate, and obtain a self-powered flexible humidity sensor based on cellulose derivative.

[0055] Comparative Example 1 A self-powered flexible humidity sensor based on cellulose derivatives comprises, from bottom to top, a flexible substrate (PET), a bottom electrode (ITO), a porous composite functional layer, and a top electrode (Zn metal sheet); the porous composite functional layer is a porous composite material formed by sodium carboxymethyl cellulose, polyvinyl alcohol, and potassium hydroxide; the mass ratio of sodium carboxymethyl cellulose, polyvinyl alcohol, and potassium hydroxide is 75 mg: 90 mg: 150 mg. The flexible substrate has a thickness of 175 μm; the bottom electrode has a thickness of 60 nm; the porous composite functional layer has a thickness of 1 μm; and the top electrode has a thickness of 10 μm. The method for preparing the self-powered flexible humidity sensor based on cellulose derivatives is as follows: (1) The bottom electrode was prepared using the same method as in Example 1; (2) Prepare CMC solution, KOH solution and PVA solution respectively, mix the three and coat them on the bottom electrode to prepare a porous composite functional layer. The process is as follows: Weigh 75 mg of CMC powder using an electronic balance and place it in a 10 mL glass bottle A. Add 3 mL of deionized water to the bottle using a pipette and place a PTFE (polytetrafluoroethylene) magnetic stir bar inside. Place glass bottle A on a heated stirring table and stir at 60°C for 5 hours until the solute is completely dissolved to obtain a CMC solution. Allow the solution to cool before use. Separately, take 300 mg of PVA powder and place it in a 10 mL glass bottle B. Add 5 mL of deionized water to the bottle using a pipette and place a PTFE magnetic stir bar inside. Place glass bottle B on a heated stirring table and stir at 90°C for 4 hours until the solute is completely dissolved to obtain a 60 mg / mL PVA solution. Allow the solution to cool. Use a pipette to add 1.5 mL of the prepared 60 mg / mL PVA solution from glass bottle B dropwise into glass bottle A. Place the bottle on a heated stirring table and stir for 0.5 hours until the solutions are completely mixed. Next, weigh 600 mg of KOH powder and place it in a 10 mL glass bottle C. Use a pipette to add 2 mL of deionized water to the bottle, gently shaking until the KOH is completely dissolved in the deionized water, obtaining a 300 mg / mL KOH solution. After the CMC solution cools to room temperature, use a pipette to slowly and evenly add 0.5 mL of the prepared 300 mg / mL KOH solution dropwise to the CMC solution. Turn on the magnetic stirrer and set an appropriate stirring speed to ensure that the CMC solution is constantly stirred during the dropwise addition, allowing the CMC solution to quickly and thoroughly mix with the KOH solution, obtaining a CMC / PVA / KOH mixed solution with a mass ratio of 1:1.2:2, i.e., a blended solution.

[0056] 0.5 mL of CMC / PVA / KOH blend solution was drop-coated onto the pretreated ITO surface, and then spin-coated at 600 r / min for 60 s (acceleration 300 r / s). The film was then annealed on a high-temperature heating stage at 60 °C for 30 min to obtain a porous composite functional layer. (3) Fix the Zn electrode onto the porous composite functional layer film using polyimide tape; (4) The flexible substrate is peeled off from the rigid substrate to obtain a self-powered flexible humidity sensor based on cellulose derivatives.

[0057] Comparative Example 2 A self-powered flexible humidity sensor based on cellulose derivatives consists of a flexible substrate (PET), a bottom electrode (ITO), a functional layer, and a top electrode (Zn metal sheet) arranged sequentially from bottom to top. The flexible substrate has a thickness of 175 μm; the bottom electrode has a thickness of 60 nm; the functional layer has a thickness of 200 nm; and the top electrode has a thickness of 10 μm. The method for preparing the self-powered flexible humidity sensor based on cellulose derivatives is as follows: (1) The bottom electrode was prepared using the same method as in Example 1; (2) The functional layer was prepared using CMC solution. The process is as follows: 0.5 mL of 15 mg / mL CMC solution was dropped onto the pretreated ITO surface. After spin coating at 600 r / min for 60 s (acceleration 300 r / s), the film was placed on a high-temperature heating stage at 60 °C for annealing for 30 min to obtain the functional layer. (3) Fix the Zn electrode onto the functional layer film using polyimide tape; (4) The flexible substrate is peeled off from the rigid substrate to obtain a self-powered flexible humidity sensor based on cellulose derivatives.

[0058] The electrical performance diagram of the self-powered flexible humidity sensor based on cellulose derivatives provided in Example 1 is shown in Figure 1. Figure 2 As shown; the electrical performance diagram of the self-powered flexible humidity sensor based on cellulose derivatives provided in Comparative Example 1 is shown in Figure 1. Figure 3 As shown in the figure; the electrical performance diagram of the self-powered flexible humidity sensor based on cellulose derivatives provided in Comparative Example 2 is shown in the figure. Figure 4 As shown. By Figures 2-4 As can be seen, the self-powered flexible humidity sensor based on cellulose derivatives provided in Example 1 has an output voltage of ~940mV, a response time of 16s, and a recovery time of 24s, which is superior to Comparative Examples 1 and 2. This is because the embodiment of the present invention prepares a porous composite functional layer, and the addition of KOH and PVA can improve the transmission performance of the self-powered flexible humidity sensor based on cellulose derivatives.

[0059] Figure 5 The images show the SEM microstructure of the porous composite functional layer of the self-powered flexible humidity sensor based on cellulose derivatives in Example 1 and Comparative Example 1. Figure 5 In the figures, a) is the porous composite functional layer of Comparative Example 1; b) is the porous composite functional layer of Example 1. Figure 5 It can be seen that the introduction of freeze-drying process can further adjust the pore size of the functional layer. By introducing freeze-drying, this invention can optimize the pore structure of the porous composite functional layer and improve the water transport performance.

[0060] The results above demonstrate that the self-powered flexible humidity sensor based on cellulose derivatives provided by this invention exhibits excellent sensing and power supply performance. This is because the polyvinyl alcohol in the porous composite functional layer has excellent adsorption and desorption properties for water molecules; the porous composite functional layer has a through-pore-like structure, which enhances the transport capacity of ions or water; the potassium hydroxide in the porous composite functional layer has an adsorption effect on water molecules, allowing for the adsorption of more water molecules; and the cellulose derivative has a fibrous nanocrystalline structure, enabling the transport of ions or water along the nanocrystalline structure, further enhancing the transmission capability of the self-powered flexible humidity sensor based on cellulose derivatives. Furthermore, the cellulose derivative has good biocompatibility. The self-powered flexible humidity sensor based on cellulose derivatives provided by this invention also has a large specific surface area and porosity, enhancing the sensor's adsorption and dissociation of moisture, thus significantly improving the device's absorption and dissociation speed, effectively improving the device's output voltage / current, sensitivity, and response / recovery time, and comprehensively enhancing the device's sensing and power supply performance.

[0061] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A self-powered flexible humidity sensor based on cellulose derivatives, characterized in that, It includes a flexible substrate, a bottom electrode, a porous composite functional layer, and a top electrode arranged sequentially from bottom to top; the porous composite functional layer is a porous composite material formed by cellulose derivatives, polyvinyl alcohol, and potassium hydroxide.

2. The self-powered flexible humidity sensor based on cellulose derivatives according to claim 1, characterized in that, The cellulose derivatives include one or more of sodium carboxymethyl cellulose, hydroxyethyl cellulose, hydroxypropyl cellulose, methyl cellulose, and hydroxypropyl methyl cellulose.

3. The self-powered flexible humidity sensor based on cellulose derivatives according to claim 1, characterized in that, The mass ratio of cellulose derivative, polyvinyl alcohol and potassium hydroxide in the porous composite functional layer is 75:(0~150):

150.

4. The self-powered flexible humidity sensor based on cellulose derivatives according to claim 1, characterized in that, The thickness of the porous composite functional layer is 200 nm to 5 μm.

5. The self-powered flexible humidity sensor based on cellulose derivatives according to claim 1, characterized in that, The flexible substrate is a polymer film; the polymer film is made of one of polyimide, polydimethylsiloxane and polyethylene terephthalate.

6. The self-powered flexible humidity sensor based on cellulose derivatives according to claim 1, characterized in that, The thickness of the flexible substrate is 1μm to 1mm.

7. The self-powered flexible humidity sensor based on cellulose derivatives according to claim 1, characterized in that, The bottom electrode is made of one of the following materials: ITO, graphene, carbon nanotubes, and silver nanowires.

8. The method for preparing the self-powered flexible humidity sensor based on cellulose derivatives according to any one of claims 1 to 7, characterized in that, Includes the following steps: A bottom electrode is fabricated on one side surface of a flexible substrate; A cellulose derivative, polyvinyl alcohol, potassium hydroxide, and water are mixed to obtain a blend solution; the blend solution is coated on the surface of the bottom electrode and then freeze-dried to obtain a porous composite functional layer. A top electrode is fabricated on the surface of the porous composite functional layer to obtain a self-powered flexible humidity sensor based on cellulose derivatives.

9. The preparation method according to claim 8, characterized in that, The freeze-drying temperature is -20 to -90°C; the freeze-drying time is 6 to 24 hours.

10. The self-powered flexible humidity sensor based on cellulose derivatives as described in any one of claims 1 to 7, or the self-powered flexible humidity sensor based on cellulose derivatives prepared by the preparation method described in any one of claims 8 to 9, is used in real-time monitoring of human body moisture status, dynamic monitoring of environmental moisture, monitoring of moisture processes in industrial production, precise monitoring of agricultural moisture, and moisture safety monitoring of electronic devices.

Images