Humidity sensor based on graphene film interdigital electrode and preparation method and application thereof

Abstract

The invention provides a humidity sensor based on a graphene film interdigital electrode and a preparation method and application thereof. The preparation method comprises the following steps: S1, preparing a graphene film; s2, performing surface treatment on the graphene film; s3, the treated graphene film is placed in a laser engraving machine to be machined, and the graphene interdigital electrode is obtained; s4, preparing a humidity-sensitive material: diluting the graphene oxide slurry to 1 wt% by using deionized water, and fully stirring; then diluting 1 wt% of graphene oxide solution to 0.01 wt%-0.03 wt%, and continuously stirring until graphene oxide is stripped into a single-layer state; and S5, preparing the humidity sensor: taking the graphene oxide solution stirred in the step S4, dripping the graphene oxide solution onto the interdigital part of the interdigital electrode, so that the graphene oxide solution uniformly overlays the interdigital part, and drying to obtain the humidity sensor based on the graphene film interdigital electrode. The humidity sensor prepared by the invention has excellent sensitivity, response / recovery time, good flexibility and extremely good environmental stability.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of humidity sensors, and particularly relates to a humidity sensor based on a graphene film interdigital electrode and a preparation method and application thereof. BACKGROUND

[0002] Humidity sensors are an integral part of emerging technologies such as the Internet of Things, intelligent electronics, environmental monitoring, and modern agriculture.

[0003] Existing humidity sensor electrode materials face multiple technical bottlenecks: the conductivity of laser-induced graphene (LIG) electrodes is low, and bending easily causes structural damage and conductivity decay; among metal electrodes, gold electrodes are costly and have poor flexibility compatibility, and copper electrodes, although less expensive, have poor corrosion resistance and are easily oxidized and fail in alkaline or salt spray environments, requiring additional encapsulation protection.

[0004] Therefore, there is a need to prepare a humidity sensor based on a graphene film interdigital electrode that can solve the contradictions of high conductivity, mechanical durability, environmental adaptability, and low cost, and provide a reliable technical path for flexible wearable devices and harsh environment monitoring. SUMMARY

[0005] The purpose of the present application is to overcome the shortcomings of the prior art and provide a humidity sensor based on a graphene film interdigital electrode and a preparation method and application thereof.

[0006] The present application provides the following technical solutions: The present application provides a preparation method for a humidity sensor based on a graphene film interdigital electrode, comprising the following steps: S1, preparing a graphene film; S2, surface treating the graphene film; S3, preparing an interdigital electrode; placing the graphene film treated in step S2 in a laser engraving machine for processing, after processing, removing the excess part of the electrode, and obtaining a graphene interdigital electrode; S4, preparing a humidity-sensitive material: diluting the graphene oxide slurry with deionized water to 1 wt%, and fully stirring; then diluting the 1 wt% graphene oxide solution to 0.01 wt% ~ 0.03 wt%, and continuing to fully stir, and exfoliating the graphene oxide into a single-layer state; S5, preparing a humidity sensor: taking the stirred graphene oxide solution in step S4, dropping it onto the interdigital electrode, making it evenly cover the interdigital electrode, and obtaining the humidity sensor based on the graphene film interdigital electrode after drying.

[0007] Further, in step S1, the preparation of the graphene film comprises the following steps: S11, graphene oxide is dispersed in deionized water to form a suspension of 2 wt%-10 wt%, the graphene oxide suspension is converted into graphene oxide colloid by stirring, and then coated to form a graphene oxide film; S12, the graphene oxide film is heated and then annealed in an inert gas atmosphere, and then the obtained sample is rolled on PET to obtain the graphene film.

[0008] Further, in step S12, the temperature is heated to 1100 ℃-1500 ℃ and then held for 2-4 h, and then annealed at 2500 ℃-3000 ℃ for 1-2 h.

[0009] The two-step reduction method (pre-reduction gas channel construction + high-temperature deep reduction) avoids film rupture and ensures structural integrity. The temperature of 1100 ℃-1500 ℃ can ensure that non-carbon elements are fully removed, avoid residual heteroatoms hindering subsequent graphitization, and prevent excessive pyrolysis from causing disordered growth of microcrystals, affecting structural density; the temperature of 2500 ℃-3000 ℃ accelerates the rearrangement of carbon atoms, and the layer size rapidly increases, and the three-dimensional ordered stacking is perfect.

[0010] Further, in step S2, the surface treatment includes wiping the graphene film with anhydrous ethanol.

[0011] Further, in step S3, the parameter settings of the laser engraving machine are as follows: mode selection cut inside, power frequency: 50-150 KHz, power: 1.5-2.5 W, structured speed: 50-150 mm / s, focal point compensation: 0-0.1 mm, repetition number: 1-10 times, pulse energy: 10-40 μJ, channel width: 15 μm.

[0012] Further, in step S4, a stirring defoaming machine is used for stirring.

[0013] Further, in step S5, the drying is carried out in a blowing drying oven at 40 ℃-60 ℃, and the drying time is 8-16 h.

[0014] The application also provides a humidity sensor based on a graphene film interdigital electrode prepared by the above preparation method.

[0015] The application also provides applications of the above humidity sensor based on a graphene film interdigital electrode in real-time monitoring of human respiration and non-contact human-computer interaction, and the monitoring of human respiration is not for the purpose of medical diagnosis and treatment.

[0016] The application also provides applications of the above humidity sensor based on a graphene film interdigital electrode in plant and animal environmental sensing.

[0017] The present application has the following beneficial effects: 1、The electrode substrate of the humidity sensor of the present application is graphene film, graphene interdigital electrodes are prepared by laser patterning, and fast and large-scale preparation can be realized; the humidity-sensitive layer adopts graphene oxide, and the graphene interdigital electrodes and the graphene oxide together form a pure carbon-based humidity sensor. The humidity sensor has excellent sensitivity, response / recovery time, good flexibility and excellent environmental stability.

[0018] 2、The graphene film prepared in the present application has extremely high electrical conductivity, flexibility and extremely strong chemical corrosion resistance. BRIEF DESCRIPTION OF DRAWINGS

[0019] In order to more clearly illustrate the technical solutions of the embodiments of the present application or the prior art, the drawings needed to be used in the embodiments or the prior art description will be briefly introduced below. Obviously, the drawings in the following description are only some embodiments of the present application, and those skilled in the art can also obtain other drawings according to these drawings without creative labor.

[0020] Figure 1 It is a schematic diagram of the size of the interdigital electrode in Example 1 of the present application; Figure 2 It is a large-scale interdigital electrode engraved by laser in Example 1 of the present application; Figure 3 It is an optical photograph and a surface SEM image of the humidity sensor prepared in Example 1 of the present application; Figure 4 It is a cross-sectional SEM image of the humidity sensor prepared in Example 1 of the present application; Figure 5 It is the sensitivity and response / recovery time of the humidity sensor prepared in Example 1 of the present application; Figure 6 It is a comparison chart of the sensitivity and response / recovery time of the humidity sensors prepared in Examples 1-3 of the present application; Figure 7 It is a comparison chart of the sensitivity and response / recovery time of the humidity sensors prepared in Examples 1, 4-5 of the present application; Figure 8 It is a performance characterization chart of the humidity sensor prepared in Example 1, Comparative Example 2 of the present application; Figure 9 It is a result characterization chart of the humidity sensor prepared in Example 1 of the present application applied to human breath monitoring; Figure 10 It is a result characterization chart of the humidity sensor prepared in Example 1 of the present application applied to a non-contact button; Figure 11The humidity sensor prepared in Embodiment 1 of the present application is applied to a specific setting diagram for transpiration monitoring with green plants as samples; Figure 12 The humidity sensor prepared in Embodiment 1 of the present application is applied to a result characterization diagram for transpiration monitoring with green plants as samples; Figure 13 The conductivity change result diagram of the graphene film interdigital electrode after multiple bending. DETAILED DESCRIPTION

[0021] The technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the drawings in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor fall within the scope of protection of the present application.

[0022] The present application provides a preparation method of a humidity sensor based on a graphene film interdigital electrode, comprising the following steps: S1, preparing a graphene film; S2, performing surface treatment on the graphene film; S3, preparing an interdigital electrode; placing the graphene film treated in step S2 into a laser engraving machine for processing, removing the excess part of the electrode after processing is completed, and obtaining a graphene interdigital electrode; S4, preparing a humidity-sensitive material: diluting the graphene oxide slurry to 1 wt% with deionized water and fully stirring; then diluting the 1 wt% graphene oxide solution to 0.01 wt%~0.03 wt% and continuing to fully stir, and peeling the graphene oxide into a single-layer state; S5, preparing a humidity sensor: taking the stirred graphene oxide solution in step S4, dropping it onto the upper part of the interdigital electrode, making it evenly cover the interdigital part, and obtaining the humidity sensor based on the graphene film interdigital electrode after drying.

[0023] In the present application, the electrode substrate of the humidity sensor is a graphene film, which has extremely high conductivity (>10 6 S / m), flexibility and extremely strong chemical corrosion resistance. The graphene interdigital electrode is prepared by laser patterning, which can realize rapid and large-scale preparation. The humidity-sensitive layer uses graphene oxide, which together with the graphene interdigital electrode forms a pure carbon-based humidity sensor. The humidity sensor has excellent sensitivity, response / recovery time, good flexibility and excellent environmental stability.

[0024] Specifically, in step S1, the preparation of the graphene film comprises the following steps: S11, graphene oxide is dispersed in deionized water to form a suspension of 4 wt%, the graphene oxide suspension is converted into graphene oxide colloid by stirring, and then coated to form a graphene oxide film; S12, the graphene oxide film is heated and then annealed in an inert gas atmosphere, and then the obtained sample is rolled on PET to obtain a graphene film.

[0025] By high temperature reduction, the oxygen-containing functional groups in graphene oxide (GO) are completely removed (the oxygen content is significantly reduced), the carrier scattering center is greatly reduced, and sp 2 The size of the hybrid carbon domain is increased, a long-range ordered conductive network is formed, the two-step reduction method (pre-reduction to construct a gas channel + high-temperature deep reduction) is combined to avoid film rupture and ensure structural integrity, and finally the high-pressure roller compaction treatment reduces the interlayer porosity, optimizes the orientation arrangement of graphene layers, and enhances the transverse conductive path. This synergistic process makes the conductivity break through 10 6 S / m, which is significantly higher than that of traditional methods.

[0026] The high-performance graphene film interdigital electrode prepared by the application has a conductivity (>10 6 S / m) which is 4 orders of magnitude higher than that of LIG, and has excellent flexibility (the conductivity does not attenuate after bending 10000 times, see Figure 13 ), and also has intrinsic corrosion resistance, and the raw material cost is much lower than that of gold electrodes.

[0027] The application will be further described below through specific examples: Example 1 The preparation process of the humidity sensor in this embodiment is as follows: The graphene film is prepared by dispersing graphene oxide in deionized water to form a suspension of 4 wt%, stirring the graphene oxide suspension into graphene oxide colloid, and then coating to form a graphene oxide film. The graphene oxide film is heated to 1300 DEG C under an argon atmosphere and kept for 2 hours. Then the graphene oxide film is annealed at 2850 DEG C under an argon atmosphere for 1 hour. The obtained sample is rolled on PET under a pressure of 200 MPa to obtain a graphene film. The graphene film is surface treated, and the graphene film is cut into a rectangular block of 25 cm x 20 cm by repeatedly wiping the surface of the graphene film with anhydrous ethanol using a dust-free paper. Preparation of interdigital electrode; the cut graphene film was placed in a laser engraving machine (ProtoLaser U4, LPKF Laser & Electronics AG, Slovenia) for processing, mode selection cut inside, power frequency: 100 KHz, power: 1.85 W, structured speed: 100 mm / s, focal point compensation: 0.05 mm, repetition number: 5 times, pulse energy: 19 μJ, channel width: 15 μm; after processing, the excess part of the electrode was removed using tweezers, and the complete graphene interdigital electrode was obtained; Preparation of humidity-sensitive material: the graphene oxide slurry with a solid content of 4% (purchased from San'ayan graphene technology research co., LTD) was diluted to 1% with deionized water, and stirred twice for 30 minutes each time using a stirring defoaming machine to ensure complete dispersion of graphene oxide. Then, the 1% graphene oxide solution was diluted to 0.02%, and the graphene oxide was exfoliated to a single layer state using a stirring defoaming machine for 2 times; Preparation of humidity sensor: 50 μL of the above-stirred graphene oxide solution was dropped into the middle of the interdigital part of the interdigital electrode, and in the process of dropping, the graphene oxide solution was uniformly diffused to the edge of the interdigital part, so that it was uniformly spread on the interdigital part, and then dried in a blast drying oven at 50 ℃ for 12 hours to obtain a humidity sensor based on a graphene film interdigital electrode.

[0028] In this embodiment, the size of the prepared interdigital electrode is as shown in Figure 1 The overall length and width of the electrode are 11.25 mm 6.25 mm, the electrode spacing is 250 μm, the interdigital width is 500 μm, the length is 5 mm, and the logarithm is 5 pairs; Figure 2 The laser-engraved large-scale interdigital electrode in this embodiment.

[0029] The conductivity of the prepared graphene film interdigital electrode was measured by four-probe thin film sheet resistance to be 1.2×10 6 S / m.

[0030] SEM analysis was performed using a Zeiss Crossbeam 350 dual-beam microscope, as shown in Figure 3 、 Figure 4As can be seen from the figure, the GO film has continuous, conformal and defect-free coverage characteristics, the unique wrinkle structure on its surface significantly increases the specific surface area, and the ultra-thin thickness (about 150 nm) ensures the rapid penetration and escape of water molecules and good adhesion to the substrate; these structural characteristics jointly act on the performance of the sensor: the wrinkle provides a large number of water molecule adsorption sites, thereby enhancing the sensitivity of the sensor, the ultra-thin thickness greatly shortens the diffusion path of water molecules in the film, laying a solid foundation for the sensor to realize fast response and recovery kinetics, and the continuity and uniform coverage of the film ensure the stability and reliability of the electrical signal transmission.

[0031] The humidity sensor prepared in Example 1 was tested for humidity sensing performance (impedance change with humidity) by using a CHI660E electrochemical workstation. Referring to Figure 5 , the sensitivity was measured to be 2920 kΩ / %RH, and the response / recovery time was 2.8 s / 2.9 s, which is superior to the mainstream industrial standard (such as the military standard SJ 20760, which requires ≤15 seconds).

[0032] Example 2: The preparation process is basically the same as that of Example 1, except that the 1% graphene oxide solution is diluted to 0.01%. The humidity sensor prepared is tested for humidity sensing performance by using a CHI660E electrochemical workstation (performance test results are shown in Figure 6 ).

[0033] Example 3: The preparation process is basically the same as that of Example 1, except that the 1% graphene oxide solution is diluted to 0.03%. The humidity sensor prepared is tested for humidity sensing performance by using a CHI660E electrochemical workstation (performance test results are shown in Figure 6 ).

[0034] Example 4: The preparation process is basically the same as that of Example 1, except that the electrode spacing of the interdigital electrode prepared is designed to be 150 μm. The humidity sensor prepared is tested for humidity sensing performance by using a CHI660E electrochemical workstation (performance test results are shown in Figure 7 ).

[0035] Example 5: The preparation process is basically the same as that of Example 1, except that the electrode spacing of the interdigital electrode prepared is designed to be 350 μm. The humidity sensor prepared is tested for humidity sensing performance by using a CHI660E electrochemical workstation (performance test results are shown in Figure 7 ).

[0036] Comparative Example: Humidity sensor with common metal electrode and humidity sensor with laser-induced graphene electrode Comparative example and example 1, the humidity-sensitive material and the step of coating the humidity-sensitive material to make the humidity sensor are the same as example 1, the difference is that the preparation step of the interdigital electrode is different; Common metal electrode: copper foil as raw material, metal interdigital electrode is prepared by laser engraving (specific parameters: mode selection cut inside, power frequency: 100 KHz, power: 1.85 W, structuring speed: 100 mm / s, focus compensation: 0.05 mm, repetition number: 5 times, pulse energy: 19 μJ, channel width: 15 μm).

[0037] Laser-induced graphene electrode: polyimide film as raw material, laser-induced graphene interdigital electrode is obtained by laser induction (specific parameters: mode selection Hatch, power frequency: 100 KHz, power: 0.2 W, structuring speed: 10 mm / s, focus compensation: 0.00 mm, repetition number: 1 time, pulse energy: 2 μJ, channel width: 15 μm).

[0038] Reference Figure 8 The humidity sensor prepared by the graphene film interdigital electrode in example 1 has more excellent performance than the traditional metal (copper as an example) and laser-induced graphene interdigital electrode of the comparative example.

[0039] Application example: Human respiratory monitoring: the humidity sensor prepared in example 1 is integrated inside the mask, and is connected to the electrochemical workstation, after the mask is normally worn, the respiratory monitoring simulation is carried out, and the humidity response characteristics are used to monitor the respiratory frequency and depth in real time.

[0040] Figure 9 The real-time response curves of the sensor to three different breathing modes are shown: rapid breathing (90 times / min), normal breathing (27 times / min) and deep breathing (11 times / min). In addition to the frequency, the sensor can also effectively respond to the change of breathing depth: the impedance change amplitude is the largest when deep breathing, and the smallest when rapid breathing.

[0041] Non-contact human-computer interaction: the humidity sensor prepared in example 1 is placed on a flat table, and is connected to the electrochemical workstation, the finger is quickly close to the top of the humidity sensor, lasts for 5s, then the finger is quickly withdrawn, the height of the finger from the surface of the sensor is changed, and the test is repeated; As Figure 10As shown, when the finger approaches the sensor surface, water molecules are adsorbed by the graphene oxide humidity-sensitive layer, resulting in a significant increase in conductivity and a significant decrease in impedance. As the finger gradually moves away (from 1 mm to 5 mm), the impedance value rises accordingly. Different distances correspond to specific impedance values, showing a good linear relationship between distance and impedance.

[0042] Plant environment sensing: integrate the humidity sensor prepared in Example 1 into the upper stem area to monitor the humidity changes mainly related to the lower leaf surface (Fig. 2b), Figure 11 , so as to track the dynamic plant (taking pothos as an example) transpiration pattern.

[0043] Figure 12 The transpiration change curve of the plant for four consecutive day-night cycles is shown: the plant is usually watered in the evening before the test, and then subjected to simulated drought conditions for three days. The results show that the transpiration reaches a peak in the afternoon of the first day, starts to decrease on the second day, and further significantly decreases on the third day (manifested as an increase in impedance value) compared with the second day. After normal watering in the evening of the third day, the transpiration in the daytime of the fourth day returns to a level comparable to that of the first day.

[0044] The humidity sensor prepared by the present application has excellent sensitivity, response / recovery time, good flexibility, and excellent environmental stability, providing a reliable technical path for flexible wearable devices and harsh environment monitoring.

[0045] The above only describes the preferred embodiments of the present application and is not intended to limit the present application. Any modification, equivalent replacement, improvement, etc. made within the spirit and principles of the present application shall be included in the protection scope of the present application.

Claims

1. A method for preparing a humidity sensor based on graphene film interdigital electrodes, characterized by, The method comprises the following steps: S1, preparing a graphene film; S2, surface treating the graphene film; S3, preparing an interdigital electrode: placing the graphene film treated in step S2 into a laser engraving machine for processing, removing the excess part of the electrode after the processing is completed, and obtaining a graphene interdigital electrode; S4, preparing a humidity-sensitive material: diluting graphene oxide slurry with deionized water to 1 wt%, and fully stirring; then diluting the 1 wt% graphene oxide solution to 0.01 wt%-0.03 wt%, and continuing to fully stir, and exfoliating the graphene oxide into a single-layer state; S5, preparing a humidity sensor: taking the graphene oxide solution stirred in step S4, dropping it onto the interdigital part of the interdigital electrode, making it evenly cover the interdigital part, and obtaining the graphene film interdigital electrode-based humidity sensor after drying.

2. The method of claim 1, wherein the graphene film interdigital electrode-based humidity sensor is prepared by the steps of: (a) preparing a graphene film on a substrate; (b) forming a first electrode on the graphene film; (c) forming a second electrode on the graphene film; and (d) forming a dielectric layer between the first electrode and the second electrode. In the step S1, the preparation of the graphene film comprises the following steps: S11, dispersing graphene oxide in deionized water to form a suspension of 2 wt%-10 wt%, stirring the graphene oxide suspension into a graphene oxide colloid, and then coating to form a graphene oxide film; S12, heating and then annealing the graphene oxide film in an inert gas atmosphere, and then rolling the obtained sample on PET to obtain the graphene film.

3. The method of claim 2, wherein the graphene film interdigital electrode-based humidity sensor is prepared by the steps of: (a) preparing a graphene film on a substrate; (b) forming a first electrode on the graphene film; (c) forming a second electrode on the graphene film; and (d) forming a dielectric layer between the first electrode and the second electrode. In the step S12, the heating is to 1100 ℃-1500 ℃, and the holding is for 2-4 h, and then the annealing is at 2500 ℃-3000 ℃ for 1-2 h.

4. The method of claim 1, wherein the graphene film interdigital electrode-based humidity sensor is prepared by the steps of: (a) preparing a graphene film on a substrate; (b) forming a first electrode on the graphene film; (c) forming a second electrode on the graphene film; and (d) forming a dielectric layer between the first electrode and the second electrode. In the step S2, the surface treatment comprises wiping the graphene film with anhydrous ethanol.

5. The method of claim 1, wherein the graphene film interdigital electrode-based humidity sensor is prepared by the steps of: (a) preparing a graphene film on a substrate; (b) forming a first electrode on the graphene film; (c) forming a second electrode on the graphene film; and (d) forming a dielectric layer between the first electrode and the second electrode. In the step S3, the parameter settings of the laser engraving machine are as follows: mode selection cut inside, power frequency: 50-150 KHz, power: 1.5-2.5 W, structuring speed: 50-150 mm / s, focal point compensation: 0-0.1 mm, repetition number: 1-10 times, pulse energy: 10-40 μJ, and channel width: 15 μm.

6. The method of claim 1, wherein the graphene film interdigital electrode-based humidity sensor is prepared by the steps of: (a) preparing a graphene film on a substrate; (b) forming a first electrode on the graphene film; (c) forming a second electrode on the graphene film; and (d) forming a dielectric layer between the first electrode and the second electrode. In the step S4, the stirring is performed by a stirring defoaming machine.

7. The method of claim 1, wherein the graphene film interdigital electrode-based humidity sensor is prepared by the steps of: (a) preparing a graphene film on a substrate; (b) forming a first electrode on the graphene film; (c) forming a second electrode on the graphene film; and (d) forming a dielectric layer between the first electrode and the second electrode. In the step S5, the drying is performed in a blowing drying oven at 40 ℃-60 ℃, and the drying time is 8-16 h.

8. A graphene film interdigital electrode-based humidity sensor prepared by the preparation method in any one of claims 1-7.

9. The application of the graphene film interdigital electrode-based humidity sensor in claim 8 in real-time monitoring of human respiration and non-contact human-computer interaction, wherein the application in real-time monitoring of human respiration does not include use for medical diagnosis and treatment.

10. The application of the graphene film interdigital electrode-based humidity sensor in claim 8 in environmental sensing of animals and plants.

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