Elastomeric stretchable hydrogen sensor and method of making same

Abstract

The application belongs to the field of gas sensing, and relates to a hydrogen sensor, and particularly provides an elastomer tensile type hydrogen sensor and a preparation method thereof, so as to solve the problems of limited detection range, mutual restriction between detection range and process complexity, and stability to be improved of the existing Pd-based nanogap type hydrogen sensor. The application comprises: a flexible substrate, a Pd-based hydrogen sensitive film arranged on the front and back surfaces of the flexible substrate, and a PEI-rGO multilayer composite strain sensitive film, the flexible substrate is used as a signal conversion medium between the hydrogen sensitive film and the strain sensitive film on the front and back surfaces of the flexible substrate, the lattice expansion strain of the hydrogen sensitive film after absorbing hydrogen is converted into an electrical signal output of the strain sensitive film, and environmental hydrogen concentration detection is realized. The hydrogen sensor can work continuously in a wide expansion range of the hydrogen sensitive film without relying on the switching of the nanogap, the wide detection range and the low process complexity can be considered, and the stability of the device is significantly improved.

Description

TECHNICAL FIELD

[0001] The application belongs to the field of gas sensing, and relates to a hydrogen sensor, and particularly provides an elastomer tensile type hydrogen sensor and a preparation method thereof. BACKGROUND

[0002] Hydrogen (H2) is a new type of clean renewable energy. Under the background of the increasingly serious problems of traditional fossil fuel reserves and the environment, hydrogen has been widely valued due to its wide flammable range, low density, non-toxicity, high combustion value and other advantages, and has a relatively wide application in many aspects such as transportation, aerospace, power systems and the like. However, due to the low density and high diffusion rate of hydrogen, it is more difficult to control than other gases, and it has a relatively large flammable range among flammable gases. At normal temperature and pressure, when the content of hydrogen in the air is between 4% and 75%, it may cause fire and explosion accidents, threatening personal and property safety. Therefore, it is of important research significance to scientifically and effectively detect the hydrogen concentration during storage and transportation, and to reduce or prevent hydrogen explosion.

[0003] In the development of hydrogen sensors, Pd-based materials (mainly including Pd and alloys of Pd and other noble metals) are widely used due to the high specific adsorption capacity of Pd metal to H2. In Pd-based hydrogen sensors, there are mainly two working modes: Pd-based resistivity type based on electron transfer caused by Pd hydrogen absorption, and Pd-based nanogap type based on volume expansion effect of sensitive material caused by Pd hydrogen absorption lattice β phase change; among them, the working mode of Pd-based nanogap type usually has high sensitivity and fast response and recovery rate, and therefore has been widely studied.

[0004] At present, the Pd-based nanogap type hydrogen sensor usually controls the on-off of the conductive path at the nanogap through the expansion and contraction of the hydrogen absorption and dehydrogenation of the thin film at the nanogap, and then realizes the conversion of hydrogen concentration to electric signal; however, the working principle of hydrogen sensing through nanogap on-off will limit the detection range of the device near the hydrogen threshold concentration of on-off, which has certain limitation to the detection range of the device; if the detection range of the device is to be expanded, the width of the nanogap needs to be reduced, which will greatly increase the preparation cost and process complexity of the device, and it is difficult to balance the detection range and process complexity; at the same time, after the hydrogen sensitive thin film at the nanogap is deformed for many times, the aging deformation of the hydrogen sensitive thin film will affect the conductive path, and affect the stability of the device. SUMMARY

[0005] The present application aims at the problems of limited detection range, mutual restriction between detection range and process complexity, and poor stability of existing Pd-based nanogap type hydrogen sensors, and provides an elastomer tensile type hydrogen sensor and a preparation method thereof.

[0006] To achieve the above object, the technical scheme adopted by the present application is as follows:

[0007] An elastomer tensile type hydrogen sensor comprises a flexible substrate, a hydrogen sensitive film and a strain sensitive film, characterized in that the flexible substrate is an elastic polymer substrate, the hydrogen sensitive film is a patterned Pd-based noble metal film, and the strain sensitive film is a polyethyleneimine / reduced graphene oxide (PEI-rGO) multilayer composite film, and the hydrogen sensitive film and the strain sensitive film are arranged on the front and back surfaces of the flexible substrate respectively.

[0008] Further, the elastic polymer substrate is made of a material with good tensile properties, and the flexible substrate is specifically made of polydimethylsiloxane (PDMS), Ecoflex or polymethyl methacrylate (PMMA), and the substrate thickness is 1-3 mm.

[0009] Further, one layer of PEI and one layer of rGO together define one layer of composite film, and the number of layers of the polyethyleneimine / reduced graphene oxide multilayer composite film is 4-8 layers.

[0010] Further, the material of the hydrogen sensitive film is Pd, Pd / Ni alloy, Pd / Au alloy, Pd / Ru alloy or Pd / Co alloy, the patterned shape is spiral, snake, zigzag, sine, back-to-back or circular ring, the film line width is 0.5-1 mm, and the film thickness is 20-50 nm; more preferably, the patterned shape is spiral to obtain the maximum tensile efficiency.

[0011] Further, the hydrogen sensitive film is located at the center position of the flexible substrate.

[0012] Further, in the elastomer tensile type hydrogen sensor, the flexible substrate serves as a signal conversion medium between the hydrogen sensitive film and the strain sensitive film on the front and back surfaces thereof, and converts the lattice expansion strain of the hydrogen sensitive film after absorbing hydrogen into the electrical signal output of the strain sensitive film.

[0013] Further, the preparation method of the elastomer tensile type hydrogen sensor comprises the following steps:

[0014] Step 1. Glass substrate is used, and the glass substrate is cleaned and subjected to hydrophobic pretreatment;

[0015] Step 2. A PEI-GO multilayer composite film is prepared on the surface of the glass substrate by using a layer-by-layer self-assembly method.

[0016] Step 3. A flexible substrate is prepared on the surface of the glass substrate with the PEI-GO multilayer composite film by using a thermal curing method, and the cured flexible substrate is peeled off from the surface of the glass substrate, so that the PEI-GO multilayer composite film on the surface of the glass substrate is transferred to the flexible substrate.

[0017] Step 4. The PEI-GO multilayer composite film on the flexible substrate is reduced to a PEI-rGO multilayer composite film by using ascorbic acid soaking or thermal annealing to form a strain-sensitive film.

[0018] Step 5. A palladium-based noble metal film is prepared on the other surface of the flexible substrate by using evaporation or magnetron sputtering to form a hydrogen-sensitive film.

[0019] Further, in step 2, the specific process of the layer-by-layer self-assembly method is as follows: first, the glass substrate is immersed in the PEI solution for 4-6 min, then the substrate is washed with deionized water and dried with N2; then, the glass substrate is immersed in the GO solution for 4-6 min, then the substrate is washed with deionized water and dried with N2; the process is repeated for several times to prepare the PEI-GO multilayer composite film.

[0020] Further, in step 3, the specific process of the thermal curing method is as follows: the flexible substrate is mixed with the main agent and the curing agent corresponding to the precursor, and is spin-coated onto the surface (front or back) of the glass substrate with the PEI-GO multilayer composite film, and then the glass substrate is heat-cured in a constant temperature drying oven at 60-80℃ for 40-60 min.

[0021] Further, in step 4, the specific process of ascorbic acid soaking is as follows: the flexible substrate is soaked in a saturated ascorbic acid (VC) solution, heated in a constant temperature water bath at 70-80℃ for 1.5-2h, and then left to stand at room temperature for 8-10h to obtain the PEI-rGO multilayer composite film.

[0022] From the working principle:

[0023] The present application provides an elastomer stretch type hydrogen sensor, which uses a flexible substrate as a signal conversion medium between the hydrogen-sensitive film and the strain-sensitive film on the front and back surfaces, so as to convert the lattice expansion strain of the hydrogen-sensitive film after absorbing hydrogen into an electrical signal output of the strain-sensitive film. Figure 2As shown, taking the Pb hydrogen-sensitive film as an example, when the sensor is exposed to an H2 environment, the hydrogen-sensitive film on the front side is converted from the alpha phase to the beta phase, and the lattice expansion in the phase change process causes the volume of the hydrogen-sensitive film to expand, which produces a tensile effect on the elastomer substrate, causing the elastomer substrate to be stretched with a tensile strain ΔStrain (positive correlation); and as the strain of the elastic substrate increases, the graphene sheets adhered to the back side of the substrate move with the substrate strain, the overlapping or contact area decreases, the tunnel effect between the graphene sheets decreases, causing the resistance of the PEI-rGO strain-sensitive film to increase (positive correlation); and when restored to an air environment, the volume expansion of the hydrogen-sensitive film is restored, causing the tensile strain of the substrate to recover, and the overlapping area between the graphene sheets increases again, so the resistance of the PEI-rGO strain-sensitive film returns to the original value; thus, the hydrogen concentration sensing is realized through the change in the resistance value of the strain-sensitive film. Further, the patterned shape of the hydrogen-sensitive film includes a spiral shape, a zigzag shape, a back-to-back shape, a snake shape, a sinusoidal shape, and a circular ring shape, and the stress-tensile strain simulation results of the hydrogen-sensitive film in each patterned shape are as shown in Figure 3 As shown, the hydrogen-sensitive film includes a spiral shape, a zigzag shape, a back-to-back shape, a snake shape, a sinusoidal shape, and a circular ring shape, and the stress-tensile strain simulation results of the hydrogen-sensitive film in each patterned shape are as shown in Figure 4 As shown in the figure, each patterned shape can achieve the above hydrogen sensing function, and the spiral shape can achieve the maximum tensile efficiency.

[0024] Based on the above technical solutions and working principles, the present application has the following advantages:

[0025] The present application provides an elastomer tensile hydrogen sensor, which includes a flexible substrate and a Pd-based hydrogen-sensitive film and a polyethyleneimine / reduced graphene oxide (PEI-rGO) multilayer composite strain-sensitive film arranged on the front and back sides of the flexible substrate. The flexible substrate serves as a signal conversion medium between the hydrogen-sensitive film and the strain-sensitive film on the front and back sides thereof. The lattice expansion effect of the Pd-based hydrogen-sensitive film after absorbing hydrogen produces a tensile strain on the flexible substrate, which is then converted by the PEI-rGO multilayer composite strain-sensitive film into a change in the resistance value of the strain-sensitive film. In other words, the lattice expansion strain of the hydrogen-sensitive film after absorbing hydrogen is converted into an electrical signal output of the strain-sensitive film, realizing the detection of the environmental hydrogen concentration. Unlike other hydrogen swelling type hydrogen sensors, which realize the on-off working mode of the conduction path connection and separation at the nanometer gap through the hydrogen absorption and expansion of the hydrogen-sensitive film at the nanometer gap, the hydrogen sensor of the present application can work continuously in a wide hydrogen expansion range without relying on the on-off of the nanometer gap, thus balancing a wide detection range and low process complexity. At the same time, the working mode of the present application, which does not rely on the nanometer gap, can avoid the problem of the hydrogen-sensitive film at the nanometer gap being affected by aging deformation to affect the conduction path, thereby improving the stability of the device.

[0026] In summary, the present application introduces strain sensing into the signal conversion path of gas sensing, expands the application range of strain sensors, and provides a new research direction for hydrogen sensor devices based on volume expansion effect. BRIEF DESCRIPTION OF DRAWINGS

[0027] Figure 1 It is a structural schematic diagram of the elastomer tensile hydrogen sensor in the application, wherein 1 is a hydrogen sensitive film, 2 is an elastomer substrate, 3 is a strain sensitive film, 3-1 is an rGO layer of the strain sensitive film, and 3-2 is a PEI layer of the strain sensitive film.

[0028] Figure 2 It is a working principle schematic diagram of the elastomer tensile hydrogen sensor in Example 1 of the application.

[0029] Figure 3 It is a graphical shape schematic diagram of the hydrogen sensitive film layer in the application, wherein (a) is a spiral shape, (b) is a zigzag shape, (c) is a back-shaped, (d) is a snake shape, (e) is a sine shape, and (f) is a circular ring shape.

[0030] Figure 4 It is a simulation result of internal stress-tensile strain after the hydrogen sensitive film layer is graphically shaped in the application.

[0031] Figure 5 It is a structural size diagram of the elastomer tensile hydrogen sensor in Example 1 of the application.

[0032] Figure 6 It is a process flow chart of the preparation method of the elastomer tensile hydrogen sensor in Example 1 of the application. DETAILED DESCRIPTION

[0033] In order to make the purpose, technical scheme and advantages of the application clearer, the application is further described in detail below in combination with the drawings and examples; it should be understood that the examples described herein are only used to explain the application and do not limit the application, that is, the described examples are only a part of the examples of the application, but not all the examples.

[0034] Example 1

[0035] This example provides an elastomer tensile hydrogen sensor, the structure of which is as shown in Figure 1As shown, it comprises: a flexible substrate 1, a hydrogen-sensitive film 2 arranged on the front surface of the substrate and located at the center position, and a strain-sensitive film 3 arranged on the back surface of the substrate; wherein the flexible substrate adopts a PDMS flexible substrate, the hydrogen-sensitive film adopts a Pd film, and the strain-sensitive film adopts an ascorbic acid-reduced PEI-rGO composite film, each layer of the composite film is composed of a PEI layer 3-2 and a rGO layer 3-1 stacked together; the length of the PDMS flexible substrate is 30 mm, and the width is 15 mm; the thickness of the Pd hydrogen-sensitive film is 20 nm, and the patterned shape is a spiral shape with a line width of 1 mm; the number of layers of the PEI-rGO composite film is 6, and the length and width of the PEI-rGO composite film are the same as those of the PDMS flexible substrate, as shown in Figure 5 .

[0036] The embodiment also provides a preparation method of the above-mentioned elastomer stretch-type hydrogen sensor, and the flow thereof is as shown in Figure 6 .

[0037] Step 1. Select a glass sheet as a substrate, clean the substrate and perform hydrophobic pretreatment; specifically, the cleaning process is: ultrasonic cleaning of the substrate with acetone, ethanol and deionized water in sequence, and the hydrophobic treatment process is: irradiating the substrate with oxygen plasma and then soaking it in trimethylchlorosilane (TMCS) for 30 min;

[0038] Step 2. Prepare a PEI-GO composite film by layer-by-layer self-assembly; specifically, first, immerse the glass substrate obtained in step 1 in a PEI solution for 5 min, then rinse the substrate with deionized water and dry it with N2; then, immerse the glass substrate soaked with PEI in a GO solution for 5 min, then rinse the substrate with deionized water and dry it with N2; repeat this process 6 times to prepare a 6-layer PEI-GO composite film;

[0039] Step 3. Prepare a PDMS flexible substrate by elastomer curing method, and transfer the PEI-GO composite film by mechanical peeling method; specifically, mix the PDMS main agent and the curing agent in a mass ratio of 10:1, stir for 10 minutes, and then spin coat onto the glass sheet with the PEI-GO composite film obtained in step 2; heat cure the glass sheet in a constant temperature drying oven at 70°C for 1 h, and after cooling to room temperature, peel off the cured PDMS flexible substrate from the surface of the glass sheet, and the PEI-GO film on the surface of the glass sheet will also be transferred to the PDMS substrate accordingly;

[0040] Step 4. Reducing the PEI-GO composite film with ascorbic acid; specifically, the flexible substrate with the composite film peeled off in step 3 was immersed in a saturated ascorbic acid (VC) solution, heated in a constant temperature water bath at 80℃ for 2h, and after being taken out, was left to stand at room temperature for 8h to obtain a PEI-rGO composite film; the PDMS flexible substrate with the PEI-rGO composite film was cut into a rectangle of 15mm x 30mm, and conductive silver paste and copper wire were used to lead out electrodes at both ends of the PEI-rGO composite film.

[0041] Step 5. Preparing a Pd hydrogen-sensitive film by magnetron sputtering; specifically, a spiral-shaped mask was used on the other side of the device without the PEI-rGO composite film obtained in step 4, and a 20nm Pd film was magnetron sputtered at a rate of 0.2A / s.

[0042] Example 2

[0043] This example provides an elastomer stretch-type hydrogen sensor, which differs from example 1 in that the flexible substrate is Ecoflex, and the others are the same as example 1.

[0044] Example 3

[0045] This example provides an elastomer stretch-type hydrogen sensor, which differs from example 1 in that the material of the hydrogen-sensitive film is Pd / Ni alloy, and the others are the same as example 1.

[0046] The above is only a specific embodiment of the present application, any feature disclosed in this specification can be replaced by other equivalent or similar purpose alternative features unless specifically described; all features disclosed, or steps in all methods or processes, except for mutually exclusive features and / or steps, can be combined in any way.​

Claims

1. A method of making an elastomeric stretchable hydrogen sensor, characterized by, The method comprises the following steps: Step 1. A glass substrate is adopted, and the glass substrate is cleaned and subjected to hydrophobic pretreatment; Step 2. A PEI-GO multilayer composite film is prepared on the surface of the glass substrate by using a layer-by-layer self-assembly method; Step 3. A flexible substrate is prepared on the surface of the glass substrate with the PEI-GO multilayer composite film by using a thermal curing method, and the flexible substrate after curing is peeled off from the surface of the glass substrate, so that the PEI-GO multilayer composite film on the surface of the glass substrate is transferred to the flexible substrate; Step 4. The PEI-GO multilayer composite film on the flexible substrate is reduced to a PEI-rGO multilayer composite film by ascorbic acid soaking or thermal annealing, so as to form a strain-sensitive film; Step 5. A patterned palladium-based noble metal film is prepared on the other surface of the flexible substrate by using evaporation or magnetron sputtering, so as to form a hydrogen-sensitive film, and the hydrogen-sensitive film and the strain-sensitive film are arranged on the front and back surfaces of the flexible substrate, respectively.

2. The method of claim 1, wherein the elastomeric stretchable hydrogen sensor is prepared by the steps of: In step 2, the specific process of the layer-by-layer self-assembly method is as follows: first, the glass substrate is immersed in a PEI solution for 4-6 min, then the substrate is washed with deionized water and dried with N2; Then, the glass substrate is immersed in a GO solution for 4-6 min, then the substrate is washed with deionized water and dried with N2; The process is repeated for multiple times, so as to prepare the PEI-GO multilayer composite film.

3. The method of claim 1, wherein the elastomeric stretchable hydrogen sensor is prepared by the steps of: In step 3, the specific process of the thermal curing method is as follows: the main agent and the curing agent of the precursor corresponding to the flexible substrate are mixed and spin-coated on the surface of the glass substrate with the PEI-GO multilayer composite film, and then the glass substrate is subjected to thermal curing at 60-80 ℃ for 40-60 min in a constant-temperature drying box.

4. The method of claim 1, wherein the elastomeric stretchable hydrogen sensor is prepared by the steps of: In step 4, the specific process of ascorbic acid soaking is as follows: the flexible substrate is soaked in a saturated ascorbic acid solution, heated in a constant-temperature water bath at 70-80 ℃ for 1.5-2 h, and then left to stand at room temperature for 8-10 h, so as to obtain the PEI-rGO multilayer composite film.

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