A preparation method of a flexible electrode

Abstract

The present invention discloses a preparation method of a flexible electrode, that is, by means of a simple vacuum filtration device, a three-electrode pattern with a working electrode and a counter electrode being a single-walled carbon nanotube (SWCNT) conductive film and a reference electrode being a silver nanowire (Ag NWs) conductive film is constructed on a filter membrane, and by utilizing the characteristic that the viscosity of Parafilm or thermoplastic polyurethane elastomer rubber (TPU) is improved at a relatively low heating temperature and the excellent flexibility of a polyethylene terephthalate / ethylene vinyl acetate (PET / EVA) composite film, the electrode pattern on the filter membrane is rapidly transferred to a PET / EVA / Parafilm or PET / EVA / TPU composite flexible substrate in one step by means of vacuum pumping. Compared with other flexible electrode preparation processes, the present invention not only has low requirements for equipment, but also the flexible substrates used can all be commercially purchased. This method has great potential for popularization in terms of both preparation cost and simplicity of the preparation process.

Description

[0001] Technical field

[0002] The present invention relates to the technical field of electrodes, and particularly relates to a preparation method of a flexible electrode. Background technology

[0003] Electrochemical sensing is based on a three-electrode working system: a working electrode, a counter electrode, and a reference electrode. It is based on the law that the measured target specifically causes regular changes in electrochemical signals to complete the detection of substances in a solution. It not only has high sensitivity, a wide detection range, but also low cost and is easy to miniaturize. Therefore, it has good application potential in point-of-care testing. In recent years, integrating the traditional three-electrode detection system onto a flexible substrate and using it for biosensing, disease detection, and environmental monitoring has been a major research hotspot (Lab Chip 2018, 18, 1812-1830). Currently, flexible sensors show great development prospects, enabling high-resolution, high-sensitivity, fast response, low manufacturing cost, and complex signal detection of flexible wearable sensors. Because these sensors can adapt to the soft, elastic, and bendable characteristics of human tissues, they have great future applications in many fields, especially in health monitoring (Anal. Chem. 2020, 92, 378-396).

[0004] Screen printing is the main production technology adopted in the preparation process of flexible electrodes. Although printing technology can achieve mass production of flexible electrodes (Sensors 2020, 20, 3609; Lab Chip 2020, 20, 9-34). However, this preparation process still requires specific printing equipment. In addition, the formulation of the ink required for printing and the complex post-treatment process after printing still consume a large amount of cost and time (PNAS 2020 117 18292-18301; Lab Chip2020,20, 9-34). In addition, methods such as chemical deposition, laser etching, and pencil-drawn electrodes can also be used to prepare flexible electrodes with excellent electrochemical performance. However, due to the characteristics of the technology itself and the requirements for manufacturing equipment, these methods all have some obvious deficiencies. For example, the chemical deposition method not only has cumbersome steps but also requires precise control of deposition conditions, so it is difficult to control the reproducibility of the prepared electrodes; the laser etching method requires expensive laser etching instruments, so the cost of preparing electrodes is high; the force of the pencil-drawn electrodes will affect the thickness of the graphite conductive layer, so the reproducibility of the electrodes is also difficult to control (ACS Appl. Mater. Interfaces 2016, 8, 51, 34978-34984; ACS Appl. Nano Mater. 2019,3, 391-398; PNAS 2020, 117, 18292-18301). It is worth noting that due to its advantages such as fast speed, uniform conductive thin film prepared, and good reproducibility, the vacuum filtration method is a commonly used method for preparing flexible electrode materials at present. However, on the one hand, when preparing flexible electrodes by the vacuum filtration method, it is necessary to drop conductive silver paste or attach a silver conductive film at the reference part after the electrode is made to stabilize the electrochemical detection potential; on the other hand, since the hydrophilicity of the filter membrane cannot be directly used as the electrode substrate, the filter membrane needs to be processed into a hydrophobic one through a certain process or directly use an expensive hydrophobic filter membrane. Therefore, these two aspects make the preparation of flexible electrodes by the vacuum filtration method expensive and cumbersome in terms of cost and process (ACS Sens. 2018, 3,2518-2525; ACS Appl. Mater. Interfaces 2018, 10, 13729-13740; Angew. Chem.,Int. Ed. 2021, 60, 2993-3000).

[0005] There are many substrates commonly used to fabricate flexible electrodes, among which paper is one of the most frequently used. However, due to the hydrophilicity of paper, some special techniques must be used to partially treat it into a hydrophobic interface during the preparation of electrodes, such as using the relatively expensive wax printing technique or spraying specific hydrophobic polymers (Anal. Chem. 2009, 81, 5821–5826; RSC Adv. 2015, 5, 78109-78127). In addition, flexible plastic films with high flexibility commonly seen in daily life, such as polyethylene (PE), polystyrene (PS), polypropylene (PP), etc., are also widely used in the preparation of flexible electrodes. It is worth noting that screen printing technology is the main fabrication process adopted during the preparation of flexible electrodes on the above flexible substrates (LabChip 2018, 18, 1812-1830). In recent years, some flexible composite films have gradually attracted attention. For example, PET / EVA composite films are also commonly used as substrates for fabricating flexible electrodes (Nano Lett. 2015, 15, 6, 4206-4213). Although, based on the characteristic that the viscosity of EVA increases when heated, the roll-to-roll hot pressing technique can quickly transfer the conductive film from one substrate to another. However, affected by the transfer temperature and the pressure of hot pressing, in addition to the conductivity of the flexible film prepared by this method being easily affected, the microscopic morphological structure of the electrode is also easily damaged, which is very unfavorable for the construction of highly sensitive electrochemical sensors. In addition, polydimethylsiloxane (PDMS) substrates with good adhesiveness, flexibility, and biocompatibility are commonly used in the preparation of wearable flexible electrodes (ACS Appl. Mater. Interfaces 2018, 10, 13729-13740; Lab Chip 2018, 18, 1812-1830). However, since this substrate is not a semi-finished product, it needs to be prepared on-site, which not only takes a long time and has cumbersome steps but also has high requirements for the preparation conditions. Therefore, there is still a great challenge in finding flexible substrates that are easy to obtain, inexpensive, and have simple requirements for instruments and realizing the rapid and low-cost preparation of flexible electrodes. Summary of the Invention

[0007] The purpose of the present invention is to overcome the technical deficiencies of the existing vacuum filtration method and flexible substrates during the preparation of flexible electrodes, and to provide a method for preparing flexible electrodes. This method uses vacuum filtration as a technical means and relies on PET / EVA / Parafilm or PET / EVA / TPU composite films as flexible substrates to rapidly and low-cost construct a three-electrode integrated electrode chip.

[0008] To achieve the above purpose, the present invention adopts the following solutions:

[0009] First, use a heat sealer to thermally press and compound commercial polyethylene terephthalate / ethylene vinyl acetate (PET / EVA) with Parafilm or thermoplastic polyurethane elastomer rubber (TPU) to form a flexible composite film of PET / EVA / Parafilm or PET / EVA / TPU. Then, design the electrode template required for suction filtration using AI software, and use an electronic paper cutter to cut the PET / EVA / Parafilm or PET / EVA / TPU composite substrate to obtain the corresponding electrode hollow template. Next, use a heat sealer to seal the template and the filter membrane at a lower temperature to form a template / filter membrane composite film. Secondly, use the vacuum suction filtration method to suction filter silver nanowires (Ag NWs) at the position of the reference electrode on the template / filter membrane composite film to form a stable Ag NWs conductive film. Furthermore, suction filter single-walled carbon nanotubes (SWCNT) into the hollow part of the template to form a highly conductive SWCNT film. Then, separate the filter membrane from the template to obtain a filter membrane with an electrode pattern, and the separated template can be reused. Finally, utilize the characteristic that Parafilm or TPU is slightly sticky when heated, and under the irradiation of an infrared lamp, quickly transfer the electrode pattern on the filter membrane to the hydrophobic PET / EVA / Parafilm or PET / EVA / TPU composite substrate by vacuum suction pressure to finally obtain a flexible electrode.

[0010] The specific steps are as follows:

[0011] (1) At a heat-sealing temperature of 110 - 135 °C, thermally press and compound PET / EVA with Parafilm or TPU together through a heat sealer to obtain a flexible PET / EVA / Parafilm or PET / EVA / TPU composite film;

[0012] (2) Use a Silhouette Portrait electronic paper cutter to cut the PET / EVA / Parafilm or PET / EVA / TPU composite film to obtain the corresponding electrode template;

[0013] (3) At a heat-sealing temperature of 65 - 75 °C, seal the above electrode template and a microporous aqueous filter membrane (pore size 0.2 - 0.8 µm, diameter 45 - 50 mm) together through a heat sealer to obtain an electrode template / filter membrane composite film;

[0014] (4) Drop 50 - 200 µL of a 2.8 mg / mL Ag NWs dispersion liquid at the hollow position of the reference electrode of the electrode template / filter membrane composite film respectively, and use a glass sintered funnel for vacuum suction filtration to form an Ag NWs conductive film; wait for 5 min before proceeding to the next step;

[0015] (5) On the electrode template / membrane composite membrane with an Ag NWs conductive film in the reference part, add 10 mL of SWCNT with a concentration of 1.0 - 3.0 mg / mL, and use a glass sand core funnel for vacuum filtration to form a SWCNT conductive film. Then, tear off the electrode template on the electrode template / membrane composite membrane to obtain a membrane with an electrode pattern; after drying at room temperature for 1 h, perform the subsequent operations, and the separated electrode template can be reused in step (3);

[0016] (6) Place the membrane with the electrode pattern on a sand core funnel, and under the action of vacuum filtration (the pressure value of vacuum filtration is 0.6 - 1 atmospheres to achieve transfer), closely adhere it to the PET / EVA / Parafilm or PET / EVA / TPU composite membrane with the side of Parafilm or TPU, and irradiate it under an infrared lamp for 2 - 8 min to separate the membrane from the PET / EVA / Parafilm or PET / EVA / TPU composite membrane. At this time, the electrode pattern on the membrane can be transferred to the PET / EVA / Parafilm or PET / EVA / TPU composite membrane.

[0017] The present invention adopts the above technical solutions. Based on the characteristics that SWCNT and Ag NWs dispersion liquids can form conductive thin films on microporous membranes under vacuum filtration, with PET / EVA / Parafilm or PET / EVA / TPU as the substrate, and using the property that Parafilm or TPU has adhesiveness at a relatively low temperature (40 - 60 °C), the conductive pattern on the microporous membrane is transferred to the PET / EVA / Parafilm or PET / EVA / TPU flexible substrate in one step by vacuum pumping, realizing the rapid and low-cost preparation of a three-electrode integrated flexible chip with a reference electrode of an Ag NWs conductive film, a working electrode, and a counter electrode of a SWCNT conductive film. Description of the Drawings

[0018] Figure 1 is a design flow chart for the preparation of a flexible electrode.

[0019] Figure 2 It is a physical picture of a PET / EVA / Parafilm-based electrode mold.

[0020] Figure 3 It is a physical picture of PET / EVA / Parafilm / membrane.

[0021] Figure 4 It is a physical picture indicating the position of the reference electrode of PET / EVA / Parafilm / membrane.

[0022] Figure 5 It is a physical picture of the electrode pattern on a porous membrane.

[0023] Figure 6 It is a flexible electrode chip with a three - electrode integration based on PET / EVA / Parafilm, where the SWCNT conductive film serves as the working electrode and the counter electrode, and the silver nanowire conductive film serves as the reference electrode.

[0024] Figure 7 For four flexible electrode chips on the same flexible substrate in 0.05 M K containing 0.1 M KCl 3 [Fe(CN) 6 electrolyte solution cyclic voltammograms, scan rate 100 mV / s.

[0025] Figure 8 For eight flexible electrode chips on two flexible substrates in 0.05 M K containing 0.1 M KCl 3 [Fe(CN) 6 electrolyte solution cyclic voltammograms, scan rate 100 mV / s. Detailed implementation mode

[0026] Example 1

[0027] A preparation method of a flexible electrode is as follows:

[0028] (1) At a plastic - sealing temperature of 130 °C, PET / EVA and Parafilm are thermally pressed and compounded together through a plastic - sealing machine to obtain a PET / EVA / Parafilm composite film with good flexibility;

[0029] (2) Use a Silhouette Portrait electronic paper cutter to cut PET / EVA / Parafilm to obtain the corresponding electrode template;

[0030] (3) At a plastic - sealing temperature of 70 °C, the above - mentioned electrode template and a microporous aqueous filter membrane (pore size 0.45 µm, diameter 50 mm) are plastic - sealed together through a plastic - sealing machine to obtain an electrode template / filter membrane composite film;

[0031] (4) At the hollow position of the reference electrode of the electrode template / filter membrane composite film, 200 µL of a 2.8 mg / mL Ag NWs dispersion liquid is respectively dropped, and a Ag NWs conductive film is formed by vacuum filtration using a glass sand - core funnel. Wait for 5 min before proceeding to the next step;

[0032] (5) On the electrode template / membrane composite membrane with an Ag NWs conductive film in the reference part, add 10 mL of SWCNT with a concentration of 1.2 mg / mL, and use a glass sand core funnel to vacuum filter to form a SWCNT conductive film. Then tear off the electrode template on the electrode template / membrane composite membrane to obtain a membrane with an electrode pattern; after drying at room temperature for 1 h, perform the subsequent operations, and the separated electrode template can be reused in step (3);

[0033] (6) Place the membrane with the electrode pattern on a sand core funnel, and under the action of vacuum filtration (the pressure value of vacuum filtration is 0.8 atmospheres), closely adhere it to the PET / EVA / Parafilm composite membrane with the Parafilm side, and irradiate it under an infrared lamp for 4 min to separate the membrane from the PET / EVA / Parafilm composite membrane. At this time, the electrode pattern on the membrane can be transferred to the PET / EVA / Parafilm composite membrane.

[0034] Example 2

[0035] A method for preparing a flexible electrode, the steps are as follows:

[0036] (1) At a plastic sealing temperature of 130 °C, thermally press and compound PET / EVA and TPU together through a plastic sealer to obtain a PET / EVA / TPU composite membrane with good flexibility;

[0037] (2) Use a Silhouette Portrait electronic paper cutter to cut PET / EVA / TPU to obtain the corresponding electrode template;

[0038] (3) At a plastic sealing temperature of 60 °C, plastic seal the above electrode template and a microporous aqueous filter membrane (pore size 0.45 µm, diameter 50 mm) together through a plastic sealer to obtain an electrode template / membrane composite membrane;

[0039] (4) Drop 200 µL of an Ag NWs dispersion with a concentration of 2.8 mg / mL at the hollow position of the reference electrode of the electrode template / membrane composite membrane, and use a glass sand core funnel to vacuum filter to form an Ag NWs conductive film. Wait for 5 min and then proceed to the next step;

[0040] (5) On the electrode template / membrane composite membrane with an Ag NWs conductive film in the reference part, add 10 mL of SWCNT with a concentration of 1.2 mg / mL, and use a glass sand core funnel to vacuum filter to form a SWCNT conductive film. Then tear off the electrode template on the electrode template / membrane composite membrane to obtain a membrane with an electrode pattern; after drying at room temperature for 1 h, perform the subsequent operations, and the separated electrode template can be reused in step (3);

[0041] (6) Place the filter membrane with the electrode pattern on a sintered glass funnel, and under the action of vacuum filtration (the pressure value of vacuum filtration is 0.8 atmospheres), closely adhere it to the PET / EVA / TPU composite membrane with the TPU side facing up, and irradiate it under an infrared lamp for 4 minutes. Then, the filter membrane can be separated from the PET / EVA / TPU composite membrane, and at this time, the electrode pattern on the filter membrane can be transferred to the PET / EVA / TPU composite membrane.

[0042] Example 3

[0043] Characterize the electrochemical performance of four flexible electrode chips on the same flexible substrate. The experimental results show that the prepared flexible electrodes can obtain the classical redox peaks of the electroactive substance K 3 [Fe(CN) 6 in an electrolyte solution containing 0.05 M K 3 [Fe(CN) 6 and 0.1 M KCl. Moreover, when comparing the cyclic voltammograms measured for four flexible electrode chips on the same flexible substrate in a mixed electrolyte solution of K 3 [Fe(CN) 6 and KCl with the same concentration, it is found that their curves coincide very well ( Figure 7 ), indicating that the electrochemical performances of the four flexible electrode chips are basically the same, demonstrating that the flexible electrodes of the same batch prepared by the present invention have good reproducibility.

[0044] Example 4

[0045] In order to investigate the reproducibility of the flexible electrodes of different batches prepared by the present invention, we characterized the electrochemical performances of eight flexible electrode chips on two flexible substrates. The experimental results show that the cyclic voltammograms measured for eight flexible electrode chips on two flexible substrates in a mixed electrolyte solution of K 3 [Fe(CN) 6 and KCl with the same concentration coincide very well ( Figure 8 ), indicating that the electrochemical performances of the eight flexible electrode chips are basically the same, demonstrating that the flexible electrodes of different batches prepared by the technical solution of the present invention have good reproducibility, and thus further indicating that this solution has great potential for mass production.

Claims

1. A preparation method of a flexible electrode, characterized in that, it comprises the following steps: (1) Thermally press and compound PET / EVA with Parafilm or TPU together through a plastic sealer to obtain a PET / EVA / Parafilm or PET / EVA / TPU composite film; (2) Cut the PET / EVA / Parafilm or PET / EVA / TPU composite film by an electronic paper cutter to obtain a corresponding electrode template; (3) Seal the above electrode template and the filter membrane together through a plastic sealer to obtain an electrode template / filter membrane composite film; (4) Drop the Ag NWs dispersion liquid at the hollow position of the reference electrode of the electrode template / filter membrane composite film, and vacuum filter through a glass sand core funnel to form an Ag NWs conductive film, and wait for 5 min before proceeding to the next step; (5) Add SWCNT onto the electrode template / filter membrane composite film with an Ag NWs conductive film in the reference part, and vacuum filter through a glass sand core funnel to form an SWCNT conductive film, then tear off the electrode template on the electrode template / filter membrane composite film to obtain a filter membrane with an electrode pattern, dry it at room temperature and then proceed to the next step, (6) Place the filter membrane with the electrode pattern on a sand core funnel, and under the action of vacuum filtration, closely adhere it to the PET / EVA / Parafilm or PET / EVA / TPU composite film with the side of Parafilm or TPU, and irradiate it under an infrared lamp, then the filter membrane can be separated from the PET / EVA / Parafilm or PET / EVA / TPU composite film, and at this time, the electrode pattern on the filter membrane can be transferred to the PET / EVA / Parafilm or PET / EVA / TPU composite film.

2. The preparation method of a flexible electrode according to claim 1, characterized in that, in step (1), the plastic sealing temperature is 110 - 135 °C.

3. The preparation method of a flexible electrode according to claim 1, characterized in that, in step (3), the pore diameter of the filter membrane is 0.20 - 0.80 µm, and the diameter is 45 - 50 mm.

4. The preparation method of a flexible electrode according to claim 1, characterized in that, in step (3), the plastic sealing temperature is 65 - 75 °C.

5. The preparation method of a flexible electrode according to claim 1, characterized in that, in step (4), the dropping amount of the AgNWs dispersion liquid is 50 - 200 µL, and the concentration is 2.8 mg / mL.

6. The preparation method of a flexible electrode according to claim 1, characterized in that, in step (5), the dropping amount of the SWCNT is 10 mL, and the concentration is 1.0 - 3.0 mg / mL.

7. The preparation method of a flexible electrode according to claim 1, characterized in that, the electrode template after separation in step (5) is reused in step (3).

8. The preparation method of a flexible electrode according to claim 1, characterized in that, in step (6), the pressure value of the vacuum filtration is 0.6 - 1 atmosphere, and the irradiation time of the infrared lamp is 2 - 8 min.

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