Preparation method of petal-shaped flexible reference electrode and application thereof

Abstract

The application relates to a preparation method of a petal-shaped flexible reference electrode and application thereof, and belongs to the field of electrochemical preparation of reference electrodes. In the application, graphene oxide / carbon cloth is used as a substrate, silver is deposited by using an electrochemical method to obtain a graphene oxide / carbon cloth-Ag electrode, the electrode is chlorinated by using an electrochemical chlorination method to obtain a petal-shaped graphene oxide / carbon cloth-Ag / AgCl reference electrode, and finally, a layer of KCl-PVA-agar conductive hydrogel liquid is uniformly coated on the surface of the electrode to obtain a petal-shaped KCl-PVA-agar conductive hydrogel / graphene oxide / carbon cloth-Ag / AgCl reference electrode. In the application, graphene oxide / carbon cloth is used as a substrate for the first time, a petal-shaped nano-structured reference electrode is prepared for the first time, and a layer of hydrogel film is uniformly coated on the surface of the reference electrode. The electrode prepared in the application has the advantages of low preparation cost, good conductivity, stable performance, long service life and the like, and can be applied to wearable devices for electromyography, electrocardiogram and electroencephalogram monitoring.

Description

Technical Field

[0001] This invention belongs to the field of electrochemical preparation of reference electrodes, specifically relating to a method for preparing a petal-shaped flexible reference electrode and its application. Background Technology

[0002] In recent years, with the development of flexible wearable sensors, which have the ability to continuously and dynamically measure multiple physiological and motion parameters, flexible wearable devices that are soft, thin, and have a stretchable structure can move with the skin and achieve close contact with the skin through direct attachment. They have shown excellent repeatability in long-term vital sign monitoring. [1] Currently, flexible sensors can measure physical quantities such as temperature, heart rate, electrocardiogram, and skin texture, as well as chemical substances such as metabolites, electrolytes, and biomolecules. They can also perform percutaneous transtissue image signal detection using methods such as ultrasound and X-ray imaging. [2] As a crucial component of flexible electronic devices, the reference electrode is essential due to its advantages such as high tensile strength, light weight, good conductivity, high sensitivity, and stable chemical properties.

[0003] Currently, the most widely used method for preparing sheet-like reference electrodes is screen printing. [3] inkjet printing [4] However, the reference electrodes prepared by these two methods have low stability and short lifespan, which is not conducive to practical applications. In the applicant's previous research... [5] A reference electrode based on silver nanowires was fabricated using PDMS as a flexible substrate and AgNWs. This reference electrode exhibited excellent performance in terms of stability, lifespan, repeatability, and storage life. However, later studies revealed that the stability of this reference electrode still could not match that of commercially available glass Ag / AgCl reference electrodes. Therefore, the primary challenge in the research of sheet-like reference electrodes remains improving electrode stability to reach the level of commercially available glass Ag / AgCl reference electrodes, thereby enhancing both the electrode's lifespan and long-term stability. Summary of the Invention

[0004] To address the performance shortcomings of existing reference electrodes, this invention discloses a method for preparing a petal-shaped flexible reference electrode, namely a KCl-PVA-agar conductive hydrogel / graphene oxide / carbon cloth-Ag / AgCl reference electrode, and its application, using polyvinyl alcohol (PVA). This invention uses graphene oxide / carbon cloth as the substrate for the reference electrode. First, silver is deposited electrochemically to obtain a graphene oxide / carbon cloth-Ag electrode. Then, the graphene oxide / carbon cloth-Ag electrode is chlorinated electrochemically to obtain a petal-shaped graphene oxide / carbon cloth-Ag / AgCl reference electrode. Finally, a layer of KCl-PVA-agar conductive hydrogel is uniformly coated on its surface to obtain the petal-shaped KCl-PVA-agar conductive hydrogel / graphene oxide / carbon cloth-Ag / AgCl reference electrode. The electrodes prepared by this invention have advantages such as low preparation cost, high tensile strength, light weight, good conductivity, stable chemical properties, and long service life. They can also be applied in wearable devices for monitoring electromyography, electrocardiography, and electroencephalography.

[0005] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0006] Step 1: Coat a graphene oxide solution uniformly onto a carbon cloth substrate to obtain a graphene oxide / carbon cloth flexible substrate.

[0007] Step 2: Preparation of graphene oxide / carbon cloth-Ag / AgCl reference electrode.

[0008] Step 2.1: A three-electrode system was adopted, with a graphene oxide / carbon cloth flexible substrate as the working electrode, a saturated calomel electrode as the reference electrode, and a platinum wire as the counter electrode. They were placed in a mixed solution of AgNO3 and KNO3, and electrochemical deposition was performed using the chronopotential method to obtain a graphene oxide / carbon cloth-Ag electrode.

[0009] Step 2.2: Using a three-electrode system, with a graphene oxide / carbon cloth-Ag electrode as the working electrode, a saturated calomel electrode as the reference electrode, and a platinum wire as the counter electrode, this three-electrode system was placed in a hydrochloric acid solution, and electrochemical chlorination was performed using a chronopotentiometric method to obtain a petal-shaped graphene oxide / carbon cloth-Ag / AgCl reference electrode.

[0010] Step 3: Preparation of KCl-PVA-agar conductive hydrogel / graphene oxide / carbon cloth-Ag / AgCl reference electrode.

[0011] 0.5000g PVA was dissolved in 20mL of 80℃ ultrapure water. Then, 0.3g of agar powder was added to 20mL of saturated KCl solution and heated until completely dissolved. The PVA solution and the saturated KCl-agar solution were mixed to obtain KCl-PVA-agar conductive hydrogel solution. After cooling and standing for 6h, a petal-shaped graphene oxide / carbon cloth-Ag / AgCl reference electrode was immersed in the conductive hydrogel solution, and a layer of hydrogel film was uniformly coated on its surface. After drying and standing, a petal-shaped KCl-PVA-agar conductive hydrogel / graphene oxide / carbon cloth flexible-Ag / AgCl reference electrode was obtained.

[0012] More specifically, the method for preparing the substrate in step 1 is as follows: take a piece of carbon cloth and cut it into several sizes of 2cm×4cm, then uniformly coat the carbon cloth substrate with graphene oxide solution to obtain a graphene oxide / carbon cloth substrate.

[0013] In the above method, in step 1, the concentration of the graphene oxide solution is 2-8 mg / mL, preferably 6 mg / mL.

[0014] In the above method, in step 2.1, the concentration of AgNO3 solution is 0.01-0.1M, the concentration of KNO3 solution is 0.1-1.0M, preferably, the concentration of AgNO3 solution is 0.05M, and the concentration of KNO3 solution is 0.5M.

[0015] In the above method, in step 2.1, silver is deposited using the chronopotential method, with a deposition potential of -0.6V and a deposition time of 1800s-3600s. Preferably, the deposition potential is -0.6V and the deposition time is 2400s.

[0016] In the above method, in step 2.2, the concentration of the hydrochloric acid solution is 0.05-0.15M, preferably 0.1M.

[0017] In the above method, in step 2.2, electrochemical chlorination is performed using a chronopotential method. The chlorination potentials are OCP+100mV, OCP+150mV, OCP+200mV, OCP+250mV, and OCP+300mV, with the optimal value being OCP+250mV. The chlorination time is 2400s-3600s, and preferably, the chlorination potential is OCP+250mV and the chlorination time is 3000s.

[0018] This invention also protects the application of a KCl-PVA-agar conductive hydrogel / graphene oxide / carbon cloth-Ag / AgCl reference electrode in the wearable industry, particularly in electromyography (EMG) monitoring, electrocardiogram (ECG) monitoring, and electroencephalogram (EEG) monitoring.

[0019] Carbon cloth, also known as carbon fiber cloth, is composed of oxidized polyacrylonitrile fiber fabric through carbonization or carbon fiber through weaving. Carbon cloth possesses properties such as high strength, high durability, low density, good conductivity, and good flexibility, thus its applications are very wide-ranging. For example, it is used in battery research as a negative electrode for electron acceptance and transfer; in supercapacitor research as a current collector, electron transport, and current collection structure or component; and as a substrate material in electrochemistry, where metal oxides are deposited on carbon cloth to test the performance of the metal oxides.

[0020] Graphene oxide is a non-traditional type of soft material with good hydrophilicity, high specific surface energy, and excellent mechanical properties. Because of the coexistence of various oxygen-containing functional groups on the basal planes and edges of the graphene oxide sheet framework, its conductivity and band gap can be modulated by controlling the type and number of these oxygen-containing functional groups. Therefore, graphene oxide is widely used in conductive materials.

[0021] KCl-PVA-agar conductive hydrogel has good conductivity, adhesion, flexibility and ion permeability. Using KCl-PVA-agar conductive hydrogel as an encapsulation film can protect the electrode from damage, reduce the contamination of the reference electrode, increase the stability of the reference electrode, and improve the service life of the reference electrode.

[0022] Compared with existing technologies, the advantages of this invention are as follows: This invention is the first to use graphene oxide / carbon cloth as a substrate, which has advantages such as excellent conductivity, light weight per unit area, and low preparation cost. This invention uses a highly flexible KCl-PVA-agar conductive hydrogel with excellent ion permeability as a surface film, which can reduce contamination of the reference electrode, increase the stability of the reference electrode, and improve the service life of the reference electrode. This invention is the first to prepare a reference electrode with a petal-shaped nanostructure, whose stability is comparable to commercial reference electrodes. The reference electrode prepared by this invention can be applied to wearable devices for monitoring electromyography, electrocardiography, and electroencephalography. Attached Figure Description

[0023] Figure 1 Scanning electron microscope image of the KCl-PVA-agar conductive hydrogel / graphene oxide / carbon cloth flexible-Ag / AgCl reference electrode;

[0024] Figure 2 A comparison of the stability of the KCl-PVA-agar conductive hydrogel / graphene oxide / carbon cloth flexible-Ag / AgCl reference electrode and the commercial hard glass Ag / AgCl reference electrode.

[0025] Figure 3 Electromyography (EMG) of a human using a KCl-PVA-agar conductive hydrogel / graphene oxide / carbon cloth flexible-Ag / AgCl electrode;

[0026] Figure 4 Electrocardiogram of a human using a KCl-PVA-agar conductive hydrogel / graphene oxide / carbon cloth flexible-Ag / AgCl electrode;

[0027] Figure 5 Electroencephalography (EEG) of a human using a KCl-PVA-agar conductive hydrogel / graphene oxide / carbon cloth flexible-Ag / AgCl electrode. Detailed Implementation

[0028] The present invention will be further described below with reference to the embodiments. Unless otherwise specified, the experimental methods described in the embodiments are conventional methods; unless otherwise specified, the experimental reagents and materials can be obtained commercially.

[0029] Example 1

[0030] The preparation method of the KCl-PVA-agar conductive hydrogel / graphene oxide / carbon cloth-Ag / AgCl reference electrode is as follows:

[0031] Step 1: Fabricate a flexible graphene oxide / carbon cloth substrate.

[0032] Take a piece of carbon cloth and cut it into several 2cm×4cm sizes. Apply a 6mg / mL graphene oxide solution evenly to the carbon cloth substrate to obtain a graphene oxide / carbon cloth substrate.

[0033] Step 2: Preparation of graphene oxide / carbon cloth-Ag / AgCl reference electrode.

[0034] Step 2.1: Preparation of graphene oxide / carbon cloth-Ag electrode.

[0035] A three-electrode system was adopted, with the graphene oxide / carbon cloth flexible substrate prepared in step 1 as the working electrode, a saturated calomel electrode as the reference electrode, and a platinum wire as the counter electrode. The substrate was placed in a mixed solution of 0.05 M AgNO3 and 0.5 M KNO3 and electrochemical deposition was performed using a chronopotential method. The deposition potential was -0.6 V and the deposition time was 2400 s. After deposition, a graphene oxide / carbon cloth-Ag electrode was obtained.

[0036] Step 2.2: Chlorinated graphene oxide / carbon cloth-Ag electrode.

[0037] Using the graphene oxide / carbon cloth-Ag electrode prepared in step 2.1 as the working electrode, a saturated calomel electrode as the reference electrode, and a platinum wire as the counter electrode, this three-electrode system was placed in a 0.1M hydrochloric acid solution and chlorinated using a chronopotential method at an OCP+250mV for 3000s. The chlorinated electrode was then stored at room temperature in a dark, dry environment for one day to obtain a petal-shaped graphene oxide / carbon cloth-Ag / AgCl reference electrode.

[0038] Step 3: Preparation of KCl-PVA-agar conductive hydrogel / graphene oxide / carbon cloth-Ag / AgCl reference electrode.

[0039] 0.5000 g PVA was dissolved in 20 mL of 80 °C ultrapure water. Then, 0.3 g agar powder was added to 20 mL of saturated KCl solution and heated until completely dissolved. The PVA solution and saturated KCl-agar solution were mixed to obtain a KCl-PVA-agar conductive hydrogel solution. After cooling and standing for 6 hours, a petal-shaped graphene oxide / carbon cloth-Ag / AgCl reference electrode was immersed in this conductive hydrogel solution, uniformly coating its surface with a hydrogel film. After drying and standing, a petal-shaped KCl-PVA-agar conductive hydrogel / graphene oxide / carbon cloth flexible-Ag / AgCl reference electrode was obtained. The scanning electron microscope image is shown below. Figure 1 As shown.

[0040] Example 2

[0041] Stability Comparison of KCl-PVA-Agar Conductive Hydrogel / Graphene Oxide / Carbon Cloth-Ag / AgCl Reference Electrode and Commercial Hard Glass Ag / AgCl Reference Electrode

[0042] The open-circuit potential (OCP) of the two reference electrodes described above was tested, and the test results are as follows: Figure 2 As shown, the results indicate that the test curves of the KCl-PVA-agar conductive hydrogel / graphene oxide / carbon cloth-Ag / AgCl reference electrode prepared in this invention are both very stable and show little difference compared to the commercial hard glass Ag / AgCl reference electrode. Therefore, the stability of the reference electrode prepared in this invention is comparable to that of the commercial hard glass Ag / AgCl reference electrode, a level that prior art reference electrodes have not yet achieved.

[0043] Example 3

[0044] Application of KCl-PVA-agar conductive hydrogel / graphene oxide / carbon cloth-Ag / AgCl flexible reference electrode in electromyography (EMG), electrocardiogram (ECG), and electroencephalogram (EEG) monitoring.

[0045] Like nerve cells, muscle fibers (cells) are also excitable cells. When excited, they generate action potentials, which are conductive potentials appearing across the cell membrane at the site of excitation. Surface electromyography (EMG) is a method of measuring bioelectrical signals during the activity of nearby muscle fibers (cells) by placing electrodes on the skin surface. Currently, most surface EMG monitoring uses nano-silver / silver chloride electrodes, which have disadvantages such as high manufacturing cost and poor stability. This invention's KCl-PVA-agar conductive hydrogel / graphene oxide / carbon cloth-Ag / AgCl flexible reference electrode has advantages such as low manufacturing cost, high stability, and strong signal transmission capability. It is applied to the measurement of the electromyographic morphology of the common peroneal nerve, tibial nerve, and superficial peroneal nerve in surface EMG monitoring, such as... Figure 3 As shown.

[0046] Electrocardiography (ECG) is a technique that uses an ECG machine to record the changes in electrical activity of the heart during each cardiac cycle from the body surface. By placing measuring electrodes on the human body surface to record the curves of cardiac electrical activity, it is of great significance for the diagnosis and analysis of various arrhythmias and conduction blocks. Currently, commonly used electrodes for biosignal transduction in ECG monitoring include silver-plated copper alloy electrodes, nickel-silver alloy electrodes, zinc-silver-copper alloy electrodes, and stainless steel electrodes. While these electrodes can achieve high-performance detection and are widely used in existing medical testing, their manufacturing costs are high. The KCl-PVA-agar conductive hydrogel / graphene oxide / carbon cloth-Ag / AgCl flexible reference electrode of this invention has low manufacturing costs, stable performance, high safety, and strong signal transmission capabilities. Compared with existing reference electrodes, it is more suitable for application in wearable health monitoring systems. The results of applying the reference electrode of this invention to ECG monitoring are as follows... Figure 4 As shown.

[0047] Scalp electroencephalography (EEG) is a graphical representation of spontaneous electrical activity in the brain obtained by amplifying and recording it using electrodes applied to the scalp. EEG does not reflect the electrical activity of a single nerve cell, but rather records the sum of electrical activity from many nerve cell groups in a specific brain region represented by the electrodes. By capturing and recording spontaneous rhythmic activities in the brain, it aids clinicians in accurate analysis. Currently, electrodes commonly used in EEG monitoring are made of materials such as stainless steel, gold, or platinum. However, prolonged direct contact with gold or platinum electrodes can irritate the skin and cause discomfort to patients. The reference electrode of this invention is more wearable, safer, and has stronger signal transmission capabilities. Following the international 10-20 system electrode placement method, the reference electrode of this invention was attached to the patient's scalp for EEG monitoring. The results are as follows... Figure 5 As shown.

[0048] The above embodiments are merely illustrative and explanatory of the present invention and are not intended to limit the invention to the scope of the described embodiments. Furthermore, those skilled in the art will understand that the present invention is not limited to the above embodiments, and many more variations and modifications can be made based on the teachings of the present invention, all of which fall within the scope of protection claimed by the present invention.

[0049] References

[0050] [1] Wan Chunxue, Wu Ziyue, Huang Xian. Research progress on flexible wearable sensing and intelligent recognition technology [J]. Science in China: Chemistry, 2022, 52(11):1913-1924.

[0051] [2]KimDH,LuN,MaR,KimYS,KimRH,WangS,WuJ,WonSM,TaoH,IslamA,YuKJ,KimT,Chowdhury R,YingM,XuL,LiM,ChungHJ,KeumH,McCormickM,LiuP,ZhangYW,OmenettoFG,HuangY,Coleman T,RogersJA.Science,2011,333:838–843

[0052] [3]LindnerE,GuzinskiM,KhanTA,etal.Referenceelectrodeswithionicliquidsaltbridge:whenwillthese innovativenovelreferenceelectrodesgainbroadacceptance[J].AcsSensors,2019,4(3):549-561.

[0053] [4]CardosoRM,KalinkeC,RochaRG,etal.Additive-manufactured(3D-printed)electrochemicalsensors:Acriticalreview[J].Analyticachimicaacta,2020,1118:73-91.

[0054] [5] Sun Jing, Wang Qingxiang, Shen Guijun, Lang Mingfei. A method for preparing and applying a reusable PDMS-based Ag / AgCl microelectrode [P]. Liaoning Province: CN108195911B, 2020-05-19.

Claims

1. A method for preparing a petal-shaped flexible reference electrode, characterized in that, Includes the following steps: Step 1: Uniformly coat a graphene oxide solution onto a carbon cloth substrate to obtain a graphene oxide / carbon cloth flexible substrate. Step 2: Preparation of graphene oxide / carbon cloth-Ag / AgCl reference electrode; Step 2.1: A three-electrode system was used, with a graphene oxide / carbon cloth flexible substrate as the working electrode, a saturated calomel electrode as the reference electrode, and a platinum wire as the counter electrode. The substrate was placed in a mixed solution of AgNO3 and KNO3, and electrochemical deposition was performed using a chronopotential method. After deposition, a graphene oxide / carbon cloth-Ag electrode was obtained. The concentration of AgNO3 solution was 0.01~0.1 M, the concentration of KNO3 solution was 0.1~1.0 M, the deposition potential was -0.6 V, and the deposition time was 1800 s~3600 s. Step 2.2: Using a three-electrode system, a graphene oxide / carbon cloth-Ag electrode is used as the working electrode, a saturated calomel electrode as the reference electrode, and a platinum wire as the counter electrode. This three-electrode system is placed in a hydrochloric acid solution, and electrochemical chlorination is performed using a chronopotential method. The concentration of the hydrochloric acid solution is 0.05~0.15 M, the chlorination potential is OCP+100 mV, OCP+150 mV, OCP+200 mV, OCP+250 mV or OCP+300 mV, and the chlorination time is 2400 s~3600 s, to obtain a petal-shaped graphene oxide / carbon cloth-Ag / AgCl reference electrode. Step 3: Preparation of KCl-PVA-agar conductive hydrogel / graphene oxide / carbon cloth-Ag / AgCl reference electrode; 0.5000 g PVA was dissolved in 20 mL of 80 ℃ ultrapure water. Then, 0.3 g agar powder was added to 20 mL of saturated KCl solution and heated until completely dissolved. The above PVA solution and saturated KCl-agar solution were mixed to obtain KCl-PVA-agar conductive hydrogel solution. After cooling and standing for 6 h, a petal-shaped graphene oxide / carbon cloth-Ag / AgCl reference electrode was immersed in the conductive hydrogel solution, and a layer of hydrogel film was uniformly coated on its surface. After drying and standing, the petal-shaped KCl-PVA-agar conductive hydrogel / graphene oxide / carbon cloth-Ag / AgCl reference electrode was obtained.

2. The method according to claim 1, characterized in that, In step 1, the concentration of the graphene oxide solution is 2~8 mg / mL.

3. The method according to claim 1, characterized in that, In step 2.1, the concentration of AgNO3 solution is 0.05 M, the concentration of KNO3 solution is 0.5 M, the deposition potential is -0.6 V, and the deposition time is 2400 s.

4. The method according to claim 1, characterized in that, In step 2.2, electrochemical chlorination is performed using a chronopotential method. The concentration of the hydrochloric acid solution is 0.1 M, the chlorination potential is OCP+250 mV, and the chlorination time is 3000 s.

5. The application of the petal-shaped flexible reference electrode prepared by the method of claim 1 in wearable devices.

6. The application of the petal-shaped flexible reference electrode prepared by the method described in claim 1 in electromyography monitoring, electrocardiogram monitoring and electroencephalogram monitoring.

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