Electrochemical flexible carbon monoxide gas sensor based on composite hydrogel

Abstract

The invention discloses an electrochemical flexible carbon monoxide gas sensor based on composite hydrogel, which is characterized in that a composite hydrogel proton exchange membrane is used as a middle layer, flexible electrode layers are fixed on the upper surface and the lower surface of the composite hydrogel proton exchange membrane through an adhesive, and the outer part of an electrode is packaged by a PDMS (Polydimethylsiloxane) packaging layer; the composite hydrogel proton exchange membrane is a gel film; the flexible electrode layer adopts carbon paper loaded with a noble metal catalyst, and is combined on the upper surface and the lower surface of the composite hydrogel proton exchange membrane through chain winding and polymer plasticizing, so that the flexible electrode layer is tightly entangled with the proton exchange membrane; the PDMS packaging layer is doped with carbon black and has the surface super-hydrophobic property. The electrochemical flexible carbon monoxide gas sensor prepared by the invention can quickly respond to carbon monoxide with medium and low concentrations, can be carried on wearable equipment to realize safety monitoring, and has a good application prospect.

Description

Technical Field

[0001] This invention belongs to the field of sensors, specifically relating to an electrochemical flexible carbon monoxide gas sensor based on composite hydrogels. Background Technology

[0002] Carbon monoxide (CO) is a colorless, odorless, and highly toxic gas widely present in industrial production, mining operations, and residential gas leaks, posing a serious threat to human life. Therefore, developing fast-response, miniaturized, flexible, and highly reliable carbon monoxide sensors is a core requirement for ensuring public and industrial safety. In recent years, the development of miniaturized and flexible carbon monoxide sensors has received considerable attention. The core reason is that traditional sensors generally have many shortcomings, severely limiting their application in practical safety monitoring scenarios such as wearable devices and miners' personal alarms. These scenarios demand extremely high levels of device portability and environmental adaptability, and require sensors with rapid response capabilities to ensure timely evacuation of personnel.

[0003] Based on their working principles, existing carbon monoxide sensors are mainly classified into five categories: optical infrared, metal oxide, catalytic combustion, carbon adsorption, and electrochemical. The industry has conducted extensive research and industrialization practices to optimize the performance of each type of sensor, and significant progress has been made in all technologies. Specific research results are as follows: Optical Infrared Type: The NDIR carbon monoxide infrared sensor module developed by Henliang Gas Sensing Technology has fast response characteristics (T90≤200ms), a measurement range of 0~3000 ppm, accuracy ≤±1%FS, repeatability ≤±1%FS, and an operating temperature range of 0~45 ℃, with excellent overall detection performance.

[0004] Metal oxide type: Van Tong P et al. (Pham Van Tong, et al. Materials Research Bulletin, 2021, 137:111179) synthesized porous In2O3 nanorods using a low-cost and simple hydrothermal method. The metal oxide carbon monoxide sensor prepared after heat treatment achieved a response value of 3.5 to 400 ppm carbon monoxide at an operating temperature of 350 ℃, and exhibited good selectivity and stability for carbon monoxide. The invention patent with publication number CN120651924A proposed a room temperature MEMS carbon monoxide sensor based on Nb-TiO2 / WO3 geometrized powder material. By doping with Nb and modifying with WO3, the sensitivity and selectivity of TiO2 to carbon monoxide were improved. Combined with the characteristics of MEMS devices such as miniaturization, easy integration, low power consumption and good stability, the consistency of the sensor was significantly improved.

[0005] Catalytic combustion type: In her master's thesis (A catalytic combustion carbon monoxide sensor based on cobalt tetroxide [D]. Nanjing University of Technology, 2013.), Huang Caixia proposed a catalytic combustion carbon monoxide sensor prepared from Pt and Co3O4, in which the Pt-based sensor achieved a sensitivity of 2.67 V·L·mg. -1 The detection limit is as low as 0.0035 mg / L, and the sensitivity of the Co3O4-based sensor reaches 1.04 V·L·mg. -1 The detection limit was 0.013 mg / L, and both sensors exhibited excellent long-term stability.

[0006] Carbon adsorption type: Zuo J et al. (Zuo J, et al. Chemosensors, 2020, 8(2):36) first demonstrated a fabrication scheme for a printed flexible carbon monoxide sensor array based on a printable semiconductor catalyst-decorated reduced graphene oxide sensor medium. The sensor can operate at room temperature and is deposited on a thin flexible substrate using high-throughput printing and coating methods, and has the potential for flexible and scalable fabrication.

[0007] Electrochemical: As the technology route with the greatest potential for wearable application scenarios, electrochemical sensors have the advantages of simple structure and easy miniaturization. Some products have already achieved performance breakthroughs: the carbon monoxide sensor developed by Winsen Electronics Technology Co., Ltd., based on MECS (Micro Electrochemical Systems) technology, weighs only about 0.19g and has a volume of about 0.1cm. 3 The linear range is 0~500 ppm, the sensitivity is >1 nA / ppm, the response time T90 is <20 seconds, and it can achieve zero response in an environment with 2000 ppm alcohol interference, demonstrating excellent anti-interference ability. The project "Research on Fuel Cell CO Sensor Based on Nafion Proton Exchange Membrane" led by Professor Suo Hui of Jilin University has optimized both the sensor structure design and the membrane electrode material preparation process, expanding the sensor's detection concentration range to 0.1~500 ppm and improving the sensitivity to 77 mA / ppm. The 90% response time and 10% recovery time for 30 ppm carbon monoxide are both less than 30 seconds, resulting in a significant improvement in detection performance.

[0008] Despite the progress made in the research and development of various carbon monoxide sensors, many inherent technical shortcomings remain, making it difficult to simultaneously meet core application requirements such as fast response, miniaturization, low power consumption, high selectivity, and high stability. Specific problems are as follows: 1. Optical infrared sensors: Although they have fast response and high detection accuracy, they are bulky and not portable, making them unsuitable for miniaturized applications such as wearable devices and personal safety monitoring.

[0009] 2. Metal oxide sensors: Traditional metal oxide sensors operate at high temperatures and consume a lot of power, posing a potential risk of ignition and explosion in unknown gas environments; even if room temperature operation is achieved through material modification, the selectivity under room temperature conditions is still difficult to guarantee, and cannot meet the needs of accurate monitoring.

[0010] 3. Catalytic combustion sensors: These have problems such as high operating temperature and high power consumption, and slow response and recovery speed (such as the Pt-based and Co3O4-based sensors mentioned above, whose response and recovery time for 0.582 mg / L carbon monoxide gas is more than 50 seconds). They are also susceptible to interference from combustible gases, which can cause false alarms.

[0011] 4. Carbon adsorption sensors: Although they can operate at room temperature and have the potential for flexibility, based on the adsorption principle of carbon materials, their response speed at room temperature is usually slow and their selectivity is insufficient, making it difficult to achieve rapid and accurate monitoring of carbon monoxide.

[0012] 5. Electrochemical sensors: Although they have strong adaptability and are currently the most promising technology for wearable applications, they still face multiple core technology bottlenecks that severely restrict their performance improvement and large-scale promotion. The specific problems are as follows: First, the contradiction between the environmental friendliness and cost of proton exchange membranes is prominent. The proton exchange membranes required by existing sensors are mostly made of Nafion (a perfluorosulfonic acid polymer), which has a very high production cost and generates a large amount of non-degradable waste during the production process, resulting in poor environmental friendliness. On the other hand, natural polymer hydrogels, as a potential alternative to Nafion, have the inherent defect of low proton conduction efficiency, which makes it difficult to meet the rapid response requirements of sensors. Secondly, the proton conduction mechanism of natural polymer hydrogels is hindered. On the one hand, their complex and disordered internal network structure makes it difficult to form efficient and rapid proton transport channels, resulting in protons being obstructed during transport and unable to reach the electrode surface quickly, thus prolonging the sensor response time. On the other hand, the hydrogel polymer backbone is mainly composed of hydroxyl and carboxyl groups with weak dissociation ability, lacking strong proton donor groups, which cannot effectively increase proton concentration and efficiently bind and dissociate protons. This results in fewer effective proton conduction sites and a lower density of transport channels, preventing the Grothuss proton conduction mechanism from functioning fully. At the same time, hydrophilic small molecule additives such as glycerol introduced to improve water retention and antifreeze properties will inhibit the hydrogen bond breaking and recombination process through strong hydrogen bonds, severely hindering the Grothuss mechanism and reducing water activity, making it difficult for hydrated protons to diffuse as a whole and inhibiting the efficiency of the vehicle mechanism, thus doubly restricting the proton conduction efficiency. Third, structural stability is poor in acidic environments. Although the proton exchange membrane of a fuel cell carbon monoxide sensor needs to be adapted to acidic working environments, the network structure of natural polymer hydrogels is easily loosened in acidic environments. The large number of protons generated by the reaction easily react with the electronegative groups of the polymer, weakening the degree of cross-linking, destroying the proton conduction pathway, and leading to a decrease in sensor response speed. After the proton conductivity decreases, the proton concentration in the hydrogel will further increase, forming a vicious cycle of "proton accumulation - structural destruction - conduction deterioration". Fourth, carbon paper substrates are prone to water flooding. Electrochemical sensors usually use highly permeable, highly conductive, and high-strength carbon paper as the membrane electrode substrate. However, in actual operation, the amount of water vapor entering the sensor is much greater than that of carbon monoxide. Unreacted water easily condenses in the micropores of the carbon paper, forming a water flooding phenomenon, hindering gas diffusion, and reducing the sensor response speed. Fifth, Pt catalysts are prone to poisoning and have insufficient catalytic efficiency. Sensors usually mount Pt catalysts on the surface of the membrane electrode substrate to catalyze the working electrode (CO + H2O = CO2 + 2H2O). + +2e - ) and counter electrode (2H + +1 / 2O2 + 2e -The electrochemical reaction of carbon monoxide (Pt) with H2O is catalytically efficient, but the active sites of Pt are easily blocked by the adsorption of large amounts of carbon monoxide, resulting in reduced catalytic efficiency and a significantly slower chemical reaction rate, which significantly affects the response speed and sensitivity of the sensor. Sixth, the interface between the membrane electrode and the hydrogel is not firmly bonded. In flexible electrochemical carbon monoxide sensors based on hydrogels, the surface properties of the hydrogel and the carbon paper electrode differ greatly, and the dry-wet interface is not tightly bonded, making it prone to separation under cyclic external force loads. Furthermore, after the hydrogel absorbs water and swells, it further exacerbates the interface separation problem, preventing protons from quickly entering the hydrogel for conduction, severely affecting the sensor's response performance and lifespan.

[0013] In summary, all existing carbon monoxide sensors suffer from insurmountable technical shortcomings. Electrochemical sensors, in particular, while possessing potential for wearable applications, are hampered by multiple technical bottlenecks that limit further performance improvements and large-scale application, failing to fully meet the demands of practical safety monitoring. Therefore, developing an electrochemical flexible carbon monoxide sensor based on novel proton exchange membrane materials and optimized electrode structure and interfacial bonding performance to address these technical challenges is of significant theoretical and practical value. Summary of the Invention

[0014] To address the problems existing in the prior art, this invention provides an electrochemical flexible carbon monoxide gas sensor based on composite hydrogel, aiming to achieve rapid response, high sensitivity, good flexibility and environmental stability, and adapt to practical safety monitoring scenarios such as wearable devices.

[0015] To achieve its objectives, the present invention employs the following technical solution: This invention first discloses an electrochemical flexible carbon monoxide gas sensor based on composite hydrogel. The sensor has a multilayer symmetrical composite structure, which consists of, from top to bottom: a PDMS encapsulation layer, a flexible carbon paper working electrode, a composite hydrogel proton exchange membrane, a flexible carbon paper counter electrode, and a PDMS encapsulation layer. The composite hydrogel proton exchange membrane is prepared by pre-structuring the composite hydrogel solution through directional freeze casting, room temperature curing, salting out with saturated sodium citrate solution, and washing and wetting with deionized water. In the composite hydrogel solution, the total mass fraction of chitosan, sulfonate-modified sodium alginate, polyglutamic acid, lysine, diethylene glycol, and acetic acid is 2.4-3.4%, with the remainder being the solvent (deionized water) of the composite hydrogel solution. The mass ratio of chitosan, sulfonate-modified sodium alginate, polyglutamic acid, lysine, diethylene glycol, and acetic acid is 3:5-8:1-1.5:0.25-0.5:2-3:1.2-1.6, and the molecular weight of polyglutamic acid is 50,000-100,000.

[0016] The composite hydrogel proton exchange membrane is bonded and fixed to the flexible carbon paper working electrode, and the composite hydrogel proton exchange membrane is bonded and fixed to the flexible carbon paper counter electrode, both using a tannic acid-polyvinyl alcohol adhesive. The tannic acid-polyvinyl alcohol adhesive is prepared by mixing polyvinyl alcohol, tannic acid, and deionized water in a ratio of 1 g: 0.8~1 g: 20 mL.

[0017] The flexible carbon paper working electrode and the flexible carbon paper counter electrode have the same structure, both using carbon paper as the substrate, with a Pt / Au bimetallic catalyst loaded on the substrate surface. The Pt / Au bimetallic catalyst is loaded onto the surface of the carbon paper substrate using KBr as a halogen regulator and ascorbic acid as a reducing agent through a halogen-regulated in-situ metal growth method.

[0018] The PDMS encapsulation layer is formed by spraying and cross-linking a PDMS suspension doped with carbon black. The mass ratio of carbon black to PDMS in the PDMS suspension doped with carbon black is 0.4~0.6:1.

[0019] The core technical solution of this invention is as follows: A chitosan-sulfonic acid-modified sodium alginate-polyglutamic acid composite hydrogel is used as the proton exchange membrane. An ordered internal structure of the hydrogel is achieved through a directional freeze-casting process, constructing an efficient proton conduction channel. A halogen-regulated in-situ metal growth method is employed to load a Pt / Au bimetallic catalyst onto a carbon paper substrate, improving catalytic efficiency and inhibiting catalyst poisoning. A tannic acid-polyvinyl alcohol adhesive is used to achieve tight bonding between the proton exchange membrane and the carbon paper electrode, solving the interface separation problem. A superhydrophobic encapsulation layer is prepared using a carbon black-doped PDMS suspension to block excessive moisture, prevent electrode flooding, and ensure stable sensor operation under fluctuating temperature and humidity conditions.

[0020] This composite hydrogel combines the anionic properties of sulfonic acid-modified sodium alginate with the cationic properties of chitosan, enabling electrostatic self-assembly and cross-linking under mild conditions to form a stable hydrogel network. Polyglutamic acid, in synergy with lysine, supports the gel framework and enhances water retention, while diethylene glycol optimizes gel flexibility and self-healing capabilities. As a proton exchange membrane, this composite hydrogel efficiently conducts protons while blocking electron flow, ensuring the smooth electrochemical reactions between the working and counter electrodes and guaranteeing a good linear relationship between the sensor output voltage and carbon monoxide concentration. Simultaneously, the carbon paper electrode loaded with a Pt / Au bimetallic catalyst enhances catalytic activity, and the PDMS encapsulation layer undergoes rapid cross-linking and self-roughening to achieve superhydrophobicity, effectively mitigating the impact of high external humidity on sensor performance.

[0021] This invention further provides a method for preparing an electrochemical flexible carbon monoxide gas sensor based on composite hydrogels, comprising the following steps: Step 1: Preparation of composite hydrogel proton exchange membrane Chitosan was dissolved in a 1% (w / w) acetic acid solution and stirred until completely dissolved to obtain a chitosan-acetic acid solution. Sulfonate-modified sodium alginate was dissolved in deionized water and stirred until transparent to obtain a sulfonate-modified sodium alginate solution. Polyglutamic acid was dissolved in deionized water to obtain a polyglutamic acid solution. The chitosan-acetic acid solution, sulfonate-modified sodium alginate solution, and polyglutamic acid solution were mixed and stirred for 1 hour. Lysine and diethylene glycol were then added, and stirring continued for 2-4 hours to form a homogeneous composite hydrogel solution. The composite hydrogel solution was filled into a brass-PTFE mold and frozen at -20 to -40 °C for 12-24 hours, followed by freezing at 4-25 °C. Thaw at ℃ for 4-8 hours, repeat the freeze-thaw cycle 2-4 times to complete the directional freeze-casting pre-structured treatment; fill the pre-structured composite hydrogel solution into a polytetrafluoroethylene mold and cure at room temperature, then soak in saturated sodium citrate solution at room temperature for 5-10 minutes for salting out, and wash and moisten with deionized water to obtain the composite hydrogel proton exchange membrane.

[0022] The preparation method of the sulfonic acid-modified sodium alginate is as follows: Sodium alginate is dissolved in 0.1 mol / L MES buffer to prepare a sodium alginate solution with a mass fraction of 1-2%. Taurine solid is added to the sodium alginate solution at a mass ratio of sodium alginate:taurine = 1:0.4-0.6. After stirring until completely dissolved, an EDC·HCl / NHS mixed solution is added dropwise. The mixture is stirred and reacted at room temperature in the dark for 12-24 hours. After the reaction is complete, the reaction solution is poured into ice-cold anhydrous ethanol to precipitate. The precipitate is collected by centrifugation and redissolved in deionized water. After dialyzing through a dialysis bag with a molecular weight cutoff of 12000-14000 Daltons for 72-84 hours, the sulfonic acid-modified sodium alginate is obtained by freeze-drying. The EDC·HCl / NHS mixed solution is prepared using 0.1 mol / L MES buffer as the solvent, and the concentrations of both EDC·HCl and NHS are 0.05%. The mass ratios of EDC·HCl, NHS, and sodium alginate in the mixture were 0.0863~0.1055:1 and 0.0518~0.0633:1, respectively.

[0023] Step 2: Fabrication of flexible carbon paper electrodes Using KBr as a halogen regulator and ascorbic acid as a reducing agent, a Pt / Au bimetallic catalyst was loaded onto the surface of a carbon paper substrate via a halogen-regulated in-situ metal growth method to prepare flexible carbon paper working electrodes and flexible carbon paper counter electrodes. The specific method is as follows: H₂PtCl₆·6H₂O was dissolved in deionized water to prepare a solution. KBr was added and stirred to dissolve the solution, resulting in a first mixed solution with a molar ratio of KBr to H₂PtCl₆·6H₂O of 10~12:1. Carbon paper was immersed in the first mixed solution and reacted for 20~30 minutes. Ascorbic acid solution was added dropwise, with a molar ratio of ascorbic acid to H₂PtCl₆·6H₂O of 12~18:1. The mixture was stirred at 40 °C for 4~6 hours, washed, and dried to obtain Pt-loaded carbon paper. A solution was prepared by dissolving HAuCl4·3H2O in deionized water. KBr was added and stirred to dissolve the solution, resulting in a second mixed solution with a molar ratio of KBr to HAuCl4·3H2O of 10~12:1. Pt-loaded carbon paper was immersed in the second mixed solution and reacted for 20~30 minutes. Ascorbic acid solution was added dropwise, with a molar ratio of ascorbic acid to HAuCl4·3H2O of 12~18:1. The mixture was stirred at 40 °C for 0.5~2 hours, washed, and dried to obtain a flexible carbon paper electrode supported on a Pt / Au bimetallic catalyst, which served as the flexible carbon paper working electrode and the flexible carbon paper counter electrode.

[0024] Step 3: Preparation of tannic acid-polyvinyl alcohol adhesive Polyvinyl alcohol powder is dissolved in deionized water and heated and stirred at 80-85 °C until completely dissolved. After cooling to room temperature, tannic acid powder is added and stirring is continued until the tannic acid is completely dissolved to obtain tannic acid-polyvinyl alcohol adhesive. The ratio of polyvinyl alcohol, tannic acid and deionized water is 1 g : 0.8~1 g : 20 mL. The prepared adhesive should be sealed and stored in a cool place and used within 24 hours after preparation. Step 4: Prepare a PDMS suspension doped with carbon black. Take a PDMS mixture with a main agent to curing agent mass ratio of 10:1, and mix the three components according to a volume ratio of PDMS mixture: n-hexane: deionized water = 10:6~6.5:50~55. Stir vigorously to form a PDMS solution. Add carbon black to the PDMS solution, with a carbon black to PDMS mixture mass ratio of 0.4~0.6:1. After stirring evenly, dilute with deionized water to a system mass fraction of 1~2% to obtain a carbon black-doped PDMS suspension. Step 5: Assemble the sensor Take a flexible carbon paper working electrode and a flexible carbon paper counter electrode, rinse them sequentially with acetone, ethanol, and deionized water, and dry them at room temperature. Then place them in a heating environment of 70-80 ℃ and spray them with the carbon black-doped PDMS suspension prepared in step 4. After each spraying, allow them to stand and dry before the next spraying, and spray them 3-4 times in total. After spraying, treat the two electrodes at 70-80 ℃ for 1-2 hours to obtain the working electrode-PDMS encapsulation layer composite and the counter electrode-PDMS encapsulation layer composite. After cleaning and drying the two composites again, spin coat the carbon paper electrode side of each composite with tannic acid-polyvinyl alcohol adhesive twice. After the first spin coating, air dry at room temperature until touch dry to complete the pre-curing. After the second spin coating, attach the composite hydrogel proton exchange membrane prepared in step 1 between the bonding interface of the two electrodes, roll to remove internal air bubbles, and cure at room temperature for 4-6 hours under compaction to obtain an electrochemical flexible carbon monoxide gas sensor based on composite hydrogel.

[0025] The electrochemical flexible carbon monoxide sensor of this invention is assembled from a PDMS encapsulation layer, a carbon paper electrode, and a composite hydrogel proton exchange membrane. A highly swellable chitosan-sulfonic acid-modified sodium alginate-polyglutamic acid composite hydrogel is constructed by introducing diethylene glycol and lysine. A directional freeze-casting process is used to achieve ordered internal structure of the hydrogel. Catalyst loading on the carbon paper electrode surface is accomplished through a halogen-regulated in-situ metal growth method. The PDMS layer is sprayed using a rapid cross-linking self-roughening technique, achieving superhydrophobic treatment with a simple process. Compared with existing technologies, the sensor provided by this invention possesses high response speed, high sensitivity, good stability, and excellent mechanical flexibility, making it stably adaptable to flexible wearable applications and capable of reliable operation under certain temperature and humidity fluctuations. Specific beneficial effects are reflected in the following aspects: 1. This invention designs a flexible carbon monoxide sensor based on the fuel cell reaction principle. The overall structure is simple and compact, with core advantages of small size, low operating temperature and high selectivity. It does not require complex auxiliary equipment and has stronger adaptability.

[0026] 2. This invention selects natural polymer materials such as chitosan, sodium alginate, and polyglutamic acid as the hydrogel crosslinking network matrix. The crosslinking operation is simple, and the materials themselves are biodegradable, non-toxic, and harmless. Compared with the mainstream Nafion materials, the environmental benefits are greatly improved. At the same time, natural polymer materials are widely available and have a significant competitive advantage in production costs compared with precious metals and synthetic polymer materials.

[0027] 3. This invention innovatively employs a synergistic process of directional freeze-casting and salting-out, causing the hydrogel polymer chains to extend in a uniform direction. Salting-out further enhances the cross-linking density, achieving an ordered internal structure within the hydrogel and constructing continuous, unidirectional proton-water channels. This structure ensures continuous and rapid proton conduction within the channels, significantly improving proton conductivity and thus accelerating sensor response. It solves the technical pain points of traditional hydrogels, such as disordered proton conduction paths and low efficiency.

[0028] 4. By attaching a small number of sulfonic acid groups to the side of the sodium alginate molecular chain, the proton concentration and the number of proton binding sites in the system are effectively increased, creating an efficient channel for proton conduction, further promoting rapid proton migration, and helping to improve the sensor response speed, thus overcoming the limitation of insufficient proton donors in traditional hydrogels.

[0029] 5. Lysine is rich in hydrophilic groups, which can work synergistically with polyglutamic acid to support the formation of a stable three-dimensional network structure. This structure can accommodate a large number of water molecules while inhibiting the sticky interference of small hydrophilic molecules. In addition, the moderate expansion of the polymer network caused by the high swelling capacity of the hydrogel can transform the originally locally connected structure into a large-scale connected state, forming a continuous hydrophilic water area, which provides a favorable microenvironment for continuous and rapid proton conduction.

[0030] 6. Diethylene glycol has a high diffusion rate, allowing it to rapidly diffuse to the micro-damage sites on the hydrogel and achieve rapid repair through strong hydrogen bonding. Simultaneously, the hydrogel's high swelling capacity can absorb small amounts of water vapor from the environment (or trace amounts of exudate in wearable applications), creating a stable microenvironment for the sensor's electrochemical reactions. These self-healing properties and microenvironment regulation capabilities effectively maintain the integrity of the proton conduction structure, ensure stable sensor response speed, and significantly enhance the long-term reliability of overall performance.

[0031] 7. This invention employs a PDMS spraying process, incorporating carbon black into the PDMS to prepare a superhydrophobic, opaque, flexible encapsulation layer. This process is simple to operate, and the resulting encapsulation layer effectively isolates light interference and prevents the infiltration of large amounts of external moisture. Its flexible, hydrophobic, and breathable properties enable effective sensor encapsulation, fundamentally avoiding the chemical reaction disorders caused by electrode flooding and light interference in traditional sensors, thus ensuring the sensor's operational stability.

[0032] 8. The in-situ metal growth method with halogen regulation can significantly improve the dispersibility of Pt catalysts. While reducing the Pt loading, it increases the diversity of chemical bonds on the electrode surface, thereby enhancing the reactivity of catalytic sites and thus enhancing the low-temperature oxidation activity of carbon monoxide, achieving rapid carbon monoxide consumption. At the same time, the simultaneous loading of Au nanoparticles on the electrode surface can effectively inhibit the adsorption of carbon monoxide on Pt active sites, solving the core technical problem of traditional Pt catalysts being easily poisoned by CO and experiencing activity decay.

[0033] 9. Using a tannic acid-polyvinyl alcohol adhesive to achieve interfacial bonding between the composite hydrogel proton exchange membrane and carbon paper can construct a tight dry-wet interface structure, while suppressing modulus mismatch and interfacial separation problems caused by the increase in hydrogel swelling, thus avoiding the decrease in response speed due to interfacial separation. The core principle is that when the composite hydrogel absorbs water, polymer molecules compete with water molecules for hydrogen bond sites, promoting the mutual diffusion and entanglement of polymer chains and tannic acid, resulting in moderate plasticization, thereby strengthening the interfacial bonding strength. Attached Figure Description

[0034] Figure 1 This is an overall structural diagram of the electrochemical flexible carbon monoxide gas sensor based on composite hydrogel of the present invention. Figure 2 The simplified chemical structural formula of sodium alginate modified with sulfonic acid group is shown below. Figure 3 A schematic diagram of interfacial bonding mediated by tannic acid-polyvinyl alcohol adhesive; Figure 4 The flexible carbon monoxide sensor prepared in Example 1 is shown to be the carbon monoxide output voltage-concentration response at carbon monoxide concentrations of 0–60 ppm. Figure 5 The response time and recovery time curves of the flexible carbon monoxide sensor prepared in Example 1 under carbon monoxide concentration variations of 0~60 ppm; Figure 6 The repeatability of the flexible carbon monoxide sensor prepared in Example 1 at a carbon monoxide concentration of 40 ppm; Figure 7 The flexible carbon monoxide sensor prepared in Example 1 was aged for 60 days, and its output voltage-concentration response at carbon monoxide concentrations of 0-60 ppm was measured. Figure 8 The response time and recovery time curves of the flexible carbon monoxide sensor prepared in Example 1 after aging for 60 days under carbon monoxide concentration variations of 0~60 ppm; Figure 9 The response of the flexible carbon monoxide sensor prepared in Example 1 to a mixture of methane, ethane and other organic gases; Figure 10 The response of the flexible carbon monoxide sensor prepared in Example 1 to different ambient humidity levels of 20-70%RH at a carbon monoxide concentration of 40 ppm; Figure 11 This is a photograph of the flexible carbon monoxide sensor prepared in Example 1. Detailed Implementation

[0035] The embodiments of the present invention will be described in detail below with reference to the accompanying drawings. The following embodiments are implemented based on the technical solution of the present invention, and detailed implementation methods and specific operation processes are given. However, the protection scope of the present invention is not limited to the following embodiments.

[0036] Example 1 like Figure 1 As shown, the electrochemical flexible carbon monoxide gas sensor based on composite hydrogel proposed in this invention has a multilayer symmetrical composite structure, consisting of, from top to bottom: a PDMS encapsulation layer, a flexible carbon paper working electrode, a proton exchange membrane based on composite hydrogel, a flexible carbon paper counter electrode, and the PDMS encapsulation layer. The proton exchange membrane and the electrode are bonded together using a tannic acid-polyvinyl alcohol adhesive.

[0037] The electrochemical flexible carbon monoxide sensor of this embodiment was prepared according to the following steps: Step 1: Preparation of composite hydrogel proton exchange membrane First, sulfonic acid-modified sodium alginate was prepared: 500 mg of sodium alginate was dissolved in 50 mL of 0.1 mol / L MES buffer solution with a pH of 4.6, and stirred continuously at room temperature until completely dissolved to prepare a 1% (w / w) sodium alginate solution. Then, 200 mg of taurine was added to the solution and stirred until completely dissolved. 47.95 mg of 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide hydrochloride (EDC·HCl) powder and 28.75 mg of N-hydroxysuccinimide (NHS) powder were added to 5 mL of 0.1 mol / L MES buffer solution to prepare an EDC·HCl / NHS mixed solution (both concentrations were 0.05 mol / L, with a mass ratio of 1.67:1, and their mass ratios to sodium alginate in the system were 0.0959:1 and 0.0575:1, respectively). Under vigorous stirring, the mixture was added dropwise to the reaction system of sodium alginate and taurine, and the reaction was carried out at room temperature in the dark for 12 hours. After the reaction was completed, the resulting mixture was slowly poured into 40 mL of ice-cold anhydrous ethanol to allow the product to precipitate completely. The mixture was then transferred to a high-speed refrigerated centrifuge and centrifuged at 8000 rpm and 4 °C for 10 minutes. The supernatant was then removed, and the precipitate was collected. The precipitate was redissolved in 25 mL of deionized water and transferred in batches to dialysis bags with a molecular weight cutoff of 14000 Daltons. The bags were dialyzed in 500 mL of deionized water for 72 hours, with the dialysate changed every 6 hours to completely remove byproducts and all unreacted small molecule reagents. Finally, the dialyzed solution was cryogenically frozen at -80 °C and then transferred to a freeze dryer and freeze-dried at -50 °C and a vacuum of less than 0.1 mbar for 48 hours to obtain purified sulfonic acid-modified sodium alginate solid product.

[0038] Dissolve 60 mg of chitosan powder in 3 mL of 1% (w / w) acetic acid solution and stir until completely dissolved to obtain a chitosan-acetic acid solution. Dissolve 120 mg of sulfonate-modified sodium alginate powder in 6 mL of deionized water and stir until transparent to obtain a sulfonate-modified sodium alginate solution. Select polyglutamic acid with a molecular weight of 50,000-100,000, dissolve 20 mg in 1 mL of deionized water to obtain a polyglutamic acid solution. Mix the chitosan-acetic acid solution, sulfonate-modified sodium alginate solution, and polyglutamic acid solution, stir for 1 hour, then add 5 mg of lysine and 50 mg of diethylene glycol, and continue stirring thoroughly for 3 hours to form a homogeneous composite hydrogel solution.

[0039] The composite hydrogel solution was filled into a brass-PTFE mold measuring 21 mm long, 21 mm wide, and 25 mm deep. The mold was frozen at -30 °C for 24 hours, then thawed at 25 °C for 4 hours. This freeze-thaw cycle was repeated four times to complete the directional freeze-casting pre-structuring process. The vertical temperature gradient promoted the formation of ice columns and the parallel growth of polymer chains. The ice columns in the cold matrix led to aqueous phase separation, shortening the distance between polymer chains, and allowing hydroxyl and carboxyl groups to form numerous hydrogen bonds in a relatively compact environment. Therefore, crystallization and hydrogen bonding synergistically provided initial cross-linking, promoting molecular chain entanglement.

[0040] The pre-structured composite hydrogel solution was filled into a polytetrafluoroethylene mold measuring 20 mm long, 15 mm wide, and 2 mm deep and cured at room temperature. It was then immersed in 0.5 mL of saturated sodium citrate solution at 25 °C for 10 minutes to salt out the polymer chains, thereby shortening the distance between them and increasing the degree of cross-linking. Afterward, it was washed and moistened with a small amount of deionized water to maintain humidity and avoid excessive cross-linking, completing the final structuring and obtaining the composite hydrogel proton exchange membrane.

[0041] Step 2: Fabrication of flexible carbon paper electrodes 26.3 mg of H₂PtCl₆·6H₂O was dissolved in 20 mL of Milli-Q grade deionized water, followed by the addition of 72.5 mg of KBr, making the molar ratio n(KBr) / n(H₂PtCl₆·6H₂O) = 12. The mixture was stirred for 10 minutes to obtain the first mixed solution. Carbon paper was immersed in the first mixed solution and reacted for 20 minutes. Then, 7.62 mL of fresh 0.1 mol / L ascorbic acid (AA) solution was added dropwise as a reducing agent, making the molar ratio n(AA) / n(H₂PtCl₆·6H₂O) = 15. The mixture was heated to 40 °C for 5 hours with continuous stirring until the carbon paper changed color from gray to yellow, indicating the formation of Pt particles. The carbon paper was washed several times with Milli-Q grade deionized water and dried at room temperature for 2 hours to obtain Pt-loaded carbon paper.

[0042] 20.0 mg of HAuCl4·3H2O was dissolved in 20 mL of Milli-Q grade deionized water, followed by the addition of 72.5 mg of KBr to achieve a molar ratio of n(KBr) / n(HAuCl4) = 12. The mixture was stirred for 10 minutes to obtain a second mixed solution. Pt-loaded carbon paper was immersed in this second mixed solution and reacted for 20 minutes. Then, 7.62 mL of fresh 0.1 mol / L ascorbic acid solution was added dropwise as a reducing agent, resulting in a molar ratio of n(AA) / n(HAuCl4) = 15. The mixture was heated to 40 °C for 1 hour with continuous stirring until the carbon paper changed color from yellow to brownish-red, indicating the formation of Au particles. The carbon paper was washed repeatedly with Milli-Q grade deionized water and dried at room temperature for 2 hours to obtain a flexible carbon paper electrode supported on a Pt / Au bimetallic catalyst, which served as both the working and counter electrodes of the flexible carbon paper.

[0043] Step 3: Preparation of tannic acid-polyvinyl alcohol adhesive While stirring, dissolve 1.0 g of polyvinyl alcohol powder in 16 mL of deionized water. Heat to 85 °C and stir continuously for 30 minutes until the polyvinyl alcohol is completely dissolved and a transparent solution is formed. Then, allow it to cool naturally to room temperature (25 °C). Add a total of 1.0 g of tannic acid powder in twenty batches, and continue stirring for 30 minutes until the tannic acid is completely dissolved and the solution is a uniform pale yellow color. Finally, add deionized water to adjust the total volume to 20 mL and stir thoroughly to obtain the tannic acid-polyvinyl alcohol adhesive. The prepared adhesive should be sealed and stored in a cool place and used within 24 hours after preparation to ensure the stability of the adhesive performance.

[0044] Step 4: Prepare a PDMS suspension doped with carbon black. Mix 18.73 g of Sylgard 184 PDMS base agent with 1.87 g of curing agent and add to 12 mL of n-hexane. Add the mixture to 100 mL of deionized water and stir vigorously for 10 minutes to form a PDMS solution. Add 10 g of carbon black to the PDMS solution, stir well, and then add 1.9 L of deionized water while stirring to dilute and obtain a carbon black-doped PDMS suspension.

[0045] Step 5: Assemble the sensor Take the flexible carbon paper working electrode and flexible carbon paper counter electrode, and clean them sequentially with acetone, ethanol, and deionized water, respectively, and dry them at room temperature. Use a spray gun to spray a PDMS suspension doped with carbon black onto the electrode substrate heated to 80 ℃. The spraying conditions are: a distance of 10 cm between the spray gun and the substrate, and a spray volume of 0.1 mL·cm³. -2The process involves a cycle with a spraying pressure of 0.1 bar, a spray gun moving speed of 30 cm / s, a spray flow rate of 20 mL / min, and a nozzle diameter of 1.2 mm. Each spray is allowed to stand for 1 hour to dry before the next spray is applied. A total of 4 sprays are applied. After spraying, the electrode is treated at 80 °C for 2 hours to achieve cross-linking and shaping of the PDMS microstructure, resulting in a working electrode-PDMS encapsulation layer composite and a counter electrode-PDMS encapsulation layer composite.

[0046] After cleaning and drying the two conjugates again, they were flattened and fixed on a vacuum spin coater. Tannic acid-polyvinyl alcohol adhesive was spin-coated twice on one side of the carbon paper electrode of each conjugate. The first spin-coating conditions were: spin-coating at 500 rpm for 5 seconds, then spin-coating at 700 rpm for 5 seconds. After spin-coating, the conjugates were air-dried at room temperature until they were touch-dry to complete the pre-curing. After pre-curing, a second spin-coating was performed under the same conditions. Then, the composite hydrogel proton exchange membrane prepared in step 1 was carefully attached between the bonding interfaces of the two conjugates. The membrane was gently rolled to remove internal air bubbles and cured at room temperature for 6 hours under compaction to obtain an electrochemical flexible carbon monoxide gas sensor based on the composite hydrogel.

[0047] Figure 2 This is a schematic diagram of the structure of sodium alginate modified with sulfonic acid groups. In its repeating unit structure, the carboxyl groups on the sodium alginate backbone are linked to sulfonic acid groups (-SO3) via amidation. - This structure forms negatively charged hydrophilic side chains. This design significantly increases the number of proton donors and proton binding sites in the material, providing highly efficient proton conduction capabilities for the composite hydrogel and serving as a key structural basis for the sensor's rapid response.

[0048] Figure 3 This diagram illustrates the bonding mechanism between the hydrogel and electrode interfaces, visually demonstrating the interfacial interaction mechanism of the tannic acid-polyvinyl alcohol binder between the composite hydrogel and the carbon paper electrode. The left side shows the initial state, with clear interfaces between the hydrogel (layer 1), binder (layer 2), and carbon paper electrode (layer 3). The right side shows the state after water absorption; the hydrogel swells upon absorbing water, promoting the diffusion, entanglement, and moderate plasticization of the polymer chains and tannic acid at the interface, forming a tight wet-dry bond structure. This mechanism effectively suppresses interfacial separation caused by hydrogel swelling, ensuring the stability of the sensor's response speed.

[0049] The output voltage of the electrochemical flexible carbon monoxide sensor prepared in Example 1 was tested within the CO concentration range of 0–60 ppm, and the results are as follows: Figure 4As shown, the sensor output voltage exhibits a good linear positive correlation with CO concentration, with a high degree of linearity, indicating that the sensor has excellent detection accuracy and quantitative capability within this concentration range. As the CO concentration increases, the output voltage rises steadily without a significant saturation trend, proving that the sensor has high sensitivity to low concentrations of CO and can achieve accurate detection of trace CO leaks.

[0050] The response time and recovery time of the sensor were tested under different CO concentrations, and the results are as follows: Figure 5 As shown, the sensor response time is generally maintained at 5-12 seconds, which is much faster than that of traditional electrochemical sensors, demonstrating the rapid response advantage brought by the efficient proton conduction of the composite hydrogel. Although the recovery time fluctuates slightly with the increase of concentration, it remains at 5-27 seconds overall, indicating that the sensor can quickly recover to the baseline state after completing the detection, has good continuous detection capability, and can be adapted to real-time monitoring scenarios.

[0051] At a CO concentration of 40 ppm, the sensor was subjected to 10 repeated measurements, and the results are as follows: Figure 6 As shown in the figure. In 10 experiments, the sensor output voltage remained stable between 35 and 48 mV, with an average value of approximately 40 mV, showing no significant attenuation or drift, demonstrating that the sensor's catalytic system, interface structure, and packaging design all possess excellent long-term reliability.

[0052] The working electrode and counter electrode were connected, and the sensor was short-circuited for 48 hours for aging, followed by 56 days of natural aging in clean air, and then short-circuited for another 48 hours. The output voltage of the aged sensor was tested within a CO concentration range of 0–60 ppm, and the results are as follows. Figure 7 As shown, the sensor output voltage maintains a good linear positive correlation with CO concentration, exhibiting high linearity and confirming the sensor's excellent long-term stability.

[0053] The response time and recovery time of the aged sensor were tested at different CO concentrations, and the results are as follows: Figure 8 As shown, the sensor maintains a high response speed and a fast recovery speed, and the numerical fluctuation is reduced, further verifying the long-term operational reliability of the sensor of this invention.

[0054] To verify the sensor's anti-interference performance, a mixed interference gas consisting of methane (0-50 ppm), ethane (0-50 ppm), acetaldehyde (50-100 ppm), sulfur dioxide (20-100 ppm), and toluene (50-100 ppm), generated by burning paper, plastic, and rubber, was introduced into the test system without the introduction of carbon monoxide. The sensor's output voltage was tested 10 times, and the results are as follows: Figure 9As shown in the figure, in 10 experiments, the sensor output voltage remained between 0 and 2 mV, and mostly remained stable between 0 and 1 mV, which is much lower than the response value for 40 ppm CO (about 40 mV). The interference on CO concentration detection is negligible, indicating that the sensor has excellent anti-interference ability and high selectivity for non-target organic interfering gases.

[0055] The sensor's output voltage was tested under different ambient humidity conditions, ranging from 20% to 70% RH, and the results are as follows: Figure 10 As shown, the sensor output voltage is stable between 33 and 43 mV, with only a slight attenuation in the low humidity range, and the overall response is stable at around 40 mV, proving that the sensor has excellent environmental humidity adaptability.

[0056] The electrochemical flexible carbon monoxide sensor prepared in Example 1 was photographed, and the results are as follows: Figure 11 As shown, it is small in size and highly flexible in installation; the surface of the encapsulation layer is opaque and allows water droplets to stand upright on the surface without penetrating, proving that the sensor's encapsulation design has achieved the goal of being superhydrophobic and opaque.

[0057] The above description is merely a preferred embodiment of the present invention and is not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. An electrochemical flexible carbon monoxide gas sensor based on composite hydrogel, characterized in that, The sensor has a multi-layer symmetrical composite structure, which consists of, from top to bottom: a PDMS encapsulation layer, a flexible carbon paper working electrode, a composite hydrogel proton exchange membrane, a flexible carbon paper counter electrode, and a PDMS encapsulation layer. The composite hydrogel proton exchange membrane is prepared by directional freeze casting pre-structuring treatment of a composite hydrogel solution, room temperature curing, salting out with saturated sodium citrate solution, and washing and wetting with deionized water; the total mass fraction of chitosan, sulfonic acid-modified sodium alginate, polyglutamic acid, lysine, diethylene glycol, and acetic acid in the composite hydrogel solution is 2.4~3.4%, and the solvent of the composite hydrogel solution is deionized water; The composite hydrogel proton exchange membrane and the flexible carbon paper working electrode, as well as the composite hydrogel proton exchange membrane and the flexible carbon paper counter electrode, are both bonded and fixed by tannic acid-polyvinyl alcohol adhesive. The flexible carbon paper working electrode and the flexible carbon paper counter electrode have the same structure, both using carbon paper as the substrate and loading a Pt / Au bimetallic catalyst on the substrate surface. The PDMS encapsulation layer is made by spraying and cross-linking a PDMS suspension doped with carbon black.

2. The electrochemical flexible carbon monoxide gas sensor based on composite hydrogel according to claim 1, characterized in that, In the composite hydrogel solution, the mass ratio of chitosan, sulfonic acid-modified sodium alginate, polyglutamic acid, lysine, diethylene glycol, and acetic acid is 3:5~8:1~1.5:0.25~0.5:2~3:1.2~1.6; the molecular weight of the polyglutamic acid is 50,000~100,000.

3. The electrochemical flexible carbon monoxide gas sensor based on composite hydrogel according to claim 1 or 2, characterized in that, The preparation method of the sulfonic acid-modified sodium alginate is as follows: Sodium alginate is dissolved in 0.1 mol / L MES buffer to prepare a sodium alginate solution with a mass fraction of 1-2%. Taurine solid is added to the sodium alginate solution at a mass ratio of sodium alginate:taurine = 1:0.4-0.

6. After stirring until completely dissolved, an EDC·HCl / NHS mixed solution is added dropwise. The reaction is carried out at room temperature in the dark for 12-24 hours. After the reaction is completed, the reaction solution is poured into ice-cold anhydrous ethanol to precipitate. The precipitate is collected by centrifugation and redissolved in deionized water. The molecular weight cutoff is 120. After dialysis with a dialysis bag containing 00~14000 Daltons for 72~84 hours, sulfonate-modified sodium alginate was obtained by freeze drying; wherein, the EDC·HCl / NHS mixed solution was prepared with 0.1mol / L MES buffer as solvent, and the concentrations of EDC·HCl and NHS were both 0.05mol / L, and the mass ratios of EDC·HCl, NHS and sodium alginate in the mixed solution were 0.0863~0.1055:1 and 0.0518~0.0633:1, respectively.

4. The electrochemical flexible carbon monoxide gas sensor based on composite hydrogel according to claim 1, characterized in that, The Pt / Au bimetallic catalyst on the surface of the flexible carbon paper working electrode and the flexible carbon paper counter electrode is loaded onto the surface of the carbon paper substrate using KBr as a halogen regulator and ascorbic acid as a reducing agent through a halogen-regulated in-situ metal growth method.

5. The sensor according to claim 4, characterized in that, The preparation steps of the Pt / Au bimetallic catalyst are as follows: H₂PtCl₆·6H₂O was dissolved in deionized water to prepare a solution. KBr was added and stirred to dissolve the solution, resulting in a first mixed solution with a molar ratio of KBr to H₂PtCl₆·6H₂O of 10~12:

1. Carbon paper was immersed in the first mixed solution and reacted for 20~30 minutes. Ascorbic acid solution was added dropwise, with a molar ratio of ascorbic acid to H₂PtCl₆·6H₂O of 12~18:

1. The mixture was stirred at 40 °C for 4~6 hours, washed, and dried to obtain Pt-loaded carbon paper. A solution was prepared by dissolving HAuCl4·3H2O in deionized water. KBr was added and stirred to dissolve the solution, resulting in a second mixed solution with a molar ratio of KBr to HAuCl4·3H2O of 10~12:

1. Pt-loaded carbon paper was immersed in the second mixed solution and reacted for 20~30 minutes. Ascorbic acid solution was added dropwise, with a molar ratio of ascorbic acid to HAuCl4·3H2O of 12~18:

1. The mixture was stirred at 40 °C for 0.5~2 hours, washed, and dried to obtain a flexible carbon paper electrode supported on a Pt / Au bimetallic catalyst, which served as the flexible carbon paper working electrode and the flexible carbon paper counter electrode.

6. The sensor according to claim 1, characterized in that, The tannic acid-polyvinyl alcohol adhesive is prepared by mixing polyvinyl alcohol, tannic acid and deionized water in a ratio of 1 g : 0.8~1 g : 20 mL.

7. The sensor according to claim 1, characterized in that, The mass ratio of carbon black to PDMS mixture in the carbon black-doped PDMS suspension is 0.4~0.6:

1.

8. A method for preparing an electrochemical flexible carbon monoxide gas sensor based on composite hydrogel as described in any one of claims 1 to 7, characterized in that, Includes the following steps: Step 1: Preparation of composite hydrogel proton exchange membrane Chitosan was dissolved in a 1% (w / w) acetic acid solution and stirred until completely dissolved to obtain a chitosan-acetic acid solution. Sulfonate-modified sodium alginate was dissolved in deionized water and stirred until transparent to obtain a sulfonate-modified sodium alginate solution. Polyglutamic acid was dissolved in deionized water to obtain a polyglutamic acid solution. The chitosan-acetic acid solution, sulfonate-modified sodium alginate solution, and polyglutamic acid solution were mixed and stirred for 1 hour. Lysine and diethylene glycol were then added, and stirring continued for 2-4 hours to form a homogeneous composite hydrogel solution. The composite hydrogel solution was filled into a brass-PTFE mold and frozen at -20 to -40 °C for 12-24 hours, followed by freezing at 4-25 °C. Thaw at ℃ for 4-8 hours, repeat the freeze-thaw cycle 2-4 times to complete the directional freeze-casting pre-structured treatment; fill the pre-structured composite hydrogel solution into a polytetrafluoroethylene mold and solidify at room temperature, then soak in saturated sodium citrate solution at room temperature for 5-10 minutes for salting out, and wash and moisten with deionized water to obtain the composite hydrogel proton exchange membrane. Step 2: Fabrication of flexible carbon paper electrodes Using KBr as a halogen regulator and ascorbic acid as a reducing agent, a Pt / Au bimetallic catalyst was loaded onto the surface of a carbon paper substrate by a halogen-regulated in-situ metal growth method to prepare a flexible carbon paper working electrode and a flexible carbon paper counter electrode. Step 3: Preparation of tannic acid-polyvinyl alcohol adhesive Polyvinyl alcohol powder is dissolved in deionized water and heated and stirred at 80-85 °C until completely dissolved. After cooling to room temperature, tannic acid powder is added and stirring is continued until the tannic acid is completely dissolved to obtain tannic acid-polyvinyl alcohol adhesive. The ratio of polyvinyl alcohol, tannic acid and deionized water is 1 g : 0.8~1 g : 20 mL. The prepared adhesive is sealed and stored in a cool place and used within 24 hours after preparation. Step 4: Prepare a PDMS suspension doped with carbon black. Take a PDMS mixture with a main agent to curing agent mass ratio of 10:1, and mix the three components according to a volume ratio of PDMS mixture: n-hexane: deionized water = 10:6~6.5:50~55. Stir vigorously to form a PDMS solution. Add carbon black to the PDMS solution, with a carbon black to PDMS mixture mass ratio of 0.4~0.6:

1. After stirring evenly, dilute with deionized water to a system mass fraction of 1~2% to obtain a carbon black-doped PDMS suspension. Step 5: Assemble the sensor Take a flexible carbon paper working electrode and a flexible carbon paper counter electrode, rinse them sequentially with acetone, ethanol, and deionized water, and dry them at room temperature. Then place them in a heating environment of 70-80 ℃ and spray them with the carbon black-doped PDMS suspension prepared in step 4. After each spraying, allow them to stand and dry before the next spraying, and spray them 3-4 times in total. After spraying, treat the two electrodes at 70-80 ℃ for 1-2 hours to obtain the working electrode-PDMS encapsulation layer composite and the counter electrode-PDMS encapsulation layer composite. After cleaning and drying the two composites again, spin coat the carbon paper electrode side of each composite with tannic acid-polyvinyl alcohol adhesive twice. After the first spin coating, air dry at room temperature until touch dry to complete the pre-curing. After the second spin coating, attach the composite hydrogel proton exchange membrane prepared in step 1 between the bonding interface of the two electrodes, roll to remove internal air bubbles, and cure at room temperature for 4-6 hours under compaction to obtain an electrochemical flexible carbon monoxide gas sensor based on composite hydrogel.

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