A co3o4-based fuel cell type nitric oxide sensor and a method for manufacturing the same

Abstract

The application provides a Co3O4-based fuel cell type nitric oxide sensor and a preparation method thereof. The preparation method comprises the following steps: S1, adding Co3O4 material into a dispersant, and ultrasonic dispersion to obtain an active slurry; S2, drop coating the active slurry on two carbon papers, drying, then drop coating Nafion solution on the surface of the carbon papers, and continuously drying to obtain an active conductive layer; S3, clamping a Nafion film between the two active conductive layers, and hot pressing to obtain a film assembly; and S4, hot melt sealing and fixing the film assembly and a copper electrode to obtain the Co3O4-based fuel cell type nitric oxide sensor. The application adopts the hot pressing mode of the Nafion film and the carbon paper electrode, which not only improves the stability and conductivity of the electrode, but also ensures the long-term reliable operation of the sensor under environmental conditions. The preparation method is simple, controllable, has good scalability, and can meet the requirements of high sensitivity, low power consumption and strong selectivity of NO detection in practical applications.

Description

Technical Field

[0001] This invention relates to the field of nitric oxide sensor technology, specifically to a Co3O4-based fuel cell-type nitric oxide sensor and its preparation method. Background Technology

[0002] Nitric oxide (NO), a highly reactive and biotoxic gaseous component of nitrogen oxides, is widely generated from industrial emissions, vehicle exhaust, and fossil fuel combustion. Even at low concentrations, long-term exposure to NO has been shown to be closely associated with various respiratory diseases, including allergic airway inflammation, chronic bronchitis, emphysema, and other progressive lung diseases, posing a persistent threat to public health. To control exposure risks in occupational environments, the time-weighted average permissible concentration of NO in the workplace is limited to no more than 25 ppm. Beyond its environmental health impacts, nitric oxide also plays a crucial role in the diagnosis and detection of respiratory diseases. For example, in inflammatory airway diseases such as asthma, the concentration of NO in exhaled breath is considered an important biomarker, used to assess inflammation levels and treatment response. This further highlights the importance of achieving highly selective and sensitive NO detection technologies under routine environmental conditions.

[0003] Currently, NO detection methods primarily employ electrochemical sensors, metal-oxide-semiconductor (MOS) sensors, and optical detection. However, these methods still face significant challenges in complex atmospheric environments. A major bottleneck lies in the poor selectivity of most sensing materials for NO, particularly susceptible to interference from nitrogen dioxide. Since NO and NO2 often coexist in practical applications, traditional sensors struggle to effectively distinguish between these two gases, leading to high cross-sensitivity, signal distortion, and increased false alarm rates. Furthermore, existing NO sensors exhibit significant shortcomings in detection limits, response stability, and power consumption. Particularly when achieving trace detection at ppb to ppm levels at room or near-room temperature, their overall performance often fails to meet the accuracy, comfort, and energy efficiency requirements of practical applications. Therefore, developing a NO sensor capable of high selectivity, high sensitivity, strong anti-interference capabilities, and low power consumption under normal environmental conditions has become an important research direction in environmental monitoring and medical diagnostics. Summary of the Invention

[0004] Technical problems to be solved To address the shortcomings of existing technologies, this invention provides a Co3O4-based fuel cell-type nitric oxide sensor and its preparation method, thus solving the problems mentioned in the background section.

[0005] Technical solution To achieve the above objectives, the present invention provides the following technical solution: According to a first aspect of the present invention, a method for preparing a Co3O4-based fuel cell-type nitric oxide sensor is provided, comprising the following steps: S1. Add Co3O4 material to the dispersant and disperse it ultrasonically to obtain an active slurry; S2. The active slurry is drop-coated onto two sheets of carbon paper, dried, and then Nafion solution is drop-coated onto the surface of the carbon paper. After drying, an active conductive layer is obtained. S3. The Nafion membrane is sandwiched between the two active conductive layers and hot-pressed to obtain the membrane assembly; S4. The membrane assembly is heat-sealed and fixed to the copper electrode to obtain the Co3O4-based fuel cell-type nitric oxide sensor.

[0006] Preferably, in step S1, the amount of Co3O4 material added to the active slurry is 2~10 mg, and the dispersant includes 460 μL of isopropanol and 40 μL of Nafion solution.

[0007] Optionally, the amount of Co3O4 material added in the active slurry is selected from any value or a range between any two values ​​of 2mg, 3mg, 4mg, 5mg, 6mg, 7mg, 8mg, 9mg, and 10mg.

[0008] Preferably, the preparation process of the Co3O4 material is as follows: a. Dissolve cobalt nitrate hexahydrate in an aqueous methanol solution to obtain solution A; b. Dissolve 2-methylimidazole in methanol to obtain solution B; c. Add solution B to solution A, stir for 30 min, perform hydrothermal reaction, dry, and then calcine in air at a heating rate of 2 °C / min to obtain the Co3O4 material.

[0009] Preferably, the molar ratio of cobalt nitrate hexahydrate to 2-methylimidazole is 1:2~4.

[0010] Preferably, the hydrothermal reaction is carried out at a temperature of 120-130°C for 3-4 hours. The roasting temperature is 300~600℃, and the roasting time is 1~2h.

[0011] Preferably, in step S2, the porosity of the carbon paper is 70-90%.

[0012] Optionally, in step S2, the porosity of the carbon paper is any value among 70%, 75%, 80%, 85%, and 90%, or a range between any two values.

[0013] According to a second aspect of the present invention, a Co3O4-based fuel cell-type nitric oxide sensor prepared according to the above preparation method is provided, comprising copper electrodes and a membrane assembly fixed in two copper electrodes, the membrane assembly comprising an active conductive layer and a Nafion membrane fixed in two active conductive layers.

[0014] Preferably, the copper electrode is a copper ring with a hollow structure. Beneficial effects

[0015] This invention provides a Co3O4-based fuel cell-type nitric oxide sensor and its preparation method. It has the following beneficial effects: This solution provides a Co3O4-based fuel cell-type nitric oxide sensor. Utilizing the specific structure and electronic properties of Co3O4 material, it can rapidly undergo redox cycles under environmental conditions, achieving ppb-level detection sensitivity without the need for an external power source. The detection limit can reach 50ppb. Under NO concentration of 20ppm, the sensor's response time reaches 7s, recovery time reaches 6s, and the NO selectivity reaches 45.9, exhibiting excellent resistance to NO2 interference.

[0016] This solution provides a method for fabricating a Co3O4-based fuel cell-type nitric oxide sensor. By hot-pressing a Nafion membrane with a carbon paper electrode, the stability and conductivity of the electrode are improved, and the long-term reliable operation of the sensor under environmental conditions is ensured. The fabrication method is simple, highly controllable, and has good scalability, which can meet the needs of high sensitivity, low power consumption, and strong selectivity for NO detection in practical applications. Attached Figure Description

[0017] Figure 1 A schematic diagram of the structure of a Co3O4-based fuel cell-type nitric oxide sensor provided by the present invention; Figure 2 X-ray diffraction pattern of Co3O4 in the fuel cell-type nitric oxide sensor provided by the present invention; Figure 3 A scanning electron microscope image of Co3O4 in the fuel cell-type nitric oxide sensor provided by the present invention; Figure 4 A comparison diagram of the selectivity of the fuel cell-type nitric oxide sensor provided by the present invention for different gases; Figure 5 This is a dynamic response diagram of the fuel cell-type nitric oxide sensor with different Co3O4 loadings to NO. Figure 6 The response recovery time of the fuel cell-type nitric oxide sensor with different Co3O4 loadings of the present invention to NO at a concentration of 20 ppm; Figure 7The NO response curve of the sensor using YL-S30T carbon paper is shown in the comparative example of this invention. Figure 1 In the diagram, 1. Copper electrode; 2. Active conductive layer; 3. Nafion film. Detailed Implementation

[0018] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0019] The technical solution of the present invention will be described below with reference to specific embodiments and accompanying drawings. Example

[0020] A schematic diagram of a Co3O4-based fuel cell-type nitric oxide sensor is shown below. Figure 1 As shown, it includes two copper electrodes 1 as positive and negative electrodes respectively, and a membrane assembly fixed between the two copper electrodes 1. The membrane assembly includes an active conductive layer 2 loaded with Co3O4 material and a Nafion membrane 3 fixed in the two active conductive layers 2.

[0021] The specific fabrication steps of the Co3O4-based fuel cell-type nitric oxide sensor are as follows: Step 1, Preparation of Co3O4 material: 4 mmol of cobalt nitrate hexahydrate was dissolved in a mixed solvent containing 20 mL of deionized water and 10 mL of methanol to obtain solution A under stirring. 8 mmol of 2-methylimidazole was dissolved in 6 mL of methanol to obtain solution B. Solution B was slowly added to solution A, and after stirring for 30 min, the mixture was transferred to a polytetrafluoroethylene-lined stainless steel reactor and reacted at 120 °C for 3 h. The resulting precipitate was washed sequentially with deionized water and anhydrous ethanol, then vacuum dried. The dried sample was placed in a muffle furnace and calcined at 400 °C for 1 h at a heating rate of 2 °C / min to obtain Co3O4 material. Its X-ray diffraction pattern and scanning electron microscope image are shown below. Figure 2 and Figure 3 As shown, according to Figure 2 It can be seen that the prepared Co3O4 material is a typical spinel phase, belonging to the cubic crystal system with space group Fd-3m, in which Co 2+ Ions occupy octahedral sites, Co 3+ Ions occupy tetrahedral sites, there are no impurity phases, and the purity is high; according to Figure 3 It can be seen that the prepared Co3O4 material has an interlaced nanosheet structure.

[0022] Step 2, Preparation of active slurry: 2 mg of Co3O4 material was dispersed in a mixed solution of 460 μL isopropanol and 40 μL Nafion solution, and ultrasonically dispersed for 2 h under ice-water bath conditions to obtain active slurry; Step 3, Preparation of active conductive layer: The active slurry is drop-coated onto two pieces of HCP120 carbon paper with a size of 15mm×15mm and dried thoroughly in an oven. After drying, 20μL of Nafion solution is drop-coated onto the surface of the carbon paper and dried in an oven for another 2 hours to obtain two active conductive layers. Step 4, preparation of membrane module: The Nafion membrane is attached to two active conductive layers and hot-pressed at 80°C for 90 seconds to obtain the membrane module; Step 5, Sensor Assembly: Seal and fix the membrane assembly to the copper electrodes on both sides using hot melt adhesive. Example

[0023] The preparation method of this embodiment is the same as that of Example 1, except that the calcination temperature in step 1 is 300℃. Example

[0024] The preparation method of this embodiment is the same as that of Example 1, except that the calcination temperature in step 1 is 500℃. Example

[0025] The preparation method of this embodiment is the same as that of Example 1, except that the calcination temperature in step 1 is 600℃. Example

[0026] The preparation method of this embodiment is the same as that of Example 1, except that in step 2, the content of Co3O4 material in the active slurry is 5mg. Example

[0027] The preparation method of this embodiment is the same as that of Example 1, except that in step 2, the content of Co3O4 material in the active slurry is 10mg.

[0028] Comparative Example 1 The preparation method of this comparative example is the same as that of Example 1, except that in step 3, HCP120 carbon paper is replaced with YSL30T carbon paper.

[0029] Figure 4 This is a comparison chart of the selectivity of the Co3O4-based fuel cell-type nitric oxide sensors prepared in Examples 1 to 4 for various gases. Figure 4 It can be seen that the sensor prepared in this invention has a higher response value to nitric oxide compared to other gases such as nitrogen dioxide, and according to... Figure 4It is also known that the Co3O4 material calcined at 400℃ has higher redox reactivity, which makes the sensor more sensitive.

[0030] Figure 5 The dynamic response diagrams of the sensors prepared in Examples 1, 5, and 6 under NO concentrations of 50 ppm, 30 ppm, 20 ppm, 10 ppm, 5 ppm, 1 ppm, 0.5 ppm, 0.3 ppm, 0.1 ppm, and 0.05 ppm are shown below. Figure 5 It can be seen that when the amount of Co3O4 material is 10mg, the excessively thick sensitive layer results in a uniform distribution of Co3O4 material on the electrode surface, thus hindering effective gas diffusion and sufficient contact at the reaction interface. The sensor exhibits the highest response value to the target gas, but its response / recovery rate is low. Compared to 10mg, sensors with 2mg and 5mg have faster response and recovery times. According to... Figure 6 It can be seen that the sensor with 2 mg of Co3O4 material has a response time of 6 s and a recovery time of 10 s, while the sensor with 5 mg of Co3O4 material has a response time of 4 s and a recovery time of 5 s. The sensor with 5 mg of Co3O4 material ensures sufficient active sites and forms a more uniform and porous sensitive layer structure, which is conducive to the rapid adsorption and desorption of gases.

[0031] according to Figure 5 and Figure 7The comparison shows that the sensor response value based on YLS30T carbon paper is significantly lower than that based on HCP120 carbon paper. This is mainly because the porosity of YLS30T carbon paper is 60-70%, its structure is relatively dense, and there are fewer gas transport channels, making it difficult for the target gas to fully diffuse to the interface between the sensitive layer and the electrode, thus reducing gas reactivity and electron transport efficiency. In contrast, the HCP120 carbon paper used in Example 1 has a porosity of 75-85%, which has higher porosity and conductivity, facilitating rapid gas molecule penetration and effective carrier migration, resulting in a higher sensing response. As an electrode support layer, the pore structure of carbon paper plays a crucial role in gas diffusion, electrolyte penetration, and charge transport. Generally speaking, the higher the porosity, the larger the average pore size, and the shorter the gas molecule diffusion path of the carbon paper, the faster the target gas reaches the surface of the sensitive material, thereby improving the sensor's response speed. However, when the pore size is too large or the pore structure is too loose, it leads to uneven distribution of the sensitive material on the carbon paper surface and insufficient interfacial contact, thereby increasing charge transport impedance and weakening the effective utilization of the electrode active area. Therefore, the pore size of carbon paper is not necessarily better the larger it is, but rather there is an optimal balance between gas diffusion and charge transport. When the porosity is ≤70%, gas transport is restricted and the response weakens, while when the porosity is ≥90%, the adhesion of the sensitive layer decreases and the current carrying path becomes discontinuous, which also reduces the corresponding stability.

[0032] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A method for preparing a Co3O4-based fuel cell-type nitric oxide sensor, characterized in that: Includes the following steps: S1. Add Co3O4 material to the dispersant and disperse it ultrasonically to obtain an active slurry; S2. The active slurry is drop-coated onto two sheets of carbon paper, dried, and then Nafion solution is drop-coated onto the surface of the carbon paper. After drying, an active conductive layer is obtained. S3. The Nafion membrane is sandwiched between the two active conductive layers and hot-pressed to obtain the membrane assembly; S4. The membrane assembly is heat-sealed and fixed to the copper electrode to obtain the Co3O4-based fuel cell-type nitric oxide sensor.

2. The method for preparing a Co3O4-based fuel cell-type nitric oxide sensor according to claim 1, characterized in that: In step S1, the amount of Co3O4 material added to the active slurry is 2~10 mg, and the dispersant includes 460 μL of isopropanol and 40 μL of Nafion solution.

3. The method for preparing a Co3O4-based fuel cell-type nitric oxide sensor according to claim 1, characterized in that: The preparation process of the Co3O4 material is as follows: a. Dissolve cobalt nitrate hexahydrate in an aqueous methanol solution to obtain solution A; b. Dissolve 2-methylimidazole in methanol to obtain solution B; c. Add solution B to solution A, stir for 30 min, perform hydrothermal reaction, dry, and then calcine in air at a heating rate of 2 °C / min to obtain the Co3O4 material.

4. The method for preparing a Co3O4-based fuel cell-type nitric oxide sensor according to claim 3, characterized in that: The molar ratio of cobalt nitrate hexahydrate to 2-methylimidazole is 1:2~4.

5. The method for preparing a Co3O4-based fuel cell-type nitric oxide sensor according to claim 3, characterized in that: The hydrothermal reaction is carried out at a temperature of 120~130℃ for 3~4 hours. The roasting temperature is 300~600℃, and the roasting time is 1~2h.

6. The method for preparing a Co3O4-based fuel cell-type nitric oxide sensor according to claim 1, characterized in that: In step S2, the porosity of the carbon paper is 70-90%.

7. A Co3O4-based fuel cell-type nitric oxide sensor obtained by the preparation method according to any one of claims 1 to 6, characterized in that: The device includes copper electrodes and a membrane assembly fixed within the two copper electrodes. The membrane assembly includes an active conductive layer and a Nafion membrane fixed within the two active conductive layers.

8. A Co3O4-based fuel cell-type nitric oxide sensor according to claim 7, characterized in that: The copper electrode is a copper ring with a hollow structure.

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