Flexible semiconductor gas sensor for detecting bromine gas and preparation method thereof

Abstract

The invention discloses a flexible semiconductor gas sensor for detecting bromine gas and a preparation method of the flexible semiconductor gas sensor, and belongs to the technical field of harmful gas detection.The flexible semiconductor gas sensor is characterized in that an MIL-68 (In) derived In2O3 and carbon nanofiber composite material is prepared by adopting an electrostatic spinning method, and the porous structure and the high specific surface area of MOF are utilized, so that the bromine gas detection sensitivity is improved; the bromine gas adsorption capacity and the surface reaction activity are obviously enhanced, and the sensitivity, the selectivity and the moisture resistance of the sensor are improved. The method is simple in preparation process, low in cost and suitable for large-scale production. And through ultraviolet excitation, the sensor can quickly respond at room temperature, and compared with a traditional semiconductor gas sensor, the energy consumption is reduced. According to the invention, electrolyte leakage of the zinc-bromine flow battery can be monitored in time, environmental pollution is prevented, and the safety and operation reliability of the system are improved.

Description

Technical Field

[0001] This invention relates to the field of hazardous gas detection technology, specifically to a room-temperature semiconductor gas-sensitive detection method based on a composite material of indium oxide (In2O3) derived from MIL-68(In) and carbon nanofibers (CNFs) for detecting gaseous bromine (Br2) in electrolyte leakage of zinc-bromine flow batteries (ZBFBs). Background Technology

[0002] Currently, research on bromine detection mainly focuses on spectroscopic methods (such as ultraviolet absorption spectrometry) and electrochemical sensor technology. Spectroscopic methods (ultraviolet absorption spectrometry) utilize the absorption characteristics of bromine in the ultraviolet region for detection. Although this method has high sensitivity and selectivity under specific conditions, its high equipment cost, complex operation, and strict environmental requirements limit its widespread application in practice.

[0003] Electrochemical sensor technology detects bromine gas through electrochemical reactions. These sensors exhibit good sensitivity and selectivity, but their response speed is slow, and their performance is unstable in high humidity environments, affecting the reliability of detection. Although these methods demonstrate high sensitivity and selectivity under specific conditions, their widespread adoption in practical applications is limited by the high cost of equipment, complex operation, and insufficient environmental adaptability.

[0004] Gas sensors based on semiconductor materials (such as tin dioxide and zinc oxide) have attracted attention due to their economic efficiency, convenience, and low power consumption. However, research on semiconductor gas-sensitive materials specifically for bromine is limited, and existing materials exhibit unsatisfactory detection performance at low or room temperature, with insufficient sensitivity and selectivity, making it difficult to meet the detection requirements in complex environments. Therefore, it is necessary to design a nanocomposite material based on semiconductor materials for Br2 detection in ZBFBs electrolyte leakage at room temperature. Summary of the Invention

[0005] To overcome the drawbacks of traditional bromine detection methods, such as high cost, complex operation, and poor universality, this paper proposes a method for fabricating and applying a flexible sensor based on a composite material of indium oxide (In2O3) derived from MIL-68(In) and carbon nanofibers (CNFs) for room temperature semiconductor gas-sensitive detection of bromine.

[0006] To achieve the above objectives, the technical solution of the present invention is as follows: A flexible semiconductor gas sensor for detecting bromine gas includes: a flexible substrate; a conductive path disposed on the surface of the flexible substrate; and a gas-sensitive film coated on the conductive path. The gas-sensitive film is a composite material of indium oxide (In2O3) derived from metal-organic framework MIL-68(In) and carbon nanofibers, wherein the In2O3 is grown in situ in the form of nanoparticles and uniformly dispersed in the carbon nanofiber network structure.

[0007] Furthermore, the composite material is prepared by a method including the following steps: S1. Provide a polymer nanofiber membrane loaded with indium source; S2. React the polymer nanofiber membrane loaded with indium source with organic ligands to grow MIL-68(In) in situ on the polymer nanofibers to obtain MOF modified nanofiber membrane. S3. The MOF-modified nanofiber membrane is subjected to the first stage of heat treatment under an oxygen-containing atmosphere to partially oxidize MIL-68(In) to In2O3. S4. The membrane that has undergone the first heat treatment is subjected to a second heat treatment under an inert atmosphere to carbonize the polymer to form carbon nanofibers and complete the crystallization of In2O3, thereby obtaining a composite material of In2O3 and carbon nanofibers.

[0008] Furthermore, the first stage of heat treatment is conducted in an air atmosphere at a temperature of 350°C to 450°C for 0.5 to 2 hours; the second stage of heat treatment is conducted in a nitrogen or argon atmosphere at a temperature of 550°C to 650°C for 0.5 to 2 hours.

[0009] Furthermore, in the composite material, the mass percentage of carbon nanofibers is 1% to 10%.

[0010] Furthermore, the gas-sensitive thin film operates under ultraviolet light excitation at a wavelength of 365 nm, with an ultraviolet light power density of 400-500 mW / cm².

[0011] Furthermore, the sensors also include: Ultraviolet light source, used to irradiate the gas-sensitive thin film; Humidity sensor, used to detect ambient humidity; The signal processing unit is configured to receive the signal from the humidity sensor and the resistance signal from the gas-sensitive film, and output the humidity-compensated bromine concentration value based on a preset humidity-concentration compensation algorithm.

[0012] Furthermore, the signal processing unit is also configured to trigger an alarm device when the bromine concentration exceeds a preset threshold.

[0013] A method for fabricating a flexible semiconductor gas sensor for detecting bromine gas includes the following steps: S01. Preparation of precursor membrane by electrospinning: Indium salt and polymer are dissolved in an organic solvent to form a spinning solution, and polymer nanofiber membrane loaded with indium source is obtained by electrospinning. S02, In-situ growth of MOF: The membrane obtained in step S01 is subjected to a solvothermal reaction with a solution of terephthalic acid to grow MIL-68(In) in-situ on the nanofibers, thereby obtaining a MOF-modified nanofiber membrane. S03, Segmented heat treatment: The MOF modified nanofiber membrane obtained in step S02 is subjected to the first stage heat treatment and the second stage heat treatment in an oxygen-containing atmosphere and an inert atmosphere, respectively, to finally obtain a composite material of In2O3 and carbon nanofibers. S04, Sensor Integration: The composite material obtained in step S03 is coated onto a flexible substrate with conductive paths to form a gas-sensitive thin film, thereby obtaining the flexible semiconductor gas-sensitive sensor.

[0014] Furthermore, in step S01, the polymer is polyacrylonitrile, the indium salt is indium nitrate, the flexible substrate is PET, and the conductive path is composed of copper tape.

[0015] A zinc-bromine flow battery electrolyte leakage monitoring system includes: a flexible semiconductor gas sensor for detecting bromine gas; and a data acquisition and display unit connected to a signal processing unit for real-time display of the bromine gas concentration value after humidity compensation.

[0016] The beneficial effects of this invention are: This invention employs electrospinning to prepare a composite material of MIL-68(In)-derived In₂O₃ and carbon nanofibers. Utilizing the porous structure and high specific surface area of ​​MOFs, the adsorption capacity for bromine gas and surface reactivity are significantly enhanced, improving the sensor's sensitivity, selectivity, and moisture resistance. This method is simple, inexpensive, and suitable for large-scale production. Furthermore, through ultraviolet light excitation, the sensor can respond rapidly at room temperature, reducing energy consumption compared to traditional semiconductor gas sensors. This invention can promptly monitor electrolyte leakage in zinc-bromine flow batteries, preventing environmental pollution and improving system safety and operational reliability. Attached Figure Description

[0017] Figure 1 XRD patterns of all samples in this embodiment of the invention.

[0018] Figure 2 SEM images of all samples in this embodiment of the invention.

[0019] Figure 3 Mapping, EDS, and HRTEM images of sample B2 in this embodiment of the invention.

[0020] Figure 4XPS image of sample B2 in an embodiment of the present invention.

[0021] Figure 5 Gas-sensitive test pattern of the sample in an embodiment of the present invention.

[0022] Figure 6 A diagram illustrating the gas-sensing mechanism of sample B2 in this embodiment of the invention.

[0023] Figure 7 A practical application diagram of sample B2 in this embodiment of the invention. Detailed Implementation

[0024] Preparation of MIL-68(In)-derived In2O3 and carbon nanofiber composite materials

[0025] Preparation of spinning solution and electrospinning: 1–5 mmol of indium nitrate (In(NO3)3) was dissolved in 10–100 mL of N,N-dimethylformamide (DMF), and then 0.892 g of polyacrylonitrile (PAN) was added with stirring until a homogeneous spinning solution was formed. The resulting solution was then treated in an electrospinning apparatus with the operating parameters set as follows: spinning distance 15 cm, voltage 15–25 kV, and flow rate 0.15 mL / h. The spun membrane was successfully prepared.

[0026] Preparation of MIL-68(In): 2-10 mmol of terephthalic acid (H₂BDC) was dissolved in an appropriate amount of DMF and stirred vigorously until a clear solution was formed. Subsequently, the dried spun membrane was added to the solution and sonicated to achieve uniform dispersion. The resulting mixture was transferred to a Teflon-lined stainless steel autoclave and reacted at 100-160°C for 24 hours to form a MIL-68(In) modified spun membrane. The reaction product was washed with deionized water and dried overnight at 80°C.

[0027] High-temperature pyrolysis treatment: The dried MIL-68(In) modified spun film was placed in a quartz boat in the center of a tube furnace, ensuring that both ends of the quartz tube were in contact with air. The tube furnace heating program was set as follows: the temperature was increased from room temperature to 220°C at a rate of 1°C / min and held for 60 minutes. Subsequently, the temperature was increased to 410-510°C at a rate of 5°C / min and held for another 60 minutes to promote the oxidation of indium atoms. Finally, under a nitrogen atmosphere, the temperature was increased to 600°C at a rate of 2°C / min and held for 60 minutes. After the heating process, the sample was allowed to cool naturally to room temperature to obtain the final product—a flexible In2O3 modified carbon nanofiber composite material, named B2. (Pure In2O3 obtained without the introduction of nitrogen during carbonization in the heat treatment process is denoted as B1. The In2O3 modified carbon nanofiber composite material obtained by introducing nitrogen in the initial stage for calcination is denoted as B3.)

[0028] Flexible sensor fabrication: The flexible sensor substrate uses PET (1-3 mm) as the substrate, with copper tape forming the conductive path. The sensing material is dispersed in deionized water and then applied to the flexible substrate via drop casting to a thickness of 100 ± 20 micrometers, followed by drying at 80°C for 24 hours. Subsequently, the prepared sensor is subjected to plasma cleaning in air for 1 minute to enhance surface activity and sensing performance.

[0029] Preparation of detection gas A self-made instrument was used to measure gases of different concentrations. The procedure for preparing the detection gas involved extracting a 1% standard gas of the target gas using a 10 mL syringe and injecting it into a 1 L gas chamber. The standard gas was then diluted with dry air to obtain a 100 ppm sample gas for detection purposes. For volatile organic compounds (VOCs) and electrolytes, a specific volume of high-purity analytical-grade aqueous solution was injected into the 1 L gas chamber using a microsyringe. The gas chamber was heated to 80°C to evaporate the liquid, generating the sample gas, and then cooled to 25°C for measurement. Various humidity conditions were simulated using a saturated salt solution, and humidity was recorded using a hygrometer after 24 hours. The flexible sensor substrate used PET as the substrate, with copper tape forming the conductive path. The sensing material was dispersed in deionized water and applied to the flexible substrate, then dried at 80°C for 24 hours. Subsequently, the prepared sensor was plasma-cleaned in an air atmosphere for 1 minute to enhance surface activity and sensing performance. The sensor response was calculated as Rg / Ra (oxidizing gas) or Ra / Rg (reducing gas), where Ra and Rg represent the resistance values ​​in air and the test gas, respectively. The response time is based on the time taken to reach 90% of the maximum response during gas injection. The UV LED has a wavelength of 365 nm, and the power density of UV irradiation on the sensor surface is 477.47 mW / cm². 2 The Fluke 8846A digital multimeter records resistance changes in real time.

[0030] Characterization Results and Discussion

[0031] X-ray diffraction analysis In this embodiment, X-ray diffraction (XRD) was used to test all samples, with diffraction angles ranging from 10 to 80°. The observed diffraction peaks matched those of cubic In₂O₃ (JCPDS No. 06-0416). Due to the low CNF content, no diffraction peaks were observed, and there were no additional peaks associated with impurities, indicating that the samples are highly crystalline.

[0032] Scanning electron microscopy and transmission electron microscopy analysis The effects of different calcination times under a nitrogen atmosphere on the nanofiber structure were presented, and the microstructure of each sample was analyzed in detail using SEM. Figure 2 As shown in (a), the synthesized precursor material B0 exhibits a distinct polygonal prism morphology, consistent with the morphology of MIL-68. Calcination of the synthesized MIL-68 in air for two hours resulted in significant wrinkling on the surface of the obtained nanofiber B1 material compared to the uncalcined state (B0). The calcination background atmosphere of the research material was changed; it was first calcined in air for one hour, then calcined again with nitrogen for one hour. Figure 2 (b) shows that some fiber structures disintegrate, increasing the chances of contact with gas. Finally, after a complete two-hour calcination in a nitrogen atmosphere, obvious nanoflowers are formed on the surface of the nanofibers.

[0033] This change in surface morphology indicates that the introduction of MOF structures not only affects the overall morphology of the fibers but may also have a profound impact on their microstructure. The introduction of MOF structures can effectively promote In₂O₃ crystallization during high-temperature calcination. Increasing surface particle size can effectively improve the specific surface area of ​​the material, which has a positive effect on gas adsorption and diffusion, thereby promoting excellent sensor performance in gas detection, including the rapid response time to Br₂. These structure-related properties, especially the adjustable surface morphology and increased surface roughness achieved through MOF structures, play a key role in optimizing nanofibers for gas sensing applications.

[0034] To further verify the composition and elemental distribution of sample B2, TEM mapping characterization was performed. Figure 3 (ae). Characterization results showed that In, O, and C were uniformly distributed throughout the sample. EDS characterization of sample B2 revealed relative percentages of O, In, and C of 66.23%, 28.71%, and 5.06%, respectively, confirming the content of these elements. From Figure 3 In the HRTEM of (g), the interplanar spacing of 0.292 nm corresponds to the In2O3 (222) crystal plane.

[0035] X-ray photoelectron spectroscopy analysis This demonstrates that the chemical valence state of the corresponding element in the sample is a key factor affecting the sensing mechanism of the gas sensor. To further verify the valence state composition of the sample, the chemical valence state of sample B2 was characterized by XPS. The scanning spectrum of sample B2 is shown below. Figure 4 As shown, the results revealed the presence of In and O in sample B2. Figure 4 (b) The XPS spectrum of sample B2 has two peaks at 451.7 eV and 444.2 eV, corresponding to In 3d 5 / 2 and In 3d 3 / 2 This indicates that In 3+ The existence of. Figure 4 Figure c shows the O 1s photoelectron spectrum of sample B2. The peaks at approximately 531.6 eV and 529.7 eV are attributed to oxygen vacancy defects (O₂, O₂, O₃ ... V ) and lattice oxygen (O L Of these, oxygen vacancy defects account for 44.2%, resulting in a high oxygen vacancy content and strong oxygen adsorption capacity in B2. In detailed analysis of C1s XPS (… Figure 4 (e) Three different carbon states can be identified in the spectrum. The C-C bond at 284.8 eV mainly originates from carbon nanofibers, while the CO bond at 286.3 eV may originate from DMF solvent residue. The OC=O at 288.7 eV mainly originates from organic ligands (H2BDC).

[0036] Gas Sensitive Test This study investigated the effect of different carbonization times on the detection capability of indium-based MOF materials for volatiles (Br2) in the discharged electrolyte at room temperature. Three experimental groups (B1, B2, and B3) were used to test the volatiles (Br2) in a 1 L chamber with 10 μL of discharged electrolyte under both UV and UV irradiation conditions. Figure 5 (a) It can be found that, regardless of the experimental conditions with or without ultraviolet light irradiation, the response of B2 to the volatilization of Br2 is much higher than that of B1 and B3. Figure 5(b) shows the dynamic resistance curves of the B2 sensor at room temperature with and without UV irradiation. To ensure the reliability of the experimental results, the recorded data were averaged after the baseline resistance stabilized during the experiment to determine the precise value. Specifically, for the resistance without UV irradiation, the average value of 100 consecutive stable data points before the reaction was calculated to be 821.97 kΩ. Under UV irradiation, the average value of 100 consecutive stable data points showed a significantly lower baseline resistance, dropping to 7.44 kΩ. The resistance decreases as UV light generates more free charge carriers (such as electrons) within the sensor material, enhancing its conductivity. Furthermore, UV light reduces the sites where electrons might be trapped, allowing for more efficient electron movement. Therefore, the sensor's electron transport capability is enhanced, resulting in a higher response, increasing from 1.44 to 3.67. The effect of UV light is further reflected in the desorption capability; without UV excitation, the sensor resistance does not spontaneously recover to the baseline position after the reaction.

[0037] To further understand the detection performance of the B2 sensor for low-concentration electrolyte (charged state) volatiles (Br2), dynamic testing of different volumes of charged electrolyte in a 1 L chamber was conducted under UV irradiation at room temperature. This allowed for the determination of the sensor's or detection device's detection limit and sensitivity, which helps in determining its suitability for the application environment. Figure 5 (c) It can be seen that the detection limit of the B2 sensor for charged electrolyte is 1 μL / L, and its response value is 1.40. A low detection limit means that the sensor can detect potential safety risks, which helps in early detection and taking necessary measures to ensure the safety of personnel and the environment. By linearly fitting the data points between 1 μL / L and 500 μL / L, the fitting equation is y=0.024x+1.196, and the R² of the least squares method is 0.994 (…). Figure 5 (d)). The repeatability of the sensor's ability to detect volatile electrolytes was verified by repeated application of the sensor. Three detection experiments were conducted on B2 using 10 μL of charged electrolyte in a 1 L chamber under UV irradiation at room temperature to detect volatiles (Br2). Figure 5As shown in (e), three repeated experiments revealed that the baseline resistance remained consistent before and after the reaction, and the reaction process exhibited high consistency, indicating that the experimental system possesses good stability and repeatability. Further investigation was conducted on the response and desorption times of 10 μL of charged electrolyte for the volatile substance bromine (Br2) within a 1 L chamber, yielding values ​​of 23.4 seconds and 104.3 seconds, respectively. These results demonstrate that the material not only exhibits excellent repeatability but also possesses rapid response and efficient desorption capabilities. The rapid response time reflects the material's high sensitivity in detecting bromine gas, enabling real-time monitoring, while the short desorption time signifies that the material can quickly recover its initial state, making it suitable for continuous cyclic use.

[0038] In practical applications, the volatile products of electrolytes often include not only gaseous bromine but also a large number of water molecules. However, high humidity generally damages the sensing performance of sensors. To explore the moisture resistance of the sensitive material and avoid the bromine detection of the sensor by water molecules, the sensor's response in high-humidity pure water vapor was tested. Figure 5(f) shows the response and resistance curves to water vapor. We can see that the material resistance fluctuates slightly under high humidity water vapor, but the baseline resistance remains unchanged after stabilization. Under high humidity conditions, water molecules rapidly undergo adsorption and desorption processes on the surface of the sensing material. This dynamic equilibrium leads to a short-term change in the charge carrier concentration on the material surface, resulting in fluctuations in resistance. MIL-68(In) derivative indium oxide (In2O3) composite carbon nanofibers (CNFs) exhibit excellent moisture resistance during detection, and their baseline resistance remains stable under the influence of high-purity water vapor. This performance is mainly attributed to the surface chemical properties, structural design, and interfacial synergistic effects of the material. From the perspective of surface chemical properties, indium oxide, as an n-type semiconductor, is rich in oxygen defects on its surface. These oxygen defects preferentially undergo chemisorption with gaseous bromine molecules (Br2) with high electron affinity, accompanied by charge transfer, while water molecules are mainly adsorbed on the surface through weaker hydrogen bonding, thus resulting in a weaker response to water vapor. Meanwhile, MIL-68(In) retains some of the porous structure of the metal-organic framework during derivatization. This microporous structure not only limits the effective adsorption of highly polar water molecules but also further enhances the selective adsorption of nonpolar bromine molecules. The carbon nanofiber substrate in the composite material further strengthens the hydrophobic properties, and the weak polarity and high conductivity of carbon materials significantly reduce the material's affinity for water molecules. In addition, the interfacial synergistic effect between the MIL-68(In) derivative and carbon nanofibers further optimizes the target molecule capture ability and significantly improves the sensitivity to gaseous bromine. Furthermore, ultraviolet light excitation in the experiment further enhances the reactive oxygen species response of the indium oxide surface, thus preferentially oxidizing gaseous bromine molecules, while the chemisorption of water molecules on the material surface is relatively stable and does not produce significant resistance changes. These factors work synergistically to enable the MIL-68(In)-derived indium oxide composite carbon nanofibers to exhibit a stable baseline resistance in a high-purity water vapor environment, while also demonstrating high selectivity for Br2. This excellent moisture resistance provides a reliable guarantee for the detection of volatiles in zinc-bromine flow battery electrolytes under complex environments.

[0039] The Br concentration in the solution of a zinc-bromine flow battery varies with the battery's charge. To further investigate the sensor's detection capability against high-concentration electrolyte volatiles, tests were conducted on 100 mL of charged electrolyte in a 1 L chamber. The response was 104984.33 (7.35 kΩ – 771634.89 kΩ). Figure 5 (g) After the response is complete, the material recovers to the baseline under room temperature UV excitation, demonstrating its excellent performance in the detection of high-concentration bromine gas, exhibiting high sensitivity, a wide response range, and excellent reversibility. These characteristics make it promising for applications in zinc-bromine flow battery monitoring, environmental gas sensors, and industrial bromine gas detection.

[0040] Various interfering gases exist in different environments and application scenarios. To explore the selectivity of the sensor, a certain concentration and volume of interfering gases and VOCs were detected under ultraviolet irradiation at room temperature. Figure 5 As shown in (h), B2 exhibits a significantly higher response to Br2 compared to other interfering gases and VOCs. The excellent selectivity of B2 can be attributed to the following reasons: First, indium oxide (In2O3) has a strong surface chemical affinity for bromine. Bromine is a strong oxidizing agent, and the surface of indium oxide has many active sites that can effectively adsorb bromine. In particular, the oxygen vacancies on the In2O3 surface are very sensitive to oxidizing gases. When bromine molecules come into contact with the In2O3 surface, a redox reaction occurs, and the migration of surface electrons leads to a significant change in the material's resistivity, thus significantly increasing the sensor's response to bromine.

[0041] The addition of composite carbon nanofibers further enhances the overall performance of the sensor. Carbon nanofibers (CNFs) possess a very high specific surface area, which significantly increases the material's adsorption capacity for gas molecules. The larger specific surface area means more active sites are available for the interaction between gas molecules and the sensing material, thereby further enhancing the sensor's detection response to bromine. Furthermore, the high conductivity of carbon nanofibers also significantly improves the sensor's response speed and sensitivity, as it promotes electron transport, facilitating smoother electron transfer resulting from the chemical reaction between bromine and indium oxide. The synergistic effect between In₂O₃ and carbon nanofibers enables the sensor to better capture bromine, providing more sensitive detection.

[0042] The strong oxidizing properties and high polarity of bromine are also reasons for its significant response. Bromine has high oxidizing power, enabling effective electron exchange with the surface of indium oxide materials, while many volatile organic compounds (VOCs) typically lack such oxidizing ability and have relatively weak polarity. This difference results in indium oxide exhibiting a higher response to bromine during detection. Bromine molecules have a high affinity for electrons, thus facilitating electron migration during interaction with the sensing material. This significant electron exchange characteristic allows bromine to induce a noticeable change in the sensor's conductivity.

[0043] Long-term stability testing verified the sensor's durability under prolonged exposure to the target gas, ensuring it would not degrade or age due to environmental factors. Therefore, when B2 was excited by UV light at room temperature, continuous detection of 100 ppm Br2 for 15 days showed minimal changes in response and baseline resistance, demonstrating long-term stability (e.g., ...). Figure 5(i) The long-term stability is mainly attributed to the chemical and structural stability of the material, the continuous effect of ultraviolet irradiation, the maintenance of the surface state, and stable electrical properties. These factors together enable the sensor to maintain a stable response and consistent resistance change over extended periods.

[0044] Gas Sensing Mechanism Based on Br2 detection results, the B2 sample obtained by calcining MIL-68(In) in air for 1 hour followed by calcination in nitrogen for 1 hour exhibited the best gas-sensing performance. The reasons for the enhanced performance of the B2 sensor are as follows: First, the resistance of the In2O3 semiconductor oxide sensor derived from MIL-68(In) decreases upon exposure to reducing gases but increases upon exposure to oxidizing gases. In the absence of ultraviolet light, B2 charge carriers are less abundant at room temperature. In air, various absorbed oxide species form on the material surface, a process of electron capture. For n-type semiconductors, conduction band electrons are captured by adsorbed oxygen, forming chemisorbed oxygen ions (such as O2). -, O - O 2- ): O2(gas)+e - →O2 - (ads) O2 - (ads) + e - →2O - (ads) Under ultraviolet radiation, photogenerated holes (h) + (hy) Electrons are generated on the surface of the sensing material at room temperature, which increases the carrier concentration and reduces the sensor resistance. Under ultraviolet irradiation, many electrons... - Formed on the sensor surface, and these e - It readily interacts with adsorbed oxygen (O2), forming more adsorbed oxygen ions (O2). - .

[0045] When the sensor is exposed to bromine gas, Br2, due to its strong oxidizing properties, preferentially adsorbs onto the active sites on the material surface. The adsorbed Br2 molecules then abstract electrons from the conduction band of indium oxide, forming bromine adsorbate species. Br2(gas) + e - → 2Br - (ads) This process leads to a significant thickening of the electron depletion layer in indium oxide, resulting in a sharp increase in electrical resistance.

[0046] Real-time monitoring system In zinc-bromine flow batteries, electrolyte leakage leading to Br2 production is a major health hazard; therefore, Br2 detection is crucial for protecting the health of researchers. A real-time Br2 monitoring system was constructed by integrating Br2 samples into the circuitry. This system consists of a data acquisition circuit, a microcontroller unit, a DHT11 temperature and humidity module, a buzzer, and an OLED. Figure 7 (a, b)). The Br2 concentration is calculated together with the temperature compensation module and the voltage signal. An important technical indicator of the sensor is the humidity compensation module, which maintains accurate readings despite varying humidity levels. The Br2 response is linearly related to both humidity and concentration. This performance allows for direct interpretation of sensor data, enabling the system to effectively detect the leakage concentration of Br2 in the zinc-bromine flow battery in real time. The response function to humidity is y. h1 =-0.017x h1 +3.228 ( Figure 7 (c)), where y h1 The humidity is x h1 The sensor response, x h1 This is the humidity value measured by the temperature and humidity module. The response function to concentration is y = 0.24x + 1.21, where y is the response value provided by the sensor and x is the concentration to be measured. This functional relationship is used to compensate for the effect of humidity on the zinc-bromine flow cell. First, based on the measured humidity value x... h1 , through y h1 The compensated response value is calculated. Then, the humidity response value is substituted into the concentration response function to obtain the humidity-compensated concentration value x. This eliminates the influence of humidity changes on the sensor's humidity measurement, ensuring the stability and reliability of the structure. The system uses an STM32F103C8T6 microcontroller. To ensure measurement accuracy, the system has been rigorously calibrated. A Br2 concentration alarm threshold of 20 µL / L is set. When the detected Br2 level exceeds the threshold, a buzzer will produce a sharp popping sound to alert researchers to take necessary action. In this operating mode, it is powered by a rechargeable lithium battery (1000 mAh) and can operate continuously for 24 hours. To simulate the real-world operating conditions of this emerging flow electrohydraulic system, the system was tested at Br2 concentrations below and above 20 µL / L, such as... Figure 7 As shown in (de). These tests were designed to verify the responsiveness and accuracy of the sensor under real-world field conditions. The goal was to ensure that the sensor could effectively monitor Br2 levels during zinc-bromine flow battery production, thereby protecting the health of researchers.

[0047] In summary, this study prepared In-based MOF-derived In₂O₃ composite carbon nanofibers using electrospinning. The In₂O₃ / CNF sample exhibited the following performance under room temperature UV irradiation: a response of 3.67 to the volatiles of 10 µL charged electrolyte in a 1 L container; response and recovery times were 23.4 s / 104.3 s; and the detection limit was 1 µL / L. Based on the sample's excellent performance under high humidity conditions, a real-time Br₂ monitoring system was constructed using an integrated humidity compensation system to display the Br₂ concentration and humidity levels during the preparation process in the zinc-bromine flow battery. When the Br₂ concentration in the environment exceeds the threshold, the system immediately issues a warning, notifying researchers to take immediate action. This system helps protect the health of researchers.

[0048] This invention prepares MIL-68(In)-derived indium oxide and carbon nanofiber composite materials by electrospinning, and utilizes the high specific surface area and porous structure of MOF structure to significantly improve the detection sensitivity and selectivity of Br2.

[0049] This invention achieves rapid baseline recovery at room temperature through ultraviolet light excitation, ensuring the stability and reliability of the sensor in high humidity environments.

[0050] The innovation of this invention lies in combining metal-organic framework-derived materials with carbon nanofibers to optimize gas-sensing and moisture-resistant properties, providing an advanced and feasible solution for the efficient and accurate detection of electrolyte leakage in zinc-bromine flow batteries.

[0051] Based on the above-described preferred embodiments of the present invention, and through the foregoing description, those skilled in the art can make various changes and modifications without departing from the inventive concept. The technical scope of this invention is not limited to the contents of the specification.

Claims

1. A flexible semiconductor gas sensor for detecting bromine gas, characterized in that, include: Flexible substrate; Conductive paths set on the surface of a flexible substrate; And a gas-sensitive film coated on the conductive path. The gas-sensitive film is a composite material of indium oxide (In2O3) derived from metal-organic framework MIL-68(In) and carbon nanofibers. In this composite material, In2O3 is grown in situ in the form of nanoparticles and uniformly dispersed in the carbon nanofiber network structure.

2. The sensor according to claim 1, characterized in that, The composite material is prepared by a method including the following steps: S1. Provide a polymer nanofiber membrane loaded with indium source; S2. React the polymer nanofiber membrane loaded with indium source with organic ligands to grow MIL-68(In) in situ on the polymer nanofibers to obtain MOF modified nanofiber membrane. S3. The MOF-modified nanofiber membrane is subjected to the first stage of heat treatment under an oxygen-containing atmosphere to partially oxidize MIL-68(In) to In2O3. S4. The membrane that has undergone the first heat treatment is subjected to a second heat treatment under an inert atmosphere to carbonize the polymer to form carbon nanofibers and complete the crystallization of In2O3, thereby obtaining a composite material of In2O3 and carbon nanofibers.

3. The sensor according to claim 2, characterized in that, The first stage of heat treatment is conducted in an air atmosphere at a temperature of 350°C to 450°C for 0.5 to 2 hours. The second stage of heat treatment is conducted in a nitrogen or argon atmosphere at a temperature of 550°C to 650°C for 0.5 to 2 hours.

4. The sensor according to claim 3, characterized in that, In composite materials, carbon nanofibers account for 1% to 10% of the mass.

5. The sensor according to claim 4, characterized in that, The gas-sensitive thin film operates under ultraviolet light excitation at a wavelength of 365 nm, with an ultraviolet light power density of 400-500 mW / cm².

6. The sensor according to claim 5, characterized in that, The sensor also includes: Ultraviolet light source, used to irradiate the gas-sensitive thin film; Humidity sensor, used to detect ambient humidity; The signal processing unit is configured to receive the signal from the humidity sensor and the resistance signal from the gas-sensitive film, and output the humidity-compensated bromine concentration value based on a preset humidity-concentration compensation algorithm.

7. The sensor according to claim 6, characterized in that, The signal processing unit is also configured to trigger an alarm device when the bromine concentration exceeds a preset threshold.

8. A method for preparing the sensor as described in any one of claims 1-7, characterized in that, Includes the following steps: S01. Preparation of precursor membrane by electrospinning: Indium salt and polymer are dissolved in an organic solvent to form a spinning solution, and polymer nanofiber membrane loaded with indium source is obtained by electrospinning. S02, In-situ growth of MOF: The membrane obtained in step S01 is subjected to a solvothermal reaction with a solution of terephthalic acid to grow MIL-68(In) in-situ on the nanofibers, thereby obtaining a MOF-modified nanofiber membrane. S03, Segmented heat treatment: The MOF modified nanofiber membrane obtained in step S02 is subjected to the first stage heat treatment and the second stage heat treatment in an oxygen-containing atmosphere and an inert atmosphere, respectively, to finally obtain a composite material of In2O3 and carbon nanofibers. S04, Sensor Integration: The composite material obtained in step S03 is coated onto a flexible substrate with conductive paths to form a gas-sensitive thin film, thereby obtaining the flexible semiconductor gas-sensitive sensor.

9. The method according to claim 8, characterized in that, In step S01, the polymer is polyacrylonitrile, the indium salt is indium nitrate, the flexible substrate is PET, and the conductive path is composed of copper tape.

10. A zinc-bromine flow battery electrolyte leakage monitoring system, characterized in that, include: The flexible semiconductor gas sensor as described in claim 6 or 7; The data acquisition and display unit is connected to the signal processing unit and is used to display the bromine concentration value after humidity compensation in real time.

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