Hydrogen sensor based on MXene-SnO2 composite sensitive material and its preparation method and application

Abstract

The present invention belongs to the technical field of gas sensors, and specifically relates to a hydrogen sensor based on MXene-SnO2 composite sensitive materials, a preparation method thereof, and an application thereof. The hydrogen sensor is mainly composed of a gas-sensitive coating and a substrate, and the gas-sensitive coating is coated on the surface of the substrate with a coating thickness of 0.5mm-0.7mm. The gas-sensitive material component is a heterojunction composite material formed by layered Ti3C2 and SnO2 nanosheets, wherein the diameter of the SnO2 nanosheet is 30-50nm and the size of the Ti3C2 is 1-2μm. The hydrogen sensor has a fast response and a short recovery time, a wide concentration detection range, a low detection limit, and excellent repeatability, stability and selectivity, and can achieve high-precision and ultra-fast detection of hydrogen leakage in the early stage of thermal runaway of lithium batteries.

Description

Technical Field

[0001] The present invention belongs to the technical field of gas sensors, and specifically relates to a hydrogen sensor based on MXene-SnO2 composite sensitive material, a preparation method thereof, and applications thereof. Background Art

[0002] In recent years, lithium-ion batteries have been widely used in new energy electric vehicles due to their high energy density, low self-discharge, and long cycle life. However, during long-term operation, batteries in electric vehicles are susceptible to damage due to improper use, such as overcharging or over-discharging, leading to thermal runaway. During thermal runaway, the electrolyte decomposes into various gases, causing the lithium battery to expand and rupture, resulting in a rapid increase in temperature and, consequently, battery pack fires and explosions. Therefore, given the rapid development of the lithium-ion battery industry, research on thermal runaway assessment and early warning technologies for lithium-ion batteries is particularly important.

[0003] Existing battery thermal runaway fault assessment methods mainly include monitoring battery surface temperature, battery pressure signals, battery internal current and voltage, battery internal resistance, etc. However, the above monitoring and assessment methods all have certain drawbacks. Among them, temperature monitoring requires a large number of temperature sensors covering the battery surface, which is costly; pressure signals are prone to lag and are easily interfered with, with a long response time and low accuracy; current detection within the battery pack is expensive, and the presence of a large number of parallel batteries in the battery pack can suppress fluctuations in the voltage signal, resulting in low resolution... Compared with the above detection methods, gas detection has the advantages of low detection limit, high resolution, and short response time. Therefore, gas detection technology has become a new research hotspot for assessing the health status of lithium batteries.

[0004] A gas sensor is a converter that converts the volume fraction of a certain gas into a corresponding electrical signal. The presence of the gas to be measured in the environment is obtained based on the strength of the electrical signal. During the entire process of thermal runaway and eventual combustion of lithium-ion batteries, the electrolyte decomposes into gases such as hydrogen, carbon dioxide, and carbon monoxide. A sudden increase in the hydrogen concentration in the battery pack environment can indicate that the electrolyte has decomposed due to thermal runaway of the battery. Therefore, a hydrogen sensor can be constructed to accurately, quickly, and continuously monitor the hydrogen content in the battery pack to determine whether the battery has thermal runaway, and then evaluate the health of the lithium battery. Ti3C2T xAs a typical MXene material, it has advantages such as a narrow band gap, large specific surface area, rich surface functional groups, and high electron transfer rate, making it suitable for constructing gas sensors for hydrogen detection. Semiconductor metal oxide-based gas sensors offer significant advantages such as simple preparation, low maintenance costs, and long service life, enabling efficient and rapid response to target gases. SnO2, a typical n-type semiconductor metal oxide, is widely used in gas sensors due to its wide band gap (3.6 eV), ultrahigh electron mobility, and strong thermal and chemical stability. Summary of the Invention

[0005] This invention provides a hydrogen sensor based on a MXene-SnO2 composite sensitive material, its preparation method, and its application. Using MXene-SnO2 as the sensitive membrane material, the hydrogen sensor exhibits an ultra-fast response to hydrogen gas based on a resistive output signal. MXene significantly enhances the sensing performance of the MXene-SnO2 composite material. Based on the oxygen adsorption theory of semiconductor sensors, this invention explains how the MXene-SnO2 heterojunction effect, formed between MXene and SnO2, enhances sensor performance.

[0006] Pure MXene gas sensors have problems such as long response time and baseline drift when detecting hydrogen. After combining MXene with SnO2, with the increase in specific surface area and the introduction of surface functional groups, more hydrogen adsorption sites are formed on the material surface. In addition, the space charge region formed at the contact surface of MXene and SnO2 can adjust the gas-sensing properties of the material, shortening the response time and improving the sensitivity.

[0007] In order to achieve the above-mentioned objectives, the first aspect of the present invention provides a hydrogen sensor based on a MXene-SnO2 composite sensitive material, which is mainly composed of a gas-sensitive coating and a substrate. The gas-sensitive coating is coated on the surface of the substrate with a coating thickness of 0.5mm-0.7mm; the gas-sensitive material component is a heterojunction composite material formed by layered Ti3C2 and SnO2 nanosheets.

[0008] The SnO2 nanosheets are obtained by high-temperature calcination, and the diameter of the SnO2 nanosheets is 30-50 nm. The SnO2 nanosheets obtained by the calcination method in the present invention have a large specific surface area and good sensing performance.

[0009] The layered Ti3C2 is obtained by a hydrochloric acid and lithium fluoride combined etching method, and the size of the Ti3C2 is 1-2 μm.

[0010] Furthermore, the substrate is a ceramic plate electrode, preferably a ceramic plate silver electrode.

[0011] A second aspect of the present invention provides a method for preparing the above-mentioned hydrogen sensor based on the MXene-SnO2 composite sensitive material, characterized in that the method comprises:

[0012] (1) lithium fluoride and dilute hydrochloric acid are mixed evenly, titanium aluminum carbide is added during the stirring process and stirred for reaction, after the reaction is completed, the mixture is washed and centrifuged, the resulting solution is ultrasonically filtered and dried to obtain layered Ti3C2;

[0013] (2) SnCl4·5H2O powder was calcined in air to obtain SnO2 nanosheets;

[0014] (3) Dissolve SnO2 nanosheets and layered Ti3C2 in anhydrous ethanol and stir to obtain MXene-SnO2 composite sensitive material;

[0015] (4) The MXene-SnO2 composite sensitive material is evenly dispersed in an anhydrous ethanol solution to obtain a dispersion, which is then evenly coated on the surface of the substrate and dried to obtain a hydrogen sensor.

[0016] Furthermore, in step (1), the concentration of dilute hydrochloric acid is 7.5-8 mol / L, the addition ratio of titanium aluminum carbide, dilute hydrochloric acid and lithium fluoride is 1.8 g:40-50 mL:1.5-2 g, the reaction temperature is 35-40° C., and the reaction time is 30-40 h.

[0017] Furthermore, in step (2), the calcination temperature is 700-850°C, the calcination time is 5-7h, and the heating rate is 1-5°C / min.

[0018] Furthermore, in step (3), the addition ratio of layered Ti3C2, SnO2 nanosheets and anhydrous ethanol is 0.005-0.015 g: 0.1 g: 10-15 mL, the reaction temperature is 35-45 ° C, and the reaction time is 1-3 h.

[0019] Furthermore, the concentration of the MXene-SnO2 composite sensitive material dispersion in step (4) is 0.01-0.015 g / mL; the coating method is a spin coating method, specifically, the dispersion is dropped onto the surface of the substrate, and then it is evenly coated using a coating machine.

[0020] The third aspect of the present invention provides an application of a hydrogen sensor based on a MXene-SnO2 composite sensitive material in detecting hydrogen leakage, especially hydrogen leakage in the early stage of thermal runaway of a lithium battery.

[0021] Compared with the prior art, the present invention has the following beneficial effects:

[0022] (1) The present invention prepares a MXene-SnO2 heterojunction composite material by etching with hydrochloric acid and lithium fluoride in combination with high-temperature calcination. The composite material has high crystallinity and large specific surface area. At the same time, the heterojunction structure formed between MXene and SnO2, the oxygen vacancies of the SnO2 nanosheets themselves, and the large number of active sites provided by MXene significantly enhance the composite material's ability to adsorb hydrogen, thereby improving the sensitivity of the hydrogen sensor.

[0023] (2) The hydrogen sensor of the present invention has a fast response and short recovery time, a wide concentration detection range, a low detection limit, and excellent repeatability, stability and selectivity, and can achieve high-precision and ultra-fast detection of hydrogen leakage in the early stage of thermal runaway of lithium batteries.

[0024] (3) In the present invention, MXene, as the main contributor of charge carriers, significantly improves the hydrogen-sensitive performance of the MXene-SnO2 system and improves the response performance of the MXene-SnO2 system to hydrogen. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 This is a flow chart of the manufacturing process of the MXene-SnO2 hydrogen sensor of the present invention;

[0026] Figure 2 This is a test flow chart of the MXene-SnO2 hydrogen sensor of the present invention;

[0027] Figure 3 This is the XRD pattern of the MXene-SnO2 composite sensitive material in Example 1;

[0028] Figure 4 a is the SEM image of the MXene-SnO2 composite sensitive material in Example 1, Figure 4 b is the TEM image of the MXene-SnO2 composite sensitive material in Example 1;

[0029] Figure 5 Response curves of the hydrogen sensor in Example 1 at different operating temperatures;

[0030] Figure 6 This is a dynamic resistance response curve of the hydrogen sensor in Example 1 to different hydrogen concentrations;

[0031] Figure 7 1 is a graph showing the response of the hydrogen sensor to different hydrogen concentrations in Example 1;

[0032] Figure 8 The figure is a fitting curve diagram of hydrogen concentration and response value of the hydrogen sensor in Example 1;

[0033] Figure 9Response and recovery time curve of the hydrogen sensor in Example 1 to 600 ppm hydrogen;

[0034] Figure 10 This is a graph showing the cyclic repeatability test of the hydrogen sensor in Example 1 at 100, 400, and 800 ppm hydrogen.

[0035] Figure 11 This is a long-term stability test curve of the hydrogen sensor in Example 1 within 30 days;

[0036] Figure 12 This is a selective test of the hydrogen sensor in Example 1 for several typical lithium battery thermal runaway early leakage gases;

[0037] Figure 13 a is the optimized structure of SnO2, Figure 13 b is the optimized structure of SnO2 adsorbing hydrogen molecules, Figure 13 c is the charge transfer density diagram of SnO2 adsorbing hydrogen molecules, Figure 13 d is the optimized structure of MXene-SnO2, Figure 13 e is the optimized structure of MXene-SnO2 adsorbing hydrogen molecules, Figure 13 f is the charge transfer density diagram of hydrogen molecules adsorbed on MXene-SnO2;

[0038] Figure 14 a is the band structure of SnO2, Figure 14 b is the band structure of MXene-SnO2, Figure 14 c is the energy band structure of SnO2 adsorbing hydrogen molecules, Figure 14 d is the energy band structure of MXene-SnO2 adsorbing hydrogen molecules;

[0039] Figure 15 a is the density of states diagram of SnO2, Sn and O, Figure 15 b is the density of states diagram of SnO2 adsorbed hydrogen, Figure 15 c is the state density diagram of MXene-SnO2, Sn, O, C and Ti, Figure 15 d is the density of states diagram of hydrogen adsorption on MXene-SnO2;

[0040] Figure 16 a is a schematic diagram of the energy band structure of SnO2 and MXene (Ti3C2), Figure 16 b is a schematic diagram of the energy band structure of MXene-SnO2. DETAILED DESCRIPTION

[0041] The principles and features of the present invention are described below with reference to examples. The examples are only used to explain the present invention and are not used to limit the scope of the present invention.

[0042] The experimental methods in the following examples are conventional methods unless otherwise specified; the reagents and materials are all commercially available unless otherwise specified. Figure 1 This is a flow chart of the manufacturing process of the MXene-SnO2 hydrogen sensor of the present invention. Figure 2 This is a test flow chart of the MXene-SnO2 hydrogen sensor of the present invention.

[0043] Example 1

[0044] A hydrogen sensor based on MXene-SnO2 composite sensitive material mainly consists of a gas-sensitive coating and a ceramic plate silver electrode. The gas-sensitive coating is coated on the surface of the ceramic plate silver electrode with a coating thickness of 0.6 mm. The gas-sensitive material component is a heterojunction composite material formed by layered Ti3C2 and SnO2 nanosheets.

[0045] The preparation method comprises the following steps:

[0046] S1 1.8 g of lithium fluoride and 45 mL of 7.8 mol / L dilute hydrochloric acid were stirred and mixed uniformly in a water bath at 36 ° C. During the stirring process, 1.8 g of titanium aluminum carbide was slowly added. The mixture was stirred and reacted in a water bath at 36 ° C for 40 h. After the reaction was completed, it was washed and centrifuged several times until the pH of the solution reached 6 to obtain a black-green solution. The black-green solution was then ultrasonically dispersed and filtered. It was vacuum-dried at 35 ° C to obtain a black powder, i.e., layered Ti3C2.

[0047] S2 SnCl4·5H2O powder was placed in a tubular calcining furnace and calcined in air at 800℃ for 6h (heating rate of 3℃ / min) to obtain SnO2 nanosheets.

[0048] S3 0.1 g SnO2 nanosheets and 0.01 g layered Ti3C2 were dissolved in 10 mL of anhydrous ethanol and stirred in a 40 °C water bath for 2 h to obtain a MXene-SnO2 composite sensitive material, i.e., 10 wt% MXene-SnO2.

[0049] S4 0.1 g of MXene-SnO2 composite sensitive material was evenly dispersed in 10 mL of anhydrous ethanol solution, and then evenly coated on the silver electrode surface of the ceramic plate by spin coating, and dried at room temperature to obtain the hydrogen sensor.

[0050] Example 2

[0051] A hydrogen sensor based on MXene-SnO2 composite sensitive material mainly consists of a gas-sensitive coating and a ceramic plate silver electrode. The gas-sensitive coating is coated on the surface of the ceramic plate silver electrode with a coating thickness of 0.5 mm. The gas-sensitive material component is a heterojunction composite material formed by layered Ti3C2 and SnO2 nanosheets.

[0052] The preparation method comprises the following steps:

[0053] S1 1.5 g of lithium fluoride and 40 mL of 7.5 mol / L dilute hydrochloric acid were stirred and mixed in a water bath at 36 ° C. During the stirring process, 1.8 g of titanium aluminum carbide was slowly added. The mixture was stirred and reacted in a water bath at 36 ° C for 30 h. After the reaction was completed, the mixture was washed and centrifuged several times until the pH of the solution reached 6 to obtain a black-green solution. The black-green solution was then ultrasonically dispersed and filtered. It was vacuum-dried at 35 ° C to obtain a black powder, i.e., layered Ti3C2.

[0054] S2 SnCl4·5H2O powder was placed in a tubular calcining furnace and calcined in air at 700℃ for 5h (heating rate of 1℃ / min) to obtain SnO2 nanosheets.

[0055] S3 Dissolve 0.1 g SnO2 nanosheets and 0.005 g layered Ti3C2 in 15 mL of anhydrous ethanol, stir and react in a 35 °C water bath for 1 h to obtain a MXene-SnO2 composite sensitive material.

[0056] S4 0.15 g of MXene-SnO2 composite sensitive material was evenly dispersed in 10 mL of anhydrous ethanol solution, and then evenly coated on the silver electrode surface of the ceramic plate by spin coating, and dried at room temperature to obtain the hydrogen sensor.

[0057] Example 3

[0058] A hydrogen sensor based on MXene-SnO2 composite sensitive material mainly consists of a gas-sensitive coating and a ceramic plate silver electrode. The gas-sensitive coating is coated on the surface of the ceramic plate silver electrode with a coating thickness of 0.7 mm. The gas-sensitive material component is a heterojunction composite material formed by layered Ti3C2 and SnO2 nanosheets.

[0059] The preparation method comprises the following steps:

[0060] S1 2 g of lithium fluoride and 50 mL of 8 mol / L dilute hydrochloric acid were stirred and mixed uniformly in a water bath at 36 ° C. During the stirring process, 1.8 g of titanium aluminum carbide was slowly added. The mixture was stirred and reacted in a water bath at 36 ° C for 40 h. After the reaction was completed, the mixture was washed and centrifuged several times until the pH of the solution reached 6 to obtain a black-green solution. The black-green solution was then ultrasonically dispersed and filtered. It was vacuum-dried at 35 ° C to obtain a black powder, i.e., layered Ti3C2.

[0061] S2 SnCl4·5H2O powder was placed in a tubular calcining furnace and calcined in air at 850℃ for 7h (heating rate of 5℃ / min) to obtain SnO2 nanosheets.

[0062] S3 Dissolve 0.1 g SnO2 nanosheets and 0.015 g layered Ti3C2 in 10 mL of anhydrous ethanol, stir and react in a 45 °C water bath for 3 h to obtain a MXene-SnO2 composite sensitive material.

[0063] S4 0.1 g of MXene-SnO2 composite sensitive material was evenly dispersed in 8 mL of anhydrous ethanol solution, and then evenly coated on the surface of the silver electrode of the ceramic plate by spin coating, and dried at room temperature to obtain the hydrogen sensor.

[0064] Transmission electron microscopy images ( Figure 4 b) It can be proved that MXene and SnO2 have been successfully composited. The lattice spacing of MXene is 1.31nm, corresponding to the (002) crystal plane of MXene, and the lattice spacing of SnO2 is 0.264nm, corresponding to the (101) crystal plane of SnO2. Figure 4 It can be seen that the MXene-SnO2 sensitive material prepared by the present invention is composed of larger multi-layered MXene sheets and relatively smaller polygonal SnO2 nanosheets. Figure 3 The results show that the MXene-SnO2 sensitive material of the present invention has high crystallinity and large specific surface area. The size of MXene is 1-2 μm, and the diameter of SnO2 nanosheets is 30-50 nm.

[0065] Hydrogen sensor performance test

[0066] Sensor testing is performed using a dynamic gas-sensing test system. The MXene-SnO2 sensitive material is thoroughly ground and evenly coated onto the silver electrode surface of a ceramic plate using a spin coating method. Multiple ceramic plates are mounted in a sealed test chamber to form a sensor array, whose operating temperature can be precisely controlled. Furthermore, nitrogen is used as the carrier gas for the target gas (hydrogen), and a gas flow control module is used to control the gas concentration and complete the sensor test.

[0067] The hydrogen sensor prepared in Example 1 was placed in a 600 ppm hydrogen atmosphere to test its optimal operating temperature. Figure 5 As shown in the figure, the sensor has the highest response value to 600ppm hydrogen at 400℃ and the best sensing performance, so 400℃ is selected as the operating temperature of the sensor.

[0068] The dynamic resistance response of the hydrogen sensor prepared in Example 1 of the present invention under different hydrogen concentration atmospheres was characterized. The results are as follows: Figure 6 As shown, the resistance response of the hydrogen sensor increases with the increase of hydrogen concentration. Figure 7The response value calculation curve of the sensor to the gradual increase of hydrogen concentration based on the above is given. At the same time, based on the dynamic response results of the MXene-SnO2 hydrogen sensor at a hydrogen concentration of 50~2000ppm, Figure 8 The function fitting curve of hydrogen concentration and response value is given. As can be seen from the figure, its nonlinear fitting equation is Y=82.4–63.5×0.99 x The correlation coefficient is 0.9833, which indicates that the sensor's detection limit is 1.81 ppm. Therefore, the hydrogen sensor of the present invention has the advantages of a wide concentration detection range and a low detection limit, and can be used to detect hydrogen leakage in the early stages of thermal runaway in lithium batteries with high precision and accuracy.

[0069] Figure 9 The response and recovery time curves for the hydrogen sensor prepared in Example 1 of the present invention to 600 ppm hydrogen are shown. As can be seen from the figure, the sensor has a hydrogen adsorption time of 11 seconds and a desorption time of 13 seconds. This demonstrates that the MXene-SnO2 nanosheet composite has excellent hydrogen response and recovery capabilities, making it suitable for ultra-fast detection of hydrogen leakage in the early stages of thermal runaway in lithium batteries. Figure 10 The graph below shows the repeatability test of the hydrogen sensor prepared in Example 1 of the present invention for 100, 400, and 800 ppm hydrogen. The sensor was sequentially exposed to three test environments with set hydrogen concentrations, and each concentration gradient was cycled three times continuously. The results show that the sensor has good response repeatability to different concentrations of hydrogen. The stability test was also conducted. Figure 11 It can be seen from the graph that the sensor has good response stability to various concentrations of hydrogen (100, 400, 800 ppm) within 30 days.

[0070] Figure 12 This figure shows the selectivity of the hydrogen sensor prepared in Example 1 of the present invention for several typical lithium battery thermal runaway early-stage leak gases. 600 ppm hydrogen, 600 ppm carbon monoxide, 600 ppm carbon dioxide, 600 ppm methane, and 600 ppm sulfur dioxide were selected for detection. As can be seen from the figure, the sensor's response to hydrogen is significantly higher than that to carbon monoxide, carbon dioxide, and other typical lithium battery thermal runaway early-stage leak gases, demonstrating the high selectivity of the MXene-SnO2 hydrogen sensor.

[0071] Explanation of the performance mechanism of hydrogen sensors

[0072] Density functional theory (DFT) is a method for studying the electronic structure of electronic systems. DFT can be used to establish microstructural models of sensitive material surfaces and target gas molecular models, simulate the adsorption of gas molecules on sensitive material surfaces, and analyze the interactions or reactions between target gas molecules and the sensitive material surface. Using DFT, we can provide a plausible explanation for the performance improvement of tin dioxide due to MXene and further validate the excellent performance of MXene-SnO2 hydrogen sensors.

[0073] Density functional theory (DFT) analysis of the MXene / SnO2 composite sensitive material of the present invention was performed based on VASP (Vienna AB-Initio Simulation Package), and the calculation parameters were set as follows: cutoff energy (400eV), vacuum layer (20Å), and k-point (2π × 0.04Å). When the maximum ionic Hermann-Feynman force and total energy are less than 10 -3 eV / Å and 10 - 6 eV / Å, the structure optimization is terminated.

[0074] The adsorption energy is calculated as follows:

[0075] E ad =E MXene-SnO2 / H2 -E MXene-SnO2 -E H2

[0076] Among them, E MXene-SnO2 / H2 is the energy of hydrogen molecules adsorbed by MXene-SnO2 composite sensitive material, E MXene-SnO2 is the energy of MXene / SnO2 composite sensitive material, E H2 is the energy of the H2 molecule.

[0077] The optimized structure of MXene-SnO2 based on VASP and the adsorption energy calculation results based on the optimized structure are shown in the figure. Figure 13 As shown. The adsorption energy of hydrogen adsorbed by the optimized SnO2 structure is E ad =-1.37eV, and the adsorption energy of hydrogen adsorbed by the optimized MXene-SnO2 structure is E ad =-4.21eV. The composite of MXene and SnO2 theoretically increases the adsorption stability of the structural system to hydrogen molecules, that is, the introduction of MXene enhances the hydrogen sensitivity of the MXene-SnO2 sensor. Figure 14 a is the band structure of SnO2, BG (Band gap) = 0.39 eV; Figure 14 b is the band structure of MXene-SnO2, BG = 0.01 eV; Figure 14c is the energy band structure of SnO2 adsorbing hydrogen molecules, BG=-0.01eV; Figure 14 d is the energy band structure of MXene-SnO2 adsorbed hydrogen molecules, with BG = -0.09 eV. After the MXene and SnO2 heterojunction forms, the MXene-SnO2 system has a smaller band gap than SnO2. The lower the band gap, the easier the electron transition. Therefore, the introduction of MXene improves the responsiveness of the MXene-SnO2 system to hydrogen.

[0078] Figure 15 a is the density of states diagram of SnO2, Sn and O, Figure 15 b is the density of states diagram of SnO2 adsorbed hydrogen, Figure 15 c is the state density diagram of MXene-SnO2, Sn, O, C and Ti, Figure 15 d is the density of states diagram of hydrogen adsorption on MXene-SnO2. Figure 15 a and Figure 15 As shown in Figure c, the state density diagram of MXene-composite SnO2 is different from that of pure SnO2, indicating that there is polarization between MXene and SnO2, and the electronic state of SnO2 near the Fermi level is mainly contributed by Sn and O elements, and the electronic state of the MXene-SnO2 system near the Fermi level is mainly contributed by Ti elements, indicating that MXene is the main contributor to the MXene-SnO2 electronic system, and the improvement of the hydrogen-sensitive performance of MXene-SnO2 is mainly attributed to the composite of MXene with SnO2.

[0079] The hydrogen detection mechanism of the MXene-SnO2 composite sensitive material of the present invention is analyzed as follows based on the oxygen adsorption theory in the sensor field.

[0080] Figure 16 The energy band structure diagram of the MXene-SnO2 composite sensitive material is presented to explain the sensing mechanism. MXene is a p-type semiconductor, and SnO2 is an n-type semiconductor. Together, they form the composite's pn heterostructure. After successful doping, the composite exhibits n-type response behavior. When the material is exposed to air, the oxygen-rich air adsorbs onto the material's surface. Due to the affinity of oxygen molecules for electrons, electrons in the material are extracted by oxygen under temperature, transforming into various oxygen ions. This is shown in the following equation:

[0081] O 2(gas) → O 2(ads) or 2O (ads)

[0082] O 2(ads) + e - → O2 - (ads)

[0083] O (ads) + e - → O - (ads)

[0084] After hydrogen is adsorbed by the MXene-SnO2 composite sensitive material, it interacts with the surface functional groups, releasing the electrons bound in the hydrogen into the conduction band of the sensitive material, increasing the carrier concentration, reducing the width of the electron depletion layer, and reducing the resistance of the material. This is shown in the following formula:

[0085] H 2(gas) → 2H (ads)

[0086] 4H (ads) + O2 - (ads) → 2H2O + e -

[0087] 2H (ads) + O - (ads) → H2O + e -

[0088] exist Figure 16 In (b), the work function of SnO2 (4.7 eV) is greater than that of MXene (3.4 eV). Consequently, the Fermi level of MXene is lower, and the bottom of the SnO2 conduction band bends downward. This further extracts electron holes from the SnO2 surface, expanding the depletion region on the SnO2 surface. To achieve Fermi level equilibrium, electrons from the MXene conduction band must be transferred to the SnO2 conduction band. This bends the energy levels at the junction of the two materials, increasing the potential barrier and further forming an electron depletion layer, which increases the base resistance of the composite sensitive material. Furthermore, MXene has a large specific surface area and numerous active sites, further enhancing the composite sensitive material's ability to adsorb hydrogen. As the amount of gas adsorbed increases, many electrons return to the sensitive material's conduction band, reducing the material's resistance in the target gas and significantly improving the sensor's response. Furthermore, the large specific surface area of MXene further enhances oxygen adsorption and the surface activity of the MXene-SnO2 hydrogen-sensitive material. In summary, MXene, as the main contributor of charge carriers, significantly improves the hydrogen-sensitive performance of the MXene-SnO2 system, and the improvement of the hydrogen-sensitive performance of the MXene-SnO2 sensor is mainly due to the pn homojunction effect between MXene and SnO2.

[0089] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A method for preparing a hydrogen sensor based on MXene-SnO2 composite sensitive material, characterized in that: The sensor is mainly composed of a gas-sensitive coating and a substrate. The gas-sensitive coating is coated on the surface of the substrate with a coating thickness of 0.5 mm to 0.7 mm. The gas-sensitive material is a heterojunction composite material formed by layered Ti3C2 and SnO2 nanosheets. The SnO2 nanosheets are obtained by high-temperature calcination, and the diameter of the SnO2 nanosheets is 30-50 nm; The layered Ti3C2 is obtained by etching with a combination of hydrochloric acid and lithium fluoride, and the size of the Ti3C2 is 1-2 μm; The preparation method comprises the following steps: (1) lithium fluoride and dilute hydrochloric acid are mixed evenly, titanium aluminum carbide is added during the stirring process and stirred for reaction, after the reaction is completed, the mixture is washed and centrifuged, the resulting solution is ultrasonically filtered and dried to obtain layered Ti3C2; (2) SnCl4·5H2O powder was calcined in air to obtain SnO2 nanosheets; (3) Dissolve SnO2 nanosheets and layered Ti3C2 in anhydrous ethanol and stir to obtain MXene-SnO2 composite sensitive material; (4) The MXene-SnO2 composite sensitive material is uniformly dispersed in an anhydrous ethanol solution to obtain a dispersion, which is then uniformly coated on the surface of the substrate and dried to obtain a hydrogen sensor; In step (2), the calcination temperature is 700-850°C, the calcination time is 5-7h, and the heating rate is 1-5°C / min; In step (3), the addition ratio of layered Ti3C2, SnO2 nanosheets and anhydrous ethanol is 0.005-0.015 g: 0.1 g: 10-15 mL, the reaction temperature is 35-45 ° C, and the reaction time is 1-3 h.

2. The preparation method according to claim 1, characterized in that In step (1), the concentration of dilute hydrochloric acid is 7.5-8 mol / L, the addition ratio of titanium aluminum carbide, dilute hydrochloric acid and lithium fluoride is 1.8 g:40-50 mL:1.5-2 g, the reaction temperature is 35-40° C., and the reaction time is 30-40 h.

3. The preparation method according to claim 1, characterized in that The concentration of the MXene-SnO2 composite sensitive material dispersion in step (4) is 0.01-0.015 g / mL.

4. Application of a hydrogen sensor based on a MXene-SnO2 composite sensitive material prepared by the preparation method according to claim 1 in detecting hydrogen leakage.

5. The use according to claim 4, characterized in that The hydrogen leakage is the early stage hydrogen leakage of thermal runaway of the lithium battery.

Images