Palladium-based composite metal oxide semiconductor material, method for preparing same, and hydrogen sensor

Abstract

The application provides a palladium-based composite metal oxide semiconductor material and a preparation method thereof and a hydrogen sensor. The preparation of the palladium-based composite metal oxide semiconductor material comprises the following steps: separating and drying a material after a hydrothermal reaction of tin dichloride, urea and nickel nitrate in deionized water to obtain a composite metal oxide; dispersing the composite metal oxide in deionized water, then adding palladium chloride and a reducing agent to perform a reaction; and separating and drying the material after the reaction to obtain the palladium-based composite metal oxide semiconductor material. The mass ratio of the tin dichloride, the nickel nitrate and the palladium chloride is (17-100):(0.05-3):1. The mass ratio of the tin dichloride and the urea is 1:(0.2-1). The palladium-based composite metal oxide semiconductor material prepared by the application has high hydrogen-sensitive selectivity, can quickly detect hydrogen with a low hydrogen concentration, has excellent detection stability, and can be widely used for preparing hydrogen sensors.

Description

Technical Field

[0001] The present invention relates to the technical field of gas sensors, and in particular to a palladium-based composite metal oxide semiconductor material and a preparation method thereof, and a hydrogen sensor. Background Art

[0002] Hydrogen energy boasts advantages such as high combustion efficiency and pollution-free products. Along with solar energy and nuclear energy, it is considered one of the three new energy sources. As an ideal and efficient fuel, hydrogen is currently widely used in rocket launches, space shuttles, missiles, and fuel-powered vehicles. Despite its growing application, concerns about hydrogen's safety have persisted throughout its development.

[0003] Hydrogen is a colorless, odorless, flammable, explosive, and easily permeable and diffusible hazardous gas. It has an extremely low density, a high diffusion coefficient, and a lower explosion limit of only 4% in air. Leakage can easily cause explosions during storage, transportation, and use. Hydrogen leaks and explosions have become a frequent occurrence in recent years, sparking public concern. Hydrogen sensors for real-time monitoring of hydrogen leaks are essential for ensuring the safe use of hydrogen energy and are of great significance for its storage and real-time monitoring.

[0004] Among the numerous hydrogen sensors, small portable gas sensors have shown outstanding advantages and achievements in trace gas detection. Metal oxide semiconductor (MOS) gas sensors have great application prospects in trace gas detection due to their excellent stability, high sensitivity and easy maintenance. Among them, tin dioxide (SnO2), as a wide bandgap n-type MOS, is considered to be a very promising sensing material due to its low cost, simple manufacturing process and good long-term stability. It has been successfully developed and widely used to detect trace hazardous gases. However, SnO2-based gas sensors still have many disadvantages such as high power consumption and poor selectivity, which greatly limit the practical application of gas sensors. In addition, how to further improve the stability of SnO2-based gas sensors has always been a hot topic in the industry. Summary of the Invention

[0005] In response to the deficiencies in the prior art, the present invention discloses a palladium-based composite metal oxide semiconductor material, a preparation method thereof, and a hydrogen sensor. The hydrogen sensor comprising the palladium-based composite metal oxide semiconductor material has excellent stability and can detect low-concentration hydrogen quickly and highly selectively.

[0006] In order to achieve the above technical objectives, on the one hand, the present invention provides a method for preparing a palladium-based composite metal oxide semiconductor material, which comprises the following steps: (1) separating and drying the materials after hydrothermal reaction of tin dichloride, urea and nickel nitrate in deionized water to obtain a composite metal oxide; (2) dispersing the composite metal oxide in deionized water, and then adding palladium chloride and a reducing agent to react; the materials after the reaction are separated and dried to obtain the palladium-based composite metal oxide semiconductor material; wherein the mass ratio of the tin dichloride, the nickel nitrate and the palladium chloride is (17-100): (0.05-3): 1; the mass ratio of the tin dichloride to the urea is 1: (0.2-1).

[0007] The palladium-based composite metal oxide semiconductor material prepared by the above technical solution uses a composite metal oxide including an n-type semiconductor tin oxide and a p-type semiconductor nickel oxide as a matrix, and doping palladium into the matrix can obtain at least two advantages: (1) a rich heterojunction barrier is formed between tin oxide, nickel oxide and palladium elements. Specifically, the semiconductor materials tin oxide and nickel oxide have different electron affinities and energy band structures, and the interface between the two will form a heterojunction; in addition, although palladium is not a semiconductor, it can form a Schottky barrier or an ohmic contact with the semiconductor materials tin oxide and nickel oxide, respectively, thereby increasing the prepared palladium-based composite metal oxide by synergistic optimization. (1) The number of heterojunctions in the composite metal oxide material, that is, the number of carrier transfer channels, is increased, and the gas-sensing performance of the composite metal oxide is further significantly improved; (2) Palladium is a hydrogen-sensitive material with a specific selective characteristic, but its stability is poor and its sensitivity is limited; in the above technical solution, a hydrothermal method is used to prepare the composite metal oxide matrix, and then the palladium element is uniformly loaded on the composite metal oxide matrix by an impregnation method, so that the overflow effect of the palladium element can be utilized. When hydrogen molecules contact the palladium surface and are adsorbed and dissociated into hydrogen atoms, the hydrogen atoms are quickly overflowed to the surface of the composite metal oxide to participate in the oxidation-reduction reaction, thereby enhancing the response of the overall composite metal oxide semiconductor material to hydrogen and improving the hydrogen sensitivity selectivity.

[0008] In the above technical solution, the dosage of the reaction raw materials tin dichloride, nickel nitrate, and palladium chloride is optimized, which not only promotes the formation of the heterojunction barrier, but also regulates the palladium loading in the palladium-based composite metal oxide semiconductor material to be between 0.5% and 4%. The preparation method of the present invention can improve the hydrogen-sensitive performance of the composite metal oxide semiconductor material by only loading an appropriate amount of palladium metal, thereby lowering the detection limit and improving the stability.

[0009] The above technical solution adds urea at a mass of 0.2-1 times the mass of tin dichloride, which can serve as a structure-directing agent and reaction regulator in the early stage of the hydrothermal reaction to guide the formation of a specific composite metal oxide nanostructure, and decomposes and evaporates after the hydrothermal reaction, so that the composite metal oxide forms a specific porous structure, thereby providing more gas adsorption sites and improving the hydrogen detection sensitivity of the composite metal oxide semiconductor material.

[0010] In a further example of the present invention, the mass ratio of the tin dichloride, the nickel nitrate and the palladium chloride is explored and optimized. Based on a large amount of experimental data, the mass ratio of the tin dichloride, the nickel nitrate and the palladium chloride is preferably (17-50): (0.05-1.5): 1, by doping an appropriate amount of palladium in the semiconductor gas-sensitive material obtained in the SnO2 / NiO composite metal oxide, showing better hydrogen sensitivity; the obtained palladium-based composite metal oxide semiconductor material is applied to the hydrogen sensor, with a lower detection limit and higher detection stability. The mass ratio of the tin dichloride, the nickel nitrate and the palladium chloride described in some preferred examples of the present invention is further preferably (17-35): (0.5-1): 1, and further preferably 32: 1: 1, which is conducive to further reducing the detection limit of the obtained palladium-based composite metal oxide semiconductor material, and reducing the response time and recovery time, and improving the stability of the response.

[0011] In a further example of the present invention, the mass ratio of tin dichloride to urea is 1:(0.3-0.5), which further promotes the improvement of the comprehensive hydrogen-sensitive performance of the prepared palladium-based composite metal oxide semiconductor material.

[0012] The purpose of using deionized water in step (1) of the present invention is to serve as a solvent to dissolve the raw materials. Those skilled in the art can set the amount of deionized water in step (1) as needed. For example, preferably, the mass ratio of deionized water to tin dichloride in step (1) is (15-100):1 to fully dissolve the reaction raw materials such as tin dichloride, nickel nitrate and urea.

[0013] In a further example of the present invention, the temperature of the hydrothermal reaction in step (1) is 100-150° C., preferably (100-130° C.), and the reaction time is 10-15 h.

[0014] It should be noted that the present invention does not limit the apparatus for conducting the hydrothermal reaction. For example, it is preferably carried out in a high-pressure reactor, a polytetrafluoroethylene-lined reactor or a stainless steel reactor. Those skilled in the art can choose according to their needs, and the scope of protection of the present invention is not limited thereby.

[0015] In a further example of the present invention, the separation operation in step (1) may be centrifugal washing, the rotation speed of the centrifugal washing is 3500-5000 rpm, the washing time is 5-15 min, and the washing is performed 3-5 times.

[0016] In a further example of the present invention, the drying operation in step (1) is carried out in an oven, preferably at 60-80° C. under air conditions for 10-20 hours.

[0017] In a further embodiment of the present invention, the mass ratio of palladium chloride to the reducing agent is 1:(0.5-3). Thus, the reducing agent allows an appropriate amount of palladium to be uniformly doped into the SnO2 / NiO composite metal oxide, thereby enhancing the hydrogen detection performance of the overall gas-sensitive material through the overflow effect of palladium metal during hydrogen detection. Preferably, the reducing agent is ascorbic acid or sodium borohydride. In some preferred embodiments of the present invention, the mass ratio of palladium chloride to the reducing agent is 1:(0.5-2).

[0018] The purpose of using deionized water in step (2) of the present invention is to disperse the reaction materials and use it as a solvent. Those skilled in the art can set an appropriate amount of deionized water as needed. For example, preferably, the mass ratio of deionized water in step (2) to the tin dichloride used in step (1) is (15-200):1, so as to facilitate the full dispersion of the composite metal oxide in the deionized water.

[0019] In a further example of the present invention, the reaction in step (2) is carried out under stirring conditions, the reaction temperature is 20-25° C., and the reaction time is 5-10 h. The specific operation is preferably carried out in a magnetic stirrer to promote the uniformity of palladium doping.

[0020] The present invention is not limited to the specific process of separation and drying of the material after the reaction in step (2). The separation operation can be optionally centrifugal washing, wherein the centrifugal washing is preferably carried out at a centrifugal washing speed of 6000-10000 rpm, a washing time of 5-20 min, and 3-5 washings; the drying operation is preferably carried out in an oven, preferably at 60-90° C. under air conditions for 8-12 h.

[0021] On the other hand, the present invention provides a palladium-based composite metal oxide semiconductor material prepared by the above-mentioned preparation method. In a further embodiment of the present invention, the palladium loading, average particle size and particle size distribution of the composite metal oxide semiconductor material are explored and optimized.

[0022] Furthermore, the palladium loading of the palladium-based composite metal oxide semiconductor material is preferably 0.5%-4%. The palladium-based composite metal oxide semiconductor material of the present invention improves the hydrogen-sensitive performance of the overall semiconductor material by uniformly loading a small amount of palladium metal, through the overflow effect of palladium metal and the synergistic optimization of the heterojunction barrier of SnO2 and NiO in the composite metal oxide. In some preferred embodiments of the present invention, the palladium loading of the palladium-based composite metal oxide semiconductor material is 1.5%-4%; in some preferred examples of the present invention, the palladium loading of the composite metal oxide semiconductor material is further preferably 2.3%-4%, and in some preferred examples of the present invention, the palladium loading of the palladium-based composite metal oxide semiconductor material is further preferably 2.3%, further improving the hydrogen-sensitive performance of the material.

[0023] Furthermore, the average particle size of the composite metal oxide semiconductor material is 80-120 nm, and the particle size distribution is uniform. It is not only easy to separate and purify during the preparation process, but also has a uniform particle size distribution, which is conducive to processing and use, and a hydrogen sensor with stable performance is prepared.

[0024] In another aspect, the present invention provides a hydrogen sensor comprising the palladium-based composite metal oxide semiconductor material.

[0025] Furthermore, the hydrogen detection lower limit of the hydrogen sensor is 0.5 ppm, the response time is 2-22 s, the recovery time is 4-25 s, and the response stability error is controlled within 10% over 30 days.

[0026] Furthermore, the hydrogen sensor is obtained by coating a mixed slurry containing the palladium-based composite metal oxide semiconductor material on the outer wall of a ceramic tube having an electrode and drying the mixture; wherein the mixed slurry is obtained by dispersing the palladium-based composite metal oxide semiconductor material in deionized water.

[0027] Furthermore, the coating thickness of the palladium-based composite metal oxide semiconductor material is 50-150 μm.

[0028] Furthermore, the hydrogen sensor further includes a sensor base for supporting a ceramic tube having electrodes. Optionally, the electrodes are Au electrodes, and the ceramic tube is an Al2O3 ceramic tube. Optionally, the drying operation utilizes a heating resistor for approximately 24 hours of heating.

[0029] Compared with existing technologies, the present invention offers the following advantages: The palladium-based composite metal oxide semiconductor material preparation method utilizes specific amounts of tin dioxide, nickel nitrate, and palladium chloride as raw materials, adds an appropriate amount of urea, and employs a hydrothermal reaction combined with reduction impregnation to produce the palladium-based composite metal oxide semiconductor material. This preparation method is simple and utilizes readily available raw materials. The resulting palladium-based composite metal oxide semiconductor material exhibits high hydrogen sensitivity selectivity, can rapidly detect low hydrogen concentrations (response time 2 seconds), and exhibits excellent detection stability. Furthermore, its uniform particle size distribution facilitates processing, making it widely applicable for the preparation of hydrogen sensors. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] The accompanying drawings, which constitute part of this application, are intended to provide a further understanding of the present invention. The exemplary embodiments of the present invention and their descriptions are intended to explain the present invention and do not constitute an undue limitation of the present invention. In the accompanying drawings:

[0031] Figure 1 The SEM image of the palladium-based composite metal oxide semiconductor material prepared in Example 4 of the present invention is shown;

[0032] Figure 2 Showing the selectivity test results of the palladium-based composite metal oxide semiconductor material of Example 4;

[0033] Figure 3 Showing the selectivity test results of the composite metal oxide semiconductor material of Comparative Example 2;

[0034] Figure 4 A dynamic resistance curve of a hydrogen sensor comprising the palladium-based composite metal oxide semiconductor material of Example 4 at an operating temperature of 300° C. to 500 ppb-100 ppm hydrogen;

[0035] Figure 5 1. The graph shows the response of the hydrogen sensor comprising the palladium-based composite metal oxide semiconductor material of Example 4 at a hydrogen concentration of 100 ppm;

[0036] Figure 6 A stability diagram of a hydrogen sensor including the palladium-based composite metal oxide semiconductor material of Example 4 is shown. DETAILED DESCRIPTION

[0037] To facilitate understanding of the present invention, the present invention will be described in more detail below, with preferred embodiments of the present invention provided. However, it should be understood that these embodiments are merely for the purpose of further explanation and are not to be construed as limiting the present invention in any form, i.e., they are not intended to limit the scope of protection of the present invention.

[0038] Unless otherwise defined, the technical terms used in the following examples have the same meanings as commonly understood by those skilled in the art to which this invention belongs. The experimental reagents used in the following examples, unless otherwise specified, are conventional biochemical reagents; the experimental methods described, unless otherwise specified, are conventional methods.

[0039] In order to further verify the technical effects of the technical solutions of the present invention, the following is a detailed description through specific embodiments and test examples.

[0040] Example 1

[0041] A method for preparing a palladium-based composite metal oxide semiconductor material comprises the following steps:

[0042] (1) 1100 mg of tin dichloride, 400 mg of urea, and 5 mg of nickel nitrate hexahydrate were dissolved in 20 ml of deionized water, stirred evenly, and then subjected to a hydrothermal reaction in a polytetrafluoroethylene-lined reactor at a temperature of 120° C. for 10 h. The reacted material was centrifugally washed three times with deionized water and dried at 80° C. for 12 h to obtain a composite metal oxide.

[0043] (2) The composite metal oxide was dispersed in 20 ml of deionized water, and then 11.05 mg of palladium chloride and 11.05 mg of ascorbic acid were added to react; the reacted material was centrifuged and washed three times, and dried at 80° C. for 12 h to obtain the palladium-based composite metal oxide semiconductor material; the particle size of the semiconductor material was 80-120 nm, the average particle size was 100 nm, and the particle size distribution was uniform.

[0044] Example 2

[0045] A method for preparing a palladium-based composite metal oxide semiconductor material comprises the following steps:

[0046] (1) 1100 mg of tin dichloride, 220 mg of urea, and 5 mg of nickel nitrate hexahydrate were dissolved in 20 ml of deionized water, stirred evenly, and then subjected to a hydrothermal reaction in a polytetrafluoroethylene-lined reactor at a temperature of 120° C. for 10 h. The reacted material was centrifugally washed three times with deionized water and dried at 80° C. for 12 h to obtain a composite metal oxide.

[0047] (2) The composite metal oxide was dispersed in 20 ml of deionized water, and then 33.15 mg of palladium chloride and 33.15 mg of ascorbic acid were added to react; the reacted material was centrifuged and washed three times, and dried at 80° C. for 12 h to obtain the palladium-based composite metal oxide semiconductor material; the particle size of the semiconductor material was 80-120 nm, the average particle size was 100 nm, and the particle size distribution was uniform.

[0048] Example 3

[0049] A method for preparing a palladium-based composite metal oxide semiconductor material comprises the following steps:

[0050] (1) 1100 mg of tin dichloride, 400 mg of urea, and 50 mg of nickel nitrate hexahydrate were dissolved in 20 ml of deionized water, stirred evenly, and then subjected to a hydrothermal reaction in a polytetrafluoroethylene-lined reactor at a temperature of 120° C. for 10 h. The reacted material was centrifugally washed three times with deionized water and dried at 80° C. for 12 h to obtain a composite metal oxide.

[0051] (2) The composite metal oxide is dispersed in 20 ml of deionized water, and then 23 mg of palladium chloride and 23 mg of ascorbic acid are added to react; the reacted material is centrifuged and washed three times, and dried at 80° C. for 12 h to obtain the palladium-based composite metal oxide semiconductor material; the particle size of the semiconductor material is 80-120 nm, the average particle size is 100 nm, and the particle size distribution is uniform.

[0052] Example 4

[0053] A method for preparing a palladium-based composite metal oxide semiconductor material comprises the following steps:

[0054] (1) 1100 mg of tin dichloride, 400 mg of urea, and 50 mg of nickel nitrate hexahydrate were dissolved in 20 ml of deionized water, stirred evenly, and then subjected to a hydrothermal reaction in a polytetrafluoroethylene-lined reactor at a temperature of 120° C. for 10 h. The reacted material was centrifugally washed three times with deionized water and dried at 80° C. for 12 h to obtain a composite metal oxide.

[0055] (2) The composite metal oxide was dispersed in 20 ml of deionized water, and then 34.5 mg of palladium chloride and 34.5 mg of ascorbic acid were added to react; the reacted material was centrifuged and washed three times, and dried at 80° C. for 12 h to obtain the palladium-based composite metal oxide semiconductor material; the particle size of the semiconductor material was 80-120 nm, the average particle size was 100 nm, and the particle size distribution was uniform. The SEM image is shown as follows: Figure 1 shown.

[0056] Example 5

[0057] A method for preparing a palladium-based composite metal oxide semiconductor material comprises the following steps:

[0058] (1) 1100 mg of tin dichloride, 400 mg of urea, and 50 mg of nickel nitrate hexahydrate were dissolved in 20 ml of deionized water, stirred evenly, and then subjected to a hydrothermal reaction in a polytetrafluoroethylene-lined reactor at a temperature of 120° C. for 10 h. The reacted material was centrifugally washed three times with deionized water and dried at 80° C. for 12 h to obtain a composite metal oxide.

[0059] (2) The composite metal oxide was dispersed in 20 ml of deionized water, and then 57.5 mg of palladium chloride and 57.5 mg of ascorbic acid were added to react; the reacted material was centrifuged and washed three times, and dried at 80° C. for 12 h to obtain the palladium-based composite metal oxide semiconductor material; the particle size of the semiconductor material was 80-120 nm, the average particle size was 100 nm, and the particle size distribution was uniform.

[0060] Example 6

[0061] A method for preparing a palladium-based composite metal oxide semiconductor material comprises the following steps:

[0062] (1) 1100 mg of tin dichloride, 1050 mg of urea, and 70 mg of nickel nitrate hexahydrate were dissolved in 20 ml of deionized water, stirred evenly, and then subjected to a hydrothermal reaction in a polytetrafluoroethylene-lined reactor at a temperature of 120° C. for 10 h. The reacted material was centrifugally washed three times with deionized water and dried at 80° C. for 12 h to obtain a composite metal oxide.

[0063] (2) The composite metal oxide was dispersed in 20 ml of deionized water, and then 58.5 mg of palladium chloride and 58.5 mg of ascorbic acid were added to react; the reacted material was centrifuged and washed three times, and dried at 80° C. for 12 h to obtain the palladium-based composite metal oxide semiconductor material; the particle size of the semiconductor material was 80-120 nm, the average particle size was 100 nm, and the particle size distribution was uniform.

[0064] Comparative Example 1

[0065] The preparation process, parameters, and control conditions in this comparative example are the same as those in Example 1, except that step (2) is not included in this comparative example, i.e., palladium chloride is not added. The particle size of the semiconductor material obtained is 80-120 nm, with an average particle size of 100 nm and a uniform particle size distribution.

[0066] Comparative Example 2

[0067] The preparation process, parameters and control conditions in this comparative example are the same as those in Example 2, except that nickel nitrate is not added in step (1) of this comparative example. The particle size of the semiconductor material is 80-120 nm, the average particle size is 100 nm, and the particle size distribution is uniform.

[0068] Comparative Example 3

[0069] The preparation process, parameters and control conditions in this comparative example are the same as those in Example 3, except that tin dichloride is not added in step (1) of this comparative example. The particle size of the semiconductor material is 40-100 nm, the average particle size is 70 nm, and the particle size distribution is uniform.

[0070] Comparative Example 4

[0071] The preparation process, parameters, and control conditions in this comparative example are the same as those in Example 3, except that tin dichloride is not added in step (1) and step (2) is not included, i.e., palladium chloride is not added. The particle size of the semiconductor material is 40-100 nm, the average particle size is 70 nm, and the particle size distribution is uniform.

[0072] Comparative Example 5

[0073] This comparative example provides a method for preparing a composite metal oxide semiconductor material. Specifically, 1100 mg of tin dichloride, 50 mg of nickel nitrate hexahydrate, 34.5 mg of palladium chloride, 400 mg of urea, and 34.5 mg of ascorbic acid are added to 20 ml of deionized water, stirred evenly, and then added to a polytetrafluoroethylene-lined reactor. The mixture is hydrothermally reacted at 120° C. for 10 hours, centrifuged and washed five times, and dried at 80° C. for 12 hours to obtain a composite metal oxide semiconductor material. The composite metal oxide semiconductor material has a particle size of 80-120 nm, an average particle size of 100 nm, and an uneven particle size distribution.

[0074] Comparative Example 6

[0075] The preparation process, parameters, and control conditions in this comparative example were the same as those in Example 4, except that the mass of palladium chloride added in step (2) in this comparative example was 3.45 mg. The particle size of the obtained semiconductor material was 80-120 nm, with an average particle size of 100 nm and a uniform particle size distribution.

[0076] Comparative Example 7

[0077] The preparation process, parameters, and control conditions in this comparative example were the same as those in Example 4, except that the mass of palladium chloride added in step (2) in this comparative example was 69 mg. The particle size of the obtained semiconductor material was 80-120 nm, with an average particle size of 100 nm and a uniform particle size distribution.

[0078] Comparative Example 8

[0079] The preparation process, parameters, and control conditions in this comparative example were the same as those in Example 4, except that the mass of urea added in step (1) in this comparative example was 110 mg. The particle size of the obtained semiconductor material was 150-200 nm, with an average particle size of 175 nm and a uniform particle size distribution.

[0080] Comparative Example 9

[0081] The preparation process, parameters, and control conditions in this comparative example were the same as those in Example 4, except that the mass of urea added in step (1) in this comparative example was 2000 mg. The particle size of the obtained semiconductor material was 30-90 nm, with an average particle size of 60 nm and a uniform particle size distribution.

[0082] Test Case

[0083] The palladium-based composite metal oxide semiconductor materials prepared in the examples and the comparative examples were used in hydrogen gas sensors. The composite metal oxide semiconductor materials were prepared as aqueous solutions and evenly coated onto ceramic tube electrodes to a thickness of approximately 100 microns. A heating resistor was also added and heated for 24 hours for stabilization to form the corresponding gas sensors. Gas sensor performance testing was conducted to characterize the hydrogen-sensing properties of the composite metal oxide semiconductor materials in the different examples and comparative examples.

[0084] The present invention uses the Weisheng Technology WS-30A gas sensitive test platform to perform performance testing of gas sensors, wherein:

[0085] 1) The selectivity test of the composite metal oxide semiconductor material was carried out under the test environment where the heating voltage was controlled at 3V and the test voltage was 5V. The selectivity test results of the palladium-based composite metal oxide semiconductor material in Example 4 are as follows: Figure 2 , Comparative Example 4 The selectivity test results of the composite metal oxide semiconductor material are as follows Figure 3 Through comparative analysis Figure 2 and Figure 3 It can be confirmed that the technical solution of the present invention significantly improves the selectivity for hydrogen by doping an appropriate amount of palladium metal into the tin oxide and nickel oxide composite metal oxide.

[0086] 2) The test method for the detection limit of the composite metal oxide semiconductor material is: the injection gas is diluted to the lowest concentration in a closed environment. The test results are shown in Table 1. Figure 4 The graph shows the dynamic resistance curve of the hydrogen sensor containing the palladium-based composite metal oxide semiconductor material of Example 4 under the working condition of 300°C for 500ppb-100ppm hydrogen. The response value is the resistance value R of the gas sensor in air. a and the resistance value R in the gas to be measured g The ratio, that is, R a / R g .

[0087] 3) The response time and recovery time of the composite metal oxide semiconductor material were tested under a test environment in which the heating voltage was controlled at 3V and the test voltage was 5V. The test results are shown in Table 1. Figure 5 The graph shows the response of the hydrogen sensor including the palladium-based composite metal oxide semiconductor material of Example 4 at a hydrogen concentration of 100 ppm.

[0088] 4) The present invention also tested the response stability of the composite metal oxide semiconductor material: the test was conducted under a test environment where the heating voltage was controlled at 3V and the test voltage was 5V. The test results were characterized by the 30-day response stability error rate, which was calculated by the deviation from the average test result; the average test result was obtained by averaging the five measurements. The stability test results are shown in Table 1; Figure 6 The stability test results of the hydrogen sensor including the palladium-based composite metal oxide semiconductor material of Example 4 are shown.

[0089] Table 1

[0090]

[0091] Analysis of Examples 1-6 and Comparative Examples 1-9 in Table 1 shows that the detection limit of the hydrogen sensor prepared using the palladium-based composite metal oxide semiconductor material of the present invention is 5 ppb-50 ppm, which is significantly lower than the hydrogen detection limit of 50-5000 ppm in the comparative example, reflecting better hydrogen sensitivity performance.

[0092] Analysis of the test results of Examples 1 to 6 in Table 1 shows that the mass ratio of the tin dichloride, the nickel nitrate, and the palladium chloride described in the preparation method of the palladium-based composite metal oxide semiconductor material of the present invention is (15-100):(0.05-3):1. Within this range, the palladium loading of the prepared palladium-based composite metal oxide semiconductor material is 0.5%-4%. The hydrogen detection lower limit of the hydrogen sensor containing the palladium-based composite metal oxide semiconductor material of the present invention is in the range of 500 ppb-50 ppm, the response time is in the range of 2-28 s, the recovery time is in the range of 4-30 s, and the 30-day response stability error rate is controlled within 10%. Furthermore, the mass ratio of the tin dichloride, the nickel nitrate, and the palladium chloride described in the preparation method of the palladium-based composite metal oxide semiconductor material of the present invention is preferably (17-50): (0.05-1.5): 1. It can be seen from the test results of Examples 2 to 6 that within this range, the palladium loading of the prepared palladium-based composite metal oxide semiconductor material is 1.5%-4%, and the hydrogen detection lower limit of the hydrogen sensor containing the palladium-based composite metal oxide semiconductor material of the present invention is in the range of 500 ppb-10 ppm, the response time is in the range of 2-20 s, the recovery time is in the range of 4-23 s, and the 30-day response stability error rate is controlled within 10%. Furthermore, the mass ratio of the tin dichloride, the nickel nitrate, and the palladium chloride described in the preparation method of the palladium-based composite metal oxide semiconductor material of the present invention is preferably (17-35): (0.5-1): 1. It can be seen from the test results of Examples 2 to 6 that within this range, the palladium loading of the prepared palladium-based composite metal oxide semiconductor material is 2.3%-4%, and the hydrogen detection lower limit of the hydrogen sensor containing the palladium-based composite metal oxide semiconductor material of the present invention is in the range of 500 ppb-5 ppm, the response time is in the range of 2-10 s, the recovery time is in the range of 4-16 s, and the 30-day response stability error rate is controlled within 5%.

[0093] Combined analysis of Example 4 and Comparative Example 6 and Comparative Example 7: Figure 1 The SEM image of the palladium-based composite metal oxide semiconductor material prepared in Example 4 is shown. Figure 2 、 Figure 4 、 Figure 5 and Figure 6It is shown that the hydrogen detection lower limit of the hydrogen sensor containing the palladium-based composite metal oxide semiconductor material of Example 4 reaches 500 ppb, the response time is 2 s, the recovery time is 4 s, and the response stability error is controlled within 5% for 30 days; when the mass of the doped palladium element is less (Comparative Example 6), the detection sensitivity of the hydrogen sensor containing the prepared semiconductor material decreases, the detection lower limit reaches 100 ppm, and the response time and recovery time become longer, and the stability decreases, that is, the overall performance deteriorates; when the mass of the doped palladium element exceeds the addition range of the present invention (Comparative Example 7), the detection lower limit of the hydrogen sensor containing the prepared semiconductor material is 50 ppm, and the response time, recovery time and stability are all worse than those of the embodiment of the present invention. It is speculated that excessive palladium doping hinders the overflow effect of the palladium element, thereby affecting the overall performance of the hydrogen sensor.

[0094] Combining Example 1 with Comparative Example 1, it can be confirmed that the present invention can effectively reduce the detection limit of the hydrogen sensor by doping the hydrogen-sensitive palladium element on the composite metal oxide matrix, and promote the reduction of the response time and facilitate the rapid recovery of the hydrogen sensor; Combining Example 2 with Comparative Example 2, and Figure 2 It can be verified that the present invention uses nickel oxide as one of the components of the composite metal oxide, which is beneficial to improving hydrogen selectivity and thus improving the sensitivity of hydrogen detection, and improving the response recovery ability of the hydrogen sensor, and more importantly, it can improve the stability of the sensor; combined with Example 3 and Comparative Example 3, it can be confirmed that tin oxide as one of the main components of the composite metal oxide can improve the hydrogen sensitivity of the prepared palladium-based composite metal oxide semiconductor material and reduce the response time and recovery time, especially improve the stability of the hydrogen sensor. Combined with Example 3 and Comparative Example 4, the preparation of the palladium-based composite metal oxide semiconductor material of the present invention adopts a staged hydrothermal reaction combined with a palladium element doping operation. Compared with the preparation method of tin dichloride, nickel nitrate, and palladium chloride in one pot, the hydrogen sensitivity of the prepared palladium-based composite metal oxide semiconductor material is significantly improved, while effectively reducing the response time and recovery time, and the stability is also improved by more than 6 times, confirming that the specific preparation process of the present invention improves the hydrogen sensitivity comprehensive performance of the prepared palladium-based composite metal oxide semiconductor material.

[0095] This verifies that the preparation method of the palladium-based composite metal oxide semiconductor material of the present invention optimizes the mass ratio of the added tin dichloride, nickel nitrate and palladium chloride, so that the prepared palladium-based composite metal oxide semiconductor material is loaded with an appropriate and small amount of palladium metal, thereby achieving the technical effect of lowering the lower limit of hydrogen detection and improving the detection stability of the hydrogen sensor.

[0096] In combination with Example 4, Comparative Examples 8 and 9, it can be verified that adding an appropriate amount of urea with a mass of 0.2-1 times the mass of tin dichloride in the hydrothermal reaction stage of the preparation method of the palladium-based composite metal oxide semiconductor material of the present invention can act as a structure directing agent and reaction regulator in the early stage of the hydrothermal reaction, guiding the formation of a specific composite metal oxide nanostructure; and decomposing and evaporating after the hydrothermal reaction, so that the composite metal oxide forms a specific porous structure to provide more gas adsorption sites, thereby ultimately improving the hydrogen detection sensitivity of the prepared palladium-based composite metal oxide semiconductor material. When the amount of urea added in the step (1) is too small (Comparative Example 8, the amount of urea added is 0.1 times the mass of tin dichloride), the composite metal oxide cannot be promoted to form a specific porous structure, thereby resulting in the prepared palladium-based composite metal oxide semiconductor material having a hydrogen detection lower limit of only 1000 ppm, a response time and a recovery time of 103 s and 115 s, respectively, and a 30-day error rate of 30%, and poor overall performance; when the amount of urea added in the step (1) is too large (Comparative Example 9, the amount of urea added is 1.82 times the mass of tin dichloride), considering that excessive urea affects the pH value of the reaction system or causes the pore structure of the composite metal oxide to be too large or uneven, thereby affecting the stability of the prepared palladium-based composite metal oxide semiconductor material, the hydrogen detection lower limit of the composite semiconductor material in Comparative Example 9 is 50 ppm, the response time and recovery time are 30 s and 37 s, respectively, and the 30-day error rate also reaches 15%, and the overall performance is worse than that of Example 4. Therefore, in the preparation method of the palladium-based composite metal oxide semiconductor material of the present invention, the mass ratio of tin dichloride to the urea is 1:(0.2-1); preferably 1:(0.3-0.5). The porous structure of the composite metal oxide formed by adding urea within this range can promote the improvement of the comprehensive hydrogen-sensitive performance of the prepared palladium-based composite metal oxide semiconductor material.

[0097] In summary, compared with Comparative Examples 1-9, the palladium-based composite metal oxide semiconductor material of the present invention has better hydrogen sensitivity, faster response rate, and higher stability, and is more efficient and safe for hydrogen detection.

[0098] It should be noted that the above is a further detailed description of the present invention in conjunction with specific embodiments, and the specific implementation of the present invention should not be considered to be limited to these descriptions. For those skilled in the art of the present invention, several simple improvements can be made without departing from the concept of the present invention, and all of these should be considered to fall within the scope of protection of the present invention.

Claims

1. A method for preparing a palladium-based composite metal oxide semiconductor material, characterized in that: The following steps are involved: (1) separating and drying the materials after hydrothermal reaction of tin dichloride, urea, and nickel nitrate in deionized water to obtain a composite metal oxide; (2) dispersing the composite metal oxide in deionized water, and then adding palladium chloride and a reducing agent to react; the reacted material is separated and dried to obtain the palladium-based composite metal oxide semiconductor material; Wherein, the mass ratio of the tin dichloride, the nickel nitrate and the palladium chloride is (17-100): (0.05-3):1; the mass ratio of the tin dichloride to the urea is 1:(0.2-1).

2. The method for preparing a palladium-based composite metal oxide semiconductor material according to claim 1, wherein The mass ratio of the tin dichloride, the nickel nitrate and the palladium chloride is (17-50): (0.05-1.5):

1.

3. The preparation method of the palladium-based composite metal oxide semiconductor material according to claim 2, wherein The mass ratio of the tin dichloride, the nickel nitrate and the palladium chloride is (17-35): (0.5-1):

1.

4. The method for preparing a palladium-based composite metal oxide semiconductor material according to claim 1, wherein The mass ratio of the palladium chloride to the reducing agent is 1:(0.5-3); And / or, the reducing agent is ascorbic acid or sodium borohydride.

5. The method for preparing a palladium-based composite metal oxide semiconductor material according to claim 1, wherein: The mass ratio of the tin dichloride to the urea is 1:(0.2-0.5).

6. The method for preparing a palladium-based composite metal oxide semiconductor material according to claim 1, wherein: The temperature of the hydrothermal reaction in step (1) is 100-150° C., and the reaction time is 10-15 hours.

7. The method for preparing a palladium-based composite metal oxide semiconductor material according to claim 1, wherein: The reaction in step (2) is carried out under stirring conditions, the reaction temperature is 15-30° C., and the reaction time is 5-10 h.

8. A palladium-based composite metal oxide semiconductor material, characterized in that: The palladium-based composite metal oxide semiconductor material is prepared by the preparation method according to any one of claims 1 to 7.

9. The palladium-based composite metal oxide semiconductor material according to claim 8, characterized in that The loading amount of palladium in the palladium-based composite metal oxide semiconductor material is 0.5%-4%.

10. The palladium-based composite metal oxide semiconductor material according to claim 8, characterized in that: The average particle size of the composite metal oxide semiconductor material is 80-120 nm.

11. A hydrogen sensor comprising the palladium-based composite metal oxide semiconductor material according to any one of claims 8 to 10.

12. The hydrogen sensor according to claim 11, characterized in that The hydrogen sensor is obtained by coating a mixed slurry containing the palladium-based composite metal oxide semiconductor material on the outer wall of a ceramic tube having an electrode and drying the mixture; wherein the mixed slurry is obtained by dispersing the palladium-based composite metal oxide semiconductor material in deionized water.

13. The hydrogen sensor according to claim 12, characterized in that The coating thickness of the palladium-based composite metal oxide semiconductor material is 50-150 μm.

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