A high-response-sensitivity catalytic combustion hydrogen sensor based on a porous alumina support body and a preparation method thereof

Abstract

The application provides a high-response-sensitivity catalytic combustion hydrogen sensor based on a porous alumina support body and a preparation method thereof, which comprises a porous alumina sheet, palladium nanoparticles, a platinum resistor and an alumina film. The platinum resistor is located on the bottom surface of the porous alumina sheet and is covered with the alumina film on the surface, and the palladium nanoparticles are attached to the hole side of the porous alumina sheet, and the palladium nanoparticles are attached to the surface and the inside of the holes of the sheet. The high-response-sensitivity catalytic combustion hydrogen sensor based on the porous alumina support body has different heat generated by flameless combustion of different hydrogen concentrations, which influences the temperature of the porous alumina sheet, and the resistance of the platinum resistor increases with the increase of the temperature, and then the quantitative detection of the hydrogen concentration is realized by monitoring the change of the platinum resistor. The porous alumina provides a large catalyst carrier area, and the arrayed hole structure is more conducive to efficient catalytic heat production than the plane, and the sensitivity of the sensor is effectively improved.

Description

Technical Field

[0001] This invention relates to the field of gas sensing technology, specifically to a high-response-sensitivity catalytic combustion hydrogen sensor based on a porous alumina support and its preparation method. Background Technology

[0002] Hydrogen energy is hailed as an ideal renewable energy source, and promoting the development of hydrogen energy and related industries has become an important strategic direction for environmental governance and energy utilization. However, hydrogen diffuses rapidly and is highly susceptible to leakage during production, transportation, and use. When the leakage concentration in the air reaches 4-75% by volume, it will explode violently upon contact with an open flame. Furthermore, the colorless and odorless nature of hydrogen makes it difficult for the human body to detect with the five senses. Therefore, developing highly sensitive, fast-response, and reliable hydrogen sensors is crucial for the safe production and application of hydrogen.

[0003] Hydrogen fuel cell vehicles, as a new energy vehicle, have become a focus of attention in the field of hydrogen energy due to their zero pollution and zero emissions. Ensuring the safety of hydrogen used in fuel cells is the foundation for promoting the development of hydrogen fuel cell vehicles. In the field of fuel cell vehicles, the stability requirements of on-board hydrogen sensors are very high. Catalytic combustion hydrogen sensors, due to their automatic compensation function, can greatly eliminate the influence of device drift and changes in ambient temperature and humidity, thus meeting the practical application requirements of high stability in the vehicle field. However, most traditional catalytic combustion hydrogen sensors adopt filament structures, and frequent vehicle vibrations can cause filament breakage and device failure, which greatly limits their large-scale application in the vehicle field. With the advancement of micro-nano fabrication technology, catalytic combustion hydrogen sensors based on microelectromechanical systems (MEMS) have emerged, which can effectively solve the defect of easy breakage of filament structures, but their manufacturing cost is high and the process is complex (Catalytic combustion gas sensor based on MEMS technology [J]. Modern Information Technology, 2018, 2(10): 179-181). Furthermore, planar MEMS catalytic combustion gas sensors suffer from heat dissipation issues during operation; the heat generated by catalytic combustion, localized within the planar structure, tends to dissipate into the ambient temperature. Consequently, the temperature change of the platinum resistance thermometer is extremely limited, resulting in low device sensitivity. Compared to filament-structured catalytic combustion gas sensors, planar MEMS catalytic combustion gas sensors do not exhibit any sensitivity advantage, representing another weakness of MEMS catalytic combustion gas sensors. Therefore, developing a low-cost, high-performance catalytic combustion hydrogen sensor is a current challenge that needs to be addressed. Summary of the Invention

[0004] The purpose of this invention is to overcome the problems of traditional filament catalytic combustion hydrogen sensors being prone to breakage and having a short lifespan, and MEMS catalytic combustion hydrogen sensors being complex in process, high in cost, and low in sensitivity. This invention provides a novel catalytic combustion hydrogen sensor based on a porous alumina support and its preparation method. The catalytic combustion hydrogen sensor of this invention has the advantages of low cost and high performance.

[0005] To achieve the above objectives, this invention proposes a catalytic combustion hydrogen sensor device based on a porous alumina support. The catalytic combustion element uses a porous alumina sheet as a substrate, and a platinum resistance thermometer and alumina film are prepared using a mask combined with physical vapor deposition. Palladium nanoparticles are deposited on the pore sides of the porous alumina sheet using cluster beam deposition. When the catalytic combustion element is in operation, hydrogen undergoes flameless combustion under the catalytic action of the palladium nanoparticles, releasing a large amount of heat, which affects the temperature of the porous alumina sheet. The resistance of the platinum resistance thermometer increases with increasing temperature, and thus the hydrogen concentration can be quantitatively detected by monitoring the change in platinum resistance. Compared with traditional MEMS catalytic combustion gas sensors and filament-type catalytic combustion gas sensors, the sensor involved in this invention has the following advantages: First, it avoids the disadvantages of traditional MEMS catalytic combustion gas sensors, such as high cost and complex manufacturing processes; second, it does not have the defect of easily broken filament structures, providing stable and reusable performance; third, it improves the sensitivity of the device and reduces the operating temperature of the device. The porous alumina support structure provides an excellent carrier for the catalyst. The heat generated by the palladium nanoparticles located in the pores is distributed throughout the axial structure of the cavity, forming a heat pipe-like effect. This can greatly avoid heat loss during flameless combustion, thereby generating a large temperature change, significantly improving the device's sensitivity, and reducing the device's initial operating temperature.

[0006] The innovation of this invention lies in the design of a porous alumina-supported catalytic combustion hydrogen sensor with excellent performance at lower operating temperatures. A porous alumina sheet is used as the supporting substrate for the platinum resistor and catalyst, and the planar platinum resistor serves as the main element for catalytic combustion. The planar structure of this catalytic combustion hydrogen sensor effectively avoids the drawback of suspended platinum resistors in vehicle-mounted gas sensors, which are prone to breakage due to frequent vibrations. Furthermore, the porous alumina-supported catalytic combustion hydrogen sensor uses a single-channel alumina sheet to support the platinum resistor and loaded palladium catalyst, avoiding complex MEMS processes and reducing device costs. More importantly, the high-response-sensitivity catalytic combustion hydrogen sensor based on a porous alumina support proposed in this invention distributes the heat generated during flameless combustion of hydrogen throughout the pores by depositing the catalyst on the pore side of the porous alumina sheet, reducing heat loss and improving sensor sensitivity.

[0007] The aforementioned high-response-sensitivity catalytic combustion hydrogen sensor based on a porous alumina support features a single-pass porous alumina sheet. One side of the sheet has micro / nano-scale pores, while the other side is a non-porous plane, defined as the bottom surface of the porous alumina sheet. The catalytic combustion element uses the bottom surface of the porous alumina sheet as a substrate, on which a platinum resistance thermometer and an alumina film are sequentially attached. The pore side of the porous alumina sheet serves as the catalyst support region, with the catalyst material attached to both the pore side and the surface of the porous alumina sheet. Quantitative detection of hydrogen concentration is achieved by monitoring changes in the platinum resistance thermometer.

[0008] Preferably, the substrate of the catalytic combustion hydrogen sensor is the bottom surface of a porous alumina sheet. The thickness of the bottom surface of the porous alumina sheet should be sufficient to provide effective support for the catalytic combustion main element; the thickness of the porous alumina sheet can be selected in the range of 10–200 μm.

[0009] Preferably, the catalyst support region of the catalytic combustion hydrogen sensor is selected from the pore side of a porous alumina sheet. The depth of the porous channel should ensure that the heat during the catalytic combustion process can be effectively transferred to the platinum resistance thermometer of the catalyst host element. The pore depth of the porous alumina sheet can be selected in the range of 5 to 180 μm.

[0010] Preferably, the catalyst support region of the catalytic combustion hydrogen sensor is selected from the pore side of a porous alumina sheet. The pore diameter of the porous alumina sheet should meet the requirement that the catalyst can be deposited into the pores to ensure heat storage during the catalytic combustion process. The pore diameter of the porous alumina sheet can be selected in the range of 50–400 nm.

[0011] Preferably, the catalyst support region of the catalytic combustion hydrogen sensor is selected from the pore side of a porous alumina sheet. The center-to-center spacing of the pores in the porous alumina sheet should ensure heat transfer between the pores; the center-to-center spacing of the pores in the porous alumina sheet can be selected in the range of 65–500 nm.

[0012] Preferably, the platinum resistance thermometer in the catalytic combustion main element is prepared by electron beam evaporation. The planar structure of the platinum resistance thermometer can be effectively supported by the substrate, which can avoid the problem of easy breakage of the suspended platinum resistance thermometer in traditional catalytic combustion sensors, leading to device failure.

[0013] Preferably, the pattern of the platinum resistance thermometer can be achieved using a metal mask, with the platinum resistance thickness controlled between 0.5 and 10 μm and the electrode gap between 0.05 and 5 mm. This platinum resistance thermometer fabrication process avoids the drawbacks of complex and costly semiconductor photolithography, enabling mass production.

[0014] As a preferred option, to ensure that the planar platinum resistance thermometer can better adhere to the bottom surface of the porous alumina sheet, the temperature can be heated to 50–300°C during the vapor deposition process, and a titanium or chromium film with a thickness of 1–10 nm can be deposited on the substrate surface as an adhesive layer.

[0015] Preferably, the alumina thin film of the catalytic host element is prepared by magnetron sputtering. Selective deposition is performed using a mask, ensuring that the alumina thin film covers only the surface of the platinum resistance thermometer, with the film thickness controlled within the range of 1–10 μm.

[0016] Preferably, the palladium nanoparticles required for the catalytic combustion element are prepared using a cluster beam deposition method. Their particle size is controlled between 1 and 100 nm, and they are attached to the pores of porous alumina sheets. Palladium nanoparticles are attached both on the surface of the porous alumina sheets and inside the pores.

[0017] The method for preparing a high-response-sensitivity catalytic combustion hydrogen sensor based on a porous alumina support includes the following steps:

[0018] 1) First, deposit metallic titanium or chromium as an adhesion layer on the bottom surface of a porous alumina sheet using electron beam evaporation. Then, further deposit platinum resistance thermometers using the same method. The pattern can be achieved through a metal mask.

[0019] 2) After the platinum resistance is deposited, an aluminum oxide thin film is prepared on the surface of the platinum resistance by magnetron sputtering, so that it is uniformly covered on the surface of the platinum resistance and the platinum resistance is not in contact with the ambient gas.

[0020] 3) Following the methods in steps 1) to 2), a catalytic combustion element based on porous alumina sheets was prepared;

[0021] 4) Palladium nanoparticles are deposited on the pore side of porous alumina sheets using cluster beam technology, so that palladium nanoparticles are attached to both the surface of the sheet and the inside of the pores.

[0022] Furthermore, in step 1), the thickness of the titanium or chromium adhesive layer is 1–10 nm; in step 1), platinum resistance is deposited using electron beam evaporation with a power of 10–100 W.

[0023] Further, in step 2), the thickness of the alumina film is 1 to 10 μm; in step 2), a magnetron sputtering coating equipment with a sputtering power source of radio frequency is used to deposit the alumina film, the target material is selected as alumina target, the sputtering power is 100 to 200 W, and the argon gas pressure in the sputtering chamber is maintained at 0.3 to 2 Pa.

[0024] Furthermore, in step 3), palladium nanoparticles are deposited on the pore side of the porous alumina sheet using a cluster beam device. Both the sputtering gas and the buffer gas are argon, with flow rates of 60–70 sccm and 70–80 sccm, respectively. The sputtering power is 5–30 W, and the sputtering time is 3500–4500 s.

[0025] Compared with the prior art, the beneficial effects achieved by the present invention are:

[0026] 1) This invention proposes a high-response-sensitivity catalytic combustion hydrogen sensor based on a porous alumina support. The sensor uses the bottom surface of a porous alumina sheet as a substrate, and platinum resistance thermometers and alumina films are deposited on the bottom surface of the porous alumina sheet using physical vapor deposition. The prepared catalytic combustion hydrogen sensor based on a porous alumina support has a planar structure and can operate stably in the frequent mechanical vibration environment of vehicles, making it widely applicable in vehicle-mounted hydrogen combustion batteries.

[0027] 2) This invention deposits a catalyst on the pore side of a porous alumina sheet. When the catalyst reacts with hydrogen molecules, the presence of pores prevents heat loss during the catalytic combustion process, significantly improving the device's sensitivity. Specifically, the catalytic combustion hydrogen sensor proposed in this invention utilizes a porous alumina sheet as its main catalytic combustion element, which features a simple process and stable structure and performance. Therefore, the novel catalytic combustion hydrogen sensor proposed in this invention is characterized by low cost, high stability, and superior performance.

[0028] 3) The catalytic combustion main element of the present invention adopts a planar structure, which has the characteristics of simple preparation process and stable structural performance. Attached Figure Description

[0029] Figure 1 This is a schematic diagram of the structure of the catalytic combustion hydrogen sensor of the present invention.

[0030] Figure 1 In the middle: 101 - bottom surface of porous alumina sheet, 102 - platinum resistance thermometer, 103 - alumina film, 104 - pore side of porous alumina sheet, 105 - palladium nanoparticles.

[0031] Figure 2a This is a comparison chart of real-time current curves of different catalytic combustion hydrogen sensors at different hydrogen concentrations.

[0032] Figure 2b Comparison of the relationship between different hydrogen concentrations and responsivity for different catalytic combustion hydrogen sensors; Detailed Implementation

[0033] The present invention will be further described below with reference to specific embodiments, but the scope of protection of the present invention is not limited thereto.

[0034] Example:

[0035] like Figure 1 As shown, this invention relates to a high-response-sensitivity catalytic combustion hydrogen sensor based on a porous alumina support. The bottom surface 101 of the porous alumina sheet serves as an insulating substrate, a planar platinum resistance thermometer 102 serves as the measuring unit, and an alumina thin film 103 covers the surface of the platinum resistance thermometer 102. (Comparison) Figure 1 In this process, palladium nanoparticles 105 are deposited on the pore side 104 of the porous alumina sheet as a catalyst, constituting a catalytic combustion element.

[0036] Example 1:

[0037] A method for fabricating a high-response-sensitivity catalytic combustion hydrogen sensor based on a porous alumina support includes the following steps:

[0038] (1) Substrate selection: A porous alumina sheet with a thickness of 50 μm is selected, and its bottom surface is used as an insulating substrate; the other side of the porous alumina sheet is distributed with micro-nano pores, the pore depth is 10-100 μm, the pore diameter is 50-400 nm, and the pore center spacing is 65-400 nm.

[0039] (2) Preparation of platinum resistance thermometers: To increase the adhesion between the platinum resistance thermometer and the substrate surface, a porous alumina sheet was heated to 200℃, and a chromium layer with a thickness of about 6 nm was deposited on the bottom surface of the porous alumina sheet as an adhesion layer using electron beam evaporation. Then, the platinum resistance thermometer was deposited using the same method with a power of about 20 W. The patterns of the adhesion layer and the platinum resistance thermometer were achieved using a metal mask. By controlling the deposition time, a platinum resistance thermometer with a thickness of about 1 μm was prepared, and the electrode gap of the platinum resistance thermometer was 0.2 mm. (See Li-Jun, Wang, Li-Yan, et al. Electrical performance of alumina films made in EBevaporation.[J].Modern Physics Letters B,2016.)

[0040] (3) Preparation of alumina thin films: Alumina thin films were prepared using magnetron sputtering equipment. An RF power supply was used for sputtering, and an alumina target was selected. The sputtering power was 170W, and the argon gas pressure in the sputtering chamber was maintained at approximately 1 Pa. The film thickness was controlled to be approximately 1 μm. The alumina layer uniformly covered the surface of the platinum resistance thermometer. (See Dey I. Microstructural studies of e-beam evaporated alumina thin films[J]. Surface Engineering, 2014.)

[0041] (4) Deposition of palladium nanoparticles: Palladium nanoparticles were deposited on the pore side of porous alumina sheets using cluster beam deposition. Argon was used as both the sputtering gas and the buffer gas, with flow rates of 60 sccm and 70 sccm, respectively. The sputtering power was 15 W and the sputtering time was 4000 s. Palladium nanoparticles were deposited on both the surface of the sheet and inside the pores. The size of the palladium nanoparticles was about 5 nm. (See ACS Applied Materials & Interfaces, 10(2018)44603–44613; CN200910028487.3).

[0042] Catalytic combustion performance test:

[0043] The performance of the catalytic combustion hydrogen sensor based on a porous alumina support prepared by the above method was tested. A voltage of approximately 1.7V was applied to the platinum resistance thermometer of the catalytic combustion hydrogen sensor to reach the initial temperature of 110℃ for the catalytic combustion reaction between palladium nanoparticles and hydrogen. To investigate the catalytic combustion effect of the two elements, two different catalytic combustion hydrogen sensors (one planar structure and the other porous alumina support type) were placed in the test chamber, and hydrogen concentrations ranging from 100 to 40000 ppm were introduced into the chamber. The current value of the platinum resistance thermometer was monitored in real time during the entire test. The comparison of real-time current curves of different catalytic combustion hydrogen sensors (one planar structure and the other porous alumina support type) at different hydrogen concentrations under this test method is shown in the figure below. Figure 2a As shown.

[0044] Figure 2a The planar catalytic element is the single-sided catalytic element obtained according to the method in Example 1 of the previously applied-for mica sheet planar structure catalytic combustion hydrogen sensor (see CN 202210366188.6). Figure 2a The porous catalytic element is the high-response-sensitivity catalytic combustion hydrogen sensor based on a porous alumina support obtained in Example 1 of this invention.

[0045] Furthermore, the differences in the responsivity performance of different catalytic combustion hydrogen sensors were compared using the sensor responsivity calculation formula, which is as follows:

[0046] Where: R e I is the responsivity, I0 is the initial current value, and I is the sensor current value exposed to the hydrogen environment.

[0047] Based on the previously applied-for mica sheet planar structure catalytic combustion hydrogen sensor (see CN202210366188.6), the performance of the planar structure catalytic element is compared with that of the porous alumina support catalytic combustion device of Embodiment 1 of this invention. Figure 2b As shown. From Figure 2b It can be seen that compared with the planar structure with mica sheets as the insulating substrate, the porous alumina support structure can significantly improve the catalytic combustion performance of hydrogen. For example, at a hydrogen concentration of 40,000 ppm, the responsivity of the planar structure with mica sheets as the insulating substrate is 7.85%, while the responsivity of the porous alumina support structure is 34.72%, which is about 5 times higher.

[0048] Furthermore, a control catalytic combustion device was prepared according to the method of Example 1 of this application, the only difference being that "after the preparation of the alumina film in step (3), palladium nanoparticles were deposited on the bottom surface of the porous alumina sheet according to the method in step (4)", thus preparing a catalytic combustion device with palladium nanoparticles deposited on the bottom surface (non-pore side) of the porous alumina support for the same time. Under the premise of maintaining the above test conditions, the performance of the porous alumina support (bottom side) catalytic combustion device was tested. At a hydrogen concentration of 40,000 ppm, the responsivity of the porous alumina support (bottom side) catalytic combustion device was 8.05%, that is, the responsivity was improved by 4.3 times.

[0049] This invention proposes a novel catalytic combustion hydrogen sensor, in which a porous alumina-supported catalytic combustion device significantly improves the catalytic combustion performance of hydrogen. Simultaneously, the planar structure of the substrate of this catalytic combustion hydrogen sensor avoids device failure caused by frequent mechanical vibrations in the automotive environment, and also avoids the complex manufacturing process and high cost of MEMS-based catalytic combustion hydrogen sensors. In summary, the high-response-sensitivity catalytic combustion hydrogen sensor based on a porous alumina support proposed in this invention features low cost, high stability, and excellent performance, and has significant practical application value in the safety monitoring of on-board hydrogen fuel cells.

[0050] The contents described in this specification are merely an enumeration of the implementation forms of the inventive concept, and the scope of protection of this invention should not be regarded as limited to the specific forms described in the embodiments.

Claims

1. A high-response-sensitivity catalytic combustion hydrogen sensor based on a porous alumina support, characterized in that, The hydrogen sensor comprises porous alumina sheets, palladium nanoparticles, platinum resistance thermometers, and alumina films; The porous alumina sheet has a single-pass structure, meaning that one side of the sheet has micro- and nano-sized pores, while the other side is a non-porous plane. This non-porous plane is defined as the bottom surface of the porous alumina sheet. Platinum resistance thermometer and alumina film carrier are sequentially attached to the bottom surface of the porous alumina sheet; palladium nanoparticles are attached to the pores of the porous alumina sheet, and palladium nanoparticles are attached to both the surface of the sheet and the inside of the pores. An aluminum oxide film covers the surface of the platinum resistance thermometer, preventing it from coming into contact with ambient gases. The porous alumina sheet with a single-channel structure serves to support the platinum resistance thermometer and the palladium nanoparticle catalyst. The sheet thickness ranges from 10 to 200 μm. The micro-nano pore structure distributed on one side of the sheet has a pore depth of 5 to 180 μm, a pore diameter of 50 to 400 nm, and a pore center-to-center spacing of 65 to 500 nm.

2. The high-response-sensitivity catalytic combustion hydrogen sensor based on a porous alumina support as described in claim 1, characterized in that, Palladium nanoparticles, with a size of 1~100 nm, act as a catalyst, enabling hydrogen and oxygen to undergo flameless combustion under relatively mild conditions, thereby generating heat.

3. The high-response-sensitivity catalytic combustion hydrogen sensor based on a porous alumina support as described in claim 1, characterized in that, The thickness of the platinum resistance thermometer is 0.5~10 μm, and the electrode gap is 0.05~5 mm.

4. The high-response-sensitivity catalytic combustion hydrogen sensor based on a porous alumina support as described in claim 1, characterized in that, The thickness of the alumina film is 1~10 μm.

5. The method for preparing a high-response-sensitivity catalytic combustion hydrogen sensor based on a porous alumina support as described in claim 1, characterized in that, Includes the following steps: 1) Platinum resistance thermometers are deposited on the bottom surface of porous alumina sheets by physical vapor deposition, and the pattern is achieved by a metal mask; 2) After the platinum resistance is deposited, an aluminum oxide film is prepared on the surface of the platinum resistance by physical vapor deposition, so that it is uniformly covered on the surface of the platinum resistance and the platinum resistance is not in contact with the ambient gas. 3) Palladium nanoparticles were deposited on the porous alumina sheet with pores using a cluster beam deposition apparatus, so that palladium nanoparticles were attached to both the surface of the sheet and the inside of the pores.

6. The method for preparing a high-response-sensitivity catalytic combustion hydrogen sensor based on a porous alumina support as described in claim 5, characterized in that, In step 1), a 1-10 nm thick titanium or chromium film is first deposited on the bottom surface of the porous alumina sheet as an adhesion layer using electron beam evaporation. Then, platinum resistance thermometers are deposited using the same method, and the pattern is achieved through a metal mask.

7. The method for preparing a high-response-sensitivity catalytic combustion hydrogen sensor based on a porous alumina support as described in claim 5, characterized in that, In step 2), a magnetron sputtering coating equipment with a sputtering power source as the radio frequency power source is used to deposit an alumina thin film. The target material is an alumina target, the sputtering power is 100~200 W, and the argon gas pressure in the sputtering chamber is maintained at 0.3~2 Pa.

8. The method for preparing a high-response-sensitivity catalytic combustion hydrogen sensor based on a porous alumina support as described in claim 5, characterized in that, In step 3), palladium nanoparticles are deposited on the pore side of the porous alumina sheet using a cluster beam device. Both the sputtering gas and the buffer gas are argon, with flow rates of 60-70 sccm and 70-80 sccm, respectively. The sputtering power is 5-30 W, and the sputtering time is 3500-4500 s.

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