A humidity gain film for a molybdenum trioxide hydrogen sensor

Abstract

The present application belongs to the field of gas sensing technology, and relates to a hydrogen sensor, and provides a humidity gain film of a molybdenum trioxide hydrogen sensor, which is used for solving the problems of slow response time and sensitivity decline of the existing hydrogen sensor caused by the influence of environmental humidity, and is jointly formed with a palladium-based hydrogen-sensitive film and a substrate to form the hydrogen sensor. Through the design of a thermal evaporation process, a molybdenum trioxide film with a thickness of 2-10 nm and a non-continuous nano-island structure on the surface is successfully deposited on the surface of the palladium-based hydrogen-sensitive film to serve as the humidity gain film. Through the unique reverse hydrogen release effect of the molybdenum trioxide film in a humidity environment, hydrogen atoms are accelerated to contact the active sites on the surface of the palladium film, and the influence of water molecules on the response speed of the palladium-based hydrogen sensor is weakened, that is, while allowing hydrogen molecules to diffuse through to the surface of the palladium-based hydrogen-sensitive film, the diffusion of water molecules is inhibited on the surface of the humidity gain film, and finally the target of rapid detection of hydrogen leakage in a humidity environment is achieved.

Description

Technical Field

[0001] The present invention belongs to the technical field of gas sensing, and relates to a hydrogen sensor. Specifically, it provides a molybdenum trioxide gain film applied to a hydrogen sensor in a humid environment. Background Art

[0002] Hydrogen is an ideal secondary energy source. It is not only abundant and easy to prepare, being obtained through water electrolysis, but also a key industrial raw material with widespread applications in petrochemicals, food processing, aerospace, and other fields. With the dwindling fossil fuel reserves and the resulting environmental pollution, the demand for hydrogen as a clean and renewable energy carrier is growing, spurring research into the development of a new generation of highly sensitive, fast-response, and low-cost hydrogen sensors. However, in practical applications, the performance of hydrogen sensors can be affected by cross-reactivity or background interference, resulting in slow response times, desensitization, and even false alarms. This is particularly true for palladium-based hydrogen sensors. When gas adsorbs on the material surface, a palladium-catalyzed surface reaction occurs. The surface reaction between H atoms and O atoms generates HO. Water molecules block the surface sites for gas adsorption, thereby affecting the absorption and equilibrium of the target gas within the sensor membrane, severely limiting the gas-sensing performance of nanofilm-based sensors.

[0003] Currently, there are few reports on addressing the effects of humidity on hydrogen sensors. For example, patent publication No. CN102037349A provides a method for utilizing the synergistic effects of a silicon dioxide layer, a hydrophobic coating, and an aluminum oxide layer to simultaneously inhibit the diffusion of oxygen and water molecules, thereby reducing the effect of water molecules on the zero drift of the hydrogen sensor. Another example is patent publication No. CN112858440A, which provides a method for utilizing a hydroxyl diffusion barrier layer to inhibit the diffusion of hydroxyl groups generated by the decomposition of water molecules to prevent hydrogen from being consumed by hydroxyl groups after cracking, thereby reducing the effect of ambient humidity on device sensitivity. However, this type of barrier coating requires a certain thickness, which also limits the diffusion of hydrogen itself, making it impossible for the device to quickly detect leaked hydrogen in ambient humidity. Summary of the Invention

[0004] The purpose of the present invention is to address the problems of slow response time and decreased sensitivity of existing hydrogen sensors due to the influence of environmental humidity, and to provide a humidity gain film for a hydrogen sensor based on molybdenum trioxide. The present invention successfully deposits a molybdenum trioxide film with a thickness of 2 to 10 nm and a discontinuous nano-island structure on the surface of a palladium-based hydrogen-sensitive film through the design of a thermal evaporation process, as a humidity gain film. The unique reverse hydrogen release effect of the molybdenum trioxide film in a humid environment accelerates the contact of hydrogen atoms with the active sites on the surface of the palladium film, thereby reducing the influence of water molecules on the response speed of the palladium-based hydrogen sensor, thereby achieving the goal of rapidly detecting hydrogen leaks in a humid environment.

[0005] To achieve the above object, the technical solution adopted by the present invention is:

[0006] A humidity gain film for a hydrogen sensor based on molybdenum trioxide, characterized in that the humidity gain film is specifically a molybdenum trioxide film, the molybdenum trioxide film 3 is arranged on the surface of a palladium-based hydrogen-sensitive film 2, and the palladium-based hydrogen-sensitive film 2 is arranged on a silicon wafer substrate 1, and the three together constitute a palladium-based hydrogen sensor.

[0007] Furthermore, the thickness of the molybdenum trioxide film is 2 to 10 nm, and the surface morphology of the molybdenum trioxide film is a discontinuous nano-island structure, which is used to allow hydrogen molecules to diffuse through the surface of the palladium-based hydrogen-sensitive membrane and suppress the diffusion of water molecules on the surface of the molybdenum trioxide film, thereby ensuring the rapid response of the sensor itself in a high-humidity environment.

[0008] Furthermore, the palladium-based hydrogen-sensitive film is a palladium nanofilm, a palladium-nickel layered nanofilm or a palladium-gold layered nanofilm, and its thickness is 10 to 30 nm.

[0009] Furthermore, the humidity gain film is deposited on the palladium-based hydrogen-sensitive film by a thermal evaporation process. The thermal evaporation process is as follows: first, the silicon wafer substrate deposited with the palladium-based hydrogen-sensitive film is fixed on the sample stage, placed in a thermal evaporation coating device, and a molybdenum trioxide evaporation boat is installed; then, the vacuum system is turned on and the vacuum degree in the chamber reaches 6×10 -4 Pa, turn on the workpiece rotation power supply and evaporation power supply, pre-evaporate for 5 to 10 minutes, open the baffle, observe the film thickness meter reading and adjust the evaporation power supply to control the evaporation rate of molybdenum trioxide to When the film thickness meter reading reaches 2 to 10 nm, the baffle is closed; finally, after the vacuum system is turned off, the palladium-based hydrogen sensor with molybdenum trioxide deposited thereon is taken out.

[0010] Furthermore, the palladium-based hydrogen-sensitive film is deposited on a silicon wafer substrate using an electron beam evaporation process.

[0011] Furthermore, the molybdenum trioxide film reacts reversibly with hydrogen (not adsorbed on the surface of the palladium-based hydrogen-sensitive film) to generate hydrogen molybdenum bronze (H x MoO3) and molybdenum trioxide containing oxygen vacancies (MoO 3-x / 2 ); Water molecules in the ambient humidity cause the reaction to proceed in reverse, and hydrogen-molybdenum bronze and molybdenum trioxide containing oxygen vacancies release hydrogen atoms in reverse, accelerating their contact with the active sites on the surface of the palladium-based hydrogen-sensitive film; thus, the molybdenum trioxide humidity gain film significantly reduces the effect of ambient humidity on the response speed of the palladium-based hydrogen sensor.

[0012] Based on the above technical solution, the beneficial effects of the present invention are:

[0013] The present invention successfully deposits a molybdenum trioxide film with a thickness of 2 to 10 nm and a discontinuous nano-island structure on the surface of a palladium-based hydrogen-sensitive film through a thermal evaporation process, thereby serving as a humidity gain film. Based on the thickness and surface morphology of the molybdenum trioxide film, under ambient humidity, on the one hand, the molybdenum trioxide humidity gain film allows hydrogen molecules to diffuse through the surface of the palladium-based hydrogen-sensitive film while isolating most water molecules, thereby reducing the influence of water molecules on the surface active sites of the palladium-based hydrogen-sensitive film. On the other hand, based on the unique reversible reaction between molybdenum trioxide and hydrogen atoms, the molybdenum trioxide film reversibly reacts with hydrogen not adsorbed on the surface of the palladium-based hydrogen-sensitive film to generate hydrogen-molybdenum bronze (H x MoO3) and molybdenum trioxide containing oxygen vacancies (MoO 3-x / 2 ), water molecules in the ambient humidity will cause the reaction to proceed in the reverse direction, and hydrogen-molybdenum bronze and molybdenum trioxide containing oxygen vacancies will release hydrogen atoms in the reverse direction. The released hydrogen atoms can quickly contact the active sites on the surface of the palladium-based hydrogen-sensitive film.

[0014] In summary, the present invention provides a humidity gain film for a hydrogen sensor based on molybdenum trioxide, which can constitute a palladium-based hydrogen sensor together with a palladium-based hydrogen-sensitive film and a silicon wafer substrate. In a humid environment, the humidity gain film can not only ensure that hydrogen molecules diffuse through the surface of the palladium-based hydrogen-sensitive film, but also isolate water molecules to reduce the influence of water molecules on the active sites on the surface of the palladium film. It can also promote the rapid contact of hydrogen atoms with the active sites on the surface of the palladium-based hydrogen-sensitive film through its unique reversible reaction with hydrogen atoms, thereby ultimately avoiding the influence of ambient humidity (water molecules) on the palladium-based hydrogen sensor and effectively improving the response speed of the device. In particular, when the ambient humidity RH is above 80%, the response speed is consistent with that under dry conditions, thereby achieving the goal of quickly detecting hydrogen leakage in a humid environment. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 Schematic diagram of the structure of the palladium-based hydrogen sensor in Example 1 of the present invention, wherein 1 is a silicon wafer substrate, 2 is a palladium-based hydrogen-sensitive film, and 3 is a molybdenum trioxide humidity gain film.

[0016] Figure 2 1 and 2 are hydrogen-sensitive response curves of the palladium-based hydrogen sensor in Example 1 of the present invention and the comparative example at various humidity levels, wherein (a) is the comparative example and (b) is Example 1.

[0017] Figure 3 1 and 2 are hydrogen-sensitive response curves of the palladium-based hydrogen sensors in Examples 2 and 3 of the present invention at various humidity levels. DETAILED DESCRIPTION

[0018] In order to make the purpose, technical solutions and beneficial effects of the present invention more clearly understood, the present invention is further described in detail below with reference to the accompanying drawings and embodiments.

[0019] Example 1

[0020] This embodiment provides a humidity gain film for a hydrogen sensor based on molybdenum trioxide. The humidity gain film is specifically a molybdenum trioxide film with a thickness of 5 nm. The molybdenum trioxide film 3 is arranged on the surface of a palladium-based hydrogen-sensitive film 2, and the palladium-based hydrogen-sensitive film 2 is arranged on a silicon wafer substrate 1. The three together constitute a palladium-based hydrogen sensor. Figure 1 As shown; the surface morphology of the molybdenum trioxide film is a discontinuous nano-island structure, which is used to allow hydrogen molecules to diffuse through the surface of the palladium-based hydrogen-sensitive membrane and suppress the diffusion of water molecules on the surface of the molybdenum trioxide film, thereby ensuring the rapid response of the sensor itself in a high humidity environment.

[0021] Furthermore, in this embodiment, first, a 1×1 cm 2 A silicon wafer was used as the silicon wafer substrate 1, which was cleaned in sequence with chemical reagents such as acetone, ethanol, and deionized water, and then blown dry with nitrogen for later use. Then, a 2nm chromium layer was deposited on the surface of the silicon wafer substrate as a seed layer based on an electron beam evaporation process, and a 15nm palladium nanofilm was deposited as a palladium-based hydrogen-sensitive film 2. Finally, a 5nm molybdenum trioxide film was deposited on the surface of the palladium-based hydrogen-sensitive film as a humidity gain layer based on a thermal evaporation process.

[0022] The palladium-based hydrogen sensor composed of the above silicon wafer substrate 1 and the palladium-based hydrogen-sensitive film 2 on its upper surface was compared to verify the beneficial effects of the present invention. The performance of the palladium-based hydrogen sensor in Example 1 and the comparative example was tested at a test temperature of 80°C, a hydrogen concentration of 24000ppm, and humidity conditions of RH0%, 50%, 80% and 100%, respectively. The hydrogen-sensitive response curves of the two at various humidities are shown in FIG. Figure 2 As shown in the figure, (a) is a comparative example and (b) is Example 1; it can be seen from the figure that the molybdenum trioxide humidity gain film provided by the present invention significantly reduces the influence of ambient humidity on the hydrogen-sensitive response speed of the device; specifically, starting from the ambient humidity RH50%, a large amount of water molecules in the palladium-based hydrogen sensor (traditional structure) of the comparative example are adsorbed on the film surface, causing the response speed of the palladium nanofilm hydrogen-sensitive device to be greatly slowed down. After the molybdenum trioxide humidity gain layer is provided, the slowdown in the response speed of the palladium-based hydrogen sensor in Example 1 is effectively reduced, especially after the ambient humidity RH80%, the response time is accelerated by about 15 to 20 seconds compared with the traditional structure, as shown in Table 1:

[0023] Table 1

[0024] Device Type RH0% RH50% RH80% RH100% Comparative Example 19.2s 56.5s 60.9s 62s Example 1 18.9s 35.9s 45.2s 45.6s

[0025] It should be noted that the response time refers to the time from when the hydrogen sensitive device changes from a carrier gas environment to a hydrogen standard gas environment to when it reaches 90% of the final hydrogen sensitive response saturation stable value.

[0026] Example 2

[0027] The difference between this embodiment and embodiment 1 is that the palladium-based hydrogen-sensitive film 2 adopts a layered palladium-nickel nanofilm with a total thickness of 13 nm.

[0028] Example 3

[0029] The difference between this embodiment and embodiment 2 is that the humidity gain film is a molybdenum trioxide film with a thickness of 2 nm.

[0030] The performance of the palladium-based hydrogen sensors in Example 2 and Example 3 was tested under the same test conditions as in Example 1. The hydrogen-sensitive response curves of the two sensors at various humidity levels are shown in FIG. Figure 3 As shown in the figure, it can be seen that the molybdenum trioxide humidity gain film in Example 2 and Example 3 has a significant gain effect, especially after the ambient humidity RH80%, the layered palladium nickel film in the traditional structure is seriously affected by water molecules, and its required response time is slowed down to three times that under dry conditions (RH0%). In Example 2 and Example 3, under the action of the molybdenum trioxide humidity gain film, the unique reverse hydrogen release effect of the molybdenum trioxide humidity gain film in a humid environment significantly reduces the influence of water molecules on the response speed of the palladium-based hydrogen-sensitive film, and its required response time is almost equivalent to that under dry conditions (RH0%).

[0031] Table 2

[0032]

[0033]

[0034] The above description is only a specific embodiment of the present invention. Any feature disclosed in this specification, unless otherwise stated, can be replaced by other equivalent or alternative features with similar purposes; all disclosed features, or all steps in the methods or processes, except for mutually exclusive features and / or steps, can be combined in any way.

Claims

1. A humidity gain film for a hydrogen sensor made of molybdenum trioxide, characterized in that: The humidity gain film is specifically a molybdenum trioxide film, which is arranged on the surface of a palladium-based hydrogen-sensitive film, and the palladium-based hydrogen-sensitive film is arranged on a silicon wafer substrate. The three together constitute a palladium-based hydrogen sensor; the thickness of the molybdenum trioxide film is 2~10nm, and the surface morphology of the molybdenum trioxide film is a discontinuous nano-island structure.

2. The humidity gain film of the molybdenum trioxide hydrogen sensor according to claim 1, characterized in that: The palladium-based hydrogen-sensitive film is a palladium nanofilm, a palladium-nickel layered nanofilm or a palladium-gold layered nanofilm, and has a thickness of 10 to 30 nm.

3. The humidity gain film of the molybdenum trioxide hydrogen sensor according to claim 1, characterized in that: The humidity gain film is deposited on the palladium-based hydrogen-sensitive film by a thermal evaporation process. The thermal evaporation process is as follows: first, the silicon wafer substrate deposited with the palladium-based hydrogen-sensitive film is fixed on the sample stage and then placed in the thermal evaporation coating equipment, and a molybdenum trioxide evaporation boat is installed; then, the vacuum system is turned on and the vacuum degree in the chamber reaches 6×10 -4 Pa, after pre-evaporation for 5 to 10 minutes, adjust the evaporation power to control the evaporation rate of molybdenum trioxide to 0.1 to 0.2 Å / s until the thickness of the molybdenum trioxide film reaches 2 to 10 nm.

4. The humidity gain film of the molybdenum trioxide hydrogen sensor according to claim 1, characterized in that: The palladium-based hydrogen-sensitive film is deposited on a silicon wafer substrate by adopting an electron beam evaporation process.

5. The humidity gain film of the molybdenum trioxide hydrogen sensor according to claim 1, characterized in that: The molybdenum trioxide film reacts reversibly with hydrogen to generate hydrogen molybdenum bronze (H x MoO3) and molybdenum trioxide containing oxygen vacancies (MoO 3-x / 2 ); Water molecules in the ambient humidity cause the reaction to proceed in reverse, and hydrogen-molybdenum bronze and molybdenum trioxide containing oxygen vacancies release hydrogen atoms in reverse.

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