A tungsten trioxide-palladium-platinum composite nano-film optical fiber hydrogen sensor

Abstract

The invention discloses a tungsten trioxide-palladium-platinum composite nanofilim optical fiber hydrogen sensor, which consists of a broadband light source, a polarizer, a polarization controller, a test gas chamber, a flowmeter, a hydrogen and nitrogen source, an optical fiber sensor with a composite nanofilim, and a demodulator; the sensor consists of a WO3-Pd2Pt-Pt composite nanofilim and a core without a cladding and is completely sealed in the test gas chamber. The light emitted by the broadband light source is incident on the polarization controller through the polarizer and then enters the left end of the sensor. The hydrogen and nitrogen source introduces a hydrogen and nitrogen mixed gas into the test gas chamber through the air inlet, and the flowmeter monitors the change in the hydrogen concentration in the test gas chamber. The right end of the test gas chamber is connected to the demodulator. Since the optical properties of the composite nanomaterial change after reacting with hydrogen, the properties of the evanescent field in this part of the region also change accordingly. By monitoring the change in the transmission spectrum, the monitoring of hydrogen at different concentrations can be achieved.

Description

Technical Field

[0001] The invention belongs to the field of hydrogen sensors, and in particular relates to a tungsten trioxide-palladium-platinum composite nano-film microstructure optical fiber hydrogen sensor. Background Art

[0002] In today's society, due to the limited availability of fossil fuels and the greenhouse effect and environmental pollution they cause, clean new energy has become a hot topic for global development and utilization. Hydrogen energy has the advantages of high combustion efficiency and no pollution. It is known as one of the nine new energy sources along with solar energy and wind energy, and is praised as the most promising secondary energy source. At the same time, hydrogen is also an important industrial raw material, and is widely used in the electronics industry, automobile industry, metallurgical industry, petrochemical industry, float glass, fine organic synthesis, aerospace, food processing, etc.

[0003] Hydrogen is a colorless, odorless, non-toxic, flammable and explosive gas. Hydrogen has a very small molecular weight and is prone to leakage during production, storage, transportation and use. Hydrogen also has a strong permeability. At the same time, the ignition point of hydrogen is 585°C. When the hydrogen content in the air is between 4% and 75%, it will explode when it encounters an open flame, which brings great inconvenience to the storage and use of hydrogen. In view of the wide use of hydrogen in food hygiene, energy and power, military defense and other fields and its potential dangers, its concentration must be tested when using hydrogen.

[0004] The current type sensor has stable performance and can be adjusted from 0 to 10 4 The rapid detection of hydrogen concentration is achieved within the range of ppm, the sensor response time is 30s, and the sensitivity is 4uA / 100ppm. Dong Hanpeng et al. prepared a three-electrode galvanic hydrogen sensor with a basic structure of H2, Pt|Nafion-117|Pt, and O2 (air) based on a polymer solid electrolyte. However, changes in temperature, pressure, and humidity have a significant impact on the measurement results of this sensor. The potential sensor measures the hydrogen concentration by measuring the potential difference between the sensing electrode and the reference electrode. It has a wide range of applications and can detect the hydrogen content in gases, aqueous solutions, and dissolved metals at room temperature or high temperature. N.Maffei et al. made a potential hydrogen sensor with a basic structure of H2, Pd|Hyceram|Ag-Hyceram|Ag. Since the sensor uses a palladium working electrode, it can measure the hydrogen content in the air, but the potential hydrogen sensor is logarithmically related to the hydrogen concentration, and it is difficult to determine a specific and reliable data relationship.

[0005] Most of the resistive hydrogen sensors are semiconductor metal oxide sensors, which use tin oxide as the sensitive material. The average response time is between 4s and 20s, and the measurable hydrogen concentration range is 10ppm to 20ppm. The selectivity of a single metal oxide for hydrogen is not high. In order to improve the selectivity, metal materials with good hydrogen selectivity, such as palladium and platinum, can be doped. Tonny-Roksana Rashid et al. covered a layer of 8nm thick palladium nanofilm on the ZnO nanobelt. The hydrogen concentration range that can be measured at room temperature is 0.2ppm to 1000ppm, and it has a fast response speed and stable performance. However, it has poor selectivity for hydrogen and is easily interfered by other reducing gases, such as methane, carbon monoxide, alcohols, etc. As for non-resistance hydrogen sensors, Ivan Ryger and others used Pt / NiO Schottky hydrogen sensors to conduct experiments on hydrogen with a concentration of 100ppm to 1000ppm at a temperature range of 50℃ to 250℃, and found that it has a good detection effect on 1000ppm hydrogen at 50℃. However, the working temperature is relatively high, which increases energy consumption, and it is easy to generate electric sparks during operation, so it is not suitable for the detection of hydrogen concentration in flammable and explosive places.

[0006] With the rapid development of sensor-related technologies, the unique advantages of fiber optic sensors have been continuously highlighted and quickly put on the agenda in situations where traditional electrical sensors are not applicable. Research based on optical hydrogen sensors has also emerged in an endless stream. The structure and manufacturing process of microlens fiber optic hydrogen sensors are relatively simple. It only requires the preparation of sensitive films on the cut optical fiber end faces. It is low-cost and easy to use. However, this type of hydrogen sensor is a light intensity sensor, which is greatly affected by the system optical path. It is only suitable for point measurement and must rely on optical switches to achieve repeated routing and addressing of the sensor. The multiplexing capacity is greatly limited. The response sensitivity and response time of this end-face film sensor interfere with each other, and it is difficult to achieve independent optimization. The evanescent field optical fiber hydrogen sensor is very sensitive to hydrogen and reacts quickly. The characteristics of the sensor can be controlled by the type and content of the catalyst. In addition, it is possible to make multiple evanescent field sensors on a single optical fiber to achieve distributed measurement. However, the manufacturing process of this sensor is relatively complex, and the attenuation after series connection is large. It is currently mainly used in laboratory research. The interference type optical fiber hydrogen sensor has the advantages of high measurement accuracy, good repeatability, and small error in theory, but this sensor is easily affected by external environmental factors (mainly temperature), so the accuracy of the sensor is low. The interference of environmental changes on the sensor can be reduced by temperature compensation. The fiber Bragg grating type optical fiber hydrogen sensor is affected by the redox principle, the sensor has a long recovery time, and is limited by the performance of hydrogen sensitive materials. The sensor does not respond to hydrogen below 0.6% at 25°C. At the same time, because LPFG is too sensitive, it only has a good response under ideal laboratory conditions. Therefore, there is no hydrogen sensor with ideal performance on the market. Chinese scholars are also continuing to study Pd alloy hydrogen sensitive sensors, and are committed to developing hydrogen sensors that can work at room temperature and have a fast response speed. Summary of the invention

[0007] In view of the deficiencies of the prior art, the present invention aims to provide a tungsten trioxide-palladium-platinum composite nanofilm (11) microstructure optical fiber hydrogen sensor. The sensing film layer structure of the hydrogen sensor is composed of a tungsten trioxide-palladium-platinum composite nanofilm (11). After the tungsten trioxide-palladium-platinum sensitive nanofilm (11) absorbs hydrogen, the refractive index and volume will change. The change of the transmission spectrum is monitored by a demodulator (8) to achieve monitoring of hydrogen of different concentrations. Thus, the problems of slow response speed to hydrogen at room temperature, high response concentration, and low precision of the traditional Pd film sensor are solved.

[0008] The present invention is realized by the following technical scheme: a tungsten trioxide-palladium-platinum composite nanofilm (11) optical fiber hydrogen sensor, which is composed of a broadband light source (1), a polarizer (2), a polarization controller (3), a test gas chamber (4), a flow meter (5), a hydrogen and nitrogen source (6), an optical fiber sensor (7) of the composite nanofilm (11), and a demodulator (8); the characteristic is that the sensor (7) is composed of a tungsten trioxide-palladium-platinum composite nanofilm (11) and a cladding removed. The exposed fiber core (10) of (12) is formed and completely sealed in the test chamber (4). The light emitted by the broadband light source (1) is incident on the polarization controller (3) through the polarizer (2), and then enters the left end of the sensor (7). The hydrogen and nitrogen sources (6) pass the hydrogen and nitrogen mixed gas into the test chamber (4) through the air inlet (13). The concentration change of hydrogen in the test chamber (4) is monitored by the flow meter (5). The right end of the test chamber (4) is connected to the demodulator (8). By monitoring the change of the transmission spectrum, the monitoring of hydrogen with different concentrations can be realized.

[0009] The sensor is a microstructured sawtooth optical fiber. The optical fiber sensor (7) is a sawtooth optical fiber with a composite nano film (11) coated on its surface. The sawtooth depth ranges from 20 to 100 microns, the sawtooth width is 100 microns, the number of sawtooths ranges from 3 to 100, and the composite nano film (11) is a layered structure of tungsten trioxide, palladium, and platinum. The composite nano film (11) of a determined thickness is coated using a sensor head coating technology.

[0010] The working principle of the present invention is as follows: light emitted by a broadband light source (1) is incident on a polarization controller (3) through a polarizer (2), and after passing through a sensor (7), an electromagnetic field, namely an evanescent field, is formed at the core (10) of the optical fiber. The field intensity of the evanescent field decays exponentially along the core diameter direction. For this purpose, the cladding (12) at the sensor (7) needs to be removed so that the tungsten trioxide-palladium-platinum composite nanofilm (11) is within the action range of the evanescent field. Since the optical properties of the composite nanomaterial (11) change after reacting with hydrogen, the property parameters of the evanescent field in this area also change accordingly. By detecting the intensity or phase of light passing through this area, the change in hydrogen concentration in the corresponding environment can be obtained. The performance test of the hydrogen sensor includes a response time test, a sensor hydrogen cycle test, and a hydrogen concentration test.

[0011] The beneficial effects of the present invention are: the special microstructure serrated structure can make multiple MZ interference structures cascade together, thereby enhancing the evanescent field and obtaining better optical transmission performance than ordinary single-mode optical fiber. WO3 has good adhesion to optical fiber, and the WO3-Pd2Pt-Pt nanocomposite film has good mechanical properties, so the sensor probe has certain long-term reliability. The volume of WO3 exposed to hydrogen has almost no expansion, and alloying Pd with Pt can greatly inhibit the change of Pd lattice constant. At the same time, the sensor also shows good resolution and accuracy in ultra-low concentration trace monitoring (0-0.1%), and has good application prospects. BRIEF DESCRIPTION OF THE DRAWINGS

[0012] Figure 1 The present invention is a schematic diagram of a tungsten trioxide-palladium-platinum composite nano-film optical fiber hydrogen sensor test system.

[0013] Figure 2 This is a schematic diagram of the microstructure of a tungsten trioxide-palladium-platinum composite nano-thin film optical fiber sensor. DETAILED DESCRIPTION

[0014] like Figure 1 As shown, a tungsten trioxide-palladium-platinum composite nanofilm (11) optical fiber hydrogen sensor is composed of a broadband light source (1), a polarizer (2), a polarization controller (3), a test chamber (4), a flow meter (5), a hydrogen and nitrogen source (6), an optical fiber sensor (7) of the composite nanofilm (11), and a demodulator (8); the characteristics are as follows: the sensor (7) is composed of a tungsten trioxide-palladium-platinum composite nanofilm (11) and a bare fiber core (10) with a cladding (12) removed and is completely sealed in the test chamber (4); light emitted by the broadband light source (1) is incident on the polarization controller (3) through the polarizer (2) and then enters the left end of the sensor (7); a hydrogen and nitrogen source (6) is introduced into the test chamber (4) through an air inlet (13) to pass a hydrogen and nitrogen mixed gas; the concentration change of hydrogen in the test chamber (4) is monitored by the flow meter (5); and the right end of the test chamber (4) is connected to the demodulator (8). By monitoring the changes in the transmission spectrum, it is possible to monitor different concentrations of hydrogen. First, a fiber cleaver is used to remove part of the cladding of the microstructured optical fiber, and then a 200nm WO3 film is deposited by thermal evaporation. During the evaporation process, oxygen is used as the process gas at a rate of 3.33x10 -6 m 3 / S rate of continuous charging. Then use Bestech magnetron sputtering system to sputter 20nm Pd2Pt and 10nm Pt films on the surface of WO3 film. During the sputtering process, the crystal oscillator system is used to monitor the thickness of the sensitive film in real time.

[0015] First, nitrogen was introduced into the test chamber (4), and after a few minutes, hydrogen with a concentration of 3% was introduced. The light intensity at the wavelength of the higher-order cladding mode of the spectrum increased significantly. After the introduction of nitrogen, the light intensity was basically restored. Compared with the peak-to-peak change of the light intensity of the spectrum, the wavelength drift of the sensor was very weak. The peak-to-peak value of the spectrum at 1567nm was selected to measure its intensity change during the cyclic hydrogen test.

[0016] A method for testing hydrogen concentration of a tungsten trioxide-palladium-platinum composite nanofilm (11) microstructure optical fiber hydrogen sensor is as follows: first, nitrogen is introduced for a period of time, and after the gas flow is stable, hydrogen is slowly introduced, while the flow rate is kept constant, and the hydrogen flow rate is gradually increased to record the sensor response at different concentrations. Hydrogen of different concentrations is introduced in sequence, and hydrogen concentration testing and analysis of the sensor is performed.

Claims

1. A tungsten trioxide-palladium-platinum composite nanofilm optical fiber hydrogen sensor, comprising a broadband light source (1), a polarizer (2), a polarization controller (3), a test gas chamber (4), a flow meter (5), a hydrogen and nitrogen source (6), a composite nanofilm (11) sensor (7), and a demodulator (8); characterized in that: The sensor (7) is composed of a tungsten trioxide-palladium-platinum composite nanofilm (11) and a bare fiber core (10) with a cladding (12) removed and is completely sealed in a test chamber (4). The sensor (7) is a zigzag optical fiber with a composite nanofilm (11) plated on its surface. A fiber cleaver removes part of the cladding of the microstructured optical fiber, and then a 200nm WO3 film is deposited by thermal evaporation. A Bestech magnetron sputtering system is used to sputter 20nm Pd2Pt and 10nm Pd2Pt on the surface of the WO3 film. The composite nanofilm (11) is a layered structure of tungsten trioxide, palladium and platinum. Light emitted by a broadband light source (1) is incident on a polarization controller (3) through a polarizing plate (2) and then enters the left end of a sensor (7). A hydrogen and nitrogen source (6) passes a hydrogen and nitrogen mixed gas into a test chamber (4) through an air inlet (13). A flow meter (5) is used to monitor the concentration change of hydrogen in the test chamber (4). The right end of the test chamber (4) is connected to a demodulator (8). After the tungsten trioxide-palladium-platinum sensitive nanofilm (11) absorbs hydrogen, its refractive index and volume will change. The demodulator (8) is used to monitor the change of the transmission spectrum to achieve monitoring of hydrogen of different concentrations.

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