Miniaturized current type hydrogen sensor based on Pt-Pd-C / Nafion membrane material, preparation method and test fixture

Abstract

The invention discloses a miniaturized current type hydrogen sensor based on a Pt-Pd-C / Nafion membrane material, a preparation method and a test fixture, and belongs to the technical field of gas sensors. The device consists of a gas diffusion cap, a membrane electrode assembly, an isolation gasket and a water storage tank with a metal shell, the gas diffusion cap is formed by stacking an upper cylinder and a lower cylinder which are made of stainless steel; through holes in the vertical direction are formed in the upper cylinder, through holes in the horizontal direction are formed in the side face of the upper cylinder, and the through holes are communicated with one another; the membrane electrode assembly is composed of a sensitive electrode, a Nafion membrane and a reference electrode from top to bottom, and the sensitive electrode and the reference electrode are made of 10-30wt% of Pt-Pd / C electrode materials; deionized water is contained in the water storage tank, and an annular boss is arranged at the position, close to the upper edge, in the water storage tank; the sensor has the advantages of being small in size, low in power consumption, capable of working at the room temperature, environmentally friendly, convenient to operate and convenient to carry.

Description

Technical Field

[0001] The present invention belongs to the technical field of gas sensors, and in particular relates to a miniaturized current-type hydrogen sensor based on a Pt-Pd-C / Nafion membrane material, a preparation method and a test fixture. Background Art

[0002] Due to the limited reserves of fossil fuels and the easy greenhouse effect and environmental pollution, various clean energy sources have become the research hotspots of application. Among them, hydrogen, as a clean energy, is known as the most promising secondary energy. It can generate a large amount of heat and electricity through combustion or as a fuel cell without producing pollutants such as carbon dioxide. It is widely used in the chemical industry and provides sustainable energy solutions for mankind. However, hydrogen is a colorless and odorless combustible gas with a small molecular weight and strong permeability. It is easy to leak during production, storage, transportation and use. When the volume concentration of hydrogen in the air is in the range of 4% to 75%, it is very easy to explode if it encounters a spark. Therefore, it is urgent to develop a hydrogen sensor with high sensitivity, good selectivity, intrinsic safety and room temperature operation to monitor the concentration changes of hydrogen in real time during production, storage, transportation and use, and ensure the safety of production and life.

[0003] Common types of hydrogen sensors include catalytic combustion sensors, electrochemical sensors, and semiconductor oxide sensors. Catalytic combustion hydrogen sensors need to be used in an environment with oxygen. They can detect all flammable gases, have poor selectivity, and are prone to ignition and explosion. Electrochemical hydrogen sensors have a limited service life, a limited temperature range, and are sensitive to environmental conditions. Semiconductor metal oxide hydrogen sensors cannot be used at room temperature, have high power consumption, and are prone to sparks during operation. They are not suitable for use in flammable and explosive places.

[0004] Among amperometric electrochemical sensors, gas sensors using proton exchange membranes as solid electrolytes have good mechanical properties, excellent chemical stability, and excellent conductivity under high water vapor conditions, and are now receiving more attention. Among them, the Nafion membrane (perfluorosulfonic acid membrane) invented by Dupont is the most mature membrane material for commercial applications. The Nafion membrane is resistant to chemical corrosion, high temperature and low temperature, has ionic conductivity and proton exchange capacity, and is selective and highly permeable to water.

[0005] Compared with traditional gas analysis equipment that is bulky, expensive, and requires professional operation, miniaturization of sensor devices has become an inevitable trend in gas sensor research. Miniaturized sensors are small in size, low in power consumption, easy to operate, and easy to carry. They can be arrayed and integrated to a certain extent, meeting the needs of many practical application scenarios and achieving mass production and commercialization. Miniaturized hydrogen sensors also have excellent gas-sensing performance. Summary of the invention

[0006] The object of the present invention is to provide a miniaturized current-type hydrogen sensor based on Pt-Pd-C / Nafion membrane material, a preparation method and a test fixture.

[0007] In the preparation of Nafion-based current-type hydrogen sensor, the present invention adopts precious metals Pt and Pd to load on the surface of carbon fiber to make Pt-Pd-C electrode material, and further improves the gas-sensing performance of the gas sensor by adjusting the total loading amount of metal Pt and Pd to 10-30wt%. The sensor obtained by the present invention has the advantages of high sensitivity, fast response speed, good selectivity and stability. At the same time, in order to miniaturize the device, the present invention redesigns and processes the corresponding sensor housing and test equipment, and the obtained miniaturized Pt-Pd-C / Nafion current-type hydrogen sensor has the characteristics of small size, low power consumption, can work at room temperature, green and environmentally friendly, easy to operate, easy to carry, and easy to integrate.

[0008] The miniaturized current-type hydrogen sensor based on Pt-Pd-C / Nafion membrane material described in the present invention is composed of a gas diffusion cap, a membrane electrode assembly, an isolation gasket, and a water storage tank with a metal shell from top to bottom; the gas diffusion cap is composed of an upper and a lower stack of two stainless steel cylinders, the lower cylinder is a hollow structure, and the outer diameter of the lower cylinder is smaller than the diameter of the upper cylinder; 3 to 5 vertical through holes are arranged on the upper cylinder, and the same number of horizontal through holes are arranged on the side of the upper cylinder, and the vertical through holes and the horizontal through holes are interconnected; the gas diffusion cap is fixed to the metal shell of the water storage tank above the membrane electrode assembly by a rubber ring; the membrane electrode assembly The device consists of a sensitive electrode, a Nafion membrane and a reference electrode from top to bottom. The diameter of the membrane electrode assembly is smaller than the inner diameter of the water storage tank and the membrane electrode assembly is not in electrical contact with the metal shell. The water storage tank is filled with deionized water. An annular boss is arranged near the upper edge of the water storage tank to provide support for the isolation gasket and the membrane electrode assembly. The isolation gasket is a circular structure made of stainless steel. A micropore is arranged at the center of the isolation gasket, so that the water vapor in the water storage tank can pass through the micropore to reach the membrane electrode assembly, maintain the humidity of the Nafion membrane, and ensure that the Nafion membrane has a high conductivity. The sensitive electrode and the reference electrode are made of 10 to 30 wt% Pt-Pd / C electrode material.

[0009] Wherein, 10-30wt% of Pt-Pd / C electrode material is prepared by the following steps:

[0010] (1) preparing a suspension in which carbon fibers are dispersed: weighing 0.25-0.45 g of CFs having a Pt-Pd / C ratio of 10-30 wt%, 2-4 mL of a 50 mmol / L H2PtCl6 aqueous solution, and 0.04-0.07 g of Pd(NO3)2·nH2O powder, and then adding 0.15-0.45 g of Na3C6H5O7·2H2O, wherein the mass ratio of the total amount of Pt and Pd metals to Na3C6H5O7·2H2O is 1:3; dissolving the obtained suspension in 40-60 mL of deionized water, and then placing it in an ultrasonic cleaner for ultrasonic treatment for 20-40 min to disperse it uniformly;

[0011] (2) preparing a reducing agent solution: weigh 0.16-0.24 g of NaOH powder and dissolve it in 40-60 mL of deionized water to prepare a reducing agent solution to inhibit the hydrolysis of NaBH4; then add 0.004-0.006 g of excess NaBH4 powder that can reduce Pt and Pd, and stir evenly;

[0012] (3) Reduction reaction: placing the beaker containing the suspension obtained in step (1) in a constant temperature magnetic stirrer at 70 to 90° C., pouring the reducing agent solution obtained in step (2) into a separatory funnel, and placing it above the beaker; controlling the flow rate of the separatory funnel so that the reducing agent drips into the beaker at a rate of one drop per second; after adding the reducing agent, continuing the reaction for 1.5 to 3.0 hours;

[0013] (4) Collection of electrode materials: The reaction solution obtained in step (3) is filtered using a vacuum filter, and the powder obtained by filtration is washed with deionized water for multiple times, and then placed in an oven at 70 to 90° C. and dried for 10 to 15 hours to obtain 10 to 30 wt % of Pt-Pd / C electrode material.

[0014] The membrane electrode assembly (2) is prepared by the following steps:

[0015] (1) Take two polytetrafluoroethylene (PTFE) membranes and two scrapers, and place two square PTFE membranes (2-4 cm*2-4 cm, 0.05-0.1 mm thick) on the center of the two scrapers, and fix the PTFE membranes on the scrapers with tape;

[0016] (2) preparing a dispersion: preparing a dispersion by mixing ethylene glycol, a 5 wt % Nafion aqueous solution and deionized water in a volume ratio of 1:2:4;

[0017] (3) Preparation of catalytic layer material: Take two portions of 80-120 μl of the dispersion and drop them on the center of the surface of two PTFE membranes respectively, and wait for them to gather into an elliptical water drop shape; then weigh two portions of 8-15 mg each of 20% Pt-Pd / C electrode material and evenly disperse them on the dispersion with a scraper, and then dry them in an oven at 85-95° C. for 10-20 minutes to obtain a catalytic layer material on the surface of the PTFE membrane;

[0018] (4) Hot pressing: The catalyst layer material as the sensitive electrode, a 2-3 cm*2-3 cm, 0.10-0.15 mm thick Nafion membrane and the catalyst layer material as the reference electrode are placed in order, aligned and placed in a hot press, the hot press pressure is set to 6-10 MPa, and hot pressing is performed at 85-95°C for 60-120 seconds; after hot pressing, the PTFE membranes on both sides of the Nafion membrane are peeled off and cut into discs with a diameter of 2.5-3.5 mm, which are used as membrane electrode assemblies (2) with an overall thickness of 25-35 μm.

[0019] The miniaturized current-type hydrogen sensor based on Pt-Pd-C / Nafion membrane material of the present invention firstly fills a water storage tank with deionized water, with the horizontal plane located below the annular boss; then sequentially places an isolation gasket on the annular boss, places a membrane electrode assembly (MEA) on the isolation gasket, and places a gas diffusion cap above the membrane electrode assembly (MEA), thereby completing the preparation of the sensor, and then places Figure 5 The test is performed in the test fixture shown. The test fixture is a battery box structure, which consists of a 3D printed shell, a spring, an upper copper sheet and a lower copper sheet; the upper surface of the upper copper sheet contacts the spring, and the lower surface of the upper copper sheet contacts the upper surface of the gas diffusion cap of the sensor; the upper surface of the lower copper sheet contacts the bottom surface of the metal shell of the sensor; the spring presses the upper copper sheet, the sensor and the lower copper sheet, so that the sensitive electrode, the gas diffusion cap, the upper copper sheet and the spring of the membrane electrode assembly form a good electrical contact, and at the same time, the reference electrode, the isolation gasket, the metal shell and the lower copper sheet of the membrane electrode assembly form a good electrical contact; the positive electrode of the electrochemical workstation is connected to the wire led out of the spring, and the negative electrode is connected to the wire led out of the lower copper sheet, and an external circuit is formed between the sensitive electrode-gas diffusion cap-upper copper sheet-spring-electrochemical workstation-lower copper sheet-metal shell-isolation gasket-reference electrode, and the response current flowing through the external circuit at different hydrogen concentrations is detected by the electrochemical workstation, thereby completing the test of hydrogen concentration. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1This is a schematic diagram of the structure of the miniaturized Pt-Pd-C / Nafion current-type hydrogen sensor assembly described in the present invention; the miniaturized current-type hydrogen sensor based on the Pt-Pd-C / Nafion membrane material described in the present invention is composed of a gas diffusion cap 1, a membrane electrode assembly (MEA) 2, an isolation gasket 3, and a water storage tank 5 with a metal shell 4 from top to bottom.

[0021] Figure 2 The schematic diagram of the gas diffusion cap structure of the present invention is composed of two stainless steel cylinders stacked on top and bottom, which are prepared by mechanical processing; the diameter of the upper cylinder is 2.5-3.5 mm, the lower cylinder is a hollow structure, the outer diameter of the lower cylinder (smaller than the diameter of the upper cylinder) is 2-3 mm, and the inner diameter of the lower cylinder is 1-2 mm; 3-5 vertical through holes are arranged on the upper cylinder, and the same number of horizontal through holes are arranged on the side of the upper cylinder, and the vertical through holes and the horizontal through holes are interconnected, and the gas to be measured passes through the through holes and contacts the Nafion membrane in the membrane electrode assembly (MEA) 2, and the gas diffusion cap also acts as an upper electrode to collect the anode current. The gas diffusion cap 1 is fixed to the metal shell 4 of the water storage tank 5 above the membrane electrode assembly 2 by a rubber ring to prevent the gas diffusion cap from falling off and to avoid the gas diffusion cap 1 from contacting the metal shell 4 to cause a short circuit.

[0022] Figure 3 It is a schematic diagram of the structure of a membrane electrode assembly (MEA) 2; from top to bottom, it consists of a sensitive electrode, a Nafion membrane and a reference electrode. The membrane electrode assembly (MEA) 2 is a circular structure as a whole with a diameter of 2.5 to 3.5 mm (the diameter is smaller than the internal diameter of the water storage tank, and the membrane electrode assembly 2 is not in electrical contact with the metal shell 4). As the core component of the sensor, it is the place where the electrode reaction occurs.

[0023] The isolation gasket 3 (circular structure, diameter of 3.0-4.0 mm, thickness of 0.5-1.0 mm; diameter equal to the inner diameter of the water storage tank) is made of stainless steel and is prepared by lathe processing; a micropore with a diameter of 0.5-0.7 mm is arranged at the center of the isolation gasket 3, so that the water vapor in the water storage tank 5 can pass through the micropore to reach the membrane electrode assembly (MEA) 2, maintain the humidity of the Nafion membrane, and ensure that the Nafion membrane has a high conductivity; the isolation gasket 3 provides support for the membrane electrode assembly (MEA) 2, and at the same time acts as a lower electrode to collect cathode current.

[0024] Figure 4The schematic diagram of the external shape of the water storage tank 5 is a cylindrical structure prepared by lathe processing; the water storage tank 5 has a total length of 2.0 to 3.0 cm and an internal diameter of 3.0 to 4.0 mm, and is filled with deionized water; an annular boss is provided inside the water storage tank 5 at a distance of 3 to 4 mm from the upper edge (the boss extends to the bottom of the water storage tank 5) to provide support for the isolation gasket 3 and the membrane electrode assembly (MEA) 2.

[0025] Figure 5 This is a schematic diagram of the structure of the Pt-Pd-C / Nafion sensor test fixture. The fixture consists of a 3D printed 3D shell (ABS material, Acrylonitrile Butadiene Styrene), a spring, an upper copper sheet and a lower copper sheet (square structure, 5mm*5mm).

[0026] Figure 6 This is a gas-sensing performance test chart of the sensor, which tests the sensor's response current to hydrogen with a concentration gradient of 300 to 6000ppm; the horizontal axis is time (Time / s), and the vertical axis is the response current (△I / nA). The hydrogen response current (△I) is defined as the sensor's current when it is in the target atmosphere (I P ) and in air atmosphere (I a ) is the difference in current intensity in the external circuit detected by the electrochemical workstation, that is, △I = I P -I a .like Figure 6 As shown in the figure, as the gas concentration increases, the response current of the sensor increases, the response and recovery time shortens, and the stable value can be reached quickly at high concentrations. At all concentrations, the response recovery time of the sensor does not exceed 50 seconds. The response current for 30ppm H2 is about 0.17nA, and the response current for 6000ppm H2 is about -1.0nA.

[0027] Figure 7 The standard curve of hydrogen concentration and current intensity is shown in Figure 1. The horizontal axis is hydrogen concentration and the vertical axis is response current. The standard curve equation is y = -0.19-2.31×10 -4 x, wherein y is the response current (nA) and x is the hydrogen concentration (ppm); while the volume of the sensor is greatly reduced, the sensor obtained by the present invention has excellent gas-sensitive performance to hydrogen. DETAILED DESCRIPTION

[0028] Example 1

[0029] The preparation method of Pt-Pd / C of the present invention comprises the following steps:

[0030] The experiment used 50mmol / L chloroplatinic acid solution (H2PtCl6) as the Pt source, Pd(NO3)2·nH2O as the Pd source, carbon fiber CFs as the carrier, trisodium citrate dihydrate (Na3C6H5O7·2H2O) as the stabilizer, and Pt and Pd were reduced and loaded on the carbon fiber by sodium borohydride (NaBH4) reduction method. The specific preparation steps are as follows:

[0031] (1) preparing a suspension in which carbon fibers are dispersed: weighing CFs (0.312 g), H2PtCl6 (50 mmol / L aqueous solution, 2.5 mL) and Pd(NO3)2·nH2O powder (0.053 g) in a 20 wt% Pt-Pd / C ratio, and then adding Na3C6H5O7·2H2O (0.234 g), wherein the mass ratio of the total amount of Pt and Pd metals to Na3C6H5O7·2H2O is 1:3; dissolving the obtained suspension in 50 mL of deionized water, and then placing it in an ultrasonic cleaner for ultrasonic treatment for 30 min to disperse it evenly;

[0032] (2) preparing a reducing agent solution: weigh 0.2 g of NaOH powder and dissolve it in 50 mL of deionized water to prepare a reducing agent solution to inhibit the hydrolysis of sodium borohydride (NaBH4); then add an excess amount of NaBH4 powder (0.005 g) that can reduce Pt and Pd, and stir evenly;

[0033] (3) Reduction reaction: Place the beaker containing the suspension obtained in step (1) in a constant temperature magnetic stirrer at 80° C. Pour the reducing agent solution obtained in step (2) into a separatory funnel and place it above the beaker; control the flow rate of the separatory funnel so that the reducing agent drips into the beaker at a rate of one drop per second; after adding the reducing agent, continue the reaction for 2 hours;

[0034] (4) Collection of electrode materials: The reaction solution obtained in step (3) was filtered using a vacuum filter, and the powder obtained by filtration was washed with deionized water several times, and then dried in an oven at 80° C. for 12 hours to obtain 20 wt % Pt-Pd / C electrode material (0.1 g).

[0035] Example 2

[0036] The preparation process of the membrane electrode assembly (MEA) 2 of the present invention comprises the following steps:

[0037] (1) Take two polytetrafluoroethylene (PTFE) membranes and two scrapers, place two square PTFE membranes (3 cm*3 cm, 0.05 mm thick) cut on the center of the two scrapers, and fix the PTFE membranes on the scrapers with tape;

[0038] (2) preparing a dispersion: preparing a dispersion by mixing ethylene glycol, a 5 wt % Nafion aqueous solution and deionized water in a volume ratio of 1:2:4;

[0039] (3) Preparation of catalytic layer material: Take two 100 μl portions of the dispersion and drop them on the center of the surface of two PTFE membranes respectively, and wait for them to aggregate into an elliptical water drop shape; then weigh two 10 mg portions of 20 wt% Pt-Pd / C electrode material and evenly disperse them on the dispersion with a scraper, and then dry them in an oven at 90° C. for 15 minutes to obtain a catalytic layer material on the surface of the PTFE membrane;

[0040] (4) Hot pressing: Catalytic layer material (as sensitive electrode), Nafion membrane (square structure, 2.5 cm*2.5 cm, 0.127 mm thick) and catalytic layer material (as reference electrode) are placed in order, aligned and put into a hot press, the hot press pressure is set to 8 MPa, and hot pressing is performed at 90°C for 90 seconds; after hot pressing, the PTFE membranes on both sides of the Nafion membrane are peeled off and cut to obtain a disc with a diameter of 2.5 mm, which is used as a membrane electrode assembly (MEA) 2, with an overall thickness of 30 μm.

[0041] Example 3

[0042] The preparation process of the Pt-Pd / C-Nafion current-type hydrogen sensor of the present invention is to first fill the water storage tank 5 with deionized water, with the horizontal plane located below the annular boss; then sequentially place the isolation gasket 3 on the annular boss, place the membrane electrode assembly (MEA) 2 on the isolation gasket 3, and place the gas diffusion cap above the membrane electrode assembly (MEA) 2 to complete the preparation of the sensor, and then place Figure 5 The test was performed in the test fixture shown.

[0043] The diameter of the upper cylinder of the gas diffusion cap 1 is 3mm, and the diameter of the lower cylinder is 2mm; three vertical through holes are arranged on the upper cylinder (the diameter of the through holes is 0.5mm), and the same number of horizontal through holes are arranged on the side of the upper cylinder; the diameter of the membrane electrode assembly 2 is 2.5mm; the diameter of the isolation gasket 3 is 3.0mm and the thickness is 0.5mm; a micropore with a diameter of 0.6mm is arranged at the center of the isolation gasket 3; the water storage tank 5 has a total length of 2.5cm and an internal diameter (not at the annular boss) of 4.0mm, and is filled with deionized water; an annular boss is arranged inside the water storage tank 5 at a distance of 3.5mm from the upper edge, and the internal diameter of the annular boss is 3.6mm, which provides support for the isolation gasket 3 and the membrane electrode assembly 2.

[0044] The current-type hydrogen sensor based on Pt-Pd / C-Nafion membrane described in the present invention has the following sensitive mechanism: the Nafion membrane is composed of a main skeleton, side chains and a network structure between ion clusters. The main skeleton is a polytetrafluoroethylene (PTFE) structure, and the fluorine atoms with high electronegativity partially replace the hydrogen atoms, tightly wrapping the CC main chain to form a protective layer with very low surface energy. The side chains are perfluorovinyl ether structures with sulfonic acid groups (-SO3H) at the ends. Since the sulfonic acid groups are hydrophilic, the H in -SO3H + It can react with H2O to form H3O + , so that protons can move quickly, forming efficient conduction of protons. In the hydrated state, the hydrophilic sulfonic acid groups tend to aggregate to form ion clusters of about 4nm, and the walls of the ion clusters carry negative charges, so they are more sensitive to OH - The migration resistance of negatively charged ions is much higher than that of cations. In addition, these ion clusters are connected by narrow water channels with a diameter of about 1 nm. The short and narrow channels also restrict the passage of ions with larger radius.

[0045] Sensing electrode: 2H2=4H + +4e - (1)

[0046] Reference electrode: O2+4e - +4H + =2H2O(2)

[0047] Overall reaction: 2H2+O2=2H2O(3)

[0048] After the sensor of the present invention is installed in the test fixture and placed in a hydrogen atmosphere, hydrogen molecules reach the sensitive electrode through the through hole on the gas diffusion cap and are catalyzed by the Pt-Pd / C electrode material to produce a reaction of protons and electrons (1). Due to the width of the channel formed by the ion clusters in the Nafion membrane and the negative charge, the migration resistance to protons is much smaller than that of other substances. Therefore, the generated protons can pass through the Nafion membrane along the concentration gradient to reach the reference electrode side. The electrons thus repelled by the negatively charged ion clusters can only be transferred from the sensitive electrode to the reference electrode through the external circuit and participate in the reaction (2). The positive electrode of the electrochemical workstation is connected to the wire led out from the spring, and the negative electrode of the electrochemical workstation is connected to the wire led out from the lower copper sheet. The response current flowing through the external circuit at different hydrogen concentrations is detected by the electrochemical workstation, thereby completing the test of the hydrogen concentration. Experiments show that the response current (△I=I P -I a) has different sizes. The greater the hydrogen concentration, the greater the response current. The hydrogen concentration and the response current are linearly related. The entire detection process does not require external bias. As long as the hydrogen gas to be detected enters the sensor through the gas diffusion cap, a current signal can be generated.

[0049] In actual application, a "hydrogen concentration-response current" standard curve can be first established, that is, the sensor installation test fixture described in the present invention is placed in an atmosphere of known hydrogen concentrations, the real-time data of hydrogen concentration and response current are recorded, and the "hydrogen concentration-response current" standard curve is established; then the sensor installation test fixture described in the present invention is placed in an atmosphere of unknown concentration of hydrogen, the real-time data of the response current is recorded, and the data is substituted into the "hydrogen concentration-response current" standard curve, and then the hydrogen concentration is calculated.

Claims

1. A miniaturized amperometric hydrogen sensor based on Pt-Pd-C / Nafion membrane material, characterized in that: The gas diffusion cap (1) is composed of a gas diffusion cap (1), a membrane electrode assembly (2), an isolation gasket (3), and a water storage tank (5) with a metal shell (4) from top to bottom. The gas diffusion cap (1) is composed of two stacked stainless steel cylinders, the lower cylinder is a hollow structure, and the outer diameter of the lower cylinder is smaller than the diameter of the upper cylinder. The upper cylinder is provided with 3 to 5 vertical through holes, and the side of the upper cylinder is provided with the same number of horizontal through holes, and the vertical through holes and the horizontal through holes are interconnected. The gas diffusion cap (1) is fixed to the metal shell (4) of the water storage tank (5) above the membrane electrode assembly (2) by a rubber ring. The membrane electrode assembly (2) is composed of a sensitive electrode, a Nafion membrane and a reference electrode from top to bottom. The electrode composition comprises a membrane electrode assembly (2) having a diameter smaller than the inner diameter of a water storage tank (5) and the membrane electrode assembly (2) is not in electrical contact with a metal housing (4); the water storage tank (5) is filled with deionized water, and an annular boss is provided near the upper edge of the water storage tank (5) to provide support for the isolation gasket (3) and the membrane electrode assembly (2); the isolation gasket (3) is a circular structure made of stainless steel, and a micropore is provided at the center of the isolation gasket (3) so that water vapor in the water storage tank (5) can pass through the micropore to reach the membrane electrode assembly (2), thereby maintaining the humidity of the Nafion membrane and ensuring that the Nafion membrane has a high conductivity; the sensitive electrode and the reference electrode materials are 10 to 30 wt% of Pt-Pd / C electrode materials.

2. A miniaturized current-type hydrogen sensor based on Pt-Pd-C / Nafion membrane material as claimed in claim 1, characterized in that: 10-30wt% Pt-Pd / C electrode material is prepared by the following steps: (1) preparing a suspension in which carbon fibers are dispersed: weighing 0.25-0.45 g of CFs having a Pt-Pd / C ratio of 10-30 wt%, 2-4 mL of a 50 mmol / L H2PtCl6 aqueous solution, and 0.04-0.07 g of Pd(NO3)2·nH2O powder, and then adding 0.15-0.45 g of Na3C6H5O7·2H2O, wherein the mass ratio of the total amount of Pt and Pd metals to Na3C6H5O7·2H2O is 1:3; dissolving the obtained suspension in 40-60 mL of deionized water, and then placing it in an ultrasonic cleaner for ultrasonic treatment for 20-40 min to disperse it uniformly; (2) preparing a reducing agent solution: weigh 0.16-0.24 g of NaOH powder and dissolve it in 40-60 mL of deionized water to prepare a reducing agent solution to inhibit the hydrolysis of NaBH4; then add 0.004-0.006 g of excess NaBH4 powder that can reduce Pt and Pd, and stir evenly; (3) Reduction reaction: placing the beaker containing the suspension obtained in step (1) in a constant temperature magnetic stirrer at 70 to 90° C., pouring the reducing agent solution obtained in step (2) into a separatory funnel, and placing it above the beaker; controlling the flow rate of the separatory funnel so that the reducing agent drips into the beaker at a rate of one drop per second; after adding the reducing agent, continuing the reaction for 1.5 to 3.0 hours; (4) Collection of electrode materials: The reaction solution obtained in step (3) is filtered using a vacuum filter, and the powder obtained by filtration is washed with deionized water for multiple times, and then placed in an oven at 70 to 90° C. and dried for 10 to 15 hours to obtain 10 to 30 wt % of Pt-Pd / C electrode material.

3. A miniaturized current-type hydrogen sensor based on Pt-Pd-C / Nafion membrane material as claimed in claim 1, characterized in that: The membrane electrode assembly (2) is prepared by the following steps: (1) Take two polytetrafluoroethylene (PTFE) membranes and two scrapers, and place two square PTFE membranes (2-4 cm*2-4 cm, 0.05-0.1 mm thick) on the center of the two scrapers, and fix the PTFE membranes on the scrapers with tape; (2) preparing a dispersion: preparing a dispersion by mixing ethylene glycol, a 5 wt % Nafion aqueous solution and deionized water in a volume ratio of 1:2:4; (3) Preparation of catalytic layer material: Take two portions of 80-120 μl of the dispersion and drop them on the center of the surface of two PTFE membranes respectively, and wait for them to gather into an elliptical water drop shape; then weigh two portions of 8-15 mg each of 20% Pt-Pd / C electrode material and evenly disperse them on the dispersion with a scraper, and then dry them in an oven at 85-95° C. for 10-20 minutes to obtain a catalytic layer material on the surface of the PTFE membrane; (4) Hot pressing: The catalyst layer material as the sensitive electrode, a 2-3 cm*2-3 cm, 0.10-0.15 mm thick Nafion membrane and the catalyst layer material as the reference electrode are placed in order, aligned and placed in a hot press, the hot press pressure is set to 6-10 MPa, and hot pressing is performed at 85-95°C for 60-120 seconds; after hot pressing, the PTFE membranes on both sides of the Nafion membrane are peeled off and cut into discs with a diameter of 2.5-3.5 mm, which are used as membrane electrode assemblies (2) with an overall thickness of 25-35 μm.

4. A method for preparing a miniaturized current-type hydrogen sensor based on Pt-Pd-C / Nafion membrane material according to any one of claims 1 to 3, characterized in that: First, a water storage tank (5) is filled with deionized water until the horizontal plane is located below the annular boss; then, an isolation gasket (3) is placed on the annular boss of the water storage tank (5), a membrane electrode assembly (2) is placed on the isolation gasket (3), and a gas diffusion cap (1) is placed above the membrane electrode assembly (2), thereby completing the preparation of the sensor.

5. A test fixture for a miniaturized current-type hydrogen sensor based on Pt-Pd-C / Nafion membrane material as claimed in any one of claims 1 to 3, characterized in that: The test fixture is a battery box structure, which is composed of a 3D-printed shell, a spring, an upper copper sheet and a lower copper sheet; the upper surface of the upper copper sheet contacts the spring, and the lower surface of the upper copper sheet contacts the upper surface of the gas diffusion cap of the sensor; the upper surface of the lower copper sheet contacts the bottom surface of the sensor metal shell (4); the spring presses the upper copper sheet, the sensor and the lower copper sheet, so that a good electrical contact is formed between the sensitive electrode of the membrane electrode assembly (2), the gas diffusion cap (1), the upper copper sheet and the spring, and a good electrical contact is formed between the reference electrode of the membrane electrode assembly (2), the isolation gasket (3), the metal shell (4) and the lower copper sheet; the positive electrode of the electrochemical workstation is connected to the wire led out of the spring, and the negative electrode is connected to the wire led out of the lower copper sheet, and an external circuit is formed between the sensitive electrode-gas diffusion cap-upper copper sheet-spring-electrochemical workstation-lower copper sheet-metal shell (4)-isolation gasket (3)-reference electrode, and the response current flowing through the external circuit at different hydrogen concentrations is detected by the electrochemical workstation.

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