CN101968461A - Room temperature hydrogen sensor based on palladium-nanometer-scale stannic oxide film type electrode - Google Patents

Abstract

The invention relates to a miniature hydrogen sensor, in particular to the preparation and performance detection of a palladium-nano tin dioxide thin film electrode in a hydrogen sensor, in which aluminum oxide is used as a film, and palladium and nano tin dioxide are deposited by an electrodeless electrolysis method As the hydrogen sensitive material on the back sheet, the invention provides a method for preparing a palladium-nano tin dioxide thin film electrode, as the hydrogen sensitive material, the performance of the hydrogen sensor is better improved, and the research and development and application of the nano tin dioxide material are helpful In order to improve the performance of tin dioxide hydrogen sensor, doping tin dioxide into palladium and other precious metals can improve sensitivity, reduce response time, and can also reduce operating temperature. The present invention has shorter response time, better stability and repeatability, especially It is suitable for detection at room temperature, and the size of the sensor is small, the processing cost is low, and it is convenient for miniaturization, integration and industrialization, and the ceramic sheet of the base carrier can also be recycled.

Description

Room temperature hydrogen sensor based on palladium-nano-tin dioxide film electrode

technical field

The invention relates to a miniature hydrogen sensor, in particular to the preparation and performance detection of a palladium-nanometer tin dioxide film electrode in the hydrogen sensor.

technical background

Hydrogen is an ideal new energy source, which is favored by people and widely used in various industrial and agricultural occasions. However, hydrogen is also a flammable and explosive gas, and it is easy to explode when mixed with air. Therefore, the research on hydrogen sensors is imminent. The hydrogen sensor is mainly used in the detection of hydrogen concentration, the separation of mixed gas and the detection of hydrogen leaks in gas filtration.

At present, there are many studies on hydrogen-sensitive materials, such as tin dioxide and metal palladium. Tin dioxide is an important semiconductor-type hydrogen-sensing material, but it lacks gas selectivity and requires high operating temperature (250-600 °C) to obtain sufficient sensitivity. Metal palladium has attracted much attention because of its reversible reaction with hydrogen. However, due to the strong adsorption capacity of pure palladium film for hydrogen, especially when the concentration of hydrogen is high, it will lose the sensing performance of hydrogen; and the palladium film is prone to hydrogen embrittlement. Therefore, the research on hydrogen sensitive materials is still going on, and the better performance of hydrogen sensors still needs to be improved and excavated.

Contents of the invention

Aiming at the deficiencies of the prior art, the present invention provides a method for preparing a palladium-nano-tin dioxide thin-film electrode, as a hydrogen-sensitive material, to better improve the performance of hydrogen sensors, and the research and development and application of nano-tin dioxide materials are helpful It is used to improve the performance of tin dioxide hydrogen sensor; doping tin dioxide with noble metals such as palladium can improve sensitivity, reduce response time, and can also reduce operating temperature.

The invention relates to a method for preparing a palladium-nanometer tin dioxide thin-film electrode in a hydrogen sensor. Alumina is used as a negative film, and palladium and nano-tin dioxide are deposited on the negative film by an electrodeless electrolysis method as a hydrogen sensitive material. as follows:

1) Preparation of nano-tin dioxide: use the hydrothermal method to synthesize nano-tin dioxide, add stannous chloride dihydrate to the ethanol solution, adjust the pH to 11, stir the obtained suspension for 1 hour, After heating at ℃ for 6 hours, centrifuging and drying at 50℃ overnight, light yellow tin dioxide was obtained;

2) Pretreatment of alumina ceramic sheets: After soaking and cleaning with aqua regia, then ultrasonic cleaning with deionized water for 1 minute, and finally burning in a high-temperature furnace at 500-600°C for about 2 hours, soaking the clean ceramic sheets separately Activate the surface in freshly prepared stannous chloride solution (30 g/L) and silver ammonia solution (10 g/L) for 10 minutes each;

3) Composite coating: On the treated ceramic substrate, the method of electrodeless composite coating is used to deposit nano-tin dioxide, palladium and gold on the ceramic substrate to form a coating layer, and the pretreated ceramic sheet is transferred to a container. Add appropriate amount of sodium gold sulfite and formaldehyde to the aqueous solution of sodium sulfite, palladium chloride, and nano-tin dioxide, and after 20 minutes, a layer of gray uniform film is formed on the surface of the ceramic sheet;

4) After drying the film at different temperatures, connect it to a wire with an alligator clip to become a palladium-nano-tin dioxide film electrode in a hydrogen sensor.

The size of the alumina ceramic sheet of the present invention is 15mm*15mm*2mm.

The ratio of palladium-tin in the coating layer of the present invention is controlled at 1:1.

The hydrogen sensor is mainly tested for its sensing performance at room temperature. The wires of the Agilent 34901A data collector can be connected to the sensor using alligator clips. The sensor is placed in the center of the quartz tube that allows the gas to flow through. The performance detection steps of the hydrogen sensor adopting the palladium-nano tin dioxide film electrode of the present invention are as follows:

● Before performance testing, feed high-purity nitrogen until the hydrogen sensor responds with a stable resistance signal;

● Continuously inject synthetic air until the signal is stable, and obtain a stable baseline resistance signal, which is recorded as R ₀ ;

● Feed hydrogen diluted with nitrogen, the hydrogen concentration is 2%, continue to feed hydrogen until the signal curve does not fall and become stable, then continue to feed synthetic air until the signal curve does not rise and become stable, repeat the operation repeatedly;

● Use synthetic air to further dilute hydrogen to obtain a series of hydrogen with different concentrations such as 1% and 0.5% for detection;

● Investigate the effects of the drying temperature of the coating film on the performance of the sensor at room temperature, 100°C, and 200°C;

● Data processing, connect the sensor electrodes to the data collector through wires, scan and collect data through computer program control, and compare and analyze the sensor response curves under different test conditions.

Advantage of the present invention: the hydrogen sensor of palladium-nanometer tin dioxide thin-film electrode of the present invention, owing to adopt nano-tin dioxide material, specific surface increases greatly and is conducive to surface electron transfer, has strengthened the absolute intensity of detection signal, and the palladium material Incorporation can improve detection sensitivity and reduce detection temperature. The sensor has high sensitivity, it takes less than 1 minute for the signal strength to reach 90%, and it takes about 1 to 2 minutes to complete the desorption. The reproducibility and stability are also good. With the increase of hydrogen concentration, the relative strength of the response signal gradually increases. Enhanced, the signal response time decreases slightly with the increase of the hydrogen concentration, which overcomes the disadvantage that the pure palladium film will lose its sensing performance for hydrogen when the hydrogen concentration is high, and also avoids the phenomenon that the palladium film is prone to hydrogen embrittlement and film shedding. At the same time, the operating temperature is lowered to room temperature, which greatly improves safety. The hydrogen sensor of the palladium-nanometer tin dioxide thin film electrode of the present invention has good measurement performance for many times in one month, the response time is short, the stability and repeatability are good, it is especially suitable for room temperature detection, and the sensor size is small , low processing cost, convenient for miniaturization, integration and industrialization, and the ceramic sheet of the base carrier can be recycled.

Description of drawings

Figure 1 is the response curve of the SnO ₂ -Pd hydrogen sensor to 1% hydrogen concentration.

Fig. 2 is the response curve of the SnO ₂ -Pd hydrogen sensor to different concentrations of hydrogen.

Figure 3 shows the effect of the drying temperature of the SnO ₂ -Pd film on the hydrogen response under different hydrogen concentrations.

Detailed ways

  The preparation method of the palladium-nano tin dioxide thin film electrode in the hydrogen sensor is to use aluminum oxide as the negative film, and adopt the method of electroless electrolysis to deposit palladium and nano tin dioxide on the negative film as the hydrogen sensitive material. The palladium in the hydrogen sensor- The process steps of nano-tin dioxide film electrode preparation include: preparation of nano-tin dioxide, pretreatment of alumina ceramic sheet, composite coating, post-treatment and other steps. The specific process is as follows:

● Preparation of nano-tin dioxide: Add stannous chloride dihydrate to ethanol solution, adjust the pH to 11, and make the Sn (divalent) concentration reach 15.8 mM. After the obtained white suspension was magnetically stirred for 1 hour, it was transferred to a stainless steel pot with Telflon coating, heated in a muffle furnace at 120°C for 6 hours, centrifuged and dried overnight at 50°C to obtain light yellow tin dioxide;

● Pretreatment of alumina ceramic sheets (15mm*15mm*2mm): After soaking and cleaning with aqua regia, ultrasonic vibration cleaning with deionized water for 1 minute, and finally burning in a high-temperature furnace at 500-600°C for about 2 hours, the Soak the clean ceramic sheet in freshly prepared stannous chloride solution (30 g/L) and silver ammonia solution (10 g/L) for 10 minutes each to activate its surface;

● Composite coating: Transfer the pretreated ceramic sheet to a small beaker filled with 0.0143 g Na ₂ SO ₃ , a small amount of PdCl ₂ , about the same amount of SnO ₂ powder as PdCl ₂ , and 1ml deionized water, and ultrasonically vibrate for 10 minutes Finally, move the small beaker to the ice-water mixture, and add 50 μL Na ₃ Au (SO ₃ ) ₂ and 50 μL formaldehyde to the small beaker, shake and mix quickly, and after standing for 20 minutes, a layer of gray uniform film;

● Post-processing: After drying the film at different temperatures, connect it to a wire with an alligator clip to become a palladium-nano tin dioxide film electrode in a hydrogen sensor.

Performance testing steps:

● Before the performance test, inject high-purity nitrogen gas, and wait until the hydrogen sensor shows a stable signal response at room temperature;

● Continuously inject synthetic air, wait for the signal to be stable, and then inject a hydrogen gas sample with a concentration of 1% for detection. The detection curve of the sensor for 1% hydrogen gas at room temperature is shown in Figure 1. It can be seen from the graph that the hydrogen sensor has high sensitivity; the response of the sensor is very fast and stable, and it takes less than 1 minute for the signal strength to reach 90% from the baseline, and the response signal value tends to be stable. The signal remains stable, showing a relatively stable platform; when the gas flow is switched from 1% hydrogen to synthetic air, the time required for the hydrogen desorption process is about 1 to 2 minutes, and the signal value of the hydrogen sensor appears a stable platform again, and the signal value Return to the initial size and complete a detection cycle;

● Introduce hydrogen gas with discontinuous concentrations of 0.5%, 1%, 2%, etc., and continue to infuse the mixed gas until the signal curve does not change and becomes stable. Then, continue to infuse synthetic air until the signal curve does not change and becomes stable. It tends to be stable, repeated operations many times, and the repeatability test results are shown in Figure 2. It can be seen from the graph in Figure 2 that the hydrogen sensor has good repeatability, and the resistance value drop caused by the same concentration of hydrogen is basically the same. The higher the hydrogen concentration, the greater the resistance value change;

● Dry the same thin-film electrode at room temperature, 100°C, and 200°C, and test the response to different concentrations of hydrogen. The results are shown in Figure 3. It can be seen from Figure 3 that after drying at 100 ℃, the response to hydrogen signal is slightly higher than that of the thin film electrode dried at room temperature; after drying at 200 ℃, the response to hydrogen signal is greatly weakened, which is probably due to the thermal morphology of nano-tin dioxide. Change, the film electrode dried at room temperature has already shown sufficient sensitivity, so generally no additional heating treatment is required, and the process is simpler.

Claims (4)

1. a palladium-nanometer tin dioxide thin-film electrode preparation method in a hydrogen sensor, is characterized in that aluminum oxide is used as a negative film, and palladium and nano tin dioxide are deposited on the negative film as a hydrogen sensitive material by means of electroless electrolysis, Proceed as follows: 1) Preparation of nano-tin dioxide: use the hydrothermal method to synthesize nano-tin dioxide, add stannous chloride dihydrate to the ethanol solution, adjust the pH to 11, stir the obtained suspension for 1 hour, After heating at ℃ for 6 hours, centrifuging and drying at 50℃ overnight, light yellow tin dioxide was obtained; 2) Pretreatment of alumina ceramic sheets: After soaking and cleaning with aqua regia, then ultrasonic cleaning with deionized water for 1 minute, and finally burning in a high-temperature furnace at 500-600°C for about 2 hours, soaking the clean ceramic sheets separately Activate the surface in freshly prepared stannous chloride solution (30 g/L) and silver ammonia solution (10 g/L) for 10 minutes each; 3) Composite coating: On the treated ceramic substrate, the method of electrodeless composite coating is used to deposit nano-tin dioxide, palladium and gold on the ceramic substrate to form a coating layer, and the pretreated ceramic sheet is transferred to a container. Add appropriate amount of sodium gold sulfite and formaldehyde to the aqueous solution of sodium sulfite, palladium chloride, and nano-tin dioxide, and after 20 minutes, a layer of gray uniform film is formed on the surface of the ceramic sheet; 4) After drying the film at different temperatures, connect it to a wire with an alligator clip to become a palladium-nano-tin dioxide film electrode in a hydrogen sensor. 2. The method for preparing the palladium-nanometer tin dioxide film electrode in the hydrogen sensor according to claim 1, characterized in that the size of the alumina ceramic sheet is 15mm*15mm*2mm. 3. The method for preparing the palladium-nano-tin dioxide film electrode in the hydrogen sensor according to claim 1, characterized in that the palladium-tin ratio in the coating layer is controlled at 1:1. 4. the performance detection method of the hydrogen sensor of the palladium-nanometer tin dioxide film electrode that preparation method obtains according to claim 1, its steps are: a. The wires of the data collector can be connected to the sensor using alligator clips, and the sensor is placed in the center of the quartz tube that allows the gas to flow through; b. Before the performance test, feed high-purity nitrogen until the hydrogen sensor responds with a stable resistance signal; c. Continuously feed synthetic air until the signal is stable, and obtain a stable resistance signal, which is recorded as R ₀ ; d. Pass in hydrogen diluted with nitrogen, the hydrogen concentration is 2%, continue to pass in hydrogen until the signal curve no longer drops and becomes stable, and then continue to pass in synthetic air until the signal curve does not rise and becomes stable, repeat operate multiple times; e. Use synthetic air to further dilute hydrogen to obtain a series of hydrogen with different concentrations such as 1% and 0.5% for detection; f. Investigate the effects of the drying temperature of the coating film on the performance of the sensor at room temperature, 100°C, and 200°C; g. Data processing: connect the sensor electrodes to the data collector through wires, scan and collect data through computer program control, and compare and analyze the sensor response curves under different test conditions.

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