CN105784813B - One kind is with MnNb2O6Electric potential type SO is blended together for the stabilizing zirconia base of sensitive electrode2Sensor, preparation method and applications - Google Patents

Abstract

_A stable zirconia _- based mixed potential SO2 sensor with _MnNb2O6 as a sensitive electrode, a preparation method and its application in low _- concentration SO2 detection belong to the technical field of gas sensors. It consists of an Al ₂ O ₃ ceramic plate with a Pt heating electrode, a YSZ substrate, a Pt reference electrode, and a MnNb ₂ O ₆ sensitive electrode; the reference electrode and the sensitive electrode are separately and symmetrically prepared on both ends of the upper surface of the YSZ substrate, _The lower surface of the YSZ substrate is bonded with an _Al2O3 ceramic plate with a Pt heating electrode. In the present invention, YSZ is used as the ion-conducting layer, and the MnNb ₂ O ₆ composite oxide material with high electrochemical catalytic activity calcined at 800, 1000 and 1200 ° C is used as the sensitive electrode to construct the sensor device, and the response value to SO ₂ is compared , to obtain devices with higher sensitivity performance.

Description

A stabilized zirconia-based mixed potential SO2 sensor using MnNb2O6 as a sensitive electrode Sensors, preparation methods and applications

technical field

The invention belongs to the technical field of gas sensors, and in particular relates to a stable zirconia _- based mixed potential SO2 sensor using _MnNb2O6 as a sensitive electrode, a preparation method and its application in low _- concentration _SO2 detection.

Background technique

Sulfur dioxide (SO ₂ ) is an important toxic and harmful gas in the atmosphere. It is mainly produced in industrial production processes such as coal and fuel combustion, as well as natural processes such as volcanic eruptions and forest fires. Sulfur dioxide contributes to the formation of acid rain, causing acidification of soil, rivers, and lakes. In addition, high concentrations of sulfur dioxide can cause nausea, chest tightness, respiratory diseases, and even worsen cardiovascular and cerebrovascular diseases. Studies have shown that repeated exposure to less than 5 ppm sulfur dioxide can cause permanent lung damage. Facing serious health threats and ecological problems, it is urgent for us to develop simple, reliable, and portable gas sensors for the selective detection of SO2.

At present, in order to realize the monitoring of gas, solid electrolyte gas sensors with low cost, miniaturization, excellent sensitivity and mechanochemical stability have received more and more attention. Many research teams have developed different _SO2 sensors using different types of solid electrolytes. Most sensors show good sensitivity to relatively high concentrations of sulfur dioxide gas. However, it is very necessary and meaningful to develop gas sensors for detecting _SO2 in the low concentration range. In our previous research work, a hybrid solid-state electrochemical gas sensor based on stabilized zirconia (YSZ) and metal oxide sensitive electrodes has been developed for the detection of low _- concentration H2S and acetone gases. According to the mixed-type sensitive mechanism, the sensitive signal of the sensor is generated at the three-phase interface of the sensitive electrode/test gas/solid electrolyte through electrochemical reaction, and the sensitivity performance of the sensor is mainly determined by the electrochemical catalytic activity of the sensitive electrode material to test gas. Therefore, it is very important to develop and search for a sensitive electrode material suitable for detecting _SO2 .

Contents of the invention

The purpose of the present invention is to provide a stable zirconia-based mixed potential SO ₂ sensor with MnNb ₂ O ₆ as the sensitive electrode, its preparation method and its practical application in low-concentration SO ₂ detection. In addition to better sensitivity, the sensor obtained by the invention also has lower detection limit, better selectivity and stability.

_The SO2 sensor involved in the present invention is based on the solid electrolyte YSZ and the high electrochemical catalytic performance _MnNb2O6 composite _oxide material is a novel SO2 sensor constructed by the sensitive electrode, YSZ (ZrO2 _{( 8} % _{Y2O3 )} ) as the ion-conducting layer.

The YSZ _- based mixed potential type SO2 sensor of the present invention, as shown in Figure ₁ , consists of an _Al2O3 ceramic plate with a Pt heating electrode, a YSZ substrate, a Pt reference electrode and a sensitive electrode in sequence; the reference electrode and the sensitive electrode The electrodes are separated from each other and symmetrically prepared at both ends of the upper surface of the YSZ substrate, and the lower surface of the YSZ substrate is bonded to the Al ₂ O ₃ ceramic plate with the Pt heating electrode; the characteristic is that the sensitive electrode material is MnNb ₂ O ₆ , and prepared by the following method:

Weigh Nb ₂ O ₅ , dissolve in 15-20 mL of hydrofluoric acid (mass fraction ≥ 40%), stir at 60-90°C for 2-4 hours; add ammonia water drop by drop to the above solution to adjust the reaction The pH value of the system is 8-10, aged for 12-14 hours, filtered and washed until neutral, and a white precipitate is obtained; dissolve the white precipitate in citric acid solution, and continue to stir at 60-80°C for 1-2 hour, then add NH ₄ NO ₃ and Mn(NO ₃ ) ₂ ·4H ₂ O and continue to stir until it becomes a gel; dry the obtained gel under vacuum at 80-90°C for 12-24 hours to obtain a dry gel, Finally, sinter at 800-1200°C for 2-4 hours to obtain MnNb ₂ O ₆ sensitive electrode material; the molar ratio of Mn(NO ₃ ) ₂ 4H ₂ O, Nb ₂ O ₅ and NH ₄ NO ₃ is 1 : 1:12-14, the molar ratio of citric acid to Nb ₂ O ₅ is 2-5:1, and the mass concentration of ammonia water is 25-28%.

SO of the present invention _The preparation steps of the sensor are as follows:

(1) Making a Pt reference electrode: Use Pt paste on one end of the upper surface of the YSZ substrate to make a 15-20 μm thick Pt reference electrode, and at the same time fold a Pt wire in half and stick it to the middle of the reference electrode as an electrode lead, and then connect the YSZ The substrate is baked at 90-120°C for 1-2 hours, and then the YSZ substrate is sintered at 1000-1200°C for 1-2 hours to remove terpineol in the platinum paste, and finally lower to room temperature;

(2) Make MnNb ₂ O ₆ sensitive electrode: adjust the MnNb ₂ O ₆ sensitive electrode material into a slurry with deionized water, the mass concentration is 2-20%; use this slurry on the YSZ substrate symmetrical to the Pt reference electrode On the other end of the surface, a sensitive electrode with a thickness of 20-30 μm is prepared, and a platinum wire is also folded in half and glued to the sensitive electrode as an electrode lead;

(3) Sinter the YSZ substrate prepared in the previous step with the reference electrode and the sensitive electrode at 800-1000°C for 1-3 hours; the preferred heating rate during high-temperature sintering is 1-2°C/min;

(4) Preparation of inorganic binder: Measure 2-4 mL of water glass (Na ₂ SiO ₃ ·9H ₂ O), weigh 0.7-1.0 g of Al ₂ O ₃ powder, mix water glass and Al ₂ O ₃ powder Mix and stir evenly to obtain the desired inorganic binder;

(5) Use an inorganic adhesive to bond the lower surface of the YSZ substrate and the _Al2O3 ceramic plate with a Pt heating electrode _;

Among them, the Al ₂ O ₃ ceramic plate with Pt heating electrode is obtained by screen printing Pt on the Al ₂ O ₃ ceramic plate, and the Al ₂ O ₃ ceramic plate with Pt heating electrode is used together as the heating plate of the device;

(6) Welding and packaging the bonded devices, so as to prepare the YSZ-based hybrid potential sensor with MnNb ₂ O ₆ as the sensitive electrode of the present invention.

In the present invention, YSZ is used as the ion-conducting layer, and the MnNb ₂ O ₆ composite oxide material with high electrochemical catalytic activity calcined at 800, 1000 and 1200 °C is used as the sensitive electrode to construct the sensor device, and the response value to SO ₂ is compared , to obtain devices with higher sensitivity performance.

Advantages of the present invention:

(1) The sensor uses a typical solid electrolyte - stabilized zirconia (YSZ), which has good thermal and chemical stability and can detect SO ₂ in harsh environments;

(2) The high-performance composite oxide MnNb ₂ O ₆ is prepared by the sol-gel method as the sensitive electrode of the sensor, the preparation method is simple, and it is beneficial to batch industrial production.

(3) By comparing the performance of sensors constructed with sensitive electrode materials obtained at three different calcination temperatures, it was found that the YSZ-based hybrid potential device with MnNb ₂ O ₆ calcined at 1000°C as the sensitive electrode showed the highest response to SO ₂ , And it has a low detection limit of 50ppb, good sensitivity, selectivity, repeatability and stability, and has potential application prospects in the detection of low _- concentration SO2.

Description of drawings

Figure 1: Schematic structure diagram of the YSZ _- based hybrid potentiometric SO sensor of the present invention.

Names of each part: Al ₂ O ₃ ceramic plate 1, Pt heating electrode 2, inorganic binder 3, YSZ substrate 4, Pt wire 5, Pt reference electrode 6, MnNb ₂ O ₆ sensitive electrode 7.

Figure 2: XRD patterns of sensitive electrode materials prepared by the present invention at different calcination temperatures (wherein, the abscissa is the angle, and the ordinate is the intensity).

As shown in Figure 2, it is the XRD pattern of the sensitive electrode material obtained at different calcination temperatures. By comparing with the standard spectrum, the sensitive material obtained at the calcination temperature above 800°C is consistent with the standard card JCPDS (File Nos.33-899) , is orthorhombic niobite-type MnNb ₂ O ₆ composite material. It shows that our sensitive electrode materials prepared at 800, 1000 and 1200℃ are pure phase MnNb ₂ O ₆ materials.

Figure 3: A comparison chart of the response value of the sensor to 5ppm SO ₂ constructed using MnNb ₂ O ₆ calcined at 800, 1000, and 1200°C as sensitive electrode materials at a working temperature of 700°C.

The sensitive performance test of the device adopts a static test method (the specific process is shown in the embodiment), and the response value of the sensor is represented by ΔV=V _SO2 -V _air . As shown in Figure 3, it is the device that embodiment 1～3 is made to 5ppm SO _The response value contrast chart, can find out from the figure, the device that embodiment 1～ ₃ makes is to 5ppm SO Response value They are -27, -9.5 and -19mV respectively. It can be seen that the YSZ _- based hybrid potentiometric sensor with calcined _MnNb2O6 at 1000 °C as the sensitive electrode material has the highest response value to _SO2 .

Figure 4: Sensitivity curve to SO ₂ of a sensor using 1000°C calcined MnNb ₂ O ₆ as a sensitive electrode material (where the abscissa is the concentration of SO ₂ , and the ordinate is the potential difference; the working temperature is 700 degrees).

The sensitivity of the sensor is the slope of the linear relationship between the sensor's response value and the corresponding concentration logarithm within a certain measurement concentration range. As shown in Figure 4, it is the sensitivity curve of the sensor to SO ₂ using MnNb ₂ O ₆ calcined at 1000°C as the sensitive electrode material. It can be seen from the figure that the sensitivity of the device to 0.05-5ppm SO ₂ is -13mV /decade, the minimum can detect 50ppb SO ₂ , this sensor shows good sensitivity and low detection limit.

Figure 5: The selectivity of the sensor using MnNb ₂ O ₆ calcined at 1000°C as the sensitive electrode material (the operating temperature is 700°C, and the concentration of the gas to be measured is 5ppm).

As shown in Figure 5, the selectivity of MnNb ₂ O ₆ as a sensor for sensitive electrode materials calcined at 1000°C is shown. It can be seen from the figure that the device exhibits the greatest sensitivity to SO ₂ , and the response of other interfering gases is uniform. It can be seen that the device has good selectivity.

Figure 6: The stability of the sensor using MnNb ₂ O ₆ calcined at 1000°C as the sensitive electrode material (the abscissa is time, and the ordinate is the potential difference and the change in potential difference).

The stability test of the device is to keep the sensor at a working temperature of 700 degrees. After 14 days of continuous high temperature testing, the response values to 2 and 5ppm SO ₂ are used as standards. During the test, a point is taken every two days to record Changes within 14 days. As shown in Figure 6, it is the stability test of the device with MnNb ₂ O ₆ calcined at 1000°C as the sensitive electrode material within 14 days. It can be seen from the figure that the device is stable for 2 and 5ppm SO ₂ The variation range of the response value is less than 26%, indicating that the device has good stability.

Detailed ways

Example 1:

The MnNb ₂ O ₆ material was prepared by the sol-gel method, and the MnNb ₂ O ₆ obtained by calcination at 1000°C was used as a sensitive electrode material to make a YSZ-based hybrid potentiometric sensor, and the gas-sensing performance of the sensor to SO ₂ was tested. The specific process is as follows :

1. Make a Pt reference electrode: use Pt slurry to make a Pt reference electrode with a size of 0.5mm×2mm and a thickness of 15μm on one end of the upper surface of the YSZ substrate with a length and width of 2×2mm and a thickness of 0.2mm, and fold it in half with a Pt wire Then stick the electrode lead wire on the middle position of the reference electrode; then bake the YSZ substrate at 100°C for 1.5 hours, and then sinter the YSZ substrate at 1000°C for 1 hour, so as to eliminate the terpineol in the platinum paste, and finally reduce the to room temperature.

2. Fabrication of MnNb ₂ O ₆ sensitive electrodes: First, MnNb ₂ O ₆ materials were prepared by sol-gel method. Weigh 3 mmol of Nb ₂ O ₅ , dissolve it in 15 mL of hydrofluoric acid (40% by mass), and stir at 80°C for 2 hours; add ammonia water with a mass concentration of 25% to the above solution drop by drop , adjust the pH value to 9, age for 14 hours, filter and wash to neutrality, and obtain a white precipitate; dissolve the above white precipitate in 1.891g of citric acid solution, continue stirring at 80°C for 2 hours, add 2.880g of NH ₄ NO ₃ and 0.7530 g Mn(NO ₃ ) ₂ ·4H ₂ O continued to stir until gelling. The obtained gel-like substance was dried in a vacuum oven at 80°C for 12 hours to obtain a dry gel, and finally sintered in a muffle furnace at 1000°C for 2 hours to obtain 1.021g of MnNb ₂ O ₆ sensitive electrode material.

Take 5mg of MnNb ₂ O ₆ powder and make a slurry with 100 mg of deionized water, and coat the MnNb ₂ O ₆ slurry with a layer of 0.5mm×2mm and 20μm thick on the other end of the upper surface of the YSZ substrate symmetrical to the reference electrode. The sensitive electrode is also folded in half with a platinum wire and glued to the sensitive electrode to lead out the electrode lead.

The prepared YSZ substrate with the reference electrode and the sensitive electrode was heated to 800°C at a heating rate of 2°C/min and kept for 2h before cooling down to room temperature.

3. Bonding ceramic plates with heating electrodes. Use an inorganic binder (Al ₂ O ₃ and water glass Na ₂ SiO ₃ 9H ₂ O, prepared at a mass ratio of 5:1) to bond the lower surface of the YSZ substrate (the side not coated with electrodes) with the same size The Al ₂ O ₃ ceramic plate (length and width 2×2mm, thickness 0.2mm) of the Pt heating electrode is bonded;

4. Device welding and packaging. Weld the device on the hexagonal socket, put on the protective cover, and complete the hybrid potential SO ₂ sensor.

Example 2:

The MnNb ₂ O ₆ material calcined at 800°C was used as the sensitive electrode material to fabricate the SO ₂ sensor. The preparation process of the MnNb ₂ O ₆ sensitive electrode material and the device fabrication process are the same as in Example 1.

Example 3:

The MnNb ₂ O ₆ material calcined at 1200°C was used as the sensitive electrode material to fabricate the SO ₂ sensor. The preparation process of the MnNb ₂ O ₆ sensitive electrode material and the device fabrication process are the same as in Example 1.

Connect the sensor to the Rigol signal tester, place the sensor in air, 50ppb, 100ppb, 200ppb, 500ppb, _800ppb , 1ppm, 2ppm and 5ppm SO2 atmospheres for voltage signal testing. The test method of the device adopts the traditional static test method, and the specific process is as follows:

1. Connect the sensor to the Rigol signal tester, and place the device in a test bottle filled with air with a volume of 1L to achieve stability, which is the electromotive force value (Vair) of the device in _air .

2. Quickly transfer the sensor to a test bottle filled with SO ₂ gas at the concentration to be measured, until the response signal is stable, which is the electromotive force value (V _SO2 ) of the device in SO ₂ .

3. Transfer the device back to the air bottle until it reaches a stable state, and the device completes a response recovery process. The electromotive force difference (ΔV=V _SO2 -V _air ) of the device in SO ₂ and air is the response value of the device to the concentration of SO ₂ . The slope of the linear relationship between the response value of the sensor in a certain measurement concentration range and the corresponding concentration logarithm is the sensitivity of the sensor.

Table 1: Comparison of the response values of sensors to 5ppm SO ₂ using MnNb ₂ O ₆ calcined at 800, 1000 and 1200°C as sensitive electrode materials

Table _{2 :} Variation of ΔV with SO2 concentration for devices using _MnNb2O6 calcined at 1000 °C as the sensitive electrode

Table 1 lists the response values of YSZ-based hybrid potentiometric sensors to 5ppm SO ₂ using MnNb ₂ O ₆ calcined at 800, 1000 and 1200°C as sensitive electrodes. It can be seen from the table that the device with MnNb ₂ O ₆ calcined at 1000°C as the sensitive electrode exhibited the highest response value, which was -27mV.

Table 2 lists the electromotive force of the YSZ-based hybrid potentiometric sensor made of MnNb ₂ O ₆ calcined at 1000°C as the sensitive electrode material in the atmosphere of different concentrations of SO ₂ and the difference of the electromotive force in air with the concentration of SO ₂ change value. It can be seen from the table that the sensitivity (slope) and detection limit of the device are -13mV/decade and 50ppb respectively. It can be seen that the device composed of the new MnNb ₂ O ₆ sensitive electrode material developed by us shows good sensitivity to SO ₂ , and a YSZ-based hybrid potential SO ₂ sensor with high sensitivity and low detection limit is obtained.

Claims (6)

_{1. A} stabilized zirconia _- based hybrid potentiometric SO2 sensor with _MnNb2O6 as the sensitive electrode, which sequentially consists of an _Al2O3 ceramic plate with a Pt heating electrode, a YSZ substrate, a Pt reference electrode, and a sensitive electrode; The reference electrode and the sensitive electrode are separated from each other and symmetrically prepared at both ends of the upper surface of the YSZ substrate, and the lower surface of the YSZ substrate is bonded with an Al ₂ O ₃ ceramic plate with a Pt heating electrode; it is characterized in that the material of the sensitive electrode is MnNb ₂ O ₆ , and prepared by the following method, Weigh Nb ₂ O ₅ , dissolve in 15-20mL of hydrofluoric acid, stir at 60-90°C for 2-4 hours; add ammonia water dropwise to the above solution, adjust the pH of the reaction system to 8- 10. Aging for 12 to 14 hours, filtered and washed to neutrality to obtain a white precipitate; dissolve the above white precipitate in citric acid solution, continue to stir at 60-80°C for 1-2 hours, then add NH ₄ NO ₃ and Mn(NO ₃ ) ₂ ·4H ₂ O continue to stir until gel-like; dry the obtained gel under vacuum at 80-90°C for 12-24 hours to obtain a dry gel, and finally dry it at 800-1200°C sintering for 2 to 4 hours to obtain MnNb ₂ O ₆ sensitive electrode materials; wherein the molar ratio of Mn(NO ₃ ) ₂ 4H ₂ O, Nb ₂ O ₅ and NH ₄ NO ₃ is 1:1:12~14, lemon The molar ratio of acid to Nb ₂ O ₅ is 2-5:1, and the mass concentration of ammonia water is 25-28%. 2. a kind of MnNb as claimed in claim ₁ O ₆ is the stable zirconia base mixed potential type SO of sensitive electrode _The preparation method of the sensor, its steps are as follows: (1) Making a Pt reference electrode: Use Pt paste on one end of the upper surface of the YSZ substrate to make a 15-20 μm thick Pt reference electrode, and at the same time fold a Pt wire in half and stick it to the middle of the reference electrode as an electrode lead, and then connect the YSZ The substrate is baked at 90-120°C for 1-2 hours, and then the YSZ substrate is sintered at 1000-1200°C for 1-2 hours to remove terpineol in the platinum paste, and finally lower to room temperature; (2) Make MnNb ₂ O ₆ sensitive electrode: adjust the MnNb ₂ O ₆ sensitive electrode material into a slurry with deionized water, the mass concentration is 2-20%; use this slurry on the YSZ substrate symmetrical to the Pt reference electrode On the other end of the surface, a sensitive electrode with a thickness of 20-30 μm is prepared, and a platinum wire is also folded in half and glued to the sensitive electrode as an electrode lead; (3) Sintering the above-mentioned YSZ substrate prepared with the reference electrode and the sensitive electrode at 800-1000°C for 1-3 hours; ( ₄ ) The lower surface of the YSZ substrate and the _Al2O3 ceramic plate with Pt heating electrodes are bonded together using an inorganic adhesive; (5) Welding and packaging the bonded devices, so as to produce a YSZ-based hybrid potentiometric sensor with MnNb ₂ O ₆ as the sensitive electrode. 3. a kind of as claimed in claim ₂ uses MnNb ₂ O ₆ as the preparation method of the stable zirconia-based mixed potential type SO sensor of sensitive electrode, it is characterized in that: the heating rate during high-temperature sintering is 1～2 ℃/ min. 4. A method for preparing a stable zirconia-based mixed potentiometric SO ₂ sensor using MnNb ₂ O ₆ as a sensitive electrode as claimed in claim 2, characterized in that: 2 to 4 mL of water glass Na ₂ SiO ₃ is measured · 9H ₂ O, and weigh 0.7-1.0g Al ₂ O ₃ powder, mix water glass and Al ₂ O ₃ powder and stir evenly to obtain the required inorganic binder. 5. The application of a stable zirconia-based hybrid potentiometric SO ₂ sensor using MnNb ₂ O ₆ as a sensitive electrode according to claim 1 in the detection of low concentration SO ₂ . 6. A kind of as claimed in claim 5 with MnNb ₂ O ₆ is the stable zirconia base mixed potential type SO sensor of sensitive electrode in the application of low concentration SO ₂ detection, it is characterized in that _{: the concentration of SO 2 is} 50ppb .