CN104897761A - YSZ-based mixed potential NO2 sensor based on graded In2O3 sensitive electrodes and its preparation method - Google Patents

Abstract

The invention belongs to the technical field of gas sensors, and in particular relates to a YSZ-based mixed potential NO ₂ sensor based on graded In ₂ O ₃ sensitive electrodes and a preparation method thereof. The sensor can be mainly used for detecting automobile exhaust. The sensor consists of an Al ₂ O ₃ ceramic plate with a Pt heating electrode, a YSZ substrate, a reference electrode and a sensitive electrode in sequence; the reference electrode is a strip-shaped Pt, and the sensitive electrode is a strip-shaped In ₂ O ₃ , and the two electrodes are separated from each other and symmetrically Both ends of the upper surface of the YSZ substrate _were prepared, and the lower surface of the YSZ substrate was bonded with an _Al2O3 ceramic plate with a Pt heating electrode. In the present invention, the YSZ substrate is used as the ion-conducting layer, In ₂ O ₃ with high electrochemical catalytic activity is used as the sensitive electrode, and the microscopic morphology of the sensitive electrode material is changed through different calcination temperatures (800°C-1200°C), so as to improve the sensitivity purpose of the feature.

Description

YSZ-based mixed potential NO2 sensor based on graded In2O3 sensitive electrodes and its preparation method

technical field

The invention belongs to the technical field of gas sensors, and in particular relates to a YSZ-based mixed potential NO ₂ sensor based on graded In ₂ O ₃ sensitive electrodes and a preparation method thereof. The sensor can be mainly used for detecting automobile exhaust.

Background technique

NO ₂ , as one of a group of highly active reactive gases (NO _x ), mainly comes from the combustion emission process, especially the exhaust emission of road motor vehicles. A large amount of NO ₂ emitted will not only cause serious air pollution problems such as acid rain, greenhouse effect, and ozone layer destruction, but also cause serious damage to human respiratory system. In order to effectively solve the related pollution problems from the source and protect human health, it is urgent to develop cheap, miniature, sensitive and reliable gas sensors for monitoring and controlling _NOx . Since the exhaust emissions of automobile engines are in a typical environment of long-term high temperature, high humidity and the coexistence of various gases, the sensors required to work normally in this environment must have good sensitivity characteristics. Over the past ten years, hybrid potentiometric gas sensors based on solid electrolyte (YSZ) and oxide sensitive electrodes have met the above requirements and have proven to be very reliable devices for applications in automotive exhaust detection. , and become a new type of gas sensor that has attracted much attention.

The sensitive mechanism of the stable zirconia _- based mixed potential NO2 sensor is: NO2 in the atmosphere diffuses to the three _- phase reaction interface through the sensitive electrode layer. During the diffusion process, the concentration of NO2 will gradually decrease due to the reaction ( ₁ ), and the oxidation _The porosity of the material sensitive electrode will determine the reduction degree of NO2 concentration. At the three-phase interface of gas/sensing electrode/YSZ, the electrochemical reduction reaction of NO and the electrochemical oxidation reaction of oxygen occur simultaneously, and the reactions ( ₂ ) and (3) constitute a local battery, when both reaction rates are equal , the reaction reaches equilibrium, and a mixed potential is formed on the sensitive electrode, and the potential difference between it and the reference electrode is used as the detection signal of the sensor. The magnitude of the detection signal is determined by the rate of electrochemical reactions (2) and (3), and the reaction rate depends on the electrochemical and chemical catalytic activity of the sensitive electrode material, the microstructure of the electrode material (such as the porosity, particle size, and morphology of the material). wait).

The reaction formula is as follows:

NO ₂ →NO+1/2O ₂ (1)

NO ₂ +2e- ^→ NO+O ^2- (2)

O ^2- → 1/2O ₂ +2e ^- (3)

At present, in order to prepare sensors with higher sensitivity characteristics, most researchers at home and abroad are devoted to the research of sensitive electrode materials. For example, the YSZ-based mixed potential NO ₂ sensor made by our research group with Cr ₂ O ₃ -WO ₃ as the sensitive electrode material has a mixed potential value of 52mV for 100ppm NO ₂ (Quan Diao, Chengguo Yin, Yingwei Liu, Jianguo Li , Xun Gong, Xishuang Liang, Shiqi Yang, Hong Chen, Geyu Lu, Mixed-potential-type NO ₂ sensor using stabilized zirconia and Cr ₂ O ₃ -WO ₃ nanocomposites, Sensor and Actuators B 180(2013) 90-95). The shortcoming of this kind of NO ₂ sensor is that the response value is low, the sensitivity is not high enough, and it cannot meet the practical requirements. In addition, since the morphology of the electrode material will affect the diffusion process of NO2 in the electrode layer, thereby affecting the electrochemical reaction of the gas at the three _- phase interface, the development of a porous sensitive electrode material with a special morphology will further improve the sensitivity of the sensor. (Sensitivity, response value, selectivity, stability, etc.) are of great significance.

Contents of the invention

The purpose of the present invention is to provide a YSZ _- based mixed potential NO sensor based _on graded In ₂ O ₃ sensitive electrodes and its preparation method, so as to improve the sensitive performance of the NO sensor and promote the practical application of this sensor in the field of automobile exhaust detection . In addition to high sensitivity, the sensor obtained by the invention also has good selectivity, repeatability and stability.

_The NO2 sensor involved in the present invention is based _on solid electrolyte YSZ and high electrochemical catalytic performance graded _In2O3 is a novel NO2 sensor built as a sensitive electrode, and the doping ratio of the substance amount of _{YSZ ( Y2O3} is 8% ZrO ₂ ) as the ion-conducting layer.

A YSZ _- based mixed potentiometric NO sensor based on graded In ₂ O ₃ sensitive electrodes according to the present invention, as shown in Figure 1, is characterized in that it consists of Al ₂ O ₃ ceramic plates with Pt heating electrodes in sequence , YSZ substrate, reference electrode and sensitive electrode; the reference electrode is strip-shaped Pt, the sensitive electrode is strip-shaped In ₂ O ₃ , the two 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 It is bonded with Al ₂ O ₃ ceramic plates with thin strip-shaped Pt heating electrodes; the sensitive electrode material is to dissolve 1~2mmol In(NO ₃ ) ₃ ·4.5H ₂ O in 30~60mL deionized water, stir Make it dissolve; then add 4-6mmol sucrose and 2.5-5mmol urea into the In(NO ₃ ) ₃ solution, stir to dissolve it; React at ~180°C for 12-18 hours, and cool naturally to room temperature after the reaction; the product in the reactor is centrifuged, washed, and dried to obtain a prepolymer precipitate, and then sintered at 800-1200°C for 2-4 hours. Among them, as shown in Figure 3a, the graded In ₂ O ₃ is constructed from nanosheets with holes and has a certain star-like structure, and the nanosheets are composed of nanoparticles.

In the present invention, the YSZ substrate is used as the ion-conducting layer, In ₂ O ₃ with high electrochemical catalytic activity is used as the sensitive electrode, and the microscopic morphology of the sensitive electrode material is changed through different calcination temperatures (800°C-1200°C), so as to improve the sensitivity purpose of the feature.

A kind of YSZ based mixed potential type NO sensor based _on graded In ₂ O ₃ sensitive electrodes according to the present invention, 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 with Pt paste as the electrode lead Then bake the YSZ substrate at 90-120°C for 1-2 hours, then sinter the YSZ substrate at 1000-1200°C for 1-2 hours, remove the terpineol in the Pt slurry, and finally cool down to room temperature;

(2) Make sensitive electrodes: adjust the sensitive electrode materials obtained above into slurry with deionized water, and the mass concentration is 2 to 20%; use the slurry of sensitive electrode materials on the YSZ substrate upper surface symmetrical to the reference electrode Prepare a sensitive electrode with a thickness of 20-30 μm at the other end, and also fold a Pt wire in half and stick it on the sensitive electrode with Pt paste as the 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; 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, and mix the obtained water glass with Al ₂ O ₃ The powders are mixed and stirred evenly to obtain an inorganic binder;

( ₅ ) The lower surface of the YSZ substrate and the _Al2O3 ceramic plate with Pt heating electrodes were bonded together using an inorganic adhesive;

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 produce the YSZ-based hybrid potential sensor with In ₂ O ₃ as the sensitive electrode of the present invention.

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 NO ₂ at high temperatures (in automobile exhaust).

(2) The hydrothermal method is used to prepare graded In ₂ O ₃ as the sensitive electrode material of the sensor, the preparation method is simple, and it is beneficial to batch industrial production.

(3) Optimizing the microstructure of the sensitive electrode material by changing different calcination temperatures (800°C to 1200°C) facilitates the gas to be measured to quickly reach the three-phase interface to participate in the electrochemical reaction and reduce the consumption in the diffusion process, so that the sensor is effective Very high sensitivity.

Description of drawings

Figure 1: Schematic diagram of the structure of the YSZ _- based hybrid potentiometric NO sensor of the present invention.

Names of each part: In ₂ O ₃ sensitive electrode 1, YSZ substrate 2, Pt reference electrode 3, Pt wire 4, Pt point 5, Al ₂ O ₃ ceramic plate 6, Pt heating electrode 7, inorganic binder 8.

Figure 2: XRD pattern of the In ₂ O ₃ sensitive electrode material prepared in the present invention.

As shown in Figure 2, it is the XRD pattern of the In ₂ O ₃ sensitive electrode material. By comparing with the standard spectrum, the In ₂ O ₃ prepared by the present invention is consistent with the standard card JCPDS#65-3170, and is cubic In ₂ O ₃ . It shows that the sensitive electrode material prepared by the present invention is In ₂ O ₃ material.

Figure 3: SEM images of sensitive electrode materials prepared by the present invention at different calcination temperatures.

As shown in Figure ₃ , a: 800 °C, b: 1000 °C, c: 1200 °C SEM images of _In2O3 sensitive electrode materials calcined, the inset is the enlarged image of the local area. It can be seen from the figure that as the calcination temperature increases, the special morphology of the material gradually disappears, and the particle size and pore size gradually increase. It can be seen that changing the sintering temperature of the sensitive material can change the sensitivity of the sensitive electrode. The microscopic morphology of the electrode is conducive to the diffusion of gas.

Figure ₄ : Concentration logarithmic curves of sensors S800, S1000 and S1200 in response to different concentrations of NO2.

As shown in Figure 4, the electromotive force difference ΔV of the devices made in Example 1, Example _{2 and Example 3 varies with the concentration of NO 2 .} The logarithm has a good linear relationship, and its slope is defined as the sensitivity of the sensor. The sensitivities of Examples 1, 2, and 3 are 61, 68, and 33 mV/decade, respectively. It can be seen that the YSZ-based hybrid potentiometric NO ₂ sensor S1000, which uses In ₂ O ₃ sintered at 1000°C as the sensitive electrode material, has the highest sensitivity.

Figure ₅ : Selectivity of the sensor S1000 with _In2O3 sintered at 1000°C as the sensitive electrode material.

As shown in Figure 5, it is the selectivity of the sensor S1000. It can be seen from the figure that the sensitivity of the device to the coexistence of NO ₂ and other gases has a small change. It can be seen that the device has a good selectivity to NO ₂ .

Figure 6: Long _- term stability of sensor S1000 against NO2.

As shown in Figure ₆ , the stability of the sensor S1000 to 100ppm and 200ppm NO2 during the 30-day test period, it can be seen from the figure that the device exhibits good long _- term stability to NO2.

Detailed ways

Example 1:

In ₂ O ₃ material was prepared by hydrothermal method, and In ₂ O ₃ was used as a sensitive electrode material to make a YSZ-based hybrid potentiometric NO ₂ sensor, and the gas-sensing performance of the sensor 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 Finally, stick the Pt paste on the middle position of the reference electrode to lead out the electrode lead; then bake the YSZ substrate at 100°C for 1.5 hours, and then sinter the YSZ substrate at 1000°C for 1.5 hours to eliminate the terpineol in the platinum paste , and finally down to room temperature.

2. Fabrication of In ₂ O ₃ sensitive electrodes: firstly prepare In ₂ O ₃ material by hydrothermal method. Dissolve 1 mmol of In(NO ₃ ) ₃ ·4.5H ₂ O in 30 mL of deionized water, stir to dissolve; then add 4 mmol of sucrose and 2.5 mmol of urea to the In(NO ₃ ) ₃ solution, stir to dissolve; The obtained mixed solution was transferred to a polytetrafluoroethylene reactor, sealed tightly and placed in an oven at 160° C. for 12 hours. After the reaction, it was naturally cooled to room temperature. After centrifugation, washing and drying, the prepolymer precipitate was obtained. Finally, the obtained precipitate was sintered at 800° C. for 2 hours with a heating rate of 2° C./min to obtain In ₂ O ₃ sensitive electrode materials.

Take 5mg of In ₂ O ₃ powder and make a slurry with 100 mg of deionized water, and coat the In ₂ O ₃ 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 with Pt paste 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 in a mass ratio of about 5:1) to bond the lower surface of the YSZ substrate (the side that is not coated with electrodes) with a tape of the same size Al ₂ O ₃ ceramic plates (length and width 2×2mm, thickness 0.2mm) with Pt heating electrodes are bonded;

4. Device welding and packaging. Weld the device on the hexagonal socket, put on the protective cover, and complete the hybrid potential NO ₂ sensor, which is marked as sensor S800.

Example 2:

The In ₂ O ₃ material sintered at 1200°C is used as the sensitive electrode material to make the NO ₂ sensor. The manufacturing process is as follows:

The In ₂ O ₃ prepared by the aforementioned method was sintered in a muffle furnace at 1200° C. to obtain the sensitive electrode material In ₂ O ₃ (1200° C.). The device manufacturing process is the same as that of Example 1, marked as sensor S1200.

Example 3:

The In ₂ O ₃ material sintered at 1000°C is used as the sensitive electrode material to make the NO ₂ sensor. The manufacturing process is as follows:

The In ₂ O ₃ prepared by the aforementioned method was sintered in a muffle furnace at 1000°C to obtain the sensitive electrode material In ₂ O ₃ (1000°C). The fabrication process of the device was the same as in Example 1, marked as sensor S1000.

Connect the sensor to the Rigol signal tester, place the sensor in the atmosphere of air, 5ppm NO ₂ , 10ppm NO ₂ , 20ppm NO ₂ , 50ppm NO ₂ , 100ppm NO ₂ , 200ppm NO ₂ , 300ppm NO ₂ for voltage signal test .

Table 1 lists the YSZ-based hybrid potentiometric sensors made of In ₂ O _{3 (800°C)} , In ₂ O _{3 (1000°C)} and In ₂ O _{3 (1200°C)} as sensitive electrode materials respectively at different concentrations of NO ₂ The difference between the electromotive force in the atmosphere and the electromotive force in the air varies with the NO ₂ concentration. It can be seen from the table that all _three devices have good response characteristics to NO2, and the sensitivity (slope) of device S1000 is the highest, which is 68mV/decade, which is greater than 61mV/decade of device S800 and 33mV/decade of device S1200. And the device S1000 has the largest response value to each concentration of NO ₂ , showing the highest sensitivity. It can be seen that the device constructed by the graded In ₂ O ₃ sensitive electrode material with special morphology has good sensitivity to NO ₂ , and the electrochemical catalytic activity and porosity of the sensitive material can be changed by changing the sintering temperature of the sensitive electrode material. Thus improving the electrode reaction efficiency of the sensor, a YSZ-based hybrid potentiometric NO ₂ sensor with high sensitivity was obtained.

Table 1 Variation of ΔV with NO ₂ concentration for sensors S800, S1000 and S1200 using In ₂ O ₃ (800°C), In ₂ O ₃ (1000°C) and In ₂ O ₃ (1200°C) as sensitive electrode materials respectively

Claims (4)

1. one kind based on graduation In ₂o ₃the YSZ base of sensitive electrode blendes together electric potential type NO ₂sensor, is characterized in that: successively by the Al with Pt heating electrode ₂o ₃ceramic wafer, YSZ substrate, reference electrode and sensitive electrode form; Reference electrode is strip Pt, and sensitive electrode is strip In ₂o ₃, two electrodes are separate and be prepared in the two ends of YSZ upper surface of base plate symmetrically, lower surface and the Al with fine strip shape Pt heating electrode of YSZ substrate ₂o ₃ceramic wafer is bonded together; Sensitive electrode material is by the In (NO of 1 ~ 2mmol ₃) ₃4.5H ₂o is dissolved in 30 ~ 60mL deionized water, stirs and makes it dissolve; Then 4 ~ 6mmol sucrose and 2.5 ~ 5mmol urea are joined In (NO ₃) ₃in solution, stir and make it dissolve; The mixed solution obtained is transferred in teflon reactor, after airtight, at 160 ~ 180 DEG C, react 12 ~ 18h, after reaction terminates, naturally cool to room temperature; In reactor product through centrifugal, washing, obtain prepolymer precipitation after drying, then sinter at 800 ~ 1200 DEG C and prepare for 2 ~ 4 hours.

2. one according to claim 1 is based on graduation In ₂o ₃the YSZ base of sensitive electrode blendes together electric potential type NO ₂the preparation method of sensor, its step is as follows:

(1) Pt reference electrode is made: use Pt to starch the thick Pt reference electrode of making 15 ~ 20 μm in one end of YSZ upper surface of base plate, be bonded at after the doubling of a Pt silk on reference electrode centre position as contact conductor with Pt slurry simultaneously, then YSZ substrate is toasted 1 ~ 2 hour under 90 ~ 120 DEG C of conditions, again YSZ substrate is sintered 1 ~ 2 hour at 1000 ~ 1200 DEG C, get rid of the terpinol in Pt slurry, be finally down to room temperature;

(2) sensitive electrode is made: by aforementioned obtained sensitive electrode material deionized water furnishing slurry, mass concentration is 2 ~ 20%; Prepare 20 ~ 30 μm of thick sensitive electrodes with the slurry of sensitive electrode material at the other end of the YSZ upper surface of base plate with reference electrode symmetry, be also bonded at after the doubling of a Pt silk on sensitive electrode as contact conductor with Pt slurry equally;

(3) the YSZ substrate of reference electrode and sensitive electrode above-mentioned preparation is had to sinter 1 ~ 3 hour at 800 ~ 1000 DEG C;

(4) use inorganic bond by the lower surface of YSZ substrate and the Al with Pt heating electrode ₂o ₃ceramic wafer is bonded together;

(5) device bonded is carried out welding, encapsulating, thus prepare based on graduation In ₂o ₃the YSZ base of sensitive electrode blendes together electric potential type NO ₂sensor.

3. as claimed in claim 2 a kind of based on graduation In ₂o ₃the YSZ base of sensitive electrode blendes together electric potential type NO ₂the preparation method of sensor, is characterized in that: measure water glass Na ₂siO ₃9H ₂o 2 ~ 4mL, and take Al ₂o ₃powder 0.7 ~ 1.0g, by the water glass that obtains and Al ₂o ₃powder mixes and stirs, and namely prepares inorganic bond.

4. as claimed in claim 2 a kind of based on graduation In ₂o ₃the YSZ base of sensitive electrode blendes together electric potential type NO ₂the preparation method of sensor, is characterized in that: with the Al of Pt heating electrode ₂o ₃ceramic wafer is at Al ₂o ₃ceramic wafer is obtained by serigraphy Pt.