CN104819998A - A kind of impedance spectroscopy NOx sensor and its solid electrolyte material preparation method - Google Patents

Abstract

The invention discloses an impedance spectrum _NOx sensor and a method for preparing the solid electrolyte material thereof. The solid electrolyte material is Gd _1-x Ca _x AlO _{3- δ} , wherein 0.05≤x≤0.25; the _NOx The sensor consists of a solid electrolyte substrate, a sensitive electrode, and a reference electrode. The sensitive electrode is NiO, while the reference electrode is the noble metal Pt. The invention adopts screen printing technology to print sensitive electrodes and reference electrodes on the upper and lower surfaces of the solid electrolyte, and draws out electrode leads for connection, and forms a fixed whole by sintering. The _NOx sensor of the present invention uses the AC impedance method to test the _NOx concentration, the frequency range of the test is 1 Hz to 10 MHz, the temperature range is 300°C to 1000°C, and the testable range of _NOx is 0 to 500 ppm. The sensor has Short response time, high sensitivity, good stability, low detection limit and other advantages.

Description

A kind of impedance spectroscopy NOx sensor and its solid electrolyte material preparation method

technical field

The invention belongs to the field of preparation of solid electrolyte materials, in particular to an impedance spectrum _NOx sensor and a preparation method of the solid electrolyte material.

Background technique

With the continuous improvement of my country's economic level, cars have entered the homes of ordinary people, and the number of cars in my country is increasing year by year, and it is expected to reach 200 million in 2020. Cars bring convenience to our daily life, but also bring serious air pollution. Among them, nitrogen oxides (NO _x ) in automobile exhaust, as one of the main air pollutants, seriously threaten environmental safety and human health. For this reason, various countries have established relevant laws and regulations to strictly control nitrogen oxides in automobile exhaust. emissions of toxic gases. In addition, researchers continue to carry out technological transformation on the combustion system of automobile engines. Compared with traditional engine control systems, the new engine electronic control fuel injection system (EFI) has added _NOx sensors for exhaust gas monitoring. So far, the NO _x sensors that have been reported mainly include: surface acoustic wave type, semiconductor oxide type, electrochemical type, solid electrolyte type, FET type, diode type and optical fiber type, etc. Because the solid electrolyte _NOx sensor has the advantages of fast response speed, high sensitivity, low detection limit, and good selectivity, it has attracted the attention of domestic and foreign researchers and conducted in-depth research in recent years.

CN 1071508 A Invented a nitrogen oxide sensor group. The set of self-contained _NOx sensors is used to sense the _NOx level in the combustion exhaust and to generate a measurable output signal related to the measured _NOx level.

CN 202814903 U discloses a limit current measurement circuit of an oxygen pump for a nitrogen and oxygen sensor. The nitrogen and oxygen sensor is used to measure the limit current of the oxygen pump so that the controller can accurately provide the working voltage for the oxygen pump, thereby ensuring the measurement accuracy of the nitrogen and oxygen sensor.

CN 1646901 A discloses a nitrogen oxide detection electrode and its nitrogen oxide sensor. The sensor uses a detection electrode to detect nitrogen oxides under high temperature conditions and in a humid atmosphere containing water vapor.

CN 101706470 A discloses a fully solidified mixed potential _NOx sensor and a preparation method thereof. The sensor is made by spark plasma sintering technology, it can detect _NOx concentration range from 1% to 75%, and the response time is less than 2 minutes.

The _NOx sensors reported above have disadvantages such as complex structure, high manufacturing cost, limited detection range, poor stability, and long response and recovery time.

The solid electrolyte material currently used in automotive exhaust _NOx sensors is mainly yttrium-doped zirconia (YSZ), but it must have a high ionic conductivity value at high temperature, and the resistance of this material decreases sharply with the decrease of temperature. increase. Perovskite oxides (ABO ₃ ) have a relatively relaxed and stable structural environment, which can accommodate a large number of oxygen ion vacancies and produce high electrical conductivity. The typical representative is the double-doped Sr and Mg LaGaO ₃ base Perovskite system, the oxygen ion conductivity of this system is three times that of YSZ at 800 °C. CN 102866192 _A discloses an amperometric NO2 sensor with a solid electrolyte and a preparation method thereof. This kind of sensor adopts casting method to prepare La _1-x Sr _x Ga _1-y Mg _y O _3-δ solid electrolyte substrate, and thick film screen printing technology to print electrodes. It has the advantages of simple structure, stable performance and lower operating temperature of the sensor. features. GdAlO ₃ , as a new member of perovskite-type oxide oxygen ion conductor, not only reduces the cost but also has better stability compared with LaGaO ₃ -based perovskite systems. Therefore, using GdAlO3 _- based oxides as solid electrolyte materials for _NOx sensors has great research value and space.

Contents of the invention

The technical problem to be solved by the present invention is to provide an impedance spectrum type _NOx sensor and a preparation method of the solid electrolyte material thereof, aiming at the shortage of current _NOx sensor materials. The sensor made of this material can monitor the concentration of NO _x gas in a medium and low temperature environment, and the sensor has the advantages of short response time, high sensitivity, good stability, and low detection limit.

Technical scheme of the present invention is:

An impedance spectrum _NOx sensor and its solid electrolyte material preparation method, the solid electrolyte material is Gd _1-x Ca _x AlO _3-δ , where 0.05≤x≤0.25.

The preparation method of the impedance spectrum type _NOx sensor and its solid electrolyte material is a citric acid-gel method, which specifically includes the following steps:

(1) Weigh gadolinium nitrate, aluminum nitrate, calcium nitrate and citric acid reagents according to the stoichiometric ratio, pour gadolinium nitrate, aluminum nitrate and calcium nitrate into a beaker at room temperature, add 100-400 mL deionized water and stir to fully dissolve , placed in a 60-90°C water bath to heat, and magnetically stirred for 0.5-2 h;

(2) Add citric acid reagent to the solution prepared in step (1), stir, and heat in a water bath at 60-90°C for 4-10 hours to form a light yellow gel;

(3) Transfer the light yellow gel obtained in step (2) to an electric constant temperature blast drying oven, and dry it at 80-150 °C for 4-20 h to obtain a brown precursor powder;

(4) Pour the brown precursor powder obtained in step (3) into an evaporating dish, spread a layer in the evaporating dish, and bake at 600-1200 ℃ for 2-6 h in an air atmosphere, with a heating rate of 2 ℃/min ~ 4 °C/min;

(5) Grind the powder obtained in step (4), take the ground powder and press it into a cylindrical sheet by isostatic pressing, and bake it at a high temperature of 1400-1700 ℃ for 4-10 hours in an air atmosphere to make a solid electrolyte substrate.

The solid electrolyte substrate prepared in step (5) has a thickness of 0.2 mm to 0.5 mm and a diameter of 8 mm to 12 mm.

The invention provides an impedance spectrum _NOx sensor and its solid electrolyte material preparation method. The _NOx sensor is composed of a solid electrolyte substrate, a sensitive electrode and a reference electrode; wherein the sensitive electrode is NiO and the reference electrode is Pt.

The composition of the sensitive electrode precursor is NiO slurry containing ethyl cellulose and terpineol.

The composition of the reference electrode precursor is platinum slurry containing ethyl cellulose, glass powder and terpineol.

The preparation method of the _NOx sensor comprises the following steps:

(1) Put the solid electrolyte substrate into a high-temperature furnace and sinter to make a dense solid electrolyte substrate, and the sintering temperature is 1400-1700 °C.

(2) Use screen printing technology to coat sensitive electrodes and reference electrodes on the upper and lower surfaces of the solid electrolyte substrate, and lead out the electrode leads for connecting to the power supply, and form a fixed whole after drying and roasting.

The electrode leads are made of Pt wire or Pt sheet.

After the electrode is coated in step (2), the drying temperature is 80-120 °C, and the drying time is 8-20 h; the roasting temperature is 800-1100 °C, the heating rate is 2-10 °C/min, and the roasting time is 10 -120 min.

The beneficial effects are:

(1) Compared with the YSZ material commonly used in the prior art, the medium and low temperature solid electrolyte material used in the NO _x sensor of the present invention is a perovskite-type composite oxide Gd _1-x Ca _x AlO _3-δ , the oxide Due to its relatively relaxed and stable structural environment, the material can accommodate a large number of oxygen ion vacancies and produce high electrical conductivity;

(2) The impedance spectrum _NOx sensor made of this solid electrolyte material is used to test the _NOx concentration by the method of AC impedance. The testable range of _x is 0 ~ 500 ppm, which has the advantages of short response time, high sensitivity, good stability, and low detection limit.

Description of drawings

Fig. 1 is the XRD pattern of the sample of Gd _1-x Ca _x AlO _3-δ (x=0-0.15) solid electrolyte material calcined at 1200 ℃ for 2 h.

Detailed ways

In order for the skilled person to further understand the technical solution of the present invention, the technical solution of the present invention will be described in more detail below in conjunction with examples.

The technical problem to be solved by the present invention is to provide a solid electrolyte impedance _NOx sensor for monitoring the _NOx gas concentration in a medium and low temperature environment. The sensor has the advantages of short response time, high sensitivity, good stability, low detection limit, etc. advantage. The present invention adopts the following technical solutions to solve the above technical problems: an impedance spectrum _NOx sensor and its solid electrolyte material preparation method, the _NOx sensor is composed of a solid electrolyte substrate, a sensitive electrode, and a reference electrode. The solid electrolyte material is Gd _1-x Ca _x AlO _3-δ , where 0.05≤x≤0.25, the sensitive electrode is NiO, and the reference electrode is the noble metal Pt. The invention adopts screen printing technology to print sensitive electrodes and reference electrodes on the upper and lower surfaces of the solid electrolyte, and draws out electrode leads for connection, and forms a fixed whole by sintering.

The working principle of the present invention is to use the electrochemical reaction impedance of the sensitive electrode, solid electrolyte and _NOx gas three _- phase interface in the _NOx sensor to detect the _NOx concentration with the change of the _NOx concentration, and respond to the same concentration of NO and NO2. The magnitude and sign of are consistent, so that the total concentration of NO _x can be determined. For impedance spectroscopy type _NOx sensors, in terms of _NO2 gas, the relative total resistance As a response signal, is the total resistance of the sensor under different _NO2 concentrations, is the total resistance of the sensor when the NO ₂ concentration is 0 mL/m ³ , and the total resistance of the sensor at different NO ₂ concentrations . The cathodic reaction occurring at the interface between the solid electrolyte and the sensitive electrode is as follows:

or ,

Anode reaction:

Example 1

The Gd _0.95 Ca _0.05 AlO _3-δ solid electrolyte substrate was prepared by the citric acid gel method, and the calcium content was 5% molar ratio.

1) Weigh 12.8638, 11.2539, 0.3542, and 15.7613 grams of gadolinium nitrate, aluminum nitrate, calcium nitrate, and citric acid reagents according to the stoichiometric ratio, and pour the above gadolinium nitrate, aluminum nitrate, and calcium nitrate reagents into a beaker at room temperature, Stir 250 mL of deionized water to fully dissolve, heat in a water bath at 80 °C, and stir magnetically for 1 h;

2) Add citric acid reagent to the solution prepared in step 1), continue heating and stirring for 6 h, and the solution gradually forms a light yellow gel;

3) Transfer the light yellow gel to an electric constant temperature blast drying oven, and dry it at 120 °C for 10 h to obtain a brown precursor powder;

4) Pour the brown precursor powder into an evaporating dish, and bake it at 1000 °C for 2 h in an air atmosphere, with a heating rate of 4 °C/min;

5) Grind the treated powder, take an appropriate amount of ground powder and press it into a cylindrical sheet by isostatic pressing, and then bake it at 1500 ℃ for 4 hours in an air atmosphere to make it with a thickness of 3 mm and a diameter of 8 mm solid electrolyte substrate;

Use screen printing technology to coat sensitive electrodes and reference electrodes on the upper and lower surfaces of the solid electrolyte substrate, and lead out the electrode leads for connecting to the power supply. After drying at 100 °C for 10 h, put it into a high-temperature furnace with a temperature increase of 5 °C/min. The temperature was raised to 1000 °C and baked for 1 h to form a fixed whole sensor.

product testing:

Put the product in the test device, which consists of three parts: gas distribution system, heating system and test system. Through the gas distribution system to simulate the exhaust gas of the automobile, the tube furnace is used for heating, and the circuit is connected to test its conductivity and its sensitivity to _NOx by CHI600E electrochemical workstation.

Example 2

The specific preparation method is basically the same as that in Example 1 of this part, except that step 5) the firing temperature of the Gd _0.95 Ca _0.05 AlO _3-δ solid electrolyte substrate is changed to 1700 °C.

Example 3

The specific preparation method is basically the same as in Example 1 of this part, except that the solid electrolyte material is replaced by Gd _0.85 Ca _0.15 AlO _3-δ .

Example 4

The specific preparation method is basically the same as in Example 3 of this part, except that the firing temperature of the Gd _0.9 Ca _0.1 AlO _3-δ solid electrolyte substrate is changed to 1700 °C.

Example 5

The specific preparation method is basically the same as in Example 3 of this part, except that the firing time of the Gd _0.9 Ca _0.1 AlO _3-δ solid electrolyte substrate is changed to 8 h.

Example 6

The specific preparation method is basically the same as in Example 1 of this part, except that the solid electrolyte material is replaced by Gd _0.85 Ca _0.15 AlO _3-δ .

Example 7

The specific preparation method is basically the same as in Example 6 of this part, except that the firing temperature of the Gd _0.85 Ca _0.15 AlO _3-δ solid electrolyte substrate is changed to 1700 °C.

Example 8

The specific preparation method is basically the same as in Example 6 of this part, except that the firing time of the Gd _0.85 Ca _0.15 AlO _3-δ solid electrolyte substrate is changed to 8 h.

Example 9

The specific preparation method is basically the same as in Example 1 of this part, except that the solid electrolyte material is replaced by Gd _0.75 Ca _0.25 AlO _3-δ .

Example 10

The specific preparation method is basically the same as in Example 9 of this part, except that the firing temperature of the Gd _0.75 Ca _0.25 AlO _3-δ solid electrolyte substrate is changed to 1700 °C.

Example 11

The specific preparation method is basically the same as in Example 1 of this part, except that the prepared solid electrolyte material is replaced by YSZ.

Table 1 The corresponding conductivity of different solid electrolytes at 800℃ and their response and recovery time to NO ₂

The preferred embodiments of the present invention have been illustrated, and various changes or modifications may be made by those skilled in the art without departing from the scope of the present invention.

Claims (9)

1. an impedance spectral pattern NO _xthe preparation method of sensor and solid electrolyte material thereof, is characterized in that: described solid electrolyte material is Gd _1-xca _xalO _3-δ, wherein 0.05≤x≤0.25.

2. impedance spectral pattern NO according to claim 1 _xthe preparation method of sensor and solid electrolyte material thereof, is characterized in that: adopt citrate-gel method to prepare Gd _1-xca _xalO _3-δsolid electrolyte material, comprises the following steps:

(1) gadolinium nitrate, aluminium nitrate, calcium nitrate and citric acid reagent is taken according to stoichiometric proportion, at room temperature, pour gadolinium nitrate, aluminium nitrate and calcium nitrate into beaker, add 100-400 mL deionized water and stirring and fully dissolve, put into 60-90 DEG C of water-baths to heat, magnetic agitation 0.5-2 h;

(2) in the obtained solution of step (1), add citric acid reagent, stir, and heat 4-10 h in 60-90 DEG C of water-baths, form light yellow gel;

(3) light yellow gel that step (2) obtains is transferred in electric heating constant-temperature blowing drying box, at 80-150 DEG C of dry 4-20 h, obtain brown precursor powder;

(4) pour the brown precursor powder that step (3) obtains into evaporating dish, tile one deck in evaporating dish, 600-1200 DEG C of roasting 2-6 h in air atmosphere, heating rate 2 DEG C/min ~ 4 DEG C/min;

(5) by the powder mull that step (4) obtains, get the powder after grinding and adopt isostatic compaction method to be pressed into cylindrical pellets, in air atmosphere, be made into solid electrolyte substrate through 1400-1700 DEG C of high-temperature roasting 4-10 h.

3. impedance spectral pattern NO according to claim 2 _xthe preparation method of sensor and solid electrolyte material thereof, is characterized in that: the solid electrolyte substrate thickness obtained by step (5) is 0.2 mm-0.5 mm, and diameter is 8 mm-12 mm.

4. an impedance spectral pattern NO as claimed in claim 1 _xthe preparation method of sensor and solid electrolyte material thereof, is characterized in that: described NO _xsensor by solid electrolyte substrate, sensitive electrode, reference electrode form; Wherein sensitive electrode is NiO, and reference electrode is Pt.

5. impedance spectral pattern NO according to claim 4 _xthe preparation method of sensor and solid electrolyte material thereof, is characterized in that: described sensitive electrode presoma composition is the NiO slurry containing ethyl cellulose and terpinol.

6. impedance spectral pattern NO according to claim 4 _xthe preparation method of sensor and solid electrolyte material thereof, is characterized in that: described reference electrode presoma composition is containing ethyl cellulose, the platinum slurry of glass dust and terpinol.

7. impedance spectral pattern NO according to claim 4 _xthe preparation method of sensor and solid electrolyte material thereof, is characterized in that: described NO _xthe preparation method of sensor comprises the following steps:

(1) solid electrolyte substrate is put into high temperature furnace sintering and make dense solid electrolyte matter substrate, sintering temperature is 1400-1700 DEG C;

(2) adopt screen printing technique at solid electrolyte substrate upper and lower surface coating sensitive electrode and reference electrode, and draw the contact conductor for connecting power supply, dry and entirety that after roasting, formation one is fixing.

8. impedance spectral pattern NO according to claim 7 _xthe preparation method of sensor and solid electrolyte material thereof, is characterized in that: described contact conductor adopts Pt silk or Pt sheet.

9. impedance spectral pattern NO according to claim 7 _xthe preparation method of sensor and solid electrolyte material thereof, is characterized in that: in step (2) after electrode coating, bake out temperature is 80-120 DEG C, and drying time is 8-20 h; Sintering temperature is 800-1100 DEG C, and heating rate is 2-10 DEG C/min, and roasting time is 10-120 min.