JPH0949816A - Nox concentration detecting device and nox sensor used for the device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a simple NOx concentration detector which can easily detect NOx concentrations by inexpensively performing simple computation in a short time. SOLUTION: A NOx concentration detecting device is provided with an electrolyte 1, a first electrode 2 and a reference electrode 3 which are provided on one of the facing surfaces of the electrolyte 1 and do not absorb NOx, a second electrode 4 which is provided on the other surface of the electrolyte 1 so that the electrode 4 can face the electrodes 2 and 3 and absorbs NOx, an impedance measuring instrument 5 which applies an AC voltage across the electrodes 2 and 4 and measures the impedance between the electrodes 3 and 4, and an arithmetic means 6 which computes the NOx concentration from the measured impedance.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention is for detecting a trace amount of NOx concentration in combustion exhaust gas containing a large amount of oxygen and carbon dioxide discharged from household combustion equipment or automobiles.
The present invention relates to an Ox detection method and device and a NOx sensor used for the same.

[0002]

2. Description of the Related Art In recent years, NOx emitted from internal combustion engines such as household combustion equipment and automobiles is not only harmful to humans, but also causes environmental pollution such as air pollution and acid rain, resulting in NOx concentration. There is a strong demand for the establishment of a technique for accurately detecting NOx, and the use of NOx sensors using electrolytes is increasing.

Conventionally, Japanese Laid-Open Patent Publication No. 6-18480 discloses this type of NOx sensor, which is generally used.

As shown in FIG. 5, this conventional NOx sensor includes an oxygen ion conductive solid electrolyte a made of stabilized zirconia and a platinum electrode b and a rhodium electrode c sandwiching the electrolyte a. It is composed of a pair of electrodes formed of compositions having different NOx decomposition characteristics.

When a measured gas containing NOx is introduced into and exposed to this NOx sensor, NOx on each of the electrodes b and c is exposed.
Electromotive force is generated between the electrodes due to the different decomposition rates. When the NOx concentration increases, the decomposition rate on each electrode b, c increases and the electromotive force generated between the electrodes b, c also increases.

Therefore, the electromotive force between the electrodes b and c is N
It depends on the Ox concentration, and the NOx concentration can be detected by measuring the potential difference between the electrodes with a voltmeter d.

Japanese Unexamined Patent Publication No. 6-18480 discloses that when the NOx sensor is operated at 620 to 930 ° C.,
0 to 100 in the gas under measurement containing about ppm of oxygen
It discloses that a NO concentration of 0 ppm can be detected.

[0008]

However, in the above structure, two different kinds of electrodes capable of decomposing NOx are required, and when either one of them changes, of course, when both electrodes change, The relationship between the NOx decomposition rate and the potential difference between the electrodes is unlikely to be the same, and there is a problem that it is not possible to accurately detect the NOx concentration because the relationship is broken.

Further, in the conventional structure, the electromotive force generated between the electrodes depends on the operating temperature of the NOx sensor, and the degree of dependence differs depending on the type of the electrode, so that the temperature of the gas to be measured changes or the heating means. However, if the operating temperature changes due to deterioration, the NOx concentration cannot be accurately detected.

Further, in the conventional configuration, 1 is contained in the gas to be measured.
When a large amount of oxygen of about 0% is included, there is also a problem that an accurate NOx concentration cannot be detected.

Therefore, the applicant of the present invention has previously proposed a NOx sensor and a detection device capable of decomposing or adsorbing NOx, only one type of electrode is required, and capable of detecting an accurate NOx concentration even if the electrode changes.

In this device, the NOx-adsorptive electrode and the NOx-adsorptive electrode face each other on both sides of the electrolyte.
The x sensor is exposed to the gas to be detected at a predetermined operating temperature, and the NOx concentration in the gas to be measured is detected from the impedance between the NOx adsorbing electrode and the counter electrode that does not adsorb NOx at this time. I am trying to do it.

Thus, NO exposed to the gas to be measured
In the x sensor, one of the counter electrodes facing each other on both sides of the electrolyte has NOx adsorption,
At a given operating temperature, NOx in the gas to be measured reacts with the electrode to decompose and adsorb it, and an impedance that depends on the NOx concentration can be obtained between the counter electrode and the counter electrode that has no NOx adsorbing property and causes almost no electrode reaction. Since only one electrode having NOx adsorbing property is required, it is possible to accurately detect the NOx concentration from the impedance without the problem that the correlation of the NOx decomposition rate between the electrodes changes due to the change of the electrode. .

However, in general, when the real part of the impedance between two electrodes of the solid electrolyte obtained by the complex impedance method is plotted on the horizontal axis and the imaginary part is plotted on the vertical axis, the solid electrolyte bulk, grain boundary and electrode reaction are observed from the high frequency side. Three arcs representing the component of are observed. The size of the line segment that cuts the real number axis from each arc is the resistance of each component. When the impedance is actually measured, the impedance of each component appears continuously according to the measurement frequency. Therefore, the resistance of each component can be obtained by fitting the obtained continuous curve so that three arcs are formed. In order to accurately determine the electrode reaction resistance of the electrode, it is necessary to subtract the bulk resistance and the grain boundary resistance from the total resistance. For this reason,
The device and operation become complicated, which causes a cost increase and the processing time becomes long.

An object of the present invention is to solve such a problem, and a NOx concentration detecting apparatus and a NOx concentration detecting apparatus which are simple in apparatus and calculation, inexpensive and short in processing time, and NOx used therein.
The main purpose is to provide a sensor.

It is another object of the present invention to provide a NOx concentration detecting device and a NOx sensor that can accurately detect the NOx concentration even if the operating temperature of the NOx sensor changes.

Even when the measured gas contains a large amount of oxygen and carbon dioxide of about 10%, accurate NOx is obtained.
An object is to provide a NOx concentration detection device and a NOx sensor that can detect the concentration.

[0018]

In order to achieve the above-mentioned object, the NOx concentration detecting apparatus of the invention of claim 1 is
Electrolyte and N provided on one surface of the electrolyte facing each other
A first electrode and a reference electrode having no Ox adsorbing property, a second electrode having NOx adsorbing property provided on the other surface of the electrolyte so as to face both the first electrode and the reference electrode, and An impedance measuring device for measuring the impedance between the reference electrode and the second electrode by applying an alternating current between the electrode and the second electrode, and N from the measured impedance.
It is characterized in that it comprises an arithmetic means for calculating the Ox concentration.

The NOx concentration detecting device of the invention of claim 2 is
Electrolyte and N provided on one surface of the electrolyte facing each other
A first electrode and a reference electrode having no Ox adsorbing property, a second electrode having NOx adsorbing property provided on the other surface of the electrolyte so as to face both the first electrode and the reference electrode, and An alternating current is applied between the electrode and the second electrode to measure impedance between the reference electrode and the first electrode and between the reference electrode and the second electrode, and the reference electrode and the first electrode. The temperature is calculated from the impedance obtained between the electrodes, and the NOx is calculated from the impedance obtained between the reference electrode and the second electrode and the calculated temperature.
It is characterized in that it is provided with a calculating means for calculating the concentration.

According to another aspect of the NOx sensor of the present invention, an electrolyte, a first electrode and a reference electrode provided on one surface of the electrolyte facing each other, and a first electrode provided on the other surface of the electrolyte. And a second electrode provided so as to face both the reference electrode and the reference electrode.

According to the invention of claim 4, in the invention of claim 3, the second electrode further comprises a NOx adsorbing oxide.

The NOx of the invention of claim 5 is the same as those of claims 3 and 4.
In any one of the invention of 1 above, the electrolyte is a solid electrolyte having oxygen ion conductivity.

According to the NOx sensor of the sixth aspect of the present invention, in addition to any one of the third to fifth aspects of the present invention, the second electrode further contains a noble metal, a NOx adsorbing oxide, and a porous oxide. .

According to a seventh aspect of the present invention, in the NOx sensor according to any one of the third to fifth aspects, the second electrode further comprises a noble metal, a NOx adsorbing oxide, and iron oxide.

According to the NOx sensor of the eighth aspect of the present invention, in addition to any one of the third to fifth aspects of the present invention, the second electrode further contains a noble metal, a NOx adsorbing oxide, and gold.

In the NOx sensor of the ninth aspect of the present invention, the second electrode may further include a noble metal and a complex oxide or a noble metal and one or more kinds of oxides. It is a waste.

According to the NOx sensor of the tenth aspect of the present invention, in addition to any one of the third to ninth aspects of the invention, the electrolyte is an oxygen ion conductive solid electrolyte.

[0028]

In the above structure of the NOx concentration detector of the present invention, the second electrode, which is opposed to the first electrode with the electrolyte interposed therebetween, has the NOx adsorbing property so that the second electrode can be operated at a predetermined operating temperature. An electrode that reacts with NOx in the gas to be measured is decomposed and adsorbed, and an impedance that depends on the NOx concentration is obtained between the counter electrode that has no NOx adsorbability and almost no electrode reaction occurs. Only one electrode is required, and there is no problem that the correlation of the NOx decomposition rate between the electrodes changes due to the change of the electrodes, the NOx concentration can be detected from the impedance, and this impedance can be used as the NOx adsorbing property. And the second electrode, which is provided separately from the first electrode opposed to the electrode having the Since the bulk resistance and grain boundary resistance between the poles are so small that they can be ignored compared to the electrode reaction resistance, the point where the arc intersects the horizontal axis on the low frequency side, that is, the overall resistance may be close to the electrode reaction resistance. Therefore, the calculation for subtracting the bulk resistance and the grain boundary resistance from the total resistance can be omitted, and the apparatus and the calculation can be inexpensive and the processing time can be short.

In the above configuration of the NOx concentration detecting device of the invention of claim 2, the impedance between the second electrode having NOx adsorbing property and the reference electrode is the same as in the invention of claim 1, from the total resistance to the bulk. The NOx concentration is detected by omitting the calculation for subtracting the grain boundary resistance, and in particular, the operating temperature is calculated from the impedance between the reference electrode and the first electrode, and the operation temperature between the reference electrode and the second electrode is calculated. By calculating the NOx concentration from the impedance and the operating temperature, an accurate NOx concentration can be detected even if the operating temperature changes.

Generally, the bulk resistance and the grain boundary resistance are determined by the solid electrolyte, and if the electrode area is constant, it depends on the operating temperature.

According to the structure of the electrode of the present invention, the operating temperature can be calculated by measuring the impedance between the reference electrode and the first electrode and determining the bulk resistance. And
An accurate NOx concentration corresponding to the operating temperature can be calculated from the impedance between the reference electrode and the second electrode.

Further, the NOx sensor according to any one of the inventions of claims 3 to 5 can be used in the NOx concentration detecting device of the invention of claims 1 and 2, and the NOx of the invention of claim 4 can be used.
In the above configuration of the x sensor, the characteristics of the electrode reaction obtained with NOx can be variously manipulated by blending the NOx adsorbing oxide of the second electrode. The NOx sensor according to the invention of claim 5 is convenient for weakening and decomposing the bond between nitrogen oxide and oxygen at the second electrode, and is advantageous for detecting NOx concentration in the presence of oxygen. Becomes

In any of the NOx sensors according to the inventions of claims 5 to 10, even if a large amount of oxygen or carbon dioxide is contained in the gas to be measured, a catalytic action is exerted on each second electrode, The NOx concentration can be selectively detected.

[0034]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Some embodiments of the present invention will be described below with reference to the drawings.

The first embodiment of the present invention shown in FIG.
A NOx sensor suitable for detecting NOx concentration is provided.

As shown in the figure, a plate-shaped solid electrolyte 1 having oxygen ion conductivity, a first electrode 2 and a reference electrode 3 formed on one surface of the electrolyte 1, and a first electrode sandwiching the electrolyte 1 The second electrode 4 is provided so as to face the electrode 2 and the reference electrode 3 and includes a NOx adsorbing oxide.

This NOx sensor is exposed to the gas to be detected at a predetermined operating temperature, and the impedance between the second electrode 4 having NOx adsorbing property and the reference electrode 3 having no NOx adsorbing property at this time The NOx concentration in the measured gas can be detected. If the impedance is measured between the first electrode 2 and the first electrode 2, the reference electrode 3 is not necessary, but it is characterized in that the reference electrode 3 is used.

In short, one of the counter electrodes facing each other on both sides of the solid electrolyte 1 has the NOx adsorbing property, so that the NOx in the gas to be measured at a predetermined operating temperature. Reacts with the electrode to decompose and adsorb it, and NOx
Since the impedance depending on the NOx concentration is obtained between the first electrode 2 and the reference electrode 3, which are the counter electrodes having no adsorptive property and hardly causing electrode reaction, only one electrode having the NOx adsorptive property is required. There is no problem that the correlation of the NOx decomposition rate between the electrodes changes due to the change of the electrodes, and the NOx concentration can be accurately detected from the impedance.

In particular, by having the reference electrode 3 as in this embodiment and measuring the impedance between the second electrode 4 and the reference electrode 3, the reference electrode 3 and the second electrode 4 are Since the bulk resistance and the grain boundary resistance between them are so small that they can be ignored as compared with the electrode reaction resistance, the point where the arc intersects the horizontal axis on the low frequency side, that is, the overall resistance can be approximated to the electrode reaction resistance. The calculation for subtracting the bulk resistance and the grain boundary resistance from the total resistance can be omitted, and the device and the calculation can be simple and inexpensive and the processing time can be short.

As described above, when the real part of the impedance between the two electrodes of the solid electrolyte obtained by the complex impedance method is plotted on the horizontal axis and the imaginary part is plotted on the vertical axis, the bulk, grain boundaries and electrodes of the solid electrolyte are plotted from the high frequency side. Three arcs representing the components in the reaction are observed. The size of the line segment that cuts the real number axis from each arc is the resistance of each component. When the impedance is actually measured, the impedance of each component appears continuously according to the measurement frequency. Therefore, the resistance of each component can be obtained by fitting the obtained continuous curve so that three arcs are formed.

Further, since the second electrode 4 contains the NOx adsorbing oxide, the NOx is mixed with the NOx adsorbing oxide.
There is the advantage that the resulting electrode reaction with x can be manipulated. Depending on the fact that the solid electrolyte 1 has oxygen ion conductivity, it is convenient for weakening and decomposing the bond between nitrogen oxide and oxygen at the second electrode 4, and the NOx concentration in the presence of oxygen This is advantageous for detection.

Example 1 First, a 12.5 mm × 25 mm × 0.5 mm thick solid electrolyte substrate made of stabilized zirconia containing 8 mol% of yttria was thoroughly washed, and as shown in FIG.
In order to form the 5 mm × 23 mm first electrode 2 and the 1 mm × 23 mm reference electrode 3, a screen printing method was used.
The platinum paste was printed at the same time and dried at about 100 ° C. Next, the first electrode 2 and the reference electrode 3 with the solid electrolyte 1 sandwiched therebetween.
In order to form the second electrode 4 of 10.5 mm × 23 mm so as to face both of them, the NOx adsorbing oxide barium-yttrium-copper oxide (Ba ₂ YCu ₃ O ₇ ) is added to platinum.
The mixed paste mixed with 0 wt% was printed and dried by the same method. This is fired in the air at 820 ° C. for 10 minutes using an electric furnace, and the thicknesses of the first electrode 2 and the reference electrode 3 after firing are each about 20 μm, and the thickness of the second electrode 4 is about 40 μm.
Met. Next, each electrode has a diameter of 0.1 mm and a length of 20 mm.
Fix the platinum lead wire with a gold paste and leave it in the air at 700 ° C.
The sample No. It was set to 1.

Next, as a comparative sample, 8.5 mm × 23 m
A sample in which a second electrode 4 having a size of m × 40 μm is provided so as to face only the first electrode 2 with the electrolyte 1 interposed therebetween is Sample No. 1
Created in the same manner as.

Next, sample No. 1 and the comparative sample were heated and held at about 450 ° C., respectively, and each of the first electrode 2 and the second electrode
A DC power source is connected between the electrodes 4 of each of the electrodes via a lead wire, and the current density becomes about 10 mA / cm ² in a quartz tube supplied with about 500 ppm NOx (helium balance) at a flow rate of about 200 cc / min. Thus, a current was passed for 10 minutes to perform pretreatment.

An impedance measuring instrument 5 was connected to each of the samples thus obtained as shown in FIG. 1
The NOx concentration detecting device according to the second embodiment of the present invention is configured by the NOx sensor of. In addition, FIG. 2B employs a calculation unit 6 that uses a microcomputer to calculate the NOx concentration by the output from the impedance measuring device 5, to which the output from the impedance measuring device 5 is input, and a predetermined value is input. Is calculated to obtain the NOx concentration output. The calculation means 6 can be applied to other various calculations and processes. However, it goes without saying that it may be a dedicated device other than the microcomputer.

In addition to the yttrium-stabilized zirconia, the electrolyte 1 may be an oxygen ion conductive solid electrolyte such as other stabilized zirconia, ceria or bismuth oxide. Further, the first electrode 2 and the reference electrode 3 may be other precious metals, base metals, or oxides having good electron conductivity, in addition to platinum. The second electrode 4 may also be a mixture of another noble metal such as rhodium or palladium and another NOx adsorbing oxide other than the mixture of platinum and barium yttrium copper oxide. Other methods for forming electrodes include electroless plating,
Although a sputtering method or the like may be used, the screen printing method is superior in that it is simple and inexpensive. It is preferable to determine the most suitable conditions for the temperature, atmosphere, etc. during firing by experiments. In addition, although a direct current was passed through the NOx sensor as a pretreatment, an alternating current may be used, and it is preferable to experimentally find optimum conditions for the treatment conditions such as temperature, atmosphere, current density and time.

Next, each sample was set to have an inner diameter of 20 mm and a length of 500 m.
It was fixed in a quartz tube of m, and heated and held at about 450 ° C. by a tubular furnace capable of controlling temperature. A mixed gas of various concentrations was supplied into the quartz tube at a flow rate of about 200 cc / min.
Then, the impedance measuring instrument 5 applies an alternating current of 5 mV between the first electrode 2 and the second electrode 4, and the impedance between the reference electrode 3 and the second electrode 4 of each sample in the frequency range of 100 mHz to 1 MHz. Measure each bulk resistance,
Grain boundary resistance and electrode reaction resistance were determined.

Sample No. when supplying NOx of 500 ppm. Bulk resistance of 1 and comparative sample is 8Ω each
And 40Ω, and the electrode reaction resistance was about 1400Ω. Almost no grain boundary resistance was observed and it was found that it was much smaller than other resistances. It was also found that all bulk resistances were smaller than the electrode resistances, and the overall resistance and the electrode reaction resistance were almost equal. Also, compared to the comparative sample,
Sample No. The bulk resistance of Sample No. 1 is smaller, and when the overall resistance is considered to be the electrode reaction resistance, Sample No. It has been found that the placement of one electrode gives a more accurate NOx concentration. However, the comparative sample can also be effectively used in terms of the method of detecting the NOx concentration, which requires only one electrode having NOx adsorbing property, and belongs to the category of the present invention.

Next, sample No. No. 1 Supply gas NO
x concentration is 500 to 3000 ppm, oxygen concentration is 0 to 10
The electrode reaction resistance when the percentage was changed was calculated. The relationship between the NOx concentration and the electrode reaction resistance is shown in FIG. In FIG. 3, the horizontal axis represents the NOx concentration and the vertical axis represents the reciprocal of the electrode reaction resistance R. Even if a large amount of oxygen is present in the gas to be measured, accurate NO
It can be seen that the x concentration can be detected.

Next, sample No. 500p for 1
The operating temperature characteristic of the bulk resistance in pmNOx was investigated. When an AC voltage is applied between the first electrode 2 and the second electrode 4, the impedance between the reference electrode 3 and the first electrode 2 is measured, and the operating temperature T is changed from 400 to 550 ° C. FIG. 4 shows the change in the bulk resistance Rb. FIG.
The activation energy E was about 1 eV. Therefore, if the bulk resistance is obtained, the operating temperature of the NOx sensor can be calculated, and the NOx concentration corresponding to the temperature can be obtained. That is, an accurate NOx concentration can be obtained even if the temperature of the gas to be measured changes or the operating temperature changes due to deterioration of the heating means.

Example 2 Sample No. 1 of Example 1 Example 1 is the same as Example 1 except that the second electrode 4 is different.

Sample No. 1 was able to detect the accurate NOx concentration even in the presence of a large amount of oxygen, but when a large amount of carbon dioxide was present in the gas to be measured, the electrode reaction resistance of the second electrode 4 increased. , No more accurate NOx concentration is shown. This is because yttrium barium copper oxide or platinum contained in the second electrode 4 is poisoned by carbon dioxide, and the surface of the electrode is covered with carbon dioxide, and NOx or oxygen interferes with the electrode reaction occurring on the electrode. It is thought to be because of this.

In this example, the sample No. 2 to Sample No. Since the second electrode 4 that is not affected by the carbon dioxide coexisting in the gas to be measured is used as in 9, the stable electrode reaction resistance can be obtained even in the presence of a large amount of carbon dioxide and oxygen. An accurate NOx concentration can be detected.

Sample No. 2 to 9 were prepared in the same manner as in Example 1.

Sample No. The second electrode 4 of 2 is platinum 5w
It consists of a mixture with t% barium yttrium copper oxide and 15 wt% porous cerium oxide added. It is considered that the addition of the porous oxide further disperses platinum and barium-yttrium-copper oxide, activates its catalytic action, and adsorbs or decomposes NOx even if carbon dioxide coexists. In addition to cerium oxide, a porous lanthanum oxide containing a rare earth element such as cerium, an oxide such as aluminum oxide, or a mixture thereof may be used.

Sample No. The second electrode 4 of No. 3 is made of a mixture obtained by adding 20 wt% of a mixed powder of barium yttrium copper oxide in which iron oxide is premixed with platinum. The mixed powder was obtained by adding 20 wt% iron nitrate hydrate to barium yttrium copper powder as an aqueous solution, evaporating the water content while dispersing, and then sintering the powder at about 900 ° C. in the air and crushing it. Other than iron nitrate, other iron compounds such as iron oxide may be mixed with barium yttrium copper powder. It is considered that the addition of iron causes NOx to be adsorbed or decomposed with little influence even when carbon dioxide coexists.

Sample No. The second electrode 4 of 4 is platinum 20
The mixture was composed of a mixture containing wt% barium-yttrium copper oxide and a mixture containing the same weight of gold as the mixture, and was fired at about 620 ° C. in the atmosphere. It is considered that the addition of gold makes it possible to detect a stable NOx concentration even when carbon dioxide coexists.

Sample No. The second electrode 4 of 5 is platinum 20
It consists of a mixture with the addition of wt% lanthanum cobalt oxide (LaCoO ₃ ). Lanthanum cobalt oxide was prepared from lanthanum nitrate and cobalt nitrate, but may be prepared from other compounds such as acetate.

Lanthanum cobalt oxide is a perovskite type complex oxide and is generally well known because it adsorbs or absorbs a large amount of NOx and the like, and it is considered that the NOx concentration can be detected even in the presence of carbon dioxide.

Sample No. The second electrode 4 of 6 is platinum 20
wt% lanthanum strontium cobalt oxide (La
_0.6 Sr _0.4 CoC ₃ ). Lanthanum strontium cobalt oxide is sample No. The lanthanum site of the lanthanum cobalt oxide used in Example 5 was partially replaced with strontium.

Sample No. The second electrode 4 of No. 7 is made of a mixture obtained by adding 20 wt% of a mixture of yttrium oxide, magnesium oxide and copper oxide to platinum.

Sample No. The second electrode 4 of 8 is platinum 20
wt% calcium oxide yttrium copper (Ca ₂ YCu
₃ Ox). Calcium yttrium oxide oxide is the barium site of yttrium copper oxide barium substituted with calcium of the same alkaline earth metal.

Sample No. The second electrode 4 of 9 is platinum 20
It comprises a mixture with addition of a mixture of a mixture of magnesium oxide and zirconium oxide in wt%.

Above No. Example 1 for samples 2-9
The impedance was measured in the same manner as in. NOx in Table 1
In a mixed gas of 500 ppm, 10% oxygen and NOx5
Electrode reaction resistances R1 and R2 in a mixed gas of 00 ppm, 10% oxygen and 6% carbon dioxide, and a ratio of electrode reaction resistance R2 when carbon dioxide is contained to electrode reaction resistance R1 when carbon dioxide is not contained. Indicates R2 / R1.

[0065]

[Table 1]

From Table 1, sample No. No. 1 was compared with platinum and barium yttrium copper oxide. It was found that the samples 2 to 9 were less affected by carbon dioxide and the ratio was close to 1. Therefore, the sample No. With the configuration of the second electrode 4 such as 2 to 9, even if a large amount of oxygen and carbon dioxide coexist in the gas to be measured, NOx is selectively decomposed and adsorbed to accurately detect the NOx concentration. I knew I could do it.

Sample No. In addition to 2 to 9, the second electrode 4 may be platinum in which at least one kind of oxide such as bismuth oxide, copper oxide, zirconium oxide, barium oxide is mixed. Alternatively, a mixture of platinum with a complex oxide such as barium platinum oxide (BaPtOx) may be used.

[0068]

According to the NOx concentration detecting apparatus of the first aspect of the present invention, there is one NOx adsorbing electrode, and when the electrode changes, the correlation of the NOx decomposition rate between the electrodes changes. In order to detect the NOx concentration from the impedance without the impedance, this impedance is obtained between the NOx adsorbing electrode and the reference electrode, and the bulk resistance and the grain boundary resistance between the reference electrode and the second electrode cause the electrode reaction. Utilizing the fact that it is negligibly smaller than the resistance, the calculation for subtracting the bulk resistance and the grain boundary resistance from the total resistance is omitted, the device and the calculation are simple, and the processing time is short.

According to the NOx concentration detector of the second aspect of the present invention, in order to detect the NOx concentration similarly to the first aspect of the invention, the operating temperature obtained from the impedance between the reference electrode and the first electrode is used. The NOx concentration can be obtained from the impedance between the reference electrode and the second electrode to accurately detect the NOx concentration even when the operating temperature changes.

Further, the NOx sensor according to any one of the inventions of claims 3 to 5 can be used in the NOx concentration detecting device of the invention of claims 1 and 2, and the NOx of the invention of claim 4 can be used.
According to the x sensor, the electrode reaction with NOx can be manipulated by mixing the NOx adsorbing oxide contained in the second electrode to achieve the required concentration detection. NO of the invention of claim 5
The x sensor is convenient for weakening and decomposing the bond between nitrogen oxide and oxygen at the second electrode, which is advantageous for detecting NOx concentration in the presence of oxygen.

N according to any one of the inventions of claims 5 to 10
According to the Ox sensor, the catalytic action works on each of the second electrodes, and the NOx concentration can be selectively detected even if the measured gas contains a large amount of oxygen or carbon dioxide.

[Brief description of drawings]

FIG. 1 is a schematic configuration diagram of a NOx sensor according to a first embodiment of the present invention.

FIG. 2 is a schematic configuration diagram of a NOx concentration detection device using a NOx sensor according to a second embodiment of the present invention.

FIG. 3 is a NOx concentration characteristic diagram of electrode reaction resistance in the NOx sensor of FIGS. 1 and 2.

FIG. 4 is a temperature characteristic diagram of the bulk resistance of the NOx sensor of FIGS. 1 and 2.

FIG. 5 is a sectional view of a conventional NOx sensor.

[Explanation of symbols]

 1 Electrolyte 2 1st electrode 3 Reference electrode 4 2nd electrode 5 Impedance measuring device 6 Computing means

 ─────────────────────────────────────────────────── ─── Continuation of front page (72) Inventor Kenzo Ochi 1006 Kadoma, Kadoma City, Osaka Prefecture Matsushita Electric Industrial Co., Ltd. (72) Akio Fukuda 1006 Kadoma, Kadoma City, Osaka Matsushita Electric Industrial Co., Ltd.

Claims (10)

[Claims] 1. An electrolyte, a first electrode and a reference electrode having no NOx adsorption property provided on one surface of the electrolyte facing each other, and both of the first electrode and the reference electrode on the other surface of the electrolyte. Impedance measurement for measuring the impedance between the reference electrode and the second electrode by applying an alternating current between the second electrode having the NOx adsorbing property provided opposite to the first electrode and the second electrode An NOx concentration detecting apparatus comprising: a container and an arithmetic means for calculating the NOx concentration from the measured impedance. 2. An electrolyte, a first electrode and a reference electrode having no NOx adsorption property provided on one surface of the electrolyte facing each other, and both of the first electrode and the reference electrode on the other surface of the electrolyte. An alternating current is applied between the first electrode and the second electrode and the NOx adsorbing second electrode provided facing each other, and between the reference electrode and the first electrode and between the reference electrode and the second electrode. An impedance measuring device for measuring the impedance between the electrodes and the temperature obtained from the impedance obtained between the reference electrode and the first electrode, and the impedance obtained between the reference electrode and the second electrode. An NOx concentration detection device, comprising: a calculation unit that calculates the NOx concentration from the calculated temperature. 3. An electrolyte, a first electrode and a reference electrode provided on one surface of the electrolyte that faces each other, and an electrolyte and a first electrode and a reference electrode provided on the other surface of the electrolyte that face both the first electrode and the reference electrode. A NOx sensor provided with a second electrode having NOx adsorption properties. 4. The NOx sensor according to claim 3, wherein the second electrode contains a NOx adsorbing oxide. 5. The NOx sensor according to claim 3, wherein the electrolyte is a solid electrolyte having oxygen ion conductivity. 6. The NOx sensor according to claim 3, wherein the second electrode contains a noble metal, a NOx adsorbing oxide, and a porous oxide. 7. The NOx sensor according to claim 3, wherein the second electrode contains a noble metal, a NOx adsorbing oxide, and iron oxide. 8. The N according to claim 3, wherein the second electrode contains a noble metal, a NOx adsorbing oxide, and gold.
Ox sensor. 9. The NOx sensor according to claim 3, wherein the second electrode contains a noble metal and a complex oxide, or a noble metal and one or more kinds of oxides. 10. The NOx according to any one of claims 3 to 9, wherein the electrolyte is a solid electrolyte having oxygen ion conductivity.
Sensor.