JP6292735B2 - NOx sensor - Google Patents

Description

  The present invention relates to a NOx sensor having a solid electrolyte body having oxygen ion conductivity and a plurality of electrodes formed on the surface of the solid electrolyte body.

  As a NOx sensor for measuring the concentration of NOx contained in automobile exhaust gas or the like, a measurement gas chamber into which exhaust gas (measurement gas) is introduced, a solid electrolyte body having oxygen ion conductivity, and the solid electrolyte body And a plurality of electrodes formed on the surface (see Patent Document 1 below). In this NOx sensor, a pump cell and a sensor cell are formed by the solid electrolyte body and the electrode. The pump cell is a cell for reducing the oxygen concentration in the gas chamber to be measured. The sensor cell is a cell for measuring the concentration of NOx contained in the gas to be measured after the oxygen concentration is reduced by the pump cell.

The pump cell decomposes O ₂ molecules into oxygen ions at an electrode (pump electrode) constituting the pump cell, and discharges the oxygen ions from the gas chamber to be measured through the solid electrolyte body. The pump electrode does not decompose NOx. For this reason, a Pt—Au alloy that is active with respect to O ₂ but inactive with respect to NOx is used for the pump electrode. Since Au is inactive to NOx, if it contains Au, it becomes an electrode inactive to NOx as described above.

  The sensor cell decomposes NOx to generate oxygen ions at an electrode (sensor electrode) constituting the sensor cell, and discharges the oxygen ions from the gas chamber to be measured through the solid electrolyte body. At this time, the NOx concentration is measured by measuring the current flowing through the sensor cell. For the sensor electrode, a Pt—Rh alloy active against NOx or Pt is used.

  When manufacturing a NOx sensor, a conductive paste to be used as a pump electrode or a sensor electrode is printed on the surface of an unfired solid electrolyte body, and combined with another ceramic material and fired. Since heat is applied to the pump electrode in this step, there is a known problem that Au contained in the pump electrode evaporates and adheres to the surface of the sensor electrode. Further, when the NOx sensor is used, since the solid electrolyte body is heated to the activation temperature using a heater, Au contained in the pump electrode is evaporated by the heat of the heater, and the surface of the sensor electrode It may adhere to. As described above, since Au is inactive with respect to NOx, if Au adheres to the surface of the sensor electrode, the ability of the sensor electrode to decompose NOx may be reduced.

  In order to solve this problem, a porous layer made of a porous material may be formed on the surface of the pump electrode (see FIG. 11). If it does in this way, it can suppress that Au evaporates from a pump electrode by a porous layer. Therefore, it can suppress that Au adheres to the surface of a sensor electrode. In addition, a porous layer may be formed on the surface of the sensor electrode, thereby preventing the evaporated Au from adhering to the sensor electrode.

JP 2011-214848 A

  However, the NOx sensor has a problem that the number of materials that can be used for the porous layer is small. That is, in order to completely cover the electrode with the porous layer, it is necessary to bring a part of the porous layer into contact with the solid electrolyte body (see FIG. 11). For this reason, it is necessary to form the porous layer using a material that adheres well to the solid electrolyte and the electrode.

  As described above, in the NOx sensor, there are restrictions on materials that can be used for the porous layer. Therefore, it is not always possible to form the porous layer with a material excellent in the effect of suppressing evaporation of Au. For this reason, there is a problem that a decrease in activity of the sensor electrode with respect to NOx cannot be sufficiently suppressed.

  Further, when the electrode is covered with the porous layer, the NOx sensor is likely to be difficult to manufacture. That is, for example, when the sensor electrode is covered with a porous layer, the higher the porosity of the porous layer, the easier it is for the evaporated Au to pass through and for the Au to adhere to the sensor electrode. In addition, when the porosity of the porous layer is low, it is difficult for the evaporated Au to pass through and it is possible to prevent Au from adhering to the sensor electrode. However, when the NOx sensor is used, the gas to be measured passes through the porous layer. Since it becomes difficult, the amount of current flowing through the sensor cell is reduced or the responsiveness is likely to be lowered. For this reason, it is necessary to adjust the porosity of the porous layer to an optimum range, and the production of the NOx sensor tends to be difficult. A similar problem occurs when the pump electrode is covered with a porous layer.

  Moreover, when covering an electrode with a porous layer, as above-mentioned, it is necessary to make a porous layer adhere | attach well on both an electrode and a solid electrolyte body. Therefore, it is necessary to optimize the film quality of the porous layer so that the film can be satisfactorily adhered to these. Therefore, the manufacture of the NOx sensor tends to be difficult.

  The present invention has been made in view of such a background, and an object of the present invention is to provide a NOx sensor that can sufficiently suppress a decrease in activity of a sensor electrode with respect to NOx and can be easily manufactured.

One embodiment of the present invention includes a measurement gas chamber into which a measurement gas is introduced,
A reference gas chamber into which the reference gas is introduced;
A solid electrolyte body interposed between the gas chamber to be measured and the reference gas chamber and having oxygen ion conductivity;
A plurality of electrodes formed on the main surface of the solid electrolyte body,
The plurality of electrodes include a reference electrode formed on a main surface of the solid electrolyte body on the reference gas chamber side, and a pump electrode and a sensor formed on the main surface of the solid electrolyte body on the gas chamber side to be measured. The pump electrode is made of an alloy of Pt and Au, the sensor electrode is made of an alloy of Pt and Rh or Pt,
The solid electrolyte body, the pump electrode, and the reference electrode form a pump cell that adjusts the oxygen concentration in the measured gas introduced into the measured gas chamber. The solid electrolyte body, the sensor electrode, and the A sensor cell for measuring the NOx concentration in the measurement gas is formed by the reference electrode,
In the measurement gas chamber, Au that adsorbs Au atoms evaporated from the pump electrode at a position where none of the plurality of electrodes formed on the main surface of the solid electrolyte body on the measurement gas chamber side is covered. The NOx sensor is characterized in that an adsorption layer is formed.

  In the NOx sensor, the Au adsorption layer is formed in the measured gas chamber. Therefore, even if Au evaporates from the pump electrode due to heat applied during manufacture or use of the NOx sensor, this Au can be adsorbed by the Au adsorption layer. Thereby, it is possible to suppress the evaporated Au from adhering to the surface of the sensor electrode, and it is possible to suppress a decrease in activity of the sensor electrode with respect to NOx.

  Further, in the NOx sensor, the Au adsorption layer is formed at a position where none of the plurality of electrodes is covered. Therefore, the choice of the material which comprises Au adsorption layer can be increased. That is, since the Au adsorption layer does not cover the electrode, the Au adsorption layer is not particularly required to be formed of a material having excellent adhesion to the electrode. Therefore, the choice of the material which forms Au adsorption layer can be increased, and it becomes possible to form Au adsorption layer with the material which was especially excellent in the adsorptivity of Au. Therefore, Au evaporated from the pump electrode can be effectively adsorbed, and the amount of Au attached to the sensor electrode can be reduced. Thereby, it is possible to sufficiently suppress the decrease in activity of the sensor electrode with respect to NOx.

  Further, if the Au adsorption layer is formed so as to cover the electrode, it is necessary to form the Au adsorption layer with a porous material, and it is necessary to adjust the porosity to an optimum range. That is, if the porosity of the Au adsorbing layer is too high, it becomes easier for Au to pass through when the NOx sensor is baked, and Au is likely to adhere to the sensor electrode. In addition, if the porosity is too low, the gas to be measured does not easily pass through the Au adsorption layer when the NOx sensor is used, which causes problems such as a decrease in responsiveness. Therefore, it is necessary to adjust the porosity of the Au adsorption layer to an optimum range. However, if the Au adsorption layer is formed at a position where none of the plurality of electrodes is covered, it is not necessary to optimize the porosity. Further, as described above, it is not necessary to make the Au adsorbing layer adhere well to both the electrode and the solid electrolyte body. Therefore, the NOx sensor can be easily manufactured.

  As described above, according to the present invention, it is possible to provide a NOx sensor that can sufficiently suppress the decrease in activity of the sensor electrode with respect to NOx and can be easily manufactured.

FIG. 3 is a cross-sectional view of a NOx sensor in the first embodiment. II-II sectional drawing of FIG. III-III sectional drawing of FIG. The IV arrow line view of FIG. 1 is an exploded perspective view of a NOx sensor in Embodiment 1. FIG. FIG. 3 is a cross-sectional view of a NOx sensor in which a pump cell and a sensor cell are formed in separate solid electrolyte bodies in Example 1. The Au adhesion amount measurement result on the sensor cell surface in Experimental Example 1. Sectional drawing of the NOx sensor in Example 2. FIG. FIG. 11 is a cross-sectional view of the NOx sensor in Embodiment 3, which is a cross-sectional view taken along the line IX-IX in FIG. XX sectional drawing of FIG. Sectional drawing of the NOx sensor in the comparative example 1. FIG.

  The NOx sensor can be a vehicle-mounted NOx sensor for measuring the NOx concentration contained in the exhaust gas of an automobile.

Example 1
Examples of the NOx sensor will be described with reference to FIGS. As shown in FIGS. 1 to 3, the NOx sensor 1 of this example includes a measured gas chamber 10, a reference gas chamber 11, a solid electrolyte body 2, and a plurality of electrodes 3 (3p, 3s, 3m, 3b). Is provided. A measurement gas g is introduced into the measurement gas chamber 10, and a reference gas such as the atmosphere is introduced into the reference gas chamber 11. The solid electrolyte body 2 is interposed between the measured gas chamber 10 and the reference gas chamber 11. The solid electrolyte body 2 has oxygen ion conductivity. The electrode 3 is formed on the main surfaces 21 and 22 of the solid electrolyte body 2.

  The plurality of electrodes 3 include a reference electrode 3b, a pump electrode 3p, and a sensor electrode 3s. The reference electrode 3 b is formed on the main surface 22 of the solid electrolyte body 2 on the reference gas chamber 11 side. The pump electrode 3p and the sensor electrode 3s are formed on the main surface 21 of the solid electrolyte body 2 on the measured gas chamber 10 side. The pump electrode 3p is made of an alloy of Pt and Au, and the sensor electrode 3s is made of an alloy of Pt and Rh or Pt.

  The solid electrolyte body 2, the pump electrode 3 p, and the reference electrode 3 b form a pump cell 4 p that adjusts the oxygen concentration in the measurement gas g introduced into the measurement gas chamber 10. The solid electrolyte body 2, the sensor electrode 3s, and the reference electrode 3b form a sensor cell 4s that measures the NOx concentration in the gas to be measured.

  In the measured gas chamber 10, the Au atoms evaporated from the pump electrode 3p are adsorbed in a position where none of the plurality of electrodes 3 formed on the main surface 21 of the solid electrolyte body 2 on the measured gas chamber 10 side is covered. An Au adsorbing layer 5 is formed.

  The NOx sensor 1 of this example is a vehicle-mounted NOx sensor for measuring the concentration of NOx contained in automobile exhaust gas.

The Au adsorption layer 5 of this example can contain, for example, a metal element selected from Pt, Pd, Ni, Rh, Ir, Ta, W, and Mo as a main component. Among these metal elements, it is preferable to use Pt with high Au adsorption efficiency.
The “main component” means a component having the highest mass ratio.

Further, Au adsorption layer ₅ of this embodiment may _also be constituted by a porous ceramic material selected CeO 2, TiO 2, _CZY, from _{Al 2} O 3, ZrO 2.

  As shown in FIGS. 1 and 4, the Au adsorption layer 5 of this example is formed at a position facing the pump electrode 3p in the thickness direction (Z direction) of the pump electrode 3p.

  As shown in FIG. 2, the NOx sensor 1 of this example includes a monitor cell 4s in addition to the pump cell 4p and the sensor cell 4s. The monitor cell 4s includes a solid electrolyte body 2, a monitor electrode 3m, and a reference electrode 3b. Similarly to the pump electrode 3p, the monitor electrode 3m is made of an alloy of Pt and Au. The monitor electrode 3m is formed on the main surface 21 of the solid electrolyte body 2 on the measured gas chamber 10 side.

When measuring the NOx concentration in the measurement gas g, a DC voltage is applied between the reference electrode 3b and the pump electrode 3p so that the pump electrode 3p has a lower potential. In this way, O ₂ is contained in the measurement gas g, is reduced to oxygen ions at the pump electrode 3p, the oxygen ions are discharged through the solid electrolyte body 2 into the reference gas chamber 11 side. Therefore, the O ₂ concentration in the measurement gas g is reduced. Since the pump electrode 3p contains inactive Au in NOx, NOx is not decomposed in the pump electrode 3p, and only O ₂ is ionized.

Thus, after reducing the O ₂ concentration in the measurement gas g, the concentration of O ₂ slightly remaining in the measurement gas g is measured using the monitor cell 4m. That is, O ₂ is reduced to oxygen ions at the monitor electrode 3m, and the oxygen ions are discharged to the reference gas chamber 11 side through the solid electrolyte body 2. The residual O ₂ concentration is measured by measuring the value of the current flowing at this time.

In the sensor cell 4s, the total concentration of O ₂ and NOx contained in the gas to be measured g whose O ₂ concentration is reduced by the pump cell 4p is measured. That is, O ₂ and NOx are decomposed at the sensor electrode 3s to generate oxygen ions. The total concentration of O ₂ and NOx is measured by measuring the current value generated when the oxygen ions flow through the solid electrolyte body 2. Then, the NOx concentration is calculated by subtracting the O ₂ concentration measured using the monitor cell 4m from the total concentration.

Since the sensor electrode 3s is active for both O ₂ and NOx, only the total concentration of these can be measured. Therefore, only the O ₂ concentration is measured using the monitor cell 4m, and the NO x concentration can be accurately measured by subtracting the O ₂ concentration from the total concentration.

  Next, the structure of the NOx sensor 1 will be described in more detail. As shown in FIGS. 1 and 5, the NOx sensor 1 of this example includes a ceramic plate-like portion 13, a first spacer 14, a second spacer 15, a heater 6, and a diffusion resistance layer 12. A gas chamber 10 to be measured is formed by the first spacer 14, and a reference gas chamber 11 is formed by the second spacer 15. Each of these spacers 14 and 15 is made of ceramic.

  The diffusion resistance layer 12 is made of alumina or the like. The diffusion resistance layer 12 limits the amount of gas to be measured g introduced from the outside of the sensor into the gas chamber 10 to be measured.

  As shown in FIG. 5, a connection terminal 16 that is electrically connected to the electrode 3 is formed on the plate-like portion 13. An Au adsorption layer 5 is formed on the main surface 130 (see FIG. 1) of the plate-like portion 13 on the measured gas chamber 10 side. The composition of the Au adsorption layer 5 of this example is the same as that of the reference electrode 3b.

  The solid electrolyte body 2 is made of zirconia, partially stabilized zirconia, or the like. As described above, a plurality of electrodes 3 (3p, 3s, 3m, 3b) are formed on the surface of the solid electrolyte body 2. As shown in FIGS. 2 and 5, the monitor electrode 3m and the sensor electrode 3s are arranged in the width direction (Y direction) orthogonal to both the longitudinal direction (X direction) of the solid electrolyte body 2 and the thickness direction (Z direction). Are next to each other. The monitor electrode 3m and the sensor electrode 3s are formed at positions adjacent to the pump electrode 3p in the X direction.

  As shown in FIG. 5, the heater 6 includes two alumina sheets 61 and 63 and an electric heating unit 62 interposed between the two alumina sheets 61 and 63. On the surface of the alumina sheet 63, a heater terminal 17 electrically connected to the electric heating portion 62 is formed. It is configured to raise the temperature of the solid electrolyte body 2 to the activation temperature by causing a current to flow through the electric heating section 62 to generate heat.

  Next, a method for manufacturing the NOx sensor of this example will be described. In order to manufacture the NOx sensor, first, an unfired solid electrolyte body 2 is prepared, and a pump electrode 3p, a sensor electrode 3s, a monitor electrode 3m, and a reference electrode 3b are respectively formed on the surfaces 21 and 22 of the solid electrolyte body 2. A conductive paste is printed.

In addition, an unfired plate-like portion 13, a first spacer 14, and a second spacer 15 are prepared. A paste that becomes the Au adsorption layer 5 is printed on the unfired plate-like portion 13. For example, this paste is prepared by mixing Pt powder, which is the main component, and alumina powder at a predetermined ratio, and further, an organic binder such as acrylic resin, a plasticizer such as DBP or DOP, an organic solvent such as terpineol, etc. Can be used.
In addition, vias 18 for electrically connecting the electrodes 3 and the connection terminals 16 are formed in the spacers 14 and 15 and the plate-like portion 13. And the unbaked said plate-shaped part 13, the 1st spacer 14, the solid electrolyte body 2, and the 2nd spacer 14 are laminated | stacked, and a sensor laminated body is formed.

  Next, two unfired alumina sheets 61 and 63 are prepared, and a conductive paste to be the electrothermal portion 62 is printed on one alumina sheet 63 of the two alumina sheets 61 and 63. Further, a paste to be used as the heater terminal 17 and the connection terminal 16 is printed on the surface of one alumina sheet 63. Vias 18 for electrical connection are formed in the alumina sheets 61 and 63. Then, the two alumina sheets 61 and 63 are laminated to form a heater laminate.

  Next, the sensor laminate and the heater laminate are laminated and compressed in the Z direction while heating the whole. Thereby, the layers are brought into close contact with each other to form an unfired NOx sensor. Thereafter, the unfired NOx sensor is fired at a predetermined temperature. The firing temperature can be, for example, about 1400 to 1500 ° C.

  The effect of this example will be described. As shown in FIG. 1, in this example, the Au adsorption layer 5 is formed in the measured gas chamber 10. Therefore, even if Au evaporates from the pump electrode 3p due to the heat of firing the ceramic when the NOx sensor 1 is manufactured or the heat generated from the heater 6 when the NOx sensor 1 is used, this Au is adsorbed by the Au adsorption layer 5. be able to. Thereby, it can suppress that Au adheres to the surface of 3 s of sensor electrodes, and it becomes possible to suppress the activity fall with respect to NOx of 3 s of sensor electrodes.

  In this example, the Au adsorption layer 5 is formed at a position where none of the plurality of electrodes 3 (3p, 3m, 3s) is covered. Therefore, the choice of the material which comprises Au adsorption layer 5 can be increased. That is, since the Au adsorbing layer 5 does not cover the electrode 3, the Au adsorbing layer 5 is not particularly required to be formed of a material having excellent adhesion to the electrode 3. Therefore, the choice of the material which forms Au adsorption layer 5 can be increased, and it becomes possible to form Au adsorption layer 5 with the material which was excellent in Au adsorption property especially. Therefore, Au evaporated from the pump electrode 3p can be effectively adsorbed, and the amount of Au adhering to the sensor electrode 3s can be reduced. Thereby, it is possible to sufficiently suppress the decrease in activity of the sensor electrode 3s with respect to NOx.

  That is, as shown in FIG. 11, if a porous layer 95 is formed on the surface of the pump electrode 93 p, and the porous layer 95 attempts to suppress evaporation of Au from the pump electrode 93 p, the porous layer 95 In order to completely cover the pump electrode 93p, a part of the porous layer 95 needs to be in close contact with the solid electrolyte body 92. Therefore, it is necessary to use a material that adheres well to both the pump electrode 93p and the solid electrolyte body 92 for the porous layer 95. Therefore, there are few choices of materials, and it is not always possible to use a material excellent in the effect of suppressing evaporation of Au. On the other hand, as shown in FIG. 1, if the Au adsorbing layer (Au adsorbing layer 5) is formed so as not to cover the electrode 3 as in this example, the adhesion to the electrode 3 is not necessarily excellent. Therefore, the choice of materials that can be used as the Au adsorption layer 5 can be expanded. Therefore, a material that is particularly excellent in the Au adsorption effect can be used as the Au adsorption layer 5. Therefore, the amount of Au adhering to the sensor electrode 3s can be reduced, and the decrease in activity of the sensor electrode 3s with respect to NOx can be sufficiently suppressed.

In addition, as shown in FIG. 11, when the porous layer 95 is formed on the surface of the pump electrode 93p, if the porosity of the porous layer 95 is too high, Au tends to evaporate when the NOx sensor 91 is baked. If the porosity is too low, the gas to be measured g hardly passes through the porous layer 95 when the NOx sensor 91 is used, causing problems such as a reduction in O ₂ discharge efficiency. Therefore, it is necessary to adjust the porosity of the porous layer 95 to an optimal value, and it becomes difficult to manufacture the NOx sensor 91. However, as shown in FIG. 1, if the Au adsorbing layer (Au adsorbing layer 5) is formed at a position not covering the electrode 3 as in this example, the porosity of the Au adsorbing layer 5 is optimized. Since there is no need in particular, it becomes possible to manufacture a NOx sensor easily.

  As shown in FIG. 1, the Au adsorption layer 5 of this example is formed at a position facing the pump electrode 3p in the Z direction. Therefore, the Au adsorption layer 5 can be provided in the vicinity of the pump electrode 3p. Therefore, Au evaporated from the pump electrode 3p can be immediately adsorbed, and Au can be prevented from moving to the sensor electrode 3s. Therefore, the amount of Au attached to the sensor electrode 3s can be reduced.

Further, in this example, as shown in FIG. 4, all parts of the pump electrode 3 p are configured to overlap the Au adsorption layer 5 when viewed from the Z direction.
Therefore, the area of the Au adsorption layer 5 can be increased, and Au evaporated from the pump electrode 3p can be more reliably adsorbed by the Au adsorption layer 5.

The Au adsorption layer 5 can be formed of a material containing, for example, Pt, Pd, Ni, Rh, and Ir as main components. Since these metals have a face-centered cubic structure like Au, they easily adsorb Au.
The Au adsorption layer 5 can also be formed of a material containing Ta, W, and Mo as main components. These metals have a relatively large adsorption energy. Therefore, Au can be effectively adsorbed by using these metals.

  The Au adsorption layer 5 preferably contains Pt as a main component. Since Pt is a noble metal element like Au, it has a high affinity with Au. Therefore, if the Au adsorption layer 5 is formed of a material containing Pt as a main component, it becomes possible to adsorb Au particularly effectively. Since Pt is also contained in the sensor electrode 3s, even if Pt evaporates from the Au adsorption layer 5 and adheres to the sensor electrode 3s, the characteristics of the sensor electrode 3s do not vary greatly.

  The Au adsorption layer 5 is most preferably composed mainly of Pt and further contains alumina. If the Au adsorption layer 5 contains alumina, the Au adsorbing layer 5 is easily adhered to the plate-like portion 13. Therefore, problems such as peeling of the Au adsorbing layer 5 due to thermal stress or the like are less likely to occur.

  The porosity of the Au adsorption layer 5 is preferably 5 to 95%. In this case, the surface area of the Au adsorption layer 5 can be increased. Therefore, Au adsorption efficiency can be increased. When the porosity of the Au adsorption layer 5 is less than 5%, the efficiency of adsorbing Au is lowered. On the other hand, if the porosity exceeds 95%, the durability tends to decrease.

The Au adsorption layer 5 preferably has the same composition as that of the reference electrode 3b.
In this case, the Au adsorption layer 5 and the reference electrode 3b can be formed using the same conductive paste. Therefore, the types of conductive paste to be prepared can be reduced in the NOx sensor 1 manufacturing factory. Therefore, it becomes easy to reduce the manufacturing cost of the NOx sensor 1.

Further, the Au adsorption layer _{5 may} be constituted by a porous ceramic material selected CeO 2, TiO 2, _CZY, from _{Al 2} O 3, ZrO 2. Since these materials are porous, they have a large surface area. Therefore, it is excellent in the adsorptivity of Au.

  As described above, according to this example, it is possible to provide a NOx sensor that can sufficiently suppress the decrease in activity of the sensor electrode with respect to NOx and can be easily manufactured.

  In this example, as shown in FIGS. 1 and 2, three types of cells 4 (pump cell 4p, sensor cell 4s, monitor cell 4m) are formed in one solid electrolyte body 2, but the present invention is not limited to this. It is not a thing. That is, as shown in FIG. 6, two solid electrolyte bodies 2a and 2b are used to form a pump cell 4p on one solid electrolyte body 2a and a sensor cell 4s and a monitor cell 4m on the other solid electrolyte body 2b. Also good. Then, the Au adsorption layer 5 may be formed at a position facing the pump electrode 3p in the Z direction. In this case, the Au adsorption layer 5 is formed on the surface of the other solid electrolyte body 2b.

(Experimental example 1)
An experiment was conducted to confirm the effect of this example. First, an unsintered sample of the NOx sensor 1 provided with the Au adsorption layer 5 and an unsintered sample of the NOx sensor not provided with the Au adsorption layer 5 were prepared. These two samples have the same structure as in FIG.

  Then, after firing the two samples, the obtained NOx sensor was disassembled, and the amount of Au deposited on the surface of the sensor electrode 3s was investigated using XPS (X-ray photoelectron spectroscopy). The result is shown in FIG.

  From the figure, it can be seen that the NOx sensor 1 having the Au adsorption layer 5 has only a small amount of Au attached to the sensor electrode 3s. Further, it can be seen that the NOx sensor in which the Au adsorption layer 5 is not formed has 20% of Au attached to the sensor electrode 3s.

  From this result, the NOx sensor 1 in which the Au adsorption layer 5 is formed has a smaller amount of Au adhering to the sensor electrode 3s than the NOx sensor in which the Au adsorption layer 5 is not formed. It can be seen that the decrease in activity can be suppressed.

(Example 2)
In the following embodiments, the same reference numerals used in the drawings among the reference numerals used in the drawings represent the same components as in the first embodiment unless otherwise specified.

In this example, the position of the Au adsorption layer 5 is changed. As shown in FIG. 8, in this example, the Au adsorption layer 5 is formed on the main surface 21 of the solid electrolyte body 2 on the measured gas chamber 10 side. The Au adsorption layer 5 is formed between the sensor electrode 3s and the monitor electrode 3m, and the pump electrode 3p. By forming the Au adsorption layer 5 at this position, the electrode 3 (3p, 3m, 3s) is prevented from being covered with the Au adsorption layer 5.
In addition, the configuration and operational effects are the same as those of the first embodiment.

(Example 2)
In this example, the position of the Au adsorption layer 5 is changed. In this example, the Au adsorption layer 5 is formed on the side surfaces 131 and 132 of the first spacer 13. By forming the Au adsorption layer 5 at this position, the electrode 3 (3p, 3m, 3s) is prevented from being covered with the Au adsorption layer 5.
In addition, the configuration and operational effects are the same as those of the first embodiment.

DESCRIPTION OF SYMBOLS 1 NOx sensor 10 Gas chamber 11 to be measured Reference gas chamber 2 Solid electrolyte body 3 Electrode 3p Pump electrode 3s Sensor electrode 3b Reference electrode 4p Pump cell 4s Sensor cell 5 Au adsorption layer

Claims (6)

A gas chamber to be measured (10) into which the gas to be measured is introduced;
A reference gas chamber (11) into which the reference gas is introduced;
A solid electrolyte body (2) interposed between the measured gas chamber (10) and the reference gas chamber (11) and having oxygen ion conductivity;
A plurality of electrodes (3) formed on the main surfaces (21, 22) of the solid electrolyte body (2),
The plurality of electrodes (3) include a reference electrode (3b) formed on a main surface (22) of the solid electrolyte body (2) on the reference gas chamber (11) side, and the solid electrolyte body (2). There are a pump electrode (3p) and a sensor electrode (3s) formed on the main surface (21) on the measured gas chamber (10) side, and the pump electrode (3p) is made of an alloy of Pt and Au. The sensor electrode (3s) is made of an alloy of Pt and Rh or Pt.
A pump cell (4p) that adjusts the oxygen concentration in the measured gas introduced into the measured gas chamber (10) by the solid electrolyte body (2), the pump electrode (3p), and the reference electrode (3b). ), And the sensor cell (4s) for measuring the NOx concentration in the measurement gas is formed by the solid electrolyte body (2), the sensor electrode (3s), and the reference electrode (3s),
The measured gas chamber (10) is covered with the plurality of electrodes (3) formed on the main surface (21) of the solid electrolyte body (2) on the measured gas chamber (10) side. The NOx sensor (1), wherein an Au adsorbing layer (5) for adsorbing Au atoms evaporated from the pump electrode (3p) is formed at a position where no pumping is performed.   The NOx sensor (1) according to claim 1, wherein the Au adsorption layer (5) is formed at a position facing the pump electrode (3p) in the thickness direction of the pump electrode (3p). ).   The NOx sensor (1) according to claim 2, wherein when viewed from the thickness direction, all the parts of the pump electrode (3p) overlap with the Au adsorption layer (5).   The Au adsorption layer (5) contains a metal element selected from Pt, Pd, Ni, Rh, Ir, Ta, W, and Mo as a main component. The NOx sensor (1) according to claim 1.   The NOx sensor (1) according to any one of claims 1 to 3, wherein the Au adsorption layer (5) contains Pt as a main component. The Au adsorption layer _{(5) is} a _{CeO 2, TiO 2, CZY,} Al 2 O 3, claim, characterized in that it is constituted by a porous ceramic material selected from ZrO _2. 1 to claim 3 NOx sensor (1) given in any 1 paragraph.

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