JP3841513B2 - Hydrocarbon sensor - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
  The present invention relates to a limiting current type hydrocarbon sensor used for detection and concentration measurement of hydrocarbons in a temperature range from room temperature to high temperature (800 ° C.), and more particularly, detection of hydrocarbon gas in a living environment, for automobiles The present invention relates to improvements in hydrocarbon sensors that can be used for combustion control (lean burn) of combustion equipment and catalyst deterioration monitoring by detecting residual hydrocarbons in exhaust gas from engines, stoves, catalytic combustion equipment, etc.
[0002]
[Prior art]
  The present inventors have already proposed a limiting current type (constant potential electrolytic type) hydrocarbon sensor using a barium cerium-based oxide exhibiting high proton conductivity as a solid electrolyte.Wish7-285800). A sensor using this electrolyte responds well to a small amount of hydrocarbons in the atmosphere, and has the ability to linearly detect hydrocarbons in the concentration range of several ppm to several percent in the atmosphere.
[0003]
  As shown in FIG. 1, the general structure of this sensor is that a barium cerium oxide (BaCeOO) is formed on a solid electrolyte layer 1 formed in a thin plate shape. ₃ setThe film-like metal electrodes 2 and 3 are bonded and fixed to both surfaces of the electrolyte layer 1 respectively, and the anode 2 of these electrodes is connected to the anode 2. Diffusion-limiting means comprising an anode chamber 40 having an anode surrounded by an insulating ceramic substrate 4 on the surface of the solid electrolyte layer, and a diffusion-controlling hole 42 having a small inner diameter communicating with the atmosphere to be measured is provided in the anode chamber. In this example, a heater 6 for heating the sensor itself is attached to the outer surface of the ceramic 4 substrate outside the anode chamber.
[0004]
  When the sensor is used, a constant potential E is applied between the electrodes 2 and 3 while the sensor itself is exposed to the atmosphere, and the sensor is heated to a constant temperature. The hydrocarbon gas in the atmosphere (denoted as CH in FIG. 1) diffuses and moves into the anode chamber 40 via the diffusion rate controlling hole 42, and the hydrocarbon CH is dissociated on the surface of the anode 2 electrode in the anode chamber. Hydrogen ion (H⁺) That is, protons are generated, and the protons move to the cathode side in the solid electrolyte layer, become hydrogen molecules at the cathode, and are released to the atmosphere. And between the metal electrodes, H per unit time flowing through the electrolyte layer. ⁺ amountA current A proportional to Here, by providing a diffusion-controlling hole, the amount of hydrocarbon corresponding to the hydrocarbon partial pressure in the atmosphere is supplied to the anode chamber by diffusion, and the amount of hydrogen ions proportional to the amount of hydrocarbon in the anode chamber moves through the electrolyte layer. Therefore, the value of the measured current is obtained in proportion to the hydrocarbon partial pressure of the atmosphere.
[0005]
  Sensors that perform quantitative detection of hydrocarbon concentration in combustion exhaust gas from internal combustion engines such as the above-mentioned automobile engines and other combustion equipment have selectivity only for hydrocarbons. Even so, it is required that the hydrocarbons in the atmosphere have high sensitivity and high data reliability. At the same time, such a sensor is also required to be small in size, easy and easy to manufacture, and low in manufacturing cost. For such applications, the above-mentioned limiting current type hydrocarbon sensor using barium-cerium-based oxide has high proton mobility, large detection current signal, and good linearity with respect to hydrocarbon concentration. Is widely expected.
[0006]
[Problems to be solved by the invention]
  Conventional sensors that use barium cerium-based oxides as solid electrolytes have good responsiveness to hydrocarbons, but when oxygen gas is present in the atmosphere, the sensor is also sensitive to this oxygen gas, The detection current between the electrodes includes a current corresponding to oxygen gas, which causes a large measurement error. In particular, when the hydrocarbon concentration is small and the oxygen concentration is high, the current output from the sensor is large, which makes it impossible to detect the hydrocarbon concentration. Such variations in the atmospheric composition can often occur in the exhaust gas of an automobile engine due to changes in the fuel-air mixture ratio and the rotational speed. As described above, in the atmosphere in which the atmosphere to be measured coexists with the hydrocarbon gas and the oxygen gas, a detection error due to oxygen occurs in the sensor, and there is a problem that the hydrocarbon concentration cannot be detected with high accuracy.
[0007]
  In view of the above problems, the present invention provides a limit current sensor that uses barium cerium-based oxide as a solid electrolyte, is insensitive to oxygen even in an oxygen-containing atmosphere, and accurately detects hydrocarbons, or its It is an object of the present invention to provide a hydrocarbon sensor capable of accurately measuring the concentration.
[0008]
[Means for Solving the Problems]
  In the limiting current type hydrocarbon sensor using barium cerium oxide as a solid electrolyte, the present invention prevents or reduces oxygen dissociation or migration on the cathode side where oxygen in the atmosphere migrates and ion dissociates. By providing the means for reducing the amount of oxygen ions at the cathode, the generation of error current originating from oxygen ion conduction is reduced or prevented.
[0009]
  Barium and cerium-based oxides also have oxygen ion conductivity due to fluctuations and malfunctions in the current value between electrodes when oxygen coexists in the atmosphere.RutaAs for the conventional sensor, the cathode side is H₂  In order to dissipate gas, it is necessary to expose the atmosphere to be measured. For this reason, oxygen in the atmosphere to be measured moves to the cathode surface and dissociates into oxygen ions, and the oxygen ions move to the anode side in the solid electrolyte. As a result, the current originating from oxygen at the electrode is added to the detection output of the hydrocarbon.
[0010]
  The present invention prevents the generation of error current by suppressing the generation of oxygen ions at the cathode even when the sensor is in an oxygen-containing atmosphere.
  To achieve this, the present invention is more specifically classified into two means.
  The first means is a means for directly preventing or reducing oxygen dissociation at the cathode of oxygen gas, which includes a cathode made of a metal inert to oxygen and a cathode shape having a smaller area than the anode. Is adopted.
[0011]
  In the present invention, the second means includes an oxygen suppressing means for suppressing oxygen transfer to the cathode as described below. For this, an oxygen diffusion rate controlling means for controlling the diffusion movement of oxygen to the cathode, an oxygen absorption means for regulating the movement of oxygen to the cathode, or an oxygen consumption means for promoting the combustion consumption of oxygen on the cathode side is adopted. The
[0012]
DETAILED DESCRIPTION OF THE INVENTION
  Details of the present invention will be described below with reference to the drawings. Structurally, there are many places common to FIG. 1 showing the conventional example, and explanation will be given using FIG. In addition, since there are many places where the constituent elements are common, common elements will be described with the same numbers. Regarding the structure of the limiting current type hydrocarbon sensor of the present invention, the solid electrolyte layer 1 is composed of BaCeO as barium cerium oxide.₃Is a sintered body having a perovskite type crystal structure. Barium cerium oxide is based on the basic composition BaCeO.₃A compound obtained by substituting a part of Ce of the compound with another rare earth element can also be used.
    In general formula, BaCe_1-XM_X O ₃      [0.16≦X≦ 0.23] can be used, and for R, rare earth metals other than Ce, such as Y, Gd, Dy, Sm, and Tb, are used.
[0013]
  The solid electrolyte layer 1 is usually formed into a layer to form an electrode. A metal film anode 2 is formed on one surface of the solid electrolyte layer 1 and a metal film cathode 3 is formed on the opposite surface. It is deposited so as to face each other through the layer 1.
  Further, on the anode 2 side, an anode chamber 40 is formed by the ceramic substrate 4 and the glass spacer 41, and a hydrocarbon diffusion control hole 42 is formed between the ceramic substrate 4 and the solid electrolyte layer 1. But communicated with the atmosphere.
[0014]
  Further, a heater 6 is attached to the sensor, for example, on the ceramic substrate 4, and the entire sensor including the solid electrolyte layer 1 is heated and held at a constant temperature by the heater 6. At the time of measurement, this entire sensor is placed in the test gas and heated and held.A constant voltage is applied to the two electrodes from the constant voltage power supply E via the leads 28 and 38, and the current value AIs detected output.
[0015]
  In the first embodiment, the hydrocarbon sensor of the present invention is such that the cathode electrode material is formed of a metal material inert to oxygen. Here, as the metal inert to oxygen, an oxygen inert metal is preferably used as compared with Pt normally used for the electrode metal of the anode 2. Specifically, preferably, a metal material selected from Ag, Cu, Ti, Fe, Co, Ni, Pd, and Ru is included. These electrode materials reduce the rate or rate of ionization of atmospheric oxygen molecules at the cathode, so that oxygen ions O at the cathode are reduced.^2-Therefore, the limit current due to oxygen ion conduction into the electrolyte layer is relatively reduced, and the influence on the detection current due to oxygen in the atmosphere is reduced.
[0016]
  The combination of the electrode metal of the anode and the cathode can be a combination of Ag and Ag, for example. Another combination of anode and cathode electrode metals may be a combination of different metals, for example, a combination of anode Pt and cathode Cu, anode Pt and cathode Ag, Pd and Au, or the like. Further, the electrode metal may be a mixture of Pd and Pt or a mixture of Ag and Au.
[0017]
    As Example 1, CoveredAn example is shown in which the detection characteristics of a sensor using an automobile exhaust gas as the detection gas, Pt as the anode, and Ag as the cathode are examined.
  BaCe as barium cerium oxide_{0. 8} Gd_{0. 2} O ₃ setThe solid electrolyte layer 1 having a thickness of 10 mm × 10 mm and a thickness of 0.45 mm is formed from the sintered body, and the electrodes are formed as a Pt film as the anode 2 on the surface of the solid electrolyte layer 1 and an Ag film as the cathode 3 on the other surface. Both the anode 2 and the cathode 3 were patterned into a 6 × 6 mm square. Furthermore, an anode chamber 40 having a hydrocarbon diffusion-controlling hole 42 on the anode side was produced by the ceramic substrate 4 and the glass spacer 5 to form a hydrocarbon sensor.
  The measurement of hydrocarbons is carried out by exposing the sensor to the exhaust gas at an applied voltage of 0.6 V between the anode 2 and the cathode 3 with the sensor temperature heated to about 600 ° C. and outputting various gas concentrations. Examined.
[0018]
  FIG. 2 shows the relationship between the hydrocarbon concentration and the output. For comparison, the output characteristics of a conventional sensor using a Pt electrode for both the anode and the cathode are also shown.
  The sensor of the present invention and the conventional sensor show good linearity in hydrocarbon concentration and detection output. When oxygen was mixed at 5% with a low hydrocarbon concentration, the current output between the electrodes rapidly increased as shown in FIG. 2 in the conventional sensor. However, in the sensor of the present invention, it is caused by oxygen. It can be seen that the increase in the current output is considerably suppressed. This clearly shows that the hydrocarbon sensor of the present invention shows a selective response to hydrocarbons better than the conventional one, and can be detected with high accuracy even when oxygen is mixed.
[0019]
  In this embodiment, forming the cathode from a metal material inert to oxygen, and further combining the anode and the cathode with different electrode metals can also be used in other means shown in the following embodiments. Is preferred.
[0020]
  In the second embodiment, the sensor according to the present invention is such that the area of the cathode 3 formed on the surface of the electrolyte layer 1 is relatively smaller than the area of the anode 2. The frequency of dissociation is reduced, and the limiting current resulting from oxygen ion conduction into the electrolyte layer is relatively reduced.
[0021]
  FIG. 3A shows a plan view of the sensor viewed from the cathode 3 side of the solid electrolyte 1. In this example, the rectangular electrode of the cathode 3 on the surface of the electrolyte 1 is the anode on the back surface of the electrolyte 1 facing this. The area is smaller than that of the square electrode 2.In the figure, 29 and 30 are electrical connection portions.In the present invention, the ratio of the electrode area of the cathode 2 to the anode 3 is suitably in the range of 30 to 80%. If the electrode area ratio of the cathode is less than 30%, the detection current for hydrocarbons is small, which is not preferable. If it exceeds 80%, the reduction in current measurement error due to oxygen is not improved. This electrode area ratio is preferably 50 to 70%.
[0022]
  As Example 2, MosquitoAn example of a sensor with a reduced sword area is shown. The structure of the sensor is a BaCe 10 mm × 10 mm 0.45 mm thick in the solid electrolyte 1._{0. 8} Y _{0. 2} O _3-α Both the anode 2 and the cathode 3 are used as the electrolyte layer of the sintered body and a platinum film is used. As in the first embodiment, the anode chamber 40 having the diffusion-determining holes for hydrocarbons is formed in the ceramic substrate 4 and the glass. A spacer 41 was used. The shape of the anode 2 and the cathode 3 is formed into a square pattern as shown in FIG. 3A, and the electrode area is 0.36 cm at the anode 2. ² InOn the other hand, the cathode 3 is 0.25 cm. ² WhenThus, the cathode 3 side was set to a small area.
[0023]
  FIG. 4 shows the relationship between the hydrocarbon concentration and the current output in the same manner as in the previous Example 1, which was examined for a sensor in which the exhaust gas of an automobile was used as the test gas and the cathode area was reduced. For comparison, the output characteristics of a sensor in which the Pt anode and the Pt cathode have the same area are also shown. In the conventional sensor, when oxygen is mixed in a state where the hydrocarbon concentration is low, the current output rapidly increases as shown in FIG. However, in the sensor of the present invention, it can be seen that the current output due to oxygen is considerably suppressed. This clearly proves that the hydrocarbon sensor of the present invention responds better than before, and can be detected with high accuracy even when oxygen is mixed.
[0024]
  In this embodiment, platinum electrodes having different electrode areas are used for the anode and the cathode. For example, Au may be used for both electrodes, or a different combination of Pt and Au. Similar effects have been confirmed.
[0025]
  Thus, reducing the area of the cathode compared to the anode is good for reducing the influence of oxygen on the detection current,However,On the other hand, hydrogen ions H moving from the anode to the cathode⁺As seen from FIG. 3B, the hydrogen ions that move from the peripheral edge of the anode 2 to the cathode 3 and reach the cathode 3 obliquely cross the electrolyte layer 1 with respect to the thickness direction, as shown in FIG. As it moves, its permeation path in the electrolyte layer becomes longer, which can cause a decrease in the sensitivity of hydrocarbon detection.The problem remains.
[0026]
  For this purpose, the outer shape of the cathode 3 is made substantially the same as the outer shape of the anode 2, and the cathode 3 is formed with one or more openings 30 or one or more notches 31 in the surface area thereof. The area of the electrode is substantially reduced. Thereby, the proton permeation path from the anode 2 to the cathode 3 is shortened on average, and a decrease in the sensitivity of the hydrocarbon can be suppressed. Such a cathode uses a strip-shaped metal film and has openings 30 as shown in FIG. 5 (A) to form a grid, or notches 31 as shown in FIG. 5 (B). A comb shape or fish bone shape is preferably employed.
[0027]
  As Example 3, an example of a limiting current type hydrocarbon sensor in which the shape of the cathode is made into a lattice by a thin metal film is shown below. First, using a printing machine, a cathode 3 is formed on the surface of the electrolyte layer 1 as shown in FIG. 5A, and 16 openings 30 are formed in the surface area using Pt paste to form a lattice pattern. The configuration of sensor elements other than the cathode was the same as in Example 1. In this case, the cathode area was 35% of the anode area.
[0028]
  Using this sensor, the relationship between the hydrocarbon concentration and the detected current was examined in the same manner as in Example 2, using the exhaust gas of an automobile as the test gas. FIG. 6 shows the relationship between the hydrocarbon concentration and the output. For comparison, the output characteristics of a sensor using a conventional Pt electrode having the same area are also shown. In the conventional sensor, when oxygen was mixed in a state where the hydrocarbon concentration was low, the output increased rapidly as shown in the figure. However, all the sensors using the grid-like cathode of the present invention can suppress the output even when oxygen is mixed, and it is understood that hydrocarbons in the oxygen mixed exhaust gas can be detected with higher accuracy than before. It was.
[0029]
  In the third embodiment, the hydrocarbon sensor of the present invention includes a sensor that provides oxygen diffusion rate limiting means on the cathode side to limit the rate at which oxygen moves from the atmosphere to the cathode side. The oxygen diffusion rate controlling means is preferably provided with a ceramic substrate 7 that covers the surface of the solid electrolyte layer 1 with a space on the cathode 3, and has diffusion rate limiting holes 72 between the ceramic substrate 7 and the solid electrolyte layer 1. What is formed is adopted.
  As another oxygen diffusion rate limiting means, a continuous air-permeable ceramic layer coated directly or indirectly on the cathode surface area on the electrolyte layer 1 is also used.
[0030]
  As an example of the oxygen diffusion rate limiting means, FIG. 7 shows the structure of a limiting current type hydrocarbon sensor. The sensor is a solid electrolyte layer 1, and an anode 2 and a cathode 3 are provided on the surface of the electrolyte layer 1 with electrodes. In this example, a cathode chamber 70 is formed from the ceramic substrate 7 and the glass spacer 71 on the cathode 3 side as an oxygen diffusion rate controlling means, and a small hole communicating with the atmosphere between the ceramic substrate 7 and the electrolyte layer 1 is formed. Are provided as oxygen diffusion rate limiting holes 72.
  On the anode 2 side, an anode chamber 40 is formed by the ceramic substrate 4 and the glass spacer 41 as a hydrocarbon diffusion rate-limiting means, as in the prior art, and a small hole 42 between the ceramic substrate 4 and the electrolyte layer 1 is formed. WithCharcoalThis is a diffusion-determining hole 42 for hydrogen fluoride.
[0031]
  As for the oxygen diffusion rate limiting means, on the cathode 3 side, oxygen in the atmosphere passes through an oxygen diffusion rate limiting hole 72 formed by the ceramic substrate 7 and the glass spacer 71, dissociates into oxygen ions by electrolysis at the cathode 3, and is solid. Conducted through the electrolyte layer 1 and released as oxygen gas at the anode. However, since the oxygen inflow rate at this time is limited by the oxygen diffusion rate limiting hole 72, the amount of oxygen ions moving in the solid electrolyte layer 1 is restricted, and the current caused by oxygen ions is minimized among the current flowing between the electrodes. Thus, the error in the detected current due to oxygen can be minimized. On the other hand, for hydrocarbons, the hydrogen ions ionized in the anode chamber 40 move through the solid electrolyte layer as described above to become gaseous hydrogen at the cathode in the cathode chamber, and gaseous hydrogen diffuses compared to oxygen. Since the coefficient is large, it passes through the oxygen diffusion rate limiting hole and is released into the atmosphere, and even if oxygen diffusion rate limiting means is provided, it does not hinder the measurement of hydrocarbons.
[0032]
  As Example 4, BaCe having an outer shape of 10 mm × 10 mm and a thickness of 0.45 mm was formed on the electrolyte layer 1._{0. 8} Dy_{0. 2} O _3-α A hydrocarbon sensor in which the anode 2 and the cathode 3 are formed of platinum electrodes using a sintered body, and as shown in FIG. 7, a cathode chamber 70 and an oxygen diffusion rate limiting hole 72 are formed as oxygen diffusion rate limiting means on the cathode side. The characteristics were investigated in the exhaust gas of automobiles. The measurement conditions were an element temperature of about 600 ° C. and an applied voltage of 0.6V.
[0033]
  FIG. 8 shows the relationship between the hydrocarbon concentration and the output when the oxygen diffusion rate limiting means is formed. For comparison, the output characteristics of a conventional sensor that does not have oxygen diffusion rate limiting means on the cathode side are also shown. In the conventional sensor, when oxygen is mixed in the atmosphere in a state where the hydrocarbon concentration is low, as shown in FIG. 8, the output increases rapidly, resulting in a large error. It can be seen that, even by mixing, the current output fluctuation is suppressed to a very low level by the oxygen diffusion rate limiting means, and the sensitivity characteristic of the output current with respect to the hydrocarbon concentration is exactly the same as that of the conventional sensor. This clearly proves that the hydrocarbon sensor of the present invention can be detected with high accuracy even when oxygen is mixed.
[0034]
  In a fourth embodiment, the present invention includes an oxygen absorbing means for restricting the movement of oxygen to the cathode. The oxygen absorbing means has a function of absorbing oxygen existing on the cathode side. As the oxygen absorbing means, a porous oxygen absorbing layer 9 attached on the electrolyte layer 1 so as to cover the cathode 3 is used. Is done. Examples of the oxygen absorbing layer 9 include an oxide porous body that is easily oxidized and reduced. As such an oxide, cerium oxide is preferably used. In addition, as the other oxygen absorbing layer 9, an alumina based molecular sieve can also be used. Such oxygen absorbing means adsorbs and fixes as an oxide when oxygen in the atmosphere moves to the cathode, reduces the amount of oxygen reaching the cathode, and at the same time, H ⁺ IThe gaseous hydrogen generated at the cathode when turned on passes through the porous oxygen absorbing means and is released into the atmosphere, so that it does not hinder the measurement of hydrocarbons.
[0035]
  The structure of the sensor of the present invention is illustrated in FIG. 9. An anode 2 and a cathode 3 are formed on the surface of the solid electrolyte layer 1, and a cerium oxide layer that absorbs oxygen is applied to the upper surface of the cathode 3. A porous oxygen absorption layer 9 is laminated, and on the other anode 2 side, an anode chamber 40 is formed by a ceramic substrate 4 and a glass spacer 41 as a hydrocarbon diffusion rate-limiting means as in the conventional one. In addition, a diffusion rate controlling hole 42 is formed between the ceramic substrate 4 and the solid electrolyte layer 1.
[0036]
  As Example 5acidAn example using the element absorbing means is shown below. In FIG. 9, the electrolyte layer 1 has a BaCe having an outer shape of 10 mm × 10 mm and a thickness of 0.45 mm._{0 . 8} Y _{0. 2} O _3-α Using a sintered body, the anode 2 and the cathode 3 are formed of platinum electrodes having the same area, and a hydrocarbon rate-limiting means is formed on the anode 2 side. A cerium oxide powder is formed on the cathode 3 on the cathode 2 side. A coated and sintered oxygen absorbing layer 9 was formed and covered. The characteristics of this hydrocarbon sensor were investigated in automobile exhaust gas. FIG. 10 shows the relationship between the hydrocarbon concentration and the output. For comparison, FIG. 10 also shows the output characteristics of a hydrocarbon sensor having the same configuration except that no oxygen absorbing means is provided.
[0037]
  In the conventional sensor, when oxygen is mixed in a state where the hydrocarbon concentration is low, as shown in FIG. 10, the current output of the sensor increases rapidly, but in the sensor of the present invention, the output at the time of oxygen mixing is considerably suppressed. You can see that This clearly shows that the hydrocarbon sensor of the present invention having the oxygen absorbing means responds better than before and can detect with high accuracy even when oxygen is mixed.
[0038]
  Regarding the fifth embodiment, the hydrocarbon sensor of the present invention includes one having oxygen consuming means for promoting the combustion consumption of oxygen on the cathode side. The oxygen consuming means has a function of consuming the oxygen present on the cathode side through combustion reaction with hydrocarbons. As the oxygen consuming means, Pt, Rh, Pd, Ru, or the like can be used as a catalyst for promoting the reaction between oxygen and hydrocarbons.
[0039]
  The oxygen consuming means forms a cathode chamber 70 on the cathode 3 by a ceramic substrate 7 and a glass spacer 71 so as to communicate with the atmosphere, and a catalyst layer 8 is applied to the inner surfaces of the ceramic substrate 7 and the glass spacer 71 in the cathode chamber. The thing of the structure which was made can be adopted. The porous catalyst layer 8 containing a catalyst such as platinum as an oxygen consuming means is formed by a physical production method such as a coating film baking method, a thermal spraying method, a vacuum deposition method, a sputtering method, or a chemical method such as a CVD method. The law is widely used. The catalyst of the catalyst layer 8 does not directly contact the cathode 3 but promotes a combustion reaction between oxygen entering the cathode chamber 70 and hydrocarbons entering at the same time, thereby oxidizing and consuming oxygen. The amount of oxygen that shifts to is reduced as much as possible.
[0040]
  As another oxygen consuming means, the above metal catalyst may be supported on an appropriate insulating ceramic continuous air-permeable support covering the entire surface of the cathode 3.
[0041]
  The structure of the sensor of the present invention is shown in FIG. 11, where the anode 2 and the cathode 3 are formed on the surface of the solid electrolyte layer 1, and the hydrocarbon diffusion limiting means is formed on the anode side by the ceramic substrate 4 and the glass 5. Has been. In the oxygen consuming means, as shown in FIG. 11, a Pt catalyst layer 8 is formed on the surface of the electrolyte layer 1 on the cathode 3 side so as to cover the cathode. The catalyst layer 8 is porous and can freely move gas. By the catalytic action of Pt, nearby oxygen reacts with the hydrocarbon and burns. In this way, the oxygen in the cathode chamber 70 that has moved from the atmosphere is removed before reaching the cathode.
  The small hole 74 also includes the cathode chamber 70, which also serves as the oxygen diffusion rate limiting hole 72.MetThe oxygen consuming means can also serve as the oxygen diffusion rate controlling means.
[0042]
  As Example 6, an example provided with oxygen consuming means is shown below. As solid electrolyte 1, BaCe having an outer shape of 10 mm × 10 mm and a thickness of 0.45 mm is used._{0. 8} Gd_{0. 2} O _3-α A sintered body is used, and Pt electrodes having the same area are used for the anode 2 and the cathode 3, and the cathode 3 has small holes 74 that can communicate with the atmosphere as a means for consuming oxygen by the ceramic substrate 7 and the glass spacer 71. A cathode chamber 70 provided with a porous platinum catalyst layer 8 was coated on the inner surface of the ceramic substrate 7 and the opening 72 communicating with the cathode chamber 70.
  Further, on the anode side, a hydrocarbon diffusion control means comprising an anode chamber 40 and hydrocarbon diffusion control holes 42 is constituted by the ceramic substrate 4 and the glass spacer 41 as in the prior art.
[0043]
  The hydrocarbon detection characteristics of this sensor were examined in the exhaust gas of automobiles as in the previous example. FIG. 12 shows the relationship between the hydrocarbon concentration and the output. For comparison, the output characteristics of a conventional sensor that does not include oxygen consuming means on the cathode side are also shown. In the conventional sensor, when oxygen is mixed in a state where the hydrocarbon concentration is low, the output increases rapidly as shown in FIG. 12, but in the sensor of the present invention, the output accompanying oxygen mixing is considerably suppressed. I understand. This clearly shows that the hydrocarbon sensor of the present invention responds better than before and can detect hydrocarbons with high accuracy even when oxygen is mixed.
[0044]
【The invention's effect】
  In the limiting current hydrocarbon sensor using barium cerium oxide as a solid electrolyte, the present invention prevents or reduces oxygen migration or dissociation on the cathode side where oxygen in the atmosphere migrates and dissociates. Since the means is configured, the oxygen ion concentration at the cathode from the atmosphere can be reduced to reduce or prevent an error current originating from oxygen ions from being generated in the detection output. Can increase accuracy and reliabilityRu.
[0045]
  In addition, the adoption of a cathode made of a metal inert to oxygen, or the adoption of a cathode having a smaller area than the anode makes it possible to manufacture a hydrocarbon sensor particularly easily and at low cost.
[0046]
  Furthermore, by providing the cathode with oxygen diffusion rate limiting means, oxygen absorbing means, or oxygen consuming means, it is possible to substantially remove oxygen before reaching the cathode, so hydrocarbon measurement in the presence of oxygen can be measured. The process can be executed with high accuracy without being substantially affected by the oxygen present in the atmosphere.
[Brief description of the drawings]
FIG. 1 is a longitudinal sectional view conceptually showing a limiting current type hydrocarbon sensor using a conventional barium cerium oxide based electrolyte layer.
FIG. 2 shows the hydrocarbon concentration and sensor current output in a hydrocarbon sensor using a silver electrode for the cathode.No sekiFIG.
FIG. 3 is a plan view (A) of a solid electrolyte layer showing electrode shapes of an anode and a cathode according to an embodiment and a partial longitudinal section (B) thereof.
FIG. 4 is a graph showing a relationship between a hydrocarbon concentration and a sensor current output in a hydrocarbon sensor having a small cathode area.
FIG. 5 is a plan view (A, B) showing the electrode shape of the cathode according to the example.
6 is a view similar to FIG. 2 in a limiting current type hydrocarbon sensor using a grid-like cathode in an example. FIG.
FIG. 7 is a schematic cross-sectional view of a limiting current type hydrocarbon sensor provided with oxygen diffusion rate limiting means on the cathode side.
FIG. 8 is a view similar to FIG. 2 in a hydrocarbon sensor provided with oxygen diffusion rate-limiting means according to an embodiment.
FIG. 9 is a schematic cross-sectional view of a limiting current type hydrocarbon sensor provided with oxygen consuming means on the cathode side.
FIG. 10 is a view showing a relationship between a hydrocarbon concentration and a sensor current output in a hydrocarbon sensor provided with an oxyfuel combustion consumption unit according to an example.
FIG. 11 is a schematic cross-sectional view of a limiting current type hydrocarbon sensor provided with oxygen absorbing means on the cathode side.
FIG. 12 is a diagram showing the relationship between the hydrocarbon concentration and the sensor current output of a hydrocarbon sensor provided with an oxygen absorbing means according to an example.
[Explanation of symbols]
    1 Solid electrolyte layer
    2 Anode
    3 Cathode
    4 Ceramic substrate
    40 Anode chamber
    42 Hydrocarbon diffusion controlled pores
    70 Cathode chamber
    72 Oxygen diffusion rate limiting hole
    8 Oxygen consumers
    9 Oxygen absorption layer

Claims (10)

Barium cerium oxide solid electrolyte layer having proton conductivity and oxygen ion conductivity, anode and cathode opposed to each other through the electrolyte layer, and hydrocarbon for controlling the diffusion and movement of hydrocarbons to the anode A hydrocarbon sensor comprising diffusion rate-limiting means and oxygen blocking / reducing means for blocking or reducing oxygen dissociation at the cathode or transfer to the cathode.   2. The hydrocarbon sensor according to claim 1, wherein the cathode is made of a metal inert to oxygen as the oxygen blocking / reducing means.   2. The hydrocarbon sensor according to claim 1, wherein as the oxygen blocking / reducing means, the area of the cathode is made smaller than the area of the anode.   4. The hydrocarbon sensor according to claim 3, wherein the cathode is provided with one or more openings or notches in a surface area thereof.   2. The hydrocarbon sensor according to claim 1, wherein as the oxygen blocking / reducing means, oxygen diffusion rate-limiting means for controlling the diffusion movement of oxygen to the cathode is used.   6. The hydrocarbon according to claim 5, wherein the oxygen diffusion rate limiting means is provided with diffusion rate limiting holes communicating with the inside and outside of a cathode chamber formed by covering the cathode with a ceramic substrate through a space. Sensor.   6. The hydrocarbon sensor according to claim 5, wherein the hydrocarbon sensor is of a limiting current type, and the oxygen diffusion rate controlling means has an oxygen absorbing means.   8. The hydrocarbon sensor according to claim 7, wherein the oxygen absorbing means is a continuously ventilated ceramic layer coated directly or indirectly on the cathode surface area.   9. The hydrocarbon sensor according to claim 8, wherein the oxygen absorbing means is made of a porous Ce-containing oxygen absorbing material covering the cathode.   2. The hydrocarbon sensor according to claim 1, further comprising oxygen consumption means for promoting catalytic combustion consumption of oxygen on the cathode side as the oxygen blocking / reducing means.

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