Gas sensor

Abstract

This gas sensor 1 detects a concentration of a gas being measured that is included in an environment being measured. The gas sensor 1 includes: at least one substrate 11; at least one reference electrode 12; at least one solid electrolyte body 13; a first detection electrode 21 for detecting a first oxygen concentration; a first diffusion porous body 22; a second detection electrode 31 for detecting a second oxygen concentration; a second diffusion porous body 32; and a gas concentration calculation part for calculating the concentration of the gas being measured by using the difference between the first oxygen concentration and the second oxygen concentration. The second diffusion porous body 32 has a catalytic function for promoting reaction.

Description

Gas Sensor

[0001] The present invention relates to a gas sensor that detects the concentration of a gas by utilizing the difference in diffusion coefficient between the gas and oxygen.

[0002] In recent years, hydrogen gas has been attracting attention as an alternative energy source to fossil fuels such as petroleum, and various systems utilizing hydrogen have been proposed. These hydrogen-based systems are equipped with gas sensors for detecting hydrogen.

[0003] Gas sensors for detecting hydrogen include various types of sensors, such as catalytic combustion type, thermal conduction type, and semiconductor type. For example, Patent Document 1 discloses a Si-MOSFET type hydrogen gas sensor that uses a platinum film as the gate electrode as an example of a semiconductor type gas sensor.

[0004] JP 2009-300297 A

[0005] When detecting hydrogen gas using various sensors such as catalytic combustion, thermal conduction, and semiconductor sensors, there are limitations on the range of gas temperatures and concentrations that can be used, and these sensors also have limitations on the environment in which they can be used, such as being unable to be used in condensation environments.

[0006] An object of the present invention is to provide a gas sensor that can be used in a wider range of environments.

[0007] [1] A gas sensor according to one aspect of the present invention detects the concentration of a target gas contained in a measurement environment. The gas sensor includes: at least one substrate; at least one reference electrode disposed on the substrate; at least one solid electrolyte body disposed on the reference electrode; a first sensing electrode disposed opposite the reference electrode across the solid electrolyte body and configured to detect a potential difference between the first sensing electrode and the reference electrode; a first diffusion porous body disposed between the first sensing electrode and the measurement environment; a second sensing electrode disposed opposite the reference electrode across the solid electrolyte body and configured to detect a potential difference between the first sensing electrode and the reference electrode; a second diffusion porous body disposed between the second sensing electrode and the measurement environment and configured to catalyze a reaction; and a gas concentration calculation unit configured to calculate a first oxygen concentration from the potential difference of the first sensing electrode, a second oxygen concentration from the potential difference of the second sensing electrode, and calculate the concentration of the target gas using the difference between the first and second oxygen concentrations.

[0008] Here, the second diffusion porous body having a catalytic function means either of the following: (1) The second diffusion porous body includes a diffusion porous body and a catalyst layer provided on the diffusion porous body to promote the reaction, or (2) The second diffusion porous body has a catalytic function to promote the reaction.

[0009] [2] The gas sensor according to one aspect of the present invention further comprises at least one of a first insulating layer made of a first insulating part and the first diffusion porous body and a second insulating layer made of a second insulating part and the second diffusion porous body, a hollow first measurement chamber is provided above the first sensing electrode and into which the gas to be measured that has passed through the first diffusion porous body flows, and a side surface of the first measurement chamber is surrounded by the first insulating layer made of the first insulating part and the first diffusion porous body, a hollow second measurement chamber is provided above the second sensing electrode and into which the gas to be measured that has passed through the second diffusion porous body flows, and a side surface of the second measurement chamber is surrounded by the second insulating layer made of the second insulating part and the second diffusion porous body, a third solid electrolyte body disposed above the first measurement chamber, and a fourth solid electrolyte body disposed above the second measurement chamber, The first pair of electrodes may be disposed on the upper and lower surfaces of the third solid electrolyte body, and the second pair of electrodes may be disposed on the upper and lower surfaces of the fourth solid electrolyte body.

[0010] [3] In the gas sensor according to any of the above aspects of the present invention, a hollow measurement chamber is provided above the first sensing electrode and into which the measurement target gas that has passed through the first diffusion porous body flows, a side surface of the measurement chamber is surrounded by an insulating layer made of an insulating portion and the first diffusion porous body, and the gas sensor has a second solid electrolyte body disposed above the measurement chamber, a third sensing electrode having the same potential as the first sensing electrode is provided on a surface of the measurement chamber facing the second solid electrolyte body, and the second sensing electrode may be provided on a surface of the second solid electrolyte body opposite to the measurement chamber.

[0011] [4] A gas sensor according to any of the above aspects of the present invention includes: an insulating layer disposed on a second solid electrolyte body disposed on the reference electrode, the insulating layer comprising an insulating portion and the second diffusion porous body; and a first solid electrolyte body disposed on the insulating layer, wherein the insulating layer has a hollow measurement chamber into which the measurement target gas that has passed through the second diffusion porous body flows, and a third detection electrode having the same potential as the second detection electrode is provided on a surface of the measurement chamber facing the first solid electrolyte body, and the first detection electrode may be provided on a surface of the first solid electrolyte body opposite to the surface on which the third detection electrode is provided.

[0012] [5] In the gas sensor according to any of the above aspects of the present invention, the gas concentration calculation unit may calculate the concentration of the target gas from the first oxygen concentration, the second oxygen concentration, and a difference in diffusion coefficient with respect to the target gas.

[0013] [6] In the gas sensor according to any one of the above aspects of the present invention, the measurement target gas may be any one of hydrogen gas, ammonia gas, and propane gas.

[0014] According to the present invention, it is possible to provide a gas sensor that can be used in a wider range of environments.

[0015] FIG. 11 is a cross-sectional view schematically illustrating the internal configuration of a gas sensor according to an embodiment. FIG. 12 is a cross-sectional view schematically illustrating the configuration of a gas concentration detection element provided in a gas sensor according to a first embodiment. FIG. 13 is a cross-sectional view schematically illustrating the configuration of a gas concentration detection element provided in a gas sensor according to a second embodiment. FIG. 14 is a cross-sectional view schematically illustrating the configuration of a gas concentration detection element provided in a gas sensor according to a third embodiment. FIG. 15 is a cross-sectional view schematically illustrating the configuration of a gas concentration detection element provided in a gas sensor according to a fourth embodiment. FIG. 16 is a cross-sectional view schematically illustrating the configuration of a gas concentration detection element provided in a gas sensor according to a modified example. FIG. 17 is a cross-sectional view schematically illustrating the configuration of a gas concentration detection element provided in a gas sensor according to a modified example. FIG. 18 is a cross-sectional view schematically illustrating the configuration of a gas concentration detection element provided in a gas sensor according to a modified example. FIG. 19 is a perspective view showing the general configuration of a limiting current type oxygen concentration detection element. FIG. 11 is a cross-sectional view schematically illustrating the configuration of an insulating layer portion of the oxygen concentration detection element shown in FIG. 10. FIG. 19 is a cross-sectional view schematically illustrating the configuration of a gas concentration detection element provided in a gas sensor according to a modified example. 10 is a cross-sectional view showing a configuration of a gas concentration detection element provided in a gas sensor according to a sixth embodiment. FIG. 11 is a cross-sectional view showing a configuration of a gas concentration detection element provided in a gas sensor according to a seventh embodiment. FIG. 12 is a cross-sectional view showing a configuration of a gas concentration detection element provided in a gas sensor according to a seventh embodiment. １ and K. ２ FIG. 10 is an image diagram for explaining the above.

[0016] Hereinafter, an embodiment of the present invention will be described with reference to the drawings. In the following description, the same components are denoted by the same reference numerals. The names and functions of the components are also the same. Therefore, detailed description thereof will not be repeated.

[0017] In this embodiment, a gas sensor that detects a gas concentration by utilizing the difference in diffusion coefficient with respect to oxygen will be described. The gas sensor has a gas concentration detection element that detects a gas concentration by utilizing the difference in diffusion coefficient with respect to oxygen. The gas sensor can detect, for example, any of hydrogen gas, ammonia gas, and propane gas as a measurement target gas. The following description will be given by taking as an example a gas sensor 1 that detects the concentration of hydrogen gas, which is one of the measurement target gases.

[0018] First, the overall configuration of the gas sensor 1 will be described. Fig. 1 shows the internal configuration of the gas sensor 1 according to one embodiment. The gas sensor 1 mainly includes a sensor unit 2, a housing 3, a sensor cover 4, an atmosphere-side cover 5, wiring 8, and a sensor control unit 9.

[0019] The sensor unit 2 has, for example, an elongated flat plate shape and is inserted and held inside a cylindrical housing 3. The sensor unit 2 includes a gas concentration detection element 10 and a heater (not shown). The gas concentration detection element 10 detects the concentration of a measurement target gas contained in a measurement environment. In this embodiment, the gas concentration detection element 10 detects the concentration of hydrogen gas contained in a mixed gas G that has flowed into the sensor cover 4.

[0020] The housing 3 is made of, for example, metal and holds the sensor unit 2 therein. The tip end side in the longitudinal direction of the sensor unit 2 (i.e., the lower end side in FIG. 1 ) protrudes from the housing 3 and is housed in a sensor cover 4.

[0021] The sensor cover 4 is attached to the tip side of the housing 3. The sensor cover 4 is arranged to surround the periphery of the tip of the sensor unit 2. The sensor cover 4 is provided with a through-hole that serves as an inlet / outlet for mixed gas G containing the measurement target gas and the like.

[0022] The mixed gas G that passes through the through-hole and flows into the sensor cover 4 reaches the surface of the sensor unit 2 and is taken in. The base end side in the longitudinal direction of the sensor unit 2 (i.e., the upper end side in FIG. 1 ) protrudes from the housing 3 and is housed in the atmosphere-side cover 5. The cylindrical atmosphere-side cover 5 has through-holes that open to the outer circumferential side and serve as atmosphere holes, allowing the atmosphere A, which serves as a reference gas, to be taken in. In another embodiment, a configuration may be employed in which a predetermined level of reference oxygen is generated within the oxygen sensor using oxygen accumulated in the reference electrode portion, and this is used as the reference gas concentration (a so-called self-generating gas sensor).

[0023] The base end side of the sensor unit 2 is connected to a sensor control unit 9 via wiring 8. The sensor control unit 9 includes a gas concentration calculation unit 41. As will be described later, the gas concentration calculation unit 41 is a component of the gas concentration detection element 10, and is connected to each electrode in the gas concentration detection element 10 via wiring 8. The gas concentration calculation unit 41 can calculate the potential difference between the electrodes included in the gas concentration detection element 10. The gas concentration calculation unit 41 can also calculate the concentration of the target gas based on an oxygen concentration (e.g., a first oxygen concentration and a second oxygen concentration) obtained based on the potential difference between the electrodes, the difference in diffusion coefficient between the target gas (e.g., hydrogen gas) and oxygen, and the reaction rate of the target gas on the catalyst.

[0024] The gas sensor 1 can be applied to any hydrogen utilization system, such as a fuel cell system. The gas sensor 1 is installed in a gas supply path or exhaust path through which a mixed gas G containing hydrogen gas flows, and can be used to detect the concentration of hydrogen gas in an atmosphere in which oxygen and multiple reducing gases coexist. The gas sensor 1 can also be used suitably in environments where conventional gas sensors cannot be used, such as condensation environments.

[0025] In the following, various embodiments will be described, each including a gas concentration detection element 10 having a different configuration. In the following description, the "gas concentration detection element" will also be simply referred to as the "detection element."

[0026] First Embodiment In the first embodiment, a gas sensor 1 will be described that includes a sensing element 10A, which is an example of a gas concentration sensing element 10. The sensing element 10A of this embodiment has a configuration that senses the oxygen concentration using the principle of a so-called zirconia oxygen sensor. Figure 2 shows the configuration of the sensing element 10A.

[0027] The sensing element 10A includes a substrate 11, a reference electrode 12, a solid electrolyte body 13, a first sensing electrode 21, a first diffusion porous body 22, a second sensing electrode 31, a second diffusion porous body 32, a catalyst layer 33, and a gas concentration calculation unit 41 (see FIG. 1 ). The substrate 11 is made of an insulating material. In one example, the substrate 11 contains alumina as a main component.

[0028] The reference electrode 12 is disposed on the substrate 11. The reference electrode 12 is formed of a platinum group element such as Pt, Pd, a Pt alloy, or a Pd alloy. The reference electrode 12 is configured to come into contact with a reference gas. The reference gas is, for example, the atmosphere. That is, the reference electrode 12 is configured to come into contact with the atmosphere A taken in through the atmosphere-side cover 5 of the gas sensor 1.

[0029] The solid electrolyte body 13 is disposed on the reference electrode 12. The solid electrolyte body 13 is made of, for example, zirconia (ZrO ２ ) with yttria (Y) as a stabilizer ２ O ３ It is composed of a partially stabilized zirconia sintered body to which zirconia (ZrO) or calcia (CaO) is added.

[0030] The first sensing electrode 21 is disposed at a position facing the reference electrode 12 with the solid electrolyte body 13 sandwiched therebetween. The first sensing electrode 21 is formed of a platinum group element such as Pt, Pd, a Pt alloy, or a Pd alloy, similar to the reference electrode 12. The first sensing electrode 21 detects a first oxygen concentration using the potential difference between itself and the reference electrode 12.

[0031] The first diffusion porous body 22 is provided between the first sensing electrode 21 and the environment to be measured. Specifically, the first diffusion porous body 22 is provided so as to cover the first sensing electrode 21 (see FIG. 2). The first diffusion porous body 22 is exposed to the space inside the sensor cover 4 into which the mixed gas G flows. Therefore, the interior of the sensor cover 4 is the environment to be measured.

[0032] The first diffusion porous body 22 is made of alumina (Al ２ O ３ The first diffusion porous body 22 is provided between the first sensing electrode 21 and the environment to be measured, thereby adjusting the speed at which the mixed gas G in the environment to be measured reaches the first sensing electrode 21. For this reason, the first diffusion porous body 22 is also called a rate-controlling layer.

[0033] The second sensing electrode 31 is disposed opposite the reference electrode 12 with the solid electrolyte body 13 sandwiched therebetween. The second sensing electrode 31 is formed of a platinum group element such as Pt, Pd, a Pt alloy, or a Pd alloy, similar to the first sensing electrode 21. The second sensing electrode 31 detects the second oxygen concentration using the potential difference between itself and the reference electrode 12.

[0034] The second diffusion porous body 32 is provided between the second sensing electrode 31 and the environment to be measured. Specifically, the second diffusion porous body 32 is provided so as to cover the second sensing electrode 31 (see FIG. 2).

[0035] The second diffusion porous body 32 is made of alumina (Al ２ O ３ The second diffusion porous body 32 is provided between the second sensing electrode 31 and the environment to be measured, thereby adjusting the speed at which the mixed gas G in the environment to be measured reaches the second sensing electrode 31. For this reason, the second diffusion porous body 32 is also called a rate-controlling layer.

[0036] A catalyst layer 33 is provided on the second diffusion porous body 32 so as to cover the entire surface exposed to the environment to be measured, and promotes the reaction. That is, the catalyst layer 33 decomposes hydrogen contained in the environment to generate hydrogen ions and promotes the reaction of the generated hydrogen ions and electrons with oxygen in the air to produce water. The catalyst layer 33 is formed of, for example, a platinum (Pt) catalyst or a palladium (Pd) catalyst.

[0037] With the above-described configuration, the solid electrolyte body 13 and a pair of electrodes (specifically, the reference electrode 12 and the first sensing electrode 21, and the reference electrode 12 and the second sensing electrode 31) sandwiching the solid electrolyte body 13 form an oxygen concentration cell, which can output an electromotive force corresponding to the oxygen concentration in the mixed gas G.

[0038] A first diffusion porous body 22 is provided between the first sensing electrode 21 and the environment to be measured. This adjusts the speed at which the mixed gas G in the environment to be measured reaches the first sensing electrode 21. Here, hydrogen (H ２ ) is oxygen (O ２ ) and other combustible gases. As a result, the mixed gas G passes through the first diffusion porous body 22 and the oxygen partial pressure ([O ２ ]' １ ) decreases under the influence of hydrogen.

[0039] On the other hand, a second diffusion porous body 32 covered with a catalyst layer 33 is provided between the second sensing electrode 31 and the environment to be measured. As a result, when the mixed gas G in the environment to be measured reaches the second sensing electrode 31, it first passes through the catalyst layer 33. In the catalyst layer 33, oxygen (O ２ ) and hydrogen (H ２ ) reacts with the element, and a part of the reaction rate α specific to the element is equilibrated. Therefore, in the second sensing electrode 31, oxygen (O ２ ) and hydrogen (H ２ ) diffusion rate to reduce the effect of oxygen partial pressure ([O ２ ]' ２ ) can be measured.

[0040] The gas concentration calculation unit 41 calculates the concentration of the measurement target gas using the difference between the first oxygen concentration and the second oxygen concentration.

[0041] The first oxygen concentration is an oxygen concentration calculated using the potential difference between the first sensing electrode 21 and the reference electrode 12. In this embodiment, the first oxygen concentration is an oxygen partial pressure ([O ２ ]' １ ) means

[0042] The second oxygen concentration is an oxygen concentration calculated using the potential difference between the second sensing electrode 31 and the reference electrode 12. In this embodiment, the second oxygen concentration is calculated based on the oxygen partial pressure ([O ２ ]' ２ ) means

[0043] More specifically, the gas concentration calculation unit 41 calculates the concentration of the target gas from the difference between the first oxygen concentration and the second oxygen concentration, the difference between the diffusion coefficient of oxygen gas and the diffusion coefficient of the target gas, and the reaction rate of the target gas on the catalyst.

[0044] Here, when the gas to be measured is hydrogen gas, the hydrogen gas concentration ([H ２ ]) is calculated using the following formula 1.

[0045]

[0046] In the above formula 1, each symbol has the following meaning: ２ ]' １ : First oxygen concentration [O ２ ]' ２ : second oxygen concentration detected by the second sensing electrode D Ｈ２ : Diffusion coefficient of hydrogen gas D Ｏ２ : Diffusion coefficient of oxygen gas α: H ２ O ２ Response rate to

[0047] The hydrogen gas concentration ([H ２ ]) may be calculated from the following formula 2 obtained based on the above formula 1.

[0048] In the above formula 2, K１ =D Ｈ２ / D Ｏ２ and K ２ = {α + (1-α) K １}. K １ and K. ２ can be determined experimentally.

[0049] In FIG. １ and K. ２ The image of the measurement is shown in FIG. ２ +1 / 2O ２ = H ２ From O, H of concentration X ２ When burned, O with a concentration of X / 2 ２ In addition, in Table 1, K １ and K. ２ The actual measurement results and an example of the calculated value of α are shown below. １ and K. ２ It can be calculated from the measured values ​​by the following formula: α = (K ２ -K １ ) / (1-K １ )

[0050]

[0051] Oxygen concentration in the oxygen-containing space [O ２ ] sensor output [O ２ ] Ｓ１ and the sensor output when hydrogen of concentration X is mixed into the space [O ２ ] Ｓ２ Also, measure [O ２ ] Ｓ１ - [O ２ ] Ｓ２ =ΔO ２ Let's say.

[0052] Here, K １ is the sensor output for the sensor without a catalyst, and ΔO ２ The ratio of (i.e., K １ =ΔO ２ / (X / 2)). Also, K ２ is the sensor output when the catalyst is present, and ΔO is the ratio of X / 2 to ２The ratio of (i.e., K ２ =ΔO ２ / (X / 2)).

[0053] The diffusion coefficients of hydrogen gas and oxygen gas in the atmosphere (m ２ / s) are as follows: Hydrogen gas: D Ｈ２ = 6.65 x 10 －５ Oxygen gas: D Ｏ２ = 1.80 x 10 －５

[0054] Diffusion coefficients of other target gases in the atmosphere (m ２ / s) are as follows: Ammonia gas: D ＮＨ３ = 0.844 × 10 －５ Propane gas: D Ｃ３Ｈ８ = 0.987 × 10 －５

[0055] As described above, the sensing element 10A according to this embodiment senses the concentration of a target gas, such as hydrogen gas, contained in a mixed gas G in a measurement environment. The sensing element 10A includes at least one substrate 11, at least one reference electrode 12, at least one solid electrolyte body 13, a first sensing electrode 21 for sensing a first oxygen concentration, a first diffusion porous body 22, a second sensing electrode 31 for sensing a second oxygen concentration, and a second diffusion porous body 32. The second diffusion porous body 32 is provided with a catalyst layer 33 that promotes a reaction. The catalyst layer 33 is provided so as to cover the entire surface of the second diffusion porous body 32 that is exposed to the measurement environment.

[0056] The sensing element 10A also has a gas concentration calculation unit 41. The gas concentration calculation unit 41 calculates the concentration of the target gas based on the difference between the first oxygen concentration and the second oxygen concentration and the difference between the diffusion coefficient of oxygen gas and the diffusion coefficient of the target gas.

[0057] According to the above configuration, the first sensing electrode 21 and the second sensing electrode 31 detect the oxygen concentration in the mixed gas G, thereby making it possible to detect the concentration of hydrogen gas contained in the mixed gas G. The sensing element 10A having the above configuration can detect a wider range of gas concentrations than methods of detecting hydrogen gas using various sensors such as catalytic combustion type, thermal conduction type, and semiconductor type. Furthermore, the sensing element 10A can be used in a wider range of temperature environments or in condensation environments.

[0058] Therefore, the gas sensor 1 including the sensing element 10A can measure the concentration of a target gas such as hydrogen gas under a wider range of environmental conditions. For example, when measuring the concentration of hydrogen gas using the gas sensor 1, the concentration of hydrogen gas can be detected regardless of the gas composition as long as the environment contains any of oxygen, water, and carbon dioxide.

[0059] This makes it possible to provide a more versatile gas sensor 1. The gas sensor 1 can be used to detect hydrogen in, for example, a hydrogen production process, a methanation process, a hydrogen engine, a hydrogen burner, and the like.

[0060] Second Embodiment In the second embodiment, a gas sensor 1 including a detection element 10B, which is an example of a gas concentration detection element 10, will be described. In the first embodiment, the detection element 10A including one base, one reference electrode, and one solid electrolyte body was described. However, the number of bases, reference electrodes, and solid electrolyte bodies is not limited to one. In this embodiment, a detection element including two bases, two reference electrodes, and two solid electrolyte bodies will be described.

[0061] 3 shows the configuration of the sensor element 10B. The sensor element 10B includes two substrates (a first substrate 11a and a second substrate 11b), two reference electrodes (a first reference electrode 12a and a second reference electrode 12b), two solid electrolyte bodies (a first solid electrolyte body 13a and a second solid electrolyte body 13b), a first sensing electrode 21, a first porous diffusion body 22, a second sensing electrode 31, a second porous diffusion body 32, a catalyst layer 33, and a gas concentration calculation unit 41 (see FIG. 1). The substrates contain alumina as a main component.

[0062] The first reference electrode 12a is disposed on the first substrate 11a. The first solid electrolyte body 13a is disposed on the first reference electrode 12a. The first sensing electrode 21 is disposed at a position facing the first reference electrode 12a with the first solid electrolyte body 13a interposed therebetween, and detects a first oxygen concentration ([O ２ ]' １ ) is detected.

[0063] The second reference electrode 12b is disposed on the second substrate 11b. The second solid electrolyte body 13b is disposed on the second reference electrode 12b. The second sensing electrode 31 is disposed at a position facing the second reference electrode 12b with the second solid electrolyte body 13b interposed therebetween, and detects a second oxygen concentration ([O ２ ]' ２ ) is detected.

[0064] The first diffusion porous body 22, the second diffusion porous body 32, the catalyst layer 33, and the gas concentration calculation unit 41 can have the same configuration as in the first embodiment.

[0065] Third Embodiment In the third embodiment, a gas sensor 1 including a sensing element 10C, which is an example of a gas concentration sensing element 10, will be described. In the first embodiment, a configuration was described in which a catalyst layer that promotes a reaction is provided on the second diffusion porous body so as to cover the entire surface exposed to the measurement environment. However, in another embodiment, the rate-limiting layer itself may have a catalytic function that promotes a reaction. Therefore, in this embodiment, a sensing element 10C having such a configuration will be described.

[0066] 4 shows the configuration of the detector element 10C, which includes one base 11, one reference electrode 12, one solid electrolyte body 13, a first detection electrode 21, a first diffusion porous body 22, a second detection electrode 31, a second diffusion porous body 132, and a gas concentration calculation unit 41 (see FIG. 1).

[0067] The second diffusion porous body 132 is provided between the second sensing electrode 31 and the environment to be measured, and has a catalytic function for promoting a reaction. The second diffusion porous body 132 is made of alumina (Al ２ O ３ The second diffusion porous body 132 is obtained by adding a catalyst such as a platinum (Pt) catalyst or a palladium (Pd) catalyst to a porous body made of a metal (ZnO) or a nickel (Ni) based on the oxygen (O ) contained in the mixed gas G when the mixed gas G in the measurement environment passes through the second diffusion porous body 132 and reaches the second sensing electrode 31. ２ ) and hydrogen (H ２ ) reacts with the second sensing electrode 31 to form an equilibrium. ２ ) and hydrogen (H ２ ) diffusion rate to reduce the effect of oxygen partial pressure ([O ２ ]' ２ ) can be measured. Therefore, the sensing element 10C does not have a catalyst layer.

[0068] Other than the above, the same configuration as in the first embodiment can be applied. (Fourth Embodiment) In the fourth embodiment, a gas sensor 1 including a sensing element 10D, which is an example of a gas concentration sensing element 10, will be described. In this embodiment, a sensing element having two substrates, two reference electrodes, and two solid electrolyte bodies will be described, as in the second embodiment. Also, in this embodiment, a configuration will be described in which the rate-limiting layer itself has a catalytic function that promotes the reaction, as in the third embodiment.

[0069] 5 shows the configuration of the detector element 10D. The detector element 10D has two substrates (a first substrate 11a and a second substrate 11b), two reference electrodes (a first reference electrode 12a and a second reference electrode 12b), two solid electrolyte bodies (a first solid electrolyte body 13a and a second solid electrolyte body 13b), a first sensing electrode 21, a first diffusion porous body 22, a second sensing electrode 31, a second diffusion porous body 132, and a gas concentration calculation unit 41 (see FIG. 1).

[0070] The second diffusion porous body 132 is provided between the second sensing electrode 31 and the environment to be measured, as in the third embodiment, and has a catalytic function to promote the reaction. Other configurations are the same as those in the second embodiment.

[0071] (Modifications) Modifications of the first to fourth embodiments will be described below. Figures 6 to 8 show the configurations of the detection elements according to the modifications. In the modifications shown below, the number of base bodies, reference electrodes, and solid electrolyte bodies differs from that of the above-described embodiments. Other configurations can be applied that are similar to those of any of the above-described embodiments.

[0072] 6 includes one base 11, one reference electrode 12, two solid electrolyte bodies (a first solid electrolyte body 13a and a second solid electrolyte body 13b), a first sensing electrode 21, a first diffusion porous body 22, a second sensing electrode 31, a second diffusion porous body 32, a catalyst layer 33, and a gas concentration calculation unit 41 (see FIG. 1). An insulator 18 is provided between the first solid electrolyte body 13a and the second solid electrolyte body 13b so as to cover the reference electrode 12.

[0073] The detector element 10F shown in FIG. 7 has one base 11, two reference electrodes (a first reference electrode 12a and a second reference electrode 12b), two solid electrolyte bodies (a first solid electrolyte body 13a and a second solid electrolyte body 13b), a first detection electrode 21, a first diffusion porous body 22, a second detection electrode 31, a second diffusion porous body 32, a catalyst layer 33, and a gas concentration calculation unit 41 (see FIG. 1).

[0074] The detector element 10G shown in FIG. 8 includes one base 11, two reference electrodes (a first reference electrode 12a and a second reference electrode 12b), two solid electrolyte bodies (a first solid electrolyte body 13a and a second solid electrolyte body 13b), a first detection electrode 21, a first diffusion porous body 22, a second detection electrode 31, a second diffusion porous body 32, a catalyst layer 33, and a gas concentration calculation unit 41 (see FIG. 1).

[0075] In the modifications shown in FIGS. 6 to 8, a second porous diffusion body 132 may be provided in place of the second porous diffusion body 32 and the catalyst layer 33.

[0076] Fifth Embodiment In the above-described embodiments, a sensing element having a configuration for detecting oxygen concentration using the principle of a zirconia oxygen sensor has been described. Hereinafter, a sensing element including a configuration for detecting oxygen concentration using the principle of a limiting current oxygen sensor in addition to the principle of a zirconia oxygen sensor will be described.

[0077] 9 shows the configuration of a gas concentration sensing element 200A according to this embodiment. The gas concentration sensing element 200A has two oxygen concentration sensing elements: a first oxygen concentration sensing element 210a that does not have a catalytic layer, and a second oxygen concentration sensing element 210b that has a catalytic layer. These two oxygen concentration sensing elements 210a and 210b both detect oxygen concentration using the principle of a limiting current type oxygen sensor.

[0078] Fig. 10 shows a schematic configuration of an oxygen concentration sensing element 210, which is an example of a limiting current type oxygen concentration sensing element. Fig. 11 shows a schematic configuration of a horizontal cross section of an insulating layer 220 of the oxygen concentration sensing element 210. The oxygen concentration sensing element 210 is formed of a plate-shaped substrate 211. A measurement chamber 215 and the like are provided at one end of the substrate 211. A connection terminal 252 is provided at the other end of the substrate 211. A plurality of connection terminals 252 are provided corresponding to the respective electrodes. The connection terminals 252 are connected to a gas concentration calculation unit 41 in the sensor control unit 9 via wiring 8.

[0079] One end of the base 211 (i.e., the end where the measurement chamber 215 is provided) may be covered with a breathable porous protective film 251. The measurement chamber 215 is formed by forming an opening in a portion of the insulating layer 220. The side of the measurement chamber 215 is surrounded by an insulating portion (e.g., first insulating portion 223) and a diffusion porous body (e.g., first diffusion porous body 222). The cross-sectional views of the oxygen concentration detection elements shown in Figure 9 and elsewhere correspond to the cross-sectional configuration taken along line A-A in Figure 11.

[0080] As shown in FIG. 9, the gas concentration detection element 200A has a first oxygen concentration detection element 210a that does not have a catalyst layer, a second oxygen concentration detection element 210b that has a catalyst layer 233, and a gas concentration calculation unit 41 (see FIG. 1).

[0081] The first oxygen concentration sensing element 210a has a first base 211a, a first reference electrode 212a, a first solid electrolyte body 213a, a first sensing electrode 221, a first insulating layer 220, a third solid electrolyte body 214a, a first ventilation layer 216a, and a first pair of electrodes 217a.

[0082] The first insulating layer 220 includes a first insulating portion 223 and a first diffusion porous body 222. A hollow first measurement chamber 215a is present above the first sensing electrode 221, into which the mixed gas G (containing the measurement target gas and oxygen gas) that has passed through the first diffusion porous body 222 flows. The side of the first measurement chamber 215a is surrounded by a first insulating layer 220 consisting of the first insulating portion 223 and the first diffusion porous body 222.

[0083] The third solid electrolyte body 214a is disposed above the first measurement chamber 215a and functions as an oxygen pump cell. The first pair of electrodes 217a are disposed on the upper and lower surfaces of the third solid electrolyte body 214a.

[0084] In the first oxygen concentration sensing element 210a, the direction and magnitude of the current flowing between the first pair of electrodes 217a arranged with the third solid electrolyte body 214a therebetween are adjusted so that the voltage (electromotive force) generated between the electrodes arranged with the first solid electrolyte body 213a therebetween (i.e., between the first reference electrode 212a and the first sensing electrode 221) becomes a predetermined value (e.g., 450 mV). This makes it possible to linearly detect the oxygen concentration in the mixed gas G in accordance with the current flowing through the third solid electrolyte body 214a.

[0085] With the above configuration, the first oxygen concentration detection element 210a detects the first oxygen concentration ([O ２ ]' １ ) is detected.

[0086] The second oxygen concentration sensing element 210b has a second base 211b, a second reference electrode 212b, a second solid electrolyte body 213b, a second sensing electrode 231, a second insulating layer 230, a fourth solid electrolyte body 214b, a second ventilation layer 216b, and a second pair of electrodes 217b.

[0087] The second insulating layer 230 includes a second insulating portion (not shown) and a second diffusion porous body 232. The second diffusion porous body 232 is provided with a catalyst layer 233 that covers the entire surface exposed to the measurement environment. That is, the catalyst layer 233 decomposes hydrogen contained in the measurement environment to generate hydrogen ions and promotes a reaction in which the generated hydrogen ions and electrons react with oxygen in the air to produce water. Like the catalyst layer 33, the catalyst layer 233 is formed of, for example, a platinum (Pt) catalyst or a palladium (Pd) catalyst.

[0088] A hollow second measurement chamber 215b is present above the second sensing electrode 231, into which the mixed gas G (containing the measurement target gas and oxygen gas) flows after passing through the catalyst layer 233 and the second diffusion porous body 232. The side of the second measurement chamber 215b is surrounded by a second insulating layer 230 made up of a second insulating portion 234 and the second diffusion porous body 232.

[0089] The fourth solid electrolyte body 214b is disposed above the second measurement chamber 215b and functions as an oxygen pump cell. The second pair of electrodes 217b are disposed on the upper and lower surfaces of the fourth solid electrolyte body 214b.

[0090] In the second oxygen concentration sensing element 210b, the direction and magnitude of the current flowing between the second pair of electrodes 217b arranged with the fourth solid electrolyte body 214b therebetween are adjusted so that the voltage (electromotive force) generated between the electrodes arranged with the second solid electrolyte body 213b therebetween (i.e., between the second reference electrode 212b and the second sensing electrode 231) becomes a predetermined value (e.g., 450 mV). This makes it possible to linearly detect the oxygen concentration in the mixed gas G in accordance with the current flowing through the fourth solid electrolyte body 214b.

[0091] With the above configuration, the second oxygen concentration detection element 210b detects the second oxygen concentration ([O ２ ]' ２ ) is detected.

[0092] The gas concentration calculation unit 41 calculates the concentration of the target gas from the difference between the first oxygen concentration detected by the first oxygen concentration detection element 210a and the second oxygen concentration detected by the second oxygen concentration detection element 210b, the difference between the diffusion coefficient of oxygen gas and the diffusion coefficient of the target gas, and the reaction rate of the target gas on the catalyst.

[0093] The calculation method here can be the method described in the first embodiment. For example, when the measurement target gas is hydrogen gas, the hydrogen gas concentration ([H ２ ]) is calculated using Equation 1 above.

[0094] In addition, in the second oxygen concentration detection element 210b of this embodiment, a second diffusion porous body 132 (see the third embodiment) having catalytic function can also be provided instead of the second diffusion porous body 232 and the catalyst layer 233.

[0095] (Modifications) FIGS. 12 and 13 show the configuration of a modification of the gas concentration detection element 200A.

[0096] In the gas concentration sensing element 200B shown in FIG. 12, the configuration of the second oxygen concentration sensing element 210c is different from that of the second oxygen concentration sensing element 210b described above. The second oxygen concentration sensing element 210c has a configuration similar to that of the element on the right side of the sensing element 10B shown in FIG. 3. In the second oxygen concentration sensing element 210c, the second oxygen concentration ([O ２ ]' ２ ) is detected.

[0097] In the gas concentration sensing element 200C shown in FIG. 13, the configuration of the first oxygen concentration sensing element 210d is different from that of the first oxygen concentration sensing element 210a described above. The first oxygen concentration sensing element 210d has a configuration similar to that of the element on the left side of the sensing element 10B shown in FIG. 3. In the first oxygen concentration sensing element 210d, a first oxygen concentration ([O ２ ]' １ ) is detected.

[0098] Sixth Embodiment In a sixth embodiment, a gas sensor 1 including a sensing element 310 that is an example of the gas concentration sensing element 10 will be described.

[0099] 14 shows the configuration of the sensor element 310. The sensor element 310 has a base 311, a reference electrode 312, a plurality of solid electrolyte bodies (a first solid electrolyte body 313a and a second solid electrolyte body 313b), a plurality of sensing electrodes (a first sensing electrode 321, a second sensing electrode 331, and a third sensing electrode 341), two diffusion porous bodies (a first diffusion porous body 322 and a second diffusion porous body 332), a catalyst layer 333, and a gas concentration calculation unit 41 (see FIG. 1).

[0100] The first solid electrolyte body 313a is disposed on the reference electrode 312. A first sensing electrode 321 is disposed on the first solid electrolyte body 313a. A hollow measurement chamber 315 is located above the first sensing electrode 321, into which the mixed gas G (containing the measurement target gas and oxygen gas) that has passed through the first diffusion porous body 322 flows. The side of the measurement chamber 315 is surrounded by an insulating layer 320 made of an insulating portion (not shown) and the first diffusion porous body 322.

[0101] The second solid electrolyte body 313b is disposed above the measurement chamber 315. A third sensing electrode 341 having the same potential as the first sensing electrode 321 is provided on the surface of the measurement chamber 315 facing the second solid electrolyte body 313b. The second sensing electrode 331 is provided on the surface of the second solid electrolyte body 313b opposite the measurement chamber 315.

[0102] The second diffusion porous body 332 is provided with a catalyst layer 333 that covers the entire surface exposed to the measurement environment. That is, the catalyst layer 333 decomposes hydrogen contained in the measurement environment to generate hydrogen ions and promotes a reaction in which the generated hydrogen ions and electrons react with oxygen in the air to produce water. The catalyst layer 333 is formed of, for example, a platinum (Pt) catalyst or a palladium (Pd) catalyst, similar to the catalyst layer 33.

[0103] With the above configuration, the first sensing electrode 321 detects the first oxygen concentration ([O ２ ]' １ ) is detected. In addition, the second sensing electrode 331 detects a second oxygen concentration ([O ２ ]' ２ ) is detected.

[0104] The gas concentration calculation unit 41 calculates the concentration of the target gas from the difference between the first oxygen concentration and the second oxygen concentration, the difference between the diffusion coefficient of oxygen gas and the diffusion coefficient of the target gas, and the reaction rate of the target gas on the catalyst.

[0105] The calculation method here can be the method described in the first embodiment. For example, when the measurement target gas is hydrogen gas, the hydrogen gas concentration ([H ２ ]) is calculated using Equation 1 above.

[0106] In addition, in the detection element 310 of this embodiment, a second diffusion porous body 132 (see the third embodiment) having catalytic function can be provided instead of the second diffusion porous body 332 and the catalyst layer 333.

[0107] Seventh Embodiment In a seventh embodiment, a gas sensor 1 including a sensing element 410 that is an example of the gas concentration sensing element 10 will be described.

[0108] 15 shows the configuration of the sensor element 410. The sensor element 410 has a base 411, a reference electrode 412, a plurality of solid electrolyte bodies (a first solid electrolyte body 413a and a second solid electrolyte body 413b), a plurality of sensing electrodes (a first sensing electrode 421, a second sensing electrode 431, and a third sensing electrode 441), two diffusion porous bodies (a first diffusion porous body 422 and a second diffusion porous body 432), a catalyst layer 433, and a gas concentration calculation unit 41 (see FIG. 1).

[0109] The second solid electrolyte body 413b is disposed on the reference electrode 412. A second sensing electrode 431 is disposed on the second solid electrolyte body 413b. A hollow measurement chamber 415 is located above the second sensing electrode 431, into which the mixed gas G (containing the measurement target gas and oxygen gas) that has passed through the second diffusion porous body 432 flows. The side of the measurement chamber 415 is surrounded by an insulating layer 430 made of an insulating portion (not shown) and the second diffusion porous body 432.

[0110] The first solid electrolyte body 413a is disposed above the measurement chamber 415. A third sensing electrode 441 having the same potential as the second sensing electrode 431 is provided on the surface of the measurement chamber 415 facing the first solid electrolyte body 413a. The first sensing electrode 421 is provided on the surface of the first solid electrolyte body 413a opposite the measurement chamber 415.

[0111] A catalyst layer 433 is provided on the second diffusion porous body 432 so as to cover the entire surface exposed to the measurement environment. As a result, the mixed gas G (containing the measurement target gas and oxygen gas) in the measurement environment passes through the catalyst layer 433, then passes through the second diffusion porous body 432 and flows into the measurement chamber 415.

[0112] With the above configuration, the first sensing electrode 421 detects the first oxygen concentration ([O ２ ]' １ ) is detected. In addition, the second sensing electrode 431 detects a second oxygen concentration ([O ２ ]'２ ) is detected.

[0113] The gas concentration calculation unit 41 calculates the concentration of the target gas from the difference between the first oxygen concentration and the second oxygen concentration, the difference between the diffusion coefficient of oxygen gas and the diffusion coefficient of the target gas, and the reaction rate of the target gas on the catalyst.

[0114] The calculation method here can be the method described in the first embodiment. For example, when the measurement target gas is hydrogen gas, the hydrogen gas concentration ([H ２ ]) is calculated using Equation 1 above.

[0115] In addition, in the detection element 410 of this embodiment, a second diffusion porous body 132 (see the third embodiment) having catalytic function can be provided instead of the second diffusion porous body 432 and the catalyst layer 433.

[0116] The embodiments disclosed herein should be considered to be illustrative in all respects and not restrictive. The scope of the present invention is defined by the claims, not by the above description, and is intended to include all modifications within the meaning and scope of the claims. Furthermore, configurations obtained by combining the configurations of the different embodiments described herein are also included in the scope of the present invention. In the present embodiment, a plate-shaped gas concentration sensing element has been described as an example of a gas concentration sensing element, but the gas concentration sensing element according to the present invention may also be a bottomed, cylindrical gas concentration sensing element.

[0117] 1: Gas sensor 10, 200, 310, 410: Gas concentration detection element 11, 211, 311, 411: Base 12, 212, 312, 412: Reference electrode 13, 213, 214, 313, 413: Solid electrolyte body 214a: Third solid electrolyte body 214b: Fourth solid electrolyte body 21, 221, 321, 421: First detection electrode 31, 231, 331, 431: Second detection electrode 22, 222, 322, 422: First diffusion porous body 32, 132, 232, 332, 432: Second diffusion porous body 33, 233, 333, 433: Catalyst layer 215, 315, 415: Measurement chamber 220, 230, 320, 430: insulating layers 341, 441: third sensing electrodes 41: gas concentration calculation section

Claims

1. A gas sensor for detecting the concentration of a target gas contained in a measurement environment, comprising: at least one substrate; at least one reference electrode disposed on the substrate; at least one solid electrolyte body disposed on the reference electrode; a first detection electrode disposed opposite the reference electrode with the solid electrolyte body interposed therebetween and detecting a potential difference between the reference electrode; a first diffusion porous body provided between the first detection electrode and the measurement environment; a second detection electrode disposed opposite the reference electrode with the solid electrolyte body interposed therebetween and detecting a potential difference between the reference electrode; a second diffusion porous body provided between the second detection electrode and the measurement environment and having a catalytic function for promoting a reaction; and a gas concentration calculation unit that calculates a first oxygen concentration from the potential difference of the first detection electrode, calculates a second oxygen concentration from the potential difference of the second detection electrode, and calculates the concentration of the target gas using the difference between the first oxygen concentration and the second oxygen concentration.

2. The gas sensor further comprises at least one of a first insulating layer consisting of a first insulating part and the first diffusion porous body and a second insulating layer consisting of a second insulating part and the second diffusion porous body, wherein a hollow first measurement chamber is located above the first sensing electrode and into which the gas to be measured that has passed through the first diffusion porous body flows, the sides of the first measurement chamber being surrounded by the first insulating layer consisting of the first insulating part and the first diffusion porous body, and a hollow second measurement chamber is located above the second sensing electrode and into which the gas to be measured that has passed through the second diffusion porous body flows, the sides of the second measurement chamber being surrounded by the second insulating layer consisting of the second insulating part and the second diffusion porous body, and wherein the gas sensor further comprises a third solid electrolyte body located above the first measurement chamber and a fourth solid electrolyte body located above the second measurement chamber, wherein a first pair of electrodes are located on the upper and lower surfaces of the third solid electrolyte body and a second pair of electrodes are located on the upper and lower surfaces of the fourth solid electrolyte body.

2. The gas sensor according to claim 1.

3. The gas sensor according to claim 1, wherein a hollow measuring chamber is provided above the first sensing electrode and into which the gas to be measured that has passed through the first diffusion porous body flows, the side of the measuring chamber is surrounded by an insulating layer consisting of an insulating part and the first diffusion porous body, and the gas sensor has a second solid electrolyte body disposed above the measuring chamber, a third sensing electrode having the same potential as the first sensing electrode is provided on the surface of the measuring chamber facing the second solid electrolyte body, and the second sensing electrode is provided on the surface of the second solid electrolyte body opposite to the measuring chamber.

4. A gas sensor according to claim 1, comprising: an insulating layer disposed on a second solid electrolyte body disposed on the reference electrode and consisting of an insulating portion and the second diffusion porous body; and a first solid electrolyte body disposed on the insulating layer, wherein the insulating layer has a hollow measurement chamber into which the gas to be measured that has passed through the second diffusion porous body flows, and a third detection electrode having the same potential as the second detection electrode is provided on a surface of the measurement chamber facing the first solid electrolyte body, and the first detection electrode is provided on the surface of the first solid electrolyte body opposite to the surface on which the third detection electrode is provided.

5. The gas sensor according to any one of claims 1 to 4, wherein the gas concentration calculation unit calculates the concentration of the target gas from the first oxygen concentration, the second oxygen concentration, and the difference in diffusion coefficient with the target gas.

6. The gas sensor according to any one of claims 1 to 4, wherein the gas to be measured is any one of hydrogen gas, ammonia gas, and propane gas.