gas sensor

Abstract

This invention provides a gas sensor capable of accurately measuring the concentration of hydrogen gas in a gas under test over a wide concentration range. [Solution] The gas sensor 100 includes a sensor element 101 and a control device. The sensor element 101 includes a base portion 101 that includes a proton-conducting first solid electrolyte 4 and second solid electrolytes 5 and 6 that have lower proton-conducting resistance than the first solid electrolyte 4; a current measuring pump cell 21 that includes an in-space measuring electrode 22 disposed on the second solid electrolyte 6 in an internal cavity 20; a voltage detection sensor cell 31 that includes a reference electrode 32 disposed on the first solid electrolyte 4 in a reference gas chamber 30, and a detection electrode 23 disposed from the reference electrode 32 at least via the first solid electrolyte 4. The concentration calculation unit of the control device calculates the hydrogen concentration in the gas to be measured based on the electromotive force V2 generated in the voltage detection sensor cell 31, and / or calculates the hydrogen concentration in the gas to be measured based on the current Ip1 flowing through the current measuring pump cell 21.

Description

[Technical Field]

[0001] The present invention relates to a gas sensor that includes a sensor element using a proton-conducting solid electrolyte and detects hydrogen gas in a gas to be measured. [Background technology]

[0002] As an example of a gas sensor that detects hydrogen gas in a gas to be measured, a gas sensor using a proton-conducting solid electrolyte (proton conductor) is known (for example, Japanese Patent Publication No. 2022-189215, Japanese Patent Publication No. 62-269054).

[0003] For example, Japanese Patent Publication No. 2022-189215 discloses a hydrogen sensor comprising a reference electrode provided on the surface of a proton-conducting solid electrolyte and a measuring electrode provided on the surface of the proton-conducting solid electrolyte in a second space different from the first space in which the reference electrode is in contact. Furthermore, it is disclosed that the hydrogen concentration in the second space is detected based on the electromotive force between the reference electrode and the measuring electrode in this hydrogen sensor. A so-called voltage-type hydrogen sensor is disclosed.

[0004] Furthermore, for example, Japanese Patent Publication No. 62-269054 discloses a hydrogen sensor element in which an anode electrode and a cathode electrode are provided on both sides of a hydrogen ion conductive solid electrolyte, and a hydrogen diffusion control body is provided to cover the anode electrode. It also discloses detecting the hydrogen concentration from the limiting current characteristics of the current flowing between the anode electrode and the cathode electrode. A so-called limiting current type hydrogen sensor is disclosed. [Prior art documents] [Patent Documents]

[0005] [Patent Document 1] Japanese Patent Publication No. 2022-189215 [Patent Document 2] Japanese Patent Publication No. 62-269054 [Overview of the project]

Problems to be Solved by the Invention

[0006] Hydrogen gas sensors are used for detecting hydrogen and measuring its concentration in various fields that utilize hydrogen. For example, hydrogen gas sensors can be used in hydrogen power generation, hydrogen production, hydrogen transportation, etc., such as fuel cells, hydrogen vehicles, iron and steel plants, and petrochemical plants that handle hydrogen. The concentration range to be measured can vary depending on the application of the hydrogen gas sensor. For example, when a hydrogen gas sensor is used to detect hydrogen leakage in industrial gases, it is assumed that the measurement range will vary significantly depending on the concentration of the hydrogen gas used. It is also conceivable that the hydrogen concentration in the gas to be measured can vary within a range from a low concentration of about 100 ppm to a high concentration exceeding several tens to 50% or more. In order to accommodate various applications, hydrogen gas sensors are required to be able to accurately measure within a wide concentration range.

[0007] Therefore, an object of the present invention is to provide a gas sensor that can accurately measure the concentration of hydrogen gas in the gas to be measured within a wide concentration range.

Means for Solving the Problems

[0008] As a result of intensive studies, the present inventors have arrived at the present invention. The present invention includes the following inventions.

[0009] (1) A gas sensor for detecting hydrogen gas in a gas to be measured, comprising a sensor element and a control device for controlling the sensor element, wherein the sensor element comprises a substrate portion including a first solid electrolyte having proton conductivity and a second solid electrolyte disposed in contact with at least a part of the first solid electrolyte and having a lower resistance value for proton conduction than the first solid electrolyte, a gas inlet opening on the surface of the substrate portion, and a gas flow cavity to be measured having an internal cavity that communicates with the gas inlet through a diffusion rate-limiting passage and in which at least the second solid electrolyte is present on the inner surface, A current measurement pump cell including an intracavity measurement electrode disposed on the second solid electrolyte within the internal cavity of the gas flow cavity to be measured, and an extracavity measurement electrode disposed at a position different from the gas flow cavity to be measured within the substrate portion and disposed via the second solid electrolyte with respect to the intracavity measurement electrode. A reference gas chamber formed inside the substrate portion, separated from the gas flow cavity to be measured, and having at least the first solid electrolyte present on an inner surface thereof. A voltage detection sensor cell including a reference electrode disposed on the first solid electrolyte within the reference gas chamber, and a detection electrode disposed at a position different from the reference gas chamber and the gas flow cavity to be measured and disposed via the first solid electrolyte or via the first and second solid electrolytes with respect to the reference electrode. Comprising The control device A pump control unit for controlling the current measurement pump cell A concentration calculation unit for calculating the hydrogen concentration in the gas to be measured Comprising Based on the electromotive force generated in the voltage detection sensor cell, the concentration calculation unit calculates the hydrogen concentration in the gas to be measured, and / or A gas sensor that calculates the hydrogen concentration in the gas to be measured based on the current flowing through the current measurement pump cell.

[0010] Usually, when the hydrogen concentration in the gas to be measured is relatively low, the concentration calculation unit calculates the hydrogen concentration in the gas to be measured based on the electromotive force generated in the voltage detection sensor cell. When the hydrogen concentration in the gas to be measured is relatively high, higher than the low concentration, the concentration calculation unit calculates the hydrogen concentration in the gas to be measured based on the current flowing through the current measurement pump cell.

[0011] (2) The concentration calculation unit When the value of the electromotive force generated in the voltage detection sensor cell is less than or equal to a predetermined threshold value, the concentration calculation unit calculates the hydrogen concentration in the gas to be measured based on the electromotive force generated in the voltage detection sensor cell. The gas sensor according to (1) above, which calculates the hydrogen concentration in the gas to be measured based on the current flowing through the current measuring pump cell when the value of the electromotive force generated in the voltage detection sensor cell is greater than the predetermined threshold.

[0012] (3) The concentration calculation unit, When the value of the current flowing through the current measuring pump cell is below a predetermined threshold, the hydrogen concentration in the gas to be measured is calculated based on the electromotive force generated in the voltage detection sensor cell. The gas sensor according to (1) above, which calculates the hydrogen concentration in the gas to be measured based on the current flowing through the current measuring pump cell when the value of the current flowing through the current measuring pump cell is greater than the predetermined threshold.

[0013] (4) The concentration calculation unit, If the hydrogen concentration calculated based on the electromotive force generated in the voltage detection sensor cell is below a predetermined threshold, the hydrogen concentration calculated based on the electromotive force generated in the voltage detection sensor cell is taken as the hydrogen concentration in the gas to be measured. The gas sensor according to (1) above, wherein if the hydrogen concentration calculated based on the electromotive force generated in the voltage detection sensor cell is greater than the predetermined threshold, the gas sensor calculates the hydrogen concentration based on the current flowing through the current measuring pump cell.

[0014] (5) The concentration calculation unit, If the hydrogen concentration calculated based on the current flowing through the current measuring pump cell is below a predetermined threshold, the hydrogen concentration is calculated based on the electromotive force generated in the voltage detection sensor cell. The gas sensor according to (1) above, wherein if the hydrogen concentration calculated based on the current flowing through the current measuring pump cell is greater than the predetermined threshold, the hydrogen concentration calculated based on the current flowing through the current measuring pump cell is set to be the hydrogen concentration in the gas to be measured.

[0015] (6) The gas sensor according to any one of (1) to (5) above, wherein the pump control unit applies a predetermined voltage between the air-fill measuring electrode and the air-fill measuring electrode of the current measuring pump cell to cause current to flow through the current measuring pump cell.

[0016] (7) The first solid electrolyte is a proton conductor selected from the group consisting of Ca-Zr-Mn-O and Ca-Zr-In-O perovskite compounds, The gas sensor according to any one of (1) to (6) above, wherein the second solid electrolyte is a proton conductor selected from the group consisting of Sr-Zr-YO, Ba-Zr-YO, Ba-Ce-YO, and Sr-Zr-Yb-O perovskite compounds.

[0017] (8) A sensor element for detecting hydrogen gas in the gas to be measured, A base portion comprising a first solid electrolyte having proton conductivity, and a second solid electrolyte disposed in contact with at least a portion of the first solid electrolyte and having a lower proton conduction resistance than the first solid electrolyte, A gas passage to be measured having a gas inlet opening to the surface of the substrate and an internal cavity communicating with the gas inlet via a diffusion-limited passage, and having at least the second solid electrolyte present on its inner surface, A current measuring pump cell includes an in-space measuring electrode disposed on the second solid electrolyte within the internal cavity of the gas flow cavity to be measured, and an out-of-space measuring electrode disposed at a position different from the gas flow cavity to be measured on the base portion, with the in-space measuring electrode separated from the in-space measuring electrode via the second solid electrolyte, A reference gas chamber is formed inside the base portion, spaced apart from the gas flow space to be measured, and having at least the first solid electrolyte present on its inner surface. A voltage detection sensor cell comprising a reference electrode disposed on the first solid electrolyte in the reference gas chamber, and a detection electrode disposed at a location different from the reference gas chamber and the gas flow space to be measured, wherein the reference electrode is disposed via the first solid electrolyte, or via the first solid electrolyte and the second solid electrolyte, A sensor element, including [Effects of the Invention]

[0018] According to the present invention, a gas sensor can be provided that can measure the concentration of hydrogen gas in a gas to be measured with high accuracy over a wide concentration range. [Brief explanation of the drawing]

[0019] [Figure 1] This is a schematic diagram of a vertical cross-section of the sensor element 101 in the longitudinal direction, showing an example of the general configuration of the gas sensor 100 of Embodiment 1. [Figure 2] This is a block diagram showing the electrical connection relationship between the control device 90 and each pump cell 21, 31 of the sensor element 101. [Figure 3] This is a schematic diagram showing an example of the relationship between the H2 concentration in the gas being measured and the pump current Ip1 in the gas sensor 100. The horizontal axis represents the H2 gas concentration (%), and the vertical axis represents the pump current Ip1 (A). [Figure 4] This is a schematic diagram showing an example of the relationship between the H2 concentration in the gas being measured and the voltage V2 in the gas sensor 100. It is a semi-logarithmic graph with a logarithmic scale on the horizontal axis and a linear scale on the vertical axis. The horizontal axis represents the H2 gas concentration (%), and the vertical axis represents the voltage V2 (V). [Figure 5] This is a schematic diagram showing an example of the relationship between the H2 concentration in the gas being measured and the voltage V2 in the gas sensor 100. Both the horizontal and vertical axes are plotted on a linear scale. The horizontal axis represents the H2 gas concentration (%), and the vertical axis represents the voltage V2 (V). [Figure 6] Figure 3 shows the relationship between the H2 concentration in the gas being measured and the pump current Ip1, and Figure 5 shows the relationship between the H2 gas concentration in the gas being measured and the voltage V2, both plotted on the same graph in the gas sensor 100. Both the horizontal and vertical axes are plotted on a linear scale. The horizontal axis represents the H2 gas concentration (%), and the vertical axis represents the pump current Ip1 (A) and voltage V2 (V). [Figure 7] This is a schematic diagram of a vertical cross-section of the sensor element 201 in the longitudinal direction, showing an example of the general configuration of the gas sensor 200 of Embodiment 2. [Modes for carrying out the invention]

[0020] The gas sensor of the present invention includes a sensor element and a control device for controlling the sensor element.

[0021] The sensor element included in the gas sensor of the present invention is A base portion comprising a first solid electrolyte having proton conductivity, and a second solid electrolyte disposed in contact with at least a portion of the first solid electrolyte and having a lower proton conduction resistance than the first solid electrolyte, A gas passage to be measured having a gas inlet opening to the surface of the substrate and an internal cavity communicating with the gas inlet via a diffusion-limited passage, and having at least the second solid electrolyte present on its inner surface, A current measuring pump cell includes an in-space measuring electrode disposed on the second solid electrolyte within the internal cavity of the gas flow cavity to be measured, and an out-of-space measuring electrode disposed at a position different from the gas flow cavity to be measured on the base portion, with the in-space measuring electrode separated from the in-space measuring electrode via the second solid electrolyte, A reference gas chamber is formed inside the base portion, spaced apart from the gas flow space to be measured, and having at least the first solid electrolyte present on its inner surface. A voltage detection sensor cell comprising a reference electrode disposed on the first solid electrolyte in the reference gas chamber, and a detection electrode disposed at a location different from the reference gas chamber and the gas flow space to be measured, wherein the reference electrode is disposed via the first solid electrolyte, or via the first solid electrolyte and the second solid electrolyte, Includes.

[0022] The control device included in the gas sensor of the present invention is A pump control unit that controls the current measuring pump cell, A concentration calculation unit that calculates the hydrogen concentration in the gas being measured, Includes, The concentration calculation unit calculates the hydrogen concentration in the gas to be measured based on the electromotive force generated in the voltage detection sensor cell, and / or Based on the current flowing through the current measuring pump cell, the hydrogen concentration in the gas being measured is calculated.

[0023] The concentration calculation unit, when the hydrogen concentration in the gas being measured is relatively low, calculates the hydrogen concentration in the gas being measured based on the electromotive force generated in the voltage detection sensor cell. If the hydrogen concentration in the gas being measured is relatively high, higher than the low concentration, the hydrogen concentration in the gas being measured is calculated based on the current flowing through the current measuring pump cell.

[0024] [Embodiment 1] An example of an embodiment of the gas sensor of the present invention will be described below with reference to the drawings. Figure 1 is a schematic longitudinal cross-sectional view showing an example of the general configuration of a gas sensor 100 including a sensor element 101. In the following, with reference to Figure 1, the top and bottom refer to the upper side of Figure 1 as the top and the lower side as the bottom, the left side of Figure 1 as the front end and the right side as the rear end.

[0025] In Figure 1, the gas sensor 100 shows an example of a gas sensor that detects hydrogen H2 in the gas to be measured using a sensor element 101 and measures its gas concentration.

[0026] Furthermore, the gas sensor 100 includes a control device 90 that controls the sensor element 101. Figure 2 is a block diagram showing the electrical connection relationship between the control device 90 and the sensor element 101.

[0027] (Sensor element) The sensor element 101 is an element having a base portion 102 that includes a first solid electrolyte having proton conductivity and a second solid electrolyte that is arranged in contact with at least a portion of the first solid electrolyte and has a lower proton conductivity resistance than the first solid electrolyte. In this embodiment, the sensor element 101 is a long plate-shaped element. A long plate-shaped element is also called a long plate shape or a strip shape. The base portion 102 contains two types of proton-conducting solid electrolytes with different proton conductivity (different resistance values).

[0028] As a solid electrolyte having proton conductivity (also called a proton-conducting solid electrolyte or proton conductor), for example, perovskite-type oxides can be used. A detailed explanation of proton conductors will be given later.

[0029] The base portion 102 has a structure in which six layers are stacked in roughly parallel order from the bottom as seen in the drawing: a first substrate layer 1, a second substrate layer 2, a first spacer layer 3, a first proton conductor layer 4, a second spacer layer 5, and a second proton conductor layer 6, each consisting of a proton-conducting solid electrolyte layer. The solid electrolyte forming these six layers is dense and airtight. The six layers may all have the same thickness, or each layer may have a different thickness. The layers are bonded together via an adhesive layer made of solid electrolyte, and the base portion 102 includes this adhesive layer. Figure 1 illustrates the layer configuration consisting of the six layers, but the layer configuration in the present invention is not limited to this, and any number of layers and layer configuration may be used. In addition, some of the layers (for example, the first substrate layer 1, the second substrate layer 2, and the first spacer layer 3) may be made of dense layers made of an insulator such as alumina.

[0030] In this embodiment, the first proton conductor layer 4 is a layer made of a first solid electrolyte (also referred to as the first solid electrolyte layer). The first substrate layer 1, the second substrate layer 2, the first spacer layer 3, the second spacer layer 5, and the second proton conductor layer 6 are layers made of a second solid electrolyte having a lower proton conduction resistance than the first solid electrolyte (also referred to as the second solid electrolyte layer).

[0031] The gas flow space 15 to be measured has a gas inlet 10 that opens to the surface of the base portion 102, and an internal space 20 that communicates with the gas inlet 10 via a diffusion-limited passage 11 (diffusion-limited section) and in which at least the second solid electrolyte is present on its inner surface. In this embodiment, the internal space 20 is a space partitioned by a second spacer layer 5 and a second proton conductor layer 6 made of the second solid electrolyte, and a first proton conductor layer 4 made of the first solid electrolyte.

[0032] In this embodiment, a gas inlet 10 is formed at one end of the sensor element 101 in the longitudinal direction (hereinafter referred to as the tip), between the lower surface of the second proton conductor layer 6 and the upper surface of the first proton conductor layer 4. The gas passage space 15 to be measured, that is, the gas passage section to be measured, is formed adjacent to the gas inlet 10 in the longitudinal direction, with a diffusion rate-limited passage 11 and an internal space 20 communicating in that order.

[0033] The gas inlet 10 and the internal cavity 20 are spaces inside the sensor element 101, provided in a manner in which the second spacer layer 5 is hollowed out, with the upper part being the lower surface of the second proton conductor layer 6 made of the second solid electrolyte, the lower part being the upper surface of the first proton conductor layer 4 made of the first solid electrolyte, and the sides being the side surfaces of the second spacer layer 5 made of the second solid electrolyte. In other words, the gas inlet 10 and the internal cavity 20 are in contact with the second spacer layer 5 and the second proton conductor layer 6 made of the second solid electrolyte and the first proton conductor layer 4 made of the first solid electrolyte, respectively.

[0034] The diffusion-limiting passage 11 is provided as two horizontally elongated slits (with their openings perpendicular to the drawing in Figure 1). The diffusion-limiting passage 11 can be in any form that provides the desired diffusion resistance, and its form is not limited to the slits described above.

[0035] Furthermore, a reference gas chamber 30 is provided inside the base portion 102, separated from the gas flow space 15 to be measured, and having at least the first solid electrolyte (first proton conductor layer 4) on its inner surface. In this embodiment, the reference gas chamber 30 is located at a position further from the tip side of the sensor element 101 than the diffusion rate-limiting passage 11 of the gas flow space 15 to be measured, between the upper surface of the second substrate layer 2 and the lower surface of the first proton conductor layer 4, and is positioned so that its sides are demarcated by the side surface of the first spacer layer 3. The reference gas chamber 30 has an opening at the other end of the sensor element 101 (hereinafter referred to as the rear end). The reference gas chamber 30 is a space that extends from the opening at the rear end of the sensor element 101 in the longitudinal direction of the sensor element 101 to the position where the internal space 20 exists (for example, near the longitudinal center of the internal space 20). For example, air is introduced into the reference gas chamber 30 as a reference gas when performing concentration measurement.

[0036] In the gas flow space 15 to be measured, the gas inlet 10 is a part that is open to the outside space, and the gas to be measured is taken into the sensor element 101 from the outside space through the gas inlet 10.

[0037] In this embodiment, the gas to be measured is introduced into the gas flow space 15 through a gas inlet 10 opening on the tip surface of the sensor element 101. However, the present invention is not limited to this embodiment. For example, the gas flow space 15 does not need to have a recess for the gas inlet 10. In this case, the diffusion-limited passage 11 substantially becomes the gas inlet.

[0038] Furthermore, for example, the gas flow space 15 to be measured may have an opening on the side of the base portion 102 along its longitudinal direction that communicates with a position close to the tip of the internal space 20, for example, a position closer to the tip than the internal measuring electrode 22 described later. In this case, the gas to be measured is introduced through the opening from the side of the base portion 102 along its longitudinal direction.

[0039] Furthermore, for example, the gas flow space 15 to be measured may be configured such that the gas to be measured is introduced through a porous material.

[0040] The diffusion rate-limiting passage 11 is a section that imparts a predetermined diffusion resistance to the gas to be measured, which is taken in from the gas inlet 10.

[0041] The internal cavity 20 is provided as a space for measuring the current corresponding to the hydrogen concentration in the gas to be measured, which is introduced through the diffusion rate-limiting passage 11. This measurement is performed by operating the current measuring pump cell 21.

[0042] The current measuring pump cell 21 is an electrochemical pump cell that includes an in-space measuring electrode (in this embodiment, an inner measuring electrode 22) disposed on a second solid electrolyte (in this embodiment, a second proton conductor layer 6) within an internal space 20 of the gas flow space 15 to be measured, and an out-of-space measuring electrode (in this embodiment, an outer electrode 23) disposed at a position different from the gas flow space 15 to be measured on the base portion 102, and separated from the inner measuring electrode 22 via the second proton conductor layer 6.

[0043] In other words, the current measuring pump cell 21 is an electrochemical pump cell composed of an inner measuring electrode 22 provided on the lower surface of the second proton conductor layer 6 facing the internal cavity 20, an outer electrode 23 provided on the upper surface of the second proton conductor layer 6 in a manner that is exposed to the external space in a region roughly corresponding to the inner measuring electrode 22, and the second proton conductor layer 6 sandwiched between these electrodes.

[0044] The inner measuring electrode 22 and the outer electrode 23 are preferably porous cermet electrodes (electrodes having a mixture of metal and ceramic components). While the ceramic component is not particularly limited, it is preferable to use a proton-conducting solid electrolyte, similar to the second proton conductor layer 6 in contact with both electrodes. For example, a second solid electrolyte, as detailed later, can be used as the ceramic component.

[0045] The inner measuring electrode 22 may contain a noble metal with catalytic activity (for example, at least one of Pt, Rh, Ir, Ru, or Pd) as its metallic component. For example, the inner measuring electrode 22 may be a porous cermet electrode made of Pt and a second solid electrolyte. The outer electrode 23 may also contain a noble metal (for example, at least one of Pt, Rh, Ir, Ru, Pd, or Au) as its metallic component. For example, the outer electrode 23 may be a porous cermet electrode made of Au and Pt and a second solid electrolyte.

[0046] In the current measuring pump cell 21, a desired pump voltage Vp1 is applied between the inner measuring electrode 22 and the outer electrode 23 by a variable power supply 24, and a pump current Ip1 is passed between the inner measuring electrode 22 and the outer electrode 23, making it possible to pump hydrogen from the internal cavity 20 into the external space.

[0047] Furthermore, an electrochemical sensor cell, i.e., a voltage detection sensor cell 31, is constructed by a reference electrode 32 disposed on a first solid electrolyte (first proton conductor layer 4 in this embodiment) within the reference gas chamber 30, and a detection electrode disposed at a location different from the reference gas chamber 30 and the gas flow space 15 to be measured, and connected to the reference electrode 32 via the first solid electrolyte, or via the first solid electrolyte and the second solid electrolyte. The reference electrode 32 is disposed in contact with the reference gas, and the detection electrode is disposed in contact with the gas to be measured. In this embodiment, the outer electrode 23 also functions as the detection electrode of the present invention. The outer electrode 23 is disposed to the reference electrode 32 via a first solid electrolyte layer (first proton conductor layer 4) and a second solid electrolyte layer (second spacer layer 5 and second proton conductor layer 6).

[0048] In other words, the voltage detection sensor cell 31 is an electrochemical sensor cell composed of a reference electrode 32, an outer electrode 23, a first proton conductor layer 4 made of a first solid electrolyte, and a second spacer layer 5 and a second proton conductor layer 6 made of a second solid electrolyte.

[0049] The reference electrode 32 is an electrode positioned on the first solid electrolyte within the reference gas chamber 30, that is, on the lower surface of the first proton conductor layer 4. The reference electrode 32 is positioned so as to be in contact with the reference gas via the reference gas chamber 30.

[0050] The reference electrode 32 is preferably a porous cermet electrode, similar to the inner measuring electrode 22 and the outer electrode 23. While the ceramic component is not particularly limited, it is preferable to use a proton-conducting solid electrolyte, similar to the first proton conductor layer 4 in contact with the reference electrode 32. For example, a first solid electrolyte, as detailed later, can be used as the ceramic component.

[0051] The reference electrode 32 may contain a catalytically active noble metal (for example, at least one of Pt, Rh, Ir, Ru, or Pd) as a metallic component. For example, the reference electrode 32 may be a porous cermet electrode made of Pt and a first solid electrolyte.

[0052] In the voltage detection sensor cell 31, an electromotive force (voltage V2) is generated between the reference electrode 32 and the outer electrode 23 due to the concentration difference between the hydrogen concentration in the gas to be measured in contact with the outer electrode 23 and the hydrogen concentration in the reference gas in the reference gas chamber 30. As mentioned above, the outer electrode 23 may be a porous cermet electrode made of Au and Pt and a second solid electrolyte. If Au is used as the metal component, the combustion of hydrogen in the gas to be measured can be suppressed at the outer electrode 23 as a detection electrode, and it is thought that the voltage detection sensor cell 31 can more accurately detect the electromotive force (voltage V2) corresponding to the hydrogen concentration in the gas to be measured.

[0053] Furthermore, the sensor element 101 is equipped with a heater section 70 that plays a role in temperature control by heating and maintaining the sensor element 101 to enhance the hydrogen ion conductivity (proton conductivity) of the solid electrolyte. The heater section 70 comprises a heater electrode 71, a heater 72, a through-hole 73, a heater lead 76, and a heater insulating layer 74.

[0054] The heater electrode 71 is an electrode formed in such a manner that it is in contact with the lower surface of the first substrate layer 1. By connecting the heater electrode 71 to an external power supply, power can be supplied to the heater unit 70 from an external source.

[0055] The heater 72 is an electrical resistor formed in such a manner that it is sandwiched between the first substrate layer 1 and the second substrate layer 2 from above and below. The heater 72 is connected to a heater electrode 71 via a heater lead 76 that is connected to the heater 72 and extends to the longitudinal rear end of the sensor element 101, and a through hole 73. The heater electrode 71 generates heat when power is supplied from the outside, heating and maintaining the temperature of the solid electrolyte forming the sensor element 101.

[0056] Furthermore, the heater 72 is embedded throughout the entire internal cavity 20, making it possible to adjust the temperature of the sensor element 101 to a temperature at which the proton-conducting solid electrolyte is activated. It is sufficient that the temperature is adjusted so that the current measuring pump cell 21 can operate. The entire area does not need to be adjusted to the same temperature, and there may be a temperature distribution on the sensor element 101. By maintaining the heater 72 at the desired temperature, the sensor element 101 can be kept at a drive temperature at which the solid electrolyte is activated and the H2 concentration can be measured accurately.

[0057] Hydrogen gas has an ignition temperature of 500°C to 571°C (see the Fire and Disaster Management Agency of the Ministry of Internal Affairs and Communications' Hazardous Materials Disaster Information Support System). Therefore, the operating temperature of the gas sensor 100 must be no higher than 500°C. On the other hand, the temperature must be such that the solid electrolyte can exhibit proton conductivity. The operating temperature of the gas sensor 100 can be set appropriately depending on the configuration of the sensor element 101, such as the materials of the first and second solid electrolytes, and the purpose and environment of use of the gas sensor 100, for example, it may be between 300°C and 450°C.

[0058] In this embodiment, the heater 72 is embedded in the base portion 102 of the sensor element 101, but the embodiment is not limited to this configuration. The heater 72 only needs to be arranged to heat the base portion 102. That is, the heater 72 only needs to be able to heat the sensor element 101 to the extent that it exhibits proton conductivity that allows the current measurement pump cell 21 described above to operate. For example, it may be embedded in the base portion 102 as in this embodiment. Alternatively, for example, the heater portion 70 may be formed as a separate heater substrate from the base portion 102 and arranged adjacent to the base portion 102.

[0059] The heater insulating layer 74 is an insulating layer formed on the upper and lower surfaces of the heater 72 and heater lead 76 using an insulator such as alumina. The heater insulating layer 74 is formed to provide electrical insulation between the first substrate layer 1 and the heater 72 and heater lead 76, and between the second substrate layer 2 and the heater 72 and heater lead 76.

[0060] (Control device) The gas sensor 100 of this embodiment includes the sensor element 101 described above and a control device 90 that controls the sensor element 101. In the gas sensor 100, each electrode 22, 23, and 32 of the sensor element 101 is electrically connected to the control device 90 via lead wires (not shown). Figure 2 is a block diagram showing the electrical connection relationship between the control device 90 and each cell 21 and 31 of the sensor element 101. The control device 90 includes the variable power supply 24 described above and a control unit 91. The control unit 91 includes a pump control unit 92 and a concentration calculation unit 93.

[0061] The control unit 91 is implemented by a general-purpose or dedicated computer, and the functions of the pump control unit 92 and the concentration calculation unit 93 are realized by the CPU, memory, etc. installed in the computer. In the case where the gas sensor 100 is used as part of various measuring devices, some or all of the functions of the control device 90 (especially the control unit 91) may be realized by the CPU, memory, etc. installed in the measuring device.

[0062] The control unit 91 is configured to acquire the pump current Ip1 in the current measuring pump cell 21 of the sensor element 101, and the electromotive force (voltage V2) in the voltage detection sensor cell 31. The control unit 91 is also configured to output a control signal to the variable power supply 24.

[0063] The pump control unit 92 is configured to control the operation of the current measuring pump cell 21 so that the concentration of hydrogen gas in the gas to be measured can be measured.

[0064] In this embodiment, the pump control unit 92 is A predetermined pump voltage Vp1 is applied between the air-filled measuring electrode (inner measuring electrode 22) and the air-filled measuring electrode (outer electrode 23) of the current measuring pump cell 21, causing a current (pump current Ip1) to flow through the current measuring pump cell 21.

[0065] When a pump voltage Vp1 is applied between the inner measuring electrode 22 and the outer electrode 23 of the current measuring pump cell 21 to pump hydrogen from the internal cavity 20 to the external space, the pump current Ip1 increases with increasing pump voltage Vp1 while the pump voltage Vp1 is low. Subsequently, as the pump voltage Vp1 increases, the pump current Ip1 no longer increases even if the pump voltage Vp1 increases, and saturates. This saturated current value is called the limit current value. The region in which the pump current Ip1 becomes the limit current value relative to the pump voltage Vp1 is called the limit current region. In the limit current region, it is considered that virtually all of the hydrogen that reaches the inner measuring electrode 22 is pumped out by the current measuring pump cell 21.

[0066] When the gas sensor 100 is driven, the pump control unit 92 applies a predetermined pump voltage Vp1 between the air-fill measuring electrode (inner measuring electrode 22) and the air-fill measuring electrode (outer electrode 23) of the current measuring pump cell 21 using a variable power supply 24, thereby pumping hydrogen from the gas to be measured out of the internal air cavity 20. At this time, the pump current Ip1 flowing through the current measuring pump cell 21 flows from the outer electrode 23 towards the inner measuring electrode 22 outside the sensor element 101.

[0067] The pump voltage Vp1 applied to the current measuring pump cell 21 should be set to a value such that all or substantially all of the hydrogen in the gas to be measured introduced into the internal cavity 20 is pumped out. The pump voltage Vp1 should be set to a value such that the pump current Ip1 becomes the limit current value mentioned above. The pump voltage Vp1 may vary depending on the purpose of use of the gas sensor 100 and the configuration of the sensor element 101, but for example, it may be between 100mV and 1000mV.

[0068] In the voltage detection sensor cell 31, an electromotive force (voltage V2) is generated because there is a concentration difference between the hydrogen concentration in the gas being measured that is in contact with the outer electrode 23 and the hydrogen concentration in the reference gas in the reference gas chamber 30. Therefore, the pump control unit 92 does not perform any control such as applying a voltage to the voltage detection sensor cell 31, as is done in the case of the current measurement pump cell 21.

[0069] The concentration calculation unit 93 is configured to calculate the hydrogen concentration (H2 concentration) in the gas being measured. The concentration calculation unit 93 calculates the hydrogen concentration in the gas being measured based on the electromotive force (voltage V2) generated in the voltage detection sensor cell 31, and / or The hydrogen concentration in the gas being measured is calculated based on the current (pump current Ip1) flowing through the current measuring pump cell 21.

[0070] The concentration calculation unit 93 acquires the voltage V2 in the voltage detection sensor cell 31 and is configured to calculate the H2 concentration in the gas to be measured based on a pre-stored conversion parameter between the voltage V2 and the H2 concentration in the gas to be measured (voltage-H2 concentration conversion parameter) and output it as a measured value of the gas sensor 100. The voltage-H2 concentration conversion parameter is pre-stored in the memory of the control unit 91, which functions as the concentration calculation unit 93. The voltage-H2 concentration conversion parameter can be appropriately determined in advance by a person skilled in the art through experiments or other means for the gas sensor 100. The voltage-H2 concentration conversion parameter may be, for example, a coefficient of an approximation formula (logarithmic function, etc.) obtained by experiment, or it may be a map showing the correspondence between the voltage V2 and the H2 concentration in the gas to be measured. The voltage-H2 concentration conversion parameter may be a parameter specific to each gas sensor 100, or it may be a parameter used in common for multiple gas sensors.

[0071] The concentration calculation unit 93 acquires the pump current Ip1 in the current measurement pump cell 21, calculates the H2 concentration in the gas to be measured based on a pre-stored conversion parameter (current-H2 concentration conversion parameter) between the pump current Ip1 and the H2 concentration in the gas to be measured, and is configured to output this as a measured value from the gas sensor 100. The current-H2 concentration conversion parameter is pre-stored in the memory of the control unit 91, which functions as the concentration calculation unit 93. The current-H2 concentration conversion parameter can be appropriately determined in advance by a person skilled in the art through experiments or other means for the gas sensor 100. The current-H2 concentration conversion parameter may be, for example, a coefficient of an approximate formula (such as a linear function) obtained experimentally, or it may be a map showing the correspondence between the pump current Ip1 and the H2 concentration in the gas to be measured. The current-H2 concentration conversion parameter may be a parameter specific to each gas sensor 100, or it may be a parameter used in common for multiple gas sensors.

[0072] The concentration calculation unit 93 normally calculates the hydrogen concentration in the gas being measured based on the electromotive force (voltage V2) generated in the voltage detection sensor cell 31 when the hydrogen concentration in the gas being measured is relatively low. If the hydrogen concentration in the gas being measured is relatively high, higher than the low concentration, the hydrogen concentration in the gas being measured is calculated based on the current (pump current Ip1) flowing through the current measuring pump cell 21.

[0073] The concentration calculation unit 93 may always perform both calculations of hydrogen concentration based on voltage V2 and calculations of hydrogen concentration based on pump current Ip1, or it may select to perform either calculations of hydrogen concentration based on voltage V2 or calculations of hydrogen concentration based on pump current Ip1 based on the hydrogen concentration in the gas being measured. Either the hydrogen concentration calculated based on voltage V2 or the hydrogen concentration calculated based on pump current Ip1 should be output as the measured value of the gas sensor 100.

[0074] (Current measuring pump cell and voltage detection sensor cell) The current measurement pump cell 21 and the voltage detection sensor cell 31 will be explained in more detail.

[0075] The pump control unit 92 operates the current measuring pump cell 21 to pump out all or substantially all of the hydrogen in the gas to be measured that has been introduced into the internal cavity 20. At this time, the pump current Ip1 flowing through the current measuring pump cell 21 is a value corresponding to the hydrogen concentration in the gas to be measured.

[0076] Figure 3 is a schematic diagram showing an example of the relationship between the H2 concentration (H2 gas concentration) in the gas being measured and the pump current Ip1 in the gas sensor 100. The horizontal axis represents the H2 gas concentration (%), and the vertical axis represents the pump current Ip1 (A). In the current measuring pump cell 21, by flowing the pump current Ip1, virtually all of the hydrogen in the gas being measured that has been introduced into the internal cavity 20 is pumped out. Therefore, as shown in Figure 3, there is a linear relationship between the H2 concentration in the gas being measured and the pump current Ip1. The gas sensor 100 can measure the H2 concentration based on this linear relationship between the H2 concentration and the pump current Ip1.

[0077] To obtain such a linear relationship with higher precision, it is preferable that the resistance value in the current measurement pump cell 21 is low and that hydrogen is pumped out smoothly. Therefore, it is preferable that the second solid electrolyte (second proton conductor layer 6) interposed between the in-space measurement electrode (inner measurement electrode 22) and the out-of-space measurement electrode (outer electrode 23) has high proton conductivity, that is, low proton conduction resistance.

[0078] Generally, the resistance of a solid electrolyte decreases with increasing temperature. However, as mentioned above, the ignition temperature of hydrogen gas is 500°C to 571°C, so the operating temperature of the gas sensor must be no higher than 500°C. Therefore, it is preferable that the second solid electrolyte (second proton conductor layer 6) has low resistance at temperatures below 500°C, for example, around 450°C or lower.

[0079] When calculating H2 concentration based on the pump current Ip1, the measurement accuracy tends to be better as the H2 concentration increases. As shown in Figure 3, the higher the H2 concentration, the larger the pump current Ip1 becomes, resulting in a higher signal-to-noise ratio and thus higher sensitivity. As a result, it is thought that high measurement accuracy can be obtained. In the case of extremely low concentrations, the pump current Ip1 becomes very small, so the accuracy is thought to be lower compared to the case of high concentrations.

[0080] Furthermore, as described above, in the voltage detection sensor cell 31, an electromotive force (voltage V2) is generated between the reference electrode 32 and the outer electrode 23 due to the concentration difference between the hydrogen concentration in the gas to be measured that is in contact with the outer electrode 23 and the hydrogen concentration in the reference gas in the reference gas chamber 30.

[0081] Figure 4 is a schematic diagram showing an example of the relationship between the H2 concentration in the gas being measured and the voltage V2 in the gas sensor 100. It is a semi-logarithmic graph with a logarithmic scale on the horizontal axis and a linear scale on the vertical axis. The horizontal axis represents the H2 gas concentration (%), and the vertical axis represents the voltage V2 (V). The voltage V2 in the voltage detection sensor cell 31 is the electromotive force generated due to the concentration difference between the hydrogen concentration in the gas being measured and the hydrogen concentration in the reference gas. Since the relationship between hydrogen concentration and electromotive force (voltage V2) follows the so-called Nernst equation, there is a linear relationship between the logarithm of the H2 concentration and the voltage V2. The gas sensor 100 can measure the H2 concentration based on this relationship between H2 concentration and voltage V2.

[0082] Figure 5 is a schematic diagram showing an example of the relationship between the H2 concentration in the gas being measured and the voltage V2 in the gas sensor 100. Both the horizontal and vertical axes are plotted on a linear scale. In other words, Figure 5 is a schematic diagram of Figure 4 when the logarithmic scale of the horizontal axis is changed to a linear scale. The horizontal axis represents the H2 gas concentration (%), and the vertical axis represents the voltage V2 (V). As shown in Figure 5, the lower the H2 concentration, the steeper the slope of the graph, and the higher the H2 concentration, the shallower the slope of the graph. In other words, the lower the H2 concentration, the larger the change in voltage V2 in response to the change in concentration, and the higher the H2 concentration, the smaller the change in voltage V2 in response to the change in concentration.

[0083] Therefore, when calculating H2 concentration based on voltage V2, the lower the H2 concentration, the better the measurement accuracy tends to be. As the H2 concentration decreases, the change in voltage V2 in response to the concentration change becomes larger, allowing for higher sensitivity to the H2 concentration. As a result, it is thought that high measurement accuracy can be obtained.

[0084] As described above, the voltage V2 is the potential difference between the reference electrode 32 and the outer electrode 23. Therefore, if the potential of the reference electrode 32, which serves as the reference for measurement, is kept constant, the voltage V2 will be the potential of the outer electrode 23, that is, a value corresponding to the hydrogen concentration in the gas being measured. Keeping the potential of the reference electrode 32 constant usually means keeping the hydrogen concentration in the reference gas in contact with the reference electrode 32 constant. To supply the sensor element 101 with a gas of a predetermined hydrogen concentration, for example, a gas cylinder filled with gas of a predetermined hydrogen concentration can be used. However, in this case, the gas sensor becomes large, limiting the installation space for the gas sensor, which is undesirable as it restricts the applications of the gas sensor. Therefore, it is preferable to use the atmosphere as the reference gas.

[0085] The atmosphere contains trace amounts of hydrogen, and slight fluctuations in its concentration may cause changes in the potential of the reference electrode 32. This is particularly likely to occur when the reference electrode 32 is in contact with a solid electrolyte that has high proton conductivity. Therefore, it is preferable that the first solid electrolyte (first proton conductor layer 4) in contact with the reference electrode 32 has low proton conductivity in the region of very low hydrogen concentrations, such as in the atmosphere; that is, it has high proton conduction resistance. Alternatively, the solid electrolyte may exhibit substantially no proton conductivity in the region of very low hydrogen concentrations, such as in the atmosphere. In this case, the level of proton conductivity in the region of hydrogen concentrations higher than that in the atmosphere (for example, the hydrogen concentration in the gas being measured) is not particularly limited.

[0086] In the present invention, the resistance value of the proton conductor used in the second solid electrolyte is lower than the resistance value of the proton conductor used in the first solid electrolyte. As described above, the first solid electrolyte preferably has high proton conduction resistance in the region of very small hydrogen concentrations, such as in the atmosphere, i.e., low proton conductivity. Furthermore, the second solid electrolyte preferably has low proton conduction resistance, i.e., high proton conductivity.

[0087] As indicators of the proton conduction resistance of the first and second solid electrolytes, for example, the so-called DC resistance value, the real part value of the impedance obtained by AC impedance measurement, etc., can be used.

[0088] DC resistance may be measured, for example, as follows. First, a sensor element 101 having a second proton conductor layer 6 made of a solid electrolyte whose resistance value is to be measured is fabricated as a measuring sensor element. The measuring sensor element is heated to the operating temperature by a heater 72. In this state, a predetermined voltage Vp1 is applied between the inner measuring electrode 22 and the outer electrode 23 in an atmospheric environment, and the pump current Ip1 flowing at that time is measured. The value obtained by dividing the applied voltage Vp1 by the measured pump current Ip1 (DC resistance value) may be used as the resistance value.

[0089] Impedance is the ratio of voltage to current in an AC circuit and is generally represented as a complex number. It is also called complex impedance. In complex impedance, the real part represents the resistance component of the impedance, and the imaginary part represents the reactance component. Impedance is measured by AC impedance measurement.

[0090] Specifically, the resistance value may be measured as follows. First, a sensor element 101 having a second proton conductor layer 6 made of a solid electrolyte whose resistance value is to be measured is fabricated as a measuring sensor element. The measuring sensor element is heated to the driving temperature using a heater 72. In this state, AC impedance measurement is performed in an atmospheric environment. The AC impedance measurement may be performed in an inert gas, in a gas atmosphere simulating the atmosphere, for example, with an oxygen concentration of 20.5%, or in an atmosphere simulating the target gas component in the gas to be measured, such as automobile exhaust gas. The AC impedance measurement can be performed using a known measuring device such as an impedance analyzer. An AC voltage is applied between the inner measuring electrode 22 and the outer electrode 23 while changing the frequency, and the frequency characteristics of the impedance are obtained. The real part of the impedance at a predetermined frequency may be taken as the resistance value of the solid electrolyte. Alternatively, an AC voltage of a predetermined frequency may be applied, the impedance at that frequency may be measured, and its real part may be taken as the resistance value.

[0091] The resistance of the first solid electrolyte may be, for example, 1 kΩ or more as the DC resistance in air. Within this range, it is considered that the potential of the reference electrode 32 can be kept constant. Alternatively, it may be 5 kΩ or more, or 10 kΩ or more. The first solid electrolyte may be any proton-conducting solid electrolyte, and there is no particular upper limit to its resistance, but it may be, for example, around 50 kΩ or less.

[0092] The resistance of the second solid electrolyte may be, for example, 500 Ω or less as the DC resistance in air. Within this range, it is thought that hydrogen can be pumped more smoothly in the current measuring pump cell 21. Alternatively, it may be 200 Ω or less, or 100 Ω or less. There is no particular lower limit to the resistance of the second solid electrolyte, but it may be, for example, around 20 Ω or more.

[0093] Further, for example, proton conductivity may be used as an index indicating the proton conductivity of the first solid electrolyte and the second solid electrolyte. Proton conductivity indicates the ease of proton conduction, contrary to the resistance value. A high proton conductivity indicates a low resistance value, and a low proton conductivity indicates a high resistance value. Therefore, in the present invention, the proton conductivity in the proton conductor used for the second solid electrolyte is higher than the proton conductivity in the proton conductor used for the first solid electrolyte. Proton conductivity can be measured by known methods.

[0094] As the proton-conductive solid electrolyte (proton conductor) used for the first solid electrolyte (in this embodiment, the first proton conductor layer 4) and the second solid electrolyte (in this embodiment, the second spacer layer 5 and the second proton conductor layer 6), for example, perovskite ceramics represented by the following composition formula can be used.

[0095] A(B 1-x C x )O 3-δ Here, A is a divalent metal selected from the group consisting of, for example, Ba, Ca, and Sr. B is a tetravalent metal selected from the group consisting of, for example, Ce and Zr. C is a trivalent metal selected from the group consisting of, for example, In, Y, Yb, Mn, and Sc, and is a so-called dopant. x may be, for example, 0 or more and 0.7 or less.

[0096] Specifically, the first solid electrolyte and the second solid electrolyte are, for example, Sr(Zr 1-x Y x )O 3-δ (Sr-Zr-Y-O system or SZY), Ba(Zr 1-x Y x )O 3-δ (Ba-Zr-Y-O system), Ba(Ce 1-x Y x )O 3-δ (Ba-Ce-Y-O system), Sr(Zr 1-x Yb x )O 3-δ (Sr-Zr-Yb-O system), Ca(Zr 1-xMn x )O 3-δ (Ca-Zr-Mn-O system or CZMN), and Ca(Zr 1-x In x )O 3-δ Each of these compounds may be selected from the group consisting of perovskite compounds of the (Ca-Zr-In-O system). However, it is assumed that the second solid electrolyte has a lower proton conduction resistance than the first solid electrolyte, i.e., higher proton conductivity.

[0097] For example, Ca(Zr 1-x Mn x )O 3-δ (Ca-Zr-Mn-O system or CZMN) and Ca(Zr 1-x In x )O 3-δ It is preferable to use a proton conductor selected from the group consisting of (Ca-Zr-In-O system) perovskite compounds. Here, x may be, for example, between 0 and 0.7. More specifically, for example, Ca(Zr 0.95 Mn 0.05 )O 3-δ You may use [this]. Also, as the second solid electrolyte, for example, Sr(Zr 1-x Y x )O 3-δ (Sr-Zr-YO system or SZY), Ba(Zr 1-x Y x )O 3-δ (Ba-Zr-YO system), Ba(Ce 1-x Y x )O 3-δ (Ba-Ce-YO system), and Sr(Zr 1-x Yb x )O 3-δ It is preferable to use a proton conductor selected from the group consisting of perovskite compounds of the (Sr-Zr-Yb-O system). Here, x may be, for example, between 0 and 0.7. More specifically, for example, Sr(Zr 0.8 Y 0.2 )O 3-δ ~Sr(Zr 0.95 Y 0.05 )O 3-δ You may use this.

[0098] Other perovskite-type compounds and non-perovskite-type compounds can also be selected as appropriate from the viewpoint of proton conductivity and resistance.

[0099] (Measurement of hydrogen concentration in the gas being measured) Next, a method for measuring the concentration of hydrogen (H2) in a gas to be measured using the gas sensor 100 having the configuration described above will be explained.

[0100] The gas to be measured is introduced from the gas inlet 10, passes through the diffusion rate-limiting passage 11, is given a predetermined diffusion resistance, and reaches the internal cavity 20.

[0101] The pump control unit 92 operates the current measuring pump cell 21 as described above, thereby pumping out all or substantially all of the hydrogen in the gas to be measured that has been introduced into the internal cavity 20. The pump current Ip1 flowing through the current measuring pump cell 21 is a current value corresponding to the amount of hydrogen in the gas to be measured that has reached the internal cavity 20. Here, the relationship between the H2 concentration in the gas to be measured and the pump current Ip1 is a linear relationship as shown in Figure 3.

[0102] Furthermore, as described above, in the voltage detection sensor cell 31, an electromotive force (voltage V2) is generated between the reference electrode 32 and the outer electrode 23 due to the concentration difference between the hydrogen concentration in the gas to be measured that is in contact with the outer electrode 23 and the hydrogen concentration in the reference gas in the reference gas chamber 30. Here, the relationship between the H2 concentration in the gas to be measured and the voltage V2 is as shown in Figure 5.

[0103] As described above, the concentration calculation unit 93 normally calculates the hydrogen concentration in the gas being measured based on the electromotive force (voltage V2) generated in the voltage detection sensor cell 31 when the hydrogen concentration in the gas being measured is relatively low. If the hydrogen concentration in the gas being measured is relatively high, higher than the low concentration, the hydrogen concentration in the gas being measured is calculated based on the current (pump current Ip1) flowing through the current measuring pump cell 21.

[0104] When the H2 concentration in the gas being measured is relatively low, as described above, the change in voltage V2 in response to the change in concentration becomes large, thus allowing for higher sensitivity to the H2 concentration. Therefore, by calculating the H2 concentration based on the voltage V2 (hereinafter also referred to as voltage measurement), higher measurement accuracy can be obtained. On the other hand, when the H2 concentration in the gas being measured is relatively high, as described above, the current value of the pump current Ip1 is large, allowing for high sensitivity. Therefore, it is considered that higher measurement accuracy can be obtained by calculating the H2 concentration based on the pump current Ip1 (hereinafter also referred to as current measurement).

[0105] Figure 6 is a schematic diagram showing the relationship between the H2 concentration in the gas being measured and the pump current Ip1 (Figure 3), and the relationship between the H2 concentration in the gas being measured and the voltage V2 (Figure 5) on the same graph for the gas sensor 100. Both the horizontal and vertical axes are plotted on a linear scale. Note that in Figure 6, the pump current Ip1 and voltage V2 are only shown schematically and do not represent the magnitude of actual values. The horizontal axis represents the H2 gas concentration (%), and the vertical axis represents the pump current Ip1 (A) and voltage V2 (V). In Figure 6, the concentration ranges in which the sensitivity of measurement based on voltage V2 is higher, and the concentration ranges in which the sensitivity of measurement based on pump current Ip1 is higher, are shown by dashed lines, respectively.

[0106] The measurement range for voltage measurement should be in a relatively low concentration range. In Figure 6, the dashed line represents the concentration range where the sensitivity of measurement based on voltage V2 is higher. The measurement range for voltage measurement should be, for example, 10% or less in terms of hydrogen concentration. Within such a range, the change in voltage V2 in response to changes in hydrogen concentration does not become too small, and it is thought that high measurement accuracy can be maintained. There is no particular lower limit to the measurement range for voltage measurement, but the hydrogen concentration may be, for example, 100 ppm or more.

[0107] The measurement range for current measurement should ideally be in a relatively high-concentration region. In Figure 6, the dashed line represents the concentration range where the sensitivity of measurement based on the pump current Ip1 is higher. The measurement range for current measurement should ideally be, for example, 1% or higher in hydrogen concentration. Within such a range, the current value of the pump current Ip2 will not become too small, and high measurement accuracy can be maintained. There is no particular upper limit to the measurement range for current measurement, but it may be, for example, 50% or lower in hydrogen concentration.

[0108] The concentration calculation unit 93 calculates the hydrogen concentration in the gas to be measured (voltage measurement) based on the electromotive force (voltage V2) generated in the voltage detection sensor cell 31 if the hydrogen concentration in the gas to be measured is below a predetermined concentration threshold (or less than a predetermined concentration threshold). If the hydrogen concentration in the gas to be measured is higher than (or equal to or greater than) the predetermined concentration threshold, the hydrogen concentration in the gas to be measured should be calculated (current measurement) based on the current (pump current Ip1) flowing through the current measuring pump cell 21.

[0109] The aforementioned concentration threshold should be appropriately selected so that the gas sensor 100 can maintain high measurement accuracy over a wide concentration range. As shown in Figure 6, the concentration range in which voltage measurement is more sensitive and the concentration range in which current measurement is more sensitive partially overlap. In this overlapping concentration range, it is considered that sufficiently high measurement accuracy can be obtained regardless of whether voltage measurement or current measurement is used. Therefore, the hydrogen concentration included in this overlapping concentration range may be appropriately selected as the concentration threshold.

[0110] The aforementioned concentration threshold may be, for example, a value of approximately 1% or more and approximately 10% or less. For example, the concentration threshold may be approximately 1% or more, approximately 3% or more, approximately 5% or more, or approximately 10% or less, approximately 8% or less, or approximately 6% or less.

[0111] The concentration calculation unit 93 is When the value of the electromotive force (voltage V1) generated in the voltage detection sensor cell 31 is less than or equal to a predetermined threshold (referred to as the voltage threshold), it is determined that the hydrogen concentration in the gas being measured is low, and the hydrogen concentration in the gas being measured is calculated based on the electromotive force (voltage V1) generated in the voltage detection sensor cell 31. If the value of the electromotive force (voltage V1) generated in the voltage detection sensor cell 31 is greater than (or equal to or equal to) the predetermined voltage threshold, it may be determined that the hydrogen concentration in the gas being measured is high, and the hydrogen concentration in the gas being measured may be calculated based on the current (pump current Ip1) flowing through the current measurement pump cell 21.

[0112] The voltage threshold can be appropriately selected so that the gas sensor 100 can maintain high measurement accuracy over a wide concentration range. The voltage threshold may be a voltage value that corresponds to the concentration threshold. For example, the voltage threshold may be a voltage value that corresponds to a hydrogen concentration of approximately 1% to 10%.

[0113] Furthermore, the concentration calculation unit 93 is When the value of the current flowing through the current measuring pump cell 21 (pump current Ip1) is less than or equal to a predetermined threshold (referred to as the current threshold), it is determined that the hydrogen concentration in the gas being measured is low, and the hydrogen concentration in the gas being measured is calculated based on the electromotive force (voltage V1) generated in the voltage detection sensor cell 31. If the value of the current flowing through the current measuring pump cell 21 (pump current Ip1) is greater than (or equal to or equal to) the predetermined current threshold, it may be determined that the hydrogen concentration in the gas being measured is high, and the hydrogen concentration in the gas being measured may be calculated based on the current flowing through the current measuring pump cell 21 (pump current Ip1).

[0114] The current threshold should be appropriately selected so that the gas sensor 100 can maintain high measurement accuracy over a wide concentration range. The current threshold may be a current value that corresponds to the concentration threshold. For example, the current threshold may be a current value that corresponds to a hydrogen concentration of approximately 1% to 10%.

[0115] Alternatively, the concentration calculation unit 93, If the hydrogen concentration calculated based on the electromotive force (voltage V1) generated in the voltage detection sensor cell 31 is below a predetermined concentration threshold (or less than a predetermined concentration threshold), it is determined that the hydrogen concentration in the gas being measured is low, and the hydrogen concentration calculated based on the electromotive force (voltage V1) generated in the voltage detection sensor cell 31 is taken as the hydrogen concentration in the gas being measured. If the hydrogen concentration calculated based on the electromotive force (voltage V1) generated in the voltage detection sensor cell 31 is higher than (or equal to or greater than) the predetermined concentration threshold, it may be determined that the hydrogen concentration in the gas being measured is high, and the hydrogen concentration in the gas being measured may be calculated based on the current (pump current Ip1) flowing through the current measurement pump cell 21.

[0116] Alternatively, the concentration calculation unit 93 may be: If the hydrogen concentration calculated based on the current flowing through the current measuring pump cell 21 (pump current Ip1) is below a predetermined concentration threshold (or less than a predetermined concentration threshold), it is determined that the hydrogen concentration in the gas being measured is low, and the hydrogen concentration is calculated based on the electromotive force (voltage V1) generated in the voltage detection sensor cell 31. If the hydrogen concentration calculated based on the current flowing through the current measuring pump cell 21 (pump current Ip1) is higher than the predetermined concentration threshold (or is equal to or greater than the predetermined concentration threshold), it may be determined that the hydrogen concentration in the gas being measured is high, and the hydrogen concentration calculated based on the current flowing through the current measuring pump cell 21 (pump current Ip1) may be used as the hydrogen concentration in the gas being measured.

[0117] The concentration threshold can be appropriately selected so that the gas sensor 100 can maintain high measurement accuracy over a wide concentration range. The concentration threshold may be, for example, a value of 1% or more and 10% or less. For example, the concentration threshold may be 1% or more, 3% or more, 5% or more, or 10% or less, 8% or less, or 6% or less.

[0118] The concentration calculation unit 93 may always perform both calculations of the hydrogen concentration based on the electromotive force (voltage V1) generated in the voltage detection sensor cell 31 and calculations of the hydrogen concentration based on the current (pump current Ip1) flowing through the current measurement pump cell 21 while the gas sensor 100 is in operation, or it may perform only one of them. If only one of them is performed, for example, it may select either the calculation of the hydrogen concentration based on the electromotive force (voltage V1) or the calculation of the hydrogen concentration based on the current (pump current Ip1) based on the electromotive force (voltage V1) generated in the voltage detection sensor cell 31, the current flowing through the current measurement pump cell 21 (pump current Ip1), or the hydrogen concentration calculated based on the current flowing through the current measurement pump cell 21 (pump current Ip1), and may switch between these while measuring the hydrogen concentration.

[0119] [Embodiment 2] As another example of an embodiment of the gas sensor of the present invention, a gas sensor 200 of Embodiment 2 is shown. Figure 7 is a schematic longitudinal vertical cross-sectional view showing an example of the schematic configuration of the gas sensor 200 including the sensor element 201. It is the same cross-section as in Figure 1. In Figure 7, the same reference numerals are used for the same components as in Figure 1.

[0120] The base portion 202 has a structure in which six layers are stacked in roughly parallel order from the bottom as seen in the drawing: a first substrate layer 1, a second substrate layer 2, a first spacer layer 3, a lower proton conductor layer 214, a second spacer layer 5, and a second proton conductor layer 6, each consisting of a proton-conducting solid electrolyte layer. The first substrate layer 1, the second substrate layer 2, the first spacer layer 3, the lower second proton conductor layer 214, the second spacer layer 5, and the second proton conductor layer 6 are all layers made of a second solid electrolyte.

[0121] In the sensor element 201, the internal cavity 20 is a cavity partitioned by a lower proton conductor layer 214 made of a second solid electrolyte, a second spacer layer 5, and a second proton conductor layer 6.

[0122] In the sensor element 201, a first proton conductor layer 204 is positioned on the lower surface of the lower proton conductor layer 214, facing the reference gas chamber 30. The first proton conductor layer 204 is a layer made of a first solid electrolyte. The first proton conductor layer 204 is preferably positioned in the longitudinal direction of the sensor element 201 at a location where an internal cavity 20 exists, for example, at a location where the inner measuring electrode 22 is generally located. The reference electrode 32 is disposed on the first proton conductor layer 204 within the reference gas chamber 30.

[0123] In the sensor element 201, the voltage detection sensor cell 31 is an electrochemical sensor cell composed of a reference electrode 32, an outer electrode 23, a first proton conductor layer 204 made of a first solid electrolyte, a lower proton conductor layer 214 made of a second solid electrolyte, a second spacer layer 5, and a second proton conductor layer 6.

[0124] Similar to the sensor element 101, the hydrogen concentration in the gas to be measured can be measured using the control device 90 with respect to the sensor element 201, as described above.

[0125] While Embodiments 1 and 2 have been shown above as examples of embodiments of the present invention, the present invention is not limited to these forms. The present invention may include gas sensors with various forms of sensor elements and control device configurations, as long as it achieves the objective of the present invention, which is to provide a gas sensor capable of accurately measuring the concentration of hydrogen gas in a gas to be measured over a wide concentration range.

[0126] In embodiments 1 and 2 described above, the outer electrode 23 served as both the outside-space measuring electrode of the current measuring pump cell 21 and the detection electrode of the voltage detection sensor cell 31, but is not limited to this. For example, the outside-space measuring electrode and the detection electrode may be formed as separate electrodes.

[0127] In the embodiments 1 and 2 described above, the outer electrode 23, which serves as the out-of-air measurement electrode of the current measuring pump cell 21, is positioned on the upper surface of the second proton conductor layer 6, in a position generally corresponding to the inner measurement electrode 22, which serves as the in-air measurement electrode, but is not limited to this. The outer electrode 23 may be positioned at a different location from the inner measurement electrode 22 in the longitudinal direction of the sensor element 101 (base portion 102). It may also be positioned at a different location from the inner measurement electrode 22 in the width direction perpendicular to the longitudinal direction. The out-of-air measurement electrode only needs to be arranged with a second solid electrolyte interposed between it and the in-air measurement electrode. Since the out-of-air measurement electrode does not need to be in contact with the gas to be measured, for example, in embodiment 2, the out-of-air measurement electrode may be placed on the second solid electrolyte in the reference gas chamber 30. If the detection electrode for the out-of-space measurement electrode of the current measurement pump cell 21 is to be positioned in a location that does not come into contact with the gas to be measured, such as inside the reference gas chamber 30, then the detection electrode of the voltage detection sensor cell 31 may be formed in a location that comes into contact with the gas to be measured, as a separate electrode from the out-of-space measurement electrode of the current measurement pump cell 21.

[0128] In embodiments 1 and 2 described above, the reference electrode 32 constituting the voltage detection sensor cell 31 was disposed on the first solid electrolyte, and the outer electrode 23 of the detection electrode was disposed on the second solid electrolyte. However, the present invention is not limited to this form. It is sufficient that the reference electrode 32 is disposed on the first solid electrolyte. The detection electrode of the voltage detection sensor cell 31 only needs to be in contact with the gas to be measured, and may be disposed in contact with either the first solid electrolyte or the second solid electrolyte. When the detection electrode is disposed on the first solid electrolyte, the out-of-space measurement electrode of the current measurement pump cell 21 may be formed on the second solid electrolyte as a separate electrode from the detection electrode of the voltage detection sensor cell 31.

[0129] In the embodiments 1 and 2 described above, the reference electrode 32 of the voltage detection sensor cell 31 is positioned in approximately the same location as the outer electrode 23, which acts as the detection electrode, in the longitudinal direction of the sensor element 101 (base portion 102), but is not limited to this. The reference electrode 32 may be positioned in a different location from the outer electrode 23 in the longitudinal direction of the sensor element 101 (base portion 102). It may also be positioned in a different location from the outer electrode 23 in the width direction perpendicular to the longitudinal direction. More preferably, the reference electrode 32 is positioned in approximately the same location as the outer electrode 23, which acts as the detection electrode, in the longitudinal direction of the sensor element 101 (base portion 102). In this case, the temperature difference between the two electrodes is reduced, and the influence of thermoelectric power generated by the temperature difference can be reduced, so it is thought that the electromotive force (voltage V2) corresponding to the hydrogen concentration in the gas to be measured can be measured with greater accuracy.

[0130] In the gas sensor 100 of Embodiment 1 described above, the pump control unit 92 applies a predetermined pump voltage Vp1 between the inner measuring electrode 22 and the outer electrode 23 of the current measuring pump cell 21 using a variable power supply 24, thereby pumping out hydrogen from the gas to be measured in the internal cavity 20 by flowing a pump current Ip1. However, it is not limited to this. For example, the pump control unit 92 may apply a predetermined pump voltage Vp1 between the inner measuring electrode 22 and the outer electrode 23 of the current measuring pump cell 21 based on the electromotive force generated between the reference electrode 32 and the inner measuring electrode 22 of the current measuring pump cell 21. The electromotive force generated between the reference electrode 32 and the inner measuring electrode 22 corresponds to a value corresponding to the hydrogen concentration in the internal cavity 20. Therefore, the pump voltage Vp1 of the variable power supply 24 may be feedback controlled so that the electromotive force remains constant. This allows the pump current Ip1 flowing through the current measuring pump cell 21 to be a value corresponding to the hydrogen concentration in the gas to be measured even more accurately.

[0131] In the embodiments 1 and 2 described above, the sensor element 101 and the sensor element 201 were elongated plate-shaped elements, but the shape of the sensor element is not limited to this. As long as there is a structure in which a gas flow space to be measured and a reference gas chamber 30 exist, it can be various shapes such as disc-shaped or cylindrical.

[0132] [Method of manufacturing a gas sensor] Next, an example of a method for manufacturing the gas sensor described above will be explained. After performing predetermined processing and printing circuit patterns on multiple unfired sheet-like molded products (so-called green sheets) containing a proton-conducting solid electrolyte as a ceramic component, the multiple sheets are laminated, the laminate is cut, and then fired to produce a sensor element. The fabricated sensor element can then be assembled to create a gas sensor.

[0133] In the following explanation, we will describe the case of fabricating a gas sensor 100 that includes a sensor element 101 consisting of six layers as shown in Figure 1, as an example.

[0134] First, one green sheet containing a first solid electrolyte, such as a Ca-Zr-Mn-O perovskite compound, as a ceramic component, and five green sheets containing a second solid electrolyte, such as a Sr-Zr-YO perovskite compound, as ceramic components are prepared. The one green sheet containing the first solid electrolyte as a ceramic component is used for the first proton conductor layer 4, and the five green sheets containing the second solid electrolyte as ceramic components are used for the other five layers. Known molding methods can be used to produce the green sheets. All six green sheets may be the same thickness, or their thickness may differ depending on the layer being formed. Each of the six green sheets is pre-formed with sheet holes, etc., to be used for positioning during printing and lamination, by known methods such as punching with a punching device, to create a blank sheet. The blank sheet used for the second spacer layer 5 is also formed with internal voids and other perforations in the same manner. Other necessary perforations are also pre-formed in the other layers.

[0135] The blank sheet used for the six layers—the first substrate layer 1, the second substrate layer 2, the first spacer layer 3, the first proton conductor layer 4, the second spacer layer 5, and the second proton conductor layer 6—is subjected to printing and drying processes for various patterns required for each layer. Known screen printing techniques can be used for printing the patterns. Known drying methods can also be used for the drying process.

[0136] This process is repeated until various patterns have been printed and dried on each of the six blank sheets. Then, the six printed blank sheets are stacked in a predetermined order, positioned using sheet holes, etc., and pressed together under predetermined temperature and pressure conditions to form a laminate. The pressing process is carried out by heating and pressurizing using a laminating machine such as a known hydraulic press. The temperature, pressure, and time for heating and pressurizing depend on the laminating machine used, but can be appropriately determined to achieve good lamination.

[0137] The resulting laminate contains multiple sensor elements 101. The laminate is cut to separate it into units of sensor elements 101. The separated laminate is fired at a predetermined firing temperature to obtain sensor elements 101. That is, the sensor element 101 is obtained by the integrated firing (co-firing) of the solid electrolyte layer and the electrodes. The firing temperature should be such that the solid electrolyte constituting the base portion 102 of the sensor element 101 is sintered to become a dense body, and the electrodes and other components maintain the desired porosity. For example, firing is performed at a firing temperature of approximately 1200°C to 1500°C.

[0138] The obtained sensor element 101 is incorporated into the gas sensor 100 in such a manner that the tip of the sensor element 101 is in contact with the gas to be measured, and the rear end of the sensor element 101 is in contact with the reference gas.

[0139] As described above, according to the present invention, by using two types of proton conductors with different resistance values ​​and equipping the device with a current measuring pump cell and a voltage detection sensor cell, it is possible to provide a gas sensor that can measure the concentration of hydrogen gas in a gas to be measured with high accuracy over a wide concentration range. [Explanation of symbols]

[0140] 1. First substrate layer 2. Second substrate layer 3. First spacer layer 4,204 First proton conductor layer 214 Lower proton conductor layer 5. Second Spacer Layer 6. Second proton conductor layer 10 Gas inlet 11 Diffusion-limited pathway 15. Gas flow space under measurement 20 Internal voids 21 Current measuring pump cell 22 Inner measurement electrode 23 Outer electrode 24. Variable power supply (for current measuring pump cells) 30 Standard gas chamber 31 Voltage detection sensor cell 32 Reference electrode 70 Heater section 71 Heater electrodes 72 Heater 73 Through Holes 74 Heater Insulation Layer 76 Heater Lead 90 Control device 91 Control Unit 92 Pump Control Unit 93 Concentration calculation section 100,200 gas sensors 101,201 Sensor elements 102,202 Base part

Claims

1. A gas sensor for detecting hydrogen gas in a gas to be measured, comprising a sensor element and a control device for controlling the sensor element, The aforementioned sensor element is A base portion comprising a first solid electrolyte having proton conductivity, and a second solid electrolyte disposed in contact with at least a portion of the first solid electrolyte and having a lower proton conduction resistance than the first solid electrolyte, A gas passage to be measured having a gas inlet opening to the surface of the substrate and an internal cavity communicating with the gas inlet via a diffusion-limited passage, and having at least the second solid electrolyte present on its inner surface, A current measuring pump cell includes an in-space measuring electrode disposed on the second solid electrolyte within the internal cavity of the gas flow cavity to be measured, and an out-of-space measuring electrode disposed at a position different from the gas flow cavity to be measured on the base portion, with the in-space measuring electrode separated from the second solid electrolyte; A reference gas chamber is formed inside the base portion, spaced apart from the gas flow space to be measured, and having at least the first solid electrolyte present on its inner surface. A voltage detection sensor cell comprising a reference electrode disposed on the first solid electrolyte in the reference gas chamber, and a detection electrode disposed at a location different from the reference gas chamber and the gas flow space to be measured, wherein the reference electrode is disposed via the first solid electrolyte, or via the first solid electrolyte and the second solid electrolyte, Includes, The control device is A pump control unit that controls the current measuring pump cell, A concentration calculation unit that calculates the hydrogen concentration in the gas being measured, Includes, The concentration calculation unit calculates the hydrogen concentration in the gas to be measured based on the electromotive force generated in the voltage detection sensor cell, and / or A gas sensor that calculates the hydrogen concentration in a gas to be measured based on the current flowing through the current measuring pump cell.

2. The concentration calculation unit, If the value of the electromotive force generated in the voltage detection sensor cell is below a predetermined threshold, the hydrogen concentration in the gas to be measured is calculated based on the electromotive force generated in the voltage detection sensor cell. The gas sensor according to claim 1, wherein when the value of the electromotive force generated in the voltage detection sensor cell is greater than the predetermined threshold, the gas sensor calculates the hydrogen concentration in the gas to be measured based on the current flowing through the current measuring pump cell.

3. The concentration calculation unit, When the value of the current flowing through the current measuring pump cell is below a predetermined threshold, the hydrogen concentration in the gas to be measured is calculated based on the electromotive force generated in the voltage detection sensor cell. The gas sensor according to claim 1, wherein when the value of the current flowing through the current measuring pump cell is greater than the predetermined threshold, the gas sensor calculates the hydrogen concentration in the gas to be measured based on the current flowing through the current measuring pump cell.

4. The concentration calculation unit, If the hydrogen concentration calculated based on the electromotive force generated in the voltage detection sensor cell is below a predetermined threshold, the hydrogen concentration calculated based on the electromotive force generated in the voltage detection sensor cell is taken as the hydrogen concentration in the gas to be measured. The gas sensor according to claim 1, wherein if the hydrogen concentration calculated based on the electromotive force generated in the voltage detection sensor cell is greater than a predetermined threshold, the hydrogen concentration is calculated based on the current flowing through the current measuring pump cell.

5. The concentration calculation unit, If the hydrogen concentration calculated based on the current flowing through the current measuring pump cell is below a predetermined threshold, the hydrogen concentration is calculated based on the electromotive force generated in the voltage detection sensor cell. The gas sensor according to claim 1, wherein if the hydrogen concentration calculated based on the current flowing through the current measuring pump cell is greater than the predetermined threshold, the hydrogen concentration calculated based on the current flowing through the current measuring pump cell is set to be the hydrogen concentration in the gas to be measured.

6. The gas sensor according to claim 1, wherein the pump control unit applies a predetermined voltage between the air-fill measuring electrode and the air-out-of-air measuring electrode of the current measuring pump cell to cause current to flow through the current measuring pump cell.

7. The first solid electrolyte is a proton conductor selected from the group consisting of Ca-Zr-Mn-O and Ca-Zr-In-O perovskite compounds. The gas sensor according to claim 1, wherein the second solid electrolyte is a proton conductor selected from the group consisting of Sr-Zr-Y-O, Ba-Zr-Y-O, Ba-Ce-Y-O, and Sr-Zr-Yb-O perovskite compounds.

8. A sensor element for detecting hydrogen gas in a gas being measured, A base portion comprising a first solid electrolyte having proton conductivity, and a second solid electrolyte disposed in contact with at least a portion of the first solid electrolyte and having a lower proton conduction resistance than the first solid electrolyte, A gas passage to be measured having a gas inlet opening to the surface of the substrate and an internal cavity communicating with the gas inlet via a diffusion-limited passage, and having at least the second solid electrolyte present on its inner surface, A current measuring pump cell includes an in-space measuring electrode disposed on the second solid electrolyte within the internal cavity of the gas flow cavity to be measured, and an out-of-space measuring electrode disposed at a position different from the gas flow cavity to be measured on the base portion, with the in-space measuring electrode separated from the second solid electrolyte; A reference gas chamber is formed inside the base portion, spaced apart from the gas flow space to be measured, and having at least the first solid electrolyte present on its inner surface. A voltage detection sensor cell comprising a reference electrode disposed on the first solid electrolyte in the reference gas chamber, and a detection electrode disposed at a location different from the reference gas chamber and the gas flow space to be measured, wherein the reference electrode is disposed via the first solid electrolyte, or via the first solid electrolyte and the second solid electrolyte, A sensor element, including

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