JP2023101434A - Gas concentration detection device - Google Patents

Abstract

To provide a gas concentration detection device of explosion-proof construction with which it is possible to detect a hydrogen concentration without using oxygen in the atmospheric air.SOLUTION: A gas concentration detection device 1 comprises a sensor element 2, a first voltage application unit 31A, a current measurement unit 32, and a second voltage application unit 31B, and a gas concentration detection unit 33. The gas concentration detection unit 33 is constituted so as to detect a hydrogen concentration on the basis of a current I that is measured by the current measurement unit 32 when, upon voltage application by the first voltage application unit 31A and voltage application by the second voltage application unit 31B, the hydrogen contained in the gas G under test in a gas chamber 24 is electrochemically oxidized using an oxidative gas that is contained in the gas G under test in a gas duct 25.SELECTED DRAWING: Figure 1

Description

The present invention relates to a gas concentration detection device.

Gas concentration detectors are used to detect concentrations of various gases such as oxygen, hydrogen, carbon monoxide, and carbon dioxide. Hydrogen can generate electricity by reacting with, for example, oxygen, and technologies using hydrogen are attracting attention for forming an energy recycling society. For example, Patent Document 1 discloses a gas concentration detection device used in equipment using hydrogen.

In the _H sensor of Patent Document 1, the hydrogen concentration is detected based on the difference between the output value of the first cell having the first electrode provided with the catalyst layer and the diffusion resistance layer and the output value of the second cell having the second electrode provided with the diffusion resistance layer. The atmosphere-side electrodes in the first cell and the second cell are arranged in an atmosphere chamber into which the atmosphere is introduced.

JP 2010-266310 A

A gas concentration detection device for detecting hydrogen such as that disclosed in Patent Document 1 is used in a state where a detection target gas containing combustible gases such as hydrogen, carbon monoxide, and hydrocarbons coexists with air containing oxygen. Therefore, if the sensor element of the gas concentration detection device is damaged for some reason, there is a risk that hydrogen and oxygen in the atmosphere will burn. Therefore, it is desired to develop an explosion-proof gas concentration detection device that does not use oxygen in the atmosphere and that can more reliably ensure safety even if the sensor element is damaged.

SUMMARY OF THE INVENTION It is an object of the present invention to provide an explosion-proof gas concentration detection device capable of detecting the concentration of hydrogen without using oxygen in the atmosphere.

One aspect of the present invention is
A gas chamber (24) into which a gas to be detected (G) is introduced via a diffusion resistor (23), a gas duct (25) into which the gas to be detected is introduced, and a solid electrolyte body (21) that separates the gas chamber and the gas duct. ) is provided with a pump electrode (213) in the gas duct, and a reference electrode (212) is provided inside the solid electrolyte body;
a first voltage applying section (31A) that applies a voltage between the detection electrode and the reference electrode while the reference electrode is on the high potential side;
a current measuring unit (32) for measuring a current (I) flowing between the detection electrode and the reference electrode via the solid electrolyte body;
a second voltage applying unit (31B) that applies a voltage between the pump electrode and the reference electrode while the reference electrode is on the high potential side;
a gas concentration detection unit (33) for detecting the hydrogen concentration based on the current measured by the current measurement unit when hydrogen contained in the detection target gas in the gas chamber is electrochemically oxidized using the oxidizing gas contained in the detection target gas in the gas duct in response to application of voltage by the first voltage application unit and voltage application by the second voltage application unit.

The gas concentration detection device is devised to detect the concentration of hydrogen without using the atmosphere. Specifically, the solid electrolyte body of the sensor element is provided with a detection electrode housed in a gas chamber and a pump electrode housed in a gas duct, and a reference electrode is embedded therein. Then, the gas concentration detection device uses the oxidizing gas contained in the detection target gas instead of the atmosphere in order to detect the concentration of hydrogen contained in the detection target gas.

In the gas concentration detection device, the application of voltage between the detection electrode and the reference electrode by the first voltage application section and the application of voltage between the pump electrode and the reference electrode by the second voltage application section electrochemically oxidize hydrogen contained in the gas to be detected in the gas chamber using oxygen generated by electrochemical reduction of the oxidizing gas contained in the gas to be detected in the gas duct. With this configuration, hydrogen contained in the gas to be detected can be electrochemically oxidized without using oxygen in the atmosphere. Then, the concentration of hydrogen is detected by the gas concentration detection unit based on the current flowing between the detection electrode and the reference electrode, which is measured by the current measurement unit.

Therefore, according to one aspect of the present invention, it is possible to provide an explosion-proof gas concentration detection device capable of detecting the concentration of hydrogen without using oxygen in the atmosphere.

In addition, although the symbols in parentheses of each component shown in one aspect of the present invention indicate the correspondence with the symbols in the drawings in the embodiment, each component is not limited only to the contents of the embodiment.

FIG. 1 is an explanatory diagram showing a gas concentration detection device according to Embodiment 1. FIG. FIG. 2 is an explanatory diagram showing the sensor element of the gas concentration detection device according to the first embodiment, taken along the line II-II in FIG. FIG. 3 is an explanatory diagram showing the sensor element of the gas concentration detection device according to the first embodiment, taken along line III-III in FIG. FIG. 4 is an explanatory diagram showing the fuel cell system using the gas concentration detection device according to the first embodiment. FIG. 5 is a graph showing the relationship between the voltage applied by the voltage application unit and the direct current by the current measurement unit when the gas to be detected contains hydrogen, hydrocarbons, carbon monoxide, water vapor, and carbon dioxide according to the first embodiment. 6 is a flowchart showing an example of a gas concentration measuring method using the gas concentration detection device according to the first embodiment; FIG. FIG. 7 is an explanatory diagram showing a gas concentration detection device according to a second embodiment. FIG. 8 is a flow chart showing an example of a gas concentration measuring method using a gas concentration detection device according to the third embodiment.

A preferred embodiment of the gas concentration detection device described above will be described with reference to the drawings.
<Embodiment 1>
The gas concentration detection device 1 of this embodiment includes a sensor element 2, a first voltage application section 31A, a current measurement section 32, a second voltage application section 31B, and a gas concentration detection section 33, as shown in FIGS. The sensor element 2 has a gas chamber 24 into which the gas G to be detected is introduced through a diffusion resistance portion 23, a gas duct 25 into which the gas G to be detected is introduced, and a solid electrolyte body 21 partitioning the gas chamber 24 and the gas duct 25. A detection electrode 211 is provided on the first surface 201 of the solid electrolyte body 21 while being accommodated in the gas chamber 24 . A second surface 202 of the solid electrolyte body 21 opposite to the first surface 201 is provided with a pump electrode 213 accommodated in the gas duct 25 . A reference electrode 212 is provided inside the solid electrolyte body 21 .

The first voltage applying section 31A is configured to apply a voltage between the detection electrode 211 and the reference electrode 212 while the reference electrode 212 is on the high potential side. Current measurement unit 32 is configured to measure current I flowing between detection electrode 211 and reference electrode 212 through solid electrolyte body 21 . The second voltage applying section 31B is configured to apply a voltage between the pump electrode 213 and the reference electrode 212 while the reference electrode 212 is on the high potential side.

The gas concentration detection unit 33 is configured to receive voltage application by the first voltage application unit 31A and voltage application by the second voltage application unit 31B, and detect the hydrogen concentration based on the current I measured by the current measurement unit 32 when the hydrogen contained in the detection target gas G in the gas chamber 24 is electrochemically oxidized using the oxidizing gas contained in the detection target gas G in the gas duct 25.

The gas concentration detection device 1 of this embodiment will be described in detail below.
(Gas concentration detector 1)
As shown in FIG. 4, the gas concentration detection device 1 of the present embodiment is used in a fuel cell system 5 that generates power using hydrogen among various hydrogen utilization systems that utilize hydrogen to generate energy. The fuel cell system 5 of the present embodiment includes a cell stack 51 that is configured by a solid oxide fuel cell (SOFC) and causes hydrogen and oxygen to react via a solid electrolyte body 21, an air preheater 53 that heats air and supplies it to the cell stack 51, a reformer 52 that supplies hydrogen obtained by reforming fuel F to the cell stack 51, and the like. In the cell stack 51, oxygen is ionized from the air electrode provided on the solid electrolyte body 21 and moves to the fuel electrode provided on the solid electrolyte body 21. At the fuel electrode, hydrogen ( _H ), carbon monoxide (CO), hydrocarbons (HC), etc. undergo an electrochemical oxidation reaction to generate water (steam, _H2O ), carbon dioxide ( _CO2 ), and the like.

The offgas O discharged from the fuel chamber 512 containing the fuel electrode in the cell stack 51 contains water vapor, carbon dioxide, etc., in addition to the hydrogen not used for power generation. A part of this offgas O is mixed with the fuel F via the ejector 54 and recirculated to the reformer 52, where the hydrogen and the like contained in the offgas O are reused. In the cell stack 51, the off-gas discharged from the air chamber 513 containing the cathode and the rest of the off-gas O discharged from the fuel chamber 512 are used for combustion by the off-gas burner 55, and the heated combustion gas C discharged from the off-gas burner 55 is used to heat the reformer 52 and the air preheater 53. The gas concentration detection device 1 of this embodiment is used to detect the concentration of hydrogen contained in the offgas O discharged from the fuel chamber 512 .

The gas concentration detection device 1 includes a sensor main body 10 arranged in a pipe through which an off-gas O containing hydrogen flows, and a sensor control unit 3 electrically connected to the sensor main body 10 . The sensor body 10 has a sensor element 2 and a housing portion for arranging the sensor element 2 in a pipe. The first voltage application section 31A, the second voltage application section 31B, the current measurement section 32 and the gas concentration detection section 33 are constructed in the sensor control unit 3. FIG. The sensor control unit 3 may be built into the controller of the fuel cell system 5 .

(Sensor element 2)
As shown in FIGS. 1 to 3, the sensor element 2 includes a solid electrolyte body 21, a detection electrode 211, a pump electrode 213, and a reference electrode 212 provided on the solid electrolyte body 21, a first insulator 22A and a second insulator 22B laminated on both sides of the solid electrolyte body 21, a diffusion resistance section 23 provided on the first insulator 22A, and a heating element 26 embedded in the second insulator 22B. The solid electrolyte body 21, the first insulator 22A and the second insulator 22B of the sensor element 2 are formed in an elongated rectangular shape.

The solid electrolyte body 21 has oxide ion (O ²⁻ ) conductivity at a predetermined activation temperature. The detection electrode 211 is provided on the first surface 201 of the solid electrolyte body 21 and the pump electrode 213 is provided on the second surface 202 of the solid electrolyte body 21 . The detection electrode 211 and the pump electrode 213 are arranged at positions facing each other at the distal end portion of the solid electrolyte body 21 in the longitudinal direction L. As shown in FIG. 1 and 3, the distal end side in the longitudinal direction L is indicated by L1, and the proximal end side in the longitudinal direction L is indicated by L2.

The reference electrode 212 is embedded in the solid electrolyte body 21 at a position sandwiched between the detection electrode 211 and the pump electrode 213 . In other words, the detection electrode 211, the pump electrode 213, and the reference electrode 212 are arranged at positions overlapping each other in the stacking direction of the solid electrolyte body 21, the first insulator 22A, and the second insulator 22B. The reference electrode 212 is sandwiched between sheets forming the solid electrolyte body 21 and embedded in the solid electrolyte body 21 . The reference electrode 212 is formed longer on the base end side in the longitudinal direction L than the detection electrode 211 and the pump electrode 213 .

A gas chamber 24 that accommodates a detection electrode 211 is formed by the first insulator 22A laminated on the first surface 201 of the solid electrolyte body 21 . The gas chamber 24 is formed at the tip of the sensor element 2 in the longitudinal direction L. As shown in FIG. Further, the first insulator 22A is provided with a diffusion resistance section 23 for introducing the gas G to be detected into the gas chamber 24 at a predetermined diffusion rate. The detection target gas G is guided to the detection electrode 211 in the gas chamber 24 via the diffusion resistance section 23 .

A gas duct 25 surrounding the pump electrode 213 is formed by the second insulator 22B laminated on the second surface 202 of the solid electrolyte body 21 . The gas duct 25 opens at the front end side of the sensor element 2 in the longitudinal direction L and is formed at the same front end portion as the gas chamber 24 . A heating element 26 for heating the solid electrolyte body 21 by generating heat when energized is embedded in the second insulator 22B. Note that the heating element 26 may be embedded in the first insulator 22A. The detection target gas G is guided from the tip of the sensor element 2 in the longitudinal direction L to the pump electrode 213 inside the gas duct 25 .

The solid electrolyte body 21 is made of a zirconia-based oxide as a solid electrolyte, containing zirconia as a main component (containing 50% by mass or more), and is made of stabilized zirconia or partially stabilized zirconia obtained by partially substituting zirconia with a rare earth metal element or an alkaline earth metal element. A part of the zirconia constituting the solid electrolyte body 21 is replaced with yttria, scandia or calcia. The detection electrode 211 and the reference electrode 212 contain a noble metal such as platinum that exhibits catalytic activity with respect to oxygen, and a zirconia-based oxide as a common material with the solid electrolyte body 21 .

The first insulator 22A, the second insulator 22B, and the diffusion resistor section 23 are made of metal oxide such as aluminum oxide. The first insulator 22A and the second insulator 22B are made of a dense metal oxide that is impermeable to the detection target gas G, and the diffusion resistance section 23 is made of a porous metal oxide that is permeable to the detection target gas G.

(First voltage application unit 31A)
As shown in FIG. 1, the first voltage applying section 31A applies a DC voltage between the detection electrode 211 and the reference electrode 212 with the reference electrode 212 on the positive side and the detection electrode 211 on the negative side. The DC voltage applied by the first voltage applying section 31A is a voltage that causes oxide ions to move from the reference electrode 212 to the detection electrode 211 in order to electrochemically oxidize the hydrogen in contact with the detection electrode 211 .

(Second voltage application unit 31B)
As shown in FIG. 1, the second voltage applying section 31B applies a DC voltage between the pump electrode 213 and the reference electrode 212 with the reference electrode 212 on the plus side and the pump electrode 213 on the minus side. The second voltage applying section 31B applies a voltage between the pump electrode 213 and the reference electrode 212 to supply oxide ions to the reference electrode 212 .

More specifically, the DC voltage applied by the second voltage applying unit 31B is of a magnitude that causes the oxidizing gas such as water vapor and carbon dioxide contained in the detection target gas G in the gas duct 25 to be electrochemically reduced to generate oxygen. With this configuration, the concentration of hydrogen contained in the gas G to be detected can be detected. The DC voltage applied by the second voltage application section 31B is a voltage that causes movement of oxide ions required for the electrochemical oxidation reaction of hydrogen in the gas chamber 24 from the pump electrode 213 to the reference electrode 212 .

(Current measuring unit 32)
As shown in FIG. 1, the current measurement unit 32 is configured to detect a DC current I flowing between the detection electrode 211 and the reference electrode 212 when a DC voltage is applied between the detection electrode 211 and the reference electrode 212 by the first voltage application unit 31A and a DC voltage is applied between the pump electrode 213 and the reference electrode 212 by the second voltage application unit 31B. This DC current I is detected as a current I flowing from the detection electrode 211 to the reference electrode 212 .

In the present embodiment, an electrochemical oxidation reaction may be simply referred to as an oxidation reaction, and an electrochemical reduction reaction may simply be referred to as a reduction reaction.

(Gas concentration detector 33)
As shown in FIGS. 1 and 5, the gas concentration detection unit 33 is configured to detect the concentration of hydrogen when the oxidation voltage Vo is applied by the first voltage application unit 31A, in which the value of the current I due to hydrogen is balanced with respect to the voltage change due to the first voltage application unit 31A, and the current I due to the reducing gas other than hydrogen is not measured due to an overvoltage state. This configuration improves the accuracy of detecting the concentration of hydrogen.

FIG. 5 shows the applied voltage [V] by the first voltage applying unit 31A and the DC current I[m] measured by the current measuring unit 32 when the voltage [V] applied between the pump electrode 213 and the reference electrode 212 by the second voltage applying unit 31B is applied by the second voltage applying unit 31B and the voltage [V] applied between the detection electrode 211 and the reference electrode 212 by the first voltage applying unit 31A is changed when the detection target gas G contains hydrogen, hydrocarbon, carbon monoxide, water vapor, and carbon dioxide. A].

Oxidizing gas such as water vapor and carbon dioxide contained in the detection target gas G in the gas duct 25 is electrochemically reduced by the voltage application by the second voltage application unit 31B to generate oxygen. Further, when a voltage lower than about 1 [V] is applied by the first voltage applying unit 31A, the oxygen in the gas duct 25 becomes oxide ions at the interface between the pump electrode 213 and the solid electrolyte and conducts through the solid electrolyte body 21 and the reference electrode 212 in order to electrochemically oxidize carbon monoxide, hydrocarbons, or hydrogen contained in the detection target gas G. At the interface between the detection electrode 211 and the solid electrolyte, carbon monoxide, hydrocarbons, or hydrogen are oxidized by oxide ions. At this time, electrons move from the pump electrode 213 to the reference electrode 212 and from the reference electrode 212 to the detection electrode 211 , while current I flows from the detection electrode 211 to the reference electrode 212 and from the reference electrode 212 to the pump electrode 213 .

In addition, the flow rate of carbon monoxide, hydrocarbons, or hydrogen introduced into the gas chamber 24 when oxide ions are supplied from the pump electrode 213 to the detection electrode 211 via the reference electrode 212 is restricted by the diffusion resistance section 23 . Therefore, the oxidation reaction of carbon monoxide, hydrocarbons, or hydrogen is rate-determined by the diffusion resistor section 23, and even if the voltage applied by the first voltage application section 31A changes so as to increase, there is a voltage range that exhibits a limiting current characteristic in which the current I measured by the current measurement section 32 does not change.

As shown in FIG. 5, the applied voltages that produce the current I due to carbon monoxide, hydrocarbons or hydrogen are appropriately different. When a lower applied voltage is applied by the first voltage applying section 31A, there is a voltage range in which the limiting current characteristic of the current I due to carbon monoxide or hydrocarbons occurs. The voltage range in which the limiting current characteristic of the current I due to hydrogen occurs is higher than the voltage range in which the current I due to carbon monoxide or hydrocarbons occurs. In other words, the hydrogen detection range Vh exists as a voltage range in which the limiting current characteristics of the current I due to hydrogen occur and in which the current I due to reducing gases other than hydrogen, such as carbon monoxide and hydrocarbons, is not measured due to an overvoltage state.

The oxidizing voltage Vo applied by the first voltage applying section 31A when detecting hydrogen is applied as a voltage within this hydrogen detection range Vh. Then, when the detection target gas G contains hydrogen, when the voltage Vo for oxidation is applied by the first voltage applying unit 31A, the magnitude of the current I measured by the current measuring unit 32 changes according to the concentration of hydrogen. Thereby, the concentration of hydrogen is detected by the gas concentration detection unit 33 .

When a voltage of about 1 [V] is applied between the detection electrode 211 and the reference electrode 212 by the first voltage application unit 31A, neither the electrochemical oxidation reaction of the reducing gas containing hydrogen nor the electrochemical reduction reaction of the oxidizing gas such as water vapor or carbon dioxide occurs, and no current I flows between the detection electrode 211 and the pump electrode 213 via the reference electrode 212. When the detection target gas G contains hydrogen, an open circuit voltage (OCV, also called natural potential or electromotive force) of about 1 [V] is generated between the detection electrode 211 and the pump electrode 213 via the reference electrode 212. In the vicinity of about 1 [V], the open circuit voltage and the voltage applied by the first voltage applying section 31A are balanced, and a state occurs in which the current I does not flow between the detection electrode 211 and the reference electrode 212.

(Gas concentration measurement method of gas concentration detection device 1)
Next, an example of a gas concentration measuring method using the gas concentration detection device 1 will be described with reference to FIG.
When the gas concentration detection device 1 is started, the heating element 26 of the sensor element 2 is energized, and the solid electrolyte body 21, the detection electrode 211, the pump electrode 213 and the reference electrode 212 of the sensor element 2 are heated to the activation temperature (step S101). Next, after the solid electrolyte body 21, the detection electrode 211, the pump electrode 213, and the reference electrode 212 reach the activation temperature, the voltage Vo for oxidation is applied between the detection electrode 211 and the reference electrode 212 by the first voltage application section 31A, and the voltage is applied between the pump electrode 213 and the reference electrode 212 by the second voltage application section 31B (step S102). Next, it is determined whether or not a predetermined sampling time has elapsed (step S103). When the predetermined sampling time has elapsed, the current measurement unit 32 measures the current I flowing between the detection electrode 211 and the reference electrode 212 (step S104). Then, the concentration of hydrogen contained in the detection target gas G is detected by the gas concentration detection unit 33 according to the magnitude of the current I (step S105).

After that, steps S104 and S105 are repeatedly executed each time a predetermined sampling time in step S103 elapses until an instruction to end the detection is issued (step S106).

(Effect)
The gas concentration detection device 1 of this embodiment is devised to detect the concentration of hydrogen without using the atmosphere. Specifically, the solid electrolyte body 21 of the sensor element 2 is provided with a detection electrode 211 housed in the gas chamber 24 and a pump electrode 213 housed in the gas duct 25, and a reference electrode 212 is embedded. Then, in order to detect the concentration of hydrogen contained in the detection target gas G, the gas concentration detection device 1 uses the oxidizing gas contained in the detection target gas G instead of the atmosphere.

In the gas concentration detection device 1, the first voltage application section 31A applies an oxidizing voltage Vo between the detection electrode 211 and the reference electrode 212, and the second voltage application section 31B applies a voltage between the pump electrode 213 and the reference electrode 212. Thus, the hydrogen contained in the detection target gas G in the gas chamber 24 is electrochemically reduced, and the oxidizing gas such as water vapor and carbon dioxide contained in the detection target gas G in the gas duct 25 is electrochemically reduced. Electrochemically oxidized. With this configuration, it is possible to electrochemically oxidize the hydrogen contained in the detection target gas G without using oxygen in the atmosphere. Then, the concentration of hydrogen is detected by the gas concentration detection unit 33 based on the current I flowing between the detection electrode 211 and the reference electrode 212 measured by the current measurement unit 32 .

Therefore, according to the gas concentration detection device 1 of this embodiment, the concentration of hydrogen can be detected without using oxygen in the atmosphere, and the gas concentration detection device 1 having an explosion-proof structure can be formed.

<Embodiment 2>
As shown in FIG. 7, this embodiment shows the gas concentration detection device 1 in which the voltage is applied between the pump electrode 213 and the reference electrode 212 by the second voltage applying section 31B in a state where a constant current I flows between the pump electrode 213 and the reference electrode 212. The amount of oxygen (oxide ions) supplied from the pump electrode 213 to the reference electrode 212 depends on the amount of oxygen generated when oxidizing gases such as water vapor and carbon dioxide contained in the detection target gas G in the gas duct 25 are reduced. In addition, a change in the temperature of the solid electrolyte body 21 and the like of the sensor element 2 may change the resistance value of the solid electrolyte body 21 and the like, which may change the amount of oxide ions that can move from the pump electrode 213 to the reference electrode 212 .

Therefore, it is possible that the amount of oxygen supplied from the pump electrode 213 to the reference electrode 212 cannot be adjusted only by adjusting the voltage applied by the second voltage applying section 31B. Therefore, a constant current I is caused to flow from the reference electrode 212 to the pump electrode 213 when the voltage is applied by the second voltage applying section 31B. Specifically, a constant current circuit 34 is provided between the pump electrode 213 and the reference electrode 212 . The constant current circuit 34 may have various configurations using constant current diodes, transistors, OP amplifiers, and the like.

In the gas concentration detection device 1 of the present embodiment, the constant current I is caused to flow from the reference electrode 212 to the pump electrode 213 by the second voltage applying section 31B, so that the potential of the reference electrode 212 is less likely to vary. Also, the amount of oxygen supplied from the pump electrode 213 to the reference electrode 212 can be appropriately adjusted.

Other configurations, effects, and the like in the gas concentration detection device 1 of the present embodiment are the same as the configuration, effects, and the like of the first embodiment. Also in the present embodiment, constituent elements indicated by the same reference numerals as those in the first embodiment are the same as those in the first embodiment.

<Embodiment 3>
As shown in FIGS. 1 and 5, this embodiment shows a gas concentration detection device 1 in which the gas concentration detection unit 33 detects not only hydrogen contained in the detection target gas G but also reducing gases other than hydrogen. The gas concentration detection unit 33 of this embodiment detects the concentration of hydrogen based on the current I measured by the current measurement unit 32 when the first voltage application unit 31A applies the first oxidation voltage Vo1 between the detection electrode 211 and the reference electrode 212. The first oxidation voltage Vo1 is a voltage in which the hydrogen contained in the detection target gas G is electrochemically oxidized using the oxygen contained in the atmosphere, the current I due to hydrogen exhibits a limiting current characteristic in which the value of the current I due to hydrogen is balanced with respect to changes in voltage, and the current I due to reducing gases other than hydrogen is not measured due to an overvoltage state.

Further, the gas concentration detection unit 33 of the present embodiment detects the concentration of reducing gases other than hydrogen using the current I measured by the current measurement unit 32 when a second oxidation voltage Vo2 lower than the first oxidation voltage Vo1 is applied between the detection electrode 211 and the reference electrode 212 by the first voltage application unit 31A. The second oxidation voltage Vo2 is a voltage at which the reducing gas other than hydrogen contained in the detection target gas G is electrochemically oxidized using oxygen contained in the atmosphere, and at which the value of the current I due to the reducing gas is balanced with respect to the voltage change, and the current I due to hydrogen exhibits the limiting current characteristic. In FIGS. 1 and 5, the first oxidation voltage Vo1 and the second oxidation voltage Vo2 are shown in parentheses.

The gas concentration detection device 1 of this embodiment is also used in a fuel cell system 5 that generates power using hydrogen. The offgas O discharged from the fuel chamber 512 of the cell stack 51 of the fuel cell system 5 contains reducing gases such as carbon monoxide (CO) and hydrocarbons (HC) supplied from the reformer 52 to the fuel electrode, in addition to hydrogen not used for power generation. The gas concentration detection device 1 of this embodiment detects hydrogen and carbon monoxide as a reducing gas other than hydrogen.

The first voltage application section 31A of this embodiment is configured to instantly switch the voltage applied between the detection electrode 211 and the reference electrode 212 between the first oxidation voltage Vo1 and the second oxidation voltage Vo2. The second oxidation voltage Vo2 is set as a voltage at which carbon monoxide as a reducing gas is oxidized. The gas concentration detection unit 33 of this embodiment is configured to detect the concentration of carbon monoxide based on a value obtained by subtracting the current I measured by the current measurement unit 32 when the first oxidation voltage Vo1 is applied from the current I measured by the current measurement unit 32 when the second oxidation voltage Vo2 is applied.

FIG. 5 shows the relationship between the applied voltage [V] and the direct current I [mA] measured by the current measurement unit 32 when the voltage applied between the detection electrode 211 and the reference electrode 212 by the first voltage application unit 31A is changed when the detection target gas G contains hydrogen, carbon monoxide, and hydrocarbons (methane, etc.). FIG. 5 shows the difference in current I when hydrogen, carbon monoxide, or methane is detected when the applied voltage is 1 [V] or less.

As in the case of the first embodiment, the voltage range in which the limiting current characteristic of hydrogen occurs is higher than the voltage range in which the limiting current characteristic of carbon monoxide occurs. A hydrogen detection range Vh exists as a voltage range in which the limiting current characteristics of the current I due to hydrogen occur and in which the current I due to carbon monoxide does not occur. The first oxidation voltage Vo1 is applied as a voltage within the hydrogen detection range Vh. The concentration of hydrogen is detected by the gas concentration detection unit 33 according to the magnitude of the current I measured by the current measurement unit 32 .

On the other hand, in the voltage range in which the limiting current characteristics of the current I due to carbon monoxide occur, there are a portion overlapping the voltage range in which the limiting current characteristics of the current I due to hydrogen occur and a portion overlapping the voltage range in which the limiting current characteristics of the current I due to hydrocarbons occur as the carbon monoxide detection range Vc. Further, the carbon monoxide detection range Vc is set to a range in which almost no current I is generated by hydrocarbons such as methane. The second oxidation voltage Vo2 is applied as a voltage within the carbon monoxide detection range Vc.

When the first voltage application unit 31A applies the second oxidation voltage Vo2 between the detection electrode 211 and the reference electrode 212, the current I measured by the current measurement unit 32 includes the current I due to carbon monoxide and the current I due to hydrogen. Therefore, when the second voltage for oxidation Vo2 is applied to detect the concentration of carbon monoxide, the first voltage for oxidation Vo1 is applied at the same time with a time lag to detect the concentration of hydrogen.

Specifically, the first voltage application unit 31A instantly switches between the state of applying the first voltage for oxidation Vo1 and the state of applying the second voltage for oxidation Vo2, and the current measurement unit 32 measures both the current I generated by the oxidation reaction of hydrogen and the current I generated by the oxidation reaction of hydrogen and carbon monoxide. Then, the gas concentration detection unit 33 detects the concentration of carbon monoxide by subtracting the current I generated by the oxidation reaction of hydrogen from the current I generated by the oxidation reaction of hydrogen and carbon monoxide.

(Gas concentration measurement method of gas concentration detection device 1)
Next, an example of a gas concentration measuring method using the gas concentration detection device 1 of this embodiment will be described with reference to FIG.
Also in the gas concentration measuring method of the present embodiment, step S201 is executed in the same manner as step S101 in FIG. 6 of the first embodiment, and after the solid electrolyte body 21, the detection electrode 211, and the reference electrode 212 reach the activation temperature, the first voltage application section 31A applies the first oxidation voltage Vo1 between the detection electrode 211 and the reference electrode 212 (step S202). Next, it is determined whether or not a predetermined sampling time has elapsed (step S203). When the predetermined sampling time has elapsed, the current measurement unit 32 measures the current I flowing between the detection electrode 211 and the reference electrode 212 (step S204). Then, the concentration of hydrogen contained in the detection target gas G is detected by the gas concentration detection unit 33 based on the current I when the first voltage for oxidation Vo1 is applied (step S205).

Next, the first voltage application unit 31A applies the second oxidation voltage Vo2 between the detection electrode 211 and the reference electrode 212 (step S206). Next, the current I flowing between the detection electrode 211 and the reference electrode 212 is measured by the current measurement unit 32 (step S207). Then, the gas concentration detection unit 33 detects the concentration of carbon monoxide contained in the detection target gas G based on the value obtained by subtracting the current I when the first oxidation voltage Vo1 is applied from the current I when the second oxidation voltage Vo2 is applied (step S208). Next, the first voltage application unit 31A applies the first oxidation voltage Vo1 between the detection electrode 211 and the reference electrode 212 (step S209).

After that, steps S204 to S209 are repeatedly executed each time a predetermined sampling time in step S203 elapses until an instruction to end detection is issued (step S210).

(Effect)
The gas concentration detection device 1 of the present embodiment is capable of detecting hydrogen and carbon monoxide contained in the detection target gas G by changing the voltage applied between the detection electrode 211 and the reference electrode 212 via the solid electrolyte body 21 by the first voltage application section 31A. When the voltage applied between the detection electrode 211 and the reference electrode 212 by the first voltage applying section 31A changes to the second oxidation voltage Vo2 which is even lower than the first oxidation voltage Vo1, hydrogen and carbon monoxide are electrochemically oxidized. There is a voltage range in which both the current I due to hydrogen and the current I due to carbon monoxide exhibit limiting current characteristics, and the second oxidation voltage Vo2 is set within this voltage range. In the gas concentration detection device 1 of the present embodiment, utilizing the fact that the state of the electrochemical oxidation reaction differs depending on the applied voltage, hydrogen is detected when the first voltage for oxidation Vo1 is applied, and carbon monoxide is detected when the second voltage for oxidation Vo2 is applied.

Therefore, according to the gas concentration detection device 1 of this embodiment, hydrogen and carbon monoxide can be detected by changing the voltage applied between the detection electrode 211 and the reference electrode 212 of the sensor element 2.

Other configurations, effects, and the like in the gas concentration detection device 1 of the present embodiment are the same as the configurations, effects, and the like of the first and second embodiments. Further, in the present embodiment as well, the components indicated by the same reference numerals as those in the first and second embodiments are the same as those in the first and second embodiments.

The present invention is not limited to only each embodiment, and further different embodiments can be configured without departing from the scope of the invention. In addition, the present invention includes various modifications, modifications within the equivalent range, and the like. Furthermore, the technical concept of the present invention also includes combinations, forms, and the like of various components assumed from the present invention.

REFERENCE SIGNS LIST 1 gas concentration detection device 2 sensor element 21 solid electrolyte body 23 diffusion resistance section 24 gas chamber 25 gas duct 31A first voltage application section 31B second voltage application section 32 current measurement section 33 gas concentration detection section

Claims (4)

A gas chamber (24) into which a gas to be detected (G) is introduced via a diffusion resistor (23), a gas duct (25) into which the gas to be detected is introduced, and a solid electrolyte body (21) that separates the gas chamber and the gas duct. ) is provided with a pump electrode (213) in the gas duct, and a reference electrode (212) is provided inside the solid electrolyte body;
a first voltage applying section (31A) that applies a voltage between the detection electrode and the reference electrode while the reference electrode is on the high potential side;
a current measuring unit (32) for measuring a current (I) flowing between the detection electrode and the reference electrode via the solid electrolyte body;
a second voltage applying unit (31B) that applies a voltage between the pump electrode and the reference electrode while the reference electrode is on the high potential side;
a gas concentration detection unit (33) for detecting the concentration of hydrogen based on the current measured by the current measurement unit when hydrogen contained in the detection target gas in the gas chamber is electrochemically oxidized using the oxidizing gas contained in the detection target gas in the gas duct in response to the voltage application by the first voltage application unit and the voltage application by the second voltage application unit. 2. The gas concentration detection device according to claim 1, wherein the gas concentration detection unit is configured to detect the concentration of hydrogen when an oxidizing voltage is applied by the first voltage application unit, in which the value of the current due to the hydrogen is balanced with respect to a change in the voltage by the first voltage application unit, and the current due to the reducing gas other than the hydrogen is not measured due to an overvoltage state. 3. The gas concentration detection device according to claim 1, wherein the voltage application by said second voltage application section is performed in a state where a constant current flows between said pump electrode and said reference electrode. The gas concentration detection device according to any one of claims 1 to 3, wherein the voltage applied by the second voltage application unit is set to a magnitude that electrochemically reduces the oxidizing gas contained in the gas to be detected in the gas duct.

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