JP5350670B2 - Control device for water vapor sensor for fuel cell, water vapor sensor for fuel cell, and fuel cell system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a control device of a steam sensor for a fuel cell in which deterioration of an electrode such as exfoliation in the steam sensor can be prevented, the steam sensor for the fuel cell, and a fuel cell system. <P>SOLUTION: The steam sensor includes a step 100 of applying pump voltage Vp+ of a positive direction to a pump cell 31 by turning on a switch SW1, a step 110 of determining whether a fixed time is progressed and moving to a step 120 when the fixed time is progressed, a step 120 of measuring pump current Ip+, a step 130 of calculating steam concentration from the pump current Ip+, a step 140 of determining whether the fixed time is progressed, namely, whether it is timing for switching an applying direction of voltage and moving to a step 150 when it is such timing, and a step 150 of turning on a switch SW2 by turning off the switch SW1 and applying pump voltage Vp- of a negative direction to the pump cell 31. <P>COPYRIGHT: (C)2010,JPO&amp;INPIT

Description

  The present invention relates to a fuel cell water vapor sensor that detects water vapor in fuel gas supplied to a fuel cell or fuel exhaust gas discharged from the fuel cell, and in particular, performs control to prevent deterioration of the fuel cell water vapor sensor. The present invention relates to a fuel cell water vapor sensor control device, a fuel cell water vapor sensor equipped with the control device, and a fuel cell system.

  Conventionally, as a sensor for detecting an air-fuel ratio of an internal combustion engine, a full-range air-fuel ratio sensor (UEGO sensor) including an oxygen pump cell and an oxygen concentration battery cell (electromotive force cell) is known. Techniques for detecting such abnormalities have also been proposed (see Patent Documents 1, 2, and 3).

  In addition, the applicant of the present application attaches the above-mentioned full-range air-fuel ratio sensor to the fuel supply path and the fuel discharge path of the fuel cell in Japanese Patent Application No. 2006-190620, and detects the water vapor concentration in the fuel gas or the fuel exhaust gas. We propose a method to do this.

  With this technology, for example, fuel gas contains only methane and water vapor, so only a pump cell is used, and a constant DC voltage (minus the electrode in the measurement chamber and plus the electrode in the fuel gas) is applied to the pump cell. Then, oxygen ions are extracted from water vapor at the three-layer interface of the electrode and pumped, and the water vapor concentration is detected from the pump current.

Apart from this, conventionally, there has also been proposed a technique for detecting water vapor using a limiting current sensor or cleaning when the sensor is deteriorated (see Patent Document 4).
JP-A-10-246720 JP 2003-90821 A JP 2007-101485 A Japanese Patent Laid-Open No. 9-257746

  However, in the technique for detecting the water vapor concentration using the above-described full-range air-fuel ratio sensor, a reducing gas in which methane and water vapor are mixed enters the measurement chamber of the full-range air-fuel ratio sensor, and measurement is performed during pumping. Since hydrogen gas is generated at the chamber-side electrode, the measurement chamber side is in a very strong reduction state. Furthermore, if pumping is continued in this state and oxygen ions are exhausted to the outside from the measurement chamber, the oxygen ions in the solid electrolyte body are excessively exhausted to the outside, resulting in deterioration of the solid electrolyte body. There is a problem that peeling or the like tends to occur on the side electrode.

  In the limit current sensor technology of the cited document 4, after the sensor deterioration occurs, voltage is applied in the reverse direction to recover the deterioration. However, in a severe environment such as a fuel cell, the electrode peeling occurs. Is not sufficient because the deterioration will continue.

  The present invention has been made to solve the above-described problems, and has as its object to control a fuel cell water vapor sensor control device, a fuel cell water vapor sensor, and a fuel capable of preventing deterioration such as electrode peeling in the water vapor sensor. It is to provide a battery system.

(1) A first aspect of the present invention is a pump cell in which a pair of porous electrodes are disposed on an oxygen ion conductive solid electrolyte body, and a diffusion rate controlling portion that controls gas diffusion on the one porous electrode side of the pump cell. And a water vapor sensor for a fuel cell that detects the concentration of water vapor in the fuel gas supplied to the fuel cell or the fuel exhaust gas discharged from the fuel cell based on the electrical signal from the pump cell. A control device for a water vapor sensor for a fuel cell that controls an alternating current between the porous electrodes of the pump cell, wherein the alternating current is controlled in accordance with the oxygen concentration on the diffusion-controlling portion side. The timing for switching the direction is controlled .

  In the present invention, since an alternating current flows between both porous electrodes of the pump cell, that is, the direction of the current flowing between both electrodes is appropriately switched to the opposite direction, it is possible to suppress deterioration of the electrodes on the diffusion rate controlling portion side. it can.

  That is, in the present invention, in a certain period, in the pump cell, a current is passed so as to pump oxygen ions from the electrode on the diffusion rate-determining part side to the electrode on the opposite side, and the water vapor concentration in the measurement gas is measured. Then, a current in the direction opposite to the current at the time of measuring the water vapor concentration is passed between both electrodes of the pump cell, and these operations are alternately repeated by an alternating current.

  Therefore, when an electric current flows in the opposite direction to the water vapor measurement, the oxygen ions are pumped from the outside to the diffusion rate-determining part side (in the following, referred to as “pumping for preventing deterioration”). Oxygen ions are not excessively discharged from the inside of the solid electrolyte body as in the case where the pumping is continued. Therefore, since the deterioration of the solid electrolyte body can be prevented, it is possible to prevent the occurrence of peeling of the porous electrode on the diffusion rate controlling portion side.

Further, in the present invention, depending on the oxygen concentration in the diffusion rate side, that controls the timing for switching the direction of the alternating current.
In the present invention, since the direction of the alternating current is switched according to the oxygen concentration on the diffusion rate controlling portion side, before the oxygen concentration on the diffusion controlling portion side is excessively decreased (therefore, oxygen ions are excessively discharged from the solid electrolyte body). Before entering the state), the direction of oxygen ion pumping can be switched. Therefore, generation | occurrence | production of peeling of a porous electrode, etc. can be prevented exactly.

  As this control content, for example, the lower the oxygen concentration, the earlier the timing of pumping oxygen ions to the diffusion rate-determining part side, or the frequency of pumping is increased, or the pumping period is lengthened. Is mentioned.

(2) A second aspect of the present invention is a pump cell in which a pair of porous electrodes are disposed on an oxygen ion conductive solid electrolyte body, and a diffusion rate controlling portion that controls gas diffusion on the one porous electrode side of the pump cell. And a water vapor sensor for a fuel cell that detects the concentration of water vapor in the fuel gas supplied to the fuel cell or the fuel exhaust gas discharged from the fuel cell based on the electrical signal from the pump cell. A control device for a fuel cell water vapor sensor for controlling the fuel cell, wherein an alternating current flows between both porous electrodes of the pump cell, and a pair of porous electrodes is provided on the oxygen ion conductive solid electrolyte body. An electromotive force cell is disposed, one porous electrode of the electromotive force cell is disposed on the diffusion-controlling portion side, the other porous electrode is disposed on the oxygen reference source side, and the electromotive force cell Depending on the output, and controlling the timing of switching the direction of the alternating current.
In the present invention, since the alternating current flows between the porous electrodes of the pump cell as in the first aspect of the invention, that is, the direction of the current flowing between the two electrodes is appropriately switched to the opposite direction. Deterioration of the electrodes and the like can be suppressed.
That is, in the present invention, in a certain period, in the pump cell, a current is passed so as to pump oxygen ions from the electrode on the diffusion rate-determining part side to the electrode on the opposite side, and the water vapor concentration in the measurement gas is measured. Then, a current in the direction opposite to the current at the time of measuring the water vapor concentration is passed between both electrodes of the pump cell, and these operations are alternately repeated by an alternating current.
Therefore, when an electric current flows in the opposite direction to the water vapor measurement, the oxygen ions are pumped from the outside to the diffusion rate-determining part side (in the following, referred to as “pumping for preventing deterioration”). Oxygen ions are not excessively discharged from the inside of the solid electrolyte body as in the case where the pumping is continued. Therefore, since the deterioration of the solid electrolyte body can be prevented, it is possible to prevent the occurrence of peeling of the porous electrode on the diffusion rate controlling portion side.
In the present invention, the oxygen ion conductive solid electrolyte body is provided with an electromotive force cell in which a pair of porous electrodes are disposed, and one porous electrode of the electromotive force cell is disposed on the diffusion rate controlling portion side, The other porous electrode is arranged on the oxygen reference source side .

Therefore, in the present invention, the oxygen concentration on the diffusion rate controlling portion side can be detected using the electromotive force of the electromotive force cell as in the full-range air-fuel ratio sensor.
Further, in the present invention, in accordance with the output of the electromotive force cell, that controls the timing of switching the direction of the alternating current.

  Since the output of the electromotive force cell corresponds to the oxygen concentration on the diffusion rate-determining part side, it is possible to suitably prevent the porous electrode from peeling off by switching the direction of the alternating current according to the output of the electromotive force cell. Can do.

( 3 ) The invention of claim 3 is characterized in that the direction of the alternating current is switched at regular intervals.
In the present invention, since the direction of the current applied to the pump cell is periodically switched to perform the water vapor concentration measurement pumping and the deterioration prevention pumping, the deterioration of the porous electrode can be prevented.

( 4 ) The invention of claim 4 is characterized in that the water vapor sensor includes a heater.
In this water vapor sensor, the pump cell and the electromotive force cell can be easily raised to the operating temperature by the heater.

( 5 ) The invention of claim 5 is characterized in that the water vapor sensor is plate-shaped.
The present invention exemplifies the shape of a water vapor sensor.
( 6 ) The invention of claim 6 is characterized in that the water vapor sensor is cylindrical.

The present invention exemplifies the shape of a water vapor sensor.
(7) The invention of claim 7 is a steam sensor for a fuel cell having a control device of the steam sensor for a fuel cell according to any one of the claims 1-6.

The present invention shows a water vapor sensor having a control device.
( 8 ) The invention of claim 8 is a fuel cell system comprising the fuel cell water vapor sensor according to claim 7 .

The present invention shows a fuel cell system including a water vapor sensor having a control device. Thereby, the reliability regarding the water vapor | steam control of a fuel cell system can be improved.
<Each configuration of the present invention will be described below>
-As a fuel cell, a solid oxide fuel cell is mentioned, for example. This solid oxide fuel cell includes a solid oxide body (solid electrolyte body), a fuel electrode, and an air electrode, and is introduced into the fuel gas and air electrode introduced into the fuel electrode when the fuel cell is operated. Electric power is generated using an oxidant gas.

  -As the pump cell, a cell in which porous electrodes are arranged on both sides of the solid electrolyte layer can be used. As this solid electrolyte layer, various oxygen ion conductive solids such as stabilized or partially stabilized zirconia are used. Electrolyte material can be used.

  As the electromotive force cell, an oxygen concentration battery cell (reference cell) in which porous electrodes are arranged on both sides of the solid electrolyte layer can be adopted as in the pump cell, and the solid electrolyte layer of the electromotive force cell is the same as that of the pump cell. Solid electrolyte material can be used.

  That is, as this electromotive force cell, an oxygen concentration battery cell (provided with an oxygen reference source) of a known full-range air-fuel ratio sensor can be adopted. Therefore, in this case, a conventional full-range air-fuel ratio sensor can be used as the water vapor sensor.

  -As the diffusion control part, it is only necessary to control the gas diffusion of fuel gas or fuel exhaust gas as the measurement gas for one porous electrode. For example, when a measurement chamber is provided to cover the porous electrode A porous layer that performs diffusion rate control may be provided between the measurement chamber and the measurement gas side (external). Or you may provide the porous layer which performs a diffusion rate control so that the porous electrode may be covered. Furthermore, a plate material or the like may be disposed close to the porous electrode through a slight gap, and diffusion rate control may be performed by the gap.

Next, the best mode of the present invention, that is, a fuel cell water vapor sensor control device, a fuel cell water vapor sensor, and a fuel cell system will be described.
[First Embodiment]
a) First, the overall configuration of the fuel cell system will be described.

  As shown in FIG. 1, a fuel cell system 1 is a system that generates power using fuel gas (for example, a mixed gas of methane and water vapor) and air, and a solid oxide that is a power generation unit in a heat insulating container 3. A fuel cell stack 5 in which stacked fuel cells (not shown) are stacked, a vaporizer 7 that vaporizes water and mixes it with fuel gas, and supplies the fuel gas to the fuel cell stack 5. An exhaust pipe 9 for discharging the used fuel exhaust gas to the outside and a burner 11 for heating the fuel cell stack 5 and the like are provided.

  A first water vapor sensor 13 for detecting water vapor in the fuel gas is disposed in the fuel gas supply path of the vaporizer 7, and a second water vapor for detecting water vapor in the fuel exhaust gas is provided in the exhaust pipe 9. A sensor 15 is arranged.

  Further, the fuel cell system 1 includes a pump 17 that supplies water to the vaporizer 7, a first blower 19 that supplies fuel gas to the vaporizer 7, and a second blower 21 that supplies air to the fuel cell stack 5. A proportional valve 23 for mixing the fuel gas with air and supplying it to the burner 11, a third blower 25 for supplying air to the proportional valve 23, and a controller 27 for controlling the operation of the fuel cell system 1. It has.

  The controller 27 includes a well-known microcomputer (not shown) and an electric circuit that drives both the water vapor sensors 13 and 15. The controller 27 includes both the water vapor sensors 13 and 15, the pump 17, and the first one. Drive signals for driving the blower 19, the second blower 21, the third blower 25, and the like are output, and electrical signals (sensor signals) from both the water vapor sensors 13, 15 are received.

b) Next, the first and second water vapor sensors 13, 15 and their electric circuits will be described.
Since the water vapor sensors 13 and 15 have the same configuration, the first water vapor sensor (simply referred to as a water vapor sensor) 13 will be described below as an example.

  As shown in FIG. 2, the water vapor sensor 13 includes a known pump cell (pump element) 31, electromotive force cell (oxygen concentration battery cell: here reference cell 33), and heater 35 stacked in a predetermined interval. Further, it has the same configuration as that of the plate-like full-range air-fuel ratio sensor (see, for example, Japanese Patent Laid-Open No. 62-148849).

  Specifically, the pump cell 31 includes an oxygen ion conductive solid electrolyte layer 37 (for example, made of stabilized or partially stabilized zirconia) and porous electrodes 39 and 41 formed on both sides thereof. Similarly, the reference cell 33 includes a solid electrolyte layer 43 and porous electrodes 45 and 47.

  In addition, a measurement chamber 49 is provided between the pump cell 31 and the reference cell 33, and the measurement chamber 49 is connected to the outside (fuel gas side) via an insulating porous diffusion limiting portion 51 that controls gas diffusion. Communicate. Furthermore, the surface of the porous electrode 39 outside the pump cell 31 (upward in the figure), that is, the outer surface of the porous electrode 39 in contact with the fuel gas is covered with a porous protective layer 53. The heater 35 is disposed outside the protective layer 53 at a predetermined interval. The heater 53 includes a heating element 57 covered with a dense insulating ceramic layer 55 such as alumina.

  On the other hand, the outside (downward in the drawing) of the reference cell 33 is covered with a solid electrolyte layer 59 made of the same material as that of the reference cell 33. A dense insulating ceramic layer 61 such as alumina is disposed around the porous electrode 47 outside the reference cell 35 so that the measurement gas does not enter (that is, in the same manner as the configuration using the oxygen reference source). .

  In particular, the water vapor sensor 13 of the present embodiment is connected to an electric circuit for driving the water vapor sensor 13 to detect the water vapor concentration in the fuel gas and preventing the water vapor sensor 13 from deteriorating.

  Specifically, for the purpose of measuring the water vapor concentration, a constant voltage (for example, 1.5 V) is applied to the pump cell 31 with the outer porous electrode 39 as the positive electrode side between the porous electrodes 39 and 41. Therefore, a constant voltage source (battery) 63 is connected through the switch SW1. On the contrary, for the purpose of preventing the deterioration of the porous electrode 41 in the measurement chamber 49, the switch SW2 is used to apply a constant voltage (for example, 1.5 V) with the porous electrode 41 as the positive electrode side. A constant voltage source 65 is connected via In this circuit, an ammeter 67 is arranged to detect forward and reverse currents flowing between the porous electrodes 39 and 41.

  On the other hand, constant current circuits 71, 73, and 75 are connected to the reference cell 33 through the switches SW4, SW5, and SW6, respectively, in order to pass a constant current between the porous electrodes 45 and 47. In this circuit, a voltmeter 77 is disposed to detect the voltage between the porous electrodes 45 and 47.

The heater 35 is connected to a variable voltage source 79 that applies an appropriate voltage so that the pump cell 31 has an appropriate operating temperature (for example, 800 ° C.).
c) Next, the operation principle of the water vapor sensor 13 will be described.

(1) Method for Measuring Water Vapor Concentration When fuel gas is supplied around the water vapor sensor 13, the fuel gas enters the measurement chamber 49 via the diffusion rate controlling unit 51.

  In this water vapor sensor 13, the predetermined pump voltage Vp is applied between the porous electrodes 39, 41 of the pump cell 31 by the operation of turning on the switch SW 1 and turning off the switch SW 2, that is, the outer porous electrode 39 Since the voltage is applied so as to be a positive electrode, the pump cell 31 can extract oxygen ions from the water vapor in the fuel gas in the measurement chamber 49. That is, in the pump cell 31, oxygen ions are pumped (pumped) from the porous electrode 41 side in the measurement chamber 49 to the outer porous electrode 39 side.

  Therefore, as shown in the timing chart of FIG. 3, the current (pump current Ip) at the time of pumping corresponds to the water vapor concentration, that is, the water vapor concentration can be expressed as a predetermined function f = (Ip). The water vapor concentration can be obtained from the pump current Ip.

(2) Degradation prevention method of water vapor sensor 13 Here, contrary to the measurement of the water vapor concentration, the switch SW1 is turned off and the switch SW2 is turned on to measure the water vapor concentration for the pump cell 31. Control is performed to prevent deterioration of the porous electrode 41 by applying a current in a direction opposite to the applied pump current.

  That is, as described above, when the water vapor sensor 13 is used, the fuel gas is introduced into the measurement chamber 49. However, this fuel gas is a reducing gas, and when pumping oxygen ions. Since oxygen is separated from the water vapor, hydrogen gas is generated in the measurement chamber 49, so that the measurement chamber 49 is strongly reduced. Therefore, if the pumping for measuring the water vapor concentration is continued, the porous electrode 41 of the pump cell 31 in the measurement chamber 49 is likely to be abnormal such as peeling.

  Therefore, here, in order to prevent an abnormality from occurring in the porous electrode 41, a voltage is applied to the pump cell 31 so that the porous electrode 41 in the measurement chamber 49 becomes a positive electrode. As a result, pumping is performed in reverse to the normal measurement of water vapor concentration. That is, oxygen ions are pumped from the outer porous electrode 39 to the porous electrode 41 side in the measurement chamber 49. Thereby, since oxygen ions in the solid electrolyte body 37 do not become excessive, even if the reduction state in the measurement chamber 49 is significant, the occurrence of peeling or the like of the porous electrode 41 in the measurement chamber 49 is prevented. can do.

d) Next, a water vapor concentration calculation process, a deterioration prevention process, and the like performed by the microcomputer will be described with reference to the flowchart of FIG.
Here, an example will be described in which the application of a voltage for measuring the water vapor concentration and the application of a reverse voltage for preventing deterioration are periodically switched at regular intervals.

  First, in step (S) 100 of FIG. 4, the switch SW1 is turned on, and the pump voltage Vp + in the positive direction (that is, the direction in which the outer porous electrode 39 side is the positive electrode) is applied to the pump cell 31.

In the following step 110, it is determined whether or not a certain time has elapsed.
In step 120, the pump current Ip + is measured.

In the subsequent step 130, the water vapor concentration is calculated from the pump current Ip + using a predetermined arithmetic expression, a map, or the like obtained in advance by experiments or the like.
In the following step 140, it is determined whether or not a certain time has elapsed, that is, whether or not it is a timing for switching the voltage application direction (for example, timing t1 in FIG. 3).

  In step 150, the switch SW1 is turned off, the switch SW2 is turned on, and the pump voltage Vp− in the reverse direction (that is, the direction in which the porous electrode 41 side in the measurement chamber 49 is the positive electrode) is applied to the pump cell 31.

  In the following step 160, it is determined whether or not a certain time has elapsed, that is, whether or not it is a timing for stopping the application of the voltage in the reverse direction (for example, timing t2).

  In the following step 170, it is determined whether or not there is an instruction for stopping the system. If the instruction is to be stopped, the process proceeds to step 180, the application of the voltage to the pump cell 31 is stopped, and this process is temporarily ended.

Although the main processing has been described here, as shown in FIG. 3, the measurement of the element temperature (the temperature of the water vapor sensor 13) may be performed after the application of the voltage in the reverse direction is completed. .
Specifically, in the process of measuring the water vapor concentration and preventing deterioration, the switches SW3 and SW4 are turned off and the switch SW5 is turned on, and a current (Icp) is supplied to the reference cell 33 to generate an electromotive force ( Vs) is measured, and at timing t2, the switch SW1 is turned on and the switch SW5 is turned off.

  Accordingly, from timing t2, the electromotive force (Vs) gradually increases due to the current (Irpvs +) from the constant current source 71 and reaches the voltage (Vrpvs) corresponding to the element temperature. Thereafter, the switch SW3 is turned off. In order to prevent polarization, the switch SW4 is turned on, and the switch SW4 is turned off at the next water vapor concentration measurement timing t3.

Therefore, since the resistance value can be found from the applied current (Irpvs +) and the voltage (Vrpvs) at that time, the element temperature can be obtained from this resistance value.
e) As described above, in the present embodiment, an alternating current in which the direction of the current is periodically switched is applied to the pump cell 31 to perform pumping when measuring the water vapor concentration, and (that is, the movement direction of oxygen ions). Pumping for prevention of deterioration is performed.

  Thereby, even if the inside of the measurement chamber 49 is in a reduced state, the oxygen ions in the solid electrolyte body 37 are not excessively reduced, and thus the occurrence of peeling of the porous electrode 41 on the measurement chamber 49 side is prevented. it can.

Further, since the element temperature can be measured using the resistance value while the alternating current is applied, it can be determined whether or not the temperature is appropriate for pumping.
[Second Embodiment]
Next, the second embodiment will be described, but the description of the same content as the first embodiment will be omitted. In addition, also in this embodiment, since the 1st, 2nd water vapor | steam sensor is the same structure, below, a 1st water vapor | steam sensor (it only describes as a water vapor | steam sensor) is demonstrated. In addition, the number similar to 1st Embodiment is used for the number of a member.

  In the present embodiment, as shown in the timing chart of FIG. 5, the voltage applied to measure the water vapor concentration and the voltage applied in the reverse direction to prevent deterioration are applied to the output voltage of the electromotive force cell 33 (that is, It is switched according to the oxygen concentration in the measurement chamber 49.

In addition, since the water vapor | steam sensor 13 used, its electric circuit, etc. are the same as that of the said 1st Embodiment, a control process is demonstrated here.
First, in step 200 of FIG. 6, the switch SW <b> 1 is turned on to apply the pump voltage Vp + in the positive direction to the pump cell 31.

In the following step 210, it is determined whether or not a certain time has elapsed, and if it has elapsed, the process proceeds to step 220.
In step 220, the pump current Ip + is measured.

In the following step 230, the water vapor concentration is calculated from the pump current Ip +.
In the following step 240, it is determined whether or not the output voltage Vs of the electromotive force cell 33 is equal to or higher than a predetermined threshold (Vs threshold), that is, whether or not it is a timing for switching the voltage application direction (for example, timing t1 in FIG. 3). If it is timing, the process proceeds to step 250.

In step 250, the switch SW1 is turned off, the switch SW2 is turned on, and the pump voltage Vp− in the reverse direction is applied to the pump cell 31.
In the next step 260, it is determined whether or not a certain time has passed, that is, whether or not it is a timing to stop the application of the voltage in the reverse direction (for example, timing t2).

  In the following step 270, it is determined whether or not there is a command for stopping the system. If the instruction is to stop, the process proceeds to step 280, the application of the voltage to the pump cell 31 is stopped, and the present process is temporarily ended.

As described above, in this embodiment, the pumping for measuring the water vapor concentration is switched from the pumping for measuring the water vapor concentration according to the output voltage Vs of the electromotive force cell 33, that is, the reduction state in the measurement chamber 49. When the degree of the above becomes serious, since the control is promptly switched to the deterioration prevention control, the deterioration of the porous electrode 41 on the measurement chamber 49 side can be suitably prevented.
[Third Embodiment]
Next, the third embodiment will be described, but the description of the same contents as the first embodiment will be omitted. In addition, also in this embodiment, since the 1st, 2nd water vapor | steam sensor is the same structure, below, a 1st water vapor | steam sensor (it only describes as a water vapor | steam sensor) is demonstrated.

In the present embodiment, as shown in FIG. 7, a water vapor sensor 71 similar to that in the first embodiment (having a structure similar to that of the full-range air-fuel ratio sensor) is used, but the reference cell 73 is not operated.
That is, as in the first embodiment, the switch SW1 and the switch SW2 are switched with respect to the pump cell 75, and an alternating current is caused to flow through the constant voltage sources 77 and 79 as shown in FIG. However, the element temperature is not measured.

  Also according to the present embodiment, the pumping for water vapor measurement and the pumping for preventing deterioration (in which the pumping direction is reversed) are periodically performed. Therefore, the same effects as those of the first embodiment can be obtained.

Here, since the reference cell 73 is not operated, a simple gas shielding plate made of alumina or the like may be employed instead of the reference cell 73.
[Fourth Embodiment]
Next, the fourth embodiment will be described, but the description of the same contents as the first embodiment will be omitted.

As shown in FIG. 9, the water vapor sensor 81 of the present embodiment is not a plate but a cylinder (test tube shape).
In this embodiment, porous electrodes 85 and 87 are formed on the outside and inside of the solid electrolyte layer 83 having a test tube shape, and a porous diffusion control layer 89 is formed on the outside of the outer porous electrode 87. Has been. A rod-shaped heater 91 is disposed inside the water vapor sensor 81.

  In the present embodiment, the solid electrolyte layer 83 provided with the porous electrodes 85 and 87 on both sides functions as a pump cell 93 that pumps oxygen ions from the outside to the inside of the water vapor sensor 83. Therefore, by measuring this pump current, The water vapor concentration can be measured.

Further, for example, similarly to the first embodiment, by periodically switching the direction of the voltage applied to the pump cell 93, it is possible to suitably prevent the deterioration of the porous electrode 87 on the diffusion rate controlling layer 89 side.
<Experimental example>
Next, experimental examples performed to confirm the effects of the present invention will be described.

In this experimental example, a continuous operation experiment for 150 hours was performed using the water vapor sensor of the first embodiment under the following experimental conditions.
[Experimental conditions]
Gas composition: H ₂ O: 50% by volume, CH ₄ : 50% by volume
Gas flow rate: 2L / min
Gas temperature: 120 ° C
Applied voltage: 1.2V alternating at 0.5 Hz In addition, as a comparative example, an experiment in which 1.2V was continuously applied was also performed (other conditions are the same as the product of the present invention).

  The results are shown in FIG. 10. The product of the present invention was suitable because the sensor output did not decrease even after 100 hours had passed. In contrast, in the comparative example, the sensor output decreased after 100 hours, and the electrode on the measurement chamber side of the pump cell peeled off after about 120 hours.

  In addition, this invention is not limited to the said embodiment at all, and it cannot be overemphasized that it can implement with a various aspect in the range which does not deviate from this invention.

It is explanatory drawing which shows the fuel cell system of 1st Embodiment. It is explanatory drawing which shows the water vapor | steam sensor of 1st Embodiment, and its electric circuit. It is a timing chart which shows operation | movement of the water vapor | steam sensor in 1st Embodiment. It is a flowchart which shows the control process of the water vapor | steam sensor in 1st Embodiment. It is a timing chart which shows operation of a water vapor sensor in a 2nd embodiment. It is a flowchart which shows the control process of the water vapor | steam sensor in 2nd Embodiment. It is explanatory drawing which shows the water vapor | steam sensor of 3rd Embodiment, and its electric circuit. It is a timing chart which shows operation of a water vapor sensor in a 3rd embodiment. It is explanatory drawing which shows the water vapor | steam sensor of 4th Embodiment. It is a graph which shows the experimental result regarding deterioration of a water vapor sensor.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Fuel cell system 5 ... Fuel cell stack 13, 15, 71, 81 ... Water vapor sensor 27 ... Controller 31, 75, 93 ... Pump cell 33, 73 ... Reference cell 35, 91 ... Heater 37, 59, 83 ... Solid electrolyte layer 39, 41, 45, 47, 85, 87 ... porous electrode

Claims (8)

A pump cell in which a pair of porous electrodes are disposed on an oxygen ion conductive solid electrolyte body, and a diffusion rate-controlling unit that controls gas diffusion on one porous electrode side of the pump cell. Control of the fuel cell water vapor sensor for controlling the operation of the fuel cell water vapor sensor for detecting the concentration of water vapor in the fuel gas supplied to the fuel cell or the fuel exhaust gas discharged from the fuel cell based on the signal A device,
Between the two porous electrodes of the pump cell has a configuration of flowing an alternating current ,
A control device for a water vapor sensor for a fuel cell, characterized in that the timing for switching the direction of the alternating current is controlled in accordance with the oxygen concentration on the diffusion rate controlling portion side . A pump cell in which a pair of porous electrodes are disposed on an oxygen ion conductive solid electrolyte body, and a diffusion rate-controlling unit that controls gas diffusion on one porous electrode side of the pump cell. Control of the fuel cell water vapor sensor for controlling the operation of the fuel cell water vapor sensor for detecting the concentration of water vapor in the fuel gas supplied to the fuel cell or the fuel exhaust gas discharged from the fuel cell based on the signal A device,
Between the two porous electrodes of the pump cell has a configuration of flowing an alternating current,
The oxygen ion conductive solid electrolyte body includes an electromotive force cell in which a pair of porous electrodes are disposed, and one porous electrode of the electromotive force cell is disposed on the diffusion-controlling portion side, and the other porous electrode A quality electrode is placed on the oxygen reference source side,
The fuel cell steam sensor control device further controls timing for switching the direction of the alternating current in accordance with the output of the electromotive force cell . 3. The fuel cell steam sensor control device according to claim 1 or 2 , wherein the direction of the alternating current is switched at regular intervals. The said water vapor sensor is provided with the heater, The control apparatus of the water vapor sensor for fuel cells of any one of Claims 1-3 characterized by the above-mentioned. The said water vapor | steam sensor is plate shape, The control apparatus of the water vapor | steam sensor for fuel cells of any one of Claims 1-4 characterized by the above-mentioned. The said water vapor sensor is cylindrical, The control apparatus of the water vapor sensor for fuel cells of any one of Claims 1-4 characterized by the above-mentioned. Steam sensor for a fuel cell characterized by comprising a control device for the water vapor sensor for a fuel cell according to any one of the claims 1-6. A fuel cell system comprising the fuel cell water vapor sensor according to claim 7 .

Images