JP4629986B2 - Fuel cell system - Google Patents

Description

  The present invention relates to a fuel cell system, and more particularly to a fuel cell system that improves the durability of an electrolyte membrane.

  In recent years, solid polymer fuel cells have attracted attention as power sources for electric vehicles. A polymer electrolyte fuel cell (PEFC) can generate power even at room temperature, and is being put into practical use for various purposes other than automobiles.

In general, a fuel cell system is a fuel cell in which a cathode is disposed on one side of a solid polymer electrolyte membrane and an anode is disposed on the other side, and oxygen in air (oxidant) supplied into a cathode gas flow path. Gas) and hydrogen (fuel gas) supplied into the anode gas flow path generate electric power through an electrochemical reaction that generates water.
In the operation of the fuel cell, the environment in the fuel cell changes greatly (below the freezing point to about 80 degrees) between power generation and when power generation is stopped due to an environmental temperature such as an outside air temperature.

  By the way, normally, in a fuel cell system, when the fuel cell is stopped, the cathode gas channel is opened to the atmosphere, and the anode gas channel is closed, so that the fuel gas flows out or is mixed with the oxidant gas. It is preventing. However, when the anode gas flow path is a closed system, the gas pressure in the anode gas flow path becomes smaller than the gas pressure in the cathode gas flow path due to condensation accompanying the temperature drop of the water vapor contained in the gas. A differential pressure (hereinafter referred to as “electrode pressure difference”) is generated between the gas pressure in the gas channel and the gas pressure in the cathode gas channel.

  In addition, when the fuel cell is stopped, the inter-electrode differential pressure may also occur when both the cathode gas channel and the anode gas channel are closed (both include the same amount of water vapor). In other words, since the volumetric contraction rate of air is larger than the volumetric contraction rate of hydrogen, the gas pressure in the cathode gas channel is smaller than the gas pressure in the anode gas channel in extremely cold regions such as Alaska. Differential pressure is generated.

  The generation of such an inter-electrode differential pressure is undesirable because it imposes a load on the solid polymer electrolyte membrane and degrades the solid polymer electrolyte membrane.

Conventionally, there is a differential pressure prevention device for preventing a differential pressure between electrodes of a fuel cell (see, for example, Patent Document 1). FIG. 5 is an overall configuration diagram of a conventional inter-electrode differential pressure preventing device.
As shown in FIG. 5, the conventional inter-electrode differential pressure prevention device 100 communicates with an anode water seal 103 that communicates with the fuel gas supply passage 102 of the fuel cell 101 and an oxidant gas supply passage 104 of the fuel cell 101. A cathode water seal 105 is provided, and the anode water seal 103 and the lower end of the cathode water seal 105 are configured to communicate with each other through a communication path 106. The anode water seal 103 and the cathode water seal 105 are filled with a liquid such as water or mercury.

According to the configuration of the inter-electrode differential pressure preventing device 100, when the inter-electrode differential pressure is generated, the pressure of the fuel gas is transmitted to the anode water seal 103 and the pressure of the oxidant gas is transferred to the cathode water seal 105. To be told. For example, when the gas pressure in the anode gas flow channel 101a is smaller than the gas pressure in the cathode gas flow channel 101b and an inter-electrode differential pressure is generated, the liquid level in the cathode water sealer 105 is lowered at the same time as the anode The liquid level in the water sealer 103 rises and a difference occurs between the positions of the liquid levels. The position of the liquid level is balanced and stable when the pressure corresponding to the difference coincides with the inter-electrode differential pressure. Due to the change in the liquid level, a part of the oxidant gas is extracted into the cathode water seal 105 and a part of the fuel gas is returned from the anode water seal 103. As a result, the differential pressure is reduced and the differential pressure between the electrodes can be eliminated / reduced.
JP-A-6-36785 (Claim 1, paragraphs 0011, 0017, 0018, FIG. 1)

However, when water is used as the liquid in the anode water seal 103 and the cathode water seal 105, when the fuel cell 101 becomes below freezing when the fuel cell 101 is stopped, the inside of the anode water seal 103 and the cathode water seal 105 There was a problem that would freeze and stop functioning.
Further, since the above-described inter-electrode differential pressure prevention device 100 is provided with various new devices such as the anode water seal 103 and the cathode water seal 105, there is a problem that the fuel cell system is enlarged as a whole.

  Therefore, an object of the present invention is to provide a fuel cell system that reliably eliminates and reduces the inter-electrode differential pressure that occurs when the fuel cell is stopped, and that realizes a simple configuration.

As means for solving the above-mentioned problems, the present invention provides an electrolyte membrane disposed between an anode and a cathode, and reacts a fuel gas supplied to the anode and an oxidant gas supplied to the cathode. A fuel cell for generating electricity; an anode gas flow path through which fuel gas flows through the anode; a cathode gas flow path through which oxidant gas flows through the cathode; and the anode gas flow upstream of the anode. A first valve provided in a path; a second valve provided in the anode gas flow path downstream of the anode; a third valve provided in the cathode gas flow path upstream of the cathode; and the cathode downstream of the fourth valve provided in the cathode gas passage, a first detecting a fuel gas pressure of the anode gas flow path between the first valve and the second valve Comprises a force detecting unit, and a second pressure detecting means for detecting an oxidant gas pressure of the cathode gas flow path between the third valve and the fourth valve to stop the power generation of the fuel cell When power generation is stopped, the first valve and the second valve are closed, and the anode gas flow path between the first valve and the second valve is closed from the atmosphere, and the third valve and the fourth valve Is opened and the cathode gas flow path between the third valve and the fourth valve is opened to the atmosphere, and after the power generation of the fuel cell is stopped, the first pressure detecting means When the fuel gas pressure detected by the second pressure detection means is lower than the oxidant gas pressure detected by the second pressure detection means , the fuel gas pressure in the anode gas flow path and the cathode gas are determined based on the detection value of the pressure detection means. Flow Comprising a differential pressure detecting means for detecting a differential pressure between the oxidant gas pressure inside the detected differential pressure of the differential pressure detecting means, a differential pressure determining means for determining whether a predetermined value or less, the When the differential pressure determining means determines that the differential pressure exceeds a predetermined value, the second valve is opened, and the anode gas flow path between the first valve and the second valve is opened to the atmosphere. A fuel cell system characterized by

According to such a fuel cell system, after the power generation of the fuel cell is stopped, the differential pressure detection means is configured such that the gas pressure in the anode gas channel (fuel gas pressure) and the gas pressure in the cathode gas channel (oxidant gas pressure) ), And the differential pressure determination means determines whether or not the detected value is equal to or less than a predetermined value. And a differential pressure elimination means (2nd valve) makes a differential pressure below a predetermined value according to the determination result (determination result that exceeds predetermined value). Thus, the load on the electrolyte membrane can be reduced by eliminating / reducing the differential pressure between the gas pressure in the anode gas passage and the gas pressure in the cathode gas passage (inter-electrode differential pressure). Therefore, it is possible to suppress the deterioration of the electrolyte membrane and improve the durability.

Further , according to such a fuel cell system, the opening means (second valve) opens the anode gas flow path to the atmosphere. By doing so, the pressure difference between the electrodes can be eliminated / reduced.
That is, according to the fuel cell system such as this, without adding a special component, it can be eliminated, reducing the inter-electrode differential pressure only in existing devices. In addition, since no gas is supplied in order to eliminate or reduce the differential pressure between the electrodes , the fuel consumption can be improved.

  In the fuel cell system, when the second valve is opened, the differential pressure detected by the differential pressure detecting means is reduced, and the fuel gas pressure in the anode gas flow path detected by the first pressure detecting means is reduced. And the oxidant gas pressure in the cathode gas flow path detected by the second pressure detecting means becomes equal, the second valve is closed and the anode between the first valve and the second valve is closed. Preferably, the gas flow path is closed, the third valve and the fourth valve are closed, and the cathode gas flow path between the third valve and the fourth valve is closed.

According to the present invention , the pressure difference between the electrodes can be eliminated / reduced. And the load to an electrolyte membrane can be reduced by eliminating and reducing the pressure difference between electrodes. Therefore, it is possible to suppress the deterioration of the electrolyte membrane and improve the durability.

Next, embodiments of the present invention will be described in detail with reference to the drawings as appropriate. FIG. 1 is a schematic configuration diagram of a fuel cell system according to the present embodiment.
The fuel cell system 1 is supplied into a hydrogen gas as a fuel gas supplied into an anode gas flow path 3 connected to an anode 21 of a fuel cell 2 and into a cathode gas flow path 5 connected to a cathode 22. Electricity is generated by an electrochemical reaction that generates water with air as an oxidant gas. In the present invention, in particular, after the fuel cell 2 is stopped, the pressure difference between the pressure of the fuel gas in the anode gas channel 3 and the pressure of the oxidant gas in the cathode gas channel 5 is eliminated / reduced. The purpose is to do.

  As shown in FIG. 1, the fuel cell system 1 includes a fuel cell 2, a pressure sensor 4 (first pressure detection means) provided in an anode gas flow path 3 connected to an anode 21 of the fuel cell 2, The pressure sensor 6 (second pressure sensor) provided in the cathode gas passage 5 connected to the cathode 22 of the fuel cell 2 and the pressure of the fuel gas flowing in the anode gas passage 3 (hereinafter referred to as “fuel gas”) Valves V1 and V2 for adjusting the pressure, and valves V3 and V4 for adjusting the pressure of the oxidant gas flowing through the cathode gas flow path 5 (hereinafter referred to as “oxidant gas pressure”); An ECU 7 that controls opening and closing of the valves V1 to V4 is provided.

  The fuel cell 2 is formed by laminating a membrane electrode assembly formed by disposing an anode 21 on one side of a solid polymer electrolyte membrane 23 and a cathode 22 on the other side through a separator. In FIG. 1, it is shown in a simplified manner.

  An anode gas flow path 3 through which fuel gas flows is connected to the anode 21 of the fuel cell 2. A high-pressure hydrogen tank 31 is disposed at the end of the anode gas passage 3 located upstream of the anode 21, and fuel gas is supplied from the tank 31 into the anode gas passage 3.

The anode gas flow path 3 located upstream from the anode 21 is provided with the valve V1, the pressure sensor 4, and the ejector 32 that sucks off-gas discharged from the fuel cell 2. The pressure sensor 4 detects the pressure of the fuel gas flowing through the anode gas flow path 3 and transmits the detected value to the ECU 7. The valve V1 is controlled to open and close based on a signal transmitted from the ECU 7.
The above-described valve V2 is provided in the anode gas flow path 3 (off-gas flow path) located on the downstream side of the anode 21. This valve V2 is a purge valve for discharging the fuel gas discharged from the anode 21 side of the fuel cell 2 to the outside, and its opening and closing is controlled based on a signal transmitted from the ECU 7. The tank 31, the valve V1, the ejector 32, and the like correspond to “ gas supply means”, and the valve V2 corresponds to “ opening means”.

  A cathode gas flow path 5 through which an oxidant gas flows is connected to the cathode 22 of the fuel cell 2. A compressor 51 is disposed at the end of the cathode gas flow path 5 located on the upstream side of the cathode 22. The compressor 51 compresses the atmosphere and supplies the atmosphere as an oxidant gas into the cathode gas flow path 5, and its drive is controlled by the ECU 7.

Further, the valve V3 and the pressure sensor 6 described above are provided in the cathode gas flow path 5 located on the upstream side of the cathode 22. The pressure sensor 6 detects the pressure of the fuel gas flowing through the cathode gas flow path 5 and transmits the detected value to the ECU 7. The valve V3 is controlled to open and close based on a signal transmitted from the ECU 7.
The cathode gas flow path 5 (off-gas flow path) located downstream from the cathode 22 is provided with the valve V4. This valve V4 is a purge valve for discharging the oxidant gas discharged from the cathode 22 side of the fuel cell 2 to the outside, and its opening and closing is controlled based on a signal transmitted from the ECU 7. The compressor 51, the valve V3, and the like correspond to “ gas supply means”, and the valve V4 corresponds to “ opening means”.

Next, the internal configuration of the ECU 7 will be described. FIG. 2 is a schematic configuration diagram of the ECU.
As shown in FIG. 2, the ECU 7 includes differential pressure detection means 71 that detects the inter-electrode differential pressure based on the detected values transmitted from the pressure sensors 4 and 6, and the detected value by the pressure sensor 4 is detected by the pressure sensor 6. When the pressure difference is smaller than the detection value, the first differential pressure determination means 72 for determining whether or not the pressure difference between the electrodes is equal to or less than a predetermined value; When the pressure difference is small, the valve V1 is driven based on the determination result of the second differential pressure determination means 73 for determining whether or not the pressure difference between the electrodes is equal to or less than a predetermined value and the first differential pressure determination means 72. The compressor 51 is driven based on the determination result of the second differential pressure determination means 73 and the signal generation circuit 74 that generates a signal to be transmitted to the V1 drive circuit 81 or the V2 drive circuit 82 that drives the valve V2. Compressor drive circuit 83, valve V V3 driving circuit 84 for driving the or,, is configured to include a signal generation unit 75 for generating a signal to be transmitted to V4 drive circuit 85 for driving the valve V4. Each predetermined value is stored in advance in the storage device of each differential pressure determination means 72, 73, and this predetermined value can be appropriately changed. Incidentally, the first and second differential pressure determination means 72 and 73 can be configured as one differential pressure determination means.

The operation of the fuel cell system 1 configured as described above will be described. FIG. 3 is a flowchart of the fuel cell system, where (a) shows a case where the pressure in the anode gas flow path is smaller than the pressure in the cathode gas flow path, and (b) shows that the pressure in the cathode gas flow path is the anode gas flow path. This is the case when the internal pressure is smaller.
In the fuel cell system 1, after the fuel cell 2 is stopped, the valves V1 and V2 are basically closed so that the anode gas flow path 3 of the fuel gas is closed, and the cathode gas flow of the oxidant gas Since the path 5 is opened, it is assumed that the valves V3 and V4 are opened.

  First, the case where the pressure in the anode gas flow path 3 is smaller than the pressure in the cathode gas flow path 5 (A <C) will be described. As described above, this state is caused by the fact that the water vapor contained in the fuel gas stops the fuel cell 2 under the condition that the anode gas flow path is closed and the cathode gas flow path is opened. It is because it condenses with the temperature fall by.

  As shown in FIG. 3A, in the fuel cell system 1, when the fuel cell 2 is stopped and the ignition is turned off (step S1), the pressure sensor 4 or 6 shown in FIG. Monitoring is performed while detecting the pressure of each gas supplied to the inside and the cathode gas flow path 5 (step S2). Note that an on-vehicle battery (not shown) is used as the power source at that time. Then, the differential pressure detecting means 71 of the ECU 7 shown in FIG. 2 detects the inter-electrode differential pressure from each detected value, and the first differential pressure determining means 72 determines whether or not the inter-electrode differential pressure is not more than a predetermined value. Determine (step S3). As a result, if the detected value of the inter-electrode differential pressure is equal to or less than the predetermined value (Yes in step S3), the process returns to step S2 and the monitoring of the pressure of each gas is continued. On the other hand, when the detected value of the inter-electrode differential pressure exceeds the predetermined value (No in step S3), the ECU 7 opens the valve V1 shown in FIG. 1 and supplies the fuel gas into the anode gas flow path 3 (step). S4) Or, the valve V2 is opened, and the downstream side (off-gas channel) of the anode gas channel 3 is opened to the atmosphere (step S4 ′). As shown in step S4, if the fuel gas is newly supplied, the pressure of the fuel gas supplied into the anode gas flow path 3 can be increased, so that the differential pressure between the electrodes can be eliminated / reduced. Further, as shown in step S4 ', by opening the valve V2 and releasing it to the atmosphere, the gas pressure in the cathode gas flow path 5 can be made equal, and the differential pressure between the electrodes can be eliminated / reduced.

  Next, a case where the internal pressure of the cathode gas channel 5 is smaller than the internal pressure of the anode gas channel 3 (C <A) will be described. In the natural state, such a state does not occur. However, assuming that a large amount of fuel gas is supplied in step S4, the internal pressure of the cathode gas passage 5 is the internal pressure of the anode gas passage 3. The case where it is smaller is described.

  As shown in FIG. 3B, in the fuel cell system 1, when the fuel cell 2 is stopped and the ignition is turned off (step S5), the pressure sensor 4 or 6 shown in FIG. Monitoring is performed while detecting the pressure of each gas supplied to the inside and the cathode gas flow path 5 (step S6). Then, the differential pressure detecting means 71 of the ECU 7 shown in FIG. 2 detects the inter-electrode differential pressure from each detected value, and the second differential pressure determining means 73 determines whether the detected inter-electrode differential pressure is equal to or less than a predetermined value. It is determined whether or not (step S7). As a result, if the detected value of the differential pressure between the electrodes is equal to or smaller than the predetermined value (Yes in step S7), the process returns to step S6 and the monitoring of the pressure of each gas is continued. On the other hand, when the detected value of the inter-electrode differential pressure exceeds a predetermined value (No in step S7), the ECU 7 drives the compressor 51 shown in FIG. Air is introduced into the cathode gas channel 5 (step S8). As shown in step S8, if the atmosphere is introduced, the pressure of the oxidant gas supplied into the cathode gas flow path 5 can be increased, so that the pressure difference between the electrodes can be eliminated / reduced. When the fuel cell 2 is stopped, the valve V4 is basically opened. However, when the fuel cell 2 is closed, the pressure difference between the electrodes can be eliminated or reduced by opening the valve V4. .

  After eliminating or reducing the inter-electrode differential pressure generated after the fuel cell 2 is stopped, for example, both the anode gas passage 3 for the fuel gas and the cathode gas passage 5 for the oxidant gas may be closed. . This is because, after the fuel cell is stopped, there is no large temperature difference between power generation and room temperature, and therefore, once the inter-electrode differential pressure is eliminated / reduced, a large differential pressure does not occur. By doing in this way, it is not necessary to always monitor a pressure with a pressure sensor, and a fuel consumption can be improved.

According to the above, the following effects can be obtained in the fuel cell system 1 according to the present embodiment.
In the fuel cell system 1, since a new gas is supplied into the gas flow path (the anode gas flow path 3 or the cathode gas flow path 5) having the lower gas pressure, the gas pressure in the gas flow path to which the gas has been supplied. , The inter-electrode differential pressure is eliminated / reduced, and the load on the solid polymer electrolyte membrane 23 can be reduced. Therefore, it is possible to improve the durability by suppressing the deterioration of the solid polymer electrolyte membrane 23.
In addition, since the fuel cell system 1 newly supplies fuel gas or oxidant gas, or only opens the off-gas flow path to the atmosphere, the differential pressure between the electrodes can be reduced with an existing system without adding special parts. Can be eliminated / reduced. In particular, if it is only opened to the atmosphere, unnecessary gas is not used, and fuel consumption can be improved.

As mentioned above, although embodiment of this invention was described, this invention is not limited to the said embodiment .
Also, it may be a less of such a reference example. FIG. 4 is a schematic configuration diagram of a fuel cell system according to a reference example.

  4 further includes a dedicated gas supply source 9 and an upstream side of the anode gas flow path 3 from the dedicated gas supply source 9 (upstream side of the fuel cell 2). ) And a gas flow path 10B communicating from the dedicated gas supply source 9 to the upstream side of the cathode gas flow path 5 (upstream side of the fuel cell 2), the gas flow paths 10A and 10B include Are provided with valves V5 and V6, respectively. In addition, as exclusive gas of the exclusive gas supply source 9, dry gas, such as nitrogen, compressed air, helium gas, argon gas, is mention | raise | lifted, for example.

  In this fuel cell system 1 ′, the process up to the determination as to whether or not the inter-electrode differential pressure is equal to or less than a predetermined value is the same as in the above-described embodiment, so that the description thereof is omitted, and first differential pressure determination means of the ECU The operation after 72 and 73 (see FIG. 2) determine that the inter-electrode differential pressure exceeds a predetermined value will be described below.

  In the fuel cell system 1 ′ shown in FIG. 4, when the pressure in the anode gas flow path 3 is smaller than the pressure in the cathode gas flow path 5, the ECU 7 controls the valve V5 to be opened via the gas flow path 10 </ b> A. The special gas is supplied to the anode gas flow path 3. By newly supplying the dedicated gas in this way, the gas pressure in the anode gas flow path 3 can be increased, and the inter-electrode differential pressure can be eliminated / reduced.

  On the other hand, when the pressure in the cathode gas flow path 5 becomes smaller than the pressure in the anode gas flow path 3 as a result of excessive supply of the dedicated gas into the anode gas flow path 3, the ECU 7 controls to open the valve V6. . Then, a dedicated gas is supplied to the cathode gas channel 5 through the gas channel 10B. By newly supplying the dedicated gas in this way, the gas pressure in the cathode gas flow path 5 can be increased, and the inter-electrode differential pressure can be eliminated / reduced.

  As described above, in the fuel cell system 1 ′ according to the modified example, it is only necessary to provide means for supplying the dedicated gas to the anode gas channel 3 and the cathode gas channel 5, respectively. Pressure can be eliminated / reduced.

  In the above embodiment, the anode gas flow path 3 is closed and the cathode gas flow path 5 is opened. However, the present invention is not limited to this. For example, the anode gas flow path 3 is opened. The cathode gas channel 5 may be closed, or both channels (the anode gas channel 3 and the cathode gas channel 5) may be closed.

1 is a schematic configuration diagram of a fuel cell system according to an embodiment. It is a schematic block diagram of ECU which concerns on this embodiment. 4 is a flowchart of a fuel cell system, where (a) is a case where the pressure in the anode gas flow path is smaller than the pressure in the cathode gas flow path, and (b) is a pressure in the cathode gas flow path smaller than the pressure in the anode gas flow path. Is the case. It is a schematic block diagram of the fuel cell system which concerns on a reference example. It is a whole block diagram of the conventional inter-electrode differential pressure preventing device.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Fuel cell system 2 Fuel cell 3 Gas flow path 4 Pressure sensor 5 Gas flow path 6 Pressure sensor 7 ECU
9 Dedicated gas supply source 10A Gas flow path 10B Gas flow path 21 Inside the anode gas flow path 22 Inside the cathode gas flow path 23 Solid polymer electrolyte membrane 31 High pressure hydrogen tank 32 Ejector 51 Compressor

Claims (2)

An electrolyte membrane is disposed between the anode and the cathode, and a fuel cell that generates electricity by reacting a fuel gas supplied to the anode and an oxidant gas supplied to the cathode ; and
An anode gas flow path through which fuel gas passes through the anode;
A cathode gas passage through which an oxidant gas passing through the cathode flows;
A first valve provided in the anode gas flow path upstream of the anode;
A second valve provided in the anode gas flow path downstream of the anode;
A third valve provided in the cathode gas flow path upstream of the cathode;
A fourth valve provided in the cathode gas flow path downstream of the cathode;
First pressure detecting means for detecting a fuel gas pressure in the anode gas flow path between the first valve and the second valve ;
Second pressure detecting means for detecting an oxidant gas pressure in the cathode gas flow path between the third valve and the fourth valve ;
With
When power generation is stopped to stop power generation of the fuel cell, the first valve and the second valve are closed, and the anode gas flow path between the first valve and the second valve is closed from the atmosphere, A fuel cell system in which a third valve and the fourth valve are opened and the cathode gas flow path between the third valve and the fourth valve is opened to the atmosphere ;
When the fuel gas pressure detected by the first pressure detection means is lower than the oxidant gas pressure detected by the second pressure detection means after stopping the power generation of the fuel cell ,
Based on the detection value of the pressure detecting means, a differential pressure detecting means for detecting a differential pressure between the fuel gas pressure and the oxidizing gas pressure in the cathode gas flow path of the anode gas flow channel,
Differential pressure determination means for determining whether or not the differential pressure detected by the differential pressure detection means is a predetermined value or less;
With
When the differential pressure determining means determines that the differential pressure exceeds a predetermined value, the second valve is opened, and the anode gas flow path between the first valve and the second valve is opened to the atmosphere.
The fuel cell system which is characterized a call.   When the second valve is opened, the differential pressure detected by the differential pressure detecting means is reduced, and the fuel gas pressure and the second pressure in the anode gas flow path detected by the first pressure detecting means are reduced. After the oxidant gas pressure in the cathode gas flow path detected by the detection means becomes equal, the second valve is closed to close the anode gas flow path between the first valve and the second valve. The third valve and the fourth valve are closed to close the cathode gas flow path between the third valve and the fourth valve.
  The fuel cell system according to claim 1.

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