JP2006236789A - Fuel cell stack - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To enable a fuel cell stack to prevent a cell from damage caused by supply shortage of reaction gas without stopping power generation. <P>SOLUTION: A supply state of reaction gas is judged for each cell (#1 to #6) constituting a fuel cell stack 2. If one cell (#3) is judged to be short of supply of reaction gas, a cathode and an anode of the cell (#3) are made short-circuited by a short-circuiting switch 10 to have it electrically cut off from the other cells (#1, #2, #4, #5, #6). <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a solid polymer membrane fuel cell stack in which a plurality of cells are stacked, and more particularly to a technique effective in preventing cell damage due to insufficient supply of reaction gas.

  A fuel cell is usually used as a fuel cell stack in which a plurality of cells are stacked. Each cell is configured by sandwiching a membrane electrode assembly from both sides with a conductive separator. The membrane electrode assembly has a structure in which an anode electrode is bonded to one surface of a solid polymer electrolyte membrane and a cathode electrode is bonded to the other surface. A fuel gas containing hydrogen is supplied to the anode electrode, and an oxidizing gas containing oxygen is supplied to the cathode electrode, so that an electrochemical reaction occurs in both electrodes and a potential difference is generated between the separators.

  End plates for sandwiching stacked cells from both sides are provided at both ends of the fuel cell stack. One end plate is connected to a fuel gas supply pipe for supplying fuel gas to the fuel cell stack and an oxidizing gas supply pipe for supplying oxidizing gas. Each reaction gas supplied to the fuel cell stack (collectively referred to as fuel gas and oxidizing gas is called a reaction gas) is distributed to each cell through a manifold formed in the fuel cell stack.

  The amount of reaction gas distributed to each cell is desirably uniform between the cells. However, the gas flow path in the cell is blocked by water generated in the cell due to power generation, and the supply amount of the reaction gas may be insufficient in some cells. Further, at the time of cold start from below freezing point, the generated water freezes in the gas flow path and becomes ice, which may block the gas flow path. Thus, when the supply amount of the reaction gas is insufficient in some cells due to some cause, the following problems may occur.

When the supply amount of fuel gas is insufficient in a certain cell, the cell cannot function as a fuel cell. At this time, if another cell is operating normally, the cell is in a state where a voltage is applied from the outside, and a reaction for emitting electrons at the anode electrode is forced. As a result, a negative voltage is generated in which the anode electrode has a higher potential than the cathode electrode, and the following abnormal reaction occurs.
(Oxidation reaction of carbon) C + 2H ₂ O → CO ₂ + 4H ⁺ + 4e ⁻
(Pt elution reaction) Pt → Pt ²⁺ + 2e ⁻
In addition, a reaction for opening a hole in the electrolyte membrane also occurs by the generated heat. These abnormal reactions deteriorate the membrane electrode assembly and damage the cell.

  Further, even when the supply amount of the oxidizing gas is insufficient in a certain cell, the cell cannot function as a fuel cell. In this case, a hydrogen pump phenomenon occurs in which hydrogen is generated at the cathode electrode of the cell. This hydrogen pump phenomenon is due to the fact that hydrogen ions that have moved from the anode electrode side through the electrolyte membrane to the cathode electrode side cannot recombine with oxygen due to lack of oxidizing gas, but recombine only with electrons. The temperature of the cell rises due to the Joule heat generated at this time and the combustion heat due to the direct reaction between oxygen and hydrogen on the cathode electrode, resulting in thermal degradation of the membrane electrode assembly.

As described above, when a shortage of reaction gas occurs in some cells, if the operation of the fuel cell stack is continued as it is, the cells may be damaged. In some cases, damage to some cells may cause a reduction in the power generation capacity of the entire fuel cell stack. For this reason, in the operation of the system using the fuel cell stack, it is necessary to detect the lack of reaction gas and to take measures after detecting the lack of reaction gas. For example, Patent Document 1 describes that an abnormality is detected by detecting a voltage for each cell, and the operation of the fuel cell stack is stopped when the abnormality is detected.
JP 2002-313396 A JP 2003-109636 A JP-A-11-233126

  However, although the conventional technique described in Patent Document 1 can prevent the cell from being damaged, the power generation by the fuel cell stack remains stopped until the restart process such as the replacement of the cell is completed. During this time, power cannot be supplied from the fuel cell stack to the power supply target.

  The present invention has been made to solve the above-described problems, and provides a fuel cell stack capable of preventing cell damage due to insufficient supply of reaction gas without stopping power generation. Objective.

In order to achieve the above object, a first invention provides a fuel cell stack of a solid polymer membrane type,
Determination means for determining the supply state of the reaction gas for each cell constituting the fuel cell stack;
As a result of the determination by the determination means, when it is determined that the supply of the reaction gas is insufficient in some cells, the short-circuit means for short-circuiting the cathode and anode of the cell,
It is characterized by having.

  In a second aspect based on the first aspect, the determination means compares the cell voltage of each cell with a predetermined reference voltage, and supplies the reaction gas to the cell whose cell voltage is equal to or lower than the reference voltage. It is characterized by judging that the cell is insufficient.

  According to a third invention, in the first or second invention, the determination means compares the cell temperature of each cell with a predetermined reference temperature, and determines a cell whose cell temperature is equal to or higher than the reference temperature as a reactive gas. It is characterized in that it is determined that the cell is in short supply.

  According to a fourth invention, in any one of the first to third inventions, the short-circuit means releases the short-circuit when a predetermined reference time has elapsed after the cathode and anode of the cell are short-circuited. When it is determined that the supply of the reaction gas continues to be insufficient in the cell, the cathode and anode of the cell are again short-circuited.

  According to the first invention, when the supply of the reaction gas is insufficient in some cells, the cells are electrically disconnected from the fuel cell stack by short-circuiting the cathode and anode of the cells. . Thus, power generation can be continued using the remaining cells excluding the cell, and damage to the cell can be prevented.

  When the supply of fuel gas among the reaction gases is insufficient, the voltage of the cell greatly decreases. According to the second aspect of the invention, it is possible to detect a cell in which the supply of fuel gas is insufficient, and to prevent damage to the cell due to the insufficient supply of fuel gas.

  If the supply of oxidizing gas among the reaction gases is insufficient, the temperature of the cell rises. According to the third aspect of the invention, it is possible to detect a cell in which the supply of the oxidizing gas is insufficient, and to prevent the cell from being damaged due to the insufficient supply of the oxidizing gas.

  In addition, according to the fourth aspect of the present invention, the short-circuit is once released when the reference time has elapsed since the short-circuiting of the cell in which the reaction gas is insufficient, thereby eliminating the shortage of supply of the reaction gas in the cell. Then, since power generation can be performed including the cell thereafter, insufficient output of the fuel cell stack can be prevented. On the other hand, when the supply shortage of the reaction gas is not solved in the cell, the cathode and the anode are short-circuited again, so that the cell is prevented from being damaged.

Hereinafter, an embodiment of the present invention will be described with reference to FIG.
FIG. 1 is a schematic configuration diagram of a fuel cell stack as an embodiment of the present invention. As shown in FIG. 1, the fuel cell stack 2 includes a plurality of cells 4 stacked in one direction. In FIG. 1, it is assumed that the fuel cell stack 2 is composed of six cells 4 for the sake of simplicity. However, an actual fuel cell stack is composed of a larger number of cells. Numbers # 1 to # 6 shown in FIG. For example, # 3 indicates that the cell 4 to which it is attached is the third cell (third cell). Hereinafter, when a specific cell 4 is distinguished from other cells 4, the number #n of the specific cell is used to call the nth cell. A load (for example, an electric motor) that is a power supply target of the fuel cell stack 2 is connected to the outermost first cell and the sixth cell.

  Although not shown, each cell 4 is configured by sandwiching a membrane electrode assembly from both sides with a conductive separator. The membrane electrode assembly has a structure in which an anode electrode is bonded to one surface of a solid polymer electrolyte membrane and a cathode electrode is bonded to the other surface. A fuel gas flow path through which fuel gas flows is formed between the anode electrode and the separator in contact therewith, and an oxidizing gas flow path through which oxidizing gas flows is formed between the cathode electrode and the separator in contact therewith. Although not shown in the fuel cell stack 2, a fuel gas manifold for distributing the fuel gas to the fuel gas flow path of each cell 4 and the oxidizing gas to the oxidizing gas flow path of each cell 4 are distributed. An oxidizing gas manifold is formed for the purpose.

  In the fuel cell stack 2, a voltage monitor 6 for measuring the voltage of the cell 4 and a temperature sensor 8 for measuring the temperature of the cell 4 are attached to each cell 4. Each voltage monitor 6 and each temperature sensor 8 are connected to a monitoring device 20 that monitors the operating state of the fuel cell stack 2. The monitoring device 20 monitors the voltage and temperature of each cell 4 based on the measurement information from the voltage monitor 6 and the temperature sensor 8.

  Each cell 4 is provided with a short-circuit switch 10 for short-circuiting the anode-side separator and the cathode-side separator. All the short-circuit switches 10 of each cell 4 are normally turned off (state shown in FIG. 1). In this state, power generation is performed in a state where the six cells 4 from the first cell to the sixth cell are connected in series. In this case, the sum of the voltages of the cells 4 becomes the voltage of the fuel cell stack 2. The short circuit switch 10 of each cell 4 is connected to the monitoring device 20. The monitoring device 20 can turn on / off each short-circuit switch 10 independently. By turning on the short-circuit switch 10, the cell 4 in which the short-circuit switch 10 is turned on is electrically disconnected from the other cells 4. FIG. 2 shows a state where only the short-circuit switch 10 of the third cell is turned on. In this state, the third cell is electrically disconnected from the other cells 4, and the sum of the voltages of the remaining first, second, fourth, fifth and sixth cells becomes the voltage of the fuel cell stack 2. . In the third cell separated from the others, the electrochemical reaction on each electrode stops regardless of the supply of the reaction gas.

  The monitoring device 20 detects an abnormality of each cell 4 from the cell voltage measured by the voltage monitor 6 and the cell temperature measured by the temperature sensor 8, specifically, the supply of reactive gas is insufficient, and according to the result. The short circuit switch 10 of each cell 4 is controlled. The monitoring device 20 controls the short-circuit switch 10 according to the routine shown in the flowchart of FIG. The routine shown in FIG. 3 is executed for each cell 4 periodically or at a predetermined time, for example, immediately after the fuel cell stack 2 is activated.

  In the first step 100 of the routine shown in FIG. 3, it is determined whether or not the cell voltage measured by the voltage monitor 6 is 0 V or less, that is, whether or not a negative voltage is generated. If no negative voltage is generated as a result of the determination, it can be determined that the cell 4 is normal. In this case, the short-circuit switch 10 is maintained off (step 110).

  On the other hand, when a negative voltage is generated, it is further determined whether or not the cell voltage measured by the voltage monitor 6 is −0.5 V or less, that is, whether or not a large negative voltage is generated ( Step 102). When there is a shortage in fuel gas, the cell voltage suddenly drops below 0V. On the other hand, when the oxidizing gas is insufficient, the decrease in the cell voltage is small. Therefore, by comparing the cell voltage when a negative voltage is generated with a certain reference value (in this example, -0.5 V, the value of the reference value is not limited to this), the cause of the negative voltage is It can be determined whether the fuel gas is insufficient.

  If the cell voltage is determined to be −0.5 V or less as a result of the determination in step 102, the short-circuit switch 10 of the cell 4 is turned on (step 104). This is because when the fuel gas is insufficient, the membrane electrode assembly deteriorates rapidly due to an abnormal chemical reaction, and thus it is necessary to immediately stop the power generation of the cell 4. By turning on the short-circuit switch 10, the electrochemical reaction in the membrane electrode assembly of the cell 4 is stopped, and deterioration of the membrane electrode assembly due to power generation in a state where the fuel gas is insufficient is prevented. In addition, power generation stops only in the cell 4 and power generation in the other remaining cells 4 is continued, so that power can be continuously supplied from the fuel cell stack 2 to the load.

  If the result of determination in step 102 is that the cell voltage measured by the voltage monitor 6 is greater than −0.5 V, the determination in step 106 is further executed. In step 106, it is determined whether the cell temperature measured by the temperature sensor 8 is 120 ° C. or higher. When a negative voltage is generated, if the voltage value is not much lower than 0 V, the supply of oxidizing gas is considered to be a cause of the negative voltage. However, unlike the case of insufficient supply of fuel gas, when the supply of oxidizing gas is insufficient, the membrane electrode assembly is unlikely to deteriorate rapidly. For this reason, as long as thermal degradation due to an excessive temperature rise of the membrane electrode assembly does not occur, the operation of the cell 4 can be continued as it is. In this step, the cell temperature when the negative voltage is generated is compared with a certain reference value (here, 120 ° C. as an example, but the value of the reference value is not limited to this). Judging the possibility of thermal degradation.

  As a result of the determination in step 106, when it is determined that the cell temperature is 120 ° C. or higher, the short circuit switch 10 of the cell 4 is turned on (step 108). Thereby, the electrochemical reaction in the membrane electrode assembly of the cell 4 is stopped, and thermal deterioration of the membrane electrode assembly due to power generation in a state where the oxidizing gas is insufficient is prevented. Also in this case, power generation stops only in the cell 4 and power generation in the other remaining cells 4 is continued, so that power can be continuously supplied from the fuel cell stack 2 to the load. On the other hand, if it is determined in step 106 that the cell temperature is less than 120 ° C., the short-circuit switch 10 is maintained off and the operation of the cell 4 is continued (step 110).

  By executing the above routine for each cell 4, it is possible to detect the cell 4 in which the supply of the reactive gas is insufficient, and the supply of the reactive gas is insufficient without stopping the power generation of the fuel cell stack 2. It is possible to prevent the cell 4 from being damaged due to the above.

  In the present embodiment, the “determination means” of the first invention is realized by the voltage monitor 6, the temperature sensor 8, and the monitoring device 20 at the time of execution of the above routine. Further, the “short-circuit means” of the first invention is realized by the short-circuit switch 10 and the monitoring device 20 at the time of execution of the above routine.

  In addition, even if it is the cell 4 where the reactive gas is insufficient at present, the shortage of the reactive gas may be resolved over time. For example, when there is a shortage of the reaction gas due to the gas flow path being blocked by the generated water, the generated water that has blocked the gas flow path is swept away by the reaction gas, thereby restoring the flow rate of the reaction gas. Sometimes. When the fuel cell stack 2 is activated, if the gas flow path is blocked by ice formed by freezing generated water, the ice is melted by the heat generated by the power generation of the other cells 4, thereby causing the flow rate of the reaction gas. May recover. As in the above example, when the flow rate of the reaction gas recovers after the short circuit, the cell 4 will not be damaged even if the power generation of the cell 4 is resumed. Further, by restarting the power generation of the cell 4, it is possible to prevent the output of the fuel cell stack 2 from being insufficient at a high load.

  Therefore, the monitoring device 20 controls the short-circuit switch 10 in accordance with the routine shown in the flowchart of FIG. 4 after short-circuiting the cell 4 that is in short supply of the reaction gas. The routine shown in FIG. 3 is executed for the cell 4 in which the short-circuit switch 10 is turned on by the routine shown in FIG.

  In the first step 200 of the routine shown in FIG. 4, it is determined whether or not a predetermined reference time has elapsed after the short-circuit switch 10 is turned on. Until the reference time elapses, the short-circuit switch 10 is kept on and maintained as it is (step 208). During this time, the cell 4 is electrically disconnected from the normal cell 4 in which there is no shortage of reaction gas, and power is generated only by the normal cell 4.

  As a result of the determination in step 200, when the reference time has elapsed since the short-circuit switch 10 was turned on, the short-circuit switch 10 is temporarily turned off (step 202). As a result, the cell 4 is again electrically joined to the other cell 4, and the power generation of the cell 4 is resumed.

  In the next step 204, the cell voltage and cell temperature of the cell 4 after the restart of power generation are measured, and it is determined based on the measured values whether or not the abnormality of the cell 4, that is, insufficient supply of the reaction gas continues. The The contents of the determination executed in step 206 are the same as the contents of the determination executed in the routine shown in FIG. 3, that is, steps 100, 102, and 104. If there is no abnormality as a result of the determination, that is, if the shortage of reactant gas supply has been resolved, the current state is maintained with the short-circuit switch 10 turned off (step 208). Thereby, the electric power generated by the cell 4 can also be output as a part of the electric power of the fuel cell stack 2, and the shortage of the output of the fuel cell stack 2 at the time of high load can be prevented.

  On the other hand, if there is an abnormality as a result of the determination in step 204, that is, if the supply of reactive gas continues to be insufficient, the short-circuit switch 10 is turned on again (step 206). Thereby, the damage of the cell 4 due to continuing power generation in a state where the reaction gas is insufficient is prevented. When the short-circuit switch 10 is turned on again, this routine is executed again for the cell 4. This routine is repeatedly executed until the supply shortage of the reaction gas in the cell 4 is resolved and the short-circuit switch 10 is turned off.

  Although the embodiments of the present invention have been described above, the present invention is not limited to the above-described embodiments, and various modifications can be made without departing from the spirit of the present invention. For example, the following modifications may be made.

  In the above embodiment, each cell 4 is provided with the temperature sensor 8, but one temperature sensor 8 may be arranged for two cells 4. For example, two cells 4 are made into one set, and the temperature sensor 8 is arranged between the separators adjacent to each other. Also in this case, by combining with the measured value of the cell voltage by the voltage monitor 4, it can be determined which of the two cells 4 is abnormal.

  In the above embodiment, the routine shown in FIG. 4 is executed until the supply shortage of the reaction gas is resolved. However, the upper limit value of the number of executions is determined, and the execution number of the routine reaches the upper limit value. After that, the short-circuit switch 10 may be kept on.

1 is a schematic configuration diagram of a fuel cell stack as an embodiment of the present invention. It is a figure which shows the state which short-circuited some cells in the fuel cell stack of FIG. It is a flowchart of the routine for control of the short circuit switch performed in embodiment of this invention. It is a flowchart of the routine for control of the short circuit switch performed in embodiment of this invention.

Explanation of symbols

2 Fuel cell stack 4 Cell 6 Voltage monitor 8 Temperature sensor 10 Short-circuit switch 20 Monitoring device # 1 to # 6 Cell number

Claims (4)

In a polymer electrolyte fuel cell stack,
Determination means for determining the supply state of the reaction gas for each cell constituting the fuel cell stack;
As a result of the determination by the determination means, when it is determined that the supply of the reaction gas is insufficient in some cells, the short-circuit means for short-circuiting the cathode and anode of the cell,
A fuel cell stack comprising:   The determination means compares a cell voltage of each cell with a predetermined reference voltage, and determines that a cell whose cell voltage is equal to or lower than the reference voltage is a cell in which supply of reaction gas is insufficient. Item 2. The fuel cell stack according to Item 1.   The determination unit compares a cell temperature of each cell with a predetermined reference temperature, and determines that a cell having a cell temperature equal to or higher than the reference temperature is a cell for which supply of a reaction gas is insufficient. Item 3. The fuel cell stack according to Item 1 or 2. The short-circuit means releases the short-circuit when a predetermined reference time has elapsed since the cathode and anode of the cell are short-circuited, and when it is determined that the shortage of reactant gas continues in the cell. The fuel cell stack according to any one of claims 1 to 3, wherein the cathode and the anode of the cell are again short-circuited.

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