JP2010282800A - Fuel cell system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To further efficiently generate power by inhibiting the power generation of a fuel cell from being unnecessarily restricted. <P>SOLUTION: The fuel cell system includes a power generation restricting means for restricting the power generation of the fuel cell body when cell voltage is lower than predetermined negative voltage. It also includes sensing means (S101-S104) for sensing the breakage of the cathode catalyst electrode layer of the cell, and correcting means (S106, S107) for subtracting current cell voltage from an initial value for the cell voltage to calculate a cell voltage drop amount when sensing the breakage of the cathode catalyst electrode layer, and then for correcting the predetermined negative voltage in accordance with the cell voltage drop mount. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a fuel cell system.

As a fuel cell, a polymer electrolyte fuel cell configured by stacking a plurality of cells is known. In such a fuel cell, each cell has an MEA (Membrane Electrode Assembly) formed by joining a pair of catalyst electrode layers (a cathode catalyst electrode layer and an anode catalyst electrode layer) to an electrolyte membrane. . In each cell, an oxidant gas containing oxygen is supplied to the cathode catalyst electrode layer, and a fuel gas containing hydrogen is supplied to the anode catalyst electrode layer, thereby generating power.

In such a fuel cell, the supply of the reaction gas to the catalyst electrode layer (or the diffusion of the reaction gas in the catalyst electrode layer) may be hindered due to freezing of the generated water generated during power generation. . In this case, an abnormal reaction occurs in the catalyst electrode layer. For example, when the amount of fuel gas supplied to the anode catalyst electrode layer is insufficient, electrons are taken out from the anode catalyst electrode layer despite the absence of hydrogen. As a result, in addition to water oxidation reaction (2H ₂ O → O ₂ + 4H ⁺ + 4e ⁻ ), carbon oxidation reaction (C + 2H ₂ O → CO ₂ + 4H ⁺ + 4e ⁻ ) and platinum elution reaction (Pt → Pt ²⁺ + 2e) ^- ) In addition, an oxidation reaction of the electrolyte component occurs. Such an abnormal reaction in the anode catalyst electrode layer causes excessive deterioration and damage of the MEA.

  For this reason, when a shortage of the amount of fuel gas supplied to the anode catalyst electrode layer occurs, it is important to detect it early. Here, in the anode catalyst electrode layer in which the supply amount of the fuel gas is insufficient, the potential increases due to the abnormal reaction as described above. As a result, a phenomenon that the anode potential becomes higher than the cathode potential (reverse potential phenomenon) occurs, and the cell voltage may become a negative voltage. At this time, the smaller the amount of fuel gas supplied to the anode catalyst electrode layer, the higher the anode potential and the smaller the negative voltage of the cell (that is, the larger the absolute value of the negative voltage). Therefore, the cell voltage is measured, and when the cell voltage becomes a negative voltage and the value becomes smaller than a predetermined threshold (hereinafter referred to as a hydrogen depletion allowable negative voltage), the anode potential is excessively high. That is, a technique for determining that the shortage of the supply amount of fuel gas to the anode catalyst electrode layer exceeds an allowable range is known (see, for example, Patent Document 1). When it is determined that the shortage of fuel gas supply to the anode catalyst electrode layer exceeds the allowable range, the power generation of the fuel cell is restricted, so that deterioration or damage of the MEA can be suppressed.

  As for the fuel cell system, a technique is known that measures the surface area of the anode catalyst and determines whether or not to execute control for restoring the characteristics of the fuel cell based on the surface area (see, for example, Patent Document 2). .)

JP 2008-277044 A JP 2007-207671 A Japanese Patent Laid-Open No. 2005-150020 JP 2008-21448 A JP 2007-52988 A

  In a fuel cell, the supply of oxidant gas to the cathode catalyst electrode layer may be hindered by freezing of produced water or the like. If power generation is continued in this state, the cathode catalyst electrode layer may be destroyed. When the cathode catalyst electrode layer is destroyed, the cathode potential is lowered. Similarly, when the surface area (hereinafter referred to as the effective surface area) of the cathode catalyst electrode layer effective for power generation is reduced due to deterioration such as corrosion, the cathode potential similarly decreases.

  When the cathode potential decreases, if the amount of fuel gas supplied to the anode catalyst electrode layer is insufficient in that state, the reverse potential phenomenon is likely to occur, and the negative voltage of the cell when the reverse potential phenomenon occurs is It is smaller than when the electrode layer is normal. Therefore, even if the actual supply amount of fuel gas to the anode catalyst electrode layer is within the allowable range, the negative voltage of the cell may be smaller than the allowable negative voltage of hydrogen. In this case, there is a possibility that the power generation of the fuel cell is limited even though the supply amount of the fuel gas to the anode catalyst electrode layer is within the allowable range.

  Even if the cathode catalyst electrode layer is destroyed or its effective surface area is reduced, if the anode potential is detected, the supply amount of fuel gas to the anode catalyst electrode layer is insufficient based on the detected value. It is possible to accurately determine whether or not the range is exceeded. However, it is difficult to detect only the anode potential as compared to detecting the negative voltage of the cell.

  The present invention has been made in view of the above problem, and an object of the present invention is to provide a technique capable of suppressing power generation of a fuel cell unnecessarily and performing more efficient power generation. To do.

  The present invention corrects the value of the hydrogen deficient allowable negative voltage (predetermined negative voltage), which is a threshold for power generation restriction, in consideration of a decrease in the cathode potential accompanying the destruction of the cathode catalyst electrode layer or the decrease in the effective surface area. .

More specifically, the fuel cell system according to the first invention is
A fuel cell body formed by laminating a plurality of cells having MEAs formed by joining a cathode catalyst electrode layer and an anode catalyst electrode layer to an electrolyte membrane;
Voltage measuring means for measuring the cell voltage;
In a fuel cell system comprising a power generation limiting means for limiting power generation of the fuel cell main body when the cell voltage becomes smaller than a predetermined negative voltage,
Detection means for detecting the destruction of the cathode catalyst electrode layer of the cell;
When a breakdown of the cathode catalyst electrode layer is detected, a cell voltage decrease amount is calculated by subtracting a current cell voltage measured by the cell voltage measuring means from an initial value of the cell voltage, and the cell voltage decrease amount Correction means for correcting the predetermined negative voltage based on:
Is further provided.

  Here, the destruction of the cathode catalyst electrode layer means that the cathode catalyst electrode layer is peeled from the electrolyte membrane. The initial value of the cell voltage is the cell voltage when the cell is in the initial state, that is, when the cathode catalyst electrode layer is not deteriorated or destroyed.

  According to the present invention, when the cathode potential decreases due to the destruction of the cathode catalyst electrode layer, the hydrogen deficient allowable negative voltage is corrected to a smaller value by the amount of decrease (the hydrogen deficient allowable negative voltage The absolute value is larger). Therefore, it is possible to prevent the power generation of the fuel cell from being restricted even though the supply amount of the fuel gas to the anode catalyst electrode layer is within the allowable range.

  In the present invention, the voltage measuring means measures a cell voltage at a portion where the water content of MEA is relatively high, and a current measuring means for measuring a cell current at a portion where the water content of MEA is relatively high; Resistance measuring means for measuring the internal resistance of the cell in a portion where the water content of MEA is relatively high may be further provided. The detecting means detects a breakage of the cathode catalyst electrode layer of the cell in a portion where the water content of MEA is relatively high, and calculates a change in current for calculating a change rate of the cell current measured by the current measuring means. You may have a speed calculation means and a resistance change speed calculation means for calculating the change speed of the internal resistance measured by the resistance measurement means. In this case, when the current change rate calculated by the current change rate calculating unit changes from negative to positive and the resistance change rate calculated by the resistance change rate calculating unit is positive, It is determined that the cathode catalyst electrode layer is broken.

  Further, in the portion where the water content of MEA is relatively high, the supply of oxidant gas to the cathode electrode layer is likely to be hindered due to freezing of the produced water. Therefore, destruction of the cathode catalyst electrode layer is likely to occur at a portion where the water content of MEA is relatively high. Therefore, in the above, the destruction of the cathode catalyst electrode layer is detected at a portion where the water content of MEA is relatively high.

  Moreover, not only when the cathode catalyst electrode layer of the cell is destroyed, but also drying of the electrolyte membrane, inhibition of reaction due to excessive water content of MEA, inhibition of supply of oxidant gas before destruction of the cathode catalyst electrode layer, etc. Also changes the cell current. Therefore, it is difficult to detect the destruction of the cathode catalyst electrode layer with high accuracy based only on the behavior of the cell current.

  In the above, the destruction of the cathode catalyst electrode layer is detected based on the behavior of the current change acceleration and the resistance change speed. Therefore, the destruction of the cathode catalyst electrode layer can be detected with higher accuracy.

A fuel cell system according to a second invention is
A fuel cell body formed by laminating a plurality of cells having MEAs formed by joining a cathode catalyst electrode layer and an anode catalyst electrode layer to an electrolyte membrane;
Voltage measuring means for measuring the cell voltage;
In a fuel cell system comprising a power generation limiting means for limiting power generation of the fuel cell main body when the cell voltage becomes lower than a predetermined negative voltage,
An effective surface area obtaining means for obtaining an effective surface area which is a surface area of a portion effective for power generation of the cathode catalyst electrode layer of the cell;
When the effective surface area of the cathode catalyst electrode layer decreases, a cell voltage decrease amount that is a decrease amount from the initial value of the cell voltage is calculated based on the decrease amount, and the predetermined negative voltage is calculated based on the cell voltage decrease amount. Correction means for correcting
Is further provided.

  Here, the initial value of the cell voltage is the cell voltage when the cell is in the initial state, that is, when the cathode catalyst electrode layer is not deteriorated or destroyed and the effective surface area of the cathode catalyst electrode layer is in the initial state. That is. According to the present invention, when the cathode potential is lowered by reducing the effective surface area of the cathode catalyst electrode layer, the hydrogen deficient allowable negative voltage is corrected to a lower value by the amount of the reduction. Therefore, it is possible to prevent the power generation of the fuel cell from being restricted even though the supply amount of the fuel gas to the anode catalyst electrode layer is within the allowable range.

  According to the present invention, since it is possible to suppress the power generation of the fuel cell from being unnecessarily restricted, it is possible to perform more efficient power generation.

It is a figure which shows schematic structure of the fuel cell system which concerns on a 1st Example. It is a figure which shows schematic structure of the cell of the fuel cell main body which concerns on a 1st Example. It is a figure which shows an example of the state of the cathode potential of the cell at the time of electric power generation, an anode potential, and a cell voltage. (A) shows a normal state, (b) shows a state when the supply amount of hydrogen gas to the anode catalyst electrode layer is insufficient, and (c) shows a state of the cathode catalyst electrode layer. This shows a state when the supply amount of hydrogen gas to the anode catalyst electrode layer is insufficient when destruction occurs. (A) is a figure which shows transition of the cell voltage and internal resistance of a cell in a wet location based on 1st Example. (B) is a figure which shows transition of the cell electric current in the wet site | part and the dry site | part in the same cell based on 1st Example. It is a flowchart which shows the hydrogen deficient allowable negative voltage correction flow which concerns on a 1st Example. It is a figure which shows the IV characteristic of the cell which concerns on a 1st Example. It is a flowchart which shows the hydrogen deficient allowable negative voltage correction flow which concerns on a 2nd Example. It is a figure which shows the relationship between the effective surface area of the cathode catalyst electrode layer which concerns on a 2nd Example, and cell voltage.

  Hereinafter, specific embodiments of the present invention will be described with reference to the drawings. The dimensions, materials, shapes, relative arrangements, and the like of the components described in the present embodiment are not intended to limit the technical scope of the invention to those unless otherwise specified.

<First Example>
A first embodiment of the present invention will be described with reference to FIGS.

(System outline configuration)
FIG. 1 is a diagram illustrating a schematic configuration of a fuel cell system according to the present embodiment. FIG. 2 is a diagram illustrating a schematic configuration of a cell of the fuel cell main body according to the present embodiment. In FIG. 1, solid arrows indicate the flow of air and hydrogen gas.

  The fuel cell main body 1 is a solid polymer fuel cell configured by stacking a plurality of cells 30. As shown in FIG. 2, each cell 30 is configured by sandwiching an MEA 31 between a pair of separators 35a and 35b. The MEA 31 is formed by joining a cathode catalyst electrode layer 33 and an anode catalyst electrode layer 34 to an electrolyte membrane 32.

  The electrolyte membrane 32 is a membrane body of a polymer material (for example, a fluorine resin) that can conduct protons. The catalyst electrode layers 33 and 34 are formed by carrying platinum or an alloy catalyst containing platinum and other metals on a carrier made of carbon black. In the catalyst electrode layers 33 and 34, platinum or an alloy catalyst containing platinum and other metals is supported in the vicinity of the contact surface with the electrolyte membrane 32.

  An air passage 36 is formed in the separator 35a on the cathode catalyst electrode layer 33 side. Air flowing through the air passage 36 is supplied to the cathode catalyst electrode layer 33 as an oxidant gas. A hydrogen gas passage 37 is formed in the separator 35b on the anode catalyst electrode layer 34 side. Hydrogen gas (or hydrogen mixed gas) flowing through the hydrogen gas passage 37 is supplied to the anode catalyst electrode layer 34 as fuel gas.

In the anode catalyst electrode layer 34, the supplied hydrogen gas is decomposed into electrons and protons. Protons move in the electrolyte membrane 32 toward the cathode catalyst electrode layer 33. On the other hand, electrons are conducted to the cathode catalyst electrode layer 33 through an external circuit (not shown). In the cathode catalyst electrode layer 33, oxygen in the supplied air is combined with protons that have moved through the electrolyte membrane 32 and electrons conducted through an external circuit, thereby generating water. By these reactions, an electromotive force is generated between the cathode catalyst electrode layer 33 and the anode catalyst electrode layer 34.

  An air passage 36 formed in the separator 35 a is connected to an air inlet and an air outlet in the fuel cell main body 1. A hydrogen gas passage 37 formed in the separator 35 b is connected to a hydrogen gas inlet and a hydrogen gas outlet in the fuel cell main body 1.

  One ends of air pipes 2 and 3 are connected to an air inlet and an air outlet in the fuel cell main body 1, respectively. An air compressor 13 is provided in the air pipe 2. Air is supplied to the fuel cell main body 1 from the air pipe 2 by pressure-feeding the air by the air compressor 13. In addition, air that has not been used for power generation in the fuel cell body 1 (hereinafter referred to as cathode off gas) is discharged to the air pipe 3. The air pipe 3 is provided with a pressure adjustment valve 11. The pressure of the air (including the cathode off gas) in the fuel cell main body 1 is adjusted by the pressure adjusting valve 11.

  Further, the humidification module 12 is provided so as to straddle the downstream side of the air compressor 2 in the air pipe 2 and the downstream side of the pressure adjustment valve 11 in the air pipe 3. In the humidification module 12, air and cathode off gas are mixed, and air is humidified by moisture contained in the cathode off gas. Thereby, the humidified air from the humidification module 12 is discharged to the air pipe 2 and supplied to the fuel cell main body 1. With such a configuration, the electrolyte membrane 32 of each cell 30 is kept wet. In addition, the humidification module 12 may humidify the air supplied to the fuel cell main body 1 by evaporating the water pumped up from the water tank etc. which were provided separately, and mixing with air.

  One ends of hydrogen gas pipes 4 and 5 are respectively connected to the hydrogen gas inlet and the hydrogen gas outlet in the fuel cell main body 1. The other end of the hydrogen gas pipe 4 is connected to a hydrogen gas supply device 6. Hydrogen gas is supplied from the hydrogen gas supply device 6 to the fuel cell body 1 through the hydrogen gas pipe 4. The hydrogen gas pipe 4 is provided with a flow rate adjusting valve 7. The flow rate of hydrogen gas supplied to the fuel cell main body 1 is adjusted by the flow rate adjusting valve 7.

  In addition, hydrogen gas that has not been used for power generation in the fuel cell main body 1 (hereinafter referred to as anode off-gas) is discharged to the hydrogen gas pipe 5. The other end of the hydrogen gas pipe 5 is connected to the downstream side of the flow rate adjusting valve 7 in the hydrogen gas pipe 4.

  The hydrogen gas pipe 5 is provided with a pressure regulating valve 8, a gas-liquid separator 9, and a hydrogen gas circulation pump 10 in order from the upstream side along the flow of the anode off gas. The pressure of the hydrogen gas (including the anode off gas) inside the fuel cell main body 1 is controlled by the pressure adjustment valve 8. A liquid layer component is removed from the anode off gas by the gas-liquid separator 9. The anode gas is pumped in the direction of the hydrogen gas pipe 4 by the hydrogen gas circulation pump 10. As a result, the anode off-gas from which the liquid layer component has been removed is supplied again to the fuel cell body 1. The flow rate of hydrogen gas supplied to the fuel cell main body 1 is also controlled by the hydrogen gas circulation pump 10.

  As described above, in this embodiment, a circulation path is formed in which the anode off-gas is re-supplied to the fuel cell main body 1, but the hydrogen gas pipe 5 is not connected to the hydrogen gas pipe 4 and no circulation path is formed. However, application of the present invention is possible. Further, a humidification module that humidifies the hydrogen gas supplied to the fuel cell main body 1 may be provided in the hydrogen gas pipe 4.

  A voltage measuring device 21, a current measuring device 22, a resistance measuring device 23, and a temperature sensor 24 are provided in the vicinity of the air outlet in the fuel cell main body 1.

  In each cell 30, moisture moves in the direction from the anode catalyst electrode layer 34 to the cathode catalyst electrode layer 33 as the platen moves in the electrolyte membrane 32. In the fuel cell main body 1, air (including the cathode off gas) flows toward the air outlet, and moisture also flows toward the air outlet together with the air flow. As a result, the portion near the air outlet in the fuel cell main body 1 has a higher water content in the MEA 31 than the other portions. That is, the voltage measuring device 21, the current measuring device 22, the resistance measuring device 23, and the temperature sensor 24 according to the present embodiment are the cell voltage, the cell current, the internal resistance of the cell 30, The temperature of each cell 30 is measured.

The fuel cell system according to this embodiment includes an ECU (Electric Control Unit) 20. A voltage measuring device 21, a current measuring device 22, a resistance measuring device 23, a temperature sensor 24, and the like are electrically connected to the ECU 20. Output signals from these measuring instruments and sensors are input to the ECU 20.

  Further, the hydrogen gas supply device 6, the flow rate adjustment valve 7, the pressure adjustment valves 8 and 11, the hydrogen gas circulation pump 10, the air compressor 13, and the humidification module 12 are electrically connected to the ECU 20. These are controlled by the ECU 20.

(Power generation restriction)
FIG. 3 is a diagram illustrating an example of the state of the cathode potential, the anode potential, and the cell voltage of the cell 30 during power generation. 3A shows a normal state, FIG. 3B shows a state when the supply amount of hydrogen gas to the anode catalyst electrode layer is insufficient, and FIG. c) shows a state where the supply amount of hydrogen gas to the anode catalyst electrode layer is insufficient when the cathode catalyst electrode layer is destroyed.

  As shown in FIG. 3A, in the fuel cell main body 1, the cathode potential (eg, 0.6V) is usually higher than the anode potential (eg, 0V). However, when the supply of hydrogen gas to the anode catalyst electrode layer 34 is hindered by freezing of the produced water and the supply amount is insufficient, an abnormal reaction occurs in the anode catalyst electrode layer 34. Thereby, as shown in FIG. 3B, the anode potential rises (for example, 1.8 V). As a result, a reverse potential phenomenon occurs, and the cell voltage may become a negative voltage (for example, -1.2 V). At this time, the smaller the amount of hydrogen gas supplied to the anode catalyst electrode layer 34, the higher the anode potential and the smaller the cell voltage (the absolute value of the cell voltage increases).

  If power generation is continued in a state where the shortage of hydrogen gas supplied to the anode catalyst electrode layer 34 exceeds the allowable range, the MEA 31 may be excessively deteriorated or damaged due to an abnormal reaction in the anode catalyst electrode layer 34. There is. Therefore, in this embodiment, when the cell voltage measured by the voltage measuring device 21 becomes a negative voltage and the value becomes smaller than the hydrogen deficient allowable negative voltage, the anode potential is excessively high, that is, the anode It is determined that the shortage of hydrogen gas supply to the catalyst electrode layer 34 exceeds the allowable range. When such a determination is made, the ECU 20 controls the amount of air and hydrogen gas supplied to the fuel cell body 1 to limit the power generation of the fuel cell body 1. Thereby, excessive deterioration and damage of MEA 31 can be suppressed.

  As described above, in this embodiment, the portion where the voltage measuring device 21 is provided in the fuel cell main body 1 is a portion where the water content of the MEA 31 is relatively large. Insufficient supply of hydrogen gas to the layer 34 is likely to occur.

(Destruction of cathode catalyst electrode layer)
On the other hand, also in the cathode catalyst electrode layer 33, the supply of air may be hindered due to freezing of the generated water, and the supply amount may be insufficient. If power generation is continued in this state, an abnormal reaction occurs in the cathode catalyst electrode layer 33. As a result, the cathode catalyst electrode layer 33 is broken, that is, the cathode catalyst electrode layer 33 is peeled off from the electrolyte membrane 32. It should be noted that such destruction of the cathode catalyst electrode layer 33 is likely to occur at a portion where the water content of the MEA 31 where the product water is likely to freeze is relatively high, as is the case with the insufficient supply of hydrogen gas to the anode catalyst electrode layer 34.

  When the cathode catalyst electrode layer 33 is destroyed, the cathode potential is lowered (for example, 0.4 V) as shown in FIG. Therefore, if the supply amount of hydrogen gas to the anode catalyst electrode layer 34 is insufficient in a state where the cathode catalyst electrode layer 33 is destroyed, a decrease in cathode potential and an increase in anode potential occur at the same time. As a result, the negative voltage of the cell 30 when the reverse potential phenomenon occurs is smaller than when the cathode catalyst electrode layer 33 is normal (for example, even if the anode potential is 1.6 V, the negative voltage of the cell is -1.2V). For this reason, even if the actual supply amount of fuel gas to the anode catalyst electrode layer 34 is within the allowable range, the negative voltage of the cell 30 may be smaller than the allowable negative voltage of hydrogen. In this case, the power generation of the fuel cell main body 1 is restricted even though the supply amount of the fuel gas to the anode catalyst electrode layer 34 is within the allowable range.

  Therefore, in this embodiment, it is determined whether or not the cathode catalyst electrode layer 33 is broken. When the breakdown of the cathode catalyst electrode layer 33 is detected, the hydrogen depletion allowable negative voltage is corrected to a smaller value (the absolute value of the hydrogen depletion allowable negative voltage is larger) by the decrease in the cathode potential due to the breakdown. Value). As a result, it is possible to suppress the power generation of the fuel cell main body 1 from being restricted even though the shortage of hydrogen gas supplied to the anode catalyst electrode layer 34 is within the allowable range.

(Destruction detection method of cathode catalyst electrode layer)
Here, a method for detecting the destruction of the cathode catalyst electrode according to the present embodiment will be described with reference to FIG. In the following, a portion where the water content of MEA is relatively high is referred to as a wet portion, and a portion where the water content of MEA is relatively low is referred to as a dry portion.

  (A) of FIG. 4 is a figure which shows transition of the cell voltage and internal resistance of a cell in a wet site | part. In FIG. 4A, L1 represents the internal resistance of the cell, L2 represents the measured voltage of the cell measured by the voltage measuring instrument, and L3 corrected the voltage drop due to the internal resistance of the cell. It represents the IR correction voltage, which is the cell voltage. FIG. 4B is a diagram showing the transition of the cell current at the wet site and the dry site in the same cell. In FIG. 4B, L4 represents the cell current at the wet site, and L5 represents the cell current at the dry site. In FIG. 4, time td indicates the timing at which the supply of air to the cathode catalyst electrode layer is hindered due to freezing of the produced water and the cathode catalyst electrode layer is destroyed at the wet site.

When the supply amount of air to the cathode catalyst electrode layer 33 decreases at the wet site, the amount of oxygen combined with electrons (O ₂ reduction reaction) in the cathode catalyst electrode layer 33 decreases. Therefore, as indicated by L4, the current at the wet site decreases immediately before time td. At this time, the amount of electrons used for the O ₂ reduction reaction at the dry site increases as the amount of electrons used for the O ₂ reduction reaction at the wet site decreases. Therefore, as indicated by L5, immediately before the time td, the current at the wet site increases.

When the cathode catalyst electrode layer 33 is destroyed at the wet site, it becomes necessary to receive electrons even though oxygen is not supplied. As a result, instead of the O ₂ reduction reaction,
A reaction (H ⁺ reduction reaction) occurs in which protons transferred from the anode catalyst electrode layer 34 to the cathode catalyst electrode layer 33 through the electrolyte membrane 32 recombine with electrons. As a result of this H ⁺ reduction reaction, the current at the wet site increases immediately after time td, as indicated by L4. At this time, the amount of electrons used for the O ₂ reduction reaction at the dry site is reduced by the amount of electrons used for the H ⁺ reduction reaction at the wet site. Therefore, as shown in L5, time t
Immediately after d, the current in the dry area decreases.

Furthermore, when the reaction at the wet site is changed from the O ₂ reduction reaction to the H ⁺ reduction reaction, moisture moves from the electrolyte membrane 32 to the cathode catalyst electrode layer 33 along with the movement of protons. Is no longer generated. Therefore, as indicated by L1, the internal resistance of the cell 30 at the wet site increases.

  That is, when the cathode catalytic electrode layer 33 is destroyed at the wet site, the change rate of the cell current at the site changes from negative to positive, and the change rate of the internal resistance of the cell 30 at the site becomes positive. . Therefore, in this embodiment, the destruction of the cathode catalyst electrode layer 33 is detected by detecting such a change in the cell current and the internal resistance of the cell 30.

  Thereby, the destruction of the cathode catalyst electrode layer 33 is detected in distinction from the drying inhibition of the electrolyte membrane 32, the reaction inhibition due to the excessive water content of the MEA 31 and the air supply inhibition before the cathode catalyst electrode layer 33 is destroyed. I can do it.

(Hydrogen shortage allowable negative voltage correction flow)
In the fuel cell main body 1, when power generation is started below freezing point, the cathode catalyst electrode layer 33 is easily broken at the wet site due to freezing of the generated water. Therefore, in this embodiment, when power generation of the fuel cell main body 1 is started below freezing point, a hydrogen deficient allowable negative voltage correction flow described below is executed.

  FIG. 5 is a flowchart showing a flow of correcting a hydrogen deficient allowable negative voltage according to the present embodiment. This flow is stored in the ECU 20 in advance, and is repeatedly executed at predetermined intervals by the ECU 20 when power generation of the fuel cell main body 1 is started below freezing point.

  In this flow, first, in step S101, the cell current change rate ΔI / Δt at the wet site is calculated based on the measured value of the current measuring device 22.

  Next, in step S102, the change rate ΔR / Δt of the internal resistance of the cell 30 at the wet site is calculated based on the measured value of the resistance measuring device 23.

  Next, in step S103, it is determined whether or not the change rate ΔI / Δt of the cell current changes from negative to positive and the change rate ΔR / Δt of the internal resistance of the cell 30 is positive. If an affirmative determination is made in step S103, it is determined in step S104 that the cathode catalyst electrode layer 33 has been destroyed at the wet site. In this case, the process of step S105 is performed next. On the other hand, when a negative determination is made in step S103, it is determined in step S108 that the cathode catalyst electrode layer 33 is not broken at the wet site. In this case, the execution of this flow is temporarily terminated.

  In step S105, the cell voltage Vc at the current wet site measured by the voltage measuring device 21 is read.

Next, in step S106, the cell voltage V read in step S105.
By subtracting c from the initial value Vci of the cell voltage, the cell voltage decrease amount ΔVc0 resulting from the cathode potential decreasing due to the destruction of the cathode catalyst electrode layer 33 is calculated. Here, the initial value Vci of the cell voltage is a cell voltage when the cell 30 is in the initial state, that is, in a state where the cathode catalyst electrode layer 33 is not deteriorated or broken. In the present embodiment, the initial value Vci of the cell voltage is stored in advance in the ECU 20 in correspondence with the cell current and the temperature of the cell 30.

FIG. 6 is a diagram illustrating the IV characteristics of the cell according to this example. In FIG. 6, the horizontal axis represents the cell current, and the vertical axis represents the cell voltage. In FIG. 6, Li represents the time when the cell is in the initial state, and Ld represents the time when the cathode catalyst electrode layer was broken. FIG. 6 shows the IV characteristics of the cell at the temperature T ₀ when the cell voltage read in step S105 is measured. In FIG. 6, I ₀ represents the cell current when the cell voltage read in step S105 is measured. That is, in step S106, as shown in FIG. 6, the cell voltage drop amount ΔVc0 when the temperature of the cell 30 is T ₀ and the cell current is I ₀ is calculated.

  Next, in step S107, the hydrogen deficient allowable negative voltage ΔVclimit is corrected based on the cell voltage decrease amount ΔVc0 calculated in step S106. That is, the hydrogen deficient allowable negative voltage ΔVclimit is corrected to a value that is smaller than the reference value by the cell voltage decrease amount ΔVc0 (the absolute value of the hydrogen deficient allowable negative voltage ΔVclimit is increased by the cell voltage decrease amount ΔVc0). Then, the corrected hydrogen deficient allowable negative voltage ΔVlimit is stored in the ECU 20.

  When the cathode catalyst electrode layer 33 is destroyed due to the execution of the above flow, whether or not the shortage of hydrogen gas supplied to the anode catalyst electrode layer 34 exceeds the allowable range is determined to be acceptable for lack of hydrogen after correction. The determination is made based on the negative voltage ΔVlimit.

  In this embodiment, when the destruction of the cathode catalyst electrode layer 33 is detected, this may be recorded in the ECU 20 or the like. As a result, the fuel cell main body 1 can be replaced based on this record at the time of vehicle inspection or the like.

(Variation of detection of cathode catalyst electrode layer failure)
In this embodiment, in order to detect the destruction of the cathode catalyst electrode layer 33, the difference between the measured voltage of the cell 30 measured by the voltage measuring device 21 and the IR correction voltage (hereinafter simply referred to as voltage difference) is used. May be. As shown in FIG. 4A, when the cathode catalyst electrode layer 33 is destroyed, the voltage difference (that is, the difference between L3 and L2) increases. Therefore, as described above, the change rate of the cell current at the wet site and the change rate of the internal resistance of the cell 30 are calculated, and the change rate of the absolute value of the voltage difference at the wet site is calculated. When the rate of change of the cell current changes from negative to positive, the rate of change of the internal resistance of the cell 30 is positive, and the rate of change of the absolute value of the voltage difference is positive, the cathode catalyst electrode layer 33 It may be determined that the destruction has occurred. According to this, the detection accuracy of destruction of the cathode catalyst electrode layer 33 can be further improved.

(Variation of insufficient determination of hydrogen gas supply to anode catalyst electrode layer)
In the present embodiment, the fuel cell main body 1 may be provided with an anode potential measuring device for measuring the anode potential at the wet site. In this case, when the destruction of the cathode catalyst electrode layer 33 is detected, the supply amount of hydrogen gas to the anode catalyst electrode layer 34 is insufficient based on whether or not the anode potential measured by the anode potential measuring device exceeds the threshold value. It is determined whether or not exceeds the allowable range. Then, based on the determination result, it is determined whether to limit the power generation of the fuel cell main body 1. This also limits the power generation of the fuel cell body 1 when the cathode catalyst electrode layer 33 is destroyed, even though the supply amount of hydrogen gas to the anode catalyst electrode layer 34 is within an allowable range. This can be suppressed.

  In the present embodiment, the voltage measuring device 21 corresponds to the voltage measuring means according to the present invention, the current measuring device 22 corresponds to the current measuring means according to the present invention, and the resistance measuring device 23 corresponds to the resistance measuring means. To do. Moreover, ECU20 which restrict | limits the electric power generation of the fuel cell main body 1 is equivalent to the electric power generation limiting means which concerns on this invention. In the flow shown in FIG. 5, the ECU 20 that executes step 101 corresponds to the current change rate calculation means according to the present invention, and the ECU 20 that executes step 102 corresponds to the resistance change rate calculation means according to the present invention. The ECU 20 that executes S101 to S104 corresponds to the detection means according to the present invention, and the ECU 20 that executes steps S106 and S107 corresponds to the correction means according to the present invention.

<Second Example>
A second embodiment of the present invention will be described with reference to FIGS. Here, only the parts different from the first embodiment will be described.

  The effective surface area of the cathode catalyst electrode layer 33 decreases with deterioration such as corrosion. When the effective surface area of the cathode catalyst electrode layer 33 decreases, the cathode potential decreases as in the case where the cathode catalyst electrode layer 33 is destroyed in the first embodiment. Therefore, the negative voltage of the cell 30 when the reverse potential phenomenon occurs due to the insufficient supply amount of the fuel gas to the anode catalyst electrode layer 34 changes according to the effective surface area of the cathode catalyst electrode layer 33.

  Therefore, in this embodiment, the effective surface area of the cathode catalyst electrode layer 33 is estimated. Then, when the effective surface area of the cathode catalyst electrode layer 33 is reduced, the cathode depletion allowable negative voltage is corrected to a smaller value corresponding to the decrease in the cathode potential accompanying the decrease (the absolute value of the hydrogen depletion allowable negative voltage is a larger value). And). As a result, it is possible to suppress the power generation of the fuel cell main body 1 from being restricted even though the shortage of hydrogen gas supplied to the anode catalyst electrode layer 34 is within the allowable range.

(Hydrogen shortage allowable negative voltage correction flow)
FIG. 7 is a flowchart showing a hydrogen deficient allowable negative voltage correction flow according to this embodiment. This flow is stored in advance in the ECU 20, and is repeatedly executed by the ECU 20 at predetermined intervals.

  In this flow, first, in step S201, the current effective surface area Sca0 of the cathode catalyst electrode layer 33 of the cell 30 whose cell voltage is measured by the voltage measuring device 21 is the operation load history of the fuel cell body 1 (that is, the cathode potential). Based on the history). The relationship between the change in the operating load of the fuel cell main body 1 and the change in the effective surface area of the cathode catalyst electrode layer 33 is obtained in advance based on experiments or the like and is stored in the ECU 20. In step 201, the current effective surface area Sca0 of the cathode catalyst electrode layer 33 may be obtained by another method.

  Next, in step S202, the cell voltage decrease amount ΔVc0 resulting from the decrease in the cathode potential due to the decrease in the effective surface area of the cathode catalyst electrode layer 33 becomes the effective surface area Sca0 of the cathode catalyst electrode layer 33 estimated in step S201. Calculated based on

In the present embodiment, the relationship between the effective surface area of the cathode catalyst electrode layer 33 and the cell voltage as shown in FIG. 8 is obtained in advance based on experiments or the like and stored in the ECU 20. In FIG. 8, the horizontal axis represents the effective surface area of the cathode catalyst electrode layer 33, and the vertical axis represents the cell voltage. In step S202, a cell voltage drop amount ΔVc0 as shown in FIG. 8 is calculated.

  Next, in step S203, the hydrogen deficient allowable negative voltage ΔVclimit is corrected based on the cell voltage decrease amount ΔVc0 calculated in step S202. That is, the hydrogen deficient allowable negative voltage ΔVclimit is corrected to a value that is smaller than the reference value by the cell voltage decrease amount ΔVc0 (the absolute value of the hydrogen deficient allowable negative voltage ΔVclimit is increased by the cell voltage decrease amount ΔVc0). Then, the corrected hydrogen deficient allowable negative voltage ΔVlimit is stored in the ECU 20.

  When the effective surface area of the cathode catalyst electrode layer 33 is reduced by executing the above flow, it is determined whether or not the shortage of hydrogen gas supplied to the anode catalyst electrode layer 34 exceeds the allowable range. The determination is made based on the allowable negative voltage ΔVlimit.

  In the present embodiment, in the flow shown in FIG. 7, the ECU 20 that executes step 201 corresponds to the effective surface area acquisition means according to the present invention, and the ECU 20 that executes steps S202 and 203 serves as the correction means according to the present invention. Equivalent to.

  The above embodiments can be combined as much as possible. For example, when destruction of the cathode catalyst electrode layer is detected by the cathode catalyst electrode layer destruction detection method according to the first embodiment, the effective surface area of the cathode catalyst electrode layer is estimated, and then the hydrogen according to the second embodiment is determined. The hydrogen deficiency allowable negative voltage may be corrected by a deficiency allowable negative voltage correction method.

DESCRIPTION OF SYMBOLS 1 ... Fuel cell main body 2, 3 ... Air pipe 4, 5 ... Hydrogen gas pipe 20 ... ECU
21 .. Voltage measuring device 22 .. Current measuring device 23 .. Resistance measuring device 24 .. Temperature sensor 30 .. Cell 31 .. MEA
32 .... Electrolyte membrane 33..Cathode catalyst electrode layer 34..Anode catalyst electrode layer 35a, 35b..Separator 36..Air passage 37..Hydrogen gas passage

Claims (3)

A fuel cell body formed by laminating a plurality of cells having MEAs formed by joining a cathode catalyst electrode layer and an anode catalyst electrode layer to an electrolyte membrane;
Voltage measuring means for measuring the cell voltage;
In a fuel cell system comprising a power generation limiting means for limiting power generation of the fuel cell main body when the cell voltage becomes smaller than a predetermined negative voltage,
Detection means for detecting the destruction of the cathode catalyst electrode layer of the cell;
When a breakdown of the cathode catalyst electrode layer is detected, a cell voltage decrease amount is calculated by subtracting a current cell voltage measured by the cell voltage measuring means from an initial value of the cell voltage, and the cell voltage decrease amount Correction means for correcting the predetermined negative voltage based on:
A fuel cell system further comprising: The voltage measuring means measures a cell voltage in a portion where the water content of MEA is relatively high;
Current measuring means for measuring a cell current in a portion where the water content of MEA is relatively high;
A resistance measuring means for measuring the internal resistance of the cell in a portion where the water content of MEA is relatively high,
The detection means detects the destruction of the cathode catalyst electrode layer of the cell in a portion where the water content of MEA is relatively high,
Current change rate calculating means for calculating the change rate of the cell current measured by the current measuring means;
Resistance change rate calculating means for calculating a change rate of internal resistance measured by the resistance measuring means,
When the current change rate calculated by the current change rate calculating unit changes from negative to positive and the resistance change rate calculated by the resistance change rate calculating unit is positive, the cathode catalyst electrode layer is destroyed. The fuel cell system according to claim 1, wherein the fuel cell system is determined to be. A fuel cell body formed by laminating a plurality of cells having MEAs formed by joining a cathode catalyst electrode layer and an anode catalyst electrode layer to an electrolyte membrane;
Voltage measuring means for measuring the cell voltage;
In a fuel cell system comprising a power generation limiting means for limiting power generation of the fuel cell main body when the cell voltage becomes smaller than a predetermined negative voltage,
An effective surface area obtaining means for obtaining an effective surface area which is a surface area of a portion effective for power generation of the cathode catalyst electrode layer of the cell;
When the effective surface area of the cathode catalyst electrode layer decreases, a cell voltage decrease amount that is a decrease amount from the initial value of the cell voltage is calculated based on the decrease amount, and the predetermined negative voltage is calculated based on the cell voltage decrease amount. Correction means for correcting
A fuel cell system further comprising:

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