JP2007005000A - Control method for fuel cell system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a fuel cell system suppressing deterioration of an electrolyte membrane. <P>SOLUTION: In the fuel cell system having the electrolyte membrane, and a fuel electrode and an oxidant electrode between which the electrolyte membrane is interposed, while the fuel cell system is stopped in such a way as idling stop, cross leak of an electrolyte is detected, supply of hydrogen to the fuel electrode and supply of air to the oxidant electrode are stopped, and when the amount of the cross leak of the electrolyte membrane exceeds the prescribed amount, voltage of fuel cell is decreased once. and then the voltage of the fuel cell 1 is increased again to quickly decompose hydrogen peroxide generated by the cross leak. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a control method for a fuel cell system.

  For example, when a fuel cell is installed in a vehicle, the output of the fuel cell is reduced to zero without supplying a reaction gas such as new hydrogen or air when the vehicle is idle to improve the fuel consumption of the fuel cell vehicle. The fuel cell is held as an open circuit voltage (hereinafter referred to as OCV).

When the fuel cell is held at an open circuit voltage, the voltage per unit cell of the fuel cell becomes lower than 0.9 V in about 100 hours. This is because hydrogen or oxygen cross-leaks through the electrolyte membrane in the fuel cell, so that oxygen is mixed into the fuel electrode or hydrogen is mixed into the oxidant electrode, and hydrogen and oxygen react at the fuel electrode or oxidant electrode. This is because hydrogen peroxide (hereinafter referred to as H ₂ O ₂ ) is generated and the electrolyte is deteriorated by H ₂ O ₂ .

Therefore, Non-Patent Document 1 discloses a method for effectively decomposing H ₂ O ₂ by increasing the voltage of the fuel cell to an OCV such as 1.4 V (approximately 0.95 V). ₂ O ₂ can be decomposed.
Satoshi Inaba “Research and Development of Polymer Electrolyte Fuel Cell Research on Degradation Factors of Polymer Electrolyte Fuel Cell” FY2013 New Energy and Industrial Technology Development Organization Report, March 2002

However, the normal OCV of the fuel cell is about 0.95 V, and in order to effectively decompose H ₂ O ₂ , it is necessary to apply a voltage from the outside, which deteriorates the energy efficiency of the fuel cell system.

Furthermore, under a voltage of about OCV (0.8 to 1.0 V), for example, when platinum is used as the catalyst in the oxidizer electrode, an oxide film is formed on the surface of the platinum, and the above-mentioned Since the potential is lower than about 1.4 V, there is a problem that the decomposition rate of H ₂ O ₂ is slowed, the electrolyte is deteriorated by H ₂ O ₂ , and the fuel cell is deteriorated.

The present invention has been invented to solve such problems. H ₂ O ₂ is decomposed by an energy efficient fuel cell system without applying voltage from the outside to suppress deterioration of the fuel cell. For the purpose.

  In the present invention, a fuel cell having an electrolyte membrane, a fuel electrode sandwiching the electrolyte membrane and an oxidant electrode, a hydrogen supply means for supplying hydrogen to the fuel electrode, and an oxidant supply for supplying oxidant to the oxidant electrode A cross-leak detection means for detecting a cross leak of the electrolyte membrane when the fuel cell system is stopped, for example, in an idle stop state, and a hydrogen supplied from the hydrogen supply means and the oxidant supply means. When the supply of oxygen and the oxidizing agent is stopped and the cross leak amount of the electrolyte membrane exceeds a predetermined amount, the voltage of the fuel cell is reduced to the first predetermined voltage, and then the fuel cell voltage is set to the first predetermined voltage. Voltage adjustment means for making the voltage higher than the voltage is provided.

According to the present invention, when the output of the fuel cell of the fuel cell system is set to zero, for example, when idling is stopped, H ₂ O ₂ generated by cross leak can be quickly decomposed without applying voltage from the outside.

  A schematic configuration of the fuel cell system according to the first embodiment of the present invention will be described with reference to FIG. In this embodiment, the fuel cell 1, a hydrogen cylinder (hydrogen supply means) 2 that supplies hydrogen to a fuel electrode 41 (to be described later) of the fuel cell 1, and exhaust hydrogen that has not been used for the power generation reaction of the fuel cell 1 are again fueled. A circulation pump 3 that circulates to the electrode 41, a compressor (oxidant supply means) 4 that supplies air to an oxidant electrode 42 (to be described later) of the fuel cell 1, and a load such as a resistor that consumes the power generated by the fuel cell 1 5, a voltage sensor 6 that detects the voltage of the fuel cell 1, and output control means 7 that controls the output of the fuel cell 1.

  Also, a hydrogen supply path 10 for supplying hydrogen from the hydrogen cylinder 2 to the fuel electrode 41 of the fuel cell 1, a circulation channel 11 for recirculating the exhausted hydrogen that has not been used for power generation of the fuel cell 1 to the fuel electrode 41, And a hydrogen discharge path 12 for sending the discharged hydrogen to a hydrogen consuming means (not shown) when the hydrogen concentration in the discharged hydrogen becomes low. A valve V1 is provided between the hydrogen cylinder 2 and the fuel electrode 41, and a valve V2 is provided in the hydrogen discharge path 12. Further, an air supply path 13 for supplying air from the compressor 4 to the oxidant electrode 42 and an air discharge path 14 for discharging exhaust air that has not been used for power generation of the fuel cell 1 to the outside of the fuel cell system are provided. Open / close valve V2 is selectively switched to recirculate the exhaust hydrogen or send it to the hydrogen consuming means.

  Moreover, the controller 20 which controls the circulation pump 3, the compressor 4, the output control means 7, and valve | bulb V1, V2 based on the output requested | required of a fuel cell system is provided.

  The fuel cell 1 is configured by stacking a plurality of unit cells 30. The unit cell 30 will be described with reference to the schematic configuration diagram of FIG.

  The unit cell 30 includes a solid polymer electrolyte membrane (hereinafter referred to as an electrolyte membrane) 31, an anode catalyst layer 32 and a cathode catalyst layer 33 that sandwich the electrolyte membrane 31, and anode gas diffusion provided outside the anode catalyst layer 32. A layer 34 and a cathode gas diffusion layer 35 provided outside the cathode catalyst layer 33. In addition, an anode separator 37 provided outside the anode gas diffusion layer 34 and having a hydrogen flow path 36 and a cathode separator 39 provided outside the cathode gas diffusion layer 35 and having an air flow path 38 are provided. Further, an edge seal 40 is provided so that hydrogen or air does not leak. Although not shown, a cooling water channel through which cooling water for cooling the unit cell 30 may be provided.

  In this embodiment, the anode catalyst layer 32 and the anode gas diffusion layer 34 are the fuel electrode 41, and the cathode catalyst layer 33 and the cathode gas diffusion layer 35 are the oxidant electrode 42.

  The electrolyte membrane 31 is a polymer electrolyte membrane such as perfluorosulfonic acid such as Nafion (registered trademark) manufactured by DuPont.

  The anode catalyst layer 32 and the cathode catalyst layer 33 are carbon black carrying platinum as a catalyst. The catalyst is not limited to platinum.

  For the anode gas diffusion layer 35 and the cathode gas diffusion layer 35, for example, carbon paper or carbon cloth is used.

  The output control means 7 is a device that controls the output of the fuel cell 1 and is a device that can switch the output of the fuel cell 1 in a stepped manner. That is, it is a device that can selectively switch the electrical connection between the fuel cell 1 and the load 5. The output control means 7 is electrically connected to, for example, a motor (not shown), and controls the output of the fuel cell 1 according to the power consumed by the motor.

  The controller 20 calculates the output of the fuel cell 1 based on the power consumed by the fuel cell system, and transmits the output value of the fuel cell 1 to the output control means 7 as a signal. Further, the amount of hydrogen or the amount of air supplied to the fuel electrode 41 and the oxidant electrode 42 is adjusted by controlling the opening degree of the valves V1 and V2, the rotational speed of the circulation pump 3 and the compressor 4, and the like.

During operation of the fuel cell 1, in the unit cell 30, cross leak occurs in which air is mixed into the fuel electrode 41 through the electrolyte membrane 31 and hydrogen is mixed into the oxidizer electrode 42. When a cross leak occurs, hydrogen and oxygen react with each other at both the fuel electrode 41 and the oxidant electrode 42 to generate H ₂ O ₂ . As described later, since H ₂ O ₂ is easily decomposed in the cathode catalyst layer 33, the concentration of H ₂ O ₂ is higher in the anode catalyst layer 32. Therefore, H ₂ O ₂ moves in the electrolyte membrane 31 from the anode catalyst layer 32 to the cathode catalyst layer 33 side by concentration diffusion.

At this time, H ₂ O ₂ generated at the fuel electrode 41 and the oxidant electrode 42 may deteriorate the electrolyte membrane 31 having a polymer structure, but the generated H ₂ O ₂ is from the viewpoint of potential. It can be decomposed by the catalyst of the cathode catalyst layer 33 having a high potential. Therefore, H ₂ O ₂ that has moved to the cathode catalyst layer 33 via the electrolyte membrane 31 is basically decomposed in the cathode catalyst layer 33. The anode catalyst layer 32 is lower than the potential (about 0.6V) of H ₂ O ₂ is decomposed, the decomposition of H ₂ O ₂ hardly occurs. As described above, H ₂ O ₂ is easily decomposed in the cathode catalyst layer 33 having a high potential. However, when the electric potential is high, an oxide film is formed on the surface of platinum, so that H ₂ O ₂ is hardly decomposed. On the other hand, during normal operation where the output required for the fuel cell 1 is relatively high, the voltage of the fuel cell 1 is low. That is, the potential of the cathode catalyst layer 33 is lowered. At this time, in the cathode catalyst layer 33, the oxide film formed on the surface of platinum as a catalyst is reduced, and the amount of oxide film formed is reduced. In particular, if it is 0.7 V or more, H ₂ O ₂ is rapidly decomposed. Therefore, deterioration of the electrolyte membrane 31 is suppressed.

However, at the time of idling stop when the output taken out from the fuel cell 1 becomes zero, the voltage of the fuel cell 1 becomes as high as about 0.95 V, and the potential of the oxidizer electrode 42 becomes high. Thereby, in the cathode catalyst layer 33, an oxide film is formed on the surface of platinum. When an oxide film is formed on the surface of platinum, the activity of platinum decreases. Therefore, when H ₂ O ₂ is generated by cross leak, the function of decomposing H ₂ O ₂ is lowered, and the electrolyte membrane 31 is deteriorated by H ₂ O ₂ . In this embodiment, the deterioration of the electrolyte membrane 31 that occurs during idle stop is suppressed.

  Next, control of the fuel cell system performed by the controller 20 will be described with reference to the flowchart of FIG. The control of this embodiment is control performed when idling is stopped. During normal operation, the fuel cell 1 and the load 5 are electrically disconnected by the output control means 7.

In step S100, when an idle stop signal is received in the fuel cell system, the valves V1 and V2 are closed, and the circulation pump 3 is operated to circulate only the discharged hydrogen to the fuel electrode 41. When the circulation pump 3 is operating until just before, it is continuously operated. Further, the compressor 4 is stopped, and the supply of air to the oxidant electrode 42 is stopped. At this time, when no cross leak occurs in the electrolyte membrane 31, the voltage of the fuel cell 1 is maintained relatively high. However, when a cross leak occurs, H ₂ O ₂ is generated at the fuel electrode 41 and the oxidant electrode 42. Therefore, when a cross leak occurs, hydrogen decreases in the fuel electrode 41 and oxygen increases, and in the oxidizer electrode 42, oxygen in the air decreases and hydrogen increases, so the voltage of the fuel cell 1 decreases.

  In step S101, the voltage of the fuel cell 1 is detected by the voltage sensor 6, and the voltage V per unit cell 30 of the fuel cell 1 is calculated. When the voltage V becomes lower than the predetermined voltage (predetermined amount, second predetermined voltage) V1, the process proceeds to step S102.

  Here, FIG. 4 shows the cross leak relative amount characteristic with respect to the temperature in the electrolyte membrane. In FIG. 4, the cross leak relative amount of the electrolyte membrane A when the relative humidity of the gas is α% is indicated by a solid line, and the cross leak relative amount of the electrolyte membrane B when the relative humidity of the gas is α% is indicated by a dashed line. It shows with. In the electrolyte membrane A, the cross leak relative amount when the relative humidity of the gas is β% (α <β) is indicated by a broken line. The electrolyte membrane A and the electrolyte membrane B are different types of electrolyte membranes, and the thicknesses of the membranes are the same.

  According to FIG. 4, when the relative humidity is α%, the electrolyte membrane A and the electrolyte membrane B have different cross leak amounts, and the cross leak amount increases as the temperature increases. Even when the same electrolyte membrane A is used, the cross leak amount increases as the relative humidity increases.

  As described above, the amount of cross leak in the electrolyte membrane 31 varies depending on the type of the electrolyte membrane 31 and the use conditions such as the humidity and temperature of hydrogen or air. In this embodiment, the predetermined voltage V1 is set according to the electrolyte membrane 31 used from the map shown in FIG. The predetermined voltage V1 is a voltage for determining whether or not a cross leak has occurred in the fuel cell 1. In this embodiment, the predetermined voltage V1 is set to 0.92 V (step S101 constitutes a cross leak detecting means).

  In step S102, the output control means 7 electrically connects the fuel cell 1 and the load 5, and the output control means 7 takes out an output corresponding to 5% of the maximum output of the fuel cell 1. The arrival time until the output corresponding to 5% of the maximum output of the fuel cell 1 is 1 second. The extracted output is consumed by the load 5.

  Here, when the voltage per unit cell 30 of the fuel cell 1 is repeatedly changed between the OCV and a predetermined voltage, that is, from the state where the output of the fuel cell 1 is zero, the voltage per unit cell 30 is predetermined. FIG. 5 shows the relationship between the voltage per unit cell 30 and the amount of change in the electrochemical surface area (hereinafter referred to as ECA) of the cathode catalyst layer 33 when it is repeatedly changed to the voltage output. The predetermined voltage is set to five types of voltages A, B, C, D, and E in descending order of the voltage of the unit cell 30, and the output output from the fuel cell 1 corresponding to each voltage is small. In order, they are a, b, c, d, and e. The amount of change in the ECA of the cathode catalyst layer 33 is indicated by the ratio of the ECA of the cathode catalyst layer 33 and the ECA of OCV obtained by cyclic voltammetry. The amount of change in ECA indicates that as the ratio increases, the elution of platinum from the cathode catalyst layer 33 increases.

  According to FIG. 5, platinum is more eluted when the voltage change is repeated between the OCV and the predetermined voltage than when the fuel cell 1 is held at the OCV. Further, the lower the predetermined voltage, the more platinum is eluted. By reducing the voltage of the unit cell 30 from the OCV to a predetermined voltage, the potential of the cathode catalyst layer 33 is reduced, and the oxide film formed on the platinum surface of the cathode catalyst layer 33 is reduced and separated. Thereafter, when the voltage of the unit cell 30 is increased again, the cathode catalyst layer 33 becomes a high potential, and platinum is ionized and eluted from the cathode catalyst layer 33 until an oxide film is formed on platinum. Therefore, when the voltage change is repeated between the OCV and a predetermined voltage, platinum is eluted from the cathode catalyst layer 33 due to the potential change of the cathode catalyst layer 33 and the oxidation / reduction of platinum.

  Further, when the predetermined voltage is smaller than B, that is, when the output taken out from the fuel cell 1 is larger than b, the amount of change in ECA increases, and the rate of increase in the elution amount of platinum increases. Further, when the predetermined voltage is made smaller than D, the change amount of ECA is small, that is, the increase rate of the elution amount of platinum is small.

As described above, elution of platinum can be reduced and a part of the oxide film on the surface of platinum is reduced by setting the predetermined voltage (first predetermined voltage) to B or higher, that is, the output taken out from the fuel cell 1 to b or lower. Thus, H ₂ O ₂ generated by cross leak can be decomposed and deterioration of the electrolyte membrane 31 can be suppressed.

  In step S102, the output of the fuel cell 1 is set to 5% of the maximum output of the fuel cell 1, and this is set so that the output of the fuel cell 1 is equal to or less than b. The output of the fuel cell 1 may be less than or equal to b, but it is desirable that the output of the fuel cell 1 be close to b. Note that the output b of the fuel cell 1 is set in advance by experiments or the like, but here the output is set so that the voltage per unit cell 30 is 0.78 V or more.

  In step S103, when the voltage per unit cell 30 reaches the predetermined voltage B, the output control means 7 disconnects the electrical connection between the fuel cell 1 and the load 5 in a step-like manner, and the output taken out from the fuel cell 1 is set to zero. To do. After the output is set to zero, the circulation pump 3 may be continuously operated or stopped. However, when hydrogen deficiency occurs in the anode catalyst layer 32, the cathode catalyst facing the anode catalyst layer 32 deficient in hydrogen. Since the potential of the layer 33 rises and carbon corrosion occurs, it is desirable to control the circulation pump 3 so that hydrogen deficiency does not occur in the anode catalyst layer 32. As a result, the potential of the oxidant electrode 42 is increased, and an oxide film is formed again on the platinum surface in the cathode catalyst layer 33 (steps S102 and S103 constitute a voltage adjusting means).

  When an output extraction signal is received from the fuel cell 1 due to, for example, depression of an accelerator during this control, this control is stopped and power generation is started in the fuel cell 1 based on the signal.

  In step S102, the output of the fuel cell 1 is set to 5% of the maximum output of the fuel cell 1. However, the output is not limited to this. The fuel cell 1 suppresses the deterioration of the electrolyte membrane 31 and suppresses the elution of platinum. Set to output.

With the above control, when the amount of cross leak in the electrolyte membrane 31 increases when the fuel cell system is idling, the fuel cell 1 is temporarily connected to the load 5, the voltage of the fuel cell 1 is lowered, and the fuel electrode 41 is reduced. Then, the potential of the oxidant electrode 42 is lowered to reduce the oxide film on the surface of platinum. Thereby, the activity of platinum as a catalyst can be increased, and H ₂ O ₂ generated by cross leak can be decomposed.

  The effect of 1st Embodiment of this invention is demonstrated.

Here, when the unit cell 30 is held at the OCV and when the voltage is cycle-changed between the OCV and the predetermined voltage B, the unit cell 30 is included in the drain water discharged from the fuel electrode 41 and the oxidant electrode 42. The relative comparison result of the discharge rate of fluorine ions (F ⁻ ) is shown in FIG. The fluorine ion discharge rate is 1 when the unit cell 30 is held in the OCV.

  As shown in FIG. 6, when the voltage is cycle-changed from the OCV to the predetermined voltage B, the fluorine ion discharge rate is suppressed. That is, it can be seen that both the fuel electrode 41 and the oxidant electrode 42 suppress the deterioration of the electrolyte membrane 31.

In this embodiment, when the voltage per unit cell 30 becomes lower than the predetermined voltage V1 at the time of idling stop of the fuel cell system, the voltage of the fuel cell 1 is temporarily reduced. As a result, by reducing a part of the oxide film formed on the surface of the platinum of the fuel electrode 41 and the oxidant electrode 42, particularly the oxidant electrode 42, the activity of the platinum is increased. The generated H ₂ O ₂ can be decomposed and deterioration of the electrolyte membrane 31 can be suppressed.

When the voltage of the fuel cell 1 is lowered, the voltage is changed in a range where the elution of platinum is reduced, for example, the voltage per unit cell 30 is not less than B shown in FIG. Since they are separated from each other, elution of platinum in the anode catalyst layer 32 and the cathode catalyst layer 33 can be reduced, and H ₂ O ₂ generated by cross leak can be decomposed to suppress deterioration of the electrolyte membrane 31.

  Further, when the voltage of the fuel cell 1 is lowered, the voltage of the fuel cell 1 is lowered in a short time, for example, 1 second, so that the amount of hydrogen consumed in the anode catalyst layer 32 when the voltage is lowered is minimized. Therefore, the energy efficiency of the fuel cell system can be improved.

  When the voltage of the fuel cell 1 is once lowered and then increased again, the electrical connection between the motor 5 and the fuel cell 1 is cut stepwise to form an oxide film instantaneously on the platinum surface. And elution of platinum can be suppressed.

  Next, a second embodiment of the present invention will be described with reference to the schematic configuration diagram of FIG.

  This embodiment includes a secondary battery (power charging / discharging means) 8 electrically connected to the fuel cell 1 by the output control means 7 in place of the load 5 in the fuel cell system of the first embodiment. Since other configurations are the same as those of the first embodiment, description thereof is omitted here.

  The secondary battery 8 is, for example, a lithium ion battery, a nickel metal hydride battery, an electric double layer capacitor, or the like, and performs charge / discharge according to the output taken out from the fuel cell system.

  Next, control of the fuel cell system performed by the controller 20 will be described with reference to the flowchart of FIG.

  Since step S200 and step S201 are the same control as step S100 and step S101 of the first embodiment, description thereof is omitted here.

In step S 202, the fuel cell 1 and the secondary battery 8 are electrically connected by the output control means 7, and an output corresponding to 5% of the maximum output of the fuel cell 1 is taken out. The arrival time until the output corresponding to 5% of the maximum output of the fuel cell 1 is 1 second. As a result, the voltage of the fuel cell 1 is lowered, and a part of the oxide film formed on the platinum surface of the cathode catalyst layer 33 is reduced to increase the activity of platinum, thereby generating H ₂ O ₂ generated by cross leak. Can be disassembled. Furthermore, the energy efficiency of the fuel cell system can be improved by charging the secondary battery 8 from the fuel cell 1. In addition, it is desirable that the output of the fuel cell 1 and the arrival time are controlled by the output control means 7 so that the charging efficiency of the secondary battery 8 is improved.

  In step S203, when the voltage per unit cell 30 reaches the predetermined voltage B, the output control means 7 disconnects the electrical connection between the fuel cell 1 and the secondary battery 8 and sets the output of the fuel cell 1 to zero. As a result, the voltage of the fuel cell 1 is increased, and an oxide film is formed on the platinum surface of the cathode catalyst layer 33.

  In step S204, the voltage of the fuel cell 1 is detected by the voltage sensor 6, and the voltage V per unit cell 30 is compared with the predetermined voltage V2. If the voltage V is higher than the predetermined voltage V2, the process returns to step S201 and the above control is repeated. On the other hand, when the voltage V is lower than the predetermined voltage V2, this control is terminated. When the voltage V is lower than the predetermined voltage V2, it is determined that hydrogen in the fuel electrode 41 or oxygen in the air in the oxidant electrode 42 is reduced, and cross leak is suppressed, so that the electrolyte membrane 31 does not deteriorate. . Preferably, as described in the first embodiment, from the viewpoint of carbon corrosion at the oxidant electrode, a state where oxygen in the air of the oxidant electrode 42 is reduced is good. The predetermined voltage V2 is set in consideration of deterioration of the electrolyte membrane 31, elution of platinum, or carbon corrosion in the cathode catalyst layer 33 at the start of the next operation, and is set to 0.6 V here.

  By the above control, when the voltage of the fuel cell 1 is lowered at the time of idling stop, the fuel cell 1 and the secondary battery 8 are electrically connected so that the electric power generated by the fuel cell 1 is converted into the secondary battery 8. To charge.

  The effect of 2nd Embodiment of this invention is demonstrated.

In this embodiment, when the H ₂ O ₂ generated by the cross leak is decomposed by lowering the voltage of the fuel cell 1 at the time of idling stop, the fuel cell 1 and the secondary battery 8 are electrically connected, and the fuel The energy efficiency of the fuel cell system can be improved by reducing the voltage of the battery 1 and charging the secondary battery 8 with the electric power generated by the fuel cell 1.

  Next, a fuel cell system according to a third embodiment of the present invention will be described with reference to FIG.

  The fuel cell system of this embodiment includes a timer (time measuring means) 9 in addition to the second embodiment. Since the configuration is the same as that of the second embodiment, a description thereof is omitted here.

  Next, control of the fuel cell system performed by the controller 20 will be described with reference to the flowchart of FIG.

In step S300, when an idle stop signal is received in the fuel cell system, the valves V1 and V2 are closed, and the circulation pump 3 is intermittently operated at a predetermined rotational speed to circulate only the discharged hydrogen to the fuel electrode 41. Further, the compressor 4 is stopped, and the supply of air to the oxidant electrode 42 is stopped. At this time, when no cross leak occurs in the electrolyte membrane 31, the voltage of the fuel cell 1 is maintained relatively high. However, when a cross leak occurs, H ₂ O ₂ is generated at the fuel electrode 41 and the oxidant electrode 42. Therefore, hydrogen decreases and oxygen increases in the fuel electrode 41, and oxygen in the air decreases and hydrogen increases in the oxidizer electrode 42, so the voltage of the fuel cell 1 decreases. By operating the circulation pump 3 intermittently at a predetermined rotational speed, the energy required to operate the circulation pump 3 can be reduced.

  In step S301, a time t after the idling stop in the fuel cell system is measured by the timer 9, and it is determined whether or not the time t has passed the predetermined time t1. Then, when the time t has passed the predetermined time t1, the process proceeds to step S302. The predetermined time t1 is a time set based on the map shown in FIG. 4 and the like, and is a time when the amount of cross leak in the electrolyte membrane 31 exceeds a predetermined amount after the idling stop.

  Since the control from step S302 to step S304 is the same as the control from step S202 to step S204 of the second embodiment, description thereof is omitted here.

  With the above control, when the voltage of the fuel cell 1 is lowered at the time of idling stop, the fuel cell 1 and the secondary battery 8 are electrically connected, so that the electric power generated by the fuel cell 1 is converted into the secondary battery 8. To charge.

  The effect of the third embodiment of the present invention will be described.

  In this embodiment, in addition to the effects of the second embodiment, by intermittently operating the circulation pump 3, the power consumed by the circulation pump 3 can be reduced, and the energy efficiency of the fuel cell system is improved. can do.

  It goes without saying that the present invention is not limited to the above-described embodiments, and includes various modifications and improvements that can be made within the scope of the technical idea.

  It can be used for a fuel cell system mounted on a fuel cell vehicle.

1 is a schematic configuration diagram of a fuel cell system according to a first embodiment of the present invention. It is a schematic block diagram of the unit cell of 1st Embodiment of this invention. It is a flowchart which shows the control in the idle stop state of 1st Embodiment of this invention. It is a map which shows the cross leak relative quantity with respect to the temperature in the electrolyte membrane of 1st Embodiment of this invention. It is a map which shows the variation | change_quantity of the electrochemical surface area of a cathode catalyst layer with respect to the voltage change of the unit cell of 1st Embodiment of this invention. It is a map which shows the discharge | emission speed | rate of the fluorine ion of the case where the unit cell of 1st Embodiment of this invention is hold | maintained at OCV, and the case where a voltage is cycle-changed from OCV to the predetermined voltage B. It is a schematic block diagram of the fuel cell system of 2nd Embodiment of this invention. It is a flowchart which shows the control in the idle stop state of 2nd Embodiment of this invention. It is a schematic block diagram of the fuel cell system of 3rd Embodiment of this invention. It is a flowchart which shows the control in the idle stop state of 3rd Embodiment of this invention.

Explanation of symbols

1 Fuel cell 2 Hydrogen cylinder (hydrogen supply means)
3 Circulating pump 4 Compressor (oxidant supply means)
5 Load 6 Voltage sensor 7 Output control means 8 Secondary battery (power charge / discharge means)
20 controller 30 unit cell 31 polymer electrolyte membrane (electrolyte membrane)
32 Anode catalyst layer 33 Cathode catalyst layer 41 Fuel electrode 42 Oxidant electrode

Claims (8)

A fuel cell having an electrolyte membrane, and a fuel electrode and an oxidizer electrode sandwiching the electrolyte membrane;
Hydrogen supply means for supplying hydrogen to the fuel electrode;
An oxidant supply means for supplying an oxidant to the oxidant electrode, and a fuel cell system comprising:
Cross leak detection means for detecting cross leak of the electrolyte membrane;
When the supply of the hydrogen and the oxidant from the hydrogen supply means and the oxidant supply means is stopped and the cross leak amount of the electrolyte membrane exceeds a predetermined amount when the fuel cell system is stopped A fuel cell system comprising voltage adjusting means for making the voltage of the fuel cell higher than the first predetermined voltage after reducing the voltage of the fuel cell to the first predetermined voltage. The cross leak detection means includes a voltage sensor for detecting the voltage of the fuel cell,
The voltage adjusting means stops the supply of the hydrogen and the oxidant from the hydrogen supply means and the oxidant supply means when the fuel cell system is stopped, and the voltage of the fuel cell is the first predetermined voltage. 2. The fuel cell system according to claim 1, wherein the voltage of the fuel cell is lowered to the first predetermined voltage when the voltage is lower than a second predetermined voltage higher than the voltage. The cross leak detecting means includes a time measuring means for measuring a time after stopping the supply of the hydrogen and the oxidant from the hydrogen supply means and the oxidant supply means,
The voltage adjusting means stops the supply of the hydrogen and the oxidant from the hydrogen supply means and the oxidant supply means when the fuel cell system is stopped, and the hydrogen supply means and the oxidant supply means 2. The voltage of the fuel cell is reduced to the first predetermined voltage when a time after the supply of the hydrogen and the oxidant from the fuel is stopped is longer than a predetermined time. Fuel cell system.   The voltage adjusting means takes out the output from the fuel cell and lowers the voltage of the fuel cell to the first predetermined voltage, then stops taking out the output from the fuel cell, and sets the voltage of the fuel cell to The fuel cell system according to any one of claims 1 to 3, wherein the fuel cell system is higher than the first predetermined voltage.   5. The fuel cell system according to claim 4, wherein the voltage adjusting means stops taking out the output from the fuel cell in a stepwise manner. Power charging / discharging means electrically connected to the fuel cell;
6. The fuel cell according to claim 1, wherein charging of the power charging / discharging unit from the fuel cell reduces the voltage of the fuel cell to the first predetermined voltage. 6. system. A circulation pump for circulating hydrogen discharged from the fuel electrode to the fuel electrode;
7. The circulating pump is operated continuously or intermittently when supply of the hydrogen and the oxidant from the hydrogen supply means and the oxidant supply means is stopped. The fuel cell system according to any one of the above.   The fuel cell system according to any one of claims 1 to 7, wherein the first predetermined voltage is 0.78V or more.

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