JP5521909B2 - FUEL CELL SYSTEM AND MOBILE BODY MOUNTING THE FUEL CELL SYSTEM - Google Patents

Description

  The present invention relates to a fuel cell system and a moving body.

  In a polymer electrolyte fuel cell, a radical inhibitor such as a cerium compound is disposed inside the fuel cell in order to suppress chemical deterioration of the electrolyte membrane caused by hydroxy radicals generated by an electrochemical reaction. The configuration is known. By disposing the radical inhibitor in the fuel cell, the radical inhibitor is gradually dissolved using the liquid water generated in the fuel cell, and the radical inhibitor is gradually supplied to the electrolyte membrane, resulting in deterioration of the electrolyte membrane. Can be suppressed. As described above, in the configuration in which the radical inhibitor is dissolved using the liquid water inside the fuel cell, the lack of water inside the fuel cell causes the radical inhibitor to dissolve, and the dissolved radical suppressor electrolyte membrane There may be a case where the supply to is insufficient.

  Various methods are known as methods for adjusting the amount of water inside the fuel cell and suppressing water shortage inside the fuel cell. For example, when it is determined that the amount of water taken out from the fuel cell is large based on the water balance in the fuel cell, and the output current of the fuel cell is below a predetermined value, the supply of air to the cathode is stopped. A configuration for performing idle stop has been proposed (see, for example, Patent Document 1). By performing such control, the amount of moisture taken out by the air supplied to the cathode is suppressed, and water shortage inside the fuel cell is suppressed.

JP 2006-92801 A JP 2004-265862 A JP 2006-127788 A

  However, when the idle stop is performed while the supply of air to the cathode is stopped, further moisture removal during the idle stop can be suppressed, but the internal state of the fuel cell at the idle stop becomes a state of water shortage. Since the deterioration of the electrolyte membrane due to the hydroxy radicals already described is a reaction that proceeds frequently when the fuel cell voltage is high, particularly when the fuel cell voltage including when the power generation of the fuel cell is stopped becomes a high voltage, It has been desired to suppress the water shortage in the fuel cell and ensure the elution of the radical inhibitor.

  The present invention has been made in order to solve the above-described conventional problems, and is an amount of liquid that can elute a radical inhibitor when the voltage of the fuel cell, including when the power generation of the fuel cell is stopped, becomes a high voltage. The purpose is to secure water in the fuel cell.

  SUMMARY An advantage of some aspects of the invention is to solve at least a part of the problems described above, and the invention can be implemented as the following forms or application examples.

[Application Example 1]
A fuel cell system comprising a fuel cell,
The fuel cell
An electrolyte membrane comprising a polymer electrolyte;
A pair of electrodes formed on each surface of the electrolyte membrane;
A porous gas diffusion layer disposed on the electrode;
A radical inhibitor disposed in at least one of the electrodes and / or in a region including a boundary with the electrode in at least one of the gas diffusion layers;
With
The fuel cell system further includes:
A water balance deriving unit for deriving a water balance in the fuel cell;
An operation state control unit for controlling an operation state in the fuel cell;
A membrane wet state detection unit for detecting a wet state in the electrolyte membrane;
With
When the operation state control unit determines that the fuel cell should be brought into a stoppage equivalent state including a predetermined low output state set in place of power generation stop or power generation stop, the water balance deriving unit derives If the water balance is a negative value, the operating state of the fuel cell is changed so that the moisture content of the one electrode or the electrode in contact with the one gas diffusion layer is increased, and the membrane wet state detection unit detects A fuel cell system that performs control for bringing the fuel cell into the stop equivalent state after the wet state in the electrolyte membrane reaches a reference wet state.

  According to the fuel cell system described in Application Example 1, when the water balance is a negative value, the fuel cell is brought into the stop equivalent state after the wet state in the electrolyte membrane reaches the reference wet state. Therefore, the radical suppressing substance can be dissolved and supplied to the electrolyte membrane before the stop equivalent state is achieved. As a result, it is possible to suppress deterioration of the electrolyte membrane due to radicals in a stop equivalent state where the fuel cell voltage becomes high.

[Application Example 2]
In the fuel cell system according to Application Example 1, the operation state control unit may increase the water content of the one electrode or the electrode in contact with the one gas diffusion layer, so that the water balance is a positive value. A fuel cell system for changing the operating state of the fuel cell. According to the fuel cell system described in Application Example 2, by changing the operation state of the fuel cell so that the water balance becomes a positive value, the radical suppression substance is secured in the electrolyte membrane before the stop equivalent state. can do.

[Application Example 3]
The fuel cell system according to Application Example 2, wherein the operation state control unit is configured to increase a humidification amount in the reaction gas supplied to the at least one electrode and / or the at least one gas diffusion layer, and the reaction gas. The fuel cell system changes the operating state of the fuel cell by a method selected from a decrease in the supply amount of the fuel cell and an increase in the back pressure in the reaction gas flow path in the fuel cell. According to the fuel cell system described in the application example 3, by changing the humidification amount or supply amount of the reaction gas or the back pressure, it is possible to secure the radical inhibitor in the electrolyte membrane before the stop equivalent state is achieved. it can.

[Application Example 4]
4. The fuel cell system according to Application Example 2 or 3, wherein the cathode provided in the fuel cell is a porous electrode, and the radical inhibitor is a gas disposed in and / or in contact with the cathode. The operation state control unit is disposed in a region including a boundary with the cathode in the diffusion layer, and the water balance becomes a positive value after the wet state in the electrolyte membrane reaches the reference wet state. The power generation of the fuel cell is performed in an operating state, and the volume of water generated in the fuel cell after power generation after the wet state in the electrolyte membrane reaches the reference wet state is the pore volume in the cathode. A fuel cell system that performs control to bring the fuel cell to the stop equivalent state when the fuel cell reaches the stop equivalent state. According to the fuel cell system described in Application Example 4, when the fuel cell is brought into a stop equivalent state, the pores of the cathode are filled with generated water, and the radical inhibitor is dissolved and supplied to the electrolyte membrane. The reliability of the operation to be performed can be further increased.

[Application Example 5]
The fuel cell system according to Application Example 1, wherein the fuel cell system is further provided in contact with the gas diffusion layer, and a fuel gas or oxidizing gas flow channel is formed between the gas diffusion layer and the gas diffusion layer. A pair of gas separators forming a refrigerant channel separated from the gas channel, wherein the gas separator is disposed on the electrode and / or the gas diffusion layer side of the pair of gas separators. The gas separator includes a pair of gas separators each including a porous body in which pores that communicate the gas flow path and the refrigerant flow path are formed, and a refrigerant pressure that adjusts a pressure of the refrigerant flowing through the refrigerant flow path. A gas separator including the porous body as a change in the operating state of the fuel cell to increase the water content of the electrolyte membrane. The way the pores of the gas diffusion layer is filled with the coolant, the fuel cell system to increase the pressure of the refrigerant. According to the fuel cell system described in Application Example 5, by supplying the refrigerant directly to the gas diffusion layer by increasing the refrigerant pressure, the radical inhibitor is dissolved in the refrigerant before the fuel cell is brought into an equivalent state of stoppage. Can be supplied to the electrolyte membrane.

[Application Example 6]
The fuel cell system according to Application Example 5, wherein the refrigerant is an acidic solution. According to the fuel cell system described in Application Example 6, the solubility of the radical inhibitor in the refrigerant can be increased.

[Application Example 7]
The fuel cell system according to Application Examples 1 to 6, wherein the reference wet state is when the electrolyte membrane is supplied with a fuel gas and an oxidizing gas having a relative humidity of 100% with respect to the fuel cell. A fuel cell system in a similar wet state. According to the fuel cell system described in Application Example 7, before the fuel cell is brought into an equivalent state of stopping, the wet state of the electrolyte membrane is sufficiently secured, and the radical inhibitor is dissolved and supplied to the electrolyte membrane. it can.

[Application Example 8]
The fuel cell system according to Application Example 7, further including a membrane resistance measurement unit that measures the resistance of the electrolyte membrane, wherein the operating state control unit has a resistance of the electrolyte membrane measured by the membrane resistance measurement unit. The wet state of the electrolyte membrane has reached the reference wet state when the resistance value of the electrolyte membrane when the fuel gas and the oxidizing gas having a relative humidity of 100% are supplied to the fuel cell is reduced. A fuel cell system to judge. According to the fuel cell system described in Application Example 8, it can be easily determined that the wet state of the electrolyte membrane has reached the reference wet state based on the membrane resistance of the electrolyte membrane.

[Application Example 9]
9. The fuel cell system according to any one of application examples 1 to 8, wherein the radical suppressing substance is disposed at least in a region including a boundary with the cathode in a gas diffusion layer disposed on the cathode and / or on the cathode. Fuel cell system. According to the fuel cell system described in Application Example 9, since the radical inhibitor is disposed in the cathode and / or the gas diffusion layer on the cathode side where generated water is generated with power generation, the generated water is used and the radical inhibitor is used. Can be easily dissolved.

[Application Example 10]
10. The fuel cell system according to any one of application examples 1 to 9, wherein the radical inhibitor is a compound of at least one element selected from cerium, manganese, and platinum. According to the fuel cell system described in Application Example 10, it is possible to suppress deterioration of the electrolyte membrane due to radicals by using the above compound.

[Application Example 11]
The fuel cell system according to any one of Application Examples 1 to 10, wherein the water balance is calculated from a sum of a water amount supplied to the fuel cell and a generated water amount generated by power generation in the fuel cell. A fuel cell system which is a value obtained by subtracting the amount of water discharged from the fuel cell. According to the fuel cell system described in the application example 11, water is easily generated based on the amount of water supplied to the fuel cell, the amount of generated water accompanying power generation, and the amount of water discharged from the fuel cell. You can ask for a balance.

  The present invention can be realized in various forms other than those described above. For example, the present invention can be realized in the form of a mobile body in which the fuel cell system of the present invention is mounted as a driving power source, a method for suppressing deterioration of an electrolyte membrane provided in the fuel cell Is possible.

1 is a block diagram illustrating a schematic configuration of a fuel cell system 10. FIG. 2 is an exploded perspective view showing a single cell 70. FIG. It is a cross-sectional schematic diagram which expands and shows the area | region containing the contact surface of MEA71 and the gas diffusion layers 72 and 73. FIG. 2 is a block diagram illustrating a schematic configuration of an electric vehicle 90. FIG. It is a flowchart showing a radical inhibitor substance ensuring process routine. It is a graph showing the relative humidity in supply gas, and the grade of deterioration of an electrolyte membrane. 2 is a schematic cross-sectional view showing a configuration of a fuel cell 115. FIG. It is a flowchart showing a radical inhibitor substance ensuring process routine. It is a flowchart showing a radical inhibitor substance ensuring process routine.

A. Overall configuration of the device:
FIG. 1 is a block diagram showing a schematic configuration of a fuel cell system 10 according to a first embodiment of the present invention. The fuel cell system 10 of this embodiment includes a fuel cell 15, a hydrogen tank 20, a compressor 30, a hydrogen circulation pump 44, a refrigerant circulation pump 60, a radiator 61, and a control unit 50.

  The fuel cell 15 is a solid polymer type fuel cell, and has a stack structure in which a plurality of single cells 70 as power generation bodies are stacked. FIG. 2 is an exploded perspective view showing the single cell 70 constituting the fuel cell 15. The unit cell 70 includes an MEA (Membrane Electrode Assembly) 71, gas diffusion layers 72 and 73, and gas separators 74 and 75. Here, the MEA 71 includes an electrolyte membrane and an anode and a cathode that are electrodes formed on each surface of the electrolyte membrane. The MEA 71 is sandwiched between the gas diffusion layers 72 and 73, and the sandwich structure composed of the MEA 71 and the gas diffusion layers 72 and 73 is sandwiched between the gas separators 74 and 75 from both sides (however, the gas diffusion layer 72 is provided). (It is not shown in FIG. 2 because it is disposed on the back surface of the surface on which the gas diffusion layer 73 is disposed).

  The electrolyte membrane constituting the MEA 71 is a proton conductive ion exchange membrane formed of a solid polymer material, for example, a fluorine-based resin, and exhibits good electron conductivity in a wet state. The cathode and the anode are layers formed on the electrolyte membrane, and include carbon particles supporting a catalytic metal (for example, platinum) that progresses an electrochemical reaction, and a polymer electrolyte having proton conductivity. The gas diffusion layers 72 and 73 are made of a member having gas permeability and electron conductivity, and are formed of, for example, a metal member such as foam metal or metal mesh, or a carbon member such as carbon cloth or carbon paper. can do.

  In the gas diffusion layers 72 and 73, water repellent layers 76 and 77 are provided in a region including a surface in contact with the electrode. FIG. 3 is an enlarged schematic cross-sectional view showing a region including a contact surface between the MEA 71 and the gas diffusion layers 72 and 73 in the single cell 70. The water repellent layers 76 and 77 are made of a water repellent paste containing conductive particles, for example, carbon particles, and a water repellent resin such as a fluorine resin, on one side of the carbon porous body that becomes the gas diffusion layers 72 and 73 ( It is formed by coating on the surface overlapping the MEA 71. The water-repellent layer provided between the electrode and the gas diffusion layer has the function of repelling liquid water and pushing it back to the electrode side, thus suppressing the electrolyte membrane from becoming deficient in water by pushing back the liquid water. doing. Further, by repelling the liquid water, the pores of the gas diffusion layers 72 and 73 are suppressed from being blocked by the liquid water, and the inhibition of the gas flow due to the blockage of the pores is suppressed. Further, by adding carbon particles to the water repellent paste, the contact resistance between the gas diffusion layers 72 and 73 and the MEA 71 is reduced and the current collecting property is improved.

  Of the gas diffusion layers 72 and 73, the water repellent layer 76 provided on the gas diffusion layer 72 disposed in contact with the cathode further includes a radical suppressing substance. When the water repellent layer 76 is formed, for example, a radical repellent substance is further added to the carbon particles and the water repellent resin to prepare a water repellent paste, and the obtained water repellent paste is applied onto the gas diffusion layer 72. Good.

The radical inhibitor is described below. In a polymer electrolyte fuel cell, when an electrochemical reaction proceeds, hydrogen peroxide (H ₂ O ₂ ) is generated by a side reaction, and further radicals are generated from the hydrogen peroxide. Among radicals, the activity of hydroxy radicals is particularly high, which is a problem. Such radicals cause a reaction for decomposing the polymer electrolyte constituting the electrolyte membrane, and cause deterioration of the electrolyte membrane. A radical inhibitor is a substance that reacts with hydrogen peroxide or radicals to inactivate radicals and the like.

  As the radical inhibitor, for example, a substance selected from a cerium compound, a manganese compound, platinum, or a platinum alloy can be used. Examples of the cerium compound include cerium nitrate, cerium acetate, cerium chloride, cerium sulfate, cerium oxide, primary cerium phosphate, secondary cerium phosphate, cerium carbonate, or a composite of cerium and tungsten, zirconium, lanthanum, etc. Can be used. As the manganese compound, for example, manganese oxide can be used. These radical suppressing substances disposed in the water-repellent layer 76 provided in the gas diffusion layer 72 are dissolved in the liquid water existing in and near the gas diffusion layer 72 and supplied to the electrolyte membrane. As a result, the deterioration of the electrolyte membrane due to radicals is suppressed.

  For example, it is considered that the suppression of the deterioration of the electrolyte membrane in the case where a cerium compound is used as the radical inhibitor is performed as follows. At least a part of the cerium compound dissolved in the liquid water and reaching the electrolyte membrane generates trivalent or tetravalent cerium ions. When hydrogen peroxide that generates peroxide radicals or peroxide radicals is generated with the power generation of the fuel cell, the cerium ions in the electrolyte membrane inactivate the peroxide radicals and the like. As an example of such a reaction, the reaction between trivalent cerium ions and hydrogen peroxide is represented by the following formula (1), and the reaction between trivalent cerium ions and peroxide radicals is represented by the following formula (2). Thus, by using a radical inhibitor, radicals can be inactivated by the radical inhibitor, or the generation of radicals can be suppressed, and the deterioration of the electrolyte due to the radicals can be suppressed.

2Ce ³⁺ + H ₂ O ₂ + 2H ⁺ → 2Ce ⁴⁺ + 2H ₂ O (1)
Ce ³⁺ + OH → Ce ⁴⁺ + OH ⁻ (2)

  Returning to FIG. The gas separators 74 and 75 are formed of a gas-impermeable conductive member, for example, a carbon-made member such as dense carbon that has been made to be gas-impermeable by compressing carbon, or a metal member such as press-formed stainless steel. ing. The gas separators 74 and 75 are members that form walls of a flow path of a reaction gas (a fuel gas containing hydrogen or an oxidizing gas containing oxygen) formed between the gas separators 74 and 75. An uneven shape for forming the flow path is formed. Between the gas separator 74 having the groove 88 formed on the surface and the MEA 71, an in-cell oxidizing gas flow path that is a flow path for the oxidizing gas is formed. In addition, an in-cell fuel gas flow path, which is a flow path for the fuel gas, is formed between the gas separator 75 having a groove 89 formed on the surface and the MEA 71. When assembling the single cell 70, a seal portion (not shown) is arranged on the outer periphery of the MEA 71, and the gas separators 74 and 75 are joined together while ensuring the sealing performance of the gas flow path in the single cell 70. .

  Here, in the gas separators 74 and 75, a recess 87 is formed on the back surface of the surface provided with the grooves 88 and 89 for forming the in-cell gas flow path (however, formed on the back surface of the gas separator 74). The recessed portion 87 is not shown). These recesses 87 are formed over a range that overlaps the entire region where the gas diffusion layers 72 and 73 are arranged on the gas separators 74 and 75, and between the adjacent single cells 70 between the cells that are the flow paths of the refrigerant. A refrigerant flow path is formed. Note that the inter-cell refrigerant flow path is not provided between the single cells 70 but may be provided, for example, every time a predetermined number of single cells 70 are stacked.

  The gas separators 74 and 75 are provided with a plurality of holes at positions corresponding to each other near the outer periphery thereof. When a fuel cell is assembled by stacking a plurality of single cells 70, holes provided at corresponding positions of the separators overlap each other to form a flow path that penetrates the fuel cell in the stacking direction of the gas separators. Specifically, the hole 83 forms an oxidant gas supply manifold that distributes the oxidant gas to each in-cell oxidant gas flow path, and the hole 84 oxidizes the oxidant gas that collects from each in-cell oxidant gas flow path. A gas exhaust manifold is formed. The hole 85 forms a fuel gas supply manifold that distributes the fuel gas to each in-cell fuel gas flow path, and the hole 86 forms a fuel gas discharge manifold that collects the fuel gas from each in-cell fuel gas flow path. Form. Moreover, the hole 81 forms a refrigerant supply manifold that distributes the refrigerant to the inter-cell refrigerant flow path, and the hole 82 forms a refrigerant discharge manifold that collects the refrigerant from the inter-cell refrigerant flow path.

  The fuel cell 15 according to the present embodiment is formed by sequentially arranging a current collector plate (terminal), an insulating plate (insulator), and an end plate each having an output terminal at both ends of a laminate formed by laminating a plurality of single cells 70. Is done. The fuel cell 15 is held in a state where a fastening pressure is applied in the stacking direction of the single cells 70 by a holding member (not shown).

  Returning to FIG. 1, the hydrogen tank 20 provided in the fuel cell system 10 is a storage device that stores hydrogen gas as fuel gas, and is connected to the hydrogen supply manifold of the fuel cell 15 via the hydrogen supply flow path 22. Yes. On the hydrogen supply flow path 22, a hydrogen cutoff valve 40 and a modulatable pressure valve 42 are provided in order from the hydrogen tank 20. The adjustable pressure valve 42 is a pressure regulating valve capable of adjusting the hydrogen pressure (hydrogen amount) supplied from the hydrogen tank 20 to the fuel cell 15. The hydrogen tank 20 may be a hydrogen cylinder that stores high-pressure hydrogen gas, or may be a tank that includes a hydrogen storage alloy and stores hydrogen by storing the hydrogen in the hydrogen storage alloy.

  A hydrogen discharge passage 24 is connected to the hydrogen discharge manifold of the fuel cell 15. A purge valve 46 is provided in the hydrogen discharge channel 24. Further, a connection flow path 25 is provided by connecting the hydrogen supply flow path 22 and the hydrogen discharge flow path 24. The connection channel 25 is connected to the hydrogen supply channel 22 on the downstream side of the adjustable pressure valve 42 and is connected to the hydrogen discharge channel 24 on the upstream side of the purge valve 46. The connection channel 25 is provided with a hydrogen circulation pump 44 that generates a driving force when hydrogen circulates in the channel.

  Hydrogen supplied from the hydrogen tank 20 via the hydrogen supply flow path 22 is supplied to the electrochemical reaction in the fuel cell 15 and discharged to the hydrogen discharge flow path 24. The hydrogen discharged to the hydrogen discharge channel 24 is guided again to the hydrogen supply channel 22 via the connection channel 25. As described above, in the fuel cell system 10, hydrogen is part of the hydrogen discharge passage 24, the connection passage 25, part of the hydrogen supply passage 22, and the fuel gas passage formed in the fuel cell 15. (These flow paths are collectively referred to as a hydrogen circulation flow path). During the power generation of the fuel cell 15, the purge valve 46 is normally closed. However, when impurities (nitrogen, water vapor, etc.) in the circulating hydrogen increase, the purge valve 46 is opened as appropriate. Part of the hydrogen gas with increased impurity concentration is discharged outside the system. Further, when the amount of hydrogen in the hydrogen circulation channel is insufficient due to the consumption of hydrogen due to the progress of the electrochemical reaction or the opening of the purge valve 46, the hydrogen tank 20 is transferred from the hydrogen tank 20 to the hydrogen circulation channel via the adjustable pressure valve 42. And hydrogen is supplemented.

  The compressor 30 is a device that takes in air from the outside, compresses it, and supplies it as the oxidizing gas to the fuel cell 15, and is connected to the oxidizing gas supply manifold of the fuel cell 15 via the air supply channel 31. . An air discharge passage 32 is connected to the oxidizing gas discharge manifold of the fuel cell 15. The air supplied from the compressor 30 via the air supply flow path 31 is subjected to an electrochemical reaction in the fuel cell 15 and discharged to the outside of the fuel cell 15 via the air discharge flow path 32.

  Here, in the air supply flow path 31, a first hygrometer 34, a first pressure gauge 35, and a flow meter 36 are provided in the order closer to the compressor 30. The first hygrometer 34, the first pressure gauge 35, and the flow meter 36 detect the dew point temperature, pressure, and flow rate of the oxidizing gas supplied to the fuel cell 15, respectively.

  A second hygrometer 37 and a second pressure gauge 38 are provided in the air discharge flow path 32. By the second hygrometer 37 and the second pressure gauge 35, the dew point temperature and pressure of the exhausted oxidant gas discharged from the fuel cell 15 are detected. Further, a back pressure valve 39 is provided downstream of the second pressure gauge 35 in the air discharge channel 32. In this embodiment, the pressure of the oxidizing gas in the fuel cell 15 is adjusted by adjusting the opening of the back pressure valve 39 based on the detection signal of the second pressure gauge 38.

  A load 57 is connected to the output terminal provided on the current collector plate of the fuel cell 15 via a wiring 56. The load 57 can be, for example, a secondary battery or a power consuming device (such as a motor). An AC impedance measuring unit 53 is connected to the output terminal of the fuel cell 15 in parallel with the load 57.

  The AC impedance measurement unit 53 derives the impedance of the fuel cell 15 by a known AC impedance method. The AC impedance measurement unit 53 includes a frequency sweep unit 54 and an impedance derivation unit 55. In the AC impedance measurement unit 53, the frequency sweep unit 54 superimposes an AC component while sweeping the frequency to the output terminal of the fuel cell 15 according to an instruction from the control unit 50, and the impedance derivation unit 55 sets the impedance in the fuel cell 15. calculate. The impedance deriving unit 55 of the present embodiment derives the membrane resistance component of the impedance of the fuel cell 15 as the resistance of the electrolyte membrane. As described above, the AC impedance measurement unit 53 functions as a membrane resistance measurement unit for measuring the resistance of the electrolyte membrane. In addition, the membrane resistance measurement part with which the fuel cell system 10 is provided is good also as measuring a membrane resistance by another method, for example, the electric current interruption method other than measuring a membrane resistance by the alternating current impedance method as mentioned above.

  The radiator 61 is provided in the refrigerant channel 62 and cools the refrigerant flowing in the refrigerant channel 62. The refrigerant flow path 62 is connected to the refrigerant supply manifold and the refrigerant discharge manifold described above of the fuel cell 15. In addition, a refrigerant circulation pump 60 is provided in the refrigerant flow path, and by driving the refrigerant circulation pump 60, the refrigerant is circulated between the radiator 61 and the fuel cell 15, and the internal temperature of the fuel cell 15 is increased. It is adjustable. In the refrigerant flow path 62, a refrigerant temperature sensor 63 for detecting the temperature of the refrigerant is provided in the vicinity of the connection portion between the fuel cell 15 and the refrigerant discharge manifold.

  The control unit 50 is configured as a logic circuit centered on a microcomputer, and more specifically, a CPU that executes predetermined calculations in accordance with a preset control program, and controls necessary for executing various arithmetic processes by the CPU. A ROM in which programs, control data, and the like are stored in advance, a RAM in which various data necessary for performing various arithmetic processes in the CPU, and an input / output port for inputting and outputting various signals are also provided. The control unit 50 outputs a drive signal to the compressor 30, the hydrogen cutoff valve 40, the adjustable pressure valve 42, the hydrogen circulation pump 44, the purge valve 46, the refrigerant circulation pump 60, the AC impedance measurement unit 53, and the like. Further, detection signals are acquired from the hygrometers 34 and 37, the pressure gauges 35 and 38, the flow meter 36, the refrigerant temperature sensor 63, and the like.

  The fuel cell system 10 of this embodiment is mounted on an electric vehicle 90 and used as a driving power source. FIG. 4 is a block diagram showing a schematic configuration of electric vehicle 90. The electric vehicle 90 includes a secondary battery 91 together with the fuel cell 15 as a driving power source. In FIG. 4, the description of the components of the fuel cell system 10 other than the fuel cell 15 is omitted. The electric vehicle 90 includes an auxiliary machine 94 and a drive inverter 93 connected to the drive motor 95 as a load that receives power supply from the fuel cell 15 and the secondary battery 91. The power output to the output shaft 98 of the drive motor 95 is transmitted to the vehicle drive shaft 99. The auxiliary machine 94 includes fuel cell auxiliary machines such as the compressor 30, the hydrogen circulation pump 44, and the refrigerant circulation pump 60, and vehicle auxiliary machines such as an air conditioner (air conditioner). The fuel cell 15 and the secondary battery 91 and each of the loads are connected in parallel to each other via a wiring 56. The wiring 56 is provided with a load connecting portion 51 that is a switch for turning on and off the connection with the fuel cell 15. The secondary battery 91 is connected to the wiring 56 through the DC / DC converter 92. In this embodiment, the control unit 50 sets the target voltage value on the output side of the DC / DC converter 92 to adjust the voltage of the wiring 56, and the power generation amount of the fuel cell 15 and the charge / discharge state of the secondary battery 91. Can be controlled. The DC / DC converter 92 also serves as a switch for controlling the connection state between the secondary battery 91 and the wiring 56, and when the secondary battery 91 does not need to be charged / discharged, The connection with the wiring 56 is disconnected.

  With the configuration as described above, the electric vehicle 90 can supply power to the load from at least one of the fuel cell 15 and the secondary battery 91. In addition, the secondary battery 91 can be charged by the fuel cell 15. Furthermore, when the electric vehicle 90 is braked, the secondary battery 91 can be charged by operating the drive motor 95 as a generator. In FIG. 4, each unit of the electric vehicle 90 is controlled by the control unit 50, but the control unit that performs control in the fuel cell system 10 and the control unit that controls each unit of the electric vehicle 90 are described. , It may be integral or separate.

B. Control when idling:
As described above, the fuel cell system 10 of this embodiment suppresses deterioration of the electrolyte membrane due to radicals by providing the water repellent layer 76 in the fuel cell 15 with a radical inhibitor. The reaction related to the deterioration of the electrolyte membrane (decomposition reaction of the polymer electrolyte by radicals) is a reaction that proceeds frequently when the fuel cell voltage is high. Therefore, when the fuel cell voltage is particularly high, specifically, when the power generation of the fuel cell is stopped or when the output of the fuel cell is extremely small, the radical inhibitor is sufficiently supplied from the water repellent layer 76 to the electrolyte membrane. It is desirable. The radical inhibitor is supplied to the electrolyte membrane by dissolving the radical inhibitor in liquid water. Therefore, in the fuel cell system 10 of the present embodiment, when the fuel cell voltage increases, specifically, when the electric vehicle 90 is in an idling state, sufficient liquid water is secured in the vicinity of the water repellent layer 76. Control is performed.

  FIG. 5 is a flowchart showing a radical inhibiting substance dissolution ensuring routine executed by the CPU of the control unit 50 of the fuel cell system 10. This routine is started when the fuel cell system 10 is started, and is repeatedly executed until the fuel cell system 10 is stopped. The fuel cell system 10 is started when the electric vehicle 90 is started (a start switch is turned on corresponding to the ignition switch) and stopped when the electric vehicle 90 is stopped (the start switch is turned off).

  When this routine is started, the CPU of the control unit 50 determines whether or not an idling command is issued in the electric vehicle 90 (step S100). Idling refers to a state where the electric vehicle 90 is stopped but the fuel cell system 10 is operating. Specifically, in step S100, it is determined that an idling command has been issued when the above-described start switch is on, the accelerator opening is zero, and the vehicle speed is zero from a positive value. The CPU of the control unit 50 repeatedly executes the process of step S100 related to whether or not the idling command has been issued until it is determined that the idling command has been issued.

If it is determined in step S100 that a degree ring command has been issued, the CPU of the control unit 50 derives a water balance in the fuel cell 15 (step S110). The water balance (WB) in the fuel cell 15 is the amount of water supplied to the fuel cell 15 (supply water amount N _in ), the amount of generated water (generated water amount N _H2O ) generated by power generation in the fuel cell 15, Is a value obtained by subtracting the amount of water discharged from the fuel cell 15 (the amount of water N _out ). The equations for deriving the water balance WB, the supply water amount N _in , the generated water amount N _H2O , and the carry-off water amount N _out are shown below as equations (3) to (6), respectively. Table 1 shows the meaning of each parameter used in the equations (3) to (6).

Among the parameters used in the above equations (3) to (6), the power generation area A is the area of the electrode that contributes to power generation, and is stored in advance in the control unit 50 together with the molecular weight M _{H2O of} water and the Faraday constant F. Has been. The current density I is derived based on the detection value of a current sensor (not shown) provided in the fuel cell system 10 for detecting the output current of the fuel cell 15 and the power generation area A. The oxidizing gas supply amount N _air is measured by the flow meter 36. The air stoichiometric ratio S _air is the ratio of the actually supplied oxidizing gas amount to the oxidizing gas amount theoretically obtained as the oxidizing gas amount (air amount) required to generate the desired electric power, and the time when the water balance is derived. It is derived on the basis of the amount of power generated in the above and the oxidizing gas supply amount N _air . The inlet water vapor pressure P _{H2O_in} is derived based on the humidity of the supplied oxidizing gas detected by the first hygrometer 34 and the pressure of the supplied oxidizing gas detected by the first pressure gauge 35. Similarly, the outlet water vapor pressure P _{H2O_out} is derived based on the humidity of the exhaust oxidant gas detected by the second hygrometer 37 and the pressure of the exhaust oxidant gas detected by the second pressure gauge 38. The inlet oxidizing gas pressure P _in is the pressure of the supplied oxidizing gas detected by the first pressure gauge 35, and the outlet oxidizing gas pressure P _out is the pressure of the exhaust oxidizing gas detected by the second pressure gauge 38.

The fuel cell system 10 of this embodiment is a so-called anode circulation type fuel cell system that circulates and uses hydrogen, which is a fuel gas. In such an anode circulation type fuel cell system, except for drainage from the hydrogen circulation channel by opening the purge valve 46 at a predetermined timing, water does not enter and exit the hydrogen circulation channel. Further, the water balance in step S110 may be derived in a short time interval of about 1 second to several seconds. Therefore, in the present embodiment, when the water balance is derived, only the amount of water supplied and the amount of water taken away are considered as the amount of water to be supplied N _in and the amount of water to be removed N _out . When the fuel cell system does not circulate the fuel gas, the supply water amount N is further added to the supply water amount by the fuel gas or the take-off water amount by the fuel gas in addition to the supply water amount by the oxidation gas or the removal water amount by the oxidation gas. _What is necessary is just to obtain _in and the amount of water N _out to be taken away.

When the water balance is derived in step S110, the CPU of the control unit 50 determines whether or not the derived water balance is a negative value (step S120). When the water balance is a negative value, that is, when the carried- _out water amount N _out exceeds the sum of the supplied water amount N _in and the generated water amount N _H2O , the CPU of the controller 50 controls the electrode on the side where the radical inhibitor is disposed. Specifically, the operating state of the fuel cell 15 is changed so that the water balance becomes a positive value so that the water content of the cathode increases (step S130).

  As a configuration for changing the operation state of the fuel cell 15 so that the water balance becomes a positive value, for example, a configuration for increasing the humidification amount of the oxidizing gas supplied to the fuel cell 15 can be cited. Specifically, for example, in the air supply passage 31 of the fuel cell system 10, a humidifier for humidifying the oxidizing gas is disposed between the compressor 30 and the first hygrometer 34. In step S130, the humidification amount of the oxidizing gas in the humidifier may be increased so that the water balance becomes a positive value. Alternatively, the operating state may be changed so as to reduce the stoichiometric ratio by reducing the drive amount of the compressor 30. With such a configuration, the flow rate of the oxidizing gas supplied with respect to the power generation amount (produced water amount) in the fuel cell 15 decreases, so that the amount of moisture taken away by the oxidizing gas decreases and the water balance becomes a positive value. Can do. Alternatively, the operating state may be changed so as to increase the back pressure in the oxidizing gas flow path by reducing the opening of the back pressure valve 39 provided in the air discharge flow path 32. With such a configuration, it is possible to suppress the amount of moisture taken out by the oxidizing gas by increasing the back pressure, and to set the water balance to a positive value.

  In step S130, when the operating state of the fuel cell 15 is changed so that the water balance becomes a positive value, the CPU of the control unit 50 acquires the membrane resistance of the electrolyte membrane from the AC impedance measurement unit 53 (step S140). . Then, it is determined whether or not the acquired film resistance is equal to or less than a predetermined reference resistance value (step S150).

  The reference resistance value used in step S150 is an electrolyte membrane when fuel gas and oxidizing gas having a relative humidity of 100% (water vapor pressure is saturated vapor pressure) are supplied to the fuel cell 15. Is set as the value of the membrane resistance. That is, the value is set as the value of the membrane resistance in the state where the wet state of the electrolyte membrane is the highest (the state where the membrane resistance is the lowest) under the power generation conditions of the fuel cell.

  If it is determined in step S150 that the membrane resistance exceeds the reference resistance value, the CPU of the control unit 50 returns to step S140 and acquires the membrane resistance again. As described above, since the operating state of the fuel cell 15 is changed so that the water balance becomes a positive value in step S130, the wet state of the electrolyte membrane gradually increases. Therefore, when the acquisition of the film resistance and the operation of comparing the acquired film resistance and the reference resistance value are repeated, the film resistance eventually becomes equal to or less than the reference resistance value.

  If it is determined in step S150 that the membrane resistance is less than or equal to the reference resistance value, the CPU of the control unit 50 acquires the amount of water produced after it is determined that the membrane resistance is less than or equal to the reference resistance value (step S160). ). The amount of water produced in the fuel cell 15 can be derived based on the current density in the fuel cell 15, that is, the output current, as shown in equation (4). When the CPU of the control unit 50 according to the present embodiment determines that the membrane resistance is equal to or less than the reference value in step S150, the amount of generated water generated by the subsequent power generation is integrated based on the output current of the fuel cell 15. In step S160, the CPU of the control unit 50 acquires the current value of the integrated value of the generated water amount thus obtained.

  Thereafter, the CPU of the control unit 50 determines whether or not the acquired amount of generated water exceeds the cathode pore volume (step S170). The cathode pore volume is the total volume of pores formed in the cathode formed as a porous electrode. As described above, the cathode is composed of carbon particles supporting a catalytic metal (for example, platinum) and a polymer electrolyte having proton conductivity. Therefore, the cathode pore volume can be obtained by subtracting the volume of the catalyst-supporting carbon and the polymer electrolyte from the apparent volume of the cathode. The apparent volume of the cathode can be obtained by multiplying the area of the cathode (the power generation area A described above) and the thickness of the cathode. What is necessary is just to measure the thickness of a cathode using SEM (scanning electron microscope), for example. The volume of the catalyst-supporting carbon and the polymer electrolyte can be determined based on the weight of the catalyst-supporting carbon and the polymer electrolyte provided in the cathode and the density of the catalyst-supporting carbon and the polymer electrolyte. In the present embodiment, the cathode pore volume calculated as described above is obtained in advance and stored in the control unit 50.

  If it is determined in step S170 that the generated water amount is equal to or less than the cathode pore volume, the CPU of the control unit 50 returns to step S160 and acquires the generated water amount again. As described above, since the operation state of the fuel cell 15 is changed so that the water balance becomes a positive value in step S130, it is determined in step S150 that the wet state of the electrolyte membrane is the highest. Thereafter, the amount of water remaining in the fuel cell 15 continues to increase by imaging the amount of generated water. Therefore, if the acquisition of the generated water amount and the operation of comparing the acquired generated water amount and the cathode pore volume are repeated, the generated water amount eventually exceeds the cathode pore volume.

  If it is determined in step S170 that the amount of generated water exceeds the cathode pore volume, the CPU of the control unit 50 executes idling (step S180) and ends this routine. Specifically, the CPU of the control unit 50 drives the load connection unit 51 to cut off the connection between the fuel cell 15 and the load. As described above, when the power generation of the fuel cell 15 is stopped, the change of the operation state set in step S130 is cancelled.

  When it is determined in step S120 that the water balance is 0 or more, the CPU of the control unit 50 can determine that the amount of water in the fuel cell 15 is sufficient, and therefore performs idling as it is (step S180). This routine is terminated.

  Further, the accelerator is stepped on again before idling after securing the amount of water in the fuel cell 15 by the radical inhibiting substance dissolution ensuring routine shown in FIG. 5, that is, during the execution of the radical inhibiting substance dissolution ensuring routine. There may be cases. In this case, the execution of the radical inhibitor dissolution ensuring routine is interrupted by the interrupt process, and the radical inhibitor dissolution ensuring routine is executed again from the beginning, and normal control for vehicle travel is started. The

  When it is determined in step S100 that an idling command has been issued, as described above, the vehicle speed is zero, and no energy is required for driving the vehicle. Therefore, the electric power generated by the fuel cell 15 during the processes after step S110 is used for charging the secondary battery 91 or supplied to auxiliary equipment including vehicle auxiliary equipment.

  According to the fuel cell system 10 of the present embodiment configured as described above, when idling is performed, the electrolyte membrane is sufficiently wetted and an amount of generated water corresponding to the cathode pore volume is further increased. Idling is performed after it is generated. For this reason, when power generation is stopped due to idling, the pores of the cathode are filled with generated water, and the radical repellent substance in the water-repellent layer 76 in contact with the cathode is dissolved, and the dissolved radical suppressor electrolyte membrane is dissolved. Can be ensured. Therefore, a radical inhibitor can be supplied to the electrolyte membrane at the time of power generation stoppage where the degradation reaction of the electrolyte membrane due to radicals is likely to proceed, and the degradation of the electrolyte membrane due to radicals is suppressed. Can do.

  In particular, in this embodiment, the radical suppressing substance is held in the water repellent layer 76 provided in the region including the contact surface with the cathode in the gas diffusion layer 72. Therefore, by changing the operating state so that the water balance becomes a positive value, the generated water that immediately becomes liquid water at the cathode is repelled by the water repellent layer 76 and remains on the water repellent layer 76. That is, the generated water spreads on the surface of the water repellent layer 76 without entering the water repellent layer 76 until the amount of generated water increases and the pressure of the generated water exceeds the water permeation start pressure of the water repellent layer 76. Stay. Therefore, after ensuring the wet state of the electrolyte membrane to the maximum extent, a sufficient amount of liquid water is supplied to the radical inhibiting substance in the water-repellent layer 76 by further ensuring the amount of generated water corresponding to the cathode pore volume. Thus, the radical inhibitor can be dissolved.

Below, the effect which suppresses the deterioration of the electrolyte membrane resulting from a radical by ensuring the moisture content in a fuel cell is further demonstrated. FIG. 6 is a graph showing the results of examining the relative humidity in the gas supplied to the fuel cell and the degree of deterioration of the electrolyte membrane. Here, hydrogen gas, which is a fuel gas, is supplied without being circulated to a fuel cell similar to the fuel cell 15 of the first embodiment, and air, which is an oxidizing gas, is supplied. A comparison is made between a fuel cell in which the relative humidity of the supplied fuel gas and oxidizing gas is 68% and a fuel cell in which both are 100%. Each fuel cell was kept at 90 ° C. and an on-off durability test was conducted. Specifically, a test was repeated in which power generation at 0.1 A / cm ² and power generation stop (OCV) were repeated. The “endurance time” shown on the horizontal axis of the graph of FIG. 6 represents the elapsed time since the start of the on-off endurance test. Here, the moisture in the fuel exhaust gas discharged from the anode and the moisture in the oxidized exhaust gas discharged from the cathode were each collected as liquid water, and the amount of fluorine in the liquid water was measured by ion chromatography. The “fluorine generation rate” shown on the vertical axis of the graph of FIG. 6 represents the amount of fluorine discharged from the fuel cell together with the exhaust gas. Among the constituent elements of the fuel cell, since the polymer electrolyte included in the electrolyte membrane and the catalyst contains fluorine, the degree of decomposition of the electrolyte membrane is estimated by measuring the amount of fluorine discharged from the fuel cell. be able to.

  As shown in FIG. 6, in the fuel cell in which the relative humidity of the supply gas is 100%, the amount of fluorine discharged from the fuel cell is extremely small compared to the fuel cell in which the relative humidity of the supply gas is 68%. It was confirmed that the decomposition of was suppressed. A fuel cell having a relative humidity of 68% in the supply gas is considered to be a fuel cell in which power generation is continued with a negative water balance. On the other hand, a fuel cell having a relative humidity of 100% in the supply gas continues power generation with a positive water balance, and corresponds to a fuel cell that performs the processing from step S160 onward. It is considered to be a state.

  As described above, by setting the inside of the fuel cell in a wet state corresponding to the state where the relative humidity of the supply gas is 100%, it is sufficient to dissolve the radical inhibitor and cause deterioration of the electrolyte membrane. It is thought that an effect is acquired. For this reason, in this embodiment, after making a determination to ensure the wet state of the electrolyte membrane in step S150, power generation is continued until the amount of generated water exceeds the cathode pore volume, thereby securing the amount of moisture in the fuel cell. However, the idling may be performed immediately when the film resistance is equal to or lower than the reference resistance value. Even with such a configuration, an effect of suppressing deterioration of the electrolyte membrane caused by radicals can be obtained by continuing the operation state in which the water balance becomes a positive value until the electrolyte membrane is in the maximum wet state. Can do.

  In addition, even if the power generation is continued after the determination to ensure the wet state of the electrolyte membrane in step S150, the power generation is continued until the generated water less than the cathode pore volume is generated. It may be good until the produced water more than the cathode pore volume is generated. However, by ensuring at least the amount of generated water corresponding to the cathode pore volume, it is possible to increase the reliability with which liquid water can sufficiently reach the radical inhibitor. Further, by stopping the power generation when the amount of generated water reaches the pore volume, the power generation amount when the power generation should be stopped can be suppressed.

C. Second embodiment:
FIG. 7 is a schematic cross-sectional view showing the configuration of the fuel cell 115 of the second embodiment. FIG. 7 shows only a part of the single cell 170 constituting the fuel cell 115 and the surroundings. The fuel cell 115 of the second embodiment is provided in a fuel cell system similar to the fuel cell system 10 of the first embodiment. In the following description, the same reference numerals are assigned to parts common to the fuel cell 15 of the first embodiment, and only the points different from the first embodiment will be described.

  The fuel cell 115 includes a gas separator 174 instead of the gas separator 74 that forms the in-cell oxidizing gas flow path. The gas separator 174 has the same shape as the gas separator 74, but as shown in FIG. 7, an in-cell oxidizing gas flow path is formed on one surface and an inter-cell refrigerant flow path is formed on the other surface. The region for forming (shown as CLT in FIG. 7) is formed of a porous body. In the gas separator 174 of the present embodiment, the regions other than the regions that form the in-cell oxidizing gas flow channel and the inter-cell refrigerant flow channel are formed by a gas-impermeable dense member similar to the gas separator 74. The porous portion provided in the gas separator 174 can be formed of a carbon porous body or a metal porous body. In the fuel cell 115, the steady-state refrigerant pressure is set so that the refrigerant pressure in the inter-cell refrigerant channel is higher than the oxidizing gas pressure in the intra-cell oxidizing gas channel. During power generation, the refrigerant circulation pump 60 is driven so that the set steady-state refrigerant pressure is realized. That is, during normal power generation, the refrigerant in the refrigerant flow path is not supplied into the single cell via the gas separator 174. In this embodiment, water is used as the refrigerant.

  FIG. 8 is a flowchart showing a radical inhibiting substance dissolution ensuring routine executed in the CPU of the control unit 50 of the fuel cell system including the fuel cell 115 of the second embodiment. This routine is repeatedly executed during the operation of the fuel cell system 10 instead of the radical inhibiting substance dissolution ensuring processing routine of FIG. In FIG. 8, steps common to those in FIG. 5 are given the same step numbers, and detailed description of the common steps is omitted.

  When this routine is started, the CPU of the control unit 50 determines the presence or absence of an idling command (step S100), and if it determines that an idling command has been issued, derives a water balance (step S110). When the water balance is a negative value, specifically, the water content of the gas diffusion layer 72 is saturated so that the water content of the cathode, which is the electrode on which the radical inhibitor is disposed, increases. The refrigerant circulation pump 60 is driven so as to be in a state, and the refrigerant pressure is increased (step S230).

Here, in the porous body in which the liquid is pressed into the gas while being exposed to the gas, the capillary pressure (Capillary Pressure, P _C ) is the pressure of the liquid to be pressed into the inside as shown in the following formula (7). It is expressed as the difference between the pressure (Loquid Pressure, P _L ) and the gas pressure (Gas Pressure).

_{P C = P L - P G} ... (7)

As described above, in the porous body in which the liquid is injected while being exposed to the gas, the degree of saturation of the porous body (the entire pores formed in the porous body depends on the capillary pressure (P _C )). It is known that the proportion of pores containing water is determined (see, for example, JT Gostick et al, Journal of Power Sources, vol. 194, (2009), pp 433-444). Therefore, the water content of the porous body can be determined by determining the pressure (P _L ) and the gas pressure (P _G ) of the liquid.

In step S230, the refrigerant pressure is increased so that the pores in the gas diffusion layer 72, which is a porous body exposed to the oxidizing gas, are filled with the refrigerant. Here, the capillary pressure (P _C ) when the water content of the gas diffusion layer 72 becomes saturated can be examined in advance. The oxidizing gas pressure that is the gas pressure (P _G ) can be detected by the second pressure gauge 38. Further, the liquid pressure (P _L ) that is the pressure of the refrigerant press-fitted from the inter-cell refrigerant flow path into the gas diffusion layer 72 through the porous body constituting the gas separator 174, the driving amount of the refrigerant circulation pump 60, and This relationship can also be obtained in advance. Therefore, in the present embodiment, a map in which the driving amount of the refrigerant circulation pump 60 for setting the water content state of the gas diffusion layer 72 to the saturated state is determined according to the oxidizing gas pressure is stored in the control unit 50 in advance. . In step S230, the oxidant gas pressure is acquired from the second pressure gauge 38, and the driving amount of the refrigerant circulation pump 60 is determined with reference to the map so that the determined driving amount is realized. The driving amount of 60 is increased.

  Thereafter, the CPU of the control unit 50 acquires the membrane resistance of the electrolyte membrane (step S140), and compares the acquired membrane resistance with a reference resistance value (step S150). By increasing the refrigerant pressure in step S230, the refrigerant is directly supplied to the gas diffusion layer 72 via the gas separator 174, and the water content of the gas diffusion layer 72 gradually increases. The liquid water supplied to the gas diffusion layer 72 moves to the cathode and the electrolyte membrane while increasing the water content of the electrolyte membrane while dissolving the radical inhibiting substance in the water repellent layer 76. Therefore, when the refrigerant pressure is increased in step S230, the wet state of the electrolyte membrane eventually reaches the upper limit value, and the membrane resistance becomes lower than the reference resistance value. When it is determined in step S150 that the film resistance has become equal to or less than the reference resistance value, the CPU of the control unit 50 executes idling (step S180) and ends this routine. As described above, the power generation of the fuel cell 115 is stopped, so that the setting of the refrigerant pressure increased in step S230 is cancelled.

  According to the fuel cell system of the second embodiment configured as described above, at least a part of the gas diffusion layer 72 is formed of a porous body, the refrigerant pressure is increased, and the refrigerant is directly supplied to the gas diffusion layer 72. By supplying, the radical suppressing substance in the water repellent layer 76 can be dissolved prior to idling. Thereby, it is possible to suppress deterioration of the electrolyte membrane due to radicals at idling when the fuel cell voltage increases.

  In this embodiment, water is used as the refrigerant, but a different configuration may be used. For example, if an acidic solution such as an aqueous nitric acid solution is used as the refrigerant, the radical inhibiting substance is easily dissolved by the refrigerant, so that the radical inhibiting substance can be supplied more sufficiently to the electrolyte membrane. Therefore, it is possible to improve the reliability for the operation of suppressing the deterioration of the electrolyte membrane during idling.

  In the second embodiment, the operation in step S230 is performed instead of step S130 in the first embodiment. However, the operation in step S230 may be performed together with the operation in step S130. That is, the control for changing the operating state of the fuel cell so that the water balance becomes a positive value and the control for increasing the refrigerant pressure so that the water content of the gas diffusion layer 72 is saturated may be performed. With such a configuration, the moisture content of the cathode and the electrolyte membrane can be increased more quickly, and idling can be performed more quickly.

D. Third embodiment:
In the first and second embodiments, every time there is an idling command, the amount of liquid water in the vicinity of the cathode is secured in the fuel cell, and the radical inhibitor disposed in the water repellent layer 76 is actively dissolved. However, a different configuration may be used. That is, once the processing for ensuring the dissolution of the radical inhibitor is performed, there is a sufficient amount of radical inhibitor in the electrolyte membrane for a while, so when there is an idling command in a short time interval The radical inhibitor dissolution ensuring process may not be executed at the time of a subsequent idling command. Such a configuration will be described below as a third embodiment.

  Since the fuel cell system of the third embodiment has the same configuration as the fuel cell system 10 of the first embodiment, the same reference numerals are used for description. FIG. 9 is a flowchart showing a radical inhibiting substance dissolution ensuring routine executed by the CPU of the control unit 50 of the fuel cell system 10 of the third embodiment. This routine is repeatedly executed during the operation of the fuel cell system 10 instead of the radical inhibiting substance dissolution ensuring processing routine of FIG. In FIG. 9, steps common to those in FIG. 5 are given the same step numbers, and detailed description of common steps is omitted.

  When this routine is started, the CPU of the control unit 50 determines the presence or absence of an idling command (step S100), and if it determines that an idling command has been issued, derives a water balance (step S110). When the water balance is a negative value, the elapsed time since the previous execution of the process for ensuring the dissolution of the radical inhibitor (steps S130 to S170) exceeds a preset reference time. It is determined whether or not (step S325).

  As will be described later, in this embodiment, after the process of step S170 is executed, measurement of elapsed time is started using a timer in the control unit 50. The reference time used in step S325 is that after the treatment for ensuring the dissolution of the radical inhibitory substance is performed once, the radical inhibitory substance having a concentration capable of suppressing the deterioration of the electrolyte film due to the radicals remains in the electrolyte membrane. It is determined as a possible time. Such a reference time may be obtained by conducting an experiment under conditions simulating actual conditions in the electric vehicle 90, or by simulation based on average driving conditions.

  In step S325, if it is determined that the elapsed time from the previous process exceeds the reference time, the amount of radical suppressing substance in the electrolyte membrane may be insufficient, so the CPU of the control unit 50 Performs the processing of steps S130 to S170. If it is determined in step S170 that the amount of generated water exceeds the cathode pore volume, the CPU of the controller 50 resets the elapsed time (step S375) and starts counting the elapsed time again. Thereafter, idling is executed (step S180), and this routine is terminated.

  If it is determined in step S120 that the water balance is 0 or more, and if it is determined in step S325 that the elapsed time from the previous time is less than or equal to the reference time, the CPU of the control unit 50 sets the elapsed time. Idling is executed without resetting (step S180), and this routine is terminated.

  According to the fuel cell system of the third embodiment configured as described above, when it can be determined that the radical inhibitor is sufficiently present in the electrolyte membrane, the process for promoting the dissolution of the radical inhibitor is performed. Perform idling without any problems. Therefore, it is possible to suppress the execution of unnecessary processing in the fuel cell system. Further, since idling is immediately performed when the elapsed time is equal to or less than the reference time, excessive power generation after the electric vehicle 90 stops can be suppressed.

  In the third embodiment, it is determined whether or not the current process is necessary based on the elapsed time from the previous execution of the process for ensuring the dissolution of the radical inhibitor, but a different configuration may be used. . For example, the determination may be made based on the travel distance of the vehicle since the process was executed last time. Or you may judge based on the integrated electric power generation amount after performing the said process last time.

  Further, the operation related to the necessity determination of the current process in the third embodiment may be applied to the second embodiment. That is, in the radical inhibiting substance dissolution ensuring processing routine shown in FIG. 8, after step S120, step S325 is performed prior to step S230, and after step S150, step S375 is performed prior to step S180. It is also good.

E. Variations:
The present invention is not limited to the above-described examples and embodiments, and can be implemented in various modes without departing from the gist thereof. For example, the following modifications are possible.

E1. Modification 1:
In the first to third embodiments, the outlet water vapor pressure _{PH2O_out} used for deriving the water balance is _determined by the humidity of the exhaust oxidant gas detected by the second hygrometer 37 and the exhaust oxidation detected by the second pressure gauge 38. Although derived based on the pressure of the gas, a different configuration may be used.

  For example, if it is known in advance that the humidity of the exhaust oxidant gas shows a specific value in the fuel cell system to be used, the specific value may be used. Specifically, for example, if the relative humidity of the exhaust oxidant gas is normally approximately 100%, the saturated water vapor pressure at the fuel cell temperature (for example, the temperature detected by the refrigerant temperature sensor 63) is used as the humidity of the exhaust oxidant gas. Use it.

Further, one value of the inlet oxidizing gas pressure P _in and the outlet oxidizing gas pressure P _out may be estimated based on the other value and the pressure loss in the fuel cell. This is because the pressure loss in the fuel cell can be obtained in advance, and it is considered that the fluctuation of the pressure loss as a whole of the fuel cell is small during the power generation of the fuel cell. For example, like the fuel cell system of the first to third embodiments, a system for regulating the back pressure of the oxidizing gas by using the detection value of the second pressure gauge 38, an inlet oxidizing gas pressure P _in the second pressure What is necessary is just to obtain | require based on the detected value of the total 38, and the pressure loss of a fuel cell. With such a configuration, hygrometers, pressure gauges, and the like can be reduced, and the system configuration can be simplified.

E2. Modification 2:
In the first to third embodiments, the water balance is calculated based on the equations (3) to (6), but different configurations may be used. For example, the water balance in the fuel cell system 10 can be estimated using parameters such as the output current value of the fuel cell 15, the oxidizing gas supply amount N _air , the outlet oxidizing gas pressure P _out , and the fuel cell temperature. It is. Therefore, a map that can determine whether the water balance is 0 or more or a negative value based on each parameter described above may be created in advance and stored in the control unit 50. Then, it may be determined whether or not the water balance becomes a negative value with reference to the map using each detected parameter.

E3. Modification 3:
In the first to third embodiments, the water balance is derived when an idling command is issued, but a different configuration may be used. For example, the CPU of the control unit 50 may always calculate the current water balance. In this case, for example, when the water balance is 0 or more, the radical inhibiting substance dissolution ensuring processing routine may not be executed. That is, when the water balance is 0 or more, idling is performed immediately when an idling command is issued without performing unnecessary processing.

E4. Modification 4:
In the first to third embodiments, in step S150, the value of the membrane resistance obtained for the entire stack is used to determine whether or not the electrolyte membrane is sufficiently wet. However, a different configuration may be used. For example, the membrane resistance may be measured for each single cell. In this case, when the membrane resistance values of all the single cells are lowered to the membrane resistance values when the fuel gas and the oxidizing gas having a relative humidity of 100% are supplied, it is judged that the wet state is sufficiently obtained. Just do it. Thereby, the reliability of the process which ensures the melt | dissolution of the radical inhibitor in all the single cells can be improved.

E5. Modification 5:
In the first to third embodiments, whether or not the electrolyte membrane is in a sufficiently wet state is determined based on the membrane resistance in step S150. However, a different configuration may be used. For example, the determination may be made based on whether the current value with respect to the output voltage of the fuel cell is greater than or equal to a reference value or the voltage value with respect to the output current is greater than or equal to the reference value. When the water content of the electrolyte membrane decreases, the battery performance (IV characteristics, which is the relationship between output current and output voltage) decreases. Therefore, when it can be determined that sufficient battery performance is maintained based on the current value and the voltage value, it can be determined that the wet state of the electrolyte membrane is sufficient.

E6. Modification 6:
In the first to third embodiments, when there is an idling command, the processing related to ensuring dissolution of the radical inhibitor is performed prior to the idling, but a different configuration may be used. As described above, the deterioration of the polymer electrolyte caused by radicals generally tends to progress as the fuel cell voltage increases. Therefore, if the same process is executed prior to the process for making the stop equivalent state when the stop equivalent state including the predetermined low output state set instead of the power generation stop or the power generation stop is performed, the electrolyte membrane The same effect can be obtained that suppresses the deterioration of.

  The stop equivalent state in which the fuel cell stops power generation includes, in addition to idling, when the fuel cell system is stopped. However, idling is more frequent than idling as a state where fuel cell power generation is not required. Therefore, in order to secure the supply of the radical inhibitor and sufficiently obtain the effect of suppressing the deterioration of the electrolyte membrane, it is desirable to perform control based on the water balance at least during idling.

  Or the intermittent driving | running performed while driving | running | working the electric vehicle 90 can be mentioned. Fuel cell systems generally have the property that energy efficiency is reduced when the load demand is small. Therefore, the electric vehicle 90 may travel in an operation mode in which driving power is obtained from the secondary battery 91 and power generation of the fuel cell 15 is stopped when the load demand is small, such as during constant speed traveling. Such an operation state in which power generation of the fuel cell is stopped because there is a load request on the vehicle but the load request is small is called intermittent operation. If the same processing as in the embodiment is performed when the system is stopped or intermittent operation is started, the same effect of suppressing the deterioration of the electrolyte membrane when the fuel cell power generation is stopped can be obtained.

  In addition, as a stop equivalent state that is a predetermined low output state set in place of the power generation stop, the fuel cell power generation is completely stopped during idling (vehicle speed zero) or intermittent operation (running) as described above. In order to avoid the fuel cell electrode from becoming a high potential, a state where power generation is continued slightly can be mentioned. When power generation of the fuel cell is stopped, the voltage of the fuel cell becomes OCV (Open circuit voltage), and the electrode is exposed to a high potential. Therefore, for the purpose of suppressing the deterioration of the electrode due to exposure to a high potential, even if the power generation of the fuel cell is not required, the power generation of the fuel cell can be continued to suppress the electrode deterioration. In some cases, the electrode potential is controlled to be low. Such control can be suitably employed when the power generation stop time is predicted to be relatively short, such as idling or intermittent operation. As described above, even when the electrode potential is suppressed to such an extent that electrode deterioration can be suppressed, the fuel cell voltage becomes higher than that during normal power generation, so that deterioration of the electrolyte membrane due to radicals is likely to proceed. Therefore, by applying the present invention, it is possible to suppress the deterioration of the electrolyte membrane in such a stop equivalent state.

E7. Modification 7:
In the first to third embodiments, the radical suppressing substance is disposed in the water repellent layer 76 provided on the gas diffusion layer 72, but a different configuration may be used. For example, a radical inhibitor may be widely disposed throughout the gas diffusion layer. By disposing at least the region including the interface with the cathode in the gas diffusion layer 72, it becomes possible to efficiently dissolve the radical inhibitor by the generated water and supply it to the electrolyte membrane.

  Or you may arrange | position a radical inhibitor in a cathode. In the case where a radical inhibitor is disposed in the cathode, a catalyst ink may be prepared by mixing a radical inhibitor in addition to the catalyst-supporting carbon and the polymer electrolyte to form the cathode. If the radical inhibitor is held in the cathode or in the gas diffusion layer including the boundary with the cathode, the same effect as in the embodiment can be obtained by securing a sufficient amount of generated water in the cathode.

E8. Modification 8:
In the first to third embodiments, the radical suppressing substance is provided in the cathode-side gas diffusion layer, but may be provided in the anode and / or the anode-side gas diffusion layer. Even when the radical suppressing substance is arranged on the anode side, an effect of suppressing deterioration of the electrolyte membrane can be obtained by securing a wet state in the vicinity of the electrolyte membrane prior to the stop equivalent state. However, it is desirable that at least the cathode in which the generated water is produced and / or the gas diffusion layer on the cathode side be provided. Thereby, at the time of normal power generation, the radical inhibitor can be dissolved little by little by the generated water and supplied to the electrolyte membrane.

E9. Modification 9:
In the first to third embodiments, the fuel cell system 10 is used as a power source for driving the electric vehicle 90, but may have a different configuration. For example, it may be used as a power source for driving a moving body other than a vehicle, or may be used as a stationary power source. If the same process is performed when the power generation is stopped or the stop equivalent state including the predetermined low output state set in place of the power generation stop is performed, the effect of suppressing deterioration of the electrolyte membrane can be obtained.

DESCRIPTION OF SYMBOLS 10 ... Fuel cell system 15,115 ... Fuel cell 20 ... Hydrogen tank 22 ... Hydrogen supply flow path 24 ... Hydrogen discharge flow path 25 ... Connection flow path 30 ... Compressor 31 ... Air supply flow path 32 ... Air discharge flow path 34 ... 1st DESCRIPTION OF SYMBOLS 1 Hygrometer 35 ... 1st pressure gauge 36 ... Flow meter 37 ... 2nd hygrometer 38 ... 2nd pressure gauge 39 ... Back pressure valve 40 ... Hydrogen shut-off valve 42 ... Modulatable pressure valve 44 ... Hydrogen circulation pump 46 ... Purge valve 50 ... Control part 51 ... Load connection part 53 ... AC impedance measurement part 54 ... Frequency sweep part 55 ... Impedance derivation part 56 ... Wiring 57 ... Load 60 ... Refrigerant circulation pump 61 ... Radiator 62 ... Refrigerant flow path 63 ... Refrigerant temperature sensor 70, 170 ... Single cell 71 ... MEA
72, 73 ... Gas diffusion layer 74, 75, 174 ... Gas separator 76, 77 ... Water-repellent layer 81-86 ... Hole 87 ... Recess 88, 89 ... Groove 90 ... Electric vehicle 92 ... DC / DC converter 93 ... Drive inverter 94 ... Auxiliary machine 95 ... Drive motor 98 ... Output shaft 99 ... Vehicle drive shaft

Claims (13)

A fuel cell system comprising a fuel cell,
The fuel cell
An electrolyte membrane comprising a polymer electrolyte;
A pair of electrodes formed on each surface of the electrolyte membrane;
A porous gas diffusion layer disposed on the electrode;
A radical inhibitor disposed in at least one of the electrodes and / or in a region including a boundary with the electrode in at least one of the gas diffusion layers;
With
The fuel cell system further includes:
A water balance deriving unit for deriving a water balance in the fuel cell;
An operation state control unit for controlling an operation state in the fuel cell;
A membrane wet state detection unit for detecting a wet state in the electrolyte membrane;
With
When the operation state control unit determines that the fuel cell should be brought into a stoppage equivalent state including a predetermined low output state set in place of power generation stop or power generation stop, the water balance deriving unit derives If the water balance is a negative value, the operating state of the fuel cell is changed so that the moisture content of the one electrode or the electrode in contact with the one gas diffusion layer is increased, and the membrane wet state detection unit detects A fuel cell system that performs control for bringing the fuel cell into the stop equivalent state after the wet state in the electrolyte membrane reaches a reference wet state. The fuel cell system according to claim 1, wherein
The operation state control unit changes the operation state of the fuel cell so that the water balance becomes a positive value in order to increase the water content of the one electrode or the electrode in contact with the one gas diffusion layer. Fuel cell system. The fuel cell system according to claim 2, wherein
The operating state control unit is configured to increase a humidification amount in a reaction gas supplied to the at least one electrode and / or the at least one gas diffusion layer, decrease a supply amount of the reaction gas, and reduce the supply amount of the reaction gas in the fuel cell. A fuel cell system that changes an operating state of the fuel cell by a method selected from an increase in back pressure in a reaction gas flow path. The fuel cell system according to claim 2 or 3, wherein
The cathode provided in the fuel cell is a porous electrode,
The radical inhibitor is disposed in the cathode and / or in a region including the boundary with the cathode in the gas diffusion layer disposed in contact with the cathode,
The operating state control unit further causes the fuel cell to generate power in an operating state in which the water balance becomes a positive value after the wet state in the electrolyte membrane reaches the reference wet state, To bring the fuel cell into the stop equivalent state when the volume of water generated in the fuel cell with power generation after the wet state reaches the reference wet state reaches the pore volume in the cathode. A fuel cell system that controls The fuel cell system according to claim 1, further comprising:
Provided in contact with the gas diffusion layer, a fuel gas or oxidizing gas channel is formed as a gas channel between the gas diffusion layer and a refrigerant channel separated from the gas channel is formed. A pair of gas separators, wherein the gas separator arranged on the gas diffusion layer side and / or the electrode on which the radical suppressing substance is arranged, the gas flow path and the refrigerant flow A pair of gas separators including a porous body in which pores that communicate with the path are formed;
A refrigerant pressure adjusting unit for adjusting the pressure of the refrigerant flowing through the refrigerant flow path;
With
The operating state control unit is configured to change the operating state of the fuel cell to increase the water content of the electrolyte membrane, so that the pores in the gas diffusion layer in contact with the gas separator having the porous body are the refrigerant. A fuel cell system that raises the pressure of the refrigerant so as to be satisfied. The fuel cell system according to claim 5, wherein
The fuel cell system, wherein the refrigerant is an acidic solution. The fuel cell system according to any one of claims 1 to 6,
The reference wet state is a state in which the electrolyte membrane is in the same wet state as when a fuel gas and an oxidizing gas having a relative humidity of 100% are supplied to the fuel cell. The fuel cell system according to claim 7, further comprising:
A membrane resistance measurement unit for measuring the resistance of the electrolyte membrane;
The operating state control unit is configured such that the resistance of the electrolyte membrane measured by the membrane resistance measurement unit is that of the electrolyte membrane when a fuel gas and an oxidizing gas having a relative humidity of 100% are supplied to the fuel cell. A fuel cell system that determines that the wet state of the electrolyte membrane has reached a reference wet state when the resistance value decreases. A fuel cell system according to any one of claims 1 to 8,
The radical suppressant is disposed in at least a region including a boundary with the cathode in a gas diffusion layer disposed on the cathode and / or on the cathode. The fuel cell system according to any one of claims 1 to 9,
The fuel cell system, wherein the radical inhibitor is a compound of at least one element selected from cerium, manganese, and platinum. The fuel cell system according to any one of claims 1 to 10,
The water balance is a value obtained by subtracting the amount of water discharged from the fuel cell from the sum of the amount of water supplied to the fuel cell and the amount of water generated by power generation in the fuel cell. Fuel cell system. A moving object,
A fuel cell system according to any one of claims 1 to 11, comprising:
A moving body using at least the fuel cell as a driving power source. The moving body according to claim 12,
The operation state control unit determines that the fuel cell should be in the stop equivalent state at least when stopping the driving of the moving body without stopping the fuel cell system.

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