JP2019083178A - Fuel cell system - Google Patents

Abstract

To provide a fuel cell system with a capability of suppressing a voltage overshoot while stabilizing the state of power generation.SOLUTION: In a fuel cell system that has a control apparatus 20 for controlling a functional state of a fuel cell 1, a carrier 31 of one electrode where water is generated by combining hydrogen with oxygen, of electrodes 2, 3 of the fuel cell 1, is made hydrophilic, and a catalyst part 32 and an ionomer part 33 are provided. The catalyst part 32 is a site where a catalytic metal is carried on the carrier 31. The ionomer part 33 is fixed around the catalyst part 32 so that at least the catalytic metal is exposed. Further, a control part 22 is disposed in the control apparatus 20 for controlling a moisture amount existing on a surface of the carrier 31. The control part 22 performs control for increasing a moisture amount during a start period until a given stable start condition is established from starting a power generation more than a moisture amount during a stable operation after establishing the given stable start condition.SELECTED DRAWING: Figure 4

Description

  The present invention relates to a fuel cell system provided with a control device that controls both the supply state of fuel gas supplied to the fuel electrode of the fuel cell and the supply state of air supplied to the air electrode.

  2. Description of the Related Art Conventionally, in a fuel cell system that extracts electric energy using a chemical reaction between hydrogen (hydrogen gas) and oxygen (air), there is a technique of adjusting the amount of water contained in a fuel electrode or an air electrode. For example, by supplying non-humidified fuel gas to the fuel electrode at start-up of the fuel cell, air remaining in the vicinity of the fuel electrode (air containing oxygen) is discharged to prevent generation of reverse current. Are known. In addition, in order to remove water (such as dew condensation water) condensed inside the fuel cell, there is also known a technique of reducing the pressure of the cooling water (see Patent Documents 1 and 2).

JP, 2016-027534, A JP 2003-151597

  By the way, water is always produced inside the electrode of the fuel cell by the chemical reaction of hydrogen and oxygen. If the generated water stays in the vicinity of the catalyst, the chemical reaction between hydrogen and oxygen is inhibited, and the power generation state may become unstable. Therefore, it has been studied to make the electrode itself water repellent and to have a structure in which generated water is smoothly removed from the inside of the electrode. However, when the electrode itself is subjected to water repellant treatment, the movement and diffusion of ions should be secured unless a large amount of electrolyte (ionomer) for conducting hydrogen ions is conducted around the catalyst metal. difficult. On the other hand, as the amount of ionomer present around the catalyst metal increases, the oxygen ions dissolved in the ionomer increase. As a result, a phenomenon in which the voltage rapidly rises (voltage overshoot) is likely to occur at the start of the fuel cell, and the deterioration of the electrode is likely to proceed.

  One of the objects of the present invention is to solve the above problems and to provide a fuel cell system capable of suppressing voltage overshoot while stabilizing the power generation state of the fuel cell. . The present invention is not limited to this object, and it is an operation and effect derived from each configuration shown in the “embodiments to be described later”, and it is also possible to exert an operation and effect that can not be obtained by the prior art. It can be positioned as a goal.

  (1) The disclosed fuel cell system is a fuel cell system provided with a control device that controls the operating state of the fuel cell. One electrode from which hydrogen and oxygen combine to form water is a hydrophilic carrier, a catalyst portion formed by supporting a catalyst metal on the carrier, and the catalyst portion so that at least the catalyst metal is exposed. And an ionomer part formed by fixing the ionomer to the periphery of the In addition, the amount of water present on the surface of the carrier at the start timing from when the control device starts power generation to when a predetermined stable start condition is satisfied, during steady operation after the stable start condition is satisfied. It has a control part which makes it increase more than the said moisture content.

(2) It is preferable that the control unit controls the amount of water so that the catalyst metal is coated with water at the start timing and the catalyst metal is exposed during the steady operation.
(3) It is preferable that the control device has an estimation unit that calculates an estimated water content, which is an estimated value of the water content existing on the surface of the carrier, based on the electrical resistance value of the electrode.
(4) It is preferable that the control unit strengthens the cooling capacity of the fuel cell when the operation of the fuel cell is stopped as the estimated amount of water is smaller. For example, it is preferable to humidify in advance by strengthening the cooling capacity immediately before the operation of the fuel cell is stopped.

(5) It is preferable that the control unit reduces the flow rate of gas supplied to the one electrode as the estimated amount of water decreases. For example, by reducing the gas flow rate at the start time, it is preferable to suppress the scattering and diffusion of the water generated by the fuel cell, and to provide an environment in which the water on the electrode surface tends to increase.
(6) It is preferable that the control unit performs feedback control of the humidity of the gas supplied to the electrode at the start time based on the estimated water content. For example, the control unit preferably performs the feedback control such that the humidity at the start timing is higher than that in the steady operation.

(7) It is preferable that the control unit strengthens the cooling capacity of the fuel cell at the time of the operation stop of the fuel cell as the cell temperature of the fuel cell is higher.
(8) The stable start condition is preferably "a predetermined time has elapsed since the start of the power generation".
(9) The volume ratio of the ionomer contained in the one electrode is preferably 10% or more.

  By making the water content at the start time of the fuel cell higher than that in the steady operation, it is possible to suppress the voltage overshoot immediately after the start, and to improve the controllability of the fuel cell. Thereby, the deterioration of the catalyst part of the electrode can be prevented, and the quality of the fuel cell can be improved. Further, since the ionomer is fixed to the electrode so that the catalyst metal is exposed, a three-phase interface can be formed in the vicinity of the catalyst, and the power generation state of the fuel cell can be stabilized.

FIG. 1 is a block diagram showing a configuration of a vehicle to which a fuel cell system is applied. It is a block diagram for demonstrating the structure of a fuel cell system. (A) is a schematic view showing a cell structure of a polymer electrolyte fuel cell (PEFC), and (B) is a schematic view showing a cell structure of an alkaline fuel cell (AFC). (A) is a schematic diagram which shows the structure of one electrode surface, (B) is a schematic diagram which shows the structure of the other electrode surface. It is a graph which illustrates the relationship between the cell resistance value of an electrode, and the presumed moisture content. (A) is a schematic diagram which shows the water-containing state of the catalyst surface at the time of starting of a fuel cell, (B) is a schematic diagram which shows the water-containing state at the time of steady state. It is a flowchart which shows the control content (at the time of stop) of a fuel cell system. It is a flowchart which shows the control content (at the time of starting) of a fuel cell system. It is a flowchart which shows the control content (at the time of starting) as a modification.

  Hereinafter, a fuel cell system as an embodiment will be described with reference to the drawings. The following embodiments are merely illustrative, and there is no intention to exclude the application of various modifications and techniques that are not specified in the following embodiments. Each structure of this embodiment can be variously modified and implemented in the range which does not deviate from those meaning. Also, they can be selected as needed or can be combined as appropriate.

[1. Constitution]
The fuel cell system according to the present embodiment is a fuel cell system provided with a control device 20 for controlling the operation state of the fuel cell 1, and is mounted on a vehicle 40 (FCV; Fuel Cell Vehicle) shown in FIG. The vehicle 40 is equipped with a motor 41 for traveling, an inverter 42, and a battery 43 for traveling. The battery 43 is a main power supply of the motor 41 which is a drive source of the vehicle 40 and is a storage device for storing the generated power of the fuel cell 1 and is, for example, a unit type lithium ion secondary battery incorporating a plurality of cells. The motor 41 is an AC motor generator (motor generator) having a function as a motor and a function as a generator. The vehicle 40 shown in FIG. 1 is equipped with a front wheel and rear wheel motor 41. The motor 41 disposed on the front side drives the front wheel, and the motor 41 disposed on the rear side drives the rear wheel. Do.

  An inverter 42 is interposed between the battery 43 and each motor 41. The inverter 42 is a converter (DC-AC inverter) that mutually converts DC power on the battery 43 side and AC power on the motor 41 side. At the time of power running of the motor 41, AC drive power is supplied from the battery 43 side to the motor 41 side. On the other hand, during regenerative power generation of the motor 41, DC regenerative power is supplied from the motor 41 side to the battery 43 side. The inverter 42 and the motor 41 are connected by a three-phase AC power line (charge / discharge circuit), and the inverter 42 and the battery 43 are connected by a DC power line. The AC voltage in the three-phase AC power line fluctuates according to the drive voltage and the generated voltage of the motor 41, and can rise up to around 600 V, for example. On the other hand, the direct current voltage in the direct current power line fluctuates in accordance with the charge and discharge voltage of the battery 43, and fluctuates, for example, in the range of 200 to 300 [V].

  The fuel cell 1 is connected to a DC power line via a transformer 44. The transformer 44 is a converter (DC-DC converter) that mutually converts the DC voltage on the fuel cell 1 side and the DC voltage on the battery 43 side. A fuel passage 11 through which a fuel gas flows, an air passage 12 through which air containing oxygen flows, and a cooling water passage 17 through which cooling water flows are connected to the fuel cell 1 of the present embodiment. A fuel tank 45 for storing an established fuel gas is connected to the fuel passage 11 via a fuel valve 46. Further, the air passage 12 is provided with an air blower 47 for feeding air at a predetermined flow rate. The flow rate of the fuel gas supplied to the fuel electrode 2 is changed by adjusting the opening degree of the fuel valve 46. Similarly, the flow rate of air supplied to the air electrode 3 is changed by adjusting the rotation speed of the air blower 47. When the vehicle 40 is equipped with an internal combustion engine, the fuel gas may be generated by reforming the fuel (gasoline, light oil, etc.) of the internal combustion engine, and the fuel tank 45 may be omitted.

  The cooling water passage 17 is a refrigerant passage for cooling the fuel cell 1 by circulating the cooling water. A cooling water pump 48, a flow path switching valve 49, and a radiator 50 are interposed in the cooling water passage 17. The cooling water pump 48 is a pumping device for increasing or decreasing the flow rate and pressure of the cooling water. The flow rate of the cooling water is adjusted by changing the pumping amount (operating speed) of the cooling water pump 48. The flow path switching valve 49 is a flow control valve that controls the ratio of the flow rate of cooling water that has passed through the fuel cell 1 to the radiator 50 side and the flow rate of bypassing the radiator 50 and returning to the fuel cell 1 again. is there. The radiator 50 is a heat exchanger that exchanges heat between the outside air and the cooling water. The cooling water is air cooled by the radiator 50. The radiator 50 is provided with a radiator core in which tubular refrigerant passages are spaced apart from each other, and cooling water passes therethrough. Further, a large number of heat dissipating fins are provided on the outer surface of the radiator core so that the heat of the radiator core is exposed to the outside air and dissipated.

  A radiator fan 51 is provided on the rear side of the vehicle 40 relative to the radiator 50, and an open / close grill 52 is disposed on the front side. The radiator fan 51 is a blower for increasing the flow velocity of the outside air passing through the radiator 50. The opening and closing grille 52 is an electric louver capable of adjusting an opening area (louver angle) into which the outside air is introduced from the front of the vehicle 40. The temperature of the cooling water can be changed by adjusting the division ratio of the cooling water in the flow path switching valve 49, the rotational speed of the radiator fan 51, the opening degree of the opening and closing grille 52, and the like. For example, as the flow rate bypassing the radiator 50 decreases, the temperature of the cooling water becomes lower, and the cooling capacity of the fuel cell 1 is strengthened. On the other hand, as the bypass flow rate is increased, the temperature of the cooling water becomes higher, and the cooling capacity is weakened. In addition, the temperature of the cooling water tends to decrease as the flow rate of the outside air passing through the radiator core increases or the outside air temperature decreases.

  The fuel cell system shown in FIG. 2 is a control device that controls both the supply state of fuel gas supplied to the fuel electrode 2 (anode) of the fuel cell 1 and the supply state of air supplied to the air electrode 3 (cathode). It is a fuel cell system provided with twenty. The type of fuel cell 1 is, for example, polymer electrolyte type (PEFC; Polymer Electrolyte Fuel Cell), phosphoric acid type (PAFC; Phosphoric Acid Fuel Cell), solid oxide type (SOFC; Solid Oxide Fuel Cell), alkali electrolyte type (PEFC) Such as Alkaline Fuel Cell).

Fuel gas is supplied to the fuel electrode 2 through the fuel passage 11, and air containing oxygen is supplied to the air electrode 3 through the air passage 12. An electrolyte unit 4 is provided between the fuel electrode 2 and the air electrode 3. The composition of the electrolyte unit 4 is determined according to the type of fuel cell 1. For example, in the case of PEFC, a polymer membrane (fluorine-based membrane) having conductivity of proton (hydrogen ion H ⁺ ) is used. In the case of the AFC, the hydroxide ion (OH ^-) electrolyte having conductivity (aqueous solution such as sodium hydroxide or potassium hydroxide) to the impregnated polymer film, is used a porous material Be done.

  The fuel electrode 2 and the air electrode 3 are provided with a resistance sensor 15 for measuring the electric resistance value between the electrodes 2 and 3 in order to grasp the amount of water adhering (remaining) on the electrode surface. Here, as shown in FIG. 2, the cell resistance value R of the fuel cell 1 (that is, the electrical resistance value between the fuel electrode 2 and the air electrode 3 sandwiching the electrolyte portion 4) is measured. Information on the cell resistance value R measured by the resistance sensor 15 is transmitted to the control device 20. Specific examples of the resistance sensor 15 include a resistance meter, a tester, an impedance measuring instrument, and the like. The resistance sensor 15 may be incorporated in the fuel cell 1 or may be provided separately from the fuel cell 1.

  The fuel cell 1 of the present embodiment is provided with a temperature sensor 16 for detecting the cell temperature T. Although the temperature sensor 16 shown in FIG. 2 is disposed at a position for detecting the temperature of the fuel electrode 2, the detection position of the temperature sensor 16 is not limited to this, and the temperature of the air electrode 3 or the electrolyte portion 4 is detected. Alternatively, the temperature of the outer surface of the cell stack (stack temperature) may be detected. Further, temperatures at a plurality of locations may be detected, and the average value thereof may be detected and calculated as the cell temperature T.

  As shown in FIG. 2, a fuel humidifier 13 is interposed in the fuel passage 11, and an air humidifier 14 is interposed in the air passage 12. The fuel humidifier 13 functions to raise the humidity of the fuel gas by supplying water droplets or water vapor to the fuel passage 11. Similarly, the air humidifier 14 has a function of increasing the humidity of the air introduced to the air electrode 3. The water supplied from the humidifiers 13 and 14 may be previously replenished to a vehicle water tank, or the condensed water recovered from the off gas of the fuel cell 1 may be reused. The control device 20 manages the operating state of the humidifiers 13 and 14. In FIG. 2, the humidifiers 13 and 14 of the type which collect | recovers condensed water from off-gas and recycle | reuse are illustrated.

  The humidifiers 13 and 14 are provided on a passage that supplies a gas to at least “one electrode where hydrogen and oxygen combine to generate water”. For example, in the case of PEFC, at least the air passage 12 is provided with the air humidifier 14 and the fuel humidifier 13 can be omitted. Further, in the case of AFC, the fuel humidifier 13 is provided at least in the fuel passage 11, and the air humidifier 14 can be omitted. The humidifiers 13 and 14 of the present embodiment have a function as a heat exchanger for cooling off gas to recover condensed water. Thereby, the water contained in the off gas is reused. The off gas after the condensed water is recovered may be introduced into the fuel passage 11 or the air passage 12 again, or may be discharged outside the vehicle through the off gas purification device.

Here, the cell structure and reaction formula of PEFC are shown in FIG. 3 (A), and the cell structure and reaction formula of AFC are shown in FIG. 3 (B). The basic structure of the fuel cell 1 is almost the same regardless of its type. That is, the fuel electrode 2 is provided with an anode electrode layer 5, a hydrogen diffusion layer 7 and a hydrogen separator 9, and the air electrode 3 is provided with a cathode electrode layer 6, an oxygen diffusion layer 8 and an oxygen separator 10.
The electrode layers 5 and 6 are a composite of a conductive support on which a catalytic noble metal (such as platinum or platinum-ruthenium) is supported and an electrolyte. The carrier functions as a channel (passage) through which electrons are conducted, and the electrolyte functions as a channel through which ions are conducted.

The diffusion layers 7 and 8 are porous bodies for maintaining the conductivity and the fluidity of water while efficiently diffusing the reactant in the electrode layers 5 and 6. These diffusion layers 7 and 8 are formed, for example, by impregnating carbon paper, carbon cloth or the like with a highly water-repellent resin.
The separators 9 and 10 are porous members for uniformly diffusing fuel gas and air into the diffusion layers 7 and 8, and are formed of a conductive material. Grooves are provided on the surfaces of the separators 9 and 10, and by bringing the surfaces into close contact with the diffusion layers 7 and 8, gas flow paths are formed. Moreover, the flow path through which a cooling water distribute | circulates is provided in the back surface and the inside of the separators 9 and 10, and the cooling water passage 17 is connected.

The ions moving inside the electrolyte unit 4 are proton H ⁺ in PEFC shown in FIG. 3A and hydroxide ions OH ⁻ in AFC shown in FIG. 3B. Therefore, an electrode from which hydrogen and oxygen combine to form water is the air electrode 3 in PEFC and the fuel electrode 2 in AFC.
In the fuel cell 1 of the present embodiment, one of the electrodes from which water is generated has a structure shown in FIG. 4 (A). That is, this structure is applied to at least the cathode electrode layer 6 of the air electrode 3 in PEFC, and applied to at least the anode electrode layer 5 of the fuel electrode 2 in AFC.

  In FIG. 4A, reference numeral 31 denotes a carbon support (carbon black, support), and reference numeral 32 denotes a catalyst portion on which a catalyst metal (platinum particles or platinum-ruthenium particles) is supported. Further, reference numeral 33 denotes an ionomer part to which an ionomer (electrolyte polymer) is fixed, and reference numeral 34 denotes a hydrophilic part. The hydrophilic portion 34 is formed by subjecting the surface of the carbon carrier 31 to a hydrophilic treatment (oxidation treatment) to bind an acidic functional group. Examples of the type of the acidic functional group include a hydroxyl group, a carboxy group, a carbonyl group and a quinone group. When the hydrophilic portion 34 is regarded as a part of the carbon carrier 31, it can be said that the carbon carrier 31 itself has hydrophilicity.

  The ionomer portion 33 is fixed around the catalyst portion 32 so that at least the catalyst metal is exposed. Preferably, the ionomer portion 33 is disposed at a distance from the catalyst portion 32 so that the hydrophilic portion 34 surrounds the catalyst portion 32. As shown in FIG. 4A, a relatively small amount of ionomer is fixed to the surface of the carbon support 31 so that the ionomer portion 33 does not cover the catalyst portion 32. The volume ratio (volume ratio in the electrode layers 5 and 6) of the ionomer of the present embodiment is less than 60%. However, when the content of the ionomer in the electrode layers 5 and 6 is too small, the binding property of the carbon carrier 31 is reduced, so the lower limit of the volume ratio is 10% (volume ratio is 10% or more).

  As described above, the structure shown in FIG. 4A is applied to at least one of the electrodes from which water is generated. The other electrode may have a similar structure, or may have a structure as shown in FIG. 4 (B). The structure shown in FIG. 4B has a structure in which a relatively large amount of ionomer is fixed to the surface of the carbon support 31 such that the carbon support 31 does not have the hydrophilic portion 34 and the ionomer 33 covers the catalytic metal. is there. In this case, the volume ratio of the ionomer is preferably larger than that of the ionomer at least at one electrode where water is generated, and may not be less than 60%.

  The control device 20 (FC-ECU) is an electronic control device [ECU (control device) for controlling the operating states of the fuel cell 1 and the humidifiers 13 and 14 and the cooling capacity of the fuel cell 1 (cooling water, operating state of the radiator 50, etc. Electronic Control Unit)]. Inside the control device 20, a processor, a memory, an interface device, etc. connected to each other via an internal bus are incorporated. The processor is, for example, a processing unit including a control unit (control circuit), an operation unit (operation circuit), a cache memory (register), and the like. The memory is a storage device in which programs and data during work are stored, and includes a ROM (Read Only Memory), a RAM (Random Access Memory), a non-volatile memory, and the like. The contents of control performed by the control device 20 are recorded and stored in the memory as firmware or an application program. The contents of the program are expanded in the memory space when the program is executed and executed by the processor.

  The fuel humidifier 13, the air humidifier 14, and the resistance sensor 15 are connected to the control device 20. The controller 20 has a function of calculating an estimated water content W which is an estimated value of the water content existing on the surface of the carbon carrier 31 based on the cell resistance value R detected by the resistance sensor 15 and the estimated water content W It also has a function to control the operating state of the humidifiers 13 and 14 and the cooling capacity of the fuel cell 1 based on that. Further, the control device 20 implements different control between the start timing of the fuel cell 1 and the steady operation.

  Here, the “start time” refers to the time when a predetermined stable start condition is satisfied after the fuel cell 1 whose operation has been stopped starts operating (for example, until a predetermined time elapses, or when power is generated at a predetermined output) Until the cell voltage falls below a predetermined value). In addition, the period until the operation of the fuel cell 1 is stopped after the predetermined stable start condition is satisfied is "during steady operation". In addition, the conditions (power generation conditions) for operating the fuel cell 1 in stop can be set arbitrarily. For example, the internal combustion engine of the vehicle to which the fuel cell system is applied is stably operating, the fuel remaining amount of the internal combustion engine is a predetermined amount or more, and the charging rate of the on-vehicle battery is a predetermined value or less And the like.

[2. Control configuration]
The control unit 20 is provided with an estimation unit 21 and a control unit 22 as elements for controlling the operation states of the humidifiers 13 and 14. Further, the control unit 22 is provided with a cooling capacity adjustment unit 23, a gas flow rate adjustment unit 24, and a humidity adjustment unit 25. These elements are obtained by classifying the functions of the control device 20 for convenience, and each element may be described as an independent program, or described as a compound program having these functions. It is also good. These programs are recorded in ROM, RAM, non-volatile memory, removable media, and executed by a processor. Alternatively, these programs are recorded on a recording medium (removable medium) such as an optical disk or a semiconductor memory, and read and executed on the memory via a recording medium drive.

  The estimation unit 21 calculates an estimated water content W present on the surface of the carbon carrier 31 based on the electrical resistance value of the electrode. Here, the estimated water content W for at least one of the electrodes from which water is generated is calculated. The water content of the other electrode may not be calculated. The estimated water content W is estimated based on the detection value of the resistance sensor 15. Here, the correspondence between the cell resistance value R and the estimated moisture amount W is illustrated in FIG. The cell resistance value R decreases as the estimated amount of water W present on the surface of the carbon carrier 31 increases, and increases as the estimated amount of water W decreases. Therefore, it can be estimated that, as the cell resistance value R detected by the resistance sensor 15 is lower, the estimated water content W is larger. The correspondence between the cell resistance value R and the estimated water content W may be obtained in advance for each of the fuel electrode 2 and the air electrode 3 (for each electrode) through a test or experiment.

  The control unit 22 controls the amount of water present on the surface of the carbon carrier 31 with respect to at least one electrode from which water is generated. The water content of the other electrode may be excluded from the control target. Here, control is performed to increase the amount of water at the start time of the fuel cell 1 more than the amount of water during steady operation. The control unit 22 of the present embodiment has a function of controlling the amount of water so that the catalyst metal of the catalyst unit 32 is coated with water at the start time, and the catalyst metal is exposed during steady operation.

Here, the water distribution of the start time on the surface of the carbon carrier 31 is shown in FIG. 6 (A), and the water distribution during steady operation is shown in FIG. 6 (B). Immediately after the fuel cell 1 is started, the catalyst portion 32 is surrounded by the water 35. As a result, for example, in the case of PEFC, the oxygen ion O ²⁻ becomes difficult to approach the surface of the catalyst metal, and the compound of hydrogen and oxygen is blocked. Similarly, hydroxide ions OH on the surface of the catalyst metal in the case of AFC ^- hardly approached, water production is blocked. Therefore, voltage overshoot that may occur immediately after start-up of the fuel cell 1 is suppressed.

On the other hand, during the steady operation of the fuel cell 1, the water 35 is removed from the periphery of the catalyst portion 32, and the catalyst metal is exposed. In addition to this, since the hydrophilic portion 34 is formed on the surface of the carbon carrier 31, the water 35 is distributed so as to spread wet along the surfaces of the ionomer portion 33 and the hydrophilic portion 34, and the catalyst portion 32 and the ionomer portion It is cross-linked by water 35 with 33. Thus, for example, in the case of PEFC, oxygen ions O ^{2 −} and protons H ⁺ easily approach the surface of the catalyst metal, and the combination of hydrogen and oxygen is promoted. Therefore, the power generation state during steady operation is stabilized.

  The control unit 22 of the present embodiment performs three types of control in order to realize the water distribution of FIG. 6A at the start time of the fuel cell 1. The first control is control to secure the remaining amount of water by keeping the state wet than usual. This control is mainly performed when the fuel cell 1 is stopped, but may be performed at the start of the fuel cell 1. The first control is performed by the cooling capacity adjustment unit 23. The second control is control for securing the remaining amount of water by changing the flow rate of gas (fuel gas or air) supplied to the fuel cell 1. This control is performed by the gas flow rate adjustment unit 24 at the start time of the fuel cell 1. The third control is control for securing the remaining amount of water by changing the humidity of the gas (fuel gas or air) supplied to the fuel cell 1. This control is performed by the humidity adjustment unit 25 at the start time of the fuel cell 1.

The cooling capacity adjustment unit 23 adjusts the cooling capacity of the fuel cell 1. Here, the cooling capacity adjustment based on the estimated water content W and the cooling capacity adjustment based on the cell temperature T are performed.
In the former adjustment of the cooling capacity, the smaller the estimated water content W, the stronger the cooling capacity of the fuel cell 1, and the larger the estimated water content W, the weaker the cooling capacity. As means for enhancing the cooling capacity, the pumping amount of the cooling water pump 48 is increased (acceleration speed is accelerated), the radiator fan 51 is accelerated, the opening area of the opening / closing grille 52 is expanded, and the radiator 50 is increased. And reducing the flow rate bypassing the By increasing the cooling capacity of the fuel cell 1, the temperature (the stack temperature and the cell temperature T) of the fuel electrode 2 and the air electrode 3 themselves is lowered, and the electrode surface becomes more wet than usual. As a result, the remaining amount of water at the next start time is secured, and the water distribution of FIG. 6A is realized.

  In the latter cooling capacity adjustment, the higher the cell temperature T, the stronger the cooling capacity of the fuel cell 1, and the lower the cell temperature T, the weaker the cooling capacity. The means for enhancing the cooling capacity is the same as the cooling capacity adjustment based on the estimated water content W. As the cell temperature T is higher, the cooling capacity of the fuel cell 1 is intensified, so that the temperature of the fuel electrode 2 or the air electrode 3 itself (stack temperature or cell temperature T) decreases and the electrode surface becomes wet than usual. . As a result, the remaining amount of water at the next start time is secured, and the water distribution of FIG. 6A is realized.

  The gas flow rate adjustment unit 24 adjusts the gas flow rate of the fuel cell 1 based on the estimated water content W. Here, the flow rate of the gas supplied to at least one of the electrodes from which water is generated is adjusted. For example, in PEFC, the flow rate of air supplied to the air electrode 3 is adjusted. To change the flow rate of air, the rotational speed of the air blower 47 may be adjusted. The gas flow rate adjustment unit 24 of the present embodiment reduces the gas flow rate as the estimated water content W decreases, and increases the gas flow rate as the estimated water content W increases. By such control, when the amount of residual water is large, the water is likely to scatter, diffuse and decrease. On the other hand, when the amount of residual water is small, scattering and diffusion of the water are suppressed, and the water tends to increase.

The humidity adjustment unit 25 adjusts the gas humidity of the fuel cell 1 based on the estimated water content W. Here, the humidity of the gas supplied to at least one of the electrodes from which water is produced is adjusted. The humidity of the gas supplied to the other electrode may be excluded from the control targets. For example, in PEFC, the humidity of air supplied to at least the air electrode 3 is adjusted.
The humidity adjustment unit 25 of the present embodiment has a function of performing feedback control of gas humidity based on the estimated water content W. That is, the humidity adjustment unit 25 performs feedback control to make the measured value asymptotically approach a predetermined “target value”, with the estimated moisture amount W estimated by the estimation unit 21 as the “measured value”.

Hereinafter, the target value during steady-state operation is referred to as "steady-state target water content W ₀ ", and the target value upon startup is referred to as "start-up target water content W ₁ ". The startup target moisture amount W ₁ is set to a value larger than at least the steady-state target moisture amount W ₀ (W ₁ > W ₀ ). The specific values of the constant target water content W ₀ and the startup target water content W ₁ may be fixed values set in advance, or the operating state of the fuel cell 1 (environmental temperature, environmental humidity, generated output, etc.) It may be a variable value set according to For example, when the environmental humidity is high and it is considered that the estimated moisture amount W on the surface of the carbon carrier 31 is likely to increase, the target moisture amounts W ₀ and W ₁ may be set to be slightly lower.

  The humidity adjustment unit 25 reduces the amount of water injected from the humidifiers 13 and 14 as the value obtained by subtracting the target value from the estimated water content W (measured value) estimated by the estimation unit 21 increases, thereby reducing the humidity of the gas. Reduce. On the other hand, as the value obtained by subtracting the target value from the estimated water content W estimated by the estimation unit 21 is smaller, the water injected from the humidifiers 13 and 14 is increased to raise the humidity of the gas. By such control, the estimated water content W estimated by the estimation unit 21 approaches the target value.

[3. flowchart]
[3-1. At FC stop]
FIG. 7 is a flowchart showing an example of control when the fuel cell 1 is stopped. The present flow is repeatedly performed in a predetermined cycle while the fuel cell 1 is in operation, but a description of control relating to power generation is omitted. In step A1, it is determined whether an FC stop condition (stop condition of the fuel cell 1) is satisfied. Specific examples of the FC stop condition include that the charging rate of the battery 43 has reached a predetermined value, and that the amount of fuel remaining in the fuel tank 45 has decreased to a predetermined value or less. If the FC stop condition is not satisfied, the condition determination is repeated until the FC stop condition is satisfied.

  On the other hand, when the FC stop condition is satisfied, various information such as the environmental temperature, the environmental humidity, and the power generation output (request output) is acquired by the control device 20 (step A2). Further, the information of the cell resistance value R detected by the resistance sensor 15 is transmitted to the estimation unit 21 (step A3). The estimation unit 21 calculates an estimated water content W based on the cell resistance value R (step A4). The estimated water content W is estimated based on, for example, the relationship between the cell resistance value R and the estimated water content W as shown in FIG.

Subsequently, the control unit 22 determines whether the estimated water content W is equal to or greater than a first predetermined value W ₁ (step A5). The first predetermined value W ₁ is the upper limit of the amount of moisture can be realized the water distribution of such starting time as shown in FIG. 6 (A). Here, if W ₁ ≦ W, the water content is slightly excessive, so that the cooling capacity adjustment unit 23 performs control to weaken the cooling capacity of the fuel cell 1 (step A 7). For example, the pumping amount of the cooling water pump 48 is reduced, or the radiator fan 51 is decelerated. Alternatively, the flow path switching valve 49 is controlled such that the opening area of the opening and closing grille 52 is narrowed or the flow rate of the cooling water bypassing the radiator 50 is increased. Further, in the subsequent step A8, a purge operation for discharging the gas (fuel gas, air) supplied to the fuel cell 1 to the outside is executed, and the process proceeds to step A12. As described above, by performing the purge operation while weakening the cooling capacity of the fuel cell 1, the stack temperature of the fuel cell 1 and the cell temperature T rise, and the excess water on the electrode surface is removed.

On the other hand, when a W _1> W in step A5 proceeds to step A6, whether the estimated amount of water W is less than the second predetermined value W ₂ is determined. The second predetermined value W ₂ has a value smaller than the first predetermined value W ₁ as shown in FIG. 5, and the lower limit of the amount of water which can realize the water distribution at the start time as shown in FIG. It is a value. Here, in the case of W <W ₂ it is to become the moisture content is somewhat insufficient to implement the control of the cooling ability adjustment section 23 enhances the cooling capacity of the fuel cell 1 (step A9). Further, the purge operation in this case is temporarily stopped to make the electrode surface more wet before the fuel cell 1 is completely stopped (step A10), and the process proceeds to step A12. As described above, by temporarily stopping the purge operation while strengthening the cooling capacity of the fuel cell 1, the stack temperature of the fuel cell 1 and the cell temperature T decrease, and the amount of water on the electrode surface increases.

If a W ≧ W ₂ in step A6 (i.e., W ₂ ≦ W <case of W ₁₎ to, since the water content is within the proper range, the cooling capacity adjusting portion 23 is in the normal cooling capacity Control for cooling the fuel cell 1 is performed (step A11), and a purge operation is performed (step A8). By such control, the gas purge proceeds with the water distribution on the electrode surface maintained in an appropriate state. In step A12, the control unit 22 determines whether the purge completion condition is satisfied. Specific examples of the purge completion condition include that the elapsed time since the establishment of the FC stop condition has reached a predetermined time, and that the cell voltage of the fuel cell 1 has dropped to a predetermined value or less. If the purge completion condition is not satisfied, the process proceeds to step A2, and the purge operation and the adjustment of the cooling capacity are continued. When the purge completion condition is satisfied, the operation of the fuel cell 1 is stopped (step A13).

[3-2. At FC startup]
FIG. 9 is a flowchart showing an example of control when the fuel cell 1 is started. The present flow is repeatedly performed at a predetermined cycle regardless of the operating state of the fuel cell 1. In step B1, it is determined whether an FC start condition (start condition of the fuel cell 1) is satisfied. Specific examples of the FC start condition include that the charge rate of the battery 43 becomes less than a predetermined value, that a start request from another electronic control unit (for example, an engine ECU or a motor ECU) or a driver is transmitted Can be mentioned. If the FC start condition is not satisfied, the condition determination is repeated until the FC start condition is satisfied.

  On the other hand, when the FC start condition is satisfied, it is determined whether the stable start condition is satisfied (step B2). As described above, the stable start condition is a condition for distinguishing between the start time and the steady operation. When the stable start condition is satisfied, a normal gas flow rate is set (step B10), and steady operation of the fuel cell 1 is performed. On the other hand, when the stable start condition is not satisfied (that is, when the start timing), the flow proceeds to the flow for performing control for adjusting the gas flow rate.

First, various information such as the environmental temperature, the environmental humidity, and the power generation output (required output) is acquired by the control device 20 (step B3). Further, information of the cell resistance value R detected by the resistance sensor 15 is transmitted to the estimation unit 21 (step B4). The estimation unit 21 calculates an estimated water content W based on the cell resistance value R (step B5). Here, the estimated water content W is estimated based on, for example, the relationship between the cell resistance value R and the estimated water content W as shown in FIG.

Subsequently, the control unit 22 determines whether the estimated water content W is equal to or more than a first predetermined value W ₁ (step B6). Here, if W ₁ ≦ W, the water content is slightly excessive, so the gas flow rate adjustment unit 24 performs control to increase the gas flow rate (step B 7). For example, the fuel valve 46 is controlled in the opening direction (when the control target is the fuel electrode 2) or the rotational speed of the air blower 47 is increased (when the control target is the air electrode 3). As a result, the water on the electrode surface is easily diffused into the gas, and the excess water on the electrode surface is removed.

On the other hand, if W ₁ > W in step B 6, the process proceeds to step B 8 to determine whether the estimated water content W is less than the second predetermined value W ₂ (where W ₂ <W ₁ ). Here, in the case of W <W ₂ it is to become the moisture content is somewhat insufficient to implement the control of the gas flow rate adjusting section 24 is reduced the gas flow rate (step B9). For example, the fuel valve 46 is controlled in the closing direction (when the control target is the fuel electrode 2) or the rotational speed of the air blower 47 is reduced (when the control target is the air electrode 3). This makes it difficult for the water on the electrode surface to diffuse into the gas, and the water content on the electrode surface increases.

Further, when a W ≧ W ₂ in step B8 (i.e., if it is W ₂ ≦ W <W ₁₎ to, since the water content is within the proper range, the gas flow rate adjusting section 24 is a gas flow rate Control to a normal gas flow rate (step B10). By such control, the water distribution on the electrode surface is maintained in an appropriate state. Note that step B10 is also executed when the stable start condition is satisfied in step B2. Therefore, the gas flow rate is adjusted only during the start time, and during normal operation, the normal gas flow rate is obtained.

  FIG. 10 is a flowchart showing another control example at the start of the fuel cell 1. The present flow is repeatedly performed at a predetermined cycle regardless of the operating state of the fuel cell 1. First, it is judged whether or not the FC start condition (start condition of the fuel cell 1) is satisfied (step C1), and when the FC start condition is satisfied, various information such as environmental temperature, environmental humidity, power generation output (request output) Is acquired by the control device 20 (step C2), and the elapsed time from the start of power generation is measured (step C3). The information on the elapsed time is used to distinguish between the start time of the fuel cell 1 and the steady operation.

The estimation unit 21 estimates the amount of water present on the surface of the carbon carrier 31 as the estimated amount of water W for at least one of the electrodes from which water is generated (step C4). Here, the estimated water content W is estimated based on the cell resistance value R detected by the resistance sensor 15. Thereafter, it is determined whether or not the stable start condition is satisfied (step C5). For example, when the elapsed time from the start of power generation exceeds a predetermined hour, is determined that the stable starting condition is satisfied, the steady-state target water content W ₀ is set (step C6). On the other hand, when the stable start condition is not established, the start time target water content W ₁ is set (step C7). Starting-time target moisture content W ₁ is a value larger than the steady target water content W _0.

Thereafter, a control signal is output from the control unit 22 to the humidity adjusting unit 25 to adjust the gas humidity, and feedback control of the water content W is performed (steps C8 and C9). That is, in the starting period of the fuel cell 1, the estimated water content W is asymptotic to startup target water content W ₁ (preferably eventually match) manner, the actuation of the humidifier 13 is controlled . Further, during steady operation after the start-up period, the operating state of the humidifiers 13 and 14 is controlled such that the estimated water amount W approaches (preferably, finally matches) the steady state target water amount W _0. Be done. Therefore, the electrodes in the start-up period of the fuel cell 1 become more wet than in steady-state operation.

[4. effect]
(1) In the fuel cell system described above, control is performed to increase the water content at the start time of the fuel cell 1 more than during steady operation. Thus, for example, in the PEFC, oxygen ions O ²⁻ coming into contact with the catalyst portion 32 at the start time of the fuel cell 1 can be reduced, and voltage overshoot immediately after start can be suppressed. Similarly, in the case of AFC, it is possible to reduce the hydroxide ion OH 2 ⁻ contacting with the catalyst portion 32 at the start time of the fuel cell 1. As described above, the controllability of the fuel cell 1 can be enhanced by performing the above-described control on at least one of the electrodes from which water is generated regardless of the type of the fuel cell 1. Further, since a sudden change in the generated voltage can be suppressed, the progress of deterioration of the catalyst portion 32 of the electrode can be prevented, and the quality of the fuel cell 1 can be improved.

  (2) In the above fuel cell system, as shown in FIG. 6A, the amount of water is controlled so that the catalyst metal of the catalyst unit 32 is covered with water at the start time. By such control, the oxygen ion concentration around the catalyst portion 32 can be more reliably reduced, and the effect of suppressing the voltage overshoot can be enhanced. In addition, during steady-state operation, as shown in FIG. 6 (B), the water content is controlled so that the catalyst metal is exposed. By such control, the oxygen ion concentration around the catalyst portion 32 can be more reliably increased, and the power generation efficiency can be enhanced.

  (3) The control device 20 described above is provided with the estimation unit 21 that calculates the estimated water content W present on the surface of the carbon carrier 31 based on the electrical resistance value of the electrode. As a result, the estimation accuracy of the estimated water content W can be improved, and the state of the water distribution on the electrode surface (wet state of the surface of the carbon carrier 31) can be grasped with high accuracy. Therefore, the voltage overshoot immediately after startup can be suppressed more reliably, and the controllability of the fuel cell 1 can be further improved.

  In the control device 20 described above, as shown in FIG. 5, the estimated water content W is calculated based on the cell resistance value R between the electrodes 2 and 3. As described above, by using the cell resistance value R, the amount of water adhering to the surface of the carbon carrier 31 can be accurately calculated. In addition, since the surface of the carbon support 31 is hydrophilic, the moisture calculated here is highly likely to be present on the “surface” of the carbon support 31. That is, the estimated water content W has a strong correlation with the exposure of the catalyst metal. Therefore, by performing control based on the estimated water content W, the strength of the catalytic reactivity in the catalyst unit 32 can be controlled.

  (4) The control unit 22 of the control device 20 is provided with a cooling capacity adjustment unit 23 that adjusts the cooling capacity of the fuel cell 1 based on the estimated water content W. In the cooling capacity adjustment unit 23, control is performed to strengthen the cooling capacity of the fuel cell 1 as the estimated amount of water W is smaller. Such control makes it easier to make the electrode surface wet just before the fuel cell 1 stops. Therefore, the remaining amount of water at the next start time can be secured, and the voltage overshoot immediately after start can be suppressed more reliably.

  (5) The control unit 22 is provided with a gas flow rate adjustment unit 24 that adjusts the gas flow rate of the fuel cell 1 based on the estimated water content W. The gas flow rate adjustment unit 24 performs control to reduce the gas flow rate of the gas supplied to at least one electrode from which water is generated as the estimated water content W is smaller. By such control, it becomes easy to make the electrode surface wet immediately after the fuel cell 1 is started. Therefore, the remaining amount of water at the start time can be secured, and the voltage overshoot immediately after start can be suppressed more reliably.

  (6) The control unit 22 is provided with the humidity adjustment unit 25 that adjusts the gas humidity of the fuel cell 1 based on the estimated water content W. The humidity adjustment unit 25 performs feedback control of the gas humidity of the gas supplied to at least one of the electrodes from which water is generated, based on the estimated water content W. By such control, it becomes easy to make the electrode surface more wet than usual immediately after start-up of the fuel cell 1, and it is possible to secure the remaining amount of water at the start-up time. Therefore, the voltage overshoot immediately after startup can be suppressed more reliably.

  (7) The cooling capacity adjustment unit 23 described above can perform the cooling capacity adjustment based on the cell temperature T. In this cooling capacity adjustment, the higher the cell temperature T, the stronger the cooling capacity of the fuel cell 1, and the lower the cell temperature T, the weaker the cooling capacity. By such control, the electrode surface can be made more wet than usual without calculating the estimated water amount W, and the remaining amount of water at the start time can be secured. Therefore, the voltage overshoot immediately after startup can be suppressed more reliably.

  (8) The control device 20 controls the surfaces of the electrodes 2 and 3 to be more wet than usual after the fuel cell 1 starts power generation until a predetermined time elapses. As described above, by increasing the amount of water until the predetermined time has elapsed, it is possible to more reliably suppress voltage overshoot immediately after startup. On the other hand, since the water content is controlled to be smaller after the predetermined time has elapsed, the power generation efficiency can be more reliably improved.

  (9) In the fuel cell 1 described above, the ionomer portion 33 having a volume ratio of 10% or more is provided on the surface of at least one of the electrodes 2 and 3 from which water is generated. Thereby, the binding property of the carbon support 31 can be improved. Further, by setting the volume ratio of the ionomer portion 33 to less than 60%, it becomes easy to generate two states, a state in which the water adhering to the surface of the carbon support 31 covers the catalyst surface and a state in which the catalyst portion 32 is exposed. be able to. Thus, in the former state, voltage overshoot can be prevented by covering the surface of the catalyst portion 32 with water, and in the latter state, power generation efficiency can be enhanced.

[5. Modified example]
Although the fuel cell system mounted on a vehicle equipped with an internal combustion engine has been illustrated in the above embodiment, the application of the fuel cell system is not limited to such a vehicle, and is applied to, for example, an electric vehicle. Is also possible. In addition, the present invention may be applied to household appliances, railways, ships, aircraft, factories, emergency power supply equipment, and the like. Regardless of the type of application target, it is possible to stabilize the power generation state of the fuel cell 1 and to suppress the voltage overshoot immediately after startup.

  In the above-described embodiment, the control in the case where the stable start condition is "a predetermined time has elapsed since the fuel cell 1 was started" is exemplified, but another condition may be used. For example, "the power generation amount of the fuel cell 1 is equal to or more than a predetermined amount", "the supply amount of fuel gas is equal to or more than a predetermined amount", and "the cell voltage is equal to or less than a predetermined value in a state where power is generated with a predetermined output. It can be considered that the water content is increased until these conditions are satisfied, with the stable start-up condition and the like. At least by increasing the wet state of the surface of the carbon carrier 31 immediately after start-up (that is, by controlling the amount of water at start-up more than at the time of steady-state), the same operation and effect as the above embodiment can be obtained. Can be earned.

  Although the electrodes 2 and 3 of the carbon support 31 (carbon black) are exemplified in the above-described embodiment, the composition of the support is not limited to this, and may be a metal support or a ceramic support. By providing at least the catalyst portion 32, the ionomer portion 33, and the hydrophilic portion 34 in the carrier, the same function and effect as the above-described embodiment can be obtained.

DESCRIPTION OF SYMBOLS 1 fuel cell 2 fuel electrode 3 air electrode 4 electrolyte part 11 fuel passage 12 air passage 13 fuel humidifier 14 air humidifier 15 resistance sensor 16 temperature sensor 17 cooling water passage 20 control device 21 estimation unit 22 control unit 23 cooling capacity adjustment unit 24 gas flow rate adjustment unit 25 humidity adjustment unit 31 carbon carrier (carrier)
32 catalyst portion 33 ionomer portion 34 hydrophilic portion 35 water

Claims (9)

In a fuel cell system provided with a control device for controlling the operating state of the fuel cell,
One electrode from which hydrogen and oxygen combine to form water is a hydrophilic carrier, a catalyst portion formed by supporting a catalyst metal on the carrier, and the catalyst portion so that at least the catalyst metal is exposed. And an ionomer part formed by fixing an ionomer to the periphery of the
The amount of water present on the surface of the carrier at the start timing from when the control device starts power generation to when a predetermined stable start condition is satisfied, the water during steady operation after the stable start condition is satisfied What is claimed is: 1. A fuel cell system comprising: a control unit that increases the amount. The fuel according to claim 1, wherein the control unit controls the water content such that the catalyst metal is coated with water at the start time and the catalyst metal is exposed during the steady operation. Battery system. The controller according to any one of the preceding claims, further comprising: an estimation unit configured to calculate an estimated amount of water, which is an estimated value of the amount of water present on the surface of the carrier, based on the electrical resistance value of the electrode. The fuel cell system described. 4. The fuel cell system according to claim 3, wherein the control unit strengthens the cooling capacity of the fuel cell at the time of operation stop of the fuel cell as the estimated amount of water is smaller. 5. The fuel cell system according to claim 3, wherein the control unit reduces the flow rate of gas supplied to the one electrode as the estimated amount of water decreases. The fuel cell according to any one of claims 3 to 5, wherein the control section performs feedback control of the humidity of the gas supplied to the electrode at the start time based on the estimated water content. system. 7. The controller according to any one of claims 1 to 6, wherein the control unit increases the cooling capacity of the fuel cell at the time of operation stop of the fuel cell as the cell temperature of the fuel cell is higher. Fuel cell system. The fuel cell system according to any one of claims 1 to 7, wherein the stable start condition is that a predetermined time has elapsed since the start of the power generation. The fuel cell system according to any one of claims 1 to 8, wherein a volume ratio of the ionomer contained in the one electrode is 10% or more.

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