JP2009230887A - Fuel cell system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To recover a catalyst layer peeled off from an electrolyte film, and thereby to suppress degradation of the power generation performance of a fuel cell. <P>SOLUTION: A fuel cell system composed of a fuel cell, determination means, and recovery means is provided. The fuel cell has a plurality of layered unit cells, and each unit cell at least includes an electrolyte film and a pair of catalyst layers between which the electrolyte film is held. The determination means determines whether the catalyst layers are peeled off from the electrolyte film in each unit cell. When the catalyst layers are determined to have been peeled off from the electrolyte film, the recovery means performs recovery operation to recover the catalyst layer from the peeled-off state. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a fuel cell system, and more particularly to recovery recovery of a catalyst layer of a fuel cell.

  In recent years, a fuel cell system using a fuel cell that generates electric power by an electrochemical reaction of reaction gases (fuel gas and oxidizing gas) as an energy source has attracted attention. The fuel cell system supplies high-pressure fuel gas from the fuel tank to the anode of the fuel cell, and also supplies air as the oxidizing gas to the cathode, and generates an electromotive force by electrochemically reacting these fuel gas and oxidizing gas. It is what

In such a fuel cell system, deterioration of the catalyst layer constituting the anode and cathode becomes a problem. For example, Patent Document 1 discloses that the performance of the catalyst is recovered by determining the oxidation state of the cathode catalyst and removing the oxide.
JP 2005-174463 A

  However, the deterioration of the catalyst layer occurs not only due to oxidation of the catalyst layer but also due to peeling of the catalyst layer from the electrolyte membrane. This exfoliation phenomenon is likely to occur when the fuel cell is used in a low temperature environment. In particular, when the fuel cell is repeatedly started below the freezing point, the water contained in the catalyst is solidified, and the volume expands and contracts due to melting of the ice. As a result, the catalyst layer is easily peeled off. The deterioration of the catalyst layer due to such peeling remains unsolved in the prior art.

  Accordingly, the present invention has been made in view of the above-described problems of the prior art, and provides a fuel cell system that recovers the separation of the catalyst layer from the electrolyte membrane, and thus suppresses a decrease in the power generation performance of the fuel cell. With the goal.

  In the present invention, the following means are adopted in order to solve the above-mentioned problems. That is, a fuel cell in which a plurality of unit cells each having a pair of catalyst layers sandwiching an electrolyte membrane are stacked, a determination means for determining whether or not the catalyst layer is peeled off from the electrolyte membrane, and the catalyst When it is determined that the layer is peeled from the electrolyte membrane, a fuel cell system is provided that includes recovery means for performing a recovery operation for recovering the catalyst layer from the peeled state.

  According to this structure, it can be detected whether the catalyst layer has peeled from the electrolyte membrane, and when there is peeling, the catalyst layer can be recovered from the peeled state again by the recovery operation. That is, the fuel cell can be self-healed. Thereby, the fall of the power generation performance of a fuel cell can be suppressed and durability can be improved.

  Further, in the above configuration, the determination unit measures current-voltage characteristics when the fuel cell is generated in a dry state rather than during normal power generation, and the catalyst layer is peeled off from the electrolyte membrane. You may make it determine.

  Since the current-voltage characteristic when the fuel cell is generated in a dry state than during normal power generation has a significant difference between the case where peeling occurs and the case where peeling does not occur, according to the above configuration, The separation of the catalyst layer can be effectively determined including the separation from the cause of deterioration (for example, oxidation) of the catalyst layer.

  In the above configuration, the recovery operation may be an operation of increasing the fastening load in the stacking direction of the single cells of the fuel cell.

  According to the said structure, since a fastening load is added to the lamination direction of the single cell of a fuel cell, a catalyst layer can be physically adhere | attached on an electrolyte membrane, and a catalyst layer can be recovered from a peeling state.

  In the above configuration, the recovery operation may be an operation for raising the operating temperature of the fuel cell higher than that during normal power generation.

  According to the above configuration, since the temperature of the catalyst layer and the electrolyte membrane in the single cell is higher than that during normal operation, the catalyst layer and the electrolyte membrane can be chemically bonded, and the catalyst layer is recovered from the peeled state. be able to.

  Further, in the above configuration, the determination may be performed when the number of times of cold start exceeds a predetermined number.

  According to the above configuration, the catalyst layer is likely to be peeled off when the low temperature start is repeated. Therefore, it is highly necessary to make the peel determination, and conversely, the case where the determination is made is defined by the number of times of the low temperature start. Thus, it is possible to prevent excessive peeling determination. Here, the low temperature start indicates a start below the temperature at which the liquid contained in the catalyst layer solidifies, and typically indicates a start below freezing point.

  In the above configuration, the determination may be performed when the power generation performance of the fuel cell in a low temperature environment is lower than a predetermined value.

  According to the above configuration, when power generation performance in a low-temperature environment, for example, current-voltage characteristics are lowered, there is a high possibility that peeling has occurred. By defining the power generation performance when the power generation performance falls below a predetermined value, it is possible to prevent excessive peeling determination. Here, the low temperature environment typically indicates an environment where the fuel cell is in a temperature range of about 0 to 50.

  In the above configuration, when the determination unit determines that the catalyst layer is still detached from the electrolyte membrane after the recovery operation, the operating humidity of the fuel cell is set to be higher than that during normal power generation. It may be.

  According to the above machine configuration, when the peeling cannot be sufficiently recovered even in the recovery operation, the operating humidity of the fuel cell is increased more than that during normal power generation. By making up, it becomes possible to obtain a desired output.

  According to the present invention, it is possible to provide a fuel cell system that recovers separation of the catalyst layer from the electrolyte membrane and thus suppresses a decrease in power generation performance of the fuel cell.

Hereinafter, fuel cells according to embodiments of the present invention will be described in the following order with reference to the drawings. In the drawings, the same parts are denoted by the same reference numerals.
1. 1. Overall configuration of fuel cell system 2. Self-healing control of fuel cell system Modified example

  In this embodiment, a solid polymer fuel cell suitable for a vehicle will be described as an example. Of course, the fuel cell system provided with the fuel cell can be mounted not only on the vehicle but also on a self-propelled mobile body such as a robot, a ship, an aircraft, etc., and power generation for a building (house, building, etc.) It can also be used as a stationary power generation system used as equipment.

1. First, the overall configuration of a fuel cell system according to an embodiment of the present invention will be described with reference to FIG. Here, FIG. 1 is a configuration diagram of the fuel cell system according to the embodiment of the present invention. The fuel cell system 1 shown in FIG. 1 supplies a fuel cell 2, an oxidizing gas piping system 3 that supplies air (oxygen) as an oxidizing gas to the fuel cell 2, and a hydrogen gas as a fuel gas to the fuel cell 2. A fuel gas piping system 4, a refrigerant piping system 5 that supplies a refrigerant to the fuel cell 2 to cool the fuel cell 2, a power system 6 that charges and discharges the power of the system 1, and a control unit that controls the entire system. 7.

  The fuel cell 2 is formed of, for example, a solid polymer electrolyte type and has a stack structure in which a large number of single cells are stacked. Each single cell has a membrane / electrode assembly (hereinafter also referred to as “MEA”) and a pair of separators arranged so as to sandwich the MEA from both sides.

  Specifically, the MEA includes a polymer electrolyte membrane and a pair of catalyst layers arranged so as to sandwich the polymer electrolyte membrane from both sides. The polymer electrolyte membrane is made of an ion exchange membrane made of a polymer material. The catalyst layer is a matrix in which the catalyst-supporting carbon and the electrolyte are mixed. For example, platinum is used as the catalyst. An electrode reaction is performed at the interface between the catalyst and the electrolyte on the catalyst-supporting carbon, and the pair of catalyst layers function as an anode and a cathode. Then, the oxidizing gas is supplied to the oxidizing gas passage 2a of the separator on the anode side, and the fuel gas is supplied to the fuel gas passage 2b of the other separator. The fuel cell 2 generates electric power by the electrochemical reaction of the supplied fuel gas and oxidizing gas. The electrochemical reaction in the fuel cell 2 is an exothermic reaction, and the temperature of the solid polymer electrolyte fuel cell 2 is approximately 60 to 80 ° C.

  The oxidizing gas piping system 3 has a supply path 11 through which the oxidizing gas supplied to the fuel cell 2 flows, and a discharge path 12 through which the oxidizing off gas discharged from the fuel cell 2 flows. The downstream end of the supply path 11 communicates with the upstream end of the oxidizing gas flow path 2a, and the upstream end of the discharge path 12 communicates with the downstream end of the oxidizing gas flow path 2a. The oxidizing off gas is in a highly moist state because it contains moisture generated by the cell reaction of the fuel cell 2.

  The supply path 11 is provided with a compressor 14 (compressor) that takes in the oxidizing gas (outside air) via the air cleaner 13, and a humidifier 15 that humidifies the oxidizing gas pumped to the fuel cell 2 by the compressor 14. Yes. The humidifier 15 exchanges moisture between the low-humidity oxidizing gas flowing in the supply passage 11 and the high-humidity oxidizing off-gas flowing in the discharge passage 12, and appropriately supplies the oxidizing gas supplied to the fuel cell 2. Humidify.

  The back pressure of the oxidizing gas supplied to the fuel cell 2 is regulated by a pressure regulating valve 16 disposed in the discharge passage 12 near the cathode outlet. The pressure regulating valve 16 is, for example, a valve driven by a step motor, and is electrically connected to the control unit 7. The valve opening degree of the pressure regulating valve 16 is configured to be adjustable by the control unit 7 in an arbitrary range including full open, half open, and full close. The oxidizing off gas passes through the pressure regulating valve 16 and the humidifier 15 and is finally exhausted into the atmosphere outside the system as exhaust gas.

The fuel gas piping system 4 includes a hydrogen supply source 21, a supply path 22 through which hydrogen gas supplied from the hydrogen supply source 21 to the fuel cell 2 flows, and a supply path for supplying hydrogen offgas (fuel offgas) discharged from the fuel cell 2. 22, a circulation path 23 for returning to the junction point A of 22, a pump 24 that pumps the hydrogen off-gas in the circulation path 23 to the supply path 22, and a purge path 25 that is branched and connected to the circulation path 23. . The hydrogen gas flowing out from the hydrogen supply source 21 to the supply path 22 by opening the main valve 26 is supplied to the fuel cell 2 through the pressure regulating valve 27 and other pressure reducing valves and the shutoff valve 28. The purge passage 25 is provided with a purge valve 33 for discharging the hydrogen off gas to a hydrogen diluter (not shown).

  The refrigerant piping system 5 includes a refrigerant channel 41 communicating with the cooling channel 2 c in the fuel cell 2, a cooling pump 42 provided in the refrigerant channel 41, and a radiator 43 that cools the refrigerant discharged from the fuel cell 2. And a bypass passage 44 that bypasses the radiator 43, and a switching valve 45 that sets the flow of cooling water to the radiator 43 and the bypass passage 44. The cooling pump 42 circulates and supplies the refrigerant in the refrigerant channel 41 to the fuel cell 2 by driving the motor.

  The power system 6 includes a high-voltage DC / DC converter 61, a battery 62, a traction inverter 63, a traction motor 64, and various auxiliary inverters 65, 66, and 67. The high-voltage DC / DC converter 61 is a direct-current voltage converter that adjusts the direct-current voltage input from the battery 62 and outputs it to the traction inverter 63 side, and the direct-current input from the fuel cell 2 or the traction motor 64. And a function of adjusting the voltage and outputting it to the battery 62. The charge / discharge of the battery 62 is realized by these functions of the high-voltage DC / DC converter 61. Further, the output voltage of the fuel cell 2 is controlled by the high voltage DC / DC converter 61.

  The traction inverter 63 converts a direct current into a three-phase alternating current and supplies it to the traction motor 64. The traction motor 64 is, for example, a three-phase AC motor. The traction motor 64 constitutes, for example, a main power source of the vehicle 100 on which the fuel cell system 1 is mounted, and is connected to the wheels 101L and 101R of the vehicle 100. Auxiliary machine inverters 65, 66, and 67 control driving of motors 14a, 24a, and 42a of compressor 14, pump 24, and cooling pump 42, respectively.

  The control unit 7 is configured as a microcomputer including a CPU, a ROM, and a RAM inside. The CPU executes a desired calculation according to the control program and performs various processes and controls. The ROM stores control programs and control data processed by the CPU. The RAM is mainly used as various work areas for control processing.

  The control unit 7 includes a pressure sensor and a temperature sensor used in the gas system (3, 4) and the refrigerant system 5, an outside air temperature sensor that detects an outside air temperature in the environment where the fuel cell system 1 is placed, and an accelerator opening of the vehicle 100. Detection signals from various sensors such as an accelerator opening sensor that detects the degree are input, and a control signal is output to each component of the fuel cell system 1.

2. Next, self-healing control of the fuel cell system according to the embodiment of the present invention will be described. The fuel cell system 1 detects whether or not the catalyst layer of each single cell of the fuel cell 2 is peeled off from the electrolyte membrane (peeling determination), and autonomously recovers this peeling when the peeling is detected ( Self-healing control). Hereinafter, this control will be described in detail with reference to FIG. Here, FIG. 2 is a flowchart for explaining self-healing control of the fuel cell system.

As shown in FIG. 2, the self-healing control is started when the fuel cell system 1 is started below freezing (step S ₁ ). This is because separation of the catalyst layer is likely to occur when the fuel cell is used in a low-temperature environment, particularly when the fuel cell is started below the freezing point. Here, whether or not the engine is started below freezing can be determined by various temperatures such as the refrigerant temperature in the refrigerant flow path 41, the stack temperature of the fuel cell 2, and the oxidizing gas (outside air) temperature passing through the air cleaner 13.

When the sub-freezing start is performed, the control unit 7 detects the total number of sub-freezing starts of the fuel cell 2 and determines whether or not it is equal to or more than a predetermined number N ₀ (N ₀ is a natural number) ( step S _2). This is because each time the number of sub-freezing starts increases, the water contained in the catalyst layer is solidified, the volume expands and contracts due to melting of the ice, and the possibility that the catalyst layer peels as a result is repeated. Because it becomes high. The predetermined number N ₀ can be arbitrarily determined by the fuel cell system according to the durability of the catalyst layer.

When the number of starting points below freezing is less than the predetermined number N ₀ (step S ₂ : NO), the normal operation is performed (step S ₇ ) assuming that there is no possibility that the catalyst layer has peeled from the electrolyte. That is, the control unit 7 causes the fuel cell 2 to generate power under normal conditions. At this time, the control unit 7 updates the total number of sub-freezing start times and stores it in an internal storage device (for example, RAM) to prepare for the next determination. When the number of times of starting below freezing is small, the determination of peeling of the catalyst layer is not performed, so that an excessive determination can be prevented.

When the number of starting points below freezing is equal to or greater than the predetermined number N ₀ (step S ₂ : YES), the control unit 7 determines whether or not the catalyst layer is peeled from the electrolyte (step S ₃ ). This determination is that if the catalyst layer is peeled off, it becomes more susceptible to drying, that is, the current-voltage characteristic when the fuel cell 2 is generated in a dry state rather than during normal power generation is peeled off. The fact that there is a significant difference between the case where it is present and the case where it does not occur is used. Specifically, the control unit 7 controls the humidifier 15 so that the oxidizing gas supplied to the fuel cell 2 is in a lower wet state than during normal operation, and the fuel cell 2 is dried from the normal state to generate power. . And determination is performed by measuring the current-voltage characteristic of the fuel cell 2 at this time. An example is shown in FIG. Here, FIG. 3 is a schematic diagram showing current-voltage characteristics when the fuel cell is generated in a dry state. The control unit 7 stores therein a reference line F ₀ shown in FIG. 3 in advance. Then, the control unit 7 determines that the peeling does not occur when the measured current-voltage characteristic is higher than the reference line F _{0, and the} peeling occurs when the measured current-voltage characteristic is low. In FIG. 3, if the measurement result is F ₁ , no peeling occurs, and if the measurement result is F ₂ , it is determined that peeling occurs. Thereby, separation of the catalyst layer can be effectively determined including separation from the cause of deterioration (for example, oxidation) of the other catalyst layer.

Returning to FIG. 2, the description will be continued. When it is determined that no peeling has occurred (step S ₃ : NO), the operation proceeds to normal operation, and the control unit 7 causes the fuel cell 2 to generate power under normal conditions. (Step S _7). At this time, the control unit 7 updates the total number of sub-freezing start times and stores it in an internal storage device (for example, RAM) to prepare for the next determination.

If the peeling is determined to have occurred (Step S _3: YES), the control unit 7 performs the peeling recovery operation (step S _4). The peeling recovery operation is an operation in which the peeled catalyst layer is adhered to the electrolyte membrane again. Here, the electrolyte membrane and the separated catalyst layer are physically bonded by increasing the fastening load in the stacking direction of the single cells of the fuel cell 2. In the present embodiment, a hydraulic mechanism is disposed on a fastening member at the stack end of the fuel cell 2 (not shown), and the hydraulic mechanism is contracted in accordance with a command from the control unit 7 to compress the fastening member. The fastening load in the stacking direction of the battery 2 is increased.

After completion of the peeling recovery operation, the control unit 7 determines whether or not the catalyst layer is still peeled from the electrolyte (step S ₅ ). The method of determination is the same as the case of Step S _3.

When it is determined that peeling has not occurred (when peeling has been recovered) (step S ₅ : NO), the operation proceeds to normal operation, and the control unit 7 causes the fuel cell 2 to generate power under normal conditions. (Step S _7). At this time, the control unit 7 updates the total number of sub-freezing start times and stores it in an internal storage device (for example, RAM) to prepare for the next determination.

If the peeling is determined to have occurred (if peeling is still not recovered) (Step S _5: YES), the process proceeds to a high humidification operation. That is, the control unit 7 increases the operating humidity of the fuel cell than during normal power generation. Specifically, the control unit 7 controls the humidifier 15 so that the oxidizing gas supplied to the fuel cell 2 is in a higher wet state than during normal operation, and the fuel cell 2 generates power at a higher humidity than in the normal state. . Humidification amount, the current during the peeling determination - is calculated by considering whether the measured value of the voltage characteristics are deviated much from the reference line F _0.

  As described above, it is detected whether or not the catalyst layer is peeled off from the electrolyte membrane, and when there is peeling, the catalyst layer can be recovered from the peeled state again by the recovery operation. That is, the fuel cell can be self-healed. Thereby, the fall of the power generation performance of a fuel cell can be suppressed and durability can be improved. Further, even when the peeling cannot be sufficiently recovered even by the recovery operation, the desired output of the fuel cell 2 can be obtained by compensating for the deterioration of the current-voltage characteristics caused by the peeling by increasing the operating humidity. .

3. Modifications of Fuel Cell According to Embodiment of Present Invention Although the embodiment of the present invention has been described above, the present invention is not limited to this embodiment, and various aspects are within the scope not departing from the gist of the present invention. Implementation is possible. For example, the following modifications are possible.

  In the above embodiment, the catalyst layer peeling determination is performed by counting the number of times of starting below freezing. However, the present invention is not limited to this, and whether or not the peeling determination is performed is related to the catalyst layer peeling. It may be determined by one or a plurality of parameters. Thereby, since peeling determination can be performed only when the probability of peeling is high, unnecessary peeling determination can be avoided. For example, the peeling determination may be performed when the power generation performance of the fuel cell 2 in a low temperature environment is lower than a predetermined value. This is because when the power generation performance in a low temperature environment is lowered, there is a high possibility that peeling has occurred.

  Further, in the above-described embodiment, as the recovery operation, the fastening load in the stacking direction of the single cells of the fuel cell 2 is increased. However, the present invention is not limited to this. By controlling the operation condition 2, the electrolyte membrane and the separated catalyst layer may be adhered. For example, the operating temperature of the fuel cell 2 may be made higher than that during normal power generation so that the catalyst layer and the electrolyte membrane are chemically bonded to recover the catalyst layer from the peeled state.

In the above-described embodiment, if the peeling of the catalyst layer has not recovered after one peeling recovery operation (step S ₄ ) (step S ₅ : YES), a high humidification operation is performed (step S ₆ ) Although it is like this, it is not limited to this. For example, when peeling has not recovered after one peeling recovery operation, this peeling recovery operation may be repeated a plurality of times instead of immediately performing a high humidification operation. Further, another recovery operation may be attempted.

The block diagram of a fuel cell system. The flowchart for demonstrating the self-healing control of a fuel cell system. The schematic diagram which shows the current-voltage characteristic at the time of generating electric power in a dry state of a fuel cell.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Fuel cell system, 2 ... Fuel cell, 2a ... Oxidation gas flow path, 2b ... Fuel gas flow path, 2c ... Cooling flow path, 3 ... Oxidation gas piping system, 4 ... Fuel gas piping system, 5 ... Refrigerant piping system , 6 ... Electric power system, 7 ... Control unit, 11 ... Supply path, 12 ... Discharge path, 13 ... Air cleaner, 14 ... Compressor, 14a ... Motor, 15 ... Humidifier, 16 ... Pressure regulating valve, 21 ... Hydrogen supply source, 22 DESCRIPTION OF SYMBOLS Supply path, 23 ... Circulation path, 24 ... Pump, 24a ... Motor, 25 ... Purge path, 26 ... Original valve, 27 ... Pressure regulating valve, 28 ... Shut-off valve, 33 ... Purge valve, 41 ... Refrigerant flow path, 42 ... Cooling pump, 42a ... motor, 43 ... radiator, 44 ... bypass flow path, 45 ... switching valve, 61 ... high pressure DC / DC converter, 62 ... battery, 63 ... traction inverter, 64 ... traction motor, 65 ... auxiliary inverter, 66 Auxiliary inverter, 67 ... auxiliary inverter, 100 ... vehicle, 100L ... wheel, 100R ... wheel

Claims (7)

A fuel cell in which a plurality of unit cells each including a pair of catalyst layers sandwiching an electrolyte membrane are stacked; and
Determining means for determining whether or not the catalyst layer is peeled off from the electrolyte membrane;
A fuel cell system comprising: recovery means for performing a recovery operation for recovering the catalyst layer from the peeled state when it is determined that the catalyst layer is peeled from the electrolyte membrane.   The determination means measures current-voltage characteristics when the fuel cell is generated in a dry state rather than during normal power generation, and determines whether or not the catalyst layer is peeled off from the electrolyte membrane. 2. The fuel cell system according to 1.   The fuel cell system according to claim 1, wherein the recovery operation is an operation of increasing a fastening load in a stacking direction of the single cells of the fuel cell.   3. The fuel cell system according to claim 1, wherein the recovery operation is an operation of raising an operating temperature of the fuel cell higher than that during normal power generation.   The fuel cell system according to any one of claims 1 to 4, wherein the determination is performed when the number of low-temperature startups exceeds a predetermined number.   The fuel cell system according to any one of claims 1 to 4, wherein the determination is performed when the power generation performance of the fuel cell in a low temperature environment falls below a predetermined value.   The operating humidity of the fuel cell is increased from that during normal power generation when the determination means determines that the catalyst layer is still detached from the electrolyte membrane after the recovery operation. The fuel cell system described in 1.

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