JP5794179B2 - Fuel cell system and fuel cell control method - Google Patents

Description

  The present invention relates to a fuel cell, and more particularly to control of an aging operation (break-in operation) of a fuel cell.

  An aging operation (break-in operation) is usually performed in order to increase all the mass transfer of the polymer membrane and the catalyst layer in the fuel cell. On the other hand, as a known technique, a technique for performing aging operation corresponding to a gas utilization rate of 100% to cause flooding is known (Patent Document 1).

JP 2003-217622 A

  However, when the gas utilization rate is increased, a part of the membrane / electrode assembly that is partially deficient in hydrogen or oxygen is generated, which may cause deterioration of the membrane / electrode assembly.

  The present invention has been made to solve at least a part of the above-described problems, and is an aging operation for obtaining the maximum power generation performance of the membrane electrode assembly without deteriorating the membrane electrode assembly. The purpose is to do.

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. According to one aspect of the present invention, a fuel cell system is provided. The fuel cell system includes a fuel cell having an electrolyte membrane and electrodes disposed on both sides of the electrolyte membrane, a fuel gas supply unit that supplies fuel gas to the fuel cell, and an oxidizing gas to the fuel cell. Corresponding to the cell temperature of the fuel cell, an oxidizing gas supply unit for supplying, a refrigerant supplying unit for supplying refrigerant to the fuel cell, a back pressure adjusting unit for adjusting a back pressure of at least one of the fuel gas and oxidizing gas A thermometer that detects the temperature of the fuel cell, and a controller that controls the operation of the fuel cell. The control unit controls at least one of the refrigerant supply unit and the back pressure adjustment unit so that the cell temperature is equal to or lower than a dew point in the fuel cell during the aging operation of the fuel cell. According to this embodiment, the fuel cell is controlled so that the cell temperature becomes a temperature equal to or lower than the dew point in the fuel cell during the aging operation, so that water vapor around the electrode aggregates and wets the membrane electrode assembly. it can. As a result, the maximum power generation performance of the membrane electrode assembly can be obtained without deteriorating the membrane electrode assembly.

[Application Example 1]
A fuel cell system, comprising a fuel cell having an electrolyte membrane and electrodes disposed on both sides of the electrolyte membrane, a fuel gas supply unit for supplying fuel gas to the fuel cell, and an oxidizing gas for the fuel cell An oxidant gas supply unit that supplies a refrigerant, a refrigerant supply unit that supplies a refrigerant to the fuel cell, a back pressure adjustment unit that adjusts a back pressure of at least one of the fuel gas oxidant gas, and a cell temperature of the fuel cell A thermometer that detects the temperature of the fuel cell, and a control unit that controls the operation of the fuel cell, the control unit during the aging operation of the fuel cell, the flow rate of the cell temperature, the fuel gas or the oxidizing gas The fuel cell system is characterized in that at least one of the back pressure and the current density of the fuel cell is controlled so that water inside the fuel cell exists as a liquid phase.
According to this application example, in the fuel cell, water vapor around the electrode aggregates during the aging operation, and the membrane electrode assembly can be wetted. As a result, the maximum power generation performance of the membrane electrode assembly can be obtained without deteriorating the membrane electrode assembly.

[Application Example 2]
The fuel cell system according to Application Example 1, wherein the control unit controls the refrigerant supply unit so that a cell temperature of the fuel cell becomes a temperature of 60 ° C. or less during an aging operation of the fuel cell. Battery system.
The temperature of the refrigerant during the aging operation is preferably 60 ° C. or less. Since the saturated water vapor pressure is smaller as the temperature is lower, the membrane electrode assembly can be wetted more by cooling the fuel cell. In addition, the temperature of the refrigerant during the aging operation is more preferably 20 ° C. or higher and 60 ° C. or lower. Here, the reason why the temperature is set to 20 ° C. or higher is that the temperature of 20 ° C. or lower is lower than the normal temperature and a cooling mechanism for cooling to 20 ° C. or lower is required.

[Application Example 3]
A method for controlling a fuel cell, wherein at least one of the cell temperature, the flow rate of the fuel gas or the oxidizing gas, the back pressure, and the current density of the fuel cell is controlled during the aging operation of the fuel cell. Then, the fuel cell control method is characterized in that water inside the fuel cell exists as a liquid phase.

  It should be noted that the present invention can be realized in various forms, for example, in the form of a fuel cell control method, a moving body, etc. in addition to a fuel cell system.

It is explanatory drawing which shows the structure of the fuel cell which concerns on embodiment of this invention. It is explanatory drawing which shows the structure of an electric power generation unit typically. It is explanatory drawing which expands and shows typically the membrane electrode assembly vicinity before and behind an aging driving | operation. It is a graph which shows the relationship between the cell temperature in an aging driving | operation, and the electric power generation characteristic after an aging driving | operation.

A. Embodiment:
FIG. 1 is an explanatory diagram showing a configuration of a fuel cell according to an embodiment of the present invention. The fuel cell system 20 includes a fuel cell 10, a fuel tank 300, an air pump 400, a cooling water pump 500, a load 600, and a control unit 700. The fuel cell 10 includes a fuel cell stack 100, current collector plates 200 and 201, insulating plates 210 and 211, end plates 230 and 231, a tension rod 240, and a nut 250.

  The fuel cell stack 100 includes a plurality of power generation units 110. Each power generation unit 110 is a single cell. The power generation units 110 are stacked and connected in series, and generate a high voltage as the fuel cell stack 100. The current collector plates 200 and 201 are arranged on both sides of the fuel cell stack 100 and are used to supply the load 600 with the voltage and current generated by the fuel cell stack 100. The load 600 includes additional devices such as a motor of a fuel cell vehicle and an air conditioner. The insulating plates 210 and 211 are disposed further outside the current collecting plates 200 and 201, respectively, and between the current collecting plates 200 and 201 and other members such as the end plates 230 and 231 and the tension rod 240. Insulate so that no current flows. End plates 230 and 231 are disposed on the outer sides of the insulating plates 210 and 211, respectively. The end plate 231 is disposed at a predetermined distance from the end plate 230 by the tension rod 240 and the nut 250.

  The fuel tank 300 is connected to the fuel cell 10 by a fuel gas supply pipe 310. The fuel gas supply pipe 310 is provided with a valve 320 for adjusting the flow rate of the fuel gas. A fuel gas exhaust pipe 330 is connected to the downstream side of the fuel cell 10, and a fuel gas exhaust valve 340 and a pressure gauge 350 are arranged in the fuel gas exhaust pipe 330. The fuel gas exhaust valve 340 adjusts the back pressure of the fuel exhaust gas. The fuel gas exhaust pipe 330 is connected to the fuel gas supply pipe 310 by a fuel gas recovery pipe 360. The fuel gas recovery pipe 360 is provided with a pump 370 for sending the fuel exhaust gas to the fuel gas supply pipe 310.

  The air pump 400 is connected to the fuel cell 10 through an oxidizing gas supply pipe 410. The oxidizing gas supply pipe 410 is provided with a valve 420 for adjusting the flow rate of the oxidizing gas. An oxidizing gas exhaust pipe 430 is connected to the downstream side of the fuel cell 10, and an oxidizing gas exhaust valve 440 and a pressure gauge 450 are arranged in the oxidizing gas exhaust pipe 430. The oxidizing gas exhaust valve 440 adjusts the back pressure of the oxidizing exhaust gas.

  The cooling water pump 500 is connected to the fuel cell 10 by a cooling water pipe 510. The cooling water pipe 510 is provided with a radiator 520 and a thermometer 530. The radiator 520 cools the cooling water discharged from the fuel cell 10. The thermometer 530 measures the temperature of the cooling water discharged from the fuel cell 10.

  The control unit 700 opens and closes the valves 320 and 420, the fuel gas exhaust valve 340, and the oxidizing gas exhaust valve 440 based on the power generation amount of the fuel cell 10, the power consumption in the load 600, the temperature of the fuel cell 10, and the back pressure. The opening degree is controlled, and the operation of the fuel cell 10 is controlled.

  FIG. 2 is an explanatory diagram schematically showing the configuration of the power generation unit 110. The power generation unit 110 includes a membrane electrode assembly 120, gas diffusion layers 132 and 133, porous body gas channels 142 and 143, separator plates 152 and 153, and a seal gasket 160. The membrane electrode assembly 120 includes an electrolyte membrane 121 and catalyst layers 122 and 123.

  In the present embodiment, as the electrolyte membrane 121, for example, a proton conductive ion exchange membrane made of a fluorine resin such as perfluorocarbon sulfonic acid polymer or a hydrocarbon resin is used. The catalyst layers 122 and 123 are formed on each surface of the electrolyte membrane 121, respectively. In the present embodiment, the catalyst layers 122 and 123 are formed of, for example, a platinum catalyst or catalyst-carrying particles (for example, carbon particles) that carry a platinum alloy catalyst made of platinum and another metal and an electrolyte (ionomer). .

  The gas diffusion layers 132 and 133 are disposed on the outer surfaces of the catalyst layers 122 and 123, respectively. In this embodiment, as the gas diffusion layers 132 and 133, carbon cloth or carbon paper using a carbon nonwoven fabric can be used. The porous gas channels 142 and 143 are disposed on the outer surfaces of the gas diffusion layers 132 and 133, respectively. Separator plates 152 and 153 are disposed on the outer surfaces of porous gas flow paths 142 and 143, respectively. A cooling water channel 155 is formed between the separator plate 152 and the separator plate 153 of the adjacent power generation unit 110. The seal gasket 160 is formed so as to surround the outer edges of the membrane electrode assembly 120, the gas diffusion layers 132 and 133, and the porous body gas flow paths 142 and 143. The seal gasket 160 is formed integrally with the membrane electrode assembly 120 by, for example, injection molding. Thereafter, gas diffusion layers 132 and 133 and porous body gas flow paths 142 and 143 are sequentially disposed on both surfaces of the membrane electrode assembly 120.

  FIG. 3 is an explanatory diagram schematically showing an enlarged view of the vicinity of the membrane electrode assembly before and after aging. In FIG. 3, the electrolyte membrane 121 and the catalyst layer 122 are illustrated. The catalyst layer 122 includes carbon particles 122C carrying a platinum catalyst 122Pt and an electrolyte solution 122IS. These elements are exaggerated for convenience of illustration. The electrolyte solution 122IS contains water and perfluorocarbon sulfonic acid ionomer.

  In the process of assembling the fuel cell 10, catalyst ink for forming the catalyst layer 122 is applied to the electrolyte membrane 121. The catalyst ink is a solution in which an electrolyte (perfluorocarbon sulfonic acid ionomer) and carbon particles 122C carrying a platinum catalyst 122Pt are suspended in a solvent (water and ethanol). Since the catalyst ink contains an excess solvent (ethanol or water), it is dried after the application of the catalyst ink. Thereafter, the fuel cell 10 is assembled. Immediately after the fuel cell 10 is assembled, the electrolyte solution 122IS in the catalyst layer 122 has a low moisture content and a low mobility such as protons. Therefore, after assembly, the aging operation (break-in operation) of the fuel cell 10 is performed. When the aging operation is performed, the mobility of protons and the like increases, and the output voltage of the fuel cell 10 can be increased.

B. Example:
B-1. Production of membrane electrode assembly:
A catalyst ink containing an electrode catalyst containing Pt and an electrolyte having proton conductivity was applied to a perfluoro-based electrolyte membrane (Dafon Nafion membrane (Nafion is a registered trademark)) using a spray, and an anode electrode A cathode electrode was formed. Next, a diffusion layer made of carbon paper was thermocompression bonded to both electrodes to produce a membrane electrode assembly.

B-2. Example 1:
The temperature of the fabricated membrane electrode assembly (hereinafter referred to as “cell temperature”) is 40 ° C., the dew points of the anode gas (hydrogen) and cathode gas (air) are both 0 ° C., and the stoichiometric ratio of the reaction gas is anode gas / An aging operation was performed in which power generation in which a current of 1.0 A / cm ² was passed under conditions of cathode gas = 1.2 / 1.5 and back pressure of 1 atm was continued for 15 minutes. Note that the stoichiometric ratio means a ratio of an actual gas flow rate to a gas flow rate necessary for flowing a certain current. In Example 1, the flow rate of the anode gas is a gas flow rate that is 1.2 times the amount of gas required to flow a current of 1.0 A / cm ² , and the flow rate of the cathode gas is 1.0 A / cm. ^This is 1.5 times the gas flow rate required to pass a current of ² .

B-3. Example 2:
Current is 1.0 A at a cell temperature of 50 ° C., a dew point of anode gas and cathode gas of 0 ° C., a stoichiometric ratio of reaction gas of anode gas / cathode gas = 1.2 / 1.5, and a back pressure of 1 atm. Aging operation was performed in which power generation at a current of / cm ² was continued for 15 minutes.

B-4. Example 3:
Current is 1.0 A at a cell temperature of 60 ° C., a dew point of anode gas and cathode gas of 0 ° C., a stoichiometric ratio of reaction gas of anode gas / cathode gas = 1.2 / 1.5, and a back pressure of 1 atm. Aging operation was performed in which power generation at a current of / cm ² was continued for 15 minutes. The power generation characteristics were evaluated under the above conditions.

B-5. Aging operation of Comparative Example 1 (conventional):
In Comparative Example 1, the cell temperature was 80 ° C., the dew point of the anode gas was 80 ° C., the dew point of the cathode gas was 80 ° C., and the stoichiometric ratio of the anode gas and the cathode gas was 5 or more. And the aging operation | movement which continues the electric power generation which supplies the electric current of 1.0 A / cm < ² > electric current on the conditions of 1 atmosphere of back pressure for 3 hours was implemented.

B-6. Comparative Example 2:
Current is 1.0 A at a cell temperature of 70 ° C., a dew point of anode gas and cathode gas of 0 ° C., a stoichiometric ratio of reaction gas of anode gas / cathode gas = 1.2 / 1.5, and a back pressure of 1 atm. Aging operation was performed in which power generation at a current of / cm ² was continued for 15 minutes.

B-7. Humidity:
The humidity of the catalyst layer 122 of Examples 1 to 3 and Comparative Example 2 was calculated as follows. First, the amount of generated water was calculated from the power generation amount in the aging operation. Since the temperature of the catalyst layer 122 is increased by an electrochemical reaction, the saturated water vapor amount at each temperature (cell temperature + 5 ° C.) was calculated assuming that the temperature increase was 5 ° C. The relative humidity was calculated from the amount of produced water and the amount of saturated water vapor. In Example 1 (cell temperature 40 ° C.), relative humidity 355.5%, in Example 2 (cell temperature 50 ° C.), relative humidity 216.8%, and in Example 3 (cell temperature 60 ° C.), relative humidity 136. In 2% and Comparative Example 2 (cell temperature 70 ° C.), the relative humidity was 88.3%. The humidity value is a calculated value. When the humidity is 100% or more, the excess water vapor becomes water droplets. Therefore, in Examples 1 to 3, it is determined that liquid phase water is generated. When the cell temperature at which the relative humidity was 100% was determined from the relationship between the cell temperature and the humidity, it was 67.5 ° C.

B-8. Power generation characteristics evaluation:
A membrane electrode assembly under the conditions of a cell temperature of 70 ° C., an anode gas dew point of 45 ° C., a cathode gas dew point of 55 ° C. and a reaction gas stoichiometric ratio of anode gas / cathode gas = 1.2 / 1.5 current density was measured voltages of the membrane electrode assembly when the ^{0.2A / cm 2, 0.5A / cm} 2. The measured voltage in Comparative Example 1 was used as a reference value, and in Examples 1 to 3 and Comparative Example 2, it was determined how much the voltage changed (increased) with respect to this voltage. The cell temperature is assumed to be equal to the temperature of the cooling water discharged from the fuel cell 10 (refrigerant outlet temperature), and the cooling water discharge temperature is set to 70 ° C. by controlling the cooling water temperature and flow rate. Controlled to be.

B-9. Power generation characteristics:
FIG. 4 is a graph showing the relationship between the cell temperature in the aging operation and the power generation characteristics after the aging operation. Here, the vertical axis represents the amount of change in voltage with respect to the voltage of the power generation characteristics after the aging operation of Comparative Example 1. In Example 1, the amount of change in the voltage of the membrane electrode assembly at a current density of ^{0.2A / cm 2, 0.5A / cm} 2 , respectively, 3.3 MV, was 10.9m V. Similarly, in Example 2, respectively, 3.1MV, a 8.5 m V, in Example 3, respectively, 3.8MV, was 7.1 m V. In Comparative Example 2, there was no change in voltage and power generation characteristics after the aging operation of Comparative Example 1.

  From the above results, it can be seen that the lower the cell temperature in the aging operation, the better the power generation characteristics after the aging operation. Further, the voltage increased in Examples 1 to 3 in which the relative humidity exceeded 100%, and the voltage did not change in the comparative example in which the relative humidity did not exceed 100%. Therefore, the relative humidity of the catalyst layer exceeded 100%. Then, it is considered that the membrane electrode assembly 120 is wetted and the effect of increasing the voltage appears. That is, the cell temperature at the time of aging operation should just be the temperature (dew point) where relative humidity exceeds 100%, and it can be said that lower temperature (60 degreeC, 50 degreeC, 40 degreeC) is so preferable. The cell temperature may be lower than 20 ° C. In this case, since it is lower than normal temperature, it can be cooled by a separately provided cooling mechanism. If cell temperature is 20 degreeC, it can cool, without providing a separate cooling mechanism. In this embodiment, since an aging operation corresponding to a gas utilization rate of 100% is not performed, a portion in which the membrane / electrode assembly is partially deficient in hydrogen or oxygen is generated, and the membrane / electrode assembly 120 is hardly deteriorated.

  In the present embodiment, the cell temperature during the aging operation is changed, but the back pressure of both or one of the anode gas and the cathode gas of the fuel cell stack may be increased. Increasing the back pressure also increases the water vapor partial pressure in the fuel cell stack. On the other hand, saturated water vapor pressure is determined only by temperature, and is not related to back pressure. That is, if the back pressure increases, the water vapor partial pressure also increases and the relative humidity increases. Therefore, by increasing the back pressure, the relative humidity of the gas in the fuel cell stack can exceed 100%, and water vapor can be condensed. Thus, in addition to lowering the cell temperature during aging operation, the back pressure during aging operation may be increased.

  The time when the aging operation is performed is, for example, the shipping time of the fuel cell 10. However, it is not limited to the shipping time, and when the fuel cell 10 is started, the aging operation may be performed every time, or when the fuel cell 10 is started after a certain period of time has elapsed since the previous stop of the fuel cell 10. Aging operation may be performed. Note that when the fuel cell 10 is restarted, the temperature of the fuel cell 10 and the cooling water is normal temperature (5 ° C. to 35 ° C.), and thus is lower than the cooling water temperature 40 ° C. of the third embodiment. Therefore, even if the temperature of the fuel cell 10 rises due to an electrochemical reaction during the aging operation, it is considered that the temperature lower than the dew point is sufficiently satisfied.

  The end of the aging operation can be determined by time using a timer, for example. In this embodiment, the aging operation time is 15 minutes, but the aging time may be determined by experiment using an actual fuel cell. When the aging operation is performed when the fuel cell 10 is started, the aging operation time may be changed depending on the elapsed time from the previous stop of the fuel cell 10.

  In the above embodiment, the temperature of the combustion cell 10 is measured using the temperature of the cooling water discharged from the fuel cell 10. However, the fuel cell 10 is provided with a thermometer in the power generation unit 110 or the like of the fuel cell 10. You may measure the temperature.

  The embodiments of the present invention have been described above based on some examples. However, the above-described embodiments of the present invention are for facilitating the understanding of the present invention and limit the present invention. It is not a thing. The present invention can be changed and improved without departing from the spirit and scope of the claims, and it is needless to say that the present invention includes equivalents thereof.

DESCRIPTION OF SYMBOLS 10 ... Fuel cell 20 ... Fuel cell system 100 ... Fuel cell stack 110 ... Power generation unit 120 ... Membrane electrode assembly 121 ... Electrolyte membrane 122, 123 ... Catalyst layer 122C ... Carbon particle 122IS ... Electrolyte solution 122Pt ... Platinum catalyst 132, 133 ... Gas diffusion layer 142, 143 ... Porous gas channel 152, 153 ... Separator plate 155 ... Cooling water channel 160 ... Seal gasket 200, 201 ... Current collector plate 210, 211 ... Insulating plate 230, 231 ... End plate 240 ... Tension rod 250 ... Nut 300 ... Fuel tank 310 ... Fuel gas supply pipe 320 ... Valve 330 ... Fuel gas exhaust pipe 340 ... Fuel gas exhaust valve 350 ... Pressure gauge 360 ... Fuel gas recovery pipe 370 ... Pump 400 ... Air pump 410 ... Oxidation gas supply pipe 420 ... Bed 430 ... ... oxidizing gas oxidizing gas exhaust pipe 440 exhaust valves 450 ... pressure gauge 500 ... cooling water pump 510 ... cooling water pipe 520 ... Radiator 530 ... thermometer 600 ... load 700 ... control unit

Claims (3)

A fuel cell system,
A fuel cell having an electrolyte membrane and electrodes disposed on both sides of the electrolyte membrane;
A fuel gas supply unit for supplying fuel gas to the fuel cell;
An oxidizing gas supply unit for supplying an oxidizing gas to the fuel cell;
A refrigerant supply unit for supplying a refrigerant to the fuel cell;
A back pressure adjusting unit for adjusting a back pressure of at least one of the fuel gas and the oxidizing gas;
A thermometer for detecting a temperature corresponding to a cell temperature of the fuel cell;
A control unit for controlling the operation of the fuel cell;
With
The control unit controls at least one of the refrigerant supply unit and the back pressure adjustment unit so that the cell temperature is equal to or lower than a dew point in the fuel cell during the aging operation of the fuel cell. system. The fuel cell system according to claim 1, wherein
The control unit controls the refrigerant supply unit so that a cell temperature of the fuel cell is equal to or lower than the dew point temperature and is equal to or higher than 20 ° C. and lower than 50 ° C. during the aging operation of the fuel cell. , Fuel cell system. A fuel cell control method comprising:
A method for controlling a fuel cell, comprising: controlling at least one of the refrigerant supply unit and the back pressure adjusting unit so that the cell temperature is equal to or lower than a dew point in the fuel cell during the aging operation of the fuel cell.

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