JP2006128030A - Fuel cell system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To prevent a catalyst layer on a side of an oxidant electrode of a membrane electrode assembly from deteriorating by a carbon corrosion reaction without requiring an additional device when starting a system. <P>SOLUTION: A control unit 19 determines whether oxygen exists in a fuel electrode 1a side and the inside of a fuel cell stack 1 is wet when starting the system. When it is determined that oxygen exists in the fuel electrode 1a side and the inside of the fuel cell stack 1 is wet, the inside of the fuel cell stack 1 is dried before supplying the fuel gas to the fuel electrode 1b side. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a fuel cell system, and more specifically, prevents a catalyst layer on the oxidizer electrode side of a membrane electrode assembly from being deteriorated by a carbon corrosion reaction at the time of system startup without requiring an additional device such as a compressor. It is related to the technology to do.

Conventionally, a fuel having a fuel electrode and an oxidant electrode that sandwich a membrane electrode assembly (MEA), and having a fuel cell that generates electricity by receiving supply of hydrogen and air to the fuel electrode and the oxidant electrode, respectively. Battery systems are known. By the way, in general, in such a fuel cell system, when the system is stopped, air enters the fuel electrode side from the oxidant electrode side, so that air exists on both the fuel electrode side and the oxidant electrode side. It becomes a state to do. When the system is restarted in such a state and hydrogen is supplied to the fuel electrode side, the carbon carrier carrying the MEA catalyst layer on the oxidant electrode side facing the air existence region on the fuel electrode side As a result of this oxidation reaction (hereinafter referred to as carbon corrosion reaction), the catalyst layer on the oxidant electrode side of the membrane electrode assembly deteriorates. From such a background, in the conventional fuel cell system, in order to suppress the progress of the carbon corrosion reaction, when the system is started, hydrogen is supplied to the fuel electrode gas flow path in a short time of 1 second or less. Among them, the air on the fuel electrode side is discharged out of the system (for example, see Patent Document 1).
US Patent Application Publication No. 2002/0076582

  However, according to the conventional fuel cell system, the carbon corrosion reaction is not completely prevented, and in order to supply hydrogen to the fuel electrode side gas flow path in a short time, the fuel electrode side gas flow path It is necessary to provide an additional device such as a compressor in the pipe for supplying hydrogen. Further, according to the conventional fuel cell system, when hydrogen gas is supplied, if the gas pressure on the fuel electrode side and the oxidant electrode side is not adjusted, the differential pressure between the fuel electrode and the oxidant electrode increases and the MEA is damaged. There is a possibility that a malfunction will occur.

  The present invention has been made in order to solve the above-described problems, and the object of the present invention is to prevent the catalyst layer on the oxidant electrode side of the membrane electrode assembly from undergoing a carbon corrosion reaction when the system is started up without requiring an additional device. It is an object of the present invention to provide a fuel cell system that can be prevented from being deteriorated by the above.

  In the fuel cell system according to the present invention, when the system is started, oxygen is present on the fuel electrode side based on the stop operation history when the previous operation was stopped, and the fuel cell temperature and the outside air humidity history from the stop to the start. It is determined whether or not the fuel cell interior is in a wet state, oxygen is present on the fuel electrode side, and if it is determined that the fuel cell interior is in a wet state, fuel on the fuel electrode side is determined. Before supplying gas, the inside of the fuel cell is dried.

  According to the fuel cell system of the present invention, when it is determined that the inside of the fuel cell is in a wet state, the fuel gas is supplied to the fuel electrode side after the inside of the fuel cell is dried, so an additional device is required. Therefore, it is possible to prevent the catalyst layer on the oxidant electrode side of the membrane electrode assembly from deteriorating due to the carbon corrosion reaction when the system is started.

  Hereinafter, the configuration of the fuel cell system according to the first and second embodiments of the present invention will be described with reference to the drawings.

[Configuration of fuel cell system]
As shown in FIG. 1, the fuel cell system according to the first embodiment of the present invention is a fuel in which a plurality of fuel cells that generate power by supplying hydrogen and air to the fuel electrode 1 a and the oxidant electrode 1 b are stacked. A battery stack 1 is provided. In this embodiment, the fuel cell is composed of a polymer electrolyte fuel cell, and the electrochemical reaction in the fuel electrode 1a and the oxidant electrode 1b and the electrochemical reaction as the whole fuel cell are represented by the following chemical reaction formula (1 ) To (3). Although not shown, a catalyst layer mainly composed of a noble metal such as Pt is formed on the surface of the proton conductive solid electrolyte membrane sandwiched between the fuel electrode 1a and the oxidant electrode 1b in order to promote a chemical reaction. Thus, a membrane electrode assembly (MEA) is formed.

[Fuel electrode] H ₂ → 2H ⁺ + 2e ⁻ (1)
[Oxidant electrode] 1/2 O ₂ + 2H ⁺ + 2e ⁻ → H ₂ O (2)
[Overall] H ₂ +1/2 O ₂ → H ₂ O (3)
[Configuration of fuel gas system]
The fuel cell system includes a fuel tank 2 and a fuel supply amount adjustment valve 3. The fuel supply amount adjustment valve 3 adjusts the supply amount of the fuel gas and the fuel electrode 1 a of the fuel cell stack 1 through the fuel supply pipe 4. To supply fuel gas. Further, the concentration of the fuel gas discharged from the fuel electrode 1 a of the fuel cell stack 1 is reduced to a safe range and then discharged out of the system through the fuel exhaust pipe 5. The fuel supply pipe 4 includes a fuel gas flow path for supplying the fuel gas from the fuel supply amount adjusting valve 3 directly to the fuel electrode 1a, and a fuel gas humidifier 6 for supplying the fuel gas from the fuel supply amount adjusting valve 3 to the fuel electrode 1a. A switching valve 7 for switching the flow path of the fuel gas to and from the fuel gas flow path supplied to the fuel electrode 1a is provided, and the humidification / humidification of the fuel gas supplied to the fuel electrode 1a by controlling the switching valve 7 is provided. It is configured to switch between non-humidification.

[Configuration of oxidant gas system]
The fuel cell system includes a blower 8, and the blower 8 supplies an oxidant gas to the oxidant electrode 1 b of the fuel cell stack 1 through an oxidant gas supply pipe 9. Further, the oxidant gas discharged from the oxidant electrode 1 b of the fuel cell stack 1 is discharged out of the system through the oxidant gas exhaust pipe 10. The oxidant gas supply pipe 9 has an oxidant gas flow path for directly supplying the oxidant gas from the blower 8 to the oxidant electrode 1 b, and the oxidant gas from the blower 8 via the oxidant gas humidifier 11. A switching valve 12 for switching the flow path of the oxidant gas to and from the oxidant gas flow path supplied to the oxidant electrode 1b is provided, and the oxidant supplied to the oxidant electrode 1b by controlling the switching valve 12 Gas humidification / non-humidification can be switched.

  Further, the oxidant gas supply pipe 9 on the inlet side of the switching valve 12 and the fuel gas supply pipe 4 on the inlet side of the fuel electrode 1a are connected via an oxidant gas supply pipe 13 for the fuel electrode, and the oxidant for the fuel electrode. The gas supply pipe 13 is provided with a pipe valve 14 for controlling the supply amount of the oxidant gas to the fuel electrode 1b. A control valve that adjusts the supply amount of the oxidant gas from the blower 8 may be provided in the oxidant gas supply pipe 9.

[Control system configuration]
The control system in the fuel cell system includes a charge consuming unit 15 that consumes fuel gas inside the fuel cell stack 1 when the system is stopped, and a temperature sensor that detects the temperature of the MEA of the fuel cell as the temperature of the fuel cell stack 1. 16, a resistance sensor 17 that detects the AC resistance of the MEA of the fuel cell as the humidity inside the fuel cell stack 1, and an oxygen concentration that detects the humidity in the gas pipe of the fuel electrode 1a as the oxygen concentration on the fuel electrode 1a side A sensor 18 and a control unit 19 for controlling the operation of the fuel cell system are provided.

  In this embodiment, the temperature of the MEA of the fuel cell is detected as the temperature of the fuel cell stack 1, but the temperature of circulating water inside the fuel cell stack 1 may be detected as the temperature of the fuel cell stack 1. Further, the AC resistance of the MEA is detected as the humidity inside the fuel cell stack 1, but the humidity in the catalyst layer or gas pipe on the oxidant electrode 1b side of the MEA may be detected as the humidity inside the fuel cell stack 1. The control unit 19 is composed of a microprocessor having a CPU, a program ROM, a working RAM, and an input / output interface.

  In the fuel cell system having such a configuration, when the system is started, the control unit 19 executes the start control process shown below, thereby eliminating the need for an additional device such as a compressor and performing MEA by the carbon corrosion reaction. This prevents the catalyst layer on the oxidant electrode 1b side from deteriorating. Hereinafter, the operation of the control unit 19 when executing the activation control process will be described in detail with reference to the flowchart shown in FIG.

[Startup control processing]
The flowchart shown in FIG. 2 starts in response to the activation command signal being input to the control unit 19, and the activation control process proceeds to step S1.

  In the process of step S1, the control unit 19 refers to the detection results of the temperature sensor 16, the resistance sensor 17, and the oxygen concentration sensor 18 as a startup operation determination, and the temperature of the fuel cell stack 1 is equal to or higher than a predetermined temperature and the MEA It is determined whether or not the AC resistance is a predetermined value or less and the oxygen concentration on the fuel electrode 1a side is a predetermined concentration or more.

  As a result of the determination, when the temperature of the fuel cell is equal to or higher than the predetermined temperature, the AC resistance of the MEA is equal to or lower than the predetermined value, and the oxygen concentration on the fuel electrode 1a side is equal to or higher than the predetermined concentration, the control unit 19 performs the start control process. The process proceeds to step S5. On the other hand, when the temperature of the fuel cell is equal to or higher than the predetermined temperature, the AC resistance of the MEA is equal to or lower than the predetermined value, and the oxygen concentration on the fuel electrode 1a side is not equal to or higher than the predetermined concentration, the control unit 19 performs the startup control process in step S2. Proceed to

  In step 2, the control unit 19 controls the switching valve 12 to purge (dry) the oxidant electrode 1b by supplying the dried oxidant gas from the blower 8 to the oxidant electrode 1b. Further, the control unit 19 purges the fuel electrode 1a by opening the piping valve 14 and supplying the dried oxidant gas to the fuel electrode 1a side. Thereby, the process of step S2 is completed, and the activation control process proceeds from the process of step S2 to the process of step 3.

  In the process of step S3, the control unit 19 refers to the detection result of the resistance sensor 17, and determines whether or not the AC resistance of the MEA has become a predetermined value or more. As a result of the determination, the control unit 19 determines that the fuel cell stack 1 has been dried in response to the MEA AC resistance becoming a predetermined value or more, and advances the activation control process to the process of step S4. Note that the control unit 19 calculates in advance the time during which the MEA has a predetermined AC resistance by experiment, and advances the activation control process to the process of step S4 as the calculated time elapses. Good.

  In the process of step S4, the control unit 19 stops the supply of the oxidant gas to the fuel electrode 1a by closing the piping valve 14. Thereby, the process of step S4 is completed, and the activation control process proceeds from the process of step S4 to the process of step S5.

  In the process of step S5, the control unit 19 controls the switching valve 7 to supply the dried fuel gas to the fuel electrode 1a. In this process, it is preferable that the control unit 19 puts the charge consuming unit 15 into an operating state and consumes the fuel gas. Thereby, the process of this step S5 is completed and a series of starting control processes are complete | finished.

  In general, as shown in FIG. 3A, the system is started in a state where air exists in both the fuel electrode side gas flow path 1c and the oxidant electrode side gas flow path 1d, and hydrogen is supplied to the fuel electrode 1a side. In such a case, the fuel cell system temporarily enters a state as shown in FIG. That is, in the region where hydrogen is supplied to the fuel electrode 1a, a reaction similar to that in the normal operation state occurs, and a potential of about 1 [V] is generated on the oxidant electrode 1b side.

  On the other hand, at the oxidant electrode 1b facing the air existing region on the fuel electrode 1a side with the interface (hereinafter referred to as hydrogen front) F between the hydrogen and air on the fuel electrode 1a side, the chemical reaction formula ( The carbon corrosion reaction of 4) occurs. At this time, in the region where the air on the fuel electrode 1a side exists, water is generated by the carbon corrosion reaction of the chemical reaction formula (5) shown below. Therefore, in the state shown in FIG. 3B, the oxidation reaction of the carbon support carrying the MEA catalyst layer occurs, so that the catalyst layer 1f on the oxidant electrode 1b side is deteriorated and the fuel cell performance is lowered. Such problems may occur.

[Carbon corrosion reaction] C + 2H ₂ O → CO ₂ + 4H ⁺ + 4e ⁻ (4)
[Fuel electrode side reaction] O ₂ + 4H ⁺ + 4e ⁻ → 2H ₂ O (5)
Thus, as a result of intensive research, the inventors of the present invention have come to the knowledge that the carbon corrosion reaction caused by the hydrogen front F is suppressed as the water content inside the fuel cell is lower. More specifically, the inventor introduced hydrogen into the fuel electrode from a state where both the fuel electrode side and the oxidant electrode side were replaced with air, and measured the amount of carbon dioxide discharged at that time with a gas analyzer. As a result, as shown in FIG. 4, the resistance (cell resistance) of the fuel cell increases immediately before hydrogen (anode gas) is introduced into the fuel electrode. It was found that the amount of carbon emissions, that is, the amount of carbon corrosion was small. And the inventor came up with the above-mentioned fuel cell system based on such knowledge.

  As is apparent from the above description, in the fuel cell system according to the first embodiment of the present invention, when the system is started, the control unit 19 has oxygen on the fuel electrode 1a side, and the fuel cell stack. 1 is determined whether or not the inside is in a wet state, and when it is determined that oxygen is present on the fuel electrode 1a side and the inside of the fuel cell stack 1 is in a wet state, fuel gas is supplied to the fuel electrode 1a side. Before supplying, the inside of the fuel cell stack 1 is dried.

  According to such a configuration, when it is determined that the inside of the fuel cell stack 1 is wet, the fuel gas is supplied to the fuel electrode 1a after the inside of the fuel cell stack 1 is dried. Without requiring an additional device, it is possible to suppress deterioration of the catalyst layer on the oxidant electrode 1b side of the MEA due to the carbon corrosion reaction when the system is started.

  Further, according to such a configuration, when the stop time of the fuel cell system is extremely short and oxygen is not mixed in the fuel electrode 1a side, or when the stop time is long and the inside of the fuel cell stack 1 is in a dry state. In some cases, the control unit 19 does not perform an operation of drying the inside of the fuel cell stack 1, and therefore can perform an appropriate startup process without waste.

  Note that when the detected values of the temperature sensor 16 and the resistance sensor 17 are equal to or greater than a predetermined value, the control unit 19 determines whether oxygen is present on the fuel electrode 1a side based on the stop operation history when the previous operation was stopped. If it is determined that oxygen is present on the fuel electrode 1a side, the inside of the fuel cell stack 1 may be dried before supplying the fuel gas to the fuel electrode 1a side. According to such a configuration, the time and means of the drying operation can be accurately and sufficiently performed, and therefore, deterioration of the catalyst layer on the oxidant electrode 1b side of the MEA can be more effectively suppressed.

  In addition, when the detected values of the temperature sensor 16, the resistance sensor 17, and the oxygen concentration sensor 18 are equal to or greater than a predetermined value, the control unit 19 dries the inside of the fuel cell stack 1 before supplying the fuel gas to the fuel electrode 1a side. You may let them. According to such a configuration, since it is possible to accurately determine whether or not to perform the activation operation, it is possible to perform an appropriate activation operation without waste.

  As shown in FIG. 5, in the fuel cell system according to the second embodiment of the present invention, in addition to the configuration of the fuel cell system according to the first embodiment, circulation for supplying circulating water to the fuel cell stack 1 is performed. A water supply pipe 21, a circulating water heating unit 22 for heating the circulating water, and an oxidant gas heating unit 23 for heating the oxidant gas are provided. In this fuel cell system, the control unit 19 supplies the oxidant gas that has been dried and heated by the oxidant gas heating unit 23 to the fuel electrode 1a and the oxidant electrode 1b in the process of step S2. At the same time, the circulating water heated by the circulating water heating unit 22 is supplied to the fuel cell stack 1 via the circulating water supply pipe 21. According to such a configuration, the inside of the fuel cell stack 1, in particular, the catalyst layer on the oxidant electrode 1b side can be dried in a shorter time, so that the fuel cell is not deteriorated at the time of startup, and in a shorter time. A startable fuel cell system can be realized.

  As mentioned above, although the embodiment to which the invention made by the present inventor is applied has been described, the present invention is not limited by the description and the drawings that form part of the disclosure of the present invention according to this embodiment. That is, it should be added that other embodiments, examples, operation techniques, and the like made by those skilled in the art based on the above embodiments are all included in the scope of the present invention.

1 is a schematic diagram showing a configuration of a fuel cell system according to a first embodiment of the present invention. It is a flowchart figure which shows the flow of the starting control process used as one Embodiment of this invention. It is a section lineblock diagram of a fuel cell for explaining composition of a conventional fuel cell system. It is a graph which shows the relationship between the cathode carbon dioxide discharge | emission amount after gas substitution, and the cell resistance just before gas substitution. It is a schematic diagram which shows the structure of the fuel cell system used as the 2nd Embodiment of this invention.

Explanation of symbols

1: Fuel cell stack 1a: Fuel electrode 1b: Oxidant electrode 2: Fuel tank 3: Fuel supply amount adjustment valve 4: Fuel supply pipe 5: Fuel exhaust pipe 6: Fuel gas humidifier 7, 12: Switching valve 8: Blower 9: Oxidant gas supply pipe 10: Oxidant gas exhaust pipe 11: Oxidant gas humidifier 13: Oxidant gas supply pipe for fuel electrode 14: Pipe valve 15: Charge consuming part 16: Temperature sensor 17: Resistance sensor 18: Oxygen concentration sensor 19: Control unit

Claims (8)

A fuel cell system having a fuel electrode and an oxidant electrode that sandwich a membrane electrode assembly, and comprising a fuel cell that generates power by receiving supply of hydrogen and air to the fuel electrode and the oxidant electrode, respectively,
Oxygen is present on the fuel electrode side on the basis of the stop operation history when the system was started, the stop operation history when the previous operation was stopped, and the fuel cell temperature and outside air humidity history from the stop to the restart, and the fuel cell It is determined whether or not the inside is in a wet state. If it is determined that oxygen is present on the fuel electrode side and the inside of the fuel cell is in a wet state, the fuel is supplied before supplying fuel gas to the fuel electrode side. A fuel cell system comprising a control unit for drying the inside of the battery. The fuel cell system according to claim 1,
A temperature detector for detecting the temperature of the fuel cell;
A humidity detector for detecting the humidity inside the fuel cell;
The control unit determines whether oxygen is present on the fuel electrode side based on a stop operation history when the previous operation was stopped when detection values of the temperature detection unit and the humidity detection unit are equal to or greater than a predetermined value. And when it is determined that oxygen is present in the fuel electrode, the inside of the fuel cell is dried before the fuel gas is supplied to the fuel electrode side. The fuel cell system according to claim 2, wherein
An oxygen concentration detector for detecting the oxygen concentration on the fuel electrode side;
When the detection values of the temperature detection unit, the humidity detection unit, and the oxygen concentration detection unit are equal to or greater than a predetermined value, the control unit dries the inside of the fuel cell before supplying the fuel gas to the fuel electrode side. A fuel cell system. The fuel cell system according to claim 2 or 3, wherein
The said humidity detection part detects the humidity inside the catalyst layer of the oxidant electrode side of the said membrane electrode assembly as humidity inside the said fuel cell, The fuel cell system characterized by the above-mentioned. The fuel cell system according to claim 2 or 3, wherein
The said humidity detection part detects the alternating current resistance of the said membrane electrode assembly as humidity inside the said fuel cell, The fuel cell system characterized by the above-mentioned. The fuel cell system according to any one of claims 1 to 5, wherein
The control unit dries the inside of the fuel cell by supplying a dried oxidant gas from at least one of the fuel electrode side and the oxidant electrode side. The fuel cell system according to claim 6,
The control unit heats and supplies the dried oxidant gas to at least one of the fuel electrode side and the oxidant electrode side. The fuel cell system according to any one of claims 1 to 7,
The fuel cell system, wherein the control unit dries the inside of the fuel cell by increasing the temperature of the fuel cell.

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