JP2005276552A - Operation method of fuel cell - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To control corrosion of a fuel cell component material which may be occurred when scavenging an anode side electrode with air at the time of shutdown. <P>SOLUTION: After shut down time t0 when an ignition switch generates an OFF signal, the air is supplied to the anode-side electrode to start scavenging after time t2 when the maximum value of a cell voltage becomes below a threshold voltage (voltage at which the corrosion of a fuel cell constituent member is suppressed). <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  According to the present invention, an electrolyte / electrode structure in which an anode side electrode and a cathode side electrode are provided on both sides of an electrolyte is sandwiched and held between a pair of separators, and a fuel gas flow is interposed between the anode side electrodes and the separators. The present invention relates to a method of operating a fuel cell in which an oxidant gas flow path is formed between the cathode side electrode and the separator while power is generated by a reaction between fuel gas and oxidant gas.

  For example, in a polymer electrolyte fuel cell, an electrolyte membrane / electrode structure in which an anode side electrode and a cathode side electrode are arranged on both sides of an electrolyte membrane made of a polymer ion exchange membrane is held by a separator. This fuel cell is usually used as a fuel cell stack by laminating a predetermined number of electrolyte membrane / electrode structures and separators.

  In a fuel cell, a fuel gas, for example, a hydrogen-containing gas, supplied to an anode side electrode via a fuel gas channel is hydrogen ionized on an electrode catalyst and is appropriately humidified to an anode side electrode via an electrolyte membrane. The electrons generated during the movement are taken out to an external circuit and used as direct current electric energy. Since the oxidant gas, for example, oxygen-containing gas such as air, is supplied to the cathode side electrode through the oxidant gas flow path, hydrogen ions, electrons and oxygen gas react at the cathode side electrode. Water is generated.

  By the way, in such a fuel cell system, in order to ensure startability of the fuel cell, when the power generation of the fuel cell is stopped or started, normal oxidant gas is used for the cathode side electrode and fuel gas is used for the anode side electrode. Instead, a so-called anode-side oxidant gas scavenging technique has been proposed in which oxidant gas is circulated to remove water generated by power generation accumulated in the electrolyte membrane / electrode structure and separator in the fuel cell (Patent Document). 1, see Patent Document 2).

JP-A-8-241726 (FIG. 3) Japanese Patent Laying-Open No. 2003-331893 (FIG. 4)

  However, in the fuel cell system according to Patent Documents 1 and 2 described above, at the moment of scavenging start by the oxidant gas when the power generation of the fuel cell is stopped, the oxidant gas is mixed in the fuel gas at the anode side electrode, On the inlet side of the scavenging gas of the electrolyte membrane / electrode structure, oxidant gas is present on both electrode sides, so that it becomes 0 [V], but on the outlet side of the scavenging gas, the anode electrode side is before the exhaust. Since the fuel gas remains, a certain voltage is generated. Eventually, a potential difference corresponding to the certain voltage is generated between the scavenging gas inlet side and the outlet side of the electrolyte membrane / electrode structure. Similarly, at the moment of supplying the fuel gas at the time of starting, a potential difference is generated due to the fuel gas mixed in the oxidant gas. The flow of electrons formed by the potential difference generated when power generation is stopped and started (using a constant voltage generated at one end of the electrolyte membrane / electrode structure as a battery, the electrons are on the negative electrode side of this battery → one separator → 0 [V] is the other end side of the electrolyte membrane / electrode structure → the other separator → the loop leading to the positive electrode side of the battery) is the electrolyte membrane / electrode structure, electrode catalyst, separator, etc. in the fuel cell. The problem of corroding the fuel cell constituent material arises.

  The present invention solves this type of problem, and prevents or suppresses corrosion of fuel cell constituent materials caused by mixing of fuel gas and oxidant gas at the time of stopping and starting power generation of the fuel cell. It is an object of the present invention to provide a method of operating a fuel cell that enables the above.

  In this section, for ease of understanding, reference numerals in the attached drawings are used for explanation. Therefore, the contents described in this section should not be construed as being limited to those having the reference numerals.

  According to the fuel cell operating method of the present invention, an electrolyte / electrode structure in which an anode side electrode and a cathode side electrode are provided on both sides of an electrolyte is sandwiched and held by a pair of separators, and the anode side electrode and the separator And a power generation cell in which an oxidant gas flow path is formed between the cathode side electrode and the separator, and generates power by reaction of the fuel gas and the oxidant gas. Cell voltage determination for determining whether or not the cell voltage of the power generation cell is equal to or lower than a threshold voltage when an operation stop signal is detected during operation (S1: YES, S11: YES) Processes (S3, S14) and scavenging processes (S4 to S6, S16) in which scavenging is performed by supplying an oxidant gas to the fuel gas flow path when the cell voltage becomes lower than the threshold voltage. S18) and characterized by having a (first aspect of the present invention).

  According to this invention, when the operation stop signal is detected, when the cell voltage of the power generation cell is equal to or lower than the threshold voltage, the scavenging is performed by supplying the oxidant gas to the fuel gas flow path. Even if an oxidant gas is mixed in the fuel gas in the anode side electrode, the cell voltage is equal to or lower than the threshold voltage, so that the situation of corroding the fuel cell constituent material can be prevented or suppressed. .

  In this case, in the cell voltage determination process, when the operation stop signal is detected, the supply of the fuel gas to the fuel gas flow path is stopped (S2), and the cell voltage of the power generation cell is preferably reduced ( Invention of Claim 2).

  Alternatively, in the cell voltage determination process, when the operation stop signal is detected, the oxidant gas flow rate is reduced and supplied to the oxidant gas flow path (S12), and the cell voltage of the power generation cell is decreased. Preferred (invention of claim 3).

  Note that, when the oxidant gas flow rate is reduced and supplied, the supply of the fuel gas to the fuel gas flow path is preferably continued (time t10 to time t12) (the invention according to claim 4).

  Further, in the operation method according to claim 3 or 4, when the oxidant gas flow rate is reduced and supplied, the load of the power generation cell is further increased (time t11 to time t13), and the cell voltage of the power generation cell is increased. It is preferable to lower (Invention of Claim 5).

  In addition, the fuel cell operating method according to the present invention includes an electrolyte / electrode structure in which an anode side electrode and a cathode side electrode are provided on both sides of an electrolyte, sandwiched between a pair of separators, and the anode side electrode A fuel gas flow path is formed between the separator and a power generation cell in which an oxidant gas flow path is formed between the cathode side electrode and the separator. When the operation start signal is detected (S21: YES), the fuel gas is supplied to the fuel gas flow path when the cell voltage of the power generation cell is equal to or lower than a threshold voltage. It is preferable to have a fuel gas supply start process (S23) for starting the process (invention of claim 6).

  According to this invention, when the operation start signal is detected, control is performed so that the cell voltage of the power generation cell is equal to or lower than the threshold voltage, and supply of fuel gas to the fuel gas passage is started. Even if a potential difference occurs due to the fuel gas mixed in the oxidant gas in the anode side electrode, the cell voltage is below the threshold voltage, so that the situation of corroding the fuel cell constituent material can be prevented or suppressed. it can.

  In this case, in the fuel gas supply start process, when the operation start signal is detected, the supply of the fuel gas to the fuel gas channel is started, and the oxidation supplied to the oxidant gas channel during normal power generation By supplying an oxidant gas having a flow rate lower than the flow rate of the oxidant gas (S22), the cell voltage of the power generation cell does not exceed the threshold even if the oxidant gas reacts (claim 7). invention).

  In this case, after starting the supply of the fuel gas to the fuel gas flow path, when it is determined that the discharge of the oxidant gas in the fuel gas flow path is completed, the supply to the oxidant gas flow path By increasing the flow rate of the oxidant gas to the flow rate supplied during normal power generation (S25), it is possible to prevent or suppress the situation where the fuel cell constituent material is corroded at the time of start-up, and the normal power generation state can be achieved in a short time ( (Invention of Claim 8)

  Note that the determination of the completion of the discharge of the oxidant gas in the fuel gas flow path is made by the pressure difference between the air supply port (36a) and the air discharge port (36b), the hydrogen supply port (34a), and the hydrogen discharge port ( 34b), or by indirectly detecting the fuel gas concentration in the fuel gas flow path or the fuel gas flow rate in the fuel gas flow path. It can also be determined by a timer which is a time measuring means.

  According to this invention, since the cell voltage when the gas species is switched in the anode side electrode is controlled to be equal to or lower than the threshold voltage, the fuel gas and oxidant gas at the time of stopping or starting the power generation of the fuel cell are controlled. It is possible to prevent or suppress the corrosion of the fuel cell constituent material that occurs due to the contamination.

  FIG. 1 is a schematic configuration diagram of a fuel cell system 10 for carrying out a method of operating a fuel cell according to an embodiment of the present invention.

  The fuel cell system 10 is mounted on a vehicle such as an automobile, and includes a fuel cell 12. In the fuel cell 12, a plurality of power generation cells 14 are stacked in the direction of arrow A, and end plates 16a and 16b are disposed at both ends in the stacking direction. The end plates 16a and 16b are stacked in the stacking direction by fastening bolts (not shown). It is tightened.

The power generation cell 14 holds, for example, an electrolyte membrane / electrode structure 24 in which an anode-side electrode 20 and a cathode-side electrode 22 are arranged on both sides of a solid polymer electrolyte membrane 18, and an electrolyte membrane / electrode structure 24 interposed therebetween. A pair of metal separators 26 and 28 are provided. A fuel gas flow path 30 for supplying, for example, hydrogen (H ₂ ) gas as a fuel gas is formed between the anode side electrode 20 and the metal separator 26, while the cathode side electrode 22 and the metal separator 28 are formed. Between the _two, an oxidant gas flow path 32 for supplying air containing, for example, oxygen (O ₂ ) as an oxidant gas is formed.

  The end plate 16 a has a hydrogen supply port 34 a for supplying hydrogen gas to the fuel gas flow path 30 of each power generation cell 14 and an air supply for supplying air to the oxidant gas flow path 32 of each power generation cell 14. A mouth 36a is provided. The end plate 16 b has a hydrogen discharge port 34 b for discharging exhaust gas containing unused hydrogen gas discharged from the fuel gas passage 30 from the fuel cell 12, and an unused portion discharged from the oxidant gas passage 32. And an air discharge port 36 b for discharging air containing oxygen from the fuel cell 12. Pressure gauges 72 and 74 for detecting the pressure of air are provided at the air supply port 36a and the air discharge port 36b, respectively. The hydrogen supply port 34a and the hydrogen discharge port 34b are provided with pressure gauges 46 and 55 for detecting the hydrogen pressure during operation or the oxygen pressure during scavenging, respectively.

  The fuel cell system 10 includes a hydrogen supply channel 38 that supplies hydrogen gas to the fuel cell 12, and an exhaust channel 54 that discharges exhaust gas to the outside through a dilution box (not shown) via an exhaust valve 52.

  In the hydrogen supply flow path 38, a hydrogen tank 42 that stores high-pressure hydrogen, a supply valve 44 that adjusts the pressure of hydrogen gas supplied from the hydrogen tank 42, and the adjusted hydrogen gas are supplied to the fuel cell 12. At the same time, an ejector 45 for sucking exhaust gas from the hydrogen circulation passage 47 and returning it to the fuel cell 12 and the pressure gauge 46 described above are provided. An exhaust passage 54 is connected to the hydrogen circulation passage 47 through an exhaust valve 52. On the hydrogen discharge port 34b side, in addition to the pressure gauge 55 described above, a concentration meter 48 for detecting the hydrogen concentration, A flow meter 50 for detecting the flow rate of hydrogen is provided.

  In addition, the fuel cell system 10 includes an air supply channel 56 for supplying air to the fuel cell 12 and an air exhaust channel 58 for discarding exhaust gas containing unused air discharged from the fuel cell 12 to the atmosphere. With. The air supply channel 56 is provided with a supercharger (or pump) 60 for compressing and supplying air from the atmosphere and adjusting the flow rate of the air.

  Further, between the air supply flow path 56 and the hydrogen supply flow path 38, air that is an oxidant gas is supplied from the hydrogen supply port 34a to the fuel gas flow path 30 of the power generation cell 14 during scavenging when the operation is stopped. An air scavenging flow path 64 provided with the supply valve 62 is provided.

  The fuel cell 12 is connected to a load 70 whose size is adjusted when power generation is stopped, and is provided with a voltmeter 65 that detects a cell voltage that is a voltage generated by each power generation cell 14. The voltmeter 65 sends the cell voltage to the controller 66. The controller 66 has an ON signal (for example, a signal that transitions from a low level to a high level) that is an operation start signal and an OFF signal that is an operation stop signal (therefore, a signal that transitions from a high level to a low level) from the ignition switch 68. Sent.

  The controller 66 is constituted by a microcomputer or the like, and is constituted by a control board on which an interface such as a CPU, a memory, a timer as a time measuring means, an A / D converter, a D / A converter, etc. is mounted and stored in the memory. By executing the program, the entire fuel cell system 10 such as the supply valves 44 and 62, the exhaust valve 52 and the supercharger 60 is controlled.

  The operation of the fuel cell system 10 configured as described above will be described below in relation to the operation method of the fuel cell according to this embodiment. B. Processing during normal power generation operation B. Processing when power generation operation is stopped (two processing examples), and C.I. A process at the start of power generation operation, so-called startup, will be described.

A. Description of processing during normal power generation operation In a normal power generation operation in which an ON signal is supplied from the ignition switch 68, the hydrogen tank is in a state where the supply valve 62 is closed, that is, in a state where the air scavenging flow path 64 is closed. The fuel gas supplied from 42 is adjusted to a predetermined pressure via the supply valve 44 and supplied to the hydrogen supply port 34 a through the ejector 45 and the hydrogen supply flow path 38.

  The fuel gas supplied to the hydrogen supply port 34a is supplied to the anode side electrode 20 along the fuel gas flow path 30 constituting each power generation cell 14 and moves along the anode side electrode 20, and then contains hydrogen gas containing moisture. The contained exhaust gas is sent from the hydrogen discharge port 34 b to the hydrogen circulation passage 47. The exhaust gas discharged to the hydrogen circulation passage 47 is returned to the hydrogen supply passage 82 under the suction action of the ejector 45 and then supplied again as the fuel gas in the fuel cell 12. The exhaust valve 52 is generally closed during normal power generation and is opened intermittently.

  On the other hand, air is supplied from the supercharger 60 as compressed air in which the outside air is compressed, and is supplied as an oxidant gas to the air supply port 36a via the air supply flow path 56. After the air supply port 36a is supplied to the cathode side electrode 22 along the oxidant gas flow path 32 constituting each power generation cell 14 and moves along the cathode side electrode 22, the exhaust gas containing unused air and moisture is The air is discharged from the air discharge port 36b to the atmosphere through the air discharge channel 58.

  Thereby, in each power generation cell 14, hydrogen, which is a fuel gas supplied to the anode side electrode 20, reacts with oxygen in the oxidant gas supplied to the cathode side electrode 22 to generate power.

  During this power generation, hydrogen gas is ionized at the anode side electrode 20 to generate hydrogen ions and electrons. The hydrogen ions reach the cathode side electrode 22 through the solid polymer electrolyte membrane 18 with moisture. The generated electrons reach the cathode side electrode 22 from the anode side electrode 20 via an external load 70 (the load includes a motor, a capacitor, an auxiliary machine, etc.). Electrons that reach the cathode side electrode 22 and the supplied oxygen and hydrogen ions are combined on the cathode side electrode 22 side of the electrolyte membrane 18 to become water.

B. Next, the first process when the power generation operation is stopped will be described with reference to the flowchart shown in FIG. 2 and the time chart shown in FIG. 3.

  During normal power generation operation, when it is detected in step S1 that an OFF signal has been supplied from the ignition switch 68, in step S2, the fuel gas supply valve 44 and the exhaust valve 52 are closed and the anode from the hydrogen supply port 34a is closed. The supply of fuel gas to the side electrode 20 is stopped (see time t0 in FIG. 3A).

  In this state, as shown in FIG. 3B, the cathode side electrode 22 continues to be supplied with air, which is an oxidant gas, and therefore remains in the fuel gas flow path 30 in the power generation cell 14. The hydrogen and the oxygen in the oxidant gas supplied to the cathode side electrode 22 react to generate power and generate a cell voltage. As can be seen from time t1 in FIG. The cell voltage starts to decrease at time t1 when hydrogen as the fuel gas becomes lean.

  Therefore, next, in step S3, it is determined whether or not the maximum value in the cell voltage of each power generation cell 14 detected by the voltmeter 65 is equal to or lower than the threshold voltage. The threshold voltage is a predetermined voltage that can suppress corrosion of the fuel cell constituent material such as the electrolyte membrane / electrode structure 24, the electrode catalyst, and the separators 26 and 28 in the fuel cell 12. In the development / design stage, a predetermined voltage can be determined in advance in consideration of the durability of the fuel cell 12 including a supplementary test by experimental confirmation. The predetermined voltage is a voltage lower than the constant voltage generated at the moment when the scavenging with the oxidant gas is started and when the fuel gas is supplied at the start.

  As shown at time t2 in FIG. 3D, when the maximum value of the cell voltage is equal to or lower than the threshold voltage, the determination in step S3 becomes affirmative.

  At the next time point t2 + α when the maximum value of the cell voltage becomes equal to or lower than the threshold voltage, in step S4, the supply valve 62 and the exhaust valve 52 are opened, as shown in FIGS. 3 (a) and 3 (b). As described above, air as an oxidant gas is supplied from the supercharger 60 through the air supply flow path 56 to the cathode side electrode 22 from the air supply port 36 a, and at the same time, the hydrogen supply flow through the air scavenging flow path 64 and the supply valve 62. The hydrogen is supplied from the hydrogen supply port 34 a to the anode side electrode 20 through the path 38. The air supplied to the cathode side electrode 22 is discharged to the outside air through the air discharge channel 58, and the air supplied to the anode side electrode 20 is exhausted from the hydrogen discharge port 34b to the exhaust channel 54 through the exhaust valve 52. .

  Simultaneously with the process of step S4, as shown at time t2 in FIG. 3C, the load 70 that has been in the on state is changed from the on state to the off state, and current is supplied from the power generation cell 14 to the load 70. Is stopped and power generation operation is stopped.

  After time t2 when the power generation operation is stopped, as shown in step S6, it is determined whether or not scavenging by the air in the fuel gas channel 30 and the oxidant gas channel 32 is completed. This scavenging completion determination is made based on whether the pressure difference between the pressure gauges 72 and 74 measured at the air supply port 36a and the air discharge port 36b is equal to or lower than a predetermined pressure value, and at the hydrogen supply port 34a and the hydrogen discharge port 34b. It is determined by whether or not the differential pressure measured by the pressure gauges 46 and 55 is equal to or less than a predetermined pressure value. When the differential pressure is equal to or lower than the predetermined pressure value, it is considered that the moisture in the oxidant gas flow path 32 and the fuel gas flow path 30 is discharged out of the fuel cell 12. Note that the determination in step S6 can also be made based on whether or not a predetermined time determined in advance by the timer of the controller 66 has elapsed.

  When the scavenging completion determination in step S6 becomes affirmative, as shown at time t3, in step 7, the supercharger 60 is stopped and the supply of air to the anode side electrode 20 and the cathode side electrode 22 is stopped. The system of the fuel cell system 10 is stopped.

  As described above, in the first process at the time of stopping the power generation operation, when the OFF signal from the ignition switch 68 that is the operation stop signal is detected during the normal operation, the process of step S3 that is the cell voltage determination process, It is determined whether or not the cell voltage of the power generation cell 14 has become equal to or lower than the threshold voltage, and at time t2 when the cell voltage has become lower than or equal to the threshold voltage, the fuel gas passage 30 is oxidant gas after step S4, which is a scavenging process. Scavenging is performed by supplying air.

  As described above, since the cell voltage when the gas type is switched from the fuel gas to the oxidant gas in the anode side electrode 20 is kept lower than the threshold voltage, corrosion in the separator 26 and the anode side electrode 20 is prevented. be able to.

  In this case, in the cell voltage determination process, the supply of the fuel gas to the fuel gas flow path 30 is stopped at the time t0 when the OFF signal that is the operation stop signal is detected, so that the cell voltage of the power generation cell 14 increases. There is nothing to do. Even if the supply of the fuel gas is stopped, the fuel gas remains in the fuel gas flow path 30. Therefore, in order to consume this fuel gas, as shown at time points t0 to t2 in FIG. It is preferable to keep the load 70 in the ON state within that time.

  Next, the second process when the power generation operation is stopped will be described with reference to the flowchart shown in FIG. 4 and the time chart shown in FIG.

  During normal power generation operation, when it is detected in step S11 that an OFF signal has been supplied from the ignition switch 68, the air flow rate by the supercharger 60 is adjusted in step S12, and the oxidation of the power generation cell 14 from the air supply port 36a. The flow rate of the oxidant gas to the agent gas flow path 32 is reduced and supplied (see time t10 in FIG. 5B). For this reason, as shown in FIG. 5D, the cell voltage starts to gradually decrease after time t10.

  Next, in step S13, the load 70 is increased (see time t11 in FIG. 5C).

  In this state, since the oxidant gas flow rate is reduced (see FIG. 5B) and the load 70 is increased, as shown in FIG. 5D after time t11, the cell The voltage drops rapidly.

  Therefore, next, in step S14, it is determined whether or not the maximum value in the cell voltage of each power generation cell 14 detected by the voltmeter 65 is equal to or lower than the above-described threshold voltage.

  As shown at time t12 in FIG. 5D, when the maximum value of the cell voltage becomes equal to or lower than the threshold voltage, the determination in step S14 becomes affirmative.

  At time t12 when the maximum value of the cell voltage is equal to or lower than the threshold voltage, the hydrogen gas supply valve 44 is closed, and the fuel to the anode electrode 20 of the power generation cell 14 as shown in FIG. Stop supplying gas. The reason why the supply of the fuel gas is continued until time t12 is that the anode-side electrode 20 may be corroded if the supply of the fuel gas is reduced when a large current is passed through the load 70. Because there is.

  After time t12 when the maximum value of the cell voltage is equal to or lower than the threshold voltage, in step S16 at the next time t13, the supply valve 62 is opened and, as shown in FIG. A certain amount of air is supplied from the supercharger 60 through the air supply flow path 56 to the cathode side electrode 22 from the air supply port 36 a, and at the same time, from the hydrogen supply port 34 a to the anode side electrode 20 through the air scavenging flow path 64 and the supply valve 62. The scavenging process using the oxidizing gas of the so-called anode side electrode 20 to be supplied is started.

  Simultaneously with the processing of step S15, as shown in FIG. 5C, the load 70 that is in the on state and in the increased state is changed from the on state to the off state, and current supply from the power generation cell 14 to the load 70 is performed. Is stopped and power generation operation is stopped.

  After time t13, in step S18, it is determined whether or not scavenging by the air in the fuel gas channel 30 and the oxidant gas channel 32 has been completed. The determination of the completion of the scavenging is performed by detecting whether or not the pressure difference between the pressure gauges 72 and 74 detected at the air supply port 36a and the air discharge port 36b is equal to or less than a predetermined value, and at the hydrogen supply port 34a and the hydrogen discharge port 34b. It is determined whether or not the differential pressure by the pressure gauges 46 and 55 is equal to or less than a predetermined value. When the differential pressure is equal to or lower than the predetermined pressure value, it is considered that the moisture in the oxidant gas flow path 32 and the fuel gas flow path 30 is discharged out of the fuel cell 12. The determination in step S18 can also be performed based on whether or not a predetermined time determined in advance by the timer of the controller 66 has elapsed.

  When the scavenging completion determination in step S18 becomes affirmative, as shown at time t14, in step 19, the supercharger 60 is stopped, the supply of air to the anode side electrode 20 and the cathode side electrode 22 is stopped, and scavenging is performed. The processing is completed, and in step S20, the system of the fuel cell system 10 is stopped.

  As described above, in the second process at the time of stopping the power generation operation, when the OFF signal from the ignition switch 68 that is an operation stop signal is detected during the normal operation, the process of step S14 that is a cell voltage determination process, It is determined whether or not the cell voltage of the power generation cell 14 has become equal to or lower than the threshold voltage, and at time t13 when the cell voltage has become equal to or lower than the threshold voltage, the fuel gas passage 30 is oxidant gas after step S16, which is a scavenging process. Scavenging is performed by supplying air.

  As described above, since the cell voltage when the gas type is switched from the fuel gas to the oxidant gas in the anode side electrode 20 is kept lower than the threshold voltage, corrosion in the separator 26 and the anode side electrode 20 is prevented. be able to.

  In this case, in the cell voltage determination process, since the oxidant gas flow rate is reduced and supplied to the oxidant gas flow path 32 at time t10 when the OFF signal that is the operation stop signal is detected, the cell voltage of the power generation cell 14 is supplied. Can be reduced.

  When supplying the oxidant gas at a reduced flow rate, it is preferable to continue supplying the fuel gas to the fuel gas passage 30 as shown between the time t10 and the time t12. By continuing the supply of fuel gas, when the anode side electrode 20 is in a so-called out-of-gas state in a state where power generation is continued, the separator 26 of the anode side electrode 20 is easily corroded, causing a decrease in power generation performance. Therefore, it is possible to avoid a decrease in power generation performance.

  As shown at time t10 to time t13, when the oxidant gas flow rate is reduced and supplied, the load 70 of the power generation cell 14 is increased as shown at time t11 to time t13 in FIG. Since the cell voltage of the cell 14 can be reduced temporarily, the responsiveness can be improved. In this case, the load 70 can be used as effective energy such as power of the supercharger 60 and power for keeping the fuel cell 12 warm. Of course, a resistor may be used as the load 70.

C. Next, the process at the start of the power generation operation will be described with reference to the flowchart shown in FIG. 6 and the time chart shown in FIG.

  While the system is stopped, the scavenging is completed by the processing in step S6 or step S18. Therefore, air is not supplied to the fuel gas passage 30 and the oxidant gas passage 32 in the power generation cell 14. Is in a state of entering.

  In step S21, when it is detected that the ON signal is supplied from the ignition switch 68, when the fuel gas is immediately supplied to the fuel gas passage 30, the oxidant gas and the fuel gas are generated in the fuel gas passage 30. At the same time, if a predetermined amount of oxidant gas is introduced into the oxidant gas flow path 32, the cell voltage may rise rapidly and exceed the threshold voltage. To avoid this, step S2 is performed. Then, with the supply valve 62 and the supply valve 44 closed, as shown at time t21 in FIG. 7B, the supercharger 60 is driven weakly and the cathode side electrode 22 is compared with that during normal power generation. A small amount of oxidant gas.

  Then, as shown at time t22, in a state where a small amount of oxidant gas is circulated, as shown in FIG. 7A, in step S23, the supply valve 44 is opened to supply the fuel gas to the anode side electrode 20. To start.

  Next, in a state after this time t22, in step S24, it is determined whether or not the discharge of the oxidant gas that is the remaining gas in the fuel gas flow channel 30 is completed. This determination is based on whether the hydrogen concentration measured by the concentration meter 48 provided at the hydrogen discharge port 34b is equal to or higher than the threshold concentration, or the flow rate measured by the flow meter 50 provided at the hydrogen discharge port 34b is the threshold flow rate. It can be determined based on whether or not the time has elapsed or whether the time measured by the timer exceeds the threshold time.

  When the determination in step S24 becomes affirmative, in step S25, the supercharger 60 is normally driven and increased from the air supply flow path 56 to the oxidant gas flow path 32 through the air supply port 36a, so that the normal flow rate is increased. By supplying the oxidant gas, the oxidant gas having a normal flow rate is supplied to the cathode-side electrode 22 (see time t23 in FIG. 8B).

  From this time t23, the above-described normal power generation in step S26 is started, and the cell voltage of the power generation cell 14 rises to the cell voltage during normal power generation.

  Thus, in this process at the start of operation, at the time t21 when the ON signal from the ignition switch 68, which is an operation start signal, is detected, the fuel gas flow path 30 is in a state where the cell voltage of the power generation cell 14 is equal to or lower than the threshold voltage. Is provided with a fuel gas supply start process (step S23) for starting the supply of fuel gas. That is, when an ON signal that is an operation start signal is detected, control is performed so that the cell voltage of the power generation cell 14 is equal to or lower than the threshold voltage, and supply of the fuel gas to the fuel gas passage 30 is started. Therefore, even if a potential difference occurs due to the fuel gas mixed in the oxidant gas in the anode electrode 20, the cell voltage is equal to or lower than the threshold voltage, so that the fuel cell constituent material such as the separator 26 is corroded. Can be prevented or suppressed.

  In this case, when an ON signal that is an operation start signal is detected, at time t21 to time t23 when supply of fuel gas to the fuel gas flow path 30 is started, as shown in FIG. By supplying the oxidant gas with a flow rate smaller than the flow rate of the oxidant gas supplied during normal power generation to the oxidant gas flow path 32, the cell voltage of the power generation cell 14 has a threshold value even if the oxidant gas reacts. Never exceed.

  In this case, at the time t23 when it is determined that the discharge of the oxidant gas in the fuel gas flow channel 30 is completed after the supply of the fuel gas to the fuel gas flow channel 30 is started, (b) in FIG. As shown in the figure, the flow rate of the oxidant gas supplied to the oxidant gas flow path 32 is increased to the flow rate supplied during normal power generation, thereby preventing or suppressing the situation where the fuel cell constituent material is corroded at the time of starting, and for a short time. In normal power generation state.

It is a schematic block diagram of the fuel cell system for enforcing the operating method of the fuel cell concerning this invention. It is a flowchart with which it uses for the 1st process description of the scavenging process at the time of an operation stop. It is a time chart used for the 1st processing explanation of the scavenging process at the time of operation stop. It is a flowchart with which it uses for 2nd process description of the scavenging process at the time of an operation stop. It is a time chart with which it uses for the 2nd process description of the scavenging process at the time of an operation stop. It is a flowchart with which process description at the time of the start of operation after a scavenging process is provided. It is a timing chart with which the process description at the time of the operation start after a scavenging process is provided.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 ... Fuel cell system 12 ... Fuel cell 14 ... Power generation cell 18 ... Solid polymer electrolyte membrane 20 ... Anode side electrode 22 ... Cathode side electrode 24 ... Electrolyte membrane and electrode structure 26, 28 ... Separator 30 ... Fuel gas flow path 32 ... oxidant gas flow path 34a ... hydrogen supply port 34b ... hydrogen discharge port 36a ... air supply port 36b ... air discharge port 38 ... hydrogen supply flow path 47 ... hydrogen circulation flow path 54 ... exhaust flow path 56 ... air supply flow path 58 ... Air discharge passage 64 ... Air scavenging passage

Claims (8)

An electrolyte / electrode structure provided with an anode side electrode and a cathode side electrode on both sides of the electrolyte is held between a pair of separators, and a fuel gas flow path is formed between the anode side electrode and the separator. On the other hand, a method of operating a fuel cell having a power generation cell in which an oxidant gas flow path is formed between the cathode side electrode and the separator, and generating power by reaction of fuel gas and oxidant gas,
A cell voltage determination process for determining whether the cell voltage of the power generation cell is equal to or lower than a threshold voltage when an operation stop signal is detected during operation;
A scavenging process in which scavenging is performed by supplying an oxidant gas to the fuel gas flow path when the cell voltage becomes equal to or lower than the threshold voltage. The driving method according to claim 1,
In the cell voltage determination process,
When the operation stop signal is detected, the supply of the fuel gas to the fuel gas flow path is stopped, and the cell voltage of the power generation cell is lowered. The driving method according to claim 1,
In the cell voltage determination process,
A method of operating a fuel cell, wherein when the operation stop signal is detected, the oxidant gas flow rate is reduced and supplied to the oxidant gas flow path to reduce the cell voltage of the power generation cell. The driving method according to claim 3, wherein
When the oxidant gas flow rate is reduced and supplied, the supply of the fuel gas to the fuel gas flow path is continued. The driving method according to claim 3 or 4,
When the oxidant gas flow rate is reduced and supplied, the load on the power generation cell is further increased to lower the cell voltage of the power generation cell. An electrolyte / electrode structure provided with an anode side electrode and a cathode side electrode on both sides of the electrolyte is held between a pair of separators, and a fuel gas flow path is formed between the anode side electrode and the separator. On the other hand, a method of operating a fuel cell having a power generation cell in which an oxidant gas flow path is formed between the cathode side electrode and the separator, and generating power by reaction of fuel gas and oxidant gas,
A fuel cell supply start process for starting supply of the fuel gas to the fuel gas flow path when a cell voltage of the power generation cell is not more than a threshold voltage when an operation start signal is detected. Driving method. The method of operating a fuel cell according to claim 6,
In the fuel gas supply start process, when the operation start signal is detected, when the supply of the fuel gas to the fuel gas channel is started, the oxidant gas supplied to the oxidant gas channel during normal power generation A method for operating a fuel cell, comprising supplying an oxidant gas having a flow rate lower than the flow rate. The operation method of a fuel cell according to claim 7,
After starting the supply of the fuel gas to the fuel gas flow path, when it is determined that the discharge of the oxidant gas in the fuel gas flow path is complete, the oxidant gas supplied to the oxidant gas flow path A method of operating a fuel cell, characterized in that the flow rate is increased to the flow rate supplied during normal power generation.

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