JP2004134199A - Starting method of fuel cell - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a starting method of a fuel cell using a simple composition and control, which enables an improvement in power generation performance by effectively suppressing a reduction in voltage of unit cells. <P>SOLUTION: The fuel cell 12 has a stack of a plurality of unit cells 14 in the direction of an arrow A, and is supplied with fuel gas from an end plate 16a on one end of the stack of the unit cells concerning the stacking direction. Open circuit voltage of at least one end cell 14a which is disposed near an end plate 16b on the other end of the stack of the unit cells, is measured. When it is judged that the measured open circuit voltage shows a prescribed value or more, load current is taken out from the fuel cell 12 and the starting of the fuel cell 12 is begun. <P>COPYRIGHT: (C)2004,JPO

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention has an electrolyte membrane / electrode structure provided with a pair of electrodes on both sides of a solid polymer electrolyte membrane, and stacks a plurality of unit cells in which the electrolyte membrane / electrode structure is sandwiched by a pair of separators. And a method of starting a fuel cell that supplies a reaction gas from one end in the stacking direction.
[0002]
[Prior art]
In general, a polymer electrolyte fuel cell has an electrolyte membrane / electrode in which an anode electrode and a cathode electrode are provided on both sides of a solid polymer electrolyte membrane composed of a polymer ion exchange membrane (cation exchange membrane). The structure is configured as a unit cell by being sandwiched between separators. This type of fuel cell is usually used as a fuel cell stack by stacking a plurality of unit cells.
[0003]
In this fuel cell, a fuel gas supplied to the anode side electrode, for example, a gas mainly containing hydrogen (hereinafter, also referred to as a hydrogen-containing gas) is ionized with hydrogen on the electrode catalyst, and is supplied to the cathode via the electrolyte membrane. Move to the side electrode side. The electrons generated during that time are taken out to an external circuit and used as DC electric energy. Since an oxidant gas, for example, a gas mainly containing oxygen or air (hereinafter also referred to as an oxygen-containing gas) is supplied to the cathode side electrode, hydrogen ions, electrons, And oxygen react to produce water.
[0004]
By the way, in this type of fuel cell, when power is supplied to an external load immediately after start-up, the supply of fuel gas becomes insufficient in the stacked unit cells, In many cases, there is a unit cell in which the flow is hindered or the generated voltage is apt to decrease. In order to solve this kind of problem, for example, a method for starting a polymer electrolyte fuel cell disclosed in Patent Document 1 is known.
[0005]
The startup method described above includes a voltage measuring step of measuring a power generation voltage of the polymer electrolyte fuel cell, and a voltage value measured in the voltage measuring step is indicated when the polymer electrolyte fuel cell is in a normal operation state. A voltage comparing step of determining whether or not the voltage is equal to or higher than a set voltage set based on the generated voltage; and if it is determined that the voltage is not equal to or higher than the set voltage in the voltage comparing step, supply of water to a plurality of channels is performed. Stopping, and when it is determined that the voltage is equal to or higher than the set voltage, a supply fuel control step of starting supply of water together with fuel gas to the plurality of channels.
[0006]
At this time, the set voltage is set based on the open circuit voltage shown when the polymer electrolyte fuel cell is in a normal operation state, and in the supply fuel control step, it is determined in the voltage comparison step that the voltage is not higher than the set voltage. In this case, the power supply to the outside is stopped, and if it is determined that the voltage is equal to or higher than the set voltage, the power supply to the outside is started.
[0007]
[Patent Document 1]
Japanese Patent No. 3213509 (FIG. 5)
[0008]
[Problems to be solved by the invention]
By the way, as the number of stacked cells increases, the influence of the voltage change of each cell on the voltage change of the battery main body decreases, and the detection sensitivity decreases. For this reason, in Patent Document 1 described above, for example, when the number of stacked cells is 100, each stacked block is divided into twenty stacked blocks so that each stacked block includes five cells, and power generation is performed for each stacked block. Voltage is being measured.
[0009]
Therefore, especially when a large number of cells are stacked for use in a vehicle, the number of divided stacked blocks becomes large, and a voltage measurement step, a voltage comparison step, and a supplied fuel control step must be performed for each stacked block. As a result, it has been pointed out that the configuration and control of the entire fuel cell become considerably complicated.
[0010]
The present invention solves this kind of problem and provides a fuel cell starting method capable of effectively suppressing a voltage drop of a unit cell and improving power generation performance with a simple configuration and control. The purpose is to.
[0011]
[Means for Solving the Problems]
In the fuel cell starting method according to claim 1 of the present invention, in the fuel cell in which the reactant gas is supplied from one end of the unit cells in the stacking direction, at least one unit disposed on the other end in the stacking direction. The open circuit voltage of the cell is measured. The open circuit voltage refers to a voltage output when power is generated in a state where no load current is taken out.
[0012]
Next, it is determined whether the measured open circuit voltage is equal to or higher than a preset voltage. Then, when it is determined that the measured open circuit voltage is equal to or higher than the set voltage, the extraction of the current from the fuel cell to the external load, that is, the start of the fuel cell is started.
[0013]
Here, a unit cell (hereinafter, also referred to as an end cell) disposed on the other end side in the stacking direction is liable to be short of fuel gas, and the fuel gas hardly flows to the end cell side. For this reason, if power generation of the fuel cell is started before the fuel gas is sufficiently supplied to the end cells, the voltage of the end cells is reduced due to the lack of fuel gas. . That is, among the stacked unit cells, the voltage drop of the end cell becomes the most remarkable, and if the open circuit voltage measured at this end cell is equal to or higher than the set voltage, the open circuit voltage of all other unit cells Is higher than the set voltage.
[0014]
Therefore, even if a large number of unit cells are stacked, it is possible to reliably detect whether or not all the unit cells are in a startable state only by measuring the open circuit voltage of the end cells. This makes it possible to effectively suppress the voltage drop of the unit cell and improve the power generation performance with a simple configuration and control.
[0015]
In the method for starting a fuel cell according to the second aspect of the present invention, the set voltage is changed based on at least a time from when the operation is stopped to when the operation is restarted, that is, a standby time.
[0016]
If the standby time is short, the fuel gas consumption is reduced, and the shortage of fuel gas in the end cells tends to be resolved. Therefore, even if the set voltage is low, the voltage drop of the end cell is effectively suppressed. On the other hand, if the standby time is long, the consumption of the fuel gas increases, and the shortage of the fuel gas in the end cells tends to occur. For this reason, by setting the set voltage high, after the fuel gas is sufficiently supplied to the end cells, starting can be started to suppress the voltage drop of the end cells.
[0017]
BEST MODE FOR CARRYING OUT THE INVENTION
FIG. 1 is a schematic configuration explanatory view of a fuel cell system 10 for performing a fuel cell starting method according to an embodiment of the present invention.
[0018]
The fuel cell system 10 is used, for example, for a vehicle, and includes a fuel cell 12. In this fuel cell 12, a plurality of unit cells 14 are stacked in the direction of arrow A to form a stack, and end plates 16a and 16b are provided at both ends in the stacking direction. Is given a predetermined tightening load.
[0019]
As shown in FIG. 2, the unit cell 14 includes an electrolyte membrane / electrode structure 22 and first and second separators 24 and 26 that sandwich the electrolyte membrane / electrode structure 22. A seal member 28 such as a gasket is interposed between the electrolyte membrane / electrode structure 22 and the first and second separators 24 and 26 so as to cover a periphery of a communication hole described later and an outer periphery of an electrode surface (power generation surface). Is equipped.
[0020]
An oxidizing gas supply passage 30a for supplying an oxidizing gas, for example, an oxygen-containing gas, communicates with one end edge of the unit cell 14 in the direction of the arrow B in the direction of the arrow A, which is a stacking direction. A cooling medium discharge communication hole 32b for discharging the medium and a fuel gas discharge communication hole 34b for discharging a fuel gas, for example, a hydrogen-containing gas, are provided in an arrow C direction (vertical direction).
[0021]
The other end edges of the unit cells 14 in the direction of arrow B communicate with each other in the direction of arrow A to provide a fuel gas supply communication hole 34a for supplying a fuel gas and a cooling medium supply communication hole for supplying a cooling medium. 32a and an oxidizing gas discharge communication hole 30b for discharging the oxidizing gas are arranged in the arrow C direction.
[0022]
The electrolyte membrane / electrode assembly 22 includes, for example, a solid polymer electrolyte membrane 36 in which a thin film of perfluorosulfonic acid is impregnated with water, an anode electrode 38 and a cathode electrode 40 sandwiching the solid polymer electrolyte membrane 36. And
[0023]
The anode electrode 38 and the cathode electrode 40 include a gas diffusion layer made of carbon paper or the like, and an electrode catalyst layer in which porous carbon particles having a platinum alloy supported on the surface are uniformly applied on the surface of the gas diffusion layer. Respectively. The electrode catalyst layers are joined to both surfaces of the solid polymer electrolyte membrane 36 so as to face each other with the solid polymer electrolyte membrane 36 interposed therebetween. An opening 44 is formed at the center of the seal member 28 so as to correspond to the anode 38 and the cathode 40.
[0024]
An oxidizing gas flow path 46 communicating with the oxidizing gas supply communication hole 30a and the oxidizing gas discharge communication hole 30b is provided on the surface 24a of the first separator 24 on the side of the electrolyte membrane / electrode structure 22. The oxidizing gas passage 46 includes, for example, a plurality of grooves (serpentine grooves) extending in the direction of arrow C while meandering in the direction of arrow B.
[0025]
A fuel gas channel 48 communicating with the fuel gas supply passage 34a and the fuel gas discharge passage 34b is formed on the surface 26a of the second separator 26 on the side of the electrolyte membrane / electrode structure 22. The fuel gas flow path 48 includes, for example, a plurality of grooves (serpentine grooves) extending in the direction of arrow C while meandering in the direction of arrow B. On a surface 26b opposite to the surface 26a of the second separator 26, a cooling medium flow path 50 communicating with the cooling medium supply communication hole 32a and the cooling medium discharge communication hole 32b is formed. The cooling medium flow path 50 is composed of, for example, a plurality of linear flow grooves extending in the direction of arrow B.
[0026]
As shown in FIG. 1, the fuel cell system 10 includes a fuel gas supply unit 52 that supplies a fuel gas to the fuel cell 12, an oxidizing gas supply unit (not shown) that supplies an oxidizing gas, and a cooling medium. A cooling medium supply unit (not shown) for supplying the cooling medium.
[0027]
The fuel gas supply unit 52 includes a high-pressure tank 54 for filling a fuel gas, for example, a hydrogen gas in a high-pressure state. The high-pressure tank 54 communicates with the fuel gas supply passage 34 a of the fuel cell 12 via a fuel gas supply pipe 56, and an ejector 58 is connected in the middle of the fuel gas supply pipe 56. A fuel gas discharge pipe 60 is connected to the fuel cell 12 so as to communicate with the fuel gas discharge communication hole 34b. The fuel gas discharge pipe 60 is provided with a purge valve 62 and an ejector 58.
[0028]
The operation of the fuel cell system 10 configured as described above will be described below.
[0029]
As shown in FIG. 1, a fuel gas such as a hydrogen-containing gas is supplied into the fuel cell 12 through a fuel gas supply unit 52, an oxidizing gas supply unit (not shown), and a cooling medium supply unit (not shown). An oxidizing gas, which is an oxygen-containing gas such as air, and a cooling medium such as pure water, ethylene glycol or oil are supplied.
[0030]
Therefore, as shown in FIG. 2, the oxidizing gas is introduced from the oxidizing gas supply passage 30 a into the oxidizing gas passage 46 of the first separator 24, and the oxidizing gas flows through the electrolyte membrane / electrode structure 22. It moves along the constituent cathode electrode 40. Further, the fuel gas is introduced from the fuel gas supply passage 34a into the fuel gas flow path 48 of the second separator 26, and moves along the anode 38 constituting the electrolyte membrane / electrode structure 22.
[0031]
Therefore, in the electrolyte membrane / electrode structure 22, the oxidizing gas supplied to the cathode electrode 40 and the fuel gas supplied to the anode electrode 38 are consumed by the electrochemical reaction in the electrode catalyst layer, and the power is generated. Is performed.
[0032]
The fuel gas supplied to the anode 38 and consumed is discharged in the direction of arrow A along the fuel gas discharge communication hole 34b. Similarly, the oxidant gas supplied to and consumed by the cathode electrode 40 is discharged in the direction of arrow A along the oxidant gas discharge communication hole 30b.
[0033]
Further, the cooling medium supplied to the cooling medium supply communication hole 32a flows into the cooling medium flow path 50 of the second separator 26, and then flows along the arrow B direction. This cooling medium is discharged from the cooling medium discharge communication hole 32b after cooling the electrolyte membrane / electrode structure 22.
[0034]
Next, a method of starting the fuel cell according to the present embodiment will be described below with reference to a flowchart shown in FIG.
[0035]
First, a time from when the operation of the fuel cell 12 stops to when it restarts, that is, a standby time is detected (step S1), and a set voltage (threshold) is set based on the standby time (step S2). . For example, when the time of 12 hours or more has elapsed before the restart, the set voltage is set to 1V.
[0036]
Then, the purge valve 62 is closed, and the fuel gas discharge pipe 60 serving as the fuel gas outlet is closed (step S3). Therefore, in the fuel cell 12, the flow of the fuel gas is blocked, and the open circuit voltage (OCV) can be detected. At this time, in the fuel cell 12, at least one unit cell (hereinafter referred to as an end cell) disposed on the other end side (end plate 16b side) opposite to one end side (end plate 16a side) in the stacking direction to which fuel gas is supplied. The open circuit voltage of the unit cell 14a is measured (step S4).
[0037]
The open circuit voltage of the end cell 14a increases from the time of power generation of the fuel cell 12, and when the open circuit voltage becomes equal to or higher than a set voltage (for example, 1 V) (YES in step S5), the process proceeds to step S6. Then, the purge valve 62 is opened. For this reason, the fuel gas is introduced into the fuel cell 12, the start of the fuel cell 12 is started, and a current can be taken out to an external load (not shown) (step S7).
[0038]
In this case, in the present embodiment, in the fuel cell 12, the open circuit voltage of the end cell 14a arranged adjacent to the end plate 16b, which is the other end side farthest from the fuel gas supply side, is measured. When the measured open circuit voltage becomes equal to or higher than the set voltage, the load current is taken out from the fuel cell 12, that is, the start is started.
[0039]
Here, since the end cell 14a is farthest from the fuel gas supply side, the fuel gas tends to run short, and the fuel gas hardly flows to the end cell 14a side. Therefore, among the stacked unit cells 14, the voltage drop of the end cell 14a becomes the most remarkable. If the open circuit voltage measured at the end cell 14a is equal to or higher than the set voltage, all the other unit cells 14a The open circuit voltage is higher than the set voltage.
[0040]
Thus, even if a large number of unit cells 14 are stacked, it is possible to reliably detect whether or not all the unit cells 14 can be started by merely measuring the open circuit voltage of the end cell 14a. Can be. Therefore, with a simple configuration and control, the voltage drop of the unit cell 14 and the end cell 14a is reliably suppressed, and the effect that the power generation performance of the entire fuel cell 12 can be effectively improved can be obtained. .
[0041]
Specifically, the operation of the fuel cell 12 was stopped (standby) for two days, and the set voltage was set to, for example, 0.8 V as a load current extraction threshold. As a result, as shown in FIG. 4, the output voltage (cell voltage) of the end cell 14b significantly decreased 15 seconds after the current was taken out. That is, in the end cell 14b, fuel gas deficiency due to fuel gas supply delay, fuel gas consumption due to long-term shutdown, decrease in fuel gas fluidity, and decrease in electrode activity at low temperature start-up, The output voltage has dropped.
[0042]
FIG. 5 shows an experimental result when the fuel cell 12 is started at room temperature after the operation is stopped for 12 hours, and the set voltage which is a threshold for current extraction is set to, for example, 0.9 V. I have. As a result, in the end cell 14a, the output voltage dropped because the fuel gas was deficient for 12 seconds after the current was taken out.
[0043]
On the other hand, FIG. 6 shows the output voltage at the end cell 14a when the operation is restarted after the operation has been stopped for 12 hours and the set voltage which is the current extraction threshold is set to 1.0 V, for example. Have been. As a result, by setting the set voltage to 1.0 V, the fuel cell 12 starts after the fuel gas is sufficiently supplied also to the end cell 14a, that is, the load current is taken out.
[0044]
Thereby, in particular, it is possible to reliably prevent the output voltage at the end cell 14a from decreasing. For this reason, a reliable starting state can be obtained with a simple configuration and control, and the power generation performance of the fuel cell 12 can be effectively improved.
[0045]
In the present embodiment, when the time until the restart is changed, the threshold value that is the set voltage is changed. For example, after the experiment shown in FIG. 4, when the operation was stopped for 13 minutes and restarted, the threshold voltage was set to 0.8V. As a result, as shown in FIG. 7, in the end cell 14a, although there was a voltage drop after the load current was taken out, the voltage was restored and a significant drop in the output voltage could be avoided.
[0046]
This is because the fuel gas is supplied to the vicinity of the catalyst of the end cell 14a by the power generation of the unit cell 14, and the shortage of the fuel gas is slightly eliminated. Therefore, when the standby time is short, the set voltage can be set low, and there is an advantage that a good start can be started in a short time.
[0047]
Furthermore, when the stoichiometric ratio of the fuel gas supplied to the fuel cell 12 (the ratio between the supplied fuel gas amount and the actually consumed fuel gas amount) becomes 0.8, as shown in FIG. When 6 minutes had elapsed after the removal, a voltage drop occurred in all the unit cells 14. As a result, unless the stoichiometric ratio of the fuel gas is set to 0.8 or more, even if the set voltage is 1.0 V, the fuel gas becomes deficient and the cell voltage decreases. Therefore, the set voltage may be changed according to the stoichiometric ratio of the supplied fuel gas.
[0048]
In this embodiment, as shown in FIG. 1 and FIG. 2, the fuel gas, the oxidizing gas and the cooling medium are supplied from the end plate 16a side, turn back on the end plate 16b side, and further from the end plate 16a side. The U-turn channel to be discharged is configured, but is not limited thereto. For example, the same effect can be obtained even with a DC type in which power is supplied from the end plate 16a side and then discharged to the outside of the fuel cell 12 from the end plate 16b side.
[0049]
In the present embodiment, the oxidizing gas passage 46 and the fuel gas passage 48 include a plurality of serpentine grooves, but the present invention is not limited to this. For example, a plurality of linear grooves may be used. May be.
[0050]
【The invention's effect】
In the method for starting a fuel cell according to the present invention, even when a large number of unit cells are stacked, only by measuring the open circuit voltage of the unit cell arranged at the end opposite to the supply side of the reaction gas, It is possible to reliably detect whether or not all the unit cells can be started. This makes it possible to effectively suppress the voltage drop of the unit cell and improve the power generation performance with a simple configuration and control.
[Brief description of the drawings]
FIG. 1 is a schematic structural explanatory view of a fuel cell system for carrying out a fuel cell starting method according to an embodiment of the present invention.
FIG. 2 is an exploded perspective view of a unit cell constituting the fuel cell system.
FIG. 3 is a flowchart illustrating the starting method.
FIG. 4 is an explanatory diagram of a cell voltage of an end cell when a threshold voltage is 0.8 V after operation is stopped for two days.
FIG. 5 is an explanatory diagram of the cell voltage of the end cell when the threshold voltage is 0.9 V after the operation is stopped for 12 hours.
FIG. 6 is an explanatory diagram of the cell voltage of the end cell when the threshold voltage is 1.0 V after the operation is stopped for 12 hours.
FIG. 7 is an explanatory diagram of a cell voltage of the end cell in a case where a restart is performed after 13 minutes and a threshold voltage is 0.8V.
FIG. 8 is a diagram illustrating the cell voltage of the end cell when the stoichiometric ratio of the fuel gas is set to 0.8.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 10 ... Fuel cell system 12 ... Fuel cell 14 ... Unit cell 16a, 16b ... End plate 22 ... Electrolyte membrane / electrode structure 24, 26 ... Separator 34a ... Fuel gas supply communication hole 34b ... Fuel gas discharge communication hole 36 ... Solid height Molecular electrolyte membrane 38 Anode side electrode 40 Cathode side electrode 46 Oxidant gas flow path 48 Fuel gas flow path 50 Cooling medium flow path 52 Fuel gas supply part 54 High pressure tank 56 Fuel gas supply pipe 58 Ejector 60: Fuel gas discharge pipe 62: Purge valve

Claims (2)

A solid polymer electrolyte membrane has an electrolyte membrane / electrode structure provided with a pair of electrodes on both sides, and the electrolyte membrane / electrode structure is stacked with a plurality of unit cells sandwiched by a pair of separators, and a reaction gas is formed. A method for starting a fuel cell supplied from one end side in a stacking direction,
Measuring an open circuit voltage of at least one unit cell disposed on the other end side in the stacking direction;
A step of determining whether the measured open circuit voltage is equal to or higher than a preset voltage,
Extracting the load current from the fuel cell when the measured open circuit voltage is determined to be equal to or higher than the set voltage,
A method for starting a fuel cell, comprising: 2. The method according to claim 1, wherein the set voltage is changed based on at least a time period from when the operation is stopped to when the operation is restarted.

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