JP2005085477A - Fuel cell - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a fuel cell not increasing the weight of a system, restraining carbon corrosion, capable of purging gas. <P>SOLUTION: In the fuel cell 1 comprising an anode gas passage 6 on one surface of an electrode layer including an electrolyte (MEA 2) and a cathode gas passage 5 on the other surface, a gas purging passage 7 for flowing the air for purging the gas in the anode gas passage 6 when stopping operation is provided. Further, a plurality of holes (communicating holes 8) for supplying the air nearly evenly from the gas purging passage 7 to the anode gas passage 6 in the passage axial direction are provided . <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a fuel cell. In particular, the present invention relates to a fuel cell configuration for scavenging the anode side when the fuel cell is stopped.

  Fuel cells that extract electrical energy from the electrochemical reaction between hydrogen and oxygen are attracting attention as a power source for future automobiles because they emit only harmless water and are highly efficient.

  The fuel cell has a problem in that, when the hydrogen region and the air region are mixed in the anode-side flow path when the operation is stopped, a voltage higher than that in a normal power generation state is generated and the corrosion of carbon is promoted. In order to solve this problem, in the stationary fuel cell, measures are taken to prevent hydrogen and oxygen from reacting in the anode side channel by scavenging the gas channel with nitrogen during the stop operation. However, it is difficult to mount a supply source of nitrogen in a moving body, and a countermeasure to replace scavenging with nitrogen is necessary.

As a countermeasure, the conventional technology reduces carbon corrosion by shortening the time during which excessive voltage is generated by performing scavenging with air in a short time with respect to the anode side flow path (for example, , Patent Document 1).
US Patent Application Publication No. 2002/0076582

  However, the amount of air supply required for the above-described conventional technology is very large, and if an air supply device necessary for satisfying the requirement is mounted on an automobile, the performance of the vehicle decreases due to an increase in weight. Alternatively, if the air supply device is small and light with low capacity, there is a problem that a sufficient effect cannot be obtained.

  In view of the above problems, an object of the present invention is to provide a fuel cell that can perform scavenging without increasing the weight of the system and suppressing carbon corrosion.

  The present invention relates to a fuel cell in which an anode gas flow path is formed on one surface of an electrode layer containing an electrolyte and a cathode gas flow path is formed on the other surface, and contains oxygen for scavenging the anode gas flow path during stop operation. A scavenging flow path for circulating gas is provided. Furthermore, a plurality of holes for supplying an oxygen-containing gas from the scavenging flow path to the anode gas flow path substantially uniformly in the flow path axial direction are provided.

  Since scavenging can be performed by supplying an oxygen-containing gas to the anode gas channel substantially evenly in the direction of the channel axis, it is possible to suppress a mixture of a hydrogen region and an air region at the anode. As a result, scavenging can be performed without increasing the weight of the system and suppressing carbon corrosion.

  A schematic configuration of a fuel cell system used in the present embodiment is shown in FIG. Here, as the fuel cell system, a fuel cell system used as a power source of a moving body, for example, an automobile will be described.

  A fuel cell 1 that generates power using air as an oxidant gas and hydrogen as a fuel gas is provided. As will be described later, the fuel cell 1 includes a cathode gas channel 5 to which air is supplied, an anode gas channel 6 to which hydrogen is supplied, and a scavenging channel 7 through which coolant or scavenging air flows.

  Further, a cathode upstream side valve 9 is provided on the upstream side of the cathode gas flow path 5, and a cathode downstream side valve 10 is provided on the downstream side. With the cathode upstream side valve 9 and the cathode downstream side valve 10, it is possible to select whether or not the inside of the cathode gas flow path 5 is closed. The cathode downstream side valve 10 can adjust the air pressure in the cathode gas flow path 5. An air supply device 15 for supplying air to the cathode gas flow path 5 is provided further upstream of the cathode upstream side valve 9. For example, a compressor or the like is used as the air supply device 15 to supply compressed air to the cathode gas flow path 5.

  Further, an anode upstream side valve 11 is provided on the upstream side of the anode gas flow path 6, and an anode downstream side valve 12 is provided on the downstream side. With the anode upstream side valve 11 and the anode downstream side valve 12, it is possible to select whether or not the inside of the anode gas flow path 6 is closed. Further, the hydrogen pressure in the anode gas flow path 6 can be adjusted by the anode downstream side valve 12. A hydrogen supply device 16 for supplying hydrogen to the anode gas flow path 6 is provided further upstream of the anode upstream side valve 11. In the hydrogen supply device 16, the pressure of high-pressure hydrogen supplied from a hydrogen tank or the like (not shown) is adjusted, and hydrogen is supplied to the anode gas flow path 6. Alternatively, a fuel reforming system may be used as the hydrogen supply device 16.

  A scavenging upstream valve 13 is provided upstream of the scavenging flow path 7, and a scavenging downstream valve 14 is provided downstream. Here, the coolant is circulated through the scavenging flow path 7 during normal operation, and the scavenging air is circulated during stop operation. Therefore, as the scavenging upstream valve 13, a scavenging upstream valve 13w that selects whether or not the coolant flows through the scavenging flow path 7, and a scavenging upstream valve 13a that selects whether or not the scavenging air flows. Is provided.

  A cooling system that adjusts the temperature of the fuel cell 1 by circulating the coolant through the scavenging flow path 7 includes a coolant pump 17, a coolant tank 18, and a radiator 19. Further, pure water is used as the cooling liquid. The coolant stored in the coolant tank 18 is taken out by the coolant pump 17 and circulated through the scavenging flow path 7 via the scavenging upstream valve 13w. In the fuel cell 1, the temperature of the coolant that has become high by absorbing heat generated by power generation is circulated to the radiator 19 through the scavenging downstream valve 14, and the coolant tank 18 is again adjusted. To recover. The coolant tank 18 is a tank capable of adjusting the tank internal pressure. For example, an opening valve 18a is provided above the coolant tank 18, and the gas in the coolant tank 18 can be discharged by opening the valve 18a.

  On the other hand, a scavenging gas pipe 20 is provided to allow the scavenging air to flow through the scavenging flow path 7. Here, the scavenging gas pipe 20 is a pipe branched from the pipe connected to the cathode gas flow path 5 from the air supply device 15 and connected to the scavenging flow path 7. The scavenging gas pipe 20 includes a scavenging upstream valve 13a. Here, the air supply device 15 disposed upstream of the cathode upstream side valve 9 is used as the air supply device for supplying the scavenging air. However, the present invention is not limited to this, and a separate air supply device for scavenging may be provided. .

  Next, FIG. 2 shows an outline of the fuel cell 1 used in such a fuel cell system. In FIG. 2, the fuel cell 1 is shown as a single fuel cell, but may be configured by stacking a plurality of fuel cells depending on the required power generation amount.

  The fuel cell 1 includes an MEA 2 composed of an electrolyte membrane, a catalyst layer, and a gas diffusion layer, and a cathode side separator 3 and an anode side separator 4 that sandwich the MEA 2. A cathode gas flow path 5 is formed between the cathode side separator 3 and the MEA 2. For example, the cathode gas flow path 5 is formed by forming a groove on the surface facing the MEA 2 of the cathode side separator 3. By causing the air supplied from the air supply device 15 to flow through the cathode gas channel 5, air is supplied to the gas diffusion layer and the catalyst layer on the MEA2 cathode side to cause an electrode reaction.

  On the other hand, an anode gas flow path 6 is formed between the anode side separator 4 and the MEA 2. For example, the anode gas flow path 6 is formed by forming a groove on the surface facing the MEA 2 of the anode side separator 4. By supplying the hydrogen supplied from the hydrogen supply device 16 to the anode gas flow path 6, hydrogen is supplied to the gas diffusion layer and the catalyst layer on the anode side of the MEA 2 to cause an electrode reaction.

  Further, a scavenging flow path 7 is formed inside the anode side separator 4. The scavenging flow path 7 is configured to be parallel to the anode gas flow path 6 and on the opposite side of the MEA 2 with respect to the anode gas flow path 6. That is, the anode-side separator 4 is composed of a region 4 a sandwiched between the MEA 2 and the anode gas flow channel 6 and the scavenging flow channel 7 and a region 4 b further outside the scavenging flow channel 7.

  A plurality of holes 8 that communicate the anode gas flow path 6 and the scavenging flow path 7 are formed in the region 4 a of the anode side separator 4. Here, the holes 8 are formed by forming the region 4a with a porous body that allows gas to pass therethrough. At this time, the region 4b may be formed of a porous body as well. That is, you may comprise the anode side separator 4 with a porous body.

  Next, a method for controlling the fuel cell 1 will be described.

  During operation other than the start / stop process, a coolant for adjusting the temperature of the fuel cell 1 is circulated through the scavenging flow path 7. That is, the scavenging upstream valve 13a is closed and the scavenging upstream valve 13w is opened. By driving the coolant pump 17, the coolant in the coolant tank 18 is taken out and circulated through the scavenging flow path 7 of the fuel cell 1.

  Further, air is supplied to the cathode gas flow path 5 and hydrogen is supplied to the anode gas flow path 6 according to the required load. Electric power is generated by causing an electrochemical reaction in the MEA 2 using the air and hydrogen. At this time, heat is generated with power generation and the temperature of the fuel cell 1 rises. However, heat exchange with the coolant flowing through the scavenging flow path 7 maintains the fuel cell 1 at a temperature suitable for operation. be able to. The coolant whose temperature has been raised by heat exchange is adjusted in the radiator 19 and then collected again in the coolant tank 18. Here, since the region 4a is formed of a porous body and pure water is used as the cooling liquid, the hydrogen flowing through the anode gas flow path 6 is used for scavenging by adjusting the cooling liquid pressure. It can be humidified by pure water flowing through the flow path 7.

  When the stop signal is detected, the supply of hydrogen to the anode gas flow path 6 is stopped. Further, the fuel cell 1 is connected to a discharge load (not shown). Further, when a signal requesting scavenging of the anode is detected, the anode upstream side valve 11 and the anode downstream side valve 12 are closed. That is, the anode gas flow path 6 is a closed space. On the other hand, the supply of air to the cathode gas channel 5 is continued. At this time, the air supply device 15 and the cathode downstream side valve 10 are controlled so that the pressure in the cathode gas passage 5 is maintained substantially the same as the pressure in the anode gas passage 6.

  Next, the coolant in the scavenging flow path 7 is scavenged with air. Here, the scavenging upstream valve 13w is closed and the scavenging upstream valve 13a is opened, thereby stopping the circulation of the coolant and starting the supply of scavenging air. Further, the scavenging downstream valve 14 is opened. Thus, the coolant in the scavenging flow path 7 is collected in the coolant tank 18 by the air supply device 16. At this time, the open valve portion 18a is opened so that the pressure in the coolant tank 18 does not increase excessively.

  When the coolant is scavenged from the scavenging flow path 7, the scavenging downstream valve 14 is closed. The pressure of the air supplied through the scavenging upstream valve 13a is adjusted to be approximately the same as the pressure of hydrogen in the anode gas flow path 6. As a result, hydrogen in the anode gas flow path 6 is consumed by causing an electrochemical reaction with oxygen on the cathode gas flow path 5 side, and the anode gas flow path 6 is converted into air that has passed through the region 4a through the holes 8. Replaced. At this time, air is supplied into the anode gas flow path 6 substantially uniformly along the power generation surface. Therefore, at the start of replacement, air is present on the anode separator 4 side and fuel gas is present on the MEA 2 side in the anode gas flow path 6. That is, a hydrogen layer and an air layer are formed in the anode gas flow path 6 along the reaction surface. As hydrogen is consumed, the space occupied by air gradually expands. At this time, the hydrogen concentration in the anode gas flow path 6 decreases, the boundary between hydrogen and air blurs, and the boundary between hydrogen and air does not exist. For this reason, it can be avoided that a battery is formed in the reaction region on the anode side due to the presence of an interface between hydrogen and air in the MEA 2.

  Note that the air supplied to the scavenging flow path 7 may be set to be equal to or greater than the hydrogen consumption. In this case, since the inside of the anode gas flow path 6 is replaced with a mixture of hydrogen and air in a short time, hydrogen and oxygen react directly on the catalyst on the anode side of the MEA 2. Therefore, it is possible to prevent a battery from being formed in the reaction region on the anode side, and to suppress carbon corrosion. At this time, the amount of hydrogen in the anode gas passage 6 is reduced to such an extent that the mixture of hydrogen and air is in a fuel lean state, and then the amount of hydrogen supplied is increased to generate the mixture. Is desirable.

  Here, since the region 4a is formed in a porous body and pure water is used as the cooling liquid, the air remains in the region 4a prior to the permeation of air from the scavenging flow path 7 to the anode gas flow path 6. The pure water that has been pushed out is pushed out into the anode gas flow path 6. At this time, since the reaction in the MEA 2 is continuously performed, pure water evaporates using heat accompanying the power generation reaction, and a water vapor layer is formed between the fuel gas and the air. As a result, the frequency at which the interface between hydrogen and air is present on the MEA 2 can be further reduced, and the formation of a battery in the reaction region on the anode side can prevent carbon from corroding.

  Next, the effect of this embodiment will be described.

  In the fuel cell 1 in which the anode gas channel 6 is configured on one surface of the electrode layer (MEA2) containing the electrolyte and the cathode gas channel 5 is configured on the other surface, the anode gas channel 6 is scavenged during the stop operation. A scavenging flow path 7 for circulating air is provided. Furthermore, a plurality of communication holes (holes 8) are provided from the scavenging flow path 7 to the anode gas flow path 6 for supplying air substantially uniformly in the flow path axial direction. As a result, air can be supplied substantially evenly in the axial direction of the anode gas flow path 6, thereby preventing the formation of a hydrogen region and an oxygen region in the reaction region on the anode side, thereby forming a battery. Can be prevented. As a result, scavenging can be performed without increasing the weight of the system and suppressing corrosion of carbon.

  In particular, a larger amount of air than the amount of hydrogen consumed is supplied from a communicating hole having a plurality of holes 8 in the axial direction and having a large total cross-sectional area. As a result, the hydrogen in the anode gas passage 6 is replaced with a mixture of hydrogen and air in a short time, thereby preventing the formation of a battery in the reaction region on the anode side and suppressing the corrosion of carbon. can do.

  Further, the scavenging flow path 7 is configured to be located on the opposite side of the MEA 2 with respect to the anode gas flow path 6. Thereby, hydrogen in the anode gas channel 6 can be replaced with air without hydrogen and air forming an interface on the reaction surface. As a result, the formation of a battery in the reaction region on the anode side can be prevented, and the corrosion of carbon can be suppressed.

  Further, a scavenging flow path 7 is formed substantially along the anode gas flow path 6, and at least a member separating the scavenging flow path 7 and the anode gas flow path 6 is formed of a porous member. As a result, the arrangement of the communication holes for supplying the air for scavenging becomes dense, so that the air can be supplied more evenly along the flow path axis. Therefore, the hydrogen region in the reaction region on the anode side of the MEA 2 And oxygen region can be prevented from being formed.

  An anode upstream valve 11 and an anode downstream valve 12 that selectively close the inlet and outlet of the anode gas flow path 6 are provided. During the stop operation, before the supply of air from the scavenging flow path 7 to the anode gas flow path 6 is started, the inlet and outlet of the anode gas flow path 6 are closed. Thereby, hydrogen remaining in the anode gas flow path 6 is consumed by power generation on the reaction surface while being pushed toward the reaction surface (MEA2) by the air supplied for scavenging. As a result, it is possible to prevent hydrogen and air from being mixed in the reaction region on the anode side while forming an interface, thereby suppressing carbon corrosion.

  When air is supplied from the scavenging flow path 7 to the anode gas flow path 6, air is also supplied to the cathode gas flow path 5 so that the pressures of the anode gas flow path 6 and the cathode gas flow path 5 are substantially the same. adjust. As described above, the pressures in the flow paths 5 and 6 of both electrodes can be kept equal to each other, so that the electrolyte layer can be prevented from being damaged.

  During operation, the coolant is circulated through the scavenging flow path 7. Since the scavenging air flow path and the coolant flow path are integrated, scavenging can be performed while suppressing carbon corrosion without increasing the size of the fuel cell 1.

  Furthermore, before the supply of the oxygen-containing gas from the scavenging flow path 7 to the anode gas flow path 6 is started, the scavenging flow path 7 is scavenged with the oxygen-containing gas. As a result, before air is supplied from the scavenging flow path 7 to the anode gas flow path 6, a water vapor layer is formed of water remaining in the holes 8, here, the holes 8 of the porous body. As a result, the formation of a hydrogen region and an oxygen region in MEA 2 can be further suppressed, so that carbon corrosion can be suppressed.

  In the above-described embodiment, the flow path of the coolant in the fuel cell 1 and the flow path of the scavenging air are the same flow path (the scavenging flow path 7), but this is not restrictive. You may form the flow path through which scavenging air distribute | circulates uniquely. In this case, a plurality of holes may be provided in which the holes 8 are provided uniformly along the anode gas flow path 6 and the scavenging air flow path and the anode gas flow path 6 communicate with each other. Even when the coolant is not circulated through the scavenging flow path 6, the scavenging flow path 7 is scavenged with air before the supply of air from the scavenging flow path 7 to the anode gas flow path 6 is started. preferable. Thereby, hydrogen mixed in the scavenging flow path 7 can be discharged through the holes 8. As a result, air can be supplied from the scavenging flow path 7 to the anode gas flow path 6 more evenly in the axial direction.

  Thus, it goes without saying that the present invention is not limited to the above-described embodiment, and various modifications can be made within the scope of the technical idea described in the claims.

  The present invention can be applied to a fuel cell that is desired to be reduced in size and weight, for example, a fuel cell mounted on a moving body as a drive source.

It is a schematic block diagram of the fuel cell system used for this embodiment. It is a schematic block diagram of the fuel cell used for this embodiment.

Explanation of symbols

1 Fuel Cell 2 MEA (Electrode Layer)
5 Cathode gas flow path 6 Anode gas flow path 7 Scavenging flow path 8 Communication hole (hole)
11 Anode upstream valve (closing means)
12 Anode downstream valve (closing means)

Claims (7)

In a fuel cell in which an anode gas flow path is formed on one surface of an electrode layer containing an electrolyte and a cathode gas flow path is formed on the other surface,
A scavenging flow path for circulating an oxygen-containing gas for scavenging the anode gas flow path during a stop operation;
The fuel cell further comprises a plurality of holes for supplying an oxygen-containing gas from the scavenging flow path to the anode gas flow path substantially uniformly in the flow path axial direction.   2. The fuel cell according to claim 1, wherein the scavenging flow path is configured to be positioned on an opposite side of the electrode layer with respect to the anode gas flow path. Forming the scavenging flow path substantially along the anode gas flow path;
The fuel cell according to claim 1, wherein at least a member that separates the scavenging flow path from the anode gas flow path is formed of a porous member. A closing means for selectively closing the inlet and outlet of the anode gas flow path;
2. The fuel cell according to claim 1, wherein the inlet and the outlet of the anode gas channel are closed before the supply of the oxygen-containing gas from the scavenging channel to the anode gas channel is started during the stop operation. .   The fuel cell according to claim 1, wherein the scavenging flow path is scavenged with an oxygen-containing gas before the supply of the oxygen-containing gas from the scavenging flow path to the anode gas flow path is started.   When the oxygen-containing gas is supplied from the scavenging flow path to the anode gas flow path, the pressure of the anode gas flow path and the cathode gas flow path is also increased by supplying the oxygen-containing gas also to the cathode gas flow path. The fuel cell according to claim 1, wherein the fuel cell is adjusted to be substantially the same.   The fuel cell according to any one of claims 1 to 6, wherein a coolant is circulated through the scavenging flow path during operation.

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