JP2012099332A - Fuel cell system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To achieve high output performance of a fuel cell regardless of the supply of a reactant gas.SOLUTION: A fuel cell system comprises: a first fuel cell stack 10A having a first catalyst layer; a second fuel cell stack 10B having a second catalyst layer with better water-holding properties than that of the first catalyst layer; oxidant-gas supply passages 32A and 32B supplying the fuel cell stacks 10A and 10B with an oxidant gas as a reactant gas and connected in parallel to the fuel cell stacks 10A and 10B, respectively; and a flow controlling unit for keeping the amount of flow of the oxidant gas supplied to the second fuel cell stack 10B larger than the amount of flow of the oxidant gas supplied to the first fuel cell stack 10A by controlling the amounts of the oxidant gas distributed to the fuel cell stacks 10A and 10B at the oxidant-gas supply passages 32A and 32B.

Description

  The present invention relates to a fuel cell system including a fuel cell stack.

  The fuel cell has a membrane electrode assembly including catalyst layers on both surfaces of the electrolyte membrane. Conventionally, by setting the water vapor adsorption amount of the catalyst layer to an appropriate value range, a fuel cell that exhibits high output performance in both a low humidification state and a high humidification state as well as in a good wet state has been proposed. (See Patent Document 1).

JP 2009-26602 A

  However, in the conventional technique, depending on the supply amount of the reaction gas, it is inevitable that it becomes dry up or flooding. When dry-up occurs, proton conductivity decreases. When flooding occurs, gas diffusion of the reaction gas is hindered, resulting in a problem that the output performance of the fuel cell decreases.

  The present invention has been made to solve the above-described problems, and an object of the present invention is to improve the output performance of a fuel cell regardless of the amount of reactant gas supplied.

  The present invention can be realized as the following forms or application examples in order to solve at least a part of the above-described problems.

Application Example 1 A fuel cell system,
A first fuel cell stack having a first catalyst layer;
A second fuel cell stack having a second catalyst layer whose water retention is higher than that of the first catalyst layer;
A passage for supplying reaction gas to the first and second fuel cell stacks, wherein the first and second fuel cell stacks are connected in parallel to the passage; and
By controlling the amount of reaction gas distributed to each fuel cell stack in the reaction gas supply passage, the flow rate of the reaction gas supplied to the second fuel cell stack is supplied to the first fuel cell stack. A fuel cell system comprising: a flow rate control unit configured to increase the flow rate of the reaction gas.

  According to the fuel cell system described in Application Example 1, the flow rate of the reaction gas supplied to the second fuel cell stack on the side where the water retention of the catalyst layer is high is the first flow rate on the side where the water retention of the catalyst layer is low. More than the flow rate of the reaction gas supplied to the fuel cell stack. Therefore, even if the flow rate of the reaction gas sent to the reaction gas supply passage (hereinafter referred to as “reaction gas total flow rate”) is large, the gas supply amount is low in the first fuel cell stack in which the water retention of the catalyst layer is low. Compared to the second fuel cell stack, it is less likely to dry up. On the other hand, even if the total flow rate of the reaction gas is small, the second fuel cell stack having a high water retention capacity of the catalyst layer has a larger gas supply amount than the first fuel cell stack, and is not easily flooded. Therefore, at least one of the first fuel cell stack and the second fuel cell stack can always maintain a good humidity environment. As a result, when compared with the conventional fuel cell system in which one fuel cell stack is connected to the reaction gas supply passage, the output performance of the entire fuel cell system can be improved if the total flow rate of the reaction gas is the same.

[Application Example 2] The fuel cell system according to Application Example 1,
The second fuel cell stack is
A fuel cell system having a structure in which water retention is increased by making the acid group density of the second catalyst layer higher than the acid group density of the first catalyst layer.

  According to the fuel cell described in Application Example 2, since a catalyst layer having a high acid group density can be produced simply by adding a simple acid treatment, the production is easy.

[Application Example 3] The fuel cell system according to Application Example 1 or 2,
The flow rate controller
A first adjusting unit that adjusts a distribution amount of the reaction gas to the first fuel cell stack so that a ratio of an actually supplied air amount to a theoretical air amount based on a load request becomes a first value; ,
The distribution amount of the reaction gas to the second fuel cell stack is set so that the ratio of the actually supplied air amount to the theoretical air amount based on the load request becomes a second value higher than the first value. A fuel cell system comprising: a second adjustment unit that adjusts.

  According to the fuel cell described in Application Example 3, since the flow rate control unit can be realized with a simple configuration, it is easy to manufacture.

[Application Example 4] The fuel cell system according to any one of Application Examples 1 to 3,
The fuel cell system, wherein the reaction gas whose flow rate is adjusted by the flow rate control unit is an oxidant gas.

  Since the generated water is generated on the cathode electrode side, the problem of the present invention becomes more important on the cathode electrode side where the wet environment is likely to change. According to the fuel cell system described in Application Example 3, since the supply amount of the oxidant gas that is the reaction gas to the cathode electrode is appropriately controlled, the output performance can be more reliably improved. .

  Furthermore, the present invention can be realized in various forms other than the first to fourth application examples, and for example, can be realized in the form of a vehicle equipped with the fuel cell system of the present invention.

1 is an overall configuration diagram of a fuel cell system according to an embodiment of the present invention. It is explanatory drawing which shows roughly the structure of the single cell 80 which is one unit of a fuel cell. It is explanatory drawing which shows the difference in the catalyst layer by the level of acid group density. It is process drawing which shows the preparation methods of catalyst ink. 4 is a flowchart showing an air flow rate control routine executed by an electronic control unit 60. It is a graph which shows the relationship between the air ratio and output voltage in both the fuel cell stack of the catalyst layer of a low acid group density and the fuel cell stack of a catalyst layer of a high acid group density.

  Next, embodiments of the present invention will be described based on examples.

A. Overall configuration:
FIG. 1 is an overall configuration diagram of a fuel cell system according to an embodiment of the present invention. This fuel cell system is mounted on a fuel cell vehicle, and includes two fuel cell stacks 10A and 10B, a reactive gas supply unit 20, a reactive gas discharge unit 40, and an electronic control unit 60.

  Each fuel cell stack 10A, 10B has a stack structure in which single cells of fuel cells are stacked. The fuel cell generates power by receiving supply of hydrogen gas as a reaction gas and an oxidant gas containing oxygen, and is a solid polymer fuel cell here. The structure of the fuel cell stacks 10A and 10B will be described in detail later.

  The reactive gas supply unit 20 includes a fuel reformer 21 for generating hydrogen gas and an oxidant gas supply device 31 for supplying oxidant gas.

  The fuel reformer 21 reforms fuel such as hydrocarbons supplied from the outside of the fuel cell system into hydrogen gas having a high hydrogen concentration by a steam reforming method or the like. The fuel reformer 21 basically generates hydrogen gas necessary for the electrochemical reaction of the entire plurality of fuel cell stacks 10A and 10B without excess or deficiency. The hydrogen gas output from the fuel reformer 21 is distributed to the fuel cell stacks 10A and 10B through the hydrogen gas supply passages 22A and 22B connected to the fuel cell stacks 10A and 10B, respectively. That is, the hydrogen gas supply passages 22 </ b> A and 22 </ b> B are connected in parallel to the fuel reformer 21.

  Hydrogen gas flow rate control valves 23A and 23B are provided in the hydrogen gas supply passages 22A and 22B, respectively, and the hydrogen gas flow rate control valves 23A and 23B distribute the hydrogen gas amount necessary for each fuel cell stack 10A and 10B. Adjusted.

  The oxidant gas supply device 31 adjusts oxidant gas such as air supplied from the outside of the fuel cell system to a predetermined pressure and temperature. The oxidant gas output from the oxidant gas supply device 31 is distributed to the fuel cell stacks 10A and 10B through the oxidant gas supply passages 32A and 32B connected to the fuel cell stacks 10A and 10B, respectively. That is, the oxidant gas supply passages 32 </ b> A and 32 </ b> B are connected in parallel to the oxidant gas supply device 31.

  The oxidant gas supply passages 32A and 32B are respectively provided with oxidant gas flow rate control valves 33A and 33B, and the oxidant gas flow rate control valves 33A and 33B provide the oxidant necessary for each fuel cell stack 10A and 10B. The distribution is adjusted to the amount of gas.

  The reactive gas discharge unit 40 includes hydrogen gas discharge passages 42A and 42B and oxidant gas discharge passages 44A and 44B. The hydrogen gas discharge passages 42A and 42B discharge the hydrogen gas discharged from the fuel cell stacks 10A and 10B. The oxidant gas discharge passages 44A and 44B discharge the oxidant gas discharged from the fuel cell stacks 10A and 10B.

  The electronic control unit 60 is configured as a microcomputer having a CPU, a RAM, and a ROM therein, and an output signal from the accelerator opening sensor 62 is obtained by developing and executing a computer program stored in the ROM on the RAM. Is output to the hydrogen gas flow rate control valves 23A and 23B and the oxidant gas flow rate control valves 33A and 33B provided in the reaction gas supply unit 20 to control the operation of the fuel cell system. The fuel cell system is provided with various actuators (not shown) in addition to the hydrogen gas flow rate control valves 23A and 23B and the oxidant gas flow rate control valves 33A and 33B, and the electronic control unit 60 controls these actuators. Thus, the entire operation of the fuel cell system is controlled.

B. Single cell configuration:
FIG. 2 is an explanatory diagram schematically showing the configuration of a single cell 80 that is one unit of the fuel cell provided in the fuel cell stacks 10A and 10B. As shown in the figure, the single cell 80 includes an electrolyte membrane 81, a pair of catalyst layers 82 and 83 having a sandwich structure sandwiching the electrolyte membrane 81, and a pair of gas diffusion layers 84 and 85 further sandwiching the sandwich structure. And separators 86a and 86b for further sandwiching these structures from the outside of the gas diffusion layers 84 and 85.

  Here, the separators 86a and 86b form flow paths 87P and 88P in the single cell of hydrogen gas and oxidant gas between the gas diffusion layers 84 and 85, respectively. The hydrogen gas supply passage 22A of the reaction gas supply unit 20 described above is connected to the hydrogen gas in-cell flow path 87P via a hydrogen gas manifold (not shown). The oxidant gas supply passages 32A and 32B of the reaction gas supply unit 20 described above are connected to the oxidant gas internal channel 88P via an oxidant gas manifold (not shown).

  The electrolyte membrane 81 is a proton conductive ion exchange membrane formed of a solid polymer material such as a fluorine resin, and exhibits good electrical conductivity in a wet state. In this example, a Nafion membrane (Nafion 112, manufactured by DuPont) having a thickness of 50 μm was used.

  The catalyst layers 82 and 83 are layers composed of carbon particles carrying a catalyst on the surface and a conductive polymer. As will be described later, the catalyst ink composed of the carbon particles carrying the catalyst and a conductive polymer is used as a gas. It is formed by coating on the diffusion layer. The catalyst layers 82 and 83 are regions where the above-described electrochemical reaction proceeds, and correspond to the main part of the present invention. The detailed structure and manufacturing method thereof will be described later.

The gas diffusion layers 84 and 85 are each formed of carbon paper that has been made water-repellent by coating the surface with polytetrafluoroethylene (PTFE, Teflon (registered trademark)). In order to form the single cell 80, first, a structure (electrode assembly) in which the electrolyte membrane 81 is sandwiched between the gas diffusion layers 84 and 85 is formed. In this case, the catalyst is formed on the carbon paper coated with PTFE. A pair of inks (inks composed of carbon particles carrying a catalyst and a conductive polymer) is prepared, and the catalyst ink applied on the carbon paper is vacuum dried at 100 ° C. The electrolyte membrane 81 is sandwiched with paper. At this time, the catalyst ink application surface is disposed so as to be in contact with the electrolyte membrane side, and hot pressing is performed at a surface pressure of 50 kg / cm ² and a temperature of 130 ° C. to obtain the electrode assembly.

  The separators 86a and 86b are formed of a gas-impermeable conductive member, for example, dense carbon that is compressed by gas to be gas-impermeable, or a metal member. The separators 86a and 86b are formed with rib portions of a predetermined shape on the surface, and as described above, the hydrogen gas in-cell flow path 87P or the oxidant gas between the adjacent gas diffusion layers. A single cell internal flow path 88P is formed. In FIG. 2, the ribs forming the gas flow path are formed only on one side of each separator 86a, 86b, but in actuality, they are formed on both sides. The ribs formed on one surface of each of the separators 86a and 86b form a hydrogen gas single-cell flow path 87P between the adjacent gas diffusion layers 84, and the ribs formed on the other surfaces of the separators 86a and 86b are An in-single cell flow path 88P for the oxidant gas is formed between the gas diffusion layers 85 provided in the adjacent single cells. Therefore, the separators 86a and 86b serve to form a gas flow path between the gas diffusion layers and to separate the flow of hydrogen gas and oxidant gas between adjacent single cells.

  In addition, the shape of the rib formed on the surface of each separator may be any shape as long as the gas flow path is formed and the fuel gas or the oxidant gas can be supplied to the gas diffusion layer. In this embodiment, the ribs formed on the surface of each separator have a plurality of groove-like structures formed in parallel.

  The configuration of the single cell 80, which is the basic structure of the fuel cell, has been described above. When actually assembling as a fuel cell stack, a plurality of sets of single cells 80 (for example, 100 sets) are stacked, and a current collector plate, an insulating plate, and an end plate (not shown) are further arranged at both ends thereof, and the fuel cell stack 10A. 10B is completed.

C. Configuration of catalyst layer:
One fuel cell stack (hereinafter referred to as “first fuel cell stack”) 10A and the other fuel cell stack (hereinafter referred to as “second fuel cell stack”) 10B are different in the following points. . That is, the acid group density of the catalyst layer 83 that functions as the oxidant gas side electrode in the second fuel cell stack 10B is equal to the acid density of the catalyst layer 83 that functions as the oxidant gas side electrode in the first fuel cell stack 10A. It is higher than the base density. In this embodiment, the acid group density of the catalyst layer 83 in the first fuel cell stack 10A is 0.3 mmol / g-C, and the acid group density of the catalyst layer 83 in the second fuel cell stack 10B is 0.85 mmol. / G-C. The acid referred to here is carboxylic acid (COOH).

  FIG. 3 is an explanatory diagram showing the difference in the catalyst layer depending on the acid group density. FIG. 3A is a diagram schematically showing the state of the catalyst layer having a low acid group density, and FIG. 3B is a diagram schematically showing the state of the catalyst layer having a high acid group density.

  As shown in FIGS. 3A and 3B, the catalyst layer is formed of catalyst particles 101 and a proton conductive polymer covering the periphery of the catalyst particles 101. The catalyst particle 101 is obtained by supporting a noble metal 105 on a support 103. In this embodiment, for example, hydrophobic carbon black (particle size of about 0.1 to 20 μm) is used as the carrier 103. Further, as the noble metal 105 to be supported, for example, platinum or a platinum alloy is used.

  In the conductive polymer, the catalytic acid group 107 is exposed toward the surface of the carrier 103, and the ionomer sulfonic acid group 109 is further provided.

  The structure of the catalyst layer is as described above. However, when the catalyst layer having a low acid group density is compared with the catalyst layer having a high acid group density, the number of catalyst acid groups 107 is different. In the example of FIG. 3A where the acid group density is low, the number of catalyst acid groups 107 is seven. In contrast, in the example of FIG. 3B where the acid group density is high, the number of catalyst acid groups 107 is twelve. As described above, the catalyst layer having a high acid group density has a larger number of catalyst acid groups 107 than the catalyst layer having a low acid group density. Since the catalytic acid group 107 strongly attracts water molecules, the high acid group density catalyst layer having a large number of catalytic acid groups 107 has higher water retention than the low acid group density catalyst layer.

  From the above, the catalyst layer 83 in the second fuel cell stack 10B (hereinafter, this catalyst layer 83 is referred to as “catalyst layer 83B”) is more water-retaining than the catalyst layer 83 in the first fuel cell stack 10A. It has a high quality.

D. Preparation method of catalyst ink:
The high acid group density of the catalyst layers 83A and 83B varies depending on the components of the catalyst ink. Therefore, a method for producing a catalyst ink will be described next.

  FIG. 4 is a process diagram showing a method for producing a catalyst ink. This process diagram is for the catalyst ink used for the catalyst layer 83B in the second fuel cell stack 10B. As shown in the drawing, first, carbon black such as Ketjen EC (Ketch Emplack International) or Vulcan (Cabot) is prepared as a carrier (first step S1). Note that carbon nanotubes or acetylene black may be used instead of carbon black.

  Next, the carbon black prepared in the first step S1 is suspended and stirred in distilled water, a Pt compound (chloroplatinic acid, etc.) is dropped, and a reducing agent such as ethanol is dropped, whereby Pt is deposited on the carbon black. Precipitate (second step S2).

  Thereafter, the mixture obtained in the second step S2 is filtered, and the solid matter is dried, thereby obtaining a Pt-supported catalyst (third step S3).

  Further, the Pt-supported catalyst obtained in the third step S3 is subjected to an acid treatment using 0.5N nitric acid at 90 ° C. for 24 hours (fourth step S4). The treatment in the fourth step S4 is for increasing the acid group density of the Pt-supported catalyst obtained in the third step S3. The first step S1 to the third step S3 are executed in the same manner when the catalyst layer 83B in the second fuel cell stack 10B is produced. Catalyst particles that are 3 mmol / g-C can be obtained. On the other hand, when producing the catalyst ink of the catalyst layer 83B in the second fuel cell stack 10B, the acid group density of the catalyst layer 83 is set to 0.85 mmol / g by further executing the fourth step S4. -C.

  Thereafter, after adding distilled water to the Pt-supported catalyst obtained in the fourth step S4, a solvent such as ethanol or 1-panol is added, and a Nafion solution (manufactured by DuPont, EW1000) is further added as a proton conductor. (5th process S5). The amount added was adjusted so that the sulfonic acid density was 0.8. Thereafter, this mixture was sufficiently stirred and subjected to dispersion treatment by ultrasonic irradiation, bead milling, etc. in order to atomize and uniformly disperse the particles (sixth step S6). Thus, the catalyst ink used for the catalyst layer 83B in the second fuel cell stack 10B can be produced.

  Note that when the catalyst layer 83A in the first fuel cell stack 10A is manufactured, the steps except the acid treatment in the fourth step S4, that is, the first step S1, the second step S2, the third step S3, the fifth step S4. By performing step S5 and sixth step S6, the catalyst ink used for the catalyst layer 83A can be produced.

E. Control processing:
FIG. 5 is a flowchart showing an air flow rate control routine executed by the electronic control unit 60. This air flow rate control routine is repeatedly executed at predetermined intervals as part of the operation control of the fuel cell stacks 10A and 10B in the electronic control unit 60.

  As shown in FIG. 3, when the process is started, the CPU of the electronic control unit 60 calculates a theoretical air amount based on the load request current (step S110). The load request current is a generated current required by the load. The load originally means all those that use the power of the fuel cell, but here, the load is mainly a motor, and the load demand is determined by the opening of the accelerator. That is, based on the output signal from the accelerator opening sensor 62, the air amount theoretically necessary to achieve the load requirement, that is, the theoretical air amount is calculated. This is based on a well-known arithmetic expression.

  Next, the CPU of the electronic control unit 60 has a ratio of the actually supplied air amount (hereinafter referred to as “actual air amount”) to the theoretical air amount (hereinafter referred to as “air ratio”) as 1.2. Thus, the oxidant gas flow rate adjustment valve 33A on the first fuel cell stack 10A side is adjusted (step S120). Since the air ratio is expressed by the following equation (1), the actual air amount is obtained from the following equation (2) obtained by modifying the following equation (1), and the oxidant gas flow rate control valve is realized so as to realize the actual air amount. Adjust 33A.

Air ratio = actual air amount / theoretical air amount (1)
Actual air volume = Air ratio / Theoretical air volume (2)

  That is, in step S120, the actual air amount is obtained by multiplying the theoretical air amount calculated in step S110 by 1.2, and the oxidant gas flow rate on the first fuel cell stack 10A side is realized so as to realize the actual air amount. The control valve 33A is adjusted.

  Subsequently, the CPU of the electronic control unit 60 adjusts the oxidant gas flow rate adjustment valve 33B on the second fuel cell stack 10B side so that the air ratio becomes 1.4 (step S130). That is, the actual air amount is obtained by multiplying the theoretical air amount calculated in step S110 by 1.4, and the oxidant gas flow rate adjustment valve 33B on the second fuel cell stack 10B side is realized so as to realize this actual air amount. Adjust.

  Step S120 and step S130 can be executed by switching the order, and are executed substantially simultaneously. After the execution of step S130, the process returns to “RETURN”, and this air flow rate control routine is temporarily terminated.

  According to the air flow rate control routine configured as described above, the first fuel cell stack 10A is supplied with air as an oxidant gas having a relatively small flow rate such as an air ratio of 1.2. A relatively large flow rate of air with an air ratio of 1.4 is supplied to the fuel cell stack 10B of No. 2. That is, a small flow rate of air is supplied to the first fuel cell stack 10A with relatively low water retention capacity of the catalyst layer 83A, and a large flow rate with respect to the second fuel cell stack 10B with relatively high water retention capacity of the catalyst layer 83B. Of air will be supplied.

  In this embodiment, the oxidant gas flow rate adjusting valves 33A and 33B provided in the oxidant gas supply passages 32A and 32B, the electronic control unit 60, and the air flow rate control routine executed by the electronic control unit 60, However, the “flow rate control unit” in Application Example 1 is configured.

F. Example effect:
As described above, in the fuel cell stack of the present embodiment, in the first fuel cell stack 10A having relatively low water retention, the air ratio of the supply air is 1.2, and the water retention is relatively high. In the second fuel cell stack 10B, the air ratio of the supply air is 1.4. For this reason, the air ratio is 1.3 when viewed as a whole of the fuel cell system, but the present embodiment is better than the case where the air ratio of each of the fuel cell stacks 10A and 10B is 1.3. Higher output performance can be obtained. The reason why high output performance can be obtained is as follows.

  Even if the discharge amount of the oxidant gas supply device 31 is large, the first fuel cell stack 10A in which the water retention of the catalyst layer 83A is low has a smaller gas supply amount than the second fuel cell stack 10B, resulting in dry-up. hard. On the other hand, even if the discharge amount of the oxidant gas supply device 31 is small, in the second fuel cell stack 10B in which the water retention of the catalyst layer 83B is high, the gas supply amount is larger than in the first fuel cell stack 10A, and flooding is performed. It ’s hard to be. Accordingly, at least one of the first fuel cell stack 10A and the second fuel cell stack 10B can always maintain a good humidity environment, and the output performance of the entire fuel cell system can be improved. Because.

  FIG. 6 is a graph showing the relationship between the air ratio and the output voltage in both the low acid group density catalyst layer fuel cell stack and the high acid group density catalyst layer fuel cell stack. As shown in the graph, in the case of a fuel cell stack with a catalyst layer with a low acid group density, the output voltage increases when the air ratio is as low as about 1.2, and in the case of a fuel cell stack with a catalyst layer with a high acid group density. The output voltage increases when the air ratio is as high as about 1.4. Also from this experimental result, it can be seen that at least one of the first fuel cell stack 10A and the second fuel cell stack 10B can always maintain a good humidity environment.

G. Variations:
The present invention is not limited to the above-described examples and embodiments, and can be implemented in various modes without departing from the gist thereof. For example, the following modifications are possible.

・ Modification 1:
In the embodiment and each modification, the acid group density of the catalyst layer 83 on the first fuel cell stack 10A side is set to 0.3 mmol / g-C, and the acid group of the catalyst layer 83 on the second fuel cell stack 10B side is set. The density was set to 0.85 mmol / g-C, but these values indicate that the acid group density of the catalyst layer 83 on the second fuel cell stack 10B side is the acid group density of the catalyst layer 83 on the first fuel cell stack 10A side. If it is higher, it can be changed to any value. In the above-described embodiments and modifications, the first and second fuel cell stacks 10A. The water retention of 10B is changed, but in place of this, the amount of the proton conductive polymer relative to the catalyst support is changed. The water retention may be changed by changing the ion exchange resin dry weight per mol). Increasing the amount of proton conductive polymer with respect to the catalyst carrier improves water retention. When the EW of the ionomer is lowered, the water retention is improved because the number of mols of ion exchange groups is increased.

Modification 2
In the above-described embodiments and modifications, the oxidant gas is supplied to the first fuel cell stack 10A having the catalyst layer 83 with a low acid group density so that the air ratio becomes 1.2. The oxidant gas is supplied to the second fuel cell stack 10B having the base density catalyst layer 83 so that the air ratio becomes 1.4. If the air ratio on the 10B side is higher than the air ratio on the first fuel cell stack 10A side and is 1.0 or more, it can be changed to any value.

・ Modification 3:
In the above-described embodiments and modifications, the reaction gas is distributed to the first and second fuel cell stacks 20A and 20B by the respective oxidant gas flow rate control valves 33A provided in the respective oxidant gas supply passages 32A and 32B. However, instead of this, a three-way valve may be provided at the connecting portion between the oxidant gas supply passages 32A and 32B.

-Modification 4:
In the embodiment and each modification, the oxidant gas (air) is adjusted as the reaction gas by the air flow rate control routine. However, instead of this, the hydrogen gas may be adjusted. In the fuel cell, the generated water is generated on the cathode electrode side, but the generated water moves to the anode electrode side through the electrolyte membrane. Therefore, the same configuration as in the above embodiment can be obtained by adjusting hydrogen gas instead of air. Can be played.

-Modification 5:
In the embodiment and the modified example, two fuel cell stacks are provided. However, instead of this, a structure in which three or more fuel cell stacks are provided may be used. Also in this case, it is sufficient that the configuration of the present invention is applied to two fuel cell stacks selected from three or more fuel cell stacks, and any configuration may be used for the remaining fuel cell stacks.

Modification 6:
The present invention may be applied to a fuel cell of a different type from the above embodiments and modifications. For example, it can be applied to a direct methanol fuel cell. Or the fuel cell which has electrolyte layers other than a solid polymer may be sufficient, and the same effect is acquired by applying this invention.

Modification 7:
The fuel cell systems according to the above-described embodiments and modifications may be mounted on other mobile objects such as ships and aircraft, and other various industrial machines, instead of being mounted on a vehicle (automobile).

  In the embodiment, a part of the configuration (air flow control routine) realized by software may be replaced with hardware. Moreover, elements other than the elements described in the independent claims among the components in the above-described embodiments and modifications are additional elements and can be omitted as appropriate. Furthermore, the present invention is not limited to these examples and modifications, and can be implemented in various modes without departing from the scope of the invention.

DESCRIPTION OF SYMBOLS 10A ... 1st fuel cell stack 10B ... 2nd fuel cell stack 20 ... Reaction gas supply part 21 ... Fuel reformer 22A ... Hydrogen gas supply passage 22B ... Hydrogen gas supply passage 23A ... Hydrogen gas flow control valve 23B ... Hydrogen Gas flow control valve 31 ... Oxidant gas supply device 32A ... Oxidant gas supply passage 32B ... Oxidant gas supply passage 33A ... Oxidant gas flow control valve 33B ... Oxidant gas flow control valve 40 ... Reactant gas discharge part 42A ... Hydrogen Gas discharge passage 42B ... Hydrogen gas discharge passage 44A ... Oxidant gas discharge passage 44B ... Oxidant gas discharge passage 60 ... Electronic control unit 62 ... Accelerator opening sensor 80 ... Single cell 81 ... Electrolyte membrane 82 ... Catalyst layer 83 ... Catalyst layer 83A ... Catalyst layer 83B ... Catalyst layer 84 ... Gas diffusion layer 85 ... Gas diffusion layer 86a ... Separator 87P ... Channel in single cell 8 P ... single cell flow path 101 ... catalyst particles 103 ... bearing member 105 ... precious metal 107 ... catalyst group 109 ... ionomer sulfonic acid

Claims (4)

A fuel cell system,
A first fuel cell stack having a first catalyst layer;
A second fuel cell stack having a second catalyst layer whose water retention is higher than that of the first catalyst layer;
A passage for supplying reaction gas to the first and second fuel cell stacks, wherein the first and second fuel cell stacks are connected in parallel to the passage; and
By controlling the amount of reaction gas distributed to each fuel cell stack in the reaction gas supply passage, the flow rate of the reaction gas supplied to the second fuel cell stack is supplied to the first fuel cell stack. A fuel cell system comprising: a flow rate control unit configured to increase the flow rate of the reaction gas. The fuel cell system according to claim 1,
The second fuel cell stack is
A fuel cell system having a structure in which water retention is increased by making the acid group density of the second catalyst layer higher than the acid group density of the first catalyst layer. The fuel cell system according to claim 1 or 2,
The flow rate controller
A first adjusting unit that adjusts a distribution amount of the reaction gas to the first fuel cell stack so that a ratio of an actually supplied air amount to a theoretical air amount based on a load request becomes a first value; ,
The distribution amount of the reaction gas to the second fuel cell stack is set so that the ratio of the actually supplied air amount to the theoretical air amount based on the load request becomes a second value higher than the first value. A fuel cell system comprising: a second adjustment unit that adjusts. The fuel cell system according to any one of claims 1 to 3,
The fuel cell system, wherein the reaction gas whose flow rate is adjusted by the flow rate control unit is an oxidant gas.

Images