WO2009031000A1

WO2009031000A1 - Fuel cell stack and fuel cell system

Info

Publication number: WO2009031000A1
Application number: PCT/IB2008/002267
Authority: WO
Inventors: Yoshihito Kanno; Kazuhisa Kunitake
Original assignee: Toyota Motor Corp
Current assignee: Toyota Motor Corp
Priority date: 2007-09-03
Filing date: 2008-09-02
Publication date: 2009-03-12
Anticipated expiration: 2010-03-03
Also published as: JP2009059650A

Abstract

A fuel cell stack 1 in which cells each having an anode and a cathode are stacked includes a fuel gas channel 21A that supplies a fuel gas to the anode, an oxidant gas channel 21B that supplies an oxidant gas to the cathode, an anode cooling medium channel 24 that conducts a cooling medium that cools the fuel gas that flows in the fuel gas channel 21A, and a cathode cooling medium channel 25 that conducts the cooling medium that cools the oxidant gas that flows in the oxidant gas channel 21B.

Description

FUEL CELL STACKAND FUEL CELL SYSTEM

BACKGROUND OF THE INVENTION

1. Field of the Invention [0001] The invention relates to a fuel cell stack and a fuel cell system in which water is produced during electricity generation.

2. Description of the Related Art

[0002] The cooling water channel in each cell of a fuel cell stack is provided so as to be used for the cooling of both the anode and the cathode, and the cooling water channels of the cells are merged by a manifold. Thus, the cooling system of the fuel cell stack is a single system (see Japanese Patent Application Publication No. 2003-17105 (JP-A-2003-17105)). In this case, the temperature of the anode and the temperature of the cathode are substantially the same. It is important to know how much product water produced at the cathode moves to the anode through the electrolyte membrane, in order to extract maximum performance of the fuel cell while avoiding flooding and dry-up (see Japanese Patent Application Publication No. 2005-32561 (JP-A-2005-32561) and Japanese Patent Application Publication No. 7-320755 (JP-A-7-320755)). The amount of movement of product water is affected by various electricity generation conditions such as the stoichiometric ratio, pressure, temperature, etc. A factor that affects the amount of movement of product water is the cooling water temperature difference.

[0003] As a method for avoiding flooding at the time of start-up of a fuel cell stack, there is a method in which a larger amount of coolant is caused to flow to an end plate on the cathode side of a fuel cell stack than to an end plate on the anode side of the fuel cell stack (see Japanese Patent Application Publication No. 2006-164681 (JP-A-2006-164681)). According to this method, the temperature of the cathode side of the fuel cell stack becomes higher than that of the anode side of the fuel cell stack, and water in each cell moves from the cathode side to the anode side, so that the flooding at the time of start-up of the fuel cell stack can be avoided.

[0004] However, in the foregoing related-art method, while the temperature in each cell becomes higher at the cathode than at the anode, the absolute values of the temperature in the individual cells cannot be made uniform. That is, temperature differences between the cells occur in the stacking direction of the fuel cell stack. This is because temperature adjustment is performed only at the end plates of the anode side and the cathode side of the fuel cell stack. If the foregoing related-art method is performed during electricity generation, the voltages of the individual cells greatly vary, and stable electricity generation cannot be accomplished.

SUMMARY OF THE INVENTION [0005] The invention provides a technology of controlling the temperatures of the anode and the cathode of each cell of a fuel cell stack.

[0006] A first aspect of the invention provides a fuel cell stack that includes: a plurality of stacked cells each having an anode, a cathode, a fuel gas channel that supplies a fuel gas to the anode, and an oxidant gas channel that supplies an oxidant gas to the cathode; an anode cooling medium channel that conducts a cooling medium that cools the fuel gas that flows in the fuel gas channel; and a cathode cooling medium channel that conducts a cooling medium that cools the oxidant gas that flows in the oxidant gas channel.

[0007] In this construction, the fuel gas that flows in the fuel gas channel is cooled by the cooling medium that flows in the anode cooling medium channel, and the oxidant gas that flows in the oxidant gas channel is cooled by the cooling medium that flows in the cathode cooling medium channel. Then, the anode is supplied with the fuel gas that is cooled by the cooling medium that flows in the anode cooling medium channel, and the cathode is supplied with the oxidant gas that is cooled by the cooling medium that flows in the cathode cooling medium channel. Therefore, the cathodes and the anodes can be cooled by using different cooling medium channels.

[0008] In the fuel cell stack of the foregoing aspect, the cooling medium that cools the fuel gas and the cooling medium that cools the oxidant gas may flow independently of each other. [0009] In the fuel cell stack of the foregoing aspect, the anode cooling medium channel and the cathode cooling medium channel may be provided between at least one pair of adjacent cells of the plurality of cells.

[0010] The fuel cell stack in accordance with the foregoing aspect may further include: a plurality of sandwiching holders that sandwichingly hold each of the plurality of cells, and one of surfaces of each of the plurality of sandwiching holders may be provided with the anode cooling medium channel, and another one of the surfaces of each of the plurality of sandwiching holders may be provided with the cathode cooling medium channel, and a heat insulating member or a space may be provided between the anode cooling medium channel and the cathode cooling medium channel.

[0011] According to this construction, since the heat insulating member or the space is provided between the anode cooling medium channel and the cathode cooling medium channel, it becomes possible to thermally insulate the cooling medium that cools the fuel gas that is supplied to the anode and the cooling medium that cools the oxidant gas that is supplied to the cathode.

[0012] A second aspect of the invention relates to a fuel cell system includes: the fuel cell stack in accordance with the foregoing first aspect; and control means that controls at least one of flow amount and temperature of the cooling medium that flows in the anode cooling medium channel, and at least one of flow amount and temperature of the cooling medium that flows in the cathode cooling medium channel.

[0013] The fuel cell system in accordance with the foregoing aspect may further include determination means for determining whether or not the fuel cell stack is in a dried-up state, and if it is determined that the fuel cell stack is in the dried-up state, the control means may control the flow amount of the cooling medium that flows in the anode cooling medium channel and the flow amount of the cooling medium that flows in the cathode cooling medium channel so that the temperature of the cooling medium that flows in the anode cooling medium channel is lower than the temperature of the cooling medium that flows in the cathode cooling medium.

[0014] In this construction, in the case where it is determined that the fuel cell stack is in the dried-up state, the temperature of the oxidant gas supplied to the cathode becomes higher than the temperature of the fuel gas supplied to the anode. As a result, the amount of movement of back-diffused water from the anode to the cathode increases, so that it becomes possible to avoid the dry-up. [0015] Furthermore, in the foregoing aspect, the anode cooling medium channel and the cathode cooling medium channel are disposed in each cell. Therefore, the temperature of the anode can be made uniform among all the cells, and the temperature of the cathode can be made uniform among all the cells. As a result, by restraining the occurrence of voltage difference between cells, it becomes possible to avoid the dried-up state while securing reliable electricity generation.

[0016] In the fuel cell system in accordance with the aspect, the determination means may determine whether or not the fuel cell stack may be in the dried-up state based on at least one of the temperature of the cooling medium that cools the fuel gas that flows in the fuel gas channel, and the temperature of the cooling medium that cools the oxidant gas that flows in the oxidant gas channel.

[0017] In the fuel cell system in accordance with the foregoing aspect, the determination means may determine whether or not the fuel cell stack is in the dried-up state based on impedance between the anode and the cathode. Furthermore, in the fuel cell system in accordance with the foregoing aspect, the determination means may determine whether or not the fuel cell stack is in the dried-up state based on an amount of output current of the fuel cell stack.

[0018] In the fuel cell system in accordance with the foregoing aspect, the determination means may determine whether or not the anode side of the fuel cell stack is in a flooded state, and if it is determined the anode side of the fuel cell stack is in the flooded state, the control means may control the flow amount of the cooling medium that flows in the anode cooling medium channel and the flow amount of the cooling medium that flows in the cathode cooling medium channel so that the temperature of the cooling medium that flows in the anode cooling medium channel becomes higher than the temperature of the cooling medium that flows in the cathode cooling medium channel. [0019] In this construction, in the case where it is determined that the anode side of the fuel cell stack is in the flooded state, the temperature of the fuel gas supplied to the anode becomes higher than the temperature of the oxidant gas supplied to the cathode.

As a result, the amount of movement of back-diffused water from the anode to the cathode decreases, and it becomes possible to avoid flooding.

[0020] In the foregoing construction, the anode cooling medium channel and the cathode cooling medium channel are disposed in each cell. Therefore, the temperature of the anode can made uniform among all the cells, and the temperature of the cathode can be made uniform among the cells. As a result, by restraining the occurrence of voltage difference between cells, it becomes possible to avoid flooding while securing stable electricity generation.

[0021] In the fuel cell system in accordance with the foregoing aspect, the determination means may determine whether or not the anode side of the fuel cell stack is in the flooded state based on cell voltage in the fuel cell stack. In the fuel cell system in accordance with the foregoing aspect, the determination means may determine whether or not the anode side of the fuel cell stack is in the flooded state based on rate of decrease of cell voltage in the fuel cell stack.

[0022] The fuel cell system of the foregoing aspect may further include: a first channel that supplies the fuel cell stack with the cooling medium that flows in the anode cooling medium channel; and a second channel that supplies the fuel cell stack with the cooling medium that flows in the cathode cooling medium channel.

[0023] A third aspect of the invention relates to a cooling method for a fuel cell stack in which a plurality of cells each having an anode and a cathode are stacked. The cooling method for the fuel cell stack in accordance with the aspect includes providing the fuel cell stack with a plurality of cooling medium channels so that a cooling medium that cools a fuel gas that is supplied to the anode and a cooling medium that cools an oxidant gas that is supplied to the cathode flow independently of each other.

BRIEF DESCRIPTION OF THE DRAWINGS [0024] The foregoing and further objects, features and advantages of the invention will become apparent from the following description of example embodiments with reference to the accompanying drawings, wherein like numerals are used to represent like elements and wherein: FIG 1 is a diagram showing an example of a construction of a fuel cell system in accordance with a first embodiment of the invention;

FIG 2 is a diagram showing an example of an internal structure of the fuel cell stack in accordance with the first embodiment of the invention;

FIG 3 is a flowchart illustrating an operation of a fuel cell system in accordance with the first embodiment of the invention;

FIG 4 is a flowchart illustrating an operation of the fuel cell system in accordance with the first embodiment of the invention;

FIG 5 is an example of a construction of a fuel cell system in accordance with a second embodiment of the invention; FIG. 6 is a diagram showing an example of an internal structure of the fuel cell stack in accordance with the second embodiment of the invention; and

FIG. 7 is a detailed diagram of an example of the example of the internal structure of the fuel cell stack in accordance with the second embodiment of the invention.

DETAILED DESCRIPTION OF EMBODIMENTS

[0025] Fuel cell systems in accordance with forms for carrying out the invention (hereinafter, referred to as "embodiments") will be described hereinafter with reference to the drawings. The constructions of the following embodiments are merely illustrative, and the invention is not limited by the constructions of the embodiments. [0026] A fuel cell system in accordance with a first embodiment of the invention will be described with reference to FIGS. 1 and 2. FIG 1 is an illustrative diagram of the fuel cell system in accordance with the first embodiment of the invention. In FIG 1, the fuel cell system has a fuel cell stack 1, a radiator 3 equipped with a cooling fan 2, a cooling liquid channel 4 that circulates a cooling liquid (cooling water) as an example of a cooling medium between inside the fuel cell stack 1 and inside the radiator 3, a cooling liquid pump 5 provided on the cooling liquid channel 4, and an ECU (electronic control unit) 6. The fuel cell system further has a bypass channel 7 that is a channel communicating with the cooling liquid channel 4 and that circulates the cooling liquid with respect to the fuel cell stack 1 without passing the cooling liquid through the radiator 3. In FIG 1, constructions in the fuel cell system that are related to the supply or discharge of gasses are omitted from illustration, and only construction portions related to the circulation of the cooling liquid are shown.

[0027] The fuel cell stack 1 is constructed by stacking a plurality of cells. As shown in FIG 2, each cell in the fuel cell stack 1 is constructed of an MEGA (membrane-electrode-gasket assembly) 20, a porous body 21 A (an example of a fuel gas channel in the invention) and a porous body 21B (an example of an oxidant gas channel in the invention) that are disposed so as to sandwich the MEGA 20, and a pair of separators 22 disposed so as to sandwich the porous body 21A and the porous body 21B. The MEGA 20 is constructed of an electrolyte membrane, two catalyst layers (an anode and a cathode) formed so as to sandwich the electrolyte membrane, and a pair of gas diffusion layers formed so as to sandwich the two catalyst layers. Incidentally, an MEA (membrane-electrode assembly) can be used instead of the MEGA.

[0028] The porous body 21 A and the porous body 21 B are made up of a metal material that has small pores. Hydrogen (an example of a fuel gas in the invention) flows within the porous body 21A, and air (an example of an oxidant gas in the invention) flows within the porous body 21B. The hydrogen that flows within the porous body 21 A is supplied from a hydrogen tank (not shown). The air that flows within the porous body 21B is supplied from an air compressor (not shown). Incidentally, instead of the porous body 21A and the separator 22, a separator equipped with a channel that conducts hydrogen can be used. Likewise, instead of the porous body 21B and the separator 22, a separator equipped with a channel that conducts air can be used.

[0029] Each anode of the fuel cell stack 1 is supplied with hydrogen from the porous body 21A. Each cathode of the fuel cell stack 1 is supplied with air from the porous body 21B.

[0030] In the fuel cell stack 1, an electrochemical reaction occurs between hydrogen and oxygen contained in the air, generating electric energy. Besides, at each cathode of fuel cell stack 1, the hydrogen ions produced from hydrogen combine with oxygen to produce water.

[0031] Molded plates 23 (an example of a sandwiching holder in the invention) provided on outer sides of the separators 22 have anode cooling liquid channels 24 (an example of an anode cooling medium channel in the invention), or cathode cooling liquid channels 25 (an example of a cathode cooling medium channel in the invention). The numbers of anode cooling liquid channels 24 and of cathode cooling liquid channels 25 shown in FIG 2 are merely illustrative. In each molded plate 23, an arbitrary number of anode cooling liquid channels 24 or cathode cooling liquid channels 25 can be formed.

The cooling liquid for cooling the hydrogen that flows in the porous body 21A flows in the anode cooling liquid channels 24. The cooling liquid for cooling the air that flows in the porous body 21B flows in the cathode cooling liquid channels 25.

[0032] The molded plates 23 can be provided for each cell. Therefore, the cooling liquid flowing in the anode cooling liquid channels 24 can cool the hydrogen that flows in the porous body 21 A of each cell, and the cooling liquid flowing in the cathode cooling liquid channels 25 can cool the air that flows in the porous body 21B of each cell.

[0033] As shown in FIG 1, the radiator 3 is connected to the fuel cell stack 1 via the cooling liquid channel 4. The cooling liquid channel 4 is provided with the cooling liquid pump 5 between the fuel cell stack 1 and the radiator 3. By driving the cooling liquid pump 5, the cooling liquid is circulated in the fuel cell stack 1, the cooling liquid channel 4, and the radiator 3. The driving of the cooling liquid pump 5 is controlled by a control signal from the ECU 6 that is electrically connected to the cooling liquid pump 5.

[0034] The cooling liquid is supplied to the fuel cell stack 1, and the temperature of the cooling liquid rises due to heat exchange within the fuel cell stack 1. The radiator 3 lowers the temperature of the cooling liquid that is supplied thereto via the cooling liquid channel 4. The radiator 3 has therein a channel in which the cooling liquid flows, and is constructed so as to allow external air to pass through the radiator 3. Specifically, heat exchange is allowed between the external air passing through the radiator 3 and the cooling liquid flowing within the radiator 3. The radiator 3 is equipped with the cooling fan 2. The cooling wind created by driving the cooling fan 2 cools the cooling liquid that flows in the radiator 3.

[0035] The cooling liquid channel 4 branches at an upstream side of the fuel cell stack 1, between the cooling liquid pump 5 and the fuel cell stack 1, and the branch channels are connected to the fuel cell stack 1, and are merged at the downstream side of the fuel cell stack 1. At the branching point at which the cooling liquid channel 4 branches, an anode-cathode selector valve 8 that adjusts the proportion of the flow amount of the cooling liquid that flows in the branch cooling liquid channel 4 according to the degree of opening of the valve. This adjustment is controlled by a control signal from the ECU 6 that is electrically connected to the anode-cathode selector valve 8.

[0036] It is to be noted herein that an anode inlet cooling liquid channel 9 (an example of a first channel in the invention) is one of the channels branching from the cooling liquid channel 4 upstream of the fuel cell stack 1, and communicates with the anode cooling liquid channels 24 in the fuel cell stack 1. A cathode inlet cooling liquid channel 10 (an example of a second channel in the invention) is the other one of the channels branching from the cooling liquid channel 4 upstream of the fuel cell stack 1, and communicates with the cathode cooling liquid channels 25 in the fuel cell stack 1.

[0037] On the downstream side of the fuel cell stack 1, an anode outlet cooling liquid channel 11 and a cathode outlet cooling liquid channel 12 merge into the cooling liquid channel 4. Of the two channels, the anode outlet cooling liquid channel 11 communicates with the anode cooling liquid channels 24 in the fuel cell stack 1, and the cathode outlet cooling liquid channel 12 communicates with the cathode cooling liquid channels 25 in the fuel cell stack 1.

[0038] The anode-cathode selector valve 8 adjusts the proportions of the flow amounts of the cooling liquid flowing through the anode inlet cooling liquid channel 9 and through the cathode inlet cooling liquid channel 10 according to the degree of opening of the valve. This adjustment is controlled by the control signal from the ECU 6 that is electrically connected to the anode-cathode selector valve 8. [0039] The anode outlet cooling liquid channel 11 is provided with an anode temperature sensor 13. The anode temperature sensor 13 measures the temperature of the cooling liquid that flows in the anode outlet cooling liquid channel 11. Besides, the cathode outlet cooling liquid channel 12 is provided with a cathode temperature sensor 14. The cathode temperature sensor 14 measures the temperature of the cooling liquid that flows in the cathode outlet cooling liquid channel 12.

[0040] Besides, the bypass channel 7 is provided on the cooling liquid channel 4 between the fuel cell stack 1 and the radiator 3. The bypass channel 7 branches from the cooling liquid channel 4, and serves as a channel for circulating the cooling liquid in the fuel cell system without passing it through the radiator 3. [0041] A radiator bypass three-way valve 15 is provided at a site where the cooling liquid channel 4 and the bypass channel 7 are connected. By switching the radiator bypass three-way valve 15, it is possible to select one of a path in which the cooling liquid circulates in the fuel cell system via the radiator 3 and a path in which the cooling liquid circulates in the fuel cell system without passing through the radiator 3 can be selected. Besides, by adjusting the degree of opening of the radiator bypass three-way valve 15, it is possible to control the flow amount of the cooling water passing through the radiator 3 and the flow amount of the cooling water that does not pass through the radiator 3. The switching and the opening degree of the radiator bypass three-way valve 15 are controlled by a control signal from the ECU 6 that is electrically connected to the radiator bypass three-way valve 15.

[0042] The ECU 6 has therein a CPU, a ROM, etc., and the CPU executes various processes, following control programs recorded in the ROM. The ECU 6 is electrically connected to the cooling liquid pump 5, the anode-cathode selector valve 8, the anode temperature sensor 13, the cathode temperature sensor 14, and the radiator bypass three-way valve 15. The ECU 6 acquires data regarding the temperatures of the cooling liquid measured by the anode temperature sensor 13 and the cathode temperature sensor 14. The ECU 6 controls the driving of the cooling liquid pump 5, the anode-cathode selector valve 8, and the radiator bypass three-way valve 15. [0043] FIG 3 is a flowchart of a first process performed by the ECU 6. This process is executed by a control program that is executed by the CPU. This process is repeatedly executed at predetermined time intervals. Herein, the predetermined time is a value set at the time of shipment from the factory, or a value set at a dealer that sells vehicles, or a value set by a user, etc. [0044] In this process, the ECU 6 determines whether or not the MEGA 20 in the fuel cell stack 1 is in a dried-up state (S301). For example, whether the MEGA 20 in the fuel cell stack 1 is in the dried-up state is determined on the basis of the temperature of the cooling liquid, the impedance between electrodes (between catalyst layers) in the fuel cell stack 1, and an output current of the fuel cell stack 1. [0045] As a first process example, the ECU 6 acquires data on the temperature of the cooling liquid measured by the anode temperature sensor 13 or the cathode temperature sensor 14, and determines, from the acquired data on the temperature, whether or not the MEGA 20 in the fuel cell stack 1 is in the dried-up state. In the case where the temperature of the cooling liquid is high, the possibility of the MEGA 20 in the fuel cell stack 1 being in the dried-up state is high. Therefore, the ECU 6 may determine whether or not the temperature of the cooling liquid is higher than or equal to a predetermined value. If the temperature of the cooling liquid is higher than or equal to the predetermined value, the ECU 6 may determine that the MEGA 20 in the fuel cell stack 1 is in the dried-up state. This predetermined value is found through experiments or simulations, and is stored beforehand in a memory of the ECU 6.

[0046] As a second process example, the ECU 6 acquires data on the impedance between the electrodes in the fuel cell stack 1 which is measured by a sensor (not shown), and determines whether or not the MEGA 20 in the fuel cell stack 1 is in the dried-up state, from the acquired data on the impedance between electrodes in the fuel cell stack 1. In the case where the impedance between electrodes in the fuel cell stack 1 is high, the possibility of the MEGA 20 in the fuel cell stack 1 being in the dried-up state is high. Therefore, the ECU 6 may determine whether or not the value of the impedance is higher than or equal to a predetermined value. If the value of the impedance is higher than or equal to the predetermined value, the ECU 6 may determine that the MEGA 20 in the fuel cell stack 1 is in the dried-up state. This predetermined value is found through experiments or simulations, and is stored beforehand in a memory of the ECU 6.

[0047] As a third process example, the ECU 6 acquires data on the output current of the fuel cell stack 1 which is measured by a sensor (not shown), and determines whether or not an MEGA 20 in the fuel cell stack 1 is in the dried-up state, from the acquired data on the output current of the fuel cell stack 1. In the case where the output current of the fuel cell stack 1 is low, the possibility of an MEGA 20 in the fuel cell stack 1 in the dried-up state is high. Therefore, the ECU 6 may determine whether the value of the output current of the fuel cell stack 1 is less than or equal to a predetermined value. If the value of the output current of the fuel cell stack 1 is less than or equal to the predetermined value, the ECU 6 may determine that an MEGA 20 in the fuel cell stack 1 is in the dried-up state. This predetermined value is found through experiments or simulations, and is stored beforehand in a memory of the ECU 6.

[0048] If the MEGA 20 in the fuel cell stack 1 is in the dried-up state (if an affirmative determination is made in the process of S301), the ECU 6 sets an anode outlet target temperature Da at a value of the cathode outlet target temperature Dc - a predetermined temperature α (S302).

[0049] In the case where an MEGA 20 in the fuel cell stack 1 is in the dried-up state, the amount of movement of back-diffused water from the cathode to the anode becomes insufficient. However, in the case where the temperature of the anode is lower than the temperature of the cathode, the amount of movement of back-diffused water increases.

[0050] Therefore, by making the temperature of the anode lower than the temperature of the cathode, the amount of movement of back-diffused water from the cathode to the anode is increased so as to recover the MEGA 20 in the fuel cell stack 1 from the dried-up state. Concretely, as the temperature of the cooling liquid that cools the hydrogen supplied to the anode is made lower by the predetermined temperature α than the temperature of the cooling liquid that cools the air supplied to the cathode, the amount of movement of back-diffused water from the cathode to the anode is increased so that the MEGA 20 in the fuel cell stack 1 is recovered from the dried-up state.

[0051] The anode outlet target temperature Da is a temperature that serves as a target for adjusting the temperature of the cooling liquid that flows in the anode outlet cooling liquid channel 11 in order to recover the MEGA 20 in the fuel cell stack 1 from the dried-up state. The cathode outlet target temperature Dc is a temperature that serves as a target for adjusting the temperature of the cooling liquid that flows in the cathode outlet cooling liquid channel 12 in order to recover the MEGA 20 in the fuel cell stack 1 from the dried-up state. The predetermined temperature α is the difference between the anode outlet target temperature Da and the cathode outlet target temperature Dc.

[0052] For example, the anode outlet target temperature Da, the cathode outlet target temperature Dc and the predetermined temperature α are found beforehand through experiments or simulations. A relation among the anode outlet target temperature Da, the cathode outlet target temperature Dc and the predetermined temperature α with the dried-up state of the MEGA 20 in the fuel cell stack 1 is stored beforehand in the form of a map in a memory of the ECU 6. Then, the ECU 6 calculates the anode outlet target temperature Da, the cathode outlet target temperature Dc and the predetermined temperature α from the map.

[0053] Next, the ECU 6 performs feedback (F/B) control of the degree of opening of the anode-cathode selector valve 8 so that the temperature Ta of the cooling liquid measured by the anode temperature sensor 13 is lower by the predetermined temperature α than the temperature Tc of the cooling liquid measured by the cathode temperature sensor 14 (S303). That is, the ECU 6 feedback-controls the degree of opening of the anode-cathode selector valve 8 so as to achieve the temperature Ta = the temperature Tc - the predetermined temperature α.

[0054] The feedback (F/B) control of the degree of opening of the anode-cathode selector valve 8 in the process of S303 will be described in detail below.

[0055] Let it assumed that the difference between the temperature of the cooling liquid that flows in the anode outlet cooling liquid channel 11 and the temperature of the cooling liquid that flows in the cathode outlet cooling liquid channel 12 is the temperature Td. A correspondence relation between the temperature Td and the degree of opening of the anode-cathode selector valve 8 is described as a map, and is stored in a memory of the ECU 6 beforehand. This map shows stepwise the correspondence relation between the temperature Td and the degree of opening of the anode-cathode selector valve 8. [0056] The ECU 6 calculates from the map the degree of opening of the anode-cathode selector valve 8 that corresponds to a temperature Td that is equal in value (or approximate in value) to the predetermined temperature α. The ECU 6 controls the anode-cathode selector valve 8 so as to achieve the calculated degree of opening of the anode-cathode selector valve 8. After controlling the degree of opening of the anode-cathode selector valve 8, the ECU 6 acquires data on the temperature Ta and data on the temperature Tc.

[0057] The ECU 6 determines whether or not the difference between the temperature Ta and the temperature Tc is equal (or approximate) in value to the predetermined temperature α, on the basis of the data on the temperature Ta and the data on the temperature Tc both acquired after the control of the degree of opening of the anode-cathode selector valve 8. If the difference between the temperature Ta and the temperature Tc is not equal (or approximate) in value to the predetermined temperature α, the ECU 6 corrects the degree of opening of the anode-cathode selector valve 8. Until the difference between the temperature Ta and the temperature Tc becomes equal (or approximate) in value to the predetermined temperature α, the ECU 6 repeats the acquisition of data on the temperature Ta and data on the temperature Tc, the determination regarding the data, and the correction of the degree of opening of the anode-cathode selector valve 8.

[0058] Next, the ECU 6 performs feedback (F/B) control of the degree of opening of the radiator bypass three-way valve 15 so that the temperature Ta is equal (or approximate) in value to the anode outlet target temperature Da (S304).

[0059] The feedback (F/B) control of the degree of opening of the radiator bypass three-way valve 15 in the process of the S304 will be described in detail below. [0060] A correspondence relation between the temperature of the cooling liquid that flows in the anode outlet cooling liquid channel 11 and the degree of opening of the radiator bypass three-way valve 15 is described as a map, and is stored in a memory of the ECU 6 beforehand. This map shows stepwise the correspondence relation between the temperature of the cooling liquid that flows in the anode outlet cooling liquid channel 11 and the degree of opening of the radiator bypass three-way valve 15.

[0061] ECU 6 calculates from the map the degree of opening of the radiator bypass three-way valve 15 that corresponds to the temperature of the cooling liquid that flows in the anode outlet cooling liquid channel 11 that is equal (or approximate) in value to the anode outlet target temperature Da. The ECU 6 controls the radiator bypass three-way valve 15 so as to achieve the calculated degree of opening of the radiator bypass three-way valve 15. After controlling the degree of opening of the radiator bypass three-way valve 15, the ECU 6 acquires data on the temperature Ta.

[0062] The ECU 6 determines whether or not the temperature Ta is equal (or approximate) in value to the anode outlet target temperature Da, on the basis of the data on the temperature Ta acquired after the control of the degree of opening of the radiator bypass three-way valve 15.

[0063] If the temperature Ta is not equal (or approximate) in value to the anode outlet target temperature Da, the ECU 6 corrects the degree of opening of the radiator bypass three-way valve 15. Until the temperature Ta becomes equal (or approximate) in value to the anode outlet target temperature Da, the ECU 6 repeats the acquisition of data on the temperature Ta, the determination regarding the data, and the correction of the degree of opening of the radiator bypass three-way valve 15.

[0064] In the case where the MEGA 20 in the fuel cell stack 1 is not in the dried-up state (where a negative determination is made in the process of S301), the ECU 6 sets the anode outlet target temperature Da so that it becomes equal in value to the cathode outlet target temperature Dc (S305).

[0065] Next, the ECU 6 performs feedback (FfB) control of the degree of opening of the anode-cathode selector valve 8 so as to achieve the temperature Ta = the temperature Tc (S306). That is, the ECU 6 controls the degree of opening of the anode-cathode selector valve 8 so that the temperature Ta is equal (or approximate) in value to the temperature Tc.

[0066] The feedback (F/B) control of the degree of opening of the anode-cathode selector valve 8 in the process of S306 will be described in detail below. [0067] A correspondence relation among the temperature of the cooling liquid that flows in the anode outlet cooling liquid channel 11, the temperature of the cooling liquid that flows in the cathode outlet cooling liquid channel 12, and the degree of opening of the anode-cathode selector valve 8 is described as a map, and is stored in a memory of the ECU 6 beforehand. This map shows stepwise the correspondence relation among the temperature of the cooling liquid that flows in the anode outlet cooling liquid channel 11, the temperature of the cooling liquid that flows in the cathode outlet cooling liquid channel 12, and the degree of opening of the anode-cathode selector valve 8.

[0068] The ECU 6 calculates from the map the degree of opening of the anode-cathode selector valve 8 that occurs in the case where the temperature of the cooling liquid that flows in the anode outlet cooling liquid channel 11 and the temperature of the cooling liquid that flows in the cathode outlet cooling liquid channel 12 are equal (or approximate) in value to each other. The ECU 6 controls the anode-cathode selector valve 8 so as to achieve the calculated degree of opening of the anode-cathode selector valve 8. After controlling the degree of opening of the anode-cathode selector valve 8, the ECU 6 acquires data on the temperature Ta and data on the temperature Tc.

[0069] The ECU 6 determines whether or not the temperature Ta and the temperature Tc are equal (or approximate) in value to each other. If the temperature Ta and the temperature Tc are not equal (or approximate) in value to each other, the ECU 6 corrects the degree of opening of the anode-cathode selector valve 8. Until the temperature Ta and the temperature Tc are equal (or approximate) in value to each other, the ECU 6 repeats the acquisition of data on the temperature Ta and data on the temperature Tc, the determination regarding the data, and the correction of the degree of opening of the anode-cathode selector valve 8.

[0070] According to the foregoing process, in the case where an MEGA 20 in the fuel cell stack 1 is in the dried-up state, the flow amount of the cooling liquid that cools the hydrogen supplied to the anode and the flows amount of the cooling liquid that cools the air supplied to the cathode are controlled. Then, by providing a temperature difference between the temperature of the anode and the temperature of the cathode, it becomes possible to recover the MEGA 20 in the fuel cell stack 1 from the dried-up state.

[0071] Always providing a temperature difference between the temperature of the cooling liquid that cools the hydrogen supplied to the anode and the temperature of the cooling liquid that cools the air supplied to the cathode is not preferable when the influence of the temperature difference on deterioration is taken into consideration. Therefore, in this embodiment, only when an MEGA 20 in the fuel cell stack 1 is in the dried-up state, a control is performed so that the temperature of the cooling liquid that cools the hydrogen supplied to the anode becomes lower than the temperature of the cooling liquid that cools the air supplied to the cathode. Then, by increasing the amount of movement of back-diffused water from the cathode to the anode, and recovering the MEGA 20 from the dried-up state, the deterioration of the current-voltage performances can be restrained. As a result, a desired electricity generation electric power can be achieved.

[0072] In this embodiment, the anode cooling liquid channels 24 are provided in each cell in the fuel cell stack 1, so that the temperature of the anode can be made uniform among all the cells of the fuel cell stack 1. Besides, in this embodiment the cathode cooling liquid channels 25 are provided in each cell in the fuel cell stack 1, so that the temperature of the cathode can be made uniform among all the cells of the fuel cell stack 1. As a result, the occurrence of a difference in voltage between cells can be restrained. Thus, it becomes possible to recover the MEGAs 20 in the fuel cell stack 1 from the dried-up state while securing stable electricity generation of the fuel cell stack 1.

[0073] FIG. 4 is a flowchart of a second process performed by the ECU 6. This process is executed by a control program that is executed by the CPU. Besides, this process is repeatedly executed at predetermined time intervals. Herein, the predetermined time is a value set at the time of shipment from the factory, or a value set at a dealer that sells vehicles, or a value set by a user, etc.

[0074] In this process, the ECU 6 determines whether or not the anode in the fuel cell stack 1 is flooded (S401). Whether the anode in the fuel cell stack 1 is in a flooded state is determined on the basis of the cell voltage in the fuel cell stack 1 or the rate of decrease of the cell voltage in the fuel cell stack 1.

[0075] As a first process example, the ECU 6 acquires data on the cell voltage in the fuel cell stack 1 measured by a sensor (not shown), and determines whether or not the anode in the fuel cell stack 1 is in the flooded state, from the acquired data on the cell voltage. In the case where the cell voltage in the fuel cell stack 1 is low, the possibility of the anode in the fuel cell stack 1 being in the flooded state is high. Therefore, the ECU 6 may determine whether or not the cell voltage in the fuel cell stack 1 is less than or equal to a predetermined value. If the cell voltage in the fuel cell stack 1 is less than or equal to the predetermined value, the ECU 6 may determine that the anode in the fuel cell stack 1 is in the flooded state. This predetermined value is found through experiments or simulations, and is stored beforehand in a memory of the ECU 6. For example, the ECU 6 may determine that the anode in the fuel cell stack 1 is in the flooded state, if the cell voltage in the fuel cell stack 1 is negative (less than or equal to 0 V).

[0076] As a second process example, the ECU 6 may acquire data on the rate of decrease of the cell voltage in the fuel cell stack 1 measured by a sensor (not shown). From the acquired data on the rate of decrease of the cell voltage, the ECU 6 determines whether the anode in the fuel cell stack 1 is in the flooded state. In the case where the rate of decrease of the cell voltage in the fuel cell stack 1 is fast, the possibility of the anode in the fuel cell stack 1 being in the flooded state is high. Therefore, the ECU 6 may determine whether the rate of decrease of the cell voltage in the fuel cell stack 1 is greater than or equal to a predetermined value. If the cell voltage in the fuel cell stack 1 is greater than or equal to the predetermined value, the ECU 6 may determine that the anode in the fuel cell stack 1 is in the flooded state. This predetermined value is found through experiments or simulations, and is stored beforehand in a memory of the ECU 6.

[0077] If the anode in the fuel cell stack 1 is in the flooded state (if an affirmative determination is made in S401), the ECU 6 sets the anode outlet target temperature Fa equal to the cathode outlet target temperature Fc + a predetermined value β (S402).

[0078] In the case where the anode in the fuel cell stack 1 is in the flooded state, the amount of movement of back-diffused water from the cathode to the anode is excessively large; however, if the temperature of the anode is higher than the temperature of the cathode, the amount of movement of back-diffused water decreases.

[0079] Therefore, by making the temperature of the anode higher than the temperature of the cathode, the amount of movement of back-diffused water from the cathode to the anode is reduced so as to recover the anode in the fuel cell stack 1 from the flooded state. Concretely, as the temperature of the cooling liquid that cools the hydrogen supplied to the anode is made higher by a predetermined temperature β than the temperature of the cooling liquid that cools the oxygen supplied to the cathode, the amount of movement of back-diffused water from the cathode to the anode is reduced so as to recover the anode in the fuel cell stack 1 from the flooded state.

[0080] The anode outlet target temperature Fa is a temperature that serves as a target for adjusting the temperature of the cooling liquid that flows in the anode outlet cooling liquid channel 11, in order to recover the anode in the fuel cell stack 1 from the flooded state. The cathode outlet target temperature Fc is a temperature that serves as a target for adjusting the temperature of the cooling liquid that flows in the cathode outlet cooling liquid channel 12, in order to recover the anode in the fuel cell stack 1 from the flooded state. The predetermined temperature β is a difference between the anode outlet target temperature Fa and the cathode outlet target temperature Fc.

[0081] For example, the anode outlet target temperature Fa, the cathode outlet target temperature Fc, and the predetermined temperature β are found beforehand through experiments or simulations. A relation of the flooding of the anode in the fuel cell stack 1 with the anode outlet target temperature Fa, the cathode outlet target temperature Fc and the predetermined temperature β is described as a map, and stored beforehand in a memory of the ECU 6. Then, the ECU 6 calculates the anode outlet target temperature Fa, the cathode outlet target temperature Fc, and the predetermined temperature β from the map.

[0082] Next, the ECU 6 performs feedback (F/B) control of the degree of opening of the anode-cathode selector valve 8 so that the temperature Ta of the cooling liquid measured by the anode temperature sensor 13 becomes higher by the predetermined temperature β than the temperature Tc of the cooling liquid measured by the cathode temperature sensor 14 (S403). That is, the ECU 6 performs feedback (F/B) control of the degree of opening of the anode-cathode selector valve 8 so as to achieve the temperature Ta = the temperature Tc + the predetermined temperature β. [0083] The feedback (F/B) control of the degree of opening of the anode-cathode selector valve 8 in the process of S403 will be described in detail below.

[0084] Let it assumed that the difference between the temperature of the cooling liquid that flows in the anode outlet cooling liquid channel 11 and the temperature of the cooling liquid that flows in the cathode outlet cooling liquid channel 12 is a temperature Tf. A correspondence relation between this temperature Tf and the degree of opening of the anode-cathode selector valve 8 is described as a map, and stored beforehand in a memory of the ECU 6. This map shows stepwise the correspondence relation between temperature Tf and the degree of opening of the anode-cathode selector valve 8.

[0085] The ECU 6 calculates from the map the degree of opening of the anode-cathode selector valve 8 that corresponds to the temperature Tf that is equal (or approximate) in value to the predetermined temperature β. The ECU 6 controls the anode-cathode selector valve 8 so as to achieve the calculated degree of opening of the anode-cathode selector valve 8. After controlling the degree of opening of the anode-cathode selector valve 8, the ECU 6 acquires data on the temperature Ta and data on the temperature Tc.

[0086] On the basis of the data on the temperature Ta and the data on the temperature Tc acquired after the control of the degree of opening of the anode-cathode selector valve 8, the ECU 6 determines whether or not the difference between the temperature Ta and the temperature Tc is equal (or approximate) in value to the predetermined temperature β. If the difference between the temperature Ta and the temperature Tc is not equal (or approximate) in value to the predetermined temperature β, the ECU 6 corrects the degree of opening of the anode-cathode selector valve 8. The ECU 6 repeats the acquisition of data on the temperature Ta and data on the temperature Tc, the determination regarding the data, and the correction of the degree of opening of the anode-cathode selector valve 8 until the difference between the temperature Ta and the temperature Tc is equal (or approximate) in value to the predetermined temperature β.

[0087] Next, the ECU 6 performs feedback (F/B) control of the degree of opening of the radiator bypass three-way valve 15 so that the temperature Ta becomes equal (or approximate) in value to the anode outlet target temperature Fa (S404).

[0088] The feedback (F/B) control of the degree of opening of the radiator bypass three-way valve 15 in the process of S404 will be described in detail below.

[0089] A correspondence relation between the temperature of the cooling liquid that flows in the anode outlet cooling liquid channel 11 and the degree of opening of the radiator bypass three-way valve 15 is described as a map, and stored beforehand in a memory of the ECU 6. This map shows stepwise the correspondence relation between the temperature of the cooling liquid that flows in the anode outlet cooling liquid channel 11 and the degree of opening of the radiator bypass three-way valve 15.

[0090] The ECU 6 calculates from the map the degree of opening of the radiator bypass three-way valve 15 that corresponds to the temperature of the cooling liquid flowing in the anode outlet cooling liquid channel 11 which is equal (or approximate) in value to the anode outlet target temperature Fa. The ECU 6 controls the radiator bypass three-way valve 15 so as to achieve the calculated degree of opening of the radiator bypass three-way valve 15. After controlling the degree of opening of the radiator bypass three-way valve 15, the ECU 6 acquires data on the temperature Ta.

[0091] On the basis of the data on the temperature Ta acquired after the control of the degree of opening of the radiator bypass three-way valve 15, the ECU 6 determines whether or not the temperature Ta is equal (or approximate) in value to the anode outlet target temperature Fa.

[0092] If the temperature Ta is not equal (or approximate) in value to the anode outlet target temperature Fa, the ECU 6 corrects the degree of opening of the radiator bypass three-way valve 15. The ECU 6 repeats the acquisition of data on the temperature Ta, the determination regarding the data, and the correction of the degree of opening of the radiator bypass three-way valve 15 until the temperature Ta becomes equal (or approximate) in value to the anode outlet target temperature Fa.

[0093] In the case where the anode in the fuel cell stack 1 is not in the flooded state (a negative determination is made in S401), the ECU 6 sets the anode outlet target temperature Fa so that the target temperature Fa becomes equal to the cathode outlet target temperature Fc (S405).

[0094] Next, the ECU 6 performs feedback (F/B) control of the degree of opening of the anode-cathode selector valve 8 so as to achieve the temperature Ta = the temperature

Tc (S406). That is, the ECU 6 controls the degree of opening of the anode-cathode selector valve 8 so that the temperature Ta becomes equal (or approximate) in value to the temperature Tc.

[0095] The feedback (F/B) control of the degree of opening of the anode-cathode selector valve 8 in the process of S406 will be described in detail below.

[0096] A correspondence relation among the temperature of the cooling liquid that flows in the anode outlet cooling liquid channel 11, the temperature of the cooling liquid that flows in the cathode outlet cooling liquid channel 12, and the degree of opening of the anode-cathode selector valve 8 is described as a map, and stored beforehand in a memory of the ECU 6. This map shows stepwise the correspondence relation among the temperature of the cooling liquid that flows in the anode outlet cooling liquid channel 11, the temperature of the cooling liquid that flows in the cathode outlet cooling liquid channel 12, and the degree of opening of the anode-cathode selector valve 8.

[0097] The ECU 6 calculates from the map the degree of opening of the anode-cathode selector valve 8 occurring in the case where the temperature of the cooling liquid flowing in the anode outlet cooling liquid channel 11 and the temperature of the cooling liquid flowing in the cathode outlet cooling liquid channel 12 are equal (or approximate) in value to each other. The ECU 6 controls the anode-cathode selector valve 8 so as to achieve the calculated degree of opening of the anode-cathode selector valve 8. After controlling the degree of opening of the anode-cathode selector valve 8, the ECU 6 acquires data on the temperature Ta, and data on the temperature Tc. [0098] The ECU 6 determines whether or not the temperature Ta and the temperature

Tc are equal (or approximate) in value to each other. If the temperature Ta and the temperature Tc are not equal (or approximate) in value to each other, the ECU 6 corrects the degree of opening of the anode-cathode selector valve 8. The ECU 6 repeats the acquisition of data on the temperature Ta and data on the temperature Tc, the determination regarding the data, and the correction of the degree of opening of the anode-cathode selector valve 8 until the temperature Ta and the temperature Tc become equal (or approximate) in value to each other.

[0099] According to the foregoing process, in the case where the anode in the fuel cell stack 1 is in the flooded state, the flow amount of the cooling liquid that cools the hydrogen supplied to the anode and the flow amount of the cooling liquid that cools the air supplied to the cathode are controlled. Then, by providing a temperature difference between the temperature of the anode and the temperature of the cathode, it becomes possible to recover the anode in the fuel cell stack 1 from the flooded state.

[0100] Always providing a temperature difference between the temperature of the cooling liquid that cools the hydrogen supplied to the anode and the temperature of the cooling liquid that cools the air supplied to the cathode is not preferable, if the effect of the temperature difference on the degradation is taken into consideration. Therefore, in this embodiment, only when the anode in the fuel cell stack 1 is in the flooded state, control is performed so that the temperature of the cooling liquid that cools the hydrogen supplied to the anode becomes higher than the temperature of the cooling liquid that cools the air supplied to the cathode. Then, by decreasing the amount of movement of back-diffused water from the cathode to the anode, the anode can be recovered from the flooded state and be recovered from a reduced cell voltage. In consequence, a desired generated electric power can be obtained.

[0101] In this embodiment, since each cell in the fuel cell stack 1 is provided with the anode cooling liquid channels 24, the temperature of the anode can be made uniform among all the cells of the fuel cell stack 1. Besides, in this embodiment, since each cell in the fuel cell stack 1 is provided with the cathode cooling liquid channels 25, the temperature of the cathode can be made uniform among all the cells of the fuel cell stack 1. In consequence, the occurrence of a difference in voltage between cells can be restrained. Thus, it becomes possible to recover the anodes in the fuel cell stack 1 from the flooded state while securing stable electricity generation of the fuel cell stack 1.

[0102] In conjunction with the first embodiment, a fuel cell system in which the anode cooling system and the cathode cooling system are within a single system is shown. In this case, the fuel cell system may be such that the anode cooling system and the cathode cooling system are two separate systems.

[0103] FIG 5 is a diagram of a fuel cell system in accordance with a modification of the first embodiment. In this fuel cell system, as compared with that shown FIG. 1, the anode cooling system is provided with a cooling fan 2, a radiator 3 a cooling liquid pump 5, and a radiator bypass three-way valve 15. A cooling liquid channel 4 downstream of the anode cooling system is provided with an anode temperature sensor 13. Besides, in this fuel cell system, as compared with that shown in FIG 1, the cathode cooling system is provided with a cooling fan 42, a radiator 43, a cooling liquid pump 45, and a radiator bypass three-way valve 55. The cooling liquid channel 4 downstream of the cathode cooling system is provided with a cathode temperature sensor 14. That is, the fuel cell system has a construction in which the cooling liquid that cools the hydrogen supplied to the anode in the fuel cell stack 1 and the cooling liquid that cools the air supplied to the cathode in the fuel cell stack 1 flow through separate circulation paths. [0104] In the first embodiment, the flow amount of the cooling liquid that cools the hydrogen supplied to the anode and the flow amount of the cooling liquid that cools the air supplied to the cathode are controlled on the basis of the degree of opening of the anode-cathode selector valve 8. In this modification, on the other hand, the flow amount of the cooling liquid that cools the hydrogen supplied to the anode and the flow amount of the cooling liquid that cools the air supplied to the cathode are controlled on the basis of the amounts of driving of the cooling liquid pumps 5, 45. The amounts of driving of the cooling liquid pumps 5, 45 are controlled by control signals from the ECU 6. Other constructions and operations are the same as shown in FIG 1. [0105] Due to this construction, the cooling liquid that flows in the cooling liquid channel 4 downstream of the anode cooling system, and the cooling liquid that flows in the cooling liquid channel 4 downstream of the cathode cooling system are restrained from affecting each other's temperatures. As a result, it becomes easy to control the temperature of the cooling liquid that flows in the cooling liquid channel 4 downstream of the anode cooling system and the temperature of the cooling liquid that flows in the cooling liquid channel 4 downstream of the cathode cooling system, and it also becomes easy to control the difference between the temperature of the cooling liquid that flows in the cooling liquid channel 4 downstream of the anode cooling system and the temperature of the cooling liquid that flows in the cooling liquid channel 4 downstream of the cathode cooling system.

[0106] A fuel cell system in accordance with a second embodiment of the invention will be described with reference to FIG. 6. In the foregoing first embodiment, as shown in FIG 2, the anode cooling liquid channels 24 and the cathode cooling liquid channels 25 are formed in separate molded plates 23. In the fuel cell system in accordance with the second embodiment, however, anode cooling liquid channels 24 and cathode cooling liquid channels 25 are formed in a molded plate 30 (an example of the sandwiching holder in the invention). Other constructions and operations are the same as in the first embodiment. Therefore, the same component elements are represented by the same reference numerals, and the description thereof will be omitted. Besides, the overall construction of the fuel cell system is the same as that in the first embodiment.

[0107] As shown in FIG 6, the anode cooling liquid channels 24 and the cathode cooling liquid channels 25 are formed in a single molded plate 30 by performing processing on the molded plate 30 so that the anode cooling liquid channels 24 are formed in one of the surfaces of the molded plate 30 and the cathode cooling liquid channels 25 are formed in the opposite surface thereof. The molded plate 30 in the fuel cell system in accordance with this embodiment is provided with an air layer (an example of a space in the invention) or a heat insulating material between the anode cooling liquid channels 24 and the cathode cooling liquid channels 25 in order to curb the heat exchange between the anode and the cathode.

[0108] FIG 7 shows a detailed diagram of the molded plate 30. As shown in FIG. 7, the anode cooling liquid channels 24 are formed in one of the surfaces of the molded plate 30, and the cathode cooling liquid channels 25 are formed in the other surface of the molded plate 30. A seal material 31, or an air layer, or a heat insulating material is provided within the molded plate 30. The air layer and the heat insulting material have a heat insulating effect for curving the heat exchange between the cooling liquid that flows in the anode cooling liquid channels 24 and the cooling liquid that flows in the cathode cooling liquid channels 25.

[0109] For example, in the case where the fuel cell system in accordance with this embodiment is mounted in a vehicle, it suffices that the heat insulating material can be used under an environment of about -40 to 150⁰C, and can easily be processed so as to be adjusted to a change in shape. In this case, the heat insulating material used may be an ion-less heat insulating material.

[0110] According to the fuel cell system of the embodiment, one of the surfaces of the single molded plate 30 is provided with the anode cooling liquid channels 24, and the other surface thereof is provided with the cathode cooling liquid channels 25. Therefore, it becomes possible to cool the hydrogen supplied to the anode and the air supplied to the cathode by using the molded plate 30. According to the fuel cell system of the embodiment, the air layer or the heat insulating material is provided between the anode cooling liquid channels 24 and the cathode cooling liquid channels 25. Therefore, the heat exchange between the cooling liquid that flows in the anode cooling liquid channels 24 and the cooling liquid that flows in the cathode cooling liquid channels 25 can be restrained, and the anode side and the cathode side can be thermally insulated from each other.

[0111] In the second embodiment, the flow amount of the cooling liquid that cools the hydrogen supplied to the anode and the flow amount of the cooling liquid that cools the air supplied to the cathode may be controlled on the basis of whether or not an MEGA 20 of fuel cell stack 1 is in the dried-up state, or whether or not an anode of the fuel cell stack 1 is in the flooded state.

[0112] In this embodiment, the flow amount of the cooling liquid that cools the hydrogen supplied to the anode and the flow amount of the cooling liquid that cools the air supplied to the cathode may be controlled by determining whether or not the MEGA 20 of the fuel cell stack 1 is in the dried-up state or determining whether or not the anode of the fuel cell stack 1 is in the flooded state on the basis of the amount of electricity generation of the fuel cell stack 1, the supplied amount of the anode gas, and the supplied amount of the cathode gas. In this case, the ECU 6 can acquire data regarding the amount of electricity generation by detecting the output voltage and the output current of the fuel cell stack 1. Besides, the ECU 6 can acquire data regarding the supplied amount of the cathode gas by detecting the amount of driving of an air compressor (not shown). Furthermore, the ECU 6 can acquire data regarding the supplied amount of the anode gas by detecting the amount of hydrogen supplied from a hydrogen tank (not shown).

[0113] For example, a relation of the dry-up of an MEGA 20 of the fuel cell stack 1 with the amount of electricity generation of the fuel cell stack 1, the supplied amount of the anode gas, and the supplied amount of the cathode gas may be found beforehand through experiments or simulations. Then, the relation of the dry-up of an MEGA 20 in the fuel cell stack 1 with the amount of electricity generated by the fuel cell stack 1, the supplied amount of the anode gas, and the supplied amount of the cathode gas may be described as a map, and stored beforehand in a memory of the ECU 6. The ECU 6 may acquire data on the amount of electricity generated by the fuel cell stack 1, data on the supplied amount of the anode gas, and data on the supplied amount of the cathode gas at predetermined intervals, and may determine from the map stored in the map whether or not the MEGA 20 in the fuel cell stack 1 is in the dried-up state.

[0114] Besides, for example, a relation of the flooding of an anode in the fuel cell stack 1 with the amount of electricity generated by the fuel cell stack 1, the supplied amount of the anode gas, and the supplied amount of the cathode gas may be found beforehand through experiments or simulations. Then, the relation of the flooding of an anode in the fuel cell stack 1 with the amount of electricity generated by the fuel cell stack 1, the supplied amount of the anode gas, and the supplied amount of the cathode gas may be described as a map, and stored beforehand in a memory of the ECU 6. The ECU 6 may acquire data on the amount of electricity generated by the fuel cell stack 1, data on the supplied amount of the anode gas, and data on the supplied amount of the cathode gas at predetermined intervals, and may determine from the map stored in the memory whether or not an anode in the fuel cell stack 1 is in the flooded state.

Claims

1. A fuel cell stack characterized by comprising: a plurality of stacked cells each having an anode, a cathode, a fuel gas channel that supplies a fuel gas to the anode, and an oxidant gas channel that supplies an oxidant gas to the cathode; an anode cooling medium channel that conducts a cooling medium that cools the fuel gas that flows in the fuel gas channel; and a cathode cooling medium channel that conducts a cooling medium that cools the oxidant gas that flows in the oxidant gas channel.

2. The fuel cell stack according to claim 1, wherein the cooling medium that cools the fuel gas and the cooling medium that cools the oxidant gas flow independently of each other.

3. The fuel cell stack according to claim 1 or 2, wherein, the anode cooling medium channel and the cathode cooling medium channel are provided between at least one pair of adjacent cells of the plurality of cells.

4. The fuel cell stack according to any one of claims 1 to 3, further comprising a plurality of sandwiching holders that sandwichingly hold each of the plurality of cells, wherein: one of surfaces of each of the plurality of sandwiching holders is provided with the anode cooling medium channel; another one of the surfaces of each of the plurality of sandwiching holders is provided with the cathode cooling medium channel; and a heat insulating member or a space is provided between the anode cooling medium channel and the cathode cooling medium channel.

5. A fuel cell system characterized by comprising: the fuel cell stack according to any one of claims 1 to 4; and control means that controls at least one of flow amount and temperature of the cooling medium that flows in the anode cooling medium channel, and at least one of flow amount and temperature of the cooling medium that flows in the cathode cooling medium channel.

6. The fuel cell system according to claim 5, wherein the control means controls the flow amount of the cooling medium that flows in the anode cooling medium channel, and the flow amount of the cooling medium that flows in the cathode cooling medium channel.

7. The fuel cell system according to claim 6, further comprising determination means for determining whether or not the fuel cell stack is in a dried-up state, wherein if it is determined that the fuel cell stack is in the dried-up state, the control means controls the flow amount of the cooling medium that flows in the anode cooling medium channel and the flow amount of the cooling medium that flows in the cathode cooling medium channel so that the temperature of the cooling medium that flows in the anode cooling medium channel is lower than the temperature of the cooling medium that flows in the cathode cooling medium.

8. The fuel cell system according to claim 7, wherein the determination means determines whether or not the fuel cell stack is in the dried-up state based on at least one of the temperature of the cooling medium that cools the fuel gas that flows in the fuel gas channel, and the temperature of the cooling medium that cools the oxidant gas that flows in the oxidant gas channel.

9. The fuel cell system according to claim 7, wherein the determination means determines whether or not the fuel cell stack is in the dried-up state based on impedance between the anode and the cathode.

10. The fuel cell system according to claim 7, wherein the determination means determines whether or not the fuel cell stack is in the dried-up state based on an amount of output current of the fuel cell stack.

11. The fuel cell system according to claim 7, wherein: the determination means determines whether or not the anode side of the fuel cell stack is in a flooded state, and if it is determined the anode side of the fuel cell stack is in the flooded state, the control means controls the flow amount of the cooling medium that flows in the anode cooling medium channel and the flow amount of the cooling medium that flows in the cathode cooling medium channel so that the temperature of the cooling medium that flows in the anode cooling medium channel becomes higher than the temperature of the cooling medium that flows in the cathode cooling medium channel.

12. The fuel cell system according to claim 11, wherein the determination means determines whether or not the anode side of the fuel cell stack is in the flooded state based on cell voltage in the fuel cell stack.

13. The fuel cell system according to claim 11, wherein the determination means determines whether or not the anode side of the fuel cell stack is in the flooded state based on rate of decrease of cell voltage in the fuel cell stack.

14. The fuel cell system according to claim 5, further comprising: a first channel that supplies the fuel cell stack with the cooling medium that flows in the anode cooling medium channel; and a second channel that supplies the fuel cell stack with the cooling medium that flows in the cathode cooling medium channel.

15. A cooling method for a fuel cell stack in which a plurality of cells each having an anode and a cathode are stacked, characterized by comprising providing the fuel cell stack with a plurality of cooling medium channels so that a cooling medium that cools a fuel gas that is supplied to the anode and a cooling medium that cools an oxidant gas that is supplied to the cathode flow independently of each other.