FUEL CELLAND FUEL CELL SYSTEM

BACKGROUND OF THE INVENTION

1. Field of the Invention

[0001] The invention relates to a fuel cell and a fuel cell system.

2. Description of the Related Art

[0002] Fuel cells, which generate electricity by an electrochemical reaction between a fuel gas (such as hydrogen) and an oxidant gas (such as oxygen), are attracting attention as energy sources. One type of fuel cell is a polymer electrolyte fuel cell that uses a solid polymer membrane as an electrolyte membrane. In this type of polymer electrolyte fuel cell, it is necessary to maintain the electrolyte membrane in a suitable wet state and suitably maintain proton conductivity of the electrolyte membrane. Consequently, it is necessary to humidify the electrolyte membrane of polymer electrolyte fuel cells during generation of electricity.

[0003] In conventional fuel cell systems provided with polymer electrolyte fuel cells, a humidifier is frequently provided that humidifies an oxidant gas (such as air containing oxygen) supplied to a cathode in order to humidify the electrolyte membrane (solid polymer membrane). The providing of this humidifier led to increased size of the fuel cell system. Consequently, in order to make fuel cell systems more compact, electricity must be generated by reducing the size of the humidifier and using low humidified gas or by eliminating the humidifier and using non-humidified gas. This requirement is particularly important in the case of installing fuel cell systems in automobiles where there are limitations on installation space.

[0004] Therefore, a technology has recently been proposed in which the electrolyte membrane is humidified by re-circulating water formed by the above-mentioned electrochemical reaction when generating electricity within the fuel cell (see, for example, Japanese Patent Application Publication No. 2006-40563 (JP-A-2006-40563) and Japanese Patent Application Publication No. 2002-42844 (JP-A-2002-42844)). The

humidification of an electrolyte membrane by re-circulating water formed as a result of generating electricity within a fuel cell is hereinafter referred to as "self-humidification".

[0005] According to the technology described in JP-A-2006-40563 and JP-A-2002-42844, self-humidification is possible on the same side of an anode and/or cathode. However, in the technology described in JP-A-2006-40563 and JP-A-2002-42844, self-humidification of an electrolyte membrane is unable to be carried out adequately or effectively, thereby leaving room for further improvement.

SUMMARY OF THE INVENTION

[0006] With the foregoing in view, the invention provides a fuel cell and a fuel cell system in which effective self-humidification of an electrolyte membrane is carried out in a polymer electrolyte fuel cell.

[0007] Therefore, according to a first aspect thereof, the invention provides a fuel cell in which a membrane electrode assembly, bonded respectively with an anode and cathode on both sides of an electrolyte membrane consisting of a solid polymer, is sandwiched between separators, including: an anode side gas flow path for allowing the flow of a fuel gas in a first direction along the surface of the anode, a cathode side gas flow path for allowing an oxidant gas to flow along the surface of the cathode in a second direction opposite the first direction, and a formed water capturing section provided at least one of farthermost downstream in the direction of flow of the fuel gas in the anode side gas flow path and farthermost downstream in the direction of flow of the oxidant gas in the cathode side gas flow path, for capturing at least one of formed water formed during generation of electricity contained in anode off gas which is exhaust gas discharged from the anode and the formed water contained in cathode off gas which is exhaust gas discharged from the cathode.

[0008] In the membrane electrode assembly, water formed at the cathode during generation of electricity moves downstream in the direction of flow of the oxidant gas or the cathode off gas due to the flow thereof. In addition, water formed at the cathode during generation of electricity penetrates to the anode side through the electrolyte

membrane and moves downstream in the direction of flow of the fuel gas or anode off gas due to the flow thereof. According the fuel cell as described above, the direction of flow of the fuel gas and the direction of flow of the oxidant gas are mutually opposed, and the above-mentioned formed water capturing section is provided at least one of farthermost downstream in the direction of flow of the fuel gas in the anode side gas flow path (namely, the site mutually opposing the farthermost upstream section in the direction of flow of the oxidant gas in the cathode side gas flow path with the membrane electrode assembly interposed there between) and farthermost downstream in the direction of flow of the oxidant gas in the cathode side gas flow path (namely, the site mutually opposing the farthermost upstream section in the direction of flow of the fuel gas in the anode side gas flow path with the membrane electrode assembly interposed there between).

[0009] Consequently, if the formed water capturing section is provided farthermost downstream in the direction of flow of the oxidant gas in the cathode side gas flow path, formed water contained in cathode off gas is captured by this formed gas capturing section, and together with suppressing discharge of formed water from the cathode side gas flow path to outside the fuel cell, the captured formed water can be allowed to effectively penetrate farthermost upstream in the direction of flow of the fuel gas in the anode side gas flow path through the electrolyte membrane. This formed water that has penetrated to the anode side can then be re-circulated as a result of being moved by the flow of the fuel gas. In addition, if the formed water capturing section is provided farthermost downstream in the direction of flow of the fuel gas in the anode side gas flow path, formed water contained in anode off gas is captured by this formed gas capturing section, and together with suppressing discharge of formed water from the anode side gas flow path to outside the fuel cell, the captured formed water can be allowed to effectively penetrate farthermost upstream in the direction of flow of the oxidant gas in the cathode side gas flow path through the electrolyte membrane. This formed water that has penetrated to the cathode side can then be re-circulated as a result of being moved by the flow of the oxidant gas.

[0010] Thus, effective self-humidification of the electrolyte membrane can be carried

out effectively in a polymer electrolyte fuel cell. Furthermore, as can be understood from the previously described contents, the formed water capturing section is preferably provided both farthermost downstream in the direction of flow of the fuel gas iri the anode side gas flow path and farthermost downstream in the direction of flow of the oxidant gas in the cathode side gas flow path.

[0011] In addition, in the above-mentioned fuel cell, the formed water capturing section is preferably a gap, in which gas containing the formed water is accumulated and which is formed in at least one of the anode side gas flow path and the cathode side gas flow path.

[0012] According to the fuel cell as described above, gas containing formed water can be accumulated in the gap, thereby enabling formed water contained in the gas to be captured.

[0013] In addition, in the above-mentioned fuel cell, the gap preferably has a shape such that flow path resistance in the gap is greater than flow path resistance at a site other than the gap in the flow path on the side on which the gap is provided.

[0014] According to the fuel cell as described above, since the gap has a shape such that flow path resistance in the gap is greater than flow path resistance at a site other than the gap in the flow path on the side on which the gap is provided, the movement of gas containing formed water that has been accumulated in the gap is suppressed, thereby enabling the formed water to be captured more effectively.

[0015] In addition, in the above-mentioned fuel cell, the gap is preferably formed so as to meander in the first direction or the second direction.

[0016] According to the fuel cell as described above, flow path resistance in the gap can be made to be greater than flow path resistance at a site other than the gap in the flow path on the side on which the gap is provided comparatively easily.

[0017] In addition, in the above-mentioned fuel cell, the gap is preferably filled with a moisture absorbent member having hygroscopicity.

[0018] According to the fuel cell as described above, since the gap is filled with a moisture absorbent member having hygroscopicity, formed water can be captured in the

formed water capturing section more effectively.

[0019] In addition, in the above-mentioned fuel cell, the moisture absorbent member is preferably a porous member.

[0020] According to the fuel cell as described above, the moisture absorbent member can be configured comparatively easily.

[0021] In addition, in the above-mentioned fuel cell, the insides of the pores of the porous member are preferably subjected to hydrophilic treatment.

[0022] According to the fuel cell as described above, the hygroscopicity of the porous member can be improved.

[0023] In addition, in the above-mentioned fuel cell, at least one of the anode side gas flow path and the cathode side gas flow path is preferably provided with a movement suppressing member that suppresses movement of the formed water in the direction of gas flow, as a formed water capturing section.

[0024] According to the fuel cell as described above, as a result of providing the movement suppressing member, movement of formed water contained in gas towards a discharge port is suppressed, thereby enabling the formed water to be captured effectively.

[0025] In addition, in the above-mentioned fuel cell, at least one of the anode side gas flow path and the cathode side gas flow path is preferably formed by interposing an electrically conductive and gas-diffusing porous body between the membrane electrode assembly and the separators, and the porous body is preferably provided with a first porous body and a second porous body having a pressure loss greater than the first porous body, as the movement suppressing member.

[0026] According to the fuel cell as described above, the movement of formed water contained in gas to a discharge port is suppressed by the second porous body, thereby enabling the formed water to be captured effectively. Furthermore, various members can be used for the first porous body and the second porous body, such as a foam metal sintered body, metal mesh or expanded metal.

[0027] In addition, in the above-mentioned fuel cell, the flow path resistance in the

direction of gas flow in the second porous body is preferably greater than the flow path resistance in the direction of gas flow in the first porous body.

[0028] According to the fuel cell as described above, pressure loss in the second porous body can be made to be greater than pressure loss in the first porous body.

[0029] In addition, in the above-mentioned fuel cell, the porosity of the second porous body is preferably lower than the porosity of the first porous body.

[0030] According to the fuel cell as described above, the pressure loss and flow path resistance in the second porous body can be made to greater than the pressure loss and flow path resistance in the first porous body.

[0031] In addition, in the above-mentioned fuel cell, the second porous body is preferably subjected to hydrophilic treatment.

[0032] According to the fuel cell as described above, formed water can be captured more effectively by the second porous body.

[0033] In addition, in the above-mentioned fuel cell, at least one of the anode side gas flow path and the cathode side gas flow path is preferably formed by interposing an electrically conductive and gas-diffusing porous body between the membrane electrode assembly and the separators, and the formed water capturing section is preferably an indentation for accumulating gas containing the formed water provided on at least one of a surface of the separator, arranged on the anode side, that contacts the porous body forming the anode side gas flow path, and a surface of the separator, arranged on the cathode side, that contacts the porous body forming the cathode side gas flow path.

[0034] According to the fuel cell as described above, gas containing the formed water is accumulated within the indentation, thereby enabling the formed water contained in the gas to be captured.

[0035] In addition, in the above-mentioned fuel cell, the separators are preferably produced by mutually bonding two metal plates in which the indentation is formed in at least one of the two metal plates.

[0036] According to the fuel cell as described above, the separator in which the indentation is formed can be produced comparatively easily.

[0037] In addition, in the above-mentioned fuel cell, the indentation is preferably subjected to hydrophilic treatment.

[0038] According to the fuel cell as described above, formed water can be captured by the indentation more effectively.

[0039] In addition, in the above-mentioned fuel cell, the formed water capturing section is preferably provided farthermost downstream in the direction of flow of the oxidant gas in the cathode side gas flow path, the separator arranged on the cathode side is preferably provided with a cathode off gas discharge port for discharging the cathode off gas from the cathode side gas flow path in a direction substantially perpendicular to the surface of the cathode, and in the separator arranged on the cathode side the cathode off gas discharge port is preferably formed farther upstream in the direction of flow of the oxidant gas than the formed water capturing section.

[0040] According to the fuel cell as described above, formed water captured by the formed water capturing section can be effectively suppressed from being discharged outside the fuel cell from the cathode off gas discharge port. In this fuel cell, formed water tends to be the greatest farthermost downstream in the direction of oxidant gas flow in the cathode side gas flow path, thereby making this effective.

[0041] In addition, in the above-mentioned fuel cell, the separator arranged on the anode side is preferably provided with a fuel gas supply port, in the anode side gas flow path, for supplying the fuel gas supplied from the outside in a direction substantially perpendicular to the surface of the anode, and the fuel gas supply port is preferably formed at a site opposing the formed water capturing section, with the membrane electrode assembly interposed therebetween, in the separator arranged on the anode side.

[0042] According to the fuel cell as described above, formed water captured by the formed water capturing section that has penetrated to the anode side through the electrolyte membrane can be re-circulated more effectively as a result of being moved by the flow of the fuel gas.

[0043] In addition, in the above-mentioned fuel cell, the formed water capturing section is preferably provided farthermost downstream in the direction of fuel gas flow in

the anode side gas flow path, the separator arranged on the anode side is preferably provided with an anode off gas discharge port for discharging the anode off gas from the anode side gas flow path in a direction substantially perpendicular to the surface of the anode, and in the separator arranged on the anode side the anode off gas discharge port is preferably formed farther upstream in the direction of fuel gas flow than the formed water capturing section.

[0044] According to the fuel cell as described above, formed water captured by the formed water capturing section can be effectively suppressed from being discharged outside the fuel cell from the anode off gas discharge port. In this fuel cell, the farthermost upstream section in the direction of flow of oxidizer gas in the cathode side gas flow path, having the greatest susceptibility to drying, can be effectively self-humidified.

[0045] In addition, in the above-mentioned fuel cell, the separator arranged on the cathode side is preferably provided with an oxidant gas supply port, in the cathode side gas flow path, for supplying the oxidant gas supplied from the outside in a direction roughly perpendicular to the surface of the cathode, and the oxidant gas supply port is preferably formed at a site opposing the formed water capturing section, with the membrane electrode assembly interposed therebetween, in the separator arranged on the cathode side.

[0046] According to the fuel cell as described above, formed water captured by the formed water capturing section that has penetrated to the cathode side through the electrolyte membrane can be re-circulated more effectively as a result of being moved by the flow of the oxidant gas.

[0047] In addition, in the above-mentioned fuel cell, the formed water capturing section preferably contains a cathode side formed water capturing section provided farthermost downstream in the direction of flow of the oxidant gas in the cathode side gas flow path, and an anode side formed water capturing section provided farthermost downstream in the direction of flow of the fuel gas in the anode side gas flow path; the separator arranged on the cathode side is preferably provided with an oxidant gas supply

port, in the cathode side gas flow path, for supplying the oxidant gas supplied from the outside in a direction substantially perpendicular to the surface of the cathode, and a cathode off gas discharge port for discharging the cathode off gas from the cathode side gas flow path in a direction substantially perpendicular to the surface of the cathode; the separator arranged on the anode side is preferably provided with a fuel gas supply port, in the anode side gas flow path, for supplying the fuel gas supplied from the outside in a direction substantially perpendicular to the surface of the anode, and an anode off gas discharge port for discharging the anode off gas from the anode side gas flow path in a direction substantially perpendicular to the surface of the anode; in the separator arranged on the cathode side the cathode off gas discharge port is formed farther upstream in the direction of the oxidant gas flow than the cathode side formed water generating section; in the separator arranged on the anode side the fuel gas supply port is formed at a site opposing the cathode side formed water charging section, with the membrane electrode assembly interposed therebetween; in the separator arranged on the anode side the anode off gas discharge port is formed farther upstream in the direction of fuel gas flow than the anode side formed water capturing section; and in the separator arranged on the cathode side the oxidant gas supply port is formed at a site opposing the anode side formed water capturing section, with the membrane electrode assembly interposed therebetween.

[0048] According to the fuel cell as described above, formed water captured by the cathode side formed water capturing section is effectively suppressed from being discharged outside the fuel cell from the cathode off gas discharge port, while formed water captured by the cathode side formed water capturing section that has penetrated to the anode side through the electrolyte membrane can be effectively re-circulated as a result of being moved by the flow of the fuel gas. In addition, formed water captured by the anode side formed water capturing section is effectively suppressed from being discharged outside the fuel cell from the anode off gas discharge port, while formed water captured by the anode side formed water capturing section that has penetrated to the cathode side through the electrolyte membrane can be effectively re-circulated as a result of being moved by the flow of the oxidant gas.

[0049] In addition, in the above-mentioned fuel cell, the formed water capturing section is preferably formed by carrying out hydrophilic treatment on the electrolyte membrane.

[0050] According to the fuel cell as described above, formed water is effectively captured by forming the formed water capturing section within the electrolyte membrane, and this formed water is able to penetrate from one side of the electrolyte membrane to the other.

[0051] In addition, in the above-mentioned fuel cell, the hydrophilic treatment is preferably treatment in which an additive containing at least one of an oxide having higher hydrophilicity than the electrolyte membrane and a metal having higher hydrophilicity than the electrolyte membrane is added to the electrolyte membrane.

[0052] According the fuel cell as described above, the formed water capturing section can be formed within the electrolyte membrane comparatively easily. Furthermore, examples of the above-mentioned oxide include titanium oxide, silicon oxide and cerium oxide (ceria). In addition, examples of the above-mentioned metal include platinum (Pt) and Pt alloys.

[0053] In addition, in the above-mentioned fuel cell, the additive preferably further has the property of suppressing the formation of radicals causing deterioration of the electrolyte membrane.

[0054] In polymer electrolyte fuel cells, hydroxy radicals are typically formed during generation of electricity, and these hydroxy radicals cause deterioration of the electrolyte membrane. According to the fuel cell as described above, deterioration of the electrolyte membrane in the formed water capturing section can be further suppressed since the additive further has the property of suppressing the formation of radicals (hydroxy radicals) causing deterioration of the electrolyte membrane.

[0055] In addition, in the above-mentioned fuel cell, the additive preferably contains at least one of ceria and Pt.

[0056] Ceria (cerium (IV) oxide) and Pt have higher hydrophilicity than the electrolyte membrane and have the property of suppressing formation of radicals causing

deterioration of the electrolyte membrane. Thus, according to the fuel cell as described above, capturing of formed water and suppression of the formation of radicals causing deterioration of the electrolyte membrane can be effectively carried out in the formed water capturing section formed in the electrolyte membrane. In addition, since Pt also has the property of acting as a catalyst that accelerates the reaction between fuel gas and oxidant gas, the use of Pt for the above-mentioned additive makes it possible to further form water within the electrolyte membrane and use that formed water for self-humidification.

[0057] In addition, a fuel cell system provided with any of the types of fuel cells as described above is also preferable.

[0058] According to the fuel cell system as described above, since a fuel cell capable of effective self-humidification of the electrolyte membrane is provided as described above, the size of the previously explained humidifier provided in the fuel cell system can be reduced or omitted. As a result, fuel consumption (energy efficiency) of the fuel cell system can be improved.

[0059] The invention is not required to be provided with all of the various characteristics described above, but rather can be configured while omitting or suitably combining a portion thereof.

BRIEF DESCRIPTION OF THE DRAWINGS

[0060] The features, advantages and technical and industrial significance of this invention will be described in the following detailed description of example embodiments of the invention with reference to the accompanying drawings, in which like numerals denote like elements, and wherein:

FIG 1 is an explanatory drawing showing the schematic configuration of a fuel cell system 1000 as a first embodiment of the invention;

FIGS. 2 A and 2B are explanatory drawings showing the schematic configuration of seal gasket-integrated membrane-electrode assembly (MEA) 41 in a cell module 40 of a first embodiment, with FIG 2A being an overhead view and FIG 2B being a

cross-sectional view taken along line A-A of FIG. 2A;

FIGS. 3 A and 3B are explanatory drawings showing the schematic configuration of a cathode side separator 42CA1 in a cell module 40 of a first embodiment, with FIG 3A being an overhead view and FIG. 3B being an overhead view of the back side thereof;

FIGS. 4 A and 4B are explanatory drawings showing the schematic configuration of an anode side separator 42AN1 in a cell module 40 of a first embodiment, with FIG 4A being an overhead view and FIG. 4B being an overhead view of the back side thereof;

FIG. 5 is an explanatory drawing showing the cross-sectional structure of a cell module 40 in a first embodiment;

FIGS. 6A to 6C are explanatory drawings showing the configuration of a cell module 4OR of a comparative example, with FIG. 6A being an overhead view, FIG. 6B being an overhead view of the back side thereof, the upper half of FIG. 6C being a cross-sectional view taken along line A-A of FIG. 6A and the lower half of FIG. 6C being a cross-sectional view taken along line B-B of FIG 6B;

FIG. 7 is an explanatory drawing showing the experimental results of a comparative experiment between a first embodiment and a comparative example;

FIGS. 8A to 8C are explanatory drawings showing the configuration of a cell module 40 of a second embodiment, with FIG 8A being an overhead view, FIG. 8B being an overhead view of the back side thereof, the upper half of FIG 8C being a cross-sectional view taken along line A-A of FIG. 8A, and the lower half of FIG 8C being a cross-sectional view taken along line B-B of FIG 8B;

FIG. 9 is an explanatory drawing showing the experimental results of a comparative experiment between a first embodiment and a second embodiment;

FIGS. 1OA to 1OC are explanatory drawings showing the configuration of a cell module 40 of a third embodiment, with FIG 1OA being an overhead view, FIG 1OB being an overhead view of the back side thereof, and the upper half of FIG. 1OC being a cross-sectional view taken along line A-A of FIG 1OA and the lower half of FIG 1OC being a cross-sectional view taken along line B-B of FIG 1OB;

FIG 11 is an explanatory drawing showing the experimental results of a comparative

experiment between a first embodiment and a third embodiment;

FIGS. 12A and 12B are explanatory drawings showing the schematic structure of a seal gasket-integrated MEA 41A in a cell module 40 of a fourth embodiment, with FIG. 12A being an overhead view and FIG. 12B being a cross-sectional view taken along line A-Aof FIG 12A;

FIGS. 13A to 13C are explanatory drawings showing the constituent components of a separator 42 A of a fourth embodiment, with FIG. 13 A being an overhead view of a cathode-opposing plate, FIG. 13B being an overhead view of an intermediate plate, and FIG. 13C being an overhead view of an anode-opposing plate;

FIG 14 is an overhead view of a separator 42A of a fourth embodiment;

FIG 15 is an explanatory drawing showing the cross-sectional structure of a cell module 40 of a fourth embodiment;

FIG. 16 is an explanatory drawing showing the schematic structure of a seal gasket-integrated MEA 41B in a cell module 40 of a fifth embodiment;

FIGS. 17A to 17C are explanatory drawings showing the constituent components of a separator 42B of a fifth embodiment, with FIG. 17A being an overhead view of a cathode-opposing plate, FIG 17B being an overhead view of an intermediate plate, and FIG 17C being an overhead view of an anode-opposing plate;

FIG 18 is an overhead view of a separator 42B of a fifth embodiment;

FIG 19 is an explanatory drawing showing the cross-sectional structure of a cell module 40 of a fifth embodiment; and

FIG 20 is an explanatory drawing showing an MEA 411 of a sixth embodiment.

DETAILED DESCRIPTION OF EMBODIMENTS [0061] The following provides an explanation of modes for carrying out the invention for each of the embodiments thereof.

A. Configuration of Fuel Cell System: FIG 1 is an explanatory drawing showing the schematic configuration of a fuel cell system 1000 to which each of the embodiments of the invention is applied.

[0062] A fuel cell stack 100 has a stack structure consisting of the lamination of a plurality of cell modules 40 for generating electricity by an electrochemical reaction between hydrogen and oxygen. Each cell module 40 generally employs a configuration in which membrane electrode assemblies respectively joined to an anode and cathode are held by a separator on both sides of an electrolyte membrane having proton conductivity. The anode and cathode are respectively provided with a catalyst layer joined to each surface of the electrolyte film, and a gas diffusion layer joined to the surface of this catalyst layer. Here, a solid polymer membrane such as Nafion (registered trademark) was used for the electrolyte membrane. A flow path for a fuel gas in the form of hydrogen to be supplied to the anode, a flow path for an oxidant gas in the form of air to be supplied to the cathode, and a flow path for cooling water (water, ethylene glycol and the like) are formed in each separator. Furthermore, the number of layers of the cell modules 40 can be set arbitrarily corresponding to required output of the fuel cell stack 100.

[0063] The fuel cell stack 100 is configured by laminating an end plate 10a, an insulating plate 20a, a current collector 30a, a plurality of cell modules 40, a current collector 30b, an insulating plate 20b and an end plate 10b in that order from one end thereof. These are provided with supply ports and discharge ports for allowing the flow of hydrogen, air and cooling water within the fuel cell stack 100. In addition, supply manifolds (hydrogen supply manifold, air supply manifold and cooling water supply manifold) for distributing and supplying hydrogen, air and cooling water to each cell module 40, and discharge manifolds (anode off gas discharge manifold, cathode off gas discharge manifold and cooling water discharge manifold) for respectively discharging anode off gas and cathode off gas discharged from the anodes and cathodes of each cell module 40 and for collecting cooling water and discharging outside the fuel cell stack 100, are formed within the fuel cell stack 100.

[0064] The end plates 10a and 10b are formed from a metal such as steel to ensure rigidity. The insulating plates 20a and 20b are formed from an insulating member such as rubber or resin. The current collectors 30a and 30b are formed from a

gas-impermeable electrically conductive member such as fine carbon or copper plates. Output terminals not shown are provided on each current collector 30a and 30b, enabling output of electrical power generated with the fuel cell stack 100.

[0065] Furthermore, although not shown in the drawings, the fuel cell stack 100 is clamped with clamping members in a state in which a prescribed clamping load is applied in the direction of lamination of the stack structure in order to control decreases in cell performance caused by, for example, an increase in contact resistance at any location within the stack structure, or to suppress leakage of gas.

[0066] Fuel gas in the form of hydrogen is supplied to anodes of the fuel cell stack 100 through a line 53 from a hydrogen tank 50 in which high-pressure hydrogen is stored. Instead of the hydrogen tank 50, hydrogen-rich gas may be supplied to the anodes by forming by a reforming reaction using an alcohol, hydrocarbon or aldehyde and the like as a raw material.

[0067] The high-pressure hydrogen stored in the hydrogen tank 50 is supplied to the anode of each cell module 40 through the hydrogen supply manifold after being adjusted for pressure and supply volume with a shut valve 51 and a regulator 52 provided at the outlet of the hydrogen tank 50. Anode off gas discharged from each cell module 40 can be discharged outside the fuel cell stack 100 through a discharge line 56 connected to the anode off gas discharge manifold. Furthermore, when anode off gas is discharged outside the fuel cell stack 100, hydrogen contained in the anode off gas is processed by a diluter and the like not shown.

[0068] In addition, a circulating line 54 for re-circulating anode off gas to the line 53 is connected to the line 53 and the discharge line 56. An exhaust valve 57 is arranged downstream from the connection between the discharge line 56 and the circulating line 54. In addition, a pump 55 is arranged in the circulating line 54. Whether anode off gas is discharged to the outside or circulated to the line 53 can be suitably switched by controlling the operation of the pump 55 and the exhaust valve 57. Unconsumed hydrogen contained in the anode off gas can be used efficiently by re-circulating the anode off gas to the line 53.

[0069] Oxidant gas containing oxygen in the form of compressed air compressed by a compressor 60 is supplied to the fuel cell stack 100 through a line 61. This compressed air is supplied to the cathode of each cell module 40 through the air supply manifold connected to the line 61. Cathode off gas discharged from the cathode of each cell module 40 is discharged outside the fuel cell stack 100 through a discharge line 62 connected to the cathode off gas discharge manifold. Cathode off gas is discharged from the discharge line 62 together with formed water formed by an electrochemical reaction between hydrogen and oxygen at the cathodes of the fuel cell stack 100.

[0070] Since heat is generated by the electrochemical reaction described above, cooling water for cooling the fuel cell stack 100 is also supplied to the fuel cell stack 100. This cooling water is pumped through a line 72 by a pump 70, cooled by a radiator 71 and supplied to the fuel cell stack 100.

[0071] Operation of the fuel cell system 1000 is controlled by a control unit 80. The control unit 80 is configured in the form of a microcomputer internally provided with a central processing unit (CPU), random access memory (RAM), read only memory (ROM), timers and the like, and controls system operation, such as the operation of various valves and pumps, in accordance with a program stored in the ROM.

[0072] Furthermore, in a fuel cell system provided with fuel cells using a solid polymer membrane for the electrolyte membrane, since it is necessary to maintain the electrolyte membrane in a suitable wet state in order to properly maintain proton conductivity of the electrolyte membrane and obtain desired electricity generation performance, a humidifier, for example, is frequently provided for humidifying the air used for the oxidant gas. The providing of this humidifier leads to an increase in size of the fuel cell system as well as a poor fuel consumption (energy efficiency). In contrast, in the fuel cell system 1000, each cell module 40 that composes the fuel cell stack 100 respectively has a structure that enables self-humidification of the electrolyte membrane provided by each cell module 40 to be carried out efficiently by re-circulating water formed during generation of electricity through each cell module 40 as will be described later. Thus, the fuel cell system 1000 is not provided with a humidifier for humidifying

the oxidant gas in the form of air or the fuel gas in the form of hydrogen, thereby reducing size and improving fuel consumption (energy efficiency).

[0073] The following provides an explanation of various cell modules 40 capable of efficiently carrying out self-humidification of the electrolyte membrane. Furthermore, although the cell modules in each of the embodiments explained below each have different structures, they are all uniformly referred to as "cell module 40".

[0074] The following provides an explanation of a first embodiment. The cell module 40 of the first embodiment is configured by holding a unit having a seal gasket arranged around the periphery of a membrane electrode assembly (MEA) (to be referred to as seal gasket-integrated MEA) with a cathode side separator and an anode side separator to be described later.

[0075] FIGS. 2A and 2B are explanatory drawings showing the schematic configuration of a seal gasket-integrated MEA 41 in the cell module 40 of the first embodiment. FIG. 2A shows an overhead view of the seal gasket-integrated MEA 41 as viewed from the anode side. In addition, FIG 2B shows a cross-sectional view taken along line A-A in FIG. 2A.

[0076] As shown in FIG. 2 A, the seal gasket-integrated MEA 41 has a rectangular shape, and a seal gasket 410 is integrally formed around the periphery of a rectangular MEA 411. Various materials having insulating properties, heat resistance and gas impermeability, such as rubber or resin, can be used for the seal gasket 410.

[0077] An air supply through hole 412i composing the air supply manifold, and an anode off gas discharge through hole 414o composing the anode off gas discharge manifold, are formed vertically arranged in the seal gasket 410 in the vicinity of the MEA 411 on the short side shown on the left in the drawing. In addition, a hydrogen supply through hole 414i composing the hydrogen supply manifold and a cathode off gas discharge through hole 412o composing the cathode off gas discharge manifold are formed vertically arranged in the seal gasket 410 in the vicinity of the MEA 411 on the short side shown on the right in the drawing. In addition, a cooling water supply through hole 416i composing the cooling water supply manifold is formed along the

upper long side of the seal gasket 410 in the seal gasket 410 in the vicinity of the MEA 411 on the long side shown on the top in the drawing. In addition, a cooling water discharge through hole 416o composing the cooling water discharge manifold is formed along the upper long side of the seal gasket 410 in the seal gasket 410 in the vicinity of the MEA 411 on the long side shown on the bottom in the drawing.

[0078] As shown in FIG. 2B, a cathode 411c (cathode side catalyst layer 41 Ice, cathode side gas diffusion layer 411cd) and an anode 411a (anode side catalyst layer 411ac, anode side gas diffusion layer 411ad) are respectively joined on both sides of an electrolyte membrane 411m.

[0079] FIGS. 3 A and 3B are explanatory drawings showing the schematic configuration of a cathode side separator 42CA1 in the cell module 40 of the first embodiment. FIG. 3A shows an overhead view of the cathode side separator 42CA1 as viewed from the side that contacts the cathode 411c of the MEA 411. In addition, FIG 3B shows an overhead view of the cathode side separator 42CA1 shown in FIG. 3A as viewed from the back side.

[0080] The cathode side separator 42CA1 has the same rectangular shape as the previously explained seal gasket-integrated MEA 41. As shown in the drawings, an air supply through hole 422i, an anode off gas discharge through hole 424o, a hydrogen supply through hole 424i, a cathode off gas discharge through hole 422o, a cooling water supply through hole 426i and a cooling water discharge through hole 426o are formed in the cathode side separator 42CA1 at locations respectively corresponding to the air supply through hole 412i, the anode off gas discharge through hole 414o, the hydrogen supply through hole 414i, the cathode off gas discharge through hole 412o, the cooling water supply through hole 416i and the cooling water discharge through hole 416o formed in the seal gasket 410 of the seal gasket-integrated MEA 41.

[0081] In addition, as shown in FIG 3A, a plurality of grooves 422dl and 422d2 and a plurality of ribs 422rl and 422r2 are formed in the surface of the cathode side separator 42CA1 so that air flows from the air supply through hole 422i along the surface of the cathode 411c of the MEA 411, thus forming a cathode side gas flow path. As shown in

the drawings, a cathode off gas discharge port 422e for discharging cathode off gas from the cathode side gas flow path is formed through the cathode side separator 42CA1 in the direction of thickness between the plurality of grooves 422dl and the plurality of grooves 422d2 and between the plurality of ribs 422rl and the plurality of ribs 422r2, namely at an intermediate location in the cathode side gas flow path. In other words, the plurality of grooves 422d2 and the plurality of ribs 422r2 are formed farther downstream in the direction of flow of air or cathode off gas than the cathode off gas discharge port 422e. Furthermore, cathode off gas discharged from the cathode off gas discharge port 422e flows out to the cathode off gas discharge through hole 422o through grooves 422d3 (see FIG 3B) formed in the surface of the cathode side separator 42CA1.

[0082] In addition, as shown in FIG. 3B, a plurality of grooves 426d and a plurality of ribs 426r are formed in the back side of the cathode side separator 42CA1 so that cooling water flows from the cooling water supply through hole 426i to the cooling water discharge through hole 426o.

[0083] FIGS. 4A and 4B are explanatory drawings showing the schematic configuration of an anode side separator 42AN1 in the cell module 40 of the first embodiment. FIG. 4A shows an overhead view of the anode side separator 42AN1 as viewed from the side that contacts the anode 411a of the MEA 411. In addition, FIG 4B shows an overhead view of the anode side separator 42AN1 as viewed from the back side shown in FIG. 4A.

[0084] The cathode side separator 42AN1 has the same rectangular shape as the previously explained seal gasket- integrated MEA 41. As shown in the drawings, an air supply through hole 422i, an anode off gas discharge through hole 424o, a hydrogen supply through hole 424i, a cathode off gas discharge through hole 422o, a cooling water supply through hole 426i and a cooling water discharge through hole 426o are formed in the anode side separator 42AN1 at locations respectively corresponding to the air supply through hole 412i, the anode off gas discharge through hole 414o, the hydrogen supply through hole 414i, the cathode off gas discharge through hole 412o, the cooling water supply through hole 416i and the cooling water discharge through hole 416o formed in

the seal gasket 410 of the seal gasket-integrated MEA 41.

[0085] In addition, as shown in FIG 4A, a plurality of grooves 424dl and 424d2 and a plurality of ribs 424rl and 424r2 are formed in the surface of the anode side separator 42AN1 so that hydrogen flows from the hydrogen supply through hole 424i along the surface of the anode 411a of the MEA 411, thus forming an anode side gas flow path. As shown in the drawings, an anode off gas discharge port 424e for discharging anode off gas from the anode side gas flow path is formed through the anode side separator 42AN1 in the direction of thickness between the plurality of grooves 424dl and the plurality of grooves 424d2 and between the plurality of ribs 424rl and the plurality of ribs 424r2, namely at an intermediate location in the anode side gas flow path. In other words, the plurality of grooves 424d2 and the plurality of ribs 424r2 are formed farther downstream in the direction of flow of hydrogen or anode off gas than the anode off gas discharge port 424e. Furthermore, anode off gas discharged from the anode off gas discharge port 424e flows out to the anode off gas discharge through hole 424o through grooves 424d3 (see FIG. 4B) formed in the surface of the anode side separator 42AN1.

[0086] In addition, as shown in FIG. 4B, a plurality of grooves 426d and a plurality of ribs 426r are formed in the back side of the anode side separator 42AN1 so that cooling water flows from the cooling water supply through hole 426i to the cooling water discharge through hole 426o.

[0087] FIG 5 is an explanatory drawing showing the cross-sectional structure of the cell module 40 in the first embodiment. A cross-sectional view taken along line A-A of FIG 3A when the seal gasket-integrated MEA 41 is held by the cathode side separator 42CA1 and the anode side separator 42AN1 is shown above the single-dot broken line depicted in the drawing. In addition, a cross-sectional view taken along line B-B of FIG 4 A when the seal gasket-integrated MEA 41 is held by the cathode side separator 42CA1 and the anode side separator 42AN 1 is shown below the single-dot broken line depicted in the drawing.

[0088] As shown in the drawing, air supplied from outside the fuel cell stack 100 branches from the air supply through hole 422i formed in the cathode side separator

42CA1 and flows into the groove 422dl from left to right in the drawing. At this time, formed water formed during generation of electricity also moves with the flow of air and cathode off gas. A portion of the cathode off gas containing the formed water flows into and accumulates in a gap within the groove 422d2 located farthermost downstream in the direction of flow of air and cathode off gas, while the remaining cathode off gas is discharged outside the fuel cell stack 100 by passing through the cathode off gas discharge port 422e formed farther upstream than the gap, through a groove 422d3 and through the cathode off gas discharge through hole 422o. Formed water contained in the cathode off gas that has accumulated in the gap within the groove 422d2 is captured here. This gap is one example of the formed water capturing section of the invention (to also be referred to as the cathode side formed water capturing section).

[0089] On the other hand, hydrogen supplied from outside the fuel cell stack 100 branches from the hydrogen supply through hole 424i formed in the anode side separator 42AN1 and flows into the groove 424dl from right to left in the drawing. At this time, formed water formed during generation of electricity also moves with the flow of hydrogen and anode off gas. A portion of the anode off gas containing the formed water flows into and accumulates in a gap within the groove 424d2 located farthermost downstream in the direction of flow of hydrogen and anode off gas, while the remaining anode off gas is discharged outside the fuel cell stack 100 by passing through the anode off gas discharge port 424e formed farther upstream than the gap, through the groove 424d2 and through the anode off gas discharge through hole 424o. Formed water contained in the anode off gas that has accumulated in the gap within the groove 424d2 is captured here. This gap is one example of the formed water capturing section of the invention (to also be referred to as the anode side formed water capturing section).

[0090] In the cell module 40 of the first embodiment as explained above, the direction of flow of air and cathode off gas in the cathode side gas flow path and the direction of flow of hydrogen and anode off gas in the anode side gas flow path are mutually opposing. In addition, the cell module 40 is provided with a cathode side formed water capturing section farthermost downstream in the direction of flow of air

and cathode off gas in the cathode side gas flow path (namely, at a site mutually opposing the farthermost upstream portion in the direction of flow of hydrogen and anode off gas in the anode side gas flow path with MEA 411 interposed there between). In addition, the anode side formed water capturing section is provided farthermost downstream in the direction of flow of hydrogen and anode off gas in the anode side gas flow path (namely, at a site mutually opposing the farthermost upstream portion in the direction of flow of air and cathode off gas in the cathode side gas flow path with MEA 411 interposed there between).

[0091] Consequently, together with being able to suppress the discharge of formed water outside the cell module 40 from the cathode side gas flow path by capturing formed water contained in cathode off gas with the cathode side formed water capturing section, the captured formed water can be allowed to effectively penetrate farthermost upstream in the direction of flow of hydrogen and anode off gas in the anode side gas flow path through the electrolyte membrane 411m. Formed water that has penetrated to the anode 411a side can be re-circulated as a result of being moved by the flow of hydrogen and anode off gas. In addition, together with being able to suppress the discharge of formed water outside the cell module 40 from the anode side gas flow path by capturing formed water contained in anode off gas with the anode side formed water capturing section, the captured formed water can be allowed to effectively penetrate farthermost upstream in the direction of flow of air and cathode off gas in the cathode side gas flow path through the electrolyte membrane 411m. Formed water that has penetrated to the cathode 411c side can be re-circulated as a result of being moved by the flow of oxidant gas. Thus, according to the cell module 40 of the first embodiment, the electrolyte membrane 411m can be effectively self-humidified.

[0092] A comparative experiment of electricity generation performance was carried out between the cell module 40 of the first embodiment and a cell module 4OR serving as a comparative example in order to verify the self-humidifying effects produced by the cell module 40 of the first embodiment as described above. In this experiment, a comparison was made of the maximum temperature of cooling water able to maintain a

prescribed lower limit voltage for a prescribed duration during non-humidified operation (power generation) between the cell module 40 of the first embodiment and the cell module 4OR of the comparative example. This is because in the cell modules 40 and 4OR, as the' temperature of the cooling water rises, namely as the temperatures of the cell modules 40 and 4OR rise, the electrolyte membrane 411m dries up (due to a shortage of moisture) resulting in a decrease in electromotive force.

[0093] FIGS. 6 A to 6C are explanatory drawings showing the configuration of the cell module 4OR of the comparative example. Similar to the cell module 40 of the first embodiment, the cell module 4OR of the comparative example is configured by holding the seal gasket-integrated MEA 41 shown in FIGS. 2A and 2B with a cathode side separator 42CAR and an anode side separator 42ANR. FIG 6A shows an overhead view of the cathode side separator 42CAR as viewed from the side that contacts the cathode 411c of the MEA 411. In addition, FIG. 6B shows an overhead view of the anode side separator 42 ANR as viewed from the side that contacts the anode 411a of the MEA 411. In addition, FIG. 6C shows the cross-sectional structure of the cell module 4OR. In FIG 6C, a cross-sectional view taken along line A-A of FIG 6A when the seal gasket-integrated MEA 41 is held by the cathode side separator 42CAR and the anode side separator 42ANR is shown above the single-dot broken line depicted in the drawing. In addition, a cross-sectional view taken along line B-B of FIG 6B when the seal gasket-integrated MEA 41 is held by the cathode side separator 42CAR and the anode side separator 42ANR is shown below the single-dot broken line depicted in the drawing.

[0094] As can be determined from a comparison between FIG 6A and FIGS. 3 A and 3B, an air supply through hole 422i, an anode off gas discharge through hole 424o, a hydrogen supply through hole 424i, a cathode off gas discharge through hole 422o, a cooling water supply through hole 426i and a cooling water discharge through hole 426o are formed in the cathode side separator 42CAR at the same locations as in the cathode side separator 42CA1. In addition, a plurality of grooves 422d and a plurality of ribs 422r are formed in the surface of the cathode side separator 42CAR so that air flows from the air supply through hole 422i to the cathode off gas discharge through hole 422o along

the surface of the cathode 411c of the MEA 411, thus forming a cathode side gas flow path. Differing from the cathode side separator 42CA1, the cathode side separator 42CAR is not provided with a cathode off gas discharge port 422e for discharging cathode off gas from an intermediate location in the cathode side gas flow path, grooves 422d3 or a cathode side formed water capturing section (see FIG. 6C). Furthermore, although not shown in the drawings, a plurality of grooves 426d and a plurality of ribs 426r are formed in the back side of the cathode side separator 42CAR so that cooling water flows from the cooling water supply through hole 426i to the cooling water discharge through hole 426o in the same manner as the cathode side separator 42CA1.

[0095] In addition, as can be determined from a comparison between FIG 6B and FIGS. 4A and 4B, an air supply through hole 422i, an anode off gas discharge through hole 424o, a hydrogen supply through hole 424i, a cathode off gas discharge through hole 422o, a cooling water supply through hole 426i and a cooling water discharge through hole 426o are formed in the anode side separator 42ANR at the same locations as in the anode side separator 42AN 1. In addition, a plurality of grooves 424d and a plurality of ribs 424r are formed in the surface of the anode side separator 42ANR so that hydrogen flows from the hydrogen supply through hole 424i to the anode off gas discharge through hole 424o along the surface of the anode 411a of the MEA 411, thus forming an anode side gas flow path. Differing from the anode side separator 42AN1, the anode side separator 42ANR is not provided with an anode off gas discharge port 424e for discharging anode off gas from an intermediate location in the anode side gas flow path, grooves 424d3 or an anode side formed water capturing section (see FIG 6C). Furthermore, although not shown in the drawings, a plurality of grooves 426d and a plurality of ribs 426r are formed in the back side of the anode side separator 42ANR so that cooling water flows from the cooling water supply through hole 426i to the cooling water discharge through hole 426o in the same manner as the anode side separator 42AN1.

[0096] FIG 7 is an explanatory drawing showing the experimental results of a comparative experiment. An increase of 5°C was obtained with the cell module 40 of

the first embodiment over the cell module 4OR of the comparative example. Namely, the cell module 40 of the first embodiment was able to maintain the same lower limit voltage at a maximum temperature 5 ⁰ C higher than the cell module 4OR of the comparative example. On the basis of this result, self-humidification of the electrolyte membrane 411m can be determined to be carried out more effectively in the cell module 40 of the first embodiment. In addition, in the case of applying the cell module 40 of the first embodiment in the fuel cell stack 100, the size of the radiator 71 in the fuel cell system 1000 can be made to be more compact than the case of applying the cell module 4OR of the comparative example in the fuel cell stack 100, thereby making it possible to reduce the size of the fuel cell system 1000.

[0097] The following provides an explanation of a second embodiment. The configuration of the cell module 40 in the second embodiment is nearly the same as the configuration of the cell module 40 of the first embodiment. However, in the cell module 40 of the second embodiment, the configurations of the cathode side separator 42CA2 and the anode side separator 42AN2 of the second embodiment differ partially from the configurations of the cathode side separator 42CA1 and the anode side separator 42AN1, respectively, in the cell module 40 of the first embodiment.

[0098] FIGS. 8A to 8C are explanatory drawings showing the configuration of the cell module 40 of the second embodiment. Similar to the cell module 40 of the first embodiment, the cell module 40 of the second embodiment is configured by holding the seal gasket-integrated MEA 41 shown in FIGS. 2A and 2B with a cathode side separator 42CA2 and an anode side separator 42AN2. FIG 8A shows a perspective view of the cathode side separator 42CA2 as viewed from the side that contacts the cathode 411c of the MEA 411. In addition, FIG 8B shows an overhead view of the anode side separator 42AN2 as viewed from the side that contacts the anode 411a of the MEA 411. In addition, FIG. 8C shows a cross-sectional structure of the cell module 40. FIG 8C shows a cross-sectional view taken along line A-A in FIG 8A when the seal gasket-integrated MEA 41 is held by the cathode side separator 42CA2 and the anode side separator 42AN2 is shown above the single-dot broken line depicted in the drawing.

In addition, a cross-sectional view taken along line B-B of FIG 8B when the seal gasket-integrated MEA 41 is held by the cathode side separator 42CA2 and the anode side separator 42AN2 is shown below the single-dot broken line depicted in the drawing.

[0099] As can be determined by a comparison between FIG 8 A and FIGS. 3 A and 3B, an air supply through hole 422i, an anode off gas discharge through hole 424o, a hydrogen supply through hole 424i, a cathode off gas discharge through hole 422o, a cooling water supply through hole 426i and a cooling water discharge through hole 426o are formed in the cathode side separator 42CA2 at the same locations as in the cathode side separator 42CA1. In addition, a plurality of grooves 422dl and 422d2 and a plurality of ribs 422rl and 422r2 are formed in the surface of the cathode side separator 42CA2 so that air flows from the air supply through hole 422i along the surface of the cathode 411c of the MEA 411, thus forming a cathode side gas flow path. Similar to the cathode side separator 42CA1, a cathode off gas discharge port 422e for discharging cathode off gas from the cathode side gas flow path is formed through the cathode side separator 42CA2 in the direction of thickness between the plurality of grooves 422dl and the plurality of grooves 422d2 and between the plurality of ribs 422rl and the plurality of ribs 422r2, namely at an intermediate location in the cathode side gas flow path. In other words, the plurality of grooves 422d2 and the plurality of ribs 422r2 are formed farther downstream in the direction of flow of air or cathode off gas than the cathode off gas discharge port 422e. However, as shown in the drawings, the cathode side separator 42CA2 in the second embodiment differs from the cathode side separator 42CA1 in that the plurality of grooves 422d2 and the plurality of ribs 422r2 are formed so that the cathode side gas flow path meanders.

[0100] Furthermore, although not shown in the drawings, similar to the cathode side separator 42CA1, a plurality of grooves 426d and a plurality of ribs 426r are formed in the back side of the cathode side separator 42CA2 so that cooling water flows from the cooling water supply through hole ,426i to the cooling water discharge through hole 426o. In addition, grooves 422d3 are formed in the back side of the cathode side separator 42CA2 to allow cathode off gas discharged from the cathode off gas discharge port 422e

to flow out to the cathode off gas discharge through hole 422o.

[0101] In addition, as can be determined from a comparison between FIG. 8B and FIGS. 4A and 4B, an air supply through hole 422i, an anode off gas discharge through hole 424o, a hydrogen supply through hole 424i, a cathode off gas discharge through hole 422o, a cooling water supply through hole 426i and a cooling water discharge through hole 426o are formed in the anode side separator 42AN2 at the same locations as in the anode side separator 42AN1. In addition, a plurality of grooves 424dl and 424d2 and a plurality of ribs 424rl and 424r2 are formed in the surface of the anode side separator 42AN2 so that hydrogen flows from the hydrogen supply through hole 424i along the surface of the anode 411a of the MEA 411, thus forming an anode side gas flow path. Similar to the anode side separator 42AN1, an anode off gas discharge port 424e for discharging anode off gas from the anode side gas flow path is formed through the anode side separator 42AN2 in the direction of thickness between the plurality of grooves 424dl and the plurality of grooves 424d2 and between the plurality of ribs 424rl and the plurality of ribs 424r2, namely at an intermediate location in the anode side gas flow path. In other words, the plurality of grooves 424d2 and the plurality of ribs 424r2 are formed farther downstream in the direction of flow of hydrogen or anode off gas than the anode off gas discharge port 424e. However, as shown in the drawings, the anode side separator 42AN2 in the second embodiment differs from the anode side separator 42AN 1 in that the plurality of grooves 424d2 and the plurality of ribs 424r2 are formed so that the anode side gas flow path meanders.

[0102] Furthermore, although not shown in the drawings, similar to the anode side separator 42AN 1, a plurality of grooves 426d and a plurality of ribs 426r are formed in the back side of the anode side separator 42AN2 so that cooling water flows from the cooling water supply through hole 426i to the cooling water discharge through hole 426o. In addition, grooves 424d3 are formed in the back side of the anode side separator 42AN2 to allow anode off gas discharged from the anode off gas discharge port 424e to flow out to the anode off gas discharge through hole 424o.

[0103] -As shown in FIG. 8C, air supplied from outside the fuel cell stack 100

branches from the air supply through hole 422i formed in the cathode side separator 42CA2 and flows into the groove 422dl from left to right in the drawing. At this time, formed water formed during generation of electricity also moves with the flow of air and cathode off gas. A portion of the cathode off gas containing the formed water flows into and accumulates in a gap having a meandered shape within the groove 422d2 located farthermost downstream in the direction of flow of air and cathode off gas, while the remaining cathode off gas is discharged outside the fuel cell stack 100 by passing through the cathode off gas discharge port 422e formed farther upstream than the gap, through the groove 422d3 and through the cathode off gas discharge through hole 422o. Formed water contained in the cathode off gas that has accumulated in the gap having a meandered shape within the groove 422d2 is captured here. This gap is one example of the formed water capturing section of the invention.

[0104] On the other hand, hydrogen supplied from outside the fuel cell stack 100 branches from the hydrogen supply through hole 424i formed in the anode side separator 42AN2 and flows into the groove 424dl from right to left in the drawing. At this time, formed water formed during generation of electricity also moves with the flow of hydrogen and anode off gas. A portion of the anode off gas containing the formed water flows into and accumulates in a gap having a meandered shape within the groove 424d2 located farthermost downstream in the direction of flow of hydrogen and anode off gas, while the remaining anode off gas is discharged outside the fuel cell stack 100 by passing through the anode off gas discharge port 424e formed farther upstream than the gap, through the groove 424d2 and through the anode off gas discharge through hole 424o. Formed water contained in the anode off gas that has accumulated in the gap having a meandered shape within the groove 424d2 is captured here. This gap is one example of the formed water capturing section of the invention.

[0105] In the cell module 40 of the second embodiment as explained above, similar to the cell module 40 of the first embodiment, together with being able to suppress the discharge of formed water outside the cell module 40 from the cathode side gas flow path by capturing formed water contained in cathode off gas with the cathode side formed

water capturing section, the captured formed water can be allowed to effectively penetrate farthermost upstream in the direction of flow of hydrogen and anode off gas in the anode side gas flow path through the electrolyte membrane 411m. Formed water that has penetrated to the anode 411a side can be re-circulated as a result of being moved by the flow of hydrogen and anode off gas. In addition, together with being able to suppress the discharge of formed water outside the cell module 40 from the anode side gas flow path by capturing formed water contained in anode off gas with the anode side formed water capturing section, the captured formed water can be allowed to effectively penetrate farthermost upstream in the direction of flow of air and cathode off gas in the cathode side gas flow path through the electrolyte membrane 411m. Formed water that has penetrated to the cathode 411c side can be re-circulated as a result of being moved by the flow of oxidant gas. Thus, according to the cell module 40 of the second embodiment, the electrolyte membrane 411m can be effectively self-humidified.

[0106] Furthermore, since the shape of the cathode side formed water capturing section in the cell module 40 of the second embodiment has a meandered shape as described above, the flow path resistance of the cathode side formed water capturing section in the cathode side flow path is greater than the flow path resistance of other sites. Similarly, since the shape of the anode side formed water capturing section has a meandered shape, the flow path resistance of the anode side formed water capturing section in the anode side flow path is greater than the flow path resistance at other sites. Thus, the effect of suppressing discharge of formed water captured in the cathode side formed water capturing section and the anode side formed water capturing section to the outside is greater in the cell module 40 of the second embodiment than in the cell module 40 of the first embodiment.

[0107] A comparative experiment of electricity generation performance was carried out between the cell module 40 of the first embodiment and the cell module 40 of the second embodiment in order to verify the self-humidifying effects produced by the cell module 40 of the second embodiment as described above. In this experiment, a comparison was made of the maximum temperature of cooling water able to maintain a

prescribed lower limit voltage for a prescribed duration during non-humidified operation (power generation) between the cell module 40 of the first embodiment and the cell module 40 of the second embodiment in the same manner as explained in the first embodiment.

[0108] FIG. 9 is an explanatory drawing showing the experimental results of the comparative experiment. An increase of 3°C was obtained with the cell module 40 of the second embodiment over the cell module 40 of the first embodiment. Namely, the cell module 40 of the second embodiment was able to maintain the same lower limit voltage at a maximum temperature 3°C higher than the cell module 40 of the first embodiment. On the basis of this result, self-humidification of the electrolyte membrane 411m can be determined to be carried out more effectively in the cell module 40 of the second embodiment than in the cell module 40 of the first embodiment. In addition, in the case of applying the cell module 40 of the second embodiment in the fuel cell stack 100, the size of the radiator 71 in the fuel cell system 1000 can be made to be more compact than the case of applying the cell module 40 of the first embodiment in the fuel cell stack 100, thereby making it possible to reduce the size of the fuel cell system 1000.

[0109] The following provides an explanation of a third embodiment. The configuration of the cell module 40 in the third embodiment is nearly the same as the configuration of the cell module 40 of the first embodiment. However, in the cell module 40 of the third embodiment, the configurations of the cathode side separator 42CA3 and the anode side separator 42AN3 of the third embodiment differ partially from the configurations of the cathode side separator 42CA1 and the anode side separator 42AN1, respectively, in the cell module 40 of the first embodiment.

[0110] FIGS. 1OA to 1OC are explanatory drawings showing the configuration of the cell module 40 of the third embodiment. Similar to the cell module 40 of the first embodiment, the cell module 40 of the third embodiment is configured by holding the seal gasket-integrated MEA 41 shown in FIGS. 2 A and 2B with a cathode side separator 42CA3 and an anode side separator 42AN2. FIG. 1OA shows a perspective view of the

cathode side separator 42CA3 as viewed from the side that contacts the cathode 411c of the MEA 411. In addition, FIG. 1OB shows an overhead view of the anode side separator 42AN3 as viewed from the side that contacts the anode 411a of the MEA 411. In addition, FIG. 1OC shows a cross-sectional structure of the cell module 40. FIG. 1OC shows a cross-sectional view taken along line A-A in FIG. 1OA when the seal gasket-integrated MEA 41 is held by the cathode side separator 42CA3 and the anode side separator 42AN3 is shown above the single-dot broken line depicted in the drawing. In addition, a cross-sectional view taken along line B-B of FIG. 1OB when the seal gasket-integrated MEA 41 is held by the cathode side separator 42CA3 and the anode side separator 42AN3 is shown below the single-dot broken line depicted in the drawing.

[0111] As can be determined by a comparison between FIG. 1OA and FIGS. 3A and 3B, an air supply through hole 422i, an anode off gas discharge through hole 424o, a hydrogen supply through hole 424i, a cathode off gas discharge through hole 422o, a cooling water supply through hole 426i and a cooling water discharge through hole 426o are formed in the cathode side separator 42CA3 at the same locations as in the cathode side separator 42CA1. In. addition, a plurality of grooves 422dl and 422d2 and a plurality of ribs 422rl and 422r2 are formed in the surface of the cathode side separator 42CA3 so that air flows from the air supply through hole 422i along the surface of the cathode 411c of the MEA 411, thus forming a cathode side gas flow path. Similar to the cathode side separator 42CA1, a cathode off gas discharge port 422e for discharging cathode off gas from the cathode side gas flow path is formed through the cathode side separator 42CA3 in the direction of thickness between the plurality of grooves 422dl and the plurality of grooves 422d2 and between the plurality of ribs 422rl and the plurality of ribs 422r2, namely at an intermediate location in the cathode side gas flow path. In other words, the plurality of grooves 422d2 and the plurality of ribs 422r2 are formed farther downstream in the direction of flow of air or cathode off gas than the cathode off gas discharge port 422e. However, as shown in the drawings, the cathode side separator 42CA3 in the third embodiment differs from the cathode side separator 42CA1 in that a moisture absorbent material 422a composed of a porous member is filled into the

plurality of grooves 422d. Various members having a large number of pores can be applied for the porous member. The insides of the pores of this moisture absorbent material (porous member) 422a is subjected to hydrophilic treatment to enhance hygroscopicity.

[0112] Furthermore, although not shown in the drawings, similar to the cathode side separator 42CA1, a plurality of grooves 426d and a plurality of ribs 426r are formed in the back side of the cathode side separator 42CA3 so that cooling water flows from the cooling water supply through hole 426i to the cooling water discharge through hole 426o. In addition, grooves 422d3 are formed in the back side of the cathode side separator 42CA3 to allow cathode off gas discharged from the cathode off gas discharge port 422e to flow out to the cathode off gas discharge through hole 422o.

[0113] In addition, as can be determined from a comparison between FIG. 1OB and FIGS. 4A and 4B, an air supply through hole 422i, an anode off gas discharge through hole 424o, a hydrogen supply through hole 424i, a cathode off gas discharge through hole 422o, a cooling water supply through hole 426i and a cooling water discharge through hole 426o are formed in the anode side separator 42AN3 at the same locations as in the anode side separator 42AN1. In addition, a plurality of grooves 424dl and 424d2 and a plurality of ribs 424rl and 424r2 are formed in the surface of the anode side separator 42AN3 so that hydrogen flows from the hydrogen supply through hole 424i along the surface of the anode 411a of the MEA 411, thus forming an anode side gas flow path. Similar to the anode side separator 42AN1, an anode off gas discharge port 424e for discharging anode off gas from the anode side gas flow path is formed through the anode side separator 42AN3 in the direction of thickness between the plurality of grooves 424dl and the plurality of grooves 424d2 and between the plurality of ribs 424rl and the plurality of ribs 424r2, namely at an intermediate location in the anode side gas flow path. In other words, the plurality of grooves 424d2 and the plurality of ribs 424r2 are formed farther downstream in the direction of flow of hydrogen or anode off gas than the anode off gas discharge port 424e. However, as shown in the drawings, the anode side separator 42AN3 in the third embodiment differs from the anode side separator 42AN1 in

that a moisture absorbent material 424a composed of a porous member is filled into the plurality of grooves 424d2. Various members having a large number of pores can be applied for the porous member. The insides of the pores of this moisture absorbent material (porous member) 424a is subjected to hydrophilic treatment to enhance hygroscopicity.

[0114] Furthermore, although not shown in the drawings, similar to the anode side separator 42AN1, a plurality of grooves 426d and a plurality of ribs 426r are formed in the back side of the anode side separator 42AN3 so that cooling water flows from the cooling water supply through hole 426i to the cooling water discharge through hole 426o. In addition, grooves 424d3 are formed in the back side of the anode side separator 42AN3 to allow anode off gas discharged from the anode off gas discharge port 424e to flow out to the anode off gas discharge through hole 424o.

[0115] As shown in FIG 1OC, air supplied from outside the fuel cell stack 100 branches from the air supply through hole 422i formed in the cathode side separator 42CA3 and flows into the groove 422dl from left to right in the drawing. At this time, formed water formed during generation of electricity also moves with the flow of air and cathode off gas. A portion of the cathode off gas containing the formed water flows into and accumulates in the moisture absorbent material 422a filled into the groove 422d2 located farthermost downstream in the direction of flow of air and cathode off gas, while the remaining cathode off gas is discharged outside the fuel cell stack 100 by passing through the cathode off gas discharge port 422e formed farther upstream than the moisture absorbent material 422a, through the groove 422d3 and through the cathode off gas discharge through hole 422o. Formed water contained in the cathode off gas that has accumulated in the moisture absorbent material 422a is captured here. This moisture absorbent material 422a is one example of the formed water capturing section of the invention.

[0116] On the other hand, hydrogen supplied from outside the fuel cell stack 100 branches from the hydrogen supply through hole 424i formed in the anode side separator 42AN3 and flows into the groove 424dl from right to left in the drawing. At this time,

formed water formed during generation of electricity also moves with the flow of hydrogen and anode off gas. A portion of the anode off gas containing the formed water flows into and accumulates in the moisture absorbent material 424a within the groove 424d2 located farthermost downstream in the direction of flow of hydrogen and anode off gas, while the remaining anode off gas is discharged outside the fuel cell stack 100 by passing through the anode off gas discharge port 424e formed farther upstream than the moisture absorbent material 424a, through the groove 424d2 and through the anode off gas discharge through hole 424o. Formed water contained in the anode off gas that has accumulated in the moisture absorbent material 424a is captured here. This moisture absorbent material 424a is one example of the formed water capturing section of the invention.

[0117] In the cell module 40 of the third embodiment as explained above, similar to the cell module 40 of the first embodiment, together with being able to suppress the discharge of formed water outside the cell module 40 from the cathode side gas flow path by capturing formed water contained in cathode off gas with the cathode side formed water capturing section, the captured formed water can be allowed to effectively penetrate farthermost upstream in the direction of flow of hydrogen and anode off gas in the anode side gas flow path through the electrolyte membrane 411m. Formed water that has penetrated to the anode 411a side can be re-circulated as a result of being moved by the flow of hydrogen and anode off gas. In addition, together with being able to suppress the discharge of formed water outside the cell module 40 from the anode side gas flow path by capturing formed water contained in anode off gas with the anode side formed water capturing section, the captured formed water can be allowed to effectively penetrate farthermost upstream in the direction of flow of air and cathode off gas in the cathode side gas flow path through the electrolyte membrane 411m. Formed water that has penetrated to the cathode 411c side can be re-circulated as a result of being moved by the flow of oxidant gas. Thus, according to the cell module 40 of the third embodiment, the electrolyte membrane 411m can be effectively self-humidified.

[0118] Furthermore, since the cell module 40 of the third embodiment is provided

with a cathode side formed water capturing section in the form of the moisture absorbent material 422a as described above, the flow path resistance of the cathode side formed water capturing section in the cathode side flow path is greater than the flow path resistance of other sites and the amount of formed water captured is also greater. Similarly, since the moisture absorbent material 424a is also provided for the anode side formed water capturing section, the flow path resistance of the anode side formed water capturing section in the anode side flow path is greater than the flow path resistance at other sites, and the amount of formed water captured is also greater. Thus, the effect of suppressing discharge of formed water captured in the cathode side formed water capturing section and the anode side formed water capturing section to the outside is greater in the cell module 40 of the third embodiment than in the cell module 40 of the first embodiment.

[0119] A comparative experiment of electricity generation performance was carried out between the cell module 40 of the first embodiment and the cell module 40 of the third embodiment in order to verify the self-humidifying effects produced by the cell module 40 of the third embodiment as described above. In this experiment, a comparison was made of the maximum temperature of cooling water able to maintain a prescribed lower limit voltage for a prescribed duration during non-humidified operation (power generation) between the cell module 40 of the first embodiment and the cell module 40 of the third embodiment in the same manner as explained in the first embodiment.

[0120] FIG 11 is an explanatory drawing showing the experimental results of the comparative experiment. An increase of 5°C was obtained with the cell module 40 of the third embodiment over the cell module 40 of the first embodiment. Namely, the cell module 40 of the third embodiment was able to maintain the same lower limit voltage at a maximum temperature 5°C higher than the cell module 40 of the first embodiment. On the basis of this result, self-humidification of the electrolyte membrane 411m can be determined to be carried out more effectively in the cell module 40 of the third embodiment than in the cell module 40 of the first embodiment. In addition, in the case

of applying the cell module 40 of the third embodiment in the fuel cell stack 100, the size of the radiator 71 in the fuel cell system 1000 can be made to be more compact than the case of applying the cell module 40 of the first embodiment or applying the cell module 40 of the second embodiment in the fuel cell stack 100, thereby making it possible to reduce the size of the fuel cell system 1000.

[0121] The following provides an explanation of a fourth embodiment of the invention. The cell module 40 of the fourth embodiment is, as described later, configured by laminating metal porous bodies on both sides of a seal gasket-integrated MEA and holding with separators.

[0122] FIGS. 12A and 12B are explanatory drawings showing the schematic structure of a seal gasket-integrated MEA 41 A in the cell module 40 of the fourth embodiment. FIG. 12A shows an overhead view of the seal gasket-integrated MEA 41A as viewed from the cathode side. In addition, FIG. 12B shows a cross-sectional view taken along line A-A in FIG 12 A.

[0123] As shown in FIG. 12A, the seal gasket-integrated MEA 41A has a rectangular shape, and a seal gasket 410A composed of silicone rubber is integrally formed around the periphery of a rectangular MEA 411. The MEA 411 is the same as the MEA 411 previously explained using FIGS. 2A and 2B, respectively having the cathode 411c (cathode side catalyst layer 411cc, cathode side gas diffusion layer 411cd) and the anode 411a (anode side catalyst layer 411ac, anode side gas diffusion layer 411ad) joined to both sides of the electrolyte membrane 411m.

[0124] The cathode off gas discharge through hole 412o composing the cathode off gas discharge manifold and the cooling water supply through hole 416i composing the cooling water supply manifold are formed vertically arranged in a region of the seal gasket 410A in the vicinity of the MEA 411 on the short side shown on the left in the drawing. In addition, the cooling water discharge through hole 416o composing the cooling water discharge manifold and the anode off gas discharge through hole 414o composing the anode off gas discharge manifold are formed vertically arranged in the seal gasket 410A in a region in the vicinity of the MEA 411 on the short side shown on

the right in the drawing. In addition, a hydrogen supply through hole 414i composing the hydrogen supply manifold is formed along the upper long side of the seal gasket 410A in the seal gasket 410A in a region in the vicinity of the MEA 411 on the long side shown on the top in the drawing. In addition, an air supply through hole 412i composing the air supply manifold is formed along the lower long side of the seal gasket 410A in the seal gasket 410A in a region in the vicinity of the MEA 411 on the long side shown on the bottom in the drawing.

[0125] In addition, as shown in FIG 12B, seal lines SL are respectively formed around the periphery of each of the above-mentioned through holes and MEA 411 by forming linear protrusions on both sides of the seal gasket 410A. The seal lines SL are able to suppress leakage to the outside of hydrogen, air and cooling water flowing into each of the through holes as well as leakage to the outside of hydrogen, air and the like flowing over the surface of the MEA 411 when the seal gasket-integrated MEA 41A and a separator 42A to be described later are laminated.

[0126] FIGS. 13A to 13C are overhead views of constituent components of the separator 42A. The separator 42A of the fourth embodiment is composed of three metal plates in which a plurality of through holes are respectively provided, namely a cathode- opposing plate 42c, an intermediate plate 42m and an anode-opposing plate 42a. The separator 42A is fabricated by interposing the intermediate plate 42m between the cathode-opposing plate 42c and the anode-opposing plate 42a and joining with a hot press. In the fourth embodiment, the cathode-opposing plate 42c, the intermediate plate 42m and the anode-opposing plate 42a use a stainless steel plate having the same rectangular shape as the seal gasket-integrated MEA 41A. Metal plates made of titanium, aluminum or other metal may also be used for the cathode-opposing plate 42c, intermediate plate 42m and anode-opposing plate 42a instead of stainless steel.

[0127] FIG. 13 A is an overhead view of the cathode-opposing plate 42c that contacts the surface of the seal gasket-integrated MEA 41A on the cathode side. The region enclosed with a broken line in the drawing represents the region corresponding to the MEA 411 in the previously explained seal gasket-integrated 41.

[0128] As shown in the drawing, an air supply through hole 422ci composing an air supply manifold, a cathode off gas discharge through hole 422co composing a cathode off gas discharge manifold, a hydrogen supply through hole 424ci composing a hydrogen supply manifold, a cooling water supply through hole 426ci composing a cooling water supply manifold, a cooling water discharge through hole 426co composing a cooling water discharge manifold, and an anode off gas discharge through hole 424co composing an anode off gas discharge manifold are formed in the cathode-opposing plate 42c at locations corresponding to each of the through holes formed in the seal gasket-integrated MEA 41A. The shape of each of these through holes is the same as the shape of each of the corresponding through holes in the seal gasket-integrated MEA 41.

[0129] In addition, an air supply port 422os, arranged at a location opposing the lower end of the MEA 411 in the vicinity of the air supply through hole 422ci, and a cathode off gas discharge port 422oe, arranged at a location at a prescribed interval below the location opposing the upper end of the MEA 411 in the vicinity of the cathode off gas discharge through hole 422co, are formed in the cathode-opposing plate 42c as shown in the drawings. In the fourth embodiment, the air supply port 422os and the cathode off gas discharge port 422oe are in the shape of slits having a width nearly equal to the length of the long side of the MEA 411.

[0130] FIG 13B is an overhead view of the intermediate plate 42m. The region enclosed with a broken line in the drawing represents the region corresponding to the MEA 411 in the previously explained seal gasket-integrated MEA 41 A.

[0131] As shown in the drawing, an air supply through hole 422mi composing an air supply manifold, a cathode off gas discharge through hole 422mo composing a cathode off gas discharge manifold, a hydrogen supply through hole 424mi composing a hydrogen supply manifold, and an anode off gas discharge through hole 424mo composing an anode off gas discharge manifold are formed in the intermediate plate 42m at locations corresponding to each of the through holes formed in the seal gasket-integrated MEA 41A. The shape of each of these through holes is the same as the shape of each of the corresponding through holes in the seal gasket-integrated MEA

41. In addition, a plurality of cooling water flow path-forming through holes 426m composing a cooling water supply manifold are also formed in the intermediate plate 42m.

[0132] In addition, in the intermediate plate 42m, a plurality of air supply flow path-forming sections 422mip are provided in a comb-like shape in the air supply through hole 422mi to allow the flow of air from the air supply through hole 422mi to the air supply port 422os formed in the cathode-opposing plate 42c. In addition, a cathode off gas discharge flow path-forming section 422mop is provided in the cathode off gas discharge through hole 422mo for allowing the flow of cathode off gas from the cathode off gas discharge port 422oe formed in the cathode-opposing plate 42c to the cathode off gas discharge through hole 422mo. In addition, a plurality of hydrogen supply flow path-forming sections 424mip are provided in a comb-like shape in the hydrogen supply through hole 424mi to allow the flow of hydrogen from the hydrogen supply through hole 424mi to a hydrogen supply port 424hs formed in the anode-opposing plate 42a to be described later. In addition, an anode off gas discharge flow path-forming section 424mop is formed in the anode off gas discharge through hole 424mo to allow the flow of anode off gas from an anode off gas discharge port 424he formed in the anode-opposing plate 42a to be described later to the anode off gas discharge through hole 424mo.

[0133] FIG. 13C is an overhead view of the anode-opposing plate 42a contacting the surface of the seal gasket-integrated MEA 41A on the anode side. The region enclosed with a broken line in the drawing represents the region corresponding to the MEA 411 in the seal gasket-integrated MEA 41A.

[0134] As shown in the drawing, an air supply through hole 422ai composing an air supply manifold, a cathode off gas discharge through hole 422co composing a cathode off gas discharge manifold, a cathode off gas discharge through hole 422ao composing a cathode off gas discharge manifold, a hydrogen supply through hole 424ai composing a hydrogen supply manifold, a cooling water supply through hole 426ai composing a cooling water supply manifold, a cooling water discharge through hole 426ao composing

a cooling water discharge manifold, and an anode off gas discharge through hole 424ao composing an anode off gas discharge manifold are formed in the anode-opposing plate 42a at locations corresponding to each of the through holes formed in the seal gasket-integrated MEA 41A. The shape of each of these through holes is the same as the shape of each of the corresponding through holes in the seal gasket-integrated MEA 41A.

[0135] In addition, a hydrogen supply port 424hs, arranged at a location opposing the upper end of the MEA 411 in the vicinity of the hydrogen supply through hole 424ai, and an anode off gas discharge port 424he, arranged at a location at a prescribed interval above the location opposing the lower end of the MEA 411 in the vicinity of the air supply through hole 422ai, are formed in the anode-opposing plate 42a as shown in the drawings. In the fourth embodiment, the hydrogen supply port 424hs and the anode off gas discharge port 424he are in the shape of slits having a width nearly equal to the length of the long side of the MEA 411 in the same manner as the air supply port 422os and the cathode off gas discharge port 422oe formed in the cathode-opposing plate 42c.

[0136] FIG. 14 is an overhead view of the separator 42A. As was previously explained, the separator 42A is formed by hot-pressing the cathode-opposing plate 42c, the intermediate plate 42m and the anode-opposing plate 42a. Here, the separator 42A is depicted from the side of the anode-opposing plate 42a.

[0137] As can be understood from the drawing, in the anode-opposing plate 42a, the hydrogen supply port 424hs is formed so as to overlap each lower end of the plurality of hydrogen supply flow path-forming sections 424mip formed in the intermediate plate 42m. In addition, in the anode-opposing plate 42a, the anode off gas discharge port 424he is formed so as to overlap the anode off gas discharge flow path-forming section 424mop formed in the intermediate plate 42m.

[0138] In addition, in the cathode-opposing plate 42c, the air supply port 422os is formed so as to overlap each upper end of the plurality of air supply flow path-forming sections 422mip formed in the intermediate plate 42m. In addition, in the cathode-opposing plate 42c, the cathode off gas discharge port 422oe is formed so as to

overlap the cathode off gas discharge flow path-forming section 422mop formed in the intermediate plate 42m.

[0139] In addition, in the intermediate plate 42m, the plurality of cooling water flow path-forming through holes 426m are formed so that the respective ends thereof on the right side in the drawing overlap the cooling water supply through hole 426ai formed in the anode-opposing plate 42a and the cooling water supply through hole 426ci formed in the cathode-opposing plate 42c, while the respective ends thereof on the left side in the drawing overlap the cooling water discharge through hole 426ao formed in the anode-opposing plate 42a and the cooling water discharge through hole 426co formed in the cathode-opposing plate 42c.

[0140] FIG. 15 is an explanatory drawing showing the cross-sectional structure of the cell module 40 of the fourth embodiment, and shows a cross-sectional view taken along line A-A in FIG. 14 when the separator 42A and the seal gasket-integrated MEA 41 A have been laminated.

[0141] In the cell module 40 of the fourth embodiment, a metal porous body having electrical conductivity and gas diffusivity (anode side metal porous body 43 a) is interposed between the anode 411a of the seal gasket-integrated MEA 41A and the anode-opposing plate 42a of the separator 42A, and an anode side flow path is formed for allowing the flow of hydrogen along the surface of the anode side gas diffusion layer 411ad. As shown in the drawing, in the anode side metal porous body 43a, an anode side metal porous body 43as, having lower porosity than other sites, is arranged at an opposing site farthermost downstream in the direction of flow of hydrogen and cathode off gas interposed between the air supply port 422os and the MEA 411. In the anode side metal porous body 43a, pressure loss and flow path resistance in the direction of gas flow in the anode side metal porous body 43as are higher than the pressure loss and flow path resistance in the direction of gas flow in a metal porous body arranged at other sites. Furthermore, hydrophilic treatment is carried out on this anode side metal porous body 43as to enhance moisture retention. This anode side metal porous body 43as is one example of a second porous body and movement suppressing member of the invention.

In addition, a metal porous body arranged in a region other than that of the anode side metal porous body 43as in the anode side metal porous body 43a is an example of a first porous body of the invention.

[0142] In addition, a metal porous body having electrical conductivity and gas diffusivity (cathode side metal porous body 43c) is also interposed between the cathode 411c of the seal gasket-integrated MEA 41A and the cathode-opposing plate 42c of the separator 42A, and a cathode side flow path is formed for allowing the flow of air along the surface of the cathode side gas diffusion layer 411cd. As shown in the drawing, in the cathode side metal porous body 43c, a cathode side metal porous body 43cs, having lower porosity than other sites, is arranged at an opposing site farthermost downstream in the direction of flow of air and anode off gas interposed between the hydrogen supply port 424hs and the MEA 411. In the cathode side metal porous body 43c, pressure loss and flow path resistance in the direction of gas flow in the cathode side metal porous body 43cs are higher than the pressure loss and flow path resistance in the direction of gas flow in a metal porous body arranged at other sites. Furthermore, hydrophilic treatment is carried out on this cathode side metal porous body 43cs to enhance moisture retention. This cathode side metal porous body 43cs is one example of a second porous body and movement suppressing member of the invention. In addition, a metal porous body arranged in a region other than that of the cathode side metal porous body 43cs in the cathode side metal porous body 43c is an example of a first porous body of the invention.

[0143] In the fourth embodiment, although a foam metal sintered body is used for the anode side metal porous body 43a (including the anode side metal porous body 43as) and the cathode side metal porous body 43c (including the cathode side metal porous body 43cs), various other members can be used instead, such as a metal mesh, expanded metal or punching metal formed into the shape of a corrugated plate.

[0144] As indicated by the arrows in the drawing, air that has been supplied from outside the fuel cell stack 100 in the cell module 40 passes through the air supply through hole 422ai of the anode-opposing plate 42a, branches from the air supply through hole

422mi of the intermediate plate 42m, passes through the air supply flow path-forming sections 422mip, and is supplied from the air supply port 422os of the cathode-opposing plate 42c in a direction perpendicular to the surface of the cathode side metal porous body 43c.

[0145] As can be understood from FIGS. 14 and 15, air supplied from the air supply port 422os flows while diffusing through the cathode side metal porous body 43c and through the cathode side gas diffusion layer 411cd, is discharged from the cathode off gas discharge port 422oe of the cathode-opposing plate 42c in a direction perpendicular to the surface of the cathode side metal porous body 43c, passes through the cathode off gas discharge flow path-forming section 422mop and the cathode off gas discharge through hole 422mo, passes through the cathode off gas discharge through hole 422ao of the anode-opposing plate 42a, and is discharged outside the fuel cell stack 100. At this time, a portion of the cathode off gas containing formed water flows and accumulates in the cathode side metal porous body 43cs farther downstream than the cathode off gas discharge port 422oe, and the formed water contained in the cathode off gas is captured by the cathode side metal porous body 43cs. The cathode side metal porous body 43cs is one example of the cathode side formed water capturing section of the invention.

[0146] In addition, as indicated by the arrows in the drawing, hydrogen supplied from outside the fuel cell stack 100 passes through the hydrogen supply through hole 424ci of the cathode-opposing plate 42c, branches from the hydrogen supply through hole 424mi of the intermediate plate 42m, passes through the hydrogen supply flow path-forming sections 424mip, and is supplied from the hydrogen supply port 424hs of the anode-opposing plate 42a in a direction perpendicular to the surface of the anode side metal porous body 43a.

[0147] As can be understood from FIGS. 14 and 15, hydrogen supplied from the hydrogen supply port 424hs flows while diffusing through the anode side metal porous body 43a and through the anode side gas diffusion layer 41 lad, is discharged from the anode off gas discharge port 424he of the anode-opposing plate 42a in a direction perpendicular to the surface of the anode side metal porous body 43a, passes through the

anode off gas discharge flow path-forming section 424mop of the intermediate plate 42m and through the anode off gas discharge through hole 424mo, through the anode off gas discharge through hole 424co of the cathode-opposing plate 42c, and is discharge outside the fuel cell stack 100. At this time, a portion of the anode off gas containing formed water flows into and accumulates in the anode side metal porous body 43 as farther downstream than the anode off gas discharge port 424he, and the _N formed water contained in the anode off gas is captured by the anode side metal porous body 43as. The anode side metal porous body 43as is one example of the anode side formed water capturing section of the invention.

[0148] In addition, as can be understood from FIGS. 14 and 15, cooling water supplied from outside the fuel cell stack 100 passes through the cooling water supply through hole 426ai of the anode-opposing plate 42a and the cooling water flow path-forming through holes 426m of the intermediate plate 42m, passes through the cooling water discharge through hole 426ao of the anode-opposing plate 42a, and is discharged outside the fuel cell stack 100.

[0149] In the cell module 40 of the fourth embodiment as explained above, together with being able to effectively suppress the discharge of formed water captured in the cathode side metal porous body 43cs (cathode side formed water capturing section) outside the cell module 40 from the cathode off gas discharge port 422oe, the formed water that has been captured in the cathode side metal porous body 43cs and penetrated to the anode side through the electrolyte membrane 411m can be effectively re-circulated as a result of being moved by the flow of hydrogen. In addition, together with being able to effectively suppress the discharge of formed water captured in the anode side metal porous body 43as (anode side formed water capturing section) outside the cell module 40 from the anode off gas discharge port 424he, the formed water that has been captured by the anode side metal porous body 43as and penetrated to the cathode side through the electrolyte membrane 411m can be effectively re-circulated as a result of being moved by the flow of air. Thus, according to the cell module 40 of the fourth embodiment, the electrolyte membrane 411m can be effectively self-humidified.

[0150] The following provides an explanation of a fifth embodiment. The cell module 40 of the fifth embodiment is configured by laminating metal porous bodies on both sides of a seal gasket-integrated MEA and holding with separators in the same manner as the cell module 40 of the fourth embodiment.

[0151] FIG. 16 is an explanatory drawing showing the schematic structure of a seal gasket-integrated MEA 41B in the cell module 40 of the fifth embodiment, and shows an overhead view as viewed from the cathode side of the seal gasket-integrated MEA 41B.

[0152] As shown in FIG. 16, the seal gasket-integrated MEA 41B has a rectangular shape, and a seal gasket 410B composed of silicone rubber is integrally formed around the periphery of a rectangular MEA 411. The MEA 411 is the same as the MEA 411 previously explained using FIGS. 2A and 2B, respectively having the cathode 411c (cathode side catalyst layer 411cc, cathode side gas diffusion layer 411cd) and the anode 411a (anode side catalyst layer 411ac, anode side gas diffusion layer 411ad) joined to both sides of the electrolyte membrane 411m.

[0153] The anode off gas discharge through hole 414o composing the anode off gas discharge manifold and the cooling water supply through hole 416i composing the cooling water supply manifold are formed vertically arranged in a region of the seal gasket 410B in the vicinity of the MEA 411 on the short side shown on the left in the drawing. In addition, the cooling water discharge through hole 416o composing the cooling water discharge manifold and the hydrogen supply through hole 414i composing the hydrogen supply manifold are formed vertically arranged in the seal gasket 410B in a region of the seal gasket 410B in the vicinity of the MEA 411 on the short side shown on the right in the drawing. In addition, the air supply through hole 412i composing the air supply manifold is formed along the upper long side of the seal gasket 410B in the seal gasket 410B in a region in the vicinity of the MEA 411 on the long side shown on the top in the drawing. In addition, a cathode off gas discharge through hole 412o composing the cathode off gas discharge manifold is formed along the lower long side of the seal gasket 410B in the seal gasket 410B in a region in the vicinity of the MEA 411 on the long side shown on the bottom in the drawing.

[0154] In addition, seal lines SL are respectively formed around the periphery of each of the above-mentioned through holes and the MEA 411 by forming linear protrusions on both sides of the seal gasket 410B in the same manner as the seal gasket 410A in the fourth embodiment. The seal lines SL are able to suppress leakage to the outside of hydrogen, air and cooling water flowing into each of the through holes as well as leakage to the outside of hydrogen, air and the like flowing over the surface of the MEA 411 when the seal gasket-integrated MEA 41B and a separator 42B to be described later are laminated.

[0155] FIGS. 17A to 17C are overhead view of constituent components of the separator 42B. The separator 42A of the fifth embodiment is composed of two metal plates in which a plurality of through holes are respectively provided, namely a cathode- opposing plate 42c and an anode-opposing plate 42a, and a plastic intermediate plate 42m. The weight of the separator 42B can be reduced by using plastic instead of metal for the intermediate plate 42m. The separator 42B is fabricated by interposing the intermediate plate 42m between the cathode-opposing plate 42c and the anode-opposing plate 42a and joining with a hot press. In the fifth embodiment, the cathode-opposing plate 42c and the anode-opposing plate 42a use a stainless steel plate having the same rectangular shape as the seal gasket-integrated MEA 41 B. Furthermore, surface irregularities are formed by press forming in the cathode-opposing plate 42c and the anode-opposing plate 42a as will be described later.

[0156] FIG. 17A is an overhead view of the cathode-opposing plate 42c that contacts the surface of the seal gasket-integrated MEA 41B on the cathode side. The region enclosed with a broken line in the drawing represents the region corresponding to the MEA 411 in the previously explained seal gasket-integrated 41.

[0157] As shown in the drawing, an air supply through hole 422ci composing an air supply manifold, a cathode off gas discharge through hole 422co composing a cathode off gas discharge manifold, a hydrogen supply through hole 424ci composing a hydrogen supply manifold, a cooling water supply through hole 426ci composing a cooling water supply manifold, a cooling water discharge through hole 426co composing a cooling

water discharge manifold, and an anode off gas discharge through hole 424co composing an anode off gas discharge manifold are formed in the cathode-opposing plate 42c at locations corresponding to each of the through holes formed in the seal gasket-integrated MEA 41B. The shape of each of these through holes is the same as the shape of each of the corresponding through holes in the seal gasket-integrated MEA 41.

[0158] In addition, an air supply port 422os, arranged at a location opposing the upper end of the MEA 411 in the vicinity of the air supply through hole 422ci, and a cathode off gas discharge port 422oe, arranged at a location opposing the lower end of the MEA 411 in the vicinity of the cathode off gas discharge through hole 422co, are formed in the cathode-opposing plate 42c as shown in the drawings. In the fifth embodiment, the air supply port 422os and the cathode off gas discharge port 422oe are in the shape of slits having a width nearly equal to the length of the long side of the MEA 411. In addition, as shown in the drawing, a plurality of indentations 427 are formed in the region between the cooling water supply through hole 426ci and the cooling water discharge through hole 426co. This plurality of indentations 427 are formed so as to contact the anode-opposing plate 42a when the cathode-opposing plate 42a, the intermediate plate 42m and the anode-opposing plate 42a are overlapped and joined by hot pressing as will, be described later. This is carried out to ensure electrical continuity between the cathode-opposing plate 42c and the anode-opposing plate 42a.

[0159] FIG 17B is an overhead view of the intermediate plate 42m. The region enclosed with a broken line in the drawing represents the region corresponding to the MEA 411 in the previously explained seal gasket-integrated MEA 41B.

[0160] As shown in the drawing, an air supply through hole 422mi composing an air supply manifold, a cathode off gas discharge through hole 422mo composing a cathode off gas discharge manifold, a hydrogen supply through hole 424mi composing a hydrogen supply manifold, and an anode off gas discharge through hole 424mo composing an anode off gas discharge manifold are formed in the intermediate plate 42m at locations corresponding to each of the through holes formed in the seal gasket-integrated MEA 41B. The shape of each of these through holes is the same as

the shape of each of the corresponding through holes in the seal gasket-integrated MEA 41. In addition, a cooling water flow path-forming through hole 426m composing a cooling water supply manifold is also formed in the intermediate plate 42m.

[0161] In addition, in the intermediate plate 42m, a plurality of air supply flow path-forming sections 422mip are provided in a comb-like shape in the air supply through hole 422mi to allow the flow of air from the air supply through hole 422mi to the air supply port 422os formed in the cathode-opposing plate 42c. In addition, a plurality of cathode off gas discharge flow path-forming sections 422mop are provided in a comb-like shape in the cathode off gas discharge through hole 422mo for allowing the flow of cathode off gas from the cathode off gas discharge port 422oe formed in the cathode-opposing plate 42c to the cathode off gas discharge through hole 422mo. In addition, a hydrogen supply flow path-forming section 424mip is provided in the hydrogen supply through hole 424mi to allow the flow of hydrogen from the hydrogen supply through hole 424mi to a hydrogen supply port 424hs formed in the anode-opposing plate 42a to be described later. In addition, an anode off gas discharge flow path-forming section 424mop is formed in the anode off gas discharge through hole 424mo to allow the flow of anode off gas from an anode off gas discharge port 424he formed in the anode-opposing plate 42a to be described later to the anode off gas discharge through hole 424mo.

[0162] FIG 17C is an overhead view of the anode-opposing plate 42a contacting the surface of the seal gasket-integrated MEA 41B on the anode side. The region enclosed with a broken line in the drawing represents the region corresponding to the MEA 411 in the seal gasket-integrated MEA 41B.

[0163] As shown in the drawing, an air supply through hole 422ai composing an air supply manifold, a cathode off gas discharge through hole 422co composing a cathode off gas discharge manifold, a hydrogen supply through hole 424ai composing a hydrogen supply manifold, a cooling water supply through hole 426ai composing a cooling water supply manifold, a cooling water discharge through hole 426ao composing a cooling water discharge manifold, and an anode off gas discharge through hole 424ao composing

an anode off gas discharge manifold are formed in the anode-opposing plate 42a at locations corresponding to each of the through holes formed in the seal gasket-integrated MEA 41B. The shape of each of these through holes is the same as the shape of each of the corresponding through holes in the seal gasket-integrated MEA 41B.

[0164] In addition, a hydrogen supply port 424hs, arranged at a location at a prescribed interval above the location opposing the lower end of the MEA 411 in the vicinity of the cathode off gas discharge through hole 422ao, and an anode off gas discharge port 424he, arranged at a location at a prescribed interval below the location opposing the upper end of the MEA 411 in the vicinity of the air supply through hole 422ai, are formed in the anode-opposing plate 42a as shown in the drawings. In the fifth embodiment, the hydrogen supply port 424hs and the anode off gas discharge port 424he are in the shape of slits having a width nearly equal to the length of the long side of the MEA 411 in the same manner as the air supply port 422os formed in the cathode-opposing plate 42c and the cathode off gas discharge port 422oe. In addition, as shown in the drawings, a plurality of protrusions 428 are formed arranged in a staggered pattern between the cooling water supply through hole 426ai and the cooling water discharge through hole 426ao in a region higher than a site opposing the plurality of indentations 427 in the cathode-opposing plate 42c as previously explained. As will be described later, this plurality of protrusions 428 are formed so as to contact the cathode-opposing plate 42c when the cathode-opposing plate 42c, the intermediate plate 42m and the anode-opposing plate 42a are overlapped and joined by hot-pressing. This is carried out to ensure electrical continuity between the cathode-opposing plate 42c and the anode-opposing plate 42a in the same manner as the previously explained indentations 427 in the cathode-opposing plate 42c.

[0165] FIG. 18 is an overhead view of the separator 42B. As was previously explained, the separator 42B is formed by hot-pressing the cathode-opposing plate 42c, the intermediate plate 42m and the anode-opposing plate 42a. Here, the separator 42B is depicted from the side of the anode-opposing plate 42a.

[0166] As can be understood from the drawing, in the anode-opposing plate 42a, the

hydrogen supply port 424hs is formed so as to overlap the hydrogen supply flow path-forming section 424mip formed in the intermediate plate 42m. In addition, in the anode-opposite plate 42a, the anode off gas discharge port 424he is formed so as to overlap the anode off gas discharge flow path-forming section 424mop formed in the intermediate plate 42m.

[0167] In addition, in the cathode-opposing plate 42c, the air supply port 422os is formed so as to overlap each lower end of the plurality of air supply flow path-forming sections 422mip formed in the intermediate plate 42m. In addition, in the cathode-opposing plate 42c, the cathode off gas discharge port 422oe is formed so as to overlap each of the upper ends of the plurality of cathode off gas discharge flow path-forming sections 422mop formed in the intermediate plate 42m.

[0168] In addition, in the intermediate plate 42m, the cooling water flow path-forming through hole 426m is formed so that the end on the right side in the drawing overlaps the cooling water supply through hole 426ai formed in the anode-opposing plate 42a and the cooling water supply through hole 426ci formed in the cathode-opposing plate 42c, while the end on the left side in the drawing overlaps the cooling water discharge through hole 426ao formed in the anode-opposing plate 42a and the cooling water discharge through hole 426co formed in the cathode-opposing plate 42c.

[0169] FIG. 19 is an explanatory drawing showing the cross-sectional structure of the cell module 40 of the fifth embodiment, and shows a cross-sectional view taken along line A-A in FIG 18 when the separator 42B and the seal gasket-integrated MEA 41B have been laminated.

[0170] In the cell module 40 of the fifth embodiment, a metal porous body having electrical conductivity and gas diffusivity (anode side metal porous body 43 a) is interposed between the anode 411a of the seal gasket-integrated MEA 41B and the anode-opposing plate 42a of the separator 42B, and an anode side flow path is formed for allowing the flow of hydrogen along the surface of the anode side gas diffusion layer 411ad.

[0171] In addition, a metal porous body having electrical conductivity and gas

diffusivity (cathode side metal porous body 43c) is also interposed between the cathode 411c of the seal gasket-integrated MEA 41B and the cathode-opposing plate 42c of the seal gasket-integrated MEA 4 IB, and a cathode side flow path is formed for allowing the flow of air along the surface of the cathode side gas diffusion layer 411cd.

[0172] In the fifth embodiment, although a foam metal sintered body is used for the anode side metal porous body 43a (including the anode side metal porous body 43as) and the cathode side metal porous body 43c (including the cathode side metal porous body 43cs), various other members can be used instead, such as a metal mesh, expanded metal or punching metal formed into the shape of a corrugated plate.

[0173] As indicated by the arrows in the drawing, air that has been supplied from outside the fuel cell stack 100 in the cell module 40 passes through the air supply through hole 422ai of the anode-opposing plate 42a, branches from the air supply through hole 422mi of the intermediate plate 42m, passes through the air supply flow path-forming sections 422mip, and is supplied from the air supply port 422os of the cathode-opposing plate 42c in a direction perpendicular to the surface of the cathode side metal porous body 43c.

[0174] Air supplied from the air supply port 422os flows while diffusing through the cathode side metal porous body 43c and through the cathode gas diffusion layer 411cd, is discharged from the cathode off gas discharge port 422oe of the cathode-opposing plate 42c in a direction perpendicular to the surface of the cathode side metal porous body 43c, passes through the cathode off gas discharge flow path-forming sections 422mop of the intermediate plate 42m and the cathode off gas discharge through hole 422mo, passes through the cathode off gas discharge through hole 422ao of the anode-opposing plate 42a, and is discharged outside the fuel cell stack 100. ■ At this time, a portion of the cathode off gas containing formed water flows and accumulates in the indentations 427 formed in the cathode-opposing plate 42c, and formed water contained in the cathode off gas is captured in the indentations 427. Furthermore, hydrophilic treatment is carried out on the inner walls of the indentations 27 to enhance moisture retention. The indentations 427 are one example of the formed water capturing section of the invention.

[0175] In addition, as can be understood from FIGS. 18 and 19, hydrogen supplied from outside the fuel cell stack 100 passes through the hydrogen supply through hole 424ci of the cathode-opposing plate 42c, branches from the hydrogen supply through hole 424mi of the intermediate plate 42m, passes through the hydrogen supply flow path-forming section 424mip, and is supplied from the hydrogen supply port 424hs of the anode-opposing plate 42a in a direction perpendicular to the surface of the anode side metal porous body 43a.

[0176] Hydrogen supplied from the hydrogen supply port 424hs flows while diffusing through the anode side metal porous body 43a and through the anode side gas diffusion layer 411ad, is discharged from the anode off gas discharge port 424he of the anode-opposing plate 42a in a direction perpendicular to the surface of the anode side metal porous body 43a, passes through the anode off gas discharge flow path-forming section 424mop of the intermediate plate 42m and through the anode off gas discharge through hole 424mo, through the anode off gas discharge through hole 424co of the cathode-opposing plate 42c, and is discharge outside the fuel cell stack 100. At this time, a portion of the anode off gas containing formed water flows into and accumulates farthermost downstream on the downstream side than the anode off gas discharge port 424he in the direction of flow of hydrogen and cathode off gas of the anode side metal porous body 43a, and the formed water contained in the anode off gas is captured here. This site is one example of the anode side formed water capturing section of the invention.

[0177] In addition, as can be understood from FIGS. 18 and 19, cooling water supplied from outside the fuel cell stack 100 passes through the cooling water supply through hole 426ai of the anode-opposing plate 42a and the cooling water flow path-forming through hole 426m of the intermediate plate 42m, passes through the cooling water discharge through hole 426ao of the anode-opposing plate 42a, and is discharged outside the fuel cell stack 100.

[0178] In the cell module 40 of the fifth embodiment as explained above, together with being able to effectively suppress the discharge of formed water captured in the

indentations 427 formed in the cathode-opposing plate 42c outside the cell module 40 from the cathode off gas discharge port 422oe, the formed water that has been captured in the indentations 427 and penetrated to the anode side through the electrolyte membrane 411m can be effectively re-circulated as a result of being moved by the flow of hydrogen. In addition, together with being able to effectively suppress the discharge of formed water captured farthermost downstream in the direction of flow of hydrogen and cathode off gas of the anode side metal porous body 43a outside the cell module 40 from the anode off gas discharge port 424he, the formed water that has been captured farthermost downstream in the direction of flow of hydrogen and cathode off gas of the anode side metal porous body 43a and penetrated to the cathode side through the electrolyte membrane 411m can be effectively re-circulated as a result of being moved by the flow of air. Thus, according to the cell module 40 of the fifth embodiment, the electrolyte membrane 411m can be effectively self-humidified.

[0179] The following provides an explanation of a sixth embodiment. In the cell modules 40 of the previously described first to fifth embodiments, effective self-humidification of the electrolyte membrane 411m was realized mainly by modifying the cathode side gas flow path and the anode side gas flow path. In the sixth embodiment, effective self-humidification of the electrolyte membrane 411m was realized by modifying the MEA 411. Furthermore, the MEA 411 of the sixth embodiment can be applied to various cell modules 40 having a configuration in which hydrogen and oxygen flow in mutually opposing directions with the MEA 411 interposed there between, or can be applied to the previously described cell modules 40 of the first to fifth embodiments as well as to the previously explained cell module 4OR of the comparative example.

[0180] FIG. 20 is an explanatory drawing showing the MEA 411 of the sixth embodiment, and shows a cross-sectional view of the MEA 411 of the sixth embodiment. Furthermore, the white arrows in the drawing indicate the movement of formed water.

[0181] As shown in the drawing, in the MEA 411 of the sixth embodiment, the cathode side catalyst layer 411cc is formed on one side of the electrolyte membrane 411m

(upper side in the drawing), while the anode side catalyst layer 411ac is formed on the other side (lower side in the drawing). Furthermore, in the example shown in the drawing, although the cathode side catalyst layer 411cc and the anode side catalyst layer 411ac are not formed over the entire surface of the electrolyte membrane 411m, the cathode side catalyst layer 411cc and the anode side catalyst layer 411ac may be formed over the entire surface of the electrolyte membrane 411m. In addition, although the cathode side diffusion layer 41 led and the anode side gas diffusion layer 411ad are not depicted in the drawing, these layers may be provided.

[0182] In the MEA 411 of the sixth embodiment, Pt particles are added as an additive to the electrolyte membrane 411m at the farthermost downstream section in the direction of flow of air (namely, farthermost upstream section in the direction of flow of hydrogen) and at the farthermost downstream section in the direction of the flow of hydrogen (namely, at the farthermost upstream section in the direction of flow of air). Since Pt has higher hydrophilicity than the electrolyte membrane 411m, formed water contained in cathode off gas formed during generation of electricity is captured in a region farthermost downstream in the direction of the flow of air where the Pt has been added to the electrolyte membrane 411m, thereby making it possible for the formed water to effectively penetrate to the farthermost upstream section in the direction of hydrogen flow on the anode side. In addition, formed water contained in anode off gas is captured in a region farthermost downstream in the direction of hydrogen flow where Pt has been added to the electrolyte membrane 411m, thereby making it possible for the formed water to effectively move to the farthermost upstream section in the direction of air flow on the cathode side. Thus, self-humidification of the electrolyte membrane 411m can be carried out effectively by applying the MEA 411 of the sixth embodiment to the cell module 40.

[0183] In addition, Pt also has the property of suppressing the formation of radicals (hydroxy radicals) causing deterioration of the electrolyte membrane 411m. Since Pt is used as an additive added to the electrolyte membrane 411m in the MEA 411 of the sixth embodiment, deterioration of the electrolyte membrane 411 by hydroxy radicals can also

be further suppressed.

[0184] In addition, since Pt also has the property of a catalyst that accelerates the reaction between hydrogen and oxygen, as a result of using Pt as an additive added to the electrolyte membrane 411m, formed water can be formed within the electrolyte membrane 411 thereby enabling it to be also used for self-humidification.

[0185] H. Modification: Although the above-mentioned explanation has described several embodiments of the invention, the invention is not limited in any way to these embodiments, but rather can be carried out in various aspects within a range that does not deviate from the gist thereof. The following provides a description of such variations.

[0186] The following provides an explanation of variations of each of the previously described embodiments. Although formed water capturing sections are provided in both the cathode side gas flow path and anode side gas flow path in the cell modules 40 of the first to fifth embodiments, the invention is not limited thereto. As a first variation thereof, a formed water capturing section is preferably provided in at least one of the cathode side gas flow path and anode side gas flow path.

[0187] In addition, although the cell modules 40 of the first to fifth embodiments form the cathode side catalyst layer 411cc, the cathode side gas diffusion layer 411cd, the anode side catalyst layer 411ac and the anode side gas diffusion layer 411ad over the entire surface of the MEA 411, these are not required to be formed at regions corresponding to formed water capturing sections. As a result thereof, resistance during penetration of formed water can be suppressed.

[0188] Although the cathode side formed water capturing section and the anode side formed water capturing section in the cell module 40 of the second embodiment are in the form of gaps having a meandered shape, the invention is not limited thereto. In a second variation, the shapes of the formed water capturing sections are preferably such that the flow path resistance thereof can be made to be greater than the flow path resistance at other sites within each gas flow path.

[0189] In a third variation, the moisture absorbent material 422a and the moisture absorbent material 424a used in the cell module 40 of the third embodiment are

preferably respectively filled into the grooves 422d2 and the grooves 424d2 of the cathode side separator 42CA2 in the cell module 40 of the second embodiment.

[0190] Although hydrophilic treatment is respectively carried out on the moisture absorbent material 422a and the moisture absorbent material 424a in the cell module 40 of the third embodiment, in a fourth variation, the hydrophilic treatment is preferably omitted. '

[0191] Although the cathode side metal porous body 43cs, having porosity lower than that of other sites, is arranged at a site of the cathode side metal porous body 43c opposing the hydrogen supply port 424hs with the MEA 411 interposed there between, and the anode side metal porous body 43as, having porosity lower than that of other sites, is arranged at a site of the anode side metal porous body 43a opposing the air supply port 422os with the MEA 411 interposed there between in the cell module 40 of the fourth embodiment as shown in FIG. 15, the invention is not limited thereto. In a fifth variation, the cathode side metal porous body 43cs and the anode side metal porous body 43as are preferably omitted. In this case, the sites where the cathode side metal porous body 43cs and the anode side metal porous body 43as were arranged may be in the form of gaps, and the cathode side metal porous body 43c and the anode side metal porous body 43a may be extended.

[0192] Although formed water contained in cathode off gas is captured with the indentations 427 provided in the separator 42B in the cell module 40 of the fifth embodiment as shown in FIG 19, in a sixth variation, indentations are preferably further provided for capturing formed water contained in anode off gas.

[0193] In addition, although the inner walls of the indentations 427 are subjected to hydrophilic treatment in the cell module 40 of the fifth embodiment, hydrophilic treatment may be omitted.

[0194] Although Pt is used as an additive added to the electrolyte membrane 411m in the sixth embodiment, the invention is not limited thereto. In a seventh variation, ceria or Pt alloy, for example, are preferably added as an additive. Since ceria and Pt alloys also have higher hydrophilicity than the electrolyte membrane 411m in the same manner

as Pt, while also having the property of suppressing formation of hydroxy radicals, similar effects can be obtained. In other words, the additive added to the electrolyte membrane 411 may be at least one of ceria and Pt alloy.

[0195] In addition, although Pt or ceria, having hydrophilicity higher than that of the electrolyte membrane 411m as well as the property of suppressing formation of hydroxy radicals, is used as an additive added to the electrolyte membrane 411m in the sixth embodiment and in the above-mentioned variations, the invention is not limited thereto. A material having hydrophilicity higher than the electrolyte membrane 411m but not having the property of suppressing the formation of hydroxy radicals may also be used as an additive. Examples of such materials include oxides such as titanium oxide or silicon oxide. Addition of such an additive to the electrolyte membrane 411m also causes formed water to be retained within the electrolyte membrane 411m and causes formed water to penetrate from one electrolyte membrane 411m to the other, thereby enabling self-humidification of the electrolyte membrane 411m.

[0196] In addition, in an eighth variation, specialized sections in the cell modules 40 of the first to sixth embodiments are preferably suitably combined. In addition, although the flow paths for air and hydrogen are straight in the first to third embodiments, in this invention, in general, so-called serpentine gas flow paths may also be applied provided the directions of thereof are mutually opposing.

[0197] Although a humidifier for humidifying air and hydrogen is not provided in the fuel cell system 1000 of each of the embodiments since the electrolyte membrane 411m can be effectively humidified in the cell module 40 that composes the fuel cell stack 100, in a ninth variation, a small humidifier is preferably provided for assisting in humidification during high-temperature operation.