WO2008142557A2

WO2008142557A2 - Separator and fuel cell

Info

Publication number: WO2008142557A2
Application number: PCT/IB2008/001314
Authority: WO
Inventors: Yasushi Araki; Fumihiko Inui
Original assignee: Toyota Jidosha Kabushiki Kaisha
Priority date: 2007-05-24
Filing date: 2008-05-23
Publication date: 2008-11-27
Also published as: JP2008293808A; WO2008142557A3

Abstract

Separators (600) are stacked alternately with power generation modules (200) that each include a power generation body (810) so as to construct a fuel cell (100). Each separator has oxidizing gas discharge manifold holes (120a to 120c) for discharging an oxidizing gas, and a power generation region that overlaps with the power generation body in the stacking direction when stacked and that includes at least a portion positioned on a side of the oxidizing gas discharge manifold hole, and a portion positioned on another side of the oxidizing gas discharge manifold hole opposite from the aforementioned side thereof.

Description

SEPARATOR AND FUEL CELL

FIELD OF THE INVENTION

[0001] The invention relates to a separator for a fuel ceU and a fuel cell that employs the separator and, more particularly, to temperature management in the fuel cell.

BACKGROUND OF THE INVENTION

[0002] A fuel cell, for example, a solid polymer type fuel cell, converts chemical energy of substances directly into electric energy by supplying reactant gases (a fuel gas containing hydrogen, and an oxidizing gas containing oxygen) to two electrodes (a fuel electrode and an oxygen electrode) that face each other across an electrolyte membrane and therefore causing an electrochemical reaction. As a main structure of such a fuel cell, Japanese Patent Application Publication No. 11-45728 (JP-A-11-45728) discloses a so-called stack structure in which power generation bodies that each include a generally flat platy electrolyte membrane, and separators are alternately stacked, and the stack is fastened in the stacking direction.

[0003] Incidentally, since the electrochemical reaction in the fuel cell is an exothermal reaction, the temperature management during operation of the fuel cell is important. In a fuel cell disclosed in Japanese Patent Application Publication No. 11-45728 (JP-A-11-45728), an oxidizing gas discharge manifold for discharging the oxidizing gas is disposed at outer peripheral edges of the separators. Therefore, there is possibility of the temperature difference between the oxidizing gas discharge manifold and the power generation body becoming large. As a result, moisture may condense into dew within the oxidizing gas discharge manifold. The condensed water can impede the flowage of the oxidizing gas, and can cause performance degradation of the fuel cell.

SUMMARY OF THE INVENTION

[0004] The invention provides a separator and a fuel cell in which the temperature difference between the oxidizing gas discharge manifold and the power generation body is restrained.

[0005] A first aspect of the invention relates to a separator of a fuel cell. This separator is stacked alternately with a power generation module that includes a power generation body so as to construct a fuel cell. The separator includes: an oxidizing gas discharge manifold hole for discharging an oxidizing gas; and a power generation region that overlaps with the power generation body in a stacking direction when stacked, and that includes at least a portion positioned at a side of the oxidizing gas discharge manifold hole, and a portion positioned at another side of the oxidizing gas discharge manifold hole opposite to the side of the oxidizing gas discharge manifold hole. [0006] In the separator in accordance with the first aspect, the oxidizing gas discharge manifold is sandwiched by the power generation region that overlaps with the power generation body. Therefore, the use of the separator in accordance with the first aspect will lessen the temperature difference between the portions that overlap with the power generation body in the stacking direction and the oxidizing gas discharge manifold. As a result, the problems and the like resulting from the temperature change can be restrained.

[0007] A second aspect of the invention relates to a separator of a fuel cell. The separator is stacked alternately with a power generation module that includes a power generation body so as to construct a fuel cell. The separator includes: an oxidizing gas discharge manifold hole for discharging an oxidizing gas which is disposed in a substantially central portion of the separator in at least one direction; and a power generation region that is disposed at a position different from a position of the oxidizing gas discharge manifold hole, and that overlaps with the power generation body when stacked. [0008] In the separator in accordance with the second aspect, the oxidizing gas discharge manifold can be distanced from the outside at least in one direction, so that the beat dissipation from the oxidizing gas discharge manifold to the outside can be restrained. Therefore, the use of the separator in accordance with the second aspect will lessen the temperature difference between the portions that overlap with the power generation body in the stacking direction and the oxidizing gas discharge manifold in the fuel cell. As a result, the problems and the like resulting from the temperature difference can be restrained.

[0009] In the separator in accordance with the foregoing aspects, the power generation region may include a first region adjacent to a side of the oxidizing gas discharge manifold hole, and a second region adjacent to another side of the oxidizing gas discharge manifold hole opposite to the side of the oxidizing gas discharge manifold hole.

Therefore, since a plurality of power generation regions are provided so as to sandwich the oxidizing gas discharge manifold from two sides, the temperature difference between the portions that overlap with the power generation body in the stacking direction and the oxidizing gas discharge manifold can be lessened.

[0010] In the separator in accordance with the foregoing aspects, the separator may further include: a first oxidizing gas supply manifold hole that is a manifold hole for supplying the oxidizing gas and that is adjacent to a side of the first region opposite from the oxidizing gas discharge manifold hole; and a second oxidizing gas supply manifold hole that is a manifold hole for supplying the oxidizing gas and that is adjacent to a side of the second region opposite from the oxidizing gas discharge manifold hole. Therefore, in the separator, the oxidizing gas supply manifold can be disposed outwardly, and the oxidizing gas discharge manifold can be disposed inwardly, so that the decline in the temperature of the oxidizing gas discharge manifold can be restrained. As a result, the temperature difference between the portions that overlap with the power generation body in the stacking direction and the oxidizing gas discharge manifold can be lessened.

[0011] In the separator in accordance with the foregoing aspects, the oxidizing gas discharge manifold hole and the power generation region may be disposed so as to be adjacent to each other at a long side of the oxidizing gas discharge manifold hole.

[0012] In the separator in accordance with the foregoing aspects, the oxidizing gas discharge manifold hole may be disposed so that the entire length of the long side of the oxidizing gas discharge manifold hole is adjacent to the power generation region.

[0013] A third aspect of the invention relates to a separator of a fuel cell. The separator is stacked alternately with a power generation module that includes a power generation body so as to construct a fuel cell. The separator includes: a power generation region that overlaps with the power generation body in a stacking direction when stacked; and an oxidizing gas discharge manifold hole for discharging an oxidizing gas which is disposed in a region surrounded by the power generation region.

[0014] In the separator in accordance with the foregoing aspects, a manifold hole other than the oxidizing gas discharge manifold hole may be formed along an outer peripheral edge of the separator.

[0015] A fourth aspect of the invention relates to a fuel cell. The fuel cell includes: a separator in any one of the foregoing aspects, and a power generation module that includes the power generation body, wherein the separator and the power generation module are alternately stacked.

[0016] The invention can also be realized in various manners other than the foregoing aspects. For example, the invention is realized as a device invention in a fuel cell constructed by stacking the separator in accordance with the foregoing aspect and a power generation module that includes a power generation body, a fuel cell system that includes the fuel cell, a vehicle in which the fuel cell is mounted, etc.

BRIEF DESCRIPTION OF THE DRAWINGS [0017] The foregoing and further features and advantages of the invention will become apparent from the following description of example embodiments with reference to the accompanying drawings, wherein like numerals are used to represent like elements and wherein:

FIG 1 is a first diagram showing an exterior construction of a fuel cell in accordance with an embodiment of the invention;

FIG 2 is a second diagram showing an exterior construction of the fuel cell in accordance with the embodiment of the invention;

FIG 3 is a first diagram illustrating a membrane-electrode assembly in the embodiment of the invention; FIGS. 4A and 4B are second diagrams illustrating the membrane-electrode assembly in the embodiment of the invention;

FIG 5 is a first diagram showing a construction of a separator in the embodiment of the invention; FIGS. 6A, 6B and 6C are second diagrams showing the construction of the separator in the embodiment of the invention;

FIGS. 7A and 7B are illustrative diagrams showing flows of an oxidizing gas;

FIG 8 is an illustrative diagram showing flows of a cooling medium; and

FIG 9 is an illustrative diagram showing a temperature distribution in a fuel cell during power generation.

DETAILED DESCRIPTION OF THE EMBODIMENTS

[0018] The construction of a fuel cell in accordance with an embodiment of the invention will be described with reference to FIGS. 1 to 6C. FIGS. 1 and 2 are diagrams showing an exterior construction of the fuel cell in accordance with the embodiment,

FIGS. 3, 4A and 4B are diagrams illustrating a membrane-electτode assembly in this embodiment. FIG. 3 shows a plan view of the membrane-electrode assembly, and FIGS.

4A and 4B show a cross-section taken on the line A-A of FIG 3 and a cross-section taken on the line B-B of FIG 3, respectively; FIG 5 and 6A to 6C are diagrams showing the construction of the separator in this embodiment. FIG 5 shows a plan view of the separator, and FIGS. 6 A to 6C show plan views of plates that constitute the separator,

[0019] As shown in FIG 1, a fuel cell 100 has a stack structure in which a plurality of membrane-electrode assemblies 200 and a plurality of separators 600 are alternately stacked. As shown in FIG 2, an anode-side porous body 840 or a cathode-side porous body 850 is disposed between a separator 600 and its adjacent membrane-electrode assembly 200. Each anode-side porous body 840 may be constructed integrally with a separator 600 as shown in FIG 2, or may also be constructed as a separate body.

[0020] Each anode-side porous body 840 is disposed between the anode side of a separator 600 and the anode side of the adjacent membrane-electrode assembly 200, and each cathode-side porous body 850 is disposed between the cathode side of a separator 600 and the cathode side of the adjacent membrane-electrode assembly 200. The anode-side porous bodies 840 and the cathode-side porous bodies 850 are formed from a porous material, such as a metal porous body or the like, which has gas diffusivity and electroconductivity. Furthermore, the anode-side porous bodies 840 and the cathode-side porous bodies 850 used herein are higher in porosity and lower in flow resistance than anode-side diffusion layers 820 and cathode-side diffusion layers 830 described below. The anode-side porous bodies 840 and the cathode-side porous bodies 850 function as channels for the reactant gases to flow through, as described below. [0021] As shown in FIG 1, the fuel cell 100 is provided with oxidizing gas supply manifolds 110a to 110c in which the oxidizing gas is supplied, oxidizing gas discharge manifolds 120a to 120c for discharging the oxidizing gas, fuel gas supply manifolds 130a, 130b in which the fuel gas is supplied, fuel gas discharge manifold 140 for discharging the fuel gas, cooling medium supply manifolds 150a, 150b for supplying a cooling medium, and cooling medium discharge manifolds 160a, 160b for discharging the cooling medium. These manifolds have a tubular shape, and are formed in the stacking direction of the fuel cell 100. Incidentally, air is generally used as an oxidizing gas, and hydrogen is generally used as a fuel gas. Besides, the oxidizing gas and the fuel gas both called reactant gas. The cooling medium used herein may be water, an antifreeze solution, such as ethylene glycol or the like, air, etc.

[0022] With reference to FIGS. 3, 4A and 4B, the construction of the membrane-electrode assemblies 200 will be described. Each membrane-electrode assembly 200, as shown in FIGS. 3, 4A and 4B, is constructed of two power generation portions 800a, 800b, and a non-power generation portion 700. [0023] As shown in FIGS. 4A and 4B, the power generation portion 800a is constructed by stacking a power generation body 810, an anode-side diffusion layer 820, and a cathode-side diffusion layer 830. In FIG 3, outer peripheral edges of the cathode-side diffusion layer 830 and the anode-side diffusion layer 820 are shown by dashed lines. The portions enclosed by these dashed lines are the power generation portion 800a and the power generation portion 800b where power generation is performed. The shape of the power generation portion 800a and the power generation portion 800b seen in the stacking direction is a generally rectangle having short and long sides. [0024] The power generation body 810 in this embodiment is an ion exchange membrane that is provided with a catalyst layer as a cathode on one of two surfaces thereof, and with a catalyst layer as an anode on the other one of the two surfaces (the catalyst layers are not shown in the drawings). The ion exchange membrane is formed from a fluorine-based resin material or a hydrocarbon-based resin material, and has a good ion conductivity in a wet state. Each catalyst layer contains, for example, platinum, or an alloy made up of platinum and one or more other metals.

[0025] The anode-side diffusion layer 820 is disposed in contact with the anode-side surface of the power generation body 810, and the cathode-side diffusion layer 830 is disposed in contact with the cathode-side surface of the power generation body 810. The anode-side diffusion layer 820 and the cathode-side diffusion layer 830 are formed, for example, from a carbon cloth woven of a yarn made of carbon fiber, or from carbon paper or carbon felt.

[0026] The power generation portion 800b has the same construction as the foregoing power generation portion 800a. Therefore, in the following description, like component elements are assigned with like reference characters, and detailed descriptions thereof are omitted.

[0027] The non-power generation portion 700 is disposed all around the outer peripheries of the power generation portion 800a and the power generation portion 800b in planar directions. Concretely, the power generation portion 800a and the power generation portion 800b are juxtaposed in the direction of a Y axis (in the vertical direction) in FIG 3. The non-power generation portion 700 is formed all around the peripheries of the two power generation portions 800a, 800b, and between the power generation portion 800a and the power generation portion 800b. The non-power generation portion 700 is constructed of two seal members that are air-tightly adhered to each other, that is, a first member 700a and a second member 700b. The first member 700a and the second member 700b are constructed so as to sandwich the outer peripheral end portions of the power generation body 810, the cathode-side diffusion layer 830 and the anode-side diffusion layer 820. This restrains the mixture of the reactant gases between the anode side and the cathode side of the power generation body 810. The first member 700a and the second member 700b are formed from a material that has insulating characteristic, gas impermeability, and heat resistance in the operation temperature range of the fuel cell, for example, a resin material such as a thermosetting resin, a general-purpose plastic, etc. [0028] In the non-power generation portion 700, penetration holes (manifold holes) corresponding to the various manifolds HOa to 160b shown in FIG 1 are formed as shown by cross-hatching in FlG 3. The non-power generation portion 700 is air-tightly adhered to adjacent separators 600 (not shown) on both sides so as to seal the gap with the separators 600, so that the leakage of the reactant gases (hydrogen and air in this embodiment) or the cooling water is prevented. Concretely, the entire peripheries of the power generation portions 800a, 800b and the entire peripheries of the individual manifold holes (except for the below-described channel portions for supplying/discharging the reactant gases) are sealed.

[0029] Of these manifold holes, the oxidizing gas discharge manifolds 120a to 120c are disposed between the power generation portion 800a and the power generation portion 800b. The oxidizing gas discharge manifolds 120a to 120c are formed along one of the long sides of the power generation portion 800a that is positioned downward in FIG 3 (in a positive direction of a Y axis) and along one of the long sides of the power generation portion 800b that is positioned upward in FIG. 3 (in the negative direction of the Y axis), extending over approximately the entire length of the long sides.

[0030] Of the manifold holes, the manifolds other than the three oxidizing gas discharge manifolds 120a to 120c are formed along the outer peripheral edge of the membrane-electrode assembly 200. Concretely, the three oxidizing gas supply manifolds HOa to 110c are disposed along the side of the membrane-electrode assembly 200 that is positioned upward in FIG 3 (in the negative direction of the Y axis). The oxidizing gas supply manifolds HOa to 110c are positioned opposite the oxidizing gas discharge manifolds 120a to 120c, respectively, across the power generation portion 800a. Other three oxidizing gas supply manifolds HOd to llOf are disposed along one of the sides of the membrane-electrode assembly 200 that is positioned downward in FIG 3 (in the positive direction of the Y axis). These oxidizing gas supply manifolds 11Od to llOf are positioned opposite the oxidizing gas discharge manifolds 120a to 120c, respectively, across the power generation portion 800b.

[0031] The two cooling medium supply manifolds 150a, 150b are disposed along one of the sides of the membrane-electrode assembly 200 that is positioned leftward in FIG 3 (in a negative direction of an X axis). Of the two manifolds, the cooling medium supply manifold 150a is formed along the left-hand short side of the power generation portion 800a, extending over substantially the entire length of the short side. The cooling medium supply manifold 150b is formed along the left-hand short side of the power generation portion 800b, extending over substantially the entire length of the short side.

[0032] The two cooling medium discharge manifolds 160a, 160b are disposed along one of the short sides of the membrane-electrode assembly 200 that is positioned rightward in FIG 3 (in the positive direction of the X axis). Of the two manifolds, the cooling medium discharge manifold 160a is formed along the right-hand short side of the power generation portion 800a, extending over substantially the entire length of the short side. The cooling medium discharge manifold 160b is formed along the right-hand short side of the power generation portion 800b, extending over substantially the entire length of the short side. [0033] The two fuel gas supply manifold 130a and 130b are disposed in an upper left corner of the membrane-electrode assembly 200 in FIG 3 (a corner in the negative direction of the X axis and the negative direction of the Y axis) and a lower left corner of the membrane-electrode assembly 200 (a corner in the negative direction of the X axis and the positive direction of the Y axis), respectively. The fuel gas supply manifold 130a supplies the fuel gas to the power generation body 810 of the power generation portion 800a, and the fuel gas supply manifold 130b supplies the fuel gas to the power generation body 810 of the power generation portion 800b.

[0034] The fuel gas discharge manifold 140 is disposed near a center portion of one the right-hand short side of the membrane-electrode assembly 200 in FIG 3, sandwiched by the cooling medium discharge manifold 160a and the cooling medium discharge manifold 160b.

[0035] Further channels for supplying/discharging the reactant gases are formed in the non-power generation portion 700, including two fuel gas supply channels 630, two fuel gas discharge channels 640, many oxidizing gas supply channels 650, and many oxidizing gas discharge channels 660. These channels 630 to 660 are formed at positions shown by single-hatching in FIG 3, in the form of grooves that do not penetrate the non-power generation portion 700 as shown in FlG 4A. The fuel gas supply channel 630 and the fuel gas discharge channels 640 are formed on a back side in FIG. 3, that is, the anode side of the non-power generation portion 700, and the oxidizing gas supply channel 650 and the oxidizing gas discharge channels 660 are formed on a front side in FIG 3, that is, the cathode side of the non-power generation portion 700.

[0036] One of the fuel gas supply channels 630 connects, in communication, the fuel gas supply manifold 130a and the anode-side porous body 840 that overlaps with the power generation portion 800a, and the other fuel gas supply channel 630 connects in communication the fuel gas supply manifold 130b and the anode-side porous body 840 that overlaps with the power generation portion 800b. One of the fuel gas discharge channels 640 connects in communication the fuel gas discharge manifold 140 and the anode-side porous body 840 that overlaps with the power generation portion 800a, and the other fuel gas discharge channel 640 connects in communication the fuel gas discharge manifold 140 and the anode-side porous body 840 that overlaps with the power generation portion 800b.

[0037] Some of the oxidizing gas supply channels 650 connect in communication the oxidizing gas supply manifolds 110a to HOc and the cathode-side porous body 850 that overlaps with the power generation portion 800a, The other oxidizing gas supply channels 650 connect in communication the oxidizing gas supply manifolds HOd to HOf and the cathode-side porous body 850 that overlaps with the power generation portion 800b. Some of the oxidizing gas discharge channels 660 connect in communication the oxidizing gas discharge manifolds 120a to 120c and the cathode-side porous body 850 that overlaps with the power generation portion 800a. The other oxidizing gas discharge channels 660 connect in communication the oxidizing gas discharge manifolds 120a to 120c connect and the cathode-side porous body 850 that overlaps with the power generation portion 800b. [0038] Next, the construction of the separators 600 will be described with reference to FIGS. 5 and 6A to 6C. Each separator 600 is constructed of an anode plate 300, a cathode plate 400, and an intermediate plate 500.

[0039] FIGS. 6A to 6C are illustrative diagrams showing the configurations of the anode plate 300 (FIG 6A), the cathode plate 400 (FIG 6B), and the intermediate plate 500 (FIG 6Q in this embodiment. Two regions shown by dashed lines in the plates 300 and 400 (FIGS. 6A and 6B) represent regions of overlap with the power generation portions 800a, 800b.

[0040] The anode plate 300 and the cathode plate 400 have manifold-forming portions that penetrate the plates in the direction of the thickness of the plates, corresponding to the manifolds HOa to 160b shown in FIG 1.

[0041] The intermediate plate 500 has manifold-forming portions that penetrate the intermediate plate 500 in the direction of the thickness thereof, corresponding to the manifolds HOa to 140 provided for supplying/discharging the reactant gas (the oxidizing gas or the fuel gas) shown in FIG 1. [0042] The intermediate plate 500 further has a plurality of cooling medium channel-forming portions 550. Each of the cooling medium channel-forming portions 550 has the shape of an elongated hole that extends across the power generation portion 800a or 800b in the left-right direction in FIG 3, with two ends thereof reaching outside the power generation portion 800a or 800b. The cooling medium channel-forming portions 550 may be disposed so as to entirely cover the power generation portions 800a and 800b.

[0043] FIG 5 shows a front view of a separator 600 made up of the foregoing plates 300, 400, 500. The separator 600 is made by joining the anode plate 300 and the cathode plate 400 to the opposite sides of the intermediate plate 500 so that the intermediate plate 500 is sandwiched, and by die-punching portions of the plates that are exposed to regions that correspond to the cooling medium supply manifolds 150a, 150b and the cooling medium discharge manifolds 160a, 160b of the intermediate plate 500. The method used to join the three plates can be, for example, thermocorapression bonding, brazing, welding, etc. This provides a separator 600 that has penetration opening portions for forming the various manifolds shown in FIG 1 when a fuel cell 100 is constructed, and that also has a plurality of cooling medium channels 670, as shown by hatching in FlG 5. The cooling medium channels 670 are internal channels extending in planar direction within the separator 600. An end of each cooling medium channel 670 communicates with the cooling medium supply manifold 150a or 150b, and another end thereof communicates with the cooling medium discharge manifold 160a or 160b.

[0044] In the separator 600, the oxidizing gas discharge manifolds 120a to 120c are disposed between the power generation portion 800a and the power generation portion 800b. Of the manifold, the manifolds other than the three oxidizing gas discharge manifolds 120a to 120c are formed along the outer peripheral edge of the separator 600. Concretely, the three oxidizing gas supply manifolds HOa to HOc are disposed along the upper side of the separator 600 in FlG 5. These oxidizing gas supply manifolds 110a to 110c are disposed opposite the oxidizing gas discharge manifolds 120a to 120c, respectively, across the power generation portion 800a. The other three oxidizing gas supply manifolds HOd to HOf are disposed along the lower side of the separator 600 in FIG 5 (the side thereof positioned in the positive direction of the Y axis). These oxidizing gas supply manifolds HOd to HOf are disposed opposite the oxidizing gas discharge manifolds 120a to 120c, respectively, across the power generation portion 800b. [0045] The two cooling medium supply manifolds 150a, 150b are disposed along the left-hand side of the separator 600 in FIG 5. Of the two manifolds, the cooling medium supply manifold 150a is formed along the left-hand side of the power generation portion 800a, extending over substantially the entire length of the left-hand side. The cooling medium supply manifold 150b is formed along the left-hand side of the power generation portion 800b, extending over substantially the entire length of the left-hand side.

[0046] The two cooling medium discharge manifolds 160a, 160b are disposed along the right-hand side of the separator 600 in FIG 5. Of the two manifolds, the cooling medium discharge manifold 160a is formed along the right-hand side of the power generation portion 800a, extending over substantially the entire length of the right-hand side. The cooling medium discharge manifold 160b is formed along the right-hand side of the power generation portion 800b, extending over substantially the entire length of the right-hand side.

[0047] The two fuel gas supply manifolds 130a, 130b are disposed in the upper left corner and the lower left corner of the separator 600 in FIG 5. The fuel gas discharge manifold 140 is disposed near a center portion of the right-hand side of the separator 600 in FIG 5, sandwiched between the cooling medium discharge manifold 160a and the cooling medium discharge manifold 160b.

[0048] The operation of the fuel cell 100 in accordance with the embodiment will be described with reference to FIGS. 7A, 7B and 8, which are operation diagrams of the fuel cell. FIGS. 7A and 7B are illustrative diagrams showing flows of the oxidizing gas. FIG 8 is an illustrative diagram showing flows of the cooling medium. To facilitate the understanding of the drawings, FIGS. 7 A, 7B and 8 show only a membrane-electrode assembly 200, and separators 600 and porous bodies 840, 850 that are disposed on both sides of the membrane-electrode assembly 200. An upper half of FIG 7A shows a sectional view corresponding to the line A-A in FIG 3, and a lower half of FIG 7A shows a sectional view corresponding to the line C-C in FIG 3. FIG 7B shows a sectional view corresponding to the line D-D in FIG 3. A left-hand half of FIG 8 shows a sectional view corresponding to the line E-E in FIG 5, and a right-hand half of FIG 8 shows a sectional view corresponding to the line F-F in FlG 5.

[0049] The fuel cell 100 generates electric power as the oxidizing gas supply manifolds HOa to HOf are supplied with the oxidizing gas and the fuel gas supply manifolds 130a, 130b are supplied with the fuel gas. Besides, during the power generation of the fuel cell 100, the cooling medium supply manifolds 150a, 150b is supplied with a cooling medium in order to restrain the temperature rise of the fuel cell 100 caused by the heat produced due to the power generation.

[0050] The oxidizing gas supplied to the three oxidizing gas supply manifolds HOa to HOc is supplied to the cathode-side porous body 850 that overlaps with the power generation portion 800a, via the oxidizing gas supply channels 650, as shown by arrows in FIG 7A. The oxidizing gas supplied to the cathode-side porous body 850 flows from up to down in FlG 3 in the cathode-side porous body 850, which functions as a channel of the oxidizing gas. Then, the oxidizing gas flows from the cathode-side porous body 850 into the oxidizing gas discharge channels 660, and is discharged through the oxidizing gas discharge channels 660 into the oxidizing gas discharge manifolds 120a to 120c. The oxidizing gas supplied to the other three oxidizing gas supply manifolds 11Od to llOf is supplied to the cathode-side porous body 850 that overlaps with the power generation portion 800b, via the oxidizing gas supply channels 650 as shown by arrows in FIG TB. The oxidizing gas supplied to the cathode-side porous body 850 flows from down to up in FIG 3 in the cathode-side porous body 850, which functions as a channel of the oxidizing gas. Then, the oxidizing gas flows from the cathode-side porous body 850 into the oxidizing gas discharge channels 660, and is discharged through the oxidizing gas discharge channels 660 into the oxidizing gas discharge manifolds 120a to 120c. In both the power generation portions 800a, 800b, a portion of the oxidizing gas flowing in the cathode-side porous body 850 diffuses in the entire cathode-side diffusion layer 830 that is in contact with the cathode-side porous body 850, and is given for use in the cathode reaction (e.g., 2H⁺+2e^"+(l/2)O₂→ H₂O).

[0051] Although not shown in a sectional view, the fuel gas supplied to the fuel gas supply manifolds 130a, 130b is supplied to the anode-side porous body 840 that overlaps with the power generation portions 800a, 800b, via the fuel gas supply channel 630, similarly to the oxidizing gas. The fuel gas supplied to the anode-side porous body 840 flows in the anode-side porous body 840, which functions as a channel of the fuel gas. Then, the fuel gas flows from the anode-side porous body 840 into the fuel gas discharge channels 640, and is discharged through the fuel gas discharge channels 640 into the fuel gas discharge manifold 140. A portion of the fuel gas flowing in the anode-side porous body 840 diffuses in the entire anode-side diffusion layer 820 that is in contact with the anode-side porous body 840, and is given for use in the anode reaction (e.g.,

[0052] The cooling medium supplied to the cooling medium supply manifolds 150a, 150b is supplied to the cooling medium channels 670. The cooling medium supplied to the cooling medium channels 670 flows from one end to another end of the cooling medium channels 670, and is discharged into the cooling medium discharge manifolds 160a, 160b. The cooling medium, while flowing near the power generation portions 800a, 800b, cools the fuel cell by absorbing heat from the power generation portions 800a, 800b of the membrane-electrode assembly 200,

[0053] According to the above-described embodiment, the temperature difference between the power generation portions 800a, 800b and the non-power generation portion 700 (e.g., the interiors and surroundings of the oxidizing gas discharge manifolds 120a to 120c) in the fuel cell can be made small. FIG 9 is an illustrative diagram showing a temperature distribution during the power generation of the fuel cell. The graph shown in FIG 9 shows the temperatures in the separator 600 at various positions Y on the line G-G shown in FlG 5. The line Ml shows a temperature distribution at the time point of the elapse of a time Ml from a start of power generation, and the line M2 shows a temperature distribution at the time point of the elapse of a time M2 from the start of power generation (M2>M1). It can be seen that as time elapses from the start of power generation, the temperature of the power generation portion 800a and the power generation portion 800b rises due to the heat of reaction. As a result, the temperature difference between the power generation portions 800a, 800b and an outer peripheral edge portion of the non-power generation portion 700 (e.g., a region in which the oxidizing gas supply manifolds HOa to HOf are formed) becomes larger. In a portion of the non-power generation portion 700 in which the oxidizing gas discharge manifolds 120a to 120c are formed, temperature becomes relatively high. This is because 1) the portion in which the oxidizing gas discharge manifolds 120a to 120c are formed is sandwiched by the two high-temperature power generation portions 800a, 800b, and 2) the portion in which the oxidizing gas discharge manifolds 120a to 120c are formed is positioned substantially in the center portion in the direction of the Y axis, and is not in contact with the outside, so that the heat dissipation to the outside is small. Thus, it can be understood that the temperature difference between the power generation portions 800a, 800b of the fuel cell and the portions of the non-power generation portion 700 that are within and around the oxidizing gas discharge manifolds 120a to 120c is small.

[0054] Besides, in this embodiment, the oxidizing gas discharge manifolds 120a to 120c have an elongated hole shape. Of the two longitudinal sides of the elongated hole shapes, one longitudinal side extends along and next to the power generation portion 800a, and the other longitudinal side extends along and next to other power generation portion 800b. In consequence, the oxidizing gas discharge manifolds 120a to 120c as a whole are relatively near to the power generation portions 800a, 800b. As a result, the temperature difference between the power generation portions 800a, 800b of the fuel cell and the interiors and surroundings of the oxidizing gas discharge manifolds 120a to 120c can be made smaller than in the case where the oxidizing gas discharge manifolds are provided in an outer peripheral edge of the separator,

[0055] This makes it possible to restrain condensation to dews that is caused by rapid cooling of the moisture (product water or the like) contained in the oxidizing gas in the oxidizing gas discharge manifolds 120a to 120c. The condensed water impedes smooth flowage of the oxidizing gas, and therefore causes a decline of the power generation performance.

[0056] In particular, in the case where the ambient temperature of the fuel cell is low (e.g., below the freezing point), the temperature difference between the power generation portions 800a, 800b and the interiors of the oxidizing gas discharge manifolds 120a to 120c tends to be large, and therefore the embodiment provides a great effect. Besides, with the demand for size reduction of the fuel cell 100, it is desired to reduce the thickness of the separator 600. However, if the separator 600 is made thin, the heat conductivity in planar direction will likely deteriorate. Therefore, in the case where the separator 600 is thin, the temperature difference between the portions that overlap with the power generation bodies in the stacking direction and the interiors of the oxidizing gas discharge manifolds 120a, 120b tends to be large, and therefore the embodiment provides a great effect. [0057] Besides, the oxidizing gas discharge manifolds 120a to 120c are provided over substantially the entire length of one long side of the rectangular power generation portion 800a, and the oxidizing gas supply manifolds HOa to 110c are provided over substantially the entire length of the other long side of the power generation portion 800a. As a result, the oxidizing gas flowing from the oxidizing gas supply manifolds HOa to 110c to the oxidizing gas discharge manifolds 120a to 120c is uniformly distributed over the entire area of the power generation portion 800a. Similarly, the oxidizing gas discharge manifolds 120a to 120c are provided over substantially the entire length of one long side of the rectangular power generation portion 800b, and the oxidizing gas supply manifolds 11Od to HOf are provided over substantially the entire length of the other long side of the power generation portion 800b. As a result, the oxidizing gas flowing from the oxidizing gas supply manifolds HOd to HOf to the oxidizing gas discharge manifolds 120a to 120c is uniformly distributed over the entire area of the power generation portion 800b.

[0058] However, the fuel gas supply manifolds 130a, 130b and the fuel gas discharge manifold 140 are smaller than the manifolds for the oxidizing gas, and are not formed over the entire length of the power generation portions 800a, 800b. Hydrogen, which is the fuel gas in this embodiment, has a faster diffusion rate than oxygen in air, which is the oxidizing gas. The diffusion rate is dependent mainly on the diffusion coefficient and the concentration gradient. The diffusion coefficient of hydrogen is about four times that of oxygen. Besides, the fuel gas use herein is pure hydrogen (having a hydrogen concentration of about 100%) while the oxidizing gas used herein is air (having an oxygen concentration of about 20%). Therefore, it can be understood that the diffusion rate of oxygen in the oxidizing gas is considerably lower than that of hydrogen in the fuel gas. Therefore, if the fuel gas is supplied from a portion of one side of each of the power generation portions 800a, 800b, sufficient hydrogen for the cell reaction can be supplied. Specifically, the electrochemical reaction of the fuel cell is generally determined by the reaction at the thiee-phase interface of the cathode electrode (2H⁺+2e^"+(l/2)θ₂->H₂θ) since the diffusion rate of oxygen molecules is slow. Hence, adoption of a channel arrangement designed with a high regard for the performance in supplying the oxidizing gas leads to improved cell performance.

[0059) Although the foregoing embodiment has a construction in which the oxidizing gas discharge manifolds 120a to 120c are sandwiched by the two power generation portions 800a, 800b and the oxidizing gas discharge manifolds 120a to 120c are disposed in a center portion of the separator 600 in the direction of the Y axis in FlG 5, a different construction may also be adopted. For example, it is permissible to adopt a construction in which oxidizing gas discharge manifolds are provided near the center of a circular power generation portion. Generally speaking, it is preferable that the power generation portion include at least a portion positioned on a side of the oxidizing gas discharge manifolds, and a portion positioned on another side of the oxidizing gas discharge manifolds that is opposite the aforementioned side thereof. Besides, it is preferable that the oxidizing gas discharge manifolds be positioned in a substantially central portion of the separator in at least one direction of the directions along the plane of the separator (the directions perpendicular to the stacking direction). [0060] Although in the foregoing embodiment, the materials for the various members of the power generation portions 800a, 800b and the various members of the separator 600 are specified, these materials are not restrictive, but various other appropriate materials may also be used. For example, although the anode-side porous body 840 and the cathode-side porous body 850 are formed from a metal porous body, the anode-side porous body 840 and the cathode-side porous body 850 can also be formed from another material, for example, a carbon porous body. Furthermore, although the separator 600 is formed from a metal, the separator 600 can also be formed from another material, for example, a carbon material. [0061] In the foregoing embodiment, the separator 600 has a construction in which three layers of metal plates are stacked, and the portions of the separator 600 corresponding to the power generation portions 800a, 800b have a flat shape. However, those portions may instead have any other appropriate shape. Concretely, it is permissible to adopt a separator (made of, for example, a carbon material) in which a surface corresponding to a power generation portion has gτoove-shape reactant gas channels, or adopt a separator (made, for example, by press-forming a metal plate) in which a portion corresponding to a power generation portion has a corrugated shape that functions as reactant gas channels.

[0062] Although in the embodiment, the anode-side porous body 840 and the cathode-side porous body 850 are provided, this construction is not restrictive. For example, in the case where separators in which reactant gas channels are formed or separators having corrugated plates that function as reactant gas channels are used, the anode-side and cathode-side porous bodies may be omitted.

[0063] While the invention has been described with reference to example embodiments thereof, it is to be understood that the invention is not limited to the described embodiments or constructions. To the contrary, the invention is intended to cover various modifications and equivalent arrangements. In addition, while the various elements of the disclosed invention are shown in various example combinations and configurations, other combinations and configurations, including more, less or only a single element, are also within the scope of the appended claims.

Claims

CLAIMS:

1. A separator that is stacked alternately with a power generation module that includes a power generation body so as to construct a fuel cell, the separator comprising: an oxidizing gas discharge manifold hole for discharging an oxidizing gas; and a power generation region that overlaps with the power generation body in a stacking direction when stacked, and that includes at least a portion positioned at a side of the oxidizing gas discharge manifold hole, and a portion positioned at another side of the oxidizing gas discharge manifold hole opposite to the side of the oxidizing gas discharge manifold hole.

2. A separator that is stacked alternately with a power generation module that includes a power generation body so as to construct a fuel cell, the separator comprising: an oxidizing gas discharge manifold hole for discharging an oxidizing gas which is disposed in a substantially central portion of the separator in at least one direction; and a power generation region that is disposed at a position different from a position of the oxidizing gas discharge manifold hole, and that overlaps with the power generation body when stacked.

3. The separator according to claim 1 or 2, wherein the power generation region includes a first region adjacent to a side of the oxidizing gas discharge manifold hole, and a second region adjacent to another side of the oxidizing gas discharge manifold hole opposite to the side of the oxidizing gas discharge manifold hole.

4. The separator according to claim 3, further comprising: a first oxidizing gas supply manifold hole that is a manifold hole for supplying the oxidizing gas and that is adjacent to a side of the first region opposite from the oxidizing gas discharge manifold hole; and a second oxidizing gas supply manifold hole that is a manifold hole for supplying the oxidizing gas and that is adjacent to a side of the second region opposite from the oxidizing gas discharge manifold hole.

5. The separator according to any one of claims 1 to 4, wherein the oxidizing gas discharge manifold hole and the power generation region are disposed so as to be adjacent to each other at a long side of the oxidizing gas discharge manifold hole.

6. The separator according to claim 5, wherein the oxidizing gas discharge manifold hole is disposed so that the entire length of the long side of the oxidizing gas discharge manifold hole is adjacent to the power generation region.

7. A separator that is stacked alternately with a power generation module that includes a power generation body so as to construct a fuel cell, the separator comprising: a power generation region that overlaps with the power generation body in a stacking direction, when stacked; and an oxidizing gas discharge manifold hole for discharging an oxidizing gas which is disposed in a region surrounded by the power generation region.

8. The separator according to any one of claims 1 to 7, wherein a manifold hole other than the oxidizing gas discharge manifold hole is formed along an outer peripheral edge of the separator.

9. A fuel cell comprising: a separator according to any one of claims 1 to 8; and a power generation module that includes the power generation body, wherein the separator and the power generation module are alternately stacked,