Fuel cell and method of manufacturing fuel cell

A technique of reducing the possibility that the thickness of an adhesive layer in a seal member becomes non-uniform is provided. There is provided a fuel cell comprising a membrane electrode gas diffusion layer assembly; a seal member; and a first separator and a second separator arranged to place the diffusion layer assembly and the seal member therebetween. The seal member includes a first adhesive layer facing the first separator, a second adhesive layer facing the second separator, and a core layer that is placed between, and is harder than, the first and second adhesive layers. Each of the first and second separators includes an opposed surface that faces the corresponding adhesive layer and a convex protruded from the opposed surface in a direction toward the seal member. A circumference of the convex in the opposed surface adheres to the corresponding facing adhesive layer.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application claims priority from Japanese patent application 2016-020651 filed on Feb. 5, 2016, the entirety of the disclosure of which is hereby incorporated by reference into this application.

BACKGROUND

The present disclosure relates to a fuel cell.

In a conventionally known configuration of a fuel cell, a membrane electrode gas diffusion layer assembly that includes a membrane electrode assembly and gas diffusion layers and a seal member in a film-like form that is arranged in a periphery of the membrane electrode gas diffusion layer assembly are placed between a pair of separators (as described in, for example, JP 2014-120368A). The seal member includes a core portion and surface layers (adhesive layers) that are arranged on respective sides of the core portion. In a process of manufacturing the fuel cell, the surface layers of the seal member are melted and are then cured, so that opposed surfaces of the separators arranged to face the respective surface layers of the seal member adhere to the surface layers.

SUMMARY

In a conventional process of bonding the opposed surfaces of the separators to the surface layers of the seal member, pressing the entire opposed surfaces against the surface layers provides the possibility that the thickness of a pressed portion (adhesive portion) of the surface layer is significantly reduced. Significant reduction of the thickness of the adhesive portion may cause various problems as described below. For example, this may cause a problem that the adhesive force between the opposed surfaces and the adhesive portions is reduced. In another example, part of the adhesive portion pressed by the opposed surface may be flowed away to the periphery and may cause a problem that the thickness of the fuel cell becomes non-uniform. The non-uniform thickness of the fuel cell may prevent an inter-cell seal member such as a gasket that is placed between separators of an adjacent pair of fuel cells from exerting the originally expected sealing function. This may lead to the possibility that a reactive gas or a cooling medium flowing in the fuel cell is leaked out. There is accordingly a need for a technique that reduces the possibility that the thickness of the adhesive portion of the surface layer in the seal member is reduced significantly.

In order to solve at least part the problems described above, the disclosure may be implemented by aspects described below.

(1) According to one aspect of the disclosure, there is provided a fuel cell. This fuel cell comprises a membrane electrode gas diffusion layer assembly including a membrane electrode assembly in which electrodes are arranged on respective surfaces of an electrolyte membrane, and gas diffusion layers that are arranged on respective surfaces of the membrane electrode assembly; a seal member in a film-like form that is arranged in a periphery of the membrane electrode gas diffusion layer assembly; and a first separator and a second separator that are arranged such as to place the membrane electrode gas diffusion layer assembly and the seal member therebetween. The seal member includes a first adhesive layer that is arranged to face the first separator, a second adhesive layer that is arranged to face the second separator, and a core layer that is placed between the first adhesive layer and the second adhesive layer and is harder than the first adhesive layer and the second adhesive layer. The first separator includes a first opposed surface that is arranged to face the first adhesive layer and a first convex that is protruded from the first opposed surface in a direction toward the seal member to dent the first adhesive layer. The second separator includes a second opposed surface that is arranged to face the second adhesive layer and a second convex that is protruded from the second opposed surface in a direction toward the seal member to dent the second adhesive layer. A circumference of the first convex in the first opposed surface adheres to the first adhesive layer, and a circumference of the second convex in the second opposed surface adheres to the second adhesive layer. In the fuel cell of this aspect, the separator (first separator or second separator) includes the convex (first convex or second convex) that is protruded from the opposed surface (first opposed surface or second opposed surface) in the direction toward the seal member. This configuration causes the convex to bump into the core layer and thereby suppresses the first separator or the second separator from being further pressed toward the seal member. This reduces a pressing amount of the first separator or the second separator into the adhesive layer (first adhesive layer or second adhesive layer). This configuration accordingly reduces the possibility that the thickness of a region of the adhesive layer that adheres to the separator is significantly reduced, compared with a configuration that each opposed surface does not include a convex.

(2) In the fuel cell of the above aspect, the first convex and the second convex may be arranged at positions that are not opposed to each other across the seal member. In the fuel cell of this aspect, the first convex and the second convex are arranged at the positions that are not opposed to each other. This configuration reduces the likelihood that an excessive load is applied to part of the seal member.

(3) In the fuel cell of the above aspect, when a plurality of the fuel cells are stacked and a predetermined load is applied to the plurality of fuel cells in a stacking direction, the first convex may be arranged in a first specific region of the first separator that applies a higher load to the seal member, compared with a periphery of the first specific region in the first separator. The second convex may be arranged in a second specific region of the second separator that applies a higher load to the seal member, compared with a periphery of the second specific region in the second separator. The configuration of the fuel cell of this aspect causes the convex to reach the core layer and thereby suppresses displacement of the separator.

(4) In the fuel cell of the above aspect, each of the first specific region and the second specific region may be a region that is overlapped with an inter-cell seal member placed between an adjacent pair of the fuel cells, when the fuel cell is viewed along the stacking direction. In general, when a plurality of the fuel cells are stacked and a predetermined load is applied to the plurality of fuel cells in the stacking direction, a higher load is applied to the seal member via the separator in the region that is overlapped with the inter-cell seal member, compared with a periphery of the overlapped region. In the fuel cell of this aspect, the convex is provided in the specific region (first specific region or second specific region) of the separator that applies a higher load to the seal member. This configuration causes the convex to reach the core layer and thereby reduces the likelihood that the thickness of part of the adhesive layer is significantly reduced. This suppresses displacement of the separator.

(5) In the fuel cell of the above aspect, the core layer may be made of a first type of thermoplastic resin, and each of the first adhesive layer and the second adhesive layer may be made of a second type of thermoplastic resin that is different from the first type of thermoplastic resin. The core layer may have a higher Vicat softening temperature than the first adhesive layer and the second adhesive layer. Even when the fuel cell is placed in a temperature environment that is higher than the Vicat softening temperature of the first adhesive layer and the second adhesive layer and is lower than the Vicat softening temperature of the core layer, this configuration causes the convex to bump into the core layer and thereby reduces the possibility that the thickness of a region of the adhesive layer that adheres to the separator is significantly reduced.

(6) In the fuel cell of the above aspect, the core layer may be made of a thermoplastic resin, and each of the first adhesive layer and the second adhesive layer may be made of a thermosetting resin. In the fuel cell of this aspect, even when the convex of the separator dents the thermosetting resin prior to curing, this configuration causes the convex to bump into the core layer and thereby reduces the possibility that the thickness of a region of the adhesive layer that adheres to the circumference of the convex in the separator is significantly reduced.

(7) According to another aspect of the disclosure, there is provided a method of manufacturing a fuel cell. The method of manufacturing the fuel cell comprises: (a) a process of providing a membrane electrode gas diffusion layer assembly and a seal member in a film-like form, wherein the membrane electrode gas diffusion layer assembly includes a membrane electrode assembly in which electrodes are arranged on respective surfaces of an electrolyte membrane, and gas diffusion layers that are arranged on respective surfaces of the membrane electrode assembly; (b) a process of placing the seal member in a periphery of the membrane electrode gas diffusion layer assembly, after the process (a); and (c) a process of arranging a first separator and a second separator such as to place the membrane electrode gas diffusion layer assembly and the seal member therebetween, and bonding the seal member to the first separator and the second separator, after the process (b). The seal member includes a first adhesive layer that is arranged to adhere to the first separator, a second adhesive layer that is arranged to adhere to the second separator, and a core layer that is placed between the first adhesive layer and the second adhesive layer. The first separator includes a first opposed surface that is arranged to face the first adhesive layer and a first convex that is protruded from the first opposed surface. The second separator includes a second opposed surface that is arranged to face the second adhesive layer and a second convex that is protruded from the second opposed surface. The process (c) comprises: melting or softening part of the first adhesive layer; pressing the first convex and a first circumference of the first opposed surface that is arranged to surround the first convex, against the melted or softened part of the first adhesive layer; after the pressing the first circumference, curing the melted or softened part of the first adhesive layer, such that at least the first circumference is bonded to the first adhesive layer; melting or softening part of the second adhesive layer; pressing the second convex and a second circumference of the second opposed surface that is arranged to surround the second convex, against the melted or softened part of the second adhesive layer, and after the pressing the second circumference, curing the melted or softened part of the second adhesive layer, such that at least the second circumference is bonded to the second adhesive layer. In the method of manufacturing the fuel cell according to this aspect, the respective separators include the convexes. This configuration reduces the possibility that the thickness of a region of the adhesive layer that adheres to the separator is significantly reduced, compared with a configuration that each separator does not include a convex.

The disclosure may be implemented by any of various aspects other than the fuel cell and the method of manufacturing the fuel cell described above, for example, a separator used for the fuel cell, a fuel cell stack by stacking a plurality of the fuel cells, and a vehicle equipped with the fuel cell stack.

DESCRIPTION OF EMBODIMENTS

A. Configuration of Fuel Cell System10

FIG. 1is a diagram illustrating the general configuration of a fuel cell system10according to an embodiment of the invention. An X axis, a Y axis and a Z axis orthogonal to one another are illustrated inFIG. 1. An X axis, a Y axis and a Z axis corresponding to those ofFIG. 1are also illustrated in other drawings as needed. InFIG. 1, a −Y-axis direction denotes a vertically upward direction, and a +Y-axis direction denotes a vertically downward direction.

The fuel cell system10includes a fuel cell stack100as fuel cells. The fuel cell stack100has a stacked configuration in which an end plate110A, an insulating plate120A, a current collector130A, a plurality of fuel cells (hereinafter also simply referred to as “cells”)140, a current collector130B, an insulating plate120B and an end plate110B are stacked in this sequence. The direction of stacking the cells140is a direction along the X-axis direction. The plurality of cells140are clamped by application of a predetermined load (clamping load) in a compressing direction of the X-axis direction (stacking direction) from the end plates110A and110B on the respective sides.

Hydrogen as a fuel gas is supplied from a hydrogen tank150provided to store high-pressure hydrogen to the fuel cell stack100via a shutoff valve151, a regulator152and piping153. The unused fuel gas (anode off-gas) that is not consumed in the fuel cell stack100is flowed through discharge piping163and is discharged out of the fuel cell stack100. The fuel cell system10may further include a recirculation mechanism configured to recirculate the anode off-gas to the piping153-side. The air as an oxidizing gas is also supplied to the fuel cell stack100via an air pump160and piping161. The unused oxidizing gas (cathode off-gas) that is not consumed in the fuel cell stack100is flowed through discharge piping154and is discharged out of the fuel cell stack100. The fuel gas and the oxidizing gas are also called reactive gases.

A cooling medium cooled down by a radiator170is further supplied to the fuel cell stack100via a water pump171and piping172, in order to cool down the fuel cell stack100. The cooling medium discharged out of the fuel cell stack100is circulated through piping173to the radiator170. The cooling medium used may be, for example, water, an antifreeze liquid such as ethylene glycol, or the air. According to this embodiment, water (also called “cooling water”) is used as the cooling medium.

Each of the cells140provided in the fuel cell stack100includes a membrane electrode gas diffusion layer assembly (MEGA)30as a power generation module, a seal member20attached to a periphery of the MEGA30, and a first separator40and a second separator50arranged to place the MEGA30and the seal member20therebetween.

The MEGA30includes a membrane electrode assembly (MEA)31and a pair of gas diffusion layers32and33arranged on respective surfaces of the MEA31. The MEGA30is formed in a rectangular outer shape in the planar view. The MEA31includes an electrolyte membrane38and electrodes37and39arranged on respective surfaces of the electrolyte membrane38. The electrolyte membrane38is formed in a rectangular outer shape in the planar view. The electrode37is an electrode on an anode side (anode-side electrode) and is placed on one surface of the electrolyte membrane38. The electrode39is an electrode on a cathode side (cathode-side electrode) and is placed on the other surface that is opposite to the one surface of the electrolyte membrane38. The second separator50is a separator on the anode side (anode-side separator) and includes a plurality of linear fuel gas flow paths52provided on its MEGA30-side surface and a plurality of linear cooling medium distributed flow paths54provided on an opposite surface that is opposite to the MEGA30-side surface. The first separator40is a separator on the cathode side (cathode-side separator) and includes a plurality of linear oxidizing gas flow paths42provided on its MEGA30-side surface.

The seal member20is placed in the periphery (outer circumference) of the MEGA30in the planar view. The seal member20is made of a synthetic resin. The seal member20is in a film-like form and also in a frame-like form. The seal member20is joined with the periphery of the MEGA30such that the MEGA30is placed inside of the frame. The detailed configuration of the seal member20will be described later.

FIG. 2is a schematic plan view illustrating the cell140that is viewed from the second separator50-side.FIG. 3is an F2-F2sectional view ofFIG. 2. InFIG. 2, the outer shape of the MEGA30and some of convexes45and55described later are shown by the broken line.FIG. 3also illustrates an enlarged view of part of the sectional view below the F2-F2sectional view. For the purpose of better understanding, the F2-F2sectional view shown inFIG. 3is a sectional view in the state that two adjacent cells140are stacked.

The first separator40and the second separator50are formed from members having the gas barrier properties and electrical conductivity. For example, the first separator40and the second separator50may be formed from carbon members of, for example, dense carbon formed by compressing carbon particles to be gas impermeable or formed from press-formed metal members of, for example, stainless steel or titanium steel or titanium. According to this embodiment, the first separator40and the second separator50are formed by press-forming titanium steel or titanium.

As shown inFIG. 2, the second separator50includes a fuel gas inlet manifold62, a cooling medium outlet manifold78and an oxidizing gas inlet manifold72that are provided on one side relative to the cooling medium distributed flow paths54. The second separator50also includes an oxidizing gas outlet manifold74, a cooling medium inlet manifold76and a fuel gas outlet manifold64that are provided on the other side relative to the cooling medium distributed flow paths54.

The fuel gas supplied through the piping153for the fuel cell (shown inFIG. 1) is distributed by the fuel gas inlet manifold62to the fuel gas flow paths52(shown inFIG. 1) of each of the cells140. An unused portion of the fuel gas that is not used in the fuel gas flow paths52is then gathered to the fuel gas outlet manifold64and is discharged out of the fuel cell stack100through the discharge piping163(shown inFIG. 1). The oxidizing gas supplied through the piping161for the oxidizing gas (shown inFIG. 1) is distributed by the oxidizing gas inlet manifold72to the oxidizing gas flow paths42(shown inFIG. 1) of each of the cells140. An unused portion of the oxidizing gas that is not used in the oxidizing gas flow paths42is then gathered to the oxidizing gas outlet manifold74and is discharged out of the fuel cell stack100through the discharge piping154(shown inFIG. 1).

In a plane of the second separator50viewed from the opposite side to the MEGA30-side, the cooling medium inlet manifold76, the cooling medium distributed flow paths54and the cooling medium outlet manifold78communicate with one another to constitute a cooling medium flow passage190. The cooling medium supplied through the piping172for the cooling medium (shown inFIG. 1) is distributed by the cooling medium inlet manifold76to the cooling medium distributed flow paths54of each of the cells140. The cooling medium is then gathered to the cooling medium outlet manifold78and is discharged out of the fuel cell stack100through the piping173(shown inFIG. 1).

The opening of each of the manifolds62,64,72,74,76and78is formed in an approximately rectangular shape. Manifold holes in similar shapes are also provided in the first separator40and the seal member20, so that the respective manifolds (manifold holes)62,64,72,74,76and78form flow passages (manifolds) arranged to pass through the fuel cell stack100in the stacking direction.

The fuel cell stack100further includes gaskets92provided as inter-cell seal members placed between the respective adjacent cells140. The gaskets92are placed to seal between the second separator50and a first separator of another adjacent cell140. As shown inFIG. 2, the gaskets92are provided at a plurality of locations. The plurality of gaskets92are made of, for example, a rubber or a thermoplastic elastomer. The plurality of gaskets92are placed between the separators40and50of two adjacent cells140and tightly adhere to the two adjacent separators40and50to prevent leakage of the reactive gases and the cooling medium to the outside. The plurality of gaskets92are attached to and placed on an opposite surface50faof the second separator50that is opposite to a surface facing the MEGA30and the seal member20. Some parts of the plurality of gaskets92are arranged to surround the manifolds62,64,72and74. Another part of the plurality of gaskets92is arranged to surround the cooling medium flow passage190.

As shown inFIG. 3, the seal member20includes a first adhesive layer21, a second adhesive layer23and a core layer22that is placed between the first adhesive layer21and the second adhesive layer23. The first adhesive layer21is placed to be adjacent to and in contact with one surface of the core layer22, and the second adhesive layer23is placed to be adjacent to and in contact with the other surface of the core layer22. Accordingly the seal member20has three-layered structure. The first adhesive layer21is arranged to face the first separator40. The second adhesive layer23is arranged to face the second separator50. The first adhesive layer21includes adhesive regions21R (regions including thick line portions in the drawing) that adhere to the first separator40. The second adhesive layer23includes adhesive regions23R (regions including thick line portions in the drawing) that adhere to the second separator50. The first adhesive layer21and the second adhesive layer23are used to respectively adhere to the facing first separator40and second separator50, and the core layer22provides a foundation structure of the seal member20. The core layer22has a smaller amount of deformation under application of a certain load than the adhesive layers21and23at a temperature to which the seal member20is exposed in the use environment of the fuel cell stack100and at a cell-forming temperature described later.

The first adhesive layer21and the second adhesive layer23may be made of a thermoplastic resin, for example, polypropylene or polyethylene mixed with a silane coupling agent or a modified polyolefin obtained by introducing a functional group to a polyolefin. A concrete example the thermoplastic resin is Admer (registered trademark) manufactured by Mitsui Chemicals, Inc. The first adhesive layer21and the second adhesive layer23may be made of a thermosetting resin, for example, polyisobutylene or an epoxy resin. The first adhesive layer21and the second adhesive layer23have the high adhesiveness to another material, in order to adhere to the corresponding first separator40and second separator50and provide the sealing property.

The core layer22is made of a thermoplastic resin. The core layer22may be made of, for example, polyethylene naphthalene (PEN) or polypropylene. The core layer22is harder than the two adhesive layers21and23. More specifically, the core layer22is harder than the first adhesive layer21and the second adhesive layer23at a temperature (cell-forming temperature) in a bonding process to respectively bond the first adhesive layer21and the second adhesive layer23to the corresponding first separator40and second separator50.

The cell-forming temperature is specified as described below, for example, when the core layer22is made of a first type of thermoplastic resin and the first adhesive layer21and the second adhesive layer23are made of a second type of thermoplastic resin that is different from the first type of thermoplastic resin. The cell-forming temperature denotes a heating temperature of a hot pressing machine (described later) used to bond the first adhesive layer21and the second adhesive layer23respectively to the first separator40and the second separator50. In this case, the cell140meets the following condition 1:

The Vicat softening temperature of the core layer22is higher than the heating temperature of the hot pressing machine, and the Vicat softening temperature of the first adhesive layer21and the second adhesive layer23is lower than the heating temperature of the hot pressing machine.

Accordingly the core layer22has the higher Vicat softening temperature than that of the first adhesive layer21and the second adhesive layer23. The Vicat softening temperature is measured in conformity with Japanese Industrial Standards JIS-K-7206.

When the core layer22is made of a thermoplastic resin and the first adhesive layer21and the second adhesive layer23are made of a thermosetting resin that is in the liquid form at room temperature (for example, at 25° C.) prior to curing, the cell-forming temperature denotes a temperature (for example, 25° C. to 40° C.) at which the first separator40and the second separator50are pressed against the two adhesive layers21and23by the hot pressing machine described later in a stage prior to a start of curing of the first adhesive layer21and the second adhesive layer23in the liquid form. This temperature in such pressing is lower than the Vicat softening temperature of the core layer22. Accordingly the core layer22is harder than the first adhesive layer21and the second adhesive layer23at the cell-forming temperature.

As described above, the seal member20includes the first adhesive layer21and the second adhesive layer23that are softened or liquefied and the core layer22that is not softened or liquefied, at the cell-forming temperature when the seal member20is bonded to the first separator40and the second separator50.

The first separator40includes an opposed surface40fbas a first opposed surface that is arranged to face the first adhesive layer21, and an opposite surface40fathat is on the opposite side to the opposed surface40fb. The opposed surface40fbis a planar surface. Portions of the opposed surface40fbthat adhere to the first adhesive layer21are called adhesive opposed surfaces40fc. The first separator40includes convexes45as first convexes that are protruded from the adhesive opposed surfaces40fcin a direction toward the seal member20. In other words, the adhesive opposed surface40fcform a circumference of the convex45(also called “first circumference”). The convex45dents the first adhesive layer21.

The second separator50includes an opposed surface50fbas a second opposed surface that is arranged to face the second adhesive layer23, and an opposite surface50fathat is on the opposite side to the opposed surface50fb. The opposed surface50fbis a planar surface. Portions of the opposed surface50fbthat adhere to the second adhesive layer23are called adhesive opposed surfaces50fc. The second separator50includes convexes55as second convexes that are protruded from the adhesive opposed surfaces50fcin a direction toward the seal member20. In other words, the adhesive opposed surface50fcforms a circumference of the convex55(also called “second circumference”). The convex55dents the second adhesive layer23. It is preferable that the convex45and the convex55are arranged at positions that are not opposed to each other across the seal member20(as shown inFIG. 3). In other words, when the cell140is viewed along the stacking direction of the plurality of cells140, it is preferable that the convex45and the convex55are arranged alternately to be not overlapped with each other. This configuration reduces the possibility that an excessively high load is applied to some portions of the seal member20by these two convexes45and55, for example, during the bonding process or in the clamped state of the fuel cell stack100.

The first separator40and the second separator50respectively include inclination suppressing elements47and57that are provided in portions overlapping with the seal member20along the stacking direction and are configured to prevent inclination of the separators40and50in a direction perpendicular to the stacking direction. The inclination suppressing element47is protruded from the opposite surface40faof the first separator40. The inclination suppressing element57is protruded from the opposite surface50faof the second separator50. A leading end in the protruding direction of each of the inclination suppressing elements47and57forms a plane. In the fuel cell stack100, the inclination suppressing element57is arranged to be in abutment with the inclination suppressing element47of the adjacent cell140.

As shown inFIG. 2, each of the convexes45and55is formed to continue along each of the manifolds62,64,72,74,76and78. More specifically, each of the convexes45and55is formed continuously without interruptions along each of the manifolds62,64,72,74,76and78. As shown inFIG. 3, each of the convexes45and55has a trapezoidal sectional shape in a direction perpendicular to the direction in which the convex45or55is continuous. Each of the convexes45and55is protruded to a height H from the adhesive opposed surface40fcor50fc. The height H is preferably determined to ensure a thickness of the adhesive layer21or23that provides the sufficient adhesive force between the adhesive layer21or23and the separator40or50in the adhesive region21R or23R. This ensures the thickness of the adhesive region21R or23R at the level that provides the sufficient adhesive force when the separator40or50is pressed against the adhesive region21R or23R of the adhesive layer21or23by the hot pressing machine described later. According to this embodiment, the height H may be set, for example, in a range of 0.02 mm to 0.08 mm. A maximum width W in the sectional shape of each of the convexes45and55is preferably set to a level that prevents the adhesive layer21or23from being pressed away to the periphery by the convex45or55and thereby having a significantly non-uniform thickness. According to this embodiment, the maximum width W may be set, for example, in a range of 0.1 mm to 1.0 mm.

FIG. 4is a process flowchart showing a process of manufacturing the cell140.FIG. 5is a diagram illustrating step S30ofFIG. 4.FIG. 6is a diagram illustrating step S40ofFIG. 4. In the seal member20of the cell140described with reference toFIG. 4, the core layer22is made of a first type of thermoplastic resin, and the two adhesive layers21and23are made of a second type of thermoplastic resin.

As shown inFIG. 4, the manufacturer first provides the MEGA30and the seal member20(step S10). The manufacturer subsequently bonds the seal member20to the periphery of the MEGA30(step S20). More specifically, the periphery of the MEGA30and the seal member20are bonded to each other by using an adhesive, for example, an ultraviolet cure resin including an olefin-based thermosetting sealing agent such as polyisobutylene (PIB).

After step S20, the manufacturer arranges the two separators40and50such that the MEGA30with the seal member20bonded thereto is placed between the two separators40and50(step S30). More specifically, as shown inFIG. 5, the second separator50is placed on the second adhesive layer23-side such that the opposed surface50fbof the second separator50is arranged to face the second adhesive layer23. The first separator40is placed on the first adhesive layer21-side such that the opposed surface40fbof the first separator40is arranged to face the first adhesive layer21. Each of the first adhesive layer21and the second adhesive layer23has a thickness T in the state without application of a load to the seal member20(in the state of the seal member20alone).

After step S30, the manufacturer bonds the seal member20to the two separators40and50(step S40). This completes manufacture of the cell140. More specifically, as shown inFIG. 6, the adhesive regions21R and23R of the seal member20are liquefied (melted) or softened by using a hot pressing machine200and are then cooled down to be cured, so that the separators40and50are bonded to the seal member20. At the cell-forming temperature of step S30, the core layer22is not liquefied (melted) or softened. The hot pressing machine200includes a pair of heat pressing members210. The heat pressing members210are heated to a predetermined temperature (for example, a temperature in a range of 120° C. to 200° C.) by a heating source and are used to press the separators40and50against the seal member20with a predetermined load (pressing force) F that does not significantly deform the core layer22. The hot pressing time may be set, for example, in a range of 2 seconds to 120 seconds. More specifically, the heat pressing members210are used to press the convexes45and55and the adhesive opposed surfaces40fcand50fclocated in the peripheries of the respective convexes45and55of the separators40and50against the seal member20. This causes at least the convexes45and55to dent the adhesive layers21and23.

When the adhesive layers21and23are heated by the heat pressing members210, areas including the adhesive regions21R and23R are melted and liquefied or are softened. The adhesive opposed surfaces40fcand50fcare further pressed against the melted or softened areas in the direction of clamping the seal member20(clamping direction). The convexes45and55bump into the core layer22during this pressing, so as to stop further move of the adhesive opposed surfaces40fcand50fcin the clamping direction. This configuration suppresses the first and the second separators40and50from further being pressed against the seal member20and thereby controls the pressing amounts of the first and the second separators40and50into the adhesive layers21and23. In other words, this configuration ensures the thickness of about at least the height H as the thickness of the adhesive layers21and23in the adhesive regions21R and23R. This configuration accordingly reduces the possibility that the thickness of the adhesive layers21and23in the adhesive regions21R and23R is reduced significantly.

Additional processes after step S40, for example, a process of bonding the gaskets92to the opposite surface50faof the separator50and a process of stacking the plurality of cells140may be performed to manufacture the fuel cell stack100. The process of bonding the gaskets92on the opposite surface50faof the separator50may be performed between step S20and step S30.

When the core layer22is made of a thermoplastic resin having a Vicat softening temperature that is higher than room temperature and the two adhesive layers21and23are made of a thermosetting resin that is in the liquid form (paste form) at room temperature prior to curing, the manufacturer may provide the core layer22at step S10and bond the core layer22to the periphery of the MEGA30at step S20. The manufacturer may subsequently apply the adhesive layers21and23in the paste form on the respective surfaces of the core layer22and then arrange the two separators40and50at step S30. The manufacturer may subsequently start pressing the separators40and50by using the hot pressing machine200at a temperature lower than the curing temperature of the adhesive layers21and23and then heat the heat pressing members210of the hot pressing machine200to the curing temperature or a higher temperature while continuing the pressing, so as to cure the adhesive layers21and23at step S40. In the process of bonding the separators40and50to the adhesive layers21and23, even when the separators40and50are pressed against the adhesive layers21and23in a temperature environment that is lower than the temperature at which curing of the thermosetting resin starts, this configuration ensures the thickness of about at least the height H as the thickness of the adhesive layers21and23in the adhesive regions21R and23R. This configuration accordingly also reduces the possibility that the thickness of the adhesive layers21and23in the adhesive regions21R and23R is reduced significantly.

A-2. Reference Example to Describe Advantageous Effects of Embodiment

FIG. 7is a diagram illustrating a reference example to describe the advantageous effects of the embodiment.FIG. 7is a diagram corresponding toFIG. 6. Separators40pand50pof the reference example differ from the separators40and50of the embodiment by only omission of convexes45and55that are protruded from adhesive opposed surfaces40pfcand50pfctoward the seal member20(shown inFIG. 6). Otherwise the configuration of the separators40pand50pand the configuration of the seal member20are similar to those of the above embodiment. The like components are thus expressed by the like reference signs and are not specifically described here.

At step S40, when the adhesive opposed surfaces40pfcand50pfcof the separators40pand50pare pressed against the seal member20by using the hot pressing machine200, substantially the entire adhesive opposed surfaces40pfcand50pfcbump into the core layer22. This stops further move of the adhesive opposed surfaces40pfcand50pfcin the clamping direction. This configuration causes greater amounts of the adhesive layers21and23placed in the adhesive regions21R and23R to be pressed away to the periphery by the adhesive opposed surfaces40pfcand50pfc. Since the greater amounts of the adhesive layers21and23are pressed away to the periphery, the thickness of the adhesive layers21and23in the adhesive regions21R and23R in this reference example becomes smaller than the thickness of the adhesive layers21and23in the above embodiment. This results in reducing the adhesive force between the adhesive layers21and23and the adhesive opposed surfaces40pfcand50pfc. The greater amounts of the adhesive layers21and23are pressed away to the periphery of the adhesive regions21R and23R, so that the thickness of the adhesive layers21and23becomes non-uniform in a cell140pof the reference example. This provides the non-uniform thickness of the cell140pand causes the stacked body of the seal member20and the separators40pand50pin the cell140pto include portions of locally reduced thickness145and portions of locally increased thickness147. When the gasket92is placed in a portion of locally reduced thickness145, the gasket92is likely to provide an insufficient height and is thus likely to fail in tightly adhering to the separator40or50of another adjacent cell140pand providing the sufficient sealing property between the adjacent cells140which is originally expected to be provided by the gasket92. This may cause a leakage of the reactive gas or the cooling medium to outside of the cell140p. When the gasket92is placed in a portion of locally increased thickness147as shown inFIG. 7, on the other hand, the gasket92is likely to be excessively compressed and damaged under application of a clamping load by the end plates110A and110B.

A-3. Advantageous Effects of Embodiment

In the embodiment described above, the separators40and50include the convexes45and55that are protruded from the opposed surfaces40fband50fbin the direction toward the seal member20(as shown inFIG. 3). This configuration ensures the thickness of about at least the height H of the convexes45and55as the thickness of the adhesive layers21and23in the adhesive regions21R and23R in the bonding process. This configuration accordingly reduces the possibility that the thickness of the adhesive layers21and23in the adhesive regions21R and23R is reduced significantly, compared with a configuration that the separators40and50do not have convexes45and55. This accordingly suppresses reduction of the adhesive force between the adhesive layers21and23and the adhesive opposed surfaces40fcand50fc. This also reduces the amounts of the adhesive layers21and23pressed away from the adhesive regions21R and23R to the periphery in the bonding process and thereby reduces the possibility that the thickness of the adhesive layers21and23becomes non-uniform. This accordingly reduces the possibility that the thickness of the seal member20becomes non-uniform.

In the embodiment described above, the convexes45and55provided in the separators40and50serve as barriers. This configuration suppresses the liquefied or softened adhesive layer21or23from flowing away in a wide area, for example, in the process of manufacturing the cell140. For example, this reduces the possibility that the liquefied or softened adhesive layer21or23reaches the flow passage for supplying the reactive gas to the MEGA30. The separators40and50include the convexes45and55that are formed continuously without interruptions. This makes the separators40and50unlikely to be bent in the stacking direction. For example, even when a force is applied to bend the separators40and50along a line F2-F2shown inFIG. 2, the presence of the convexes45and55makes the separators40and50unlikely to be bent.

In the embodiment describe above, the presence of the convexes45and55increases the adhesive surface areas that adhere to the adhesive layers21and23and thereby improves the adhesive force between the separators40and50and the adhesive layers21and23. The side face of each of the convexes45and55is arranged to include a component in a direction of peeling off the separator40or50from the adhesive layer21or23(X-axis direction). Even when a force is applied in a direction of peeling off the separator40or50from the adhesive layer21or23, the side face of the convex45or55that adheres to the adhesive layer21or23reduces the possibility that the separator40or50is peeled off from the adhesive layer21or23.

B. Other Embodiments with Regard to Positions of Convexes

The convexes45and55may be arranged in a specific region of the opposed surfaces40fband50fbof the separators40and50when a plurality of cells140are stacked and a predetermined load is applied to the plurality of cells140to compress the cells140in the stacking direction. The specific region herein denotes a region in the separator40or50that applies a higher load to the seal member20than the circumference of the specific region. The following describes concrete examples of the specific region.

B-1. First Concrete Example

FIG. 8is a diagram illustrating a first concrete example of the specific region. In the above embodiment, the convexes45and55are arranged at the positions that do not overlap with the gasket92when the cell140is viewed along the stacking direction of the plurality of cells140(X-axis direction) (as shown inFIG. 3). As shown inFIG. 8, however, the convexes45and55may be arranged at positions that overlap with the gasket92. The cell140has the following relationship in the state that the plurality of cells140are stacked and a predetermined load is applied to the plurality of cells140in the compressing direction of the stacking direction (X-axis direction). When the cell140is viewed along the stacking direction, a specific region PTA of the separators40and50that is overlapped with the gasket92applies a higher load to the seal member20, compared with regions PTB that are located in the periphery of the specific region PTA and are not overlapped with the gasket92. The adhesive layers21and23of the seal member20are pressed by the specific region PTA of the separators40and50and are thereby deformed in the compressing direction. The convexes45and55provided in the specific region PTA, however, bump into the core layer22. This configuration reduces the possibility that the thickness of part of the adhesive layers21and23of the seal member20is significantly reduced. The adhesive layers21and23of the seal member20thus ensure the thickness of about the height of the convexes45and55. This configuration suppresses a portion of the separators40and50that is overlapped with the gasket92in the stacking direction from being displaced in the stacking direction. This configuration accordingly maintains the degree of compression of the gasket92to the level that ensures the sealing property. In other words, this suppresses reduction of the pressure applied to the separators40and50by the gasket92(sealing linear pressure). With regard to the above embodiment, this concrete example and other concrete examples described below, it is preferable that the core layer22has the higher hardness as the measurement value using a durometer than those of the adhesive layers21and23in a temperature range (for example, −30° C. to 100° C.) to which the seal member20is exposed in the use environment of the fuel cell system10. This configuration more effectively suppresses deformation of the core layer22when the convexes45and55bump into the core layer22and thereby more effectively ensures the thickness of about the height H of the convexes45and55as the thickness of the adhesive layers21and23. The specific region PTA corresponds to the “first specific region” and the “second specific region” described in SUMMARY.

B-2. Second Concrete Example

FIG. 9is a diagram illustrating a second concrete example. The fuel cell stack100may include wall-like members94configured to keep constant intervals between the separators40and50of the respective adjacent cells140. The wall-like member94is placed between the separators40and50of the adjacent cells140to be in contact with the separators40and50of the adjacent cells140. The wall-like member94may be a rubber member made of, for example, butyl rubber or ethylene propylene rubber. In the clamped state of the fuel cell stack100, when the cell140is viewed along the stacking direction, a specific region PTAa of the separators40and50that is overlapped with the wall-like member94applies a higher load to the seal member20, compared with regions PTBa that are located in the periphery of the specific region PTAa and are not overlapped with the wall-like member94. When the cell140is viewed along the stacking direction of the plurality of cells140(X-axis direction), convexes45and55may be provided at positions on the opposed surfaces40fband50fbof the separators40and50that are overlapped with the wall-like member94. In the clamped state of the fuel cell stack100, the seal member20is pressed by the specific region PTAa and is thereby deformed in the compressing direction. The convexes45and55provided in the specific region PTAa, however, bump into the core layer22. The adhesive layers21and23of the seal member20thus ensure the thickness of about the height of the convexes45and55. This configuration suppresses a portion of the separators40and50that is overlapped with the wall-like member94in the stacking direction from being displaced in the stacking direction. This configuration accordingly controls the degree of displacement of the wall-like member94in the stacking direction. The specific region PTAa corresponds to the “first specific region” and the “second specific region” described in SUMMARY.

B-3. Third Concrete Example

FIG. 10is a diagram illustrating a third concrete example and a fourth concrete example. In the fuel cell stack100, a seal structure, in place of the gasket92, may be provided integrally with the separator40or50to seal between the adjacent separators40and50.FIG. 10illustrates a configuration that a second separator50cis provided integrally with a seal structure58. The seal structure58is a projection that is provided to be protruded from the opposite surface50fa. The seal structure58is formed by press-forming the second separator50c. The seal structure58has spring elasticity and is elastically deformed to be compressed in the stacking direction in the clamped state of the fuel cell stack100. In the clamped state of the fuel cell stack100, the vicinity of a connecting region59of the second separator50cthat is connected with the seal structure58is a specific region (second specific region). Accordingly the vicinity of the connecting region59applies a higher load to the seal member20, compared with a region located in the periphery of the connecting region59. By the same reason as that of the first concrete example, a convex55may be placed in the specific region of the second separator50c. In the first separator40, a convex45may be placed in a region (first specific region) that overlaps in the stacking direction with a contact portion that comes into contact with the seal structure58of the adjacent second separator50cdirectly or via another member (for example, a thin-film rubber member). This first specific region applies a higher load to the seal member20, compared with the periphery of the first specific region of the first separator40.

B-4. Fourth Concrete Example

Convexes45and55may be arranged in the vicinity of areas where the inclination suppressing portions47and57are connected with the opposite surfaces40faand50fa(i.e., in first and second specific regions) as shown inFIG. 10. This first specific region applies a higher load to the seal member20, compared with a region of the separator40that is located in the periphery of the first specific region. The second specific region also applies a higher load to the seal member20, compared with a region of the separator50that is located in the periphery of the second specific region. Even when the seal member20is deformed in the compressing direction by placing the convex45in the first specific region and placing the convex55in the second specific region, the adhesive layers21and23of the seal member20thus ensure the thickness of about the height of the convexes45and55. This configuration controls the degree of displacement of the inclination suppressing portions47and57in the stacking direction.

The above embodiment describes one exemplified configuration of the fuel cell. The configuration of the cell may, however, be modified, altered or changed in any of various ways. For example, some components may be added, may be omitted or may be exchanged.

C-1. First Modification

In the embodiment described above, each of the convexes45and55has the trapezoidal sectional shape in the direction perpendicular to the direction in which the convex45or55is continuous (as shown inFIG. 3). The sectional shape is, however, not limited to this embodiment. For example, the sectional shape of the convex45or55may be a semicircular shape or a triangular shape. Each of the convexes45and55may be a single convex or may consist of multiple convexes. In other words, each of the convexes45and55may be arranged to form a single line along each of the manifolds62,64,72,74,76and78or may be arranged to form double or multiple lines along each of the manifolds62,64,72,74,76and78. In the above embodiment, each of the convexes45and55is formed continuously without interruptions along each of the manifolds62,64,72,74,76and78. This configuration is, however, not essential. For example, when the cell140is viewed along the stacking direction, convexes45or55in a dot-like shape or in an oval shape may be arranged along each of the manifolds62,64,72,74,76and78. Accordingly the convexes45or55may be arranged at predetermined intervals along each of the manifolds62,64,72,74,76and78. In the above embodiment, the convex45and the convex55are arranged alternately to be not overlapped with each other when the cell140is viewed along the stacking direction of the plurality of cells140(as shown inFIG. 2). This configuration is, however, not essential. For example, the convex45and the convex55may be arranged at positions that are overlapped with each other or may be arranged at positions that intersect with each other, when the cell140is viewed along the stacking direction of the plurality of cells140.

The disclosure is not limited to any of the embodiments, the examples and the modifications described above but may be implemented by a diversity of other configurations without departing from the scope of the disclosure. For example, the technical features of any of the embodiments, the examples and the modifications corresponding to the technical features of each of the aspects described in SUMMARY may be replaced or combined appropriately, in order to solve part or all of the problems described above or in order to achieve part or all of the advantageous effects described above. Any of the technical features may be omitted appropriately unless the technical feature is described as essential herein.