SINGLE CELL FOR FUEL CELL

A single cell for a fuel cell includes a power generating unit and two separators that hold the power generating unit in between. Each separator includes a facing surface, which faces the power generating unit. Each facing surface includes groove passages and ribs. Each of the ribs includes a top wall portion, two side wall portions, and corner portions. The top wall portion is in contact with the power generating unit. The side wall portions are located at the opposite sides of the top wall portion. Each corner portion is located between the top wall portion and one of the side wall portions. A restricting portion is provided at a section of each corner portion that faces the groove passage. The restricting portion restricts the gas diffusion layer from sinking into the groove passage. The restricting portion is a conductive porous body.

BACKGROUND

The present disclosure relates to a single cell for a fuel cell.

2. Description of Related Art

Japanese Laid-Open Patent Publication No. 2013-239316 discloses a fuel cell. The fuel cell includes a power generating unit, which is referred to as an electrolyte membrane electrode structure, and a plastic frame member arranged at the outer periphery of the power generating unit.

The fuel cell also includes two separators that hold the power generating unit and the frame member between them.

The power generating unit includes a solid polymer electrolyte membrane, an anode, and a cathode. The anode and the cathode hold the solid polymer electrolyte membrane between them.

The anode and the cathode each include a catalyst layer and a gas diffusion layer stacked on the catalyst layer.

Each separator includes groove passages in a surface that faces the power generating unit. A fuel gas or an oxidant gas (hereinafter, referred to as a reactant gas) flows through the groove passages.

In such a fuel cell, sections of the gas diffusion layer that face the groove passages may be deformed to bend and thus sink into the groove passages. The sunk sections of the gas diffusion layer act as resistance to the flow of reactant gas flowing through the groove passages and thus can increase the pressure loss of the reactant gas.

SUMMARY

Accordingly, it is an objective of the present disclosure to provide a single cell for a fuel cell that restricts a gas diffusion layer from sinking into groove passages, while maintaining the diffusivity of the reactant gas.

In one general aspect, a single cell for a fuel cell includes a power generating unit and two separators. The power generating unit includes a membrane electrode assembly and two gas diffusion layers. The gas diffusion layers hold the membrane electrode assembly in between. The two separators hold the power generating unit in between. Each separator includes a facing surface that faces the power generating unit. Each facing surface includes groove passages and ribs. The groove passages are configured to allow a reactant gas to flow therethrough. The ribs are located between the groove passages and protrude toward the power generating unit. The ribs each include a top wall portion, two side wall portions, and corner portions. The top wall portion is in contact with the power generating unit. The two side wall portions are located at opposite sides of the top wall portion in an arrangement direction of the groove passages. The corner portions are each located between the top wall portion and one of the side wall portions. A restricting portion is provided at a section of each corner portion that faces the groove passage. The restricting portion restricts the gas diffusion layer from sinking into the groove passage. The restricting portion is a conductive porous body.

DETAILED DESCRIPTION

A single cell90for a fuel cell according to one embodiment will now be described with reference toFIGS.1and2. For illustrative purposes, some parts of the structures in the drawings are exaggerated or simplified, and the dimensional ratios of the structures may be different from the actual ratios. The term “orthogonal” is not necessarily used in a strict sense, but may be used in cases where elements are generally orthogonal to each other within ranges in which such configuration achieves the operational advantages of the respective embodiments.

As shown inFIGS.1and2, the single cell90for a fuel cell includes a power generating unit10, a frame member20that holds the power generating unit10, separators30,40, and restricting portions70,80. The power generating unit10and the frame member20are held between the separators30,40. The restricting portions70,80are not illustrated inFIG.1.FIG.2shows a state in which multiple single cells90are stacked in the vertical direction with the separators30facing downward in the vertical direction.

The single cell90is a rectangular plate as a whole.

In the following description, the direction in which the separator30, the layer including the power generating unit10and the frame member20, and the separator40are stacked will be referred to as a first direction X. In the present embodiment, the first direction X is the vertical direction. Among directions orthogonal to the first direction X, a longitudinal direction of the single cell90will be referred to as a second direction Y. Also, a direction that is orthogonal to both the first direction X and the second direction Y will be referred to as a third direction Z.

The single cell90has inlet manifolds91,93,95for introducing reactant gas and cooling medium into the single cell90and outlet manifolds92,94,96for discharging the reactant gas and the cooling medium in the single cell90to the outside. In the present embodiment, the inlet manifold91and the outlet manifold92are manifolds through which fuel gas, which is reactant gas, flows. The fuel gas is, for example, hydrogen gas. The inlet manifold93and the outlet manifold94are manifolds through which cooling medium flows. The cooling medium is, for example, coolant. The inlet manifold95and the outlet manifold96are manifolds through which oxidant gas, which is reactant gas, flows. The oxidant gas is, for example, air.

The inlet manifolds91,93,95and the outlet manifolds92,94,96each have a rectangular shape in plan view, and extend in the first direction X through the single cell90.

The inlet manifold91and the outlet manifolds94,96are located on a first side in the second direction Y of the single cell90(on the left side in the left-right direction inFIG.1). The inlet manifold91and the outlet manifolds94,96are arranged in that order from a first side in the third direction Z (the back side of the sheet ofFIG.1) toward a second side in the third direction Z (the front side of the sheet ofFIG.1).

The outlet manifold92and the inlet manifolds93,95are located on a second side in the second direction Y of the single cell90(on the right side in the inFIG.1). The outlet manifold92and the inlet manifolds93,95are arranged in that order from the second side in the third direction Z (the front side of the sheet ofFIG.1) toward the first side in the third direction Z (the back side of the sheet ofFIG.1).

Each component of the single cell90will now be described.

Power Generating Unit 10

As shown inFIGS.1and2, the power generating unit10includes a solid polymer electrolyte membrane (hereinafter referred to as an electrolyte membrane 11) and electrodes12,13respectively provided on opposite surfaces of the electrolyte membrane11. In the present embodiment, the electrode that is joined to a first side in the first direction X (the lower side in the up-down direction inFIG.1) of the electrolyte membrane11is an anode12. Also, the electrode joined to a second side in the first direction X (the upper side in the inFIG.1) of the electrolyte membrane11is a cathode13.

The anode12includes a catalyst layer14joined to the first side (lower side inFIG.1) of the electrolyte membrane11and a gas diffusion layer16joined to the catalyst layer14.

The cathode13includes a catalyst layer15joined to the second side (upper side inFIG.1) of the electrolyte membrane11and a gas diffusion layer17joined to the catalyst layer15.

Specifically, a membrane catalyst layer assembly including the electrolyte membrane11and the two catalyst layers14,15is held between the two gas diffusion layers16and17. In the present embodiment, the membrane catalyst layer assembly corresponds to a membrane electrode assembly according to the present disclosure.

Frame Member 20

As shown inFIG.1, the frame member20has a rectangular shape elongated in the second direction Y and is made of, for example, plastic.

The frame member20includes through-holes21,22,23,24,25,26, which are parts of the respective manifolds91,92,93,94,95,96.

The frame member20includes an opening27in a center. The power generating unit10is joined to the peripheral edge of the opening27from a second side in the first direction X (upper side as viewed inFIG.1).

As shown inFIGS.1and2, the separator30is formed by pressing, for example, a metal member that is made of titanium or stainless steel and has a rectangular shape in plan view.

The separator30includes through-holes31,32,33,34,35,36, which are parts of the respective manifolds91,92,93,94,95,96(refer toFIG.1).

The separator30includes a first surface30A and a second surface30B. The first surface30A includes a facing surface30a, which faces the anode12of the power generating unit10in the first direction X. The second surface30B includes an opposite surface30b, which is located on a side opposite to the facing surface30a.

The first surface30A is provided with groove passages37A, through which the fuel gas flows, and two connecting portions37B. Also, the first surface30A is provided with ribs37C, which are located between the groove passages37A and protrude toward the gas diffusion layer16of the power generating unit10. InFIG.1, the groove passages37A, the connecting portions37B, and the ribs37C are illustrated in a simplified manner.

The groove passages37A and the ribs37C are provided in the facing surface30a.

The groove passages37A are arranged side by side in the third direction Z while being spaced apart from each other (refer toFIG.2). Each of the groove passages37A extends linearly in the second direction Y (refer toFIG.1). In the present embodiment, the second direction Y corresponds to an extending direction of groove passages according to the present disclosure, and the third direction Z corresponds to an arrangement direction of the groove passages according to the present disclosure.

The ribs37C are arranged side by side in the third direction Z while being spaced apart from each other (refer toFIG.2). Each of the ribs37C extends linearly in the second direction Y (refer toFIG.1).

As shown inFIG.2, each of the ribs37C includes a top wall portion51, two side wall portions52, and corner portions53. The side wall portions52are located at opposite sides of the top wall portion51in the third direction Z. Each corner portion53is located between the top wall portion51and a side wall portion52.

The top wall portion51is in contact with the gas diffusion layer16of the power generating unit10. In the present embodiment, the top wall portion51is in contact with the gas diffusion layer16over the entire rib37C in the second direction Y.

The two side wall portions52are inclined such that the distance between them in the third direction Z increases toward the side opposite to the gas diffusion layer16in the first direction X.

The corner portions53are curved so as to separate away from the gas diffusion layer16in the first direction X as the corner portions53extend away from the top wall portion51in the third direction Z increases.

As shown inFIG.1, the two connecting portions37B respectively extend from the opposite sides of the groove passages37A in the second direction Y toward the through-holes31,32. The fuel gas is introduced from the inlet manifold91to the groove passages37A via one of the connecting portions37B. The fuel gas flowing through the groove passages37A is discharged to the outlet manifold92via the other connecting portion37B.

As shown inFIGS.1and2, the second surface30B is provided with groove passages38A and two connecting portions38B, through which the cooling medium flows, and ribs38C, which are located between the groove passages38A and protrude away from the ribs37C in the first direction X. InFIG.1, the groove passages38A, the connecting portions38B, and the ribs38C are illustrated in a simplified manner.

As shown inFIG.2, each groove passage38A is formed by the back side of the corresponding rib37C. Also, each rib38C is formed by the back side of the corresponding groove passage37A.

As indicated by broken lines inFIG.1, the two connecting portions38B respectively extend from the opposite sides of the groove passages38A in the second direction Y toward the through-holes33,34. The cooling medium is introduced from the inlet manifold93to the groove passages38A via one of the connecting portions38B. The cooling medium flowing through the groove passages38A is discharged to the outlet manifold94via the other connecting portion38B.

As shown inFIGS.1and2, the separator40is formed by pressing, for example, a metal member that is made of titanium or stainless steel and has a rectangular shape in plan view.

The separator40includes through-holes41,42,43,44,45,46, which are parts of the respective manifolds91,92,93,94,95,96(refer toFIG.1).

The separator40includes a first surface40A and a second surface40B. The first surface40A includes a facing surface40a, which faces the cathode13of the power generating unit10in the first direction X. The second surface40B includes an opposite surface40b, which is located on a side opposite to the facing surface40a.

The first surface40A is provided with groove passages47A and two connecting portions47B, through which the oxidant gas flows. Also, the first surface40A is provided with ribs47C, which are located between the groove passages47A and protrude toward the gas diffusion layer17of the power generating unit10. InFIG.1, the groove passages47A, the connecting portions47B, and the ribs47C are illustrated in a simplified manner.

The groove passages47A and the ribs47C are provided in the facing surface40a.

The groove passages47A are arranged side by side in the third direction Z while being spaced apart from each other (refer toFIG.2). Each of the groove passages47A extends linearly in the second direction Y (refer toFIG.1).

The ribs47C are arranged side by side in the third direction Z while being spaced apart from each other (refer toFIG.2). Each of the ribs47C extends linearly in the second direction Y (refer toFIG.1).

As shown inFIG.2, each of the ribs47C includes a top wall portion61, two side wall portions62, and corner portions63. The side wall portions62are located at opposite sides of the top wall portion61in the third direction Z. Each corner portion63is located between the top wall portion61and a side wall portion62.

The top wall portion61is in contact with the gas diffusion layer17of the power generating unit10. In the present embodiment, the top wall portion61is in contact with the gas diffusion layer17over the entire rib47C in the second direction Y.

The two side wall portions62are inclined such that the distance between them in the third direction Z increases toward the side opposite to the gas diffusion layer17in the first direction X.

The corner portions63are curved so as to separate away from the gas diffusion layer17in the first direction X as the corner portions63extend away from the top wall portion61in the third direction Z increases.

As indicated by broken lines inFIG.1, the two connecting portions47B respectively extend from the opposite sides of the groove passages47A in the second direction Y toward the through-holes45,46. The oxidant gas is introduced from the inlet manifold95to the groove passages47A via one of the connecting portions47B. The oxidant gas flowing through the groove passages47A is discharged to the outlet manifold96via the other connecting portion47B.

As shown inFIGS.1and2, the second surface40B is provided with groove passages48A and two connecting portions48B, through which the cooling medium flows, and ribs48C, which are located between the groove passages48A and protrude away from the ribs47C in the first direction X. InFIG.1, the groove passages48A, the connecting portions48B, and the ribs48C are illustrated in a simplified manner.

As shown inFIG.2, each groove passage48A is formed by the back side of the corresponding rib47C. Also, each rib48C is formed by the back side of the corresponding groove passage47A.

As shown inFIG.1, the two connecting portions48B respectively extend from the opposite sides of the groove passages48A in the second direction Y toward the through-holes43,44. The cooling medium is introduced from the inlet manifold93to the groove passages48A via one of the connecting portions48B. The cooling medium flowing through the groove passages48A is discharged to the outlet manifold94via the other connecting portion48B.

As shown inFIG.2, the restricting portions70, which are conductive porous bodies, are provided at sections of the corner portions53that face the groove passages37A.

Each restricting portion70is provided on both corner portions53at the opposite sides of the corresponding groove passage37A. The restricting portion70continuously extends in the third direction Z from one of the corner portions53to the other corner portion53along the gas diffusion layer16.

The restricting portion70is in contact with the gas diffusion layer16over the entire area in the third direction Z. That is, the gaps between the corner portions53and the gas diffusion layer16in the first direction X are filled with the restricting portion70. In the present embodiment, the restricting portion70is provided over the entire length of the groove passage37A in the second direction Y.

The restricting portions70are configured to restrict the gas diffusion layer16from sinking into the groove passages37A.

As shown inFIG.2, the restricting portions80, which are conductive porous bodies, are provided at sections of the corner portions63that face the groove passages47A.

Each restricting portion80is provided on both corner portions63at the opposite sides of the corresponding groove passage47A. The restricting portion80continuously extends in the third direction Z from one of the corner portions63to the other corner portion63along the gas diffusion layer17.

The restricting portion80is in contact with the gas diffusion layer17over the entire area in the third direction Z. That is, the gaps between the corner portions63and the gas diffusion layer17in the first direction X are filled with the restricting portion80. In the present embodiment, the restricting portion80is provided over the entire length of the groove passage47A in the second direction Y.

The restricting portions70,80are, for example, porous bodies made of particulate or fibrous conductive members and a resin that binds the conductive members together.

Examples of the material for particulate conductive members include a metal such as gold (Au), platinum (Pt), titanium (Ti), titanium nitride (TiN), copper (Cu), and cobalt (Co); a compound containing any of these metals; and carbon powder such as graphene or graphite.

Examples of the material for fibrous conductive members include carbon fibers such as carbon nanotubes and graphite nanofibers.

Examples of the resin include thermoplastic resins such as polyethylene (PE), polypropylene (PP), polystyrene (PS), polyamide (PA), polycarbonate (PC), polyphenylene ether (PPE), polyethylene terephthalate (PET), polyethylene naphthalate (PEN), polyethersulfone (PES), polyphenylene sulfide (PPS), polyphenylsulfone (PPSU), polyetherether ketone (PEEK), polyimide (PI), liquid crystal polymer (LCP), and cycloolefin polymer (COP); thermosetting resins such as epoxy resin; polymer alloys obtained by combining any of the above-listed resins; and fluoropolymers such as polytetrafluoroethylene (PTFE), perfluoroethylene propylene copolymer (FEP), perfluoroalkoxy alkane (PFA), ethylene tetrafluoroethylene copolymer (ETFE), and polyvinylidene fluoride (PVDF). In place of the resins described above, a rubber such as ethylene propylene diene rubber (EPDM), fluorine rubber, or silicone rubber may be used.

The porosity of the restricting portions70,80is preferably greater than or equal to the porosity of the gas diffusion layers16,17. In addition, the porosity of the restricting portions70,80is more preferably greater than or equal to the porosity of the gas diffusion layers16,17within a range greater than or equal to 70%. The porosity of the restricting portions70,80is further more preferably set to be greater than or equal to the porosity of the gas diffusion layers16,17within a range greater than or equal to 70% and less than or equal to 80%. In the present embodiment, the porosity of the restricting portions70,80and the porosity of the gas diffusion layers16,17are all set to 70%.

A measurement L of the restricting portions70,80in the first direction X is set to be within a range of 30 µm to 150 µm.

Operation of the present embodiment will now be described.

As shown inFIG.2, when multiple single cells90are stacked with the separators30facing downward in the vertical direction, the restricting portions70restrict the gas diffusion layers16from sinking into the groove passages37A. In the configuration of the present embodiment, the gaps between the corner portions53and the gas diffusion layer16in the first direction X are filled with the restricting portions70. Therefore, the gas diffusion layer16applies load on the corner portions53of the separator30via the restricting portions70. The gaps between the corner portions63and the gas diffusion layer17in the first direction X are filled with the restricting portions80. Therefore, the corner portions63of the separator40apply load to the gas diffusion layer17via the restricting portions80. This configuration reduces, the contact resistance between the separator30and the gas diffusion layer16and the contact resistance between the separator40and the gas diffusion layer17.

The restricting portions70,80are conductive porous bodies. Some of the fuel gas flowing through the groove passages37A thus passes through the inside of the restricting portions70and is diffused into the gas diffusion layer16. Also, some of the oxidant gas flowing through the groove passages47A passes through the inside of the restricting portions80and is diffused into the gas diffusion layer17.

The present embodiment has the following advantages.

(1) The separator30includes the facing surface30a, which faces the power generating unit10. The facing surface30aincludes the ribs37C. Each of the ribs37C is located between two of the groove passages37A, through which fuel gas flows, and protrudes toward the gas diffusion layer16of the power generating unit10. Each of the ribs37C includes a top wall portion51, two side wall portions52, and corner portions53. The top wall portion51is in contact with the gas diffusion layer16of the power generating unit10. The side wall portions52are located at the opposite sides of the top wall portion51in the third direction Z. Each corner portion53is located between the top wall portion51and one of the side wall portions52. A restricting portion70is provided at sections of the corner portions53that face the groove passage37A. The restricting portion70restricts the gas diffusion layer16from sinking into the groove passage37A. The restricting portion70is a conductive porous body.

The above-described configuration operates in the above-described manner. The configuration thus restricts the gas diffusion layer16from sinking into the groove passages37A, while maintaining the diffusivity of fuel gas.

(2) Each restricting portion70is provided over the entire length of the corresponding groove passage37A in the second direction Y.

This configuration restricts the gas diffusion layer16from sinking into the groove passages37A over the entire groove passages37A in the extending direction, while maintaining the diffusivity of the fuel gas.

(3) The porosity of the restricting portions70,80is greater than or equal to the porosity of the gas diffusion layers16,17.

If the porosity of the restricting portions70(80) is lower than the porosity of the gas diffusion layers16,17, the restricting portion70(80) may become an obstacle when the fuel gas (oxidant gas) flowing through the groove passages37A (47A) is diffused into the gas diffusion layer16(17). This may reduce the diffusivity of fuel gas (oxidizing gas).

In this regard, with the above-described configuration, the porosity of the restricting portion70(80) is greater than or equal to the porosity of the gas diffusion layer16(17). Thus, some of the fuel gas (oxidant gas) flowing through the groove passages37A (47A) easily passes through the inside of the restricting portion70(80). This prevents the above-described disadvantages from occurring.

(4) The restricting portions70,80each include particulate or fibrous conductive members and a resin that binds the conductive members together.

With this configuration, the regulating portions70,80are formed easily.

Modifications

The shapes of the inlet manifolds91,93,95and the outlet manifolds92,94,96are not limited to rectangular shapes in plan view as in the above-described embodiments. For example, the shapes of the manifolds91,92,93,94,95,96may be a quadrangular shape including a square in plan view, or may be a polygonal shape including a triangle and a pentagon in plan view. The shapes may be circular shapes in plan view such as an oval and a stadium shape.

The flows of the reactant gas and the cooling medium through the manifolds91,92,93,94,95,96are not limited to those described in the above-described embodiment. For example, the manifold96may be used as an inlet manifold for the oxidant gas, and the manifold95may be used as an outlet manifold for the oxidant gas. Accordingly, the manifold94may be used as an inlet manifold for the cooling medium, and the manifold93may be used as an outlet manifold for the cooling medium. That is, the oxidant gas that flows through the groove passages47A and the cooling medium that flows through the groove passages38A,48A may flow in the same direction as the fuel gas flowing through the groove passages37A.

The groove passages37A (38A) are not limited to extending linearly in the second direction Y as in the above-described embodiment. For example, the groove passages37A (38A) may extend in wavy shapes in a planar direction of the facing surface30a(the opposite surface30b). In this case, the ribs37C (ribs38C) extend in wavy shapes in a planar direction of the facing surface30a(opposite surface30b).

The groove passages47A (48A) are not limited to extending linearly in the second direction Y as in the above-described embodiment. For example, the groove passages47A (48A) may extend in wavy shapes in a planar direction of the facing surface40a(the opposite surface40b). In this case, the ribs47C (the rib48C) extend in wavy shapes in a planar direction of the facing surface40a(the opposite surface40b).

The shape of the ribs37C is not limited to the one described in the above-described embodiment. For example, the side wall portions52are not limited to being inclined as in the above-described embodiment, but may be orthogonal to the top wall portion51. Also, the corner portions53are not limited to being curved as in the above-described embodiment, but may be provided between the top wall portion51and the side wall portions52bent and extending from the top wall portion51.

The shape of the ribs47C is not limited to the one described in the above-described embodiment. For example, the side wall portions62are not limited to being inclined as in the above-described embodiment, but may be orthogonal to the top wall portion61. Also, the corner portions63are not limited to being curved as in the above-described embodiment, but may be provided between the top wall portion61and the side wall portions62bent and extending from the top wall portion61.

The restricting portions70,80do not necessarily include a resin that binds conductive members together as in the above-described embodiment. For example, the restricting portions70,80may be made of only conductive members.

Each restricting portion70does not necessarily need to continuously extend in the third direction Z from one of the two corner portions53, which are arranged at the opposite sides of the corresponding groove passage37A, to the other corner portion53along the gas diffusion layer16as in the above-described embodiment. For example, the restricting portion70may be provided only at the corner portions53. Specifically, as shown inFIG.3, the restricting portion70may be split into two sections in each groove passage37A and located between the groove passage37A and the gas diffusion layer16. The sections of the restricting portion70are provided at the corner portions53while being spaced apart from each other in the third direction Z.

This configuration reduces the material for the restricting portions70.

Each restricting portion80does not necessarily need to continuously extend in the third direction Z from one of the two corner portions63, which are arranged at the opposite sides of the corresponding groove passage47A, to the other corner portion63along the gas diffusion layer17as in the above-described embodiment. For example, the restricting portion80may be provided only at the corner portions63. Specifically, as shown inFIG.3, the restricting portion80may be split into two sections in each groove passage47A and located between the groove passage47A and the gas diffusion layer17. The sections of the restricting portion70are provided at the corner portions63while being spaced apart from each other in the third direction Z.

This configuration reduces the material for the restricting portions80.

The porosity of the restricting portions70,80is not limited to 70% as in the above-described embodiment, but may be changed as long as the porosity is greater than or equal to the porosity of the gas diffusion layers16,17. In addition, the porosity of the restricting portions70,80may be less than the porosity of the gas diffusion layers16,17as long as the porosity of the restricting portions70,80is within a range in which the advantages of the above-described embodiment are achieved.

Each restricting portion70does not necessarily need to be provided over the entire length of the corresponding groove passage37A in the second direction Y. Instead, the restricting portion70may be split into two or more sections that are spaced apart from each other in the second direction Y.

Each restricting portion80does not necessarily need to be provided over the entire length of the corresponding groove passage47A in the second direction Y. Instead, the restricting portion80may be split into two or more sections that are spaced apart from each other in the second direction Y.

The single cells90do not necessarily need to be stacked with the separators30facing downward in the vertical direction as in the above-described embodiment, but may be stacked with the separators40facing downward in the vertical direction.

With this configuration, the restricting portions80prevent the gas diffusion layer17from sinking into the groove passages47A. In this case, since the restricting portions80are conductive porous bodies, some of the oxidant gas flowing through the groove passages47A passes through the inside of the restricting portions80and is diffused into the gas diffusion layer17. The configuration thus restricts the gas diffusion layer17from sinking into the groove passages47A, while maintaining the diffusivity of oxidant gas.

The separators30,40do not necessarily need to be formed by pressing metal plates, but may be formed by cutting or etching.

The material for the separators30,40is not limited to titanium or stainless steel, but may be aluminum. Also, a material other than metal such as carbon may be used.