FUEL CELL STACK

A fuel cell stack includes single cells stacked in a first direction. Each single cell includes a power generating unit, a first separator, and a second separator. The first separator and the second separator hold the power generating unit between the first separator and the second separator. The first separator of each single cell includes first protrusions that protrude toward the second separator of another single cell that is adjacent in the first direction. The first protrusions are in contact with the second separator. Each of the first protrusions includes a top wall portion and two side wall portions. At least one of the two side wall portions includes a step portion having a shape of a step in the first direction.

BACKGROUND

The present disclosure relates to a fuel cell stack.

2. Description of Related Art

Japanese National Phase Laid-Open Patent Publication No. 2020-522089 discloses a fuel cell stack. The fuel cell stack includes multiple single cells stacked together. Each single cell includes two separators. A membrane electrode assembly and two gas diffusion layers, which sandwich the membrane electrode assembly in the stacking direction of the single cells, are disposed between the two separators.

Each separator includes a facing surface, which faces a gas diffusion layer. The facing surface has groove-shaped passages for conducting a reaction medium. Each separator includes groove-shaped passages in an opposite surface located on a side opposite to the facing surface. The passages in the opposite surfaces of single cells adjacent to each other form cavities between the separators. The cavities conduct a cooling medium.

Each separator includes a protruding bead and a recess portion on the facing surface. The recess portion is disposed between the bead and a passage.

The bead is provided over the entire periphery of the passages.

The bottom walls of the recess portions formed in the respective separators are in contact with each other (refer to FIG. 6A of Japanese National Phase Laid-Open Patent Publication No. 2020-522089).

In the fuel cell stack including such separators, the recess portions in contact with each other prevent the cooling medium flowing through the cavity from flowing toward the bead. That is, the recess portions prevent the so-called side flows.

In such a fuel cell stack, the depths of the recess portions of the separators vary. That is, the recess portions include relatively deep ones and relatively shallow ones. A gap is likely to be created between the bottom walls of relatively shallow recess portions. As a result, cooling medium that flows sideways from the cavity leaks out through the gap, reducing the side flow limiting effect of the recess portions. This may reduce the cooling efficiency of the cooling medium and thus reduce the power generation efficiency of the fuel cell.

SUMMARY

Accordingly, it is an objective of the present disclosure to provide a fuel cell stack capable of limiting side flows of a cooling medium.

In one general aspect, a fuel cell stack including single cells stacked in a first direction is provided. Each single cell includes a power generating unit, a first separator, and a second separator. The first separator and the second separator hold the power generating unit between the first separator and the second separator. The first separator and the second separator each include a facing surface that faces the power generating unit, and an opposite surface that is located on a side opposite to the facing surface. The opposite surface of the first separator and the opposite surface of the second separator are each provided with groove passages that extend in a second direction, a cooling medium flowing through the groove passages. The first separator of each single cell includes first protrusions that protrude toward the second separator of another single cell that is adjacent in the first direction. The first protrusions are in contact with the second separator. The groove passages include groove passages that are located at outermost positions in a third direction. The third direction intersect with both of the first direction and the second direction. The first protrusions are provided on an outer side of at least one of the groove passages that are located at the outermost positions in the third direction. The first protrusions are arranged side by side in the second direction. Each of the first protrusions includes a top wall portion and two side wall portions located on opposite sides of the top wall portion in the second direction. At least one of the two side wall portions includes a step portion having a shape of a step in the first direction.

DETAILED DESCRIPTION

Fuel cell stacks according to respective embodiments will now be described with reference toFIGS.1to4. 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.

First Embodiment

First the fuel cell stack according to the first embodiment will be described with reference toFIGS.1to3.

As shown inFIGS.1and2, the fuel cell stack is formed by stacking multiple single cells90each having a rectangular plate-shape as a whole.

In the following description, the direction in which the single cells90are stacked will be referred to as a first direction X. 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 or 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 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 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).

The single cell90includes a membrane electrode assembly10(hereinafter, referred to as MEA10), a frame member20, which holds the MEA10, a first separator30, and a second separator40. The separators30,40hold the MEA10and the frame member20between them.

Each component will now be described.

As shown inFIG.1, the MEA10includes a solid polymer electrolyte membrane (not shown; hereinafter referred to as an electrolyte membrane) and electrodes11,12respectively provided on opposite surfaces of the electrolyte membrane. In the present embodiment, the electrode that is joined to a first side in the first direction X (the upper side in the up-down direction inFIG.1) of the electrolyte membrane is a cathode11. Also, the electrode joined to a second side in the first direction X (the lower side in the inFIG.1) of the electrolyte membrane is an anode12.

The electrodes11,12each include a catalyst layer (not shown) joined to the electrolyte membrane and a gas diffusion layer (not shown), which is joined to the catalyst layer.

The MEA10corresponds to a power generating unit of the fuel cell according to the present disclosure.

As shown inFIGS.1and2, 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 respective parts of the manifolds91,92,93,94,95,96.

The frame member20includes an opening27in a center. The MEA10is joined to the peripheral edge of the opening27from the first side in the first direction X (upper side as viewed inFIG.1).

As shown inFIGS.1and2, the first 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 first separator30includes through-holes31,32,33,34,35,36, which are respective parts of the manifolds91,92,93,94,95,96.

The first separator30includes a first surface30A and a second surface30B. The first surface30A includes a facing surface30a, which faces the anode12of the MEA10in 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. InFIG.1, the groove passages37A and the connecting portions37B are illustrated in a simplified manner.

The groove passages37A are provided in the facing surface30a. Each of the groove passages37A extends linearly in the second direction Y (refer toFIG.1). The groove passages37A are arranged side by side in the third direction Z while being spaced apart from each other (refer toFIG.2).

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 first protrusions50. InFIG.1, the groove passages38A and the connecting portions38B are illustrated in a simplified manner. InFIGS.1and2, the first protrusions50are illustrated in a simplified manner.

The groove passages38A are provided in the opposite surface30b. Each of the groove passages38A extends linearly in the second direction Y (refer toFIG.1). The groove passages38A are arranged side by side in the third direction Z while being spaced apart from each other (refer toFIG.2).

As shown inFIG.2, each groove passage37A is formed by the back side of the protrusion positioned between two groove passages38A adjacent to each other in the third direction Z. Also, each groove passage38A is formed by the back side of the protrusion positioned between two groove passages37A adjacent to each other in the third direction Z.

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 first protrusions50are provided on the outer sides of two outer-side groove passages38a, which are the outermost groove passages38A in the third direction Z. In the present embodiment, the first protrusions50are provided on the outer sides of the respective outer-side groove passages38a(refer toFIG.1). The outer side in the third direction Z refers to a side away from the center of the single cell90in the third direction Z.FIG.2illustrates the outer-side groove passage38alocated on the first side in the third direction Z (the back side of the sheet ofFIG.1) of the two outer-side groove passages38aand the first protrusions50located on the outer side of that outer-side groove passage38a.

The first protrusions50protrude from each single cell90toward the second separator40of another single cell90that is adjacent in the first direction X (seeFIG.2).

The first protrusions50extend in the third direction Z.

As shown inFIG.1, the first protrusions50are arranged side by side in the second direction Y while being spaced apart from each other. The first protrusions50are provided over the entire range in which the outer-side groove passage38ais formed in the second direction Y.

As shown inFIG.3, each of the first protrusions50includes a first top wall portion51and two first side wall portions52located on opposite sides of the first top wall portion51in the second direction Y.

The first top wall portions51of each single cell90are in contact with the second surface40B of the second separator40of another single cell90that is adjacent in the first direction X.

Each first side wall portion52includes a first step portion53having the shape of a step in the first direction X. In the present embodiment, the two first side wall portions52each include a first step portion53.

The first step portion53is located at a center of the first side wall portion52in the first direction X. Each first side wall portion52includes a portion located closer to the first top wall portion51than the first step portion53in the first direction X (hereinafter, referred to as a distal portion52a), and a portion located closer to the proximal end of the first protrusion50than the first step portion53in the first direction X (hereinafter, referred to as a proximal portion52b).

The distal portion52ais located closer to the center of the first protrusion50than the proximal portion52bin the second direction Y.

As shown inFIGS.1and2, the second 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 second separator40includes through-holes41,42,43,44,45,46, which are respective parts of the manifolds91,92,93,94,95,96.

The second separator40includes a first surface40A and a second surface40B. The first surface40A includes a facing surface40a, which faces the cathode11of the MEA10in 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. InFIG.1, the groove passages47A and the connecting portions47B are illustrated in a simplified manner.

The groove passages47A are provided in the facing surface40a. Each of the groove passages47A extends linearly in the second direction Y (refer toFIG.1). The groove passages47A are arranged side by side in the third direction Z while being spaced apart from each other (refer toFIG.2).

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. InFIG.1, the groove passages48A and the connecting portions48B are illustrated in a simplified manner.

The groove passages48A are provided in the opposite surface40b. Each of the groove passages48A extends linearly in the second direction Y (refer toFIG.1). The groove passages48A are arranged side by side in the third direction Z while being spaced apart from each other (refer toFIG.2).

The groove passages48A include two outer-side groove passages48a, which are the outermost groove passages48A in the third direction Z.

As shown inFIG.2, each groove passage47A is formed by the back side of the protrusion positioned between two groove passages48A adjacent to each other in the third direction Z. Also, each groove passage48A is formed by the back side of the protrusion positioned between two groove passages47A adjacent to each other in the third direction Z.

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, a gasket70is provided on the outer side of the first protrusions50in the third direction Z. The gasket70provides a seal between the separator30of the single cell90and the second separator40of another single cell90that is adjacent in the first direction X. The first protrusions50are configured to partially fill a space S formed between the gasket70and the outer-side groove passages38a,48ain the third direction Z.

Operation of the first embodiment will now be described.

The fuel cell stack includes the single cells90, which are fastened together in the first direction X. If the length of the first protrusions50in the first direction X varies, that is, if the height H (seeFIG.3) of the first protrusions50varies, the first protrusions50include relatively high ones and relatively low ones. A gap is likely to be created between a relatively low first protrusion50of each single cell90and the second separator40of another single cell90that is adjacent in the first direction X.

In this regard, when the first protrusions50are pressed against the second separator40in the present embodiment, the first step portions53of the first side wall portions52of a relatively high first protrusion50are smoothly deformed to bend in the first direction X. As a result, the height H of the relatively high first protrusions50is reduced. Therefore, a gap is unlikely to be formed between a relatively low first protrusion50and the second separator40. Accordingly, the cooling medium is unlikely to flow to the outside of the first protrusions50through gaps. This limits side flows of the cooling medium.

The first embodiment has the following advantages.

(1-1) The first separator30of each single cell90includes the multiple first protrusions50. The first protrusions50protrude toward the second separator40of another single cell90that is adjacent in the first direction X, and abut the second separator40. The first protrusions50are provided on the outer sides of two of the outer-side groove passages38a, which are located on the outermost positions in the third direction Z. The first protrusions50are arranged side by side in the second direction Y. Each of the first protrusions50includes a first top wall portion51and two first side wall portions52located on opposite sides of the first top wall portion51in the second direction Y. The two first side wall portion52each include a first step portion53having the shape of a step in the first direction X.

This configuration operates in the above-described manner. This limits side flows of the cooling medium.

(1-2) The first protrusions50are provided over the entire range in which the outer-side groove passage38ais formed in the second direction Y.

With this configuration, the above-described advantage is achieved over the entire range in which the outer-side groove passages38aare formed in the second direction Y. Accordingly, side flows of the cooling medium are further limited.

Second Embodiment

A fuel cell stack according to the second embodiment will now be described with reference toFIGS.1and4. Differences from the first embodiment will mainly be discussed. The same reference numerals are given to those components of the fuel cell stack according to the second embodiment that are the same as or equivalent to the corresponding components of the fuel cell stack according to the first embodiment, and redundant explanations are omitted.

As shown inFIGS.1and4, the second separator40includes second protrusions60, which respectively protrude toward the first protrusions50in the first direction X.

The second protrusions60represented by the long-dash double-short-dash lines inFIG.1are provided on the outer sides of the two outer-side groove passages48a. In the present embodiment, the second protrusions60are provided on the outer sides of the respective outer-side groove passages48a.

The second protrusions60extend in the third direction Z.

The second protrusions60are arranged side by side in the second direction Y while being spaced apart from each other. The second protrusions60are provided over the entire range in which the outer-side groove passage48ais formed in the second direction Y. In the present embodiment, the second protrusions60are provided at positions each corresponding to one of the first protrusions50in the first direction X.

As shown inFIG.4, each of the second protrusions60includes a second top wall portion61and two second side wall portions62located on opposite sides of the second top wall portion61in the second direction Y.

The second top wall portion61is in contact with the first top wall portion51of the corresponding first protrusions50.

Each second side wall portion62includes a second step portion63having the shape of a step in the first direction X. In the present embodiment, the two second side wall portions62each include a second step portion63.

The second step portion63is located at a center of the second side wall portion62in the first direction X. Each second side wall portion62includes a portion located closer to the second top wall portion61than the second step portion63(hereinafter, referred to as a distal portion62a), and a portion located closer to the proximal end of the second protrusion60than the second step portion63in the first direction X (hereinafter, referred to as a proximal portion62b).

The distal portion62ais located closer to the center of the second protrusion60than the proximal portion62bin the second direction Y.

Operation of the second embodiment will now be described.

When the first protrusions50are pressed against the second protrusions60, the first step portions53of the first side wall portions52of relatively high first protrusions50and the second step portions63of the second side wall portions62of relatively high second protrusions60are smoothly deformed to bend in the first direction X.

The second embodiment has the following advantages.

(2-1) The second separator40of each single cell90includes multiple second protrusions60, which abut the first protrusions50of another single cell90that is adjacent. The second protrusions60each protrude toward the first protrusions50in the first direction X.

With this configuration, the height H of the first protrusions50can be reduced as compared with a case in which the second separator40does not include the second protrusions60(seeFIGS.3and4). Therefore, the first protrusions50are formed easily. Accordingly, the first separator30is manufactured easily.

(2-2) Each of the second protrusions60includes a second top wall portion61and two second side wall portions62located on opposite sides of the second top wall portion61in the second direction Y. The two second side wall portions62each include the second step portion63having the shape of a step in the first direction X.

This configuration operates in the above-described manner. Accordingly, it is possible to prevent the formation of a gap between the first protrusion50and the second protrusion60while limiting the amount of bending deformation of both the first step portions53of the first side wall portions52of the first protrusion50and the second step portions63of the second side wall portions62of the second protrusion60.

(2-3) The second protrusions60are provided over the entire range in which the outer-side groove passage48ais formed in the second direction Y.

With this configuration, the above-described advantage is achieved over the entire range in which the outer-side groove passages48aare formed in the second direction Y. This further limits side flows of the cooling medium.

The above-described embodiments may be modified as follows. The above-described embodiments and the following modifications can be combined as long as the combined modifications remain technically consistent with each other.

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, but may be stadium shapes in plan view, for example.

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 embodiments. 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 embodiments. For example, the groove passages37A (38A) may extend in wavy shapes in a planar direction of the facing surface30a(the opposite surface30b).

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

The shape of the first protrusions50is not limited to the one described in the above-described embodiments. For example, each first side wall portion52may be provided with two or more first step portions53. In addition, the first protrusion50is not limited to the configuration in which the first step portion53is provided on each of the two first side wall portions52. The first step portion53may be provided on only one of the first side wall portions52.

The shape of the second protrusions60is not limited to the one described in the second embodiment. For example, each second side wall portion62may be provided with two or more second step portions63. In addition, the second protrusion60is not limited to the configuration in which the second step portion63is provided on each of the two second side wall portions62. The second step portion63may be provided on only one of the second side wall portions62.

The second step portions63may be omitted from the second protrusions60.

The first protrusions50do not necessarily need to be provided on the outer sides of the respective outer-side groove passages38aas in the above-described embodiments. The first protrusions50may be provided on the outer side of one of the outer-side groove passages38a. In this case, the second protrusions60are not limited to being provided on the outer sides of both of the outer-side groove passages48a, and the arrangement thereof may be changed in accordance with the first protrusions50.

The fuel cell stack is not limited to the one in which one second protrusion60is provided at a position corresponding to each of the first protrusions50in the first direction X as described in the second embodiment. Some of the second protrusions60may be omitted. In this case, the separator30includes first protrusions50that do not face the second protrusions60in the first direction X. The first protrusions50that do not face the second protrusions60may be any protrusion as long as they are in contact with the second surfaces40B of the separator40.

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 or carbon.

The first separator according to the present disclosure is not limited to an anode-side separator as in the above-described embodiments, but may be used as a cathode-side separator. In this case, the second separator according to the present disclosure is used as an anode-side separator.