Fuel cell stack

A fuel cell stack includes a plurality of power generation units, a reactant gas channel, and a coolant channel. The plurality of power generation units are stacked in a stacking direction to provide a stacked body and each includes a first separator, a first electrolyte electrode assembly, a second separator, a second electrolyte electrode assembly, and a third separator. The first electrolyte electrode assembly is provided on the first separator. The second separator is provided on the first electrolyte electrode assembly. The second electrolyte electrode assembly is provided on the second separator. The first electrolyte electrode assembly and the second electrolyte electrode assembly each include an electrolyte and a pair of electrodes sandwiching the electrolyte therebetween. The third separator is provided on the second electrolyte electrode assembly.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application claims priority under 35 U.S.C. § 119 to Japanese Patent Application No. 2013-028888, filed Feb. 18, 2013, entitled “Fuel Cell Stack.” The contents of this application are incorporated herein by reference in their entirety.

BACKGROUND

The present disclosure relates to a fuel cell stack.

2. Description of the Related Art

For example, a solid polymer electrolyte fuel cell includes a membrane electrode assembly (MEA) and a pair of separators sandwiching the MEA therebetween. The MEA includes an electrolyte membrane, which is made from a solid polymer ion-exchange membrane, an anode separator disposed on one side of the electrolyte membrane, and a cathode electrode disposed on the other side of the electrolyte membrane. Usually, a plurality of fuel cells are stacked so as to form a fuel cell stack. The fuel cell stack is, for example, mounted on a fuel-cell electric vehicle and used as an automobile fuel cell system.

A fuel cell stack includes a stacked body in which a plurality of fuel cells are stacked; and a terminal plate, an insulator, and an end plate that are stacked at each end of the stacked body in the stacking direction. For example, Japanese Patent No. 4727972 describes a fuel cell stack in which a so-called dummy cell is disposed on at least one end portion of a stacked body in the stacking direction. The dummy cell, which has the same structure as a fuel cell, is disposed between the stacked body and a terminal plate. The dummy cell includes a metal plate instead of an electrolyte membrane and does not generate water because the dummy cell does not generate electric power. Therefore, the dummy cell functions as a heat insulating layer.

A type of fuel cell stack having a skip cooling structure is known. The fuel cell stack includes a plurality of power generation units each including a first separator, a first electrolyte electrode assembly, a second separator, a second electrolyte electrode assembly, and a third separator that are stacked in this order; and a coolant channel through which a coolant flows is only formed in each of spaces between the power generation units.

In the fuel cell stack having a skip cooling structure, the cooling conditions of the first electrolyte electrode assembly and the second electrolyte electrode assembly that are disposed at ends in the stacking direction differ from those of the first electrolyte electrode assembly and the second electrolyte electrode assembly that are disposed in a central portion in the stacking direction. Therefore, the dummy cells, which function as heat insulating layers, are disposed at ends, in the stacking direction, of the fuel cell stack having a skip cooling structure.

SUMMARY

According to one aspect of the present invention, a fuel cell stack includes a plurality of power generation units, a reactant gas channel, and a coolant channel. The plurality of power generation units are stacked in a stacking direction to provide a stacked body and each includes a first separator, a first electrolyte electrode assembly, a second separator, a second electrolyte electrode assembly, and a third separator. The first electrolyte electrode assembly is provided on the first separator. The second separator is provided on the first electrolyte electrode assembly. The second electrolyte electrode assembly is provided on the second separator. The first electrolyte electrode assembly and the second electrolyte electrode assembly each include an electrolyte and a pair of electrodes sandwiching the electrolyte therebetween. The third separator is provided on the second electrolyte electrode assembly. The reactant gas channel through which a reactant gas is to flow along a power generation surface is provided between the first separator and the first electrolyte electrode assembly, between the first electrolyte electrode assembly and the second separator, between the second separator and the second electrolyte electrode assembly, and between the second electrolyte electrode assembly and the third separator. The coolant channel is provided between the plurality of power generation units and through which a coolant is to flow. The stacked body has the second separators at one end and at another end opposite to the one end of the stacked body in the stacking direction, respectively.

DESCRIPTION OF THE EMBODIMENTS

As illustrated inFIGS. 1 and 2, a fuel cell stack10according to a first embodiment the present disclosure includes a stacked body13in which a plurality of power generation units12in upright positions are stacked in a horizontal direction (direction of arrow A).

At one end of the stacked body13in the stacking direction (direction of arrow A), a terminal plate100a, an insulator (insulation plate)102a, and an end plate104aare stacked outward in this order. At the other end of the stacked body13in the stacking direction, a terminal plate100b, an insulator (insulation plate)102b, and an end plate104bare stacked outward in this order.

For example, the fuel cell stack10is held in a box casing (not shown) having the end plates104aand104b, which are rectangular, as its end plates. Alternatively, the fuel cell stack10is integrally fastened by using a plurality of tie rods (not shown) extending in the direction of arrow A.

As illustrated inFIGS. 2 to 5, each of the power generation units12includes a first metal separator14, a first membrane electrode assembly16a, a second metal separator18, a second membrane electrode assembly16b, and a third metal separator20. The first metal separator14, the first membrane electrode assembly16a, the second metal separator18, the second membrane electrode assembly16b, and the third metal separator20are stacked in a horizontal direction. Electrode surfaces of the first and second membrane electrode assemblies16aand16bare in vertical positions and have horizontally-elongated shapes.

The first metal separator14, the second metal separator18, and the third metal separator20are each made from a horizontally-elongated metal plate, such as a steel plate, a stainless steel plate, an aluminum plate, a galvanized steel plate, or any of such thin metal plates having an anti-corrosive coating on the surface thereof. The first metal separator14, the second metal separator18, and the third metal separator20, which have rectangular shapes in plan view, are formed by press-forming thin metal plates so as to have corrugated cross-sectional shapes. Instead of the metal separators, carbon separators may be used.

As illustrated inFIG. 3, an oxidant gas inlet manifold22aand a fuel gas outlet manifold24bare formed in the power generation unit12so as to extend in the direction of arrow A through one end portion of the power generation unit12in the longitudinal direction (direction of arrow B), that is, one end portion of each of the first metal separator14, the second metal separator18, and the third metal separator20in the longitudinal direction. An oxidant gas, such as an oxygen-containing gas, is supplied through the oxidant gas inlet manifold22a. A fuel gas, such as a hydrogen-containing gas, is discharged through the fuel gas outlet manifold24b.

A fuel gas inlet manifold24aand an oxidant gas outlet manifold22bare formed in the power generation unit12so as to extend in the direction of arrow A through the other end portion of the power generation unit12in the longitudinal direction (direction of arrow B). The fuel gas is supplied through the fuel gas inlet manifold24a. The oxidant gas is discharged through the oxidant gas outlet manifold22b.

A pair of coolant inlet manifolds25aare formed in the power generation unit12so as to extend in the direction of arrow A through end portions of the power generation unit12in the transversal direction (direction of arrow C) near the oxidant gas inlet manifold22a. A coolant is supplied through the pair of coolant inlet manifolds25a. A pair of coolant outlet manifolds25bare formed in the power generation unit12so as to extend in the direction of arrow A through end portions of the power generation unit12in the transversal direction near the fuel gas inlet manifold24a. The coolant is discharged through the pair of coolant outlet manifolds25b.

As illustrated inFIG. 6, a first oxidant gas channel26, through which the oxidant gas inlet manifold22ais connected to the oxidant gas outlet manifold22b, is formed on a surface14aof the first metal separator14facing the first membrane electrode assembly16a.

The first oxidant gas channel26includes a plurality of wave-shaped channel grooves (or linear channel grooves)26aextending in the direction of arrow B. An inlet embossed portion28aand an outlet embossed portion28bare respectively disposed near an inlet and outlet of the first oxidant gas channel26. The inlet and outlet embossed portions28aand28beach have a plurality of column-shaped protrusions protruding toward the first membrane electrode assembly16a.

A plurality of inlet connection grooves30a, which constitute a bridge portion, are formed between the inlet embossed portion28aand the oxidant gas inlet manifold22a. A plurality of outlet connection grooves30b, which constitute a bridge portion, are formed between the outlet embossed portion28band the oxidant gas outlet manifold22b.

As illustrated inFIG. 3, a coolant channel38, through which the coolant inlet manifolds25aare connected to the coolant outlet manifolds25b, is formed on a surface14bof the first metal separator14. The coolant channel38is formed between the back side of the first oxidant gas channel26and the back side of a second fuel gas channel58(described below).

A first fuel gas channel40, through which the fuel gas inlet manifold24ais connected to the fuel gas outlet manifold24b, is formed on a surface18aof the second metal separator18facing the first membrane electrode assembly16a. The first fuel gas channel40includes a plurality of wave-shaped channel grooves (or linear channel grooves)40aextending in the direction of arrow B. A plurality of supply holes42aare formed near the fuel gas inlet manifold24a. A plurality of discharge holes42bare formed near the fuel gas outlet manifold24b.

As illustrated inFIG. 7, a second oxidant gas channel50, through which the oxidant gas inlet manifold22ais connected to the oxidant gas outlet manifold22b, is formed on a surface18bof the second metal separator18facing the second membrane electrode assembly16b. The second oxidant gas channel50includes a plurality of wave-shaped channel grooves (or linear channel grooves)50aextending in the direction of arrow B. A plurality of inlet connection grooves52aare formed near the oxidant gas inlet manifold22a. A plurality of outlet connection grooves52bare formed near the oxidant gas outlet manifold22b.

As illustrated inFIG. 3, the second fuel gas channel58, through which the fuel gas inlet manifold24ais connected to the fuel gas outlet manifold24b, is formed on a surface20aof the third metal separator20facing the second membrane electrode assembly16b. The second fuel gas channel58includes a plurality of wave-shaped channel grooves (or linear channel grooves)58aextending in the direction of arrow B.

A plurality of supply holes60aare formed near the fuel gas inlet manifold24a. A plurality of discharge holes60bare formed near the fuel gas outlet manifold24b. As illustrated inFIGS. 3 and 4, the supply holes60aare disposed inward from the supply holes42aof the second metal separator18(nearer to the fuel gas channel). The discharge holes60bare disposed inward from the discharge holes42bof the second metal separator18(nearer to the fuel gas channel).

A part of the coolant channel38is formed on a surface20bof the third metal separator20, which is the back side of the second fuel gas channel58. The coolant channel38is formed between the surface20bof the third metal separator20and the surface14bof the first metal separator14that is disposed adjacent to the third metal separator20.

A first sealing member68is integrally formed on the surfaces14aand14bof the first metal separator14so as to surround the outer periphery of the first metal separator14. A second sealing member70is integrally formed on the surfaces18aand18bof the second metal separator18so as to surround the outer periphery of the second metal separator18. A third sealing member72is integrally formed on the surfaces20aand20bof the third metal separator20so as to surround the outer periphery of the third metal separator20.

Each of the first sealing member68, the second sealing member70, and the third sealing member72is made from an elastic material such as a sealing material, a cushioning material, or a packing material. Examples of such materials include EPDM, NBR, fluorocarbon rubber, silicone rubber, fluorosilicone rubber, butyl rubber, natural rubber, styrene rubber, chloroprene-rubber, and acrylic rubber.

As illustrated inFIG. 6, the first sealing member68includes a first protruding sealing portion68aon the surface14aof the first metal separator14. The first protruding sealing portion68aconnects the outer peripheries of the oxidant gas inlet manifold22a, the oxidant gas outlet manifold22b, and the first oxidant gas channel26. As illustrated inFIG. 3, the first sealing member68includes a second protruding sealing portion68bon the surface14bof the first metal separator14. The second protruding sealing portion68bconnects the outer peripheries of the coolant inlet manifolds25a, the coolant outlet manifolds25b, and the coolant channel38.

As illustrated inFIG. 3, the second sealing member70includes a first protruding sealing portion70aon the surface18aof the second metal separator18. The first protruding sealing portion70asurrounds the supply holes42a, the discharge holes42b, and the first fuel gas channel40so that they are connected to each other.

As illustrated inFIG. 7, the second sealing member70includes a second protruding sealing portion70bon the surface18bof the second metal separator18. The second protruding sealing portion70bconnects the outer peripheries of the oxidant gas inlet manifold22a, the oxidant gas outlet manifold22b, and the second oxidant gas channel50.

As illustrated inFIG. 3, the third sealing member72includes a first protruding sealing portion72aon the surface20aof the third metal separator20. The first protruding sealing portion72asurrounds the supply holes60a, the discharge holes60b, and the second fuel gas channel58so that they are connected to each other.

The third sealing member72includes a second protruding sealing portion72bon the surface20bof the third metal separator20. The second protruding sealing portion72bconnects the outer peripheries of the coolant inlet manifolds25a, the coolant outlet manifolds25b, and the coolant channel38.

As illustrated inFIG. 2, the first membrane electrode assembly16aand the second membrane electrode assembly16beach include a solid polymer electrolyte membrane74, and a cathode electrode76and an anode electrode78sandwiching the solid polymer electrolyte membrane74therebetween. The solid polymer electrolyte membrane74is, for example, a thin film that is made of a perfluorosulfonate polymer and that is impregnated with water. Each of the first and second membrane electrode assemblies16aand16bis a stepped MEA, in which the cathode electrode76has planar dimensions smaller than those of the anode electrode78and the solid polymer electrolyte membrane74. Alternatively, the cathode electrode76, the anode electrode78, and the solid polymer electrolyte membrane74may have the same planar dimensions. Further alternatively, the anode electrode78may have planar dimensions smaller than those of the cathode electrode76and the solid polymer electrolyte membrane74.

The cathode electrode76and the anode electrode78each include a gas diffusion layer (not shown) and an electrode catalyst layer (not shown). The gas diffusion layer is made of carbon paper or the like. The electrode catalyst layer is formed on a surface of the gas diffusion layer by uniformly coating the surface with porous carbon particles whose surfaces support a platinum alloy. The electrode catalyst layers are disposed on both sides of the solid polymer electrolyte membrane74.

The first membrane electrode assembly16aincludes a first resin frame member80that is disposed outward from an end of the cathode electrode76on the outer periphery of the solid polymer electrolyte membrane74. The first resin frame member80is integrally formed by, for example, injection molding or the like. The second membrane electrode assembly16bincludes a second resin frame member82that is disposed outward from an end of the cathode electrode76on the outer periphery of the solid polymer electrolyte membrane74. The second resin frame member82is integrally formed by, for example, injection molding or the like. The first resin frame member80and the second resin frame member82are each made of a resin material, such as a commodity plastic, an engineering plastic, or a super engineering plastic.

As illustrated inFIG. 3, on a surface of the first resin frame member80facing the cathode electrode76, an inlet buffer portion84ais disposed between the oxidant gas inlet manifold22aand the inlet of the first oxidant gas channel26. An outlet buffer portion84bis disposed between the oxidant gas outlet manifold22band the outlet of the first oxidant gas channel26. The inlet buffer portion84aand the outlet buffer portion84beach include a plurality of protrusions and a plurality of linear channels. The same applies to other buffer portions described below.

As illustrated inFIG. 8, on a surface of the first resin frame member80on the anode electrode78side, an inlet buffer portion86ais disposed between the fuel gas inlet manifold24aand the first fuel gas channel40. An outlet buffer portion86bis disposed between the fuel gas outlet manifold24band the first fuel gas channel40.

As illustrated inFIG. 3, on a surface of the second resin frame member82of the second membrane electrode assembly16bon the cathode electrode76, an inlet buffer portion88ais disposed between the oxidant gas inlet manifold22aand the second oxidant gas channel50. An outlet buffer portion88bis disposed between the oxidant gas outlet manifold22band the second oxidant gas channel50.

As illustrated inFIG. 9, on a surface of the second resin frame member82on the anode electrode78side, an inlet buffer portion90ais disposed between the fuel gas inlet manifold24aand the second fuel gas channel58. An outlet buffer portion90bis disposed between the fuel gas outlet manifold24band the second fuel gas channel58.

When two power generation units12are stacked each other, the coolant channel38is formed between the first metal separator14of one of the power generation units12and the third metal separator20of the other power generation unit12.

As illustrated inFIGS. 1 and 2, the second metal separator18as an end separator is disposed at each end of the stacked body13in the stacking direction. As illustrated inFIG. 2, a first end power generation unit12ais disposed at one end of the power generation units12in the stacking direction. The first end power generation unit12aincludes the third metal separator20, the second membrane electrode assembly16b, and the second metal separator18that are stacked outward. A second end power generation unit12bis disposed at the other end of the power generation units12in the stacking direction. The second end power generation unit12bincludes the first metal separator14, the first membrane electrode assembly16a, and the second metal separator18that are stacked outward.

On the second metal separator18of the first end power generation unit12a, a heat insulating layer98a, the terminal plate100a, the insulator (insulation plate)102a, and the end plate104aare stacked outward in the stacking direction. On the second metal separator18of the second end power generation unit12b, a heat insulating layer98b, the terminal plate100b, the insulator (insulation plate)102b, and the end plate104bare stacked outward in the stacking direction. The heat insulating layers98aand98bare each made of an electrically conducting porous material. The heat insulating layers98aand98b, which have a heat insulating effect, are each made from, for example, a porous metal material, a stack of corrugated thin metal plates, or a honeycomb metal. One of the heat insulating layers98aand98bmay be omitted.

As illustrated inFIG. 1, terminal portions106aand106bare respectively disposed at substantially the centers of the terminal plates100aand100b. The terminal portions106aand106bextend outward in the stacking direction. The terminal portions106aand106bare respectively inserted into cylindrical insulators108so as to protrude to the outside of the end plates104aand104b. The insulators102aand102bare each made of an insulating material, such as a polycarbonate (PC) or a phenol resin. The insulators102aand102bmay have inner spaces for heat insulation.

The insulators102aand102brespectively include rectangular recessed portions110aand110bin middle portions thereof. Holes112aand112bare formed at substantially the centers of the recessed portions110aand110b. The terminal plates100aand100bare disposed in the recessed portions110aand110b. The terminal portions106aand106bof the terminal plates100aand100bare respectively inserted into the holes112aand112bwith the cylindrical insulators108therebetween.

Holes114aand114bare respectively formed at substantially the centers of the end plates104aand104bso as to be coaxial with the holes112aand112b. In the end plate104a, the oxidant gas inlet manifold22a, the fuel gas inlet manifold24a, the pair of coolant inlet manifolds25a, the oxidant gas outlet manifold22b, the fuel gas outlet manifold24b, and the pair of coolant outlet manifolds25bare formed. The outer peripheries of the terminal plates100aand100bare located inward from the oxidant gas inlet manifold22a, the fuel gas inlet manifold24a, the coolant inlet manifolds25a, the oxidant gas outlet manifold22b, the fuel gas outlet manifold24band the coolant outlet manifolds25b.

For example, a protruding portion120ais formed on an outer peripheral portion of a surface of the insulator102athat is in contact with the second metal separator18so as to correspond to the protruding/recessed shape of the surface18aof the second metal separator18. For example, a protruding portion120bis formed on an outer peripheral portion of a surface of the insulator102bthat is in contact with the second metal separator18so as to correspond to the protruding/recessed shape of the surface18bof the second metal separator18.

The operation of the fuel cell stack10will be described below.

First, as illustrated inFIG. 1, an oxidant gas, such as an oxygen-containing gas, is supplied to the oxidant gas inlet manifold22athrough the end plate104a. A fuel gas, such as a hydrogen-containing gas, is supplied to the fuel gas inlet manifold24athrough the end plate104a. A coolant, such as pure water, ethylene glycol, an oil, or the like, is supplied to the pair of coolant inlet manifolds25a.

As illustrated inFIGS. 3 and 5, the oxidant gas flows from the oxidant gas inlet manifold22a, through the inlet buffer portion84a, and to the first oxidant gas channel26of the first metal separator14. Moreover, the oxidant gas flows from the oxidant gas inlet manifold22a, through the inlet buffer portion88a, and to the second oxidant gas channel50of the second metal separator18.

The oxidant gas moves along the first oxidant gas channel26in the direction of arrow B (horizontal direction), and is supplied to the cathode electrode76of the first membrane electrode assembly16a. Moreover, the oxidant gas moves along the second oxidant gas channel50in the direction of arrow B, and is supplied to the cathode electrode76of the second membrane electrode assembly16b.

As illustrated inFIGS. 3 and 4, the fuel gas flows from the fuel gas inlet manifold24a, through the supply holes42a, and to the inlet buffer portion86a. Then, the fuel gas flows from the inlet buffer portion86ato the first fuel gas channel40of the second metal separator18. Moreover, the fuel gas flows from the fuel gas inlet manifold24a, through the supply holes60a, and to the inlet buffer portion90a. Then, the fuel gas is supplied from the inlet buffer portion90ato the second fuel gas channel58of the third metal separator20.

The fuel gas flows along the first fuel gas channel40in the direction of arrow B, and is supplied to the anode electrode78of the first membrane electrode assembly16a. Moreover, the fuel gas flows along the second fuel gas channel58in the direction of arrow B, and is supplied to the anode electrode78of the second membrane electrode assembly16b.

Accordingly, in each of the first membrane electrode assembly16aand second membrane electrode assembly16b, the oxidant gas supplied to the cathode electrode76and the fuel gas supplied to the anode electrode78are consumed in electrochemical reactions in the electrode catalyst layers, and thereby electric power is generated.

Next, the oxidant gas, which has been supplied to the cathode electrodes76of the first membrane electrode assembly16aand the second membrane electrode assembly16band consumed, is discharged through the outlet buffer portions84band88bto the oxidant gas outlet manifold22b(seeFIG. 3).

The fuel gas, which has been supplied to the anode electrodes78of the first membrane electrode assembly16aand the second membrane electrode assembly16band consumed, is discharged through the outlet buffer portions86band90band the discharge holes42band60bto the fuel gas outlet manifold24b.

As illustrated inFIG. 3, the coolant supplied to the pair of coolant inlet manifolds25aflows through the coolant inlet manifolds25ato the coolant channel38. The coolant temporarily flows inward in the direction of arrow then flows in the direction of arrow B, and cools the first membrane electrode assembly16aand the second membrane electrode assembly16b. Then, the coolant flows outward in the direction of arrow C, and is discharged to the pair of coolant outlet manifolds25b.

In the first embodiment, as illustrated inFIG. 2, the first end power generation unit12ais disposed at one end of the power generation units12in the stacking direction. The first end power generation unit12aincludes the third metal separator20, the second membrane electrode assembly16b, and the second metal separator18that are stacked outward. The second end power generation unit12bis disposed at the other end of the power generation units12in the stacking direction. The second end power generation unit12bincludes the first metal separator14, the first membrane electrode assembly16a, and the second metal separator18that are stacked outward.

Therefore, as illustrated inFIG. 10, the coolant channel38is formed between the first end power generation unit12aand an adjacent power generation unit12. The coolant supplied to this coolant channel38cools the second membrane electrode assembly16bof the first end power generation unit12aand the first membrane electrode assembly16aof the adjacent power generation unit12.

The coolant channel38is formed between the second end power generation unit12band an adjacent power generation unit12. The coolant supplied to this coolant channel38cools the first membrane electrode assembly16aof the second end power generation unit12band the second membrane electrode assembly16bof the adjacent power generation unit12.

Accordingly, the coolant flowing through these coolant channels38can cool the first membrane electrode assemblies16aand the second membrane electrode assemblies16b, which are located on both sides of the coolant channels38, of the power generation units12, the first end power generation unit12a, and the second end power generation unit12b.

FIG. 11is a schematic sectional view of a fuel cell stack10rein which a first end power generation unit12a1and an second end power generation unit12b1, each of which is the same as the power generation unit12, are disposed at ends of the stacked body13in the stacking direction.

In the fuel cell stack10re, the first membrane electrode assembly16aof the first end power generation unit12a1and the second membrane electrode assembly16bof the second end power generation unit12b1are disposed farther from the coolant channels38than other first membrane electrode assemblies16aand other second membrane electrode assemblies16bare. Thus, the cooling conditions of the first end power generation unit12a1and the second end power generation unit12b1differ from those of the power generation units12, and therefore the first and second end power generation units12a1and12b1cannot be cooled uniformly with the power generation units12.

In contrast, with the first embodiment, as illustrated inFIG. 10, the power generation units12, the first end power generation unit12a, and the second end power generation unit12bof the fuel cell stack10are cooled uniformly. Therefore, the first embodiment has an advantage in that cooling can be performed under optimal conditions without the need of a dummy cell and with a compact and economical structure.

As illustrated inFIG. 12, a fuel cell stack130according to a second embodiment of the present disclosure includes a plurality of power generation units132that are stacked. The components the same as those of the fuel cell stack10according to the first embodiment will be denoted by the same numerals, and detailed description of such components will be omitted.

Each of the power generation units132includes a first metal separator134, a first membrane electrode assembly136a, a second metal separator138, a second membrane electrode assembly136b, and a third metal separator140.

The solid polymer electrolyte membrane74of each of the first membrane electrode assembly136aand the second membrane electrode assembly136bhas planar dimensions that are larger than those of the cathode electrode76and the anode electrode78. A resin frame portion142(frame-shaped resin member) is integrally formed on the outer periphery of the solid polymer electrolyte membrane74by, for example, injection molding a resin material. The resin material is, for example, a commodity plastic, an engineering plastic, or a super engineering plastic, or the like.

Manifolds, including a fuel gas inlet manifold, a fuel gas outlet manifold, an oxidant gas inlet manifold, an oxidant gas outlet manifold, a coolant inlet manifold, and a coolant outlet manifold, are formed in outer peripheral portions of the frame portion142, although they are not illustrated. These manifolds are not formed in the first metal separator134, the second metal separator138, and the third metal separator140. The metal separators134,138, and140have smaller sizes so that they can be disposed inward from the manifolds.

A first sealing member144is integrally formed with the frame portion142of the first membrane electrode assembly136a. The first sealing member144includes a first sealing portion144athat is disposed on a surface thereof facing the first metal separator134. The first sealing portion144ais in contact with the first metal separator134so as to surround the outer periphery of the first metal separator134.

The first sealing member144further includes a second sealing portion144band a third sealing portion144cthat are disposed on a surface thereof facing the second metal separator138. The second sealing portion144bis in contact with the second metal separator138so at to surround the outer periphery of the second metal separator138. The third sealing portion144cis located outward from the outer periphery of the second metal separator138. The third sealing portion144cis in contact with the frame portion142of an adjacent second membrane electrode assembly136b.

A second sealing member146is integrally formed with the frame portion142of the second membrane electrode assembly136b. The second sealing member146includes a first sealing portion146aand a second sealing portion146bthat are disposed on a surface thereof facing the third metal separator140. The first sealing portion146ais in contact with the third metal separator140so as to surround the outer periphery of the third metal separator140. The second sealing portion146bis located outward from the outer periphery of the third metal separator140. The second sealing portion146bis in contact with the first sealing member144of the frame portion142of an adjacent first membrane electrode assembly136a.

A first end power generation unit132ais disposed at one end of the power generation units132in the stacking direction. The first end power generation unit132aincludes the third metal separator140, a second membrane electrode assembly136b, and the second metal separator138that are stacked outward. A second end power generation unit132bis disposed at the other end of the power generation units132in the stacking direction. The second end power generation unit132bincludes a first metal separator134, a first membrane electrode assembly136a, and the second metal separator138that are stacked outward.

On the second metal separator138of the first end power generation unit132a, the heat insulating layer98a, the terminal plate100a, the insulator102a, and the end plate104aare stacked outward in the stacking direction. On the second metal separator138of the second end power generation unit132b, the heat insulating layer98b, the terminal plate100b, the insulator102b, and the end plate104bare stacked outward in the stacking direction.

With the second embodiment, the coolant flowing through the coolant channels38can cool the first membrane electrode assemblies136aand the second membrane electrode assemblies136b, which are located on both sides of the coolant channels38, of the power generation units132, the first end power generation unit132a, and the second end power generation unit132b.

Accordingly, the power generation units132, the first end power generation unit132a, and the second end power generation unit132bof the fuel cell stack130can be cooled uniformly. Thus, the second embodiment has an advantage in that cooling can be performed under optimal conditions without the need of a dummy cell and with a compact and economical structure, which is the same as that of the first embodiment.

According to an aspect of the present disclosure, a fuel cell stack includes a plurality of power generation units each including a first separator, a first electrolyte electrode assembly, a second separator, a second electrolyte electrode assembly, and a third separator that are stacked in this order, the first electrolyte electrode assembly and the second electrolyte electrode assembly each including an electrolyte and a pair of electrodes sandwiching the electrolyte therebetween. A reactant gas channel through which a predetermined reactant gas flows along a power generation surface is formed in each of a space between the first separator and the first electrolyte electrode assembly, a space between the first electrolyte electrode assembly and the second separator, a space between the second separator and the second electrolyte electrode assembly, and a space between the second electrolyte electrode assembly and the third separator. A coolant channel through which a coolant flows is formed in each of spaces between the power generation units.

An end separator disposed at one end of the power generation units in a stacking direction is the second separator, and an end separator disposed at the other end of the power generation units in the stacking direction is the second separator.

It is preferable that, on each of the end separators, a terminal plate, an insulation plate, and an end plate be stacked outward in the stacking direction.

In the fuel cell stack, a first end power generation unit is disposed at one end of the power generation units in the stacking direction. The first end power generation unit includes the third metal separator, the second membrane electrode assembly, and the second metal separator that are stacked outward. A second end power generation unit is disposed at the other end of the power generation units in the stacking direction. The second end power generation unit includes the first metal separator, the first membrane electrode assembly, and the second metal separator that are stacked outward.

Therefore, a coolant channel is formed between the first end power generation unit and an adjacent power generation unit. A coolant supplied to the coolant channel cools the second membrane electrode assembly of the first end power generation unit and the first membrane electrode assembly of the adjacent power generation unit. A coolant channel is formed between the second end power generation unit and an adjacent power generation unit. A coolant supplied to the coolant channel cools the first membrane electrode assembly of the second end power generation unit and the second membrane electrode assembly of the adjacent power generation unit.

Accordingly, the coolant flowing through these coolant channels can cool the first membrane electrode assemblies and the second membrane electrode assemblies that are located on both sides of the coolant channels. Thus, the power generation units, the first end power generation unit, and the second end power generation unit of the fuel cell stack are cooled uniformly. Therefore, cooling can be performed under optimal conditions without the need of a dummy cell and with a compact and economical structure.