Fuel cell stack

A fuel cell stack includes a stack body formed by stacking a plurality of fuel cells together in a stacking direction. A second end plate is provided at one end of the stack body in the stacking direction. A pair of coolant supply passages are provided at upper and lower positions of the second end plate for allowing a coolant to flow into the fuel cells. A coolant supply manifold member is attached to the second end plate, and an insulating plate is provided between the second end plate and the coolant supply manifold member.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is based upon and claims the benefit of priority from Japanese Patent Applications No. 2014-069568 filed on Mar. 28, 2014, No. 2014-082929 filed on Apr. 14, 2014, and No. 2014-175623 filed on Aug. 29, 2014, the contents all of which are incorporated herein by reference.

BACKGROUND OF THE INVENTION

Field of the Invention:

The present invention relates to a fuel cell stack including a plurality of fuel cells for generating electrical energy by electrochemical reactions of a fuel gas and an oxygen-containing gas. The fuel cells are stacked together in a stacking direction, and end plates are provided at both ends of the fuel cell stack in the stacking direction.

Description of the Related Art:

For example, a solid polymer electrolyte fuel cell employs a polymer ion exchange membrane as an electrolyte membrane, and the polymer electrolyte membrane is interposed between an anode and a cathode to form a membrane electrode assembly (MEA). The membrane electrode assembly and a pair of separators sandwiching the membrane electrode assembly make up a power generation cell for generating electricity. In use, typically, a predetermined number of the power generation cells are stacked together to form a fuel cell stack, e.g., mounted in a fuel cell vehicle (fuel cell electric automobile, etc.).

In the fuel cell, a fuel gas flow field for supplying a fuel gas to the anode and an oxygen-containing gas flow field for supplying an oxygen-containing gas to the cathode are provided in the surfaces of the separators. Further, a coolant flow field for supplying a coolant is provided between the adjacent separators along surfaces of the adjacent separators.

In the fuel cell, internal manifold structure has been adopted. In the internal manifold structure, fuel gas passages for allowing the fuel gas to flow through the fuel cell, oxygen-containing gas passages for allowing the oxygen-containing gas to flow therethrough, and coolant passages for allowing the coolant to flow therethrough extend through the fuel cells in the stacking direction. The fuel gas passages are a fuel gas supply passage and a fuel gas discharge passage. The oxygen-containing gas passages are an oxygen-containing gas supply passage and an oxygen-containing gas discharge passage. The coolant passages are a coolant supply passage and a coolant discharge passage.

In the fuel cell, at least one of the end plates is equipped with a fluid manifold connected to each passage for supplying or discharging fluid (fuel gas, oxygen-containing gas, or coolant). Further, a fluid supply pipe and a fluid discharge pipe are connected to the fluid manifold.

In this regard, a reactant gas as one of the oxygen-containing gas and the fuel gas is humidified beforehand, and the humidified reactant gas is then supplied to the fuel cell. Further, in the fuel cell, water tends to be produced at the cathode by electrochemical reaction, and back diffusion of the produced water toward the anode tends to occur. Consequently, water vapor may be retained in the fluid manifold, and the water vapor may be condensed to produce liquid water (condensed water). Under the circumstances, the fuel cell may be undesirably connected electrically to external equipment, etc. due to connection through the liquid water (i.e., liquid junction may occur).

As a fuel cell aimed to prevent production of water droplets in the reactant gas, for example, a solid polymer electrolyte fuel cell disclosed in Japanese Laid-Open Patent Publication No. 10-012262 is known. The fuel cell has a pressing plate for pressing a stack body of the fuel cell in a stacking direction. The pressing plate has a heating section at a position where a pipe connector is provided, for heating at least one of the oxygen-containing gas and the fuel gas.

The heating section has a cylindrical outer shape having substantially the same thickness as a body portion of the pressing plate. A cylindrical hollow area is provided in the heating section. The heating section has a gas conduction section for sealing the hollow area in an air-tight manner from the inside. At the center of the gas conduction section, a through hole as a passage of the oxygen-containing gas is formed. Further, according to the disclosure, since a heating medium heated by cooling the stack body is supplied to the hollow area, the oxygen-containing gas flowing through the gas conduction section is heated by the heating medium, and it is possible to suppress production of liquid water.

Moreover, in the fuel cell, a pair of coolant supply passages and a pair of coolant discharge passages may be arranged separately at both sides (in one of two pairs of opposite sides) of the separator. The coolant supply passages and the coolant discharge passages extend through the fuel cell in the stacking direction for allowing the coolant to flow through the fuel cell. In this regard, the fuel cell adopts a structure where the pair of coolant supply passages are connected together by a single coolant manifold, and the pair of coolant discharge passages are connected together by a single coolant manifold.

For example, in a fuel cell stack disclosed in Japanese Patent No. 5054080, electrolyte electrode assemblies and separators are stacked together, and rectangular end plates are provided at both ends of the fuel cell stack in the stacking direction. On two long opposite sides of the fuel cell stack, a pair of coolant supply passages are arranged oppositely at one end side of the long sides, and a pair of coolant discharge passages are arranged oppositely at the other end side thereof.

Further, a pair of manifold sections are provided at one of the end plates. The manifold sections are connected to at least the pair of coolant supply passages or the pair of coolant discharge passages. Moreover, a coupling section is provided for coupling the pair of manifold sections together. The width of the coupling section along the long side is smaller than the dimension of the pair of manifold sections.

As described above, since the pair of manifold sections are coupled by the coupling section having a narrow width, the manifold does not have a rectangular shape as a whole. According to the disclosure, increase in the pressure loss of the coolant flowing into the manifold is suppressed effectively, and the coolant can be supplied smoothly and uniformly to the fuel cell.

SUMMARY OF THE INVENTION

However, in Japanese Laid-Open Patent Publication No. 10-012262, the heating section and the gas conduction section are provided for heating the reactant gas such as the oxygen-containing gas. Therefore, the structure is complicated, and uneconomical.

Further, in the fuel cell, in addition to the manifolds for the reactant gases, the coolant manifold as a passage of the coolant is provided. The coolant manifold tends to be electrically connected to the inside of the fuel cell through the coolant, and liquid junction between the fuel cell and external equipment may occur through the coolant. However, in the above fuel cell, it is not possible to suppress liquid junction between the fuel cell and the external equipment.

The present invention has been made to solve the problems of this type, and an object of the present invention is to provide a fuel cell stack having simple and economical structure in which it is possible to suitably achieve a desired electrical insulating performance between fluid manifolds and end plates.

Further, an object of the present invention is to provide a fuel cell stack having simple and economical structure in which a coolant can flow smoothly and uniformly inside a coolant manifold.

A fuel cell stack according to an aspect of the present invention includes a stack body formed by stacking a plurality of fuel cells together in a stacking direction for generating electrical energy by electrochemical reactions of a fuel gas and an oxygen-containing gas. A fluid passage extends through the stack body in the stacking direction for allowing a fluid, which is a coolant, the fuel gas, or the oxygen-containing gas, to flow through the fuel cells.

End plates are provided at both ends of the stack body in the stacking direction. At least one of the end plates has a fluid manifold member connected to the fluid passage. An insulating plate is provided between the one of the end plates and an attachment surface of the fluid manifold member.

Further, a fuel cell stack according to another aspect of the present invention includes a plurality of fuel cells stacked together in a stacking direction and end plates provided at both ends of the fuel cells in the stacking direction. Each of the fuel cells is formed by stacking a membrane electrode assembly and separators. The membrane electrode assembly includes a pair of electrodes and an electrolyte membrane interposed between the electrodes. A coolant flow field is formed between adjacent ones of the separators for allowing a coolant to flow along separator surfaces.

A pair of coolant supply passages are provided at an inlet side of the coolant flow field and arranged respectively on both sides of the coolant flow field in a flow field width direction. A pair of coolant discharge passages are provided at an outlet side of the coolant flow field and arranged respectively on both sides of the coolant flow field in the flow field width direction. A coolant manifold connected to the pair of coolant supply passages or the pair of coolant discharge passages is provided on one of the end plates. A pipe section as a coolant supply port or a passage discharge port is provided at a central portion of the coolant manifold in the flow field width direction. A protrusion bulging toward the pipe section is provided on a manifold inner surface facing the pipe section.

Further, in a fuel cell stack according to another aspect of the present invention, a pipe section as a coolant supply port or a passage discharge port is provided at a central portion of the coolant manifold in the flow field width direction. Protrusions bulging toward an inside of the coolant manifold are provided respectively on both sides of the pipe section.

In the present invention, the insulating plate is provided between the fluid manifold member and the end plate. Therefore, with the simple and economical structure, a desired electrical insulating performance between the fluid manifold member and the end plate is achieved suitably. Accordingly, it is possible to suitably suppress electrical connection between the fuel cell and the external equipment through liquid water.

Further, in the present invention, a pipe section is provided on the coolant manifold, and a protrusion bulging toward the pipe section is provided on a manifold inner surface facing the pipe section. In the structure, for example, the coolant supplied from the single coolant supply port into the coolant manifold is distributed toward each coolant supply passage by the guiding action of the protrusion. Further, by the guiding action of the protrusion, the coolant discharged from each coolant discharge passage to the coolant manifold flows toward the single coolant discharge port.

Thus, with the simple and economical structure, the coolant supplied into the coolant manifold can smoothly and uniformly flow toward the pair of coolant supply passages. Further, the coolant can flow from the pair of coolant discharge passages to the coolant manifold smoothly and uniformly. Accordingly, improvement in the cooling performance in each fuel cell is achieved suitably.

Further, in the present invention, a pipe section is provided on the coolant manifold, and protrusions bulging toward the inside of the coolant manifold are provided respectively on both sides of the pipe section. In the structure, for example, the coolant supplied from the single coolant supply port into the coolant manifold is distributed toward each coolant supply passage by the guiding action of the protrusions. Further, by the guiding action of the protrusions, the coolant discharged from each coolant discharge passage to the coolant manifold flows toward the single coolant discharge port.

Thus, with the simple and economical structure, the coolant supplied into the coolant manifold can smoothly and uniformly flow toward the pair of coolant supply passages. Further, the coolant can flow from the pair of coolant discharge passages to the coolant manifold smoothly and uniformly. Accordingly, improvement in the cooling performance in each fuel cell is achieved suitably.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

A fuel cell stack10according to a first embodiment of the present invention shown inFIGS. 1 and 2is mounted, e.g., in a fuel cell electric vehicle (not shown). The fuel cell stack10includes a stack body12asformed by stacking a plurality of fuel cells12in a horizontal direction indicated by an arrow B such that electrode surfaces of the fuel cells12are oriented upright. It should be noted the fuel cell stack10may be formed by stacking a plurality of fuel cells12in the direction of gravity.

As shown inFIG. 2, at one end of the fuel cells12in a stacking direction (one end of the stack body12as), a first terminal plate14ais provided. A first insulating plate16ais provided outside the first terminal plate14a, and a first end plate18ais provided outside the first insulating plate16a. At the other end of the fuel cells12in the stacking direction (the other end of the stack body12as), a second terminal plate14bis provided. A second insulating plate16bis provided outside the second terminal plate14b, and a second end plate18bis provided outside the second insulating plate16b.

A first power output terminal20aextends outward from a substantially central position of the first end plate18ahaving a laterally elongated shape (rectangular shape). The first power output terminal20amay extend from a position deviated from the central position of the first end plate18a. The first power output terminal20ais connected to the first terminal plate14a. A second power output terminal20bextends outward from a substantially central position of the second end plate18bhaving a laterally elongated shape (rectangular shape). The second power output terminal20bis connected to the second terminal plate14b.

Coupling bars22each having a constant length are provided between the first end plate18aand the second end plate18bat substantially central positions of respective sides of the first end plate18aand the second end plate18b. Both ends of each of the coupling bars22are fixed respectively to the first end plate18aand the second end plate18busing screws24, whereby a tightening load is applied to the stack body12asin the direction indicated by the arrow B.

The fuel cell stack10includes a casing26as necessary. Two sides (surfaces) of the casing26at both ends in a vehicle width direction indicated by an arrow B are the first end plate18aand the second end plate18b.Two sides (surfaces) of the casing26at both ends in a vehicle length direction indicated by an arrow A are a front side panel28aand a rear side panel28b. The front side panel28aand the rear side panel28bare laterally elongated plates. Two sides (surfaces) of the casing26at both ends in a vehicle height direction indicated by an arrow C are an upper side panel30aand a lower side panel30b. The upper side panel30aand the lower side panel30bare laterally elongated plates.

Each side of the first end plate18aand the second end plate18bhas screw holes32. The front side panel28a, the rear side panel28b, the upper side panel30a, and the lower side panel30bhave holes34at positions facing the respective screw holes32. Screws36inserted through the holes34are screwed into the screw holes32to fix the components of the casing26together.

As shown inFIG. 3, the fuel cell12includes a membrane electrode assembly40, and a first metal separator (cathode separator)42and a second metal separator (anode separator)44sandwiching the membrane electrode assembly40.

The first metal separator42and the second metal separator44are made of metal plates such as steel plates, stainless steel plates, aluminum plates, plated steel sheets, or metal plates having anti-corrosive surfaces by surface treatment. Each of the first metal separator42and the second metal separator44has a rectangular planar surface, and is formed by corrugating a thin metal plate by press forming to have ridges and recesses in cross section and a wavy or serpentine shape on the surface. Instead of the first metal separator42and the second metal separator44, for example, carbon separators may be used.

Each of the first metal separator42and the second metal separator44has a laterally elongated shape. The long sides of the first metal separator42and the second metal separator44extend in the horizontal direction indicated by the arrow A, and the short sides of the first metal separator42and the second metal separator44extend in the direction of gravity indicated by the arrow C. Alternatively, the short sides may extend in the horizontal direction and the long sides may extend in the direction of gravity.

At one end of the fuel cell12in a long-side direction indicated by the arrow A, an oxygen-containing gas supply passage (fluid passage)46aand a fuel gas supply passage (fluid passage)48aare provided. The oxygen-containing gas supply passage46aand the fuel gas supply passage48aextend through the fuel cell12in the direction indicated by the arrow B. The oxygen-containing gas is supplied through the oxygen-containing gas supply passage46a. A fuel gas such as a hydrogen-containing gas is supplied through the fuel gas supply passage48a.

At the other end of the fuel cell12in the long-side direction, a fuel gas discharge passage (fluid passage)48bfor discharging the fuel gas and an oxygen-containing gas discharge passage (fluid passage)46bfor discharging the oxygen-containing gas are provided. The fuel gas discharge passage48band the oxygen-containing gas discharge passage46bextend through the fuel cell12in the direction indicated by the arrow B.

At opposite ends of the fuel cell12in the short-side direction indicated by the arrow C, two pairs of coolant supply passages (fluid passages)50afor supplying a coolant are oppositely arranged on one side (i.e., on one end side in the horizontal direction) i.e., on a side closer to the oxygen-containing gas supply passage46aand the fuel gas supply passage48a. The two pairs of coolant supply passages50aextend through the fuel cell12in the direction indicated by the arrow B for supplying the coolant. The two pairs of coolant supply passages50aare provided respectively on upper and lower opposite sides.

The two coolant supply passages50aprovided at the upper positions of the fuel cell12are separated from each other in the horizontal direction as independent passages of the coolant. The two coolant supply passages50aprovided at the lower positions of the fuel cell12are separated from each other in the horizontal direction as independent passages of the coolant.

At opposite ends of the fuel cell12in the short-side direction, two pairs of coolant discharge passages (fluid passages)50bfor discharging the coolant are oppositely arranged on the other side (i.e., on the other end side in the horizontal direction), i.e., on a side closer to the fuel gas discharge passage48band the oxygen-containing gas discharge passage46b. The two pairs of coolant discharge passages50bextend through the fuel cell12in the direction indicated by the arrow B for discharging the coolant. The coolant discharge passages50bare provided respectively on upper and lower opposite sides. The two coolant discharge passages50bprovided at the upper positions of the fuel cell12are separated from each other in the horizontal direction as independent passages of the coolant, and the two coolant discharge passages50bprovided at the lower positions of the fuel cell12are separated from each other in the horizontal direction as independent passages of the coolant.

The membrane electrode assembly40includes a cathode54and an anode56, and a solid polymer electrolyte membrane52interposed between the cathode54and the anode56. The solid polymer electrolyte membrane52is formed by impregnating a thin membrane of perfluorosulfonic acid with water, for example.

Each of the cathode54and the anode56has a gas diffusion layer (not shown) such as a carbon paper. Porous carbon particles supporting platinum alloy on a surface thereof are deposited uniformly on the surface of the gas diffusion layer, to thereby form an electrode catalyst layer (not shown). The electrode catalyst layer of the cathode54and the electrode catalyst layer of the anode56are fixed to both surfaces of the solid polymer electrolyte membrane52, respectively.

The first metal separator42has an oxygen-containing gas flow field58on its surface42afacing the membrane electrode assembly40. The oxygen-containing gas flow field58is connected to the oxygen-containing gas supply passage46aand the oxygen-containing gas discharge passage46b.The oxygen-containing gas flow field58includes a plurality of wavy flow grooves (or straight flow grooves) extending in the direction indicated by the arrow A.

The second metal separator44has a fuel gas flow field60on its surface44afacing the membrane electrode assembly40. The fuel gas flow field60is connected to the fuel gas supply passage48aand the fuel gas discharge passage48b. The fuel gas flow field60includes a plurality of wavy flow grooves (or straight flow grooves) extending in the direction indicated by the arrow A.

A coolant flow field62is formed between the adjacent first and second metal separators42,44, more specifically, between a surface42bof the first metal separator42and a surface44bof the second metal separator44. The coolant flow field62is connected to the coolant supply passages50aand the coolant discharge passages50b. The coolant flow field62extends in the horizontal direction, and in the coolant flow field62, the coolant flows over the electrode area of the membrane electrode assembly40.

A first seal member64is formed integrally with the surfaces42a,42bof the first metal separator42, around the outer circumferential end of the first metal separator42. A second seal member66is formed integrally with the surfaces44a,44bof the second metal separator44, around the outer circumferential end of the second metal separator44.

Each of the first seal member64and the second seal member66is an elastic seal member which is made of seal material, cushion material, packing material, or the like, such as an EPDM (ethylene propylene diene monomer), an NBR (nitrile butadiene rubber), a fluoro rubber, a silicone rubber, a fluorosilicone rubber, a Butyl rubber, a natural rubber, a styrene rubber, a chloroprene rubber, an acrylic rubber, or the like.

As shown inFIG. 2, an oxygen-containing gas supply manifold member68a, an oxygen-containing gas discharge manifold member68b, a fuel gas supply manifold member70a, and a fuel gas discharge manifold member70bare attached to the first end plate18a. The oxygen-containing gas supply manifold member68a, the oxygen-containing gas discharge manifold member68b, the fuel gas supply manifold member70a, and the fuel gas discharge manifold member70bare made of electrically insulating resin.

The oxygen-containing gas supply manifold member (fluid manifold member)68aand the oxygen-containing gas discharge manifold member (fluid manifold member)68bare connected to the oxygen-containing gas supply passage46aand the oxygen-containing gas discharge passage46b, respectively. The fuel gas supply manifold member (fluid manifold member)70aand the fuel gas discharge manifold member (fluid manifold member)70bare connected to the fuel gas supply passage48aand the fuel gas discharge passage48b, respectively.

As shown inFIG. 1, a resin coolant supply manifold member (fluid manifold member)72aformed by injection molding is provided at the second end plate (one of end plates)18b. The coolant supply manifold member72ais connected to the upper and lower pairs of coolant supply passages50a. A resin coolant discharge manifold member (fluid manifold member)72bformed by injection molding is provided at the second end plate18b. The coolant discharge manifold member72bis connected to the upper and lower pairs of coolant discharge passages50b. Preferably, the coolant supply manifold member72aand the coolant discharge manifold member72bhave electrically insulating property.

As shown inFIGS. 4 to 6, the coolant supply manifold member72ais fixed to the second end plate18bsuch that an insulating plate74amade of electrically insulating resin or the like is interposed between the coolant supply manifold member72aand the second end plate18b. The insulating plate74ais a substantially flat plate, and has a coolant inlet port76aconnected to the two separate coolant supply passages50aat the upper positions and a coolant inlet port76aconnected to the two separate coolant supply passages50aat the lower positions.

As shown inFIGS. 4 and 5, the insulating plate74ahas a contact surface74aswhich contacts the second end plate18b. A first recess78ais formed in the contact surface74as, excluding portions77athereof that surround the upper and lower pairs of coolant supply passages50aand portions77bconnecting both ends of the surrounding portions77a(seeFIG. 5). The first recess78ahas a substantially rectangular shape, and the first recess78ais formed at the central portion of the contact surface74as.

As shown inFIGS. 4 and 6, a second recess80ais formed on a surface of the insulating plate74athat contacts the coolant supply manifold member72a. The second recess80ais connected to an internal space72acof the coolant supply manifold member72a. The second recess80ahas a substantially rectangular shape, and for example, the size of the opening of the second recess80ais substantially equal to the size of the opening of the first recess78a.

A plurality of holes82aare formed in the outer circumferential edge portion of the insulating plate74a.As shown inFIG. 4, screws (bolts)84ainserted into the respective holes82aare screwed into screw holes85aof the second end plate18bto thereby fix the insulating plate74ato the second end plate18b. A plurality of screw holes86aare formed on a surface74afof the insulating plate74afacing the coolant supply manifold member72a, around the second recess80aand the coolant inlet ports76a(seeFIG. 6).

The coolant supply manifold member72ahas a flange88aaround the internal space72ac. The flange88ahas a plurality of holes90acorresponding to the screw holes86a.Screws92ainserted through the holes90aare screwed into the screw holes86ato thereby fix the coolant supply manifold member72ato the insulating plate74a. It should be noted that screw holes may be formed in the second end plate18bfor allowing the screws92ato be inserted into the screw holes, whereby the coolant supply manifold member72aand the insulating plate74acan be tightened together.

An inlet pipe section94ais provided at an intermediate position of the coolant supply manifold member72ain the direction indicated by the arrow C (center of the coolant flow field62in the flow field width direction). The inlet pipe section94ais provided along the horizontal direction, or inclined from the horizontal direction.

As shown inFIG. 4, a first gap96ais formed between a surface of the second end plate18band the contact surface74asof the insulating plate74athrough the first recess78a. A second gap98ais formed between the surface74afof the insulating plate74aand an attachment surface72asof the coolant supply manifold member72athrough the second recess80a. It should be noted that only at least one of the first gap96aand the second gap98amay be provided. Further, seal members (not shown) are formed between the coolant supply manifold member72aand the insulating plate74a, and between the insulating plate74aand the second end plate18b, around the area where coolant flows.

As shown inFIG. 1, the coolant discharge manifold member72bis fixed to the second end plate18bthrough an insulating plate74bmade of electrically insulating resin, etc. The constituent elements of the coolant discharge manifold member72bthat are identical to those of the coolant supply manifold member72aare labeled with the same reference numerals (with suffix b instead of a), and detailed description thereof is omitted. An outlet pipe section94bis provided at an intermediate position of the coolant discharge manifold member72bin the direction indicated by the arrow C as a coolant discharge port. The outlet pipe section94bis provided along the horizontal direction, or inclined from the horizontal direction.

Operation of the fuel cell stack10will be described below.

Firstly, as shown inFIG. 2, an oxygen-containing gas is supplied from the oxygen-containing gas supply manifold member68aat the first end plate18ato the oxygen-containing gas supply passage46a. A fuel gas such as a hydrogen-containing gas is supplied from the fuel gas supply manifold member70aat the first end plate18ato the fuel gas supply passage48a.

Further, as shown inFIG. 1, a coolant such as pure water, ethylene glycol, oil, or the like is supplied from the inlet pipe section94ato the internal space72acof the coolant supply manifold member72aat the second end plate18b. The coolant is distributed to the upper pair of coolant supply passages50aand the lower pair of coolant supply passages50aconnected to the internal space72ac.

Thus, as shown inFIG. 3, the oxygen-containing gas flows from the oxygen-containing gas supply passage46ainto the oxygen-containing gas flow field58of the first metal separator42. The oxygen-containing gas flows along the oxygen-containing gas flow field58in the direction indicated by the arrow A, and the oxygen-containing gas is supplied to the cathode54of the membrane electrode assembly40for inducing an electrochemical reaction at the cathode54.

In the meanwhile, the fuel gas is supplied from the fuel gas supply passage48ato the fuel gas flow field60of the second metal separator44. The fuel gas flows along the fuel gas flow field60in the direction indicated by the arrow A, and the fuel gas is supplied to the anode56of the membrane electrode assembly40for inducing an electrochemical reaction at the anode56.

Thus, in the membrane electrode assembly40, the oxygen-containing gas supplied to the cathode54and the fuel gas supplied to the anode56are consumed in the electrochemical reactions at the electrode catalyst layers of the cathode54and the anode56for generating electricity.

Then, the oxygen-containing gas consumed at the cathode54of the membrane electrode assembly40is discharged along the oxygen-containing gas discharge passage46bin the direction indicated by the arrow B. In the meanwhile, the fuel gas consumed at the anode56of the membrane electrode assembly40is discharged along the fuel gas discharge passage48bin the direction indicated by the arrow B.

Further, the coolant supplied to the upper pair of coolant supply passages50aand the lower pair of coolant supply passages50aflows into the coolant flow field62between the first metal separator42and the second metal separator44. After the coolant temporarily flows inward in the direction indicated by the arrow C such that the coolant from the upper pair of coolant supply passages50aand the coolant from the lower pair of coolant supply passages50amove closer to each other, the coolant moves in the direction indicated by the arrow A to cool the membrane electrode assembly40. Then, the coolant diverges to flow away from each other in the direction indicated by the arrow C, and the coolant is discharged along the upper pair of coolant discharge passages50band the lower pair of coolant discharge passages50bin the direction indicated by the arrow B.

As shown inFIG. 1, the coolant is discharged from the upper pair coolant discharge passages50band the lower pair of coolant discharge passages50binto an internal space72bcof the coolant discharge manifold member72b. After the coolant flows toward the center of the internal space72bc, the coolant is discharged to the outside from the outlet pipe section94b.

In the first embodiment, as shown inFIG. 1, the insulating plate74ais provided between the coolant supply manifold member72aand the second end plate18b. Further, the insulating plate74bis provided between the coolant discharge manifold member72band the second end plate18b.

Thus, with the simple and economical structure, a desired electrical insulation between the coolant supply manifold member72aand the second end plate18b, and between the coolant discharge manifold member72band the second end plate18bis achieved suitably.

Further, as shown inFIGS. 4 and 5, in the insulating plate74astacked on the coolant supply manifold member72a, the first recess78ais formed at the contact surface74asthereof excluding the portions of the contact surface74asthat surround the upper pair of coolant supply passages50aand the lower pair of coolant supply passages50a. In the structure, the first gap96ais formed between the surface of the second end plate18band the contact surface74asof the insulating plate74athrough the first recess78a, and electrical resistance between the second end plate18band the insulating plate74ais thus increased. The coolant discharge manifold member72bfunctions in the same manner as the coolant supply manifold member72a.

Accordingly, it becomes possible to suitably suppress electrical connection between the fuel cell stack10and external equipment (not shown) through the coolant flowing through the coolant supply manifold member72aand the coolant discharge manifold member72b.

Further, as shown inFIGS. 4 and 6, the second recess80ais formed in the insulating plate74a, and the second recess80ais connected to the internal space72acof the coolant supply manifold member72a. Moreover, the second gap98ais provided between the surface74afof the insulating plate74aand the attachment surface72asof the coolant supply manifold member72athrough the second recess80a.

In the structure, electrical resistance of the insulating plate74abecomes large, the volume of the internal space72acis increased, and it is possible to effectively achieve size reduction of the coolant supply manifold member72a. Further, since the shape of the internal space72acis simplified, forming is performed easily. Moreover, the same advantages are obtained also on the part of the coolant discharge manifold member72b.

In the first embodiment, though the coolant supply manifold member72aand the coolant discharge manifold member72bare used as fluid manifold members, the present invention is not limited in this respect. For example, the present invention may be applicable to the fluid manifold member forming passages of the fuel gas and the oxygen-containing gas.

As shown inFIG. 7, a fuel cell stack100according to a second embodiment of the present invention is mounted, e.g., in a fuel cell electrical vehicle (not shown). The constituent elements that are identical to those of the fuel cell stack10according to the first embodiment are labeled with the same reference numerals and detailed description thereof will be omitted. Also in the third embodiment described later, the constituent elements that are identical to those of the fuel cell stack10according to the first embodiment are labeled with the same reference numerals and detailed description thereof will be omitted.

As shown inFIGS. 7 and 8, a resin coolant supply manifold member (coolant manifold)102ais attached to the second end plate18b. The coolant supply manifold member102ais connected to two pairs of coolant supply passages50a(one pair of two coolant supply passages50aat upper positions and the other pair of two coolant supply passages50aat lower positions) arranged respectively on the opposite long sides of the second end plate18b. A resin coolant discharge manifold member (coolant manifold)102bis attached to the second end plate18b. The coolant discharge manifold member102bis connected to two pairs of coolant discharge passages50b(one pair of two coolant discharge passages50bat upper positions and the other pair of two coolant discharge passages50bat lower positions) arranged respectively on the opposite long sides of the second end plate18b.

The coolant supply manifold member102aincludes upper and lower flanges104aconnected respectively to the upper and lower pairs of coolant supply passages50a. The flanges104aare formed integrally with a substantially rectangular cylindrical supply body section106a. An inlet pipe section108aas a coolant supply port is provided at an intermediary position of the supply body section106a(at the central portion of the coolant flow field62in the flow field width direction).

A protrusion110abulging toward the inlet pipe section108ais provided on a manifold inner surface of the supply body section106afacing the inlet pipe section108a, at substantially the center between the upper and lower coolant supply passages50a. The protrusion110ais formed by recessing an outer wall surface of the supply body section106atoward the inlet pipe section108ato have a smooth curved surface, e.g., circular arc surface bulging into the interior of the manifold. The protrusion110ahas a vertically symmetrical shape. It should be noted that the protrusion110amay have a vertically asymmetrical shape. In this case, as shown by a two dot chain line inFIG. 8, preferably, the slope on the upper side is steep, and the slope on the lower side is gentle in comparison with the upper side. Each of the flanges104ais fixed to the second end plate18busing a plurality of bolts84a.

The coolant discharge manifold member102bincludes upper and lower flanges104bconnected respectively to upper and lower pairs of coolant discharge passages50b. The flanges104bare formed integrally with a substantially rectangular cylindrical discharge body section106b. An outlet pipe section108bas a coolant discharge port is provided at an intermediary position of the discharge body section106b.

A protrusion110bbulging toward the outlet pipe section108bis provided on a manifold inner surface of the discharge body section106bfacing the outlet pipe section108b, at substantially the center of the upper and lower coolant discharge passages50b. The protrusion110bis formed by recessing an outer wall surface of the discharge body section106btoward the outlet pipe section108bto have a smooth curved surface, e.g., circular arc surface bulging into the interior of the manifold. It is noted that the protrusion110bis provided on the discharge body section106bas necessary, and the protrusion110bmay not be provided. Each of the flanges104bis fixed to the second end plate18busing a plurality of bolts84b.

In the second embodiment, the coolant supply manifold member102aand the coolant discharge manifold member102bare provided on the second end plate18b. In the coolant supply manifold member102a, the protrusion110abulging toward the inlet pipe section108ais provided on the manifold inner surface of the supply body section106afacing the inlet pipe section108a.

In the structure, as shown inFIG. 8, the coolant supplied from the inlet pipe section108ainto the supply body section106a(into the manifold) flows toward the protrusion110afacing the inlet pipe section108a.Therefore, since the coolant is blown onto the protrusion110a, by the guiding action of the protrusion110a, the coolant bifurcates so as to flow toward the upper side in the vertical direction (direction indicated by an arrow C1) and toward the lower side in the vertical direction (direction indicated by an arrow C2).

Thus, since the coolant is suitably distributed and supplied in the direction indicated by the arrow C1and in the direction indicated by the arrow C2, bad distribution (instability of distribution) of the coolant is suppressed reliably. Accordingly, the coolant is reliably supplied to the upper two coolant supply passages50aand the lower two coolant supply passages50a.

In the second embodiment, with the simple and economical structure, the coolant supplied into the coolant supply manifold member102aflows toward the upper and lower pairs of coolant supply passages50asmoothly and uniformly. Accordingly, improvement in the cooling performance of each fuel cell12is achieved suitably.

In the coolant discharge manifold member102b, the protrusion110bbulging toward the outlet pipe section108bis provided on the manifold inner surface of the discharge body section106bfacing the outlet pipe section108b.

In the structure, the coolant introduced from the upper two coolant discharge passages50band the lower two coolant discharge passages50binto the discharge body section106bflows toward the protrusion110bfacing the outlet pipe section108b. Thus, by the guiding action of the protrusion110b, the coolant flows from the vertically downward direction to the horizontal direction, or from the vertically upward direction to the horizontal direction. Accordingly, the coolant is suitably discharged from the outlet pipe section108bfacing the protrusion110b.

Therefore, with the simple economical structure, the coolant flows smoothly and uniformly from the upper and lower pairs of the coolant discharge passages50binto the coolant discharge manifold member102b, and the coolant is discharged into the outlet pipe section108b. Accordingly, the cooling performance of each fuel cell12is improved suitably.

FIG. 9is a front view showing a fuel cell stack120according to a third embodiment of the present invention.

In the fuel cell stack120, a resin coolant supply manifold member (coolant manifold)122and a resin coolant discharge manifold member102bare attached to the second end plate18b. An inlet pipe section124as a coolant supply port is provided on the coolant supply manifold member122at a position closer to the lower coolant supply passages50aof the supply body section106a.

The inlet pipe section124is inclined downwardly at an angle α° relative to the flow direction of the coolant in the coolant flow field62indicated by an arrow B. A protrusion126bulging toward the inlet pipe section124is provided on the manifold inner surface of the supply body section106afacing the inlet pipe section124. The center of the protrusion126is situated at a position closer to the upper coolant supply passages50a. The protrusion126is formed by recessing an outer wall surface of the supply body section106atoward the inlet pipe section124(i.e., forming a slope on the outer wall surface of the supply body section106a) to have a smooth curved surface, e.g., circular arc surface bulging into the manifold. In the protrusion126, the slope on the upper side is steep in comparison with the lower side.

It should be noted that, in the case where the inlet pipe section124is provided at a position closer to the upper coolant supply passages50ain the coolant supply manifold member122, the angle of the inlet pipe section124and the angle of the protrusion126are set in a manner opposite to the angle described above (see two dot chain line inFIG. 9).

In the third embodiment, the coolant supplied obliquely upward from the inlet pipe section124to the inside of the supply body section106a(into the manifold) at the angle α° flows toward the protrusion126facing the inlet pipe section124. Accordingly, the coolant is blown onto the protrusion126, and thus, by the guiding action of the protrusion126, the coolant is distributed so as to flow in the vertically upward direction indicated by the arrow C1and in the vertically downward direction indicated by the arrow C2.

Thus, since the coolant is suitably distributed and supplied in the direction indicated by the arrow C1and in the direction indicated by the arrow C2, bad distribution (instability of distribution) of the coolant is suppressed reliably. In the structure, the coolant is reliably supplied to the upper two coolant supply passages50aand the lower two coolant supply passages50a. Accordingly, the same advantages as in the case of the second embodiment are obtained. It should be noted that the coolant discharge manifold member102bmay have the same structure as the above described coolant supply manifold member122.

As shown inFIG. 10, a fuel cell stack130according to a fourth embodiment of the present invention is mounted, e.g., in a fuel cell electrical vehicle (not shown). The constituent elements that are identical to those of the fuel cell stack100according to the second embodiment are labeled with the same reference numerals and detailed description thereof will be omitted. Also in the fifth embodiment described later, the constituent elements that are identical to those of the fuel cell stack100according to the second embodiment are labeled with the same reference numerals and detailed description thereof will be omitted.

As shown inFIGS. 10 and 11, a resin coolant supply manifold member (coolant manifold)132ais attached to the second end plate18b. The coolant supply manifold member132ais connected to a pair of upper and lower coolant supply passages50aarranged respectively on the opposite long sides of the second end plate18b. A resin coolant discharge manifold member (coolant manifold)132bis attached to the second end plate18b. The coolant discharge manifold member132bis connected to a pair of upper and lower coolant discharge passages50barranged respectively on the opposite long sides of the second end plate18b.Alternatively, as with in the first and second embodiments, two coolant supply passages50amay be arranged on each of the opposite long sides, and two coolant discharge passages50bmay be arranged on each of the opposite long sides. Further, in the first and second embodiment, one coolant supply passage50amay be arranged on each of the opposite long sides, and one coolant discharge passage50bmay be arranged on each of the opposite long sides.

The coolant supply manifold member132aincludes a supply body section106a. A protrusion110abulging toward an inlet pipe section108ais provided on a manifold inner surface132asof the supply body section106afacing the inlet pipe section108a, at substantially the center between the upper and lower coolant supply passages50a. Protrusions134abulging toward an inside132ainof the manifold are provided respectively on both sides of the inlet pipe section108aof the supply body section106a. Each of the protrusions134ais formed on the manifold inner surface132asto have a smooth curved surface, e.g., circular arc surface.

The coolant discharge manifold member132bincludes a discharge body section106b. A protrusion110bbulging toward an outlet pipe section108bis provided on a manifold inner surface132bsof the discharge body section106bfacing the outlet pipe section108b, at substantially the center between the upper and lower coolant discharge passages50b. Protrusions134bbulging toward an inside132binof the manifold are provided respectively on both sides of the outlet pipe section108bof the discharge body section106b. Each of the protrusions134bis formed on the manifold inner surface132bsto have a smooth curved surface, e.g., circular arc surface.

In this case, as shown inFIGS. 10 and 11, in the fourth embodiment, the coolant supply manifold member132aand the coolant discharge manifold member132bare provided on the second end plate18b. In the coolant supply manifold member132a, the protrusions134abulging toward the manifold inside132ainare provided respectively on both sides (upper and lower sides) of the inlet pipe section108aof the supply body section106a.

Thus, as shown inFIG. 11, coolant supplied from the inlet pipe section108ainto the supply body section106a(manifold inside132ain) flows along the shape of the protrusions134aarranged respectively on both sides (upper and lower sides) of the inlet pipe section108a.Accordingly, by the guiding action of the protrusions134a,the coolant is distributed so as to flow in the vertically upward direction (indicated by an arrow C1) and in the vertically downward direction (indicated by an arrow C2).

Owing thereto, the coolant is suitably and smoothly distributed and supplied in the direction indicated by the arrow C1and in the direction indicated by the arrow C2, and bad distribution (instability of distribution) of the coolant is thus suppressed reliably. Accordingly, the coolant is reliably supplied to the upper coolant supply passage50aand the lower coolant supply passage50a.

In the fourth embodiment, with the simple and economical structure, the coolant supplied into the coolant supply manifold member132aflows toward the pair of upper and lower coolant supply passages50asmoothly and uniformly. Accordingly, improvement in the cooling performance of each fuel cell12is achieved suitably.

Meanwhile, in the coolant discharge manifold member132b, the protrusions134bbulging toward the manifold inside132binare provided respectively on both sides (upper and lower sides) of the outlet pipe section108bof the discharge body section106b.

In the structure, as shown inFIG. 11, the coolant introduced from the upper coolant discharge passage50band the lower coolant discharge passage50binto the discharge body section106bflows along the shape of the protrusions134b. Thus, by the guiding action of the protrusions134b,the coolant flows from the vertically downward direction to the horizontal direction, or from the vertically upward direction to the horizontal direction. Accordingly, the coolant is suitably discharged from the outlet pipe section108bfacing the protrusion110b.

Therefore, with the simple economical structure, the coolant flows smoothly and uniformly from the pair of upper and lower coolant discharge passages50binto the coolant discharge manifold member132b, and the coolant is discharged into the outlet pipe section108b. Accordingly, the cooling performance of each fuel cell12is improved suitably.

FIG. 12is a front view showing a fuel cell stack140according to a fifth embodiment of the present invention, as viewed from a coolant manifold member side. The constituent elements that are identical to those of the fuel cell stack130according to the fourth embodiment are labeled with the same reference numerals and detailed description thereof will be omitted.

In the fuel cell stack140, a resin coolant supply manifold member (coolant manifold)142and a resin coolant discharge manifold member132bare attached to the second end plate18b. An inlet pipe section144as a coolant supply port is provided on the coolant supply manifold member142at a position closer to the lower coolant supply passage50aof the supply body section106a.

The inlet pipe section144is inclined downwardly at an angle α1° relative to the flow direction of the coolant in the coolant flow field62indicated by an arrow A. A protrusion146bulging toward the inlet pipe section144is provided on a manifold inner surface142sof the supply body section106afacing the inlet pipe section144. The center of the protrusion146is situated at a position closer to the upper coolant supply passage50a. The protrusion146is formed by recessing an outer wall surface of the supply body section106atoward the inlet pipe section144(i.e., forming a slope on the outer wall surface of the supply body section106a) to have a smooth curved surface, e.g., circular arc surface bulging toward a manifold inside142in. In the protrusion146, the slope on the upper side is steep in comparison with the lower side.

Protrusions148,150bulging toward the manifold inside142inare provided respectively on both sides of the inlet pipe section144of the supply body section106a. Each of the protrusions148,150is formed on the manifold inner surface142sto have a smooth curved surface, e.g., circular arc surface.

It should be noted that, in the case where the inlet pipe section144is provided at a position closer to the upper coolant supply passage50ain the coolant supply manifold member142, the angle of the inlet pipe section144, the angle of the protrusion146, and the angles of the protrusions148,150are set in a manner opposite to the angles described above (see two dot chain line inFIG. 12). In the fifth embodiment, the coolant supplied obliquely upward from the inlet pipe section144to the inside of the supply body section106a(to the manifold inside142in) at the angle α1° flows along the shape of the protrusions148,150. Accordingly, by the guiding action of the protrusions148,150, the coolant is distributed so as to flow in the vertically upward direction indicated by the arrow C1and in the vertically downward direction indicated by the arrow C2.

Thus, since the coolant is suitably distributed and supplied in the direction indicated by the arrow C1and in the direction indicated by the arrow C2, bad distribution (instability of distribution) of the coolant is suppressed reliably. In the structure, the coolant is reliably supplied to the upper coolant supply passage50aand the lower coolant supply passage50a. Accordingly, the same advantages as in the case of the fourth embodiment are obtained. It should be noted that the coolant discharge manifold member132bmay have the same structure as the above described coolant supply manifold member142.

While the invention has been particularly shown and described with a reference to preferred embodiments, it will be understood that variations and modifications can be effected thereto by those skilled in the art without departing from the scope of the invention as defined by the appended claims.