Fuel cell

A fuel cell includes a resin-framed membrane electrode assembly, first and second separators, and a resin frame member. The resin frame member is provided to surround an outer periphery of a solid polymer electrolyte membrane. The first and second separators sandwich the resin-framed membrane electrode assembly therebetween in a stacking direction to define a reactant gas flow channel between each of the first and second separators and the resin-framed membrane electrode assembly. The first and second separators include a reactant gas manifold hole which passes through the first and second separators in the stacking direction. The resin frame member includes a bridge portion having connecting flow channels connecting the reactant gas flow channel and the reactant gas manifold hole. At least one of the connecting flow channels has a sloped surface.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application claims priority under 35 U.S.C. § 119 to Japanese Patent Application No. 2016-027593, filed Feb. 17, 2016, entitled “Fuel Cell”. The contents of this application are incorporated herein by reference in their entirety.

BACKGROUND

The present application relates to a fuel cell.

2. Description of the Related Art

In general, a solid polymer-type fuel cell includes a solid polymer electrolyte membrane formed of a polymer ion exchange membrane. The fuel cell is equipped with an electrolyte membrane-electrode assembly (MEA) in which an anodic electrode is disposed on one of the surfaces of the solid polymer electrolyte membrane and a cathodic electrode is disposed on the other surface of the solid polymer electrolyte membrane. The anodic electrode and the cathodic electrode each include a catalyst layer (electrode catalyst layer) and a gas diffusion layer (porous carbon).

The MEA sandwiched between separators (bipolar plates) constitutes a power generation cell (unit fuel cell). A particular number of power generation cells are stacked and used as a vehicle-mount fuel cell stack, for example.

A fuel cell often includes an inner manifold in order to supply reactant gas, namely, fuel gas and oxidant gas, to the anodic electrodes and the cathodic electrodes of the respective power generation cells that are stacked.

The inner manifold has reactant gas inlet manifold holes (fuel gas inlet manifold holes and oxidant gas inlet manifold holes) and reactant gas outlet manifold holes (fuel gas outlet manifold holes and oxidant gas outlet manifold holes) that penetrate in the stacking direction of the power generation cell. A reactant gas inlet manifold hole is in communication with the inlet side of a reactant gas flow channel (fuel gas flow channel or oxidant gas flow channel) through which reactant gas is supplied along the electrode surface, and a reactant gas outlet manifold hole is in communication with the outlet side of the reactant gas flow channel.

In this case, the reactant gas inlet manifold hole and the reactant gas outlet manifold hole are connected to the reactant gas flow channel via connecting flow channels that have parallel grooves and the like in order to smoothly and uniformly supply the reactant gas. In order to enable smooth sealing without clogging the connecting flow channels, a fuel cell is proposed in Japanese Patent No. 5824575, for example.

According to this fuel cell, the MEA is a resin-framed MEA that includes a resin frame member around the outer periphery of the MEA. The resin frame member has such an outer shape that the resin frame member is disposed on the inner side of the reactant gas manifold holes formed in the outer periphery of the metal separators. The resin frame member is equipped with a buffer portion positioned outside the power generation region and connected to the reactant gas flow channel and a part of the connecting flow channel (bridge portion) that connects the buffer portion to the reactant gas manifold hole.

The document describes that since a resin frame member having relatively high rigidity is used, the resin frame member is prevented from being deformed and clogging of the connecting flow channel can be reliably prevented with a simple and economic structure.

SUMMARY

According to one aspect of the present invention, a fuel cell includes a resin-framed membrane electrode assembly and separators. The resin-framed membrane electrode assembly includes a solid polymer electrolyte membrane, electrodes disposed on both surfaces of the solid polymer electrolyte membrane, and a resin frame member that surrounds an outer periphery of the solid polymer electrolyte membrane. The separators stacked on two sides of the resin-framed membrane electrode assembly. Each of the separators includes a reactant gas flow channel through which reactant gas is distributed along an electrode surface and a reactant gas manifold hole through which the reactant gas is distributed in a stacking direction of the resin-framed membrane electrode assembly and the separators. The resin frame member includes a bridge portion that connects the reactant gas flow channel to the reactant gas manifold hole. The bridge portion includes a plurality of connecting flow channels that connect the reactant gas flow channel to the reactant gas manifold hole. The connecting flow channels each have a sloped surface at a bottom thereof.

According to another aspect of the present invention, a fuel cell includes a resin-framed membrane electrode assembly, first and second separators, and a resin frame member. The resin-framed membrane electrode assembly includes a solid polymer electrolyte membrane, first and second electrodes, and the resin frame member. The first and second electrodes sandwich the solid polymer electrolyte membrane therebetween in a stacking direction. The resin frame member is provided to surround an outer periphery of the solid polymer electrolyte membrane. The first and second separators sandwich the resin-framed membrane electrode assembly therebetween in the stacking direction to define a reactant gas flow channel between each of the first and second separators and the resin-framed membrane electrode assembly. The first and second separators include a reactant gas manifold hole which passes through the first and second separators in the stacking direction. The resin frame member includes a bridge portion having connecting flow channels connecting the reactant gas flow channel and the reactant gas manifold hole. At least one of the connecting flow channels has a sloped surface along a flow direction of reactant gas from the reactant gas manifold hole toward the reactant gas flow channel.

DESCRIPTION OF THE EMBODIMENTS

Referring toFIGS. 1 and 2, multiple power generation cells (fuel cells)10according to a first embodiment of the present application are stacked in the arrow A direction (horizontal direction) or the arrow C direction (gravitational direction), for example, to form a fuel cell stack. The fuel cell stack is, for example, used as a vehicle-mount fuel cell stack mounted onto a fuel cell electric vehicle (not illustrated in the drawing).

Each power generation cell10includes a resin-framed MEA12, and a first metal separator14and a second metal separator16between which the resin-framed MEA12is sandwiched. The first metal separator14and the second metal separator16each have a horizontally long (or vertically long) rectangular shape and their outer dimensions are larger than the outer dimension of the resin-framed MEA12(refer toFIG. 1).

The first metal separator14and the second metal separator16each include a metal thin sheet such as a steel sheet, a stainless steel sheet, an aluminum sheet, a plated steel sheet, or any of the foregoing with its metal surface subjected to an anti-corrosion treatment. The metal thin sheet is press-formed so as to have a corrugated cross section. Alternatively, for example, carbon separators may be used instead of the first metal separator14and the second metal separator16.

In each of the first metal separator14and the second metal separator16, reactant gas manifold holes, namely, an oxidant gas inlet manifold hole18aand a fuel gas outlet manifold hole20b, are formed at one end portion in the arrow B direction, which is the long side direction of each separator. The oxidant gas inlet manifold hole18aof the first metal separator14and the oxidant gas inlet manifold hole18aof the second metal separator16are in communication with each other in the arrow A direction. The fuel gas outlet manifold hole20bof the first metal separator14and the fuel gas outlet manifold hole20bof the second metal separator16are in communication with each other in the arrow A direction. The oxidant gas inlet manifold holes18aare used to supply the oxidant gas (reactant gas), for example, oxygen-containing gas. The fuel gas outlet manifold holes20bare used to discharge the fuel gas (reactant gas), for example, hydrogen-containing gas.

In each of the first metal separator14and the second metal separator16, reactant gas manifold holes, namely, a fuel gas inlet manifold hole20aand an oxidant gas outlet manifold hole18b, are formed at the other end portion in the arrow B direction so that the fuel gas inlet manifold hole20aand the oxidant gas outlet manifold hole18bare aligned in the arrow C direction. The fuel gas inlet manifold hole20aof the first metal separator14and the fuel gas inlet manifold hole20aof the second metal separator16are in communication with each other in the arrow A direction. The oxidant gas outlet manifold hole18bof the first metal separator14and the oxidant gas outlet manifold hole18bof the second metal separator16are in communication with each other in the arrow A direction. The fuel gas inlet manifold holes20aare used to supply fuel gas and the oxidant gas outlet manifold holes18bare used to discharge the oxidant gas.

In each of the first metal separator14and the second metal separator16, two cooling medium inlet manifold holes22aare respectively formed at an upper end portion and a lower end portion in the short side direction (arrow C direction) on the side close to the oxidant gas inlet manifold hole18a. The cooling medium inlet manifold holes22aof the first metal separator14are in communication with the cooling medium inlet manifold holes22aof the second metal separator16in the arrow A direction. In each of the first metal separator14and the second metal separator16, two cooling medium outlet manifold holes22bare respectively formed at an upper end portion and a lower end portion in the short side direction on the side close to the fuel gas inlet manifold hole20a. The cooling medium outlet manifold holes22bof the first metal separator14are in communication with the cooling medium outlet manifold holes22bof the second metal separator16in the arrow A direction. The cooling medium inlet manifold holes22aare used in pair to supply the cooling medium and the cooling medium outlet manifold holes22bare used in pair to discharge the cooling medium.

As illustrated inFIG. 3, an oxidant gas flow channel24that extends in the arrow B direction, for example, is formed in a surface14aof the first metal separator14. The surface14ais a surface that faces the resin-framed MEA12. The oxidant gas flow channel24includes multiple wavy grooves (or linear grooves)24aparallel to one another.

An inlet buffer portion26ais disposed in the inlet-side end portion of the oxidant gas flow channel24. The inlet buffer portion26ais located outside the power generation region. An outlet buffer portion26bis disposed in the outlet-side end portion of the oxidant gas flow channel24. The outlet buffer portion26bis also outside the power generation region.

The inlet buffer portion26aand the outlet buffer portion26beach have multiple embosses protruding toward the resin-framed MEA12. Alternatively, multiple linear projections may be provided together with or instead of the embosses. The embosses of the inlet buffer portion26aand the outlet buffer portion26band embosses on a surface14b(surface facing a cooling medium flow channel38) of the first metal separator14are provided in an alternating manner.

As illustrated inFIG. 1, a fuel gas flow channel32that extends in the arrow B direction, for example, is formed in a surface16aof the second metal separator16. The surface16ais a surface that faces the resin-framed MEA12. The fuel gas flow channel32includes multiple wavy grooves (or linear grooves)32athat are parallel to one another.

An inlet buffer portion34ais disposed at an inlet-side end portion of the fuel gas flow channel32. The inlet buffer portion34ais located outside the power generation region. An outlet buffer portion34bis disposed at an outlet-side end portion of the fuel gas flow channel32. The outlet buffer portion34bis located outside the power generation region.

The inlet buffer portion34aand the outlet buffer portion34beach have multiple embosses protruding toward the resin-framed MEA12. Alternatively, multiple linear projections may be formed together with or instead of the embosses. The embosses of the inlet buffer portion34aand the outlet buffer portion34band embosses on a surface16b(surface facing the cooling medium flow channel38) of the second metal separator16are provided in an alternating manner.

Multiple supply holes (through holes)36aare formed near the fuel gas inlet manifold hole20a. Multiple discharge holes (through holes)36bare formed near the fuel gas outlet manifold hole20b.

A cooling medium flow channel38is formed between the surface14bof the first metal separator14and the surface16bof the second metal separator16adjacent to each other. The cooling medium flow channel38is in communication with the cooling medium inlet manifold holes22aand the cooling medium outlet manifold holes22b. The cooling medium flow channel38is formed as the rear-side shape of the oxidant gas flow channel24formed in the first metal separator14and the rear-side shape of the fuel gas flow channel32formed in the second metal separator16come together.

As illustrated inFIGS. 1 and 2, a first seal member40that covers a portion of the surface14aand a portion of the surface14bof the first metal separator14surrounds the outer peripheral end portions of the first metal separator14. The first seal member40is integral. A second seal member42that covers a portion of the surface16aand a portion of the surface16bof the second metal separator16surrounds the outer peripheral end portions of the second metal separator16. The second seal member42is also integral.

Referring toFIGS. 2 and 3, the first seal member40includes a protruding seal40adisposed on the surface14aand arranged to contact a flat surface of the second seal member42on the adjacent second metal separator16.

Referring toFIG. 3, the protruding seal40asurrounds the oxidant gas flow channel24, the oxidant gas inlet manifold hole18a, and the oxidant gas outlet manifold hole18b. Multiple inlet passages43aare formed near the oxidant gas inlet manifold hole18aby cutting-out the protruding seal40a. Multiple outlet passages43bare formed near the oxidant gas outlet manifold hole18bby cutting-out the protruding seal40a.

The oxidant gas inlet manifold hole18aand the oxidant gas flow channel24are in communication with each other via the inlet passages43a. The oxidant gas outlet manifold hole18band the oxidant gas flow channel24are in communication with each other via the outlet passages43b.

Referring toFIGS. 1 and 2, the second seal member42includes a protruding seal42adisposed on the surface16a. The protruding seal42aon surface16asurrounds the supply holes36a, the discharge holes36b, and the fuel gas flow channel32and so that they are in communication with each other.

Examples of the first seal member40and the second seal member42include elastic seal members such as sealing materials, cushion materials, and packing materials formed of EPDM, NBR, fluororubber, silicone rubber, fluorosilicone rubber, butyl rubber, natural rubber, styrene rubber, chloroprene rubber, and acryl rubber.

As illustrated inFIGS. 2, 4, and 5, the resin-framed MEA12includes a MEA12a, which is a stepped MEA. A stepped MEA is a type of MEA that has a difference in level (step), in other words, a MEA in which one of the electrodes has a different size from the other electrode in plan. The details are provided below.

The MEA12aincludes, for example, a solid polymer electrolyte membrane (cation exchange membrane)44, which is a water-impregnated perfluorosulfonic acid thin membrane. A cathodic electrode46is disposed on one of the surfaces of the solid polymer electrolyte membrane44. An anodic electrode48is disposed on the other surface of the solid polymer electrolyte membrane44. The solid polymer electrolyte membrane44may be a fluorine-based electrolyte or hydrocarbon (HC)-based electrolyte.

The dimension of the anodic electrode48in plan (outer dimension) is smaller than the dimensions of the solid polymer electrolyte membrane44and the cathodic electrode46in plan (outer dimensions). The cathodic electrode46and the solid polymer electrolyte membrane44are designed to have the same dimension in plan.

Alternatively, the cathodic electrode46may be designed to have a smaller dimension than the solid polymer electrolyte membrane44and the anodic electrode48in plan. The MEA12ais not limited to the stepped MEA and the anodic electrode48and the cathodic electrode46may be designed to have the same dimension in plan.

The cathodic electrode46and the anodic electrode48each include a gas diffusion layer (not illustrated) formed of carbon paper or the like and an electrode catalyst layer (not illustrated) formed by evenly applying porous carbon particles having surfaces supporting a platinum alloy onto a surface of the gas diffusion layer. The electrode catalyst layer is formed on each surface of the solid polymer electrolyte membrane44.

The resin-framed MEA12includes a resin frame member50that surrounds and is joined to the outer periphery of the solid polymer electrolyte membrane44.

As illustrated inFIGS. 1, 2, 4, and 5, the resin frame member50has an angled-U cross-sectional shape and covers the outer peripheral end portion of the MEA12a. Since the MEA12aconstitutes the stepped MEA, the resin frame member50having an angled-U shape can be firmly joined to the MEA12a.

As illustrated inFIG. 1, an oxidant gas inlet bridge portion (projection)52aand an oxidant gas outlet bridge portion (projection)52bthat project in the outer arrow B direction are formed at diagonal positions of the resin frame member50. A fuel gas inlet bridge portion (projection)54aand a fuel gas outlet bridge portion (projection)54bthat protrude in the outer arrow B direction are formed at other diagonal positions of the resin frame member50.

The oxidant gas inlet bridge portion52ais on a surface50aof the resin frame member50and contacts the first metal separator14. In the oxidant gas inlet bridge portion52a, oxidant gas inlet connecting flow channels56a1,56a2,56a3, and56a4that connect the oxidant gas inlet manifold hole18ato the inlet buffer portion26a(refer toFIG. 3) are formed.

The oxidant gas inlet connecting flow channels56a1to56a4are formed of grooves formed by cutting-out a surface of the oxidant gas inlet bridge portion52ainto slits that are parallel to each other in the vertical direction and each extend in the arrow B direction. InFIGS. 1 and 4, four oxidant gas inlet connecting flow channels56a1to56a4are illustrated but the number of the flow channels can be increased or decreased depending on the need.

As illustrated inFIG. 4, a sloped surface56aris formed at the bottom of each of the oxidant gas inlet connecting flow channels56a1to56a4. The sloped surface56arhas a tapered shape formed such that the depth of the flow channel decreases continuously as it extends from the oxidant gas inlet manifold hole18ato the oxidant gas flow channel24. The sloped surface56armay be formed through out the entire length of each of the oxidant gas inlet connecting flow channels56a1to56a4or may be formed up to a certain point in each of the oxidant gas inlet connecting flow channels56a1to56a4(refer toFIG. 4).

As illustrated inFIG. 1, the oxidant gas outlet bridge portion52bis on the surface50aof the resin frame member50and contacts the first metal separator14. In the oxidant gas outlet bridge portion52b, oxidant gas outlet connecting flow channels56b1,56b2,56b3, and56b4that connect the oxidant gas outlet manifold hole18bto the outlet buffer portion26bare formed.

The oxidant gas outlet connecting flow channels56b1to56b4are formed of grooves formed by cutting-out a surface of the oxidant gas outlet bridge portion52binto slits that are parallel to each other in the vertical direction and each extend in the arrow B direction. InFIG. 1, four oxidant gas outlet connecting flow channels56b1to56b4are illustrated but the number of the flow channels can be increased or decreased depending on the need.

A sloped surface56bris formed at the bottom of each of the oxidant gas outlet connecting flow channels56b1to56b4. The sloped surface56brhas a tapered shape formed such that the depth of the flow channel decreases continuously as it extends from the oxidant gas outlet manifold hole18btoward the oxidant gas flow channel24. The sloped surface56brmay be formed through out the entire length of each of the oxidant gas outlet connecting flow channels56b1to56b4or may be formed up to a certain point in each of the oxidant gas outlet connecting flow channels56b1to56b4.

As illustrated inFIG. 1, the fuel gas inlet bridge portion54ais disposed on another surface50bof the resin frame member50and contacts the second metal separator16. As illustrated inFIGS. 5 and 6, fuel gas inlet connecting flow channels58a1,58a2,58a3, and58a4that connect the fuel gas inlet manifold hole20ato the inlet buffer portion34aare formed in the fuel gas inlet bridge portion54a.

The fuel gas inlet connecting flow channels58a1to58a4are formed of grooves formed by cutting-out a surface of the fuel gas inlet bridge portion54ainto slits that are parallel to each other in the vertical direction and each extend in the arrow B direction. The fuel gas inlet connecting flow channels58a1to58a4are placed away from the outer peripheral end portion of the fuel gas inlet bridge portion54atoward the inner side. Although four fuel gas inlet connecting flow channels58a1to58a4are illustrated inFIG. 6, the number of the flow channels may be increased or decreased depending on the need.

As illustrated inFIG. 5, a sloped surface58aris formed at the bottom of each of the fuel gas inlet connecting flow channels58a1to58a4. The sloped surface58arhas a tapered shape formed such that the depth of the flow channel continuously decreases as it extends from the fuel gas inlet manifold hole20atoward the fuel gas flow channel32. The sloped surface58armay be formed through out the entire length of each of the fuel gas inlet connecting flow channels58a1to58a4or may be formed up to a certain point in each of the fuel gas inlet connecting flow channels58a1to58a4(refer toFIG. 5).

As illustrated inFIG. 1, the fuel gas outlet bridge portion54bis disposed on another surface50bof the resin frame member50and in contact with the second metal separator16. As illustrated inFIG. 6, fuel gas outlet connecting flow channels58b1,58b2,58b3, and58b4that connect the fuel gas outlet manifold hole20bto the outlet buffer portion34bare formed in the fuel gas outlet bridge portion54b.

The fuel gas outlet connecting flow channels58b1to58b4are formed of grooves formed by cutting-out a surface of the fuel gas outlet bridge portion54binto slits that are parallel to each other in the vertical direction and each extend in the arrow B direction. The fuel gas outlet connecting flow channels58b1to58b4are placed away from the outer peripheral end portion of the fuel gas outlet bridge portion54btoward the inner side. Although four fuel gas outlet connecting flow channels58b1to58b4are illustrated inFIG. 6, the number of flow channels may be increased or decreased depending on the need.

A sloped surface58bris formed at the bottom of each of the fuel gas outlet connecting flow channels58b1to58b4. The sloped surface58brhas a tapered shape formed such that the depth of the flow channel continuously decreases as it extends from the fuel gas outlet manifold hole20btoward the fuel gas flow channel32. The sloped surface58brmay be formed through out the entire length of each of the fuel gas outlet connecting flow channels58b1to58b4or may be formed up to a certain point in each of the fuel gas outlet connecting flow channels58b1to58b4.

As illustrated inFIG. 2, the resin frame member50is joined to the first metal separator14in contact with the surface50aby using an adhesive60a. The resin frame member50is joined to the second metal separator16in contact with the surface50bby using an adhesive60b. The adhesives60aand60bmay be a liquid seal or a hot melt agent. Alternatively, only one of the adhesives60aand60bmay be used.

The structure of the resin frame member50is not limited to one described above and resin frame members with various shapes can be used. A resin frame member may be joined to the outer periphery of the MEA12aso as to constitute the resin-framed MEA12.

Operation of the power generation cell10configured as such will now be described.

First, as illustrated inFIG. 1, oxidant gas such as oxygen-containing gas is supplied through the oxidant gas inlet manifold hole18aand fuel gas such as hydrogen-containing gas is supplied through the fuel gas inlet manifold hole20a. A cooling medium such as pure water, ethylene glycol, or oil is supplied through the cooling medium inlet manifold holes22athat form a pair and are aligned in the vertical direction.

As illustrated inFIGS. 3 and 4, the oxidant gas is supplied to the inlet passages43aof the first metal separator14through the oxidant gas inlet manifold hole18a. The oxidant gas inlet bridge portion52aof the resin frame member50is adjacent to the downstream of the inlet passages43a.

As a result, as illustrated inFIG. 4, the oxidant gas flows through the oxidant gas inlet connecting flow channels56a1to56a4of the oxidant gas inlet bridge portion52aand is introduced into the oxidant gas flow channel24through the inlet buffer portion26a. As illustrated inFIG. 1, the oxidant gas moves along the oxidant gas flow channel24in the arrow B direction and is supplied to the cathodic electrode46of the MEA12a.

As illustrated inFIGS. 1 and 5, the fuel gas is supplied to the surface16bof the second metal separator16through the fuel gas inlet manifold hole20a. The fuel gas passes through the supply holes36aand is supplied to the surface16a. The fuel gas inlet bridge portion54aof the resin frame member50is in contact with the surface16aand overlaps the supply holes36aand the fuel gas inlet connecting flow channels58a1to58a4are formed in the fuel gas inlet bridge portion54a.

As a result, as illustrated inFIG. 5, the fuel gas flows thorough the fuel gas inlet connecting flow channels58a1to58a4and is introduced to the fuel gas flow channel32through the inlet buffer portion34a. Thus, the fuel gas moves along the fuel gas flow channel32in the arrow B direction and is supplied to the anodic electrode48of the MEA12a.

As a result, in the MEA12a, the oxidant gas supplied to the cathodic electrode46and the fuel gas supplied to the anodic electrode48are consumed in the electrode catalyst layers by electrochemical reactions and power is generated.

The oxidant gas supplied to the cathodic electrode46and partly consumed flows through the oxidant gas outlet connecting flow channels56b1to56b4from the outlet buffer portion26bof the first metal separator14, as illustrated inFIGS. 1 and 3. The oxidant gas is discharged to the oxidant gas outlet manifold hole18band distributed in the arrow A direction.

Similarly, the fuel gas supplied to the anodic electrode48and partly consumed flows through the fuel gas outlet connecting flow channels58b1to58b4from the outlet buffer portion34bof the second metal separator16, as illustrated inFIGS. 1 and 6. The fuel gas is then discharged to the fuel gas outlet manifold hole20bthrough the discharge holes36band distributed in the arrow A direction.

As illustrated inFIG. 1, the cooling medium supplied through the cooling medium inlet manifold holes22aforming a pair and aligned in the vertical direction is introduced into the cooling medium flow channel38between the first metal separator14and the second metal separator16. The cooling medium is supplied to the cooling medium flow channel38through the cooling medium inlet manifold hole22a, flows along the inner arrow C direction temporarily, and then moves in the arrow B direction to cool the resin-framed MEA12. The cooling medium moves in the outer arrow C direction and then is discharged through the cooling medium outlet manifold holes22bforming a pair and aligned in the vertical direction.

In this case, in the first embodiment, as illustrated inFIG. 1, the oxidant gas inlet connecting flow channels56a1,56a2,56a3, and56a4are formed in the oxidant gas inlet bridge portion52aof the resin frame member50. As illustrated inFIG. 4, a sloped surface56aris formed at the bottom of each of the oxidant gas inlet connecting flow channels56a1to56a4.

The sloped surface56arhas a tapered shape formed such that the depth of the flow channel continuously decreases as it extends from the oxidant gas inlet manifold hole18atoward the oxidant gas flow channel24. Thus, the oxidant gas supplied through the oxidant gas inlet manifold hole18acan reliably and smoothly flow into the oxidant gas inlet connecting flow channels56a1to56a4along the sloped surfaces56arwithout disturbing the flow. Thus, the oxidant gas distribution property from the oxidant gas inlet bridge portion52ato the inlet buffer portion26acan be satisfactorily improved and the pressure loss can be decreased, which is advantageous.

The oxidant gas outlet connecting flow channels56b1,56b2,56b3, and56b4are formed in the oxidant gas outlet bridge portion52bof the resin frame member50. The sloped surface56bris formed at the bottom of each of the oxidant gas outlet connecting flow channels56b1to56b4. According to this structure, the oxidant gas can be smoothly and reliably discharged through the oxidant gas outlet connecting flow channels56b1to56b4to the oxidant gas outlet manifold hole18bwithout disturbing the flow, and the flow distribution property of the oxidant gas can be effectively improved and the pressure loss can be decreased.

As illustrated inFIG. 6, the fuel gas inlet connecting flow channels58a1,58a2,58a3, and58a4are formed in the fuel gas inlet bridge portion54aof the resin frame member50. As illustrated inFIG. 5, the sloped surface58aris formed at the bottom of each of the fuel gas inlet connecting flow channels58a1to58a4.

The sloped surface58arhas a tapered shape formed such that the depth of the flow channel continuously decreases as it extends from the fuel gas inlet manifold hole20atoward the fuel gas flow channel32. Thus, the fuel gas supplied through the fuel gas inlet manifold hole20acan smoothly and reliably flow into the fuel gas inlet connecting flow channels58a1to58a4along the sloped surfaces58ar. As a result, the flow distribution property of the fuel gas from the fuel gas inlet bridge portion54ato the inlet buffer portion34acan be satisfactorily improved and the pressure loss can be decreased, which is advantageous.

The fuel gas outlet connecting flow channels58b1,58b2,58b3, and58b4are formed in the fuel gas outlet bridge portion54bof the resin frame member50. The sloped surface58bris formed at the bottom of each of the fuel gas outlet connecting flow channels58b1to58b4. According to this structure, the fuel gas can be smoothly and reliably discharged from the fuel gas outlet connecting flow channels58b1to58b4to the fuel gas outlet manifold hole20bwithout disturbing the flow. Thus, the flow distribution property of the fuel gas can be effectively improved and the pressure loss can be decreased.

FIG. 7is a cross-sectional view of an oxidant gas inlet bridge portion52aof a power generation cell (fuel cell)70according to a second embodiment.FIG. 8is a cross-sectional view of a fuel gas inlet bridge portion54aof the power generation cell70.

The same constitutional elements as those of the power generation cell10of the first embodiment are represented by the same reference numerals and the detailed description thereof is omitted.

The power generation cell70is equipped with a resin-framed MEA72. The resin-framed MEA72includes a MEA12aand a resin frame member74joined to the MEA12a. As illustrated inFIG. 7, oxidant gas inlet connecting flow channels56a1,56a2,56a3, and56a4are formed in the oxidant gas inlet bridge portion52aof the resin frame member74. Sloped surfaces56a1r,56a2r,56a3r, and56a4rare respectively formed at the bottoms of the oxidant gas inlet connecting flow channels56a1,56a2,56a3, and56a4.

The sloped surfaces56a1r,56a2r,56a3r, and56a4rare sloped at angles of α1°, α2°, α3°, and α4°, respectively, with respect to the reference line O1that extends in the arrow B direction. These slopes start from the same starting point P1. The slope angles α1°, α2°, α3°, and α4° are preferably in the ascending order. The sloped surface56a1ris closest to the center and the sloped surface56a4ris farthest to the center. The slope angles α1°, α2°, α3°, and α4° are set based on the oxidant gas flow rate, the flow distribution state, etc., in the oxidant gas inlet connecting flow channels56a1,56a2,56a3, and56a4. In other words, the angles illustrated in the drawing are set for the sake of convenience and visibility and are not limiting.

As illustrated inFIG. 8, fuel gas inlet connecting flow channels58a1,58a2,58a3, and58a4are formed in a fuel gas inlet bridge portion54aof the resin frame member74. Sloped surfaces58a1r,58a2r,58a3r, and58a4rare respectively formed at the bottoms of the fuel gas inlet connecting flow channels58a1,58a2,58a3, and58a4.

The sloped surfaces58a1r,58a2r,58a3r, and58a4rare sloped at angles of α5°, α6°, α7°, and α8° with respect to the reference line O2that extends in the arrow B direction. These slopes start from the same starting point P2. The slope angles α5° to α8° are preferably in the ascending order. The sloped surface58a1ris closest to the center and the sloped surface58a4ris farthest to the center. The slope angles α5°, α6°, α7°, and α8° are set based on the fuel gas flow rate, the flow distribution state, etc., of the fuel gas in the fuel gas inlet connecting flow channels58a1,58a2,58a3, and58a4. In other words, the angles illustrated in the drawing are set for the sake of convenience and visibility and are not limiting.

Oxidant gas outlet connecting flow channels56b1to56b4are formed in an oxidant gas outlet bridge portion52bof the resin frame member74. The oxidant gas outlet connecting flow channels56b1to56b4have the same structure as the oxidant gas inlet connecting flow channels56a1to56a4. Fuel gas outlet connecting flow channels58b1to58b4are formed in a fuel gas outlet bridge portion54bof the resin frame member74. The fuel gas outlet connecting flow channels58b1to58b4have the same structure as the fuel gas inlet connecting flow channels58a1to58a4.

According to the second embodiment having this structure, as illustrated inFIG. 7, the oxidant gas inlet connecting flow channels56a1to56a4are formed in the oxidant gas inlet bridge portion52aof the resin frame member74. Then the sloped surfaces56a1rto56a4rrespectively having different slope angles α1° to α4° are formed at the bottoms of the oxidant gas inlet connecting flow channels56a1to56a4.

Thus, the oxidant gas supplied through the oxidant gas inlet manifold hole18acan smoothly and reliably flow into the oxidant gas inlet connecting flow channels56a1to56a4by moving along the sloped surfaces56a1rto56a4r. As a result, the oxidant gas flow distribution property from the oxidant gas inlet bridge portion52ato the inlet buffer portion26acan be satisfactorily improved, which is advantageous.

Furthermore, as illustrated inFIG. 8, the fuel gas inlet connecting flow channels58a1to58a4are formed in the fuel gas inlet bridge portion54aof the resin frame member74. The sloped surfaces58a1rto58a4rrespectively having different slope angles α5° to α8° are formed at the bottoms of the fuel gas inlet connecting flow channels58a1to58a4.

As a result, the flow distribution property is improved and the fuel gas supplied through the fuel gas inlet manifold hole20acan smoothly and reliably flow into the fuel gas inlet connecting flow channels58a1to58a4as it flows along the sloped surfaces58a1rto58a4r. Thus, the fuel gas flow distribution property from the fuel gas inlet bridge portion54ato the inlet buffer portion34acan be satisfactorily improved.

The power generation cells10and70each include one MEA and a pair of separators holding the MEA; however, the structure is not limited to this. For example, a fuel cell having a curtailed cooling structure may be employed, which includes power generation units (fuel cells) each formed of a first metal separator, a first resin-framed MEA, a second metal separator, a second resin-framed MEA, and a third separator stacked in that order, and a cooling medium flow channel disposed between the power generation units.

A fuel cell described in the present application includes a resin-framed membrane-electrode assembly (MEA) and separators stacked on two sides of the resin-framed MEA. The resin-framed MEA includes a solid polymer electrolyte membrane, electrodes disposed on both surfaces of the solid polymer electrolyte membrane, and a resin frame member that surrounds an outer periphery of the solid polymer electrolyte membrane.

The separators each include a reactant gas flow channel through which reactant gas is distributed along an electrode surface and a reactant gas manifold hole through which the reactant gas is distributed in a stacking direction of the resin-framed membrane electrode assembly and the separators. The resin frame member includes a bridge portion that connects the reactant gas flow channel to the reactant gas manifold hole. The bridge portion includes multiple connecting flow channels that connect the reactant gas flow channel to the reactant gas manifold hole. The connecting flow channels each have a sloped surface at a bottom thereof.

In this fuel cell, a slope angle of the sloped surface is preferably different for every connecting flow channel.

In this fuel cell, the sloped surface is preferably formed such that a depth of the connecting flow channel continuously decreases as the connecting flow channel extends from the reactant gas manifold hole toward the reactant gas flow channel.

According to the above-described structure, because sloped surfaces are formed at the bottoms of the connecting flow channels of the bridge portion in the resin frame member, the reactant gas can smoothly flow into the connecting flow channels. Thus, the flow distribution property of the reactant gas from the bridge portion can be satisfactorily improved.