Fuel cell and production apparatus for the fuel cell

A fuel cell includes a frame equipped membrane electrode assembly and a metal separator. The frame equipped membrane electrode assembly includes a membrane electrode assembly and a frame shaped insulating member connected to the membrane electrode assembly. The frame shaped insulating member is provided around the membrane electrode assembly. The metal separator includes a first bipolar plate and a second bipolar plate joined together, and the frame shaped insulating member includes a welding portion welded to the first bipolar plate by resistance welding.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is based upon and claims the benefit of priority from Japanese Patent Applications No. 2015-072943 filed on Mar. 31, 2015 and No. 2016-054800 filed on Mar. 18, 2016, 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 including a frame equipped membrane electrode assembly and a metal separator. The frame equipped membrane electrode assembly includes a membrane electrode assembly, in which electrodes are disposed on both sides of an electrolyte membrane, and a frame shaped insulating member connected to the membrane electrode assembly. The frame shaped insulating member is provided around the membrane electrode assembly. Further, the present invention relates a production apparatus for the fuel cell.

Description of the Related Art

In general, a solid polymer fuel cell employs a solid polymer electrolyte membrane. The solid polymer electrolyte membrane is a polymer ion exchange membrane. In this fuel cell, the solid polymer electrolyte membrane is interposed between an anode and a cathode to form a membrane electrode assembly (MEA). The membrane electrode assembly is sandwiched between separators (bipolar plates) to form a fuel cell. In use, generally, a predetermined number of the fuel cells are stacked together to form a fuel cell stack. For example, the fuel cell stack is mounted in a vehicle as an in-vehicle fuel cell stack.

Normally, the fuel cell stack is formed by stacking a large number (several tens to several hundreds) of fuel cells. For this purpose, for example, Japanese Laid-Open Patent Publication No, 2012-089505 discloses a fuel cell and a method of producing the fuel cell. According to the disclosure, it is possible to assemble a plurality of fuel cells easily and quickly, and perform the assembling operation of the fuel cells efficiently.

In this fuel cell, each of cell units is formed by stacking a membrane electrode assembly and a separator together. The cell units are joined together integrally using joint pins. Each of the joint pins has a large diameter flange which is engaged with the cell units at one end. Further, the joint pin includes a head portion engaged with the cell units at the other end. The large diameter flange has a recess for suction/holding of the joint pin. Further, according to the disclosure, the recess is sucked to fixedly position the joint pin. In this state, the cell units can be provided integrally with respect to each joint pin.

SUMMARY OF THE INVENTION

The present invention has been made in relation to the technique of this type, and an object of the present invention is to provide a fuel cell and a production apparatus for the fuel cell in which it is possible to perform assembling operation of the fuel cell efficiently and suitably at low cost.

A fuel cell according to the present invention includes a frame equipped membrane electrode assembly and a metal separator. The frame equipped membrane electrode assembly includes a membrane electrode assembly and a frame shaped insulating member connected to the membrane electrode assembly. The membrane electrode assembly includes an electrolyte membrane and electrodes on both sides of the electrolyte membrane. The frame shaped insulating member is provided around the membrane electrode assembly.

Further, the metal separator includes a first bipolar plate and a second bipolar plate joined together, and the frame shaped insulating member includes a welding portion welded to the first bipolar plate by resistance welding.

Further, preferably, the first bipolar plate includes a protrusion which contacts the welding portion of the frame shaped insulating member. Further, preferably, the second bipolar plate includes a hole at a position in alignment with the protrusion as viewed in a direction in which the first bipolar plate and the second bipolar plate are stacked together.

Further, preferably, the metal separator includes a reactant gas seal line configured to prevent leakage of a reactant gas, and a coolant seal line configured to prevent leakage of a coolant, and the protrusion and the hole are provided outside the reactant gas seal line and the coolant seal line.

Further, a fuel cell production apparatus according to the present invention includes a pedestal section and a resistance welding electrode member. The frame equipped membrane electrode assembly is placed on the pedestal section, and the metal separator is placed on the frame equipped membrane electrode assembly. The resistance welding electrode member contacts the protrusion stacked on the welding portion. The pedestal section includes an insulating pedestal on which at least the membrane electrode assembly is placed, and a metal pedestal on which the welding portion is placed.

Further, in the fuel cell production apparatus, preferably, the metal pedestal includes a positioning pin, and positioning holes are formed in the frame shaped insulating member and the metal separator, respectively, and configured to insert the positioning pin into the positioning holes.

Further, in the fuel cell production apparatus, preferably, a jig is provided on a side opposite to the pedestal section. The frame equipped membrane electrode assembly and the metal separator are interposed between the pedestal section and the jig. In this case, preferably, one of terminals of a power supply is connected to the resistance welding electrode member, and another of the terminals of the power supply is connected to the jig.

Further, in the fuel cell production apparatus, preferably, the resistance welding electrode member includes a first resistance welding electrode member which contacts a first protrusion and a second resistance welding electrode member which contacts a second protrusion which is different from the first protrusion. In this case, preferably, one of the terminals of the power supply is connected to the first resistance welding electrode member, and the other of the terminals of the power supply is connected to the second resistance welding electrode member.

Further, in the fuel cell production apparatus, preferably, the resistance welding electrode member includes a first resistance welding electrode member and a second resistance welding electrode member, and in a state where the first and second resistance welding electrode members are insulated from each other, the first and second resistance welding electrode members contact the same protrusion at the same time. In this case, preferably, one of the terminals of the power supply is connected to the first resistance welding electrode member, and the other of the terminals of the power supply is connected to the second resistance welding electrode member.

In the present invention, the welding portion is provided in the frame shaped insulating member connected to the outer portion of the membrane electrode assembly. The welding portion is welded to the first bipolar plate by resistance welding. In the structure, the cooling process as in the case of welding (joining) by high frequency heating becomes unnecessary, and the time period required for welding is reduced effectively. Moreover, no dedicated member is required for the welding portion, and the structure can be simplified advantageously. Accordingly, it becomes possible to perform the assemble operation of the fuel cells efficiently and suitably at low cost.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

As shown inFIG. 1, a plurality of fuel cells10according to an embodiment of the present invention are stacked together in a horizontal direction indicated by an arrow A or in the gravity direction indicated by an arrow C to form a fuel cell stack12. For example, the fuel cell stack12is an in-vehicle fuel cell stack. The fuel cell stack12is mounted in a fuel cell electric vehicle (not shown), etc.

In the fuel cell stack12, at one end of the fuel cells10in a stacking direction, a terminal plate14ais provided. An insulator16ais provided outside the terminal plate14a, and an end plate18ais provided outside the insulator16a. At the other end of the fuel cells10in the stacking direction, a terminal plate14bis provided. An insulator16bis provided outside the terminal plate14b, and an end plate18bis provided outside the insulator16b. Terminals20a,20bare provided at substantially the central positions of the terminal plates14a,14b. The terminals20a,20bextend toward the outside in the stacking direction. The terminals20a,20bprotrude outward from the end plates18a,18b.

The end plates18a,18bhave a laterally or horizontally (or vertically) elongated rectangular shape. Coupling bars22are provided at intermediate positions of respective sides of the end plates18a,18b, Both ends of each coupling bar22are fixed to inner surfaces of the end plates18a,18busing bolts24for applying a tightening load to the plurality of stacked fuel cells10in the stacking direction indicated by the arrow A. The fuel cell stack12may include a casing including the end plates18a,18b, and the plurality of fuel cells10may be placed in the casing.

As shown inFIG. 2, each of the fuel cells10includes a frame equipped membrane electrode assembly (frame equipped MEA)26and metal separators28. The frame equipped membrane electrode assemblies26and metal separators28are stacked alternately to form the fuel cell stack12. At one end of the fuel cells10in the horizontal direction indicated by the arrow B, an oxygen-containing gas supply passage30a, a coolant supply passage32a, and a fuel gas discharge passage34bare provided. The oxygen-containing gas supply passage30a, the coolant supply passage32a, and the fuel gas discharge passage34bextend through the fuel cells10in the direction indicated by the arrow A.

An oxygen-containing gas is supplied to the fuel cells10through the oxygen-containing gas supply passage30a, a coolant is supplied to the fuel cells10through the coolant supply passage32a, and a fuel gas such as a hydrogen-containing gas is discharged from the fuel cells10through the fuel gas discharge passage34b. The oxygen-containing gas supply passage30a, the coolant supply passage32a, and the fuel gas discharge passage34bare arranged in the vertical direction indicated by the arrow C.

At the other end of the fuel cells10in the direction indicated by the arrow B, a fuel gas supply passage34a, a coolant discharge passage32b, and an oxygen-containing gas discharge passage30bare provided. The fuel gas is supplied to the fuel cells10through the fuel gas supply passage34a. The coolant is discharged from the fuel cells10through the coolant discharge passage32b. The oxygen-containing gas is discharged from the fuel cells10through the oxygen-containing gas discharge passage30b. The fuel gas supply passage34a, the coolant discharge passage32b, and the oxygen-containing gas discharge passage30bextend through the fuel cells10in the direction indicated by the arrow A, and are arranged in the direction indicated by the arrow C.

As shown inFIGS. 2 and 3, the frame equipped membrane electrode assembly26includes a membrane electrode assembly (MEA)26a. The membrane electrode assembly26aincludes a solid polymer electrolyte membrane (cation exchange membrane)36, and an anode38and a cathode40sandwiching the solid polymer electrolyte membrane36. The solid polymer electrolyte membrane36is formed by impregnating a thin membrane of perfluorosulfonic acid with water, for example. A fluorine based electrolyte may be used as the solid polymer electrolyte membrane36. Alternatively, an MC (hydrocarbon) based electrolyte may be used as the solid polymer electrolyte membrane36.

As shown inFIG. 3, the anode38includes a first electrode catalyst layer38ajoined to one surface36aof the solid polymer electrolyte membrane36, and a first gas diffusion layer38bstacked on the first electrode catalyst layer38a. The outer size of the first gas diffusion layer38bis larger than the outer sizes of the solid polymer electrolyte membrane36and the first electrode catalyst layer38a. Alternatively, the outer size of the first gas diffusion layer38bmay be the same as the outer sizes of the solid polymer electrolyte membrane36and the first electrode catalyst layer38a.

The cathode40includes a second electrode catalyst layer40ajoined to the other surface36bof the solid polymer electrolyte membrane36and a second gas diffusion layer40bstacked on the second electrode catalyst layer40a. The outer size of the second gas diffusion layer40bis larger than the outer sizes of the solid polymer electrolyte membrane36and the second electrode catalyst layer40a. Alternatively, the outer size of the second gas diffusion layer40bmay be the same as the outer sizes of the solid polymer electrolyte membrane36and the second electrode catalyst layer40a. It should be noted that the plane surfaces of the anode38and the cathode40may have different sizes from each other.

The first electrode catalyst layer38ais formed by porous carbon particles deposited uniformly on the surface of the first gas diffusion layer38bwith platinum alloy supported on the porous carbon particles. The second electrode catalyst layer40ais formed by porous carbon particles deposited uniformly on the surface of the second gas diffusion layer40bwith platinum alloy supported on the porous carbon particles. Each of the first gas diffusion layer38band the second gas diffusion layer40bcomprises a carbon paper or a carbon cloth, etc. The first electrode catalyst layer38aand the second electrode catalyst layer40aare formed on both surfaces36a,36bof the solid polymer electrolyte membrane36, respectively.

A frame shaped insulating member42is connected to the membrane electrode assembly26ato form the frame equipped membrane electrode assembly26. The frame shaped insulating member42is provided around the membrane electrode assembly26a. An inner edge of the frame shaped insulating member42is sandwiched between outer edges of the first gas diffusion layer38band the second gas diffusion layer40b(overlapped portion). It should be noted that the joint structure for joining the frame shaped insulating member42to the first gas diffusion layer38band the second gas diffusion layer40bis not limited to this structure. As long as the frame shaped insulating member42can be joined to the first gas diffusion layer38band the second gas diffusion layer40bsuitably, any joint structure can be adopted. For example, the frame shaped insulating member42is made of PPS (polyphenylene sulfide), PPA (polyphthalamide), PEN (polyethylenenaphthalate), PES (polyether sulfone), LCP (liquid crystal polymer), PVDF (polyvinylidene fluoride), HDPE (high density polyethylene), PE (polyethylene), PP (polypropylene), POM (polyoxymethylene), silicone resin, fluororesin, or m-PPE (modified polyphenylene ether resin), etc. Further, the frame shaped insulating member42is not limited to PET (polyethylene terephthalate), PET (polybutylene terephthalate), modified polyolefin, or a resin film. Alternatively, the frame shaped insulating member42may be made of seal material, cushion material, or packing material such as an EPDM rubber (ethylene propylene diene monomer rubber), 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, or an acrylic rubber.

As shown inFIG. 2, the outer size of the frame shaped insulating member42and the outer size of the metal separator28are substantially the same. It should be noted that the outer size of the frame shaped insulating member42may be larger than the outer size of the metal separator28. The oxygen-containing gas supply passage30a, the coolant supply passage32a, the fuel gas discharge passage34b, the fuel gas supply passage34a, the coolant discharge passage32b, and the oxygen-containing gas discharge passage30bextend through the frame shaped insulating member42. A pair of circular positioning holes44for positioning the MEA are formed at one pair of diagonal positions of the frame shaped insulating member42.

The frame shaped insulating member42has welding portions45welded to a first bipolar plate46described later by resistance welding. The welding portions45are provided at four positions, adjacent to the other pair of diagonal positions of the frame shaped insulating member42and adjacent to the positioning holes44. The number and the positions of the welding portions45can be changed variously.

The metal separator28shown on the far left portion of the drawing inFIG. 3is a first metal separator disposed on a first side of the frame equipped MEA26, (the left side as shown in the drawing) and includes both the first bipolar plate46and a second bipolar plate48, portions of the first and second bipolar plates being in abutting contact with one another and joined together. The first bipolar plate46and the second bipolar plate48are made of metal plates such as steel plates, stainless steel plates, aluminum plates, plated steel sheets, titanium steel plates or metal plates having anti-corrosive surfaces by surface treatment, and have corrugated surfaces in cross section formed by press forming. The fuel cell12also includes a second metal separator28disposed on a second side of the frame equipped MEA26, (the right side as shown in the drawing) and this second metal separator has a structure substantially identical to the first metal separator as described herein, including both a third bipolar plate46and a fourth bipolar plate48, with portions of the third and fourth bipolar plates being in abutting contact with one another and joined together.

As shown inFIG. 4, the first bipolar plate46has a fuel gas flow field50on its surface46afacing the anode38of the membrane electrode assembly26a. The fuel gas flow field50is connected to the fuel gas supply passage34aand the fuel gas discharge passage34b. The fuel gas flow field50includes a plurality of fuel gas flow grooves extending in the direction indicated by the arrow B.

Circular positioning holes52aare formed at one pair of diagonal positions (adjacent to the fuel gas supply passage34aand the fuel gas discharge passage34b) of the first bipolar plate46. The positioning holes52aare provided coaxially with the positioning holes44of the frame shaped insulating member42as viewed in the stacking direction. The diameter of the positioning holes52ais larger than the diameter of the positioning holes44. The first bipolar plate46includes a plurality of circular protrusions53, e.g. at four positions (the number of the positions is not limited). The protrusions53contact the welding portions45of the frame shaped insulating member42, respectively (seeFIG. 3) as viewed in the stacking direction.

As shown inFIG. 2, the outer end of a surface46bof the first bipolar plate46is joined to the outer end of a surface48bof the second bipolar plate48by welding, brazing, etc. in a liquid tight manner. A coolant flow field54is formed between the surface46bof the first bipolar plate46and the surface48bof the second bipolar plate48. The coolant flow field54is connected to the coolant supply passage32aand the coolant discharge passage32b, and includes a plurality of coolant flow grooves extending in the direction indicated by the arrow B.

The second bipolar plate48has an oxygen-containing gas flow field56on its surface48afacing the cathode40of the membrane electrode assembly26a. The oxygen-containing gas flow field56is connected to the oxygen-containing gas supply passage30aand the oxygen-containing gas discharge passage30b. The oxygen-containing gas flow field56includes a plurality of flow grooves extending in the direction indicated by the arrow B.

As shown inFIG. 5, circular positioning holes52bare formed at one pair of diagonal positions (adjacent to the fuel gas supply passage34aand the fuel gas discharge passage34b) of the second bipolar plate48. The positioning holes52bare provided coaxially with the positioning holes52aof the first bipolar plate46as viewed in the stacking direction. The diameter of the positioning holes52bis the same as the diameter of the positioning holes52a. Holes58are formed in the second bipolar plate48at positions in alignment with the respective protrusions53of the first bipolar plate46as viewed in the stacking direction.

A first seal member60is formed integrally with the surfaces46a,46bof the first bipolar plate46, around the outer end of the first bipolar plate46. Alternatively, a member separate from the first bipolar plate46may be provided as the first seal member60provided on the surfaces46a,46bof the first bipolar plate46. A second seal member62is formed integrally with at least the surface48aof the second bipolar plate48, around the outer end of the second bipolar plate48. Alternatively, a member separate from the second bipolar plate48may be provided as the second seal member62provided at least on the surface48aof the second bipolar plate48.

Each of the first seal member60and the second seal member62is made of seal material, cushion material, or packing material such as an EPDM rubber (ethylene propylene diene monomer rubber), an MDR (nitrile butadiene rubber), a fluoro rubber, a silicone rubber, a fluorosilicone rubber, a butyl rubber, a natural rubber, a styrene rubber, a chloroprene rubber, or an acrylic rubber.

As shown inFIG. 4, the first seal member60includes a fuel gas (reactant gas) seal line60aon a surface46aof the first bipolar plate46, for preventing leakage of the fuel gas (reactant gas). As shown inFIG. 2, the first seal member60includes a coolant seal line60bon a surface46bof the first bipolar plate46, for preventing leakage of the coolant.

As shown inFIGS. 2 and 5, the second seal member62includes an oxygen-containing gas (reactant gas) seal line62aon a surface48aof the second bipolar plate48, for preventing leakage of the oxygen-containing gas (reactant gas). The protrusions53and the holes58are provided outside the fuel gas seal line60a, the coolant seal line60b, and the oxygen-containing gas seal line62a. The positioning holes44,52a,52bare provided outside the fuel gas seal line60a, the coolant seal line60b, and the oxygen-containing gas seal line62a.

FIG. 6is an exploded perspective view showing main components of a production apparatus70according to a first embodiment of the present invention, for producing the fuel cell10.

The production apparatus70includes a pedestal section (lower jig)72. The frame equipped membrane electrode assembly26is placed on the pedestal section72, and the metal separator28is placed on the frame equipped membrane electrode assembly26. As shown inFIGS. 6 and 7, the pedestal section72includes an insulating pedestal74and a metal pedestal76. At least the membrane electrode assembly26ais placed on the insulating pedestal74. The welding portions45of the frame shaped insulating member42are placed on the metal pedestal76. The insulating pedestal74can be made of any of various insulating resins. Preferably, the outer end of the insulating pedestal74is placed outside the fuel gas seal line60aand the oxygen-containing gas seal line $2a, and inside the welding portions45(seeFIG. 7).

Positioning pins78are formed integrally with the metal pedestal76at one pair of diagonal positions. The positioning pins78are inserted into the positioning holes44,52a,52b. As shown inFIG. 8, the opening diameter of the positioning hole44is the same as the diameter of the positioning pin78, and the opening diameter of the positioning holes52a,52bare larger than the diameter of the positioning pin78. A collar member82made of insulating resin is externally fitted around the positioning pin78, between outer circumference of the positioning pin78and inner circumference of the positioning holes52a,52b. The axial length of the collar member82is larger than the thickness of the metal separator28.

As shown inFIG. 6, the production apparatus70includes an upper jig84placed on the metal separator28. The outer size of the upper jig84is the same as the outer size of the metal separator28, and the upper jig84is made of electrically conductive metal. Positioning holes86are formed in the upper jig84. The positioning holes86are coaxial with the positioning holes52a,52b, and the opening diameter of the positioning holes86is the same as the opening diameter of the positioning holes52a,52b, A plurality of holes88are formed in the upper jig84. The holes88are coaxial with the holes58of the second bipolar plate48. Preferably, the opening diameter of the holes88is larger than the opening diameter of the holes58.

An electrode member90for performing resistance welding (hereinafter referred to as the resistance welding electrode member90, or simply referred to as the electrode member90) contacts the protrusion53of the first bipolar plate46stacked on the welding portion45of the frame shaped insulating member42, from a recessed side of the protrusion53. The electrode member90is connected to the upper jig84. One of the terminals of a power supply92is electrically connected to the electrode member90through a lead wire94, and the other of the terminals of the power supply92is electrically connected to the upper jig84through a lead wire95. The electrode member90has a cylindrical shape, and the diameter of the electrode member90is smaller than the opening diameter of the hole58.

Next, operation of producing the fuel cell10using the production apparatus70will be described below.

Firstly, the outer end of the first bipolar plate46and the outer end of the second bipolar plate48are joined together integrally (e.g., by welding or brazing) to form the metal separator28. In the meanwhile, on the part of the frame equipped membrane electrode assembly26, for example, in a state where the solid polymer electrolyte membrane36is joined to the anode38, the anode38and the cathode40are adhered to the frame shaped insulating member42. The frame shaped insulating member42is sandwiched by the anode38and the cathode40. It should be noted that the solid polymer electrolyte membrane36may be joined to the cathode40beforehand. Alternatively, the solid polymer electrolyte membrane36may be fixed to the frame shaped insulating member42. In this manner, the frame equipped membrane electrode assembly26is fabricated.

Next, as shown inFIGS. 6 through 8, the frame equipped membrane electrode assembly26is placed on the pedestal section72of the production apparatus70, and the metal separator28is placed on the frame equipped membrane electrode assembly26. At this time, as shown inFIG. 8, the positioning pins78of the metal pedestal76are fitted to the positioning holes44provided in the frame shaped insulating member42of the frame equipped membrane electrode assembly26, for positioning the frame equipped membrane electrode assembly26.

Further, after the collar members82are externally fitted to the positioning pins78, the collar members82are inserted into both of the positioning holes52aof the first bipolar plate46and the positioning holes52bof the second bipolar plate48. Therefore, the metal separator28is positioned on the frame equipped membrane electrode assembly26through the positioning pins78and the collar members82.

Further, the upper jig84is placed on the metal separator28. As shown inFIG. 8, an upper portion of each of the collar members82is inserted to the positioning hole86over the length S. Thus, the upper jig84is positioned relative to the pedestal section72. As shown inFIG. 7, the electrode member90having a spherical front end passes through the hole58of the second bipolar plate48, and contacts the protrusion53of the first bipolar plate46, from the recessed side of the protrusion53.

In this state, when the power supply92is turned on, energy is concentrated at the protrusion53of the first bipolar plate46, and the protrusion53is heated. Thus, the welding portion45of the frame shaped insulating member42is melted, and adhered to the protrusion53. That is, the protrusion53of the first bipolar plate46and the welding portion45of the frame shaped insulating member42are joined together by resistance welding, e.g., by micro spot welding.

In the first embodiment, welding portion45is provided in the frame shaped insulating member42connected to the outer portion of the membrane electrode assembly26a. The frame shaped insulating member42includes the welding portions45welded to the first bipolar plate46by resistance welding. In the structure, the cooling process as in the case of welding (joining) by high frequency heating becomes unnecessary, and the time period required for welding is reduced effectively. Moreover, no dedicated member is required for the welding portion45, and the structure can be simplified advantageously.

Specifically, in the first embodiment, as shown in FIG.7, the first bipolar plate46has the protrusions53which contact the welding portions45of the frame shaped insulating member42. The second bipolar plate48has the holes58in alignment with the protrusions53as viewed in the direction in which the first bipolar plate46and the second bipolar plate48are stacked together. This structure is advantageous in that it becomes possible to perform the assembling operation of the fuel cells10efficiently and suitably at low cost.

Further, as shown inFIG. 3, the metal separator28has the fuel gas seal line60a, the oxygen-containing gas seal line62a, and the coolant seal line60b. The protrusions53and the holes58are provided outside the fuel gas seal line60a, the oxygen-containing gas seal line62a, and the coolant seal line60b. In the structure, it is possible to prevent entry of dust, etc. which tends to be produced at the time of resistance welding, into the fuel gas flow field50, the oxygen-containing gas flow field56, or the coolant flow field54as much as possible.

Further, as shown inFIG. 7, the end of the insulating pedestal74extends outside the fuel gas seal line60aand the oxygen-containing gas seal line62a, and is provided inside the welding portions45. The welding portions45are placed on the metal pedestal76. Thus, it becomes possible to suitably protect the membrane electrode assembly26awithout causing flow of the electrical current through the membrane electrode assembly26a. Further, by using the metal pedestal76, since heat is conducted easily at the time of welding, improvement in the cooling performance is achieved, and improvement in the efficiency of operation is achieved easily to a greater extent.

Next, operation of the fuel cells10having the structure as described above will be described below.

As shown inFIG. 1, at the end plate18a, an oxygen-containing gas is supplied to the oxygen-containing gas supply passage30a, and a fuel gas such as a hydrogen-containing gas is supplied to the fuel gas supply passage34a. Further, a coolant such as pure water, ethylene glycol, or oil, etc. is supplied to the coolant supply passage32a.

As shown inFIG. 2, the oxygen-containing gas flows from the oxygen-containing gas supply passage30ainto the oxygen-containing gas flow field56of the second bipolar plate48. Thus, the oxygen-containing gas flows along the oxygen-containing gas flow field56in the direction indicated by the arrow B, and the oxygen-containing gas is supplied to the cathode40of the membrane electrode assembly26a.

In the meanwhile, the fuel gas flows from the fuel gas supply passage34ainto the fuel gas flow field50of the first bipolar plate46. The fuel gas flows along the fuel gas flow field50in the direction indicated by the arrow B, and the fuel gas is supplied to the anode38of the membrane electrode assembly26a.

Thus, in the membrane electrode assembly26a, as shown inFIG. 3, the fuel gas supplied to the anode38and the oxygen-containing gas supplied to the cathode40are partially consumed in electrochemical reactions in the first electrode catalyst layer38aand the second electrode catalyst layer40afor generating electrical energy in the fuel cells10.

Then, as shown inFIG. 2, the oxygen-containing gas partially consumed at the cathode40is discharged into the oxygen-containing gas discharge passage30b. Likewise, the fuel gas partially consumed at the anode38is discharged into the fuel gas discharge passage34b.

In the meanwhile, the coolant supplied to the coolant supply passage32aflows into the coolant flow field54formed between the first bipolar plate46and the second bipolar plate48which are joined together. In this coolant flow field54, the coolant flows in the horizontal direction indicated by the arrow B to cool the entire power generation surface of the membrane electrode assembly26a. Then, the coolant is discharged into the coolant discharge passage32b.

FIG. 9is a cross sectional view showing main components of a production apparatus100according to a second embodiment of the present invention, for producing the fuel cell10. The constituent elements of the production apparatus100that are identical to those of the production apparatus70according to the first embodiment are labeled with the same reference numerals and detailed description thereof will be omitted.

The production apparatus100is a series spot welding apparatus. For example, the production apparatus100includes a pair of electrode members90a,90b. The electrode member90ais electrically connected to one of the terminals of the power supply92through a lead wire94a, and the electrode member90bis electrically connected to the other of the terminals of the power supply92through a lead wire94b. A metal pedestal76of a pedestal section72functions as a backup electrode.

In the second embodiment having the structure as described above, the pair of electrode members90a,90bpasses through the holes58of the second bipolar plate48, and contact the protrusions53of the first bipolar plate46, from recessed sides of the protrusions53. Thus, the protrusions53are heated, and the welding portions45of the frame shaped insulating member42are melted, and adhered to the protrusions53. Accordingly, the welding process can be applied to the welding portions45at the two positions at the same time, and further improvement in the work efficiency is achieved advantageously.

Although the pair of electrode members90a,90bis provided in the second embodiment, the present invention is not limited in this respect. Alternatively, three or more electrode members may be used.

FIG. 10is a cross sectional view showing main components of a production apparatus110according to a third embodiment of the present invention, for producing the fuel cell10. The constituent elements of the production apparatus100that are identical to those of the production apparatus70according to the first embodiment are labeled with the same reference numerals, and detailed description thereof is omitted.

The production apparatus110is a series spot welding apparatus, and as resistance welding electrode members, the production apparatus110includes a pair of electrode members112a,112b, for example. The electrode member112ais electrically connected to one of terminals of a power supply92through a lead wire94a, and the electrode member112bis electrically connected to the other of the terminals of the power supply92through a lead wire94b.

As shown inFIG. 11, each of the electrode members112a,112bhas a semicircular shape in cross section. The electrode members112a,112bare provided adjacent to each other to form a circular shape as a whole. Though not shown, when the electrode members112a,112bare provided, the electrode members112a,112bare insulated from each other.

In the third embodiment having the structure described above, the pair of electrode members112a,112bare provided adjacent to each other, and in this state, the electrode members112a,112bpass through the same hole58of the second bipolar plate48, and contact the protrusion53of the first bipolar plate46from a recessed side of the protrusion53. Therefore, the protrusion53is heated by the pair of electrode members112a,112b. The welding portion45of the frame shaped insulating member42is melted, and adhered to the protrusion53.

As in the case of the above protrusion53, in each of the other protrusions53, the welding portion45is joined by the pair of electrode members112a,112b. In the structure, it is possible to apply the welding process to the welding portions45at the four positions at the same time, and improvement in the work efficiency is achieved advantageously.

In the first to third embodiments, the holes58are provided in the second bipolar plate48. However, the present invention is not limited in this respect. For example, cutout portions like recesses may be provided instead of the holes58. Further, the outer size of the second bipolar plate48may be smaller than the outer size of the first bipolar plate46, and the protrusion53may be provided outside the second bipolar plate48. That is, the second bipolar plate48does not require any machining operation for making holes, cutouts, etc.

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.