Metal separator, fuel cell, and method of producing metal separator

A metal separator is stacked on each of both surfaces of a membrane electrode assembly to form a fuel cell. A method of producing the metal separator includes a metal plate processing step of producing a metal plate including a fluid passage and a fluid flow field, and a rubber adding step of adhering a plurality of rubber extension parts extending from the fluid passage toward the fluid flow field, to the metal plate. In the rubber adding step, a primer is coated on the metal plate in an island pattern, and the metal plate and the rubber extension parts are adhered together through the primer in a dot pattern.

CROSS-REFERENCE TO RELATED APPLICATION

This application is based upon and claims the benefit of priority from Japanese Patent Application No. 2020-036391 filed on Mar. 4, 2020, the contents of which are incorporated herein by reference.

BACKGROUND OF THE INVENTION

Field of the Invention

The present invention relates to a metal separator stacked on each of both surfaces of a membrane electrode assembly to form a fuel cell. Further, the present invention relates to the fuel cell including this metal separator, and a method of producing the metal separator.

Description of the Related Art

A fuel cell includes a membrane electrode assembly (MEA) formed by stacking an anode, a solid polymer electrolyte membrane, and a cathode. The MEA is sandwiched between a pair of metal separators (bipolar plates) to form the fuel cell. In the fuel cell stack formed by stacking a plurality of fuel cells, a coolant flow field as a passage of a coolant is formed between metal separators of fuel cells that are adjacent to each other. The metal separator includes coolant passages extending in a stacking direction of the fuel cell, for allowing a coolant to flow through the coolant flow field.

As disclosed in Japanese Laid-Open Patent Publication No. 2007-134204, in some of metal separators of this type, in order to provide both of a leakage prevention function of preventing leakage of reactant gases and a coolant used in power generation and an insulating function, a rubber member (seal member) is provided on a metal plate (base member). The rubber member is formed integrally with the metal plate through a primer coated on a surface of the metal plate. This rubber member is also provided between coolant passages and a coolant flow field to form a bridge section as a passage of the coolant.

SUMMARY OF THE INVENTION

In this regard, in the metal separator of this type, a primer is coated uniformly on a metal plate to form rubber. However, the primer coated on the metal plate may be lost locally due to die closing, etc. for forming rubber at the time of production. In this case, there is a concern that leaked current through the coolant and/or the produced water may be concentrated at the position where the primer is lost during power generation of the fuel cell, and pitting corrosion, etc. may occur due to corrosion resulting from the electric potential difference.

Further, during power generation, water which has been vaporized, etc. (coolant) may enter the portion between the metal plate and the rubber member, and the water vapor may be condensed to form blisters (water swelling) between the metal plate and the rubber member. When the rubber member is swollen toward the fluid channel due to formation of the blisters, the channel cross sectional area is reduced, and the flow of the fluid (the reactant gases and the coolant) is obstructed.

The present invention has been made to solve the above problem, and an object of the present invention is to provide a metal separator, a fuel cell, and a method of producing the metal separator in which, with simple structure, it is possible to suitably discharge water from a portion between a metal plate and a rubber member, and suppress formation of blisters, or prevent pitting corrosion.

In order to achieve the above object, according to a first aspect of the present invention, provided is a metal separator stacked on each of both surfaces of a membrane electrode assembly to form a fuel cell, the membrane electrode assembly including an electrolyte membrane and electrodes provided on both surfaces of the electrolyte membrane. The metal separator includes: a metal plate including a fluid passage configured to allow fluid to flow in a stacking direction, the metal plate forming a fluid flow field configured to allow the fluid to flow along a separator surface; and a plurality of rubber extension parts adhered to the metal plate, and extending from the fluid passage toward the fluid flow field. Between the plurality of rubber extension parts, a metal surface of the metal plate is exposed, and a channel configured to connect the fluid passage and the fluid flow field is formed. The plurality of rubber extension parts are adhered to the metal plate through a plurality of dot primers between the metal plate and the rubber extension parts.

Further, in order to achieve the above object, according to a second aspect of the present invention, provided is a fuel cell comprising a metal separator stacked on each of both surfaces of a membrane electrode assembly, the membrane electrode assembly including an electrolyte membrane and electrodes provided on both surfaces of the electrolyte membrane. The metal separator includes: a metal plate including a fluid passage configured to allow fluid to flow in a stacking direction, the metal plate forming a fluid flow field configured to allow the fluid to flow along a separator surface; and a plurality of rubber extension parts adhered to the metal plate, and extending from the fluid passage toward the fluid flow field. Between the plurality of rubber extension parts, a metal surface of the metal plate is exposed, and a channel configured to connect the fluid passage and the fluid flow field is formed. The plurality of rubber extension parts are adhered to the metal plate through a plurality of dot primers between the metal plate and the rubber extension parts.

Further, in order to achieve the above object, according to a third aspect of the present invention, provided is a method of producing a metal separator stacked on each of both surfaces of a membrane electrode assembly to form a fuel cell, the membrane electrode assembly including an electrolyte membrane and electrodes provided on both surfaces of the electrolyte membrane. The method includes: a metal plate processing step of producing a metal plate including a fluid passage configured to allow fluid to flow in a stacking direction, the metal plate forming a fluid flow field configured to allow the fluid to flow along a separator surface; and a rubber adding step of providing, on the metal plate, a plurality of rubber extension parts extending from the fluid passage toward the fluid flow field. Between the plurality of rubber extension parts, a metal surface of the metal plate is exposed, and a channel configured to connect the fluid passage and the fluid flow field is formed. In the rubber adding step, the plurality of rubber extension parts are adhered to the metal plate through a plurality of dot primers.

In the metal separator, the fuel cell, and the method of producing the metal separator, with the simple structure, it is possible to suitably discharge water from the portion between the metal plate and the rubber member. Further, by eliminating local concentration of leakage current, it is possible to prevent pitting corrosion due to corrosion resulting from the electric potential difference.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

As shown inFIG.1, a fuel cell10according to an embodiment of the present invention forms a unit of a power generation cell which performs power generation based on reactions of a fuel gas (anode gas) and an oxygen-containing gas (cathode gas) as reactant gases. A plurality of the fuel cells10are stacked together in the direction indicted by the arrow A to form a fuel cell stack (not shown). For example, the fuel cell stack is mounted in a fuel cell automobile (not shown), and used as a power source of in-vehicle devices such as a motor.

The fuel cell10includes a frame equipped membrane electrode assembly12(hereinafter referred to as the frame equipped MEA12), and a pair of metal separators14stacked on both surfaces of the frame equipped MEA12, respectively. The frame equipped MEA12according to the embodiment of the present invention includes a membrane electrode assembly16(hereinafter referred to as the MEA16) and a resin frame member18fixed to an entire outer peripheral portion of the MEA16. It should be noted that, instead of using the frame equipped MEA12, an MEA16which does not have any resin frame member18may be applicable to the fuel cell10.

As shown inFIGS.1and2, the MEA16includes an electrolyte membrane20(cation ion exchange membrane), an anode22stacked on one surface of the electrolyte membrane20, and a cathode24stacked on the other surface of the electrolyte membrane20.

For example, the sold polymer electrolyte membrane is a thin membrane of perfluorosulfonic acid containing water. A fluorine based electrolyte may be used as the electrolyte membrane20. Alternatively, an HC (hydrocarbon) based electrolyte may be used as the electrolyte membrane20.

Each of the anode22and the cathode24includes electrolyte catalyst layers (not shown) disposed on both surfaces of the electrolyte membrane20, and gas diffusion layers (not shown) provided outside the electrode catalyst layers (sides opposite to of the electrolyte membrane20). For example, the gas diffusion layer is made of carbon paper, etc. The electrode catalyst layer is formed by depositing porous carbon particles uniformly on the surface of the gas diffusion layer, and platinum alloy is supported on surfaces of the carbon particles.

The MEA16according to the embodiment of the present invention is an MEA having different sizes of components, where the surface size of the cathode24is smaller than the surface sizes of the electrolyte membrane20and the anode22. It should be noted that the MEA16may be an MEA having different sizes of components where the surface size of the anode22is smaller than the surface sizes of the electrolyte membrane20and the cathode24. Alternatively, the MEA16may have the same size of components (where the electrolyte membrane20, the anode22, and the cathode24have the same surface size).

The resin frame member18of the frame equipped MEA12is joined to an outer peripheral surface of the electrolyte membrane20using adhesive, outside the outer peripheral portion of the cathode24of the MEA16. Examples of the material of the resin frame member18include general purpose plastics, engineering plastics, super engineering plastics, etc. having electrically insulating properties. The resin frame member18may be made of a film, etc.

The resin frame member18(frame equipped MEA12) is disposed inside the plurality of fluid passages26provided in the outer peripheral portion of the metal separator14having a rectangular shape. It should be noted that the resin frame member18and the metal separator14may have the same surface size, and the resin frame member18may have the same fluid passages26as in the case of the metal separator14.

The plurality of fluid passages26of each of the metal separators14allow reactant gases and a coolant to flow in the stacking direction of the plurality of fuel cells10. That is, fuel gas passages28(a fuel gas supply passage28aand a fuel gas discharge passage28b) form one of reactant gas passages26a, and allow the fuel gas such as the hydrogen gas to flow in the direction indicated by the arrow A. Oxygen-containing gas passages30(an oxygen-containing gas supply passage30aand an oxygen-containing gas discharge passage30b) form the other of the reactant gas passages26a, and allow the oxygen-containing gas such as the air to flow in the direction indicated by the arrow A. Coolant passages32(coolant supply passages32aand coolant discharge passages32b) form fluid passages26, and allow the coolant such as water to flow in the direction indicated by the arrow A.

Specifically, in the outer peripheral portion at one end of each of the metal separators14in the long side direction (indicated by the arrow B), the fuel gas supply passage28aand the oxygen-containing gas discharge passage30bare provided. In the outer peripheral portion at the other end of each of the metal separators14in the long side direction (indicated by the arrow B), the oxygen-containing gas supply passage30aand the fuel gas discharge passage28bare provided.

Further, in the outer peripheral portion of the fuel cell10in the short side direction (direction indicated by the arrow C), the plurality of coolant supply passages32aand the plurality of coolant discharge passages32bare provided. The plurality of coolant supply passages32aare disposed closer to the side indicated by the arrow B1than the center of the metal separator14in the long side direction is, and a pair of the coolant supply passages32aare disposed at each of both ends in the short side direction. A partition wall34for dividing the pair of coolant supply passages32ais provided between the pair of coolant supply passages32a. On the other hand, the plurality of coolant discharge passages32bare disposed closer to the side indicated by the arrow B2than the center of the metal separator14in the long side direction is, and a pair of the coolant discharge passages32bare provided at each of both ends in the short side direction. The partition wall34for dividing the pair of coolant discharge passages32bis provided between the pair of coolant discharge passages32b.

It should be noted that the positions and the shapes of the coolant passages32(the coolant supply passages32aand the coolant discharge passages32b) are not limited to those described above. For example, the coolant supply passages32aand the coolant discharge passages32bmay be provided at both ends of the fuel cell10in the longitudinal direction, and the coolant supply passages32aand the coolant discharge passages32bmay be arranged together with the fuel gas supply passage28a, the fuel gas discharge passage28b, the oxygen-containing gas supply passage30a, and the oxygen-containing gas discharge passage30bin the direction indicated by the arrow C.

The fuel gas passages28are connected to a fuel gas flow field42formed between the anode22and an anode separator40(metal separator14). The anode separator40has a plurality of ridges extending in the direction indicated by the arrow B on its surface40afacing the anode22, and grooves (wavy flow grooves or straight flow grooves in a plan view) formed between these ridges form the fuel gas flow field42. The fuel gas flow field42is a fluid flow field38(one of reactant gas flow fields38a) for allowing a fuel gas which is one of reactant gases to flow along a separator surface.

Further, a rubber member52described later is provided on an outer peripheral portion of the fuel gas flow field42of the anode separator40, for preventing leakage of the fuel gas. A bridge section43is formed between the fuel gas passages28and the fuel gas flow field42. The bridge section43includes flow grooves as a passage of the fuel gas, and the flow grooves are formed by a plurality of ridge shaped rubber extension parts (not shown) of the rubber member52. Specifically, the bridge section43comprises a plurality of flow grooves formed by a metal exposed surface, i.e., a plurality of rubber extension parts of the anode separator40. In the bridge section43inFIG.1, the plurality of flow grooves are covered by a lid. Alternatively, the plurality of rubber extension parts may be brought into contact with the resin frame member18without using any lid.

The oxygen-containing gas passages30are connected to an oxygen-containing gas flow field46formed between the cathode24and a cathode separator44(metal separator14). The cathode separator44has a plurality of ridges extending in the direction indicated by the arrow B on its surface44afacing the cathode24, and grooves (wavy flow grooves or straight flow grooves in a plan view) formed between these ridges form the oxygen-containing gas flow field46. The oxygen-containing gas flow field46is the fluid flow field38(the other of reactant gas flow fields38a) for allowing an oxygen-containing gas which is the other of reactant gases to flow along a separator surface.

The rubber member52is provided also on an outer peripheral portion of the oxygen-containing gas flow field46of the cathode separator44, for preventing leakage of the oxygen-containing gas. A bridge section47is formed between the oxygen-containing gas passages30and the oxygen-containing gas flow field46. The bridge section47includes flow grooves as a passage of the oxygen-containing gas, and the flow grooves are formed by a plurality of ridge shaped rubber extension parts (not shown) of the rubber member52. Specifically, the bridge section47comprises a plurality of flow grooves formed by the metal exposed surface, i.e., a plurality of rubber extension parts of the cathode separator44. Also in the bridge section47inFIG.1, the plurality of flow grooves are covered by a lid. Alternatively, the plurality of rubber extension parts may be brought into contact with the resin frame member18without using any lid.

The coolant passages32are connected to a coolant flow field48formed between the anode separator40and the cathode separator44that are adjacent to each other. The coolant flow field48forms the fluid flow field38as a passage of a coolant along separator surfaces. When the back surface of the fuel gas flow field42formed on a surface40bof the anode separator40and the back surface of the oxygen-containing gas flow field46formed on a surface44bof the cathode separator44are overlapped with each other, the coolant flow field48is formed between the anode separator40and the cathode separator44. The coolant flows from the each of coolant supply passages32ainto the coolant flow field48in the direction indicated by the arrow B2, and then, the coolant flows from the coolant flow field48into each of the coolant discharge passages32b.

Each of the metal separators14(the anode separator40and the cathode separator44) includes a thin metal plate50(base material) such as a steel plate, a stainless steel plate, an aluminum plate, a plated steel sheet. The metal plate50is formed to have a plurality of ridges and grooves by press forming. The metal plate50has a corrugated shape in cross section.

Further, each of the metal separators14(the anode separator40and the cathode separator44) is provided with the rubber member52which covers the metal plate50, outside of the fluid flow field38(the fuel gas flow field42, the oxygen-containing gas flow field46, or the coolant flow field48). The rubber member52achieves both of a leakage prevention function of preventing leakage of the reactant gases and the coolant and an insulating function. Hereinafter, the rubber member52provided on the anode separator40will be referred to as an anode rubber member54, and the rubber member52provided on the cathode separator44will be referred to as a cathode rubber member56.

The material of the rubber member52is not limited specially. For example, the rubber member52is made of seal material, cushion material, or packing material such as an EPDM, an NBR, 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 inFIGS.1to3, the cathode rubber member56includes a flat seal56faformed around the oxygen-containing gas flow field46on the surface44aof the cathode separator44, and a flat seal56fbformed around the coolant flow field48on the surface44bof the cathode separator44. Each of the flat seals56fa,56fbincludes marginal seals56rformed around the coolant supply passages32aand the coolant discharge passages32b. The marginal seals56rsurround the inner marginal portions of the coolant supply passages32aand the coolant discharge passages32bcontinuously.

Further, several protruding seals56sare formed integrally with the flat seal56fbof the cathode rubber member56. The protruding seals56sprotrude from the flat seal56fb, and prevent leakage of the fuel gas and the coolant in an air-tight and liquid-tight manner. The protruding seals56sinclude an outer protrusion56s1which is provided on the outer marginal portion of the metal plate50, and contacts the anode rubber member54, and fluid passage protrusions56s2formed around the reactant gas passages26a, respectively.

Further, as shown inFIGS.3and5, the cathode rubber member56includes a plurality of rubber extension parts53(cathode side rubber extension parts57) arranged on the flat seal56fb(marginal seal56r) on the surface44bof the cathode separator44. Each of the cathode side rubber extension parts57is in the form of a block extending in the direction indicated by an arrow C between the coolant passage32(the coolant supply passage32a, the coolant discharge passage32b) and the coolant flow field48.

Specifically, each of the cathode side rubber extension parts57protrudes beyond the marginal seal56r(flat seal56fb) from the metal plate50in the direction indicated by the arrow A (thickness direction). Further, the size of each of the cathode side rubber extension parts57in the width direction (direction indicated by the arrow C) is set to be larger than (twice or more, for example) the size of the cathode side rubber extension part57in the direction in which the cathode side rubber extension part57extends (direction indicated by the arrow B). That is, each of the cathode side rubber extension parts57has a narrow shape and is elongated in the direction indicated by the arrow C.

The cathode side rubber extension parts57are provided at equal intervals (at intervals of L1) in the direction indicated by the arrow B. No cathode rubber member56is provided between the adjacent cathode side rubber extension parts57, and a metal exposed surface51where the metal plate50is exposed is formed between the adjacent cathode side rubber extension parts57. The space formed by the adjacent cathode side rubber extension parts57and the metal exposed surface51forms a groove58bas a passage of the coolant (see alsoFIG.6).

At least one, e.g., two cutouts57bare formed in each of the cathode side rubber extension parts57. The cutouts57bextend in the direction indicated by the arrow B to connect the adjacent grooves58b. Each of the cathode side rubber extension parts57includes three protruding ends57adivided by the two cutouts57bprovided in the direction indicate by the arrow C. Each of the cutouts57bconnects the plurality of grooves58b, for allowing the coolant to flow. It should be noted that the number of the cutouts57bis not limited to two. One cutout57bor three or more cutouts57bmay be provided.

As shown inFIGS.2and4, the anode rubber member54includes a flat seal54faformed around the fuel gas flow field42on the surface40aof the anode separator40, and a flat seal54fbformed around the coolant flow field48on the surface40bof the anode separator40. Each of the flat seals54fa,54fbincludes marginal seals54rformed around the coolant supply passages32aand the coolant discharge passages32b. The marginal seals54rsurround the inner marginal portions of the coolant supply passages32aand the coolant discharge passages32bcontinuously.

Further, a protruding seal54sis formed integrally with the flat seal54faof the anode rubber member54. The protruding seal54sprotrudes from the flat seal54fato prevent leakage of the oxygen-containing gas, the fuel gas, and the coolant in an air-tight and liquid-tight manner. The protruding seals54shave an inner protrusion54s1which contact the resin frame member18, a passage protrusion54s2which is provided around each of the fluid passages26and contacts the cathode rubber member56, and an outer protrusion54s3which is provided on the outer marginal portion of the metal plate50, and contacts the cathode rubber member56.

Further, the anode rubber member54includes a plurality of rubber extension parts53(anode side rubber extension parts55) arranged in the flat seal54fbon the surface40bof the anode separator40. Each of the anode side rubber extension parts55extends in the direction indicated by the arrow C between the coolant supply passages32a, the coolant discharge passages32b, and the coolant flow field48. Each of the anode side rubber extension parts55extends from the metal plate50in the direction indicated by the arrow A, and has the same thickness as the marginal seal54r(flat seal54fb).

Further, each of the anode side rubber extension parts55has a narrow shape, and is elongated in the direction indicated by the arrow C. In the state where the anode separator40and the cathode separator44are stacked together, each of the anode side rubber extension parts55is disposed at a position facing each of the cathode side rubber extension parts57. That is, the protruding end57aof each of the cathode side rubber extension parts57contacts a surface55fof each of the anode side rubber extension parts55, in the flat seal54fb.

The size of each of the anode side rubber extension parts55in the width direction (direction indicated by the arrow B) is set to be larger than (twice or more, for example) the size of the anode side rubber extension part55in the direction in which the anode side rubber extension part55extends (direction indicated by the arrow C). That is, each of the anode side rubber extension parts55has a narrow shape, and is elongated in the direction indicated by the arrow C. Further, the size W1of each of the anode side rubber extension parts55in the width direction is larger (wider) than the size W2of each of the cathode side rubber extension part57in the width direction. Therefore, even if the assembling position between the metal separators14is shifted in the long side direction, no pressure losses occur in the coolant flow field48.

The anode side rubber extension parts55are provided at intervals (at intervals of L2) in the direction indicated by the arrow B. No anode rubber member54is provided between the adjacent anode side rubber extension parts55, and the metal exposed surface51where the metal plate50is exposed is formed between the adjacent anode side rubber extension parts55. In the anode separator40, the space formed by the adjacent anode side rubber extension parts55and the metal exposed surface51forms a groove58aas a passage of the coolant (see alsoFIG.6).

As shown inFIGS.2,5, and6, in the state where the fuel cells10are stacked together, the above metal separators14(the anode separator40and the cathode separator44) form a bridge structure59where the coolant can flow between the coolant passages32and the coolant flow field48. The bridge structure59is formed by alternately stacking the anode side rubber extension parts55and the cathode side rubber extension parts57arranged in the direction indicated by the arrow B.

Therefore, the bridge structure59includes a fluid channel58formed by grooves58aon the anode separator40side and grooves58bon the cathode separator44side, between the rubber extension parts53(the anode side rubber extension part55and the cathode side rubber extension part57) that are adjacent to each other in the direction indicated by the arrow B. In each fluid channel58in the direction indicated by the arrow A, the marginal seal54rand the metal exposed surface51of the anode separator40and the marginal seal56rand the metal exposed surface51of the cathode separator44face each other.

Further, in the fuel cell10according to the embodiment of the present invention, the metal separator14provided with the rubber member52adhered to the surface of the metal plate50is used. In this case, in the metal separator14, a primer60which enhances adhesiveness is coated on the surface of the metal plate50before adhering the rubber member52to the metal plate50, so that adhesion between the metal plate50and the rubber member52is improved through the primer60.

Further, the primer60according to the embodiment of the present invention is coated on a bridge part50aof the metal plate50(see also the two dot chain line inFIGS.3and4) in a dot pattern (island pattern). Hereinafter, the primer60coated on the bridge part50awill be also referred to as a dot primer61. The bridge part50ais a portion between the coolant passages32(each of the coolant supply passages32aand the coolant discharge passages32b) and the coolant flow field48. It should be noted that the dot primers61are also provided in a portion where the marginal seals54r,56rof the fluid channel58are formed. On the other hand, the primer60is coated on the entire surface (coated on all over the surface) of the metal plate50in the portion of the metal separator14other than the bridge part50a. Hereinafter, the primer60coated in the portion other than the bridge part50awill also be referred as a planar primer62.

For example, a plurality of the dot primers61are arranged on the metal plate50, in the direction indicated by the arrow B and the direction arrow C in a matrix pattern. Stated otherwise, the plurality of dot primers61are arranged at equal intervals in the longitudinal direction and the lateral direction. It should be noted that the plurality of dot primers61may be arranged not only in the matrix pattern but also in an irregular pattern.

Further, inFIG.5, the dot primers61have a substantially quadrangular shape, and have the same area. It should be noted that the shape of each of the dot primers61is not limited specifically, and may have a circular shape or any other polygonal shape. The dot primers61may have the same shape and/or area, or may have different shapes and/or areas. Further, the maximum length of each of the dot primers61is smaller than the width of the anode side rubber extension part55and the cathode side rubber extension part57.

Preferably, the thickness of each of the dot primers61is in the range of 3 μm to 15 μm. If the thickness of the dot primers61is larger than 15 μm, there is a possibility that, in the state where the fuel cells10are stacked together, variation in the line pressure applied to the rubber extension part53becomes large, and the seal compression load characteristics are decreased.

Preferably, the ratio of the total area of the plurality of dot primers61(primer area ratio) to the area of the adhesion surface of the rubber extension parts53is set within the range of 10% to 30%. If the primer area ratio is less than 10%, there is a possibility that the adhesiveness of adhering the metal plate50and the rubber member52together through the dot primers61is decreased. On the other hand, if the primer area ratio is more than 30%, when the water vapor flows between the metal plate50and the rubber extension part53as described later and is liquefied, the liquid water does not flow easily from the metal plate50and the rubber extension part53.

The plurality of dot primers61are coated on the bridge part50aof the metal separator14, whereby the dot primers61are formed not only in the adhesion portion of each of the rubber extension parts53but also in the metal exposed surface51between the rubber extension parts53. Therefore, it is possible to efficiently perform operation of coating the primer60on the metal plate50.

Although the primer60coated on the metal plate50is not limited specifically, it is preferable to use a silane coupling agent. In the embodiment of the present invention, the primer60prepared by mixing the silane coupling agent as main material, a film forming agent, solvents, catalyst, etc. together is used.

By joining of the rubber member52, a first adhesion portion64aand a second adhesion portion64bare formed in a joint border64between the metal plate50and the rubber extension part53in the bridge part50a. In the first adhesion portion64a, the metal plate50and the rubber extension parts53are joined together through the dot primers61. In the second adhesion portion64b, the metal plate50and the rubber extension parts53are joined together without any dot primers61. The first adhesion portion64aadheres the metal plate50and the rubber member52together by a joining force which is higher than that of the second adhesion portion64b.

Unlike the plurality of first adhesion portions64a(dot primers61) formed in a matrix pattern, the second adhesion portion64b(without any primers) is formed in a continuous manner seamlessly so as to fill an area between the first adhesion portions64a. This second adhesion portion64bcontacts the metal exposed surface51of the metal plate50which is exposed to both sides of each of the rubber extension parts53in the width direction or toward the coolant flow field48.

Next, a method of producing the above-described metal separator14will be described with reference toFIG.7. In the method of producing the metal separator14, a metal plate processing step (step S1) is performed, and thereafter, a rubber adding step (step S2) is performed. Further, in the metal plate processing step, a corrugating step is performed, and thereafter, a fluid passage forming step is performed to form the metal plate50. Further, in the rubber adding step, a primer coating step is performed, and thereafter, a member adhering step is performed to join the metal plate50and the rubber member52together.

In the corrugating step, a plate (not shown) forming the metal separator14is prepared, and this plate is set in a mold die of a pressing machine (not shown). The pressing machine operates the mold die after the plate is set in the mold die to perform press forming to form corrugations constituting the flow fields (the fuel gas flow field42, the oxygen-containing gas flow field46, and the coolant flow field48) of the metal separator14.

In the fluid passage forming step, the corrugated plate produced in the corrugating step is set in the pressing machine (not shown). After the plate is set in the pressing machine, fluid passages26are formed to penetrate through the corrugated plate by a pierce mold die. It should be noted that, in the production of the metal separator14, the fluid passage26may be formed beforehand, and the fluid fields may be formed subsequently. Alternatively, pressing (formation of corrugation) and formation of the fluid passages26may be performed at the same time.

In the primer coating step, using a coating machine (not shown), the primer60is coated on the surface of the outer peripheral portion of the metal plate50which has been processed beforehand. For example, the coating machine is of an ink jet type which makes it possible to inject liquid droplets of the primer60from the front end of a nozzle. Then, the coating machine coats the primer60on the bridge part50aof the metal plate50in a discrete manner to form the plurality of dot primers61. Further, the coating machine forms the planar primer62by continuously coating the primer60onto the adhesion portion of the rubber member52other than the bridge part50ain the surface direction of the metal plate50.

In the member adhering step, the metal plate50coated with the primer60is set in a mold die (not shown), and rubber material is injected between the outer peripheral portion of the metal plate50and the mold die recess to form the rubber member52. At this time, the primer60of the metal plate50can improve the adhesiveness of the rubber member52.

Further, since the planar primer62is formed in the portion other than the bridge part50a, the metal plate50and the rubber member52are adhered together firmly. On the other hand, the dot primers61are coated on the joint border64between the metal plate50and the rubber extension part53. Therefore, the plurality of first adhesion portions64a, and the second adhesion portion64bprovided continuously around the first adhesion portions64aare present.

It should be noted that the structure of adhering the metal plate50and the rubber extension parts53through the dot primers61is not limited to the bridge part50aof the coolant. For example, in the bridge sections43,47having the fluid channels58as the passages of the fuel gas and the oxygen-containing gas as the reactant gases, the metal plate50and the rubber extension part53may be adhered together through the dot primers61.

The fuel cell10and the metal separator14according to the embodiment of the present invention basically have the above structure. Hereinafter, effects and advantages of the fuel cell10and the metal separator14will be described.

As shown inFIG.1, a fuel gas, an oxygen-containing gas, and a coolant are supplied from the outside of the fuel cell stack to the plurality of fuel cells10forming the fuel cell stack. In each of the fuel cells10, the fuel gas flows through the fuel gas supply passage28ain the stacking direction (direction indicated by the arrow A), and then, the fuel gas flows into the fuel gas flow field42. The fuel gas flows along the fuel gas flow field42in the direction indicated by the arrow B, and the fuel gas is supplied to the anode22of the MEA16. Further, in each of the fuel cells10, the oxygen-containing gas flows through the oxygen-containing gas supply passage30ain the stacking direction (direction indicated by the arrow A), and the oxygen-containing gas flows into the oxygen-containing gas flow field46. The oxygen-containing gas flows along the oxygen-containing gas flow field46in the direction indicated by the arrow B, and the oxygen-containing gas is supplied to the cathode24of the MEA16.

Then, the MEA16performs power generation by electrochemical reactions of the fuel gas supplied to the anode22and the oxygen-containing gas supplied to the cathode24. The fuel gas which flowed through the fuel gas flow field42is discharged into the fuel gas discharge passage28b, and flows through the fuel gas discharge passage28bin the stacking direction (indicated by the arrow A. Then, the fuel gas is discharged to the outside of the fuel cell stack. In the meanwhile, the oxygen-containing having the low electrical conductivity which flowed through the oxygen-containing gas flow field46is discharged into the oxygen-containing gas discharge passage30b, and flows through the oxygen-containing gas discharge passage30bin the stacking direction (indicated by the arrow A. Then, the oxygen-containing gas is discharged to the outside of the fuel cell stack.

Further, the coolant comprises liquid having low electrical conductivity such as pure water including ethylene glycol. The coolant flows through the coolant supply passage32ain the stacking direction (direction indicated by the arrow A), and flows into the coolant flow field48. The coolant moves along the coolant flow field48in the direction indicated by the arrow B, to regulate the temperature of the frame equipped MEA12. The coolant having flowed through the coolant flow field48flows into the coolant discharge passage32b, flows through the coolant discharge passage32bin the stacking direction indicated by the arrow A, and is then discharged to the outside of the fuel cell stack.

In the fuel cell10, the coolant flows through each of the fluid channels58of the bridge structure59provided between the coolant supply passage32aand the coolant flow field48and between the coolant flow field48and the coolant discharge passage32b. As shown inFIG.6, each of the fluid channels58is surrounded by the metal exposed surface51of the metal plate50of the metal separator14and the rubber extension parts53of the rubber members52.

In this regard, in the state of being stacked together, the anode side rubber extension parts55and the cathode side rubber extension parts57forming the fluid channel58are applied with a compression load, and the shapes thereof are slightly collapsed in the width direction. Therefore, the coolant of the liquid in the fluid channel58cannot enter the joint border64easily, and flows in the direction in which the fluid channel58extends (in the direction indicated by the arrow C).

On the other hand, the vaporized coolant may penetrate through the rubber member52, and enter the joint border64between the metal plate50and the rubber extension part53(the anode side rubber extension part55and the cathode side rubber extension part57). As shown inFIGS.8A and8B, the coolant which enters the joint border64may be condensed into liquid water, and may form blisters.

In order to suppress formation of the blisters, in the present invention, the primer60is coated on the adhesion position of the rubber extension parts53in an island pattern. That is, the joint border64includes the first adhesion portion64awhere firm joining is attained by the dot primers61, and the second adhesion portion64bwhere the dot primers61are not present. In the structure, the liquid water can move through the joint border64smoothly by the second adhesion portion64b. Therefore, the liquid water produced in the joint border64is guided through the second adhesion portion64b. Accordingly, the liquid water is discharged easily from the joint border64to the metal exposed surface51(or the coolant flow field48) around the rubber extension parts53, and it is possible to avoid stagnation of the liquid water in the joint border64. Therefore, in the fuel cell10, it is possible to suitably suppress formation of blisters in the joint border64. Further, in the fuel cell10, since the liquid water is discharged from the joint border64, local concentration of the leakage current is prevented. Therefore, it is possible to prevent pitting corrosion due to corrosion resulting from the electric potential difference.

It should be noted that the present invention is not limited to the above embodiment. Various modification can be made in line with the gist of the present invention.

Further, for example, the bridge structure59formed by coating the primer60in an island pattern is not limited to the bridge part50abetween the coolant passages32and the coolant flow field48. That is, in the metal separator14, the above bridge structure59may be adopted in the bridge section43formed by the rubber member52between the fuel gas passages28and the fuel gas flow field42. Likewise, in the metal separator14, the above bridge structure59may be adopted in the bridge section47formed by the rubber member52between the oxygen-containing gas passages30and the oxygen-containing gas flow field46. In this manner, even if the water (liquid) produced in the fluid route for the fuel gas or the oxygen-containing gas is vaporized and the water vapor enters the portion between the rubber member52of the bridge sections43,47and the metal plate50, it is possible to suitably discharge the water vapor from the bridge sections43,47.

The above fuel cell10has structure where the dot primers61are coated also on the metal exposed surface51(bridge part50a). However, the fuel cell10(metal separator14) may have structure where the primer60(planar primer62) is coated at a portion where the rubber covering is required in the metal exposed surface51. Also in this case, since adhesion is performed by the dot primers61between the metal plate50and the rubber extension parts53, it is possible to suitably discharge the liquid water from the joint border64.

The technical concept and the advantages understood from the above embodiment will be described below.

According to a first aspect of the present invention, the metal separator14is provided. The metal separator14is stacked on each of both surfaces of the membrane electrode assembly16to form the fuel cell10. The membrane electrode assembly16includes the electrolyte membrane20, and the electrodes (the anode22, the cathode24) provided on both surfaces of the electrolyte membrane. The metal separator14includes the metal plate50and the plurality of rubber extension parts53. The metal plate50has the fluid passage26configured to allow fluid to flow in a stacking direction. The metal plate50forms the fluid flow field38configured to allow the fluid to flow along a separator surface. The plurality of rubber extension parts53are adhered to the metal plate50, and extend from the fluid passage26toward the fluid flow field38. Between the plurality of rubber extension parts53, the metal surface (metal exposed surface51) of the metal plate50is exposed, and the channel (fluid channel58) configured to connect the fluid passage26and the fluid flow field38is formed. The plurality of rubber extension parts53are adhered to the metal plate50through the plurality of dot primers61between the metal plate50and the rubber extension parts53.

In the metal separator14, with the simple structure where the metal plate50and the rubber extension parts53are adhered together through the plurality of dot primers61, it is possible to suitably discharge the liquid from the portion between the metal plate50and the rubber extension parts53. That is, in the metal separator14, even if the vaporized liquid enters the joint border64between the metal plate50and the rubber extension part53and is liquefied, the liquid can be discharged to the outside of the joint border64(e.g., metal exposed surface51) through the portion where the dot primers61are not coated. Therefore, in the metal separator14, it is possible to suppress formation of the blisters between the metal plate50and the rubber extension parts53. Further, in the metal separator14, by eliminating local concentration of leakage current, it is possible to prevent pitting corrosion due to corrosion resulting from the electric potential difference.

Further, the joint border64between the metal plate50and the rubber extension part53includes the first adhesive portion64awhere the rubber the metal plate50and the rubber extension part53are adhered together through each of the plurality of dot primers61, and the second adhesion portion64bwhere the plurality of dot primers61are not coated and the metal plate50and the rubber extension part53are directly adhered together. In the structure, in the metal separator14, the liquid produced between the metal plate50and the rubber extension part53can be discharged more easily through the second adhesion portion64b.

Further, the ratio of the total area of the plurality of dot primers61to the area of an adhesion surface of the rubber extension part53is within the range of 10% to 30%. In the structure, in the metal separator14, the rubber extension part53can be suitably adhered to the metal plate50, and the liquid produced between the metal plate50and the rubber extension part53can be discharged more reliably.

Further, the plurality of dot primers61are also coated on the metal surface (metal exposed surface51). By adopting the structure, in the metal separator14, it is possible to increase the efficiency of the primer coating step of coating the plurality of dot primers61.

Further, the rubber extension part53is a part of the rubber member52provided on the metal plate50, and the adhesion portion of the rubber member52excluding the adhesion portions of the plurality of rubber extension parts53is adhered to the metal plate50through the planar primer62coated in a planar shape. By adopting this structure, in the metal separators14, it is possible to firmly join the metal plate50and the rubber member52together.

Further, the plurality of dot primers61are arranged in a matrix pattern. In the structure, in the case where liquid is produced between the metal plate50and the rubber extension part53, the liquid can more smoothly move through the portions which are continuous between the dot primers61and in which the dot primers61are not coated.

Further, the metal separator14includes, as the fluid passage26, the coolant passage32for a coolant, and in the state where a plurality of the fuel cells10are stacked together, the metal separator14includes, as the fluid flow field38, the coolant flow field48for the coolant between the metal separator14and another metal separator14that is adjacent to the metal separator14, and the rubber extension part53adhered by the plurality of dot primers61is provided between the coolant passage32and the coolant flow field48. By adopting the structure, in the metal separator14, it is possible to suppress formation of the blisters at positions where the coolant flows, and prevent pitting corrosion due to the corrosion resulting from the electric potential difference.

Further, the metal separator14includes, as the fluid passage26, the reactant gas passage26afor a reactant gas, and includes, as the fluid flow field38, the reactant gas flow field38afor the reactant gas between the metal separator14and the membrane electrode assembly16. The rubber extension part53adhered by the plurality of dot primers61is provided between the reactant gas passage26aand the reactant gas flow field38a. By adopting the structure, in the metal separator14, it is possible to suppress formation of the blisters at positions where the reactant gas flows, and prevent pitting corrosion due to the corrosion resulting from the electric potential difference.

Further, according to a second aspect of the present invention, the fuel cell10is provided. The fuel cell10is formed by stacking a metal separator14on each of both surfaces of the membrane electrode assembly16. The membrane electrode assembly16includes the electrolyte membrane20, and the electrodes (the anode22and the cathode24) provided on both surfaces of the electrolyte membrane20. The metal separator14includes the metal plate50and the plurality of rubber extension parts53. The metal plate50has the fluid passage26configured to allow fluid to flow in a stacking direction. The metal plate50forms the fluid flow field38configured to allow the fluid to flow along a separator surface. The plurality of rubber extension parts53are adhered to the metal plate50, and extend from the fluid passage26toward the fluid flow field38. Between the plurality of rubber extension parts53, the metal surface (metal exposed surface51) of the metal plate50is exposed, and the channel (fluid channel58) configured to connect the fluid passage26and the fluid flow field38is formed. The plurality of rubber extension parts53are adhered to the metal plate50through the plurality of dot primers61between the metal plate50and the rubber extension parts53.

Further, according to a third aspect of the present invention, the method of producing the metal separator14is provided. The metal separator14is stacked on each of both surfaces of the membrane electrode assembly16to form the fuel cell10. The membrane electrode assembly16includes the electrolyte membrane20, and the electrodes (the anode22and the cathode24) provided on both surfaces of the electrolyte membrane20. The method includes the metal plate processing step of producing the metal plate50, and the rubber adding step of providing the plurality of rubber extension parts53on the metal plate50. The metal plate50has the fluid passage26configured to allow fluid to flow in a stacking direction. The metal plate50forms the fluid flow field38configured to allow the fluid to flow along a separator surface. The rubber extension parts53extends from the fluid passage26toward the fluid flow field38. Between the plurality of rubber extension parts53, the metal surface (metal exposed surface51) of the metal plate50is exposed, and the channel (fluid channel58) configured to connect the fluid passage26and the fluid flow field38is formed. In the rubber adding step, the plurality of rubber extension parts53are adhered to the metal plate50through the plurality of dot primers61.