Frame-equipped membrane electrode assembly and fuel cell

Abstract

Framed membrane electrode assembly (10, 110, 210) comprising: a membrane electrode assembly (10a, 110a, 210a) comprising an electrolyte membrane (18), a first electrode (20, 120, 220) provided on one surface of the electrolyte membrane (18), and a second electrode (22, 122, 222) provided on the other surface of the electrolyte membrane (18); and a frame member (24, 224) provided over an entire circumference of an outer peripheral portion of the membrane electrode assembly (10a, 110a, 210a), wherein a surface dimension of the second electrode (22, 122, 222) is larger than a surface dimension of the first electrode (20, 120, 220); the frame element (24, 224) includes a first frame-shaped layer (24a) and a second frame-shaped layer (24b); an inner peripheral portion (24an) of the first frame-shaped layer (24a) is connected to the outer peripheral portion of the membrane electrode assembly (10a, 110a, 210a); the first frame-shaped layer (24a) and the second frame-shaped layer (24b) are connected to each other in the thickness direction; the inner peripheral portion (24an) of the first frame-shaped layer (24a) is arranged between an outer peripheral portion (20c, 120c, 220c) of the first electrode (20, 120, 220) and an outer peripheral portion (22c, 122c, 222c) of the second electrode (22, 122, 222); an inner end (24be) of the second frame-shaped layer (24b) is arranged over an entire circumference outside an outer end (20e, 120e, 220e) of the first electrode (20, 120, 220); and an outer end (22e, 122e, 222e) of the second electrode (22, 122, 222) is arranged over the entire circumference outside the inner end (24be) of the second frame-shaped layer (24b), characterized in that the outer peripheral portion (20c, 120c, 220c) of the first electrode (20, 220) or second electrode (122) overlaps the inner peripheral portion (24an) of the first frame-shaped layer (24a) on its side remote from the electrolyte membrane (18).

Description

BACKGROUND OF THE INVENTIONField of the Invention:The present invention relates to a frame-equipped membrane electrode assembly and a fuel cell.Description of Related Art:Generally, a solid polymer electrolyte fuel cell uses a solid polymer electrolyte membrane. The solid polymer electrolyte membrane is a polymer ion exchange membrane. In the fuel cell, an anode is provided on one surface of the solid polymer electrolyte membrane, and a cathode is provided on the other surface of the solid polymer electrolyte membrane, each for forming a membrane electrode assembly (MEA).The membrane electrode assembly is sandwiched between separators (bipolar plates) to form a power generation cell (unit fuel cell). In use, a predetermined number of power generation 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 stackIn recent years, in an attempt to reduce the amount of the relatively expensive solid polymer electrolyte membranes and protect the thin solid polymer electrolyte membrane having a low strength, a frame-equipped MEA including a resin frame member in its outer periphery has been applied (see, for example, U.S. Pat. No. 8,399,150 B2).DE 10 2016 212 912 A1 shows a frame-equipped membrane electrode arrangement and a fuel cell according to the preamble of claims 1 and 21 There, and in US 2011 / 0136038 A1, an electrode overlaps a part of the first frame-shaped layer on the side facing the electrolyte membrane.SUMMARY OF THE INVENTIONIf the difference between the pressure of a reaction gas supplied to an anode and the pressure of a reaction gas supplied to a cathode is large, if the pressure difference acts on a thin resin frame member, the resin frame member may be deformed too much, and the resin frame member may be undesirably damaged.The present invention has been made in consideration of the above problem, and an object of the present invention is to provide a membrane electrode assembly equipped with a plastic frame and a fuel cell, whereby it is possible to avoid deformation of a frame member in the presence of the difference between the pressure of a reaction gas supplied to an anode and the pressure of a reaction gas supplied to a cathode, and improve the durability of the frame member.To achieve the above object, the present invention provides a frame-equipped membrane electrode assembly according to claim 1. The frame-equipped membrane electrode assembly includes a membrane electrode assembly and a frame member. The membrane electrode assembly includes an electrolyte membrane, a first electrode provided on one surface of the electrolyte membrane, and a second electrode provided on the other surface of the electrolyte membrane. The frame member is provided over an entire periphery of an outer peripheral portion of the membrane electrode assembly. A surface dimension of the second electrode is greater than a surface dimension of the first electrode. The frame member includes a first frame-shaped layer and a second frame-shaped layer. An inner peripheral portion of the first frame-shaped layer is connected to the outer peripheral portion of the membrane electrode assembly. The first frame-shaped layer and the second frame-shaped layer are connected to each other in the thickness direction. The inner peripheral portion of the first frame-shaped layer is disposed between an outer peripheral portion of the first electrode and an outer peripheral portion of the second electrode. An inner end of the second frame-shaped layer is disposed outside an outer end of the first electrode over an entire circumference, and an outer end of the second electrode is disposed outside the inner end of the second frame-shaped layer over the entire circumference.In the frame-equipped membrane electrode assembly according to the present invention, the outer end of the second electrode, which is the larger electrode, is disposed over the entire circumference outside the inner end of the second frame-shaped layer, which is the thinner frame-shaped layer. In the structure, a portion of the first frame-shaped layer corresponding to a position between the outer end of the first electrode and the inner end of the second frame-shaped layer is supported by the outer peripheral portion of the second electrode. In the structure, if the pressure of the reaction gas applied from the first electrode is higher than the pressure of the reaction gas applied from the second electrode, it is possible to avoid deformation of the frame member in the presence of the pressure difference applied from the first electrode and improve the durability of the frame member.Preferably, the inner peripheral portion of the first frame-shaped layer is joined to a surface of an outer peripheral portion of the electrolyte membrane adjacent to the first electrode.Preferably, an outer end of the electrolyte membrane is arranged outside the outer end of the first electrode.Preferably, an adhesive layer is provided on an entire surface of the first frame-shaped layer; an outer peripheral portion of the first frame-shaped layer is bonded to an entire surface of the second frame-shaped layer through the adhesive layer; and the inner peripheral portion of the first frame-shaped layer is bonded to the outer peripheral portion of the electrolyte membrane through the adhesive layer.Preferably, the outer peripheral portion of the second electrode covers a step formed by a surface of the first frame-shaped layer and the inner end of the second frame-shaped layer and extending outward beyond the inner end of the second frame-shaped layer.Preferably, the first electrode includes a step at a position corresponding to an inner end of the first frame-shaped layer; and the second electrode includes a step at a position corresponding to the inner end of the second frame-shaped layer.Preferably, the first electrode is an anode and the second electrode is a cathode.Preferably, the inner peripheral portion of the first frame-shaped layer is joined to a surface of an outer peripheral portion of the electrolyte membrane adjacent to the second electrode.Preferably, an outer end of the electrolyte membrane and the outer end of the first electrode are provided at the same position as viewed in the thickness direction of the membrane electrode assembly.Preferably, an adhesive layer is provided on an entire surface of the first frame-shaped layer; an outer peripheral portion of the first frame-shaped layer is bonded to the one entire surface of the second frame-shaped layer through the adhesive layer; and the inner peripheral portion of the first frame-shaped layer is bonded to the outer peripheral portion of the electrolyte membrane through the adhesive layer.Preferably, a gap is formed between the outer end of the first electrode and the inner end of the second frame-shaped layer.Preferably, the first electrode is an anode and the second electrode is a cathode.Preferably, the inner peripheral portion of the first frame-shaped layer is joined to a surface of an outer peripheral portion of the electrolyte membrane adjacent to the first electrode on a surface opposite to the second frame-shaped layer.Preferably, when viewed in the thickness direction of the membrane electrode assembly, an outer end of the electrolyte membrane and the outer end of the second electrode are at the same position.Preferably, an outer peripheral portion of the first frame-shaped layer is bonded to an entire surface of the second frame-shaped layer by a first adhesive layer provided on one surface of the first frame-shaped layer; and the inner peripheral portion of the first frame-shaped layer is bonded to the outer peripheral portion of the electrolyte membrane by a second adhesive layer provided on the other surface of the first frame-shaped layer.Preferably, a gap is formed over the entire circumference between the outer end of the first electrode and the inner end of the second frame-shaped layer.Preferably, the first electrode is an anode and the second electrode is a cathode.Further, the present invention provides a fuel cell according to claim 21. The fuel cell includes a frame-equipped membrane electrode assembly and separators provided on both sides of the frame-equipped membrane electrode assembly, respectively. The frame-equipped membrane electrode assembly includes: a membrane electrode assembly; and a frame member provided over an entire periphery of an outer peripheral portion of the membrane electrode assembly. The membrane electrode assembly includes an electrolyte membrane, a first electrode provided on one surface of the electrolyte membrane, and a second electrode provided on the other surface of the electrolyte membrane. A surface dimension of the second electrode is greater than a surface dimension of the first electrode. The frame member includes a first frame-shaped layer and a second frame-shaped layer; an inner peripheral portion of the first frame-shaped layer is connected to the outer peripheral portion of the membrane electrode assembly; the first frame-shaped layer and the second frame-shaped layer are connected to each other in the thickness direction; the inner peripheral portion of the first frame-shaped layer is disposed between an outer peripheral portion of the first electrode and an outer peripheral portion of the second electrode; an inner end of the second frame-shaped layer is disposed outside an outer end of the first electrode over an entire circumference; and an outer end of the second electrode is disposed outside the inner end of the second frame-shaped layer over the entire circumference.A bead seal is preferred.The above and other objects, features and advantages of the present invention will become more apparent from the following description taken in conjunction with the accompanying drawings, in which a preferred embodiment of the present invention is shown by way of example.BRIEF DESCRIPTION OF THE DRAWINGSFIG. 1 is an exploded perspective view showing main components of a power generation cell according to an embodiment of the present invention; FIG. 2 is a cross-sectional view showing the power generation cell taken along line II-II in FIG. 1 ; FIG. 3 is an overall schematic view showing a fuel cell system; FIG. 4 is a cross-sectional view showing a power generation cell according to a second embodiment of the present invention; and FIG. 5 is a cross-sectional view showing a power generation cell according to a third embodiment of the present invention.DESCRIPTION OF THE PREFERRED EMBODIMENTAs shown in FIGS. 1 and 2, a power generation cell (fuel cell) 12 according to a first embodiment includes a frame-equipped membrane electrode assembly 10 (hereinafter referred to as "frame-equipped MEA 10"), and a first separator 14 and a second separator 16 provided on both sides of the frame-equipped MEA 10, respectively. For example, the power generation cell 12 is a laterally elongated (or longitudinally elongated) rectangular solid polymer electrolyte fuel cell. A plurality of the power generation cells 12 are stacked together in the horizontal direction indicated by arrow A or the gravity direction indicated by arrow C to form a fuel cell stack 11 a. For example, the fuel cell stack 11 ais mounted as an in-vehicle fuel cell stack in a fuel cell electric vehicle (not shown).In the power generation cell 12, the frame-equipped MEA 10 is laminated between the first separator 14 and the second separator 16. The first separator 14 and the second separator 16 each have a laterally elongated (or longitudinally elongated) rectangular shape. For example, each of the first separator 14 and the second separator 16 is a steel sheet, a stainless steel sheet, an aluminum sheet, a galvanized steel sheet, a surface treatment anticorrosive surface metal sheet, a carbon member, or the like.The rectangular frame-equipped MEA 10 includes a membrane electrode assembly 10 a(hereinafter referred to as the "MEA 10 a"). The MEA 10 aincludes an electrolyte membrane 18, an anode 20 provided on one surface of the electrolyte membrane 18, and a cathode 22 provided on the other surface of the electrolyte membrane 18. In the first embodiment, the anode 20 is referred to as the "first electrode" of the present invention, and the cathode 22 is referred to as the "second electrode" of the present invention.For example, the electrolyte membrane 18 is a solid polymer electrolyte membrane (cation exchange membrane). The solid polymer electrolyte membrane is formed by impregnating a perfluorosulfonic acid thin membrane with water, for example. The electrolyte membrane 18 is disposed between the anode 20 and the cathode 22. A fluorine-based electrolyte may be used as the electrolyte membrane 18. Alternatively, a HC (hydrocarbon)-based electrolyte may be used as the electrolyte membrane 18. An outer end 18 eof the electrolyte membrane 18 is disposed outside an outer end 20 eof the anode 20.The surface dimension (outer dimension) of the anode 20 is larger than the surface dimensions of the electrolyte membrane 18 and the cathode 22, and therefore, the outer end of the anode 20 is disposed outside an outer end 18 eof the electrolyte membrane 18 and an outer end 22 eof the cathode 22 over the entire circumference.As shown in FIG. 2, the anode 20 includes a first electrode catalyst layer 20 athat is bonded to a surface 18 aof the electrolyte membrane 18, and a first gas diffusion layer 20 bthat is stacked on the electrode catalyst layer 20 a. The surface dimension of the first electrode catalyst layer 20 aand the surface dimension of the first gas diffusion layer 20 bare equal to and smaller than the surface dimensions of the electrolyte membrane 18 and the cathode 22.The surface dimension of the cathode 22 is larger than the surface dimensions of the electrolyte membrane 18 and the anode 20.The cathode 22 includes a second electrode catalyst layer 22 athat is bonded to a surface 18 bof the electrolyte membrane 18, and a second gas diffusion layer 22 bthat is stacked on the second electrode catalyst layer 22 a. The surface dimension of the second electrode catalyst layer 22 a, the surface dimension of the second gas diffusion layer 22 b, and the surface dimension of the electrolyte membrane 18 are the same. It should be noted that the surface dimensions of the second electrode catalyst layer 22 aand the second gas diffusion layer 22 bmay be larger than the surface dimension of the electrolyte membrane 18.For example, the first electrode catalyst layer 20 ais formed of porous carbon particles uniformly dispersed on the surface of the first gas diffusion layer 20 btogether with an ion conductive polymer binder, and platinum alloy supported on the porous carbon particles. For example, the second electrode catalyst layer 22 ais formed by porous carbon particles uniformly supported on the surface of the second gas diffusion layer 22 btogether with an ion conductive polymer binder, and platinum alloy supported on the porous carbon particles.Each of the first gas diffusion layer 20 band the second gas diffusion layer 22 bincludes a carbon paper or a carbon cloth, etc. The surface dimension of the second gas diffusion layer 22 bis larger than the surface dimension of the first gas diffusion layer 20 b. The first electrode catalyst layer 20 aand the second electrode catalyst layer 22 aare respectively formed on both surfaces of the electrolyte membrane 18.The frame-equipped MEA 10 is formed around the entire outer periphery of the electrolyte membrane 18 and includes a rectangular frame member 24 connected to the anode 20 and the cathode 22. The frame member 24 includes two frame-shaped layers. Specifically, the frame member 24 includes a first frame-shaped layer 24 aand a second frame-shaped layer 24 b. The first frame-shaped layer 24 aincludes an inner peripheral portion 24 anconnected to an outer peripheral portion of the MEA 10 a. The second frame-shaped layer 24 bis connected to the first frame-shaped layer 24 a.The first frame-shaped layer 24 aand the second frame-shaped layer 24 bare bonded to each other over the entire circumference (over the entire surface of the second frame-shaped layer 24 badjacent to the first frame-shaped layer 24 a) by an adhesive layer 24 cmade of adhesive 24 d. The second frame-shaped layer 24 bis joined to the outer peripheral portion of the first frame-shaped layer 24 a. In the structure, an outer peripheral portion 24 gof the frame member 24 is thicker than the inner peripheral portion of the frame member 24 b(inner peripheral portion 24 an the first frame-shaped layer 24 a).The first frame-shaped layer 24 aand the second frame-shaped layer 24 bare made of plastic material. Examples of materials of the first frame-shaped layer 24 aand the second frame-shaped layer 24 binclude PPS (polyphenylene sulfide), PPA (polyphthalamide), PEN (polyethylene naphthalate), PES (polyether sulfone), LCP (liquid crystal polymer), PVDF (polyvinylidene fluoride), a silicone resin, a fluororesin, m-PPE (modified polyphenylene ether) resin, PET (polyethylene terephthalate), PBT (polybutylene terephthalate), or modified polyolefin.The inner peripheral portion 24 an the first frame-shaped layer 24 ais disposed between an outer peripheral portion 20 cof the anode 20 and an outer peripheral portion 22 cof the cathode 22. Specifically, the inner peripheral portion 24 an the first frame-shaped layer 24 ais interposed between the outer peripheral portion 18 cof the electrolyte membrane 18 and the outer peripheral portion 20 cof the anode 20. The inner peripheral portion 24 aon the first frame-shaped layer 24 ais joined to the surface 18 aof the electrolyte membrane 18 facing the anode 20. The inner peripheral portion 24 aof the first frame-shaped layer 24 aand the outer peripheral portion 18 cof the electrolyte membrane 18 are joined to each other by the adhesive layer 24 c. The inner peripheral portion 24 anof the first frame-shaped layer 24 aincludes an overlapping part 24 akthat overlaps with the outer peripheral portion 20 cof the anode 20 over the entire circumference as viewed in the thickness direction of the MEA 10 a. The inner peripheral portion 24 anof the first frame-shaped layer 24 amay be interposed between the electrolyte membrane 18 and the cathode 22 in a state where the adhesive layer 24 cis bonded to the surface 18 bof the electrolyte membrane 18.A step is provided for the anode 20 at a position corresponding to an inner end 24 aeof the first frame-shaped layer 24 a. Specifically, the anode 20 has an inclined portion 24 cthat is inclined from the electrolyte membrane 18 between a portion 21 athat overlaps with the inner peripheral portion 24 anof the first frame-shaped layer 24 aand a portion 21 bthat overlaps with the electrolyte membrane 18. Therefore, in the inclined portion 21 c, the first electrode catalyst layer 20 aand the first gas diffusion layer 20 bare inclined away from the electrolyte membrane 18.In the anode 20, the surface of the region 21 athat overlaps with the inner peripheral portion 24 anon the first frame-shaped layer 24 aadjacent to the first separator 14 is spaced apart from the electrolyte membrane 18 as compared with the surface of the region 21 bthat overlaps with the electrolyte membrane 18 adjacent to the first separator 14.A step is provided for the cathode 22 at a position corresponding to an inner end 24 beof the second frame-shaped layer 24 b. Specifically, the cathode 22 has an inclined portion 23 cthat is inclined from the first frame-shaped layer 24 abetween a portion 23 athat overlaps with the inner peripheral portion of the second frame-shaped layer 24 band a portion that overlaps with the outer peripheral portion of the electrolyte membrane 18. Therefore, in the inclined portion 23 c, the second electrode catalyst layer 22 aand the second gas diffusion layer 22 bare inclined away from the electrolyte membrane 18. The outer peripheral portion 22 cof the cathode 22 covers the step formed by a surface (surface 24 as) of the first frame-shaped layer 24 aand the inner end 24 beof the second frame-shaped layer 24 band extends outward beyond the inner end 24 beof the second frame-shaped layer 24 b. In the cathode 22, the surface of the region 23 athat overlaps with the inner peripheral portion of the second frame-shaped layer 24 badjacent to the second separator 16 is spaced apart from the first frame-shaped layer 24 a, as compared with the surface of the region 23 bthat overlaps with the electrolyte membrane 18 adjacent to the second separator 16.The cathode 22 may also have a slant portion at a position corresponding to the slant portion 21 cof the anode 20. That is, the cathode 22 may have an inclined portion inclined from the electrolyte membrane 18 between a portion overlapping with the inner peripheral portion 24 anof the first frame-shaped layer 24 aand a portion overlapping with the electrolyte membrane 18 (portion inclined toward the direction opposite to the inclined portion 21 c).Instead of employing the above structure, the anode 20 may also have a flat shape from the region 21 binterlacing with the electrolyte membrane 18 to the region 21 overlapping with the inner peripheral portion 24 anon the first frame-shaped layer 24 a, and the cathode 22 may have an inclined region inclined from the electrolyte membrane 18 between the region 23 binterlacing with the electrolyte membrane 18 and the region 23 ainterlacing with the inner peripheral portion 24 anon the first frame-shaped layer 24 a.The second frame-shaped layer 24 bis joined to the outer peripheral portion of the first frame-shaped layer 24 a. The thickness T 2 of the second frame-shaped layer 24 bis greater than the thickness T 1 of the first frame-shaped layer 24 a. It should be noted that the thickness of the first frame-shaped layer 24 amay be equal to the thickness of the second frame-shaped layer 24 b. An inner end 24 beof the second frame-shaped layer 24 bis disposed outside the inner end 24 aof the first frame-shaped layer 24 aover the entire circumference (toward away from the MEA 10 a).The inner end 24 beof the second frame-shaped layer 24 bis disposed outside the outer end 20 eof the anode 20 over the entire circumference and outside the inner end 24 aeof the first frame-shaped layer 24 a. The inner end 24 beof the second frame-shaped layer 24 bis disposed inside the outer end 18 eof the electrolyte membrane 18. The inner end 24 beof the second frame-shaped layer 24 bmay also be disposed outside the outer end 18 eof the electrolyte membrane 18. The outer end 22 eof the cathode 22 is disposed outside the inner end 24 beof the second frame-shaped layer 24 bover the entire circumference. Therefore, when viewed in the thickness direction of the MEA 10 a, the outer peripheral portion 22 cof the cathode 22 has an overlapping part 22 kthat overlaps with the inner peripheral portion of the second frame-shaped layer 24 b.The adhesive layer 24 cis provided over the entire surface 24 asof the first frame-shaped layer 24 aadjacent to the second frame-shaped layer 24 b(cathode side). The outer peripheral portion of the first frame-shaped layer 24 ais bonded to the one entire surface of the second frame-shaped layer 24 bthrough the adhesive layer 24 c. The inner peripheral portion 24 aon the first frame-shaped layer 24 ais joined to the outer peripheral portion 18 cof the electrolyte membrane 18 through the adhesive layer 24 c. As the adhesive 24d of the adhesive layer 24c, for example, liquid adhesive or a hot melt layer is provided. The adhesive is not limited to liquid or solid adhesives, and is not limited to thermoplastic or thermosetting adhesives, etc.An overlapping part K where the anode 20, the first frame-shaped layer 24 a, and the cathode 22 overlap each other is held between a rib 39 of the first separator 14 protruding toward the anode 20 and a rib 37 of the second separator 16 protruding toward the cathode 22. The overlap part K may be held between a bead seal provided for the first separator 14 and a bead seal provided for the second separator 16.As shown in FIG. 1, at one end of the power generation cell 12 in the horizontal direction indicated by the arrow B, an oxygen-containing gas supply passage 30 a, a coolant supply passage 32 a, and a fuel gas discharge passage 34 bare provided. The oxygen-containing gas supply passage 30 a, the coolant supply passage 32 a, and the fuel gas discharge passage 34 bextend through the power generation cell 12 in the stacking direction indicated by the arrow A. The oxygen-containing gas is supplied through the oxygen-containing gas supply passage 30 a, and the coolant is supplied through the coolant supply passage 32 a. A fuel gas such as a hydrogen-containing gas is discharged through the fuel gas discharge passage 34 b. The oxygen-containing gas supply passage 30 a, the coolant supply passage 32 a, and the fuel gas discharge passage 34 bare arranged in the vertical direction indicated by the arrow C.At the other end of the power generation cell 12 in the direction indicated by the arrow B, a coolant supply passage 34 afor supplying the fuel gas, a coolant discharge passage 32 bfor discharging the coolant, and an oxygen-containing gas discharge passage 30 bfor discharging the oxygen-containing gas are provided. The fuel gas supply passage 34 a, the coolant discharge passage 32 b, and the oxygen-containing gas discharge passage 30 bextend through the power generation cell 12 in the direction indicated by the arrow A. The fuel gas supply passage 34 a, the coolant discharge passage 32 b, and the oxygen-containing gas discharge passage 33 bare arranged in the direction indicated by the arrow C.The first separator 14 has, on its surface 14 afacing the frame-equipped MEA 10, a fuel gas flow field 38 The fuel gas flow field 38 is connected to the fuel gas supply channel 34 aand the fuel gas discharge channel 34 b. Specifically, the fuel gas flow field 38 is formed between the first separator 14 and the frame-equipped MEA 10. The fuel gas flow field 38 includes straight flow grooves (or wavy flow grooves) extending in the direction indicated by the arrow B.The second separator 16 has, on its surface 16 afacing the frame-equipped MEA 10, an oxygen-containing gas flow field 36. Specifically, the oxygen-containing gas flow field 36 is formed between the second separator 16 and the frame-equipped MEA 10. The oxygen-containing gas flow field 36 includes a plurality of straight flow grooves (or wavy flow grooves) extending in the direction indicated by the arrow B.A coolant flow field 40 is formed between a surface 14 bof the first separator 14 and a surface 16 bof the second separator 16. The coolant flow field 40 is connected to the coolant supply passage 32 aand the coolant discharge passage 32 b. The coolant flow field 40 extends in the direction indicated by the arrow B.As shown in FIG. 2, a plurality of ribs 39 forming the fuel gas flow field 38 are provided on the surface 14 aof the first separator 14 (the surface facing the frame-equipped MEA 10). The ribs 39 protrude to the anode 20 and contact the anode 20, and a plurality of ribs 37 forming the oxygen-containing gas flow field 36 are provided on the surface 16 aof the second separator 16 (the surface facing the frame-equipped MEA 10). The ribs 37 protrude toward the cathode 22 and contact the cathode 22, and the MEA 10 ais held between the ribs 37, 39.A plurality of bead seals 42 are provided on the surface 14 aof the first separator 14 around the outer peripheral portion of the first separator 14 to prevent leakage of the fuel gas to the outside. The bead seals 42 are press formed to expand toward the frame member 24. The bead seal 42 on the inner side is formed around the fuel gas flow field 38, the fuel gas supply passage 34 a, and the fuel gas discharge passage 34 b, while allowing the fuel gas flow field 38 to communicate with the fuel gas supply passage 34 aand the fuel gas discharge passage 34 b. Although two bead seals 42 are provided in the embodiment, only one bead seal 42 need be provided.A resin member 43 (or rubber member) adheres, by printing, coating, etc., to the front end surface of the rib of each of the bead seals 42. the bead seals 42 contact the first frame-shaped layer 24 a(a portion overlapped with the second frame-shaped layer 24 b) air-tightly or liquid-tightly by the resin member 43. Instead of the bead seals 42, for example, elastic solid seals protruding toward the frame member 24 may be provided for the first separator 14.A channel 38 aformed between the first separator 14 and the frame member 24 within the bead seals 42 (MEA 10 aside) is connected to the fuel gas flow field 38. Therefore, the fuel gas is supplied to the passage 38a.Bead seals 44 are provided on the surface 16 aof the second separator 16 around the outer peripheral portion of the second separator 16 to prevent leakage of the oxygen-containing gas. The bead seals 44 are press formed to expand toward the frame member 24. The bead seal 44 on the inner side is formed around the oxygen-containing gas flow field 36, the oxygen-containing gas supply channel 30 a, and the oxygen-containing gas discharge channel 30 b, while allowing the oxygen-containing gas flow field 36 to communicate with the oxygen-containing gas supply channel 30 aand the oxygen-containing gas discharge channel 30 b. Although two bead seals 44 are provided in the embodiment, only one bead seal 44 need be provided.A resin member 45 (or rubber member) is adhered to the front end surface of the rib of the bead seal 44 by printing, coating, etc. The bead seals 44 contact the second frame-shaped layer 24 b(a portion overlapped with the first frame-shaped layer 24 a) air-tightly or liquid-tightly by the resin member 45. the resin member 45 may be bonded to the second frame-shaped layer 24 b.Instead of the bead seals 44, elastic solid seals protruding toward the frame member 24 may be provided for the second separator 16.For example, for the plastic members 43, 45, polyester fiber, silicone, EPDM, FKM, etc. are used. The plastic members 42, 45 are not essential and need not be provided (in this case, the bead seals 42 directly contact the first frame-shaped layer 24a, and the bead seals 44 directly contact the second frame-shaped layer 24b).The bead seals 42 and the bead seals 44 face each other through the frame member 24. The outer peripheral portion of the frame member 24 (a region where the first frame-shaped layer 24 aand the second frame-shaped layer 24 binterlate with each other) is held between the bead seals 42 of the first separator 14 and the bead seals 44 of the second separator 16. If the above solid gaskets are provided for the first separator 14 and the second separator 16, the outer peripheral portion of the frame member 24 (the region where the first frame-shaped layer 24 aand the second frame-shaped layer 24 binterlate with each other) is held between the solid gasket of the first separator 14 and the solid gasket of the second separator 16.A channel 36 aformed between the second separator 16 and the frame member 24 inside the bead seals 44 (MEA 10 aside) is connected to the oxygen-containing gas flow field 36. Therefore, the oxygen-containing gas is supplied to the passage 36a.In FIG. 3, a fuel cell system 11 includes the above-described fuel cell stack 11 a, an oxygen-containing gas supplier 50 for supplying the oxygen-containing gas to the fuel cell stack 11 a, a fuel gas supplier 52 for supplying the fuel gas to the fuel cell stack 11 a, and a coolant supplier 54 for supplying the coolant to the fuel cell stack 11 a.The oxygen-containing gas supply device 50 includes an oxygen-containing gas supply pipe 64 athat is connected to the oxygen-containing gas supply passage 30 a(see FIG. 1 ) through an oxygen-containing gas supply manifold 58 aprovided for the fuel cell stack 11 a, and an oxygen-containing gas discharge pipe 64 bthat is connected to the oxygen-containing gas discharge passage 30 b(see FIG. 1 ) through an oxygen-containing gas discharge collector 58 bthat is provided for the fuel cell stack 11 a. An air pump 66 is provided for the oxygen-containing gas supply pipe 64 a. A back pressure regulating valve 68 is provided in the oxygen-containing gas discharge pipe 64 b.A humidifier 67 is provided for the oxygen-containing gas supply pipe 64 aand the oxygen-containing gas discharge pipe 64 b. The structure of the humidifier 67 is not particularly limited as long as the humidifier 67 can wet the air supplied to the fuel cell stack 11 a. In the oxygen-containing gas supply pipe 64 a, the air pump 66 is provided upstream of the humidifier 67. In the oxygen-containing gas discharge pipe 64 b, the back pressure regulating valve 68 is provided downstream of the humidifier 67. A control unit 70 of the fuel cell system 11 controls the operation speed of the air pump 66 and the valve opening degree of the back pressure regulating valve 68 to control the pressure and the flow rate of the oxygen-containing gas flowing through the oxygen-containing gas flow field 36.The fuel gas supply device 52 includes a fuel gas supply pipe 72 aconnected to the fuel gas supply passage 34 a(see FIG. 1 ) through a fuel gas supply manifold 68 aprovided for the fuel cell stack 11 a, and a fuel gas discharge pipe 72 bconnected to the fuel gas discharge passage 34 b(see FIG. 1 ) through a fuel gas discharge collector 60 bprovided for the fuel cell stack 11 a.A hydrogen tank 74 for storing high-pressure hydrogen is provided upstream of the fuel gas supply pipe 72 a. In the fuel gas supply pipe 72 a, a stop valve 76, a regulator valve 77, and an ejector 78 are provided between the fuel gas supply manifold 60 aand the hydrogen tank 74. A hydrogen circulation passage 80 is connected to the ejector 78 and the fuel gas discharge pipe 72 b. A hydrogen pump 82 for hydrogen circulation is provided in the hydrogen circulation channel 80. The control unit 70 controls the driving speed of the hydrogen pump 82 to control the flow rate of the fuel gas flowing through the fuel gas flow field 38.The coolant supply device 54 includes a coolant circulation channel 84 for circulating and supplying the coolant to the fuel cell stack 11 a. The coolant circulation passage 84 is connected to the coolant supply passage 32 a(see FIG. 1 ) through a coolant supply manifold 62 aprovided for the fuel cell stack 11 a. The coolant circulation passage 84 is connected to the coolant discharge passage 32 b(see FIG. 1 ) through a coolant discharge header 62 b. A radiator 86 and a coolant pump 88 are provided for the coolant circulation passage 84.Next, the operation of the fuel cell system 1 including the power generation cell 12 (the fuel cell stack 11 a) having the above structure will be described.As shown in FIG. 3, in the oxygen-containing gas supply device 50, the air is supplied to the oxygen-containing gas supply pipe 64 aunder the operation of the air pump 66. After the air has passed through the humidifier 67 and the air is humidified, the air is supplied to the oxygen-containing gas supply channel 30 a(see FIG. 1 ) through the oxygen-containing gas supply manifold 58 a. The humidifier 67 adds water and heat to the supplied air, which is discharged from the oxygen-containing gas discharge collector 84 b. Meanwhile, in the fuel gas supply device 52, under the operation of the stop valve 76, the fuel gas is supplied from the hydrogen tank 74 to the fuel gas supply pipe 72 a. Here, the fuel gas whose pressure has been regulated (reduced) by the regulator valve 77 and the fuel gas from the hydrogen pump 82 are united at the ejector 78, and the fuel gas is supplied into the fuel gas supply manifold 60 a. The fuel gas is supplied to the fuel gas supply passage 34 a(see FIG. 1 ) through the fuel gas supply manifold 60 a. Further, in the coolant supply device 54, under the operation of the coolant pump 88, the coolant is supplied from the coolant circulation passage 84 to the coolant supply passage 32 a(see FIG. 1 ). Here, the coolant is supplied from the coolant supply manifold 62 ato the coolant flow field 40 provided in the fuel cell stack 11 a. After the coolant has passed through the coolant flow field 40, the coolant is discharged from the coolant discharge header 62 bto the coolant circulation channel 84 outside the fuel cell stack 11 a. Then, after the coolant is cooled by the radiator 86, the coolant is supplied again to the coolant supply manifold 62 aby the coolant pump 88.As shown in FIG. 1, oxygen-containing gas is supplied to the oxygen-containing gas supply passage 30 a, and a fuel gas such as hydrogen gas is supplied to the fuel gas supply passage 34 a. Further, a coolant such as pure water, ethylene glycol, or oil is supplied to the coolant supply passage 32 a.Therefore, the oxygen-containing gas flows from the oxygen-containing gas supply channel 30 ato the oxygen-containing gas flow field 36 of the second separator 16, and moves in the direction indicated by the arrow B, and the oxygen-containing gas is supplied to the cathode 22 of the MEA 10 a. Meanwhile, the fuel gas flows from the fuel gas supply channel 34 ato the fuel gas flow field 38 of the first separator 14, the fuel gas moves along the fuel gas flow field 38 in the direction indicated by the arrow B, and the fuel gas is supplied to the anode 20 of the MEA 10 a.Thus, in the MEA 10 a, the oxygen-containing gas supplied to the cathode 22 and the fuel gas supplied to the anode 20 are partially consumed in the second electrode catalyst layer 22 aand the first electrode catalyst layer 20 aby electrochemical reactions to generate electric energy.In this case, the pressure of the first reaction gas (fuel gas) supplied to the fuel gas flow field 38 is higher than the pressure of the second reaction gas (oxygen-containing gas) supplied to the oxygen-containing gas flow field 36. In FIG. 2, the first reaction gas flows through the channel 38 aformed between the first separator 14 and the frame member 24. Therefore, the pressure of the first reaction gas is higher than the pressure of the second reaction gas. Therefore, the differential pressure P is applied to the frame member 24 provided between the channel 36 aand the channel 38 afrom the first frame-shaped layer 24 toward the second frame-shaped layer 24 b(i.e., from the first separator 14 to the second separator 16). Preferably, the differential pressure P is 5 to 300 kPa, and preferably 10 to 200 kPa.Then, in FIG. 1, the oxygen-containing gas supplied to and partially consumed by the cathode 22 is discharged in the direction of the arrow A along the oxygen-containing gas discharge passage 30 b. Similarly, the fuel gas supplied to the anode 20 and partially consumed there is discharged along the fuel gas discharge passage 34 bin the direction indicated by the arrow A. The fuel gas flowing through the fuel gas discharge passage 34 bis discharged from the fuel gas discharge collector 60 b.Further, the coolant supplied to the coolant supply passage 32 aflows into the coolant flow field 40 between the first separator 14 and the second separator 16, and then the coolant flows in the direction indicated by the arrow B. After the coolant cools the MEA 10 a, the coolant is discharged through the coolant discharge passage 32 b.The frame-equipped MEA 10 and the power generation cell 12 according to the first embodiment provide the following advantages.In the frame-equipped MEA 10, the outer end of the larger electrode (cathode 22) is disposed outside the inner end of the frame-shaped layer having the larger inner circumference over the entire circumference (second frame-shaped layer 24 b). In the structure, a portion of the first frame-shaped layer 24 athat corresponds to a position between the outer end 20 eof the anode 20 and the inner end 24 beof the second frame-shaped layer 24 b(a portion of the first frame-shaped layer 24 athat does not overlap with the second frame-shaped layer 24 b) is supported by the outer peripheral portion 22 cof the cathode 22. Therefore, it is possible to avoid deformation of the frame member 24 in the presence of the differential pressure applied from the anode, and improve the durability of the frame member 24.In the power generation cell 12, the bead seals 42, 44 are integrally formed with each of the first separator 14 and the second separator 16. The bead seals 42, 44 protrude toward the frame member 24 to prevent leakage of the reaction gas. The bead seal 42 of the first separator 14 and the bead seal 44 of the second separator 16 hold, from both sides in the thickness direction, a portion where the first frame-shaped layer 24 aand the second frame-shaped layer 24 bof the frame member 24 overlap. In the structure, the outer peripheral portion of the relatively thick frame member 24 is held between the bead seals 42, 44. Therefore, it becomes possible to obtain the appropriate sealing surface pressure. Further, since the inner peripheral portion of the relatively thin frame member 24 is disposed between the anode 20 and the cathode 22, it is possible to effectively reduce the thickness of the joint portion between the frame member 24 and the MEA 10 a.(Second Embodiment)As shown in FIG. 4, a power generation cell (fuel cell) 112 according to a second embodiment includes a resin frame-equipped membrane electrode assembly 110 (hereinafter referred to as "frame-equipped MEA 110"), and a first separator 14 and a second separator 16 provided on both sides of the frame-equipped MEA 110. In the following description, it is assumed that the elements of the second embodiment, which are not particularly mentioned, have the same structure as the same-name elements of the first embodiment.The frame-equipped MEA 110 has a rectangular shape, and includes a membrane electrode assembly 110 a(hereinafter referred to as the "MEA 110 a") and a frame member 24 aconnected to an outer peripheral portion of the MEA 110 a. The MEA 110 aincludes an electrolyte membrane 18, an anode 120 provided on one surface 18 aof the electrolyte membrane 18, and a cathode 122 provided on the other surface 18 bof the electrolyte membrane 18. In the second embodiment, the anode 120 is the "first electrode" and the cathode 122 is the "second electrode" of the present invention. The outer end 18 eof the electrolyte membrane 18 and an outer end 120 eof the anode 120 are provided at the same position as viewed in the thickness direction of the MEA 110 a.The anode 120 includes a first electrode catalyst layer 120 athat is bonded to a surface 18 aof the electrolyte membrane 18, and a first gas diffusion layer 120 bthat is stacked on the first electrode catalyst layer 120 a. The anode 120 is parallel to the electrolyte membrane 18 over the entire circumference.The cathode 122 includes a second electrode catalyst layer 122 athat is bonded to a surface 18 bof the electrolyte membrane 18, and a second gas diffusion layer 122 bthat is stacked on the second electrode catalyst layer 122 a. The surface dimension of the cathode 122 is larger than the surface dimensions of the electrolyte membrane 18 and the anode 120. Therefore, an outer end 122 eof the anode 122 is disposed outside the outer end 120 eof the anode 120 over the entire circumference.A step is provided for the cathode 122 at a position corresponding to the inner end 24 aeof the first frame-shaped layer 24 a. Specifically, the cathode 122 has an inclined portion 23 cthat is inclined from the electrolyte membrane 18 between a portion overlapping with the inner peripheral portion 24 anof the first frame-shaped layer 24 and a portion overlapping with the outer peripheral portion 18 cof the electrolyte membrane 18. In the cathode 122, the surface of the region 122 athat overlaps with the inner peripheral portion 24 anon the first frame-shaped layer 24 aadjacent to the second separator 16 is spaced apart from the electrolyte membrane 18 as compared with the surface of the region 123 bthat overlaps with the electrolyte membrane 18 adjacent to the second separator 16.The outer end 122 eof the cathode 122 is provided, over the entire circumference, outside the inner end 24 beof the second frame-shaped layer 24 b. Therefore, an outer peripheral portion 122 cof the cathode 122 includes an overlapping part 122 kthat overlaps the inner peripheral portion of the second frame-shaped layer 24 bover the entire circumference as viewed in the thickness direction of the MEA 110 a.In the second embodiment, the first frame-shaped layer 24 athat has a frame-shaped layer having the same thickness as the second frame-shaped layer 24 bor the smaller thickness (having the smaller inner circumference) is provided adjacent to the cathode (the second separator 16), and the second frame-shaped layer 24 bthat has the frame-shaped layer having the larger thickness is provided adjacent to the anode (the first separator 14). The inner peripheral portion 24 an the first frame-shaped layer 24 ais disposed between an outer peripheral portion 120 cof the anode 120 and the outer peripheral portion 122 cof the cathode 122.The first frame-shaped layer 24 aand the second frame-shaped layer 24 bare bonded to each other over the entire circumference (over the entire surface of the second frame-shaped layer 24 badjacent to the first frame-shaped layer 24 a) by an adhesive layer 24 c. The inner peripheral portion 24 an the first frame-shaped layer 24 ais bonded to the surface of the outer peripheral portion 18 cof the electrolyte membrane 18 adjacent to the cathode 122 through the adhesive layer 24 c. The inner peripheral portion 24 aon the first frame-shaped layer 24 ais joined to the outer peripheral portion 18 cof the electrolyte membrane 18 through the adhesive layer 24 c.The inner end 24 beof the second frame-shaped layer 24 bis disposed outside the outer end 120 eof the anode 120 over the entire circumference. Therefore, a gap G is formed between the outer end 120 eof the anode 120 and the inner end 24 beof the second frame-shaped layer 24 bover the entire circumference.As described above, in the frame-equipped MEA 110 and the power generation cell 112 according to the second embodiment, the outer end of the larger electrode (cathode 122) is disposed outside the inner end of the thinner frame-shaped layer (the second frame-shaped layer 24 b) over the entire circumference. In the structure, a portion of the first frame-shaped layer 24 acorresponding to a position between the outer end 120 eof the anode 120 and the inner end 24 beof the second frame-shaped layer 24 b(portion of the first frame-shaped layer 24 anot overlapping with the second frame-shaped layer 24 b) is supported by the outer peripheral portion 122 cof the cathode 122. Accordingly, in the same manner as in the first embodiment, even in the second embodiment, it is possible to avoid deformation of the frame member 24 in the presence of the differential pressure applied from the anode and improve the durability of the frame member 24. Moreover, in the second embodiment, the structure identical to the structure of the first embodiment offers the same advantages as in the case of the first embodiment.(Third Embodiment)As shown in FIG. 5, a power generation cell (fuel cell) 212 according to a third embodiment includes a resin frame-equipped membrane electrode assembly 210 (hereinafter referred to as the "frame-equipped MEA 210") and a first separator 14 and a second separator 16 provided on both sides of the frame-equipped MEA 210. In the following description, it is assumed that the elements of the third embodiment, which are not particularly mentioned, have the same structure as the same-name elements of the first embodiment.The frame-equipped MEA 210 has a rectangular shape, and includes a membrane electrode assembly 210 a(hereinafter referred to as the "MEA 210 a") and a frame member 224 joined to an outer peripheral portion of the MEA 210 a. The MEA 210 aincludes an electrolyte membrane 18, an anode 220 provided on one surface 18 aof the electrolyte membrane 18, and a cathode 222 provided on the other surface 18 bof the electrolyte membrane 18. In the third embodiment, the anode 220 is the "first electrode", and the cathode 222 is the "second electrode". The outer end 18 eof the electrolyte membrane 18 and an outer end 222 eof the cathode 222 are provided at the same position as viewed in the thickness direction of the MEA 210 a.The anode 220 includes a first electrode catalyst layer 220 athat is bonded to a surface 18 aof the electrolyte membrane 18, and a first gas diffusion layer 22 bthat is stacked on the first electrode catalyst layer 220 a. A step is provided for the anode 220 at a position corresponding to the inner end 24 aeof the first frame-shaped layer 24 a. Specifically, the anode 220 has a slant portion 221 cthat is slanted from the electrolyte membrane 18 between a portion 221 athat overlaps with the inner peripheral portion 24 anon the first frame-shaped layer 24 aand a portion 221 bthat overlaps with the electrolyte membrane 18. Therefore, in the inclined portion 221 c, the first electrode catalyst layer 220 aand the first gas diffusion layer 220 bare inclined from the electrolyte membrane 18.In the anode, the surface of the region 221 athat overlaps with the inner peripheral portion 24 anon the first frame-shaped layer 24 aadjacent to the first separator 14 is spaced apart from the electrolyte membrane 18 as compared with the surface of the region 221 bthat overlaps with the electrolyte membrane 18 adjacent to the first separator 14.The cathode 222 includes a second electrode catalyst layer 222 athat is joined to the other surface 18 bof the electrolyte membrane 18, and a second gas diffusion layer 222 bthat is stacked on the second electrode catalyst layer 222 a. The surface dimension of the cathode 222 is greater than the surface dimension of the anode 220. Therefore, the outer end 222 eof the cathode 222 is disposed outside an outer end 220 eof the anode 220 over the entire circumference. The surface dimension of the electrolyte membrane 18 and the surface dimension of the cathode 222 are the same.The cathode 222 has a flat shape from a region 223 a, which overlaps with the inner peripheral portion 24 anon the first frame-shaped layer 24 a, to the inside of the electrolyte membrane 18.The outer end 222 eof the cathode 222 is disposed outside the inner end 24 beof the second frame-shaped layer 24 bover the entire circumference. Therefore, the outer peripheral portion 222 cof the cathode 222 has an overlapping part 222 kthat overlaps with the inner peripheral portion of the second frame-shaped layer 24 bover the entire circumference when viewed in the thickness direction of the MEA 210 a.In the third embodiment, the first frame-shaped layer 24 athat has a frame-shaped layer having the same thickness as the second frame-shaped layer 24 bor the smaller thickness (having the smaller inner circumference) is provided adjacent to the cathode (the second separator 16), and the second frame-shaped layer 24 bthat has a frame-shaped layer having the larger thickness is provided adjacent to the anode (the first separator 14). The inner peripheral portion 24 an the first frame-shaped layer 24 ais disposed between an outer peripheral portion 220 cof the anode 220 and the outer peripheral portion 222 cof the cathode 222.The first frame-shaped layer 24 aand the second frame-shaped layer 24 bare bonded to each other over the entire circumference by a first adhesive layer 24 e. Specifically, the outer peripheral portion of the first frame-shaped layer 24 ais joined to the one entire surface of the second frame-shaped layer 24 bby the first adhesive layer 24 eprovided on one surface of the first frame-shaped layer 24 a. The first adhesive layer 24 eis provided in the frame shape around the outer peripheral portion of the one surface of the first frame-shaped layer 24 a. An inner end 24 eof the first adhesion layer 24 eis disposed outside the outer end 220 eof the anode 220, and inside the inner end 24 beof the second frame-shaped layer 24 b.The inner peripheral portion 24 aon the first frame-shaped layer 24 ais bonded to the surface 18 aof the outer peripheral portion 18 cof the electrolyte membrane 18 adjacent to the anode 220 through a second adhesive layer 24 f. The inner peripheral portion 24 an the first frame-shaped layer 24 ais joined to the surface of the outer peripheral portion 18 cof the electrolyte membrane 18 adjacent to the anode 220 by the second adhesive layer 24 fprovided on the other surface of the first frame-shaped layer 24 a(the surface opposite to the second frame-shaped layer 24 b).The inner end 24 beof the second frame-shaped layer 24 bis disposed outside the outer end 220 eof the anode 220 over the entire circumference. Therefore, a gap G is formed between the outer end 220 eof the anode 220 and the inner end 24 beof the second frame-shaped layer 24 bover the entire circumference.As described above, in the frame-equipped MEA 210 and the power generation cell 212 according to the third embodiment, the outer end of the larger electrode (cathode 222) is disposed outside the inner end 24 beof the thinner frame-shaped layer (the second frame-shaped layer 24 b) over the entire circumference. In the structure, a portion of the first frame-shaped layer 24 acorresponding to a position between the outer end 220 eof the anode 220 and the inner end 24 beof the second frame-shaped layer 24 b(portion of the first frame-shaped layer 24 anot overlapping with the second frame-shaped layer 24 b) is supported by the outer peripheral portion 222 cof the cathode 222. Therefore, in the same manner as in the first embodiment, even in the third embodiment, it is possible to avoid deformation of the frame member 224 in the presence of the differential pressure of the reaction gas applied from the anode, and improve the durability of the frame member 224.Moreover, in the third embodiment, the structure identical to the structure of the first embodiment offers the same advantages as in the case of the first embodiment.A frame-equipped membrane electrode assembly (10) includes a membrane electrode assembly (10a) and a frame member (24). The frame member (24) includes a first frame-shaped layer (24a) and a second frame-shaped layer (24b). An inner peripheral portion (24an) of the first frame-shaped layer (24a) is connected to an outer peripheral portion of the membrane electrode assembly (10a). The inner peripheral portion (24an) of the first frame-shaped layer (24a) is disposed between an outer peripheral portion (20c) of an anode (20) and an outer peripheral portion (22c) of a cathode (22). An inner end (24be) of the second frame-shaped layer (24b) is disposed outside an outer end (20e) of the anode (20) over the entire circumference. The outer end (22e) of the cathode (22) is disposed over the entire circumference outside the inner end (24be) of the second frame-shaped layer (24b).

Claims

A frame-equipped membrane electrode assembly (10, 110, 210) comprising: a membrane electrode assembly (10a, 110a, 210a) including an electrolyte membrane (18), a first electrode (20, 120, 220) provided on one surface of the electrolyte membrane (18), and a second electrode (22, 122, 222) provided on the other surface of the electrolyte membrane (18); and a frame member (24, 224) provided over an entire periphery of an outer peripheral portion of the membrane electrode assembly (10a, 110a, 210a), wherein a surface dimension of the second electrode (22, 122, 222) is larger than a surface dimension of the first electrode (20, 120, 220); the frame member (24, 224) includes a first frame-shaped layer (24a) and a second frame-shaped layer (24b); an inner peripheral portion (24an) of the first frame-shaped layer (24a) is connected to the outer peripheral portion of the membrane electrode assembly (10a, 110a, 210a); the first frame-shaped layer (24a) and the second frame-shaped layer (24b) are connected to each other in the thickness direction; the inner peripheral portion (24an) of the first frame-shaped layer (24a) is disposed between an outer peripheral portion (20c, 120c, 220c) of the first electrode (20, 120, 220) and an outer peripheral portion (22c, 122c, 222c) of the second electrode (22, 122, 222); an inner end (24be) of the second frame-shaped layer (24b) is disposed outside an outer end (20e, 120e, 220e) of the first electrode (20, 120, 220) over an entire circumference; and an outer end (22e, 122e, 222e) of the second electrode (22, 122, 222) is disposed outside the inner end (24be) of the second frame-shaped layer (24b) over the entire circumference, characterized in that the outer circumferential portion (20c, 120c, 220c) of the first electrode (20, 220) or second electrode (122) overlaps the inner circumferential portion (24an) of the first frame-shaped layer (24a) on the side thereof remote from the electrolyte membrane (18).The frame-equipped membrane electrode assembly (10) according to claim 1, wherein the inner peripheral portion of the first frame-shaped layer (24a) is joined to a surface of an outer peripheral portion of the electrolyte membrane (18) adjacent to the first electrode (20).The frame-equipped membrane electrode assembly (10) of claim 2, wherein an outer end of the electrolyte membrane (18) is disposed outside the outer end of the first electrode (20).The frame-equipped membrane electrode assembly (10) according to claim 2, wherein an adhesive layer (24c) is provided on an entire surface of the first frame-shaped layer (24a); an outer peripheral portion of the first frame-shaped layer (24a) is bonded to an entire surface of the second frame-shaped layer (24b) through the adhesive layer (24c); and the inner peripheral portion of the first frame-shaped layer (24a) is bonded to the outer peripheral portion of the electrolyte membrane (18) through the adhesive layer (24c).The frame-equipped membrane electrode assembly (10) according to claim 2, wherein the outer peripheral portion of the second electrode (22) covers a step formed by a surface of the first frame-shaped layer (24a) and the inner end of the second frame-shaped layer (24b), and extends outward beyond the inner end of the second frame-shaped layer (24b).The frame-equipped membrane electrode assembly (10) according to claim 2, wherein the first electrode (20) includes a step at a position corresponding to an inner end of the first frame-shaped layer (24a); and the second electrode (22) includes a step at a position corresponding to the inner end of the second frame-shaped layer (24b).The frame-equipped membrane electrode assembly (10) of claim 2, wherein the first electrode (20) is an anode; and the second electrode (22) is a cathode.The frame-equipped membrane electrode assembly (110) according to claim 1, wherein the inner peripheral portion of the first frame-shaped layer (24a) is joined to a surface of an outer peripheral portion of the electrolyte membrane (18) adjacent to the second electrode (122).The frame-equipped membrane electrode assembly (110) according to claim 8, wherein an outer end of the electrolyte membrane (18) and the outer end of the first electrode (120) are provided at the same position as viewed in the thickness direction of the membrane electrode assembly (110a).The frame-equipped membrane electrode assembly (110) according to claim 8, wherein an adhesive layer (24c) is provided on an entire surface of the first frame-shaped layer (24a); an outer peripheral portion of the first frame-shaped layer (24a) is bonded to an entire surface of the second frame-shaped layer (24b) through the adhesive layer (24c); the inner peripheral portion of the first frame-shaped layer (24a) is bonded to the outer peripheral portion of the electrolyte membrane (18) through the adhesive layer (24c).The frame-equipped membrane electrode assembly (110) according to claim 8, wherein a gap (G) is formed between the outer end of the first electrode (120) and the inner end of the second frame-shaped layer (24b).The frame-equipped membrane electrode assembly (110) of claim 8, wherein the first electrode (120) is an anode; and the second electrode (122) is a cathode.The frame-equipped membrane electrode assembly (210) according to claim 1, wherein the inner peripheral portion of the first frame-shaped layer (24a) is joined to a surface of an outer peripheral portion of the electrolyte membrane (18) adjacent to the first electrode (220) on a surface opposite to the second frame-shaped layer (24b).The frame-equipped membrane electrode assembly (210) according to claim 13, wherein, when viewed in the thickness direction of the membrane electrode assembly (210a), an outer end of the electrolyte membrane (18) and the outer end of the second electrode (222) are at the same position.The frame-equipped membrane electrode assembly (210) according to claim 13, wherein an outer peripheral portion of the first frame-shaped layer (24a) is bonded to an entire surface of the second frame-shaped layer (24b) by a first adhesive layer (24e) provided on one surface of the first frame-shaped layer (24a); and the inner peripheral portion of the first frame-shaped layer (24a) is bonded to the outer peripheral portion of the electrolyte membrane (18) by a second adhesive layer (24f) provided on the other surface of the first frame-shaped layer (24a).The frame-equipped membrane electrode assembly (210) according to claim 13, wherein a gap is formed over the entire circumference between the outer end of the first electrode (220) and the inner end of the second frame-shaped layer (24b).The frame-equipped membrane electrode assembly (210) of claim 13, wherein the first electrode (220) is an anode; and the second electrode (222) is a cathode.The frame-equipped membrane electrode assembly (210) of claim 13, wherein the first electrode (220) is a cathode; and the second electrode (222) is an anode.The frame-equipped membrane electrode assembly (10) according to claim 1, wherein a thickness of the second frame-shaped layer and a thickness of the first frame-shaped layer are the same.The frame-equipped membrane electrode assembly (10) of claim 1, wherein the second frame-shaped layer is thicker than the first frame-shaped layer.A fuel cell (12, 112, 212) comprising: a frame-equipped membrane electrode assembly (10, 110, 210); and separators (14, 16) provided on both sides of the frame-equipped membrane electrode assembly (10, 110, 210), respectively, wherein the frame-equipped membrane electrode assembly (10, 110, 210) comprises: a membrane electrode assembly (10a, 110a, 210a) including an electrolyte membrane (18), a first electrode (20, 120, 220) provided on one surface of the electrolyte membrane (18), and a second electrode (22, 122, 222) provided on the other surface of the electrolyte membrane (18); and a frame member (24, 224) provided over an entire periphery of an outer peripheral portion of the membrane electrode assembly (10a, 110a, 210a), wherein a surface dimension of the second electrode (22, 122, 222) is larger than a surface dimension of the first electrode (20, 120, 220); the frame member (24, 224) includes a first frame-shaped layer (24a) and a second frame-shaped layer (24b); an inner peripheral portion (24an) of the first frame-shaped layer (24a) is connected to the outer peripheral portion of the membrane electrode assembly (10a, 110a, 210a); the first frame-shaped layer (24a) and the second frame-shaped layer (24b) are connected to each other in a thickness direction; the inner peripheral portion (24an) of the first frame-shaped layer (24a) is disposed between an outer peripheral portion (20c, 120c, 220c) of the first electrode (20, 120, 220) and an outer peripheral portion of the second electrode (22, 122, 222); an inner end (24be) of the second frame-shaped layer (24b) is disposed outside an outer end (20e, 120e, 220e) of the first electrode (20, 120, 220) over an entire periphery; and an outer end (22e, 122e, 222e) of the second electrode (22, 122, 222) is disposed outside the inner end (24be) of the second frame-shaped layer (24b) over the entire circumference, characterized in that the outer circumferential portion (20c, 120c, 220c) of the first electrode (20, 220) or second electrode (122) overlaps the inner circumferential portion (24an) of the first frame-shaped layer (24a) on the side thereof remote from the electrolyte membrane (18).The fuel cell (12, 112, 212) according to claim 21, wherein a bead seal (42, 44) is integrally formed with each of the separators (14, 16) so as to protrude from the frame member (24, 224) to prevent leakage of a reaction gas; and an overlapping area of the frame member (24, 224) where the first frame-shaped layer (24a) and the second frame-shaped layer (24b) overlap each other is held from both sides in the thickness direction between the bead seal (42) of one of the separators (14) and the bead seal (44) of the other of the separators (16).The fuel cell (12, 112, 212) according to claim 21, wherein an overlapping part where the outer peripheral portion of the first electrode, the inner peripheral portion of the first frame-shaped layer, and the outer peripheral portion of the second electrode overlap each other is held between a rib provided in one of the separators and protruding toward the first electrode and a rib provided in the other of the separators and protruding toward the second electrode.

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