Resin-framed stepped membrane electrode assembly for fuel cell

A resin-framed stepped membrane electrode assembly for a fuel cell, includes a stepped membrane electrode assembly and a resin frame member. The resin frame member surrounds a membrane outer periphery end of a solid polymer electrolyte membrane and includes an inner protruding portion protruding from the membrane outer periphery end toward a second electrode and is joined to the stepped membrane electrode assembly with an adhesive. The inner protruding portion includes a bank portion, a groove portion, and a ledge portion. The roughness of the bank surface is smaller than a roughness of the groove surface.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application claims priority under 35 U.S.C. § 119 to Japanese Patent Application No. 2016-045388, filed Mar. 9, 2016, entitled “Resin-framed Stepped Membrane Electrode Assembly For Fuel Cell.” The contents of this application are incorporated herein by reference in their entirety.

BACKGROUND

The present disclosure relates to a resin-framed stepped membrane electrode assembly for fuel cell.

2. Description of the Related Art

Typically, a solid polymer electrolyte fuel cell includes a solid polymer electrolyte membrane formed of a polymer ion exchange membrane. A fuel cell includes a membrane-electrode assembly (MEA) that includes a solid polymer electrolyte membrane, an anode electrode disposed on one the surfaces of the solid polymer electrolyte membrane, and a cathode electrode disposed on the other surface of the solid polymer electrolyte membrane. The anode electrode and the cathode electrode each include a catalyst layer (electrode catalyst layer) and a gas diffusion layer (porous carbon).

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

The MEA may be configured as a stepped MEA. A stepped MEA is a type of MEA in which one of the gas diffusion layers is designed to have smaller flat dimensions than the solid polymer electrolyte membrane and the other gas diffusion layer is designed to have larger flat dimensions than the aforementioned gas diffusion layer. In order to decrease the amount of the costly solid polymer electrolyte membrane to be used and in order to protect the solid polymer electrolyte membrane, which is a thin film with low strength, a resin frame member is attached around the outer periphery of the MEA. Such a resin-framed MEA has been available.

In order to reduce occurrence of cracks and strain in the solid polymer electrolyte membrane of a resin-framed MEA, the joint strength between the stepped MEA and the resin frame member is preferably maintained at a satisfactory level. For example, Japanese Unexamined Patent Application Publication No. 2013-168353 discloses such a resin-framed stepped MEA (resin-framed MEA) for a fuel cell.

The resin frame member of this resin-framed MEA includes an inner periphery protruding portion. The inner periphery protruding portion protrudes toward the outer periphery of a second electrode smaller than a first electrode and is bonded and joined to an outer peripheral portion of the solid polymer electrolyte membrane. The bonded surface of the inner periphery protruding portion has a textured portion. Thus, the inner periphery protruding portion of the resin frame member can be strongly and easily bonded and joined to the outer peripheral portion of the solid polymer electrolyte membrane and the joint strength of the entire resin-framed MEA can be reliably maintained, according to the description of the aforementioned publication.

SUMMARY

According to one aspect of the present invention, a resin-framed stepped membrane electrode assembly for a fuel cell, includes a stepped membrane electrode assembly and a resin frame member. The stepped membrane electrode assembly includes a solid polymer electrolyte membrane, a first electrode, and a second electrode. The first electrode is disposed on a surface of the solid polymer electrolyte membrane and includes a first electrode catalyst layer and a first gas diffusion layer. The second electrode is disposed on another surface of the solid polymer electrolyte membrane and includes a second electrode catalyst layer and a second gas diffusion layer. The first electrode has flat dimensions larger than flat dimensions of the second electrode. The second electrode catalyst layer includes an outer periphery exposed portion extending outward from an outer peripheral end of the second gas diffusion layer. The resin frame member surrounds an outer periphery of the solid polymer electrolyte membrane. The resin frame member includes an inner protruding portion protruding toward the second electrode and joined to the stepped membrane electrode assembly with an adhesive. The inner protruding portion includes a bank portion, a groove portion, and a ledge portion. The bank portion is disposed in an inner peripheral end portion of the inner protruding portion. The bank portion faces the outer periphery exposed portion of the second electrode catalyst layer. The groove portion is disposed on an outer peripheral side of the bank portion. The ledge portion is disposed on an outer peripheral side of the groove portion so as to contact an outer peripheral surface of the solid polymer electrolyte membrane, the outer peripheral surface being an exposed portion extending outward from the second electrode catalyst layer. A surface roughness of a tip of the bank portion is smaller than a surface roughness of a bottom surface of the groove portion.

According to another aspect of the present invention, a resin-framed stepped membrane electrode assembly for a fuel cell, includes a stepped membrane electrode assembly and a resin frame member. The stepped membrane electrode assembly includes a solid polymer electrolyte membrane, a first electrode, and a second electrode. The solid polymer electrolyte membrane has a first surface and a second surface opposite to the first surface in a stacking direction. The first electrode is stacked on the first surface in the stacking direction and includes a first electrode catalyst layer and a first gas diffusion layer. The second electrode is stacked on the second surface in the stacking direction and includes a second electrode catalyst layer and a second gas diffusion layer. The first electrode is larger than the second electrode viewed in the stacking direction. The second electrode catalyst layer includes an outer periphery exposed portion extending from a diffusion outer peripheral end of the second gas diffusion layer in a direction substantially perpendicular to the stacking direction viewed in the stacking direction. The resin frame member surrounds a membrane outer periphery end of the solid polymer electrolyte membrane viewed in the stacking direction and includes an inner protruding portion protruding from the membrane outer periphery end toward the second electrode viewed in the stacking direction and is joined to the stepped membrane electrode assembly with an adhesive. The inner protruding portion includes a bank portion, a groove portion, and a ledge portion. The bank portion is disposed between the diffusion outer peripheral end and the membrane outer periphery end in the direction viewed in the stacking direction and has a bank surface opposite to the outer periphery exposed portion in the stacking direction. The groove portion is disposed between the bank portion and the membrane outer periphery end in the direction viewed in the stacking direction and has a groove surface opposite to the solid polymer electrolyte membrane in the stacking direction. The roughness of the bank surface is smaller than a roughness of the groove surface. The ledge portion is disposed between the groove portion and the membrane outer periphery end in the direction viewed in the stacking direction so as to contact to the solid polymer electrolyte membrane in the stacking direction.

DESCRIPTION OF THE EMBODIMENTS

Referring toFIGS. 1 and 2, a resin-framed stepped membrane-electrode assembly (MEA)10for a fuel cell according to one embodiment is set in a landscape-oriented (or portrait-oriented) oblong solid polymer electrolyte fuel cell12. Two or more solid polymer electrolyte fuel cells12are stacked in, for example, the arrow A direction (horizontal direction) or the arrow C direction (direction of gravitational force) so as to form a fuel cell stack. The fuel cell stack is mounted in a fuel cell electric vehicle (not illustrated) to serve as a vehicle-mounted fuel cell stack, for example.

In the fuel cell12, the resin-framed stepped MEA10is sandwiched between a first separator14and a second separator16. The first separator14and the second separator16each have a landscape-oriented (or portrait-oriented) oblong shape. The first separator14and the second separator16are each formed of, for example, a steel sheet, a stainless steel sheet, an aluminum sheet, a plated steel sheet, a metal sheet subjected to anti-corrosion surface treatment, a carbon member, or the like.

The oblong resin-framed stepped MEA10includes a stepped MEA10a. As illustrated inFIG. 2, the stepped MEA10aincludes a solid polymer electrolyte membrane (cation exchange membrane)18which is a water-impregnated perfluorosulfonic acid thin membrane. The solid polymer electrolyte membrane18is sandwiched between an anode electrode (first electrode)20and a cathode electrode (second electrode)22. The solid polymer electrolyte membrane18may be a fluorine-based electrolyte or hydrocarbon (HC)-based electrolyte.

The cathode electrode22has smaller flat dimensions (outer dimensions) than the solid polymer electrolyte membrane18and the anode electrode20. Alternatively, the anode electrode20may be designed to have smaller flat dimensions than the solid polymer electrolyte membrane18and the cathode electrode22. In such a case, the anode electrode20serves as a second electrode and the cathode electrode22serves as a first electrode.

The anode electrode20includes a first electrode catalyst layer20ajoined to a surface18aof the solid polymer electrolyte membrane18and a first gas diffusion layer20bdisposed on the first electrode catalyst layer20a. The first electrode catalyst layer20aand the first gas diffusion layer20bhave the same flat dimensions and are designed to have the same (or smaller) flat dimensions as (than) the solid polymer electrolyte membrane18.

The cathode electrode22includes a second electrode catalyst layer22ajoined to a surface18bof the solid polymer electrolyte membrane18and a second gas diffusion layer22bdisposed on the second electrode catalyst layer22a. The second electrode catalyst layer22aprotrudes outward from an outer periphery end22beof the second gas diffusion layer22band is designed to have larger flat dimensions than the second gas diffusion layer22band smaller flat dimensions than the solid polymer electrolyte membrane18. The second electrode catalyst layer22aincludes an outer periphery exposed portion22aothat extends outward so as to be exposed from the outer periphery end22be.

The first electrode catalyst layer20ais formed by, for example, evenly applying to a surface of the first gas diffusion layer20ba mixture of an ion-conductive polymer binder and porous carbon particles carrying a platinum alloy on their surfaces. The second electrode catalyst layer22ais formed by, for example, evenly applying to a surface of the second gas diffusion layer22ba mixture of an ion-conductive polymer binder and porous carbon particles carrying a platinum alloy on their surfaces.

The first gas diffusion layer20band the second gas diffusion layer22bare each formed of a carbon paper, a carbon cloth, or the like. The flat dimensions of the second gas diffusion layer22bare set to be smaller than the flat dimensions of the first gas diffusion layer20b. The first electrode catalyst layer20aand the second electrode catalyst layer22aare respectively formed on the two surfaces18aand18bof the solid polymer electrolyte membrane18.

The resin-framed stepped MEA10includes a resin frame member (including a resin film)24that surrounds the outer periphery of the solid polymer electrolyte membrane18and is bonded to an outer peripheral portion18beof the solid polymer electrolyte membrane18.

As illustrated inFIGS. 2 to 4, the resin frame member24has a frame shape and has an outer peripheral portion24athat extends a particular length inward from the outer peripheral end. An inner protruding portion24bthat protrudes toward the cathode electrode22is integrated with an inner end portion of the outer peripheral portion24a.

As illustrated inFIG. 2, the inner protruding portion24bhas a ledge portion24b1that contacts the outer peripheral portion18beof the solid polymer electrolyte membrane18through a first step portion24s1. The thickness S1of the ledge portion24b1is set to be larger than the thickness S2of the cathode electrode22(S1>S2). A thin-walled groove portion24b2lies at the inner end portion of the ledge portion24b1and a second step portion24s2is provided between the groove portion24b2and the ledge portion24b1. A bank portion24b3lies at the inner end portion of the groove portion24b2. The bank portion24b3faces the outer periphery exposed portion22aoof the second electrode catalyst layer22aand extends throughout the entire circumference of the outer periphery exposed portion22ao.

As illustrated inFIG. 3, the outer peripheral portion24aof the resin frame member24has a thickness t, which is the dimension in the height direction (arrow A direction). The ledge portion24b1is set to be thinner than the outer peripheral portion24aby a thickness t1in the height direction. The groove portion24b2is set to be thinner than the ledge portion24b1by a thickness t2in the height direction. The bank portion24b3is set to be thicker than the groove portion24b2by a thickness t3in the height direction and the height of the bank portion24b3is smaller than the height of the ledge portion24b1.

A textured surface, for example, a first grain-finished surface26a, is formed in a surface of the ledge portion24b1facing the stepped MEA10a. A textured surface, for example, a second grain-finished surface26b, is formed in a surface of the groove portion24b2facing the stepped MEA10a. A surface26cof the bank portion24b3facing the stepped MEA10ais formed to be substantially flat.

The surface roughness of the surface (tip)26cof the bank portion24b3is smaller than the surface roughness of the second grain-finished surface (bottom surface)26bof the groove portion24b2. The surface roughness of the first grain-finished surface26aof the ledge portion24b1is larger than the surface roughness of the second grain-finished surface26bof the groove portion24b2.

As illustrated inFIG. 2, the gap between the outer peripheral portion18beon the surface18bside of the stepped MEA10aand the groove portion24b2is filled with an adhesive28awhich forms an adhesive layer28. Examples of the adhesive28ainclude polymers and fluorine-based elastomers. The adhesive28ais not particularly limited and may be liquid or solid or thermoplastic or thermosetting.

The resin frame member24and the first gas diffusion layer20bof the anode electrode20are integrated with each other with a resin-impregnated portion30that contains an adhesive resin. The resin-impregnated portion30can be, for example, formed by thermally deforming a resin protrusion30tintegral with the resin frame member24. The adhesive28aused to form the adhesive layer28may be used to form the resin-impregnated portion30.

As illustrated inFIG. 1, an oxidant gas inlet manifold32a, a cooling medium inlet manifold34a, and a fuel gas outlet manifold36bare formed in one end portion of the fuel cell12in the arrow B direction (horizontal direction). The oxidant gas inlet manifold32a, the cooling medium inlet manifold34a, and the fuel gas outlet manifold36beach penetrate the first separator14and the second separator16in the arrow A direction, which is the stacking direction. Oxidant gas, for example, oxygen-containing gas, is supplied through the oxidant gas inlet manifold32a. A cooling medium is supplied through the cooling medium inlet manifold34a. Fuel gas, for example, hydrogen-containing gas, is discharged through the fuel gas outlet manifold36b. The oxidant gas inlet manifold32a, the cooling medium inlet manifold34a, and the fuel gas outlet manifold36bare aligned with each other in the arrow C direction (vertical direction).

A fuel gas inlet manifold36a, a cooling medium outlet manifold34b, and an oxidant gas outlet manifold32bare formed in the other end portion of the solid polymer electrolyte fuel cell12in the arrow B direction. The fuel gas inlet manifold36a, the cooling medium outlet manifold34b, and the oxidant gas outlet manifold32beach penetrate the first separator14and the second separator16in the arrow A direction (stacking direction). Fuel gas is supplied through the fuel gas inlet manifold36a. A cooling medium is discharged through the cooling medium outlet manifold34b. Oxidant gas is discharged through the oxidant gas outlet manifold32b. The fuel gas inlet manifold36a, the cooling medium outlet manifold34b, and the oxidant gas outlet manifold32bare aligned with one another in the arrow C direction.

An oxidant gas flow channel38is formed in a surface16aof the second separator16facing the resin-framed stepped MEA10. The oxidant gas flow channel38is in communication with the oxidant gas inlet manifold32aand the oxidant gas outlet manifold32b. The oxidant gas flow channel38includes multiple straight (or wavy) channel grooves that extend in the arrow B direction.

A fuel gas flow channel40is formed in a surface14aof the first separator14facing the resin-framed stepped MEA10. The fuel gas flow channel40is in communication with the fuel gas inlet manifold36aand the fuel gas outlet manifold36b. The fuel gas flow channel40includes multiple straight (or wavy) flow channel grooves that extend in the arrow B direction.

A cooling medium flow channel42is formed between a surface14bof the first separator14and a surface16bof the second separator16adjacent to each other. The cooling medium flow channel42is in communication with the cooling medium inlet manifold34aand the cooling medium outlet manifold34b.

As illustrated inFIGS. 1 and 2, a first seal member44covers outer peripheral end portions of the surfaces14aand14bof the first separator14to become combined with the first separator14. A second seal member46covers outer peripheral end portions of the surfaces16aand16bof the second separator16to become combined with the second separator16.

As illustrated inFIG. 2, the first seal member44includes a first protruding seal44ain contact with the resin frame member24of the resin-framed stepped MEA10and a second protruding seal44bin contact with the second seal member46of the second separator16. The second seal member46constitutes a flat seal having a flat surface in contact with the second protruding seal44band this flat surface extends along the plane of the separator. Alternatively, instead of the second protruding seal44b, a protruding seal (not illustrated) may be provided to the second seal member46.

Examples of elastic seal members that can be used as the first seal member44and the second seal member46include sealing members, cushion materials, and packing materials formed of EPDM, NBR, fluororubber, silicone rubber, fluorosilicone rubber, butyl rubber, natural rubber, styrene rubber, chloroprene rubber, or acrylic rubber.

Next, a method for producing the resin-framed stepped MEA10is described.

First, the stepped MEA10ais prepared. Separately, the resin frame member24is prepared by injection molding using a die (not shown). In preparing the stepped MEA10a, a slurry containing a mixture of carbon black and PTFE particles is applied to flat surfaces of carbon paper sheets and dried to form undercoat layers which constitute the first gas diffusion layer20band the second gas diffusion layer22b.

A solvent is added to an electrode catalyst, and a binder solution is added to the resulting mixture to form a cathode electrode ink and an anode electrode ink. The cathode electrode ink is applied to a PET film by screen printing so as to form a cathode electrode sheet. Similarly, the anode electrode ink is applied to a PET film by screen printing so as to form an anode electrode sheet.

Next, the solid polymer electrolyte membrane18as sandwiched between the cathode electrode sheet and the anode electrode sheet is hot pressed, and the PET films are separated to form a catalyst-coated membrane (CCM). The CCM is then sandwiched between the first gas diffusion layer20band the second gas diffusion layer22band hot-pressed to integrate the CCM with the first gas diffusion layer20band the second gas diffusion layer22b. As a result, a stepped MEA10ais obtained.

As illustrated inFIG. 4, the resin frame member24has the thin-walled inner protruding portion24b. The inner protruding portion24bincludes the ledge portion24b1, which is adjacent to the outer peripheral portion24awith the first step portion24s1therebetween, and the groove portion24b2that lies at the inner end portion of the ledge portion24b1. The second step portion24s2is provided between the ledge portion24b1and the groove portion24b2. The inner protruding portion24balso includes the bank portion24b3at the inner end portion of the groove portion24b2. If needed, the resin protrusion30tillustrated inFIG. 2is formed as part of the resin frame member24.

A surface of the ledge portion24b1of the resin frame member24formed by injection molding is subjected to a grain finishing treatment to form the first grain-finished surface26aand the second grain-finished surface26bis formed on the bottom surface of the groove portion24b2. The first grain-finished surface26ahas a larger surface roughness than the second grain-finished surface26b. The grain finishing treatment can be performed by using a plasma apparatus or the like, for example. Alternatively, although not illustrated in the drawings, textured patterns corresponding to the first grain-finished surface26aand the second grain-finished surface26bmay be formed in the molding surfaces of the injection molding dies so that the first grain-finished surface26aand the second grain-finished surface26bcan be formed at the time of preparing the resin frame member24by injection molding.

Next, as illustrated inFIG. 5, the adhesive28ais applied to the bottom surface (second grain-finished surface26b) of the groove portion24b2of the inner protruding portion24bof the resin frame member24by using, for example, a dispenser not shown in the drawing. Then the first step portion24s1of the resin frame member24, an outer peripheral end portion20beof the first gas diffusion layer20bconstituting the stepped MEA10a, and an outer peripheral end portion18eof the solid polymer electrolyte membrane18are aligned.

As illustrated inFIG. 6, the adhesive28ais heated and at the same time loaded with a pressure (using a press or the like) in the thickness direction. As a result, the adhesive28ais pressurized and melted. The adhesive28ais stretched inside the groove portion24b2. Thus, the inner protruding portion24bof the resin frame member24becomes bonded to the outer peripheral portion18beof the solid polymer electrolyte membrane18with the adhesive layer28.

The inner peripheral surface of the bank portion24b3of the resin frame member24and the tip surface of the outer periphery end22beof the second gas diffusion layer22bare bonded to each other with the adhesive layer28. The resin frame member24and the first gas diffusion layer20bof the anode electrode20are integrated with each other with a resin-impregnated portion30. Thus, the resin-framed stepped MEA10is made.

In this embodiment, as illustrated inFIG. 3, the inner protruding portion24bconstituting the resin frame member24has the bank portion24b3at the inner peripheral end portion and the groove portion24b2is formed on the outer peripheral side of the bank portion24b3. The surface roughness of the surface26cof the bank portion24b3is smaller than the surface roughness of the second grain-finished surface26bof the groove portion24b2.

Since the surface roughness of the bank portion24b3is set to be small, dust rarely attaches thereto. As a result, attachment of dust and the like to the solid polymer electrolyte membrane18can be prevented by a simple structure and damage on the solid polymer electrolyte membrane18can be minimized.

In contrast, the surface roughness of the groove portion24b2is set to be large and thus the adhesive28asmoothly flows within the groove portion24b2. At the same time, air inside the adhesive28amoves along with the flow of the adhesive28aand is satisfactorily discharged to outside. As a result, variation in quality, such as gas barrier properties and adhesion durability, can be reduced and the stepped MEA10acan be strongly bonded to the resin frame member24to achieve high quality.

Moreover, the first grain-finished surface26ais formed in the surface of the ledge portion24b1facing the stepped MEA10aand the surface roughness of the first grain-finished surface26ais larger than the surface roughness of the second grain-finished surface26bof the groove portion24b2. Since the adhesive28adoes not reach the ledge portion24b1and thus the surface roughness of the ledge portion24b1can be set to be large, gas can be smoothly released. Thus, it becomes possible to reliably form a high-quality adhesive layer28free of air bubbles and the like.

The operation of the fuel cell12having such a structure will now be described.

First, as illustrated inFIG. 1, oxidant gas such as oxygen-containing gas is supplied through the oxidant gas inlet manifold32aand at the same time fuel gas such as hydrogen-containing gas is supplied through the fuel gas inlet manifold36a. A cooling medium such as pure water, ethylene glycol, or oil, is supplied through the cooling medium inlet manifold34a.

As a result, the oxidant gas is introduced into the oxidant gas flow channel38of the second separator16through the oxidant gas inlet manifold32a, moves in the arrow B direction, and is supplied to the cathode electrode22of the stepped MEA10a. The fuel gas is introduced into the fuel gas flow channel40of the first separator14through the fuel gas inlet manifold36a. The fuel gas moves in the arrow B direction along the fuel gas flow channel40and is supplied to the anode electrode20of the stepped MEA10a.

Thus, in each stepped MEA10a, the oxidant gas supplied to the cathode electrode22and the fuel gas supplied to the anode electrode20are consumed by electrochemical reactions within the second electrode catalyst layer22aand the first electrode catalyst layer20aand power is generated as a result.

The oxidant gas supplied to the cathode electrode22and partly consumed is discharged through the oxidant gas outlet manifold32bin the arrow A direction. Similarly, the fuel gas supplied to the anode electrode20and partly consumed is discharged through the fuel gas outlet manifold36bin the arrow A direction.

The cooling medium supplied to the cooling medium inlet manifold34ais introduced into the cooling medium flow channel42between the first separator14and the second separator16and is distributed in the arrow B direction. This cooling medium cools the stepped MEA10aand is discharged through the cooling medium outlet manifold34b.

A resin-framed stepped membrane electrode assembly (MEA) for a fuel cell according to the present disclosure includes a stepped membrane electrode membrane (MEA) and a resin frame member. The stepped MEA includes a first electrode that is disposed on a surface of the solid polymer electrolyte membrane and includes a first electrode catalyst layer and a first gas diffusion layer, and a second electrode that is disposed on another surface of the solid polymer electrolyte membrane and includes a second electrode catalyst layer and a second gas diffusion layer.

The first electrode has flat dimensions larger than flat dimensions of the second electrode. The second electrode catalyst layer includes an outer periphery exposed portion that extends outward from an outer peripheral end of the second gas diffusion layer. The resin frame member surrounds an outer periphery of the solid polymer electrolyte membrane and includes an inner protruding portion protruding toward the second electrode and joined to the stepped MEA with an adhesive.

The inner protruding portion includes a bank portion disposed in an inner peripheral end portion of the inner protruding portion, the bank portion facing the outer periphery exposed portion of the second electrode catalyst layer. A groove portion is disposed on an outer peripheral side of the bank portion. A ledge portion is disposed on an outer peripheral side of the groove portion so as to contact an outer peripheral surface of the solid polymer electrolyte membrane, the outer peripheral surface being an exposed portion extending outward from the second electrode catalyst layer. A surface roughness of a tip of the bank portion is smaller than a surface roughness of a bottom surface of the groove portion.

Since the surface roughness of the bank portion is designed to be small, dust rarely attaches thereto. Thus, attachment of dust or the like on the solid polymer electrolyte membrane can be prevented by a simple structure and damage on the solid polymer electrolyte membrane can be minimized.

In contrast, the surface roughness of the groove portion is designed to be large. Thus, the adhesive flows smoothly inside the groove portion and air within the adhesive layer can be smoothly discharged to outside. Thus, variation in quality, such as gas barrier properties and adhesion durability, can be reduced, and the stepped MEA can be strongly bonded to the resin frame member to achieve high quality.

In the inner protruding portion of the resin-framed stepped MEA for a fuel cell described above, a height of the bank portion is preferably smaller than a height of the ledge portion.

In the inner protruding portion of the resin-framed stepped MEA for a fuel cell described above, a surface roughness of a tip of the ledge portion is preferably larger than the surface roughness of the bottom surface of the groove portion.