Membrane electrode structure for fuel cell and fuel cell system

Abstract

To provide a durable membrane electrode structure for a fuel cell, capable of suitably performing gas humidity exchange.SOLUTION: A membrane electrode structure for a fuel cell comprises: a membrane electrode assembly including an electrolyte membrane and gas diffusion electrode layers on both sides of the electrolyte membrane; and a frame member having an inner edge at which the membrane electrode assembly is arranged. The frame member includes approximately planar first and second frame members overlapping with each other. The electrolyte membrane is extended to a non-power generation region outside outer edges of the gas diffusion electrode layers. The first and second frame members have first and second holding parts, respectively, for holding the electrolyte membrane in the non-power generation region. On the first and second holding parts, first and second open holes penetrating the first and second holding parts are provided at positions different from each other in plan view.SELECTED DRAWING: Figure 4

Description

[Technical Field]

[0001] The present invention relates to a membrane electrode assembly for a fuel cell and a fuel cell system. [Background technology]

[0002] In recent years, technological developments related to fuel cells that contribute to energy efficiency have been underway to ensure that more people have access to affordable, reliable, sustainable, and advanced energy. Known technologies related to power generation cells used in this type of fuel cell include a power generation cell that exchanges humidity between the anode and cathode side gases outside the power generation region (see, for example, Patent Document 1). In the power generation cell described in Patent Document 1, a substantially plate-shaped resin frame is placed around the cathode side gas diffusion layer and overlaps the anode side gas diffusion layer, and multiple through-holes are formed in the resin frame, forming a membrane electrode structure that exchanges humidity between the anode side gas and the cathode side gas through the multiple through-holes. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2017-183031 Summary of the Invention [Problem to be solved by the invention]

[0004] However, when a plurality of through holes for humidity exchange are provided in the resin frame as described in Patent Document 1, the strength of the resin frame decreases, making it difficult to obtain sufficient durability. [Means for solving the problem]

[0005] A fuel cell membrane electrode assembly according to one embodiment of the present invention includes a membrane electrode assembly formed by stacking an electrolyte membrane, a first gas diffusion electrode layer disposed on a first surface of the electrolyte membrane, and a second gas diffusion electrode layer disposed on a second surface opposite the first surface of the electrolyte membrane, and a frame member having an inner edge portion forming an opening in which the membrane electrode assembly is disposed. The frame members each have an inner edge portion and include a first frame member and a second frame member that are generally plate-shaped and overlap each other. The electrolyte membrane extends into a non-power generation region that is outside the outer edges of the first gas diffusion electrode layer and the second gas diffusion electrode layer. The first frame member and the second frame member have a first clamping portion and a second clamping portion, respectively, that sandwich the electrolyte membrane in the non-power generation region. The first clamping portion and the second clamping portion are provided with a first through-hole that penetrates the first clamping portion and a second through-hole that penetrates the second clamping portion, respectively, at different positions in a plan view seen from the stacking direction of the membrane electrode assembly.

[0006] Another aspect of the present invention is a fuel cell system including a fuel cell stack constructed by stacking power generation cells having the above-described fuel cell membrane electrode structure, in which the reactant gas is anode gas, and the system further includes a gas reflux section that refluxes the anode gas flowing out from the fuel cell stack to the fuel cell stack. [Effects of the Invention]

[0007] According to the present invention, sufficient durability of the membrane electrode assembly can be ensured while humidity exchange of gas can be performed satisfactorily. [Brief explanation of the drawings]

[0008] [Figure 1] 1 is a diagram showing a schematic configuration of a main part of a fuel cell system according to an embodiment of the present invention; [Figure 2] FIG. 2 is a perspective view showing a schematic overall configuration of a fuel cell stack included in the fuel cell system of FIG. [Figure 3] FIG. 3 is a cross-sectional view taken along line III-III in FIG. 2. [Figure 4] FIG. 3 is a perspective view showing a schematic configuration of an electrode assembly included in the fuel cell stack of FIG. 2. [Figure 5A]FIG. 3 is a rear view of a separator included in the fuel cell stack of FIG. 2. [Figure 5B] FIG. 3 is a front view of a separator included in the fuel cell stack of FIG. 2. [Figure 6] FIG. 4 is a cross-sectional view taken along line IV-IV in FIG. [Figure 7A] Arrow VII view of Figure 4. [Figure 7B] FIG. 7B is a diagram showing a modification of FIG. 7A. [Figure 8A] FIG. 5 is a diagram showing a modification of FIG. 4. [Figure 8B] FIG. 5 is a diagram showing another modified example of FIG. 4. [Figure 9] FIG. 5 is a diagram showing yet another modified example of FIG. 4. [Figure 10] FIG. 5B is a diagram showing a modification of FIG. 5A. [Figure 11] FIG. 11 is a rear view of the electrode assembly facing the separator of FIG. 10 . DETAILED DESCRIPTION OF THE INVENTION

[0009] Hereinafter, an embodiment of the present invention will be described with reference to FIGS. 1 to 11. FIG. 1 is a block diagram that schematically shows the configuration of a main part of a fuel cell system 500 according to an embodiment of the present invention. The fuel cell system 500 is mounted on, for example, a vehicle and generates electric power for driving the vehicle. As shown in FIG. 1, the fuel cell system 500 has a fuel cell stack 100 formed by stacking a plurality of power generation cells, a fuel gas supply / discharge unit 510, an oxidant gas supply / discharge unit 520, and a coolant supply / discharge unit 530. The fuel gas and oxidant gas are sometimes called anode gas and cathode gas, respectively.

[0010] The fuel gas supply / discharge unit 510 has a tank 511 that stores high-pressure fuel gas, an injector 512 that discharges the fuel gas, and an ejector 513. The fuel gas in the tank 511 is supplied to the fuel cell stack 100 via the injector 512, the ejector 513, and a supply pipe 510a. The fuel gas is an anode gas containing hydrogen (e.g., hydrogen gas). Fuel gas (fuel exhaust gas) containing moisture is discharged from the fuel cell stack 100 via a discharge pipe 510b. In the ejector 513, negative pressure generated by the flow of the fuel gas discharged from the injector 512 causes the fuel exhaust gas to be sucked through a circulation pipe 510c. This causes the fuel gas to be returned to the fuel cell stack 100. Although not shown, a gas-liquid separator is provided in the discharge pipe 510b, and the gas-liquid separator removes excess moisture contained in the fuel exhaust gas.

[0011] The oxidant gas supply / discharge unit 520 has a compressor 521 that compresses the oxidant gas to a high pressure. The oxidant gas compressed by the compressor 521 is supplied to the fuel cell stack 100 via a supply pipe 520a. The oxidant gas is a cathode gas (e.g., air) containing oxygen. The oxidant gas (oxidant exhaust gas) containing moisture is discharged from the fuel cell stack 100 via a discharge pipe 520b. A humidifier 522 (dotted line) that humidifies the oxidant gas may be provided in the supply pipe 520a. However, in this embodiment, the humidification of the oxidant gas is promoted as described below, so the humidifier 522 can be omitted.

[0012] The cooling medium supply / discharge unit 530 has a pump (not shown), and the cooling medium discharged from the pump is supplied to the fuel cell stack 100 via a supply pipe 530a. The cooling medium is, for example, water. The cooling medium is discharged from the fuel cell stack 100 via a discharge pipe 530b. The discharged cooling medium is cooled by heat exchange in a radiator and is supplied again to the fuel cell stack 100 via the supply pipe 530a.

[0013] FIG. 2 is a perspective view showing a schematic view of the overall configuration of the fuel cell stack 100. For convenience, the three mutually orthogonal axial directions shown in the figure are defined as the front-rear direction, the left-right direction, and the up-down direction, and the configuration of each part will be described in accordance with these definitions. These directions are not necessarily the same as the front-rear direction, the left-right direction, and the up-down direction of a vehicle. For example, the front-rear direction in FIG. 1 may be the front-rear direction, the left-right direction, or the up-down direction of a vehicle.

[0014] 2, the fuel cell stack 100 has a cell stack 101 formed by stacking a plurality of power-generating cells 1 in the front-to-rear direction, and end units 102 arranged at both the front and rear ends of the cell stack 101, and has a generally rectangular parallelepiped shape as a whole. Although not shown in the figure, a generally box-shaped case with open front and rear faces is arranged around the cell stack 101. The front end face of the case and the front end unit 102, and the rear end face of the case and the rear end unit 102 are fastened together with bolts.

[0015] The power generation cell 1 comprises an electrode assembly 2 having a membrane electrode assembly including an electrolyte membrane and electrodes, and a pair of front and rear separators 3, 3 arranged on both the front and rear sides of the electrode assembly 2 and sandwiching the electrode assembly 2. The electrode assemblies 2 and the separators 3 are arranged alternately in the front-rear direction. The electrode assemblies 2 constitute a membrane electrode structure (UEA; Unitized Electrode Assembly). The electrode assemblies 2 can also be called membrane electrode members.

[0016] FIG. 3 is a cross-sectional view of a main portion of the cell stack 101 at the center in the left-right direction (a cross-sectional view taken along line III-III in FIG. 2). As shown in FIG. 3, the separator 3 has a front plate 3F and a rear plate 3R, which are a pair of front and rear metal thin plates with a corrugated cross section. The front plate 3F extends in the vertical and horizontal directions and has a front surface 3Fa and a rear surface 3Fb. The rear plate 3R extends in the vertical and horizontal directions and has a front surface 3Ra and a rear surface 3Rb. The opposing rear surface 3Fb of the front plate 3F and the front surface 3Ra of the rear plate 3R are joined at their outer peripheral edges by welding or the like. This integrally bonds the front plate 3F and the rear plate 3R. The separator 3 is made of a conductive material with excellent corrosion resistance, such as stainless steel, titanium, or a titanium alloy.

[0017] A cooling flow path PAw through which a coolant flows is formed inside the separator 3 surrounded by the front plate 3F and the rear plate 3R, that is, between the rear surface 3Fb of the front plate 3F and the front surface 3Ra of the rear plate 3R. The flow of the coolant cools the power generation surface of the power generation cell 1. The surfaces of the separator 3 facing the electrode assembly 2 (the front surface 3Fa and the rear surface 3Rb) are formed unevenly by press molding or the like to form gas flow paths between the separator 3 and the electrode assembly 2. More specifically, the front plate 3F and the rear plate 3R each have a protrusion 31 that protrudes toward the front and rear electrode assemblies 2, and a recess 32 that is formed concave and convex and continues from the protrusion 31.

[0018] The rear convex portion 31 abuts against the front surface 2a of the electrode assembly 2, and the front convex portion 31 abuts against the rear surface 2b of the electrode assembly 2. A compressive load F is applied to the cell stack 101 in the front-to-rear direction when the fuel cell stack 100 is assembled, and in this state, the case surrounding the cell stack 101 is fastened to the front and rear end units 102. Therefore, after the assembly of the fuel cell stack 100 is complete, the compressive load F is maintained on the fuel cell stack 100, and a predetermined surface pressure acts on the electrode assembly 2 in the front-to-rear direction via the convex portions 31.

[0019] An anode flow path PAa through which a fuel gas flows is formed between the front surface 2a of the electrode assembly 2 and the rear plate 3R of the separator 3 facing this front surface 2a by the recess 32. A cathode flow path PAc through which an oxidizer gas flows is formed between the rear surface 2b of the electrode assembly 2 and the front plate 3F of the separator 3 facing this rear surface 2b by the recess 32. The fuel gas and the oxidizer gas may sometimes be referred to as reactant gases without being distinguished from each other.

[0020] Fig. 4 is a perspective view showing a schematic configuration of the electrode assembly 2. As shown in Fig. 4, the electrode assembly 2 has a substantially rectangular assembly 20 and a frame 21 that supports the assembly 20. As shown in the detailed view of portion A in Fig. 2, the assembly 20 has an electrolyte membrane 23, an anode electrode 24 provided on a front surface 23f of the electrolyte membrane 23, and a cathode electrode 25 provided on a rear surface 23r of the electrolyte membrane 23.

[0021] The electrolyte membrane 23 is, for example, a solid polymer electrolyte membrane, and a thin film of a perfluorosulfonic acid polymer containing water can be used. The electrolyte membrane 23 is not limited to a fluorine-based electrolyte membrane, and a hydrocarbon-based electrolyte membrane can also be used.

[0022] The anode 24 is formed on the front surface 23f of the electrolyte membrane 23 and includes an electrode catalyst layer 241 that serves as a reaction field for an electrode reaction, and a gas diffusion layer 242 that is provided in front of the electrode catalyst layer 241 and diffuses and supplies a fuel gas. The cathode 25 is formed on the rear surface 23r of the electrolyte membrane 23 and includes an electrode catalyst layer 251 that serves as a reaction field for an electrode reaction, and a gas diffusion layer 252 that is provided on the rear surface of the electrode catalyst layer 251 and diffuses and supplies an oxidant gas. An intermediate layer (base layer) may be provided between the electrode catalyst layers 241, 251 and the gas diffusion layers 242, 252.

[0023] The electrode catalyst layers 241, 251 contain a catalytic metal that promotes an electrochemical reaction between hydrogen contained in the fuel gas and oxygen contained in the oxidant gas, a proton-conductive electrolyte (e.g., ionomer), and electron-conductive carbon particles, etc. The gas diffusion layers 242, 252 are made of a gas-permeable conductive material, such as a porous carbon material.

[0024] At the anode electrode 24, the fuel gas (hydrogen) supplied via the anode flow path PAa is ionized by the action of a catalyst and moves toward the cathode electrode side through the electrolyte membrane 23. The electrons generated at this time pass through an external circuit and are extracted as electrical energy. At the cathode electrode 25, the oxidant gas (oxygen) supplied via the cathode flow path PAc reacts with the hydrogen ions introduced from the anode electrode 24 and the electrons transferred from the anode electrode 24 to generate water. The generated water (referred to as "generated water") provides an appropriate humidity to the electrolyte membrane 23, and excess water is discharged to the outside of the electrode assembly 2 along with the gas flow. The generated water on the cathode side also flows toward the anode side by reverse diffusion through the electrolyte membrane 23. Therefore, both the fuel gas and the oxidant gas contain generated water. Condensed water is also contained in the fuel gas and the oxidant gas.

[0025] As shown in FIG. 4, the frame 21 is a thin plate having a substantially rectangular shape and is made of insulating and gas-impermeable resin, rubber, or the like. For example, PEN (polyethylene naphthalate) or PPS (polyphenylene sulfide) can be used as the constituent material. A substantially rectangular opening 21a is formed in the center of the frame 21, and the joining body 20 is provided to cover the entire opening 21a. The frame 21 has a substantially rectangular outer edge 221 and an inner edge 222. The outer edge 221 refers to the outer edge of the frame 21 and its surrounding area, and the inner edge 222 refers to the inner edge of the frame 21 (the edge of the opening 21a) and its surrounding area.

[0026] Point P in Fig. 4 is a center point passing through the vertical and horizontal midpoints of opening 21a. Three through holes 201 to 203 that penetrate frame 21 in the front-to-rear direction are opened in a vertical line on the left side of opening 21a of frame 21. Three through holes 204 to 206 that penetrate frame 21 in the front-to-rear direction are opened in a vertical line on the right side of opening 21a. For convenience, through holes 201 to 206 are shown as being substantially rectangular, but the shape and arrangement of through holes 201 to 206 are not limited to this.

[0027] As shown in FIG. 2, the front and rear separators 3 of the electrode assembly 2 are provided with through holes 301 to 306, respectively, which penetrate the separators 3 in the front-rear direction at positions corresponding to the through holes 201 to 206 of the frame 21. The through holes 301 to 306 are connected to the through holes 201 to 206 of the frame 21, respectively. A collection of these mutually communicating through holes 201 to 206 and 301 to 306 form flow paths PA1 to PA6 (indicated by arrows for convenience) which penetrate the cell stack 101 and extend in the front-rear direction. The flow paths PA1 to PA6 are sometimes called manifolds. The flow paths PA1 to PA6 are connected to a manifold external to the fuel cell stack 100.

[0028] Although not shown in the figures, the front and rear end units 102 of the cell stack 101 each have a plurality of plates stacked in the front-to-rear direction. Specifically, the end unit 102 has a terminal plate arranged adjacent to the cell stack 101, an insulating plate arranged on the outer side of the terminal plate in the front-to-rear direction, and an end plate arranged on the outer side of the insulating plate in the front-to-rear direction.

[0029] The terminal plate is a roughly rectangular metal plate-like member that has a terminal portion for extracting the power generated by the electrochemical reaction in the cell stack 101. The insulating plate is a roughly rectangular non-conductive resin or rubber plate-like member that electrically insulates the terminal plate from the end plates. The end plates are plate-like members made of metal or high-strength resin.

[0030] The rear end unit 102 is a wet-side end unit through which the reactant gas and the cooling medium pass, and the front end unit 102 is a dry-side end unit through which the reactant gas and the cooling medium do not pass. The rear end unit 102 has a plurality of through-holes 102a-102f that pass through the end unit 102 in the front-rear direction at positions corresponding to the through-holes 201-206, 301-306 of the cell stack 101. For convenience, the through-holes 102a-102f are shown as being substantially rectangular, but the shape of the through-holes 102a-102f is not limited to this.

[0031] Flow paths PA1 and PA6 (solid arrows) are flow paths for supplying and discharging fuel gas, respectively, and supply pipe line 510a and discharge pipe line 510b in FIG. 1 are connected to through holes 201 and 206, respectively. Flow paths PA4 and PA3 (dotted arrows) are flow paths for supplying and discharging oxidant gas, respectively, and supply pipe line 520a and discharge pipe line 520b in FIG. 1 are connected to through holes 204 and 203, respectively. Flow paths PA5 and PA2 (dashed arrows) are flow paths for supplying and discharging coolant, respectively, and supply pipe line 530a and discharge pipe line 530b in FIG. 1 are connected to through holes 205 and 202, respectively.

[0032] The structure of the separator 3 will be described in more detail. FIG. 5A is a rear view (viewed from the rear) of the separator 3, and FIG. 5B is a front view (viewed from the front). Specifically, FIG. 5A shows the rear surface 3Rb (FIG. 3) of the separator 3 (rear plate 3R) facing the anode electrode 24 on the front surface 2a of the electrode assembly 2, and FIG. 5B shows the front surface 3Fa (FIG. 3) of the separator 3 (front plate 3F) facing the cathode electrode 25 on the rear surface 2b of the electrode assembly 2. The region AR1 in the figure is the region where power generation occurs in the opposing electrode assembly 2 assembly 2, and is called the active region (power generation region). The region AR2 outside the active region AR1 (outside in the left-right and up-down directions) is the region where power generation does not occur, and is called the inactive region (non-power generation region).

[0033] 5A, although some of the illustration is omitted, a plurality of protrusions 31 (FIG. 3) are provided in the active area AR1 of the separator 3 (rear plate 3R) over substantially the entire area thereof at equal intervals in the vertical direction and protrude rearward. Each of the plurality of protrusions 31 extends in the horizontal direction, and a recess 32 (FIG. 3) is provided between adjacent protrusions 31 in the vertical direction. An anode flow path PAa is formed between the plurality of recesses 32 and the front surface 2a of the assembly 20.

[0034] 5B, although some of the illustration is omitted, a plurality of protrusions 31 (FIG. 3) are provided in the active area AR1 of the separator 3 (front plate 3F) over substantially the entire area thereof at equal intervals in the vertical direction and protrude forward. Each of the plurality of protrusions 31 extends in the horizontal direction, and a recess 32 (FIG. 3) is provided between adjacent protrusions 31 in the vertical direction. A cathode flow path PAc is formed between the plurality of recesses 32 and the rear surface 2b of the assembly 20.

[0035] 5A, a rear surface 3Rb of the separator 3 (rear plate 3R) is provided by press molding with a plurality of sealing bead portions, i.e., metal bead seals, that protrude rearward toward the frame 21. The plurality of bead portions extend along the periphery of the rear plate 3R and include an outer bead portion 331 that entirely surrounds the through holes 301-306, an inner bead portion 332 that surrounds the through holes 311 and 316 and the active area AR1 inside the outer bead portion 331, and end bead portions 333 that individually surround the through holes 312-315 between the outer bead portion 331 and the inner bead portion 332. The tops of the bead portions 331-333 are in close contact with the front surface 2a of the electrode assembly 2 (frame 21), thereby forming an enclosed space through which fuel gas flows from the through hole 311 to the anode flow path PAa and the through hole 316. To improve the sealing performance, a sealing material may be fixed to the tops of the bead portions 331 to 333.

[0036] 5B, a front surface 3Fa of the separator 3 (front plate 3F) is provided by press molding with a plurality of sealing bead portions, i.e., metal bead seals, that protrude forward toward the frame 21. The plurality of bead portions extend along the periphery of the front plate 3F and include an outer bead portion 334 that entirely surrounds the through holes 301 to 306, an inner bead portion 335 that surrounds the through holes 313 and 314 and the active area AR1 inside the outer bead portion 334, and end bead portions 336 that individually surround the through holes 311, 312, 315, and 316 between the outer bead portion 334 and the inner bead portion 335. The tops of the bead portions 334 to 336 are in close contact with the rear surface 2b of the electrode assembly 2 (frame 21), thereby forming an enclosed space through which oxidant gas flows from the through hole 314 to the cathode flow path PAc and the through hole 316. To improve the sealing performance, a sealing material may be fixed to the tops of the bead portions 334 to 336.

[0037] As shown in FIG. 5A, the anode-side non-active area AR2 includes a gas flow region AR3 between the through-holes 311, 316 and the active area AR1 inside the inner bead portion 332, through which fuel gas flows. The separator 3 has a plurality of generally cylindrical protrusions 337 protruding from this gas flow region AR3 toward the rear electrode assembly 2. As shown in FIG. 5B, the cathode-side non-active area AR2 includes a gas flow region AR3 between the through-holes 313, 314 and the active area AR1 inside the inner bead portion 335, through which oxidant gas flows. The separator 3 has a plurality of generally cylindrical protrusions 338 protruding from this gas flow region AR3 toward the front electrode assembly 2.

[0038] In this way, a plurality of protrusions 337, 338 are provided in the gas flow region AR3 of the separator 3 toward the electrode assembly 2. This allows the reactant gases (fuel gas, oxidant gas) to flow evenly in the vertical direction in the gas flow region AR3. Such a gas flow region AR3 is sometimes called a buffer region, and the protrusions 337, 338 are sometimes called buffer portions.

[0039] The fuel gas flows to the right from through-hole 311 to through-hole 316, and the oxidant gas flows to the left from through-hole 314 to through-hole 313. Therefore, the fuel cell stack 100 is a crossflow type in which the fuel gas and the oxidant gas flow in opposite directions via the electrode assembly 2. Because water is produced on the cathode side, the oxidant gas flowing through the active region AR1 is humidified by the produced water, and the humidity gradually increases in the direction of flow (to the right). Meanwhile, the produced water diffuses from the cathode side to the anode side through the electrolyte membrane 23 due to the humidity gradient with the cathode side. Therefore, the fuel gas is humidified by the produced water due to reverse diffusion, and the humidity gradually increases in the direction of flow (to the left).

[0040] Therefore, near the left end of the active area AR1, the humidity of the fuel gas is higher than that of the oxidant gas, and near the right end, the humidity of the oxidant gas is higher than that of the fuel gas. When a difference in humidity occurs between the fuel gas and the oxidant gas, moisture moves from the higher humidity to the lower humidity through the electrolyte membrane 23, reducing the difference in humidity. This phenomenon of humidity change is called humidity exchange.

[0041] In the above-described power generating cell 1, if the humidity of the reactant gas is too low, the electrolyte membrane 23 dries out, inhibiting the movement of protons and resulting in a decrease in power generation performance. Conversely, if the humidity is too high, the supply of the reactant gas is inhibited, which also results in a decrease in power generation performance. Therefore, to improve the power generation performance of the power generating cell 1, the reactant gas on the anode side and the cathode side needs to have an appropriate humidity.

[0042] In this regard, if through-holes are provided in the gas flow region AR3 of the frame 21 and humidity exchange between the fuel gas and the oxidant gas is performed through the through-holes, the humidity exchange region is expanded beyond the active region AR1. This expands the range of humidity distribution, i.e., the range of humidity distribution that is neither too low nor too high, and improves power generation performance. However, providing through-holes in the gas flow region AR3 of the frame 21 reduces the strength of the frame 21. Therefore, there is a risk that the electrode assembly 2 may not be sufficiently durable in an environment where a pressure difference acts between the front and rear of the frame 21 and a compressive load F (FIG. 3) acts. Therefore, in this embodiment, the electrode assembly 2 as a membrane electrode structure is configured as follows to ensure sufficient durability and perform good humidity exchange of the reactant gases.

[0043] 6 is a cross-sectional view of the electrode assembly 2 near the inner edge 222 of the frame 21 (a cross-sectional view taken along line VI-VI in FIG. 4). The right side of FIG. 6 is the outer edge 221 side of the frame 21, and the left side is the center point P side. The outer edge 221 side may be referred to as the outside, and the center point P side may be referred to as the inside. As shown in FIG. 6, the cathode-side electrode catalyst layer 251 of the electrode assembly 2 extends outward more than the anode-side electrode catalyst layer 241, and the right end (outer edge 251a) of the electrode catalyst layer 251 is located to the right of the right end (outer edge 241a) of the electrode catalyst layer 241.

[0044] The electrolyte membrane 23 extends outward beyond the electrode catalyst layers 241, 251, and the right end (outer edge 23a) of the electrolyte membrane 23 is located to the right of the right ends of the electrode catalyst layers 241, 251. As indicated by the dotted line in FIG. 4, the electrolyte membrane 23 has a generally rectangular shape as a whole in a plan view seen from the stacking direction of the electrode assembly 2. More specifically, the electrolyte membrane 23 extends in the vertical and horizontal directions so as to cover the gas flow regions AR3 (FIGS. 5A and 5B) on the inner left-right sides of the through-holes 201-206, and the outer edge 23a of the electrolyte membrane 23 is located near the inner left-right edges of the through-holes 201-206. As shown in FIG. 6, the right end (outer edge 242a) of the anode-side gas diffusion layer 242 and the right end (outer edge 252a) of the cathode-side gas diffusion layer 252 are located at the same left-right position as the outer edge 251a of the electrode catalyst layer 251. Therefore, the electrolyte membrane 23 protrudes outward beyond the anode electrode 24 and the cathode electrode 25 .

[0045] The frame 21 is composed of a pair of front and rear frames, i.e., a front frame 211 and a rear frame 212, which are bonded via an adhesive layer 210. The front frame 211 is bonded to the front surface 23f of the electrolyte membrane 23 via the adhesive layer 210. The left end (inner edge portion 222) of the front frame 211 extends leftward (inward) from the outer edge 241a of the electrode catalyst layer 241 and is interposed between the electrode catalyst layer 241 and the electrolyte membrane 23. The left end (inner edge portion 222) of the rear frame 212 extends leftward (inward) from the outer edge 251a of the electrode catalyst layer 251 and is interposed between the electrode catalyst layer 251 and the gas diffusion layer 252. The opening 21a (inner edge) of the front frame 211 is located to the left (inner) of the opening 21a of the rear frame 212, and an active area AR1 is formed inside (left side) the inner edge of the front frame 211, where the anode electrode 24, electrolyte membrane 23, and cathode electrode 25 overlap without the frame 21 in between.

[0046] The electrolyte membrane 23 is sandwiched between the front frame 211 and the rear frame 212. The portions of the frames 211 and 212 outside the gas diffusion layers 242 and 252 where the electrolyte membrane 23 is sandwiched are called sandwiching portions 215 and 216. The region where the electrolyte membrane 23 is sandwiched between the sandwiching portions 215 and 216, that is, the region from the outer edges 242a and 252a of the gas diffusion layers 242 and 252 to the outer edge 23a of the electrolyte membrane 23, is called the sandwiching region AR4. The sandwiching region AR4 is included in the inactive region AR2, and a portion of it overlaps with the gas flow region AR3 (FIGS. 5A and 5B) between the through-holes 201-206 and the active region AR1.

[0047] The clamping portions 215, 216 of the front frame 211 and the rear frame 212 are provided with a plurality of through-holes 213, 214 that penetrate the frames 211, 212, respectively. As shown in Fig. 4, the through-holes 213, 214 are opened over the entire area of the right clamping area AR4 of the clamping areas AR4 on both the left and right sides of the opening 21a, i.e., the clamping area AR4 on the left side of the through-holes 204-206. For convenience, Fig. 4 shows only some of the through-holes 214 of the rear frame 212. In addition to or instead of the right clamping area AR4, the through-holes 213, 214 may be opened over the entire area of the left clamping area AR4.

[0048] FIG. 7A is a front view (view along arrow VII in FIG. 4) of a main portion of the electrode assembly 2 showing the arrangement of the through holes 213 and 214, corresponding to a plan view seen from the stacking direction of the electrode assembly 2. As shown in FIG. 7A, in the sandwiching region AR4 of the frame 21, the substantially rectangular through holes 213 and 214 are arranged alternately in the left-right and up-down directions. In other words, the through holes 213 and 214 are arranged alternately in the left-right and up-down directions. Therefore, the through holes 213 and 214 do not overlap each other in plan view. In this case, since it is not necessary to provide the gas diffusion layers 242 and 252 so as to overlap the through holes 213 and 214 in plan view, the gas diffusion layers can be made smaller, leading to cost reductions.

[0049] By providing the through holes 213, 214 alternately in this manner, the strength of the entire frame is improved compared to when the through holes are provided so as to overlap in plan view from the front to the rear surface of the frame 21. This increases the durability of the electrode assembly 2. Furthermore, deformation of the frame 21 can be suppressed, and sufficient sealing performance can be maintained between the frame 21 and the bead portions 331-333 of the separator 3.

[0050] FIG. 6 is a cross-sectional view of the electrode assembly 2 on the upstream side of the oxidant gas (downstream side of the fuel gas). The oxidant gas is supplied to the gas flow region AR3 in an unhumidified state. In contrast, the fuel gas after passing through the active region AR1 has been humidified by reverse diffusion. Therefore, the humidity of the fuel gas is higher than that of the oxidant gas. In this case, moisture contained in the fuel gas moves to the cathode side through the through-holes 213, the electrolyte membrane 23, and the through-holes 214, as shown by arrow A in FIG. 6. As a result, the humidity of the oxidant gas increases while the humidity of the fuel gas decreases, and humidity exchange occurs between the fuel gas and the oxidant gas.

[0051] On the other hand, on the upstream side of the fuel gas (downstream side of the oxidant gas), the humidity of the oxidant gas is higher than that of the fuel gas due to the generation of water. However, because the fuel gas is supplied to the gas flow region AR3 in a humidified state via the circulation pipe 510c (FIG. 1), the difference in humidity between the fuel gas and the oxidant gas is smaller than on the upstream side of the oxidant gas. For this reason, as shown in FIG. 4, the through holes 213, 214 in the left clamping region AR4 can be omitted.

[0052] The arrangement and shape of the through holes 213, 214 are not limited to those shown in Fig. 7A. For example, as shown in Fig. 7B, the through holes 213, 214 may be arranged alternately in the up, down, left, and right directions, and may be arranged in a staggered pattern in the up, down, left, and right directions. The through holes 213, 214 may have a shape other than a rectangle, such as a circle, an ellipse, or a polygonal shape other than a rectangle.

[0053] The opening areas of the through holes 213, 214 may be varied in the flow direction of the reactant gas rather than being constant throughout the sandwiching region AR4. FIG. 8A is a rear view (viewed from behind) of an example electrode assembly 2. In the example of FIG. 8A, a plurality of through holes 214 are formed from the through hole 204 for supplying the oxidant gas in the rear frame 212 to the assembly 20 to the left of the through hole 204. The opening areas of these through holes 214 gradually decrease from right to left, that is, from the upstream side to the downstream side of the oxidant gas. Therefore, the opening area of the through hole 214a on the right side is smaller than the opening area of the through hole 214b on the left side.

[0054] 8A shows only some of the through holes 213 with dotted lines, but similar to the through hole 214, a plurality of through holes 213 are also formed in the front frame 211 so that the opening area gradually decreases from right to left and so that the opening areas of the through holes 213 are alternately arranged with the through holes 214. In FIG. 8A, the through holes 213, 214 are provided from the through hole 204 of the frame 21 to the opening 21a, but the vicinity of the through holes 204 to 206 is located further upstream of the oxidant gas than the vicinity of the opening 21a. For this reason, the through holes 213, 214 may be provided from the through holes 203 to 206 to the opening 21a, that is, over the entire clamping region AR4, so that the opening area gradually decreases from right to left.

[0055] 8A, humidity exchange between the oxidant gas and the fuel gas is promoted on the upstream side of the oxidant gas. This increases the humidity of the oxidant gas on the upstream side of the oxidant gas, and decreases the humidity of the fuel gas on the upstream side of the oxidant gas. As a result, the range in which a good humidity distribution is achieved can be expanded.

[0056] FIG. 8B is a diagram showing a modified example of FIG. 8A. In the example of FIG. 8B, the through-holes 213, 214 are provided so that the opening area gradually decreases from near the upper and lower ends of the frame 21 to the vertical center, that is, from the outside to the inside of the frame 21. Because the through-hole 213 is located below and to the left of the through-hole 214, the oxidant gas flows leftward and downward through the gas flow region AR3. Therefore, even in the example of FIG. 8B, the through-holes 213, 214 are provided so that the opening area decreases in the flow direction of the oxidant gas (from near the upper end to the vertical center). This promotes humidity exchange on the upstream side of the oxidant gas (downstream side of the fuel gas), and the range with a good humidity distribution can be expanded.

[0057] In the above, the through holes 213, 214 are provided in the region of the sandwiching region AR4 between the through holes 204-206 of the frame 21 and the opening 21a, but the through holes 213, 214 may be provided in other regions of the sandwiching region AR4. Fig. 9 is a rear view (viewed from behind) of an example electrode assembly 2. In the example of Fig. 9, a plurality of through holes 214 are provided between the through holes 204, 205 adjacent to each other in the vertical direction of the rear frame 212. Similarly, a plurality of through holes 213 are provided in the front frame 211 between the through holes 204, 205, alternately with the through holes 124.

[0058] Multiple through holes 213, 214 may be provided not only between the through holes 204, 205 but also between the through holes 205, 206. As in FIGS. 7A to 8B, the through holes 213, 214 may be provided not only between the through holes 204, 205 but also in the region between the through holes 204-206 and the opening 21a. In FIG. 9, the outer edge 23a of the electrolyte membrane 23 is positioned outward from the through holes 201-206. Furthermore, in addition to the opening 21a, openings 231-236 are formed in the electrolyte membrane 23 by punching or other processing, corresponding to the positions and shapes of the through holes 201-206. According to the configuration of FIG. 9, the through holes 213, 214 are positioned outward in the left-right direction compared to those in FIGS. 7A to 8B, thereby expanding the range of humidity exchange in the sandwiching region AR4 in the left-right direction. This allows for a wider range of favorable humidity distribution.

[0059] In the above, the buffer section is configured by providing approximately cylindrical protrusions 337, 338 in the gas flow area AR3 of the separator 3 (FIGS. 5A and 5B), but the configuration of the buffer section is not limited to that described above. FIG. 10 is a rear view (view from behind) of a separator 3 having another buffer section. As shown in FIG. 10, a plurality of elongated protrusions 339 are provided on the rear surface 3Rb of the separator 3 (rear plate 3R) on both the left and right sides of the active area AR1 along the fuel gas flow direction.

[0060] More specifically, the multiple protrusions 339 on the left side extend rightward or diagonally downward to the right so that the flow path area gradually increases from the fuel gas supply through-hole 311 to the inlet (left end) of the active area AR1, and the gas flow area AR3 has a generally trapezoidal shape in plan view. Furthermore, the protrusions 339 on the right side extend rightward or diagonally downward to the right so that the flow path area gradually decreases from the outlet (right end) of the active area AR1 to the fuel gas discharge through-hole 316, and the gas flow area AR3 has a generally trapezoidal shape in plan view.

[0061] Similarly, on the front surface 3Fa of the separator 3 (front plate 3F), a plurality of elongated protrusions 340 are provided on both the left and right sides of the active area AR1 in the oxidant gas flow direction. More specifically, the plurality of protrusions 340 on the right side extend leftward or diagonally downward to the left so that the flow path area gradually increases from the oxidant gas supply through-hole 314 to the inlet (right end) of the active area AR1, and the gas flow area AR3 has a substantially trapezoidal shape in plan view. Furthermore, the left side protrusion 340 extends leftward or diagonally downward to the left so that the flow path area gradually decreases from the outlet (left end) of the active area AR1 to the oxidant gas discharge through-hole 313, and the gas flow area AR3 has a substantially trapezoidal shape in plan view.

[0062] FIG. 11 is a front view (view from the rear) of the electrode assembly 2 facing the separator 3 in FIG. 10. As shown in FIG. 11, through-holes 213 and 214 are opened in the frame 21 of the electrode assembly 2 in a region (region AR30 shown by hatching in FIG. 11) where the gas flow region AR3 on the anode side (rear side of the separator 3) and the gas flow region AR3 on the cathode side (front side of the separator) overlap. In this case, the right end of the electrolyte membrane 23 is located a predetermined length ΔL to the left of the through-holes 204 to 206. This allows the electrolyte membrane 23 to be shortened in the left-right direction, thereby reducing costs.

[0063] According to this embodiment, the following effects can be achieved. (1) The electrode assembly 2, which serves as a membrane electrode structure for a fuel cell, includes an assembly 20 formed by stacking an electrolyte membrane 23, an anode electrode 24 disposed on a front surface 23f of the electrolyte membrane 23, and a cathode electrode 25 disposed on a rear surface 23r of the electrolyte membrane 23, and a frame 21 having an inner edge 222 that forms an opening 21a in which the assembly 20 is disposed (FIGS. 3 and 4). The frame 21 includes a substantially plate-shaped front frame 211 and a rear frame 212 that overlap each other and each have an inner edge 222 (FIG. 6). The electrolyte membrane 23 extends into an inactive area AR2 (non-power generation area) that is located outside the outer edges 241a, 242a of the anode electrode 24 and the outer edges 251a, 252a of the cathode electrode 25 (FIG. 6). The front frame 211 and the rear frame 212 each have clamping portions 215, 216 that clamp the electrolyte membrane 23 in the inactive area AR2. The sandwiching portions 215 and 216 are provided with a through-hole 213 penetrating the sandwiching portion 215 and a through-hole 214 penetrating the sandwiching portion 216 at mutually different positions in a plan view seen from the stacking direction of the bonded body 20 (FIGS. 6, 7A, and 7B).

[0064] By opening the through-holes 213, 214 at different positions in the pair of frames 211, 212 that sandwich the electrolyte membrane 23 in this manner, the strength of the frame 21, which allows humidity exchange via the electrolyte membrane 23 in the inactive area AR2, is improved. This ensures sufficient durability of the electrode assembly 2 while allowing good humidity exchange between the fuel gas and the oxidizer gas. Furthermore, because the electrolyte membrane 23 of the assembly 20 is sandwiched between the anode electrode 24 and the cathode electrode 25 and protrudes outward, the electrodes 24, 25 can be made smaller, leading to cost reductions.

[0065] (2) The through holes 213 and the through holes 214 are provided alternately in the clamping portions 215 and 216 in a plan view (FIGS. 7A and 7B). This prevents the through holes 213 and 214 from overlapping each other in a plan view, thereby improving the durability of the electrode assembly 2.

[0066] (3) The frame 21 is provided with through-holes 201, 203, 204, and 206 through which the reactant gas flows (FIG. 4). The inactive region AR2 includes a gas flow region AR3 through which the reactant gas flows, located between these through-holes 201, 203, 204, and 206 and the active region AR1 (power generation region) in which the electrolyte membrane 23, the anode electrode 24, and the cathode electrode 25 are stacked (FIGS. 5A and 5B). The through-holes 213 and 214 are provided in the gas flow region AR3 (FIG. 6). Since water is generated in accordance with the flow of the reactant gas, the humidity changes along the flow direction of the reactant gas. However, by providing the through-holes 213 and 214 in the gas flow region AR3, humidity exchange can be performed effectively in regions with large humidity differences.

[0067] (4) The through-holes 201, 203, 204, and 206 include the through-holes 201, 206 for fuel gas supply and fuel gas discharge, through which fuel gas flows, and the through-holes 204, 203 for oxidizer gas supply and oxidizer gas discharge, through which oxidizer gas flows (FIG. 4). The gas flow region AR3 includes a gas flow region AR3 (first gas flow region) through which fuel gas flows between the anode-side through-holes 201, 206 and the active region AR1, and a gas flow region AR3 (second gas flow region) through which oxidizer gas flows between the cathode-side through-holes 204, 203 and the active region AR1 (FIGS. 5A and 5B). The through-holes 213 and 214 are provided in a region AR30 where the anode-side and cathode-side gas flow regions AR3 overlap in a plan view (FIG. 11). This allows for a smaller electrolyte membrane 23 and reduced costs.

[0068] (5) The through holes 213 and 214 are each a plurality of through holes provided in the gas flow region AR3 (FIGS. 8A and 8B). The plurality of through holes 213 and the plurality of through holes 214 are provided so that the opening area decreases in the flow direction of the reactant gas (FIGS. 8A and 8B). This promotes humidity exchange on the upstream side of the flow direction of the reactant gas, and expands the range where good humidity distribution is achieved.

[0069] (6) The frame 21 is provided with a plurality of through holes 201-206 through which the reaction gas and the cooling medium flow (FIG. 4). The through holes 213, 214 are provided between a pair of adjacent through holes 204, 205 among the plurality of through holes 201-206 (FIG. 9). As a result, the through holes 213, 214 are positioned further outward in the left-right direction, and the range of humidity exchange in the sandwiching area AR4 is expanded in the left-right direction, thereby expanding the range in which good humidity distribution is achieved.

[0070] (7) The gas flow region AR3 is formed so that the flow direction of the fuel gas facing the front frame 211 and the flow direction of the oxidant gas facing the rear frame 212 are opposite to each other (FIG. 6). In other words, it is configured as a cross-flow type. This allows the through holes 213, 214 to be provided in an area where there is a large difference in humidity between the fuel gas and the oxidant gas, thereby enabling effective humidity exchange.

[0071] (8) The gas flow region AR3 includes a gas flow region AR3 that is upstream in the fuel gas flow direction and downstream in the oxidizer gas flow direction, and is located on the left side of the electrolyte membrane 23, and a gas flow region AR3 that is downstream in the fuel gas flow direction and upstream in the oxidizer gas flow direction, and is located on the right side of the electrolyte membrane 23 ( FIGS. 4, 5A, and 5B ). The through-holes 213 and 214 are not provided in the right gas flow region AR3 of these gas flow regions AR3, but are provided in the left gas flow region AR3 ( FIG. 4 ). This minimizes the area in which the humidity exchange through-holes 213 and 214 are provided, allowing the electrode assembly 2 to maintain sufficient strength.

[0072] (9) The fuel cell system 500 includes a fuel cell stack 100 configured by stacking power generation cells 1 each having the above-described electrode assembly 2 (FIG. 1). The fuel cell system further includes a circulation pipe 510c and an ejector 513 (FIG. 1) as a gas return section that returns the fuel gas flowing out from the fuel cell stack 100 to the fuel cell stack 100. As a result, the fuel gas is supplied to the fuel cell stack 100 in a humidified state via the circulation pipe 510c, so there is no need to actively humidify the fuel gas with water generated from the oxidant gas, and a through-hole for humidity exchange upstream of the fuel gas can be omitted.

[0073] The above embodiment can be modified in various ways. Some modified examples will be described below. In the above embodiment, the through-holes 213 (first through-holes) and the through-holes 214 (second through-holes) are provided in the clamping portion 215 (first clamping portion) of the front frame 211 (first frame member) and the clamping portion 216 (second clamping portion) of the rear frame 212 (second frame member), which constitute the frame 21 as a frame member, so as not to overlap each other in a plan view. However, the first through-holes and the second through-holes may partially overlap in a plan view. In this case, it is preferable that the through-holes partially overlap in a portion having a relatively high rigidity, such as the center of the clamping region AR4.

[0074] In the above-described embodiment (FIGS. 4, 6 to 9, and 11), through-holes 213 and 214 for humidity exchange are provided on the right side of opening 21a of frame 21 (on the upstream side of the oxidizer gas and the downstream side of the fuel gas). However, instead of or in addition to this configuration, through-holes for humidity exchange may be provided on the left side of opening 21a (on the downstream side of the oxidizer gas and the upstream side of the fuel gas). In the above-described embodiment, through-holes 201, 203, 204, and 206 are provided in frame 21 as communication holes through which reactant gases flow. More specifically, through-holes 201 and 206 (first communication holes) through which fuel gas as a first reactant gas flows and through-holes 203 and 204 (second communication holes) through which oxidizer gas as a second reactant gas flows are provided in frame 21. However, the position, number, shape, and arrangement of these communication holes are not limited to those described above.

[0075] In the above embodiment, the first reactive gas is a fuel gas (anode gas) and the second reactive gas is an oxidizer gas (cathode gas), but the first reactive gas may be an oxidizer gas and the second reactive gas may be a fuel gas, and the configuration of the first reactive gas and the second reactive gas is not limited to that described above. In the above embodiment (FIG. 9), a plurality of through holes 201-206 (communicating holes) through which the reactive gas and the cooling medium flow are provided in frame 21, and through holes 213, 214 are provided between a pair of adjacent through holes 204, 205 (pair of communicating holes), but through holes 213, 214 for humidity exchange may be provided between another pair of adjacent through holes.

[0076] In the above embodiment, the anode electrode 24 (first gas diffusion electrode layer) is arranged on the front surface 23f (first surface) of the electrolyte membrane 23, and the cathode electrode 25 (second gas diffusion electrode layer) is arranged on the rear surface 23r (second surface). However, the cathode electrode 25 may be arranged on the front surface 23f, and the anode electrode 24 may be arranged on the rear surface 23r.

[0077] In the above embodiment, an example of applying the fuel cell stack 100 to a vehicle has been described, but a fuel cell stack having a fuel cell membrane electrode junction of the present invention can also be applied to moving bodies other than vehicles, such as aircraft and ships, robots, and various industrial machines.

[0078] The above description is merely an example, and the present invention is not limited to the above-described embodiment and modifications as long as the features of the present invention are not impaired. One or more of the above-described embodiment and modifications can be arbitrarily combined, and modifications can also be combined with each other. [Explanation of symbols]

[0079] 1 power generation cell, 2 electrode assembly, 20 bonded body, 21 frame, 21a opening, 23 electrolyte membrane, 23f front surface, 23r rear surface, 24 anode electrode, 25 cathode electrode, 100 fuel cell stack, 201 to 206 through holes, 211 front frame, 212 rear frame, 213, 214 through holes, 214a, 214b through holes, 215, 216 clamping portion, 222 inner edge portion, 500 fuel cell system, 510c circulation pipe, 513 ejector, AR1 active area, AR2 inactive area, AR3 gas flow area, AR30 area

Claims

1. a membrane electrode assembly formed by stacking an electrolyte membrane, a first gas diffusion electrode layer disposed on a first surface of the electrolyte membrane, and a second gas diffusion electrode layer disposed on a second surface of the electrolyte membrane opposite to the first surface; a frame member having an inner edge portion that forms an opening in which the membrane electrode assembly is placed, The frame members each have the inner edge portion and include a first frame member and a second frame member that are substantially plate-shaped and overlap each other, the electrolyte membrane extends into a non-power generation region that is outside the outer edge of the first gas diffusion electrode layer and the outer edge of the second gas diffusion electrode layer; the first frame member and the second frame member have a first clamping portion and a second clamping portion that clamp the electrolyte membrane in the non-power generation region, respectively; a first through-hole penetrating the first clamping portion and a second through-hole penetrating the second clamping portion, the first through-hole being located at a position different from the other in a plan view seen from the stacking direction of the membrane electrode assembly, and a second through-hole being located at a position different from the other in a plan view seen from the stacking direction of the membrane electrode assembly.

2. 2. The fuel cell membrane electrode assembly according to claim 1, The membrane electrode assembly for a fuel cell, wherein the first through-holes and the second through-holes are provided alternately in the first clamping portion and the second clamping portion in the plan view.

3. 3. The fuel cell membrane electrode assembly according to claim 1, the frame member is provided with a communication hole through which a reaction gas flows; the non-power generation region includes a gas flow region, through which the reactant gas flows, between the communication hole and a power generation region in which the electrolyte membrane, the first gas diffusion electrode layer, and the second gas diffusion electrode layer are stacked, The membrane electrode assembly for a fuel cell, wherein the first through-hole and the second through-hole are provided in the gas flow region.

4. 4. The fuel cell membrane electrode assembly according to claim 3, the communication holes include a first communication hole through which a first reactant gas flows and a second communication hole through which a second reactant gas flows; the gas flow regions include a first gas flow region through which the first reactant gas flows between the first communication hole on the first gas diffusion electrode layer side and the power generation region, and a second gas flow region through which the second reactant gas flows between the second communication hole on the second gas diffusion electrode layer side and the power generation region, The membrane electrode assembly for a fuel cell, wherein the first through-hole and the second through-hole are provided in a region where the first gas flow region and the second gas flow region overlap in the plan view.

5. 4. The fuel cell membrane electrode assembly according to claim 3, the first through holes and the second through holes are a plurality of first through holes and a plurality of second through holes provided in the gas flow region, The membrane electrode assembly for a fuel cell, wherein the plurality of first through holes and the plurality of second through holes are provided so that the opening areas thereof become smaller in the flow direction of the reactant gas.

6. 3. The fuel cell membrane electrode assembly according to claim 1, the frame member is provided with a plurality of communication holes through which a reaction gas and a cooling medium flow; The membrane electrode assembly for a fuel cell, wherein the first through-hole and the second through-hole are provided between a pair of adjacent communication holes among the plurality of communication holes.

7. 4. The membrane electrode assembly for a fuel cell according to claim 3, The gas flow region is formed so that the flow direction of the first reactant gas flowing toward the first frame member and the flow direction of the second reactant gas flowing toward the second frame member are opposite to each other.

8. 8. The fuel cell membrane electrode assembly according to claim 7, the gas flow region includes a gas flow region on one side of the electrolyte membrane, the gas flow region being upstream in the flow direction of the first reactant gas and downstream in the flow direction of the second reactant gas, and a gas flow region on the other side of the electrolyte membrane, the gas flow region being downstream in the flow direction of the first reactant gas and upstream in the flow direction of the second reactant gas, 2. A membrane electrode assembly for a fuel cell, wherein the first through-hole and the second through-hole are not provided in the gas flow region on one side, but are provided in the gas flow region on the other side.

9. A fuel cell system including a fuel cell stack constructed by stacking power generating cells each having the fuel cell membrane electrode assembly according to claim 3, the reactant gas is an anode gas; The fuel cell system further comprises a gas recirculation unit that recirculates anode gas flowing out from the fuel cell stack to the fuel cell stack.

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