power cell

Abstract

This power generation cell is provided with: a membrane electrode structure having a membrane electrode assembly and a frame member; and a first separator and a second separator disposed so as to face a first surface and a second surface of the membrane electrode structure, respectively. The membrane electrode assembly has an electrolyte membrane, a first electrode catalyst layer and a second electrode catalyst layer, and a first gas diffusion layer and a second gas diffusion layer. When a direction toward the center of an opening of the frame member is defined as a first direction and a direction away from the center of the opening is defined as a second direction, an end part of the frame member on the first direction side is interposed between the first electrode catalyst layer and the electrolyte membrane, an end part of the first electrode catalyst layer on the second direction side is positioned on the first direction side from an end part of the first gas diffusion layer on the second direction side, and an end part of the second electrode catalyst layer on the second direction side and an end part of the electrolyte membrane on the second direction side are positioned on the first direction side from an end part of the second gas diffusion layer on the second direction side.

Description

Technical Field

[0001] The present invention relates to a power generation cell of a fuel cell.

Background Art

[0002] In recent years, in order to enable more people to access affordable, reliable, sustainable and advanced energy, technological development has been carried out on fuel cells that contribute to energy efficiency. As a technology related to a power generation cell used in this type of fuel cell, there is known a power generation cell in which a resin frame member is sandwiched between a gas diffusion layer of an anode electrode and a gas diffusion layer of a cathode electrode, which are sandwiched by a pair of separators (see, for example, Patent Document 1). In the power generation cell described in Patent Document 1, an electrode catalyst layer is interposed between the gas diffusion layer and the frame member, and an end portion of the electrode catalyst layer is exposed to a gas flow path.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] In the power generation cell described in Patent Document 1 above, iron ions elute from the separator into the water accumulated in the gas flow path, and the iron ions may penetrate into the electrolyte membrane through the electrode catalyst layer, causing the electrolyte membrane to deteriorate.

Means for Solving the Problems

[0005] A power generation cell according to one aspect of the present invention comprises a membrane electrode structure having a membrane electrode assembly and a frame member provided with an opening in which the membrane electrode assembly is arranged, and a first separator and a second separator arranged opposite to a first surface and a second surface opposite to the first surface of the membrane electrode structure, respectively. The membrane electrode assembly has an electrolyte membrane, a first electrode catalyst layer and a second electrode catalyst layer arranged in close contact with one and the other surface of the electrolyte membrane, respectively, and a first gas diffusion layer and a second gas diffusion layer arranged between the first electrode catalyst layer and the first separator and between the second electrode catalyst layer and the second separator, respectively. The first separator has a first rib portion that contacts the surface of the first gas diffusion layer under pressure, and a first recess that is concave and connected to the first rib portion, forming a first channel through which the first reaction gas flows between it and the first surface. The second separator has a second rib portion that contacts the surface of the second gas diffusion layer under pressure, and a second recess that is concave and connected to the second rib portion, forming a second channel through which the second reaction gas flows between it and the second surface. When the direction toward the center of the opening is defined as the first direction and the direction away from the center of the opening as the second direction, the end of the frame member on the first direction side is interposed between the first electrode catalyst layer and the electrolyte membrane. The end of the first electrode catalyst layer, which is the end of the first electrode catalyst layer on the second direction side, is located laterally in the first direction than the end of the first gas diffusion layer, which is the end of the first gas diffusion layer on the second direction side. The end of the second electrode catalyst layer, which is the end of the second electrode catalyst layer on the second direction side, and the end of the electrolyte membrane, which is the end of the electrolyte membrane on the second direction side, are located on the first direction side than the end of the second gas diffusion layer, which is the end of the second gas diffusion layer on the second direction side. [Effects of the Invention]

[0006] According to the present invention, the degradation of the electrolyte membrane can be suppressed. [Brief explanation of the drawing]

[0007] [Figure 1] A schematic perspective view showing the overall configuration of a fuel cell stack having a power generation cell according to an embodiment of the present invention. [Figure 2] A cross-sectional view along line II-II in Figure 1. [Figure 3]Figure 1 is a perspective view showing the schematic configuration of the integrated electrode assembly included in the fuel cell stack. [Figure 4A] This is a cross-sectional view along the line IV-IV in Figure 3, showing the main components of a power generation cell according to an embodiment of the present invention. [Figure 4B] This figure shows the state when a gas differential pressure acts on the power generation cell in Figure 4A. [Figure 5A] Figure 4A shows a reference example. [Figure 5B] Figure 4B shows a reference example. [Figure 6A] This figure shows the first modified example of Figure 4A. [Figure 6B] This figure shows a second modified example of Figure 4A. [Modes for carrying out the invention]

[0008] Embodiments of the present invention will be described below with reference to Figures 1 to 6B. The power generation cell according to the embodiment of the present invention is included in a fuel cell stack, which is the main body of the fuel cell. The fuel cell is mounted on a vehicle, for example, and generates electricity for driving the vehicle. First, the overall configuration of the fuel cell stack will be described in general terms. Note that the fuel cell stack is sometimes simply referred to as a fuel cell.

[0009] Figure 1 is a schematic perspective view showing the overall configuration of a fuel cell stack 100 according to an embodiment of the present invention. For convenience, the three mutually orthogonal axial directions shown in the figure will be defined as the longitudinal direction, the left-right direction, and the vertical direction, and the configuration of each part will be described according to this definition. These directions are not necessarily the same as the longitudinal, left-right, and vertical directions of a vehicle. For example, the longitudinal direction in Figure 1 may be the longitudinal direction of a vehicle, the left-right direction, or the vertical direction.

[0010] As shown in Figure 1, the fuel cell stack 100 has a cell stack 101 formed by stacking multiple power generation cells 1 in the front-rear direction, and end units 102 positioned at both the front and rear ends of the cell stack 101, and the whole has a substantially rectangular parallelepiped shape. The length of the cell stack 101 in the left-right direction is longer than the length in the up-down direction. For convenience, Figure 1 shows a single power generation cell 1. The power generation cell 1 has an integrated electrode assembly 2 having a membrane electrode assembly including an electrolyte membrane and an electrode, and a pair of front and rear separators 3, 3 positioned on both the front and rear sides of the integrated electrode assembly 2 and sandwiching the integrated electrode assembly 2. The integrated electrode assembly 2 and the separators 3 are arranged alternately in the front-rear direction. Although not shown in the figure, a substantially box-shaped case with open front and rear sides 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 via bolts.

[0011] Figure 2 is a cross-sectional view of a portion of the cell laminate 101 (a cross-sectional view along the line II-II in Figure 1). As shown in Figure 2, the separator 3 has a front plate 31 and a rear plate 32, which are a pair of thin metal plates with a corrugated cross-section. The outer edges of the front plate 31 and the rear plate 32 are joined together by welding or the like, thereby forming the separator 3. The separator 3 is made of a conductive material with excellent corrosion resistance, such as stainless steel, titanium, or titanium alloy.

[0012] A cooling channel PAw is formed inside the separator 3, which is enclosed by the front plate 31 and the rear plate 32, through which a cooling medium flows. The flow of the cooling medium cools the power generation surface of the power generation cell 1. For example, water can be used as the cooling medium. The surfaces (front and rear) of the separator 3 facing the integrated electrode assembly 2 are formed to be uneven by press molding or the like so as to form a gas flow path between them and the integrated electrode assembly 2. More specifically, the front plate 31 and the rear plate 32 each have rib portions 301 that protrude toward the front and rear integrated electrode assembly 2, and recesses 302 that are formed in a concave shape connected to the rib portions 301.

[0013] The rear rib portion 301 abuts against the front surface 2a of the integrated electrode assembly 2, and the front rib portion 301 abuts against the rear surface 2b of the integrated electrode assembly 2. When the fuel cell stack 100 is assembled, a compressive load F is applied to the cell stack 101 in the front-rear direction, and in this state, the case and the front and rear end units 102 are fastened. Therefore, after the assembly of the fuel cell stack 100 is completed, the compressive load F on the fuel cell stack 100 is retained. For this reason, a predetermined surface pressure acts on the integrated electrode assembly 2 in the front-rear direction via the rib portion 301.

[0014] A concave portion 302 forms an anode flow path PAa through which fuel gas flows between the rear plate 32 of the separator 3 facing the front surface 2a of the integrated electrode assembly 2 and the front surface 2a of the integrated electrode assembly 2. A concave portion 302 forms a cathode flow path PAc through which oxidant gas flows between the front plate 31 of the separator 3 facing the rear surface 2b of the integrated electrode assembly 2 and the rear surface 2b of the integrated electrode assembly 2. As the fuel gas, for example, hydrogen gas containing hydrogen can be used, and as the oxidant gas, for example, air containing oxygen can be used.

[0015] FIG. 3 is a perspective view showing a schematic configuration of the integrated electrode assembly 2. As shown in FIG. 3, the integrated electrode assembly (UEA; Unitized Electrode Assembly) 2 is a membrane electrode structure, and includes a substantially rectangular membrane electrode assembly (MEA; Membrane Electrode Assembly) 20 and a frame frame 21 that supports the membrane electrode assembly 20. As shown in the detailed view of part A in FIG. 2, the membrane electrode assembly 20 includes an electrolyte membrane 23, an anode electrode provided on the front surface of the electrolyte membrane 23, and a cathode electrode provided on the rear surface of the electrolyte membrane 23.

[0016] The electrolyte membrane 23 is, for example, a solid polymer electrolyte membrane, and a thin film of a perfluorosulfonic acid polymer containing moisture can be used. Not limited to fluorine-based electrolyte membranes, hydrocarbon-based electrolyte membranes can also be used.

[0017] The anode electrode is formed on the front surface of the electrolyte membrane 23 and includes an electrode catalyst layer 24 that serves as a reaction field for the electrode reaction, and a gas diffusion layer 26 that is provided on the front surface of the electrode catalyst layer 24 and supplies fuel gas by diffusion. Among the electrode catalyst layer 24 and the gas diffusion layer 26, the electrode catalyst layer 24 may particularly be referred to as the anode electrode. An intermediate layer (underlayer) can also be provided between the electrode catalyst layer 24 and the gas diffusion layer 26. The cathode electrode is formed on the rear surface of the electrolyte membrane 23 and includes an electrode catalyst layer 25 that serves as a reaction field for the electrode reaction, and a gas diffusion layer 27 that is provided on the rear surface of the electrode catalyst layer 25 and supplies oxidant gas by diffusion. Among the electrode catalyst layer 25 and the gas diffusion layer 27, the electrode catalyst layer 25 may particularly be referred to as the cathode electrode. An intermediate layer (underlayer) can also be provided between the electrode catalyst layer 25 and the gas diffusion layer 27.

[0018] The electrode catalyst layers 24 and 25 contain a catalyst metal that promotes the electrochemical reaction between hydrogen contained in the fuel gas and oxygen contained in the oxidant gas, an electrolyte (such as an ionomer) having proton conductivity, and carbon particles having electron conductivity. The gas diffusion layers 26 and 27 are composed of a conductive member having gas permeability, such as a carbon porous body.

[0019] In the anode electrode (electrode catalyst layer 24), the fuel gas (hydrogen) supplied through the anode flow channel PAa and the gas diffusion layer 26 is ionized by the action of the catalyst, passes through the electrolyte membrane 23, and moves to the cathode electrode side. The electrons generated at this time pass through the external circuit and are taken out as electrical energy. In the cathode electrode (electrode catalyst layer 25), the oxidant gas (oxygen) supplied through the cathode flow channel PAc and the gas diffusion layer 27 reacts with the hydrogen ions led from the anode electrode and the electrons that have moved from the anode electrode, and water is generated. The generated water gives appropriate humidity to the electrolyte membrane 23, and the excess water is discharged to the outside of the integrated electrode assembly 2 along the gas flow.

[0020] The frame 21 in Figure 3 is a thin plate with a thickness of approximately 0.05 to 0.1 mm and is roughly rectangular in shape, and is made of an insulating resin or rubber. For example, PEN (polyethylene naphthalate) or PPS (polyphenylene sulfide) can be used as constituent materials. A roughly rectangular opening 210 is provided in the center of the frame 21, and a membrane electrode assembly 20 is provided so as to cover the entire opening 210. The frame 21 has a roughly rectangular outer edge portion 221 and a roughly rectangular inner edge portion 222 inside the outer edge portion 221. The outer edge portion 221 refers to the outer edge of the frame 21 and its surrounding area, and the inner edge portion 222 refers to the inner edge of the frame 21 (the edge of the opening 210) and its surrounding area.

[0021] Point P in Figure 3 is the center point passing through the midpoint of the opening 210 in both the vertical and horizontal directions. On the left side of the opening 210 in the frame 21, three through holes 201 to 203 are opened vertically, penetrating the frame 21 in the front-to-back direction, and on the right side of the opening 210, three through holes 204 to 206 are opened vertically, penetrating the frame 21 in the front-to-back direction.

[0022] As shown in Figure 1, through holes 311 to 316 are opened in the front and rear separators 3 of the integrated electrode assembly 2 at positions corresponding to the through holes 201 to 206 of the frame 21, respectively, and the through holes 311 to 316 penetrate the separators 3 in the front-to-back direction. The through holes 311 to 316 communicate with the through holes 201 to 206 of the frame 21, respectively. The collection of these interconnected through holes 201 to 206 and 311 to 316 forms flow channels PA1 to PA6 (indicated by arrows for convenience) that penetrate the cell stack 101 and extend in the front-to-back direction. Flow channels PA1 to PA6 are sometimes called manifolds. Flow channels PA1 to PA6 are connected to a manifold outside the fuel cell stack 100.

[0023] The flow path PA1 (solid arrow) extending forward through through holes 201 and 311 is a fuel gas supply flow path. The flow path PA6 (solid arrow) extending backward through through holes 206 and 316 is a fuel gas discharge flow path. The fuel gas supply flow path PA1 and the fuel gas discharge flow path PA6 communicate with the anode flow path PAa (Figure 2), which is located opposite the front surface of the membrane electrode assembly 20. As shown by the solid arrow, fuel gas flows to the right through the anode flow path PAa via the fuel gas supply flow path PA1 and the fuel gas discharge flow path PA6. Communication between the anode flow path PAa and the other flow paths PA2 to PA5 is blocked via a seal (not shown).

[0024] The flow path PA4 (dotted arrow) extending forward through through holes 204 and 314 is an oxidant gas supply flow path. The flow path PA3 (dotted arrow) extending backward through through holes 203 and 313 is an oxidant gas discharge flow path. The oxidant gas supply flow path PA4 and the oxidant gas discharge flow path PA3 communicate with the cathode flow path PAc (Figure 2), which is provided opposite the rear surface of the film electrode assembly 20. As shown by the dotted arrow, the oxidant gas flows to the left through the cathode flow path PAc via the oxidant gas supply flow path PA4 and the oxidant gas discharge flow path PA3. Communication between the cathode flow path PAc and the other flow paths PA1, PA2, PA5, and PA6 is blocked via a seal portion (not shown).

[0025] The flow path PA5 (dotted arrow) extending forward through through holes 205 and 315 is a cooling medium supply flow path. The flow path PA2 (dotted arrow) extending backward through through holes 202 and 312 is a cooling medium discharge flow path. The cooling medium supply flow path PA5 and the cooling medium discharge flow path PA2 are in communication with a cooling flow path PAw (Figure 2) provided inside the separator 3, and the cooling medium flows through the cooling flow path PAw via the cooling medium supply flow path PA5 and the cooling medium discharge flow path PA2. Communication between the cooling flow path PAw and the other flow paths PA1, PA3, PA4, and PA6 is blocked via a seal portion (not shown).

[0026] The end units 102, located on both the front and rear sides of the cell stack 101, each have a terminal plate 4, an insulating plate 5, and an end plate 6. The rear end unit 102 has multiple through holes 102a to 102f that penetrate the end unit 102 in the front-rear direction. Through hole 102a opens on the extension of the fuel gas supply channel PA1 and communicates with the fuel gas supply channel PA1. Through hole 102b opens on the extension of the cooling medium discharge channel PA2 and communicates with the cooling medium discharge channel PA2. Through hole 102c opens on the extension of the oxidizer gas discharge channel PA3 and communicates with the oxidizer gas discharge channel PA3. Through hole 102d opens on the extension of the oxidizer gas supply channel PA4 and communicates with the oxidizer gas supply channel PA4. Through hole 102e opens on the extension of the cooling medium supply channel PA5 and communicates with the cooling medium supply channel PA5. The through-hole 102f opens on the extension of the fuel gas exhaust passage PA6 and communicates with the fuel gas exhaust passage PA6.

[0027] More specifically, a fuel gas tank containing high-pressure fuel gas is connected to the through-hole 102a via an ejector, injector, etc., and fuel gas is supplied to the fuel cell stack 100 through the through-hole 102a. Fuel gas is discharged from the through-hole 102f. A compressor for supplying oxidizer gas is connected to the through-hole 102d, and compressed oxidizer gas is supplied to the fuel cell stack 100 through the through-hole 102d. Oxidizer gas is discharged from the through-hole 102c. A pump for supplying cooling medium is connected to the through-hole 102e, and cooling medium is supplied to the fuel cell stack 100 through the through-hole 102e. Cooling medium is discharged from the through-hole 102b. The discharged cooling medium is cooled by heat exchange in a radiator and supplied back to the fuel cell stack 100 through the through-hole 102e.

[0028] The above is a general overview of the fuel cell stack 100. Next, a more detailed description of the power generation cell 1 according to this embodiment will be given. The power generation cell 1 according to this embodiment is particularly characterized in the configuration of the area surrounding the opening 210 of the frame 21.

[0029] Figure 4A is a cross-sectional view along line IV-IV in Figure 3, that is, a cross-sectional view showing the structure around the left inner edge 222 of the frame 21. Note that the structure around the inner edge 222 is the same around the entire circumference of the inner edge 222 along the opening 210. Hereafter, the direction to the right in Figure 4A, that is, the direction toward the center point P in Figure 3 (towards the center), will be referred to as the inward direction or inner side, and the right side of Figure 4A will be referred to as the inside. Also, the direction to the left in Figure 4A, that is, the direction toward the outer edge 221 in Figure 3, will be referred to as the outward direction or outer side, and the left side of Figure 4A will be referred to as the outside.

[0030] Figure 4A shows both a separator 3 (rear plate 32) that abuts the front surface 2a of the integrated electrode assembly 2, more specifically the front surface 260 of the gas diffusion layer 26, and a separator 3 (front plate 31) that abuts the rear surface 2b of the integrated electrode assembly 2, more specifically the rear surface 270 of the gas diffusion layer 27. Similar to Figure 2, the separator 3 is provided with rib portions 301 that abut the front surface 2a and rear surface 2b of the integrated electrode assembly 2, respectively, and recesses 302 that are recessed in a direction away from the front surface 2a and rear surface 2b of the integrated electrode assembly 2. Although not shown in the figure, the separator 3 abuts the front surface 21a and rear surface 21b of the frame 21 via the rib portions 301, more specifically via the rib portions 301 and the sealing portion, on the outside of the membrane electrode assembly 20 (to the left in Figure 4A).

[0031] As shown in Figure 4A, the left end 23a (outer end) of the electrolyte membrane 23 and the left ends 24a and 25a of the electrode catalyst layers 24 and 25 are located at the same position in the left-right direction. On the other hand, the left end 26a of the anode-side gas diffusion layer 26 is located a predetermined length to the left (outer) than the left end 24a of the electrode catalyst layer 24, and the left end 27a (outer end) of the cathode-side gas diffusion layer 27 is located a predetermined length to the left than the left end 25a of the electrode catalyst layer 25. The positions of the left ends 26a and 27a of the gas diffusion layers 26 and 27 are equal to each other.

[0032] The frame 21 has a front frame 211 and a rear frame 212 that are joined together by overlapping each other via adhesive 213. The inner edge 222 of the front frame 211 protrudes to the right (inward) than the inner edge 222 of the rear frame 212. Although not shown in the figures, the left-right positions of the outer edge 221 of the front frame 211 (Figure 3) and the outer edge 221 of the rear frame 212 are equal.

[0033] The inner edge 222 of the front frame 211, particularly the right end of the front frame 211, is interposed between the electrolyte membrane 23 and the anode-side electrode catalyst layer 24. Therefore, the right end (inner end) of the front frame 211 is located to the right of the left ends 23a, 24a, and 25a of the electrolyte membrane 23 and the electrode catalyst layers 24 and 25. The integrated electrode assembly 2 described above is manufactured, for example, by the following procedure.

[0034] First, an electrode catalyst layer 25 is applied to the surface (front) of the cathode-side gas diffusion layer 27. Next, an electrolyte membrane 23 is bonded to the surface (front) of the electrode catalyst layer 25. Then, the inner edge 222 of the front frame 211 is bonded to the surfaces (front) of the gas diffusion layer 27 and the electrolyte membrane 23 via an adhesive 213. Next, the anode-side gas diffusion layer 26, which has an electrode catalyst layer 24 pre-coated on its surface, is laminated onto the electrolyte membrane 23 and the front frame 211, while bonding the electrolyte membrane 23 and the electrode catalyst layer 24. At this time, the left end of the anode-side electrode catalyst layer 24 and the gas diffusion layer 26 are bent forward as shown in the figure, and are positioned forward by an amount equivalent to the thickness of the front frame 211 compared to their position before bending. As a result, a step is provided on the front surface 260 of the gas diffusion layer 26.

[0035] The rear plate 32 of the separator 3 is configured in a stepped shape to correspond to the step in the front surface 260. That is, the rear plate 32 has a rib portion 301a that abuts against the front surface 260 of the gas diffusion layer 26 before bending, and a rib portion 301b that abuts against the front surface 260 after bending. Note that the gas diffusion layer 27 on the cathode side is not bent, and therefore the rib portion 301 of the front plate 31 is not stepped. A surface pressure P0 due to the compressive load F shown in Figure 2 acts on the front surface 260 of the gas diffusion layer 26 on the anode side and the rear surface 270 of the gas diffusion layer 27 on the cathode side via the rib portion 301 (see Figure 4B). That is, a surface pressure P0 acts such that it clamps the integrated electrode assembly 2 in the front-rear direction.

[0036] Position P1, which is the left end (outer end) of the rib portion 301b of the rear plate 32, is located to the right of the left end 26a (left end face) of the gas diffusion layer 26, and the gas diffusion layer 26 protrudes to the left (outward) of the rib portion 301b. Similarly, position P2, which is the left end of the rib portion 301 of the front plate 31, is located to the right of the left end 27a (left end face) of the gas diffusion layer 27, and the gas diffusion layer 27 protrudes to the left of the rib portion 301.

[0037] On the other hand, position P1 is located to the left of the left end portion 24a (left end face) of the anode-side electrode catalyst layer 24, and position P2 is located to the left of the left end portion 25a (left end face) of the cathode-side electrode catalyst layer 25. As a result, the left ends 23a, 24a, and 25a of the electrolyte membrane 23 and the electrode catalyst layers 24 and 25 are sandwiched between the front rib portion 301 and the rear rib portion 301, respectively, where the surface pressure P0 acts, via the gas diffusion layers 26 and 27 without any gaps in between. Therefore, the left ends 23a, 24a, and 25a of the electrolyte membrane 23 and the electrode catalyst layers 24 and 25 can be firmly held.

[0038] Since the separators 3 positioned on both the front and rear sides of the gas diffusion layers 26 and 27 contain iron as a component, generated water and condensed water produced by the electrochemical reaction between the fuel gas and the oxidizer gas accumulate in the anode channel PAa and cathode channel PAc, and iron ions may dissolve into this stagnant water. These iron ions can degrade the electrolyte membrane 23, so it is preferable to prevent water containing iron ions from penetrating the electrolyte membrane 23. In this embodiment, the electrode catalyst layers 24 and 25 containing ionomers are positioned to the right of the left ends 26a and 27a of the gas diffusion layers 26 and 27, and are sandwiched between the front and rear separators 3 via the gas diffusion layers 26 and 27 by the rib portions 301. Therefore, the electrode catalyst layers 24 and 25 are not exposed on the left side (outside) of the gas diffusion layers 26 and 27.

[0039] In this way, the electrode catalyst layers 24 and 25, which serve as entry points for iron ions, are not exposed, thus blocking the entry points for iron ions. This prevents moisture containing iron ions from entering the interior through the interface between the gas diffusion layers 26 and 27 and the frame 21 (front frame 211). In particular, since the gas diffusion layers 26 and 27 contain water-repellent carbon, they can effectively prevent moisture containing iron ions from entering through the interface between the gas diffusion layers 26 and 27 and the frame 21.

[0040] In such a power generation cell 1, when the fuel cell stack 100 is operating, fuel gas is guided to the anode channel PAa in the front recess 302 of the integrated electrode assembly 2, and oxidizer gas is guided to the cathode channel PAc in the rear recess 302. The pressure of the fuel gas is higher than the pressure of the oxidizer gas. Therefore, as shown in Figure 4B, a differential pressure ΔP acts from the space SPa of the anode channel PAa to the space SPc of the cathode channel PAc.

[0041] As a result, the frame 21 (front frame 211) flexes backward with position P2, which is the end of the rib portion 301 of the separator 3 (front plate 31), as the pivot point. Consequently, a gap GP is created between the rear surface near the left end 26a of the gas diffusion layer 26 on the anode side and the frame 21. However, since a surface pressure P0 acts to the right of position P1 of the left end of the rib portion 301, the gap GP does not extend to the right (inward) of position P1. Therefore, the electrode catalyst layer 24 is not exposed to the anode channel PAa. Since no gap GP is created on the cathode side in the first place, the electrode catalyst layer 25 is not exposed to the cathode channel PAc. As a result, even when the frame 21 is flexed due to the differential pressure ΔP between spaces SPa and SPc, it is possible to prevent moisture containing iron ions from entering the electrode catalyst layers 24 and 25.

[0042] Figure 5A shows the main components of power generation cell 1A as a reference example of Figure 4A. In Figure 5A, the electrolyte membrane 23 and electrode catalyst layers 24 and 25 extend to the left ends 26a and 27a of the gas diffusion layers 26 and 27, respectively. Therefore, the left end 24a of the electrode catalyst layer 24 is exposed to the anode channel PAa, and the left ends 23a and 25a of the electrolyte membrane 23 and electrode catalyst layer 25 are exposed to the cathode channel PAc. In this configuration, moisture containing iron ions may penetrate the electrolyte membrane 23, potentially causing degradation of the electrolyte membrane 23. Even if only the electrode catalyst layers 24 and 25 are exposed and the electrolyte membrane 23 is not, iron ions may penetrate into the inside of the membrane electrode assembly 20 via the electrode catalyst layers 24 and 25, potentially causing degradation of the electrolyte membrane 23.

[0043] In the configuration shown in Figure 5A, when the fuel cell stack 100 is used in cold regions, moisture that seeps in from the left end 24a of the electrode catalyst layer 24 may freeze, resulting in the formation of ice 300 between the gas diffusion layer 26 and the frame 21. In this case, the following problems may occur.

[0044] Figure 5B shows the state in power generation cell 1A of Figure 5A where a differential pressure ΔP acts between the space SPa of the anode channel PAa and the space SPc of the cathode channel PAc, causing the frame 21 to bend. As shown in Figure 5B, when the fuel cell stack 100 is started in a sub-zero state with ice 300 present between the gas diffusion layer 26 and the frame 21, causing the frame 21 to bend, there is a risk that a part of the electrode catalyst layer 24 (referred to as detached material 240) may be pulled by the ice 300 and detach from the gas diffusion layer 26. When the ice 300 melts in this state, the detached material 240, along with water, is guided to the drainage channel of the fuel cell stack 100. The drainage channel is a channel for discharging excess water generated in the fuel cell stack to the outside. A filter is provided in the middle of this drainage channel. Therefore, if the detached material 240 reaches the drainage channel, there is a risk that the filter will become clogged.

[0045] In this embodiment, as shown in Figure 4B, the electrode catalyst layer 24 is not exposed even when the frame 21 is bent. Therefore, even when ice is generated during use in cold regions, it is possible to prevent a portion of the electrode catalyst layer 24 from falling off due to the ice.

[0046] This embodiment can provide the following effects and advantages. (1) The power generation cell 1 comprises an integrated electrode assembly 2 as a membrane electrode structure having a membrane electrode assembly 20 and a frame 21 provided with an opening 210 in which the membrane electrode assembly 20 is arranged, and separators 3 arranged opposite to the front surface 2a and rear surface 2b of the integrated electrode assembly 2, respectively (Figure 1). The membrane electrode assembly 20 has an electrolyte membrane 23, anode-side and cathode-side electrode catalyst layers 24, 25 arranged in close contact with the front and rear surfaces of the electrolyte membrane 23, respectively, and gas diffusion layers 26, 27 arranged between the anode-side electrode catalyst layer 24 and the separator 3 and between the cathode-side electrode catalyst layer 25 and the separator 3, respectively (Figure 2). The anode-side separator 3 has a rib portion 301 that contacts the front surface 260 of the gas diffusion layer 26 under pressure, and a recess 302 that is recessed and connected to the rib portion 301, forming an anode channel PAa through which fuel gas flows between it and the front surface 2a of the integrated electrode assembly 2 (Figures 2 and 4A). The cathode-side separator 3 has a rib portion 301 that contacts the rear surface 270 of the gas diffusion layer 27 under pressure, and a recess 302 that is recessed and connected to the rib portion 301, forming a cathode channel PAc through which oxidant gas flows between it and the rear surface 2b of the integrated electrode assembly 2 (Figures 2 and 4A). The inner edge portion 222 of the frame 21 is interposed between the electrode catalyst layer 24 and the electrolyte membrane 23 (Figure 4A). The left end 24a of the anode-side electrode catalyst layer 24 is located to the right (inward) of the left end 26a of the anode-side gas diffusion layer 26, and the left end 25a of the cathode-side electrode catalyst layer 25 and the left end 23a of the electrolyte membrane 23 are located to the right (inward) of the left end 27a of the cathode-side gas diffusion layer 27 (Figure 4A).

[0047] With this configuration, the electrode catalyst layers 24 and 25 are not exposed to the anode channel PAa and cathode channel PAc from the ends of the gas diffusion layers 26 and 27. Therefore, it is possible to prevent iron ions from leaching from the separator 3 into the water accumulated in the channels PAa and PAc, and prevent that water containing iron ions from penetrating the electrolyte membrane 23 via the electrode catalyst layers 24 and 25. This prevents the degradation of the electrolyte membrane 23.

[0048] (2) The left end 24a of the anode-side electrode catalyst layer 24 is located to the right (inside) of position P1, which is the left end (outer end) of the rib portion 301 that abuts the anode-side gas diffusion layer 26, and the left end 25a of the cathode-side electrode catalyst layer 25 and the left end 23a of the electrolyte membrane 23 are located to the right (inside) of position P2, which is the left end (outer end) of the rib portion 301 that abuts the cathode-side gas diffusion layer 27 (Figure 4A). As a result, even if the frame 21 is deflected due to the differential pressure ΔP between the fuel gas in the anode channel PAa and the oxidant gas in the cathode channel PAc, a surface pressure P0 from the rib portion 301 acts on the electrode catalyst layers 24 and 25 inside the rib portion 301, so that the electrode catalyst layers 24 and 25 do not deflect (Figure 4B). As a result, it is possible to effectively prevent moisture containing iron ions from entering the inside of the membrane electrode assembly 20 through the electrode catalyst layers 24 and 25. Furthermore, even if moisture accumulated in the flow paths PAa and PAc freezes when the fuel cell stack 100 is used in cold regions, the electrode catalyst layers 24 and 25 will not detach along with the ice 300. This prevents clogging of the filter due to a portion of the electrode catalyst layers 24 and 25 entering the drainage path.

[0049] (3) The left end 26a of the anode-side gas diffusion layer 26 is located to the left (outside) of the position P1 of the left end of the rib portion 301, and the left end 27a of the cathode-side gas diffusion layer 27 is located to the left (outside) of the position P2 of the left end of the rib portion 301 (Figure 4A). This makes it possible to lengthen the distance from the left ends 26a and 27a of the gas diffusion layers 26 and 27 to the left ends 24a and 25a of the electrode catalyst layers 24 and 25. As a result, the distance from the flow channels PAa and PAc to the electrode catalyst layers 24 and 25 is increased, which effectively prevents iron ions from entering the electrode catalyst layers 24 and 25.

[0050] The above embodiment can be modified into various forms. Several modifications are described below. Figure 6A shows a first modified form of the power generation cell 1. Figure 6A differs from Figure 4A in that the left end 23a of the electrolyte membrane 23 is located to the left (outward) of the left end 25a of the cathode-side electrode catalyst layer 25. However, even in the example of Figure 6A, the left end 23a of the electrolyte membrane 23 is located to the right of the left end positions P1 and P2 of the rib portion 301 of the separator 3. Alternatively, instead of extending the electrolyte membrane 23 to the left (outward), the position of the left end 25a of the cathode-side electrode catalyst layer 25 may be shifted to the right, making the left-right length of the electrode catalyst layer 25 shorter than that of Figure 4A.

[0051] Figure 6B shows a second modified example of the power generation cell 1. Figure 6B differs from Figure 4A in that the anode-side electrode catalyst layer 24 is positioned behind the frame 21 instead of in front of it. In this example, electrode catalyst layers 24 and 25 are provided on both sides of the electrolyte membrane 23, and then the frame 21 is positioned on the surface (front) of the electrode catalyst layer 24. In Figure 6B, as in Figure 6A, the left end 23a of the electrolyte membrane 23 protrudes to the left (outward) of the left ends 24a and 25a of the electrode catalyst layers 24 and 25, but the left end 23a of the electrolyte membrane 23 does not need to protrude.

[0052] In the above embodiment, the rear plate 32 of separator 3 is positioned as the first separator, facing the front surface 2a (first surface) of the integrated electrode assembly 2 as a membrane electrode structure, and the front plate 31 of separator 3 is positioned as the second separator, facing the rear surface 2b (second surface) of the integrated electrode assembly 2. However, the configuration of the first and second separators is not limited to those described above. That is, the configuration of the rib portion 301 (first rib portion) of the rear plate 32 of separator 3 that contacts the surface of the gas diffusion layer 26 (first gas diffusion layer) under pressure and the recess 302 (first recess) that forms the anode channel PAa (first channel) through which fuel gas flows, and the configuration of the rib portion 301 (second rib portion) of the front plate 31 of separator 3 that contacts the surface of the gas diffusion layer 27 (second gas diffusion layer) under pressure and the recess 302 (second recess) that forms the cathode channel PAc (second channel) through which oxidizer gas flows are not limited to those described above.

[0053] In the above embodiment, the frame frame 21 is composed of a front frame 211 and a rear frame 212, but the configuration of the frame members is not limited to those described above. In the above embodiment (Figure 4A), the inner end (first direction side) of the front frame 211, i.e., the right end of the inner edge portion 222, is interposed between the electrode catalyst layer 24 and the electrolyte membrane 23, but the inner edge portion 222 of the rear frame 212 may be interposed between the electrode catalyst layer 24 and the electrolyte membrane 23. In the above embodiment, the first reaction gas is a fuel gas (anode gas) and the second reaction gas is an oxidizing gas (cathode gas), but the first reaction gas may be an oxidizing gas and the second reaction gas may be a fuel gas, and the configuration of the first reaction gas and the second reaction gas is not limited to those described above.

[0054] In the above embodiment (Figure 4A), the position of the outer (second direction side) end 24a (end of the first electrode catalyst layer) of the anode-side electrode catalyst layer 24 (first electrode catalyst layer), the position of the outer (second direction side) end 25a (end of the second electrode catalyst layer) of the cathode-side electrode catalyst layer 25 (second electrode catalyst layer), and the position of the outer (second direction side) end 23a (end of the electrolyte membrane) of the electrolyte membrane 23 are set to the same position in the left-right direction. However, if the end of the first electrode catalyst layer is located inward from the outer end 26a (end of the first gas diffusion layer) of the anode-side gas diffusion layer 26 (first gas diffusion layer), and the end of the second electrode catalyst layer is located inward from the outer end 27a (end of the second gas diffusion layer) of the cathode-side gas diffusion layer 27 (second gas diffusion layer), then the ends of the first electrode catalyst layer, the end of the second electrode catalyst layer, and the end of the electrolyte membrane do not need to be in the same position in the left-right direction. In the above embodiment, the outer (second direction side) end (first rib end) of the rib portion 301 (first rib portion) of the rear plate 32 indicated at position P1 is located to the right of the left end 26a of the gas diffusion layer 26, and the outer (second direction side) end (second rib end) of the rib portion 301 (second rib portion) of the front plate 31 indicated at position P2 is located to the right of the left end 27a of the gas diffusion layer 27. However, the left ends 26a and 27a of the gas diffusion layers 26 and 27 may be located at the same positions as positions P1 and P2.

[0055] In the above embodiment, an example of applying the fuel cell stack 100 to a vehicle was described, but the fuel cell stack having the power generation cell of the present invention can also be applied to mobile bodies other than vehicles such as aircraft and ships, robots, and various industrial machines.

[0056] The above description is merely an example, and the present invention is not limited by the embodiments and modifications described above, as long as the features of the present invention are not impaired. It is also possible to arbitrarily combine one or more of the above embodiments and modifications, and to combine modifications with each other.

[0057] 1 Power generation cell, 2 Integrated electrode assembly, 2a Front, 2b Rear, 3 Separator, 20 Membrane electrode assembly, 21 Frame, 23 Electrolyte membrane, 23a Left end, 24,25 Electrode catalyst layer, 24a,25a Left end, 26,27 Gas diffusion booster, 26a,27a Left end, 31 Front plate, 32 Rear plate, 100 Fuel cell stack, 210 Opening, 301 Rib section, 302 Recess, PAa Anode channel, PAc Cathode channel, P1,P2 Position

Claims

1. A membrane electrode structure comprising a membrane electrode assembly and a frame member having an opening in which the membrane electrode assembly is arranged, The membrane electrode structure comprises a first separator and a second separator, respectively, positioned opposite to the first surface and the second surface opposite to the first surface. The membrane electrode assembly comprises an electrolyte membrane, a first electrode catalyst layer and a second electrode catalyst layer disposed in close contact with one and the other surface of the electrolyte membrane, respectively, and a first gas diffusion layer and a second gas diffusion layer disposed between the first electrode catalyst layer and the first separator and between the second electrode catalyst layer and the second separator, respectively. The first separator has a first rib portion that pressurizes and contacts the surface of the first gas diffusion layer, and a first recess that is provided in a concave shape adjacent to the first rib portion and forms a first flow channel through which the first reaction gas flows between itself and the first surface. The second separator has a second rib portion that pressurizes and contacts the surface of the second gas diffusion layer, and a second recess that is provided in a concave shape adjacent to the second rib portion and forms a second flow channel through which the second reaction gas flows between it and the second surface. When the direction toward the center of the opening is defined as the first direction, and the direction away from the center of the opening is defined as the second direction, The end of the frame member on the first direction side is interposed between the first electrode catalyst layer and the electrolyte membrane. The end of the first electrode catalyst layer, which is the end on the second direction side of the first electrode catalyst layer, is located on the first direction side of the first gas diffusion layer, which is the end on the second direction side of the first gas diffusion layer. A power generation cell characterized in that the end of the second electrode catalyst layer, which is the end on the second direction side of the second electrode catalyst layer, and the end of the electrolyte membrane, which is the end on the second direction side of the electrolyte membrane, are located on the first direction side of the end of the second gas diffusion layer, which is the end on the second direction side of the second gas diffusion layer.

2. In the power generation cell according to claim 1, The end of the first electrode catalyst layer is located on the first direction side of the first rib end, which is the end of the first rib portion in the second direction that abuts the first gas diffusion layer. The power generation cell is characterized in that the end of the second electrode catalyst layer and the end of the electrolyte membrane are located on the first direction side of the second rib end, which is the end of the second rib portion that abuts the second gas diffusion layer.

3. In the power generation cell according to claim 2, The end of the first gas diffusion layer is located on the second side of the end of the first rib, The power generation cell is characterized in that the end of the second gas diffusion layer is located on the second direction side of the end of the second rib.

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