Power generation cell

Abstract

To prevent an end part of a membrane electrode assembly from being peeled.SOLUTION: A power generation cell includes: a membrane electrode structure having a membrane electrode assembly and a frame member that supports a peripheral part of the membrane electrode assembly; and first and second separators disposed to face a first surface and a second surface of the membrane electrode structure, respectively. The first and second separators have a plurality of flow path ribs that protrude toward the membrane electrode assembly and extend substantially parallel to each other to form partition walls of a plurality of power generation flow paths of a first gas and a second gas having a lower pressure than the first gas. An end part of a first gas diffusion layer of the membrane electrode assembly along a flow direction of the first gas is located inside the end part of a second gas diffusion layer of the membrane electrode assembly along the flow direction of the second gas and inside the end part of a flow path rib.SELECTED DRAWING: Figure 6A

Description

[Technical Field]

[0001] The present invention relates to a power generating cell of a fuel cell. [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 technology 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 between a pair of separators (see, for example, Patent Document 1). In the power generation cell described in Patent Document 1, the end of the gas diffusion layer is positioned in the flow path between the separator and the frame member. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Patent No. 6843730 Summary of the Invention [Problem to be solved by the invention]

[0004] However, when a fuel cell is used in a low-temperature environment, ice may form on the edges of the gas diffusion layer after the fuel cell has finished operating. If the fuel cell is started in this state, the frame member may bend due to the differential gas pressure, and part of the membrane electrode assembly may peel off along with the ice. [Means for solving the problem]

[0005] A power generation cell according to one embodiment of the present invention comprises a membrane electrode assembly, a membrane electrode structure having a frame member having an opening covered by the membrane electrode assembly and supporting a peripheral portion of the membrane electrode assembly, and a first separator and a second separator arranged opposite a first surface and a second surface of the membrane electrode structure, respectively. The membrane electrode assembly includes an electrolyte membrane, a first electrode catalyst layer and a second electrode catalyst layer disposed in close contact with one side and the other side of the electrolyte membrane, and a first 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 plurality of first flow path ribs projecting toward the membrane electrode assembly and extending substantially parallel to each other to form partition walls of a plurality of power generation flow paths for a first gas. The second separator has a plurality of second flow path ribs projecting toward the membrane electrode assembly and extending substantially parallel to each other to form partition walls of a plurality of power generation flow paths for a second gas having a lower pressure than the first gas. An end of the first gas diffusion layer in the flow direction of the first gas is located closer to the center of the opening than an end of the second gas diffusion layer in the flow direction of the second gas, and is also located more inner than the ends of the second flow path ribs. [Effects of the Invention]

[0006] According to the present invention, even if a fuel cell is started with ice adhering to the end of the gas diffusion layer, it is possible to prevent a part of the membrane electrode assembly from peeling off together with the ice. [Brief explanation of the drawings]

[0007] [Figure 1] 1 is a perspective view showing a schematic overall configuration of a fuel cell stack having a power generating cell according to an embodiment of the present invention; [Figure 2] FIG. 2 is a cross-sectional view taken along line II-II in FIG. [Figure 3] FIG. 2 is a perspective view showing a schematic configuration of an integrated electrode assembly included in the fuel cell stack of FIG. 1. [Figure 4] FIG. 2 is a front view of a separator included in the fuel cell stack of FIG. 1. [Figure 5] Enlarged view of part V in Figure 4. [Figure 6A] 1 is a cross-sectional view showing the configuration of a main part of a power generating cell according to an embodiment of the present invention. [Figure 6B] 6B is a diagram showing a state in which a differential pressure acts on the power generation cell of FIG. 6A. FIG. [Figure 7A] FIG. 6B is a diagram showing a reference example of FIG. 6A. [Figure 7B] 7B is a diagram showing a state in which a differential pressure acts on the power generation cell of FIG. 7A. FIG. [Figure 8] FIG. 6B is a diagram showing a modification of FIG. 6A. [Figure 9A] FIG. 6B is a diagram showing another modification of FIG. 6A. [Figure 9B] FIG. 6B is a diagram showing yet another modified example of FIG. 6A. DETAILED DESCRIPTION OF THE INVENTION

[0008] Hereinafter, an embodiment of the present invention will be described with reference to Figs. 1 to 9B. A power generating cell according to an embodiment of the present invention is included in a fuel cell stack, which is the main body of a fuel cell. The fuel cell is mounted on, for example, a vehicle and generates electric power for driving the vehicle. First, the overall configuration of the fuel cell stack will be described in brief. Note that the fuel cell stack may also be simply called a fuel cell.

[0009] FIG. 1 is a 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 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. The front-rear direction corresponds to the stacking direction of the power-generating cells. These directions are not necessarily the same as the front-rear direction, the left-right direction, and the up-down direction of a vehicle.

[0010] As shown in FIG. 1 , a fuel cell stack 100 includes a cell stack 101 formed by stacking multiple power-generating cells 1 in the front-rear direction and end units 102 disposed at both front-rear ends of the cell stack 101, forming a generally rectangular parallelepiped structure. The left-right length of the cell stack 101 is longer than the up-down length. For convenience, FIG. 1 shows only a single power-generating cell 1. The power-generating cell 1 includes an integrated electrode assembly 2 having a membrane electrode assembly including an electrolyte membrane and electrodes, and a pair of front and rear separators 3, 3 disposed on both the front and rear sides of the integrated electrode assembly 2 and sandwiching the integrated electrode assembly 2. The integrated electrode assemblies 2 and the separators 3 are alternately disposed in the front-rear direction. Although not shown, a generally box-shaped case with open front and rear faces is disposed around the cell stack 101. The front end of the case is fastened to the front end unit 102, and the rear end of the case is fastened to the rear end unit 102, respectively, via bolts.

[0011] FIG. 2 is a cross-sectional view (a cross-sectional view taken along line II-II in FIG. 1) of a portion of the cell stack 101. As shown in FIG. 2, the separator 3 has a front plate 31 and a rear plate 32, which are a pair of front and rear thin metal plates each having a corrugated cross section. The front plate 31 has a front surface 31a and a rear surface 31b. The rear plate 32 has a front surface 32a and a rear surface 32b. The outer peripheral 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 a titanium alloy.

[0012] A cooling flow path PAw through which a coolant flows is formed inside the separator 3 surrounded by the front plate 31 and the rear plate 32, and the flow of the coolant cools the power generation surface of the power generation cell 1. Water, for example, can be used as the coolant. The separator 3 is formed with projections and recesses by press molding or the like so as to form gas flow paths between the separator 3 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 assemblies 2, and recesses 302 that are connected to the rib portions 301 and are formed with a concave shape.

[0013] The rib portion 301 of the rear plate 32 abuts against the front surface 2a of the integrated electrode assembly 2, and the rib portion 301 of the front plate 31 abuts against the rear surface 2b of the integrated 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 and the front and rear end units 102 are fastened together. Therefore, after assembly of the fuel cell stack 100 is complete, the compressive load F is maintained on the fuel cell stack 100. As a result, a predetermined surface pressure P0 acts on the integrated electrode assembly 2 in the front-to-rear direction via the rib portion 301.

[0014] An anode flow path PAa through which a fuel gas flows is formed by the recess 302 between the rear plate 32 of the separator 3 and the front surface 2a of the integrated electrode assembly 2. A cathode flow path PAc through which an oxidant gas flows is formed by the recess 302 between the front plate 31 of the separator 3 and the rear surface 2b of the integrated electrode assembly 2. For example, hydrogen gas containing hydrogen can be used as the fuel gas, and air containing oxygen can be used as the oxidant gas.

[0015] 3 is a perspective view showing a schematic configuration of the unitized electrode assembly 2. As shown in FIG. 3, the unitized electrode assembly (UEA) 2 has a substantially rectangular membrane electrode assembly (MEA) 20 and a frame 21 that supports the membrane electrode assembly 20. The unitized electrode assembly 2 can also be called a membrane electrode structure. As shown in the detailed view of part A in FIG. 2, the membrane electrode assembly 20 has 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 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 diffuses and supplies a fuel gas. Of the electrode catalyst layer 24 and the gas diffusion layer 26, the electrode catalyst layer 24 in particular may be referred to as the anode electrode. An intermediate layer (base layer) may 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 diffuses and supplies an oxidant gas. Of the electrode catalyst layer 25 and the gas diffusion layer 27, the electrode catalyst layer 25 in particular may be referred to as the cathode electrode. An intermediate layer (base layer) may be provided between the electrode catalyst layer 25 and the gas diffusion layer 27.

[0017] The electrolyte membrane 23 is, for example, a solid polymer electrolyte membrane, and a thin film of a water-containing perfluorosulfonic acid polymer can be used. It is not limited to a fluorine-based electrolyte membrane, and a hydrocarbon-based electrolyte membrane can also be used. The electrode catalyst layers 24, 25 contain a catalytic metal that promotes the 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. The gas diffusion layers 26, 27 are made of a gas-permeable conductive material, such as a porous carbon material.

[0018] At the anode electrode (electrode catalyst layer 24), fuel gas (hydrogen) supplied via the anode flow path PAa and gas diffusion layer 26 is ionized by the action of the catalyst and moves through the electrolyte membrane 23 to the cathode electrode side. The electrons generated at this time pass through an external circuit and are extracted as electrical energy. At the cathode electrode (electrode catalyst layer 25), oxidant gas (oxygen) supplied via the cathode flow path PAc and gas diffusion layer 27 reacts with hydrogen ions introduced from the anode electrode and electrons transferred from the anode electrode, producing water. The produced water provides an appropriate humidity to the electrolyte membrane 23, and excess water is discharged to the outside of the integrated electrode assembly 2 along the gas flow.

[0019] The frame 21 in FIG. 3 is a generally rectangular, thin film plate (film member) with a thickness of 0.1 mm or less, and is made of insulating resin, rubber, or the like. Examples of materials that can be used include PEN (polyethylene naphthalate) and PPS (polyphenylene sulfide). A generally rectangular opening 210 is provided in the center of the frame 21, and the membrane electrode assembly 20 is provided to cover the entire opening 210. The frame 21 has a generally rectangular outer edge 221 and a generally rectangular inner edge 222 inside the outer edge 221. 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 210) and its surrounding area.

[0020] Point P in Fig. 3 is a center point passing through the vertical and horizontal midpoints of opening 210. On the left side of opening 210 in frame 21, three through holes 201 to 203 that penetrate frame 21 in the front-to-rear direction are opened in a line up in the vertical direction, and on the right side of opening 210, three through holes 204 to 206 that penetrate frame 21 in the front-to-rear direction are opened in a line up in the vertical direction.

[0021] 1, through holes 311 to 316 that penetrate the separators 3 in the front-rear direction 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. The through holes 311 to 316 are connected to the through holes 201 to 206 of the frame 21, respectively. A collection of these mutually connected through holes 201 to 206 and 311 to 316 form flow paths PA1 to PA6 (indicated by arrows for convenience) that penetrate the cell stack 101 and extend in the front-rear direction. The flow paths PA1 to PA6 are sometimes called manifolds.

[0022] End units 102, arranged on both the front and rear sides of the cell stack 101, each include a conductive terminal plate, an insulating insulator arranged on the inside of the end plate in the front-rear direction, and a metal end plate arranged on both front-rear sides of the insulator. The rear end unit 102 has a plurality of through holes 102a-102f that penetrate the end unit 102 in the front-rear direction. The flow paths PA1-PA6 are connected to manifolds external to the fuel cell stack 100 via the through holes 102a-102f.

[0023] Flow path PA1 (solid arrow) extending forward via through-holes 201 and 311 is a fuel gas supply flow path. Flow path PA6 (solid arrow) extending rearward via 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 are connected to an anode flow path PAa ( FIG. 2 ) provided opposite the front surface of the membrane electrode assembly 20, and 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 portion (not shown).

[0024] A flow path PA4 (dotted arrow) extending forward via the through-holes 204 and 314 is an oxidant gas supply flow path. A flow path PA3 (dotted arrow) extending rearward via the 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 are connected to a cathode flow path PAc ( FIG. 2 ) provided opposite the rear surface of the membrane electrode assembly 20, and as shown by the dotted arrow, the oxidant gas flows leftward through the cathode flow path PAc via the oxidant gas supply flow path PA4 and the oxidant gas discharge flow path PA3. The communication between the cathode flow path PAc and the other flow paths PA1, PA2, PA5, and PA6 is blocked by a seal (not shown).

[0025] A flow path PA5 (indicated by a dashed-dotted arrow) extending forward through through-holes 205 and 315 is a cooling medium supply flow path. A flow path PA2 (indicated by a dashed-dotted arrow) extending rearward 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 communicate with a cooling flow path PAw ( FIG. 2 ) provided inside 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 by a seal portion (not shown).

[0026] The above is a schematic configuration of the fuel cell stack 100. The configuration of the separator 3 will be described in more detail. FIG. 4 is a front view (viewed from the front) of the separator 3. That is, FIG. 4 is a diagram showing the surface of the separator 3 (front surface 31a of the front plate 31) that faces the cathode electrode on the rear surface 2b of the integrated electrode assembly 2. Point P in the figure is the center point of the separator 3.

[0027] In Figure 4, the region AR1 facing the membrane electrode assembly 20 of the integrated electrode assembly 2 is called the central region of the separator 3, and the regions AR2 on the left and right outer sides of the central region AR1 are called edge regions. As shown in Figures 2 and 4, a plurality of ribs 301 (Figure 2) protrude forward at equal intervals in the vertical direction over almost the entire central region AR1 of the separator 3, although some are not shown. A power generation region AR3 is provided on the left and right inner side of the central region AR1. In the power generation region AR3, electricity is generated by an electrochemical reaction between hydrogen contained in the fuel gas and oxygen contained in the oxidant gas.

[0028] Each of the plurality of rib portions 301 extends in the left-right direction, and a recess 302 (FIG. 2) is provided between adjacent rib portions 301 in the up-down direction. A plurality of cathode flow channels PAc extending substantially parallel to each other in the left-right direction are formed between the plurality of recesses 302 and the membrane electrode assembly 20. Therefore, the rib portion 301 forms a partition wall of the cathode flow channels PAc. The oxidant gas flows from right to left along the cathode flow channels PAc, as indicated by the arrows in FIG. 4. Note that the cathode flow channels PAc may extend in the left-right direction while meandering in the up-down direction, rather than extending linearly in the left-right direction.

[0029] 4, a plurality of bead portions, i.e., metal bead seals, are provided on the front surface 31a in the end region AR2 of the separator 3 (front plate 31) and protrude forward toward the frame 21. The plurality of bead portions include an outer bead portion 331 and a plurality of individual bead portions 332.

[0030] The individual bead portions 332 each have a substantially rectangular shape and individually surround the through holes 311 to 316. The outer bead portions 331 extend in the left-right direction above and below the central region AR1 along the upper and lower edge portions of the separator 3, and also extend in a zigzag pattern, passing on the outside in the left-right direction of the individual bead portions 332 around the through holes 311, 313, 314, and 316, and on the inside in the left-right direction of the individual bead portions 332 around the through holes 312 and 315.

[0031] In the end region AR2 of the separator 3 (front plate 31), a guide portion 333 is provided to protrude forward from the through hole 314 to the entire inlet area at the right end (left end in the drawing) of the cathode flow channel PAc, and from the entire outlet area at the left end (right end in the drawing) of the cathode flow channel PAc to the through hole 313. A plurality of tunnel portions 40 that cross the individual bead portions 332 are provided between the through hole 314 and the guide portion 333 and between the through hole 313 and the guide portion 333.

[0032] In the right-side end region AR2, a connecting flow path PAc1 is formed between vertically adjacent guide portions 333, 333, connecting the cathode flow path PAc to the outlet of tunnel portion 40 connected to through-hole 314. In the left-side end region AR2, a connecting flow path PAc2 is formed between vertically adjacent guide portions 333, 333, connecting the cathode flow path PAc to the inlet of tunnel portion 40 connected to through-hole 313. Therefore, guide portion 333 forms a partition wall between flow paths PAc1 and PAc2.

[0033] The number of connecting flow paths PAc1, PAc2 is smaller than the number of cathode flow paths PAc (recesses 302). For example, the number of connecting flow paths PAc1, PAc2 is 1 / 2 or less, 1 / 5 or less, or 1 / 10 or less of the number of cathode flow paths PAc. Therefore, the cathode flow paths PAc are provided at a higher density than the connecting flow paths PAc1, PAc2. A branching section 41 that branches the oxidant gas flow and guides it to the cathode flow path PAc is provided between the connecting flow path PAc1 on the right and the cathode flow path PAc. A confluence section 42 that confluences the oxidant gas flow and guides it to the connecting flow path PAc2 is provided between the cathode flow path PAc on the left and the connecting flow path PAc2.

[0034] Although not shown, outer bead portions 331, individual bead portions 332, tunnel portions 40, guide portions 33, rib portions 301, and recesses 302 are also provided on the rear surface 32b of the separator 3 (rear plate 32), similar to Fig. 4. The recesses 302 form a plurality of anode flow channels PAa in the vertical direction, and a connecting flow channel PAa1 is provided between the through-hole 311 and the anode flow channel PAa, and a connecting flow channel PAa2 is provided between the anode flow channel PAa and the through-hole 316. Furthermore, a branch portion 41 is provided between the connecting flow channel PAa1 and the anode flow channel PAa, and a junction portion 42 is provided between the anode flow channel PAa and the connecting flow channel PAa2.

[0035] Fig. 5 is an enlarged view of part V in Fig. 4, showing the configuration of the junction 42 of the cathode flow path PAc. In Fig. 5, the rib portion 301 and the guide portion 333 are shown by hatching for convenience. As shown in Fig. 5, the guide portion 333 has a bent portion 333a that bends leftward and downward from the left end portion of the central region AR1 of the separator 3, and a linear portion 333b that extends in a substantially linear manner leftward and downward from the left end portion of the bent portion 333a.

[0036] A plurality of (e.g., three) rib portions 301 are included between a pair of vertically adjacent bent portions 333a, 333a. Therefore, the plurality of cathode flow paths PAc communicate with a single connecting flow path PAc2. The inlet of the connecting flow path PAc2, i.e., the flow path between the pair of bent portions 333a, 333a, forms the confluence portion 42. In other words, the confluence portion 42 refers to the range from the end of the cathode flow path PAc to the point where the width of the connecting flow path PAc2 becomes constant.

[0037] The width W1 of the cathode flow channel PAc is very small and is narrower than the width W2 of the connecting flow channel PAc2 at the junction 42. The width W2 of the connecting flow channel PAc2 gradually decreases downstream in the flow direction from the junction 42, i.e., leftward and downward. In the straight portion 333b, the width W2 of the connecting flow channel PAc2 is approximately constant.

[0038] The power generating cell 1 according to this embodiment is characterized by the configuration of the periphery of the opening 210 of the frame 21 in FIG. 3. This point will be described below. FIG. 6A is a cross-sectional view showing the configuration of a main part of the power generating cell 1. This cross-sectional view is taken along line VI-VI in FIG. 3, i.e., a cross-sectional view showing the configuration of the periphery of the inner edge 222 on the left side of the frame 21. Note that the configuration of the periphery of the inner edge 222 is the same along the entire periphery of the inner edge 222 along the opening 210. Hereinafter, the rightward direction in FIG. 4A, i.e., the direction toward the center point P in FIG. 3 (the center side), will be referred to as the inner direction or inward, and the rightward side in FIG. 4A will be referred to as the inside. Furthermore, the leftward direction in FIG. 4A, i.e., the direction toward the outer edge 221 in FIG. 3, will be referred to as the outward direction or outward, and the leftward direction in FIG. 4A will be referred to as the outside.

[0039] 6A also shows the separator 3 (rear plate 32) abutting against the front surface 2a of the integrated electrode assembly 2, more specifically, the front surface 260 of the gas diffusion layer 26, and the separator 3 (front plate 31) abutting against the rear surface 2b of the integrated electrode assembly 2, more specifically, the rear surface 270 of the gas diffusion layer 27. The cross-sectional view of this separator 3 corresponds to the cross-sectional view taken along line VI-VI in FIG.

[0040] The separator 3 is provided with rib portions 301 that respectively abut against the front surface 2a and rear surface 2b of the integrated electrode assembly 2, and recesses 302 that are recessed in directions away from the front surface 2a and rear surface 2b of the integrated electrode assembly 2. Although not shown, the separator 3 abuts against the front surface 21a and rear surface 21b of the frame 21 via guide portions 333 on the outside of the membrane electrode assembly 20 (left side in FIG. 6A ). There are no gas diffusion layers 26, 27 between the guide portions 333 and the front surface 21a and rear surface 21b of the frame 21, and the guide portions 333 are taller (longer in the front-to-rear direction) than the rib portions 301.

[0041] 6A, the left end 23a (outer end) of the electrolyte membrane 23, the left end 25a of the cathode-side electrode catalyst layer 25, and the left end 27a of the gas diffusion layer 27 are located at the same position in the left-right direction. The left end 24a of the anode-side electrode catalyst layer 24 and the left end 26a of the gas diffusion layer 26 are located a predetermined length to the right (inside) of the left end 23a of the electrolyte membrane 23. The left end 24a of the electrode catalyst layer 24 and the left end 26a of the gas diffusion layer 26 are located at the same position.

[0042] The frame 21 has a front frame 211 and a rear frame 212 that are overlapped and joined together with adhesive 213. An inner edge 222 of the front frame 211 protrudes rightward (inward) from an inner edge 222 of the rear frame 212. Although not shown, the outer edge 221 of the front frame 211 (FIG. 3) and the outer edge 221 of the rear frame 212 are positioned at the same left-right position.

[0043] 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, 25a of the electrolyte membrane 23 and the electrode catalyst layers 24, 25. The above-described integrated electrode assembly 2 is manufactured, for example, by the following procedure.

[0044] First, the electrode catalyst layer 25 is applied to the surface (front surface) of the cathode-side gas diffusion layer 27. Next, the electrolyte membrane 23 is bonded to the surface (front surface) of the electrode catalyst layer 25. Next, the inner edge portion 222 of the front frame 211 is bonded to the surface (front surface) of the electrolyte membrane 23 via an adhesive 213. Next, the anode-side gas diffusion layer 26, on whose surface the electrode catalyst layer 24 has been applied in advance, is laminated on the surface (front surface) of 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 ends of the anode-side electrode catalyst layer 24 and gas diffusion layer 26 are bent forward as shown in the figure, and are positioned forward by an amount corresponding to the thickness of the front frame 211 relative to their positions before bending. For this reason, a step is provided on the front surface 260 of the gas diffusion layer 26.

[0045] The rear plate 32 of the separator 3 is configured to have a stepped shape corresponding to the step in the front surface 260. That is, the rear plate 32 has a rib portion 301a that contacts the front surface 260 of the gas diffusion layer 26 before bending, and a rib portion 301b that contacts the front surface 260 after bending. The cathode-side gas diffusion layer 27 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 in FIG. 2 acts on the front surface 260 of the anode-side gas diffusion layer 26 and the rear surface 270 of the cathode-side gas diffusion layer 27 via the rib portion 301 (see FIG. 6B). That is, a surface pressure P0 that sandwiches the integrated electrode assembly 2 in the front-rear direction acts.

[0046] The position of the left end 27a (left end face) of the gas diffusion layer 27 on the cathode side is the same as or slightly to the right of position P1, which is the position of the left end (outer end) of the rib portion 301 on the front plate 31 of the separator 3, i.e., the start position of the junction 42. The position of the left end 26a (left end face) of the gas diffusion layer 26 on the anode side is a predetermined length to the right of position P1 and position P2, which is the position of the left end (outer end) of the rib portion 301 on the rear plate 32 of the separator 3, i.e., the start position of the junction 42. The left end 26a of the gas diffusion layer 26 is located to the right of the left end 27a of the gas diffusion layer 27.

[0047] As a result, the left end portions 23a, 24a, 25a of the electrolyte membrane 23 and the electrode catalyst layers 24, 25 are sandwiched between the front rib portion 301 and the rear rib portion 301, on which the surface pressure P0 acts, without any gaps, via the gas diffusion layers 26, 27. Therefore, the left end portions 23a, 24a, 25a of the electrolyte membrane 23 and the electrode catalyst layers 24, 25 can be firmly held.

[0048] In this power-generating cell 1, when the fuel cell stack 100 is in operation, fuel gas is introduced into the anode flow path PAa and the connecting flow path PAa1 in the front recess 302 of the integrated electrode assembly 2. Oxidant gas is introduced into the cathode flow path PAc and the connecting flow path PAc2 in the rear recess 302. The pressure of the fuel gas is higher than the pressure of the oxidant gas. Therefore, as shown in FIG. 6B , a differential pressure ΔP acts from the space SPa of the connecting flow path PAa1 at the anode-side branching portion 41 to the space SPc of the connecting flow path PAc2 at the cathode-side joining portion 42.

[0049] This may cause the frame 21 (front frame 211) to bend rearward. However, the gas diffusion layers 26, 27 are located to the right of positions P1, P2 of the left ends of the rib portions 301. Therefore, the gas diffusion layers 26, 27 are firmly held between the rib portions 301, 301, and bending of the frame 21 between the gas diffusion layers 26, 27 can be suppressed. In particular, the left end (outer end) 26a of the anode-side gas diffusion layer 26 is located to the right of the left end (outer end) 27a of the cathode-side gas diffusion layer 27, so that the frame 21 and the electrode catalyst layer 24 can be maintained in good contact with each other.

[0050] When the fuel cell stack 100 is used in a cold climate, moisture that has seeped in through 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. Even if the fuel cell stack 100 is started in this state, as shown in FIG. 6B , no bending occurs at the left end 26a of the gas diffusion layer 26 where the ice 300 is present. However, if bending occurs at the left end 26a of the gas diffusion layer 26, the following problems may occur.

[0051] 7A is a diagram showing a reference example of FIG. 6A. In the example of FIG. 7A, the left end 23a of the electrolyte membrane 23, the left end 25a of the cathode-side electrode catalyst layer 25, and the left end 27a of the gas diffusion layer 27 protrude leftward (outward) from position P1 of the left end of the rib portion 301 of the separator 3 (front plate 31). Furthermore, the left end 24a of the anode-side electrode catalyst layer 24 and the left end 26a of the gas diffusion layer 26 protrude leftward (outward) from position P2 of the left end of the rib portion 301 of the separator 3 (rear plate 32). The left ends 23a, 24a, 25a, 26a, and 27a of the elements of the integrated electrode assembly 2 are positioned at the same level.

[0052] FIG. 7A shows a sub-freezing state in which ice 300 exists between the gas diffusion layer 26 and the frame 21. When the fuel cell stack 100 is started in this state, the frame 21 may bend as shown in FIG. 7B. This may cause a portion of the electrode catalyst layer 24 (referred to as exfoliated material 240) to be pulled by the ice 300 and peel off from the gas diffusion layer 26. When the ice 300 melts in this state, the exfoliated material 240 is guided together with water into the drainage flow path of the fuel cell stack 100. The drainage flow path is a flow path for discharging excess water generated within the fuel cell stack to the outside. A filter is provided along this drainage flow path. Therefore, if the exfoliated material 240 reaches the drainage flow path, the filter may become clogged.

[0053] 6B, even when a pressure difference ΔP acts, the frame 21 does not bend between the gas diffusion layers 26, 27, and the electrolyte membrane 23 and the electrode catalyst layer 24 can be maintained in close contact with each other. Therefore, even when ice adheres to the end of the electrode catalyst layer 24 during use in cold climates, it is possible to prevent a portion of the electrode catalyst layer 24 from falling off due to the ice.

[0054] FIG. 8 is a diagram showing a modified example of FIG. 6A. FIG. 8 differs from FIG. 6A in the positions of the left end portions 23a, 24a, and 25a of the electrolyte membrane 23 and the electrode catalyst layers 24 and 25. That is, in FIG. 8, the left end portion 23a of the electrolyte membrane 23 and the left end portion 25a of the cathode-side electrode catalyst layer 25 are located to the right of the left end portion 27a of the gas diffusion layer 27. Furthermore, the left end portion 24a of the anode-side electrode catalyst layer 24 is located to the right of the left end portion 26a of the gas diffusion layer 26. Note that, as in FIG. 6A, the left end portions 26a, 27a of the gas diffusion layers 26 and 27 are located to the right of positions P1 and P2 of the left end portions of the rib portion 301, and the left end portion 26a of the anode-side gas diffusion layer 26 is located to the right of the left end portion 27a of the cathode-side gas diffusion layer 27.

[0055] The separators 3 disposed on both sides of the gas diffusion layers 26, 27 in the front-rear direction contain iron. Therefore, water produced by the electrochemical reaction between the fuel gas and the oxidizer gas accumulates in the anode flow path PAa and the cathode flow path PAc, and iron ions may be eluted into the accumulated water. Because these iron ions can cause deterioration of the electrolyte membrane 23, it is preferable to prevent water containing iron ions from penetrating the electrolyte membrane 23. In this regard, in the example shown in FIG. 8 , the electrode catalyst layers 24, 25 containing ionomer are positioned to the right of the left ends 26a, 27a of the gas diffusion layers 26, 27, and are sandwiched between the rib portions 301 of the front and rear separators 3 via the gas diffusion layers 26, 27. Therefore, the electrode catalyst layers 24, 25 are not exposed to the left (outside) of the gas diffusion layers 26, 27.

[0056] In this way, the electrode catalyst layers 24, 25, which serve as a path for iron ion penetration, are not exposed, thereby blocking the path for iron ion penetration. This makes it possible to prevent moisture containing iron ions from penetrating inside through the boundary surface between the gas diffusion layers 26, 27 and the frame 21 (front frame 211). In particular, because the gas diffusion layers 26, 27 contain carbon, which has a water-repellent effect, it is possible to effectively prevent moisture containing iron ions from penetrating through the boundary surface between the gas diffusion layers 26, 27 and the frame 21.

[0057] 9A and 9B are diagrams showing further modified examples of FIG. 6A. In FIGS. 9A and 9B, the rear frame 212 extends further to the right than in FIG. 6A, and the front frame 211 and the rear frame 212 are sandwiched between the gas diffusion layers 26 and 27. Furthermore, in FIG. 9A, the electrolyte membrane 23 and the electrode catalyst layers 24 and 25 are sandwiched between the front frame 211 and the rear frame 212. On the other hand, in FIG. 9B, the electrolyte membrane 23 and the cathode-side electrode catalyst layer 25 are sandwiched between the front frame 211 and the rear frame 212, and the anode-side electrode catalyst layer 24 is sandwiched between the front frame 211 and the gas diffusion layer 26.

[0058] 9A and 9B, the left end portions 26a and 27a of the gas diffusion layers 26 and 27 are located to the right of positions P1 and P2 of the left end portions of the rib portion 301, and the left end portion 26a of the anode-side gas diffusion layer 26 is located to the right of the left end portion 27a of the cathode-side gas diffusion layer 27. Furthermore, the left end portions 23a, 24a, and 25a of the electrolyte membrane 23 and the electrode catalyst layers 24 and 25 are not exposed to the gas flow paths PAa and PAc.

[0059] According to this embodiment, the following effects can be achieved. (1) The power-generating cell 1 includes an integrated electrode assembly 2 as a membrane electrode structure, the integrated electrode assembly 2 having an opening 210 covered by the membrane electrode assembly 20 and a frame 21 supporting the peripheral edge of the membrane electrode assembly 20, and separators 3, 3 disposed opposite a front surface 2a and a rear surface 2b of the integrated electrode assembly 2, respectively (FIGS. 1 and 3). The membrane electrode assembly 20 includes an electrolyte membrane 23, electrode catalyst layers 24, 25 disposed in close contact with the front surface and rear surface of the electrolyte membrane 23, respectively, and gas diffusion layers 26, 27 disposed between the electrode catalyst layer 24 and the separator 3 and between the electrode catalyst layer 25 and the separator 3, respectively (FIG. 2). The separator 3 (rear plate 32) has multiple ribs 301 that protrude toward the membrane electrode assembly 20 and extend substantially parallel to one another, forming partition walls for multiple power-generation flow paths (anode flow paths PAa) for fuel gas (FIG. 2). The separator 3 (front plate 31) protrudes toward the membrane electrode assembly 20 and has multiple ribs 301 extending generally parallel to one another to form partition walls for multiple power generation flow paths (cathode flow paths PAc) for oxidant gas, which has a lower pressure than the fuel gas (FIG. 2). The left end 26a (outer end) of the anode-side gas diffusion layer 26 along the fuel gas flow direction is located to the right (inner) of the left end 27a (outer end) of the cathode-side gas diffusion layer 27 along the oxidant gas flow direction, which is closer to the center of the opening 210, and is also located to the right (inner) of position P1 of the left end of the cathode-side rib 301 (FIG. 6A).

[0060] With this configuration, when a gas pressure difference ΔP acts on the integrated electrode assembly 2, the frame 21 does not bend between the gas diffusion layers 26, 27, and therefore the frame 21 and the anode-side electrode catalyst layer 24 can be maintained in close contact with each other. This prevents a part of the membrane electrode assembly 20 (the end of the electrode catalyst layer 24) from peeling off together with the ice 300, even when the fuel cell is started with ice adhering to the end of the anode-side gas diffusion layer 26. As a result, clogging of the filter in the drainage path can be prevented.

[0061] (2) The left end 26a of the anode-side gas diffusion layer 26 is located to the right (inner) of the position P2 of the left end of the anode-side rib portion 301 (FIG. 6A). As a result, the differential pressure ΔP does not act on the gas diffusion layer 26, so the gas diffusion layer 27 does not bend, and the frame 21 and the electrode catalyst layer 24 can be maintained in good contact with each other.

[0062] (3) The separator 3 (front plate 31) has a plurality of guide portions 333 provided upstream and downstream of the rib portion 301 in the flow direction of the oxidizer gas ( FIG. 4 ). The width of the gap (gas flow paths PAa, PAc) between adjacent pairs of rib portions 301, 301 is narrower than the width of the gap (connection flow paths PAa1, PAa2, PAc1, PAc2) between adjacent pairs of guide portions 333, 333 ( FIGS. 4 and 5 ). With this configuration, the guide portions 333 function as ribs at the gas branching portion 41 and merging portion 42, but the width between the guide portions 333, 333 is wide, and the rib density of the guide portions 333 is lower than the rib density of the rib portion 301. Therefore, the frame 21 is prone to bending at the branching portion 41 and the merging portion 42. In this regard, in this embodiment, as described above, the left end portion 26a of the gas diffusion layer 26 is positioned to the right of the left end portion 27a of the gas diffusion layer 27, and is also positioned to the right of the position P1 of the left end portion of the rib portion 301, thereby effectively preventing the frame 21 from bending between the gas diffusion layers 26 and 27.

[0063] (4) The left end 24a (outer end) of the anode-side electrode catalyst layer 24 is located to the right (inner) of the left end 26a (outer end) of the anode-side gas diffusion layer 26 (FIGS. 8, 9A, and 9B). The left end 25a (outer end) of the cathode-side electrode catalyst layer 25 is located to the right (inner) of the left end 27a (left end) of the cathode-side gas diffusion layer 27 (FIGS. 8, 9A, and 9B). This prevents the electrode catalyst layers 24 and 25 from being exposed to the gas flow paths PAa and PAc, preventing moisture containing iron ions from penetrating into the electrolyte membrane 23 through the electrode catalyst layers 24 and 25.

[0064] The above embodiment can be modified in various ways. Some modifications will be described below. In the above embodiment, the rear plate 32 of the separator 3 is disposed as a first separator facing the front surface 2a (first surface) of the integrated electrode assembly 2 serving as a membrane electrode structure, and the front plate 31 of the separator 3 is disposed as a second separator facing the rear surface 2b (second surface) of the integrated electrode assembly 2. However, the configurations of the first and second separators are not limited to those described above. That is, the first separator may have any configuration as long as it has a plurality of first flow path ribs (rib portions 301) that protrude toward the integrated electrode assembly 2 and form partition walls between a plurality of power generation flow paths for a first gas (e.g., fuel gas) that extend substantially parallel to one another. The second separator may have any configuration as long as it has a plurality of second flow path ribs (rib portions 301) that protrude toward the integrated electrode assembly 2 and form partition walls between a plurality of power generation flow paths for a second gas (e.g., oxidant gas) that extend substantially parallel to one another.

[0065] In the above embodiment, the membrane electrode assembly 20 is configured by the electrolyte membrane 23, the electrode catalyst layer 24 (first electrode catalyst layer) and the electrode catalyst layer 25 (second electrode catalyst layer) that are disposed in close contact with the front surface (one surface) and the rear surface (the other surface) of the electrolyte membrane 23, and the gas diffusion layer 26 (first gas diffusion layer) and the gas diffusion layer 27 (second gas diffusion layer). Here, the membrane electrode assembly 20 may have any configuration as long as it satisfies the end condition that the end of the first gas diffusion layer along the flow direction of the first gas (e.g., fuel gas) is located more inward (toward the center of the opening 210 of the frame 21 as a frame member) than the end of the second gas diffusion layer along the flow direction of the second gas (e.g., oxidant gas) and more inward than the end of the second flow path rib.

[0066] In the above embodiment, a plurality of guide portions 333 (outer flow path ribs) are provided at the branch portion 41, which is upstream of the rib portion 301 in the flow direction of the oxidant gas, and at the junction portion 42, which is downstream of the rib portion 301, so that the above-mentioned end condition is satisfied on both the upstream and downstream sides. However, the above-mentioned end condition may be satisfied on at least one of the upstream and downstream sides. In the above embodiment, the guide portion 333 has a bent portion 333a and a straight portion 333b, but the configuration of the outer flow path ribs is not limited to the above. In the above embodiment, a fuel gas is used as the first gas and an oxidant gas is used as the second gas, but the configuration of the first gas and the second gas having a lower pressure than the first gas is not limited to the above.

[0067] 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 power generating cell of the present invention can also be applied to moving bodies other than vehicles, such as aircraft and ships, robots, and various industrial machines.

[0068] 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.

[0069] 1 power generation cell, 2 integrated electrode assembly, 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 layer, 26a, 27a left end, 31 front plate, 32 rear plate, 100 fuel cell stack, 210 opening, 301 rib portion, 333 guide portion, PAa anode flow path, PAc cathode flow path, PAc2 connecting flow path, P1, P2 positions

Claims

1. a membrane electrode assembly; and a frame member having an opening covered by the membrane electrode assembly and supporting a peripheral portion of the membrane electrode assembly; a first separator and a second separator disposed opposite a first surface of the membrane electrode assembly and a second surface opposite the first surface, respectively; the membrane electrode assembly includes an electrolyte membrane, a first electrode catalyst layer and a second electrode catalyst layer respectively disposed in close contact with one surface and the other surface of the electrolyte membrane, and a first gas diffusion layer and a second gas diffusion layer respectively disposed between the first electrode catalyst layer and the first separator and between the second electrode catalyst layer and the second separator; the first separator has a plurality of first flow path ribs that protrude toward the membrane electrode assembly, extend substantially parallel to one another, and form partition walls for a plurality of power generation flow paths for a first gas; the second separator has a plurality of second flow path ribs that protrude toward the membrane electrode assembly, extend substantially parallel to one another, and form partition walls of a plurality of power generation flow paths for a second gas that has a lower pressure than the first gas; a power generation cell characterized in that an end of the first gas diffusion layer along the flow direction of the first gas is located more inward than an end of the second gas diffusion layer along the flow direction of the second gas, closer to the center of the opening, and more inward than an end of the second flow path rib.

2. The power generating cell according to claim 1 , A power generation cell, wherein the end of the first gas diffusion layer is located further inward than the end of the first flow path rib.

3. The power generating cell according to claim 1 , the second separator has a plurality of outer flow path ribs provided on the upstream side or downstream side of the second flow path rib in the flow direction of the second gas, A power generation cell, wherein the width of a gap between a pair of adjacent second flow path ribs is narrower than the width of a gap between a pair of adjacent outer flow path ribs.

4. The power generating cell according to any one of claims 1 to 3, an end of the first electrode catalyst layer is located more inward than the end of the first gas diffusion layer, A power generating cell, wherein an end of the second electrode catalyst layer is located more inward than the end of the second gas diffusion layer.

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