JP6229339B2 - Fuel cell stack - Google Patents

Description

  The present invention relates to a fuel cell stack having a structure in which a single cell of a polymer electrolyte fuel cell is used as a power generation element and a plurality of single cells are stacked.

  As this type of fuel cell stack, there is one described in Patent Document 1. The fuel cell stack described in Patent Document 1 is configured by sandwiching a membrane electrode assembly between a pair of separators to form a fuel cell (single cell) and laminating a plurality of these fuel cells. The separator constituting the fuel battery cell has a main surface portion formed in a cross-sectional wave shape in order to form a flow path for the reaction gas and the cooling fluid on both sides thereof.

  The fuel cell stack has a joining portion that joins the current collector plate disposed at the end in the stacking direction and the separator of the fuel cell adjacent to the current collector plate, and the current density is between the current collector plate and the separator. The structure is such that many joints are distributed in relatively high portions. Thereby, in the fuel cell stack, the through electric resistance between the current collector plate and the separator is reduced, and the power generation performance is improved.

Japanese Patent No. 5076360

  However, in the fuel cell stack as described above, the problems caused by the corrugated shape of the cross section of the separator and the swelling of the membrane electrode assembly have not been considered.

  In other words, in this type of fuel cell stack, considering the gas diffusibility in the membrane electrode assembly and the electrical resistance loss between the membrane electrode assembly and the separator, the waveform pitch of the separator is small and the number of irregularities is large. Is preferred. However, when the waveform pitch is small, even if a slight shift in the in-plane direction occurs between the separators in two adjacent single cells due to the swelling of the membrane electrode assembly, the waveforms of each other will bite. There is a problem that the separator may be deformed, and it has been a problem to solve such a problem.

  The present invention has been made paying attention to the above conventional problems, and prevents the separators from being displaced in the in-plane direction due to swelling of the membrane electrode assembly even when the corrugated pitch of the separator is reduced. And it aims at providing the fuel cell stack which can prevent the deformation | transformation of the separator by this shift | offset | difference.

The fuel cell stack according to the present invention has a structure in which a rectangular unit cell formed by sandwiching a membrane electrode assembly between a pair of separators is used as a power generation element, and a plurality of the unit cells are stacked. In this fuel cell stack, the separator has a flow path forming portion having a corrugated cross section for forming a flow path for the reaction gas inside the single cell and forming a flow path for the cooling fluid outside the single cell. together, the manifold holes of the reactant gas has respectively at both ends, the flow path forming portion each said flow path formed by the, forms a linear shape toward the manifold holes at one end to the manifold holes in the other end ing.

The fuel cell stack has a joining portion for joining the corrugated convex portions of the separator between two single cells adjacent in the stacking direction, and from the inlet side in the flow direction of the cathode gas that is the reaction gas. The area of the joint portion per unit area is gradually reduced toward the outlet side, and the above structure is a means for solving the conventional problems. In addition, in order to enlarge the area of the junction part per unit area, the area of the junction part itself can be increased, or the number of junction parts having a certain size can be increased.

  Since the fuel cell stack according to the present invention employs the above-described configuration, the joining portion is arranged according to the amount of swelling in the membrane electrode assembly, so that the membrane electrode can be used even when the waveform pitch of the separator is reduced. It is possible to prevent in-plane displacement between the separators due to swelling of the joined body, and to prevent deformation of the separator due to this displacement.

It is the perspective view (A) explaining the fuel cell stack of this invention, and the perspective view (B) of a decomposition | disassembly state. FIG. 2 is a plan view showing the single cell shown in FIG. 1 in an exploded state. It is sectional drawing (A) of the principal part of a fuel cell stack, and sectional drawing (B) which shows the state which the separator shifted | deviated. Graph (A) showing relationship between swelling amount of membrane electrode assembly and position in gas flow direction in first embodiment, plan view of separator (B) plan view of separator showing other example of joint (C) It is. It is the graph (A) which shows the relationship between the swelling amount of the membrane electrode assembly in 2nd Embodiment, and the position of a gas flow direction, and the top view (B) of a separator. It is each sectional drawing (A) (B) explaining the specific example of a separator.

<First Embodiment>
The fuel cell stack FS shown in FIG. 1 includes at least two or more cell modules M in which a plurality of single cells C are stacked and integrated as shown in FIG. And a seal plate P to be interposed. The unit cell C and the seal plate P in the illustrated example each have a rectangular plate shape having substantially the same vertical and horizontal dimensions. In FIG. 1B, two cell modules M and one seal plate P are shown, but in reality, a larger number of cell modules M and seal plates P are stacked.

  The fuel cell stack FS has end plates 56A and 56B arranged at both ends in the stacking direction of the cell modules M, and fastened to the stacking end surfaces (upper and lower surfaces in FIG. 1) on the long side of the single cell C. The plates 57A and 57B are provided, and the reinforcing plates 58A and 58B are provided on the laminated end surface on the short side. Each of the fastening plates 57A, 57B and the reinforcing plates 58A, 58B has a size over the entire length in the stacking direction of the stacked body A composed of the cell module M and the seal plate P, and is connected to both end plates 56A, 56B by bolts (not shown). .

  In this way, the fuel cell stack FS has a case-integrated structure as shown in FIG. 1A. Each cell module M and the seal plate P are constrained and pressurized in the stacking direction, and each unit cell C is predetermined. In order to maintain good gas sealing performance and electrical conductivity.

  As shown in FIG. 2, the single cell C has a structure in which the membrane electrode assembly 2 is sandwiched between separators 3 and 4 on the anode side and the cathode side. The membrane electrode assembly 2 of this embodiment integrally has a resin frame 1 around it. Each of the frame 1 and the separators 3 and 4 has a rectangular plate shape having substantially the same vertical and horizontal dimensions.

  The membrane electrode assembly 2 is generally called a MEA (Membrane Electrode Assembly), and as shown in FIG. 3A, an electrolyte layer 11 made of a solid polymer is combined with a fuel electrode layer (anode) 12 and air. It has a structure sandwiched between the polar layer (cathode) 13. Although not shown, the fuel electrode layer 11 and the air electrode layer 13 are each provided with a catalyst layer and a gas diffusion layer made of a porous material from the membrane electrode assembly 2 side. In this membrane electrode assembly 2, an anode gas (hydrogen) is supplied to the fuel electrode layer 12, and a cathode gas (air) is supplied to the air electrode layer 13 to generate power by an electrochemical reaction.

  Each of the separators 3 and 4 is a metal plate member having an inverted shape, and is made of stainless steel, for example, and can be formed into an appropriate shape by pressing. Each of the separators 3 and 4 has a central portion corresponding to the membrane electrode assembly 2 formed in a wave shape in a cross section in the short side direction. This wave shape is continuous in the long side direction as shown in the figure. The separators 3 and 4 will be described in detail later.

  The frame 1 of the membrane electrode assembly 2 and the separators 3 and 4 have three manifold holes H1 to H3 and H4 to H6, respectively, at both ends on the short side. The manifold holes H1 to H3 shown on the left side of FIG. 2 are for cathode gas supply (H1), cooling fluid supply (H2), and anode gas discharge (H3), and communicate with each other in the stacking direction. A flow path is formed. Also, the manifold holes H4 to H6 shown on the right side of FIG. 2 are for anode gas supply (H4), cooling fluid discharge (H5), and cathode gas discharge (H6), and communicate with each other in the stacking direction. The flow path is formed. The supply and discharge may be partially or entirely reversed in positional relationship.

  Further, a seal member S is continuously arranged around the peripheral edge of the frame 1 and the separators 3 and 4 and around the manifold holes H1 to H6. These sealing members S also function as adhesives, and airtightly join the frame 1 and membrane electrode assembly 2 to the separators 3 and 4. Further, the seal member S disposed around the manifold holes H1 to H6 has an opening at a corresponding portion in order to supply fluid according to each layer while maintaining the airtightness of each manifold.

  The unit cell C is formed by stacking a predetermined number of cell modules M. At this time, a flow path for cooling fluid (for example, water) is formed between adjacent single cells C, and a flow path for cooling fluid is also formed between adjacent cell modules M. Therefore, the seal plate P is disposed between the cell modules M, that is, in the flow path of the cooling fluid.

  The seal plate P is formed by molding a single conductive metal plate, is formed in the same rectangular plate shape and in the same size as the above-described single cell C in plan view, and on both short sides, Manifold holes H1 to H6 similar to the single cell C are formed. This seal plate P is provided with a seal member (not shown) around each of the manifold holes H1 to H6, and an outer peripheral seal member 51 and an inner peripheral seal member 52 are provided in parallel on the entire periphery thereof, The outer peripheral seal member 51 prevents rainwater and the like from entering from the outside, and the inner peripheral seal member 52 prevents leakage of the cooling fluid flowing through the flow path between the cell modules M.

  Here, the fuel cell stack FS has a structure in which a single cell C formed by sandwiching the membrane electrode assembly 2 between a pair of separators 2 and 3 is used as a power generation element, and a plurality of the single cells C are stacked. In addition, the separators 3 and 4 have a cross-sectional corrugated flow path forming portion 23 for forming a reaction gas flow path inside the single cell C and forming a cooling fluid flow path outside the single cell C. , 24.

  As described above, each separator 3, 4 has a corrugated section at the central portion corresponding to the membrane electrode assembly 2, and the central portions are the flow path forming portions 23, 24. Moreover, as shown in FIG. 3A, the flow path forming portions 23 and 24 of this embodiment have a sine wave cross section and are continuous in the long side direction as shown in FIG.

  More specifically, the anode-side separator 3 shown on the upper side in FIG. 3 (A) is formed on the surface (lower surface) of the membrane electrode assembly 2 by the corrugated convex portion 23A of the flow path forming portion 23. And the anode gas flow path GA is formed between the corrugated recess 23B and the membrane electrode assembly 2. On the other hand, the cathode-side separator 4 shown on the lower side in FIG. 3A is formed on the surface (upper surface) of the membrane electrode assembly 2 by the corrugated convex portion 24A of the flow path forming portion 24. And the cathode gas flow path GC is formed between the corrugated recess 24B and the membrane electrode assembly 2.

  The corrugated convex portions 23A and 24A and the corrugated concave portions 23B and 24B are formed into the corrugated concave portions 23B and 24B and the corrugated convex portions 23A and 24A on the opposite surface because the separators 3 and 4 have a reverse shape. .

  The separators 3 and 4 are configured such that, in the two single cells C and C adjacent in the stacking direction, the corrugated convex portion 23A of the anode separator 23 and the corrugated convex portion 24A of the cathode separator 4 are brought into contact with each other. A cooling fluid flow path F is formed therebetween. Moreover, since both the separators 3 and 4 have a sinusoidal cross section of the flow path forming portions 23 and 24, there is no flat surface at the tops of the corrugated convex portions 23A and 24A, and the membrane electrode assembly 2 and the other separator. Is generally line contact.

  That is, in this kind of separator (3, 4), when the tops of the corrugated convex portions (23A, 24A) are flat, the corrugated convex portions (23A, 24A) are brought into contact with the membrane electrode assembly (2). The diffusivity of the reaction gas is reduced in the portion covered with the flat surface of If the contact area between the separator (3, 4) and the membrane electrode assembly (2) is reduced in order to solve this problem, the gas diffusibility is improved, but the electrical resistance loss is increased due to the reduction in the adhesion area.

  Therefore, the separators 3 and 4 have a sine wave shape in the cross section of the flow path forming portions 23 and 24, thereby reducing the contact area between the corrugated convex portions 23A and 24A and the membrane electrode assembly 2. Good gas diffusibility is ensured in the electrode assembly 2. Moreover, the separators 2 and 3 reduce the corrugated pitches 23A and 24A and the membrane electrodes by reducing the corrugated pitch (the length of a set of irregularities) of the flow path forming portions 23 and 24 and increasing the number of irregularities. A large total contact area with the joined body 2 is ensured, and an electric resistance loss is reduced.

  However, when the cross-sections of the flow path forming portions 23 and 24 are made sinusoidal and the waveform pitch is reduced as described above, the separators 3 and 4 are caused by swelling of the membrane electrode assembly as shown in FIG. When a stress that shifts in the in-plane direction is generated, deformation occurs so that each other's waveform bites. When such deformation occurs, the conductivity between the separators 3 and 4 decreases, and the flow path F of the cooling fluid formed between the separators 3 and 4 is also deformed to flow the cooling fluid. May become difficult and cooling efficiency may be reduced.

  On the other hand, as shown in FIGS. 3A and 4, the fuel cell stack FS described above has corrugated convex portions 23 </ b> A and 24 </ b> A of the separators 3 and 4 between two single cells C adjacent in the stacking direction. It has the junction part 31 which joins each other. The fuel cell stack FS has a configuration in which the area of the joined portion 31 per unit area is increased with respect to a region where the swelling amount in the membrane electrode assembly 2 is relatively large. More desirably, the area of the bonding portion 31 per unit area is increased with respect to a region where the swelling amount of the membrane electrode assembly 2 during power generation is relatively large.

  In the fuel cell stack FS, the joint 31 can be formed by at least one of welding and a conductive adhesive. To increase the area of the joint 31 per unit area, the joint 31 itself. Can be increased, or the number of joints 31 having a certain size can be increased. In addition, when forming the junction part 31 by welding, the separators 3 and 4 are metal.

  The embodiment shown in FIG. 4 is suitable for the fuel cell FS in which the humidification of the cathode gas (air) is high. In the fuel cell FS in which the humidification of the cathode gas is high, as shown in FIG. 4A, the amount of swelling in the thickness direction of the membrane electrode assembly 2 changes in the gas flow direction and decreases from the inlet side to the outlet side. To do. This change in the amount of swelling can be determined by the load change at each site in the stacking direction.

  Therefore, the cathode-side separator 4 shown in FIGS. 4B and 4C has a joint portion 31 with an anode-side separator (not shown) disposed on the lower surface side thereof, and swells in the membrane electrode assembly. For the region on the inlet side where the amount (or the amount of swelling during power generation) is relatively large, the area of the junction 31 per unit area is increased and the area of the junction 31 per unit area toward the outlet side Is gradually reduced.

  The joint 31 in the separator 4 shown in FIG. 4B is formed by continuous welding such as seam welding using a roller electrode, or adhesion using a conductive adhesive, and its area (length) is changed. ing. In the illustrated separator 4, the same number (four in the illustrated example) of joints 31 are provided at predetermined intervals in each corrugated recess 24 </ b> B, and the area (length) of each joint 31 from the inlet side to the outlet side. Is gradually becoming smaller. The corrugated recess 24B forms a gas flow path GC of the cathode gas shown in FIG. 3A, and is joined to the anode-side separator at the corrugated convex portion (24A) on the back side.

  The joint 31 in the separator 4 shown in FIG. 4 (C) is formed by local welding such as spot welding or adhesion using a conductive adhesive, and has a certain size and the interval thereof is changed. Yes. In the illustrated separator 4, the same number (15 in the illustrated example) of joints 31 are arranged in each corrugated recess 24 </ b> B, and the interval between the joints 31 is gradually increased from the inlet side toward the outlet side. Yes.

  In the fuel cell stack FS described above, the separators 3 and 4 have the flow path forming portions 23 and 24 having a corrugated cross section, and the corrugated convex portions 23A and 24A are disposed between the two single cells C adjacent in the stacking direction. It has the junction part 31 to join. This fuel cell stack FS has a larger amount of swelling in the membrane electrode assembly 2 because the area of the joined portion 31 per unit area is larger than a region where the swelling amount in the membrane electrode assembly 2 is relatively large. Since the joining portion 31 is arranged accordingly, even when the waveform pitch of the separators 3 and 4 is reduced, the in-plane displacement between the separators 3 and 4 due to swelling of the membrane electrode assembly 2 is prevented. And the deformation | transformation of the separators 3 and 4 by this shift | offset | difference, ie, the deformation | transformation which a mutually corrugated wave, can be prevented.

  In addition, the fuel cell stack FS prevents the separators 3 and 4 from being deformed, thereby ensuring conductivity between the separators 3 and 4, and a cooling fluid flow path F formed between the separators 3 and 4. (See FIG. 3B) can also be prevented to prevent a decrease in cooling efficiency.

  Furthermore, since the flow path forming portions 23 and 24 of the separators 3 and 4 have a sinusoidal cross section in the fuel cell stack FS, the separators 3 and 4 that are likely to be displaced in the in-plane direction, in other words, the flow The separators 3 and 4 having a small waveform pitch of the path forming portions 23 and 24 and a large number of irregularities, that is, the gas diffusibility in the membrane electrode assembly 2 is good, and the electric resistance loss between the path formation portions 23 and 24 is low. Small separators 3 and 4 can be employed.

  The fuel cell stack FS employs the separators 3 and 4 described above, and prevents the separators 3 and 4 from shifting in the in-plane direction due to swelling of the membrane electrode assembly 2. The deformation of 4 can be prevented beforehand. That is, the fuel cell stack FS achieves both gas diffusibility, reduction in electrical resistance loss, and prevention of displacement and deformation of the separators 3 and 4. Further, the fuel cell stack FS increases the area of the junction 31 per unit area with respect to the region where the swelling amount of the membrane electrode assembly 2 during power generation is relatively large, thereby reducing the area of the junction 31. It becomes more suitable, and the deformation preventing effect of the separators 3 and 4 is further enhanced.

  Further, since the fuel cell stack FS has the joint 31 formed by at least one of welding and a conductive adhesive, the joint 31 can be easily formed in the manufacturing process of the single cell C or the fuel cell stack FS. In addition, the through electric resistance between the separators 3 and 4 is very small, and further improvement in power generation performance can be realized.

Second Embodiment
The embodiment shown in FIG. 5 is suitable for the fuel cell FS in which the humidification of the cathode gas (air) is low. In the fuel cell FS in which the humidification of the cathode gas is low, as shown in FIG. 5 (A), the amount of swelling in the thickness direction of the membrane electrode assembly 2 changes in the gas flow direction and rises from the inlet side to the middle part It becomes a peak and decreases from the middle part to the outlet side.

  Therefore, the cathode-side separator 4 shown in FIG. 5B is swelled in the membrane electrode assembly (or during power generation) with respect to the junction 31 with the anode-side separator (not shown) disposed on the lower surface side. The area of the joint portion 31 per unit area is increased with respect to a peak region having a relatively large amount of swelling. Moreover, the separator 4 reduces the area of the junction 31 on the entrance side of the peak region, and gradually decreases the area of the junction 31 from the peak region toward the exit side.

  The joint portion 31 in the separator 4 shown in FIG. 5B is formed by continuous welding such as seam welding using a roller electrode, or adhesion using a conductive adhesive, and its area (length) is changed. ing. In the illustrated separator 4, the same number (four in the illustrated example) of joints 31 are provided in each corrugated recess 24B at a predetermined interval, and the area (length) of the second joint 31 corresponding to the peak region is maximized. I have to.

  In the fuel cell stack FS provided with the separator 4, the separators 3, 4 caused by swelling of the membrane electrode assembly 2 are obtained even when the waveform pitch of the separators 3, 4 is reduced, as in the previous embodiment. In the in-plane direction, and the deformation of the separators 3 and 4 due to the deviation can be prevented.

<Reference example>
6A and 6B are cross-sectional views (A) and (B) for explaining specific examples of the separator. In the illustrated separator 3, a corrugated convex portion 23 </ b> A and a corrugated concave portion 23 </ b> B are formed by press working using a stainless steel plate having a thickness of 0.1 mm as a material.

  When the separator 3 has a corrugated pitch Pt shown in FIG. 6B, that is, when the interval between the center lines of the adjacent corrugated convex portions 23A is 1.4 mm, as shown in a dotted circle in the figure, the corrugated convex portions 23A There will be almost no flat surface at the top. This also affects the molding limit in press working.

  Therefore, as shown in FIG. 6A, when the corrugated pitch Pt is increased to about 1.8 mm, a flat surface is formed at the top of the corrugated recess 23A (indicated by a dotted circle). If there is such a flat surface, when the corrugated convex portions of the separator are brought into contact with each other, the corrugated convex portion is not easily dropped into the corrugated concave portion even if they are displaced in the in-plane direction.

  However, in the separator 3, when the corrugated pitch Pt is increased, the contact area between the corrugated convex portion 23A and the gas diffusion layer of the membrane electrode assembly 2 decreases, and the electrical resistance loss between the membrane electrode assembly and the separator 3 increases. To do. Further, when the waveform pitch Pt is increased in order to prevent the electrical resistance loss, the gas diffusibility in the portion covered with the plane of the waveform convex portion is lowered and the concentration overvoltage is increased.

  Therefore, the separator 3 reduces the corrugated pitch Pt and increases the number of concaves and convexes, thereby ensuring the overall contact area while maintaining gas diffusibility at the portion where the corrugated convex portions are in contact with each other. It is possible to achieve both reduction of loss and reduction of concentration overvoltage. The fuel cell stack of the present invention uses the separators 3 and 4 described above, and solves the problems caused by the wave shape of the cross section of the separator and the swelling of the membrane electrode assembly. In addition, each numerical value of the thickness of the above-described separator material and the waveform pitch Pt is an example, and is not limited to this.

  The fuel cell stack according to the present invention is not limited to the above embodiments, and the material, shape, size, number, and the like of each member are changed without departing from the gist of the present invention. can do. For example, it is possible to provide both a joint by welding and a joint by adhesion using a conductive adhesive in one separator, and what kind of joint is provided is required performance, manufacturing conditions, etc. Depending on the case, it can be appropriately selected.

C Single cell F Cooling fluid flow path FS Fuel cell stack GA, GC Gas flow path 2 Membrane electrode assembly 3 Anode side separator 4 Cathode side separator 23, 24 Flow path forming part 23A, 24A Waveform convex part 23B, 24B Waveform Recess 31 Joint

Claims (3)

A fuel cell stack having a structure in which a rectangular unit cell formed by sandwiching a membrane electrode assembly between a pair of separators is used as a power generation element, and a plurality of the unit cells are stacked,
The separator has a flow path forming portion with a sinusoidal cross section for forming a flow path for the reaction gas inside the single cell and a flow path for the cooling fluid outside the single cell, and at both ends. Each has a manifold hole for reaction gas,
Each of the flow paths formed by the flow path forming portion has a linear shape from the manifold hole on one end side to the manifold hole on the other end side,
Between the two single cells adjacent to each other in the stacking direction has a joint that joins the corrugated convex portions of the separator,
A fuel cell stack, wherein the area of the junction per unit area is gradually decreased from the inlet side toward the outlet side in the flow direction of the cathode gas as the reaction gas .   The fuel cell stack according to claim 1, wherein the joint portion is formed by at least one of welding and a conductive adhesive.   The fuel cell stack according to claim 1 or 2, wherein the separator is made of metal, and the joint is formed by welding.

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