Fuel-cell single cell

A fuel-cell single cell has a membrane electrode assembly sandwiched between a pair of separators, and a sealing member that seals a gas channel formed between the membrane electrode assembly and the separators. An uneven portion is formed in a part of the membrane electrode assembly where the sealing member is disposed. A sealing member sump to trap the sealing member is provided at a side exposed to reactant gas pressure and a holder part for the sealing member are provided within a part of the separators where the sealing member is disposed. The uneven portion is opposed to the holder part.

BACKGROUND

Technical Field

The present invention relates to an improvement of fuel cells such as polymer electrolyte fuel cells, and to a fuel-cell single cell which is stacked to constitute a fuel cell stack.

Related Art

Fuel cells have been known which use hydrogen-containing anode gas and oxygen-containing cathode gas as reactant gas to generate electric energy by an electrochemical reaction. Such fuel cells are divided into various types according to the electrolyte used, one of which uses a polymer electrolyte membrane.

Patent Document 1 discloses a fuel cell stack that is constituted by a stacked plurality of fuel-cell single cells, each of which includes a membrane electrode assembly (MEA) composed of a polymer electrolyte membrane and anode and cathode electrodes disposed on both sides thereof, and separators disposed on both sides of the membrane electrode assembly.

CITATION LIST

Patent Literature

SUMMARY OF INVENTION

In such fuel cell stacks as disclosed in Patent Document 1, the components including a membrane electrode assembly and separators are bonded to each other by means of an adhesive in order to provide a sealing property between the components. However, in such fuel cell stacks, since the adhesive is disposed at the edge part of the components and around a manifold of reactant gas, the adhesive that sticks out to the outside of the components or to the manifold may decrease the sealing performance.

One or more embodiments of the present invention provides a fuel-cell single cell that may be capable of achieving improved sealing performance.

A fuel-cell single cell according to one or more embodiments of the present invention includes a membrane electrode assembly sandwiched between a pair of separators, and a sealing member that seals a gas channel formed between the membrane electrode assembly and the separators. Further, in the fuel-cell single cell, an uneven portion is formed in the part of the membrane electrode assembly where the sealing member is disposed, and a sealing member sump is provided at a side exposed to reactant gas pressure and a holder part for the sealing member are provided within the part of the separators where the sealing member is disposed, in which the uneven portion is opposed to the holder part. In this configuration, a material that also serves as an adhesive can be used for the sealing member. The term “a side exposed to reactant gas pressure” refers to a side on which the pressure of reactant gas acts, specifically the inner side of gas channels and manifold holes for supplying or discharging the reactant gas.

With the above-described configuration, the pressure of the reactant gas acts on the end of the sealing member filling the sealing member sump so that the sealing member is in tight contact with the separators and the membrane electrode assembly. The fuel-cell single cell according to one or more embodiments of the present invention can therefore have improved sealing performance. Further, in the fuel-cell single cell, the uneven portion is formed in the part of the membrane electrode assembly where the sealing member is disposed. This increases the contact area between the membrane electrode assembly and the sealing member and thereby enables retaining both of a function of improving the adhesion strength and a function of transferring a load in the stacking direction. Furthermore, the contact area with the sealing member is increased and a long penetration path in the interface between them is secured, thereby provide a structure, in which a gas leak does not occur.

DETAILED DESCRIPTION

Embodiments of the present invention will be described below with reference to the drawings. In embodiments of the invention, numerous specific details are set forth in order to provide a more thorough understanding of the invention. However, it will be apparent to one of ordinary skill in the art that the invention may be practiced without these specific details. In other instances, well-known features have not been described in detail to avoid obscuring the invention. A fuel cell stack FS ofFIGS. 1(A)-1(B)includes, particularly as illustrated inFIG. 1(B), a stacked plurality of cell modules M, each of which includes a stacked predetermined number of fuel-cell single cells C, and a sealing plate P interposed between the plurality of cell modules M.FIG. 1(B)illustrates only two cell modules M and one sealing plate P, but in practical use, more cell modules M and sealing plates P are stacked.

The fuel cell stack FS further includes end plates56A,56B disposed in both ends of the cell modules M in the stacking direction, fastening plates57A,57B disposed on both surfaces corresponding to the long sides of the fuel-cell single cells C (the upper and lower surfaces inFIGS. 1(A)-1(B)), and reinforcing plates58A,58B disposed on both surfaces corresponding to the short sides. The fastening plates57A,57B and the reinforcing plates58A,58B are coupled to both of the end plates56A,56B by bolts (not shown).

As described above, the fuel cell stack FS has a case-integrated structure as illustrated inFIG. 1(A), in which the cell modules M and the sealing plate P are restrained and pressed in the stacking direction so that a predetermined contact pressure is applied on each of the fuel-cell single cells C. With this structure, the gas sealing and the electrical conductivity are maintained at high level.

As illustrated inFIG. 2, each of the fuel-cell single cells C includes a membrane electrode assembly1, a pair of separators2,2sandwiching the membrane electrode assembly1. The membrane electrode assembly1and the separators2,2form gas channels GC, GA respectively for cathode gas and anode gas therebetween.

The membrane electrode assembly1, which is generally referred to as an MEA (membrane electrode assembly), includes an electrolyte layer of a solid polymer that is interposed between a cathode layer and an anode layer, although they are not shown in detail in the figure. In one or more embodiments of the present invention, the membrane electrode assembly1further includes a resin frame1A integrally formed at the outer periphery thereof.

The frame1A is integrally formed with the membrane electrode assembly1, for example, by injection molding. In one or more embodiments of the present invention, the frame1A is formed in a rectangular shape, and the membrane electrode assembly1is located at the center. In the frame1A, manifold holes H1to H3and H4to H6are provided, which are arranged such that each short side has three manifold holes. Areas between the manifold holes and the membrane electrode assembly1serve as diffuser parts. The frame1A and the separators2,2have a rectangular shape with substantially the same size and shape.

Further, the frame1A includes a plurality of round protrusions1B arranged in a matrix in the diffuser parts. When the single cells C deform in the thickness direction due to a change of the membrane electrode assembly1over time or the like, these protrusions1B come in contact with the separators2,2to secure the space where the reaction gas flows.

The separators2are metal plates in which one plate has reversed faces to those of the other plate. For example, the separators2are made of stainless steel, and may be formed in any suitable shape by press working. The separators2of one or more embodiments of the present invention have an uneven cross-sectional shape at least in the center part corresponding to the membrane electrode assembly1. The uneven cross-sectional shape of the separators2continues in the length direction. The apexes of the corrugation are in contact with the membrane electrode assembly1while the bottoms of the corrugation form the cathode and anode gas channels (GC, GA) between the bottoms and the membrane electrode assembly1. Further, each of the separators2has manifold holes H1to H6similarly to the frame1A at both ends.

The frame1A and membrane electrode assembly1and the two separators2,2are laminated together as illustrated inFIG. 3(A)to form the fuel cell C. A predetermined number of fuel cells C (four fuel cells inFIGS. 3(A)-3(B)) are stacked to from the cell module M. In this regard, two adjacent fuel-cell single cells C form a channel F for cooling fluid (e.g. water) therebetween, and two adjacent cell modules M also form a channel F for cooling fluid therebetween.

The manifold holes H1to H3on the left inFIG. 2are configured respectively to supply anode gas (H1), to discharge cooling fluid (H2) and to discharge cathode gas (H3) from the top. These manifold holes are communicated with corresponding manifold holes in the stacking direction to form respective channels. The manifold holes H4to H6on the right inFIG. 2are configured respectively to supply the cathode gas (H4), to supply the cooling fluid (H5) and to discharge the anode gas (H6) from the top. These manifold holes are communicated with corresponding manifold holes in the stacking direction to form respective channels. The positional relationship of the manifold holes H1to H6may be partly or fully reversed in respect of supply and discharge.

Further, in the fuel-cell single cell C, as illustrated inFIG. 2, sealing members S1, S2are provided between the frame1A and the separators2at the edge part thereof and around the manifold holes H1to H6. InFIG. 2, the sealing members S1, S2are partly overlapped with each other. The sealing members S1, S2, which also have a function as an adhesive, airtightly separate the gas channels GC, GA for the cathode gas and the anode gas from each other within respective interlayers. Further, openings are provided at suitable locations around the manifold holes H1to H6to lead corresponding fluids to the interlayers. In the fuel cell stack FS, the separators2of adjacent fuel-cell single cells are airtightly joined to each other at the outer periphery thereof so as to seal the channel F for the cooling fluid.

The sealing plate P is formed as a separate piece from the above-described fuel-cell single cells C. As illustrated inFIG. 1(B), manifold holes H1to H6are formed on both ends of a plate base50similarly with the frame1A and the separators2.

The plate base50is molded from a single electrically-conductive metal plate. The plate base50is formed in substantially the same shape and size as the above-described fuel-cell single cells C in the plan view. Since the plate base50is constituted by the electrically-conductive metal plate, it can provide stable electrical connection over time.

In the sealing plate P, sealing members51are formed around each of the manifold holes H1to H6. Further, an outer sealing member52is formed along the outermost edge of the plate base50, and an inner sealing member53is formed along the inner side of the outer sealing member52with a predetermined distance. These sealing members are individually formed all over the periphery in an endless shape. The sealing members51around the manifold holes H1to H6are formed independently from each other. These sealing members51to53are different components from the above-described sealing members S1, S2interposed between the frame1A and separators2.

As illustrated inFIG. 3(A), the sealing plate P prevents a leak of the cooling fluid flowing through the cooling fluid channel between the cell modules M by means of the inner sealing member53, and also keeps back rainwater from the outside by means of the outer sealing member52. The sealing plate P also provides electrical insulation. InFIG. 3(A), reference sign9designates an adhesive.

In the above-described fuel cell stack FS, each of the cell modules M is constituted by a stacked predetermined number of fuel-cell single cells C, and the sealing plate is configured to be easily detachable from the cell modules M. Therefore, if there is a defect in one of the fuel-cell single cells C, it is possible to exchange only the cell module M that includes the faulty fuel-cell single cell C. Therefore, it is advantageous that the other fuel-cell single cells C and cell modules M can be further used continuously.

As described above, each of the fuel-cell single cells C of the above-described fuel cell stack FS includes the membrane electrode assembly1sandwiched between the separators2,2, and the sealing members S1, S2that seals the gas channels (GC, CA) formed between the membrane electrode assembly1and the separators2. The membrane electrode assembly1includes the resin frame1A at the outer periphery thereof.

As illustrated inFIG. 3(B)andFIGS. 4(A)-4(B), each of the above-described fuel-cell single cells C includes a sealing member sump2A to hold the sealing members S1, S2, which is formed at a side exposed to reactant gas pressure within the part of the separators2where the sealing member S is disposed. The term “a side exposed to reactant gas pressure” refers to a side on which the pressure of the reactant gas acts, for example the inner side of the gas channels GC, GA and the inner side of the manifold holes H1to H6.

That is, for the sealing members51disposed at the edge part of the frame1A and the separators2, the sealing member sumps2A are disposed at the side with the reactant gas, i.e. at least at the side with the gas channels GC, GA. For the sealing members S2disposed around the manifold holes H1to H6, since the reactant gas or the cooling fluid may be present on both sides thereof, the sealing member sumps2A are disposed at least at the side exposed to higher pressure or at both sides.

In the embodiment ofFIG. 3(B), for the sealing members S1disposed on the edge part of the frame1A and the separators2, the sealing member sumps2A are formed at both sides of the part of the separators2where the sealing members S1are disposed. Specifically, a part of the separators2is bent outward with respect to the membrane electrode assembly1so that the bent part serves as the sealing member sump2A. Further, in the separators2, the flat parts between both sealing member sumps2A,2A serve as holder parts2B for the sealing members S1. In the embodiment ofFIG. 3(B), the sealing member sump2A is not provided for the sealing members S2disposed around the manifold holes H1to H6.

According to one or more embodiments of the present invention, the fuel-cell single cell C may include an uneven portion that is formed in at least one of the membrane electrode assembly1and the separators2within the part where the sealing members S1, S2are disposed. In one or more embodiments of the present invention, since the membrane electrode assembly1includes the frame1A, the uneven portion is formed in at least one of the frame1A and the separators2.

In the embodiment ofFIG. 3(B), uneven portions are provided within the parts where the sealing members S1, S2are disposed, by forming a plurality of protrusions10A in the frame1A at predetermined intervals. That is, the uneven portions of the frame1A are opposed to holder parts2B of the separators2. On the other side (outer side) from the holder parts2B, the inner sealing member53and the sealing member51of the sealing plate P are disposed.

In the embodiments ofFIGS. 4(A) and 4(B), double-sided sealing member sumps2A and holder parts2B are provided in the separators2for the sealing members S1, S2disposed respectively in the edge part of the frame1A and the separators2and around the manifold holes H1to H6. In the embodiments ofFIGS. 4(A)-4(B), the above-described uneven portion is not provided, but the inner sealing member53of the sealing plate P is disposed on the other side of the holder parts2B. Particularly in the embodiment ofFIG. 4(A), recesses2C are formed in the holder parts2B to position the inner sealing member53of the sealing plate P.

In the embodiments ofFIGS. 5(A) and 5(B), the separators2include sealing member sumps2A and holder parts2B. Further, uneven portions are provided in the part of the frame1A where the sealing members S1, S2are disposed by forming a plurality of recesses10B at predetermined intervals. In the embodiments ofFIG. 5(A), the recesses10B are identically formed on both sides of the frame1A. In the embodiments ofFIG. 5(B), the recesses10B are alternately formed on both sides of the frame1A.

The above-described fuel-cell single cells C can be manufactured by the following method. To manufacture the fuel-cell single cell C that includes the membrane electrode assembly1sandwiched between the pair of separators2,2, and the sealing members S1, S2that seal the gas channels CG, AG formed between the membrane electrode assembly1and the separators2,2, the sealing member sumps2A for the sealing members S1, S2are formed at a side exposed to reactant gas pressure within the part of the separators2where the sealing members S1, S2are disposed.

After the sealing members S1, S2are disposed within the sealer disposing part of the separators2, the separators2and the membrane electrode assembly1are joined to each other to form the gas channels CG, Ag sealed by the sealing members S1, S2between them. Along with this, the sealing members S1, S2are trapped in the sealing member sumps2A so that they can receive a reactant gas pressure.

In the above-described fuel-cell single cells C, since the sealing member sumps2A for the sealing members S1, S2are provided at a side exposed to reactant gas pressure within the part of the separators2where the sealing members S1, S2are disposed, the ends of the sealing members S1, S2are formed into nubs filling the sealing member sumps2A as illustrated inFIG. 3(B),FIGS. 4(A)-4(B)andFIGS. 5(A)-5(B).

Therefore, in the fuel-cell single cells C, a reactant gas pressure acts on the ends (end faces) of the sealing members S1, S2filling the sealing member sumps2A to press the sealing members S1, S2so that they are in tight contact with the separators2and the frame1A of the membrane electrode assembly1. As a result, an improvement of the sealing performance can be achieved. Further, by the method of producing the fuel-cell single cell C, such fuel-cell single cells with high sealing performance can be readily produced.

In the fuel-cell single cell C, the uneven portions are formed in at least one of the frame1A of the membrane electrode assembly1and the separators2, specifically within the parts of the frame1A where the sealing member S1, S2are disposed in the embodiments ofFIG. 3(B)andFIGS. 5(A)-5(B). They increase the contact area between the frame1A and the sealing members S1, S2, and thereby can retain both of a function of improving the adhesion strength and a function of transferring a load in the stacking direction. In particular, the uneven portions constituted by the protrusions10A as illustrated inFIG. 3(B)can reduce the gap between the frame1A and the separators2, which further improves the function of transferring a load in the stacking direction.

Further, in the fuel-cell single cells C, the uneven portions formed in the frame1A as described above can secure a long penetration path in the interface between the frame1and the separators2as well as increasing the contact area with the sealing members S1, S2. That is, in this type of fuel-cell single cells, the tensile shear adhesion strength of the sealing members S1, S2to the frame1A is gradually reduced through exposure to pulsation of the reactant gas or the like over a long time, and the reactant gas or a product eventually penetrates into the interface between them.

In contrast, in the fuel-cell single cells C, the uneven portions secure a sufficient length of the interface from the gas channels GC, GA to the outside between the frame1A and the sealing members S1, S2. Therefore, the reactant gas or a product does not reach the outside (a gas leak does not occur) even when the fuel-cell single cell C is used beyond its service life.

FIGS. 6(A)-6(C)are graphs illustrating the durability of the sealing members S1, S2of the fuel-cell single cell C according to one or more embodiments the present invention. As illustrated inFIG. 6(A), it is possible to extend the durability life by forming the uneven portion in the frame1A so as to increase the contact area with the sealing members S1, S2. As illustrated inFIG. 6(B), it is possible to extend the durability life by increasing the number of protrusions/recesses because it results in the increased contact area between the frame1A and the sealing members S1, S2. As illustrated inFIG. 6(C), it is possible to extend the durability life by increasing the contact area (the number of protrusions/recesses) between the frame1A and the sealing members S1, S2so as to increase the penetration length in the interface.

Further, in the fuel-cell single cell C, the uneven portions of the frame1A of the membrane electrode assembly1are opposed to the holder parts2B of the separators2as illustrated inFIG. 3(B)andFIGS. 5(A)-5(B). Therefore, the fuel-cell single cells C can firmly hold the sealing members S1, S2in the predetermined places and also adequately transfer a load in the stacking direction when they are assembled into the fuel cell stack FS.

Further, in the fuel-cell single cell C, the sealing members51to53of the sealing plate P are disposed on the outer face of the holder parts2B as illustrated inFIG. 3(B)andFIGS. 4(A)-4(B). That is, the sealing members S1, S2interposed between the frame1A and the separators2are aligned with the sealing members51to53of the sealing plate P in the stacking direction. With this configuration, the fuel-cell single cells C can firmly hold the sealing members51to53of the sealing plate P in the predetermined places and also adequately transfer a load in the stacking direction through the sealing plate P.

Further, in the fuel-cell single cell C, the membrane electrode assembly1integrally includes the resin frame1A, and the sealing members S1, S2are interposed between the frame1A and the separators2. This structure provides high sealing performance at the outer side of the power generating area of the membrane electrode assembly1and can also facilitate forming machined parts including the sealing member sumps2A, the holder parts2B and the uneven portions (protrusions10A and recesses10B) without causing any negative influence on the power generating area.

In association with the improvement in durability of the above-described fuel-cell single cell C, the durability of the fuel cell stack FS, which is constituted by stacked fuel-cell single cells C, is also improved. Further, the improvement in load transfer in the stacking direction can equalize the surface pressure and the contact resistance between the fuel-cell single cells C and also equalize the power generation performance of each of the fuel-cell single cells C.

The configuration of the fuel-cell single cell is not limited to those of the above-described embodiments, and detail of the configuration may be suitably changed and the configurations of the above-described embodiments may be suitably combined with each other without departing from the gist of the present invention. For example, in one or more of the above-described embodiments, the uneven portion is formed within the part of the frame1A of the membrane electrode assembly1where the sealing members are disposed. Instead, the uneven portion may be formed within the part of the separators2where the sealing members are disposed. The uneven portion may be formed by a physical process or by a chemical process of surface modification (e.g. UV, plasma, corona, etc.).

REFERENCE SIGNS LIST