Fuel cell and fuel cell stack

A fuel cell includes: a membrane electrode assembly having an electrolyte membrane, an anode disposed on one side of the electrolyte membrane, and a cathode disposed on the other side thereof; a porous passage that is disposed on at least one side of the membrane electrode assembly, and through which a fuel gas is supplied to the anode or an oxidant gas is supplied to the cathode; and a manifold portion-, through which the fuel gas or the oxidant gas is supplied to the porous passage, and that is provided so as to pass through the fuel cell in a stacking direction, in which the electrolyte membrane, the anode, the cathode, and the porous passage are stacked, wherein a manifold portion-side end portion of the porous passage has a gas inlet at least one of stacking surfaces of the porous passage that face in the stacking direction.

This is a 371 national phase application of PCT/IB2011/002934 filed 5 Dec. 2011, claiming priority to Japanese Patent Application No. 2010-271956 filed 6 Dec. 2010, the contents of which are incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates to a fuel cell and a fuel cell stack. More specifically, the invention relates to a fuel cell including a metal porous body that serves as a gas passage layer, and a fuel cell stack including the fuel cell.

2. Description of Related Art

A polymer electrolyte fuel cell includes a membrane electrode assembly that is fowled by stacking a catalyst layer and a gas diffusion layer, in this order, on each side of an ion-permeable electrolyte membrane. The membrane electrode assembly is held between two gas passage layers, and the membrane electrode assembly held between the gas passage layers are held between two separators. In this way, a single cell is formed. Multiple cells are assembled together to form a fuel cell stack. Fuel gas that contains hydrogen is supplied to an anode (negative electrode), and an electrochemical reaction expressed by formula (1) below occurs, thereby producing protons from the fuel gas at the anode. The produced protons pass through the electrolyte membrane to reach a cathode (positive electrode). Oxidant gas that contains oxygen is supplied to the cathode (positive electrode), and an electrochemical reaction expressed by formula (2) below occurs, in which the oxygen reacts with protons from the anode (negative electrode), so that water is produced. The electrochemical reactions that occur at the electrolyte membrane-side surfaces of the paired electrodes are used to obtain electric energy from the electrodes.
Anode reaction: H2→2H++2e−(1)
Cathode reaction: 2H++2e−+(½)O2→H2O  (2)

A fuel cell configured as described above is available, in which a metal porous body that is excellent in gas diffusion properties and electrical conductivity is used as the gas passage layer in order to supply fuel gas or oxidant gas to the electrode and collect electricity generated through the electrochemical reactions. Examples of the metal porous body include an expanded metal and a sintered metal foam. Conventional methods for producing the metal porous body include cutting and expanding a titanium sheet, a stainless steel sheet, or the like. For example, slits are made in a titanium sheet, a stainless steel sheet, or the like in a staggered manner and the sheet with slits is expanded by being stretched so that a mesh metal sheet, that is, an expanded metal is obtained.

The metal porous body obtained by cutting and expanding a metal sheet, in the above-described manner is cut into pieces having a given size in accordance with the external dimensions of the fuel cell. The obtained pieces are disposed on the respective sides of the membrane electrode assembly so that the fuel cell is faulted. The metal porous body may be cut into pieces by a laser cutter, or with the use of a die (Japanese Patent Application Publication No. 2010-80201 (JP-A-2010-80201)). With this method, a surface pressure or heat applied to the metal porous body may break an end surface of the metal porous body, which is a cut end surface, thereby causing clogging of pores. As shown inFIG. 7, an end surface40of a metal porous body functions as an inlet for gas that is supplied through a gas supply manifold portion20. Therefore, clogging of the pores in an end surface portion of the metal porous body increases loss of gas introduction pressure, which may decrease, for example, the amount of gas that is supplied to the electrode, gas diffusivity, and electric power generation performance of the fuel cell.

SUMMARY OF THE INVENTION

The invention provides a fuel cell in which a sufficient amount of fuel gas or oxidant gas is supplied to an electrode regardless of the degree of clogging at an end surface portion of a metal porous body, and also provides a fuel cell stack including the fuel cell.

A first aspect of the invention is a fuel cell that includes: a membrane electrode assembly including an electrolyte membrane, an anode disposed on one side of the electrolyte membrane, and a cathode disposed on the other side of the electrolyte membrane; a porous passage that is disposed on at least one side of the membrane electrode assembly, and through which a fuel gas is supplied to the anode or an oxidant gas is supplied to the cathode; and a manifold portion, through which the fuel gas or the oxidant gas is supplied to the porous passage; and that is provided so as to pass through the fuel cell in a stacking direction, in which the electrolyte membrane, the anode, the cathode, and the porous passage are stacked, wherein a manifold portion-side end portion of the porous passage has a gas inlet at at least one of stacking surfaces of the porous passage that face in the stacking direction.

According to the first aspect, the porous passage that supplies the fuel gas or the oxidant gas has gas inlets at an end surface and at at least one of the stacking surfaces that face in the direction in which the membrane electrode assembly and the porous flow path are stacked. Therefore, regardless of the degree of clogging at the end surface portion of the porous passage, the fuel gas or the oxidant gas is reliably introduced into the porous passage through the stacking surface. Further, the gas inlet is not merely provided at the stacking surface of the porous passage, that is, the gas inlet is provided at the stacking surface(s) of the end portion of the porous passage, so that a power generation area of the membrane electrode assembly is not reduced. Thus, it is possible to improve the gas introduction efficiency while maintaining a sufficient size of power generation area. This makes it possible to reliably supply the fuel gas or the oxidant gas to the membrane electrode assembly and to improve the power generation performance of the fuel cell stack.

The fuel cell according to the first aspect may further include: a sealing member that is disposed between an outer end surface of the membrane electrode assembly and the manifold portion; and a shield member that is disposed between the sealing member and the porous passage, wherein a manifold portion-side end portion of the shield member extends further outward, with respect to the fuel cell, than a manifold portion-side end portion of the sealing member.

According to the fuel cell configured as described above, it is possible to prevent the situation where the sealing member adjacent to the porous passage permeates and clogs the pores of the porous passage, which may result in blockage of the gas inlet. Consequently, it is possible to reliably cause the fuel gas or the oxidant gas to flow from the gas inlet to the membrane electrode assembly and to be supplied thereto.

Further, in the fuel cell according to the first aspect, the manifold portion-side end portion of the porous passage may project into the manifold portion. Further, in the fuel cell, the manifold portion-side end portion of the shield member may extend further outward, with respect to the fuel cell, than the manifold portion-side end portion of the porous passage.

According to the fuel cell configured as described above, the fuel gas or the oxidant gas that passes through the manifold portion naturally flows into the porous passage. Therefore, the efficiency of the gas introduction from the manifold portion is improved. Further, the shield member can change the flow direction of the gas. This further facilitates the gas introduction into the porous passage, and promotes the gas introduced into the porous passage to flow further inward (inward in the fuel cell). Thus, it is possible to efficiently introduce a sufficient amount of fuel gas or oxidant gas into the porous passage and facilitate gas flow through the porous passage, thereby improving the power generation performance of the fuel cell stack.

The fuel cell according to the first aspect may further include: a sealing member that is disposed adjacent to a manifold portion-side end portion of the membrane electrode assembly, wherein a manifold portion-side end portion of one of the anode and cathode that is in contact with the porous passage extends further outward, with respect to the fuel cell, than a manifold portion-side end portion of the sealing member.

In the fuel cell according to the first aspect, a configuration may be employed, in which a separator having a projecting portion is disposed on one side of the membrane electrode assembly with the porous passage interposed between the separator and the membrane electrode assembly, the manifold portion and a space formed by the projecting portion of the separator communicate with each other, and the porous passage is provided such that a manifold portion-side edge of the porous passage is located at a position within a width of the projecting portion of the separator.

According to the fuel cell configured as described above, it is possible to introduce the fuel gas or the oxidant gas into the porous passage while suppressing a pressure loss of the gas inside the manifold portion.

A second aspect of the invention is a fuel cell stack including the fuel cell according to the first aspect.

According to the invention, it is possible to reliably supply the fuel gas or the oxidant gas to the membrane electrode assembly regardless of a cutting condition and porosity of an end surface portion of the porous passage, thereby providing a fuel cell stack with improved power generation performance.

DETAILED DESCRIPTION OF EMBODIMENTS

Hereafter, a first embodiment of the invention will be described with reference toFIGS. 1, 2A, 2B, 3A and 3B.FIG. 1shows a fuel cell stack1.FIG. 2Ais a plan view of a fuel cell2(hereinafter also referred to as “cell2”) viewed from the cathode side.FIG. 2Bis a plan view of the cell2viewed from the anode side. That is,FIG. 2Ashows one side of the cell2, andFIG. 2Bshows the other side of the cell2.FIG. 3Ais a sectional view taken along the line A-A inFIGS. 2A and 2B.FIG. 3Bis a sectional view taken along the line A2-A2inFIGS. 2A and 2B. As shown inFIG. 1, the fuel cell stack1is formed by stacking a plurality of unit cells2. The stacked cells2are electrically connected in series. Electric currents obtained through electric power generation at the cells2are collected at two current collector plates30that are provided at respective ends in a stacking direction of the stacked cells2. The collected electric currents are supplied to electric apparatuses such as an electric load and a secondary battery. Note that, although the fuel cell stack1is formed by stacking the multiple fuel cells2in the first embodiment, the fuel cell stack1may include only one fuel cell2.

The current collector plate30of the fuel cell stack1has a fuel gas inlet32a, an oxidant gas inlet34a, and a coolant inlet36athrough which a fuel gas, an oxidant gas, and a coolant are respectively introduced into the fuel cell stack1. Further, the current collector plate30has a fuel gas outlet32b, an oxidant gas outlet34b, and a coolant outlet36bthrough which the fuel gas, the oxidant gas, and the coolant are respectively discharged from the fuel cell stack1.

As shown inFIG. 2A, the cell2has, at an end portion of the outer periphery thereof, a fuel gas supply manifold portion18a, an oxidant gas supply manifold portion20a, and a coolant supply manifold portion22a. The cell2also has, at another end portion of the outer periphery thereof, a fuel gas discharge manifold portion18b, an oxidant gas discharge manifold portion20b, and a coolant discharge manifold portion22bat positions that are opposed to the positions of the above corresponding supply manifold portions. These supply and discharge manifold portions are each provided so as to pass through the cell2in the direction in which the cells2are stacked (hereinafter, referred to as “stacking direction”). When the cells2are stacked, passages for the fuel gas, the oxidant gas, and the coolant are formed.

The fuel gas supply manifold portion18a, the oxidant gas supply manifold portion20a, and the coolant supply manifold portion22acommunicate with the fuel gas inlet32a, the oxidant gas inlet34a, and the coolant inlet36a, respectively, which are formed in the current collector plate30of the fuel cell stack1. Similarly, the fuel gas discharge manifold portion18b, the oxidant gas discharge manifold portion20b, and the coolant discharge manifold portion22bcommunicate with the fuel gas outlet32b, the oxidant gas outlet34b, and the coolant outlet36b, respectively, which are formed in the current collector plate30of the fuel cell stack1.

The fuel gas is supplied to each cell2through the fuel gas supply manifold portion18athereof, flows diagonally inside the cell2, and is discharged from the cell2through the fuel gas discharge manifold portion18bthereof. Similarly, the oxidant gas is supplied to each cell2through the oxidant gas supply manifold portion20athereof, flows diagonally inside the cell2, and is discharged from the cell2through the oxidant gas discharge manifold portion20bthereof. The coolant is supplied to each cell2through the coolant supply manifold portion22athereof, flows through gaps between this cell2and another cell2that is positioned next to this cell2, and is discharged from this cell2through the coolant discharge manifold portion22bthereof. Note that in the first embodiment, the fuel gas supply manifold portion18aand the oxidant gas supply manifold portion20aare positioned diagonally opposite to the fuel gas discharge manifold portion18band the oxidant gas discharge manifold portion20b, respectively. However, the positions of the manifold portions and the flow directions of the gases may be changed as needed, as long as the fuel gas flows on one side of separator and the oxidant gas flows on the other side of the separator.

As shown inFIG. 2B, when viewed from the anode side, the cell2has various manifold portions at the end portions of the outer periphery thereof. The cell2has a recess, which is a projection on the back side, at a central portion thereof that forms passages extending from the coolant supply manifold portion22ato the coolant discharge manifold portion22b. Assuming that the cathode side is a front side and the anode side is a back side, the recess (projection) is formed by recessed portions42and projected portions44. The fuel gas flows along the recessed portions42and the coolant flows along the projected portions44. Further, stepped portions46are provided between the manifold portions at the end portions of the outer periphery and the recess (projection) at the central portion. One of the stepped portions46communicates with the fuel gas supply manifold portion18aand the recessed portions42, and causes the fuel gas supplied through the fuel gas manifold portion18afurther inward.

FIG. 3Ais a sectional view taken along the line A-A inFIG. 2A, and the arrows indicate how the oxidant gas is supplied to the cathode. The cell2includes a membrane electrode assembly6, a cathode-side porous passage8, an anode-side groove passage10, a sealing member12, separators14aand14b, and a shield member16. Note thatFIGS. 3A, 3B, 4, 5, and 6each show only left portions of the two cells2stacked. Note that reference numerals are assigned only to the components of the upper cell2.

The membrane electrode assembly6is fowled of an ion-conductive electrolyte membrane3, a cathode4that is disposed on one side of fife electrolyte membrane3, and an anode5that is disposed on the other side of the electrolyte membrane3. Protons and electrons are produced from the fuel gas supplied to the anode5. The protons pass through the electrolyte membrane3to reach the cathode4. These protons react with the oxidant gas supplied to the cathode4, whereby electric energy and water are produced. Examples of materials for the membrane electrode assembly6include the following. That is, an ion-exchange resin having a fluorine-containing polymer as a skeleton may be used as the material for the electrolyte membrane3. For the anode4and the cathode5, a conductive support formed by causing a carbon material (e.g. carbon black) to support a metal catalyst such as Pt or Au, may be used.

The porous passage8is fowled of a metal porous body such as an expanded metal or a metal sintered body, and is provided on the cathode side of the membrane electrode assembly6. An end portion of the porous passage8projects into the oxidant gas supply manifold portion20a. The cathode-side porous passage8communicates with the oxidant gas supply manifold portion20a. Through the porous passage8, the oxidant gas introduced through the oxidant gas supply manifold portion20ais supplied to the cathode5of the membrane electrode assembly6.

The separator14ais formed of a conductive flat plate made of metal such as aluminum or stainless steel, and is disposed on the surface of the porous passage8, which is on the opposite side of the porous passage8from the membrane electrode assembly6. The separator14ahas an opening at a position corresponding to the oxidant gas supply manifold portion20a, whereby the passage for the oxidant gas is formed. Similarly, the separator14ahas openings at positions corresponding to the fuel gas supply manifold portion18a, the coolant supply manifold portion22a, the fuel gas discharge manifold portion18b, the oxidant gas discharge manifold portion20b, and the coolant discharge manifold portion22b(not shown inFIGS. 3A and 3B).

As shown inFIG. 3B, between the oxidant gas supply manifold portion20aand the projected portions44at the central portion of the cell2, the stepped portion46of the separator14bis formed so as to project in the stacking direction toward the adjacent cell. The separator14bis in contact with the membrane electrode assembly6and the sealing member12at the oxidant gas supply manifold portion20aside thereof. The separator14bis separate from the membrane electrode assembly6at the stepped portion46, and is in contact with the membrane electrode assembly6also at the projected portions44at the central portion of the cell2. Thus, a space50is formed between the separator14band a separator14aof the adjacent cell, through which the coolant flows. That is, the coolant supplied through the coolant supply manifold portion22a(not shown inFIG. 3B) flows between the separator14band the adjacent cell2to cool the cells2. Note that, in the first embodiment; the projections and recesses are fowled on both sides of the separator14b, and the projections and recesses on one side match the recesses and projections on the other side, respectively. Alternatively, the separator14bmay be formed such that one side thereof is flat and the other side thereof has projections and recesses.

The shield member16and the sealing member12are disposed between the porous passage8and the separator14bat the oxidant gas supply manifold portion20aside of the cell2. The shield member16is made of metal such as aluminum or stainless steel. An oxidant gas supply manifold portion20a-side end portion of the shield member16extends further outward, with respect to the cell2, than the end portion of the porous passage8. The other end portion of the shield member16extends further inward, with respect to the cell2, than the end portion of the cathode4so as to be held between the cathode4and the porous passage8. With the structure described above, it is possible to prevent the situation where the sealing member12permeates and clogs the pores of the porous passage8to reduce porosity. Note that the feature that the end portion of the shield member16extends outward with respect to the cell2means that the end portion of the shield member16extends outward, with respect to the cell2, in the plane of the shield member16.

The sealing member12is provided, adjacent to an end surface of the membrane electrode assembly6and the groove passages10, on the opposite side of the shield member16from the porous passage8, so as to seal a gap between the oxidant gas supply manifold portion20a, and the membrane electrode assembly6and the groove passages10. Therefore, the oxidant gas supplied through the oxidant gas supply manifold portion20ais supplied to the membrane electrode assembly6through the porous passage8without leaking to the anode5or the groove passages10.

Gaskets13are disposed between the separator14bof the cell2and the separator14aof the adjacent cell2. The gaps fowled between these separators14band14aform passages for the coolant.

In the fuel cell2according to the first embodiment, the oxidant gas supplied to the oxidant gas supply manifold portion20ais supplied to the cathode4through an end portion of a separator14a-side stacking surface of the cathode-side porous passage8, the stacking surface being a surface facing in the stacking direction. Therefore, even if the porosity of an end surface portion of the porous passage8is low, a sufficient amount of oxidant gas is introduced into the porous passage8and supplied to the cathode4, whereby it is possible to improve the power generation performance of the fuel cell stack1. Moreover, it is possible to prevent the situation where the sealing member12adjacent to the porous flow path8permeates the porous passage8to cause clogging that may result in blockage of the gas inlet. Thus, it is possible to reliably cause the fuel gas or the oxidant gas to flow from the gas inlet to the membrane electrode assembly6and to be supplied thereto. Further; the end portion of the stacking surface of the porous passage8serves as the gas inlet. Therefore, the gas inlet is adjacent to the oxidant gas supply manifold portion20aand no complicated structure is required. Accordingly, it is possible to increase the gas introduction efficiency without reducing the power generation area (surface area), thereby achieving high power generation performance. Note that in the first embodiment, as indicated by the arrows inFIG. 3A, the oxidant gas is supplied from the anode side toward the cathode side. Alternatively, the oxidant gas may be supplied from the cathode side toward the anode side. When the oxidant gas is supplied from the anode side toward the cathode side as in the first embodiment, the direction in which the oxidant gas flows inside the manifold portion20aand the direction in which the oxidant gas is introduced into the porous passage8are opposite to each other. Therefore, the gas does not rapidly flow into the porous passage8, which makes it possible to supply gas uniformly to each cell2of the fuel cell stack1. On the other hand, when the oxidant gas is supplied from the cathode side toward the anode side, the shield member16functions as a guide, so that the gas is more efficiently introduced into the porous passage8.

Next, a second embodiment will be described with reference toFIG. 4. LikeFIG. 3A,FIG. 4is a sectional view taken along the line A-A inFIGS. 2A and 2B. Portions the same in structure as those inFIG. 3Awill not be described below.

In the second embodiment, the shield member16is not provided at the boundary between the porous passage8and the sealing member12, and the end portion of the cathode electrode4is extended in the direction of the oxidant gas supply manifold portion20a. At the oxidant gas supply manifold portion20aside, the end portion of the cathode4extends further outward, with respect to the cell2, than the end portion of the sealing member12. Thus, the cathode4covers the electrolyte membrane3and the sealing member12, thereby providing a shielding effect. Note that the feature that the end portion of the cathode electrode4extends outward with respect to the cell2means that the end portion of the cathode electrode4extends outward, with respect to the cell2, in the plane of the cathode electrode4. When a diffusion layer (not shown) is interposed between the cathode electrode4and the porous passage8, the end portion of the diffusion layer, in addition to or instead of the cathode electrode4, may extend further outward, with respect to the cell2, than the end portion of the sealing member12.

With the fuel cell having the above structure, the cell structure is simplified, so that it is possible to reduce the number of components. Further, the power generation area is not reduced by the shield member. Thus, it is possible to efficiently supply the fuel gas or the oxidant gas to the porous passage while ensuring a sufficient size of power generation area in the membrane electrode assembly.

A third embodiment will be described with reference toFIG. 5. LikeFIG. 3A,FIG. 5is a sectional view taken along the line A-A inFIGS. 2A and 2B. Portions the same in structure as those inFIG. 3Awill not be described below.

The end portion of the porous passage8is disposed further inward, with respect to the cell2, than the end portion of the shield member16at the oxidant gas supply manifold portion20aside. The separator14ahas a projecting portion at a position corresponding to the end portion of the porous passage8, and the end portion of the porous passage8is disposed at a position corresponding to the projecting portion of the separator14a. Therefore, the oxidant gas supplied through the oxidant gas supply manifold portion20ais introduced through the end surface and the upper surface of the end portion of the porous passage8and is supplied to the membrane electrode assembly6.

The separator14bhas a key-like bent portion along the outer periphery of the groove passages10. The projecting portion of the separator14ais fitted into the key-like bent portion of the separator14b. The coolant flows through the gaps between the separator14band the separator14aof the adjacent cell2.

With the fuel cell2according to the third embodiment, the oxidant gas supplied to the oxidant gas supply manifold portion20ais efficiently supplied to the cathode4through a portion of the upper surface of the porous passage8(the surface on the separator14aside), which is located at a position corresponding to the projecting portion of the separator14aand which serves as the gas inlet. Therefore, even when the porosity of the end surface portion of the porous passage8is low, a sufficient amount of oxidant gas is introduced into the porous passage8and supplied to the cathode4. Further, a pressure loss of the gas passage in the oxidant gas supply manifold portion20ais reduced. Consequently, the power generation performance of the fuel cell stack1is improved.

Next, a fourth embodiment will be described with reference toFIG. 6. LikeFIG. 3A,FIG. 6is a sectional view taken along the line A-A inFIGS. 2A and 2B. Portions the same in structure as those inFIG. 3Awill not be described below.

The end portion of the porous passage8is disposed further outward, with respect to the fuel cell2, than the end portion of the shield member16, projecting into the oxidant gas supply manifold portion20a. Note that in the fourth embodiment, the oxidant gas supply manifold portion20ais a throughhole that is fondled by the manifold holes provided in the separators14a,14b, which are aligned in the stacking direction, so as to pass through the fuel cell stack. At an end portion of the fuel cell stack in the stacking direction, the oxidant gas supply manifold portion20acommunicates with the oxidant gas inlet34afowled in the current collector plate30.

With the fuel cell2according to the fourth embodiment, the oxidant gas supplied to the oxidant gas supply manifold portion20ais introduced into the porous passage8from its lower surface in the stacking direction. Then, the oxidant gas flows in two directions. That is, the oxidant gas flowing in one direction passes through the porous passage8, is discharged into the oxidant gas supply manifold portion20a, and flows toward the next cell2, while the oxidant gas flowing in the other direction flows inside the porous passage8. Further, a portion of the oxidant gas once discharged from the porous passage8into the oxidant gas supply manifold portion20aturns around to be introduced into the porous passage8from its upper surface in the stacking direction. The oxidant gas thus introduced into the porous passage8from its upper and lower surfaces flows through the porous passage8, and is supplied to the membrane electrode assembly6. Thus, a sufficient amount of oxidant gas is introduced into the porous passage8from both the upper and lower stacking surfaces thereof. As result, regardless of the porosity of the end surface portion of the porous passage8, it is possible to reliably introduce the oxidant gas into the porous passage8, cause the oxidant gas to flow through the porous passage8, and supply the oxidant gas to the cathode4, thereby improving the power generation performance of the fuel cell stack1. Note that the flow direction and the flow rate of the oxidant gas may be changed depending on the pore size and shape of the porous passage8.

Note that in the above description of the first to fourth embodiments, specific description has been made of the mode of supplying the oxidant gas from the oxidant gas supply manifold portion20ato the cathode side porous flow path8. However, such embodiments are applicable also in the case of supplying the fuel gas from the fuel gas supply manifold portion18ato an anode-side porous passage10. In addition, in these embodiments, specific description has been made of the case where the oxidant gas flows through the oxidant gas supply manifold portion20afrom the anode side to the cathode side. However, the direction of flow of the oxidant gas is not limited to this. The oxidant gas may flow from the cathode side to the anode side.

The invention has been described with reference to example embodiments for illustrative purposes only. It should be understood that the description is not intended to be exhaustive or to limit form of the invention and that the invention may be adapted for use in other systems and applications. The scope of the invention embraces various modifications and equivalent arrangements that may be conceived by one skilled in the art.