Fuel cell stack

A fuel cell stack is provided having a plurality of unit cells stacked in a horizontal direction. Each unit cell includes an electrolyte membrane having two surfaces and a peripheral edge, electrodes provided on both surfaces of the electrolyte membrane, frame-shaped members provided on both surfaces of the electrolyte membrane adjacent to the respective electrodes and adjacent the peripheral edge of the electrolyte membrane, separators provided on the electrodes and the frame-shaped members and having a reactant gas passage for supplying a reactant gas to each of the electrodes, and a manifold formed in the stacking direction in fluid communication with the reactant gas passage. The manifold includes a horizontal edge portion in fluid communication with the reactant gas passage.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority to Japanese Patent Application No. 2008-077757 filed Mar. 25, 2008, and Japanese Application No. 2008-310622 filed Dec. 5, 2008, each of which is incorporated by reference herein in its entirety.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a fuel cell stack.

2. Description of the Related Art

In a conventional fuel cell stack, fuel cells are stacked in a horizontal direction, and a cathode gas inlet manifold is disposed in an upper portion of one of the ends of the fuel cell stack. Also, a buffer portion is provided on a cathode separator which is a component of a fuel cell stack so that the width of a passage increases from the cathode gas inlet manifold to a gas passage. In addition, a cathode gas outlet manifold is disposed in a lower portion of the other end of the fuel cell stack. Further, a buffer portion is provided on the cathode separator so that the width of the passage increases from the gas passage to the cathode gas outlet manifold.

As a result, a cathode gas smoothly flows from the cathode gas inlet manifold to the cathode gas outlet manifold. See, for example, Japanese Unexamined Patent Application Publication No. 2006-236612. However, the above-mentioned conventional fuel cell stack has a problem in that when condensed water is produced in the fuel cell stack after power generation is stopped, the condensed water collects in the gas passage of the separator, potentially blocking gas flow from the cathode into the cathode gas outlet manifold. This problem is particularly significant when the fuel cell stack is operating in ambient temperatures below the freezing point of water, such that the condensed water collected in the gas passage of the separator can freeze.

SUMMARY OF THE INVENTION

The present invention has been achieved in consideration of the problem of conventional fuel cell stacks, and it is an object of the present invention to suppress the condensed water produced in a fuel cell stack from collecting in a gas passage of a separator after power generation is stopped.

In one embodiment of the invention, a fuel cell stack is provided having a plurality of unit cells stacked in a horizontal direction. Each unit cell includes an electrolyte membrane having two surfaces and a peripheral edge, electrodes disposed on both surfaces of the electrolyte membrane, frame-shaped members disposed on both surfaces of the electrolyte membrane adjacent to the respective electrodes and adjacent to the peripheral edge of the electrolyte membrane, separators disposed on the electrodes and the frame-shaped members and having a reactant gas passage for supplying a reactant gas to each of the electrodes, and a manifold formed in the horizontal stacking direction in fluid communication with the reactant gas passage. The manifold comprises a horizontal edge portion in fluid communication with the reactant gas passage.

In another embodiment of the invention, a fuel cell stack is provided having a plurality of unit cells stacked in a horizontal direction. Each units cell includes an electrolyte membrane, electrodes disposed on both surfaces of the electrolyte membrane so that a peripheral portion of the electrolyte membrane is exposed, frame-shaped members disposed on both surfaces of the electrolyte membrane so as to be disposed on the peripheral portion thereof, and separators disposed on the electrodes and the frame-shaped members and each containing a reactant gas passage in which a reactant gas to be supplied to each of the electrodes flows. A manifold is provided in the stacking direction of the unit cells to communicate with the reactant gas passage so that at least a portion of liquid water produced by power generation of the unit cells flows into the manifold. The manifold has a peripheral portion communicating with the reactant gas passage such that the direction of surface tension exerted on the liquid water is substantially opposite to the direction of gravitational force exerted on the liquid water to enable the gravitational force to overcome the surface tension so that the liquid water can flow into the manifold.

In another embodiment of the invention, a fuel cell stack is provided having a plurality of unit cells stacked in a horizontal direction. Each of the unit cell includes an electrolyte membrane having two surfaces and a peripheral edge, electrodes disposed on both surfaces of the electrolyte membrane, frame-shaped members disposed on both surfaces of the electrolyte membrane adjacent to the respective electrodes and adjacent to the peripheral edge of the electrolyte membrane, separators disposed on the electrodes and the frame-shaped members and having a reactant gas passage for supplying a reactant gas to each of the electrodes, and a manifold formed in the horizontal stacking direction in fluid communication with the reactant gas passage. The manifold includes means for facilitating drainage of liquid water from the reactant gas passage.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

First Embodiment

A fuel cell (unit cell)1includes an electrolyte membrane12sandwiched between an anode electrode13a(fuel electrode) and a cathode electrode13b(oxidizer electrode) so that an anode gas (fuel gas) containing hydrogen and a cathode gas (oxidizer gas) containing oxygen are supplied to the anode electrode and the cathode electrode, respectively, to generate electricity. An electrode reaction proceeding on each of the anode electrode13aand the cathode electrode13bis as follows:
Anode electrode: 2H2→4H++4e−(1)
Cathode electrode: 4H++4e−+O2→2H2O  (2)

A fuel cell produces an electromotive force of about 1 volt according to the electrode reactions (1) and (2).

When the fuel cell1is used as a power source for automobiles, a fuel cell stack10is used in which a plurality of the fuel cells1, often as many as several hundreds, are stacked, because a large amount electric power is required. Therefore, a fuel cell system for supplying an anode gas and a cathode gas to the fuel cell stack10is formed to extract electric power for driving a vehicle.

FIG. 1is a perspective view of a fuel cell stack10used as such a fuel cell system for moving vehicles such as an automobile and the like. The fuel cell stack10includes a plurality of unit cells1stacked in the horizontal direction, a pair of collecting plates2aand2b, a pair of insulating plates3aand3b, a pair of end plates4aand4b, and nuts5screwed onto four tension rods (not shown) for holding the components of the fuel cell stack10together.

The unit cell1is a unit cell of a solid polymer-type fuel cell which produces electromotive force. The unit cell1produces an electromotive voltage of about 1 volt. The detailed configuration of the unit cell1will be described later.

The pair of collecting plates2aand2bare disposed on the outsides of the stack of the plurality of unit cells1. The collecting plates2aand2bare composed of a gas-impermeable conductive material, for example, dense carbon. Each of the collecting plates2aand2bhas an output terminal6provided at the upper end. In the fuel cell stack10, electrons e−produced in the unit cells1are extracted and output through the output terminals6.

The pair of insulating plates3aand3bare disposed on the outsides of the respective collecting plates2aand2b. Each of the insulating plates3aand3bis composed of an insulating material, for example, rubber.

The pair of end plates4aand4bare disposed on the outsides of the respective insulating plates3aand3b. Each of the end plates4aand4bis composed of a metallic material with rigidity, for example, steel.

In the end plate4aof the pair of end plates4aand4b, a cooling water inlet manifold41aand a cooling water outlet manifold41b, an anode gas inlet manifold42aand an anode gas outlet manifold42b, and a cathode gas inlet manifold43aand a cathode gas outlet manifold43b, are formed. Each of the manifolds is extended to the inside of the fuel cell stack10in the stacking direction of the unit cells1. In addition, the cathode gas inlet manifold43aand the cathode gas outlet manifold43bare larger than the anode gas inlet manifold42aand the anode gas outlet manifold42b. This is because the amount (volumetric flow rate) of the cathode gas used is larger than that of the anode gas used during power generation of the fuel cells.

The cooling water inlet manifold41a, the anode gas outlet manifold42b, and the cathode gas inlet manifold43aare formed at an end (as shown on the right side in the drawing) of the end plate4a. The cooling water outlet manifold41b, the anode gas inlet manifold42a, and the cathode gas outlet manifold43bare formed at the other end (as shown on the left side in the drawing) of the end plate4a.

When hydrogen gas is supplied to the anode gas inlet manifold42aas the fuel gas, the hydrogen gas can be supplied directly from a hydrogen storage device or from a hydrogen-containing gas which is produced by reforming hydrogen-containing fuel. Examples of the hydrogen storage device include a high-pressure tank, a liquefied hydrogen tank, a hydrogen storage alloy tank, and the like. Examples of the hydrogen-containing fuels include natural gas, methanol, gasoline, and the like. In addition, air is generally used as the oxidizer gas to be supplied to the cathode gas inlet manifold43a.

The nuts5are screwed onto external threads formed at both ends of the four tension rods (not shown) which are passed through the fuel cell stack10. The fuel cell stack10is tightened in the stacking direction by fastening the nuts5to the tension rods. The tension rods are composed of a metallic material with rigidity, for example, steel. The surfaces of the tension rods are subjected to insulating treatment for preventing electric short-circuiting between the unit cells.

The detailed configuration of the unit cell1is described below with reference toFIGS. 2 and 3.FIG. 2is an exploded perspective view of the unit cell1, andFIG. 3is a sectional view of the unit cell1.

The unit cell1includes a membrane electrode assembly (MEA)11, and an anode separator20and a cathode separator30which are disposed on opposite surfaces of the MEA11. The MEA11includes an electrolyte membrane12, an anode electrode13a, a cathode electrode13b, and a pair of frame-shaped members14aand14b. The electrolyte membrane12is a proton conductive ion-exchange membrane made of a solid polymer material (e.g., a fluorocarbon resin) that has a thickness of less than 0.1 millimeter. The frame-shaped members14aand14bhave the function to maintain the mechanical strength of the MEA11and to support the electrolyte membrane12. The frame-shaped members14aand14bare described below as the reinforcements14aand14b. In the MEA11, the reinforcement14aand the anode electrode13aare disposed on one of the sides of the electrolyte membrane12and the reinforcement14band the cathode electrode13bare disposed on the other side of the electrolyte membrane12.

In addition, a cooling water inlet manifold41a, an anode gas outlet manifold42b, and a cathode gas inlet manifold43aare formed at one of the sides of the periphery of the electrolyte membrane12. Similarly, a cooling water outlet manifold41b, an anode gas inlet manifold42a, and a cathode gas outlet manifold43bare formed at the other side of the periphery of the electrolyte membrane12. Further, through holes51are formed at the four corners of the electrolyte membrane12for receiving the tension rods.

The electrolyte membrane12exhibits high electric conductivity in a wet state. Therefore, in order to improve the power generation efficiency by utilizing the performance of the electrolyte membrane12, it is necessary to maintain the electrolyte membrane12in an optimum moisture state. In this embodiment, the anode gas and cathode gas introduced into the fuel cell stack10are humidified. Further, it is necessary to use pure water to humidify the anode gas and cathode gas for maintaining the optimum moisture condition of the electrolyte membrane12. This is because when water contaminated with impurities is introduced into the fuel cell stack10, the impurities accumulate on the electrolyte membrane12, thereby decreasing the power generation efficiency.

The anode electrode13aand the cathode electrode13bare disposed on opposite surfaces of the electrolyte membrane12(i.e., the anode electrode13aon one side and the cathode electrode13bon the other side) so as to each be in contact with the electrolyte membrane12. Each of the anode electrode13aand the cathode electrode13bincludes a catalyst layer131and a gas diffusion layer132. The catalyst layer131is formed on the electrolyte membrane side of each the electrodes13aand13b. The gas diffusion layer132is formed on the separator side of each the electrodes13aand13b. The catalyst layer131is composed of platinum-carrying carbon black particles. The gas diffusion layer132is composed of a member having sufficient gas diffusibility and conductivity, for example, a carbon cloth woven with carbon fiber threads.

The reinforcements (frame-shaped members)14aand14bare disposed such that one is on either surface of the electrolyte membrane12and adjacent to the peripheral edge of the electrolyte membrane12. The reinforcement14ais disposed so as to surround the peripheral edge of the anode electrode13aand the reinforcement14bis disposed so as to surround the peripheral edge of the cathode electrode13b.

In addition, the cooling water inlet manifold41a, the anode gas outlet manifold42b, and the cathode gas inlet manifold43aare formed at one of the sides of each of the reinforcements14aand14b. Similarly, the cooling water outlet manifold41b, the anode gas inlet manifold42a, and the cathode gas outlet manifold43bare formed at the other side of each of the reinforcements14aand14b. Further, the through holes51are formed at the four corners of each of the reinforcements14aand14bin order to pass the tension rods.

The anode separator20includes an outer frame portion20aand a passage portion20b. The outer frame portion20ais in contact with the reinforcement14athrough a gasket15a. In addition, the cooling water inlet manifold41a, the anode gas outlet manifold42b, and the cathode gas inlet manifold43aare formed at one of the sides of the outer frame portion20a. Similarly, the cooling water outlet manifold41b, the anode gas inlet manifold42a, and the cathode gas outlet manifold43bare formed at the other side of the outer frame portion20a. Further, the through holes51are formed at the four corners of the outer frame portion20ain order to pass the tension rods.

The passage portion20bis in contact with the anode electrode13a. As illustrated inFIG. 3, the passage portion20bhas a gas passage21provided on the side of the anode separator20in contact with the anode electrode13ain order to supply the anode gas to the anode electrode13a. The passage portion20balso has a cooling water passage61provided on the side of the separator20opposite to the side in contact with the anode electrode13aso that the cooling water for cooling the fuel cell stack heated during power generation flows through the cooling water passage61. Details of the passage portion20are described below with reference toFIGS. 4A and 4B.

The cathode separator30also includes an outer frame portion30aand a passage portion30b. The outer frame portion30ais in contact with the reinforcement14bthrough a gasket15b. In addition, the cooling water inlet manifold41a, the anode gas outlet manifold42b, and the cathode gas inlet manifold43aare formed at one of the sides of the outer frame portion30a. Similarly, the cooling water outlet manifold41b, the anode gas inlet manifold42a, and the cathode gas outlet manifold43bare formed at the other side of the outer frame portion30a. Further, the through holes51are formed at the four corners of the outer frame portion30ain order to pass the tension rods.

The passage portion30bis in contact with the cathode electrode13b. As illustrated inFIG. 3, the passage portion30bhas a gas passage31provided on the side of the cathode separator30in contact with the cathode electrode13bin order to supply the cathode gas to the cathode electrode13b. The passage portion30balso has a cooling water passage62provided on the side of the cathode separator30opposite to the side in contact with the cathode electrode13b.

The cooling water passages61and62provided in the adjacent anode separator20and cathode separator30, respectively, are formed opposite to each other to form a cooling water passage60. Note that becauseFIG. 3shows both the anode separator20and the cathode separator30in the same view, the cooling water passages61and62appear to be the same passage; however the cooling water passage61is provided in the anode separator20and the cooling water passage62is provided in the cathode separator30. The anode separator20and the cathode separator30are made of a material such as a metal or carbon.

When fuel cells10are used as a power source for automobiles, several hundreds of unit cells1are required to be stacked together because a large amount of electric power is required, and a large amount of water is discharged during power generation because a large quantity of electricity is generated.

The anode gas and cathode gas to be supplied and discharged cannot hold an amount of water which exceeds the saturated water vapor pressure. Therefore, condensation may occur in a fuel cell stack10mounted on an automobile depending on the temperature and humidity conditions during power generation, and thus a large amount of liquid water may collect in the gas passages of the separators20and30. Unlike in a stationary fuel cell, in a fuel cell mounted on an automobile, system start is required at any ambient temperature. If liquid water remains in the gas passages, the liquid water may be frozen when the ambient temperature of the fuel cell is a below the freezing temperature of water. Then, when a system start is required under a condition in which liquid water is frozen, gas supply to the anode electrode and the cathode electrode is inhibited, thereby decreasing the power generation performance.

Further, if liquid water remains in the gas passages21and31of each of unit cells1in a fuel cell stack10, the unit cells1subjected to sufficient gas supply may be mixed with unit cells1subjected to insufficient gas supply. Therefore, in each of the unit cells1subjected to insufficient gas supply, the reactions represented by the above formulae (1) and (2) are inhibited, and thus the voltage becomes negative, resulting in deterioration of those unit cells1.

In this embodiment, therefore, a notch100is provided at a predetermined position of the reinforcement14aor14bin order to decrease the liquid water remaining in the gas passages21and31by enhancing the ability of the liquid water to flow out of the unit cell1. The shape and features of embodiments of the notch100are described below.

FIGS. 4A and 4Bare plan views of the anode separator20and the reinforcement14aas viewed from the anode electrode side.FIG. 4Ashows the anode separator20and the reinforcement14ain a stacked state, andFIG. 4Bshows the anode separator20and the reinforcement14ain a disassembled state.

The configuration of the anode separator20is described. As shown inFIG. 4B, the cathode gas outlet manifold43b, the cooling water outlet manifold41b, and the anode gas inlet manifold42aare formed at an end of the outer frame20aof the anode separator20in that order from above as shown inFIG. 4B. In addition, a plurality of groove-like gas passages21and gas diffusion portion22are formed in the surface of the reactant gas passage portion20b. The gas passages21are formed between a plurality of ribs23which project from the gas passage surface21atoward the anode electrode side to be in contact with the anode electrode. The cooling water passage61(not shown) is formed at the back side of the ribs23when a plurality of unit cells is stacked. The gas diffusion portion22has a plurality of diffusers24for uniformly distributing the anode gas introduced from the anode gas inlet manifold42ainto the gas passages21.

Next, the position of the notch100formed in the reinforcement14ais described. The notch100is formed in the anode gas inlet manifold42aso as to be positioned on the lower side in the vertical direction when unit cells1are stacked to form a fuel cell stack10. Because the notch100is designed to take advantage of gravity in facilitating drainage of liquid water from the gas diffusion portion22, the vertical direction is understood to be generally in the upward and downward direction with respect to gravity, and the horizontal direction is understood to be generally in the lateral direction perpendicular to the vertical direction and thus perpendicular to the force vector of gravity.

The notch100is formed in the opening120which forms the anode gas inlet manifold42a. Further, the notch100is formed in a manifold peripheral portion130communicating with the gas diffusion portion22of the reactant gas passage portion20b. Also, the notch100is formed to overlap the gas diffusion portion22of the anode separator20as viewed from the stacking direction when the anode separator20and the reinforcement14aare stacked together as shown inFIG. 4A. As a result, when the anode separator20and the reinforcement14aare stacked together, the notch100communicates with the anode gas inlet manifold42a, and a space101is formed in a communication portion between the anode gas inlet manifold42aand the gas diffusion portion22.

In this embodiment, the notch100is formed so that a top surface101aof the space101is substantially perpendicular to the gravitational direction. Consequently, a horizontal portion100ais formed in the periphery of the notch100, the top surface101abeing disposed in the horizontal portion100aof the notch100.

FIG. 5is a sectional view taken along line V-V inFIG. 4Aas viewed from below in the vertical direction. As shown inFIG. 5, when the notch100is formed in the anode gas inlet manifold42aof the reinforcement14a, the notch100communicates with the anode gas inlet manifold42aand forms the space101. In a stacked state, the width of the space101(height from the bottom of the gas diffusion portion22to the anode electrode13a) is larger than the width of the gas diffusion portion22(height from the bottom of the gas diffusion portion22to the reinforcement14a).

The advantage of the formation of the notch100is described below.FIGS. 6A and 6Bare drawings illustrating a liquid water flow when the notch100is formed.FIG. 12is a drawing illustrating a liquid water flow when the notch100is not formed.

For the sake of easy understanding of the invention, a liquid water flow when the notch100is not formed is first described with reference toFIG. 12. As shown inFIG. 12, liquid water produced in the gas passage due to generation reactions gravitationally collects in a lower portion of the gas diffusion portion22of the anode separator20. In this case, the liquid water flowing into the anode gas inlet manifold42aflows, due to the influence of surface tension, upward along a peripheral portion130of the opening120of the anode gas inlet manifold42awithout flowing into the anode gas inlet manifold42a, the peripheral portion130being the portion of the opening120in contact with the gas diffusion portion22. When the liquid water is present along the peripheral portion130of the anode gas inlet manifold42a, the liquid water may be frozen due to a decrease in the ambient temperature of the fuel cells. If the liquid water becomes frozen, the flow of the anode gas flowing into the gas diffusion portion22from the anode gas inlet manifold42may be inhibited.

On the other hand, when the notch100is formed as in the present embodiment of the invention, the liquid water flowing into the anode gas inlet manifold42abehaves as shown inFIG. 6A. First, as in the embodiment ofFIG. 12, the liquid water flows toward the anode gas inlet manifold42aalong the vertically lower side of the anode separator20. Then, the liquid water flows along the peripheral edge of the notch100.

In this embodiment, the upper surface101aof the space101includes a horizontal portion100ain the notch100. Because of the narrowness of the gas diffusion portion22, surface tension of the water exerts a force around the periphery of the notch100to prevent the water from flowing into the manifold42a. However, when liquid water reaches the horizontal portion100a, gravity exerted on the liquid water in a direction opposite to the direction of the surface tension overcomes the surface tension and enables the liquid water to flow into the manifold42a. In other words, the directions of the surface tension and gravity are canceled by each other. That is, by forming the horizontal portion100ain the upper surface101aof the notch100, the gravity is sufficient to overcome the surface tension exerting on the liquid water. When the liquid water reaches the horizontal portion100a, a the gravitation force from the weight of the water exceeds the surface tension, and thus the liquid water flows into the space101. Namely, the horizontal portion100ais formed in the upper surface101aso that the directions of the surface tension and gravity exerting on the liquid water are substantially opposite to each other and canceled by each other.

After the liquid water flows into the space101and its surface tension has been broken, the liquid water is discharged to the anode gas inlet manifold42aas shown inFIG. 6B. As a result, it is possible to prevent the liquid water from moving along the upper side of the edge of the anode gas inlet manifold42aand inhibiting gas flow into the gas diffusion portion22. Therefore, the flow of the reactant gas flowing into the gas diffusion portion22from the anode gas inlet manifold42ais not inhibited by the liquid water.

In the above-described embodiment, the notch100is formed in the anode gas inlet manifold42aof the reinforcement14aso as to overlap the gas diffusion portion22of the anode separator20when the anode separator20and the reinforcement14aare stacked together. In addition, the upper surface101aof the space101formed by the notch100is formed to be substantially perpendicular to the gravitational direction, thereby providing the horizontal portion100aat the upper side of the periphery of the notch100in the gravitational direction.

Gravity exerts downward force on the liquid water in the vertical direction according to the mass of the liquid water. Therefore, when the liquid water reaches the horizontal portion100a, gravity exerts downward force on the liquid water in the vertical direction. In this case, the directions of gravity and surface tension exerting on the liquid water are substantially opposite to each other. As a result, the liquid water overcomes the force exerted by surface tension and moves downwardly. Therefore, the liquid water which generally flows along the upper side of the edge of the anode gas inlet manifold42aof the anode separator20, due to the influence of surface tension, can instead be allowed to flow into the space101from the horizontal portion101aof the notch100due to the influence of gravity. Therefore, the end of the anode gas inlet manifold42can be prevented from being clogged with frozen liquid water. Consequently, the flow of the reactant gas flowing into the gas diffusion portion22from the anode gas inlet manifold42ais not inhibited, thereby maintaining sufficient gas supply to the anode electrode13a.

In this embodiment, an arrangement is described in which the notch100is provided in the anode gas inlet manifold42aof the reinforcement14a. However, the notch100may be of course provided in the cathode gas inlet manifold43aof the reinforcement14b. Since the anode gas inlet manifold42ais smaller than the cathode gas inlet manifold43a, the anode gas inlet manifold42ais more likely to be clogged by freezing of residual liquid water. Therefore, in particular, it is most effective to provide the notch100in the anode gas inlet manifold42a.

Second Embodiment

FIGS. 7A and 7Bshow a second embodiment of the present invention. The second embodiment is different from the first embodiment in that the shape of the notch100is changed. The difference is described below; the portions having the same functions as in the first embodiment are denoted by the same reference numerals and appropriately not described below.

FIGS. 7A and 7Bare each a plan view of the anode separator20and the reinforcement14aas viewed from the anode electrode side.FIG. 7Ashows the anode separator20and the reinforcement14ain a stacked state, andFIG. 7Bshows the anode separator20and the reinforcement14ain a disassembled state.

As shown inFIG. 7A, in this embodiment, the notch100is formed so as to have minimal or no overlap with diffusers24of the gas diffusion portion22when the anode separator20and the reinforcement14aare stacked together. Residual liquid water flows between the adjacent diffusers24. Therefore, when the notch100does not overlap the diffusers24, the liquid water can be more effectively allowed to flow into the space101formed by the notch100.

In this embodiment, the horizontal portion100ais formed near the top of the notch100in the vertical direction. In addition, the notch100has a portion inclined to the anode gas inlet manifold42afrom the horizontal portion100a. According to this embodiment, in addition to the advantage of the first embodiment, the liquid water can be more efficiently allowed to flow into the space101because the notch100is formed so as not to overlap, or so as to minimally overlap, the diffusers24. Further, since the notch100has the portion inclined to the anode gas inlet manifold42a, the liquid water more easily moves toward the manifold42a.

Third Embodiment

FIGS. 8A and 8Bshow a third embodiment of the present invention. The third embodiment is different from the first embodiment in that the shape of the notch100is changed. The difference is described below.

FIGS. 8A and 8Bare each a plan view of the anode separator20and the reinforcement14aas viewed from the anode electrode side.FIG. 8Ashows the anode separator20and the reinforcement14ain a stacked state, andFIG. 8Bshows the anode separator20and the reinforcement14ain a disassembled state.

As shown inFIG. 8A, in this embodiment, the notch100is formed so as not to overlap the diffusers24of the gas diffusion portion22when the anode separator20and the reinforcement14aare stacked together. Also, the notch100is formed to be positioned between the anode gas inlet manifold42aand the diffusers24. Like in the first embodiment, the notch100has the horizontal portion100a.

According to this embodiment, in addition to the advantage of the first embodiment, the liquid water can be more efficiently allowed to flow into the space101because the notch100is formed so as not to overlap the diffusers24. Further, since the notch100is formed to be positioned between the anode gas inlet manifold42aand the diffusers24, the notch100is smaller than that in the first embodiment. Therefore, the mechanical strength of the MEA11can be improved as compared with the first embodiment.

Fourth Embodiment

A fourth embodiment of the present invention is described with reference toFIGS. 9A and 9B. The fourth embodiment is different from the first embodiment in the shape of the notch100. The difference is described below.

FIGS. 9A and 9Bare each a plan view of the anode separator20and the reinforcement14aas viewed from the anode electrode side.FIG. 9Ashows the anode separator20and the reinforcement14ain a stacked state, andFIG. 9Bshows the anode separator20and the reinforcement14ain a disassembled state.

As described above, liquid water produced in a gas passage21by generation reaction gravitationally collects in a lower portion (in the gravitational direction) of the gas diffusion portion22of the anode separator20and moves toward the anode gas inlet manifold42a. Therefore, as shown inFIG. 9A, in this embodiment, the notch100is formed at the lowest position in the anode gas inlet manifold42aof the reinforcement14a. Like in the first embodiment, the notch100has the horizontal portion100a.

According to this embodiment, the notch100is formed to be positioned on the lower side of the gas diffusion portion22where liquid water collects when the anode separator20and the reinforcement14aare stacked together. Therefore, in addition to the advantage of the first embodiment, the liquid water remaining in the lowest portion of the separator can be more efficiently allowed to flow into the space101, because there is no need to overcome surface tension for the liquid water remaining in the lowest portion of the separator.

Fifth Embodiment

A fifth embodiment of the present invention is described with reference toFIGS. 10A and 10B. The fifth embodiment is different from the first embodiment in that a notch100is formed in the anode gas inlet manifold42aof the anode separator20. The difference is described below.

FIGS. 10A and 10Bare each a plan view of the anode separator20and the reinforcement14aas viewed from the anode electrode side.FIG. 10Ashows the anode separator20and the reinforcement14ain a stacked state, andFIG. 10Bshows the anode separator20and the reinforcement14ain a disassembled state.

As shown inFIGS. 10A and 10B, in this embodiment, the notch100is formed in the anode gas inlet manifold42aof the anode separator20. The notch100is formed in the periphery of the anode gas inlet manifold42aof the anode separator20so as to project toward the gas diffusion portion22.

In addition, the notch100is disposed on the lowest side of the gas diffusion portion20in the vertical direction. Therefore, a space101communicating with both the anode gas inlet manifold42aand the gas diffusion portion22is formed.

FIG. 11is a drawing showing a section taken along line XI-XI inFIG. 10Aas viewed from the lower side in the vertical direction. As shown inFIG. 11, the notch100is formed in the periphery of the anode gas inlet manifold42aof the anode separator20, and thus the space101is wider than the gas diffusion portion22as in the first embodiment. Further, the upper surface101aof the space101is formed to be substantially perpendicular to the gravitational direction to form a horizontal portion100ain the periphery of the notch100, as shown inFIG. 10.

In this configuration, liquid water reaching the horizontal portion100aof the notch100flows into the space101due to its own weight. Therefore, like in the first embodiment, liquid water can be discharged to the anode gas inlet manifold42a. In the fifth embodiment, the same advantage as the first embodiment can be obtained.

The present invention is not limited to the above-mentioned embodiments and various modifications can be made within the scope of the technical idea of the invention. For example, the notch100may be provided in the anode gas outlet manifold42bor the cathode gas outlet manifold43b.

While the invention has been disclosed with reference to certain preferred embodiments, numerous modifications, alterations, and changes to the described embodiments are possible without departing from the sphere and scope of the invention, as defined in the appended claims and equivalents thereof. Accordingly, it is intended that the invention not be limited to the described embodiments, but that it have the full scope defined by the language of the following claims.