JP4585737B2 - Fuel cell - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention includes an electrolyte membrane / electrode structure provided with electrodes on both sides of a solid polymer electrolyte membrane, and sandwiches the electrolyte membrane / electrode structure, and a predetermined reaction gas is provided on each surface facing each electrode. The present invention relates to a fuel cell including a set of metal separators in which a reaction gas channel to be supplied is formed.
[0002]
[Prior art]
For example, a solid polymer fuel cell employs a solid polymer electrolyte membrane made of a polymer ion exchange membrane (cation exchange membrane). In this fuel cell, an electrolyte membrane / electrode structure comprising an anode catalyst and a cathode electrode each made of an electrode catalyst and porous carbon is provided on both sides of a solid polymer electrolyte membrane. ). Usually, a fuel cell stack in which a predetermined number of the fuel cells are stacked is used.
[0003]
In this type of fuel cell, a fuel gas (reactive gas) supplied to the anode electrode, for example, a gas mainly containing hydrogen (hereinafter also referred to as a hydrogen-containing gas) is hydrogen ionized on the electrode catalyst, It moves to the cathode side electrode side through the electrolyte membrane. Electrons generated in the meantime are taken out to an external circuit and used as direct current electric energy. The cathode side electrode is supplied with an oxidant gas (reaction gas), for example, a gas mainly containing oxygen or air (hereinafter also referred to as oxygen-containing gas). Hydrogen ions, electrons and oxygen react to produce water.
[0004]
In the above fuel cell, a fuel gas channel (reactive gas channel) for flowing a fuel gas opposite to the anode side electrode and an oxidant gas for flowing the cathode gas facing the cathode side electrode in the plane of the separator. The oxidant gas flow path (reaction gas flow path) is provided. Further, between the separators, a coolant flow path for allowing a coolant to flow as needed is provided along the surface direction of the separator.
[0005]
This type of separator is usually made of a carbon-based material, but it has been pointed out that the carbon-based material cannot be thinned due to factors such as strength. Therefore, recently, a separator made of a thin metal plate (hereinafter also referred to as a metallic separator) which is superior in strength and easy to be thinned than this type of carbon separator is used, and this metallic separator is subjected to press working to obtain a desired By shaping the reaction gas flow path, a contrivance has been made to reduce the thickness of the metal separator to reduce the size and weight of the entire fuel cell.
[0006]
For example, the fuel cell 1 shown in FIG. 11 includes an electrolyte membrane / electrode structure 5 configured by interposing an electrolyte membrane 4 between an anode side electrode 2 and a cathode side electrode 3, and the electrolyte membrane / A pair of metal separators 6 a and 6 b that sandwich the electrode structure 5 is provided.
[0007]
The separator 6a is provided with a fuel gas flow path 7a for supplying a fuel gas (for example, hydrogen-containing gas) on the surface facing the anode side electrode 2, while the separator 6b is opposed to the cathode side electrode 3. An oxidant gas flow path 7b for supplying an oxidant gas (for example, an oxygen-containing gas such as air) is provided on the surface. The separators 6a and 6b are provided with flat portions 8a and 8b that are in contact with the anode side electrode 2 and the cathode side electrode 3, and on the back surfaces (surfaces opposite to the contact surfaces) of the flat portions 8a and 8b. Cooling medium flow paths 9a and 9b for flowing the cooling medium are formed.
[0008]
[Problems to be solved by the invention]
However, in the oxidant gas flow path 7b and the fuel gas flow path 7a, the relative humidity increases from the inlet side toward the outlet side due to generation of generated water, consumption of reaction gas, and the like. For this reason, the outlet side is more likely to condense than the inlet side, and the thin metal separators 6a and 6b in which the cooling medium flows along the back surface increase the cooling efficiency and cause condensation in a high humidity state. .
[0009]
In particular, in the flat portions 8a and 8b on the reaction gas outlet side, the cooling medium flows directly on the back surface side, so that the contact surface side is likely to condense, and the flow rate of the reaction gas is reduced, so that dew condensation water is generated. It is difficult to be discharged and often stays. Accordingly, in the electrolyte membrane / electrode structure 5, stagnant water is generated corresponding to the portion where the flat portions 8 a and 8 b on the reaction gas outlet side abut, and the portion where the reaction gas is not diffused by the stagnant water, that is, unreacted. The reaction surface portion S exists. As a result, in the electrolyte membrane / electrode structure 5, the effective area for the catalytic reaction is reduced, and a problem that good and efficient power generation performance cannot be maintained has been pointed out.
[0010]
The present invention solves this type of problem, and with a simple configuration, it is possible to prevent condensation of reaction product water within the electrode surface as much as possible, and to ensure good power generation performance. An object of the present invention is to provide a simple fuel cell.
[0011]
[Means for Solving the Problems]
In the fuel cell according to claim 1 of the present invention, the electrolyte membrane / electrode structure provided with electrodes on both sides of the solid polymer electrolyte membrane is sandwiched between a pair of metal separators, A flat portion that abuts each electrode, and a concave portion that forms a reaction gas flow path by being spaced apart from the electrode with the flat portion interposed therebetween. And the flat part is set so that the width dimension which contact | abuts to an electrode may become small toward the downstream from the upstream of a reactive gas flow path.
[0012]
Thus, for example, in the product water often occur to the downstream side of the easy reaction gas channel relative humidity is high, it is possible to the metal separator to greatly reduce the contacting area with the electrode. Furthermore, the area where the cooling medium contacts the electrode is also reduced, and the electrode surface is less likely to be cooled, thereby preventing the occurrence of condensation. As a result, it is possible to effectively reduce the unreacted surface portion of the electrode surface due to stagnant water and to ensure a good reaction effective area on the electrode surface, thereby suppressing an increase in concentration overvoltage.
[0013]
On the other hand, on the upstream side of the reaction gas channel, condensation is difficult to occur due to low relative humidity. Therefore, it is possible to effectively reduce the resistance overvoltage by setting the area of the flat portion where the metal separator is in contact with the electrode. For this reason, it is possible to reliably maintain good power generation performance of the fuel cell with a simple configuration.
[0014]
DETAILED DESCRIPTION OF THE INVENTION
FIG. 1 is an exploded perspective view of a main part of a fuel cell 10 according to the first embodiment of the present invention.
[0015]
The fuel cell 10 includes an electrolyte membrane / electrode structure 12, and first and second metal separators 14 and 16 that sandwich the electrolyte membrane / electrode structure 12. Between the electrolyte membrane / electrode structure 12 and the first and second metal separators 14, 16, a seal member 18 such as a gasket is provided so as to cover the periphery of the communication hole and the outer periphery of the electrode surface (power generation surface) described later. Is intervening.
[0016]
One end edge of the electrolyte membrane / electrode structure 12 and the first and second metal separators 14 and 16 in the direction of arrow B communicates with each other in the direction of arrow A, which is the stacking direction, and an oxidant gas, for example, oxygen An oxidant gas supply communication hole 20a for supplying a contained gas, a cooling medium discharge communication hole 22b for discharging a cooling medium, and a fuel gas discharge communication hole 24b for discharging a fuel gas, for example, a hydrogen-containing gas, are provided. Are arranged in the direction of arrow C (vertical direction).
[0017]
Fuel gas supply for supplying fuel gas to the other end edge of the electrolyte membrane / electrode structure 12 and the first and second metal separators 14 and 16 in the direction of arrow B in communication with each other in the direction of arrow A The communication holes 24a, the cooling medium supply communication holes 22a for supplying the cooling medium, and the oxidant gas discharge communication holes 20b for discharging the oxidant gas are arranged in the direction of arrow C.
[0018]
The electrolyte membrane / electrode structure 12 includes, for example, a solid polymer electrolyte membrane 26 in which a perfluorosulfonic acid thin film is impregnated with water, and an anode side electrode 28 and a cathode side electrode that sandwich the solid polymer electrolyte membrane 26. 30.
[0019]
The anode side electrode 28 and the cathode side electrode 30 are a gas diffusion layer made of carbon paper or the like, and an electrode catalyst layer in which porous carbon particles having a platinum alloy supported on the surface are uniformly applied to the surface of the gas diffusion layer, Respectively. The electrode catalyst layers are bonded to both surfaces of the solid polymer electrolyte membrane 26 so as to face each other with the solid polymer electrolyte membrane 26 interposed therebetween. An opening 34 is formed at the center of the seal member 18 corresponding to the anode side electrode 28 and the cathode side electrode 30.
[0020]
On the surface 14a of the first metal separator 14 on the electrolyte membrane / electrode structure 12 side, for example, an oxidant gas flow path 36 including a plurality of grooves extending in the direction of arrow B is provided. The gas flow path 36 communicates with the oxidant gas supply communication hole 20a and the oxidant gas discharge communication hole 20b.
[0021]
As shown in FIGS. 2 and 3, the first metal separator 14 includes a flat portion 38 that contacts the cathode side electrode 30 of the electrolyte membrane / electrode structure 12, and the cathode side electrode 30 across the flat portion 38. And a concave portion 40 that forms the oxidant gas flow path 36 by being separated from the oxidant gas flow path 36. The flat portion 38 is integrally formed by subjecting the first metal separator 14 to a press molding process or the like. From the upstream side to the downstream side of the oxidant gas flow path 36 (in the direction of arrow B1), the flat portion 38 is formed on the cathode side electrode 30. The abutting width dimension L is set to be small (see FIG. 4).
[0022]
The flat portions 38 are spaced apart from each other by a predetermined interval in the direction of the arrow C and parallel to each other in the direction of the arrow B, and the leading end side in the direction of the arrow B2 that is the upstream side of the oxidant gas flow path 36 is as shown in FIG. Furthermore, it is comprised in the substantially trapezoid shape set to the largest width dimension L1. As shown in FIG. 6, the flat portion 38 has a substantially arc shape in which the tip end in the arrow B1 direction, which is the downstream side of the oxidant gas flow path 36, is set to the minimum width dimension L2. The width dimension L of the flat portion 38 is set so as to decrease continuously or stepwise from the maximum width dimension L1 toward the minimum width dimension L2.
[0023]
A fuel gas flow path 42 communicating with the fuel gas supply communication hole 24a and the fuel gas discharge communication hole 24b is formed on the surface 16a of the second metal separator 16 on the electrolyte membrane / electrode structure 12 side. The fuel gas passage 42 includes a plurality of grooves extending in the direction of arrow B. A cooling medium flow path 44 communicating with the cooling medium supply communication hole 22a and the cooling medium discharge communication hole 22b is formed on the surface 16b of the second metal separator 16. The cooling medium flow path 44 includes a plurality of grooves extending in the arrow B direction.
[0024]
As shown in FIG. 7, on the surface 16 a side of the second metal separator 16, there is a flat portion 46 that contacts the anode side electrode 28 of the electrolyte membrane / electrode structure 12, and the anode side across the flat portion 46. A recessed portion 48 that forms the fuel gas flow path 42 by being separated from the electrode 28 is provided.
[0025]
The flat portions 46 are spaced apart from each other by a predetermined interval in the arrow C direction, and extend in parallel to each other in the arrow B direction. Each flat portion 46 is set so that the width dimension L in contact with the anode side electrode 28 decreases from the upstream side to the downstream side of the fuel gas passage 42 (in the direction of arrow B1). The flat portion 46 is configured in the same manner as the flat portion 38 of the first metal separator 14, and a detailed description thereof is omitted.
[0026]
The operation of the fuel cell 10 configured as described above will be described below.
[0027]
As shown in FIG. 1, a fuel gas such as a hydrogen-containing gas is supplied to the fuel gas supply communication hole 24a, and an oxidant gas such as an oxygen-containing gas is supplied to the oxidant gas supply communication hole 20a. Further, a coolant such as pure water, ethylene glycol, or oil is supplied to the coolant supply passage 22a.
[0028]
The oxidant gas is introduced from the oxidant gas supply communication hole 20 a into the oxidant gas flow path 36 of the first metal separator 14 and moves along the cathode side electrode 30 constituting the electrolyte membrane / electrode structure 12. On the other hand, the fuel gas is introduced into the fuel gas flow path 42 of the second metal separator 16 from the fuel gas supply communication hole 24 a and moves along the anode side electrode 28 constituting the electrolyte membrane / electrode structure 12.
[0029]
Therefore, in the electrolyte membrane / electrode structure 12, the oxidant gas supplied to the cathode side electrode 30 and the fuel gas supplied to the anode side electrode 28 are consumed by an electrochemical reaction in the electrode catalyst layer to generate power. Is done.
[0030]
Next, the fuel gas consumed by being supplied to the anode side electrode 28 is discharged in the direction of arrow A along the fuel gas discharge communication hole 24b. Similarly, the oxidant gas consumed by being supplied to the cathode side electrode 30 is discharged in the direction of arrow A along the oxidant gas discharge communication hole 20b.
[0031]
The cooling medium supplied to the cooling medium supply communication hole 22a is introduced into the cooling medium flow path 44 of the second metal separator 16 and then circulates in the direction of arrow B. The cooling medium is discharged from the cooling medium discharge communication hole 22b after the electrolyte membrane / electrode structure 12 is cooled.
[0032]
Here, for example, in the cathode side electrode 30 constituting the electrolyte membrane / electrode structure 12, generated water is generated by the reaction, and this generated water increases along the flow direction of the oxidant gas. For this reason, in the oxidant gas flow path 36 formed in the first metal separator 14, condensed water is likely to be generated on the outlet side (oxidant gas discharge communication hole 20 b side).
[0033]
Therefore, in the first embodiment, the flat portion 38 constituting the oxidant gas flow path 36 has a smaller width dimension L that contacts the cathode side electrode 30 from the upstream side to the downstream side of the oxidant gas flow path 36. (See FIGS. 3 and 4). For this reason, the area of the flat portion 38 where the first metal separator 14 contacts the cathode electrode 30 is greatly reduced on the downstream side of the oxidant gas flow path 36 where a large amount of generated water is generated and the relative humidity tends to be high. can do.
[0034]
Therefore, the unreacted surface portion of the cathode side electrode 30 due to the accumulated water is greatly reduced to the minimum width dimension L2, as shown in FIG. As a result, it is possible to satisfactorily secure the effective reaction area of the cathode-side electrode 30, and the effect of suppressing an increase in concentration overvoltage can be obtained.
[0035]
On the other hand, on the upstream side of the oxidant gas flow path 36, the relative humidity is low so that it is difficult for condensation to occur, and the area of the flat portion 38 where the first metal separator 14 contacts the cathode side electrode 30 can be set large. Become. For this reason, there exists an advantage that the resistance overvoltage in the upstream of the oxidant gas flow path 36 can be reduced effectively.
[0036]
Thereby, in the first embodiment, particularly when the first metal separator 14 is used, even when it is difficult to discharge condensed water due to an increase in generated water and a decrease in the flow rate of the oxidizing gas. By setting the width dimension L of the flat portion 38 so as to decrease from the upstream side toward the downstream side, the unreacted surface portion can be effectively reduced with a simple configuration, and the power generation performance of the fuel cell 10 Can be reliably maintained.
[0037]
Similarly, in the fuel gas passage 42 formed in the second metal separator 16, the relative humidity on the downstream side tends to be higher than the upstream side due to consumption of the fuel gas. At that time, as shown in FIG. 7, by simply setting the width dimension L of the flat portion 46 so as to decrease from the upstream toward the downstream, the stagnant water can be significantly reduced to maintain good power generation performance. Can do.
[0038]
FIG. 8 is a partially enlarged perspective view of a first metal separator 60 constituting a fuel cell according to the second embodiment of the present invention, and FIG. 9 is a partial cross-sectional view of the first metal separator 60. FIG. The same components as those of the fuel cell 10 according to the first embodiment are denoted by the same reference numerals, and detailed description thereof is omitted. Similarly, in the third embodiment described below, detailed description thereof is omitted.
[0039]
The first metal separator 60 is separated from the cathode side electrode 30 with the flat portion 62 in contact with the cathode side electrode 30 constituting the electrolyte membrane / electrode structure 12 sandwiched by the flat portion 62. And a concave portion 64 that forms the gas flow path 36.
[0040]
The flat portion 62 is set so that the width dimension L contacting the cathode side electrode 30 decreases from the upstream side to the downstream side of the oxidant gas flow path 36. The flat portion 62 is set to have a polygonal cross section in order to form the downstream minimum width dimension L2, and the downstream cross-sectional area of the oxidant gas flow path 36 is the upstream oxidant gas. It is set to be equal to or smaller than the channel cross-sectional area of the channel 36.
[0041]
As a result, in the second embodiment, it is possible to effectively reduce the accumulated water by providing the flat portion 62 set to the minimum width dimension L2 on the downstream side of the oxidant gas flow path 36 where the relative humidity becomes high. The effect similar to 1st Embodiment is acquired, such as being able to maintain a sufficient power generation performance.
[0042]
Moreover, in the second embodiment, the channel cross-sectional area of the oxidant gas channel 36 is set equal to or less than the upstream to downstream. For this reason, it is possible to prevent a decrease in the flow rate of the oxidant gas and to supply the oxidant gas smoothly and reliably over the entire surface of the cathode side electrode 30, thereby maintaining the power generation performance high. is there.
[0043]
FIG. 10 is an explanatory front view of a first metal separator 80 constituting the fuel cell according to the reference example .
[0044]
The first metal separator 80 is provided with first flat portions 82 and second flat portions 84 alternately in parallel with the flow direction of the oxidant gas, and between the first and second flat portions 82 and 84. A concave portion 86 that forms the oxidant gas flow path 36 is provided. The first flat portion 82 is configured to be long in the direction of the arrow B, while the second flat portion 84 is set at substantially the same position as the first flat portion 82 on the upstream side and the first flat portion 82 on the downstream side. It is configured in a short length that terminates on the way.
[0045]
For this reason, in the reference example , the areas of the first and second flat portions 82 and 84 that contact the cathode-side electrode 30 decrease from the upstream toward the downstream, effectively generating the accumulated water on the downstream side. The same effects as those of the first and second embodiments can be obtained.
[0046]
【The invention's effect】
In the fuel cell according to the present invention, for example, the area where the metal separator abuts on the electrode can be significantly reduced on the downstream side of the reaction gas flow path where a large amount of produced water is generated and the relative temperature tends to be high. As a result, it is possible to effectively reduce the unreacted surface portion of the electrode surface due to stagnant water and to ensure a good reaction effective area on the electrode surface, thereby suppressing an increase in concentration overvoltage.
[0047]
On the other hand, on the upstream side of the reaction gas channel, condensation is difficult to occur due to low relative humidity. Therefore, it is possible to effectively reduce the resistance overvoltage by setting the area of the flat portion where the metal separator is in contact with the electrode. For this reason, it is possible to reliably maintain good power generation performance of the fuel cell with a simple configuration.
[Brief description of the drawings]
FIG. 1 is an exploded perspective view of a main part of a fuel cell according to a first embodiment of the present invention.
FIG. 2 is a partial cross-sectional explanatory view of the fuel cell.
FIG. 3 is a front explanatory view of a first metal separator constituting the fuel cell.
FIG. 4 is a partially enlarged perspective view of the first metal separator.
FIG. 5 is a cross-sectional view taken along line VV in FIG.
6 is a cross-sectional view taken along line VI-VI in FIG.
FIG. 7 is an explanatory front view of a second metal separator constituting the fuel cell.
FIG. 8 is a partially enlarged perspective view of a first metal separator constituting a fuel cell according to a second embodiment of the present invention.
FIG. 9 is a partial cross-sectional explanatory view of the first metal separator.
FIG. 10 is a front explanatory view of a first metal separator constituting a fuel cell according to a reference example .
FIG. 11 is a partial cross-sectional explanatory view of a fuel cell according to the prior art.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 10 ... Fuel cell 12 ... Electrolyte membrane and electrode structure 14, 16, 60, 80 ... Metal separator 20a ... Oxidant gas supply communication hole 20b ... Oxidant gas discharge communication hole 22a ... Cooling medium supply communication hole 22b ... Cooling medium Discharge communication hole 24a ... Fuel gas supply communication hole 24b ... Fuel gas discharge communication hole 26 ... Solid polymer electrolyte membrane 28 ... Anode side electrode 30 ... Cathode side electrode 36 ... Oxidant gas flow path 38, 46, 62, 82, 84 ... Flat part 40, 48, 64 ... Concave part 42 ... Fuel gas flow path 44 ... Cooling medium flow path

Claims (1)

An electrolyte membrane / electrode structure provided with electrodes on both sides of the solid polymer electrolyte membrane, and a reaction gas that sandwiches the electrolyte membrane / electrode structure and supplies a predetermined reaction gas to the surface facing each electrode A fuel cell comprising a set of metal separators formed with flow paths,
The metal separator is formed on one surface by a pressing process so as to be integrally formed with the metal separator and is in contact with the electrode,
A concave portion that forms the reactive gas flow path by being spaced apart from the electrode across the flat portion;
With
In addition, the other surface is provided with a cooling medium flow path that is formed on the back surface side of the flat portion to flow the cooling medium, and
The flat portion is set so that a width dimension in contact with the electrode decreases from an upstream side to a downstream side of the reactive gas flow path,
The concave portion is set so that the width dimension on the side away from the electrode increases from the upstream side to the downstream side of the reactive gas flow path,
In addition, the fuel cell is characterized in that the width dimension of the cooling medium flow path on the side in contact with the electrode decreases from upstream to downstream.

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