JP2009048905A - Fuel cell - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To suppress drying-up of an anode side and flooding of a cathode side with a simple structure while suppressing heavy weight, large size, complication, and cost increase of a fuel cell. <P>SOLUTION: The solid polymer fuel cell 10 is constructed by laminating repeatedly a plurality of layers of an anode side gas diffusion layer 31, anode side water repellent layer 33, electrolyte membrane-electrode assembly 20, cathode side water repellent layer 34, cathode side gas diffusion layer 32, and separator 40. The anode side water repellent layer 33 and the cathode side water repellent layer 34 are formed of carbon black and PTFE, but the carbon black of the cathode side water repellent layer 34 has smaller particle size than the carbon black of the anode side water repellent layer 33. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a fuel cell in which an electrolyte membrane that conducts protons through water is disposed between an anode electrode and a cathode electrode.

  In a fuel cell, an electrochemical reaction is performed in an electrolyte membrane / electrode assembly composed of an anode electrode, an electrolyte membrane, and a cathode electrode. A specific reaction is, for example, as follows. By supplying hydrogen gas to the anode electrode, a reaction occurs in which the hydrogen gas is ionized into hydrogen ions and electrons, and the ionized hydrogen ions move through the electrolyte membrane to the cathode electrode side. Further, when oxygen is supplied to the cathode electrode, a reaction for generating water from oxygen, hydrogen ions and electrons occurs.

  Among such fuel cells, in the polymer reaction of a polymer electrolyte fuel cell, hydrogen ions ionized at the anode electrode hydrate with water in the electrolyte membrane, so that the electrolyte membrane moves from the anode electrode to the cathode. Move to the electrode. For this reason, on the anode electrode side of the electrolyte membrane, the water content decreases as the above-described electrochemical reaction proceeds. Thus, when the state (dry-up) in which the moisture content of the electrolyte membrane is reduced occurs, water for moving hydrogen ions is insufficient. As a result, the resistance when hydrogen ions permeate the electrolyte membrane increases, which causes a reduction in the power generation efficiency of the fuel cell.

  On the other hand, on the cathode electrode side where water is generated, the generated water may stay in the vicinity of the cathode electrode due to a large amount of generated water generated due to high load operation. Thus, when a state where water is excessively retained (flooding) occurs, the water blocks the oxygen supply path, and the supply of oxygen to the catalyst layer constituting the cathode electrode is hindered. As a result, the reaction at the cathode electrode is reduced, which causes a reduction in the power generation efficiency of the fuel cell.

As described above, in the polymer electrolyte fuel cell, it is an essential problem to appropriately secure the moisture content of the electrolyte membrane / electrode assembly, and various countermeasures are taken against the problem. ing. For example, Patent Document 1 below discloses a fuel cell provided with temperature adjusting means for raising the temperature of the cathode electrode higher than that of the anode electrode. This utilizes the property of the electrolyte membrane that can contain more water at higher temperatures. By making the temperature of the cathode electrode higher than that of the anode electrode, the water is higher on the cathode electrode side and lower on the anode electrode side. This technique further increases the concentration gradient and creates an environment in which the water produced on the cathode side that may be flooded is likely to diffuse to the anode side that is likely to be dry-up, and suppresses flooding and dry-up. The following two means are shown as the temperature adjusting means.
(1) First means: Materials having different thermal conductivities are used for each of the anode side and cathode side separators.
(2) Second means: Two cooling water flow paths are provided inside the separator, and cooling water having different temperatures is allowed to flow between the anode side flow path and the cathode side flow path.

JP 2001-015138 A

  However, in the above-mentioned first means, while excellent conductivity and corrosion resistance are required as a material for the separator, the degree of freedom in selecting the material is reduced. Further, in the second means described above, the cooling water circulation system is complicated, resulting in high cost and complicated control.

  In view of the above-mentioned various problems, the problem to be solved by the present invention is to reduce the weight, size, complexity, and cost of the fuel cell while keeping the anode electrode side dry and This is to suppress the occurrence of flooding on the cathode electrode side.

  SUMMARY An advantage of some aspects of the invention is to solve at least a part of the problems described above, and the invention can be implemented as the following forms or application examples.

Application Example 1 A fuel cell in which an electrolyte membrane that conducts protons through water is disposed between an anode electrode and a cathode electrode,
An anode-side pore layer disposed between an anode-side gas diffusion layer for supplying fuel gas and the anode electrode, and delivering the fuel gas from the anode-side gas diffusion layer to the anode electrode;
A cathode-side pore layer that is disposed between a cathode-side gas diffusion layer that supplies an oxidizing gas and the cathode electrode, and delivers the oxidizing gas from the cathode-side gas diffusion layer to the cathode electrode;
The cathode-side pore layer has a larger thermal resistance than the anode-side pore layer.

  In the fuel cell having such a configuration, the cathode-side pore layer has a larger thermal resistance than the anode-side pore layer. Therefore, the heat generated by the electrochemical reaction in the anode electrode, the electrolyte membrane, and the cathode electrode is more on the cathode electrode side. It is less likely to dissipate heat than the anode electrode side, and the temperature on the cathode electrode side becomes higher than the temperature on the anode electrode side. As a result, the electrolyte membrane can contain more water on the cathode side where the generated water is generated, and a high water concentration gradient on the cathode electrode side and a low water concentration gradient on the anode electrode side increases. It is possible to create an environment that easily diffuses from the cathode electrode side to the anode electrode side. Accordingly, it is possible to suppress at least one of dry-up on the anode electrode side and flooding on the cathode electrode side with a simple configuration.

[Application Example 2] The fuel cell according to Application Example 1, wherein the anode side pore layer and the cathode side pore layer include a carbon member, and the particle size of the carbon member of the cathode side pore layer is the carbon of the anode side pore layer. A fuel cell smaller than the particle size of the member.

  In the fuel cell having such a configuration, since the particle size of the carbon member included in the cathode side pore layer is smaller than the particle size of the carbon member included in the anode side pore layer, the cathode side pore layer is more carbon than the anode side pore layer. The contact point between members increases and thermal resistance becomes large. Therefore, since the temperature on the cathode electrode side becomes higher than the temperature on the anode electrode side, the dryness on the anode electrode side and the flooding on the cathode electrode side can be prevented with only a very simple configuration of reducing the particle size of the carbon member. At least one of the occurrences can be suppressed. The fuel cell is not increased in weight, size, complexity, and cost.

Application Example 3 The fuel cell according to Application Example 2, wherein the carbon member included in the anode-side pore layer includes carbon long fibers.

  In the fuel cell having such a configuration, since the carbon member included in the anode-side pore layer includes carbon long fibers, the number of contact points between the carbon members of the anode-side pore layer is reduced, and the thermal resistance is reduced. As a result, the difference in thermal resistance between the anode-side pore layer and the cathode-side pore layer is increased, and the temperature difference between the anode-side pore layer and the cathode-side pore layer is increased. Generation of at least one of dry-up on the side and flooding on the cathode electrode side can be suppressed.

Application Example 4 The fuel cell according to any one of Application Examples 1 to 3, wherein the cathode-side pore layer is thicker than the anode-side pore layer.

  In the fuel cell having such a configuration, the cathode-side pore layer has a larger thermal resistance than the anode-side pore layer because the cathode-side pore layer is thicker than the anode-side pore layer. Accordingly, since the temperature on the cathode electrode side is higher than the temperature on the anode electrode side, at least one of dry-up on the anode electrode side and flooding on the cathode electrode side can be achieved with only a simple configuration for adjusting the thickness of the pore layer. Occurrence can be suppressed.

[Application Example 5] The fuel cell according to any one of Application Example 1 to Application Example 4, wherein at least the cathode-side pore layer includes another member having a thermal resistance higher than that of the carbon member. A fuel cell in which the mixing ratio of other members is higher than the mixing ratio of other members in the anode-side pore layer.

  In the fuel cell having such a configuration, since the mixing rate of other members having a higher thermal resistance than the carbon member is higher in the cathode side pore layer than in the anode side pore layer, the cathode side pore layer is hotter than the anode side pore layer. Resistance increases. Therefore, since the temperature on the cathode electrode side is higher than the temperature on the anode electrode side, at least one of dry-up on the anode electrode side and flooding on the cathode electrode side occurs only with a simple configuration in which other members are mixed. Can be suppressed.

A. Example:
Examples of the present invention will be described. FIG. 1 is an explanatory diagram showing the configuration of a fuel cell 10 as an embodiment of the present invention. The fuel cell 10 is a solid polymer fuel cell. The fuel cell 10 has a plurality of anode side gas diffusion layers 31, anode side water repellent layers 33, electrolyte membrane / electrode assemblies 20, cathode side water repellent layers 34, cathode side gas diffusion layers 32, and separators 40 that are repeatedly stacked. Composed. FIG. 1 shows a part of the stacked layers.

  The electrolyte membrane / electrode assembly 20 is a portion where an electrochemical reaction of the fuel cell is performed, and is composed of an anode electrode 21, an electrolyte membrane 22, and a cathode electrode 23. The electrolyte membrane 22 is an ion exchange membrane formed of a solid polymer material, and conducts protons that are compatible with water well in a wet state. In this example, a fluororesin was used.

  The anode electrode 21 and the cathode electrode 23 are formed by supporting a catalyst on a conductive carrier. In this embodiment, an electrode paste is prepared using carbon particles carrying a platinum catalyst and an electrolyte of the same material as the electrolyte constituting the electrolyte membrane 22, and this electrode paste is applied to the electrolyte membrane 22 and dried.・ Used one that was fixed.

  The anode-side gas diffusion layer 31 and the cathode-side gas diffusion layer 32 flow of a reactive gas (a fuel gas containing hydrogen or an oxidizing gas containing oxygen) used for an electrochemical reaction in the electrolyte membrane / electrode assembly 20. It becomes a road and collects electricity. In this embodiment, carbon paper is used, but other conductive members having gas permeability, such as carbon cloth, carbon nanotube, metal fiber cloth, metal porous body (foam metal), etc. may be used. .

  The anode-side water-repellent layer 33 and the cathode-side water-repellent layer 34 have finer pores than the anode-side gas diffusion layer 31 and the cathode-side gas diffusion layer 32, and the reaction gas is sent to the anode-side gas diffusion layer 31 or the cathode. It is a layer that plays a role of transferring from the side gas diffusion layer 32 to the anode electrode 21 or the cathode electrode 23, and corresponds to a pore layer in the claims. The anode-side water-repellent layer 33 and the cathode-side water-repellent layer 34 have a moisture adjustment function for adjusting the amount of moisture in the electrolyte membrane 22, the anode electrode 21 and the anode-side gas diffusion layer 31, or the cathode electrode 23 and the cathode-side gas. The anode-side gas diffusion layer 31 and the cathode-side gas diffusion layer 32 are made to be electrolyte membranes by a conductive function that secures a contact area necessary for good conduction with the diffusion layer 32 and a fastening force from both ends of the fuel cell 10. -It also has a damage prevention function that prevents the electrode assembly 20 from being damaged.

  Details of the anode-side water-repellent layer 33 and the cathode-side water-repellent layer 34 are shown in FIG. In this embodiment, the anode-side water-repellent layer 33 and the cathode-side water-repellent layer 34 have the same thickness and are respectively disposed between the anode-side gas diffusion layer 31 and the anode electrode 21 and the cathode-side gas diffusion layer 32 as shown in the figure. And the cathode electrode 23. The above-mentioned thickness can be about several tens of μm to several hundreds of μm, but in this example, it was set to 50 μm.

  Both the anode-side water-repellent layer 33 and the cathode-side water-repellent layer 34 are formed including a carbon member and a water-repellent material. In this embodiment, carbon black is used as the carbon member and PTFE (polytetrafluoroethylene) is used as the water repellent material. However, other materials may be used as long as the above functions can be ensured. In addition, since the water content adjusting function described above is not essential, it is not essential that the anode-side water-repellent layer 33 or the cathode-side water-repellent layer 34 includes a water-repellent material. The anode-side water-repellent layer 33 and the cathode-side water-repellent layer 34 can be manufactured, for example, by spraying or printing a paste made of the above-described material on the anode electrode 21 or the cathode electrode 23. The pores of these water repellent layers are, for example, about 0.1 μm to 10 μm.

  The anode-side water-repellent layer 33 and the cathode-side water-repellent layer 34 are characterized in that the particle diameters of the carbon members included in them are different. That is, the particle size of the carbon member included in the cathode-side water-repellent layer 34 is smaller than the particle size of the carbon member included in the anode-side water-repellent layer 33. The effect will be described later as an effect of the present invention. The particle size of the carbon member may be appropriately set in consideration of the contact property (conductivity) with the cathode electrode 23 and the cathode side gas diffusion layer 32 or the anode electrode 21 and the anode side gas diffusion layer 31. However, it is generally set to about 0.5 μm to 25 μm. In this example, the particle size of the carbon member of the cathode side water repellent layer 34 was 1 μm, and the particle size of the carbon member of the anode side water repellent layer 33 was 20 μm.

  In this embodiment, the anode-side water-repellent layer 33 and the cathode-side water-repellent layer 34 are formed as layers independent of the anode-side gas diffusion layer 31 and the cathode-side gas diffusion layer 32. The layer 31 or the cathode side gas diffusion layer 32 is provided with at least one of the above-mentioned reaction gas delivery function, moisture adjustment function, conductive function, and damage prevention function, so that the anode side gas diffusion layer 31 and the anode side water repellent layer 33 are provided. Alternatively, at least one of the cathode side gas diffusion layer 32 and the cathode side water repellent layer 34 may be formed as an integral layer.

  Here, the description returns to FIG. The separator 40 is a part forming the wall surfaces of the anode-side gas diffusion layer 31 and the cathode-side gas diffusion layer 32 serving as a reaction gas flow path, and also performs a current collecting function. When a material showing acidity is used for the electrolyte membrane 22, corrosion resistance is also required. In this embodiment, titanium is used, but a gas-impermeable conductive member such as stainless steel, dense carbon that has been made impermeable to gas by compressing carbon, or calcined carbon may be used.

  In addition, the separator 40 includes a cooling water passage 42 for adjusting the operating temperature of the fuel cell. In this embodiment, as the separator 40, a flat plate provided on the anode electrode 21 side, a flat plate provided on the cathode electrode 23 side, and a predetermined shape serving as a cooling flow path disposed therebetween. A three-layer separator integrated with an intermediate plate having a through hole was used. The separator 40 is not limited to such a configuration. For example, the separator 40 has various configurations such as two plates having an uneven shape on the surface and the uneven shape serves as a cooling channel. These separators can be used.

  In addition, between the separators 40, the outer periphery of the electrolyte membrane / electrode assembly 20, the anode-side gas diffusion layer 31, and the cathode-side gas diffusion layer 32 is ensured to be sealed in the in-cell gas flow path. A sealing portion 50 is provided integrally with the electrolyte membrane / electrode assembly 20. In this example, fluororubber was used.

  The separator 40 and the seal portion 50 described above are provided with through holes, and these communicate with each other to form an oxidizing gas supply manifold 44 and an oxidizing gas discharge manifold 46. As shown in the drawing, the oxygen as the oxidizing gas supplied to the oxidizing gas supply manifold 44 is supplied to the cathode-side gas diffusion layer 32 through the inside of the separator 40 and used for the fuel cell reaction at the cathode electrode 23. . The exhaust gas (cathode exhaust gas) is discharged from the cathode-side gas diffusion layer 32 to the oxidizing gas discharge manifold 46 through the inside of the separator 40. Although explanation is omitted, fuel gas and cooling water are also supplied to the anode electrode 21 or the cooling water flow path 42 through the manifold formed in the separator 40 and the seal portion 50 in other cross sections (not shown) and discharged. Is done.

  In the fuel cell 10 having such a configuration, the particle size of the carbon member included in the cathode side water repellent layer 34 is smaller than the particle size of the carbon member included in the anode side water repellent layer 33. There are more contact points between the carbon members than the anode-side water-repellent layer 33, and the thermal resistance is increased. That is, the heat generated by the electrochemical reaction is less radiated on the cathode electrode 23 side than on the anode electrode 21 side, and the temperature on the cathode electrode 23 side becomes higher than the temperature on the anode electrode 21 side. As a result, the electrolyte membrane can contain more water on the cathode electrode 23 side where the generated water is generated, and the water concentration gradient that is higher on the cathode electrode 23 side and lower on the anode electrode 21 side is even greater. Therefore, it is possible to create an environment in which the generated water generated at the cathode electrode 23 that may be flooded easily diffuses from the cathode electrode 23 toward the anode electrode 21 that may be dried up. Therefore, it is possible to suppress at least one of dry-up on the anode electrode 21 side and flooding on the cathode electrode 23 side with only a very simple configuration of reducing the particle size of the carbon member. In addition, since only the particle size of the carbon member is adjusted, the fuel cell is not increased in weight, size, complexity, and cost, and is easy to manufacture. Does not adversely affect sex.

  Further, by adjusting the carbon particle size of the anode-side water-repellent layer 33 and the cathode-side water-repellent layer 34, a temperature difference is produced between the cathode electrode 23 side and the anode electrode 21 side. Compared with the case where a temperature difference is generated by using different materials on the cathode electrode 23 side, the freedom of selection of the material of the separator 40 is increased, and the cost and weight of the separator 40 can be reduced. Furthermore, when a metal member is used for the separator 40, the anode electrode 21 side and the cathode electrode 23 side can be joined more easily than when different materials are used for the anode electrode 21 side and the cathode electrode 23 side.

  Further, in the fuel cell 10 having such a configuration, the reaction is less likely to occur and the temperature on the cathode electrode 23 side where high activity is required is higher than the temperature on the anode electrode 21 side as compared with the anode electrode 21 of the fuel cell 10. Thus, the activity of the cathode electrode 23 can be relatively increased. Accordingly, the reactivity of the electrochemical reaction can be improved and an efficient operation can be performed. For the same reason, the time required for the startup operation of the fuel cell 10 can be shortened.

B. Variations:
Several modifications of the present invention will be described.
B-1. Modification 1:
In this embodiment, the anode-side water-repellent layer 33 and the cathode-side water-repellent layer 34 are composed of only the same carbon member (carbon black in the embodiment), but the present invention is not limited to such a configuration. For example, carbon long fibers may be added to carbon black in the anode-side water repellent layer 33. Various carbon long fibers such as VGCF (vapor growth carbon fiber) and carbon nanotubes can be used.

  In this way, the carbon long fiber has the effect of reducing the contact point between the carbon members and reducing the thermal resistance due to the length of the fiber length, so the heat of the anode-side water repellent layer 33 is reduced. The resistance can be reduced, and the difference in thermal resistance between the anode-side water-repellent layer 33 and the cathode-side water-repellent layer 34 can be increased as compared with the embodiment. That is, the temperature difference between the anode electrode 21 side and the cathode electrode 23 side can be increased. Therefore, the dry-up on the anode electrode 21 side and the flooding on the cathode electrode 23 side can be suppressed more effectively.

B-2. Modification 2:
In this embodiment, as a means for increasing the thermal resistance of the cathode-side water-repellent layer 34 compared to the anode-side water-repellent layer 33, the anode-side water-repellent layer 33 and the cathode-side water-repellent layer 34 have different carbon particles. (Carbon black was used in the examples), but it is not limited to such a configuration. For example, the cathode-side water-repellent layer 34 may be configured so that the thickness in the stacking direction of the fuel cell 10 is larger than the thickness of the anode-side water-repellent layer 33. For example, the anode-side water-repellent layer 33 may have a thickness of 100 μm with respect to the cathode-side water-repellent layer 34 having a thickness of 50 μm. The thickness of the cathode-side water-repellent layer 34 may be set as appropriate as long as it does not hinder the drainage performance of the cathode electrode 23.

  Even in this case, the thick cathode-side water-repellent layer 34 has higher thermal resistance than the anode-side water-repellent layer 33, and the temperature on the cathode electrode 23 side becomes higher than the temperature on the anode electrode 21 side. Therefore, dry-up on the anode electrode 21 side and flooding on the cathode electrode 23 side can be suppressed with only a simple configuration of adjusting the thickness. Of course, in addition to the configuration using the carbon member having a particle diameter smaller than that of the anode-side water-repellent layer 33 for the cathode-side water-repellent layer 34 shown in the embodiment, the thickness of the cathode-side water-repellent layer 34 of this modification is further increased. Needless to say, it is more effective if the anode side water repellent layer 33 is thicker than the anode side water repellent layer 33.

B-3. Modification 3:
Further, as a means for increasing the thermal resistance of the cathode-side water-repellent layer 34 more than that of the anode-side water-repellent layer 33, at least a member having a higher thermal resistance than the carbon member is mixed in the cathode-side water-repellent layer 34. The mixing ratio of the member in the water-repellent layer 34 may be higher than that of the anode-side water-repellent layer 33. The member may be mixed into the anode-side water-repellent layer 33 at a lower rate than the cathode-side water-repellent layer 34 or may not be mixed at all. As the member, for example, PTFE added to the anode-side water-repellent layer 33 and the cathode-side water-repellent layer 34 in the embodiment may be used, or other resin may be used.

  Even in this case, the cathode-side water-repellent layer 34 in which more members having high thermal resistance are mixed has a higher thermal resistance than the anode-side water-repellent layer 33, and the temperature on the cathode electrode 23 side is on the anode electrode 21 side. It becomes higher than the temperature. Therefore, dry-up on the anode electrode 21 side and flooding on the cathode electrode 23 side can be suppressed with only a simple configuration of adjusting the mixing rate. Of course, it goes without saying that it is more effective if combined with the configurations of the embodiments and other modifications.

  The embodiment of the present invention has been described above, but the present invention is not limited to such an example, and it is needless to say that the present invention can be implemented in various modes without departing from the gist of the present invention. For example, the present invention is not limited to the polymer electrolyte fuel cell using hydrogen gas as a fuel shown in the examples, but various fuels using an electrolyte membrane that conducts protons through water, such as a direct methanol fuel cell. It can be applied to batteries.

It is explanatory drawing which shows the structure of the fuel cell 10 as an Example of this invention. FIG. 3 is an explanatory diagram showing detailed configurations of an anode-side water-repellent layer 33 and a cathode-side water-repellent layer.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 ... Fuel cell 20 ... Electrolyte membrane electrode assembly 21 ... Anode electrode 22 ... Electrolyte membrane 23 ... Cathode electrode 31 ... Anode side gas diffusion layer 32 ... Cathode side gas diffusion layer 33 ... Anode side water repellent layer 34 ... Cathode side water repellent Water layer 40 ... Separator 42 ... Cooling water flow path 44 ... Oxidizing gas supply manifold 46 ... Oxidizing gas discharge manifold 50 ... Seal part

Claims (5)

A fuel cell in which an electrolyte membrane that conducts protons through water is disposed between an anode electrode and a cathode electrode,
An anode-side pore layer disposed between an anode-side gas diffusion layer for supplying fuel gas and the anode electrode, and delivering the fuel gas from the anode-side gas diffusion layer to the anode electrode;
A cathode-side pore layer that is disposed between a cathode-side gas diffusion layer that supplies an oxidizing gas and the cathode electrode, and delivers the oxidizing gas from the cathode-side gas diffusion layer to the cathode electrode;
The cathode-side pore layer has a larger thermal resistance than the anode-side pore layer. The fuel cell according to claim 1, wherein
The anode side pore layer and the cathode side pore layer include a carbon member,
The fuel cell, wherein a particle size of the carbon member of the cathode side pore layer is smaller than a particle size of the carbon member of the anode side pore layer.   The fuel cell according to claim 2, wherein the carbon member included in the anode-side pore layer includes carbon long fibers.   The fuel cell according to any one of claims 1 to 3, wherein a thickness of the cathode-side pore layer is larger than a thickness of the anode-side pore layer. A fuel cell according to any one of claims 1 to 4, wherein
At least the cathode-side pore layer includes another member having a higher thermal resistance than the carbon member,
The fuel cell has a higher mixing rate of the other member in the cathode-side pore layer than a mixing rate of the other member in the anode-side pore layer.

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