JP2006019162A - Fuel cell - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To make possible to keep proper humidity in a fuel cell regardless of its conditions of power generation. <P>SOLUTION: A plurality of unit gas diffusion layers 14 and 16 having regions of high gas-permeability 32 and 34 and a region of low gas-permeability are stacked to construct a gas diffusion layer. At least one layer 16 of the unit gas diffusion layers 14 and 16 is movable in a plane perpendicular to the stacking direction in relation to the adjacent layer 14. Relative displacement of the adjacent unit gas diffusion layers 14 and 16 by a moving device 36 changes overlapping states of each regions 32 and 34 between the unit gas diffusion layers 14 and 16, and results in change of gas-permeability of the whole of the gas diffusion layers. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a fuel cell, and more particularly to a fuel cell in which a gas diffusion layer is disposed between a catalyst layer in contact with an electrolyte membrane and a separator in which a gas flow path is formed.

  The electrolyte membrane of a fuel cell requires water molecules for the movement of hydrogen ions therein, and exhibits high hydrogen ion conductivity only when it contains moisture. For this reason, moisture is essential to maintain the battery performance of the fuel cell. On the other hand, however, if there is excessive moisture in the fuel cell, the gas flow path is blocked by water, and the flow of the reaction gas (fuel gas or oxidizing gas) to the electrode is hindered. Battery performance is degraded. Therefore, it is important for the fuel cell to maintain high cell performance by removing excess water and keeping the inside in a moderately wet state.

As a technique for removing excess moisture in the fuel cell, for example, a conventional technique described in Patent Document 1 is known. This prior art is characterized by the structure of the gas diffusion layer constituting the electrode. The electrode of the fuel cell includes a catalyst layer provided in contact with the electrolyte membrane and a gas diffusion layer disposed between the catalyst layer and the gas flow path. In the prior art, the gas diffusion layer has a two-layer structure of a dense inner layer and a water-repellent and porous outer layer, thereby improving the drainage of moisture generated on the surface of the catalyst layer.
JP 2000-182625 A JP 2000-58073 A Japanese Patent Laid-Open No. 10-172586

  However, in the above prior art, when the power generation state of the fuel cell changes, the inside of the fuel cell cannot always be maintained in an appropriate wet state. This is because the drainage performance of the gas diffusion layer is determined by the structure of the gas diffusion layer, whereas the amount of water generated in the fuel cell varies depending on the power generation situation. For example, when the load is high with a large amount of moisture generated, the gas diffusion layer is required to reliably drain excess water, whereas when the load is low with a small amount of moisture generated, the gas diffusion layer has an electrolyte membrane. Water retention is required to prevent drying. In the above prior art, the structure of the gas diffusion layer is fixed, and the drainage performance is constant regardless of the power generation status of the fuel cell, so it is difficult to meet all the demands according to the power generation status.

  The present invention has been made to solve the above-described problems, and an object of the present invention is to provide a fuel cell that can always maintain the inside of the fuel cell in an appropriate wet state regardless of the power generation state. And

In order to achieve the above object, a first invention provides a fuel cell in which a gas diffusion layer is disposed between a catalyst layer in contact with an electrolyte membrane and a separator in which a gas flow path is formed.
The gas diffusion layer is configured by laminating a plurality of unit gas diffusion layers having a high permeability region having a high gas permeability and a low permeability region having a low gas permeability,
Moving means for moving at least one of the unit gas diffusion layers in a plane perpendicular to the stacking direction with respect to an adjacent layer, and changing an overlapping state of the regions between the adjacent unit gas diffusion layers; It is characterized by providing.

  According to a second aspect of the present invention, in the first aspect of the present invention, the moving means is configured such that the high permeability region between the adjacent unit gas diffusion layers is higher when the power generation load of the fuel cell is higher than when the power generation load is low. The unit gas diffusion layers adjacent to each other are relatively moved so as to increase the overlapping rate.

  According to a third aspect of the present invention, in the first aspect, the moving means has the high transmission between the adjacent unit gas diffusion layers when the humidity or temperature in the fuel cell is higher than when the humidity or temperature is low. The unit gas diffusion layers adjacent to each other are moved relative to each other so as to increase the overlapping ratio of the active regions.

  According to a fourth invention, in any one of the first to third inventions, the unit gas diffusion layer arranged at the outermost of the unit gas diffusion layers has the high permeability region facing the gas flow path. It is characterized by being arranged like this.

  According to a fifth invention, in any one of the first to fourth inventions, an opening that penetrates the unit gas diffusion layer is provided as the highly permeable region.

According to a sixth aspect of the present invention, there is provided a fuel cell in which a gas diffusion layer is disposed between a catalyst layer in contact with an electrolyte membrane and a separator having a gas flow path in order to achieve the above object.
The gas diffusion layer is configured by laminating a plurality of unit gas diffusion layers in which a plurality of through holes having a substantially constant shape are formed in a regular arrangement,
Moving means for moving at least one of the unit gas diffusion layers relative to an adjacent layer in a plane perpendicular to the stacking direction to change an overlapping state of the through holes between the adjacent unit gas diffusion layers It is characterized by having.

  According to a seventh aspect, in the sixth aspect, the moving means is configured such that the rate of overlap of the through holes between the adjacent unit gas diffusion layers when the power generation load of the fuel cell is higher than when the power generation load is low. The unit gas diffusion layers adjacent to each other are moved relative to each other so as to be high.

  In an eighth aspect based on the sixth aspect, the moving means has the through-holes between the adjacent unit gas diffusion layers when the humidity or temperature in the fuel cell is higher than when the humidity or temperature is low. The unit gas diffusion layers adjacent to each other are moved relative to each other so as to increase the overlapping ratio.

  According to a ninth invention, in any one of the sixth to eighth inventions, the unit gas diffusion layer is formed of a mesh.

  According to a tenth aspect of the present invention, in any one of the first to ninth aspects, at least one of the unit gas diffusion layers is disposed along the gas flow path, and the moving means includes the gas flow path. The unit gas diffusion layer disposed along the gas flow path is moved with the wall portion of the separator constituting the base point as a base point.

  An eleventh invention is characterized in that, in any one of the first to tenth inventions, the moving means is composed of a water-absorbing polymer that expands and contracts according to the amount of water absorption.

  A twelfth aspect of the invention is characterized in that, in any one of the first to tenth aspects of the invention, the moving means is made of a shape memory alloy that expands and contracts according to temperature.

  In the first invention, the apparent gas permeability in the entire gas diffusion layer is changed by changing the overlapping state of the regions between the adjacent unit gas diffusion layers. For example, when the low permeability region of the other unit gas diffusion layer is overlapped with the high permeability region of one unit gas diffusion layer, and when the other unit gas diffusion layer of the other unit gas diffusion layer is superposed on the high permeability region of one unit gas diffusion layer. In the case where the highly permeable regions are stacked, the latter has higher apparent gas permeability in the entire gas diffusion layer. The higher the apparent gas permeability in the entire gas diffusion layer, the more the moisture is removed from the catalyst layer by the reaction gas, so the drainage is improved. Conversely, the lower the apparent gas permeability is, the more moisture from the reaction gas is. Water retention is improved because the removal of water is suppressed. Therefore, according to the first invention, the relative movement between the adjacent unit gas diffusion layers is controlled in accordance with the power generation status of the fuel cell, and the gas permeability in the entire gas diffusion layer is changed, so that the power generation status is changed. Regardless, the inside of the fuel cell can always be maintained in a moderately moist state.

  The amount of water generated with the power generation of the fuel cell increases as the power generation load of the fuel cell increases. According to the second invention, since the overlapping rate of the highly permeable regions between the adjacent unit gas diffusion layers is controlled according to the power generation load, the inside of the fuel cell is always maintained in a moderately moist state regardless of the power generation load. can do.

  The higher the humidity or temperature in the fuel cell, the more water is generated in the fuel cell with power generation. According to the third aspect of the invention, since the overlapping rate of the highly permeable regions between the adjacent unit gas diffusion layers is controlled according to the humidity or temperature in the fuel cell, the inside of the fuel cell is always maintained in an appropriate wet state. can do.

  According to the fourth aspect of the invention, since the highly permeable region of the outermost unit gas diffusion layer faces the gas flow path, the outer side of the highly permeable region of the outermost unit gas diffusion layer is on the inner side. By overlapping the highly permeable regions of the unit gas diffusion layer, water can be efficiently drained from the catalyst layer to the gas flow path.

  In addition, according to the fifth aspect of the present invention, by making the opening penetrating the unit gas diffusion layer a highly permeable region, two regions having different gas permeability (a high permeable region and a low permeable region) can be simplified. Can be configured.

  In the sixth invention, the gas permeability in the entire gas diffusion layer is changed by changing the overlapping state of the through holes between the adjacent unit gas diffusion layers. For example, when the overlap between the through hole of one unit gas diffusion layer and the through hole of the other unit gas diffusion layer is shifted, the through hole of one unit gas diffusion layer and the through hole of the other unit gas diffusion layer When the two are completely stacked, the latter has higher gas permeability in the entire gas diffusion layer. As the gas permeability in the entire gas diffusion layer increases, the drainage improves, and conversely, as the gas permeability decreases, the drainage improves. Therefore, according to the sixth aspect of the present invention, the relative movement between the adjacent unit gas diffusion layers is controlled according to the power generation status of the fuel cell, and the gas permeability in the entire gas diffusion layer is changed, so that the power generation status is changed. Regardless, the inside of the fuel cell can always be maintained in a moderately moist state.

  The amount of water generated with the power generation of the fuel cell increases as the power generation load of the fuel cell increases. According to the seventh invention, since the overlapping rate of the through holes between the adjacent unit gas diffusion layers is controlled in accordance with the power generation load, the inside of the fuel cell is always maintained in an appropriate wet state regardless of the power generation load. Can do.

  The higher the humidity or temperature in the fuel cell, the more water is generated in the fuel cell with power generation. According to the eighth invention, since the overlapping rate of the through holes between the adjacent unit gas diffusion layers is controlled in accordance with the humidity or temperature in the fuel cell, the inside of the fuel cell is always maintained in an appropriate wet state. Can do.

  Further, according to the ninth invention, the mesh has a large number of through-holes having a fixed shape formed in a regular arrangement and can be used as a unit gas diffusion layer as it is, so that the gas diffusion layer can be easily configured. it can.

  According to the tenth invention, by moving the unit gas diffusion layer disposed along the gas flow path with the wall portion of the separator constituting the gas flow path as a base point, the moving means can be configured with a simple structure. Can be realized.

  According to the eleventh aspect, since the water-absorbing polymer automatically expands and contracts according to the humidity inside the fuel cell, it is possible to easily realize the relative movement between the adjacent unit gas diffusion layers according to the power generation situation.

  According to the twelfth invention, since the shape memory alloy automatically expands and contracts according to the temperature inside the fuel cell, the relative movement between the adjacent unit gas diffusion layers according to the power generation situation can be easily realized.

Embodiment 1 FIG.
Hereinafter, Embodiment 1 of the present invention will be described with reference to FIGS.

  FIG. 1 is a schematic configuration diagram of a fuel cell 2 as Embodiment 1 of the present invention. The fuel cell 2 is configured such that both sides of the electrolyte membrane 4 are sandwiched between electrodes 10 and 20 and both sides are sandwiched between separators 6 and 8. Normally, the fuel cell 2 is not used alone, but is used as a fuel cell stack in which the fuel cell 2 is one cell and a plurality of cells are stacked in one direction. Here, for the sake of simplicity, description will be given focusing on one cell (fuel cell 2).

  The electrolyte membrane 4 is a non-conductive ion exchange membrane, such as a solid polymer membrane, and hydrogen ions move through the membrane in a wet state. One electrode 10 arranged outside the electrolyte membrane 4 is a cathode, and the cathode 10 is a catalyst layer 12 arranged on one surface of the electrolyte membrane 4 and gas diffusion layers 14 and 16 having a two-layer structure arranged outside the catalyst layer 12. It consists of. The other electrode 20 is an anode, and the anode 20 includes a catalyst layer 22 disposed on the other surface of the electrolyte membrane 4 and gas diffusion layers 24 and 26 having a two-layer structure disposed on the outside thereof.

  The separators 6 and 8 are plates made of a material that is impermeable to both gas and water and has conductivity, such as carbon, metal, or conductive resin. Gas flow paths 18 and 28 are formed on the contact surfaces of the separators 6 and 8 with the electrodes 10 and 20. The gas flow path 18 formed in the separator 6 in contact with the cathode 10 is an oxidizing gas flow path for supplying an oxidizing gas (for example, air) containing oxygen, and the gas flow path formed in the separator 8 in contact with the anode 20. 28 is a fuel gas flow path for supplying a fuel gas containing hydrogen.

  Of the two-layer gas diffusion layers 14 and 16 constituting the cathode 10, the inner gas diffusion layer 14 is disposed so as to cover the entire surface of the catalyst layer 12, and is integrally bonded to the catalyst layer 12. The separator 6 is disposed in contact with the surface of the gas diffusion layer 14. On the other hand, the outer gas diffusion layer 16 is provided along the oxidizing gas flow path 18, and both sides thereof are sandwiched between the inner gas diffusion layer 14 and the separator 6. The outer gas diffusion layer 16 and the inner gas diffusion layer 14 are not bonded, and the outer gas diffusion layer 16 can move relative to the inner gas diffusion layer 14 along the oxidizing gas flow path 18. ing.

  Similarly, of the gas diffusion layers 24 and 26 having a two-layer structure constituting the anode 20, the inner gas diffusion layer 24 is disposed so as to cover the entire surface of the catalyst layer 22, and is integrally bonded to the catalyst layer 22. Yes. The separator 8 is disposed so as to contact the surface of the gas diffusion layer 24. The outer gas diffusion layer 26 is provided along the fuel gas flow path 28, and both sides thereof are sandwiched between the inner gas diffusion layer 24 and the separator 8. The outer gas diffusion layer 26 and the inner gas diffusion layer 24 are not bonded, and the outer gas diffusion layer 26 can move relative to the inner gas diffusion layer 24 along the oxidizing gas flow path 28. ing.

  2 and 4 are detailed views of the gas diffusion layers 14 and 16 on the cathode 10 side as viewed from the direction A in FIG. 1 (above the oxidizing gas flow path 18). 3 is a cross-sectional view in the B direction of FIG. 2, and FIG. 5 is a cross-sectional view in the C direction of FIG. The difference between the structure shown in FIGS. 2 and 3 and the structure shown in FIGS. 4 and 5 is due to the difference in the amount of expansion and contraction of the water-absorbing polymer 36 described later. Hereinafter, the configuration of the gas diffusion layers 14 and 16 on the cathode 10 side will be described in detail with reference to these drawings. The configuration of the gas diffusion layers 24 and 26 on the anode 20 side is the same as the configuration of the gas diffusion layers 14 and 16 on the cathode 10 side, which will be described below.

  A plurality of openings 34 are formed in the outer gas diffusion layer 16 at regular intervals along the oxidizing gas flow path 18. On the other hand, in the inner gas diffusion layer 14, a plurality of openings 32 are formed at regular intervals so as to correspond to the openings 34 formed in the outer gas diffusion layer 16 only in the portion located below the oxidizing gas flow path 18. Is formed. At the upstream end or the downstream end along the gas flow path 18 of the outer gas diffusion layer 16, a tip end portion of the water-absorbing polymer 36 that expands and contracts in accordance with the moisture absorption is joined. The water-absorbing polymer 36 is located in the oxidizing gas flow path 18, and its base end is joined to the wall (not shown) of the separator 6.

  As the water absorbing polymer 36 expands and contracts, the outer gas diffusion layer 16 moves along the oxidizing gas flow path 18 and the relative position to the inner gas diffusion layer 14 changes. FIG. 3 shows a state in which the water-absorbing polymer 36 is extended to the maximum. At this time, the opening 34 of the outer gas diffusion layer 16 is positioned directly above the opening 32 of the inner gas diffusion layer 14. Yes. FIG. 5 shows a state in which the water-absorbing polymer 36 is contracted to the minimum. At this time, the opening 34 of the outer gas diffusion layer 16 is completely removed from the opening 32 of the inner gas diffusion layer 14. By setting the positional relationship between the upper and lower openings 32 and 34 in this way, the overlapping ratio of the upper and lower openings 32 and 34 changes linearly according to the amount of expansion and contraction of the water absorbent polymer 36.

  Next, the operation of the fuel cell 2 configured as described above, particularly the operation according to the load of the fuel cell 2 will be described. The amount of water generated in the catalyst layer 12 of the cathode 10 with power generation increases as the load of the fuel cell 2 increases. When the amount of moisture generated in the catalyst layer 12 increases, the water-absorbing polymer 36 disposed in the oxidizing gas flow path 18 absorbs moisture and expands. As a result, when the load of the fuel cell 2 increases, the outer gas diffusion layer 16 moves on the inner gas diffusion layer 14 as shown in FIGS. 2 and 3, and the opening 34 of the outer gas diffusion layer 16 moves to the inner gas. It comes to be located right above the opening 32 of the diffusion layer 14. Since the opening 34 of the outer gas diffusion layer 16 faces the gas flow path 18, a line directly connecting the catalyst layer 12 and the gas flow path 18 is formed by connecting the upper and lower openings 32 and 34 in a straight line. Thus, the diffusion of moisture from the catalyst layer 12 to the gas flow path 18 is promoted through this line. That is, the apparent gas permeability of the gas diffusion layers 14 and 16 as a whole is increased.

  On the other hand, when the load of the fuel cell 2 is low and the amount of water produced in the catalyst layer 12 is small, the water-absorbing polymer 36 disposed in the oxidizing gas channel 18 deprives moisture due to a decrease in the relative humidity of the oxidizing gas. It contracts. As a result, when the load on the fuel cell 2 decreases, the outer gas diffusion layer 16 moves on the inner gas diffusion layer 14 toward the water absorbent polymer 36 as shown in FIGS. Deviation occurs between the position of the opening 34 and the position of the opening 32 of the inner gas diffusion layer 14. Thus, in order for the water | moisture content produced | generated by the catalyst layer 12 to reach the gas flow path 18 by interrupting | blocking communication of the upper and lower openings 32 and 34, the inner side gas diffusion layer 14 and / or the outer side gas diffusion layer 16 are used. You have to pass through. That is, the apparent gas permeability of the entire gas diffusion layers 14 and 16 is reduced.

  As described above, the fuel cell 2 of the present embodiment can automatically control the apparent gas permeability of the entire gas diffusion layers 14 and 16 according to the load of the fuel cell 2. First, when the load of the fuel cell 2 becomes high, the opening 34 of the outer gas diffusion layer 16 is positioned immediately above the opening 32 of the inner gas diffusion layer 14 due to the extension of the water-absorbing polymer 36, thereby causing gas diffusion. The apparent gas permeability of the entire layers 14 and 16 is increased, and the removal of moisture from the catalyst layer 12 by the oxidizing gas is promoted. Thereby, the drainage of the gas diffusion layers 14 and 16 at the time of high load with a large amount of generated moisture is improved, and it becomes possible to drain excessive water reliably and maintain high power generation performance.

  Conversely, when the load of the fuel cell 2 is reduced, the position of the opening 34 of the outer gas diffusion layer 16 is shifted from the position of the opening 32 of the inner gas diffusion layer 14 due to the shrinkage of the water absorbing polymer 36, thereby The apparent gas permeability of the entire 14, 16 is lowered, and the removal of moisture from the catalyst layer 12 by the oxidizing gas is suppressed. Thereby, the water retention of the gas diffusion layers 14 and 16 at the time of low load with a small amount of moisture generation is improved, and it becomes possible to prevent the electrolyte membrane 4 from being dried and to maintain high power generation performance.

  2 to 5 show only the case where the water-absorbing polymer 36 is extended to the maximum and the case where the water-absorbing polymer 36 is contracted to the minimum, the water-absorbing polymer 36 expands and contracts according to the amount of generated water and opens the outer gas diffusion layer 16. The overlapping ratio between the portion 34 and the opening 32 of the inner gas diffusion layer 14 changes according to the amount of expansion and contraction of the water absorbent polymer 36. Therefore, when the load of the fuel cell 2 changes and the amount of generated water changes, the overlapping ratio of the upper and lower openings 32 and 34 changes accordingly, and the apparent gas permeability of the entire gas diffusion layers 14 and 16 changes. Will change. Thereby, it becomes possible to always maintain the inside of the fuel cell 2 in an appropriate wet state regardless of the load state of the fuel cell.

  In the present embodiment, each of the inner gas diffusion layer 14 and the outer gas diffusion layer 16 corresponds to the “unit gas diffusion layer” of the first invention, and the inner gas diffusion layer 14 and the outer gas diffusion layer 16 are combined. The entirety corresponds to the “gas diffusion layer” of the first invention. The openings 32 and 34 of the gas diffusion layers 14 and 16 correspond to the “highly permeable region” of the first invention, and the regions other than the openings 32 and 34 of the gas diffusion layers 14 and 16 are the first. This corresponds to the “low permeability region” of the first invention. As in the present embodiment, by providing the openings 32 and 34 penetrating the gas diffusion layers 14 and 16, two regions having different gas permeability (a high permeability region and a low permeability region) can be easily configured. can do.

  In the present embodiment, the openings 32 and 34 are opened in the gas diffusion layers 14 and 16, but the gas diffusion layers 14 and 16 may be configured as shown in FIG. FIG. 6 is a view showing a modification of the gas diffusion layers 14 and 16 and corresponds to FIG. 5 of the above embodiment. In this modification, the inner gas diffusion layer 14 is configured by alternately combining a high permeability region 42 having a high gas permeability and a low permeability region 44 having a low gas permeability. Similarly, the outer gas diffusion layer 16 is configured by alternately combining the high permeability region 46 and the low permeability region 48 at the same pitch as the inner gas diffusion layer 14. The difference in gas permeability between the high-permeability regions 42 and 46 and the low-permeability regions 44 and 48 is realized by making the material, density, pore diameter, etc. of the porous material forming each region different. Also in this modified example, the amount of expansion / contraction of the water-absorbing polymer 36 changes according to the amount of generated water, whereby the overlapping ratio between the high-permeability regions 42 and 46 changes, and the apparent gas in the gas diffusion layers 14 and 16 as a whole. Permeability will change.

Embodiment 2. FIG.
Next, a second embodiment of the present invention will be described with reference to FIGS.

  The fuel cell according to the present embodiment is different from the first embodiment in the configuration of the gas diffusion layer, and the other configurations are the same as those in the first embodiment. FIGS. 7 and 9 are diagrams showing the configuration of the gas diffusion layer according to the second embodiment. FIG. 7 is a diagram viewed from the direction A in FIG. 1 (above the oxidizing gas flow path 18) in the first embodiment. Equivalent to. 8 is a cross-sectional view in the D direction of FIG. 7, and FIG. 10 is a cross-sectional view in the E direction of FIG. The difference between the structure shown in FIGS. 7 and 8 and the structure shown in FIGS. 9 and 10 is due to the difference in the amount of expansion and contraction of the water-absorbing polymer 36 described later. In the figure, the same reference numerals are given to the same parts as those in the embodiment. In the following, an example in which the configuration of the present invention is applied to the cathode-side gas diffusion layer will be described, but it is of course applicable to the anode-side gas diffusion layer.

  The gas diffusion layers 52 and 56 according to the present embodiment also have a two-layer structure as in the first embodiment. The inner gas diffusion layer 52 is disposed so as to cover the entire surface of the catalyst layer 12 and is integrally bonded to the catalyst layer 12. The outer gas diffusion layer 56 is disposed so as to be movable along the surface of the inner gas diffusion layer 52, and its end is joined to the wall portion of the separator 6 via the water-absorbing polymer 36. In the present embodiment, as the gas diffusion layers 52 and 56, meshes made of metal or carbon are used. Meshes 54 and 58 are regularly formed on the mesh.

  The relative position of the outer gas diffusion layer 56 with respect to the inner gas diffusion layer 52 changes as the water-absorbing polymer 36 expands and contracts. FIG. 8 shows a state in which the water-absorbing polymer 36 is extended to the maximum. At this time, the mesh 58 of the outer gas diffusion layer 56 and the mesh 54 of the inner gas diffusion layer 52 are completely overlapped. On the other hand, FIG. 10 shows a state where the water-absorbing polymer 36 is contracted to the minimum. At this time, the mesh 58 of the outer gas diffusion layer 56 and the mesh 54 of the inner gas diffusion layer 52 are displaced.

  As described in the first embodiment, the amount of expansion / contraction of the water-absorbing polymer 36 changes according to the load of the fuel cell. When the load of the fuel cell rises, the water-absorbing polymer 36 absorbs and expands the water generated by power generation, so that the outer gas diffusion layer 56 is placed on the inner gas diffusion layer 52 as shown in FIGS. The upper and lower meshes 54 and 58 are completely overlapped. When a mesh is used as the gas diffusion layers 52 and 56 as in this embodiment, the gas permeability is determined by the ratio of the mesh area to the entire mesh area (porosity). For this reason, when the upper and lower meshes 54 and 58 are completely overlapped as described above, the porosity is maximized, and substantially the same gas permeation as when only one of the gas diffusion layers 52 and 56 is provided. Sex will be obtained.

  On the other hand, when the load of the fuel cell is reduced, the water-absorbing polymer 36 is deprived of moisture by the oxidizing gas whose relative humidity has been reduced, so that the outer gas diffusion layer 56 becomes the inner gas as shown in FIGS. The diffusion layer 52 moves to the water-absorbing polymer 36 side, and the upper and lower meshes 54 and 58 are displaced from each other. Thereby, the porosity of the mesh in the gas diffusion layers 52 and 56 as a whole is lowered, and the apparent gas permeability is lowered.

  As described above, according to the configuration of the gas diffusion layers 52 and 56 according to the present embodiment, as in the first embodiment, the apparent gas permeability of the entire gas diffusion layers 52 and 56 according to the load of the fuel cell. Can be controlled automatically. As a result, it is possible to improve the drainage performance of the gas diffusion layers 52 and 56 during high loads with a large amount of moisture generated, and to reliably drain excess moisture and maintain high power generation performance. In addition, it is possible to improve the water retention of the gas diffusion layers 52 and 56 at the time of low load where the amount of generated moisture is small, and to prevent the electrolyte membrane from being dried and to maintain high power generation performance.

  In the present embodiment, each of the inner gas diffusion layer 52 and the outer gas diffusion layer 56 corresponds to the “unit gas diffusion layer” of the sixth invention, and the inner gas diffusion layer 52 and the outer gas diffusion layer 56 are combined. The entirety corresponds to the “gas diffusion layer” of the sixth invention. The mesh meshes 54 and 58 used for the gas diffusion layers 52 and 56 correspond to the “through holes” of the sixth invention.

  In the present embodiment, the outer gas diffusion layer 56 is moved in parallel. However, as shown in FIG. 11, when the gas diffusion layers 52 and 56 are round (for example, the gas diffusion layers 52 and 56 are round cylinders). The outer gas diffusion layer 56 may be rotated in the circumferential direction according to the load of the fuel cell. In this case, when the load is high, the upper and lower meshes 54, 58 are completely overlapped as shown in the enlarged view of FIG. 12, and when the load is low, the upper and lower meshes 54, 58 are shown as shown in the enlarged view of FIG. Try to cause a shift. In FIG. 11, the inner gas diffusion layer 52 and the outer gas diffusion layer 56 are displayed while being shifted in the horizontal direction. However, the two gas diffusion layers 52 and 56 are actually overlapped with each other. In this state, the outer gas diffusion layer 56 rotates.

Others.
Although the embodiments of the present invention have been described above, the present invention is not limited to the above-described embodiments, and various modifications can be made without departing from the spirit of the present invention. For example, the following modifications may be made.

  In the above embodiment, a water-absorbing polymer is used as means for moving the outer gas diffusion layer, but a shape memory alloy may be used instead. Even if the shape memory alloy is deformed at a predetermined temperature or lower, the shape memory alloy has a property of returning to a shape before deformation when the temperature is higher than the predetermined temperature. Therefore, by using a shape memory alloy as a means for moving the outer gas diffusion layer, when the load of the fuel cell is increased and the temperature in the gas flow path is increased, the load of the fuel cell is decreased and the gas flow path is decreased. The position of the outer gas diffusion layer can be automatically changed when the inner temperature is lowered.

  An artificial muscle may be used as a means for moving the outer gas diffusion layer. Artificial muscles can be expanded and contracted by electrical signals. Therefore, by configuring the electric signal to be supplied to the artificial muscle according to the load of the fuel cell, the position of the outer gas diffusion layer can be automatically changed according to the load of the fuel cell.

  In the above embodiment, the gas diffusion layer has a two-layer structure of the outer gas diffusion layer and the inner gas diffusion layer, but more unit gas diffusion layers may be stacked. In this case, the unit gas diffusion layer that can be moved by the moving means is not limited to one layer, and a plurality of unit gas diffusion layers may be configured to be movable.

  In the second embodiment, a mesh is used as the gas diffusion layer. However, the mesh is not limited to a mesh as long as it is a member in which a large number of substantially uniform through holes (mesh in a mesh) are formed in a regular arrangement. . For example, a punching plate may be used as the gas diffusion layer. The higher the overlapping ratio of the upper and lower through holes, the higher the apparent porosity of the entire gas diffusion layer. Therefore, by controlling the overlapping rate of the upper and lower through holes according to the load of the fuel cell, the gas permeability can be changed according to the load of the fuel cell.

It is a figure which shows schematic structure of the fuel cell as Embodiment 1 of this invention. It is the figure seen from the A direction of FIG. 1 (at the time of high load). FIG. 3 is a cross-sectional view in the B direction of FIG. 2. It is the figure seen from the A direction of FIG. 1 (at the time of low load). FIG. 5 is a cross-sectional view in the direction C of FIG. 4. It is a figure which shows the modification of the gas diffusion layer concerning Embodiment 1 of this invention. It is a figure which shows the structure of the gas diffusion layer concerning this Embodiment 2, and is equivalent to the figure seen from the A direction of FIG. 1 (at the time of high load). It is a D direction sectional view of Drawing 7. It is a figure which shows the structure of the gas diffusion layer concerning this Embodiment 2, and is equivalent to the figure seen from the A direction of FIG. 1 (at the time of low load). FIG. 10 is a cross-sectional view in the E direction of FIG. 9. It is a figure which shows the modification of the gas diffusion layer concerning Embodiment 2 of this invention. It is an enlarged view which shows the positional relationship at the time of high load of the gas diffusion layer shown in FIG. It is an enlarged view which shows the positional relationship at the time of the low load of the gas diffusion layer shown in FIG.

Explanation of symbols

2 Fuel cell 4 Electrolyte membrane 6, 8 Separator 10 Cathode 12, 22 Catalyst layer 14, 24 Inner gas diffusion layer 16, 26 Outer gas diffusion layer 18 Oxidizing gas channel 20 Anode 28 Fuel gas channel 32, 34 Opening 36 Water absorption Polymer 42, 46 High permeability region 44, 48 Low permeability region 52 Inner gas diffusion layer (mesh)
56 Outer gas diffusion layer (mesh)
54,58 mesh

Claims (12)

In a fuel cell in which a gas diffusion layer is disposed between a catalyst layer in contact with an electrolyte membrane and a separator in which a gas flow path is formed,
The gas diffusion layer is configured by laminating a plurality of unit gas diffusion layers having a high permeability region having a high gas permeability and a low permeability region having a low gas permeability,
Moving means for moving at least one of the unit gas diffusion layers in a plane perpendicular to the stacking direction with respect to an adjacent layer, and changing an overlapping state of the regions between the adjacent unit gas diffusion layers; A fuel cell comprising the fuel cell.   The moving means is configured so that the overlapping unit of the highly permeable regions between the adjacent unit gas diffusion layers is higher when the power generation load of the fuel cell is higher than when the power generation load is low. 2. The fuel cell according to claim 1, wherein the gas diffusion layer is relatively moved.   The moving means is arranged so that the overlapping rate of the highly permeable regions between the adjacent unit gas diffusion layers is higher when the humidity or temperature in the fuel cell is higher than when the humidity or temperature is low. 2. The fuel cell according to claim 1, wherein the unit gas diffusion layers are moved relative to each other.   4. The unit gas diffusion layer disposed at the outermost portion of the unit gas diffusion layers is disposed such that the highly permeable region faces the gas flow path. 5. 2. The fuel cell according to item 1.   The fuel cell according to any one of claims 1 to 4, wherein an opening that penetrates the unit gas diffusion layer is provided as the highly permeable region. In a fuel cell in which a gas diffusion layer is disposed between a catalyst layer in contact with an electrolyte membrane and a separator in which a gas flow path is formed,
The gas diffusion layer is configured by laminating a plurality of unit gas diffusion layers in which a plurality of through holes having a substantially constant shape are formed in a regular arrangement,
Moving means for moving at least one of the unit gas diffusion layers relative to an adjacent layer in a plane perpendicular to the stacking direction to change an overlapping state of the through holes between the adjacent unit gas diffusion layers A fuel cell comprising:   The moving means has the unit gas diffusion adjacent to each other so that the overlapping rate of the through holes between the adjacent unit gas diffusion layers is higher when the power generation load of the fuel cell is higher than when the power generation load is low. The fuel cell according to claim 6, wherein the layers are moved relative to each other.   The moving means is adjacent to each other so that the overlapping rate of the through-holes between the adjacent unit gas diffusion layers is higher when the humidity or temperature in the fuel cell is higher than when the humidity or temperature is low. 7. The fuel cell according to claim 6, wherein the unit gas diffusion layer is relatively moved.   The fuel cell according to any one of claims 6 to 8, wherein the unit gas diffusion layer is formed of a mesh.   At least one of the unit gas diffusion layers is disposed along the gas flow path, and the moving means is disposed along the gas flow path with a wall portion of the separator constituting the gas flow path as a base point. The fuel cell according to any one of claims 1 to 9, wherein the unit gas diffusion layer formed is moved.   The fuel cell according to any one of claims 1 to 10, wherein the moving means is composed of a water-absorbing polymer that expands and contracts according to the amount of water absorption. The fuel cell according to any one of claims 1 to 10, wherein the moving means is made of a shape memory alloy that expands and contracts according to temperature.

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