JP2014072165A - Fuel cell and manufacturing method therefor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To suppress tearing of a membrane due to dry shrinkage of a membrane electrode assembly.SOLUTION: A fuel cell includes a membrane electrode assembly, first and second gas diffusion layers arranged, respectively, on two surfaces of the membrane electrode assembly, a seal portion provided at the outer edge on one surface of the membrane electrode assembly, and arranged to bring the membrane electrode assembly into a slack state at normal humidity between the first gas diffusion layer, and a pair of separator plates for holding the membrane electrode assembly, the first and second gas diffusion layers, and the seal portion.

Description

  The present invention relates to a fuel cell, and more particularly to a structure of a peripheral portion of a fuel cell.

  A fuel cell including a separator, a laminated member, and a seal member is known (Patent Document 1). In this fuel cell, the seal member is formed integrally with an end portion of the separator and the laminated member. . The laminated member includes at least an electrolyte membrane disposed on one side of the separator and a diffusion layer disposed between the electrolyte membrane and the separator. The peripheral edge of one surface of the electrolyte membrane is in contact with the surface on one side of the separator.

JP 2008-123895 A

  A fuel cell used for an automobile or the like is repeatedly operated and stopped, and the electrolyte membrane is wetted or dried. When the electrolyte membrane dries, it shrinks by drying. At this time, tensile stress is applied, and the electrolyte membrane may be broken depending on the state of the electrolyte membrane.

  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.

(1) According to one aspect of the present invention, a fuel cell is provided. The fuel cell according to this aspect includes a membrane electrode assembly, first and second gas diffusion layers disposed on two surfaces of the membrane electrode assembly, and an outer edge portion of one surface of the membrane electrode assembly. A seal portion disposed between the first gas diffusion layer and the membrane electrode assembly so that the membrane electrode assembly is slackened at normal humidity. And a pair of separator plates that sandwich the first and second gas diffusion layers and the seal portion. According to the fuel cell of this embodiment, the membrane electrode assembly has a slack, and the slack enters the gap between the first gas diffusion layer and the seal, and the membrane electrode assembly is dried and contracted during drying. Even if this occurs, it is possible to suppress the occurrence of stress in the membrane / electrode assembly by extending the slack that has entered the gap, and it is possible to suppress tearing by drying shrinkage of the membrane / electrode assembly.

(2) In the fuel cell of the above aspect, the membrane electrode assembly may be rectangular, and the gap may be formed in parallel with the short side of the rectangle. The amount of drying shrinkage in the direction parallel to the long side of the membrane electrode assembly is larger than the amount of drying shrinkage in the direction parallel to the short side. The gap between the seal portion and the first gas diffusion layer exists on all four sides. According to the fuel cell of this embodiment, the gap into which the slack of the membrane electrode assembly enters is formed in parallel with the rectangular short side of the membrane electrode assembly, so that the gap in the direction parallel to the long side of the membrane electrode assembly Even if the amount of drying shrinkage is large and the amount of slackening increases when wet, it becomes possible to absorb the large amount of slackening in the gap.

(3) According to one form of this invention, the manufacturing method of a fuel cell is provided. The fuel cell manufacturing method of this embodiment includes a step of preparing first and second gas diffusion layers having different sizes, and a step of disposing a membrane electrode assembly between the first and second gas diffusion layers. And a seal portion is disposed on the outer edge of one surface of the membrane electrode assembly so that the membrane electrode assembly is loosened at normal humidity between the first gas diffusion layer and the first gas diffusion layer. And a step of unitizing the fuel cell by sandwiching the membrane electrode assembly, the first and second gas diffusion layers, and the seal portion with a pair of separator plates. According to the fuel cell manufacturing method of this embodiment, it is possible to manufacture a fuel cell having a slack in the membrane electrode assembly after unitization. Even when drying shrinkage occurs in the membrane / electrode assembly during drying, it is possible to suppress the occurrence of stress in the membrane / electrode assembly by stretching the slack, and to suppress the tearing due to the drying / shrinkage of the membrane / electrode assembly. It becomes possible.

(4) In the fuel cell manufacturing method of the above aspect, the step of drying and shrinking the membrane electrode assembly when the relative humidity of the membrane electrode assembly is 0%, and the relative humidity of the unitized fuel cell are normally controlled. And the step of placing the seal portion may be performed in a state where the membrane electrode assembly is dried and contracted. According to the method of manufacturing a fuel cell of this embodiment, even if the membrane electrode assembly is loose when the fuel cell is manufactured, the membrane electrode assembly is not loosened when the relative humidity is 0%. A membrane / electrode assembly that reduces the stress applied to the membrane / electrode assembly during contraction can be achieved.

(5) In the method of manufacturing a fuel cell according to the above aspect, the membrane electrode assembly is further provided by a dimensional change amount of the membrane electrode assembly when the relative humidity at the time of manufacturing the fuel cell is changed to 0%. A step of determining the length in the longitudinal direction of the second gas diffusion layer to be longer than the length in the longitudinal direction of the second gas diffusion layer. According to the fuel cell manufacturing method of this aspect, it is possible to match the positions of the end of the membrane electrode assembly and the end of the second gas diffusion layer.

(6) In the method of manufacturing a fuel cell according to the above aspect, the step of measuring the relationship between the number of cycles in which the membrane / electrode assembly is wetted / dried and the stress at which the membrane / electrode assembly tears, A step of obtaining a stress value at which the membrane / electrode assembly is not torn by the number of wet / dry cycles within the useful life of the membrane / electrode assembly, and the amount of distortion of the membrane / electrode assembly caused by the stress. And determining a length in the longitudinal direction of the electrode assembly so as to be longer than a length in the longitudinal direction of the membrane electrode assembly. According to the fuel cell manufacturing method of this aspect, it is possible to suppress the tearing of the membrane electrode assembly within the service life of the fuel cell.

  The present invention can be realized in various forms. For example, the present invention can be realized in forms such as a fuel cell manufacturing method in addition to a fuel cell.

It is a figure which shows typically the cross section of the edge part of the single cell of the fuel cell of 1st Embodiment. It is a top view when the single cell of the fuel cell of 1st Embodiment is seen from the 1st gas diffusion layer side. It is a graph which shows the relationship between the relative humidity of a membrane electrode assembly, and distortion. It is a graph which shows the relationship between the frequency | count of the drying / wetting cycle applied to a membrane electrode assembly, and the stress which a membrane electrode assembly tears. It is a graph which shows the relationship between the distortion concerning a membrane electrode assembly, and the stress concerning a membrane electrode assembly. It is explanatory drawing which shows the manufacturing process of the 1st manufacturing method of the single cell in a present Example. It is explanatory drawing which shows the manufacturing process of the 3rd manufacturing method of the single cell in a present Example.

First Embodiment FIG. 1 is a diagram schematically showing a cross section of an end portion of a single cell of a fuel cell according to a first embodiment. The single cell 10 includes a membrane electrode assembly 100, a first gas diffusion layer 110, a second gas diffusion layer 120, a first separator plate 130, a second separator plate 140, a seal portion 150, . The membrane electrode assembly 100 includes a catalyst layer and catalyst layers respectively formed on both surfaces of the electrolyte membrane. The electrolyte membrane is formed of an electrolyte membrane having proton conductivity such as perfluorocarbon sulfonic acid polymer. The catalyst layer contains carbon and ionomer carrying a catalyst. A platinum catalyst or a platinum alloy catalyst can be used as the catalyst. Carbon particles and carbon nanotubes can be used as the carbon. As the ionomer, a perfluorocarbon sulfonic acid polymer can be used.

  The first gas diffusion layer 110 and the second gas diffusion layer 120 are porous members for diffusing the reaction gas, and are disposed on each surface of the membrane electrode assembly 100, respectively. As the first gas diffusion layer 110 and the second gas diffusion layer 120, for example, a carbon cloth or carbon paper using a carbon non-woven fabric can be used. In this embodiment, a carbon cloth using carbon paper is used. Yes. In addition, as the first gas diffusion layer 110 and the second gas diffusion layer 120, a porous body made of metal or resin can be used in addition to carbon cloth or carbon paper. In the present embodiment, the size of the first gas diffusion layer 110 in the longitudinal direction is smaller than the size of the membrane electrode assembly 100 in the longitudinal direction. The size of the first gas diffusion layer 110 in the longitudinal direction is substantially the same as the size of the membrane electrode assembly 100 in the longitudinal direction.

  A seal portion 150 is formed on the outer edge portion of the membrane electrode assembly 100 on the first gas diffusion layer 110 side. The seal portion 150 is a resin member provided in order to suppress leakage of the anode gas to the outside. In this embodiment, the seal portion 150 is provided so that a gap 160 is formed between the seal portion 150 and the first gas diffusion layer 110.

  The membrane / electrode assembly 100 swells or shrinks by drying depending on the wet state. The membrane electrode assembly 100 in the swollen state has a slack 100 a, and the slack 100 a enters the gap 160. On the other hand, in the dry-shrinked state, the slack 100a is straightened to relieve the stress due to the dry shrinkage and suppress the tearing of the membrane electrode assembly 100. In FIG. 1, the slack 100a is exaggerated.

  A first separator plate 130 is disposed outside the first gas diffusion layer 110 and the seal portion 150, and a second separator plate 140 is disposed outside the second gas diffusion layer 120. The first separator plate 130 and the second separator plate 140 have an uneven shape. A first reaction gas flow path 135 is formed between the first separator plate 130 and the first gas diffusion layer 110, and between the second separator plate 140 and the second gas diffusion layer 120. The second reaction gas channel 145 is formed.

  FIG. 2 is a plan view of the single cell of the fuel cell according to the first embodiment as viewed from the first gas diffusion layer side. In FIG. 2, the description of the first separator plate 130 is omitted. Note that the second separator plate 140 is in an invisible state because it is on the back side. The single cell 10 has a rectangular shape with a length in the longitudinal direction L1 and a length in the short direction L2. A frame-shaped seal portion 150 is disposed on the periphery of the unit cell 10. A first gas diffusion layer 110 is disposed inside the seal portion 150. At this time, a gap 160 is formed between both ends in the longitudinal direction of the first gas diffusion layer 110 and the seal portion 150, and the relaxed membrane electrode assembly 100 can be seen in the gap 160. A gap is also formed between both ends of the first gas diffusion layer 110 in the short direction and the seal portion 150. However, a configuration may be employed in which no gap is formed between both ends of the first gas diffusion layer 110 in the short direction and the seal portion 150.

FIG. 3 is a graph showing the relationship between the relative humidity and strain of the membrane electrode assembly 100. The horizontal axis in FIG. 3 is the relative humidity RH (%) of the membrane electrode assembly 100, and the vertical axis is the strain S (%) when the length of the membrane electrode assembly during shrink drying is 100%. . Therefore, the distortion when the relative humidity is 0% is 0 (%). In general, when the membrane electrode assembly 100 is wet, the length increases. When the length L0 of the membrane electrode assembly 100 at the time of shrinkage drying is L0 and the length of the membrane electrode assembly 100 at the relative humidity Rt% is Lt, there is the following relationship between S, L0, and Lt. .
ΔLt = Lt−L0 (1)
St = (ΔLt / L0) × 100 (%) (2)

  Therefore, the size of the membrane electrode assembly 100 when the relative humidity is 0% is set to be substantially the same as that of the second gas diffusion layer 120, and the size of the membrane electrode assembly 100 at the time of fabrication is set to the second gas diffusion layer. It is made larger by the strain ΔLt than the size of the layer 120. Then, the membrane electrode assembly 100 and the end of the second gas diffusion layer are aligned, and the remaining membrane electrode assembly 100 is loosened to prepare a single cell. In this way, even if the relative humidity of the membrane electrode assembly 100 becomes 0% and the membrane electrode assembly 100 is dried and contracted to become approximately the same size as the second gas diffusion layer 120, the membrane electrode assembly 100 is Becomes difficult to be stressed. As a result, the tearing of the membrane electrode assembly 100 can be suppressed.

Second embodiment:
When the membrane / electrode assembly 100 is dried, the membrane / electrode assembly 100 contracts and stress is applied to the membrane / electrode assembly 100. Here, the membrane electrode assembly 100 deteriorates over time when the expansion and contraction are repeated. Therefore, the membrane electrode assembly 100 may be torn even in a state where a stress smaller than that required for tearing the membrane electrode assembly 100 is applied immediately after manufacturing. The second embodiment suppresses the tearing of the membrane electrode assembly 100 within the service life.

  FIG. 4 is a graph showing the relationship between the number of wet and dry cycles applied to the membrane electrode assembly and the stress at which the membrane electrode assembly 100 tears. The horizontal axis in FIG. 4 represents the number of wet and dry cycles applied to the membrane electrode assembly, and the vertical axis represents the stress that the membrane electrode assembly 100 tears. In addition, in this measurement, it measures in the state without slack at the time of wetness. The relationship between the number of wet and dry cycles of the single cell 10 and the stress at which the membrane electrode assembly 100 tears is obtained in advance by experiments. Then, the number N of dry / wet cycles executed within the service life can be obtained by experiments or the like, and the stress δf at which the membrane electrode assembly 100 tears when the service life has just passed can be obtained from the number N of the cycles.

  FIG. 5 is a graph showing the relationship between the stress applied to the membrane electrode assembly and the strain at which the membrane electrode assembly tears. The horizontal axis in FIG. 5 is the strain that causes the membrane electrode assembly to tear, and the vertical axis is the stress applied to the membrane electrode assembly 100. When a large stress is applied to the membrane electrode assembly 100, the membrane electrode assembly 100 is deformed and a large strain is generated. From the stress δf obtained from the graph of FIG. 4, the strain St (%) can be calculated using the graph of FIG.

  In the second embodiment, the relative humidity Rt at which the strain St is obtained is obtained using FIG. Then, in the state of the relative humidity Rt, the size of the membrane electrode assembly 100 is formed to be larger than the second gas diffusion layer 120 by the strain St to form a cell. As a result, even when the membrane / electrode assembly has a relative humidity of 0%, the size of the membrane / electrode assembly 100 falls within the size of the second gas diffusion layer 120, and no stress greater than δf is applied. Therefore, even if the wet and dry cycle is repeated and the membrane electrode assembly deteriorates over time, the stress of δf or more is not applied within the service life, so that the membrane electrode assembly 100 is prevented from tearing within the service life. It becomes possible.

First manufacturing method:
FIG. 6 is an explanatory view showing a manufacturing process of the first manufacturing method of a single cell in this example. The first manufacturing method is a manufacturing method corresponding to the first embodiment. In the step (A), the membrane electrode gas diffusion layer assembly 170 is produced at normal humidity. The membrane electrode gas diffusion layer assembly 170 is obtained by integrating the membrane electrode assembly 100, the first gas diffusion layer 110, and the second gas diffusion layer 120. However, the membrane electrode assembly 100 and the first gas diffusion layer 110 and the membrane electrode assembly 100 and the second gas diffusion layer 120 are not bonded with an adhesive or the like. The normal humidity is a relative humidity (65 ± 20)% (JIS standard JIS Z 8703). The temperature at normal humidity is (20 ± 15) ° C.

  In the step (B), the relative humidity of the membrane electrode assembly 100 is set to 0%. As a result, the membrane electrode assembly 100 is dried and contracted. Examples of a method for setting the relative humidity to 0% include a method of evacuating or replacing with a gas not containing moisture such as nitrogen. The relative humidity may not be strictly 0%, but may be a low relative humidity of several percent (for example, 5%) or less. When the membrane electrode assembly 100 and the end portions of the first and second gas diffusion layers 110 and 120 are aligned, the membrane electrode assembly 100 is lengthened in advance, and the relative When the humidity is 0%, the membrane electrode assembly 100 protruding from the end portions of the first and second gas diffusion layers 110 and 120 may be cut off. Further, a portion where stress concentration is expected, such as the corner portion 150a of the seal portion 150 or the corner portion 110a of the gas diffusion layer, may be chamfered. If there is no problem with fastening or leakage, the membrane electrode assembly 100 may be inside the seal portion 150 or the end portion of the second gas diffusion layer 120.

  In the step (C), the seal portion 150 is disposed at the outer edge portion of the membrane electrode assembly 100, and the first and second separator plates 130 are further sandwiched between the membrane electrode gas diffusion layer assembly 170 and the seal portion 150. 140 are placed and heated to press to form a cell.

  In the step (D), the relative humidity of the membrane electrode assembly 100 is returned to normal humidity. Thereby, the membrane electrode assembly 100 swells. Since the end portion of the membrane electrode assembly 100 is fixed by the seal portion 150 and the central portion is sandwiched between the first gas diffusion layer 110 and the second gas diffusion layer 120, the membrane electrode assembly 100. The swollen and extended portion of the gas enters the gap 160 between the seal portion 150 and the first gas diffusion layer 110 as a slack 100a.

  When the membrane / electrode assembly 100 is dried and contracted, the slackness 100a that has entered the gap 160 returns to the original non-intrusion state to relieve the stress, thereby suppressing the tearing of the membrane / electrode assembly 100. Is possible.

Second manufacturing method:
Similar to the first manufacturing method, the second manufacturing method is a manufacturing method corresponding to the first embodiment, and is a modification of the first manufacturing method. In the first manufacturing method, the membrane electrode gas diffusion layer assembly 170 was first produced at normal humidity, but in the second embodiment, the membrane electrode gas diffusion layer assembly 170 was produced at a relative humidity of 0% from the beginning. To do. That is, only the steps (B) to (D) except the step (A) of the first embodiment are included. When aligning the membrane electrode assembly 100 with the end portions of the first and second gas diffusion layers 110 and 120, in the first manufacturing method, the membrane electrode assembly 100 is temporarily enlarged in step (A). In the step (B), the membrane electrode assembly 100 is further cut. According to the second manufacturing method, the step of cutting the membrane electrode assembly 100 is only one time of the step (B), and the labor of cutting the membrane electrode assembly 100 is saved. Further, in the first manufacturing method, a piece generated when the membrane electrode assembly 100 is cut a second time is difficult to reuse, and the use of the second manufacturing method can waste the membrane electrode assembly 100. It becomes possible to reduce.

Third manufacturing method:
FIG. 7 is an explanatory view showing a manufacturing process of the third manufacturing method of a single cell in this example. The third manufacturing method is a manufacturing method corresponding to the second embodiment. In the step (A), the strain St (%) to be relaxed and the relative humidity Rt (%) at which the strain St (%) is obtained. Specifically, the number of wet and dry cycles in the service life is obtained, and the stress δf is calculated from the relationship between the number of dry and wet cycles applied to the membrane electrode assembly shown in FIG. 4 and the stress at which the membrane electrode assembly is torn. Then, the strain St (%) of the membrane electrode assembly 100 is calculated using the relationship between the strain of the membrane electrode assembly and the stress applied to the membrane electrode assembly shown in FIG. Further, the relative humidity Rt (%) is obtained using the relationship between the relative humidity and strain of the membrane electrode assembly shown in FIG.

  In the step (B), the membrane electrode assembly 100 is produced. This step (B) may be performed at normal humidity. In the step (C), the relative humidity of the membrane electrode assembly 100 is lowered to the relative humidity Rt (%) obtained in the step (A). Thereby, the membrane electrode assembly 100 contracts.

  In the step (D), the seal portion 150 is disposed on the outer edge portion of the membrane electrode assembly 100, and the first and second separator plates 130 are further sandwiched between the membrane electrode gas diffusion layer assembly 170 and the seal portion 150. 140 are placed and heated to press to form a cell.

  In the step (E), the relative humidity of the membrane electrode assembly 100 is returned to normal humidity. Thereby, the membrane electrode assembly 100 swells. Since the end portion of the membrane electrode assembly 100 is fixed by the seal portion 150 and the central portion is sandwiched between the first gas diffusion layer 110 and the second gas diffusion layer 120, the membrane electrode assembly 100. The swollen and extended portion of the gas enters the gap 160 between the seal portion 150 and the first gas diffusion layer 110 as a slack 100a.

    When the membrane electrode assembly 100 is dried and contracted, the slackness 100a that has entered the gap 160 returns to a state where it has not entered, thereby relaxing the stress. At this time, since the stress applied to the membrane electrode assembly 100 is within δf within the service life, it is possible to suppress the tearing of the membrane electrode assembly 100 within the service life.

  The embodiments of the present invention have been described above based on some embodiments. However, the embodiments of the present invention described above are for facilitating the understanding of the present invention and limit the present invention. It is not a thing. The present invention can be changed and improved without departing from the spirit and scope of the claims, and it is needless to say that the present invention includes equivalents thereof.

DESCRIPTION OF SYMBOLS 10 ... Single cell 100 ... Membrane electrode assembly 100a ... Slack 110 ... 1st gas diffusion layer 110a ... Corner | angular part 120 ... 2nd gas diffusion layer 130 ... 1st separator plate 135 ... 1st reaction gas flow path 140 ... second separator plate 145 ... second reaction gas flow path 150 ... seal part 150a ... corner part 160 ... gap 170 ... membrane electrode gas diffusion layer assembly Lt / L0 ... Δ
N: Number of times RH ... Relative humidity Rt ... Relative humidity δf ... Stress

Claims (6)

A fuel cell,
A membrane electrode assembly;
First and second gas diffusion layers respectively disposed on two surfaces of the membrane electrode assembly;
A seal portion provided at an outer edge portion of one surface of the membrane electrode assembly so that the membrane electrode assembly is loosened at normal humidity with the first gas diffusion layer. A seal portion to be disposed;
A pair of separator plates that sandwich the membrane electrode assembly, the first and second gas diffusion layers, and the seal portion;
A fuel cell comprising: The fuel cell according to claim 1, wherein
The membrane electrode assembly is rectangular,
The fuel cell, wherein the gap is formed in parallel with the rectangular short side. A fuel cell manufacturing method comprising:
Preparing first and second gas diffusion layers of different sizes;
Disposing a membrane electrode assembly between the first and second gas diffusion layers;
A step of disposing a seal portion on the outer edge of one surface of the membrane electrode assembly so that the membrane electrode assembly is loosened at normal humidity with the first gas diffusion layer; ,
A step of unitizing the fuel cell by sandwiching the membrane electrode assembly, the first and second gas diffusion layers, and the seal portion with a pair of separator plates;
A method for manufacturing a fuel cell. The method of manufacturing a fuel cell according to claim 3, further comprising:
Drying and shrinking the membrane electrode assembly by setting the relative humidity of the membrane electrode assembly to 0%;
Returning the relative humidity of the unitized fuel cell to normal humidity;
With
The step of arranging the seal part is a method for manufacturing a fuel cell, wherein the membrane electrode assembly is dried and contracted. The method of manufacturing a fuel cell according to claim 4, further comprising:
The length of the membrane electrode assembly in the longitudinal direction is the same as that of the second gas diffusion layer by the amount of dimensional change of the membrane electrode assembly when the relative humidity at the time of manufacturing the fuel cell is changed to 0% relative humidity. A method for manufacturing a fuel cell, comprising a step of determining the length to be longer than a length in a longitudinal direction. The method of manufacturing a fuel cell according to claim 3, further comprising:
Measuring the relationship between the number of cycles to wet and dry the membrane electrode assembly and the stress at which the membrane electrode assembly tears in advance;
A step of obtaining a stress value at which the membrane / electrode assembly does not tear at the number of wet / dry cycles within the useful life of the membrane / electrode assembly from the relationship;
Determining the length of the membrane electrode assembly in the longitudinal direction to be longer than the length of the membrane electrode assembly by the amount of strain of the membrane electrode assembly caused by the stress;
A method for manufacturing a fuel cell.

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