JP5806141B2 - Fuel cell - Google Patents

Description

  The present invention relates to a fuel cell having a membrane electrode assembly.

  Conventionally, as a fuel cell, a membrane electrode assembly and separators disposed on both sides of the membrane electrode assembly are provided, and a gas flow path forming member that is a conductive porous body is provided between the membrane electrode assembly and the separator. What is provided is known. As a gas flow path forming member, a metal plate that has been processed so as to have a plurality of protruding pieces alternately protruding on the front and back surfaces has been proposed (Patent Document 1). According to this configuration, it is possible to achieve both an improvement in gas diffusibility and an improvement in drainage by securing a cross-sectional area of the flow path.

JP 2002-184422 A

  In the fuel cell described above, a gas diffusion layer is provided between the membrane electrode assembly and the separator, and the protrusion of the gas flow path forming member is in contact with the gas diffusion layer. On the other hand, in the fuel cell, a configuration in which the gas diffusion layer is removed is being studied for the purpose of miniaturization, simplification, and high performance. At that time, the microporous layer (MPL: Micro Porous Layer) applied to the gas diffusion layer is arranged in a sheet form, but the MPL It becomes easy to bend. When the MPL is bent, the generated water stays in the bent portion between the MPL and the membrane electrode assembly, resulting in a problem that the drainage performance is lowered.

  An object of the present invention is to provide a fuel cell that does not have a gas diffusion layer and to improve drainage.

  The present invention can be realized as the following forms or application examples in order to solve at least a part of the above-described problems.

Application Example 1 A fuel cell,
A membrane electrode assembly;
A microporous layer disposed outside the membrane electrode assembly;
A gas flow path forming portion that forms a gas flow path having an opening that opens to the microporous layer side, and is disposed in a form in which no gas diffusion layer is interposed on the side opposite to the membrane electrode assembly of the microporous layer; ,
With
The diameter of the opening is a fuel cell in a range of 0.1 μm to 400 μm.

  According to the fuel cell of Application Example 1, since the diameter of the opening of the gas flow path forming part is 400 μm or less, the gas flow path forming part can press the microporous layer at a fine pitch. . For this reason, the microporous layer does not bend even without the gas diffusion layer. Accordingly, the generated water does not accumulate between the microporous layer and the membrane / electrode assembly, so that the drainage can be improved.

[Application Example 2] The fuel cell according to Application Example 1,
A fuel cell, wherein a total area ratio of the openings to a region corresponding to a power generation region on the surface of the gas flow path forming portion is 20% or more.
According to this structure, the gas supply property to a membrane electrode assembly can be ensured.

[Application Example 3] The fuel cell according to Application Example 2,
The gas flow path forming portion is a linear groove formed by a rib,
The diameter of the opening is a width of the groove.
According to this configuration, drainage can be improved in a fuel cell having a linear gas flow path formed by ribs.

[Application Example 4] The fuel cell according to Application Example 2,
The gas flow path forming part is a foam sintered body,
The said opening is a fuel cell which is an opening in the interface between the said microporous layer and the said foaming sintered compact.
According to this configuration, drainage can be improved in the fuel cell in which the gas flow path forming portion is configured by the foamed sintered body.

[Application Example 5] The fuel cell according to Application Example 4,
A fuel cell, wherein a surface of the foamed sintered body is hydrophilic.
According to this configuration, drainage can be further improved.

Application Example 6 The fuel cell according to Application Example 2,
The gas flow path forming part is an expanded metal,
The diameter of the opening is a fuel cell, which is the distance of the shortest part of the opening at the interface between the microporous layer and the expanded metal .
According to this configuration, the drainage can be improved in the fuel cell in which the gas flow path forming portion is configured by the expanded metal.

[Application Example 7] The fuel cell according to Application Example 6,
A fuel cell, wherein the surface of the expanded metal is hydrophilic.
According to this configuration, drainage can be further improved.

  The present invention can be realized in various forms in addition to the application example described above. For example, the present invention is realized as a device invention of a fuel cell system including the fuel cell according to the application example and a vehicle equipped with the fuel cell according to the application example.

It is explanatory drawing which shows typically the cross section of the single cell inside the fuel cell in 1st Example of this invention. It is a figure for demonstrating an aperture ratio. It is explanatory drawing which shows the subject of the single cell as a comparative example. It is a graph which shows cell resistance when the flow path width t2 of an oxidant gas flow path is changed in the fuel cell of 1st Example. It is a graph which shows the relationship between the current density and cell voltage when the channel width t2 of an oxidant gas channel is changed in the fuel cell of 1st Example. It is explanatory drawing which shows typically the cross section of a part of single cell inside the fuel cell in 2nd Example of this invention. It is explanatory drawing which shows typically the cross section of a part of single cell inside the fuel cell in 3rd Example of this invention. It is a perspective view of the expanded metal as a gas flow path formation part.

  Hereinafter, a fuel cell according to an embodiment of the present invention will be described based on examples with reference to the drawings.

A. First embodiment:
A-1: Configuration of fuel cell:
FIG. 1 is an explanatory view schematically showing a cross section of a single cell 10 inside a fuel cell in a first embodiment of the present invention. The fuel cell of the present embodiment is a polymer electrolyte fuel cell, and has a stack structure in which a plurality of single cells 10 shown in FIG. 1 are stacked and connected in series. The single cell 10 is configured by sandwiching a membrane-electrode assembly (MEA) 20 by separators 30 and 40 from both sides.

  The MEA 20 is a joined body in which catalyst layers 22 and 23 are formed on both surfaces (both sides) of the solid polymer electrolyte membrane 21. A solid polymer electrolyte membrane (hereinafter simply referred to as “electrolyte membrane”) 21 is a proton conductive ion exchange membrane formed of a solid polymer material, for example, a fluororesin, and has good electrical conductivity in a wet state. Indicates. In this example, a Nafion membrane (manufactured by DuPont) was used. The catalyst layers 22 and 23 are layers having platinum as a catalyst or an alloy made of platinum and another metal, and serve as an anode (hydrogen electrode) and a cathode (oxygen electrode).

  A gas diffusion layer 26 is disposed between the MEA 20 and the separator 30. On the other hand, no gas diffusion layer is provided between the MEA 20 and the separator 40. The gas diffusion layer 26 is formed of a gas diffusible conductive member, for example, a carbon cloth woven with yarns made of carbon fibers. The gas diffusion layer 26 can be replaced with carbon paper containing carbon fibers. Moreover, it can also replace with the carbon sheet which arrange | positioned carbon fiber in a fixed direction, adhere | attached with the adhesive agent, and made it into a sheet form.

  A first MPL 24 mainly composed of a water-repellent resin and a conductive material such as carbon black is formed on the surface of the gas diffusion layer 26 facing the anode (catalyst layer 22). The water-repellent resin is, for example, polytetrafluoroethylene (PTFE: Polytetrafluoroethylene). The surface of the first MPL 24 is in contact with the catalyst layer 22. The first MPL 24 enhances the drainage capacity of the gas diffusion layer 26 and prevents excessive water scattering. The separator 30 is in contact with the surface of the gas diffusion layer 26 opposite to the first MPL 24.

  A sheet-like second MPL 25 is formed between the MEA 20 and the separator 40. The second MPL 25 has a resin sheet having a number of fine openings such as PTFE and polypropylene as a skeleton, and a conductive material such as carbon black supported on the sheet. The second MPL 25 need not be limited to this configuration, and may be configured to include, for example, an electrolyte component (ionomer). The catalyst layer 23 is in contact with one surface of the second MPL 25, and the separator 40 is in contact with the other surface of the second MPL 25. The second MPL 25 corresponds to the “microporous layer” in the invention according to Application Example 1.

  The separators 30 and 40 are made of a dense carbon plate. Each of the separators 30 and 40 is formed with a plurality of long protruding ribs 32 and 42 by press molding, whereby a linear groove (between the adjacent ribs 32 and 32 ( (Concave portion) is formed. This groove is an opening that opens to the catalyst layers 22 and 23 side, and functions as a flow path for a reaction gas used for an electrochemical reaction in the MEA 20. That is, the groove disposed between the anode-side separator 30 and the MEA 20 serves as a fuel gas flow path 34 through which a fuel gas containing hydrogen passes. Moreover, the groove | channel arrange | positioned between the cathode side separator 40 and MEA20 becomes the oxidant gas flow path 44 through which oxidant gas containing oxygen, such as air, passes. The rib 42 provided in the separator 40 corresponds to the “gas flow path forming portion” in the invention according to Application Example 1.

  In the present embodiment, the width t2 of the oxidant gas flow path 44, that is, the distance between the adjacent ribs 32, 32 is 300 [μm]. The numerical value of 300 [μm] is not limited to this in the present invention. The distance can be any numerical value as long as it is within a range of 0.1 [μm] to 400 [μm]. The distance corresponds to the “diameter of the opening” in the invention according to Application Example 1. That is, in the case where the gas flow path is a line as in the present embodiment, the “diameter of the opening” corresponds to the distance in the width direction, not the length direction. The distance in the width direction can be said to be the distance of the shortest part of the opening. On the other hand, the width t1 of the fuel gas channel 34 is not particularly defined in the present embodiment, and is, for example, 800 [μm].

  Furthermore, in this embodiment, the opening ratio of the oxidant gas flow path 44 in the separator 40 is 25%.

  FIG. 2 is a diagram for explaining the aperture ratio. When the separator 40 is viewed from the stacking direction (Z direction in FIG. 1), the region RY projected on the surface of the separator 40 of the catalyst layer 23 is as illustrated. Since the catalyst layers 23 and 24 are regions where the electrochemical reaction proceeds, this region RY can be said to be a region corresponding to the power generation region. The aperture ratio K can be obtained according to the following equation (1).

K = Sa / Sry (1)
Here, Sry is the total area of the region RY corresponding to the power generation region. Sa is the total area of the openings of the oxidizing gas channel 44 in the region RY. That is, the opening ratio K is a ratio of the total area of the opening of the oxidant gas flow path 44 in the region RY to the region RY corresponding to the power generation region. The total area of the openings is a value obtained by adding the areas of the openings that are open to the second MPL 25 in the oxidant gas flow path 44 over all the oxidant gas flow paths 44.

  In this embodiment, the aperture ratio K is 25%. The aperture ratio K can be set to 20% instead of 25%. In this embodiment, the numerical aperture K can be any value as long as it is 20% or more.

A-2. Example effect:
Next, the operation and effect of the fuel cell of the first embodiment will be described. FIG. 3 is an explanatory diagram showing a problem of the single cell 910 as a comparative example. This single cell 910 differs from the single cell 10 of the first embodiment only in the shape of the separator 940 on the cathode (catalyst layer 23) side, and the other parts are the same. The separator 940 has the same shape as the separator 30 on the anode (catalyst layer 22) side in the first embodiment, and has an oxidizing gas channel 942 having a channel width of 800 [μm]. That is, the separator 30 in the first embodiment has the oxidizing gas channel 44 having a channel width in the range of 0.1 [μm] to 400 [μm], whereas the separator 30 in this comparative example is 0. It has an oxidizing gas channel 942 having a channel width of 800 [μm] which is outside the range of 1 [μm] to 400 [μm].

  When the gas diffusion layer is not provided between the MEA 20 and the separator 40, the second MPL 25 is easily bent as shown in FIG. That is, when the channel width of the oxidant gas channel 942 is wide, a portion of the second MPL 25 that is not weighted by the rib 42, that is, a portion corresponding to the opening portion of the oxidant gas channel 942 is easily bent. Thereby, a space is formed between the second MPL 25 and the catalyst layer 23, and the generated water W stays in the space portion. As a result, in the fuel cell, a flooding phenomenon in which the moisture near the electrolyte membrane 21 is excessive occurs. In addition, the cell resistance increases due to the decrease in the contact area between the second MPL 25 and the catalyst layer 23.

  FIG. 4 is a graph showing the cell resistance when the channel width t2 of the oxidant gas channel 44 is changed in the fuel cell of the first embodiment. The values in this graph were investigated by experiments for power generation and non-power generation. As shown in the graph, when the channel width t2 is 400 [μm] or less, the cell resistance is hardly increased. On the other hand, when the flow path width t2 exceeds 400 [μm], the cell resistance gradually increases during power generation.

  FIG. 5 is a graph showing the relationship between the load (current density) and the cell voltage when the channel width t2 of the oxidant gas channel 44 is changed in the fuel cell of the first embodiment. As shown in this graph, when the road width t2 exceeds 400 [μm], the current density-cell voltage characteristics deteriorate rapidly. That is, as shown in FIG. 4, when the flow path width t2 exceeds 400 [μm], the cell resistance increases, and as shown in FIG. 5, the power generation performance decreases.

  From the above, it can be experimentally found that the fuel cell of the first embodiment has no decrease in power generation performance because the channel width t2 of the oxidant gas channel 44 is 400 [μm] or less. . When the channel width t2 of the oxidant gas channel 44 is 400 [μm] or less, the ribs 42 can press the second MPL 25 at a minute pitch. It is possible to prevent the second MPL 25 from being bent. For this reason, since the generated water does not accumulate between the second MPL 25 and the catalyst layer 23, the drainage of the fuel cell can be improved.

  Further, in the first embodiment, the flow path width t2 is set to 0.1 [μm] or more, but this numerical value of 0.1 [μm] substantially matches the pore size of a general MPL. For this reason, the fuel cell of the first embodiment can ensure gas supply to the catalyst layer 23. The channel width t2 may be in the range from the pore diameter of the second MPL 25 to 400 [μm] instead of in the range of 0.1 [μm] to 400 [μm].

  Furthermore, in the first embodiment, the gas supply performance to the catalyst layer 23 can be ensured by setting the opening ratio K of the oxidant gas flow path 44 in the separator 40 to 20% or more. That is, in the first embodiment, the lower limit value of the channel width t2 is set to 0.1 [μm], and the opening ratio K of the oxidant gas channel 44 is set to 20% or more, whereby the gas supply to the catalyst layer 23 is performed. Sufficient sex can be secured.

  In the first embodiment, the gas diffusion layer is not provided on the cathode side but the gas diffusion layer is provided on the anode side. However, the present invention is not limited to this. A structure having a gas diffusion layer on the cathode side and no gas diffusion layer on the anode side, or a structure having no gas diffusion layer on both the cathode side and the anode side can be employed. In these configurations, like the cathode side of the first embodiment, a sheet-like MPL is disposed on the side having no gas diffusion layer, and the distance between ribs in the separator facing the MPL is set to 0.1 [μm. ] To 400 [μm]. In addition, the opening ratio K of the oxidant gas flow path 44 in the separator facing the MPL is preferably 20% or more.

B. Second embodiment:
FIG. 6 is an explanatory view schematically showing a cross section of a part of the single cell 110 inside the fuel cell in the second embodiment of the present invention. The single cell 110 in the second embodiment differs from the single cell 10 in the first embodiment in the configuration of the cathode-side separator 140 and the gas flow path forming portion 142. Since the other configuration of the single cell 110 in the second embodiment is the same as that of the single cell 10 in the first embodiment, the same components as those in FIG. 1 are denoted by the same reference numerals in FIG. The description is omitted. In FIG. 6, the description of the respective parts 22, 24, 26, 30 on the anode side in FIG. 1 is omitted.

  In the single cell 10 (FIG. 1) of the first embodiment, the separator 40 and the “gas flow path forming portion” constituted by the ribs 42 are integrated. In the cell 110, the separator 140 and the gas flow path forming part 142 are in contact with each other, but are separate. The separator 140 is made of the same material as the separator 40 of the first embodiment, and the shape thereof is a flat plate shape. The gas flow path forming part 142 is a foamed sintered metal body and is disposed along the surface of the separator 140. The surface of the gas flow path forming portion 142 opposite to the separator 140 is in contact with the second MPL 25.

  In this embodiment, a titanium foam sintered metal body is used as the foam sintered metal body. The titanium foam sintered metal body has a large number of holes, and the diameter of the holes falls within the range of 0.1 [μm] to 400 [μm]. In addition, it is not necessary for the diameter of all the holes formed in the foam sintered metal body to fall within the range of 0.1 [μm] to 400 [μm], and most of the holes (for example, 90% or more) The diameter only needs to be within the above range.

  As described above, since the diameter of the hole portion of the foam sintered metal body is configured to fall within the range of 0.1 [μm] to 400 [μm], the foam sintered metal body and the second MPL 25 are arranged. It is clear that the opening diameter at the boundary surface between the two is 400 [μm] or less. Even in the lower limit value of the opening, most of the openings are 0.1 [μm]. Furthermore, the opening ratio of the foamed sintered metal body with respect to the entire boundary surface between the foamed sintered metal body and the second MPL 25 is 25% or more.

  In this embodiment, a titanium foam sintered metal body is used, but a foam metal such as stainless steel, nickel or copper may be used. Moreover, the gas flow path forming part 142 is not limited to the foam sintered metal body, and may be replaced with a foam sintered body that is not metal as long as it is conductive. Further, the configuration in which the gas flow path forming portion is formed of the foamed sintered body is not necessarily limited to the cathode side as in this embodiment, and can be applied to the anode side.

  In the fuel cell of the second embodiment configured as described above, the opening diameter t12 of the foamed sintered metal body is in the range of 0.1 [μm] to 400 [μm], so that Similarly, the second MPL 25 can be pressed at a minute pitch. Accordingly, similarly to the first embodiment, the generated water can be prevented from staying between the second MPL 25 and the catalyst layer 23, and the drainage of the fuel cell can be improved. Furthermore, the gas supply property to the catalyst layer 23 can be ensured similarly to the first embodiment.

  In addition, in a present Example, the opening diameter of a foaming sintered compact can take a various dimension within the range of 0.1 [micrometers]-400 [micrometers]. This is because the opening diameter of the surface of the foam sintered body can take various dimensions depending on where the hole is cut, and it can be said that the opening diameter of the foam sintered body has randomness. According to this structure, drainage property and gas supply property can be further improved. This is because liquid water is likely to be drained by capillary force from the opening having a small diameter, and gas is likely to selectively pass through the opening having a large diameter.

  As a modification of the second embodiment, the surface of the foamed sintered body constituting the gas flow path forming portion 142 may be hydrophilic. Specifically, the surface of the foam sintered body can be made hydrophilic by performing hydrophilic treatment such as UV treatment or plasma treatment. According to this configuration, the drainage can be further improved.

  In the second embodiment, the gas diffusion layer is not provided on the cathode side but the gas diffusion layer is provided on the anode side. However, the present invention is not limited to this. A structure having a gas diffusion layer on the cathode side and no gas diffusion layer on the anode side, or a structure having no gas diffusion layer on both the cathode side and the anode side can be employed. In these configurations, like the cathode side of the second embodiment, a sheet-like MPL is disposed on the side having no gas diffusion layer, and a foamed sintered metal body or the like is formed between the MPL and the separator. A bonded body may be arranged, and the opening diameter of the foamed sintered body may be in the range of 0.1 [μm] to 400 [μm]. Moreover, it is preferable that the aperture ratio of this foam sintered body shall be 20% or more.

C. Third embodiment:
FIG. 7 is an explanatory view schematically showing a cross section of a part of the single cell 210 inside the fuel cell in the third embodiment of the present invention. The unit cell 210 in the third embodiment differs from the unit cell 110 in the second embodiment in the configuration of the gas flow path forming part 242 on the cathode side. Since the other configuration of the unit cell 210 in the third embodiment is the same as that of the unit cell 110 in the second embodiment, the same components as those in FIG. The description is omitted.

  The cathode-side gas flow path forming portion 142 in the single cell 10 (FIG. 1) of the second embodiment was formed of a foamed sintered body. On the other hand, the gas flow path forming part 242 on the cathode side in the present embodiment is made of expanded metal.

  FIG. 8 is a perspective view of an expanded metal as the gas flow path forming part 242. The expanded metal is obtained by processing a single metal plate into a mesh shape by cutting and folding, and has a configuration in which a plurality of corrugated plate portions 301 are arranged in parallel in the w direction. Each corrugated plate part 301 has a configuration in which a peak part 301a and a valley part 301b are repeatedly arranged in the u direction in order.

  As shown in FIG. 8, the expanded metal is disposed so that the end of each crest 301 a and the end of each trough 301 b of the corrugated plate 301 are in contact with the separator 140 or the second MPL 25. Thereby, the gas flow path is constituted by the peak portion 301a and the valley portion 301b, and the direction of the gas flow channel is the direction toward the second MPL 25. In the second MPL 25, the distance t22 between the portion where the peak portion 301a contacts and the portion where the valley portion 301b contacts is the distance of the shortest portion of the opening of the gas flow path forming portion 242, and can be said to be the opening diameter. The distance t22 was set in the range of 0.1 μm to 400 μm, as in the first and second examples.

  In the fuel cell of the third embodiment configured as described above, the opening diameter of the gas flow path forming part 242 is in the range of 0.1 [μm] to 400 [μm], so that the first and second Similar to the embodiment, the second MPL 25 can be pressed at a minute pitch. Therefore, similarly to the first and second embodiments, the generated water can be prevented from staying between the second MPL 25 and the catalyst layer 23, and the drainage of the fuel cell can be improved. Furthermore, the gas supply property to the catalyst layer 23 can be ensured similarly to the first and second embodiments.

  As a modified example of the third embodiment, the surface of the extended metal constituting the gas flow path forming part 142 may be hydrophilic. Specifically, the surface of the expanded metal can be made hydrophilic by applying hydrophilic treatment such as UV treatment or plasma treatment to the metal plate that is the raw material of the expanded metal. According to this configuration, the drainage can be further improved.

  In the third embodiment, the gas diffusion layer is not provided on the cathode side but the gas diffusion layer is provided on the anode side. However, the present invention is not limited to this. A structure having a gas diffusion layer on the cathode side and no gas diffusion layer on the anode side, or a structure having no gas diffusion layer on both the cathode side and the anode side can be employed. In these configurations, like the cathode side of the third embodiment, a sheet-like MPL is arranged on the side not having the gas diffusion layer, an expanded metal is arranged between the MPL and the separator, and the expanded metal is used. What is necessary is just to let the opening diameter of the gas flow path formation part 242 be in the range of 0.1 [μm] to 400 [μm]. The ratio of the openings is preferably 20% or more.

D. Variation:
The present invention is not limited to the above-described embodiments and modifications, and can be carried out in various modes without departing from the scope of the invention. For example, the following modifications are possible. .

・ Modification 1:
In each of the above-described embodiments and modifications, the polymer electrolyte fuel cell is used as the fuel cell, but various fuel cells such as a phosphoric acid fuel cell, a molten carbonate fuel cell, and a solid oxide fuel cell are used. The present invention may be applied.
Modification 2
Of the constituent elements in the above-described embodiments and modifications, elements other than those described in the independent claims are additional elements and can be omitted as appropriate.

10 ... Single cell 20 ... Membrane electrode assembly (MEA)
DESCRIPTION OF SYMBOLS 21 ... Solid polymer electrolyte membrane 22 ... Catalyst layer 23 ... Catalyst layer 24 ... 1st MPL
25. Second MPL
26 ... Gas diffusion layer 30 ... Separator 32 ... Rib 34 ... Fuel gas flow path 40 ... Separator 42 ... Rib 44 ... Oxidant gas flow path 110 ... Single cell 140 ... Separator 142 ... Gas flow path forming part 210 ... Single cell 242 ... Gas flow path forming part

Claims (7)

A fuel cell,
A membrane electrode assembly;
A microporous layer disposed outside the membrane electrode assembly;
A gas flow path forming portion that forms a gas flow path having an opening that opens to the microporous layer side, and is disposed in a form in which no gas diffusion layer is interposed on the side opposite to the membrane electrode assembly of the microporous layer; ,
With
The diameter of the opening is a fuel cell in a range of 0.1 μm to 400 μm. The fuel cell according to claim 1,
The fuel cell, wherein the total area ratio of the openings to the region corresponding to the power generation region on the surface of the gas flow path forming part on the microporous layer side is 20% or more. The fuel cell according to claim 2, wherein
The gas flow path forming portion is a linear groove formed by a rib,
The diameter of the opening is a width of the groove. The fuel cell according to claim 2, wherein
The gas flow path forming part is a foam sintered body,
The said opening is a fuel cell which is an opening in the interface between the said microporous layer and the said foaming sintered compact. The fuel cell according to claim 4, wherein
A fuel cell, wherein a surface of the foamed sintered body is hydrophilic. The fuel cell according to claim 2, wherein
The gas flow path forming part is an expanded metal,
The diameter of the opening is a fuel cell, which is the distance of the shortest part of the opening at the interface between the microporous layer and the expanded metal . The fuel cell according to claim 6, wherein
A fuel cell, wherein the surface of the expanded metal is hydrophilic.

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