JP5593604B2 - Membrane electrode assembly, separator and fuel cell - Google Patents

Description

  The present invention relates to a membrane electrode assembly, a separator, and a fuel cell.

Patent Document 1 discloses a fuel cell in which a highly water repellent layer is provided between a cathode gas catalyst layer and a cathode gas diffusion layer.
JP 2007-328935 A (paragraph 0016)

  However, in the conventional fuel cell described above, when the temperature of the fuel cell is low (for example, the stack temperature is about 5 to 10 ° C.) immediately after the low temperature start, the liquid water generated in the fuel cell is converted into the cathode gas. The present inventors have found that the cathode gas diffusion layer may be damaged due to accumulation between the catalyst layer and the highly water-repellent layer.

  The present invention has been made paying attention to such conventional problems, and provides a membrane electrode assembly, a separator, and a fuel cell that do not cause damage to a gas diffusion layer even at low temperatures. Objective.

  The present invention solves the above problems by the following means.

The present invention is not capable of transmitting microporous layer generates water due to power generation of the fuel cell is too long and the water repellent in the microporous layer, want earthenware pots generate electricity by temporarily accumulated between the catalyst layer and the microporous layer sometimes, at least the cathode of the more pressure exerted on the microporous layer, the membrane electrode assembly the breakdown voltage of the gas diffusion layer in this case is configured to be larger when the accumulated product water passes through the pre-Symbol microporous layer Provided on the side surface, and when the generated water accumulates between the catalyst layer and the microporous layer, a strength enhancing portion that increases the surface pressure strength of the gas diffusion layer is provided . And is formed so as to protrude to the gas diffusion layer side of the flat portion of the separator rib that is in contact with the gas diffusion layer .

  According to the present invention, when the generated water passes from the catalyst layer to the microporous layer, the strength of the gas diffusion layer is maintained, so that damage to the gas diffusion layer can be reduced.

Hereinafter, the best mode for carrying out the present invention will be described with reference to the drawings.
(Basic form)
1A and 1B are views showing the appearance of a fuel cell according to the present embodiment, in which FIG. 1A is a perspective view and FIG. 1B is a side view.

  First, the basic configuration of the fuel cell will be described. The fuel cell stack 1 includes a plurality of stacked power generation cells 10, a current collecting plate 20, an insulating plate 30, an end plate 40, and four tension rods 50.

  The power generation cell 10 is a unit cell of a fuel cell. Each power generation cell 10 generates an electromotive voltage of about 1 volt (V). Details of the configuration of each power generation cell 10 will be described later.

The current collecting plate 20 is disposed outside each of the stacked power generation cells 10. The current collecting plate 20 is formed of a gas impermeable conductive member, for example, dense carbon. The current collecting plate 20 includes an output terminal 21 in a part of the upper side. The fuel cell stack 1 takes out and outputs the electrons e ⁻ generated in each power generation cell 10 through the output terminal 21.

  The insulating plates 30 are respectively arranged outside the current collecting plates 20. The insulating plate 30 is formed of an insulating member such as rubber.

  The end plate 40 is disposed outside the insulating plate 30. The end plate 40 is made of a rigid metal material such as steel.

  One end plate 40 (the left front end plate 40 in FIG. 1A) has an anode supply port 41a, an anode discharge port 41b, a cathode supply port 42a, a cathode discharge port 42b, and a cooling water supply. A port 43a and a cooling water discharge port 43b are provided. In the present embodiment, the anode discharge port 41b, the cooling water discharge port 43b, and the cathode supply port 42a are provided on the right side in the drawing. The cathode discharge port 42b, the cooling water supply port 43a, and the anode supply port 41a are provided on the left side in the drawing.

  The tension rods 50 are disposed near the four corners of the end plate 40, respectively. The fuel cell stack 1 has a hole (not shown) penetrating therethrough. The tension rod 50 is inserted through the through hole (see FIG. 1B). The tension rod 50 is formed of a rigid metal material such as steel. The tension rod 50 is insulated on the surface in order to prevent an electrical short circuit between the power generation cells 10. A nut 51 is screwed into the tension rod 50 (see FIG. 1B). The tension rod 50 and the nut 51 tighten the fuel cell stack 1 in the stacking direction to generate a stacking pressure.

  As a method of supplying hydrogen as the anode gas to the anode supply port 41a, for example, a method of directly supplying hydrogen gas from a hydrogen storage device or a hydrogen-containing gas reformed by reforming a fuel containing hydrogen is supplied. There are methods. Examples of the hydrogen storage device include a high-pressure gas tank, a liquefied hydrogen tank, and a hydrogen storage alloy tank. Examples of the fuel containing hydrogen include natural gas, methanol, and gasoline. Air is generally used as the cathode gas supplied to the cathode supply port 42a.

  In the fuel cell stack 1, as shown in FIG. 1B, a current collecting plate 20, an insulating plate 30, and an end plate 40 are disposed on both sides of the plurality of stacked power generation cells 10.

  A sub-end plate 41 is disposed outside the insulating plate 30 on one side of the fuel cell stack, and a fluctuation absorbing member 42 made of, for example, a disc spring is disposed outside the sub-end plate 41. A plate 40 is provided. The fuel cell stack having such a stacked structure is fastened in the stacking direction by four tension rods 50. Thus, since the fluctuation | variation absorption member 42 is provided, the fluctuation | variation of the surface pressure which acts on a fuel cell stack can be absorbed.

  FIG. 2 is an enlarged view of the power generation cell.

  The power generation cell 10 has a structure in which an anode separator 12 a and a cathode separator 12 b are disposed on both surfaces of a membrane electrode assembly (MEA) 11. In the MEA 11, electrode catalyst layers 112 (112a, 112b) are formed on both surfaces of an electrolyte membrane 111 made of an ion exchange membrane. On the electrode catalyst layer 112 (112a, 112b), a microporous layer (MPL) 113 (113a, 113b) is formed. A gas diffusion layer (Gas Diffusion Layer; GDL) 114 (114a, 114b) is formed on the MPL 113 (113a, 113b).

  The electrode catalyst layer 112 is formed by, for example, hot pressing or directly spraying a mixed layer composed of a catalyst in which platinum Pt or a platinum-based alloy is supported on a carbon carrier powder, an electrolyte particle (ionomer), and a water repellent agent on the electrolyte membrane. Formed with.

  The MPL 113 is a mixed layer of a binder / water repellent mainly composed of conductive carbon powder such as carbon black and polytetrafluoroethylene (PTFE). The MPL 113 prevents the GDL 114 fibers from being short-circuited through the electrolyte membrane 111. Further, the MPL 113 increases the contact area between the electrode catalyst layer 112 and the GDL 114. Further, the MPL 113 adjusts the drainage of the electrode catalyst layer 112 to optimize the wet environment of the electrode catalyst layer 112 during power generation and prevent flooding and dryout. Furthermore, the MPL 113 promotes the distribution of the reaction gas and improves the power generation performance of the fuel cell.

  The GDL 114 is formed of a member having sufficient gas diffusibility and conductivity, such as carbon fiber.

  The anode gas supplied from the anode supply port 41a flows through this GDL 114a, reacts with the anode electrode catalyst layer 112 (112a), and is discharged from the anode discharge port 41b. The cathode gas supplied from the cathode supply port 42a flows through this GDL 114b, reacts with the cathode electrode catalyst layer 112 (112b), and is discharged from the cathode discharge port 42b.

  The anode separator 12a is overlapped on one side (left side in FIG. 2) of the MEA 11 via the GDL 114a and the MPL 113a. The cathode separator 12b is stacked on one side (the right side in FIG. 2) of the MEA 11 via the GDL 114b and the MPL 113b. The anode separator 12a and the cathode separator 12b are formed by a separator base made of metal such as titanium, stainless steel, and aluminum. The anode separator 12a and the cathode separator 12b are formed by subjecting such a separator substrate to cold pressing, chemical etching, sandblasting, or the like. The anode separator 12a and the cathode separator 12b are conductive because their surfaces are coated with a noble metal such as gold or with a conductive carbon material. The anode separator 12a and the cathode separator 12b may be formed by resin molding using a conductive carbon powder such as carbon black as another form.

  Here, in order to describe in detail the problem to be solved in the present embodiment, it will be described with reference to FIG.

  When the anode gas and the cathode gas are supplied, the fuel cell generates power by the following reaction.

Liquid water H ₂ O is generated by this reaction. Liquid water H ₂ O passes through MPL 113 and GDL 114 and is discharged.

  Incidentally, as described above, the MPL 113 is a mixed layer of carbon powder and PTFE and is water repellent.

When the power generation reaction of the fuel cell proceeds and the temperature of the fuel cell rises, the generated liquid water H ₂ O becomes water vapor, passes through the MPL 113 and the GDL 114, and is discharged to the outside. However, if the temperature of the fuel cell is low (for example, the stack temperature is about 5 to 10 ° C.) immediately after the low temperature start, liquid water H ₂ O that is repelled by the MPL 113 and cannot permeate the MPL 113 accumulates. . As shown in FIG. 3, the liquid water concentrates under the channel 122 of the cathode separator 12b where no stacking pressure is applied. When the amount of liquid water increases and the liquid water pressure exceeds the water pressure resistance P of the MPL 113, the liquid water permeates the MPL 113. At this time, if the strength (maximum allowable surface pressure) of the GDL 114 is lower than the water pressure resistance P, the GDL 114 may be damaged.

  Therefore, in this embodiment, the strength (maximum allowable surface pressure) of the GDL 114 is always larger than the water pressure resistance P.

(First embodiment)
FIG. 4 is a diagram showing the correlation between the separator channel width and the GDL strength (maximum allowable surface pressure).

  As can be seen from FIG. 4, even with the same GDL, the maximum allowable surface pressure increases as the flow path width of the separator decreases. However, if the separator channel width is narrow, the ventilation resistance of the reaction gas flowing through the separator channel increases. Therefore, considering the ventilation resistance, it is desirable that the flow path width of the separator is large.

  FIG. 5 is a diagram showing a first embodiment of a fuel cell according to the present invention. FIG. 5 (A) shows an initial state before liquid water is generated, and FIG. 5 (B) shows liquid water generated. Shown later.

  Therefore, in this embodiment, the corner R portion 121 a is provided at the edge portion of the rib 121 of the separator 12.

  In this way, in the initial state, as shown in FIG. 5A, the flow path width is W1, and the gas flow resistance of the reaction gas can be kept low.

When the temperature of the fuel cell continues to be low just after the low temperature start and liquid water H ₂ O that cannot pass through the MPL 113 is accumulated as shown in FIG. 5B, the GDL 114 is pushed up. Accordingly, the distance between the support portions of the GDL 114 is reduced to the distance W2, so that the maximum allowable surface pressure of the GDL 114 is increased and the strength is increased, and the GDL 114 can be prevented from being damaged. Specific dimensions may be set through experiments.

  Since the reaction gas flow rate is small immediately after the low temperature start, there is little influence even if the ventilation resistance increases.

(Second Embodiment)
FIG. 6 is a view showing a second embodiment of the fuel cell according to the present invention.

  In this embodiment, the corner R portion 121a of the separator rib 121 is formed so as to protrude to the GDL side from the rib flat portion 121b.

  Even if the corner R portion 121a of the separator rib 121 is configured in such a shape, the same effect as in the first embodiment can be obtained.

(Third embodiment)
FIG. 7 is a view showing a third embodiment of the fuel cell according to the present invention. FIG. 7 (A) shows an initial state before liquid water is generated, and FIG. 7 (B) shows that liquid water is generated. Shown later.

  In the present embodiment, as shown in FIG. 7A, a convex surface 122a protruding to the GDL side is formed inside the channel 122 of the separator 12.

If constituted in this way, the state where the temperature of the fuel cell is low immediately after the low temperature start continues, and the convex surface of the GDL 114 pushed up by the liquid water H ₂ O that cannot pass through the MPL 113 as shown in FIG. 122a contacts. For this reason, it is possible to prevent the GDL 114 from being damaged.

(Fourth embodiment)
FIG. 8 is a view showing a fuel cell according to a fourth embodiment of the present invention. FIG. 8 (A) is an explanatory view of a solution problem of this fourth embodiment, and FIGS. 8 (B-1) and (B-2) are FIG. It is explanatory drawing of contact angle (theta).

  At the location of the MPL 113 located under the rib 121 of the separator 12, the stacking pressure of the fuel cell acts, and the holes inside the MPL 113 are crushed to reduce the diameter. The water pressure resistance P of the MPL 113 is expressed by the following equation (1).

  Therefore, when the maximum hole diameter D is small, the water pressure resistance P is increased. Conversely, if the maximum hole diameter D is increased, the water pressure resistance P decreases.

  Therefore, in this embodiment, when the stack temperature is low, the threading between the tension rod 50 and the nut 51 is loosened to reduce the stacking pressure. As a method for loosening the screwing, the nut 51 may be rotated by a motor or the like.

  According to this embodiment, since the stacking pressure is reduced when the stack temperature is low, the MPL holes below the ribs of the separator 12 are temporarily increased, and the water pressure resistance P at low temperature start is reduced, The pressure acting on the GDL 114 can be reduced. Therefore, the GDL 114 can be prevented from being damaged.

(Fifth embodiment)
FIG. 9 is a view showing a fifth embodiment of the fuel cell according to the present invention, FIG. 9A is a longitudinal sectional view, and FIG. 9B is a bottom view.

  In the present embodiment, the through hole 113c is formed in the MPL 113 at a portion located below the channel 122 of the separator 12.

  With this configuration, the maximum pore diameter of the MPL 113 is increased, so that the water pressure resistance P is decreased. Then, the pressure which acts on GDL114 is reduced. Therefore, damage to the GDL 114 can be prevented.

(Sixth embodiment)
FIG. 10 is a view showing a sixth embodiment of the fuel cell according to the present invention.

  In the present embodiment, the waterproof pressure reduction portion 113d is formed in the MPL 113 at a portion located under the channel 122 of the separator 12. Specifically, by mixing a hydrophilic material in this part, a part having a small contact angle θ can be locally provided in the MPL 113, and the water pressure resistance of the MPL 113 can be reduced. Examples of the hydrophilic material include a fluorine electrolyte membrane and a thin film thereof. The formation of the water pressure resistance reduction portion 113d by the electrolyte also increases the water retention of the MPL 113, so that the MPL 113 can be prevented from being extremely dried, and this also provides the effect of reducing the water pressure resistance of the MPL 113.

(Seventh embodiment)
FIG. 11 is a view showing a seventh embodiment of the fuel cell according to the present invention.

  The GDL 114 of this embodiment is impregnated with carbon particles 114c.

  According to this embodiment, the mechanical strength of the GDL 114 is improved by the binding force between the carbon particles impregnated in the GDL 114 and the binder. For this reason, the maximum bending stress of the GDL 114 increases and the maximum allowable stress increases.

(Eighth embodiment)
FIG. 12 is a view showing an eighth embodiment of the fuel cell according to the present invention.

  The GDL 114 of this embodiment has a two-layer structure of an outer GDL base material 114-1 and an inner GDL base material 114-2. The outer GDL base material 114-1 is impregnated with carbon particles 114c, and the inner GDL base material 114-2 is not impregnated with carbon particles 114c.

  If comprised in this way, bending strength can be enlarged, reducing the mixing amount of the carbon particle 114c as much as possible, and improvement of ventilation resistance and drainage can also be aimed at it. In addition, since the two GDL base materials 114-1 and 114-2 are bonded together, the carbon particles can be easily mixed with the outer GDL base material 114-1.

  In this embodiment, a two-layer structure is illustrated, but a multilayer structure may be used. Even in such a case, it is preferable to impregnate the outermost GDL base material with the carbon particles 114c. Moreover, you may use a base material with high mechanical strength for the GDL base material of outermost layer.

  Without being limited to the embodiments described above, various modifications and changes are possible within the scope of the technical idea, and it is obvious that these are also included in the technical scope of the present invention.

  For example, in the first embodiment, the structure in which the corner R portion is provided at the edge portion of the separator rib as the strength enhancing portion is exemplified, but a linear chamfer portion may be used.

It is a figure which shows the external appearance of the fuel cell in one Embodiment. It is an enlarged view of a power generation cell. It is a figure explaining the problem to solve. It is a figure which shows the correlation with the flow path width of a separator, and the intensity | strength (maximum permissible surface pressure) of GDL. It is a figure which shows 1st Embodiment of the fuel cell by this invention. It is a figure which shows 2nd Embodiment of the fuel cell by this invention. It is a figure which shows 3rd Embodiment of the fuel cell by this invention. It is a figure which shows 4th Embodiment of the fuel cell by this invention. It is a figure which shows 5th Embodiment of the fuel cell by this invention. It is a figure which shows 6th Embodiment of the fuel cell by this invention. It is a figure which shows 7th Embodiment of the fuel cell by this invention. It is a figure which shows 8th Embodiment of the fuel cell by this invention.

Explanation of symbols

11 Membrane electrode assembly (MEA)
111 Electrolyte membrane 112 (112a, 112b) Catalyst layer 113 (113a, 113b) Microporous layer (MPL)
113c Through-hole 113d Water pressure reduction part 114 (114a, 114b) Gas diffusion layer (GDL)
114c Carbon particle 12 (12a, 12b) Separator 121 Separator rib 121a Corner R part (strength enhancement part)
121b Rib flat portion 122 Separator channel 122a Convex surface (strength enhancing portion)

Claims (7)

A catalyst layer, a microporous layer, and a gas diffusion layer are laminated in this order on at least the cathode side of the electrolyte membrane, and the water generated by the power generation of the fuel cell is repelled by the microporous layer. During the power generation that cannot pass through the layer and is temporarily accumulated between the catalyst layer and the microporous layer, the generated product water is more than the pressure applied to the microporous layer when passing through the microporous layer. The gas diffusion layer is provided at least on the surface on the cathode side of the membrane electrode assembly configured to increase the pressure resistance of the gas diffusion layer, and when the generated water accumulates between the catalyst layer and the microporous layer, the gas Equipped with a strength enhancement part that increases the surface pressure strength of the diffusion layer,
The strength-enhancing portion is a corner rib R portion of the separator rib, and is formed so as to protrude to the gas diffusion layer side than the flat portion of the separator rib that is in contact with the gas diffusion layer.
A separator characterized by that. The strength enhancing portion is formed on the edge of the separator rib and is formed by removing corners.
The separator according to claim 1. A catalyst layer, a microporous layer, and a gas diffusion layer are laminated in this order on at least the cathode side of the electrolyte membrane, and the water generated by the power generation of the fuel cell is repelled by the microporous layer. During the power generation that cannot pass through the layer and is temporarily accumulated between the catalyst layer and the microporous layer, the generated product water is more than the pressure applied to the microporous layer when passing through the microporous layer. A membrane electrode assembly configured to increase the pressure resistance of the gas diffusion layer in
A separator that is provided on at least the cathode side surface of the membrane electrode assembly, and abuts the membrane electrode assembly with a predetermined stacking pressure;
A surface pressure reducing means for reducing the stacking pressure of the separator when starting at 5 to 10 ° C . ;
A fuel cell. The microporous layer has a through hole in a portion located under the channel of the separator,
The fuel cell according to claim 3. The microporous layer has a water pressure lowering portion in which water resistance is reduced by mixing a hydrophilic material in a portion located under the channel of the separator.
The fuel cell according to claim 3 or 4, wherein Carbon particles are mixed in the gas diffusion layer,
The fuel cell according to any one of claims 3 to 5, wherein: The gas diffusion layer is configured by laminating a plurality of base materials, and among the plurality of base materials, carbon particles are mixed in the outermost layer base material that is farthest from the microporous layer.
The fuel cell according to any one of claims 3 to 6, wherein:

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