JP2016035918A - Fuel cell membrane-electrode assembly and polymer electrolyte fuel cell - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a fuel cell membrane-electrode assembly capable of reliably suppressing an electrolyte membrane from being deformed without deteriorating characteristics of a membrane-electrode assembly, such as gas diffusion properties and drainage properties.SOLUTION: A membrane-electrode assembly (MEA) 110 includes: an electrolyte membrane (PEM10); an anode electrode 11 having an anode catalyst layer 11a provided so as to correspond to one main surface of the PEM10; and a cathode electrode 12 having a cathode catalyst layer 12a provided so as to correspond to another main surface. In the membrane-electrode assembly, the Young's moduli of the anode catalyst layer 11a and the cathode catalyst layer 12a in a surface direction are higher than the Young's modulus of the PEM10 in a surface direction.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a fuel cell membrane-electrode assembly (hereinafter, appropriately referred to as a membrane-electrode assembly) and a polymer electrolyte fuel cell using the fuel cell membrane-electrode assembly.

  In recent years, attention has been paid to a fuel cell in which a fuel and an oxidant are electrochemically reacted to directly convert chemical energy into electric energy regardless of the Carnot cycle. In principle, the fuel cell has high energy conversion efficiency at a low temperature, and the power generation unit is extremely small, so that high performance can be maintained even in a region where the output scale is small. In particular, since fuel cells produce only harmless water during power generation, they are expected to be applied as power sources for vehicles from the viewpoint of environmental impact.

  A polymer electrolyte fuel cell (PEFC) which is one of the fuel cells has a stack structure in which several tens to several hundreds of cells (single cells) are stacked. Each cell has a basic structure of a membrane-electrode assembly in which a solid polymer electrolyte membrane is sandwiched between a pair of electrodes, and this basic structure is sandwiched between a pair of separators.

In the membrane-electrode assembly as described above, each electrode generally has a structure in which a catalyst layer and a gas diffusion layer are laminated in order from the solid polymer electrolyte membrane (hereinafter referred to as an electrolyte membrane as appropriate) side. take.
The catalyst layer includes catalyst particles and a polymer electrolyte, and the gas diffusion layer is made of carbon paper or carbon cloth. Such a catalyst layer and a gas diffusion layer should enhance the adhesion between them and prevent the catalyst layer from peeling or cracking.
Various techniques for meeting such demand have already been proposed. That is, a proposal to provide a binder layer (buffer layer) containing a thickener on the gas diffusion layer and to laminate an electrode catalyst layer containing catalyst particles and a polymer electrolyte on the binder layer (buffer layer). (For example, refer to Patent Document 1).

  On the other hand, even when the catalyst layer has a structure having a microporous layer (MPL), the fuel cell membrane-electrode does not cause a decrease in power generation performance due to the collapse of the pores present in the MPL A joined body has been proposed (see, for example, Patent Document 2).

JP 2007-317391 A JP, 2014-022140, A

However, in the technique disclosed in Patent Document 1, when the catalyst layer is not rigid, in order to securely hold the electrolyte membrane that is easily deformed by swelling or differential pressure so as not to be deformed, carbon paper, carbon cloth, etc. It is necessary to hold in the gas diffusion layer. And in order to hold | maintain with a gas diffusion layer in this way, the buffer layer etc. for adhere | attaching the base layer and catalyst layer which were apply | coated to the gas diffusion layer are needed.
However, since such a buffer layer crushes the pores of the gas diffusion layer, there arises a problem of deteriorating important characteristics of the membrane-electrode assembly such as gas diffusibility and drainage.

On the other hand, the electrolyte membrane in the membrane-electrode assembly for a fuel cell has physical properties such that rigidity (elastic modulus) is remarkably lower than that of other members, and the dimensional change is large depending on the degree of dryness and wetness. For this reason, when the electrolyte membrane changes in size, if there is a crack in the electrode layer (catalyst layer, diffusion layer) or MPL adjacent to the electrolyte membrane, the stress concentration is concentrated on the electrolyte membrane having a lower elastic modulus than the adjacent member. As a result, cracks may occur in the electrolyte membrane.
When cracks occur in the electrolyte membrane, gas cross-leakage occurs and the power generation function is impaired.

In general, a single cell of a membrane-electrode assembly for a fuel cell is used by forming a fuel cell stack by laminating a number of such single cells. When the fuel cell stack is configured as described above, the distribution of the load to the portion where the cracks are generated as described above is biased due to the variation in the thickness of each layer of each single cell. At the portion where the load is increased, the electrolyte membrane is cracked and gas cross leak occurs.
However, the technique disclosed in Patent Document 2 cannot sufficiently solve this problem.

  The present invention has been made to solve the above-described problems, and can reliably suppress the deformation of the electrolyte membrane without deteriorating the characteristics of the membrane-electrode assembly such as gas diffusibility and drainage. An object of the present invention is to provide a fuel cell membrane-electrode assembly and a polymer electrolyte fuel cell using the fuel cell membrane-electrode assembly.

In order to achieve the above object, the following techniques are proposed here.
(1) Electrode (for example, PEM10 described later) and electrodes (for example, an anode described later) having catalyst layers (for example, anode catalyst layer 11a and cathode catalyst layer 12a described later) provided corresponding to the electrolyte membrane Electrode 11, cathode electrode 12);
A fuel cell membrane-electrode assembly (for example, a membrane-electrode assembly 110 described later),
A membrane-electrode assembly for a fuel cell, wherein the catalyst layer has a Young's modulus in the surface direction higher than the Young's modulus in the surface direction of the electrolyte membrane.

  In the fuel cell membrane-electrode assembly (1), deformation of the electrolyte membrane is suppressed by the rigid catalyst layer having a relatively high Young's modulus. In this case, since the pores of the gas diffusion layer (for example, anode diffusion layer 11b and cathode diffusion layer 12b described later) of the electrode are not crushed by the buffer layer or the like, the membrane-electrode such as gas diffusibility and drainage There is no possibility that important characteristics of the joined body are impaired.

(2) A pair of the catalyst layers are provided so as to correspond to both main surfaces of the electrolyte membrane, and a gas diffusion layer (for example, an anode diffusion layer 11b, which will be described later) is provided for each of the pair of catalyst layers. A cathode diffusion layer 12b) is provided;
One catalyst layer (for example, a cathode catalyst layer 12a described later) of the pair of catalyst layers has a larger area than a gas diffusion layer (for example, a cathode diffusion layer 12b described later) corresponding to the self-layer. The fuel cell membrane-electrode assembly according to (1) above, wherein the Young's modulus in the surface direction is higher than the Young's modulus in the surface direction of the electrolyte membrane.

  In the fuel cell membrane-electrode assembly of (2) above, in particular in the fuel cell membrane-electrode assembly of (1), one catalyst layer has a larger area than the gas diffusion layer corresponding to its own layer. In addition, it has a higher Young's modulus than the electrolyte membrane and is rigid. The deformation of the electrolyte membrane is effectively suppressed by such one catalyst layer.

  (3) The other catalyst layer (for example, an anode catalyst layer 11a described later) of the pair of catalyst layers has an area of a gas diffusion layer (for example, an anode diffusion layer 11b described later) corresponding to the self-layer. And the Young's modulus in the surface direction is lower than the Young's modulus in the surface direction of the one catalyst layer (for example, the cathode catalyst layer 12a described later). Membrane-electrode assembly.

  In the fuel cell membrane-electrode assembly of (3) above, in the fuel cell membrane-electrode assembly of (2) above, in particular, the other catalyst layer on the other main surface side of the electrolyte membrane is in the plane direction. The Young's modulus is lower than the Young's modulus in the surface direction of the one catalyst layer. However, since the gas diffusion layer having substantially the same area as the self-layer is provided, the other catalyst layer alone is not as rigid as the one catalyst layer, and the electrolyte membrane is combined with a certain rigidity of the gas diffusion layer. Can be effectively suppressed. Therefore, it is possible to appropriately suppress deformation of the electrolyte membrane without making both of the corresponding catalyst layers on both major surfaces of the electrolyte membrane rigid and rigid to the same extent.

  (4) The fuel cell membrane according to (1), wherein the catalyst layer has a Young's modulus in the surface direction higher than the Young's modulus in the surface direction of the electrolyte membrane regardless of temperature and humidity. Electrode assembly.

  In the fuel cell membrane-electrode assembly of (4) above, in particular, in the membrane-electrode assembly of the fuel cell of (1), the electrolyte membrane is strongly suppressed from deformation regardless of environmental temperature and humidity. Is done.

  (5) Of the pair of catalyst layers, the one catalyst layer (for example, the cathode catalyst layer 12a described later) has an area larger than the area of the gas diffusion layer corresponding to the self-layer and the surface direction. The fuel cell membrane-electrode assembly according to (2) above, wherein the Young's modulus is higher than the Young's modulus in the surface direction of the other catalyst layer (for example, an anode catalyst layer 11a described later).

In the fuel cell-electrode assembly of (5) above, in particular, in the fuel cell membrane-electrode assembly of (2), the one catalyst layer (for example, a cathode catalyst layer 12a described later) of the pair of catalyst layers. Has an area larger than the area of the gas diffusion layer corresponding to the self-layer, and the Young's modulus in the surface direction is Young's in the surface direction of the other catalyst layer (for example, the anode catalyst layer 11a described later). Higher than the rate.
By adopting such a configuration, the one catalyst layer in which a unique portion in which there is no diffusion layer supporting the self layer is formed behind is made more rigid, and the swelling of the electrolyte membrane is resisted even in the unique portion. On the other hand, the stress due to deformation is released to the other catalyst layer side, and as a result, deformation of the electrolyte membrane can be appropriately suppressed.

  (6) The membrane-electrode assembly for a fuel cell according to (5), wherein the one catalyst layer of the pair of catalyst layers has a thickness greater than that of the other catalyst layer. .

In the fuel cell-electrode assembly of the above (6), in particular, in the fuel cell membrane-electrode assembly of the above (5), the one catalyst layer of the pair of catalyst layers has a thickness of the other. Thicker than the thickness of the catalyst layer.
By adopting such a configuration, it is possible to increase the rigidity of the one catalyst layer in which a unique portion having no diffusion layer supporting the self layer is formed behind, and to resist swelling of the electrolyte membrane in the unique portion. Like that.

  (7) In any one of the above (2) to (6), the pair of catalyst layers each have a difference in Young's modulus in the plane direction from the electrolyte membrane within a range of 50 MPa to 200 MPa. A membrane-electrode assembly for a fuel cell.

  In the fuel cell-electrode assembly according to (7) above, in particular, in the fuel cell membrane-electrode assembly according to any one of (2) to (6), each of the pair of catalyst layers is in the plane direction with respect to the electrolyte membrane. The difference in Young's modulus is in the range of 50 MPa to 200 MPa. When the difference in Young's modulus is within the above range, the effect of suppressing the deformation of the electrolyte membrane is sufficient, and the outer peripheral end of the smaller gas diffusion layer (for example, the cathode catalyst layer 12a described later) is damaged. The risk of being easy to do is avoided.

  (8) A pair of the catalyst layers are provided so as to correspond to both main surfaces of the electrolyte membrane, respectively, and the pair of catalyst layers respectively correspond to the corresponding microporous layers (for example, a microporous layer 11b1 described later, A gas diffusion layer is provided through the microporous layer 12b1), and a composite layer (for example, an anode-side composite layer 11c and a cathode-side composite layer 12c described later) is formed by the microporous layer and the gas diffusion layer. The Young's modulus in the thickness direction of the composite layer is smaller than the Young's modulus in the thickness direction of the electrolyte membrane, and the Young's modulus in the thickness direction of the catalyst layer is smaller than the Young's modulus in the thickness direction of the electrolyte membrane. The membrane-electrode assembly for a fuel cell according to the above (1), which is also large.

In the fuel cell-electrode assembly of the above (8), in particular, in the membrane-electrode assembly for a fuel cell of the above (1), a pair of catalyst layers are provided so as to correspond to both main surfaces of the electrolyte membrane, Each of the pair of catalyst layers is provided with a gas diffusion layer through a corresponding microporous layer, and the microporous layer and the gas diffusion layer form a composite layer, and the Young's modulus in the thickness direction of the composite layer Is smaller than the Young's modulus in the thickness direction of the electrolyte membrane, and the Young's modulus in the thickness direction of the catalyst layer is larger than the Young's modulus in the thickness direction of the electrolyte membrane.
By adopting such a configuration, it is possible to absorb the stress due to the swelling of the electrolyte membrane by the shrinkage of the composite layer, and to effectively suppress the deformation of the electrolyte membrane by the relatively rigid catalyst layer.

  (9) The membrane-electrode assembly for a fuel cell according to (8), wherein a Young's modulus in the thickness direction of the composite layer is in a range of 0.1 MPa to 35 MPa.

  In the fuel cell-electrode assembly of (9) above, the Young's modulus in the thickness direction of the composite layer is in the range of 0.1 MPa to 35 MPa, particularly in the fuel cell membrane-electrode assembly of (8). When the Young's modulus in the thickness direction of the composite layer is within the above range, even if the catalyst layer (the anode catalyst layer 11a or the cathode catalyst layer 12a) is cracked, the composite layer absorbs the stress and the electrolyte The suppressing effect on the deformation of the film is sufficient.

  (10) A polymer electrolyte fuel cell comprising the fuel cell membrane-electrode assembly according to any one of (1) to (9) above.

  In the polymer electrolyte fuel cell of the above (10), the membrane-electrode assembly for the fuel cell has the effects related to the corresponding one of the above (1) to (9).

  According to the present invention, a membrane-electrode assembly for a fuel cell that can reliably suppress deformation of the electrolyte membrane without deteriorating the characteristics of the membrane-electrode assembly such as gas diffusibility and drainage, and this fuel cell A polymer electrolyte fuel cell using the membrane-electrode assembly can be realized.

It is a figure which shows the fuel cell membrane-electrode assembly as one embodiment of the present invention in a schematic cross-sectional view and explains the operation. It is a figure which compares and compares the Young's modulus of the surface direction of a catalyst layer with the surface direction of an electrolyte membrane in various temperature and humidity in the membrane-electrode assembly for fuel cells as one Embodiment of this invention. Comparison of the dimensional change in the surface direction of the CCM (catalyst layer forming electrolyte membrane) in the fuel cell membrane-electrode assembly as one embodiment of the present invention with the dimensional change in a single PEM (solid polymer electrolyte membrane) FIG. It is a figure which shows the membrane-electrode assembly for fuel cells as other embodiment of this invention, and its equivalent model. It is a figure showing the simulation result of the Young's modulus by the equivalent model of the membrane-electrode assembly for fuel cells of FIG. It is a figure for demonstrating the Young's modulus of the thickness direction of the composite layer which adapts to the membrane-electrode assembly for fuel cells of FIG. It is a figure for demonstrating the phenomenon which arises about the membrane-electrode assembly for fuel cells of FIG. It is a figure for demonstrating the phenomenon which arises about the membrane-electrode assembly for fuel cells of FIG. It is a figure for demonstrating the phenomenon which arises about the membrane-electrode assembly for fuel cells of FIG. It is a figure for demonstrating the phenomenon which arises about the membrane-electrode assembly for fuel cells of FIG.

Hereinafter, the present invention will be clarified by describing an embodiment of the present invention in detail with reference to the drawings.
FIG. 1 is a diagram schematically showing a fuel cell membrane-electrode assembly as an embodiment of the present invention in cross-sectional view and explaining the operation.
Part (a) of FIG. 1 shows a membrane-electrode assembly for a fuel cell as one embodiment of the present invention, and part (b) of FIG. 1 may occur when the technique of the present invention is not applied. Indicates a problem. In the parts (a) and (b), the corresponding parts are denoted by the same reference numerals.
The membrane-electrode assembly for a fuel cell in part (a) of FIG. 1 is on one main surface side (upper side in the figure) of a solid polymer electrolyte membrane (hereinafter referred to as PEM) 10 which is an electrolyte membrane. An anode electrode 11 is provided, and a cathode electrode 12 is provided on the other main surface side (lower side in the figure). The anode electrode 11 includes an anode catalyst layer 11a in contact with one main surface of the PEM 10, and an anode diffusion layer 11b provided corresponding to the anode catalyst layer 11a. The cathode electrode 12 includes a cathode catalyst layer 12a in contact with the other main surface of the PEM 10 and a cathode diffusion layer 12b provided corresponding to the cathode catalyst layer 12a.
In this embodiment, the anode diffusion layer 11b and the cathode diffusion layer 12b are gas diffusion layers made of carbon paper or carbon cloth.

  The PEM 10, the anode catalyst layer 11 a and the cathode catalyst layer 12 a constitute a catalyst layer forming electrolyte membrane (hereinafter referred to as CCM) 100, and the PEM 10, the anode electrode 11 and the cathode electrode 12 constitute a membrane-electrode junction A body (MEB: Electron Assembly Assembly) 110 is constructed.

A first separator 110a is provided on the anode diffusion layer 11b side and a second separator 110b is provided on the cathode diffusion layer 12b side so as to sandwich the membrane-electrode assembly 110. The membrane-electrode assembly 110 and the first separator 110a and the second separator 110b constitute one cell (single cell).
The first separator 110a is provided with a plurality of flow channel grooves 111, 111 that serve as a flow channel for flowing fuel gas (hydrogen), and the second separator 110b is a flow channel for flowing oxidant (air). A plurality of flow channel grooves 112, 112 are provided.

In this example, the PEM 10, the anode catalyst layer 11a, and the anode diffusion layer 11b have the same area (in this example, a plane projection area, that is, a plane projection region; the same applies hereinafter), but the cathode catalyst layer 12a is from the PEM 10. The area of the cathode diffusion layer 12b is even smaller.
Therefore, as shown in the figure, the edge of each layered body is uneven on the left end side in the figure on the anode side (upper side in the figure) and the cathode side (lower side in the figure) with respect to the PEM 10.
For this reason, in the present embodiment, the first separator 110a and the second separator 110b are arranged so that the end edges are aligned even on the left end side in the figure, and the portions where the end edges of the respective layered bodies are not aligned as described above. A sealing member 130 is provided so as to cover the end of the membrane-electrode assembly 110.
Instead of the seal member 130 or together with the seal member 130, a silicon-based liquid seal material (functionally a frame is used so as to rotate the outer peripheral portion between the first separator 110a and the second separator 110b. Material) may be applied.

In the above configuration, in the membrane-electrode assembly 110 according to this embodiment shown in FIG. 1A, the solid polymer electrolyte membrane (PEM10) is, for example, a polymer electrolyte such as perfluorosulfonic acid. A thin film made of is used. As this solid polymer electrolyte membrane, a commercially available product can be used. For example, “Nafion” manufactured by DuPont can be used.
Further, as the gas diffusion layer (the anode diffusion layer 11b and the cathode diffusion layer 12b), for example, carbon paper on which an underlayer containing carbon particles is formed can be used.
Further, as the catalyst layers (the anode catalyst layer 11a and the cathode catalyst layer 12a), for example, a catalyst layer containing catalyst particles made of porous carbon particles carrying a platinum alloy and the above-described polymer electrolyte is used. Can do.
In the present embodiment, the Young's modulus in the surface direction of the anode catalyst layer 11a and the cathode catalyst layer 12a is particularly higher than the Young's modulus in the surface direction of the PEM 10.

On the other hand, FIG. 1B shows a problem that may occur when the Young's modulus in the surface direction of the anode catalyst layer 11a and the cathode catalyst layer 12a is lower than the Young's modulus in the surface direction of the PEM 10. .
In the example shown in part (b) of FIG. 1, the anode electrode 11 constitutes a so-called step MEA having a larger main surface over the entire circumference (not shown) than the cathode electrode 12. The pressure of the reaction gas flowing to the anode electrode 11 side is larger than the pressure of the reaction gas flowing to the cathode electrode 12 side. For this reason, a differential pressure is generated in the pressure applied to the swelling and the main surfaces of the PEM 10 to cause the PEM 10 to bend.

  In this case, if the Young's modulus in the surface direction of the anode catalyst layer 11a and the cathode catalyst layer 12a (particularly in the illustrated case, the cathode catalyst layer 12a) is lower than the Young's modulus in the surface direction of the PEM 10, it resists deformation due to this deflection. I can't. For this reason, in the figure, the PEM 10 is damaged together with the catalyst layer (in this case, the cathode catalyst layer 12a) due to the deformation as shown in the solid circle C1.

In the figure, the part of the circle C1 is particularly the part of the PEM 10 at the outer peripheral end of the cathode diffusion layer 12b. However, there is a possibility that such breakage may occur in the part of the circle C2 or the part of the circle C3 in the figure. Is the same. The reason why the phenomenon in the part of the circle C1 may occur in the part of the circle C2 or the part of the circle C3 is that the PEM 10 is depressed if there are cracks or holes in the cathode catalyst layer 12a.
Note that the PEM 10 does not sink into the cathode catalyst layer 12a when the cathode catalyst layer 12a is flat. That is, the part of the circle C2 and the part of the circle C3 are parts having a specific positional relationship with the cathode catalyst layer 12a.

In the membrane-electrode assembly 110 shown in FIG. 1 (a), the Young's modulus in the surface direction of the anode catalyst layer 11a and the cathode catalyst layer 12a is different from that in FIG. 1 (b). It is higher than the Young's modulus in the surface direction of PEM10.
For this reason, deformation of the PEM 10 is suppressed by the rigid anode catalyst layer 11a and cathode catalyst layer 12a having a relatively high Young's modulus in the plane direction. In this case, since the pores of the gas diffusion layer (the anode diffusion layer 11b and the cathode diffusion layer 12b) are not crushed by the buffer layer or the like, important characteristics of the membrane-electrode assembly such as gas diffusibility and drainage are obtained. There is no risk of damage.

  Further, the cathode catalyst layer 12a has a larger area than the cathode diffusion layer 12b, and its Young's modulus in the surface direction is higher than the Young's modulus in the surface direction of the cathode diffusion layer 12b. For this reason, deformation of the PEM 10 is suppressed by the rigid cathode diffusion layer 12b having a relatively high Young's modulus. Also in this case, since the pores of the cathode diffusion layer 12b are not crushed by the buffer layer or the like, there is no possibility that important characteristics of the membrane-electrode assembly such as gas diffusibility and drainage are impaired.

  On the other hand, the anode catalyst layer 11a is provided with an anode diffusion layer 11b having substantially the same area as the self layer. The Young's modulus in the surface direction of the anode catalyst layer 11a is lower than the Young's modulus in the surface direction of the cathode catalyst layer 12a. However, the deformation of the electrolyte membrane can be effectively suppressed together with a certain rigidity by the gas diffusion layer (anode diffusion layer) 11b having substantially the same area as the self layer. For this reason, even if both the corresponding anode catalyst layer 11a and cathode catalyst layer 12a on both main surfaces of the PEM 10 are not necessarily rigid to the same extent, deformation of the PEM 10 can be appropriately suppressed. It is.

  In other words, the cathode catalyst layer 12a has an area larger than the area of the cathode diffusion layer 12b corresponding to the cathode layer, and the Young's modulus in the surface direction is larger than the Young's modulus in the surface direction of the anode catalyst layer 11a. Is also expensive. As a result, the cathode catalyst layer 12a in which a peculiar portion without a diffusion layer supporting the self-layer is generated in the back is made more rigid so that the peculiar portion can resist the swelling of the PEM 10 and the like. The stress due to the deformation is released to the layer 11a side, and as a result, the deformation of the PEM 10 can be appropriately suppressed.

Next, the manufacturing method of CCM100 (PEM10, the anode catalyst layer 11a, the cathode catalyst layer 12a) is demonstrated.
A slurry obtained by uniformly dispersing carbon black as conductive particles having a mass ratio of 4: 6 and polytetrafluoroethylene (PTFE) particles as a water repellent agent in ethylene glycol as a solvent was applied to one side of carbon paper. Then, it was dried to form a base layer, and a gas diffusion layer composed of carbon paper and the base layer was produced.
A catalyst paste was screen-printed on the resulting gas diffusion layer underlayer and dried under reduced pressure to prepare an anode and a cathode. The catalyst paste is made of carbon black (furnace black) with platinum particles supported at a platinum / carbon mass ratio of 1: 1 to form catalyst particles, and Nafion (trade name of DuPont) is used as a proton conducting component. The catalyst particles were uniformly mixed in the solution.

In order to increase the Young's modulus in the surface direction of the catalyst layer and increase the rigidity, the fluorine-based electrolyte membrane (PEM) is sandwiched between the anode electrode and the cathode electrode, and then at a temperature of 160 degrees Celsius, which is a higher temperature than before. CCM100 was produced by hot pressing for a minute. By increasing the temperature in the hot press in this way, crystallization of the proton dielectric component is promoted, and the Young's modulus of the catalyst layer can be increased.
FIG. 2 shows the results of verifying the Young's modulus in the surface direction of the catalyst layer and the fluorine-based PEM 10 in the CCM 100 manufactured as described above.

FIG. 2 is a diagram showing the results of verifying the Young's modulus in each surface direction between the catalyst layer of the CCM 100 and the PEM 10 in the fuel cell membrane-electrode assembly of the present embodiment at various temperatures and humidity.
As easily understood from FIG. 2, the Young's modulus in the surface direction of the catalyst layer is the surface direction of the PEM 10 in the region where the temperature is minus 40 degrees Celsius to 100 degrees Celsius and the relative humidity is 95% from the dry state. It exceeds the Young's modulus.
From this result, it can be seen that in the membrane-electrode assembly of this embodiment, the deformation of the PEM 10 is suppressed by a relatively rigid catalyst layer in a wide range of temperature and humidity.

  Here, the difference in Young's modulus in each plane direction between the PEM 10 and the catalyst layer of the CCM 100 is preferably in the range of 50 MPa to 200 MPa. When the difference in Young's modulus is 50 MPa or less, the effect of suppressing deformation of the PEM 10 is insufficient, and when it is 200 MPa or more, the outer peripheral edge of the smaller gas diffusion layer (cathode catalyst layer 12a) is damaged. This is because it becomes easier.

  In other words, the ratio of the Young's modulus in each plane direction between the PEM 10 and the catalyst layer of the CCM 100 is preferably in the range of 1: 1.5 to 1: 3. When the Young's modulus of the catalyst layer of CCM100 is 1: 1.5 or less with respect to PEM10, the effect of suppressing deformation of PEM10 is insufficient, and when it is 1: 3 or more, the smaller gas diffusion layer is used. The outer peripheral end of the (cathode catalyst layer 12a) is easily damaged.

Next, a method for measuring the Young's modulus in the plane direction described above will be described.
(1) About PEM10, stress is applied to a surface direction, the amount of distortion at this time is measured, and Young's modulus is calculated based on stress and distortion.
(2) For the catalyst layer such as the cathode catalyst layer 12a, it is difficult to directly measure the Young's modulus in the surface direction. For this reason, the total Young's modulus of PEM10 and a catalyst layer is measured, and a Young's modulus is calculated by calculation. In this calculation, the target Young's modulus is calculated assuming an equivalent model in which the PEM 10 and the catalyst layer are regarded as parallel springs.

FIG. 3 is a test result regarding the membrane-electrode assembly for a fuel cell according to the present embodiment, and is a diagram showing the dimensional change amount in the surface direction of the CCM 100 in comparison with the dimensional change amount of the PEM 10 alone.
As shown in the figure, in the test result of the PEM 10 alone, the dimensional change rate is 5% or more in a dry state environment of 70 degrees Celsius, 95 percent relative humidity and minus 35 degrees Celsius.
On the other hand, in the CCM 100 of this embodiment, the dimensional change rate was suppressed within ± 2%. That is, this value is within ± 5 percent which is the breaking strain limit of the catalyst layer. This confirms that the dimensional change rate is more effectively suppressed in the CCM 100 than in the PEM 10 alone because the catalyst layer having a higher Young's modulus than the PEM 10 is bonded.

As described above with reference to FIG. 1, a single cell of a fuel cell is constituted by the membrane-electrode assembly 110 (MEA), the first separator 110a, and the second separator 110b. A plurality of single cells are stacked and electrically connected in series to form a stack. This is a polymer electrolyte fuel cell as one embodiment of the present invention.
Such a polymer electrolyte fuel cell has the characteristics described above with respect to the membrane-electrode assembly 110 (its CCM 100).

  The method of increasing the Young's modulus in the surface direction of the catalyst layer is not necessarily limited to the method of setting the hot press temperature higher than the conventional method as described above. Depending on the selection of the materials of the catalyst layer and the electrolyte membrane, the Young's modulus in the surface direction of the catalyst layer can be increased relative to the electrolyte membrane. Specific examples of this method are listed below.

(1) Change the ratio of ionomer (polymer electrolyte) and conductive material. That is, the Young's modulus in the surface direction of the catalyst layer can be increased by increasing the amount of the conductive material (carbon) than usual (usually ionomer: carbon = 1: 1).

(2) In Nafion (trade name of DuPont), which is a fluorine ionomer, the Young's modulus increases as the ion exchange capacity (IEC) decreases. Utilizing this property, the Young's modulus in the surface direction of the catalyst layer can be increased.

(3) Due to the molecular structure, ionomers such as polyarylene and PEEK (polyetheretherketone) which are hydrocarbons have higher Young's modulus than fluorine-based ionomers. Using such properties, it is possible to increase the Young's modulus in the surface direction of the catalyst layer relative to the electrolyte membrane.

(4) The present invention is established if the Young's modulus in the surface direction of the catalyst layer is higher than the Young's modulus in the surface direction of the electrolyte membrane. Focusing on this point, the Young's modulus in the surface direction of the catalyst layer is set as usual, and the Young's modulus in the surface direction of the electrolyte membrane is relatively lowered. For example, fluorine ionomers are used for the electrolyte membrane and the catalyst layer, and the IEC (ion exchange capacity) of the electrolyte membrane is made higher than the IEC of the catalyst layer so that the Young's modulus in the surface direction of the electrolyte membrane is relative to the catalyst layer. Set low. Alternatively, the Young's modulus in the surface direction of the electrolyte membrane can be set low relative to the catalyst layer by using a hydrocarbon ionomer in the catalyst layer and using a fluorine ionomer in the electrolyte membrane. .

As a whole, the embodiment described with reference to FIGS. 1 to 3 has an anisotropy in the electrolyte membrane (PEM) because the reinforcing member is included therein. That is, the Young's modulus in the plane direction is higher than the Young's modulus in the thickness direction.
In addition, when Nafion (trade name of DuPont) is applied as the electrolyte membrane, Young's modulus is determined according to the form of the reinforcing layer in which the structural and structural reinforcement measures are taken and the components of Nafion (trade name of DuPont) itself. It takes various values and is not uniquely determined.

In one embodiment described above, in one aspect, the one catalyst layer (cathode catalyst layer 12a) of the pair of catalyst layers (anode catalyst layer 11a and cathode catalyst layer 12a) is Young in the surface direction. The rate is higher than the Young's modulus in the surface direction of the other catalyst layer (anode catalyst layer 11a).
By adopting such a configuration, the cathode catalyst layer 12a, which is the one catalyst layer in which a unique portion (a portion outside the cathode diffusion layer 12b) in which no support member is behind is generated, is made more rigid so that While it is possible to resist the swelling of the PEM 10 in the portion, the stress due to the deformation is released to the anode catalyst layer 11a side as the other catalyst layer, and as a result, the deformation of the electrolyte membrane can be appropriately suppressed. It becomes possible.

In one embodiment described above, in one aspect thereof, one catalyst layer (cathode catalyst layer 12a) of the pair of catalyst layers (anode catalyst layer 11a and cathode catalyst layer 12a) has a thickness of the other. It is thicker than the thickness of the catalyst layer (anode catalyst layer 11a).
By adopting such a configuration, the rigidity of one catalyst layer (cathode catalyst layer 12a) in which a unique portion without a diffusion layer supporting the self-layer is formed behind is increased, and the electrolyte membrane swells even in the unique portion. It is possible to effectively prevent deformation of the electrolyte membrane.

Next, a membrane-electrode assembly for a fuel cell as another embodiment of the present invention will be described with reference to the drawings.
FIG. 4 is a view showing a membrane-electrode assembly for fuel cells and an equivalent model thereof as another embodiment of the present invention.
4A is a view schematically showing a fuel cell membrane-electrode assembly as another embodiment of the present invention in a cross-sectional view.
In FIG. 4A, the same reference numerals are assigned to the corresponding parts in FIG.
The fuel cell membrane-electrode assembly (MEA) 110m in part (A) of FIG. 4 is provided with the anode electrode 11 on one main surface side (upper side in the figure) of the PEM 10, and on the other main surface side (in the figure). A cathode electrode 12 is provided on the lower side.
The anode electrode 11 includes an anode catalyst layer 11a in contact with one main surface of the PEM 10 and an anode-side composite layer 11c provided corresponding to the anode catalyst layer 11a. The anode-side composite layer 11c includes a fine porous layer 11b1 that is in contact with the anode catalyst layer 11a and an anode diffusion layer 11b2 that is in contact with the outside of the fine porous layer 11b1.
The cathode electrode 12 includes a cathode catalyst layer 12a in contact with the other main surface of the PEM 10 and a cathode-side composite layer 12c provided corresponding to the cathode catalyst layer 12a. The cathode-side composite layer 12c is composed of a fine porous layer 12b1 in contact with the cathode catalyst layer 12a and a cathode diffusion layer 12b2 in contact with the outside of the fine porous layer 12b1.
The fine porous layers (11b1, 12b1) in the anode side composite layer 11c and the cathode side composite layer 12c are also referred to as base layers.

  4A, in other words, a pair of catalyst layers (anode catalyst layer 11a and cathode catalyst layer 12a) are provided so as to correspond to both main surfaces of the electrolyte membrane (PEM10). A pair of catalyst layers (anode catalyst layer 11a, cathode catalyst layer 12a) are respectively provided with gas diffusion layers (anode diffusion layer 11b2, cathode) through corresponding microporous layers (microporous layer 11b1, microporous layer 12b1). A diffusion layer 12b2), and a composite layer (anode-side composite) composed of a microporous layer (microporous layer 11b1, microporous layer 12b1) and a gas diffusion layer (anode diffusion layer 11b2, cathode diffusion layer 12b2). Layer 11c and cathode-side composite layer 12c).

Part (B) of FIG. 4 is a diagram showing an equivalent model of MEA 110m in part (A) of FIG. In this equivalent model, each layer of the membrane-electrode assembly for a fuel cell is associated with a spring, and the Young's modulus viewed in the thickness direction of each layer is represented.
That is, the anode-side composite layer 11c and the cathode-side composite layer 12c described above are made to correspond to one spring (11c, 12c), respectively, and a spring (11c, 12c) corresponding to the PEM 10 at the center position ( 10), and a spring (11a) corresponding to the anode catalyst layer 11a connected to one end and the other end of the spring (10) and a spring (12a) corresponding to the cathode catalyst layer 12a are connected to each other as shown in FIG. Such a series connection body of springs is configured.

In order to reliably suppress the deformation of the PEM 10 in the MEA 110m represented by the spring series connection body as shown in FIG. 4B, among the Young's modulus (compression elastic modulus) seen in the thickness direction of each layer, the above It is important to control the Young's modulus of each spring (11c, 12c) located at both ends of the series connection body.
Specifically, the control is performed as follows. That is, the thickness of the composite layer (11c, 12c) in the thickness direction is smaller than the Young's modulus in the thickness direction of the PEM 10, and the thickness of the catalyst layers (the anode catalyst layer 11a and the cathode catalyst layer 12a). The Young's modulus in the direction is controlled to be larger than the Young's modulus in the thickness direction of the PEM 10.

Here, the selection of the Young's modulus in the thickness direction of the catalyst layers (the anode catalyst layer 11a and the cathode catalyst layer 12a) will be described with reference to FIG.
FIG. 5 is a diagram showing a simulation result of Young's modulus by an equivalent model of the fuel cell membrane-electrode assembly in part (B) of FIG.
In FIG. 5, the horizontal axis represents the Young's modulus (compression elastic modulus: MPa) of the composite layer (the anode side composite layer 11c or the cathode side composite layer 12c), and the vertical axis represents the catalyst layer (the anode catalyst layer 11a or the cathode catalyst layer 12a). ) Represents the rate of increase of stress applied to the PEM 10 when a crack is generated. That is, on this vertical axis, the reference value, which is a value when there is no change, is 100%, and the degree of increase (decrease) from this value is expressed in%.

  As easily understood from FIG. 5, the stress applied to the PEM 10 when the Young's modulus in the thickness direction of the composite layers (11 c, 12 c) is in the range of 0.1 MPa to 35 MPa (the range indicated by the arrow R). Is substantially maintained at the reference value, that is, 100%. In other words, if the Young's modulus in the thickness direction of the composite layers (11c, 12c) is within the range of 0.1 MPa to 35 MPa, deformation of the PEM 10 can be effectively suppressed.

  As apparent from the description with reference to FIGS. 4 and 5, the Young's modulus of each spring (11c, 12c) located at both ends of the series connection body, that is, the thickness direction of the composite layer (11c, 12c). The Young's modulus is set within the range of 0.1 MPa to 35 MPa. When the Young's modulus in the thickness direction of the composite layer (11c, 12c) is within the above range, even if a crack occurs in the catalyst layer (the anode catalyst layer 11a or the cathode catalyst layer 12a), the deformation of the PEM 10 is suppressed. The effect will be sufficient. This is because the composite layer absorbs stress and avoids applying unnecessary stress to the PEM 10.

FIG. 6 illustrates the Young's modulus E = σ / γ in the thickness direction of the composite layer (11c, 12c) suitable for the fuel cell membrane-electrode assembly described with reference to FIGS. FIG.
As shown in the figure, the strain γ increases as the stress σ increases. The stress σ and the strain γ are not necessarily in a linear relationship. The strain γ is preferably used at 50% or less.

7, 8, 9, and 10 are diagrams for explaining the phenomenon that occurs in the fuel cell membrane-electrode assembly of FIG.
7, FIG. 9, and FIG. 10, the same reference numerals are assigned to the parts (A) of FIG. 4 and the corresponding parts in FIG.
The fuel cell membrane-electrode assembly (MEA) 110m of FIGS. 7, 9, and 10 is provided with the anode electrode 11 on one main surface side (upper side in the drawing) of the PEM 10, and the other main surface side. A cathode electrode 12 is provided (lower side in the figure).
The anode electrode 11 includes an anode catalyst layer 11a in contact with one main surface of the PEM 10 and an anode-side composite layer 11c provided corresponding to the anode catalyst layer 11a. This anode-side composite layer 11c is the same as that already described with reference to part (A) of FIG.

A first separator 110a similar to that already described with reference to FIG. 1 is provided outside the anode-side composite layer 11c.
The cathode electrode 12 includes a cathode catalyst layer 12a in contact with the other main surface of the PEM 10 and a cathode-side composite layer 12c provided corresponding to the cathode catalyst layer 12a. The cathode-side composite layer 12c is also the same as described above with reference to the part (A) of FIG.
A second separator 110b similar to that already described with reference to FIG. 1 is provided outside the cathode-side composite layer 12c.

  As symbolically illustrated by a bidirectional arrow line at the location of the PEM 10 in FIG. 7, the PEM 10 undergoes dimensional changes in the surface direction and the thickness direction depending on the degree of wetness and the like. In FIG. 7, it is assumed that a crack having a width d is generated in the cathode catalyst layer 12a. The width d is assumed to be about 5 μm to 50 μm.

  FIG. 8 is a diagram illustrating the state of the stress σ applied to the PEM 10 in accordance with the degree of the crack width d. As can be seen from FIG. 8, when the crack width d is in the range of 5 μm to 50 μm, the stress σ also increases non-linearly as the crack width d increases, but when the crack width d exceeds 50 μm, the stress σ tends to show saturation.

FIG. 9 assumes that the crack of the width d described in FIG. 7 has occurred in the cathode catalyst layer 12a, and further, compressive stress P1 is applied to the anode-side composite layer 11c, and compression is applied to the cathode-side composite layer 12c. It is assumed that the stress P2 has been applied.
Under these conditions, when the compression elastic modulus (Young's modulus) of the anode side composite layer 11c and the cathode side composite layer 12c is in the range of 0.1 MPa to 35 MPa, the anode side composite layer 11c and the cathode side composite layer 12c It is possible to effectively contract the stress due to the swelling of the PEM 10 by appropriately contracting corresponding to the compressive stresses P1 and P2.

10 assumes that the crack of the width d described in FIG. 7 has occurred in the cathode catalyst layer 12a, and further, compressive stress P1 is applied to the anode-side composite layer 11c, and compression is applied to the cathode-side composite layer 12c. It is assumed that the stress P2 has been applied.
In FIG. 10, it is assumed that the compression elastic modulus (Young's modulus) of the anode side composite layer 11c and the cathode side composite layer 12c is larger than 35 MPa under these conditions. When the compression elastic modulus (Young's modulus) of the anode side composite layer 11c and the cathode side composite layer 12c is greater than 35 MPa, the anode side composite layer 11c and the cathode side composite layer 12c correspond to the compressive stresses P1 and P2. Since the film does not contract, a film in which the PEM 10 swells enters a cracked part (part indicated by a broken-line circle SC) and stress concentration occurs.

  As is apparent from the above description with reference to FIGS. 7, 8, 9, and 10, the compression elastic modulus (Young's modulus) of the anode side composite layer 11c and the cathode side composite layer 12c is from 0.1 MPa. When it is within the range of 35 MPa, deformation of the PEM 10 can be effectively suppressed.

10 ... PEM (solid polymer electrolyte membrane)
DESCRIPTION OF SYMBOLS 11 ... Anode electrode 11a ... Anode catalyst layer 11b, 11b2 ... Anode diffusion layer 11b1 ... Fine porous layer 11c ... Anode side composite layer 12 ... Cathode electrode 12a ... Cathode catalyst layer 12b, 12b2 ... Cathode diffusion layer 12b1 ... Fine porous layer 12c ... cathode side composite layer 100 ... CCM (catalyst layer forming electrolyte membrane)
110, 110m ... MEA (membrane-electrode assembly)
110a ... 1st separator 110b ... 2nd separator

Claims (10)

An electrolyte membrane;
An electrode having a catalyst layer provided corresponding to the electrolyte membrane;
A fuel cell membrane-electrode assembly comprising:
A membrane-electrode assembly for a fuel cell, wherein the catalyst layer has a Young's modulus in the surface direction higher than the Young's modulus in the surface direction of the electrolyte membrane. A pair of the catalyst layers are provided so as to correspond to both main surfaces of the electrolyte membrane, and a gas diffusion layer corresponding to each of the pair of catalyst layers is provided,
One catalyst layer of the pair of catalyst layers has an area larger than the area of the gas diffusion layer corresponding to the self-layer, and the Young's modulus in the surface direction is the Young's modulus in the surface direction of the electrolyte membrane. The membrane-electrode assembly for a fuel cell according to claim 1, wherein the membrane-electrode assembly is higher.   The other catalyst layer of the pair of catalyst layers has an area substantially equal to the area of the gas diffusion layer corresponding to the self-layer, and the Young's modulus in the surface direction is the surface direction of the one catalyst layer. The membrane-electrode assembly for a fuel cell according to claim 2, wherein the membrane-electrode assembly is lower than Young's modulus.   2. The membrane-electrode junction for a fuel cell according to claim 1, wherein the catalyst layer has a Young's modulus in the surface direction higher than a Young's modulus in the surface direction of the electrolyte membrane regardless of temperature and humidity. body.   The one catalyst layer of the pair of catalyst layers has an area larger than the area of the gas diffusion layer corresponding to the self-layer, and the Young's modulus in the surface direction is the surface direction of the other catalyst layer. The membrane-electrode assembly for a fuel cell according to claim 2, wherein the Young's modulus is higher than that of the fuel cell.   6. The fuel cell membrane-electrode assembly according to claim 5, wherein the one catalyst layer of the pair of catalyst layers has a thickness greater than that of the other catalyst layer. 7.   6. The fuel cell according to claim 2, wherein each of the pair of catalyst layers has a difference in Young's modulus in a plane direction with respect to the electrolyte membrane within a range of 50 MPa to 200 MPa. Membrane-electrode assembly.   The catalyst layers are provided in pairs so as to correspond to both main surfaces of the electrolyte membrane, the pair of catalyst layers are provided with gas diffusion layers via corresponding microporous layers, and the fine The porous layer and the gas diffusion layer form a composite layer, and the Young's modulus in the thickness direction of the composite layer is smaller than the Young's modulus in the thickness direction of the electrolyte membrane, and the Young's modulus in the thickness direction of the catalyst layer The membrane-electrode assembly for a fuel cell according to claim 1, wherein the rate is larger than the Young's modulus in the thickness direction of the electrolyte membrane.   The membrane-electrode assembly for a fuel cell according to claim 8, wherein the Young's modulus in the thickness direction of the composite layer is in the range of 0.1 MPa to 35 MPa.   A solid polymer fuel cell comprising the membrane-electrode assembly for a fuel cell according to any one of claims 1 to 9.

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