JP5542278B2 - Gas diffusion layer for fuel cell and polymer electrolyte fuel cell - Google Patents

Description

  The present invention relates to a fuel cell gas diffusion layer and a polymer electrolyte fuel cell, and more particularly to a fuel cell gas diffusion layer disposed between a catalyst layer and a gas flow path layer in a compressed state from both sides. The present invention also relates to a polymer electrolyte fuel cell including the gas diffusion layer.

  A single cell of a fuel cell (hereinafter referred to as a fuel cell) includes an electrolyte membrane, a catalyst layer provided on both sides of the electrolyte membrane, and a separator provided on the outside of the catalyst layer and having a gas flow path. A gas diffusion layer is provided between the catalyst layer and the gas flow path of the separator. In general, a fuel cell mounted on a vehicle such as an automobile is used as a fuel cell stack in which a plurality of fuel cells are stacked. The fuel cell stack is compressed with a predetermined pressure determined in advance from both sides in order to keep the contact resistance in each fuel cell and between each fuel cell low. Specifically, the end plates provided on both sides of the fuel cell stack are strongly fastened with fastening members such as bolts so that the surface pressure applied to the interface of each layer constituting each fuel battery cell becomes a predetermined pressure.

  In recent years, as the fuel cell increases in area, the fastening force of the fastening member increases, and an increase in the size and weight of the fastening member has been regarded as a problem. Therefore, it is required to reduce this fastening force. On the other hand, since the gas flow channel generally has a groove structure with unevenness in the thickness direction, the surface pressure of the portion that contacts the convex portion of the gas flow channel increases, and the surface of the portion corresponding to the concave portion of the gas flow channel Pressure is lowered. Therefore, if the fastening force of the fastening member is reduced to reduce the surface pressure of the fuel cell, the surface pressure is insufficient at the portion corresponding to the recess of the gas flow path, and particularly at the interface between the gas diffusion layer and the catalyst layer. Increase in contact resistance is likely to occur. Further, surface irregularities also exist in the gas diffusion layer and the catalyst layer, and these surface irregularities also cause a local contact resistance increase under low surface pressure conditions.

  As a technique related to the present invention, Patent Document 1 discloses a gas diffusion medium for a fuel cell including a hard layer provided on the gas flow path side and a compressible layer provided on the catalyst layer side. Patent Document 1 discloses that a typical diffusion medium exhibits a compressive strain in a range of 10 to 50% when a compressive load is in a range of 0.34 to 2.76 MPa. It is disclosed that intrusion into the gas flow path can be prevented. Further, in US Pat. No. 6,057,059, the hard layer has an elastic modulus that is at least 6 times greater than the compressible layer, and the thickness of the hard layer is 8% of the total thickness of the diffusion medium, and It is disclosed that it is 70% or less.

JP 2009-501423 A

  As described above, the technique of Patent Document 1 is provided with a hard layer in order to prevent a highly compressible diffusion medium from entering the gas flow path, for example, 0.3 MPa or less. Therefore, no consideration is given to setting the surface pressure of the fuel cell low. Therefore, the conventional techniques including Patent Document 1 do not disclose effective means for suppressing an increase in the contact resistance between the fuel cell, particularly the gas diffusion layer and the catalyst layer, under low surface pressure conditions.

  The object of the present invention is to prevent an increase in local contact resistance by avoiding a decrease in local surface pressure at the interface with the catalyst layer even when the surface pressure of the fuel cell is reduced. To provide a gas diffusion layer for a fuel cell capable of maintaining a low contact resistance. Moreover, it is providing the polymer electrolyte fuel cell provided with the said gas diffusion layer.

The fuel cell gas diffusion layer according to the present invention is disposed between the gas flow path layer and the catalyst layer having the surface unevenness depth Hc in a state of being compressed at a predetermined pressure determined in advance from both sides. In a gas diffusion layer for a fuel cell for diffusing and supplying a gas flowing through a gas flow path layer to a catalyst layer, a hard layer provided on the gas flow path layer side and having a surface unevenness depth Hb, and provided on the catalyst layer side A soft layer whose elastic modulus in the thickness direction is less than 1/12 of the elastic modulus in the thickness direction of the hard layer, and the soft layer has an elastic modulus in the thickness direction of the catalyst layer as Ezc and an elastic modulus in the surface direction. and exc, EZB elastic modulus in the thickness direction of the hard layer, the elastic modulus of the surface direction EXB, have a thickness of greater than Hc × (Ezc / exc) + Hb × (Ezb / Exb), surface irregularity depth of the hard layer Less than 1 / 10th of the thickness and larger than the surface irregularity depth of the catalyst layer A particulate conductive material having a particle diameter, or a fibrous conductive material having a fiber diameter that is less than 1/10 of the surface irregularity depth of the hard layer and larger than the surface irregularity depth of the catalyst layer; And a resin .

  According to the said structure, the soft layer which has the elasticity modulus of the thickness direction which is less than 1/12 of the elasticity modulus of the thickness direction of a hard layer, and the thickness exceeding Hcx (Ezc / Exc) + Hbx (Ezb / Exb) Even if the surface pressure of the fuel cell is set to a low surface pressure such as 0.3 MPa or less, the influence of the surface unevenness of the hard layer, the catalyst layer, and the gas flow path layer is sufficiently affected. Can be relaxed. That is, the soft layer can sufficiently enter the surface irregularities of the hard layer and the catalyst layer even under low surface pressure conditions, and can ensure a large contact area with the hard layer and the catalyst layer. Therefore, at the interface between the soft layer and the catalyst layer of the gas diffusion layer and at the interface between the soft layer and the hard layer, the surface pressure is made uniform, and the local contact resistance is avoided by avoiding the decrease in the local surface pressure. It is possible to prevent an increase in

Further, the polymer electrolyte fuel cell according to the present invention is disposed between the gas flow path layer and the catalyst layer having the surface unevenness depth Hc in a compressed state from both sides at a predetermined pressure. is, in a polymer electrolyte fuel cell comprising a fuel cell gas diffusion layer for diffusing supply gas flowing in the gas flow path layer in the catalyst layer, gas diffusion layer is provided on the gas flow path layer side surface a hard layer having an uneven depth Hb, provided the catalyst layer side, and a soft layer is less than 1/12 of the thickness direction of the elastic modulus in the thickness direction of the elastic modulus is hard layer, a soft electrolyte layer is Assuming that the elastic modulus in the thickness direction of the catalyst layer is Ezc, the elastic modulus in the surface direction is Exc, the elastic modulus in the thickness direction of the hard layer is Ezb, and the elastic modulus in the surface direction is Exb, Hc × (Ezc / Exc) + Hb × ( EZB / EXB) have a thickness of greater than, the surface roughness depth of the hard layer 1 / Particulate conductive material having a particle diameter less than 10 and larger than the surface unevenness depth of the catalyst layer, or less than 1/10 of the surface unevenness depth of the hard layer and larger than the surface unevenness depth of the catalyst layer It is characterized by comprising a fibrous conductive material having a fiber diameter and an insulating resin .

  According to the gas diffusion layer for a fuel cell according to the present invention, even when the surface pressure of the fuel cell is reduced, a local surface pressure is prevented from being lowered, particularly at the interface with the catalyst layer. It is possible to prevent an increase in contact resistance and maintain a low contact resistance. Therefore, the fastening force of the fuel cell can be reduced, and the fastening member can be reduced in size and weight.

It is sectional drawing which shows the fuel cell provided with the gas diffusion layer for fuel cells which is embodiment of this invention. FIG. 3 is a cross-sectional view showing a state of an interface between a soft layer and a catalyst layer and an interface between a soft layer and a hard layer in a fuel cell including a fuel cell gas diffusion layer according to an embodiment of the present invention. It is a figure which shows the relationship between the surface pressure and the contact resistance in the interface of a gas diffusion layer and a catalyst layer in the fuel cell provided with the gas diffusion layer for fuel cells which is embodiment of this invention. In a fuel cell including a gas diffusion layer for a fuel cell according to an embodiment of the present invention, contact with the thickness of the soft layer under a low surface pressure condition where the surface pressure at the interface between the gas diffusion layer and the catalyst layer is 0.1 MPa It is a figure which shows the relationship with resistance. In a fuel cell comprising a fuel cell gas diffusion layer according to an embodiment of the present invention, the elastic modulus of the soft layer is determined under a low surface pressure condition where the surface pressure at the interface between the gas diffusion layer and the catalyst layer is 0.1 MPa. It is a figure which shows the relationship with contact resistance. It is sectional drawing which shows the state of the interface of a soft layer and a catalyst layer, and the interface of a soft layer and a hard layer in the structure where the thickness of a soft layer does not see the conditions of Formula (2). It is a figure which shows the relationship between the surface pressure and the contact resistance in the interface of a gas diffusion layer and a catalyst layer in the structure where the thickness of a soft layer does not see the conditions of Formula (2).

  Hereinafter, embodiments of a gas diffusion layer for a fuel cell and a polymer electrolyte fuel cell including the gas diffusion layer according to the present invention will be described in detail with reference to the drawings. Hereinafter, the gas diffusion layer for a fuel cell according to the present invention is referred to as a gas diffusion layer 30 applied to each fuel cell 11 constituting the vehicle fuel cell stack 10 (hereinafter referred to as the fuel cell stack 10). Although described, the application range is not limited to a fuel cell for vehicles.

  As shown in FIG. 1, the fuel cell stack 10 includes a plurality of stacked fuel cells 11, a pair of end plates 12 disposed on both sides of the fuel cells 11, and fastening members and manifolds (not shown). ing. The end plate 12 compresses the stack of the fuel cells 11 using a fastening member (not shown) in order to keep the contact resistance in each fuel cell 11 and between the fuel cells 11 low. In addition, as a surface pressure concerning each layer of the fuel cell 11 in a compressed state, 0.05 MPa to 0.5 MPa can be exemplified, and 0.1 MPa to 0.3 MPa is more preferable. Below, the fuel cell 11 demonstrates as what is compressed by the surface pressure of 0.3 Mpa or less.

  The fuel cell stack 10 is connected to a fuel gas hydrogen gas supply device, an oxidizing gas air supply channel, a cooling water supply device, etc., not shown, via a manifold. .

  The fuel cell 11 is a polymer electrolyte fuel cell, and includes an electrolyte membrane 13 that is a polymer membrane, a catalyst layer 14 provided on both sides of the electrolyte membrane 13, and a separator 15 provided outside the catalyst layer 14. The gas diffusion layer 30 provided between the catalyst layer 14 and the separator 15 is provided. The separator 15 has a gas flow path 16 for flowing hydrogen gas or air on the surface in contact with the gas diffusion layer 30.

  The electrolyte membrane 13 is an ion exchange membrane that selectively permeates hydrogen ions (hereinafter referred to as protons) in a wet state, and has a function of moving protons generated at the anode electrode to the cathode electrode. As the electrolyte membrane 13, for example, a polymer membrane such as a sulfonic acid type perfluorocarbon polymer such as Nafion (registered trademark of DuPont), a polysulfone resin, a perfluorocarbon polymer having a phosphonic acid group or a carboxylic acid group is used. Can do.

  The catalyst layer 14 is a layer provided on both sides of the electrolyte membrane 13, and the reaction involved is different between the anode electrode side and the cathode electrode side. The catalyst layer 14 on the anode electrode side has a function of ionizing hydrogen gas supplied from the gas flow path 16 through the gas diffusion layer 30 into protons and electrons. On the other hand, in the catalyst layer 14 on the cathode electrode side, protons and electrons ionized on the anode electrode side react with oxygen in the air supplied from the gas flow path 16 through the gas diffusion layer 30 to generate water. . An electromotive force is generated by this series of reactions. Each catalyst layer 14 is mainly composed of carbon such as carbon black, acetylene black, or carbon nanotube (hereinafter referred to as supported carbon) carrying a noble metal catalyst such as platinum, ruthenium, or rhodium. . The catalyst layer 14 can be formed using, for example, a hot press after applying supported carbon dispersed in a solvent on both surfaces of the electrolyte membrane 13.

  The catalyst layer 14 has a thickness of about 5 μm to 30 μm, for example, and a thickness of about 10 μm is particularly suitable. Further, as will be described later in detail, the surface of the catalyst layer 14 on the gas diffusion layer 30 side is not flat but has surface irregularities.

  The separator 15 has a function of preventing a mixed flow of hydrogen gas and air and a function of collecting electricity generated by a reaction in the electrolyte membrane 13 and the catalyst layer 14. In general, the separator 15 is provided with a cooling water passage (not shown) and has a function of cooling the fuel cell 11. Further, the separator 15 is made of, for example, a stainless thin plate, and is provided at both ends of the fuel cell 11 so as to sandwich the electrolyte membrane 13 and the catalyst layer 14 via the gas diffusion layer 30.

  As described above, the gas flow path 16 is a flow path for flowing hydrogen gas or air, and is formed on the surface of the separator 15 in contact with the gas diffusion layer 30. Specifically, hydrogen gas flows through the gas flow path 16 on the anode electrode side, and air flows through the gas flow path 16 on the cathode electrode side. In addition, each gas flow channel 16 can adopt a structure in which grooves having irregularities in the thickness direction, for example, a serpentine flow channel structure or a straight flow channel structure, and the convex portion is in contact with the gas diffusion layer 30. doing.

  The gas diffusion layer 30 has a function of diffusing and supplying hydrogen gas or air flowing through the gas flow path 16 on the surface of the separator 15 to the catalyst layer 14 (diffusion supply), and the gas flow path 16 which is a gas flow path layer. And the catalyst layer 14. The gas diffusion layer 30 also serves as an electron transfer medium between the catalyst layer 14 and the separator 15. Therefore, the gas diffusion layer 30 is compressed at a predetermined pressure in order to maintain low contact resistance between the catalyst layer 14 and the separator 15, particularly between the catalyst layer 14 where contact resistance is likely to increase. Has been placed. Specifically, as described above, the entire fuel cell 11 is compressed by the pair of end plates 22.

  In addition, the gas diffusion layer 30 achieves uniform surface pressure even under low surface pressure conditions such as 0.3 MPa or less, and particularly reduces the local surface pressure at the interface with the catalyst layer 14. It has a function of avoiding an increase in local contact resistance. In order to realize this function, the gas diffusion layer 30 has a two-layer structure including a hard layer 31 provided on the gas flow path 16 side and a soft layer 32 provided on the catalyst layer 14 side. The elastic modulus and thickness in the thickness direction of the layer 32 are defined as described later.

  The hard layer 31 is a layer that is in contact with the gas flow path 16 and is harder than the soft layer 32 and has a higher elastic modulus. In this specification, the elastic modulus means Young's modulus obtained by dividing the compressive force by strain. As the hard layer 31, for example, a conductive material made of a fibrous conductive material such as carbon paper, carbon cloth, or carbon felt, and preferably coated with an insulating resin such as polytetrafluoroethylene is used. . The hard layer 31 can also be composed of a particulate conductive material such as carbon black and an insulating resin such as polytetrafluoroethylene. Alternatively, a paste obtained by kneading a particulate conductive material or an insulating material may be applied to a fibrous conductive material. The hard layer 31 is produced, for example, by laminating a fibrous conductive material with the constituent material of the soft layer 32 or by applying one constituent material of the hard layer 31 or the soft layer 32 to the other constituent material. .

  The hard layer 31 has, for example, a thickness of about 100 μm to 300 μm, and particularly preferably a thickness of about 150 μm to 200 μm. Further, as will be described in detail later, the surface of the hard layer 31 is not flat but has surface irregularities.

The soft layer 32 is a layer that is in contact with the catalyst layer 14, and is a layer that is more flexible and easier to compress than the hard layer 31. Further, the soft layer 32 is more flexible than the catalyst layer 14. That is, the elastic modulus of the soft layer 32 is lower than that of the hard layer 31 and the catalyst layer 14, and particularly the elastic modulus (Eza) in the thickness direction is the elastic modulus in the thickness direction of the hard layer 31 as shown in Equation (1). It is required to be less than 1/12 of (Ezb).
Eza <Ezb / 12 (1)
In addition, as a preferable range of an elasticity modulus (Eza), less than 1/12-1/24 of an elasticity modulus (Ezb) can be illustrated, for example, it sets in the range of 0.1 MPa-10 MPa.

  The expression (1) that defines the elastic modulus (Eza) of the soft layer 32 is derived from the calculation results based on Holm's contact resistance theory and the like, as well as the simulation results and actual experimental results for various elastic moduli. . That is, according to the experimental results and the like, the soft layer 32 has 0.3 MPa when the elastic modulus (Eza) satisfies the condition of the expression (1) and the thickness Ta satisfies the expression (2) as described later. An increase in contact resistance can be prevented even under the following low surface pressure conditions. On the other hand, when the elastic modulus (Eza) does not satisfy the condition of the formula (1), that is, when the elastic modulus (Eza) is 1/12 or more of the elastic modulus (Ezb) of the hard layer 31, the low surface pressure condition is used. An increase in contact resistance cannot be prevented.

  The soft layer 32 can be composed of a fibrous or particulate conductive material similar to the hard layer 31. However, in order to make the elastic modulus (Eza) smaller than that of the hard layer 31, for example, a material having a low fiber density or a material having a high flexibility is used, and a particulate conductive material such as carbon black is particularly suitable. . In addition, the soft layer 32 has a particle diameter that is less than 1/10 of the surface unevenness depth Hb of the hard layer 31 and larger than the surface unevenness depth Hc of the catalyst layer 14 from the viewpoint of uniform surface pressure and the like. A particulate conductive material, or a fibrous conductive material having a fiber diameter less than 1/10 of the surface irregularity depth Hb of the hard layer 31 and larger than the surface irregularity depth Hc of the catalyst layer 14; It is preferably composed of an insulating resin such as tetrafluoroethylene. The particle diameter and fiber diameter conditions are also derived from the above calculation results, simulation results, and experimental results.

  Here, the configuration of the gas diffusion layer 30, particularly the configuration of the soft layer 32, will be further described with reference to FIG. 2 is a cross-sectional view showing the interface between the soft layer 32 and the catalyst layer 14 and the interface between the soft layer 32 and the hard layer 31. FIG. 2 (a) is an uncompressed state and FIG. ) Indicates the compression state.

  As shown in FIG. 2A, surface irregularities exist on the surface of the catalyst layer 14 and the surface of the hard layer 31 with which the soft layer 32 contacts. The surface unevenness depth Hc of the catalyst layer 14 and the surface unevenness depth Hb of the hard layer 31 are different depending on the thicknesses. However, since the hard layer 31 is usually thicker, the surface unevenness depth has a relationship of Hc <Hb. It becomes. The surface unevenness depths Hc and Hb used in formula (2) described later are the lengths of the surface unevenness in the thickness direction in an uncompressed state or a very low compressed state (hereinafter abbreviated as a finely compressed state). For example, an optical microscope, a scanning electron microscope (SEM), a surface roughness meter with a tip diameter of 10 μm or less, a scanning probe microscope (SPM), etc., in which the probe tip pressure is controlled to 0.01 to 0.1 MPa. Can be measured.

The soft layer 32 has a thickness Ta that satisfies the expression (2) based on the surface irregularities of the catalyst layer 14 and the hard layer 31. In addition, thickness Ta means the thickness in an uncompressed state or a fine compression state.
Ta> {Hc × (Exc / Ezc)} + {Hb × (Exb / Ezb)} (2)
Here, Ex1 is the elastic modulus in the surface direction of the catalyst layer 14, Ex2: the elastic modulus in the surface direction of the hard layer 31. Hc and Hb are the surface unevenness depths of the catalyst layer 14 and the hard layer 31 in the uncompressed state or the slightly compressed state as described above. In the formula (2), for example, the maximum surface unevenness depth is A value, median, mode, average, or the like can be used. Among these, it is preferable to use a median value, a mode value, or an average value, and it is more preferable to use an average value.

  Expression (2) that defines the thickness Ta of the soft layer 32 is derived by calculation based on the Poisson's ratio, and is supported by simulations and actual experiments at various thicknesses. (Exc / Ezc) and (Exb / Ezb) in the formula (2) represent the ratio of the elongation in the surface direction and the elongation in the thickness direction of each layer in the compressed state of the catalyst layer 14 and the hard layer 31. is there. And the surface uneven | corrugated depth of each layer in a compression state can be estimated by multiplying the said ratio by the surface uneven | corrugated depth of an uncompressed state or a fine compression state. That is, the thickness Ta of the soft layer 32 is required to have a thickness that exceeds the sum of the surface unevenness of the catalyst layer 14 and the surface unevenness of the hard layer 32 in the compressed state.

  That is, as shown in FIG. 2B, the soft layer 32 is 0.3 MPa or less as long as the elastic modulus (Eza) satisfies the condition of the expression (1) and the thickness Ta satisfies the expression (2). Even under such a low surface pressure condition, it corresponds to the surface unevenness of the catalyst layer 14 and the surface unevenness of the hard layer 31, and is in contact with both layers without any gap. On the other hand, when the thickness Ta does not satisfy the condition of the formula (2), even when the elastic modulus (Eza) satisfies the condition of the formula (1), an increase in contact resistance cannot be prevented under a low surface pressure condition.

  The thickness of the gas diffusion layer 30 is preferably 50 μm to 500 μm, more preferably 100 μm to 300 μm, from the viewpoint of gas diffusibility and the like. And as thickness Ta of the soft layer 32, although it changes also with the thickness of the gas diffusion layer 30 whole, it is preferable that it is 50-200 micrometers, and it is more preferable that it is 70-100 micrometers.

  Here, with reference to FIG. 2 and FIG. 6 as a comparative example, the function and effect of the gas diffusion layer 30 having the above configuration, particularly the function and effect of the soft layer 32 will be described. FIG. 6 is a diagram corresponding to FIG. 2, and is a diagram illustrating an interface state when a soft layer 51 that does not satisfy the condition of Expression (2) is used instead of the soft layer 32.

  As shown in FIG. 2A, the soft layer 32 in which the elastic modulus (Eza) satisfies the condition of the expression (1) and the thickness Ta satisfies the condition of the expression (2) is as shown in FIG. In addition, for example, even under low surface pressure conditions such as 0.3 MPa, the surface irregularities of the catalyst layer 14 and the hard layer 31 can sufficiently enter. That is, the soft layer 32 can be in contact with the catalyst layer 14 and the hard layer 31 without a gap, and a large contact area with both layers can be secured even under low surface pressure conditions. Therefore, if the gas diffusion layer 30 is used, it is possible to avoid a decrease in local surface pressure, prevent an increase in local contact resistance, and maintain the contact resistance in a low state.

  On the other hand, as shown in FIG. 6A, when the thickness of the soft layer 51 does not satisfy the condition of the formula (2), the soft layer 51 includes the catalyst layer 14 and the hard layer as shown in FIG. The surface 31 does not sufficiently enter the surface uneven portion of the layer 31 and a large gap is formed between both layers, and a large contact area cannot be ensured particularly under low surface pressure conditions. Therefore, when the gas diffusion layer 50 shown in FIG. 6 is used, the surface pressure becomes non-uniform and causes an increase in local contact resistance.

  Next, the function and effect of the gas diffusion layer 30 will be further described with reference to FIGS. 3 to 5 and FIG. 7 as a comparative example. In each figure, ▲ indicates an actual measurement value, and a dotted line indicates a calculated value.

  3 is a diagram showing the relationship between the contact pressure and the contact pressure at the interface between the gas diffusion layer 30 and the catalyst layer 14, and FIGS. 4 and 5 show the interface between the gas diffusion layer 30 and the catalyst layer 14. FIG. 6 is a diagram showing the relationship between the thickness of the soft layer 32 and the contact resistance and the relationship between the elastic modulus of the soft layer 32 and the contact resistance under the condition that the surface pressure is 0.1 MPa. FIG. 7 is a diagram corresponding to FIG. 3, and shows a case where a soft layer 51 that does not satisfy the condition of Expression (2) is used instead of the soft layer 32.

  As shown in FIG. 3, when the soft layer 32 (Eza = 1 MPa, Ta = 98 μm) in which the elastic modulus (Eza) satisfies the condition of the expression (1) and the thickness Ta satisfies the condition of the expression (2) is used. Even under low surface pressure conditions such as 0.3 MPa, the contact resistance hardly increases and the low contact resistance can be maintained. On the other hand, as shown in FIG. 7, when the soft layer 52 that does not satisfy the conditions of the expressions (1) and (2) is used, if the surface pressure becomes smaller than 0.3 MPa, the contact resistance increases rapidly. cause.

Further, as shown in FIG. 4, when the soft layer 32 (Eza = 1 MPa) satisfying the conditions of the expressions (1) and (2) is used, the contact resistance tends to decrease as the thickness Ta increases. Obtained. Specifically, when the thickness Ta is changed from 52 μm to 98 μm, the contact resistance is changed from 85 mΩ · cm ² to 40 mΩ · cm ² , and when the thickness Ta is about doubled, the contact resistance is about ½. Results were obtained. In addition, the tendency illustrated in FIG. 4 shows that the thickness Ta of the catalyst layer 14 in the range where the thickness Ta is about 50 μm to 100 μm and the soft layer 32 satisfies the conditions of the expressions (1) and (2), the hard layer Even if the surface irregularity depth Hb of 32 or the elastic modulus (Ezb) of the hard layer 31 is changed, it hardly changes.

Further, as shown in FIG. 5, when the soft layer 32 (Ta = 98 μm) satisfying the conditions of the expressions (1) and (2) is used, the elastic modulus (Eza) is lowered, that is, the flexibility. The higher the value, the lower the contact resistance. Specifically, varying elastic modulus (Eza) from 10MPa to 1 MPa, the contact resistance results in changes from 50 m [Omega · cm ² to 40m · cm ² was obtained. In addition, the tendency illustrated in FIG. 5 shows that the surface unevenness depth Hc of the catalyst layer 14 is within the range where the elastic layer (Eza) is about 1 MPa to 10 MPa and the soft layer 32 satisfies the conditions of the expressions (1) and (2). Even if the surface unevenness depth Hb of the hard layer 32 or the elastic modulus (Ezb) of the hard layer 31 is changed, it hardly changes.

  As described above, if the gas diffusion layer 30 including the hard layer 31 and the soft layer 32 satisfying the conditions of the expressions (1) and (2) is used as the gas diffusion layer of the solid polymer fuel cell, Even when the surface pressure of the fuel cell is reduced, it is possible to avoid a decrease in the local surface pressure, prevent an increase in the local contact resistance, and maintain the contact resistance in a low state. . Therefore, the fastening force of the fuel cell can be reduced, and the fastening member can be reduced in size and weight.

  In the above description, the gas flow path 16 is formed in the separator 15. However, as a fuel cell to which the gas diffusion layer of the present invention is applied, a fuel cell including a gas flow path layer that is a separate member from the separator. It may be.

  DESCRIPTION OF SYMBOLS 10 Fuel cell stack, 11 Fuel cell, 12 End plate, 13 Electrolyte membrane, 14 Catalyst layer, 15 Separator, 16 Gas flow path, 30 Gas diffusion layer, 31 Hard layer, 32 Soft layer, Hc Surface unevenness depth of catalyst layer , Hb Hard layer surface unevenness depth, Ta soft layer thickness.

Claims (2)

And a gas flow path layer, between the catalyst layer having a surface roughness depth Hc, is disposed in a compressed state at a predetermined pressure that is determined in advance from both sides, the catalyst layer of the gas flowing through the gas flow path layer In the fuel cell gas diffusion layer for diffusion supply to
Provided in the gas flow path layer side, and a hard layer having a surface roughness depth Hb,
Provided on the catalyst layer side, comprises a soft layer elastic modulus in the thickness direction is less than 1/12 of the elastic modulus in the thickness direction of the hard layer, and
The soft layer is
EZC the thickness direction of the elastic modulus of the catalyst layer, the elastic modulus of the surface direction and Exc, the thickness direction of the elastic modulus of the hard layer EZB, the elastic modulus of the surface direction Exb, Hc × (Ezc / Exc ) + Hb have a thickness of more than × (Ezb / Exb),
Particulate conductive material having a particle diameter that is less than 1/10 of the surface unevenness depth of the hard layer and larger than the surface unevenness depth of the catalyst layer, or 1/10 of the surface unevenness depth of the hard layer Less than and a fibrous conductive material having a fiber diameter larger than the surface irregularity depth of the catalyst layer;
An insulating resin;
A gas diffusion layer for a fuel cell, comprising: And a gas flow path layer, between the catalyst layer having a surface roughness depth Hc, is disposed in a compressed state at a predetermined pressure that is determined in advance from both sides, the catalyst layer of the gas flowing through the gas flow path layer In a polymer electrolyte fuel cell comprising a gas diffusion layer for a fuel cell for diffusion supply to
The gas diffusion layer is provided in the gas flow path layer side, and a hard layer having a surface roughness depth Hb, provided the catalyst layer side, in the thickness direction modulus of elasticity in the thickness direction of the hard layer A soft layer that is less than 1/12,
The soft layer is
EZC the thickness direction of the elastic modulus of the catalyst layer, the elastic modulus of the surface direction and Exc, the thickness direction of the elastic modulus of the hard layer EZB, the elastic modulus of the surface direction Exb, Hc × (Ezc / Exc ) + Hb have a thickness of more than × (Ezb / Exb),
Particulate conductive material having a particle diameter that is less than 1/10 of the surface unevenness depth of the hard layer and larger than the surface unevenness depth of the catalyst layer, or 1/10 of the surface unevenness depth of the hard layer Less than and a fibrous conductive material having a fiber diameter larger than the surface irregularity depth of the catalyst layer;
An insulating resin;
A polymer electrolyte fuel cell comprising:

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