JP2022092379A - Gas diffusion layer - Google Patents

Abstract

To provide a gas diffusion layer with high drainage properties.SOLUTION: A gas diffusion layer for a fuel cell includes a porous carbon substrate that is configured by stacking a plurality of carbon fibers bound together with a bonding material. The porous carbon substrate has an inner layer portion and two surface layer portions sandwiching the inner layer portion. The height of substrate fibers on at least one of the surface layer portions of the porous carbon substrate in the stacking direction is lower than the height of the substrate fibers on the inner layer portions in the stacking direction.SELECTED DRAWING: Figure 10

Description

The present disclosure relates to a gas diffusion layer.

A fuel cell (FC) is a fuel cell stack (hereinafter, may be simply referred to as a stack) in which a plurality of single cells (hereinafter, may be referred to as a cell) are laminated, and a fuel gas such as hydrogen and oxygen are used. It is a power generation device that extracts electric energy by an electrochemical reaction with an oxidant gas such as air. In the following, the fuel gas and the oxidant gas may be simply referred to as "reaction gas" or "gas" without particular distinction. Further, both a single cell and a fuel cell stack in which single cells are stacked may be referred to as a fuel cell.
The single cell of this fuel cell usually comprises a membrane electrode assembly (MEA).
The membrane electrode assembly has a catalyst layer and a gas diffusion layer (GDL, hereinafter may be simply referred to as a diffusion layer) on both sides of a solid polymer electrolyte membrane (hereinafter, also simply referred to as “electrolyte membrane”), respectively. It has a structure formed in order. Therefore, the membrane electrode assembly may be referred to as a membrane electrode gas diffusion layer assembly (MEGA).
The single cell has two separators that sandwich both sides of the membrane electrode gas diffusion layer junction, if necessary. The separator usually has a structure in which a groove as a flow path of the reaction gas is formed on the surface in contact with the gas diffusion layer. This separator also functions as a current collector for the generated electricity.
At the fuel electrode (anode) of the fuel cell, hydrogen (H ₂ ) as a fuel gas supplied from the gas flow path and the gas diffusion layer is protonated by the catalytic action of the catalyst layer, passes through the electrolyte membrane, and passes through the electrolyte membrane to the oxidant electrode (oxidant electrode). Move to the cathode). The simultaneously generated electrons work through an external circuit and move to the cathode. Oxygen (O ₂ ) as an oxidant gas supplied to the cathode reacts with protons and electrons on the cathode to produce water. The generated water gives an appropriate humidity to the electrolyte membrane, and the excess water permeates the gas diffusion layer and is discharged to the outside of the system.

Various techniques have been proposed for fuel cells mounted on and used in fuel cell vehicles (hereinafter sometimes referred to as vehicles).
For example, Patent Document 1 discloses a base material for a gas diffusion layer in which the porosity is high on the rib side of the separator and the porosity decreases as the distance from the rib of the separator increases.

Further, in Patent Document 2, in order to keep the gas diffusion layer of the fuel cell thinner than the conventional one and to maintain a good balance of water repellency, water retention and conductivity, the members having different porosities of the conductive particles and the polymer material are used. A technique for laminating and rolling more than one layer is disclosed.

Further, Patent Document 3 discloses a fuel cell including a water absorbing material whose volume varies depending on the absorption / release of water between the separator and the diffusion layer.

Japanese Unexamined Patent Publication No. 2014-011163 Japanese Unexamined Patent Publication No. 2014-035797 JP-A-2017-152181

The gas diffusion layer of the fuel cell is required not to retain the liquid water generated during power generation and to improve the drainage property during scavenging.
In Patent Document 1, the pore ratio of the gas diffusion layer is high on the rib side surface of the separator, and as a result, the surface unevenness of the gas diffusion layer becomes large, so that the unevenness of the ribs may easily bite into the gas diffusion layer. be. The present disclosers have visualized that the unevenness of the ribs bites into the gas diffusion layer, so that the pores of the gas diffusion layer, that is, the drainage path is crushed or blocked, and the drainage property is deteriorated. Confirmed.
Regarding Patent Document 2, just because members having different porosities are laminated does not mean that the drainage property is improved. In addition, a rolling process and other materials (conductive materials, polymer resins, etc.) are required, which is complicated and costly.
In Patent Document 3, when the absorbent material expands, the base material is also compressed, so that gas diffusion deteriorates and the surface pressure increases locally. Therefore, the diffusion layer bends and the diffusion layer blocks the flow path, resulting in deterioration of performance. .. In addition, the adsorbent causes a poor flow of gas required for power generation under the ribs of the separator, and an increase in electrical resistance due to additional members affects power generation performance. Furthermore, the manufacturing process is complicated and the manufacturing cost is high.

The present disclosure has been made in view of the above circumstances, and an object of the present disclosure is to provide a gas diffusion layer having high drainage property.

In the present disclosure, it is a gas diffusion layer for a fuel cell provided with a porous carbon base material formed by binding a plurality of carbon fibers with a binder and laminating the plurality of the carbon fibers. hand,
The porous carbon substrate has an inner layer portion and two surface layer portions sandwiching the inner layer portion.
Provided is a gas diffusion layer characterized in that the height in the stacking direction of the base fiber of the surface layer portion of at least one of the porous carbon base material is lower than the height of the base fiber in the inner layer portion in the stacking direction. do.

According to the gas diffusion layer of the present disclosure, it is possible to easily drain the liquid water generated in a large amount during high-load power generation without retaining it, so that the power generation performance of the fuel cell can be improved.

FIG. 1 is a cross-sectional image of a conventional fuel cell. FIG. 2 is a graph showing the air permeability of the diffusion layer at 1.8 MPa (left) and the air permeability of the diffusion layer at 3.0 MPa (right). FIG. 3 is a visualization image of liquid water drainage on the surface of the diffusion layer under a rib (made of transparent glass) during power generation of a fuel cell. FIG. 4 is a visualization image of liquid water drainage on the surface of the diffusion layer under a rib (made of transparent glass) during scavenging of a fuel cell. FIG. 5 is a schematic diagram of a conventional diffusion layer that simply shows the results of liquid water visualization of the conventional diffusion layer. FIG. 6 is an image of the surface of the porous carbon substrate when the porous carbon substrate is vacuum impregnated with colored liquid water. FIG. 7 is a schematic diagram showing an example of the diffusion layer of the present disclosure for explaining the effect of the present disclosure. FIG. 8 shows that the height of the base material fiber on the surface (surface layer portion) is the same as that of a conventional fuel cell using a diffusion layer having the same height of the base material fiber on the surface (surface layer portion) and the height of the base material fiber on the inside (inner layer portion). It is a current density-voltage curve at the time of each power generation of the fuel cell of this disclosure using the diffusion layer lower than the height of the base material fiber of the inner (inner layer part). FIG. 9 is a schematic plan view showing an example of the diffusion layer of the present disclosure. FIG. 10 is a schematic cross-sectional view showing an example of the diffusion layer of the present disclosure. FIG. 11 is a schematic cross-sectional view showing another example of the diffusion layer of the present disclosure. FIG. 12 is a schematic cross-sectional view showing another example of the diffusion layer of the present disclosure. FIG. 13 is a schematic cross-sectional view showing another example of the diffusion layer of the present disclosure. FIG. 14 is a schematic cross-sectional view showing an example of a fuel cell using the diffusion layer of the present disclosure. FIG. 15 is a schematic cross-sectional view showing another example of the fuel cell using the diffusion layer of the present disclosure.

In the present disclosure, it is a gas diffusion layer for a fuel cell provided with a porous carbon base material formed by binding a plurality of carbon fibers with a binder and laminating the plurality of the carbon fibers. hand,
The porous carbon substrate has an inner layer portion and two surface layer portions sandwiching the inner layer portion.
Provided is a gas diffusion layer characterized in that the height in the stacking direction of the base fiber of the surface layer portion of at least one of the porous carbon base material is lower than the height of the base fiber in the inner layer portion in the stacking direction. do.

FIG. 1 is a cross-sectional image of a conventional fuel cell. In the fuel cell shown in FIG. 1, a gas diffusion layer (diffusion layer) 11 and a separator 12 are arranged in this order on both sides of the membrane electrode assembly 10, and an absorbing member (water absorbing material) is provided between one of the gas diffusion layer 11 and the separator 12. 14 is arranged and the flow path 15 is formed.
The fuel cell of FIG. 1 is a technique for improving drainage by inserting a water absorbing material 14 whose volume fluctuates due to absorption and release of water between a separator 12 and a diffusion layer 11. However, when the water absorbing material 14 contains water, the water absorbing material 14 expands and a local surface pressure is applied to the portion under the rib of the separator 12, so that the rib of the separator 12 bites into the diffusion layer 11 and the diffusion layer 11 There is a problem that the pressure loss increases because a part of the water enters the flow path 15. Further, the pores of the diffusion layer 11 under the rib are crushed and the air permeability of the diffusion layer 11 is significantly reduced. FIG. 2 is a graph showing the air permeability of the diffusion layer at 1.8 MPa (left) and the air permeability of the diffusion layer at 3.0 MPa (right). As shown in FIG. 2, it can be seen that the air permeability decreases as the pressure applied to the diffusion layer increases.
Further, by inserting the absorbing member 14 under the rib as shown in FIG. 1, the flow of electrons is obstructed, the electrical (thermal) resistance increases, and the power generation performance decreases. Further, since the absorbing member 14 is locally inserted, the manufacturing process is complicated and the manufacturing cost is inevitably increased.

When the researchers observed the drainage under the ribs from the surface of the diffusion layer with a power generation jig with a visualization flow path, the drainage from the diffusion layer spreads as a liquid film on the outermost surface side of the diffusion layer base material. , I found by visualization that the base fiber was in the way and could not be drained well.
FIG. 3 is a visualization image of liquid water drainage on the surface of the diffusion layer under a rib (made of transparent glass) during power generation of a fuel cell.
FIG. 4 is a visualization image of liquid water drainage on the surface of the diffusion layer under the rib (made of transparent glass) during scavenging of the fuel cell.
When the behavior of liquid water drainage under the ribs during power generation and scavenging was observed from the surface of the diffusion layer, a liquid film was observed on the surface of the diffusion layer where the liquid water was on the base fiber portion (the portion surrounded by carbon fibers). rice field.
Further, as shown in FIG. 4, during scavenging, it was observed that the liquid water moved along the base fiber of the carbon fiber in the direction perpendicular to the gas flow direction.
From this, it is considered that the water inside the diffusion layer cannot be drained well by the base fiber on the surface during power generation and scavenging.
FIG. 5 is a schematic diagram of a conventional diffusion layer that simply shows the results of liquid water visualization of the conventional diffusion layer. As shown in FIG. 5, the carbon fibers (carbon fibers) 2 on the surface of the porous carbon substrate 1 arranged on the microporous layer (MPL) 4 form irregularities, which hinder drainage. ..
FIG. 6 is an image of the surface of the porous carbon substrate when the porous carbon substrate is vacuum impregnated with colored liquid water.
As shown in FIG. 6, it can be seen that the colored water is firmly contained in the inside of the porous carbon base material, but the liquid water hardly comes to the surface portion of the porous carbon base material.

Based on these new findings, the surface roughness (diffusion layer) of the liquid water retention part (diffusion layer surface on the flow path side) of the diffusion layer is to be improved in order to reduce the power generation performance of the fuel cell due to the retention of liquid water and improve the drainage property during scavenging. It was found that the drainage property of liquid water is improved by lowering the height of the base fiber).

FIG. 7 is a schematic diagram showing an example of the diffusion layer of the present disclosure for explaining the effect of the present disclosure. As shown in FIG. 7, the height of the base fiber containing the carbon fiber (carbon fiber) 2 on the surface (surface layer portion) of the porous carbon base material 1 which is a diffusion layer arranged on the microporous layer (MPL) 4. Porous carbon by lowering the height (for example, fiber diameter) of the base fiber containing the carbon fiber (carbon fiber) 2 inside (inner layer) of the porous carbon base material 1 (for example, fiber diameter). It is possible to reduce the unevenness of the surface of the base material 1 and improve the drainage property.
In the present disclosure, in the gas diffusion layer formed by laminating carbon fibers, a base material containing carbon fibers only on the surface (surface layer portion) facing the flow path so as not to obstruct the flow of liquid water. The fiber diameter of the fiber is made smaller than the fiber diameter of the base fiber containing the carbon fiber inside the diffusion layer (inner layer portion) to reduce the unevenness of the surface layer portion. As a result, it is possible to prevent the liquid water inside the diffusion layer (inner layer portion) from being obstructed by the surface layer portion of the diffusion layer, and to facilitate the drainage of the water inside the diffusion layer (inner layer portion). As a result, the scavenging time can be shortened, the occurrence of gas blockage due to the retention of liquid water is suppressed, and the power generation performance of the fuel cell is improved.
Further, it is possible to suppress the generation of local surface pressure by suppressing the biting of the ribs of the separator into the diffusion layer as in the prior art, thereby suppressing the decrease in the air permeability of the gas in the diffusion layer. It is possible to suppress an increase in the resistance of the fuel cell.

FIG. 8 shows that the height of the base material fiber on the surface (surface layer portion) is the same as that of a conventional fuel cell using a diffusion layer having the same height of the base material fiber on the surface (surface layer portion) and the height of the base material fiber on the inside (inner layer portion). It is a current density-voltage curve at the time of each power generation of the fuel cell of this disclosure using the diffusion layer lower than the height of the base material fiber of the inner (inner layer part). As shown in FIG. 8, the fuel cell of the present disclosure has a higher voltage with respect to the current density than the conventional fuel cell. It was found that the difference in performance was particularly remarkable during power generation under a high load (high current density range) where liquid water was likely to be generated.

FIG. 9 is a schematic plan view showing an example of the diffusion layer of the present disclosure.
FIG. 10 is a schematic cross-sectional view showing an example of the diffusion layer of the present disclosure.
As shown in FIG. 9, the diffusion layer of the present disclosure is composed of a porous carbon substrate 1 containing carbon fibers 2 and a binder 3.
As shown in FIG. 10, in the diffusion layer of the present disclosure, the height of the base material fiber in the surface layer portion containing the carbon fiber 2 is lower than the height of the base material fiber in the inner (inner layer portion).

FIG. 11 is a schematic cross-sectional view showing another example of the diffusion layer of the present disclosure. In FIG. 11, the same description as in FIG. 10 will be omitted.
FIG. 11 shows an example in which the height in the stacking direction of the base material fibers on the upper and lower surfaces of the diffusion layer is lower than that of the base fibers on the inner layer of the diffusion layer.

FIG. 12 is a schematic cross-sectional view showing another example of the diffusion layer of the present disclosure. In FIG. 12, the same description as in FIG. 10 will be omitted.
FIG. 12 shows a change in the cross-sectional shape of the base fiber of the surface layer portion of the diffusion layer from a circular shape to an elliptical shape.

FIG. 13 is a schematic cross-sectional view showing another example of the diffusion layer of the present disclosure. In FIG. 13, the same description as in FIG. 10 will be omitted.
In FIG. 13, the surface layer portion of the diffusion layer is composed of two layers, and the height of the base fiber obtained by combining the two layers is lower than that of the base fiber of the inner layer portion of the diffusion layer.

FIG. 14 is a schematic cross-sectional view showing an example of a fuel cell using the diffusion layer of the present disclosure.
In the fuel cell shown in FIG. 14, a conventional diffusion layer in which the height of the surface base material fiber is the same as the height of the inner layer base material fiber on both surfaces of the membrane electrode assembly 10 including the anode catalyst layer, the electrolyte membrane, and the cathode catalyst layer. 11 is arranged, and separators 12 are arranged on both sides thereof, and the surface layer base fiber height is lower than the inner base fiber height only in the region under the rib that abuts on one of the separators 12, and the diffusion layer of the present disclosure is disclosed. This is an example in which 13 is applied.

FIG. 15 is a schematic cross-sectional view showing another example of the fuel cell using the diffusion layer of the present disclosure. In FIG. 15, the same description as in FIG. 14 will be omitted.
FIG. 15 is an example of a fuel cell in which the diffusion layer 13 of the present disclosure is applied to an air outlet where liquid water easily collects.

The gas diffusion layer may be provided with a porous carbon base material and may be made of only a porous carbon base material.
The porous carbon substrate is formed by binding a plurality of carbon fibers with a binder and laminating a plurality of the carbon fibers.
The number of carbon fibers is not particularly limited as long as it can form a porous structure.
The carbon fiber may have a water-repellent layer on its surface. A conventionally known water repellent agent may be used for the water repellent layer.
The binder may be a resin carbide, and the raw material of the resin carbide may be, for example, PEN (polyethylene naphthalate), PES (polyether sulfone), PET (polyethylene terephthalate) or the like.

The porous carbon substrate has an inner layer portion and two surface layer portions sandwiching the inner layer portion.
The inner layer portion and the surface layer portion each contain a base fiber.
The base material fiber contains at least carbon fiber, and may contain carbon fiber having a water-repellent layer formed on the surface, a binder, and the like, if necessary.
The cross-sectional shape of the base fiber may be circular or elliptical.
The surface layer portion may have a one-layer structure or a two-layer structure. The one-layer structure of the surface layer portion may be composed of one base fiber. The two-layer structure of the surface layer portion may be formed by laminating, for example, two base fibers.
The inner layer portion may be composed of one base fiber, or may be formed by laminating two or more base fibers.

In the porous carbon base material, the height of the base material fiber in at least one surface layer portion in the stacking direction is lower than the height in the stacking direction of the base material fiber in the inner layer portion.
The height of the surface layer portion in the stacking direction is not particularly limited as long as it is lower than the height of the inner layer portion in the stacking direction.
In the porous carbon base material, the height in the stacking direction of the base fiber of the two surface layer portions may be lower than the height of the base material fiber in the inner layer portion in the stacking direction.
When the cross-sectional shape of the base fiber is circular, the height of the base fiber in the stacking direction may be the size of the fiber diameter.
When the cross-sectional shape of the base fiber is elliptical, the height in the stacking direction of the base fiber may be the size of the shorter diameter of the ellipse.

The gas diffusion layer is for a fuel cell.
The gas diffusion layer of the present disclosure may be arranged at any position on the catalyst layer of the fuel cell.
The gas diffusion layer of the present disclosure may be arranged only in the region under the rib that abuts on the rib of the separator of the fuel cell, and if necessary, the conventional surface layer portion and the inner layer portion are arranged in the remaining region where the diffusion layer is required. A diffusion layer having the same base fiber height may be arranged.
The gas diffusion layer of the present disclosure may be arranged only in the region under the air outlet where the liquid water in the gas flow path of the fuel cell separator is likely to collect, and if necessary, the remaining region where the diffusion layer is required may be conventionally arranged. A diffusion layer having the same base fiber height in the surface layer portion and the inner layer portion may be arranged.

The fuel cell may be a fuel cell stack in which a plurality of single cells of the fuel cell are stacked.
The number of stacked single cells is not particularly limited, and may be, for example, 2 to several hundreds or 2 to 200.
The fuel cell stack may include end plates at both ends of the single cell stacking direction.

A single cell of a fuel cell comprises at least a membrane electrode gas diffusion layer junction.
The membrane electrode gas diffusion layer junction has an anode side gas diffusion layer, an anode catalyst layer, an electrolyte membrane, a cathode catalyst layer, and a cathode side gas diffusion layer in this order.
The membrane electrode gas diffusion layer assembly includes a membrane electrode assembly, and the membrane electrode assembly has an anode catalyst layer, an electrolyte membrane, and a cathode catalyst layer in this order.

The cathode (oxidizing agent electrode) includes a cathode catalyst layer and a cathode side gas diffusion layer.
The anode (fuel electrode) includes an anode catalyst layer and an anode-side gas diffusion layer.

The cathode catalyst layer and the anode catalyst layer are collectively referred to as a catalyst layer.
The catalyst layer may include a catalyst such as a metal that promotes an electrochemical reaction, an electrolyte, and a carrier such as carbon particles having electron conductivity.
As the catalyst (catalyst metal), for example, platinum (Pt) and an alloy composed of Pt and another metal (for example, a Pt alloy in which cobalt, nickel and the like are mixed) can be used.

The catalyst is supported on a carrier such as carbon particles, and in each catalyst layer, a carrier carrying a catalyst metal (catalyst-supported carrier) and an electrolyte may be mixed.
As the carrier for supporting the catalyst, for example, water-repellent carbon particles whose water repellency has been enhanced by heat-treating carbon particles (carbon powder) commercially available may be used.

The electrolyte membrane may be, for example, a solid polymer electrolyte membrane. Examples of the solid polymer electrolyte membrane include a fluorine-based electrolyte membrane such as a thin film of perfluorosulfonic acid containing water, a hydrocarbon-based electrolyte membrane, and the like. The electrolyte membrane may be, for example, a Nafion membrane (manufactured by DuPont) or the like.

The single cell may have a microporous layer (MPL) between the catalyst layer and the gas diffusion layer, if necessary. The microporous layer may contain a mixture of a water repellent resin such as PTFE and a conductive material such as carbon black.

The single cell may be provided with two separators sandwiching both sides of the membrane electrode gas diffusion layer junction, if necessary. One of the two separators is the anode side separator and the other is the cathode side separator. In the present disclosure, the anode-side separator and the cathode-side separator are collectively referred to as a separator.
The separator has a plurality of ribs and a plurality of grooves.
The separator may have a supply hole and a discharge hole for allowing the reaction gas and the refrigerant to flow in the stacking direction of the single cell. As the refrigerant, for example, a mixed solution of ethylene glycol and water can be used in order to prevent freezing at a low temperature. The reaction gas is a fuel gas or an oxidant gas. The fuel gas may be hydrogen or the like. The oxidant gas may be oxygen, air, dry air or the like.
Examples of the supply hole include a fuel gas supply hole, an oxidant gas supply hole, a refrigerant supply hole, and the like.
Examples of the discharge hole include a fuel gas discharge hole, an oxidant gas discharge hole, a refrigerant discharge hole, and the like.
The separator may have one or more fuel gas supply holes, one or more oxidant gas supply holes, or one or more refrigerant supply holes. It may have one or more fuel gas discharge holes, one or more oxidant gas discharge holes, or one or more refrigerant discharge holes.
The separator may have a reaction gas flow path on the surface in contact with the gas diffusion layer. Further, the separator may have a refrigerant flow path for keeping the temperature of the fuel cell constant on the surface opposite to the surface in contact with the gas diffusion layer.
When the separator is an anode-side separator, it may have one or more fuel gas supply holes, or may have one or more oxidant gas supply holes, and one or more refrigerant supply holes. May have one or more fuel gas discharge holes, may have one or more oxidant gas discharge holes, and may have one or more refrigerant discharge holes. The anode-side separator may have a fuel gas flow path for flowing fuel gas from the fuel gas supply hole to the fuel gas discharge hole on the surface in contact with the anode-side gas diffusion layer, and the anode-side gas diffusion may be performed. A gas flow path for flowing a gas from the gas supply hole to the gas discharge hole may be provided on the surface opposite to the surface in contact with the layer.
When the separator is a cathode side separator, it may have one or more fuel gas supply holes, or may have one or more oxidant gas supply holes, and one or more refrigerant supply holes. May have one or more fuel gas discharge holes, may have one or more oxidant gas discharge holes, and may have one or more refrigerant discharge holes. The cathode side separator may have an oxidant gas flow path for flowing the oxidant gas from the oxidant gas supply hole to the oxidant gas discharge hole on the surface in contact with the cathode side gas diffusion layer. A refrigerant flow path for flowing a refrigerant from the refrigerant supply hole to the refrigerant discharge hole may be provided on the surface opposite to the surface in contact with the gas diffusion layer on the cathode side.
The separator may be a gas-impermeable conductive member or the like. The conductive member may be, for example, a dense carbon obtained by compressing carbon to make it impermeable to gas, a press-molded metal (for example, iron, aluminum, stainless steel, etc.) plate or the like. Further, the separator may have a current collecting function.

The fuel cell stack may have a manifold such as an inlet manifold in which each supply hole communicates and an outlet manifold in which each discharge hole communicates.
Examples of the inlet manifold include an anode inlet manifold, a cathode inlet manifold, and a refrigerant inlet manifold.
Examples of the outlet manifold include an anode outlet manifold, a cathode outlet manifold, and a refrigerant outlet manifold.

1 Porous carbon base material (diffusion layer)
2 Carbon fiber (including those coated with a water repellent agent on the surface)
3 Resin carbide (binding material)
4 Microporous layer (MPL)
10 Membrane electrode assembly 11 Conventional diffusion layer (the height of the base material fiber in the surface layer is the same as the height of the base material fiber in the inner layer)
12 Separator 13 Diffusion layer of the present disclosure (the height of the base material fiber in the surface layer portion is lower than the height of the base material fiber in the inner layer portion)
14 Absorbent member (water absorption material)
15 Channel

Claims (1)

A gas diffusion layer for a fuel cell provided with a porous carbon base material formed by binding a plurality of carbon fibers with a binder and laminating the plurality of the carbon fibers.
The porous carbon substrate has an inner layer portion and two surface layer portions sandwiching the inner layer portion.
A gas diffusion layer characterized in that the height in the stacking direction of the base fiber of the surface layer portion of at least one of the porous carbon base material is lower than the height of the base fiber in the inner layer portion in the stacking direction.

Images