JP4423063B2 - Membrane / electrode assembly and polymer electrolyte fuel cell using the same - Google Patents

Description

  The present invention relates to a polymer electrolyte fuel that uses pure hydrogen or hydrogen gas such as reformed hydrogen obtained by reforming methanol or fossil fuel as a fuel and an oxidant gas such as air or oxygen as reaction gases. It relates to batteries. More specifically, the present invention relates to a membrane / electrode assembly used in a polymer electrolyte fuel cell.

Generally, a polymer electrolyte fuel cell generates electricity and heat simultaneously by electrochemically reacting a fuel gas such as hydrogen and an oxidant gas such as air.
Here, the structure of a general polymer electrolyte fuel cell is shown in FIG.

On both surfaces of the polymer electrolyte membrane 1 that selectively transports hydrogen ions, catalyst layers 2a and 2b mainly composed of carbon powder carrying a platinum-based metal catalyst are disposed in close contact with each other. Further, on the outside of the catalyst layers 2a and 2b, a pair of gas diffusion layers 3a and 3b having gas permeability and conductivity are disposed in close contact with the catalyst layers 2a and 2b. The gas diffusion layers 3a and 3b are composed of porous base materials 10a and 10b having conductivity and coating layers (water-repellent carbon layers) 11a and 11b having conductive particles.
The electrodes 4a and 4b are composed of gas diffusion layers 3a and 3b and catalyst layers 2a and 2b. A membrane / electrode assembly (hereinafter referred to as MEA) is composed of a polymer electrolyte membrane 1 and a pair of electrodes 4a and 4b sandwiching the polymer electrolyte membrane 1.

  Between the MEAs, there is a separator plate 6 having a gas flow path 7a for supplying fuel gas on one side, a gas flow path 7b for supplying oxidant gas on the other side, and a cooling unit 8 inside. Composite separator plates (6a and 6b) are arranged alternately. Adjacent MEAs are electrically connected in series by a separator plate 6 and a composite separator plate. The composite separator plate has a gas flow path 7a for supplying fuel gas on one side, an anode side separator plate 6a having a flow path for supplying cooling water on the other side, and an oxidant gas on one side. The separator plate 6b is composed of a cathode separator plate 6b having a flow passage for supplying cooling water to the other surface, and the separator plates are overlapped so that the surfaces having the flow passage for cooling water face each other. Configured. Between the anode side separator plate 6a and the cathode side separator plate 6b, a seal member 9 for preventing leakage of cooling water is disposed. The gas flow paths 7a and 7b also have a role of carrying away water and surplus gas generated by the electrode reaction. The battery stack in which the MEA and the separator plate are alternately stacked is fastened in the stacking direction with a predetermined pressure, so that the MEA and the separator plate come into contact with each other in a planar shape with a predetermined pressure.

The gas diffusion layer in the membrane-electrode assembly described above is (1) supplying a reaction gas from the gas flow path to the electrode (catalyst layer), (2) keeping the electrolyte membrane or catalyst layer in a wet state, (3) catalyst Water vapor or water (reaction product water) generated by the reaction in the layer is quickly discharged to the gas flow path, and (4) secures electronic conductivity between the MEA and the separator plate.
Therefore, the base material constituting the gas diffusion layer needs to be excellent in gas permeation performance, moisture permeation performance, and electronic conductivity. Typical base materials include carbon cloth, carbon paper, carbon felt, and the like.
Further, in order to stably maintain a high output voltage for a long time, it is necessary to be excellent in the ability to diffuse the reaction gas and the ability to remove the generated water vapor and water. In order to improve these, conventionally, a base material for a gas diffusion layer in which carbon fibers having hydrophilicity and carbon fibers having water repellency are woven is used (for example, Patent Documents 1 and 2).

Further, as a method of decreasing the amount of water discharged from the anode and relatively increasing the amount of water discharged from the cathode, it has been proposed to make the average pore diameter of the water repellent carbon layer on the anode side smaller than that of the cathode ( For example, Patent Document 3).
Furthermore, as a method of supplying the reaction gas uniformly and discharging the generated water smoothly, a fluid flow groove is provided in the base material for the gas diffusion layer to eliminate sagging of the base material for the gas diffusion layer, It has been proposed to increase the rate at which the gas contacts the substrate (eg, Patent Documents 4 and 5).
Further, in order to obtain good gas permeability, it has been proposed that the average pore diameter of the base material for the gas diffusion layer determined by the mercury porosimeter method is in the range of 5 to 40 μm (for example, Patent Document 6). .

However, in Patent Documents 1 and 2, since the fiber diameters of hydrophilic carbon fibers and water-repellent carbon fibers are different, it is difficult to produce a base material for a gas diffusion layer that is uniform in the plane. is there. Moreover, a manufacturing process is complicated in the process of immersing and firing carbon fibers having a fiber diameter of about 100 to 500 μm in a water-repellent treatment liquid, which is not practical. In addition, a method of obtaining carbon fiber having water repellency by graphitization has been proposed, but this method cannot provide water repellency necessary for stable power generation. Moreover, water tends to stay in the hydrophilic part.
In Patent Document 3, the average pore diameter of the water-repellent carbon layer is defined, but the water discharging ability in the base material for the gas diffusion layer cannot be improved. Moreover, since the effect of confining water is increased, the absolute amount of water contained in the polymer electrolyte membrane and the catalyst layer is increased, and a flooding phenomenon is likely to occur.

In Patent Document 4, a base material for a gas diffusion layer is produced using PVdF resin and carbon particles. However, since the amount of the resin is relatively large, the electron conductivity is lowered. In patent document 5, since a plane part and a convex part are joined with an adhesive agent, the electronic conductivity in a joining interface falls. In Patent Documents 4 and 5, there is a problem that in a long-term continuous operation, the base material for the gas diffusion layer gradually changes with time, and the convex portion is compressed by the fastening pressure to block the gas flow path.
In Patent Document 6, since the gas diffusion layer base material has many small pores, excess water such as reaction product water tends to stay inside the porous base material. In addition, since the base material for the gas diffusion layer is composed of relatively brittle carbon fibers, there is a possibility that the base material itself may be destroyed when mercury is injected. For this reason, the data of the average pore diameter calculated | required by the mercury porosimeter method lacks reliability.

Further, in Patent Document 7, a correlation between the pore distribution of the catalyst layer and the output characteristics of the battery is obtained. For the above reason, the pore distribution of the porous base material for the gas diffusion layer and the battery The correlation with output characteristics remains unclear.
JP 7-105957 A JP 2002-15747 A JP 2001-57218 A JP 2002-100372 A JP 2002-164058 A JP 2003-183994 A Japanese Patent Laid-Open No. 2002-237306

  Therefore, in order to solve the above-described conventional problems, the present invention provides a porous base material for a gas diffusion layer, which has an excellent ability to diffuse a reaction gas and to remove water vapor and water (reaction product water) generated by the reaction. It aims at providing the membrane electrode assembly which has this. Another object of the present invention is to provide a polymer electrolyte fuel cell having stable output performance by using this membrane-electrode assembly.

The membrane-electrode assembly of the present invention is a membrane-electrode assembly comprising a hydrogen ion conductive polymer electrolyte membrane and a pair of electrodes having a gas diffusion layer and a catalyst layer made of a porous substrate,
Pore distribution in the porous substrate, it has at least two distribution centers,
In the pore distribution of the porous substrate measured by the bubble point half-dry method using the bubble point method (ASTM F316-86, JIS K3832), the fine pore diameter of 40 μm or less with respect to the pore diameter of 200 μm or less. The proportion of the pores is 30% or more, and the proportion of the pores having a pore diameter of 80 to 100 μm is 40% or more,
Wherein the porous substrate is made of woven fabric, the thickness of the yarn constituting the woven fabric is 100-200 [mu] m, and the basis weight of the woven fabric characterized in that it is a 60 to 90 g / m ^2.

The membrane / electrode assembly of the present invention is a membrane / electrode assembly comprising a hydrogen ion conductive polymer electrolyte membrane and a pair of electrodes having a gas diffusion layer and a catalyst layer made of a porous substrate. And
The pore distribution in the porous substrate has at least two distribution centers;
In the pore distribution of the porous substrate measured by the bubble point half-dry method using the bubble point method (ASTM F316-86, JIS K3832), the fine pore diameter of 40 μm or less with respect to the pore diameter of 200 μm or less. The proportion of the pores is 30% or more, and the proportion of the pores having a pore diameter of 80 to 100 μm is 40% or more,
The porous substrate is made of a nonwoven fabric, and the basis weight of the nonwoven fabric is 50 to 80 g / m ² ;
And the thickness of the said nonwoven fabric is 100-300 micrometers, It is characterized by the above-mentioned.

It is preferable that the porous substrate contains 5 to 30% by weight of a fluororesin.
The present invention also provides a laminate in which a plurality of unit cells each including a pair of conductive separators having a gas flow path for supplying a reaction gas are sandwiched between the membrane / electrode assembly and the membrane / electrode assembly. The present invention relates to a polymer electrolyte fuel cell comprising:

  Since the present invention uses a porous base material for a gas diffusion layer that has at least two distribution centers in the pore distribution and separately secures a gas flow path and a moisture discharge path, the reaction gas diffusion And a membrane / electrode assembly excellent in the ability to remove water vapor and water produced by the reaction. In addition, a polymer electrolyte fuel cell using this membrane-electrode assembly can obtain a stable battery voltage in the initial and long-time continuous operation.

Further, since the porous base material for the gas diffusion layer has many relatively large pores, clogging due to clogged pieces of carbon fiber can be prevented.
Furthermore, since large pores are present in a dispersed manner, it is possible to improve not only the thickness direction of the porous base material for the gas diffusion layer but also the gas diffusion ability and moisture removal ability in the plane direction.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
The present invention relates to a porous substrate for a gas diffusion layer (for example, carbon having electronic conductivity) in which water does not stay and excess water is quickly discharged outside in a highly humidified operation of a polymer electrolyte fuel cell. The present invention relates to a membrane / electrode assembly having (fiber).
The present inventors conducted a comparative study on the correlation between the pore distribution of various porous substrates for gas diffusion layers and the output characteristics of a fuel cell using the same. As a result, it was found that stable output characteristics can be obtained when the pore distribution of the porous base material for the gas diffusion layer has at least two distribution centers.

As an example of the embodiment of the present invention, FIG. 2 shows a case where the pore distribution has two distribution centers (peaks). FIG. 2 shows the pore distribution curve of a porous substrate having two local maxima X and Y.
The maximum point X is preferably present in a pore diameter range of 40 μm or less. The maximum point Y is preferably present in the pore diameter range of 80 to 100 μm.

Here, FIGS. 3 and 4 are schematic views showing the function of the porous base material for the gas diffusion layer having the pore distribution as described above. 3 shows the case of a woven fabric, and FIG. 4 shows the case of a non-woven fabric.
A relatively small pore having a pore diameter of 40 μm or less is referred to as a pore A, and a relatively large pore having a pore diameter in the range of 80 to 100 μm is referred to as a pore B.

  The humidified reaction gas (fuel gas, oxidant gas, water vapor) supplied into the MEA reaches the catalyst layer through the pores A in the porous base material for the gas diffusion layer. On the other hand, the water generated by the reaction in the catalyst layer is water vapor immediately after generation, but most of the water is aggregated into water in the process of passing through the water-repellent carbon layer. For this reason, in the porous base material for the gas diffusion layer, this water is discharged out of the MEA system through the pores B and reaches the gas flow path of the separator plate. That is, the pore A serves as a gas (reaction gas) flow path, and the pore B serves as a liquid (reaction product water) discharge path.

Since the pore A is too small as a water flow path, excess water existing outside the MEA system does not enter the inside of the MEA through the pore A. Even if a small amount of excess water penetrates into the pores A and the porous substrate is clogged with this water, the pores A are secured as a reaction gas flow path. Can be blown away.
Further, since the pore B functions as a water discharge path to the outside of the MEA system, the reaction gas and water outside the MEA system do not reach the catalyst layer through the pore B (reversely flow).

  As shown in FIG. 5, when the maximum point in the pore distribution curve of the porous base material for the gas diffusion layer is only X (when the porous base material is composed of only the pores A), sufficient ventilation However, since the discharge path of the reaction product water is not sufficiently secured, water tends to accumulate in the pores A. That is, the flow path of the reactive gas is blocked, a flooding phenomenon occurs, and power generation stops.

As shown in FIG. 6, when the maximum point in the pore distribution curve of the porous base material for the gas diffusion layer is only Y (when the porous base material is composed of only the fine pores B), the water is discharged. Although a sufficient path can be obtained, since there are too many pores B, excess water existing outside the MEA system easily enters the inside of the MEA. That is, the gas diffusing capacity decreases, a flooding phenomenon occurs, and power generation stops.
In addition, since the mechanical strength of the porous base material for the gas diffusion layer consisting only of the pores B is lowered, the porous base material sags easily and blocks the gas flow path of the separator plate. In addition, when a water-repellent carbon layer is applied to the surface of the porous base material for the gas diffusion layer, some of the carbon particles block the pores and the porous base material is likely to be clogged.

  In addition, the pore distribution of a porous base material for a gas diffusion layer made of a conventional carbon fiber having conductivity has a uniform normal distribution as shown in FIG. From continuous operation for a long period of time, carbon fiber fragments generated by the deterioration of the porous base material for the gas diffusion layer block the pores, and the entire porous base material tends to be clogged. For this reason, gas diffusivity falls and electric power generation performance falls easily.

In contrast, since the membrane / electrode assembly of the present invention has a porous base material for a gas diffusion layer having at least two distribution centers in the pore distribution, not only the pore A having a relatively small diameter, There are many pores B having a relatively large diameter. Therefore, when a long-term durability test is performed, even if the carbon fiber fragments block the pores A, the pores B cover the gas diffusing ability of the pores A, so that a life characteristic superior to the conventional one is obtained. It is done.
Furthermore, since the pores B having a relatively large diameter in the porous base material for the gas diffusion layer are appropriately dispersed and arranged, not only in the thickness direction of the porous base material for the gas diffusion layer but also in the plane direction It becomes possible to enhance the gas diffusing ability and moisture removing ability.

  For measurement of the pore distribution of the porous base material for the gas diffusion layer, it is preferable to use a bubble point half dry method based on ASTM F316-86 or JIS K3832. Unlike the mercury porosimeter method, this method does not destroy the porous substrate for the gas diffusion layer made of relatively brittle carbon fibers during the measurement, so that the pore distribution can be accurately measured.

In the pore distribution obtained by this measuring method, the proportion of the pore A having a pore diameter of 40 μm or less to the pore having a pore diameter of 200 μm or less is 30% or more, and the pore B having a pore diameter of 80 to 100 μm is occupied. The ratio is preferably 40% or more.
When the proportion of the pores A having a pore diameter of 40 μm or less is less than 30%, the gas diffusing ability is lowered and the reaction gas is difficult to diffuse into the catalyst layer.
Moreover, when the ratio which the pore B with a pore diameter of 80-100 micrometers occupies is less than 40%, the discharge capability of water falls and water becomes easy to retain in a porous base material.

  If the pore diameter exceeds 100 μm, the diameter of the water droplets discharged out of the MEA system becomes too large, so that the water droplets are difficult to move, and the water discharging ability is reduced. Therefore, it is desirable that the pore diameter is 100 μm or less as a discharge path for surplus water in the porous base material for the gas diffusion layer in the polymer electrolyte fuel cell.

It is preferable that the porous substrate is made of a woven fabric, the thickness of the yarn constituting the woven fabric is 100 to 200 μm, and the basis weight of the woven fabric is 60 to 90 g / m ² .
It is preferable that the porous substrate is made of a nonwoven fabric, the basis weight of the nonwoven fabric is 50 to 80 g / m ² , and the thickness of the nonwoven fabric is 100 to 300 μm.
At this time, a woven fabric and a nonwoven fabric having the pore distribution as described above are obtained.

It is preferable that the porous substrate contains 5 to 30% by weight of a water repellent. As the water repellent, a fluororesin is preferably used from the viewpoint of chemical stability. Among these, it is more preferable to use polytetrafluoroethylene (PTFE) having excellent heat resistance and weather resistance.
When the content of the fluororesin is less than 5% by weight, sufficient water repellency cannot be obtained. On the other hand, when the content of the fluororesin exceeds 30% by weight, the porosity is lowered and the gas diffusing ability is lowered. That is, the diffusion rate of the reaction gas is limited, and the battery voltage decreases.

  Further, when PTFE is used as the water repellent, the portion where the PTFE particles between the carbon fibers are attached has a small pore diameter, and it tends to be a reaction gas flow path combined with the water repellent effect. On the other hand, the portion where the PTFE particles are not attached has a large pore diameter and is more hydrophilic than the portion where the PTFE particles are attached, and therefore tends to be a water discharge route.

As the porous base material, conductive carbon fiber is used. Examples of the carbon fiber include polyacrylonitrile (PAN), cellulose, viscose rayon, pitch, and phenol resin. Of these, polyacrylonitrile is particularly preferred because of its high mechanical strength and electrical conductivity and low impurities.
The membrane / electrode assembly of the present invention is suitably used for a polymer electrolyte fuel cell for stationary use, automobile use, or mobile use.

Hereinafter, embodiments of the present invention will be described in detail.
Example 1
(1) Production of porous substrate for gas diffusion layer A single fiber of polyacrylic carbonaceous fiber having a diameter of 7 μm was wound to obtain a single yarn. At this time, the thickness of the single yarn was changed variously as shown in Tables 1-5. This single yarn was woven in a plain weave using a general loom to obtain a woven fabric. The weight per unit area was varied as shown in Tables 1 to 5 by changing the weft density (the number of warp yarns and weft yarns per unit length) when the single yarn was plain-woven with a loom. This woven fabric was heated and carbonized at 900 ° C. in a nitrogen atmosphere, and then graphitized by heating at 2000 ° C. in an argon atmosphere to obtain a porous substrate for a gas diffusion layer.

(2) Preparation of gas diffusion layer Acetylene black, water, polytetrafluoroethylene (PTFE), and surfactant (Triton X-100) were mixed at a weight ratio of 15: 80: 4: 1 to obtain a carbon ink. . After applying this carbon ink on the porous substrate obtained above using a doctor blade, this was baked at 325 ° C. for 1 hour, and conductive particles (carbon particles) were placed on one side of the porous substrate. A covering layer having a gas diffusion layer was obtained.

(3) Production of MEA Catalyst powder was obtained by supporting 25% by weight of platinum particles having an average particle diameter of about 30 mm on acetylene black carbon powder. Then, the catalyst powder dispersed in isopropanol and the perfluorocarbon sulfonic acid powder dispersed in ethyl alcohol were mixed to obtain a catalyst ink. This catalyst ink was applied to both sides of a polymer electrolyte membrane (manufactured by Japan Gore-Tex, Gore Select membrane, film thickness 30 μm) by screen printing to form a catalyst layer. Incidentally, amount of platinum contained in the catalyst layer after forming the catalyst layer 0.5 mg / cm ^2, the amount of perfluorocarbon sulfonic acid was adjusted to be 1.2 mg / cm ^2.
On the catalyst layer formed on both surfaces of the polymer electrolyte membrane, the gas diffusion layer obtained above was joined by hot pressing to produce an MEA. At this time, the gas diffusion layer was disposed on the catalyst layer so that the side provided with the coating layer was in contact with the catalyst layer.

(4) Assembly of test battery (unit cell) In order to seal the fuel gas and the oxidant gas, a gasket made of silicone rubber was arranged around the MEA. A unit cell was manufactured by supplying a reaction gas to the electrode and arranging a pair of conductive separator plates having gas flow paths for carrying away water and surplus gas generated in the electrode reaction on both sides of the MEA. The unit cell was fastened at a pressure of 10 kgf / cm ² .

The following evaluation was performed about the porous base material and unit cell for gas diffusion layers obtained above.
[Evaluation]
(A) Measurement of pore distribution of porous base material for gas diffusion layer The pore distribution measuring apparatus includes Porous Materials Inc. A palm porometer CFP-1100A manufactured by the company was used. The measurement principle of this device is based on JIS standard (ASTMF 316-86, JIS K3832), and after the porous substrate is completely wetted with the test solution, the pressure is gradually increased to apply the surface tension and application of the test solution. The pore distribution was determined from the pressure and supply flow rate of the gas (bubble point half-dry method). The sample size was 24 mm in diameter. Five samples of the same kind were measured each, and the average value was taken as the measured value of the sample.

(B) Life evaluation of the unit cell Hydrogen was supplied to the anode side of the unit cell and air was supplied to the cathode side, and the unit was operated with full humidification. The battery temperature was kept at 80 ° C., and the humidification conditions were as follows: hydrogen gas was set at 80 ° C. dew point, and air was set at 80 ° C. dew point. The operating conditions were a fuel utilization rate of 80%, an air utilization rate of 50%, and a current density of 0.35 A / cm ² . And if the voltage 1000 hours after an operation start was 750 mV or more, it was judged that lifetime performance was favorable.
The results evaluated above are shown in Tables 1-5. In addition, about the lifetime characteristic in a table | surface, when the battery voltage after 1000 hours was 750 mV or more, it was set as (circle) and when less than 750 mV, it was set as x.

From Tables 1 to 5, regarding the pore distribution, the proportion of pores having a pore size of 40 μm or less to pores having a pore size of 200 μm or less is 30% or more, and the proportion of pores having a pore size of 80 to 100 μm is occupied. It was found that good life characteristics can be obtained when it is 40% or more.
In the case where the porous base material for the gas diffusion layer is made of woven fabric, such a pore distribution is obtained when the single yarn thickness is 100 to 200 μm and the basis weight is 60 to 90 g / cm ² . It turns out that it is obtained.

Example 2
A single fiber of polyacrylic carbonaceous fiber having a diameter of 7 μm was immersed in a polyvinyl alcohol aqueous solution as a binder and dispersed, and paper was made by a paperboard method, and several sheets were stacked to prepare a nonwoven fabric made of carbon fibers.
The nonwoven fabric was carbonized by heating at 1000 ° C. in a nitrogen gas atmosphere, and then graphitized by heating at 2000 ° C. in an argon atmosphere to obtain a porous substrate for a gas diffusion layer.
At this time, the amount of carbonaceous fibers per unit volume and the number of sheets to be superposed were controlled to produce various porous substrates having different basis weights and thicknesses as shown in Tables 6-10.
Single cells were produced in the same manner as in Example 1 except that these porous base materials for the gas diffusion layer were used. Then, these porous substrates and single cells were evaluated by the same method as in Example 1. The evaluation results are shown in Tables 6-10.

From Tables 6 to 10, regarding the pore distribution, the proportion of pores having a pore size of 40 μm or less to pores having a pore size of 200 μm or less is 30% or more, and the proportion of pores having a pore size of 80 to 100 μm is It was found that good life characteristics can be obtained when it is 40% or more.
When the porous substrate for the gas diffusion layer is made of a nonwoven fabric, such a pore distribution is obtained when the thickness is 100 to 300 μm and the basis weight is 50 to 80 g / cm ^2. I understood.

Example 3
The case of using a water-repellent woven fabric as a porous substrate for a gas diffusion layer was examined.
Among the woven fabrics produced in Example 1, a woven fabric having a single yarn thickness of 150 μm and a basis weight of 80 g / cm ^{2 with} the best life characteristics was prepared.
This woven fabric was immersed in an aqueous dispersion of FEP (fluorinated ethylene / propylene) (ND-1E manufactured by Daikin Industries, Ltd.) to obtain a porous substrate containing a fluororesin as a water repellent. At this time, the amount of ion-exchanged water added to the FEP was adjusted, and the content of FEP in the woven fabric was variously changed as shown in Table 11. These porous substrates were baked at 350 ° C. for 2 hours to remove moisture.

  Single cells were produced in the same manner as in Example 1 except that these porous base materials for the gas diffusion layer were used. Then, these porous substrates and single cells were evaluated by the same method as in Example 1. The results are shown in Table 11.

  When the content of FEP is increased, the FEP particles enter large pores having a diameter exceeding 100 μm, and pores having a pore diameter of 40 μm or less and 80 to 100 μm are increased, thereby improving the life characteristics. However, when the content of FEP is excessive, the porous substrate is clogged, and the pores having these pore diameters are rapidly reduced, so that the life characteristics are deteriorated.

Example 4
The case where the water-repellent treated non-woven fabric was used as the porous base material for the gas diffusion layer was examined. Among the nonwoven fabrics produced in Example 2, a nonwoven fabric having a thickness of 200 μm and the basis weight of 70 g / cm ² with which the best life characteristics were obtained was prepared. And by the method similar to Example 3, this nonwoven fabric was water-repellent-treated and the porous base material was obtained. At this time, the amount of ion-exchanged water added to the FEP was adjusted, and the content of FEP in the nonwoven fabric was variously changed as shown in Table 12.
Single cells were produced in the same manner as in Example 1 except that these porous base materials for the gas diffusion layer were used. Then, these porous substrates and single cells were evaluated by the same method as in Example 1. These evaluation results are shown in Table 12.

  When the FEP content is increased, the FEP particles enter large pores having a diameter exceeding 100 μm, and pore diameters of 40 μm or less and 80-100 μm pores are increased, so that the life characteristics are improved. However, when the FEP content is excessive, the porous substrate is clogged, and pores having these pore diameters are rapidly reduced, so that the life characteristics are deteriorated.

  The membrane / electrode assembly of the present invention can be applied to a polymer electrolyte fuel cell. The gas diffusion layer in the membrane / electrode assembly of the present invention can be applied to gas diffusion layers for various fuel cells such as liquid fuel cells and phosphoric acid fuel cells. The membrane / electrode assembly of the present invention can also be applied to gas generators and gas purifiers such as oxygen, ozone, or hydrogen, and various gas sensors such as oxygen sensors or alcohol sensors.

It is principal part sectional drawing of a general polymer electrolyte fuel cell. It is a pore distribution map of the porous base material for gas diffusion layers in the membrane-electrode assembly of the present invention. It is a schematic diagram which shows the function of the porous base material (woven fabric) for gas diffusion layers in the membrane electrode assembly of this invention. It is a schematic diagram which shows the function of the porous base material (nonwoven fabric) for gas diffusion layers in the membrane / electrode assembly of the present invention. FIG. 3 is a pore distribution diagram of a porous base material for a gas diffusion layer composed only of pores A. FIG. 3 is a pore distribution diagram of a porous base material for a gas diffusion layer composed only of pores B. It is a pore distribution map of the conventional porous base material for gas diffusion layers.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Hydrogen ion conductive polymer electrolyte membrane 2a, 2b Catalyst layer 3a, 3b Gas diffusion layer 4a, 4b Electrode 5a, 5b Gasket 6 Separator plate 6a Anode side separator plate 6b Cathode side separator plate 7a, 7b Gas flow path 8 Cooling part 9 Seal member 10a, 10b Porous base material 11a, 11b Coating layer (water-repellent carbon layer)

Claims (4)

A membrane / electrode assembly comprising a hydrogen ion conductive polymer electrolyte membrane and a pair of electrodes sandwiching the polymer electrolyte membrane and having a gas diffusion layer and a catalyst layer made of a porous substrate,
Pore distribution in the porous substrate, it has at least two distribution centers,
In the pore distribution measured by the bubble point half-dry method, the proportion of pores having a pore diameter of 40 μm or less to pores having a pore diameter of 200 μm or less is 30% or more, and pores having a pore diameter of 80 to 100 μm Is 40% or more,
Membrane wherein the porous substrate is made of woven fabric, the thickness of the yarn constituting the woven fabric is 100-200 [mu] m, and the basis weight of the woven fabric characterized in that it is a 60 to 90 g / m ² -Electrode assembly. A membrane / electrode assembly comprising a hydrogen ion conductive polymer electrolyte membrane and a pair of electrodes sandwiching the polymer electrolyte membrane and having a gas diffusion layer and a catalyst layer made of a porous substrate,
The pore distribution in the porous substrate has at least two distribution centers;
In the pore distribution measured by the bubble point half-dry method, the proportion of pores having a pore diameter of 40 μm or less to pores having a pore diameter of 200 μm or less is 30% or more, and pores having a pore diameter of 80 to 100 μm Ri der ratio is more than 40% occupied,
The membrane / electrode assembly, wherein the porous substrate is made of a nonwoven fabric, the basis weight of the nonwoven fabric is 50 to 80 g / m ² , and the thickness of the nonwoven fabric is 100 to 300 μm . The membrane / electrode assembly according to claim 1 or 2, wherein the porous substrate contains 5 to 30 wt% of a fluororesin. A plurality of unit cells each including a pair of conductive separators having a gas flow path for supplying a reaction gas sandwiching the membrane-electrode assembly according to any one of claims 1 to 3 and the membrane-electrode assembly. A polymer electrolyte fuel cell comprising the battery laminate.

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