JP2021184339A - Manufacturing method of gas diffusion layer for fuel cell - Google Patents

Abstract

To provide a manufacturing method of a gas diffusion layer for a fuel cell capable of producing a fine porous layer having excellent water repellency.SOLUTION: A manufacturing method of a gas diffusion layer for a fuel cell includes a step of heating and firing a porous base material layer coated on one surface with a coating liquid for forming a fine porous layer, and in the firing step, and when a firing temperature is A (°C) and a firing time is B (seconds), the following equations (1) to (4) are satisfied. B≥100 (1). A≥355-[(B-80)/40]×5(100≤B≤200) (2). A≥340(B>200) (3). A<390 (4).SELECTED DRAWING: Figure 1

Description

The present invention relates to a method for manufacturing a gas diffusion layer for a fuel cell.

The anode and cathode, which are the electrodes of the fuel cell, generally have a structure in which a catalyst layer and a gas diffusion layer are laminated in this order from the electrolyte membrane side. The catalyst layer contains an electrode catalyst such as platinum and a platinum alloy for accelerating the electrode reaction, a polyelectrolyte for ensuring proton conductivity, and a conductive material for ensuring electron conductivity.

In fuel cells, water is generated as power is generated. Most of the generated water is discharged from the fuel cell together with the unreacted gas discharged from the electrodes and the humidified water supplied as steam. However, a part of the humidified water supplied to the electrode as water vapor together with the generated water, hydrogen gas, oxidant gas and other reaction gases may be condensed in the fuel cell and exist in the electrode in a liquid state. be. At this time, when the condensed water (liquid water) stays in the electrode, the liquid water is clogged, that is, so-called flooding occurs, the supply of the reaction gas to the electrode is hindered, and the power generation performance is deteriorated. In particular, when the fuel cell is operated under high humidification conditions, a large amount of liquid water is generated, so it is necessary to ensure the dischargeability of the liquid water of the electrode.

As a gas diffusion layer for suppressing this flooding, a fine porous layer (microporous layer: MPL layer) having a pore size smaller than that of the porous substrate layer is laminated on the porous substrate layer having a porous structure. Those having the above-mentioned structure are known (see, for example, Patent Document 1). It is considered that by providing this fine porous layer, the ultrafine porous structure of the fine porous layer inhibits the retention of liquid water and improves the drainage property of the gas diffusion layer.

Further, in Patent Document 1, a first coating liquid for forming the fine porous layer is applied to one surface of the porous base material layer, and the first coating liquid is applied. Disclosed is a method for producing a gas diffusion layer for a fuel cell, which comprises heating and firing a coated porous base material layer, and performing the firing at a temperature of 250 ° C. or higher, preferably 400 ° C. or higher. There is.

Japanese Unexamined Patent Publication No. 2019-149289

In the gas diffusion layer for a fuel cell provided with a fine porous layer, excellent water repellency is required from the viewpoint of suppressing the retention of liquid water. However, in the method for producing a gas diffusion layer for a fuel cell described in Patent Document 1, the firing conditions for forming the fine porous layer having excellent water repellency have not been investigated, and the fine porous layer having excellent water repellency has not been investigated. There is room for improvement in the manufacturing method.

The present disclosure has been made in view of the above-mentioned conventional problems, and an object of the present disclosure is to provide a method for producing a gas diffusion layer for a fuel cell capable of producing a fine porous layer having excellent water repellency.

The method for manufacturing a gas diffusion layer for a fuel cell according to claim 1 is a step of heating and firing a porous base material layer coated on one surface with a coating liquid for forming a fine porous layer. In the step of firing, the following formulas (1) to (4) are satisfied when the firing temperature is A (° C.) and the firing time is B (seconds).
B ≧ 100 ... (1)
A ≧ 355 [(B-80) / 40] × 5 (100 ≦ B ≦ 200) ・ ・ ・ (2)
A ≧ 340 (B> 200) ・ ・ ・ (3)
A <390 ... (4)

According to the above configuration, the porous base material layer in which the coating liquid for forming the fine porous layer is applied to one surface is fired under the conditions satisfying the above-mentioned formulas (1) to (4). To form a fine porous layer. This makes it possible to produce a fine porous layer having excellent water repellency.

According to the present disclosure, it is possible to provide a method for producing a gas diffusion layer for a fuel cell, which can produce a fine porous layer having excellent water repellency.

It is a drawing for demonstrating an example of the manufacturing method of the gas diffusion layer for a fuel cell of this disclosure. It is sectional drawing which shows the structure of the single cell of a fuel cell. It is a graph which shows the relationship between the firing time and firing temperature at the time of manufacturing a gas diffusion layer for a fuel cell, and the evaluation of water repellency. It is a graph which shows the relationship between a calcination temperature and a fall angle when an aqueous solution of 15% by mass of ethanol is used. It is a graph which shows the relationship between the firing temperature and the fall angle when the aqueous solution of 10% by mass of ethanol is used. It is a graph which shows the relationship between the firing temperature and the fall angle when the aqueous solution of 20% by mass of ethanol is used.

Hereinafter, the method for manufacturing the gas diffusion layer for a fuel cell of the present disclosure will be described in detail. However, the present invention is not limited to the following embodiments. In the following embodiments, the components (including element steps and the like) are not essential unless otherwise specified. The same applies to the numerical values and their ranges, and does not limit the present invention.
In the present disclosure, the numerical range indicated by using "~" includes the numerical values before and after "~" as the minimum value and the maximum value, respectively.
In the numerical range described stepwise in the present disclosure, the upper limit value or the lower limit value described in one numerical range may be replaced with the upper limit value or the lower limit value of the numerical range described in another stepwise description. ..

<Manufacturing method of gas diffusion layer for fuel cell>
The method for producing a gas diffusion layer for a fuel cell according to the present disclosure includes a step of heating and firing a porous base material layer coated on one surface with a coating liquid for forming a fine porous layer. In the firing step, when the firing temperature is A (° C.) and the firing time is B (seconds), the following formulas (1) to (4) are satisfied.
B ≧ 100 ... (1)
A ≧ 355 [(B-80) / 40] × 5 (100 ≦ B ≦ 200) ・ ・ ・ (2)
A ≧ 340 (B> 200) ・ ・ ・ (3)
A <390 ... (4)

The fine porous layer is formed by firing the porous base material layer coated on one surface with the coating liquid for forming the fine porous layer. Further, by firing the above-mentioned porous base material layer under the conditions satisfying the above-mentioned formulas (1) to (4), a fine porous layer having excellent water repellency can be produced. The reason for this is presumed as follows. The water repellency of the fine porous layer is greatly affected by the firing temperature and firing time when firing the above-mentioned porous substrate layer, and the heat energy given by firing even when the heat energy given by firing is small. Even in the case of a large amount, the water repellency of the fine porous layer is reduced. More specifically, by firing the above-mentioned porous base material layer under the conditions satisfying the above-mentioned formulas (1) to (3), the heat energy given by the firing does not become too small, and the microporous material is formed. The layer has excellent water repellency. Further, by firing the above-mentioned porous base material layer under the condition satisfying the above-mentioned formula (4), the heat energy given by the firing does not become too large, and the coating liquid for forming the fine porous layer is formed. Since the decomposition of the components contained in is suppressed, the fine porous layer has excellent water repellency.

In the production method of the present disclosure, since the above-mentioned porous base material layer is fired under the condition satisfying the above-mentioned formula (1), the firing time is 100 seconds or more. In the production method of the present disclosure, the firing time is not particularly limited as long as the formula (1) is satisfied, and for example, from the viewpoint of productivity, it is preferably 300 seconds or less, and more preferably 240 seconds or less.

In the production method of the present disclosure, the firing temperature at the time of firing the above-mentioned porous base material layer may be any condition as long as it satisfies the above-mentioned formulas (2) to (4).
For example, when B, which is the firing time, is 100 (seconds), the firing temperature may be 352.5 ° C. or higher and lower than 390 ° C. from the formulas (2) and (4).
When B is 200 (seconds), the firing temperature may be 340 ° C. or higher and lower than 390 ° C. from the formulas (2) and (4).

In the production method of the present disclosure, since the above-mentioned porous base material layer is fired under the condition satisfying the above-mentioned formula (4), the firing temperature is less than 390 ° C. In the production method of the present disclosure, the upper limit of the firing temperature is not particularly limited as long as the formula (4) is satisfied, and for example, from the viewpoint of further suppressing the decomposition of the components contained in the coating liquid for forming the fine porous layer. The firing temperature may be 385 ° C. or lower, or 380 ° C. or lower.

The range satisfying the above equations (1) to (4) corresponds to the range of the shaded area shown in FIG. The dotted line portion shown in FIG. 3 means that the range of the shaded line portion does not include A = 390 ° C.

Hereinafter, preferable conditions of the porous base material layer and the coating liquid for forming the fine porous layer used in the production method of the present disclosure, and firing conditions will be described.

(Porous substrate layer)
The porous base material layer is a base material having a porous structure having conductivity, and is used for forming a gas diffusion layer for a fuel cell. More specifically, the gas diffusion layer for a fuel cell is formed by providing the fine porous layer on the porous base material layer.

The porous substrate layer has a function of dispersing the oxidant gas or the fuel gas and supplying the dispersed oxidant gas to the cathode catalyst layer, or supplying the dispersed fuel gas to the anode catalyst layer. Has a function. Further, the porous base material layer also has a function of discharging excess water to the outside of the single cell.

The porous substrate layer preferably has excellent gas diffusivity and conductivity when supplying gas to the cathode catalyst layer or the anode catalyst layer, and strength when used as a gas diffusion layer. Examples of the porous base material layer include a carbonaceous porous body such as carbon paper, carbon cloth, and carbon felt, and a metal such as titanium, aluminum, copper, nickel, silver, titanium, niobium, tantalum, iron, gold, and platinum. , Stainless steel, nickel-chromium alloys, copper alloys, aluminum alloys, zinc alloys, metal alloys such as lead alloys, and the like, and examples thereof include metal meshes or metal porous bodies.

(Coating liquid for forming a fine porous layer)
The coating liquid for forming the fine porous layer is a liquid applied to one surface of the porous base material layer, and the fine porous layer is formed by firing the applied coating liquid. ..

The fine porous layer is a layer formed on one surface of the porous base material layer, and has a pore diameter smaller than that of the porous base material layer. The fine porous layer makes it easy to discharge the water generated in the cathode catalyst layer to the outside of the single cell through the porous substrate layer while circulating the oxidant gas dispersed through the porous substrate layer. Promotes the function of promoting or facilitating the discharge of water generated in the anode catalyst layer to the outside of a single cell through the porous base material layer while circulating the fuel gas dispersed through the porous base material layer. Has the function of

The coating liquid for forming the fine porous layer (hereinafter, also simply referred to as “coating liquid”) is not particularly limited as long as it is a liquid capable of forming the fine porous layer on the porous base material layer. For example, the coating liquid may contain a conductive material, a binder, and a solvent. The coating liquid may be in the form of a paste or slurry in which the above-mentioned components are mixed and dispersed.

The conductive material may be any material having excellent conductivity and a large specific surface area. Examples of the conductive material include carbon black, and acetylene black is particularly preferable from the viewpoint of conductivity. The average particle size of the conductive material may be 20 nm to 150 nm.
Examples of the binder include fluorine-based polymer materials such as polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), polyhexafluoropropylene, and tetrafluoroethylene-hexafluoropropylene copolymer, polypropylene, polyethylene and the like. Examples thereof include polyolefin-based polymer materials. As the binder, a fluorine-based polymer material is preferable, and PTFE is more preferable.
Examples of the solvent include water, methanol, ethanol and the like.

The content of the conductive material contained in the coating liquid is preferably 70% by mass to 90% by mass with respect to the total solid content.
The content of the binder contained in the coating liquid is preferably 15% by mass to 25% by mass with respect to the total solid content.
In the present disclosure, the solid content means a non-volatile component such as a conductive material, a binder, and a dispersant described later. In one form, the solids may be conductive materials, binders and dispersants.

The coating liquid may contain other components other than the conductive material, the binder and the solvent. Examples of other components include dispersants such as surfactants and other additives. The coating liquid preferably does not contain metal from the viewpoint of avoiding contamination.
The surfactant is not particularly limited, and examples thereof include nonionic surfactants such as ester type, ether type, and ester / ether type.

The content of the dispersant contained in the coating liquid is preferably 5% by mass to 15% by mass with respect to the total solid content.

The proportion of the solid content contained in the coating liquid is preferably 15% by mass to 25% by mass.
The viscosity of the coating liquid is preferably in the range in which the penetration into the porous base material layer is suppressed and the coating film having a set thickness on the porous base material layer is maintained. For example, the viscosity of the coating liquid is preferably 500 mPa · s to 2500 mPa · s at a ^{shear rate of 50s-1.}
The storage elastic modulus of the coating liquid is preferably 500 Pa to 5500 Pa.
The viscosity and storage elastic modulus are measured with a viscometer.

(Example of manufacturing method of gas diffusion layer for fuel cell)
Hereinafter, an example of the method for manufacturing the gas diffusion layer for a fuel cell of the present disclosure will be shown with reference to FIG. The manufacturing apparatus 1000 shown in FIG. 1 includes a coating apparatus 100, a firing apparatus 200, a transfer apparatus 300, and a cutting apparatus 400 in this order from the upstream side. In the manufacturing apparatus 1000, the long sheet-shaped porous substrate layer BS used for forming the porous substrate layer of the gas diffusion layer is unwound from the substrate roll (not shown) by the transport apparatus 300. The coating step, the firing step, and the cutting step are executed by being sent to the coating device 100, the firing device 200, and the cutting device 400 in this order.

In the transfer of the porous base material layer BS by the transfer device 300, the pair of upper and lower drive transfer rolls 302 and the driven transfer roll 304 are sequentially drawn in with the long sheet-shaped gas diffusion layer formed by the firing device 200 sandwiched between them. In conjunction with this, the porous substrate layer BS is unwound from the substrate roll. The porous base material layer BS is a sheet-shaped porous base material layer.

(Coating process)
The coating process is performed by the coating apparatus 100. The coating apparatus 100 includes a backup roll 102 and a die head 104 arranged so as to face the backup roll 102. The die head 104 is filled with a coating liquid 106 for forming a fine porous layer on one surface of the porous base material layer BS.
The fine porous layer has a porous structure having a pore size smaller than that of the porous base material layer BS. The arrangement position of the die head 104 is not limited to the position shown in FIG. 1, and is not particularly limited as long as it is arranged so as to face the backup roll 102.

In the coating step, the coating liquid 106 is applied by the die head 104 to the surface of the porous substrate layer BS fed from the substrate roll, which is opposite to the surface of the porous substrate layer BS on the side opposite to the surface in contact with the backup roll 102. Coating basis weight may be, for example, ^{2mg / cm 2 ~6mg / cm 2} . The thickness of the coating film Mc of the applied coating liquid 106 is the speed at which the porous substrate layer BS passes between the die head 104 and the backup roll 102 and the discharge speed of the coating liquid 106 discharged from the die head 104. Determined by.

(Baking process)
The porous base material layer BS to which the coating liquid 106 has been applied is conveyed to the firing apparatus 200, and the firing step is performed by the firing apparatus 200.
The firing device 200 is composed of a general firing furnace. In the firing step, the coated porous base material layer BS of the coating liquid 106 is heated by the heater 202 to perform the firing treatment of the coating film Mc with the coating liquid 106. As a result, the coating film Mc of the coating liquid 106 is fixed on the porous base material layer BS as a fine porous layer, and the gas diffusion in the form of a long sheet in which the porous base material layer and the fine porous layer are laminated. A layer is formed.

The heating time (firing time) for firing in the firing device 200 corresponds to the time until the coated porous base material layer BS sent to the firing device 200 is sent out to the outside. The firing time satisfies the formula (1) as described above and is 100 seconds or more. The firing time can be adjusted by adjusting the speed and length of movement of the coated porous substrate layer BS in the firing apparatus 200.

The heating temperature (firing temperature) in the firing apparatus 200 is a temperature for heat-sealing the carbon particles of the coating liquid 106 and the binder, and the firing temperature is the above-mentioned formulas (2) to (4) as described above. Meet.

By adjusting the firing time and firing temperature in the firing apparatus 200 as described above, a fine porous layer having excellent water repellency can be produced on the porous substrate layer BS.

In the firing step, it is preferable that the heater 202 heats the coated porous base material layer BS only from the side opposite to the side on which the coating liquid is applied, that is, the porous base material layer BS side. The more sufficient the firing by heating, the higher the water repellency of the obtained fine porous layer, and therefore the water repellency of the obtained fine porous layer is higher on the side in contact with the base material layer than on the opposite side in contact with the catalyst layer. Become. Since the water repellency on the catalyst layer side of the fine porous layer is inferior to that on the base material layer side, the moisturizing property of the catalyst layer is enhanced, and at the same time, it is possible to suppress the dry gas from removing the water on the catalyst layer side. , Dry-up resistance is greatly improved, and power generation performance is also improved.

Before the coating step, a water-repellent treatment for imparting water repellency to the porous base material layer BS may be applied. As a method of applying the water-repellent treatment, a coating liquid for the water-repellent treatment for imparting water repellency is applied to the surface of the porous base material layer BS, and the coating for the water-repellent treatment is applied as necessary. A method of drying the working liquid can be mentioned. The surface of the porous substrate layer BS to which the coating liquid for water repellent treatment is applied may be the surface to which the coating liquid 106 is applied, or the surface opposite to the surface to which the coating liquid 106 is applied. It may be a surface.

The coating liquid for the water-repellent treatment may be a liquid containing a water-repellent agent. Examples of the water repellent include fluorine-based polymer materials such as PTFE, PVDF, polyhexafluoropropylene, and tetrafluoroethylene-hexafluoropropylene copolymer, and polyolefin-based polymer materials such as polypropylene and polyethylene. As the water repellent, a fluorine-based polymer material is preferable, and PTFE is more preferable.

As an example, the coating liquid for water repellent treatment may be a diluted liquid having a concentration of 3% by mass to 5% by mass containing PTFE having a particle size of 100 nm to 400 nm.
Further, the viscosity of the coating liquid for water repellent treatment may be, for example, 1 mPa · s to 100 mPa · s at a ^{shear rate of 50s-1.}

By applying the coating liquid for water repellent treatment to the porous base material layer BS, the coating liquid permeates from the coated surface into the porous base material layer BS by capillarity. This makes it possible to perform a water-repellent treatment in which a water-repellent agent is distributed on the surface and the inside of the porous base material layer BS to impart water repellency.

(Cut process)
In the cutting step, a gas diffusion layer having a desired shape is formed by cutting the long sheet-shaped gas diffusion layer conveyed from the firing device 200 via the transfer device 300 into a desired shape.
The cutting device 400 may be a general cutting machine.

(Example of fuel cell)
Hereinafter, an example of a fuel cell provided with a gas diffusion layer will be described with reference to FIG. FIG. 2 is a cross-sectional view showing the configuration of a single cell of a fuel cell. By using the gas diffusion layer for a fuel cell obtained by the production method of the present disclosure as at least one of the gas diffusion layer 32 and the gas diffusion layer 42, the fuel cell as shown in FIG. 2 can be manufactured.

As shown in FIG. 2, the single cell 1 has a structure in which the membrane electrode assembly 5 is sandwiched between the cathode separator 6 and the anode separator 7. The membrane electrode assembly 5 includes a solid polymer electrolyte membrane 2, a cathode (oxidizing agent electrode) 3 provided on one surface of the solid polymer electrolyte membrane 2, and an anode (fuel electrode) provided on the other surface. It is equipped with 4. The cathode 3 has a multilayer structure in which the cathode catalyst layer 31 and the gas diffusion layer 32 are laminated in order from the solid polymer electrolyte membrane 2 side. The anode 4 has a multilayer structure in which the anode catalyst layer 41 and the gas diffusion layer 42 are laminated in order from the solid polymer electrolyte membrane 2 side.

The gas diffusion layer 32 included in the cathode 3 includes a fine porous layer 33 and a porous base material layer 34, and the gas diffusion layer 42 included in the anode 4 also has a fine porous layer 43 and a porous base material layer 44. I have. The fine porous layer 33 is in contact with the cathode catalyst layer 31, and the porous substrate layer 34 is in contact with the cathode separator 6. Similarly, the fine porous layer 43 is in contact with the anode catalyst layer 41, and the porous substrate layer 44 is in contact with the anode separator 7.
The separators 6 and 7 have an oxidant gas flow path 6a and a fuel gas flow path 7a, respectively.
The gas diffusion layer for a fuel cell manufactured by the manufacturing method of the present disclosure may be for a cathode or for an anode.

In the single cell 1, the cathode 3 and the anode 4 are arranged on both sides of the solid polymer electrolyte membrane 2, and usually they are integrally bonded by a hot press method to form a membrane electrode assembly 5, and then a membrane electrode assembly is formed. It is manufactured by arranging the cathode separator 6 and the anode separator 7 on both sides of 5. In the single cell 1, a fuel gas containing hydrogen is supplied to the anode 4 side, and an oxidant gas such as air containing oxygen is supplied to the cathode 3 side. As a result, an electrochemical reaction occurs at the contact surface between the solid polymer electrolyte membrane 2 and the cathode catalyst layer 31 and the anode catalyst layer 41.

Hereinafter, the present invention will be described with reference to experimental examples, but the present invention is not limited to the following experimental examples.

[Experimental example]
First, regarding the porous base material layer, the concentration of 3% by mass to 5% by mass containing PTFE having a particle size of 200 nm to 300 nm on the surface opposite to the surface to which the coating liquid for forming the fine porous layer described later is applied. A coating liquid for water-repellent treatment of% was applied, and then the porous substrate layer was subjected to water-repellent treatment by heating and drying at 80 ° C. The viscosity of the coating liquid for water repellent treatment was 50 mPa · s at ^{a shear rate of 50s-1.}

A coating liquid for forming a fine porous layer containing acetylene black having an average particle size of 35 nm, which is a conductive material, PTFE as a binder, a solvent, and a dispersant was prepared. In this coating liquid, the total solid content of the conductive material, the binder and the dispersant is 100% by mass, the content of the conductive material is 80% by mass, the content of the binder is 15% by mass, and the dispersion is performed. The content of the agent is 5% by mass. The solid content of this coating liquid was 20% by mass, the viscosity was ^{1500 mPa · s at a shear rate of 50 s-1} , and the storage elastic modulus was 3000 Pa.

After the prepared coating liquid was applied to the porous base material layer, the porous base material layer coated with the coating liquid was fired under the conditions of the firing time and the firing temperature indicated by the circle or cross symbol in FIG. .. As a result, a gas diffusion layer for a fuel cell having a fine porous layer was manufactured.

(Evaluation of water repellency based on power generation performance)
Using gas diffusion layers for fuel cells manufactured by changing the conditions of firing time and firing temperature, a single cell as shown in FIG. 2 is configured with the other components being the same, and then power is generated under the same conditions. The water repellency was evaluated by measuring the output voltage when the performance was evaluated. The results are shown in FIG.

In FIG. 3, the case where the evaluation of water repellency was good was marked as round, and the case where the evaluation of water repellency was poor was marked as cross.

(Evaluation of water repellency by measuring the fall angle)
In the evaluation of water repellency based on power generation performance, the water repellency is evaluated after forming a single cell, so it is desirable that the water repellency can be evaluated more easily from the viewpoint of efficiency. Therefore, the gas diffusion layer for a fuel cell manufactured under the conditions that the firing time was 160 seconds and the firing temperature was 340 ° C, 350 ° C, 360 ° C, 370 ° C, 380 ° C, 390 ° C or 400 ° C was used. Water repellency was evaluated by measuring the fall angle.

An aqueous solution of 15% by mass of ethanol was prepared as a liquid for measuring the falling angle.
Next, the gas diffusion layer for the fuel cell was arranged on a flat surface so that the fine porous layer was on the upper surface, and 25 μmL of the liquid for measuring the rolling angle was allowed to stand on the fine porous layer. Then, when the plane was angled, the angle at which the static liquid started to move was measured to obtain the fall angle.

As shown in FIG. 4, when an aqueous solution of 15% by mass of ethanol is used as the liquid for measuring the falling angle, the firing temperature is 350 ° C. to 380 ° C. as compared with the case where the firing temperature is 340 ° C., 390 ° C. or 400 ° C. The fall angle showed a substantially constant small value, and it was presumed that the fine porous layer was excellent in water repellency in the range of the shaded area in FIG. This result showed the same tendency as the evaluation of water repellency by power generation performance.

Next, as a liquid for measuring the falling angle, aqueous solutions having ethanol concentrations of 10% by mass and 20% by mass were prepared, respectively. Then, the water repellency was evaluated by measuring the falling angle in the same manner as when an aqueous solution of 15% by mass of ethanol was used.

As shown in FIGS. 5 and 6, when an aqueous solution of 10% by mass of ethanol or an aqueous solution of 20% by mass of ethanol is used as the liquid for measuring the falling angle, the value of the falling angle fluctuates greatly even when the firing temperature is changed. Therefore, it was not possible to evaluate the water repellency to determine whether it was a good product or a defective product.

From the above points, the fall angle of the gas diffusion layer for a fuel cell is measured using an aqueous solution having an ethanol concentration of more than 10% by mass and less than 20% by mass, for example, an aqueous solution of 15% by mass of ethanol. It was confirmed that the evaluation of aqueous solution can be easily carried out. Further, as shown in FIG. 4, when the falling angle is equal to or less than a specific value X, it is judged to be a good product having excellent water repellency, and when the falling angle is larger than the specific value X, it is judged to be a defective product having insufficient water repellency. It has become possible to make a judgment, and it has been found that the water repellency can be clearly evaluated by a simple method without producing a single cell and evaluating the power generation performance.

Claims (1)

It includes a step of heating and firing a porous base material layer coated on one surface with a coating liquid for forming a fine porous layer.
In the firing step, a method for manufacturing a gas diffusion layer for a fuel cell that satisfies the following formulas (1) to (4) when the firing temperature is A (° C.) and the firing time is B (seconds).
B ≧ 100 ... (1)
A ≧ 355 [(B-80) / 40] × 5 (100 ≦ B ≦ 200) ・ ・ ・ (2)
A ≧ 340 (B> 200) ・ ・ ・ (3)
A <390 ... (4)

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