JP4423543B2 - Electrode for polymer electrolyte fuel cell - Google Patents

Description

  The present invention relates to an electrode for a polymer electrolyte fuel cell.

As shown in FIG. 6, an electrode (gas diffusion electrode) 100 for a polymer electrolyte fuel cell includes a catalyst layer 103 disposed on both sides of a cation exchange membrane 101 and gas diffusion layers stacked on these catalyst layers 103. Layer 107.
In a battery using this electrode, for example, hydrogen is supplied to the anode and oxygen is supplied to the cathode, for example, and an electrochemical reaction proceeds to generate power. In each electrode, the following electrochemical reaction occurs.
Anode: H ₂ → 2H ⁺ + 2e ⁻
Cathode: 1 / 2O ₂ + 2H ⁺ + 2e ⁻ → H ₂ O
All _{reaction: H 2 + 1 / 2O 2} → H 2 O

Incidentally, the gas diffusion layer 107 has a function of supplying an oxidant gas such as oxygen or a fuel gas such as hydrogen to the catalyst layer 103. Further, the gas diffusion layer 107 has a function of transmitting electricity generated by the electrode reaction of the catalyst layer 103 to the separator. Therefore, carbon fiber sheets such as carbon paper and carbon felt are widely used as the gas diffusion layer 107 so as to fulfill these functions.
However, the carbon fiber sheet is rough and has irregularities on the surface. For this reason, as shown in FIG. 6, the contact between the gas diffusion layer 107 made of a carbon fiber sheet and the catalyst layer 103 becomes insufficient, and the output characteristics of the polymer electrolyte fuel cell using the same are not necessarily sufficient. (In addition, an enlarged cross-sectional view of the contact portion between the catalyst layer 103 and the gas diffusion layer 107 is shown in the circular box in FIG. 6. In this figure, reference numeral 108 indicates a carbon fiber sheet).

Therefore, as schematically shown in FIG. 7, it is proposed to form a carbon layer 111 by applying a paste in which carbon particles and PTFE (polytetrafluoroethylene) are mixed on the gas diffusion layer 107. . This is because the surface of the gas diffusion layer 107 is coated with the carbon layer 111 so as to have a relatively smooth surface state, and sufficient contact between the gas diffusion layer 107 and the catalyst layer 103 is ensured (this Reference is made to the electrode structure disclosed in Patent Document 1 relating to the technology).
Japanese Patent Laid-Open No. 9-245801

In this case, as the carbon layer 111, for example, the carbon particles contained in the carbon layer 111 are about 90 to 95% by weight (in other words, PTFE, based on the sum of PTFE and carbon particles in the carbon layer 111). When the amount of the PTFE and the carbon particles is about 5 to 10% by weight, the contact resistance between the carbon layer 111 and the catalyst layer 103 can be kept low.
However, when the carbon layer 111 has a high carbon particle ratio, the water repellency of the carbon layer 111 decreases. Accordingly, there is a problem that water stays inside the carbon layer 111 and the supply of gas to the catalyst layer 103 is hindered by this water, and the voltage drop is particularly large in a high current density region.

On the other hand, in order to prevent this influence, for example, the carbon particles contained in the carbon layer 111 are about 60 to 70% by weight (in other words, PTFE, based on the sum of PTFE and carbon particles in the carbon layer 111). About 30 to 40% by weight with respect to the sum of PTFE and carbon particles). In this way, water retention in the carbon layer 111 can be suppressed.
However, there is a problem that the contact resistance between the carbon layer 111 and the catalyst layer 103 increases as the content of PTFE, which is an insulator, increases.
As described above, when the single carbon layer 111 is provided, the output characteristics of the polymer electrolyte fuel cell are not improved so much even if the ratio between the carbon particles and PTFE is changed.

  The present invention has been completed based on the above circumstances, and an object thereof is to improve the output characteristics of a polymer electrolyte fuel cell.

  The inventors of the present invention have intensively studied to develop an electrode for a polymer electrolyte fuel cell that can solve such problems. As a result, it was found that when the carbon layer provided between the catalyst layer and the gas diffusion layer is formed in multiple layers, the output characteristics of the polymer electrolyte fuel cell are remarkably improved. The present invention has been made based on this finding.

That is, the invention of claim 1 includes a gas diffusion layer configured to include a carbon fiber sheet, and a catalyst layer including a catalyst-supporting carbon particle and a solid polymer electrolyte, and the gas diffusion layer and the catalyst layer Between the electrode for a polymer electrolyte fuel cell provided with a carbon layer containing carbon particles and a water repellent resin, wherein the carbon layer is in contact with the gas diffusion layer; The water repellent resin contained in the second layer has a total amount of the water repellent resin and the carbon particles contained in the second layer. The water-repellent resin contained in the first layer is 20 to 40% by weight based on the total amount of the water-repellent resin and the carbon particles contained in the layer . The dry thickness of the first layer is 40-60 μm , Dry film thickness of the second layer is an electrode for a polymer electrolyte fuel cell, which is a 5 to 15 [mu] m.

According to the structure of this claim, the carbon layer provided between the catalyst layer and the gas diffusion layer is two layers. And the water-repellent resin contained in the 2nd layer which contact | connects a catalyst layer among 2 layers is 5 to 10 weight% with respect to the total amount of the water-repellent resin and carbon particle contained in the layer, and gas The water repellent resin contained in the first layer in contact with the diffusion layer is 20 to 40% by weight based on the total amount of the water repellent resin and carbon particles contained in the layer.
Therefore, on the catalyst layer side, the contact resistance with the catalyst layer can be kept low, and on the gas diffusion layer side, it is possible to prevent a decrease in gas diffusibility due to water retention.
Therefore, the output characteristics of the polymer electrolyte fuel cell can be improved by using the electrode having the structure of this claim.
According to the configuration of the present claim, the carbon layer has a two-layer structure including the first layer that contacts the gas diffusion layer and the second layer that contacts the catalyst layer, so that the structure is complicated. It is easier to manufacture.
In the polymer electrolyte fuel cell, oxidant gas and fuel gas are supplied from the gas diffusion layer to the catalyst layer. If these gases strike the catalyst layer vigorously, the catalyst layer is dried or the cation exchange membrane is dried. As a result, the output may be reduced. Therefore, conventionally, particularly on the cathode side, it has been necessary to increase the humidification temperature to operate the fuel cell.

According to the structure of this claim, since the first layer has a thickness of 40 μm or more, the first layer can sufficiently weaken the momentum of the gas striking the catalyst layer. For this reason, drying of the catalyst layer and drying of the cation exchange membrane can be prevented. Therefore, an operation in which the humidification temperature on the cathode side is lowered as compared with the prior art becomes possible.
On the other hand, when the thickness of the first layer is larger than 60 μm, the electrical resistance of the first layer itself is increased, and the electricity generated by the electrode reaction of the catalyst layer is not easily transmitted to the separator. On the other hand, if the thickness is too large, gas diffusion to the reaction interface is hindered, and the output tends to decrease. For this reason, in this claim, it is set to 60 μm or less.

Hereinafter, the electrode 1 of the present invention will be described with reference to FIG.
An electrode 1 for a polymer electrolyte fuel cell according to the present invention includes, for example, a gas diffusion layer 5 having a carbon fiber sheet 3 and a catalyst containing carbon particles carrying a catalyst, as schematically shown in FIG. The layers 7 are arranged one above the other. Further, a carbon layer 9 containing carbon particles and a water repellent resin is provided between the gas diffusion layer 5 and the catalyst layer 7.
The carbon layer 9 has a two-layer structure of a first layer 9A and a second layer 9B. (In addition, an enlarged cross-sectional view of a contact portion between the catalyst layer 7 and the gas diffusion layer 5 is shown in the circular enclosure of FIG. 2).

  The carbon fiber sheet 3 is not particularly limited, such as fiber diameter and fiber length, and known ones can be used, and a wide variety of carbon papers, carbon woven fabrics, carbon felts, etc. are widely used. can do.

In the present invention, the carbon layer 9 is formed on the carbon fiber sheet 3. For example, the carbon layer 9 can be formed by the following steps.
First, as shown in FIG. 1 (A), the carbon fiber sheet 3 is immersed in a PTFE dispersion 11 (for example, 2.5 wt%, but the concentration is not particularly limited), and then dried (for example, About 110 ° C.). Although it is desirable to improve the water repellency of the carbon fiber sheet 3 by preliminarily performing the water repellent treatment on the carbon fiber sheet 3 in this manner, the water repellent treatment is not necessarily required.

Next, a paste containing carbon particles and a water repellent resin is applied to one side of the carbon fiber sheet 3 thinly coated with PTFE in this way to form the first layer 9A (see FIG. 1B).
As long as this paste contains carbon particles and a water-repellent resin, it may contain other additives such as a resin for a binder.

  The carbon particles are not particularly limited, and for example, any of furnace black, acetylene black, lamp black, thermal black, and channel black can be used.

The average particle size of the carbon particles is not particularly limited, but is preferably 10 to 50 μm. If the average particle size is less than 10 μm, the particles are aggregated to increase the secondary particles, and if the average particle size is more than 50 μm, the dispersibility of the particles is reduced, so that a uniform paste is used. You can't get it.
The average particle diameter means a value of d50 measured by a laser diffraction scattering method.

The water-repellent resin is not particularly limited and can be used widely. For example, polytetrafluoroethylene, polyhexafluoropropylene, polyvinylidene fluoride, a copolymer of tetrafluoroethylene and hexafluoropropylene, or these Can be used. Among these, it is particularly preferable to use polytetrafluoroethylene (PTFE).
The binder resin is not particularly limited and can be used widely. For example, a wide variety of water-soluble and pyrolyzed by firing described below can be used. For example, polyethylene glycol, polyvinyl alcohol, polystyrene sulfonate, a copolymer of a vinyl compound and a carboxylic acid monomer Or the like can be used.

The ratio of the solid content weight of the water-repellent resin in the paste to the carbon particle weight is 20:80 to 40:60 (weight ratio), and preferably 25:75 to 35:65 (weight ratio) ( Since the first layer 9A is formed by drying this paste, the water-repellent resin contained in the first layer 9A is 20 to 40% by weight with respect to the sum of the water-repellent resin and the carbon particles. %, Preferably 25 to 35% by weight). If the solid content weight ratio of the water-repellent resin is larger than this range, the amount of the water-repellent resin in the first layer 9A becomes too large, and since the water-repellent resin is insulating, the electrical conductivity of the first layer 9A This is because the output characteristics of the fuel cell tend to deteriorate. On the other hand, if the weight ratio of the solid content of the water-repellent resin is smaller than this range, the water repellency of the carbon layer 9 is lowered, and water stays in the carbon layer 9 during the operation of the fuel cell and the gas diffusibility is lowered. This is because it tends to cause a decrease in output.
The thickness of the first layer 9A after drying is 40 to 60 μm. In this way, by setting the dry film thickness of the first layer 9A to 40 to 60 μm, the first layer 9A can sufficiently weaken the momentum of the gas striking the catalyst layer 7 while ensuring the electrical conductivity of the first layer 9A. Can do. For this reason, drying of the catalyst layer and drying of the cation exchange membrane can be prevented.

Next, a paste containing carbon particles and a water-repellent resin and having a lower water-repellent resin concentration than the paste used for forming the first layer 9A is applied on the first layer 9A. 9B is formed (see FIG. 1C).
For this paste, the same carbon particles, water repellent resin, binder resin and the like as the paste for the first layer 9A can be used.

  The ratio of the solid content weight of the water repellent resin in the paste for the second layer 9B and the weight of the carbon particles is 5:95 to 10:90 (weight ratio), preferably 7:93 to 8.5. 91.5 (weight ratio) (The second layer 9B is formed by drying this paste, so that the water-repellent resin contained in the second layer 9B is composed of the water-repellent resin and the carbon particles. And 5 to 10% by weight, preferably 7 to 8.5% by weight). This is because when the solid content weight ratio of the water-repellent resin is larger than this range, the water-repellent resin is insulative, and the contact resistance with the catalyst layer 7 tends to increase. This is because when the solid content weight ratio of the water-repellent resin is smaller than this range, the binding force of the water-repellent resin between the carbon particles is reduced, and the second layer 9B becomes brittle. In addition, water generated during operation of the fuel cell tends to accumulate in the second layer 9B, and the electrode reaction tends to be inhibited.

The thickness of the second layer 9B after drying is 5 to 15 μm, and more preferably 8 to 12 μm.
If it is thicker than this range, the water repellent resin concentration of the second layer 9B is lower than that of the first layer 9A, so water may stay in the second layer 9B and the electrode reaction may be hindered. is there. On the other hand, even if it is attempted to form a film thinner than this range, it is difficult to form the second layer 9B uniformly on the first layer 9A, and it is only partially formed. This is because it is difficult to sufficiently suppress the above.

Furthermore, it is desirable to fire the carbon fiber sheet 3 provided with the first layer 9A and the second layer 9B thus obtained. By baking, the binder resin is selectively removed as carbon oxide or the like, and fine pores are formed therein, and the gas diffusivity in the first layer 9A and the second layer 9B is improved by the pores. Because it can.
Moreover, the surfactant component contained in the water-repellent resin can be removed by baking. This surfactant is added as an additive at the time of polymerization of the water-repellent resin or thereafter, because the surfactant tends to inhibit the electrode reaction and is desirably removed.
Although it does not specifically limit as a calcination temperature, 320-420 degreeC is preferable and 370-390 degreeC is especially preferable. Below 320 ° C., the binder resin is not fired or tends to take a long time for firing, which is not preferable. On the other hand, at 420 ° C. or more, thermal decomposition of other constituent materials of the electrode, such as water-repellent resin, occurs. Because there is a fear.

As described above, after the first layer 9A and the second layer 9B are formed on the carbon fiber sheet 3 as the gas diffusion layer 5, the catalyst layer 7 is disposed on (or below) the second layer 9B. In this way, the electrode 1 is formed.
As the catalyst layer 7, a wide variety of those prepared by a known method can be used. For example, catalyst particles (for example, carbon particles supporting platinum) prepared in advance, a water repellent, and a PTFE dispersion as a binder (binder) are mixed and formed into a sheet on a support. It can produce by doing.

  Further, for example, the catalyst layer 7 can also be formed by the following method disclosed in JP 2000-012041 A. That is, first, a cation exchange resin, carbon particles not supporting a catalyst, and a solvent are mixed to prepare a mixed slurry. The mixed slurry is coated on a support (for example, FEP (fluorinated ethylene propylene)) to form a sheet, and this sheet is immersed in a solution containing catalyst metal ions (platinum ions or the like). Furthermore, the sheet is reduced in a hydrogen atmosphere, and catalyst metal is deposited in the sheet to form a catalyst layer.

The catalyst metal in the catalyst layer is not particularly limited by any method, and a wide variety of known metals can be used. However, the catalyst for electrochemical oxygen reduction reaction and hydrogen oxidation reaction can be used. A metal having high activity is suitable. For example, platinum group metals such as platinum, rhodium, ruthenium, iridium, palladium, osmium, and alloys thereof are preferable.
In particular, as a catalyst metal used for the anode-side electrode, an alloy containing platinum metal, for example, an alloy containing platinum and ruthenium is preferable because of its high resistance to CO poisoning (carbon monoxide resistance).

Furthermore, the fuel cell 13 is assembled using the above-described electrode 1 for a fuel cell, for example, as follows.
That is, as shown in FIG. 2, the electrode 1 is stacked on both sides of the cation exchange membrane 15, and a separator (bipolar plate) 17 having a gas flow path formed on the surface by groove processing on both sides is adhered and stacked. Thus, the fuel cell 13 is obtained.
The cation exchange membrane 15 is not particularly limited, and is a well-known polymer electrolyte membrane, for example, a fluororesin ion exchange membrane having a sulfonic acid group (for example, perfluorosulfonic acid type cation exchange membrane), styrene- A divinylbenzene-based sulfonic acid type cation exchange membrane can be used.

Hereinafter, the present invention will be described in more detail with reference to examples.
<1. Preliminary water repellent treatment of carbon paper>
First, carbon paper (Dainippon Ink Co., Ltd., Auspon E02, thickness 0.2 mm) was immersed in a 2.5 wt% PTFE dispersion (aqueous dispersion) and then dried at 110 ° C. for preliminary repelling. Water treatment was performed.

<Preparation of mixed dispersion (paste) for first layer>
The mixed dispersion for the first layer was prepared as follows. Carbon particles (Vulcan XC-72 (manufactured by Cabot)), 2.5 wt% PTFE dispersion (aqueous dispersion, Mitsui DuPont, 30-J (product number)) and CMC (carboxymethylcellulose, manufactured by Daicel Chemical Industries, DN -400H (product number)) and water were mixed to prepare a mixed dispersion for the first layer. The composition of the mixed dispersion for the first layer is as follows: carbon particles: PTFE (solid content): CMC: water (total amount of water in the mixed dispersion including water in the PTFE dispersion) = 70: 30: 20 : 1225 (weight ratio).

<Preparation of mixed dispersion (paste) for second layer>
The mixed dispersion for the second layer was prepared as follows. Carbon particles (Vulcan XC-72 (manufactured by Cabot)), 2.5 wt% PTFE dispersion (aqueous dispersion, Mitsui DuPont, 30-J (product number)) and CMC (carboxymethylcellulose, manufactured by Daicel Chemical Industries, DN -400H (product number)) and water were mixed to prepare a mixed dispersion for the second layer. The composition of the mixed dispersion for the second layer is as follows: carbon particles: PTFE (solid content): CMC: water (total amount of water in the mixed dispersion including water in the PTFE dispersion = 95: 5: 20: It was set to 1225 (weight ratio).

<Fabrication of fuel cell A>
The mixed dispersion for the first layer was applied on water-repellent treated carbon paper and then dried at 110 ° C. to form the first layer on the carbon paper. The coating amount of the mixed dispersion was adjusted so that the film thickness after drying was 40 μm.
And the mixed dispersion for 2nd layers was apply | coated on the 1st layer, and it was made to dry at 110 degreeC after that. The coating amount of the mixed dispersion was adjusted so that the film thickness after drying was 10 μm.
In this way, a carbon paper on which the first layer (40 μm) and the second layer (10 μm) were formed was produced.
Next, this carbon paper was baked at 380 ° C. for 30 minutes. As a result, CMC was selectively removed and fine pores were formed in the carbon layer (first layer and second layer).
And the carbon paper after baking was arrange | positioned on both surfaces of the assembly of the catalyst layer-cation exchange membrane-catalyst layer produced separately, and also the separator which formed the gas flow path on the surface by the groove processing on the both outer sides ( A single-cell fuel cell A was obtained by closely laminating bipolar plates).
A catalyst layer-cation exchange membrane-catalyst layer assembly was prepared as follows.
First, 80 g of a cation exchange resin solution (manufactured by Aldrich, Nafion 5 wt% solution) was collected in a container. After adding 6 g of TEC10V30E (manufactured by Tanaka Kikinzoku Co., Ltd.) as platinum-supporting carbon to the solution, a dispersion was prepared by stirring for 1 hour while irradiating ultrasonic waves using a wing-type stirrer. Next, after this paste (dispersion) is dispersed with a mixer for 30 minutes, it is heated at 60 ° C. until the concentration of solids (sum of carbon and cation exchange resin solids) becomes 20 wt% with a hot stirrer. Concentrated by heating. Subsequently, the dispersion liquid was applied onto a polymer sheet (Daikin Industries, Tetrafluoroethylene-hexafluoropropylene copolymer film) using a 120 μm applicator, and dried at room temperature to obtain about 15 μm. A catalyst layer for a fuel cell electrode was prepared.
Next, a catalyst layer-membrane-catalyst layer assembly of a catalyst layer and a polymer electrolyte membrane was produced by the following procedure. First, as a pretreatment, a polymer electrolyte membrane (Nafion 115 membrane manufactured by DuPont, film thickness of about 120 μm) is held with 0.5 mol / l sulfuric acid at 80 ° C. for 1 hour, and then deionized at 80 ° C. for 1 hour. The remaining sulfuric acid was removed by immersion in water. Subsequently, the catalyst layer was placed symmetrically on both sides of the membrane, and then the membrane and the catalyst layer were joined together by thermocompression bonding (135 ° C., 1.5 MPa). In this way, a catalyst layer-cation exchange membrane-catalyst layer assembly was obtained.

  And the current-voltage characteristic of the fuel cell A was measured. Air humidified at 80 ° C. is supplied to the cathode side, and hydrogen gas humidified at 80 ° C. is supplied to the anode side. The air utilization rate is 40%, the hydrogen utilization rate is 80%, and the operating temperature is 80 ° C. .

<Fabrication of fuel cell B>
The mixed dispersion for the first layer was applied on the water-repellent treated carbon paper, and then dried at 110 ° C. to form only the first layer (the film thickness after drying was 50 μm). Thereafter, it was baked at 380 ° C. for 30 minutes. A fuel cell B was produced in the same manner as the fuel cell A except that this carbon paper was used. The current-voltage characteristics of the fuel cell B were measured under the same conditions as the fuel cell A.

<Fabrication of fuel cell C>
The mixed dispersion for the second layer was applied on the water-repellent treated carbon paper, and then dried at 110 ° C. to form only the second layer (the film thickness after drying was 50 μm). Thereafter, it was baked at 380 ° C. for 30 minutes. A fuel cell C was produced in the same manner as the fuel cell A except that this carbon paper was used. The current-voltage characteristics of the fuel cell C were measured under the same conditions as the fuel cell A.
The thicknesses of the first layer and the second layer of the fuel cells A to C are summarized in Table 1 below.

<Measurement results of current-voltage characteristics of fuel cells A to C>
FIG. 3 shows measurement results of current-voltage characteristics of the fuel cells A to C. The fuel cell A using the carbon paper having the first layer and the second layer has a cell voltage which is higher than that of the fuel cell B having only the first layer and the fuel cell C having only the second layer at any current density. It was expensive.
In the fuel cell A, since the second layer having a low water-repellent resin concentration is in contact with the catalyst layer and the first layer having a high water-repellent resin concentration is in contact with the carbon paper, the contact resistance is suppressed on the catalyst layer side. It is considered that water retention was prevented on the side (gas diffusion layer).

<Examination of the effect of the thickness of the first layer>
Next, when the first layer and the second layer are provided, the influence of the thickness of the first layer on the characteristics of the fuel cell was examined.
Here, fuel cells D to I in which the thickness of the first layer was changed as described in Table 2 were produced. In these fuel cells, the thickness of the first layer was changed by changing the amount of the first layer mixed dispersion applied on the carbon paper. The other points were fabricated in the same manner as the fuel cell A.
Then, the current-voltage characteristics of the fuel cells A and D to I were measured. Humidified air was supplied to the cathode side, and the humidification temperature at that time was changed to 40 to 85 ° C. On the other hand, hydrogen gas humidified at 80 ° C. was supplied to the anode side. The air utilization rate was 40%, the hydrogen utilization rate was 80%, the operating temperature was 80 ° C., and the current density was 300 mAcm ⁻² .

その結果、図４に示すようなグラフが得られた。これより、カソードの加湿温度が６０℃以下において、第１層の厚みが４０〜６０μｍの燃料電池Ａ、Ｇ、Ｈは、０．４５Ｖ以上のセル電圧を確保することができた。これは、第１層の厚みを４０μｍ以上とすることで、触媒層に当たるガスの勢いを第１の層で十分に弱めることができたためと考えられる。一方、第１の層の厚みが６０μｍよりも大きい場合には、第１層自体の電気的な抵抗が上昇し、さらに、ガスの拡散性が低下して、反応界面まで十分にガスが到達しなかったために、セル電圧が低下傾向にあるものと推測される。

As a result, a graph as shown in FIG. 4 was obtained. As a result, when the humidification temperature of the cathode was 60 ° C. or less, the fuel cells A, G, and H having the first layer thickness of 40 to 60 μm were able to secure a cell voltage of 0.45 V or more. This is presumably because the momentum of the gas striking the catalyst layer could be sufficiently weakened by the first layer by setting the thickness of the first layer to 40 μm or more. On the other hand, when the thickness of the first layer is larger than 60 μm, the electrical resistance of the first layer itself is increased, the gas diffusibility is lowered, and the gas sufficiently reaches the reaction interface. Therefore, it is estimated that the cell voltage tends to decrease.

<Examination of the influence of the thickness of the second layer>
Next, when the first layer and the second layer are provided, the influence of the thickness of the second layer on the characteristics of the fuel cell was examined.
Here, fuel cells J to M in which the thickness of the second layer was changed as shown in Table 3 were produced. In these fuel cells, the thickness of the second layer was changed by changing the coating amount of the mixed dispersion for the second layer. The other points were fabricated in the same manner as the fuel cell A.
The thicknesses of the first layer and the second layer are summarized in Table 3, and the relationship between the thickness of the second layer and the cell voltage is shown in FIG. From FIG. 5, it was found that the cell voltage increases with increasing thickness until the thickness of the second layer is about 10 μm, but the cell voltage decreases when the thickness of the second layer is more than 10 μm. The reason is that the second layer works effectively because the second layer has a thickness of up to about 10 μm, because good electronic conductivity can be secured by the mixed layer of carbon having a low PTFE content and PTFE. When the thickness of the second layer becomes larger than this, the thickness of the second layer having low water repellency increases, so that water generated at the reaction interface quickly moves from the second layer to the first layer and is discharged out of the cell. It is considered that water is retained in the second layer and hinders gas diffusibility.

Sectional drawing which shows the manufacturing process of the electrode for fuel cells Cross section of fuel cell Graph showing current-voltage characteristics Graph showing the relationship between cathode humidification temperature and cell voltage Graph showing the relationship between the thickness of the second layer and the cell voltage Cross section of conventional fuel cell Cross section of conventional fuel cell

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Electrode 3 ... Carbon fiber sheet 5 ... Gas diffusion layer 7 ... Catalyst layer 9 ... Carbon layer 9A ... 1st layer 9B ... 2nd layer 13 ... Fuel cell 15 ... Cation exchange membrane 17 ... Separator

Claims (1)

A gas diffusion layer configured to include a carbon fiber sheet, and a catalyst layer including a catalyst-supported carbon particle and a solid polymer electrolyte,
An electrode for a polymer electrolyte fuel cell provided with a carbon layer containing carbon particles and a water-repellent resin between the gas diffusion layer and the catalyst layer,
The carbon layer has a two-layer structure including a first layer that contacts the gas diffusion layer and a second layer that contacts the catalyst layer,
The water repellent resin contained in the second layer is 5 to 10% by weight based on the total amount of the water repellent resin and carbon particles contained in the layer,
The water repellent resin contained in the first layer is 20 to 40% by weight based on the total amount of the water repellent resin and carbon particles contained in the layer ,
The electrode for a polymer electrolyte fuel cell , wherein the dry film thickness of the first layer is 40 to 60 μm, and the dry film thickness of the second layer is 5 to 15 μm .

Images