JP2010129380A - Gas diffusion electrode, and manufacturing method thereof - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a gas diffusion electrode capable of improving power generation characteristics of a solid polymer fuel cell, and to provide a manufacturing method thereof. <P>SOLUTION: The gas diffusion electrode 22 includes a gas diffusion layer substrate 8 and a conductive covering layer 6. The conductive covering layer 6 consists of a permeation portion 6a permeated inside from the surface of the gas diffusion layer substrate 8 and a covered portion 6b formed on the surface of the gas diffusion layer substrate 8. The permeation portion 6a has a prescribed amount of permeation thickness from the surface of the gas diffusion layer substrate 8. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a gas diffusion electrode for a fuel cell and a manufacturing method thereof, and more particularly to a gas diffusion electrode with improved drainage and a manufacturing method thereof.

  In a fuel cell, a fuel gas such as hydrogen gas and an oxygen-containing oxidant gas are electrochemically reacted through an electrolyte, and electric energy is directly taken out between electrodes provided on both surfaces of the electrolyte. In particular, a polymer electrolyte fuel cell using a polymer electrolyte membrane has attracted attention as a power source for a mobile body because of its low operating temperature and easy handling.

  A polymer electrolyte fuel cell has a catalyst layer containing platinum or the like on both sides of a hydrogen ion conductive polymer electrolyte membrane, and a gas diffusion layer having electron conductivity and air permeability in contact with the catalyst layer. Have. The catalyst layer and the gas diffusion layer constitute a fuel electrode (hereinafter also referred to as “anode” or “negative electrode”) and an oxidant electrode (hereinafter also referred to as “cathode” or “positive electrode”), respectively. Then, separators having gas supply grooves are provided outside the fuel electrode and the oxidant electrode, respectively, and the fuel electrode and the oxidant electrode respectively include fuel gas containing hydrogen and oxygen from the gas supply groove of the separator. By supplying the oxidant gas, power is generated by the electrochemical reaction of the following formulas (1) and (2).

[Fuel electrode reaction]: H ₂ → 2H ⁺ + 2e ⁻ (1)
[Oxidant electrode reaction]: 2H ⁺ + 2e ⁻ + 1 / 2O ₂ → H ₂ O (2)
In a polymer electrolyte fuel cell, a flooding (water overflow) phenomenon is well known as a cause of a remarkable decrease in power generation performance. The flooding phenomenon is a phenomenon in which the ability to discharge generated water due to a power generation reaction is insufficient, and gas generation is hindered mainly due to excess water in the cathode, resulting in a decrease in power generation performance.

  The water produced by the power generation reaction of the cathode catalyst layer is discharged as water vapor in the circulating gas, or is discharged to the anode side through the polymer electrolyte membrane. Part of the generated water is liquid and passes through the gas diffusion layer on the cathode side, and is discharged into the gas supply groove of the cathode side separator. Therefore, in order to prevent the flooding phenomenon, research and development have been conducted on a gas diffusion layer through which generated water permeates.

  As for the gas diffusion layer, there is known a gas diffusion layer including a gas diffusion layer base material and a conductive coating layer formed on the gas diffusion layer base material. In the gas diffusion layer having such a structure, when both the gas state and the liquid state water pass through the conductive coating layer, a permeation resistance related to the thickness of the conductive coating layer, the pore diameter distribution, and the like is generated. Usually, the thinner the conductive coating layer, the smaller the transmission resistance. Further, during power generation, electrons also pass through the conductive coating layer, but the electron transmission resistance is formed by the bulk resistance of the conductive coating layer and the interface contact resistance between the gas diffusion layer substrate and the catalyst layer. Usually, the influence of interfacial contact resistance is large, and in order to make better contact with the gas diffusion layer base material, the thicker the conductive coating layer, the lower the resistance. Therefore, there is a demand for a conductive coating layer having excellent characteristics in consideration of water permeability and the like.

Regarding a conventional gas diffusion electrode having a conductive coating layer, a carbon slurry, which is a material of the conductive coating layer, is directly coated on a gas diffusion layer base material, thereby forming a conductive coating layer containing carbon particles. There is a gas diffusion electrode (Patent Document 1).
JP 2005-235525 A

  However, in the technique described in Patent Document 1, the surface of the gas diffusion layer base material to which the carbon slurry as the material is directly applied in order to form the conductive coating layer has no pore shape or surface water repellency. It is uniform. Therefore, when carbon slurry, which is the material of the conductive coating layer, is directly applied on such a gas diffusion layer substrate, the amount of penetration of the carbon slurry into the gas diffusion layer substrate in the thickness direction is It varies depending on the pore distribution of the layer substrate, the surface water repellency and the physical properties of the slurry ink. For this reason, if the amount of permeation is large, the permeation resistance of water or gas increases and the power generation performance decreases. It was difficult to make the amount penetrated. Further, the above penetration amount is usually difficult to control because it greatly varies depending on the application state of the slurry ink.

  In order to solve the above-described problems, the gas diffusion electrode of the present invention includes a gas diffusion layer base material, a permeation portion that penetrates from the surface of the gas diffusion layer base material, and a coating portion formed on the surface. The conductive coating layer is composed of the conductive coating layer, and the permeation portion of the conductive coating layer is characterized in that the permeation thickness from the surface of the gas diffusion layer base material is a predetermined amount.

  The gas diffusion electrode manufacturing method of the present invention is a method for manufacturing the gas diffusion electrode described above, wherein after the liquid containing the material of the permeation portion has a predetermined constant thickness on the flat plate, The gist is to include a step of pressing at least one of the material and the flat plate toward the other and allowing the material of the permeation portion to permeate at a predetermined constant thickness from the surface of the gas diffusion layer base material.

  According to the gas diffusion electrode of the present invention, the permeation thickness of the conductive coating layer permeated into the conductive porous substrate can be made constant, so that the most suitable permeation amount for power generation performance can be achieved. .

  According to the gas diffusion electrode manufacturing method of the present invention, the gas diffusion electrode according to the present invention can be manufactured by a relatively simple process.

  A gas diffusion electrode according to an embodiment of the present invention will be described with reference to the drawings.

  FIG. 1 is a schematic cross-sectional view of a polymer electrolyte fuel cell 1 having a gas diffusion electrode according to an embodiment of the present invention. The fuel cell 1 includes a polymer electrolyte membrane 2 having hydrogen ion conductivity at the center. A fuel electrode catalyst layer 3 is formed on one surface of the polymer electrolyte membrane 2, and an oxidant electrode catalyst layer 4 is formed on the other surface. Conductive coating layers 5 and 6 are provided on the outer side of the fuel electrode catalyst layer 3 and the outer side of the oxidant electrode catalyst layer 4, respectively, in contact with these catalyst layers.

  A gas diffusion layer base material 7 for the fuel electrode is provided outside the conductive coating layer 5 on the fuel electrode side, and a gas diffusion layer base material 8 for the oxidant electrode is provided outside the conductive coating layer 6 on the oxidant side. Is provided.

  The fuel electrode side gas diffusion layer 21 is constituted by the fuel electrode side conductive coating layer 5 and the gas diffusion layer base material 7. The oxidant-side conductive coating layer 6 and the oxidant-electrode gas diffusion layer base material 8 constitute an oxidant-side gas diffusion layer 22. The gas diffusion layer 21 or the gas diffusion layer 22 on the fuel electrode side or the oxidant side corresponds to the gas diffusion electrode of the present invention. In addition, the above-described polymer electrolyte membrane 2 having the catalyst layers 3 and 4 formed on both sides thereof is called a catalyst coating membrane (CCM) 30.

  A fuel electrode separator 9 is provided outside the gas diffusion layer base material 7 of the fuel electrode, and an oxidant electrode separator 10 is provided outside the gas diffusion layer base material 8 of the oxidant electrode. The fuel electrode separator 9 is formed with a gas flow channel groove 11 for supplying fuel gas, and the oxidant electrode separator 10 is formed with a gas flow channel groove 12 for supplying oxidant gas.

  A front view of the oxidant electrode separator 10 is shown in FIG. 2A, a cross-sectional view of the oxidant electrode separator 10 taken along line XX is shown in FIG. A cross-sectional view as seen from the line is shown in FIG. As shown in FIGS. 2A to 2C, the oxidant electrode separator 10 includes a gas inlet 13, a gas inlet side manifold 14, a gas outlet 15, and a gas outlet side manifold 16. A gas passage groove 12 is formed by connecting to the gas outlet side manifold 16.

  In FIG. 1, the gas diffusion layer 21 on the fuel electrode side is formed by coating the conductive coating layer 5 on the surface of the gas diffusion layer substrate 7. Similarly, the gas diffusion layer 22 on the oxidant electrode side is formed by coating the conductive coating layer 6 on the surface of the gas diffusion layer base material 8. At the time of application, a part of the material of the conductive coating layers 5, 6, from the surface of the gas diffusion layer bases 7, 8, whether on the fuel electrode side or the oxidant electrode side, 8 penetrates into the inside of the conductive coating layers 5 and 6, and the remaining material of the conductive coating layers 5 and 6 is formed on the surfaces of the gas diffusion layer base materials 7 and 8.

  In this way, the conductive coating layers 5 and 6 that are constituent elements of the gas diffusion layers 21 and 22 were formed on the surfaces of the gas diffusion layer base materials 7 and 8 and the permeation portion that penetrated into the inside. It consists of a covering part. In the gas diffusion electrode of this embodiment, the permeation portion of the conductive coating layers 5 and 6 has a predetermined amount of permeation thickness from the surface of the gas diffusion layer base material. This will be described with reference to FIG.

  FIG. 3 is a schematic cross-sectional view (FIG. 3A) of the polymer electrolyte fuel cell 1 shown in FIG. 1, the gas diffusion layer 22 on the oxidant electrode side in the fuel cell 1, and the vicinity thereof. FIG. 3B is an enlarged cross-sectional view schematically showing (b) of FIG. In the following, the gas diffusion layer 22 on the oxidant electrode side will be described with reference to FIG. 3, but the gas diffusion electrode of the present invention can also be applied to the gas diffusion layer 21 on the fuel electrode side. it can.

  In FIG. 3, the permeation portion 6a is formed by the permeation of the material of the conductive coating layer 6 from the surface of the gas diffusion layer substrate 8 on the side facing the catalyst layer 4. Moreover, the coating | coated part 6b is formed covering this osmosis | permeation layer a. The conductive coating layer 6 is composed of the permeation portion 6a and the coating portion 6b. In the illustrated embodiment, the permeation portion 6 a has a predetermined fixed amount of permeation thickness from the most convex portion of the unevenness on the surface of the gas diffusion layer base material 8.

  In accordance with the present invention, a description will be given of the operational effect of the permeation portion having a constant permeation thickness in the conductive coating layer of the gas diffusion electrode. According to the gas diffusion electrode of the present invention, since the permeation portion 6a of the conductive coating layer 6 into the gas diffusion layer base material 8 is a constant amount, an appropriate permeation thickness considering the permeation resistance of water and gas can be obtained. can do. Therefore, power generation performance can be improved.

  Further, by forming the permeation portion 6a of the conductive coating layer 6 in a process different from the formation of the cover portion 6b, the previously formed permeation portion 6a can be used in the subsequent formation of the cover portion 6b. It plays the role which prevents the material of the coating | coated part 6b permeating the inside of the gas diffusion layer base material 8. FIG. For this reason, the conductive coating layer 6 has optimum characteristics (resistance, gas permeability, water permeability, heat permeability, etc.) according to the function required for the permeation part 6a and the function required for the cover part 6b. ) Can be obtained and the structure of the permeation part 6a and the covering part 6b can be obtained. Therefore, the power generation characteristics can be further improved.

  For example, in the gas diffusion layer 22, the conductive coating layer 6 generally has a pore structure smaller than that of the gas diffusion layer substrate 8, and usually has a gas permeability and water permeability that are lower than those of the gas diffusion layer substrate 8. Therefore, a structure having a thinner film and a larger pore is required. On the other hand, the conductive coating layer 6 has a function of controlling the humidified state of the catalyst layer 4 by using characteristics such as low water permeability, and a certain thickness is required. In order to satisfy these contradictory requirements, it is important to increase the degree of freedom in designing the coating layer. Here, according to this embodiment, since the penetration part 6a to the gas diffusion layer base material 8 of the conductive coating layer 6 and the coating part 6b can be individually designed, the permeability of gas and water is increased. However, the structure of the conductive coating layer 6 necessary for moisturizing the catalyst layer 4 and the structure of the conductive coating layer 6 necessary for suppressing electric resistance are respectively applied to the coating portion 6b on the gas diffusion layer substrate 8. And it becomes possible to make an individual design so that it can be achieved by the penetration part 6a. Therefore, it is possible to provide a higher performance electrode assembly for a fuel cell and further a high performance fuel cell.

  According to the present invention, the permeation portion 6a having a certain amount of permeation thickness into the gas diffusion layer substrate 8 is obtained by making the liquid containing the material of the permeation portion a predetermined constant thickness on a flat plate, And it can implement | achieve suitably by the process which presses at least one of a flat plate toward the other, and permeate | transmits the material of an osmosis | permeation part from the surface of this gas diffusion layer base material by predetermined fixed thickness. This will be described with reference to FIG.

  FIG. 4 is a schematic explanatory view of the manufacturing procedure of the permeation portion 6a of the conductive coating layer 6. FIG. First, a water-repellent film 42 such as a polytetrafluoroethylene film is placed on the surface plate 41, and an ink slurry liquid film 43 that is a material of the permeation portion 6a is formed on the water-repellent film 42 (FIG. 4A). ). The water repellent film 42 is provided so that the permeation part 6a can be easily separated from the water repellent film 42 after the permeation part 6a is formed. If there is no water-repellent film 42 and the ink slurry liquid film 43 is formed directly on the surface plate 41 to produce the infiltration portion 6a, the infiltration portion 6a adheres to the surface of the surface plate 41 and peels off. It may be difficult.

  The ink slurry liquid film 43 is a slurry containing carbon particles for imparting conductivity to the permeation portion 6a and a fluororesin (for example, polytetrafluoroethylene) for imparting water repellency. The film thickness of the ink slurry liquid film 43 is set to match the penetration thickness of the penetration portion 6a to be produced. This film thickness control can be controlled by applying the ink slurry liquid film 43 on the water-repellent film 42 using, for example, a knife coater. However, the film thickness control is not limited to the knife coater.

  Next, a porous gas diffusion layer base material 8, for example, carbon paper, is prepared separately from the ink slurry liquid film 43, and the gas diffusion layer base material 8 is placed on the ink slurry liquid film from above the ink slurry liquid film 43. It pushes toward 43 (FIG.4 (b)). Since the ink slurry liquid film 43 has a certain degree of viscosity, pressing the gas diffusion layer base 8 causes the ink slurry liquid film 43 to enter the gas diffusion layer base 8 while maintaining a predetermined constant thickness. The permeation part 6a is formed by permeation. Thereafter, the gas diffusion layer base material 8 is lifted and separated from the water-repellent film 42 (FIG. 4C). By performing such a process in the course of the manufacturing process of the gas diffusion electrode, the gas diffusion layer substrate 8 having the permeation portion 6a having a certain amount of permeation thickness as obtained in the present invention can be obtained.

  Thereafter, the gas diffusion layer 22 is obtained by coating and forming the covering portion 6b on the permeation portion 6a.

  In addition, the preparation point of the permeation | transmission part 6a of the electroconductive coating layer 6 is not limited to what was shown in FIG. For example, in the industrial production process, the permeation portion can be produced by allowing the slurry ink to permeate the long gas diffusion layer base material with a roll coater at a predetermined thickness.

  In the gas diffusion layer 22 of this embodiment shown in FIG. 3, the penetration thickness of the penetration portion 6 a of the conductive coating layer 6 is from a thickness corresponding to 75% of the surface roughness R of the gas diffusion layer base material 8. It is preferable to be within a range up to a half thickness of the thickness t of the gas diffusion layer substrate 8. This is because the contact resistance at the permeation portion 6a is reduced and the gas / water permeability at the permeation portion 6a and the covering portion is improved.

  Since the gas diffusion layer base material 8 is porous, the surface thereof is not flat and has a predetermined roughness. If the permeation thickness of the permeation portion 6a of the conductive coating layer 6 is less than 75% of the surface roughness R of the gas diffusion layer base material 8, the permeation portion is formed only on the convex portion of the surface roughness. Since 6a is formed, there is no effect in reducing contact resistance. Further, when the permeation thickness of the permeation portion 6 a of the conductive coating layer 6 is thicker than half the thickness of the gas diffusion layer base material 8, the permeation portion 6 a included in the gas diffusion layer base material 8. It is difficult to sufficiently fulfill the function as the gas diffusion layer substrate 8.

  Moreover, it is preferable that the thickness of the coating | coated part 6b of the electroconductive coating layer 6 exists in the range of 0-150 micrometers. The covering portion 6b can be omitted as necessary in the present invention, and the thickness of the covering portion 6b at this time is 0 μm. On the other hand, when the thickness of the covering portion 6b exceeds 150 μm, the gas permeability decreases. Therefore, in order to obtain the effect expected in the present invention, the range of 0 to 150 μm is desirable.

  The gas diffusion layer 22 of the present embodiment is preferably configured such that the average porosity of the permeation portion 6a of the conductive coating layer 6 is higher than the average porosity of the coating portion 6b. This is because the liquid water dischargeability from the covering portion 6b can be improved by such a configuration, thereby ensuring a gas permeation path and improving the gas permeability. Such adjustment of the porosity of the permeation portion 6a and the covering portion 6b is performed by adjusting the solid content contained in the ink slurry when the permeation portion 6a is produced by the process shown in FIG. It is possible to carry out by making the amount less than the covering portion.

  Next, a gas diffusion electrode according to another embodiment of the present invention will be described with reference to FIG. FIG. 5 is a schematic cross-sectional view (FIG. 5A) of the polymer fuel cell 1 using the gas diffusion layer 22 of the present embodiment, and the gas diffusion layer on the oxidant electrode side in the fuel cell 1. 22 and an enlarged cross-sectional view (FIG. 5B) schematically showing the vicinity thereof. In FIG. 5, the same members as those in FIGS. 1 to 4 are denoted by the same reference numerals, and therefore, the description overlapping with those already described is omitted below.

  In the present embodiment shown in FIG. 5, the conductive coating layer 6 has a permeation portion 6 a but does not have a coating portion. However, it can also have this coating. In this embodiment, the porosity of the permeation portion 6a of the conductive coating layer 6 is higher than the porosity of the single conductive particles contained in the material that permeates the permeation portion. As shown in a schematic enlarged view of the permeation part 6a in FIG. 5 (c), this means that the carbon fibers 61 forming the skeleton of the gas diffusion layer base material 8 into which the ink slurry is permeated in the permeation part 6a This is possible by taking a form in which conductive particles 62 (carbon particles) contained in the slurry are attached. Since the porosity in such a form is basically the porosity of the carbon fibers forming the skeleton of the gas diffusion layer base material 8, it is more than the porosity formed by the stacking of the conductive particles. High porosity. Thereby, the gas diffusion electrode of the present embodiment can increase the porosity of the permeation portion 6a and improve the discharge characteristics of gas and liquid water. The above-described embodiment can be realized by, for example, introducing an ink slurry having a low solid content into the permeation portion, and drying the permeation portion. After the drying, the introduced conductive particles 62 are held in the skeleton of the fibers 61 of the gas diffusion layer base 8, and thus have a pore distribution derived from the skeleton of the fibers 61 of the gas diffusion layer base 8. The porosity of the permeation portion 6a is increased.

  Further, in the gas diffusion electrode according to another embodiment of the present invention, the water repellency of the permeation portion 6a of the conductive coating layer 6 may be lower than the water repellency of the coating portion 6b. Such a configuration can be realized by changing the component composition of the ink slurry that permeates the permeation part 6a and the ink slurry that permeates the coating part 6b when the gas diffusion electrode is manufactured. For example, the amount of polytetrafluoroethylene contained in the carbon ink can be relatively decreased and the amount of carbon particles can be relatively increased as compared with the ink slurry to be covered with the covering portion 6b. That's fine. According to the gas diffusion electrode of the present embodiment, by improving the dischargeability of liquid water from the covering portion 6b, a gas permeation path can be secured and the gas permeability can be improved.

  Next, a gas diffusion electrode according to another embodiment of the present invention will be described with reference to FIG. FIG. 6 is a schematic cross-sectional view (FIG. 6A) of a polymer electrolyte fuel cell 1 using the gas diffusion electrode according to the present embodiment, and gas diffusion on the oxidant electrode side in the fuel cell 1. It is an expanded sectional view (Drawing 6 (b)) showing typically layer 22 and these neighborhood. In FIG. 6, the same members as those in FIGS. 1 to 4 are denoted by the same reference numerals, and therefore, the description that has already been described with respect to those members is omitted.

  In this embodiment shown in FIG. 6, the conductive coating layer 6 is provided not only on the surface facing the catalyst layer in the gas diffusion layer substrate 8 but also on the surface facing the separator 10. Specifically, on the separator 10 side, a conductive coating comprising a permeation portion 6c that has permeated from the surface of the gas diffusion layer base material 8 and a coating portion 6d formed on the surface of the gas diffusion layer base material 8 is provided. Layer 6 is provided. The permeation portion 6c and the covering portion 6d can have the same configuration as the permeation portion 6a and the covering portion 6b described so far. And the gas diffusion electrode of this embodiment reduces the contact resistance of the separator 10 and the gas diffusion layer base material 8 by providing such a conductive coating layer 6 on the side facing the separator 10. Therefore, the power generation characteristics of the battery can be improved. Although the gas diffusion electrode of the oxidant electrode has been described with reference to FIG. 6, the gas diffusion electrode of the fuel electrode can have the configuration of the present embodiment shown in FIG. 6 in the present invention.

  In the gas diffusion electrode of the present embodiment shown in FIG. 6, the conductive coating layer 6 on the side facing the separator 10 has a permeation portion 6c thickness of 10 to 50 μm and a coating portion 6d thickness of 0 to 20 μm ( 0 μm means the case where the covering portion 6 d is omitted. By making it within these ranges, gas / water permeability can be ensured while reducing the contact resistance between the separator 10 and the gas diffusion layer substrate 8.

  Next, a gas diffusion electrode according to another embodiment of the present invention will be described with reference to FIG. FIG. 7 is a schematic cross-sectional view of a gas diffusion electrode according to this embodiment. In FIG. 7, the same members as those in FIGS. 1 to 4 are denoted by the same reference numerals, and therefore, the description overlapping with those already described is omitted below.

  In the present embodiment shown in FIG. 7, the coating portion on the side facing the catalyst layer is composed of a plurality of layers having different characteristics, more specifically, a coating portion 6 b formed in contact with the infiltration portion 6 a, and this It consists of two layers with the covering part 6e formed in contact with the covering part 6b. In the present invention, the illustrated covering portion is not limited to the two-layer example, and may have a configuration of three or more layers. As described above, since the covering portion is composed of a plurality of layers having different characteristics, the liquid water dischargeability from the covering portion can be further improved. This makes it possible to secure a gas permeation path and further improve gas permeability.

  In the present embodiment shown in FIG. 7, the covering portion composed of a plurality of layers is configured such that the porosity of each layer increases stepwise from the side farther from the gas diffusion layer base material 8 toward the side closer to the gas diffusion layer base material 8. Can do. In the example of FIG. 7, it is set as the structure where the porosity of the coating | coated part 6b is larger than the porosity of the coating | coated part 6e. With such a configuration, it is possible to improve the discharge performance of the liquid water from the coating portion, thereby ensuring a gas permeation path and improving the gas permeability.

  In the present embodiment shown in FIG. 7, the covering portion composed of a plurality of layers may be configured such that the water repellency of each layer decreases stepwise from the side farther from the gas diffusion layer substrate 8 toward the side closer to the gas diffusion layer substrate 8. it can. In the example of FIG. 7, the water repellency of the cover 6b is smaller than the water repellency of the cover 6e. With such a configuration, it is possible to improve the discharge performance of the liquid water from the coating portion, thereby ensuring a gas permeation path and improving the gas permeability.

  Next, the manufacturing method of the gas diffusion electrode of this invention is demonstrated. In the gas diffusion electrode manufacturing method of the present invention, after the liquid containing the material of the permeation portion has a predetermined constant thickness on the flat plate, at least one of the gas diffusion layer substrate and the flat plate is pressed toward the other, A step of permeating the material of the permeation portion with a predetermined constant thickness from the surface of the gas diffusion layer base material can be included. An example of such a process is as described above with reference to FIG.

  A flow chart of an example of the manufacturing process of the ink slurry used for forming the conductive coating layer of the gas diffusion electrode of FIG. 4 will be described with reference to FIG. First, an aqueous surfactant solution is prepared and prepared (step S11). Next, carbon particles as conductive particles are mixed in this surfactant aqueous solution (step S12). Next, the mixed liquid is pulverized to refine the carbon particles (step S13). After pulverization, polytetrafluoroethylene (PTFE) is mixed as a water repellent material (step S14). Next, dilution water and a thickening agent are added and mixed to obtain an ink slurry (step S15).

  FIG. 9 shows a flow chart of an example of the manufacturing process of the gas diffusion electrode using the ink slurry obtained through each step of FIG. In FIG. 9, first, the gas diffusion layer base material 8 is cut out from the material of the gas diffusion layer base material to a size necessary for the gas diffusion layer base material and washed to prepare the gas diffusion layer base material 8 (step S21). Next, as shown in FIG. 4A, an ink slurry liquid film 43 for the permeation portion is formed (coated) on the surface plate 41 with a predetermined thickness (step S21). Next, by transferring the permeation portion coating ink, the permeation portion ink slurry is permeated into the gas diffusion layer base 8 as shown in FIG. 4B (step S23). Next, the carbon particles in the ink slurry that has been subjected to primary drying and baking and have permeated the permeation portion 6a are adhered to the carbon fibers of the gas diffusion layer base material 8 (step S24). Next, the ink of the covering portion is applied onto the permeation portion 6a of the gas diffusion layer base material 8 on which the permeation portion 6a is formed by baking (step S25). The covering portion ink may have the same material component composition as that of the penetrating portion ink, or may be a different material component composition. The coating of the ink on the covering portion can be performed using a conventionally known method. Next, the gas diffusion layer base material 8 on which the ink in the covering portion is formed is secondarily dried and fired to fix the carbon particles in the covering portion (step S26). The gas diffusion layer (GDL) obtained in this way is cut to a predetermined size (step S27). The gas diffusion electrode is completed through the above steps.

  Examples of gas diffusion electrodes according to the present invention will be described below.

1. Production of gas diffusion layer base material (carbon paper) (step S21)
(Preparation of gas diffusion electrode material)
Carbon paper TGP-H-060 manufactured by Toray Industries, Inc. was cut into a 10 cm square, immersed in ethanol, put into an ultrasonic cleaning device, and cleaned. After washing, it was put into a drying oven at 80 ° C. and dried for about 10 minutes.

2. Preparation of conductive coating layer (steps S11-15)
(Preparation of ink slurry)
As a surfactant, 2 g of Triton X-100 manufactured by Dow Chemical Co., Ltd. and 200 g of pure water were mixed and stirred at 150 rpm for 30 minutes with a propeller stirrer. 20 g of XC-72R carbon black was added and mixed, and the mixture was stirred with a propeller stirrer at 150 rpm for 30 minutes. The ink slurry was pulverized using a jet mill, and the carbon average particle size became 1 μm. 8 g of Polyflon D-1E manufactured by Daikin Industries is added to the ink slurry and mixed with a propeller stirrer at 150 rpm for 30 minutes. It was set as the wearing ink slurry.

3. Production of gas diffusion electrode (steps S22 to S27)
(Penetration part ink application)
On the PTFE sheet placed on the surface plate, after coating the ink slurry obtained in the ink slurry preparation described above to a thickness of 50 μm, the above-described gas diffusion layer base material (carbon paper) is applied onto the coating slurry. And then dried after pressurization. After removing the PTFE sheet, baking treatment was performed at 350 ° C. for 30 minutes.

(Coating part ink application)
After the ink slurry obtained in the preparation of the ink slurry described above was applied to have a thickness of 50 μm on the carbon layer formation of the carbon paper obtained by the above-described penetration part ink coating, it was dried and again 350 ° C. The baking process for 30 minutes was performed.

(Cutting gas diffusion electrode)
The carbon paper with a carbon layer obtained by the coating portion ink application was cut into a predetermined size to obtain a gas diffusion electrode.

4). CCM prototype (catalyst prototype)
Carbon black manufactured by Ketjen Black International Co., Ltd. 400 g of dinitrodiammine platinum aqueous solution (Pt concentration 1%) was added to 4 g of Ketjen Black EC and stirred for 1 hour. Further, 50 g of methanol as a reducing agent was mixed and stirred for 1 hour. Thereafter, the mixture was heated to 80 ° C. in 30 minutes, stirred for 6 hours as it was, and then cooled to room temperature in 1 hour. After filtering the precipitate, the obtained solid was dried under reduced pressure at 85 ° C. for 12 hours and pulverized in a mortar to obtain an electrode catalyst (average particle diameter of Pt particles 2.6 nm, Pt support concentration 50% by mass). It was.

(Preparation of catalyst layer preparation)
Five times the amount of purified water was added to the mass of the electrode catalyst obtained in the trial production of the catalyst, and a vacuum degassing operation was added for 5 minutes. To this, 0.5 times the amount of n-propyl alcohol was added, and 20% Nafion made by DuPont was added (the proton conductive polymer electrolyte solid mass ratio to the carbon mass in the electrode catalyst layer was set to 0.9). The obtained mixed slurry was well dispersed with an ultrasonic homogenizer, and a catalyst slurry was prepared by applying a vacuum degassing operation. An amount of the catalyst slurry corresponding to the desired thickness was printed on one side of the polytetrafluoroethylene sheet by screen printing and dried at 60 ° C. for 24 hours. The size of the formed catalyst layer was 5 cm × 5 cm. Further, the coating layer on the polytetrafluoroethylene sheet was adjusted so that the Pt amount was 0.2 mg / cm 2 (the average thickness of the anode catalyst layer was 6 μm).

(CCM prototype)
As a solid polymer electrolyte membrane, DuPont Nafion NRE211 (film thickness 25 μm) and an electrode catalyst layer formed on the previously prepared polytetrafluoroethylene sheet were superposed. At that time, the anode catalyst layer, the solid polymer electrolyte membrane, and the cathode catalyst layer were laminated in this order. Thereafter, hot pressing was performed at 130 ° C. and 2.0 MPa for 10 minutes, and only the polytetrafluoroethylene sheet was peeled off to obtain CCM.

5. MEA evaluation (MEA evaluation)
A fuel cell single cell is assembled using MEA in which the above gas diffusion electrode and the above CCM are joined. Atmospheric pressure, hydrogen gas is introduced into the anode electrode / air is introduced into the cathode electrode, the cell temperature is 70 ° C., and the load current density is 1 A. After performing an aging treatment at / cm2 for 12 hours, the power generation performance of the cell was evaluated.

  FIG. 10 shows the results of evaluating the power generation performance of the cell. In FIG. 10, the evaluation about what applied the ink slurry same as this invention directly on the gas diffusion layer base material about the osmosis | permeation part of a gas diffusion electrode as a comparative example is shown collectively. From FIG. 10, the power generation characteristics of the example greatly improved in both the high humidification condition and the low humidification condition as compared with the comparative example.

  As mentioned above, although the embodiment to which the invention made by the present inventors was applied has been described, the present invention is not limited by the description and the drawings that form part of the disclosure of the present invention according to this embodiment. That is, it should be added that other embodiments, examples, operation techniques, and the like made by those skilled in the art based on the above embodiments are all included in the scope of the present invention.

1 is a schematic cross-sectional view of a unit cell of a polymer electrolyte fuel cell to which a gas diffusion electrode according to the present invention is applied. It is explanatory drawing of an oxidizing agent electrode separator. It is explanatory drawing of the gas diffusion electrode of embodiment of this invention. It is explanatory drawing of the manufacturing process of the gas diffusion electrode of this invention. It is explanatory drawing of the gas diffusion electrode of embodiment of this invention. It is explanatory drawing of the gas diffusion electrode of embodiment of this invention. It is explanatory drawing of the gas diffusion electrode of embodiment of this invention. It is a flowchart of an example of the manufacturing process of an ink slurry. It is a flowchart of an example of the manufacturing process of a gas diffusion electrode. It is a graph which shows the power generation performance evaluation result of a cell.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Fuel cell 2 Polymer electrolyte membrane 3 Fuel electrode catalyst layer 4 Oxidant electrode catalyst layer 5 Conductive porous layer 6 Conductive porous layer 6a Penetration part 6b Covering part 7 Fuel electrode gas diffusion layer base material 8 Oxidant electrode Gas diffusion layer base material 9 Fuel electrode separator 10 Oxidant electrode separator

Claims (11)

A gas diffusion layer substrate;
A conductive coating layer comprising a permeation portion that has penetrated from the surface of the gas diffusion layer base material and a coating portion formed on the surface;
The gas diffusion electrode, wherein the permeation portion of the conductive coating layer has a predetermined amount of permeation thickness from the surface of the gas diffusion layer base material. The penetration thickness of the penetration portion of the conductive coating layer ranges from a thickness corresponding to 75% of the surface roughness of the gas diffusion layer base material to a half thickness of the gas diffusion layer base material. Within
2. The gas diffusion electrode according to claim 1, wherein a thickness of a covering portion of the conductive coating layer is in a range of 0 to 150 μm.   The gas diffusion electrode according to claim 1 or 2, wherein an average porosity of the permeation portion of the conductive coating layer is higher than an average porosity of the coating portion.   The porosity of the penetration part of the said conductive coating layer is higher than the porosity of the electroconductive particle single substance contained in the material osmose | permeated to this penetration part, The any one of Claims 1-3 characterized by the above-mentioned. The gas diffusion electrode according to Item.   The gas diffusion electrode according to any one of claims 1 to 4, wherein the water repellency of the permeation portion of the conductive coating layer is lower than the water repellency of the coating portion.   A gas diffusion electrode comprising the conductive coating layer according to claim 1 on not only one surface of the gas diffusion layer substrate but also the other surface.   The gas diffusion electrode according to claim 6, wherein the conductive coating layer provided on the other surface has a permeation portion thickness of 10 to 50 μm and a coating portion thickness of 0 to 20 μm. .   The gas diffusion electrode according to any one of claims 1 to 4, wherein the covering portion of the conductive covering layer is composed of a plurality of layers having different characteristics.   The gas diffusion electrode according to claim 8, wherein the covering portion of the conductive coating layer has a porosity of each layer that increases stepwise from a side farther than the gas diffusion layer base material toward a side closer to the gas diffusion layer base material. .   9. The gas diffusion electrode according to claim 8, wherein the coating portion of the conductive coating layer has a stepwise decrease in water repellency from the side farther from the gas diffusion layer base toward the side closer to the gas diffusion layer base material. A method for producing the gas diffusion electrode according to claim 1, comprising:
After the liquid containing the material of the permeation portion has a predetermined constant thickness on the flat plate, at least one of the gas diffusion layer base and the flat plate is pressed toward the other, and the material of the permeation portion is changed to the gas diffusion layer base. A method for producing a gas diffusion electrode, comprising a step of permeating at a predetermined constant thickness from a surface.

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