JP2006120461A - Membrane/electrode assembly for fuel cell and its manufacturing method, gas diffusion layer and its manufacturing method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a membrane/electrode assembly for a fuel cell and its manufacturing method advantageous for restraining a flooding phenomenon of water produced by power generation reaction blocking a gas channel, a gas diffusion layer for a fuel cell and its manufacturing method. <P>SOLUTION: The membrane/electrode assembly is formed by successively laminating a catalyst layer 601 for an oxidant, a gas diffusion layer for the oxidant with gas permeability, an electrolyte film 603, a catalyst layer for fuel, and a gas diffusion layer for fuel with gas permeability. At least either the gas diffusion layer for the oxidant or the gas diffusion layer for the fuel has gas channels and communicating holes 300 communicated with each other in a thickness direction. A hydrophilic part 500 with water absorption property is provided at least at either the catalyst layer 601 for the oxidant or a hole part contrary to the side opposing the catalyst layer for the fuel out of the communicating holes 300. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a membrane / electrode assembly for a fuel cell and a method for producing the same, a gas diffusion layer, and a method for producing the same.

  Conventionally, solid polymer fuel cells generate power by supplying a fuel gas such as hydrogen gas to the anode side and an oxidant gas such as air to the cathode side. A power generation reaction is performed using the catalyst in the catalyst layer. By this power generation reaction, water is generated in the vicinity of the catalyst layer. In order to perform a power generation reaction smoothly, it is necessary to smoothly supply gas and discharge water. Therefore, as a conventional technique, a technique of adding a water repellent material such as polytetrafluoroethylene (PTFE) to the inside or the surface of the gas diffusion electrode is used. However, as a problem in that case, since gas is supplied and discharged through the gas passage made water repellent by the water repellent material, a large amount of gas is required and a large amount of water is generated. The generated water blocks the gas passage and causes a problem of hindering the gas supply. This is a so-called flooding phenomenon. The flooding phenomenon is particularly likely to occur in a high current region. In order to alleviate the flooding phenomenon, it is effective to add a large amount of PTFE inside or on the surface of the gas diffusion electrode. However, the addition of excess PTFE causes an increase in the electrical resistance of the gas diffusion layer. Further, excessive addition of PTFE accelerates the discharge of water even in an operation in a low current density region, so that the electrolyte membrane may be dried and the proton conductivity of the electrolyte membrane may be reduced.

  The following techniques are disclosed as conventional techniques for solving such problems.

1. A technology that continuously changes the amount of water repellent material from the side of the gas diffusion layer in contact with the catalyst layer to the side of contact with the gas distribution plate. Patent Documents 1 and 2
2. A technique of forming a plurality of through-holes penetrating from one surface of the gas diffusion layer to the other surface and increasing gas permeability by the through-holes. Patent Document 3
3. A technique in which a pore-forming material for forming pores for enhancing water discharge is included in an electrode catalyst layer, and a water retention layer for enhancing water retention is provided between the catalyst layer and the diffusion layer. Patent Document 4
JP 2003-109604 A JP 2003-151565 A JP 2002-110182 A JP 2004-158387 A

  As described above. According to this technique, it is merely an extension of a technique of adding a water repellent such as PTFE to the inside or surface of a gas diffusion electrode that has been generally performed. Usually, the step of imparting water repellency to a gas diffusion electrode is performed by a method of dipping or coating a solution containing a water repellent on a carbon sheet substrate such as carbon paper or carbon cloth, and the water repellent concentration is continuous. It is common to change to. Also, depending on the impregnation method and amount of the water repellent, the water repellent concentration and the pore size may change, and an improvement effect on the flooding characteristics may be observed. This technique does not provide a solution to a fundamental problem such as a gas supply hindrance caused by the generated water blocking the gas passage. In particular, when a large amount of generated water is generated as in a high current density region, it does not provide a solution to a fundamental problem such as obstruction of gas supply due to blockage of the gas passage.

  2. As described above. With regard to the technology, the gas permeability is improved by the through-hole formed separately in the gas diffusion layer, but on the other hand, the gas is excessively supplied or the water is easily evaporated from the electrolyte membrane through the through-hole. There is a risk of excessive drying of the electrolyte membrane and a decrease in proton conductivity of the electrolyte membrane.

  3. As described above. With regard to the technology related to the above, the effect of improving the water discharge performance of the catalyst layer and the water retention of the electrolyte membrane can be expected, but the water discharged from the catalyst layer will eventually be discharged out of the membrane / electrode assembly through the diffusion layer. It is necessary to let When the flooding phenomenon occurs at the interface between the catalyst layer and the gas diffusion layer, this technique does not provide a sufficient solution to the flooding phenomenon.

  The present invention has been made in view of the above circumstances, and is a membrane / electrode assembly for a fuel cell that is advantageous for suppressing the flooding phenomenon in which water generated by a power generation reaction blocks the gas passage of the gas diffusion layer. It is another object of the present invention to provide a gas diffusion layer for a fuel cell and a method for manufacturing the same.

  (1) The inventor has been intensively developing a membrane / electrode assembly and a gas diffusion layer for a fuel cell. As shown in FIG. 12, the conventional gas diffusion layer usually has a carbon material such as carbon fiber and carbon black (CB), and forms a gas passage made water repellent by PTFE, Both gas supply and water discharge are performed through the water-repellent gas passage. The water generated by the power generation reaction becomes spherical (droplet-like) due to the effect of the water repellent, and its surface area is reduced, so that a gas supply channel in the gas diffusion electrode is secured. However, when the amount of generated water increases, the generated water tends to block the gas passage and hinder gas supply. In particular, when operating in a high current density region, the required gas and the amount of water produced are relatively greater than when operating at a low current density, as shown in FIG. The generated water blocks the gas passage and obstructs the gas supply.

  Therefore, the present inventor forms a gas passage and a communication hole communicating in the thickness direction of the gas diffusion layer for the oxidant or the gas diffusion layer for the fuel, and at least the catalyst layer for the oxidant or the fuel catalyst among the communication holes. Knowledge that a membrane / electrode assembly for a fuel cell can be provided that is advantageous in suppressing flooding if a hydrophilic portion having water absorption is provided in the hole portion on the opposite side to the side facing the layer. did.

  Further, in manufacturing at least one of the oxidant gas diffusion layer and the fuel gas diffusion layer, a first step of forming the gas diffusion layer material having the gas passage and the thickness of the gas diffusion layer material A second step of forming a communication hole communicating in the direction in the gas diffusion layer material, and at least a portion of the communication hole opposite to the side facing the oxidant catalyst layer or the fuel catalyst layer; It has been found that the above-described gas diffusion layer for a fuel cell can be provided by sequentially carrying out the third step of providing a hydrophilic portion having a.

(2) The fuel cell membrane / electrode assembly according to the present invention of aspect 1 is formed by sequentially stacking an oxidant gas diffusion layer, an oxidant catalyst layer, an electrolyte membrane, a fuel catalyst layer, and a fuel gas diffusion layer. In the membrane / electrode assembly formed as
At least one of the gas diffusion layer for oxidant and the gas diffusion layer for fuel is
With a gas passage communicating in the thickness direction and a communication hole communicating in the thickness direction,
Among the communicating holes, at least a hole portion opposite to the side facing the oxidant catalyst layer or the fuel catalyst layer is provided with a hydrophilic portion having water absorption.

(3) A method for producing a membrane / electrode assembly for a fuel cell according to the present invention of aspect 2 includes an oxidant gas diffusion layer, an oxidant catalyst layer, an electrolyte membrane, a fuel catalyst layer, and a fuel gas diffusion layer. In a manufacturing method for manufacturing a membrane-electrode assembly for a fuel cell by sequentially laminating
At least one of the gas diffusion layer for oxidant and the gas diffusion layer for fuel is
A first step of preparing a gas diffusion layer material to be one of the gas passages communicating in the thickness direction;
A second step of drilling in the gas diffusion layer material through holes communicating in the thickness direction of the gas diffusion layer material;
And a third step of sequentially providing a hydrophilic portion having water absorption in a hole portion on a side opposite to the side facing the oxidant catalyst layer or the fuel catalyst layer among the communication holes. Is.

(4) The gas diffusion layer according to the present invention of aspect 3 has one side in the thickness direction facing the catalyst layer, the other side in the thickness direction facing the gas flow plate, and supplies the gas from the gas flow plate to the catalyst layer In a gas diffusion layer for a fuel cell having gas permeability,
It has a gas passage that communicates in the thickness direction and a communication hole that communicates in the thickness direction, and at least a portion of the communication hole opposite to the side facing the catalyst layer has a hydrophilic portion having water absorption. It is characterized by this.

(5) In the method for producing a gas diffusion layer for a fuel cell according to the present invention of aspect 4, the one side in the thickness direction faces the catalyst layer, the other side in the thickness direction faces the gas flow plate, and the gas flow layer In the method for producing a gas diffusion layer for a fuel cell having gas permeability for supplying a gas of a plate to the catalyst layer,
A first step of preparing a gas diffusion layer material that has at least one of an oxidant gas diffusion layer and a fuel gas diffusion layer and has a gas passage communicating in the thickness direction;
A second step of perforating the gas diffusion layer material with a communicating hole communicating in the thickness direction of the gas diffusion layer material;
A third step of sequentially providing a hydrophilic portion having water absorption on an inner wall surface of a portion of the communication hole opposite to the side facing the catalyst layer is sequentially performed.

  (6) According to the invention according to each aspect, at least one of the oxidant gas diffusion layer and the fuel gas diffusion layer has a gas passage communicating in the thickness direction and a communication hole communicating in the thickness direction. A hydrophilic portion having water absorption is provided at least in the hole portion on the opposite side to the side facing the catalyst layer (oxidant catalyst layer or fuel catalyst layer). Water generated by a power generation reaction in the vicinity of the catalyst layer enters the communication hole by capillary action or the like, and is held in a hydrophilic portion having water absorption provided in the communication hole. Gas (generally, an oxidant gas such as air or a fuel gas such as a hydrogen-containing gas) is formed on the surface of the communication hole formed in the gas diffusion layer opposite to the side facing the catalyst layer. Since it flows, the water | moisture content currently hold | maintained at the hydrophilic part is carried to the gas downstream side by gas. As a result, the discharge of water generated by the power generation reaction in the vicinity of the oxidant catalyst layer or the fuel catalyst layer is improved, and the flooding phenomenon is suppressed. It is presumed that water generated by the power generation reaction enters the gas passage of the gas diffusion layer due to a capillary phenomenon or the like and is discharged to the outside of the gas diffusion layer also through the gas passage.

  ADVANTAGE OF THE INVENTION According to this invention, since the discharge | emission property of the water produced | generated by electric power generation reaction improves, the membrane-electrode assembly and gas diffusion layer for fuel cells which are advantageous in suppressing a flooding phenomenon can be provided.

  According to the present invention, at least one of the oxidant gas diffusion layer and the fuel gas diffusion layer has the gas passage and the communication hole. The gas passage has a three-dimensional hole structure (for example, a network structure) communicating in the thickness direction, and a structure in which the communication hole extends along the one thickness direction can be adopted. A hydrophilic portion having water absorption is provided in at least a portion of the communication hole opposite to the side facing the oxidant catalyst layer or the fuel catalyst layer. The hydrophilic portion can have conductivity in addition to water absorption. Examples of the hydrophilic part having water absorption include those having a functional group having hydrophilicity such as OH group and COOH group. Carbon black or silica tends to have hydrophilic functional groups such as OH groups and / or COOH groups on the surface, and is generally more hydrophilic than carbon fibers. In particular, carbon black has both hydrophilicity and conductivity. Furthermore, examples of the hydrophilic material constituting the hydrophilic part having water absorption include starch / acrylic acid copolymer, polyacrylate, and polyvinyl alcohol.

  Examples of the communication hole include a form formed by irradiation with a high energy density irradiation source or insertion of a needle-like member. In this case, a communication hole extending substantially straight in the thickness direction of the oxidant gas diffusion layer or the fuel gas diffusion layer can be drilled. If the communication hole extends in a straight line, the distance that the water moves when the water is discharged is presumed to be advantageous for improving the water discharge performance. Examples of the average inner diameter of the communication holes (the average inner diameter of the surface of the communication holes facing the gas distribution plate) include 0.1 to 1000 microns, 1 to 500 microns, and 5 to 100 microns. Examples of the upper limit value of the average inner diameter of the communication holes include 1000 microns, 700 microns, 500 microns, 200 microns, and 100 microns. Examples of the lower limit value that can be combined with the upper limit value of the average inner diameter of the communication holes include 0.1 micron, 1 micron, 3 microns, and 10 microns. If the inner diameter of the communication hole is too large, the electrolyte membrane may be dried excessively. If the inner diameter of the communication hole is too small, the water discharging ability may be reduced. Considering these, the average inner diameter of the communication holes can be selected as appropriate.

Examples of the high energy density irradiation source include a laser beam and an electron beam. Examples of the laser beam include a YAG laser beam, a CO ₂ laser beam, and an excimer laser beam. Examples of the needle-like member include those having a substantially uniform diameter in the length direction and those having a diameter reduced to a conical shape in the length direction. By pressurizing a gas diffusion layer material with a pressurized body having a plurality of needle-like members, if the needle-like member is inserted into the gas diffusion layer material in the thickness direction, a plurality of communication holes are combined into the gas diffusion layer material. Can be formed.

In consideration of drainage, the communication hole preferably penetrates the gas diffusion layer in the thickness direction, but it does not necessarily have to penetrate. When the thickness of the gas diffusion layer is relatively displayed as 100, the depth of the communication hole can be set to 20 to 100 and 50 to 100. The number of communication holes formed per unit area of the gas diffusion layer is different depending on the inner diameter of the communication holes, for example, 1 to 5000 / cm ² , 1 to 3000 / cm ² , and 5 to 2000. / cm ^2, 10 to 1000 pieces / cm ^2, 20 to 500 pieces / cm ^2, can be 100 to 400 cells / cm ^2, but is not limited thereto.

  Preferably, at least one of the oxidant gas diffusion layer and the fuel gas diffusion layer has a gas passage communicating in the thickness direction and a communication hole communicating in the thickness direction. The hydrophilic portion includes a first hydrophilic portion provided in at least a hole portion of the communication hole opposite to the side facing the catalyst layer, and the one surface (the one side) provided integrally with the first hydrophilic portion. And the second hydrophilic portion coated on the surface facing the gas flow plate. In this case, the hydrophilic part can exemplify a form embedded in the whole communication hole or a form in which a hole part on the opposite side of the communication hole opposite to the side facing the catalyst layer is embedded. Since the opening area of the communication hole is reduced or eliminated by the hydrophilic portion, the gas permeability is suppressed from being excessive, and therefore, the electrolyte membrane is prevented from being excessively dried. Here, the hydrophilic part can employ a form in which the entire opening of the hole part on the side opposite to the side facing the catalyst layer in the communication hole is blocked.

  According to the manufacturing method for manufacturing a fuel cell membrane / electrode assembly or gas diffusion layer according to the present invention, at least one of the oxidant gas diffusion layer and the fuel gas diffusion layer communicates in the thickness direction. A first step of preparing one gas diffusion layer material having a gas passage, a second step of drilling a gas diffusion layer material in the thickness direction of the gas diffusion layer material by a punching means, and a communication hole Of these, at least a third step of sequentially providing a hydrophilic portion having water absorption in a hole portion opposite to the side facing the oxidant catalyst layer or the fuel catalyst layer is performed.

  Preferably, the hydrophilic portion is a first hydrophilic portion provided in at least a hole portion on the side opposite to the side facing the catalyst layer in the communication hole, and the one surface provided integrally with the first hydrophilic portion. And a second hydrophilic portion coated on the surface of the one facing the gas distribution plate. The water generated by the power generation reaction can reach the second hydrophilic portion through the first hydrophilic portion existing in the communication hole. The 2nd hydrophilic part is provided in the gas distribution board side through which gas flows. Therefore, water is carried to the gas downstream side by the gas flowing through the gas distribution plate.

  According to a preferred embodiment of the present invention, in the membrane / electrode assembly and the gas diffusion layer, the gas supply and the water discharge are performed using different pores instead of using the same pores. To the goal. FIG. 1 shows a preferred embodiment. According to this embodiment, as shown in FIG. 1, the gas diffusion layer 400 is formed of an aggregate such as carbon fiber, and has a gas passage 410 formed of pores. Then, the communication hole 300 mainly functioning as the drain hole 300A is drilled by the punching means so that it penetrates the gas diffusion layer 400 in the thickness direction. In this case, the gas passage 410 and the communication hole 300 are functionally separated in the gas diffusion layer 400. That is, the gas passage 410 is mainly caused to perform the gas supply function to the catalyst layer 601 and the communication hole 300 is mainly responsible for the drainage function. In order to satisfactorily develop the capillary phenomenon in the communication hole 300 (drainage hole 300A), it is preferable to make the communication hole 300 (drainage hole 300A) hydrophilic.

  When hydrophilicity is imparted to the communication hole 300 (drainage hole 300A), when water comes into contact with the communication hole 300 (drainage hole 300A), a suction force acts due to a capillary phenomenon, and the water enters the communication hole 300 (drainage hole 300A). Is taken in. However, when the taken-in water is discharged to the outside of the communication hole 300 (drain hole 300A), the suction force due to the capillary phenomenon works, and thus the discharge of water from the drain hole 300A is inhibited. Therefore, as shown in FIG. 1, a hydrophilic portion 500 made of a hydrophilic material as a base material is disposed in the communication hole 300 (drain hole 300 </ b> A). In this case, as shown in FIG. 1, on the surface 400c of the gas diffusion layer 400 opposite to the side facing the catalyst layer 601 (that is, the surface 400c of the gas diffusion layer 400 facing the gas distribution plate 702). The hydrophilic portion 500 is preferably formed. The hydrophilic portion 500 is basically not formed on the side of the gas diffusion layer 400 that faces the catalyst layer 601. However, not only the surface 400c of the gas diffusion layer 400 opposite to the side facing the catalyst layer 601 (that is, the surface 400c of the gas diffusion layer 400 facing the gas flow plate 702), but also of the gas diffusion layer 400 The hydrophilic portion 500 can also be formed on the side facing the catalyst layer 601.

  Here, since the hydrophilic portion 500 has hydrophilicity, it absorbs water generated based on the power generation reaction in the vicinity of the catalyst layer 601 and also has a function of releasing it to the outside of the gas diffusion layer 400. Can work.

  In other words, the generated water can be guided to the surface 400c of the gas diffusion layer 400 opposite to the catalyst layer 601 (the surface 400c of the gas diffusion layer 400 facing the gas flow plate 702). Here, since the spheroidization of water is suppressed by the hydrophilic portion 500, the water discharge area can be increased by the hydrophilic portion 500, the water can be easily evaporated, and the water is effectively discharged out of the system together with off-gas. Can be made. At the same time, if the hydrophilic portion 500 based on a hydrophilic material is disposed in the communication hole 300 (drainage hole 300A), the opening of the communication hole 300 is blocked and the opening area of the communication hole 300 is reduced. Therefore, it can be expected that excessive drying of the electrolyte membrane 603 is suppressed, and the proton conductivity of the electrolyte membrane 603 can be maintained high.

According to a preferred embodiment of the manufacturing method for manufacturing the gas diffusion layer 400 described above, a gas diffusion layer having a sheet shape in which a conductive material such as carbon fiber or carbon black is mixed with a water repellent represented by a fluororesin such as PTFE. Make the material. The water-repellent gas passage 410 formed in the gas diffusion layer material is used as a gas supply channel. A gas diffusion layer material mixed with a water repellent such as PTFE can be irradiated with a high energy density beam (high energy density irradiation source, punching means) such as a YAG laser or a CO ₂ laser. In this case, a plurality of communication holes 300 that can function as drain holes are formed in the gas diffusion layer material. At this time, the gas diffusion layer material is partially burned by the heat of the high energy density beam, so that the communication hole 300 is formed. Further, the water repellent such as PTFE existing around the inner wall surface of the communication hole 300 is burned out, and the water repellency around the communication hole 300 is lost or lowered. In this state, a paste containing a hydrophilic material on the surface of the gas diffusion layer material opposite to the side facing the catalyst layer 601 (that is, the surface of the gas diffusion layer material facing the gas distribution plate 702). In the gas diffusion layer 400, the material is applied to the surface 400c of the gas diffusion layer 702 facing the gas distribution plate 702. Thereby, the hydrophilic part 500 having water absorption can be formed in the communication hole 300. The hydrophilic portion 500 can function as a water absorption / release layer that absorbs and releases the generated power generation reaction.

(First step)
First, the gas diffusion layer material according to the example is prepared. The outline of the procedure is as follows. Short fibers (thickness 13 microns, length 3 millimeters) such as carbon fibers as conductive fibers and pulp as a dissipative organic disappearance substance are mixed at a weight ratio of 6: 4 and beaten in water. Thus, a papermaking slurry (liquid material) in which carbon fibers and pulp were uniformly dispersed was produced. The papermaking slurry was made into a mesh member to prepare a paper sheet (thickness 0.3 mm). Papermaking means separating a solid substance and a liquid component contained in a papermaking slurry.

  Then, carbon black (Cabot: VALCAN XC-72R) as a conductive material and a water repellent (Daikin Industries: PTFE dispersion D-1) were mixed at a weight ratio of 2: 1 to prepare a dispersed paste. . The paste is impregnated with the roll coat on the surface of the paper sheet, dried and baked at 380 ° C., the pulp contained in the paper sheet is burned off, and then hot pressed, and the thickness is uniform in the plane. The gas diffusion layer material 100 (see FIG. 2) according to the example was prepared. The gas diffusion layer material 100 is formed of an aggregate of short fibers such as carbon fibers and carbon black, and includes a gas passage 410 that is a space gap between the short fibers such as carbon fibers and carbon black. The gas passage 410 has a three-dimensional network structure and can function as a gas supply channel.

(Second step)
As shown in FIG. 2, a gas diffusion layer material 100 (60 mm × 60 mm × 0.3 mm) described above is used by using a YAG laser oscillator 200 (Kataoka Seisakusho: Q200α) as a high energy density beam that can function as a punching means. ) Was irradiated with a laser beam 110. Thus, a plurality of communication holes 300 (diameter 0.2 mm) were drilled in the gas diffusion layer material 100 at a predetermined uniform pitch (2 mm pitch) (see FIGS. 3 and 5). The communication hole 300 penetrates straight or substantially straight along the thickness direction of the gas diffusion layer material 100. The number of communication holes 300 was 20 × 20 = 400. As described above, the gas diffusion layer material 100 is partially burned by the heat of the laser beam 110, whereby the communication hole 300 is formed. Further, the water repellent such as PTFE present around the inner wall surface of the communication hole 300 is burned out, and the water repellency at the periphery 300 f of the communication hole 300 is lost or lowered. The communication hole 300 formed by the laser beam 110 extends straight so as to penetrate along the thickness direction of the gas diffusion layer material 100.

(Third step)
A carbon black (Cabot Corporation: VALCAN XC-72R) that can function as a conductive material and a hydrophilic material, and an alkylsilicate inorganic binder (Jojo Electric: FJ803) that can function as a hydrophilic material in a solid content ratio of 1: 1.4. A mixed paste mixed at (weight ratio) was prepared. Then, as shown in FIG. 4, by using an applicator having a gap of 100 micrometers, the mixed paste is applied to the surface 100c of the gas diffusion layer material 100 facing the gas distribution plate 702, and the mixed paste is connected to the communication hole. While being inserted into 300, the opposite surface 100 c of the gas distribution plate 702 of the gas diffusion layer material 100 was covered to form the hydrophilic portion 500. The hydrophilic portion 500 is a gas that is integrated with the first hydrophilic portion 501 provided in at least the hole portion of the communication hole 300 opposite to the side facing the catalyst layer 601 and the first hydrophilic portion 501. It has the 2nd hydrophilic part 502 coat | covered by the film | membrane form on the surface 100c which the gas distribution plate 702 of the diffusion layer raw material 100 opposes. Then, the gas diffusion layer 400 was formed by heating at 100 ° C. in an air atmosphere to cure the inorganic binder.

  The water generated by the power generation reaction in the vicinity of the catalyst layer 601 is absorbed into the communication hole 300 by a capillary phenomenon or the like. Since the water is retained in the hydrophilic portion 500 having water absorption in the communication hole 300, the water moves from the first hydrophilic portion 501 to the second hydrophilic portion 502. Here, since a gas (generally, an oxidant gas such as air) flows through the gas passage 702x of the gas diffusion layer 702, moisture held in the second hydrophilic portion 502 of the hydrophilic portion 500 enters the gas passage 702x. Released and carried downstream by the gas. As a result, the discharge property of discharging the water generated by the above-described power generation reaction to the outside of the gas diffusion layer 400 is improved, and the flooding phenomenon that the water blocks the gas passage 410 of the gas diffusion layer 400 is suppressed.

  According to the present embodiment, the gas diffusion layer material 100 contains carbon black having hydrophilicity in addition to carbon fibers having poor hydrophilicity. The hydrophilic part 500 does not contain carbon fibers. Here, if the weight percentage of carbon black in the gas diffusion layer material 100 is W1, and the weight percentage of carbon black in the hydrophilic portion 500 is W2, W2 is set larger than W1 (W2> W1).

  When the water generated by the power generation reaction in the vicinity of the catalyst layer 601 is absorbed by the gas passage 410 of the gas diffusion layer 400 due to a capillary phenomenon or the like, and is discharged to the outside of the gas diffusion layer 400 through the gas passage 410 as well. Inferred. According to the present embodiment, as shown in FIG. 4, the hydrophilic portion 500 blocks at least the opening of the hole portion on the opposite side to the side facing the catalyst layer 601 in the communication hole 300, Even if gas flows to 702x, excessive drying of the electrolyte membrane 603 is suppressed, and as a result, the proton conductivity of the electrolyte membrane 603 is maintained.

(Comparative Example 1)
In Comparative Example 1, a gas diffusion layer was produced basically in the same procedure as in Example 1. However, 3. The procedure is not performed. Therefore, although the communication hole is formed in the gas diffusion layer by the laser beam, the first hydrophilic portion 501 and the second hydrophilic portion 502 are not provided because the mixed paste is not applied.

(Comparative Example 2)
In Comparative Example 2, a gas diffusion layer was basically produced by the same procedure as in Example 1. However, 2. And 3. The procedure is not performed. Therefore, the communication hole by the laser beam is not perforated, the first hydrophilic portion 501 and the second hydrophilic portion 502 are not provided, and correspond to a normal gas diffusion layer.

(Test Example 1)
In order to confirm the magnitude of the capillary phenomenon of the gas diffusion layer 400, water droplets are dropped on the hydrophilic drainage holes 300A in the gas diffusion layer 400 manufactured as described above, and the water droplets are gas diffused by the capillary phenomenon. An investigation was made as to whether or not it would be absorbed inside the layer 400. The procedure was as follows. First, the gas diffusion layer 400 was installed on the filter paper. In this case, the surface of the gas diffusion layer 400 that faces the catalyst layer is disposed on the upper side, and the surface that faces the gas distribution plate is disposed on the lower side. Then, each drop of water with a dropper, a portion of the drain hole 300A (that is, a portion filled with a hydrophilic material in a hole drilled by a laser beam; a portion aiming at a function as a drain hole in the gas diffusion layer 400) Then, water was dropped on each of the water repellent surfaces (that is, portions where the laser beam was not perforated, in other words, portions intended to function as the gas passage 410).

  And the gas diffusion layer 400 was image | photographed with the video camera from diagonally upward, and the time change of the water droplet in the gas diffusion layer 400 was observed. As an observation result, according to still images at intervals of about 0.6 seconds, the water droplets dropped on the water-repellent surface of the gas diffusion layer 400 are spherical, and even after 30 minutes, the water droplets do not change with time. In effect, the shape is maintained as it is. On the other hand, when water is dropped on the hydrophilic drainage hole 300A in the gas diffusion layer 400, the water droplet is initially spherical, but with time, it is absorbed by the hydrophilic drainage hole 300A and the size of the waterdrop. Gradually decreased, and eventually disappeared from the surface of the gas diffusion layer 400. From this, according to the gas diffusion layer 400 according to the present embodiment, the drain hole 300A formed through the laser beam irradiation process and the coating process has a function of discharging water by a capillary phenomenon as expected. I understood.

(Test Example 2)
A fuel cell membrane / electrode assembly (MEA) using the gas diffusion layer produced by the procedure of the above-described embodiment, the gas diffusion layer according to Comparative Example 1, and the gas diffusion layer according to Comparative Example 2 Was made. As shown in FIG. 6, the MEA 600 is formed by sequentially stacking an oxidant catalyst layer 601, an oxidant gas diffusion layer 401, an electrolyte membrane 603, a fuel catalyst layer 605, and a fuel gas diffusion layer 402. . The oxidant gas diffusion layer 401 is formed of the gas diffusion layer 400 subjected to the above-described perforation process and coating process, and has conductivity and gas permeability, and communicates in the thickness direction thereof. Thus, a plurality of communication holes 300 (not shown in FIG. 6) drilled with a laser beam are provided. A hydrophilic portion 500 having water absorption is provided on an inner wall surface of a portion of the communication hole 300 of the oxidant gas diffusion layer 401 opposite to the side facing the oxidant catalyst layer 601. As shown in FIG. 1, the hydrophilic portion 500 includes a first hydrophilic portion 501 provided so as to close at least a hole portion of the communication hole 300 opposite to the side facing the catalyst layer 601, And a film-like second hydrophilic portion 502 provided integrally with the hydrophilic portion 501. The fuel gas diffusion layer 402 is formed of a gas diffusion layer that has not been subjected to the above-described perforation process and coating process, and has conductivity and gas permeability.

  Then, a power generation operation was actually performed as a fuel cell, and it was examined whether or not the mitigation of the flooding phenomenon of the gas diffusion layer 400 could be observed. The evaluation procedure is as follows.

First, a catalyst layer containing platinum-supported carbon (Johnson McKay: HiSPEK 4000) in which platinum is supported on carbon black and a polymer electrolyte (Asahi Kasei: SS-1080) is formed on both surfaces of the electrolyte membrane (DuPont: Nafion 112). Was transferred by hot pressing (temperature: 130 ° C., pressure: 3 MPa). Thereafter, the gas diffusion layer produced by the procedure of the example, the gas diffusion layer according to Comparative Example 1, and the gas diffusion layer according to Comparative Example 2 were each set to a size of 36 millimeters in diameter (area 10 cm ² ). The gas diffusion layers 401 and 402 were joined to the two catalyst layers 601 and 605 transferred to the electrolyte membrane 603 by hot pressing (120 ° C., 3 MPa), respectively, and the MEA 600 was manufactured.

The produced MEA 600 was sandwiched between a fuel gas distribution plate 701 and an oxidant gas distribution plate 702 to form a single cell fuel cell. As shown in FIG. 6, the fuel gas distribution plate 701 has a fuel passage 701 x facing the fuel gas diffusion layer 402. The gas distribution plate 702 for the oxidant gas has an oxidant gas passage 702x that faces the gas diffusion layer 401 for the oxidant. FIG. 6 schematically shows a cross-sectional structure of a single cell fuel cell. The fuel cell was evaluated for discharge. As the discharge conditions, the anode gas / cathode gas was pure hydrogen (1.2 atm) / pure oxygen (1.2 atm). 1.2 atm corresponds to 1.2 × 10 ⁵ Pa. The gas utilization was 80% for the anode, 75% and 30% for the cathode. Table 1 shows humidification conditions.

(Test results)
A flooding phenomenon is likely to occur in a high current density region, and when the output is less than 0.4 volts, the cell voltage rapidly decreases due to the flooding phenomenon. As an index indicating the characteristics of the flooding phenomenon, the current density is increased at a constant rate of 1 ampere / cm ² / min to cause the flooding phenomenon, and the current density (flooding current value) when the cell voltage crosses 0.35 volts. We decided to do the evaluation according to the size.

FIG. 7 shows the current density (flooding current value) at a cell voltage of 0.35 volts and the cell resistance at a current density of 0.5 amperes / cm ² under each discharge condition. The vertical axis in FIG. 7 indicates operating conditions (dry, middle, wet). Here, the value of U indicates the gas utilization rate at the cathode. The horizontal axis in FIG. 7 shows the current density when the cell voltage crosses 0.35 volts (flooding current value) and the cell resistance at a current density of 0.5 amperes / cm ² . The bar graph shows the flooding current value, and the line graph shows the cell resistance. This cell resistance corresponds to the dryness of the electrolyte membrane. In general, if the humidification condition is dry, the flooding phenomenon is unlikely to occur, but if the humidification condition is wet, the flooding phenomenon is likely to occur. Here, as described above, the gas diffusion layer according to Comparative Example 1 has been subjected to drilling with a laser beam, but has not been applied with the hydrophilic portion 500 based on a hydrophilic material. It is. As described above, the gas diffusion layer according to Comparative Example 2 is an unprocessed (ordinary gas diffusion layer) in which neither drilling by a laser beam nor coating of a hydrophilic material is performed.

  As can be understood from the test results of FIG. 7, the gas diffusion layer according to the example is the same as the gas diffusion layer according to Comparative Example 1 and the gas diffusion layer according to Comparative Example 2 in any of dry, middle, and wet conditions. Compared to this, it was found that a high current value was developed and an improvement effect of reducing the flooding phenomenon was observed. Furthermore, regarding the cell resistance corresponding to the dryness of the electrolyte membrane, the gas diffusion layer according to Comparative Example 2 in which the perforation treatment was not performed was the best. Both the gas diffusion layer according to the example and the gas diffusion layer according to comparative example 1 are subjected to the perforation process, but the cell resistance in the gas diffusion layer according to the example is lower than that in the gas diffusion layer according to comparative example 1. It was good. This is presumably due to the fact that in the gas diffusion layer according to the example, excessive drying of the electrolyte membrane is suppressed, and the ion conductivity is ensured to be high.

  FIG. 8 shows a second embodiment. The second embodiment basically has the same configuration and operation effect as the first embodiment. Hereinafter, a description will be given centering on portions different from the first embodiment. As shown in FIG. 8, the hydrophilic portion 500 includes a first hydrophilic portion 501 embedded in almost the entire communication hole 300 drilled with a laser beam, and the first hydrophilic portion 501 integrally provided on the one surface. And a film-like second hydrophilic portion 502 that is covered. In this way, the hydrophilic portion 500 closes the entire hole portion of the communication hole 300.

  That is, as shown in FIG. 8, not only the surface 400c of the gas diffusion layer 400 opposite to the side facing the catalyst layer 601 (that is, the surface 400c of the gas diffusion layer 400 facing the gas distribution plate 702). The hydrophilic portion 500 having hydrophilicity is also formed on the gas diffusion layer 400 on the side facing the catalyst layer 601.

  In forming the hydrophilic portion 500, carbon black (Cabot Corporation: VALCAN XC-72R) that can function as a hydrophilic material and an alkyl silicate inorganic binder (Joban Electric: FJ803) that can function as a hydrophilic material in a solid content ratio. A mixed paste mixed at 1: 1.4 (weight ratio) was prepared. Then, the mixed paste is applied to the surface 100c of the gas diffusion layer material 100 facing the gas flow distribution plate by an applicator having a gap of 100 micrometers, and the gas diffusion is performed while filling the communication holes 300 with the mixed paste. A surface portion 100c of the gas distribution plate of the layer material 100 facing the surface 100c was coated to form a hydrophilic portion 500. Then, the gas diffusion layer 400 was formed by heating at 100 ° C. in an air atmosphere to cure the inorganic binder.

  Also in this embodiment, the water generated by the power generation reaction enters the communication hole 300 by a capillary phenomenon or the like, and is held in the hydrophilic part 500 having water absorption existing in the communication hole 300. The surface of the communication hole 300 formed in the gas diffusion layer 400 opposite to the side facing the oxidant catalyst layer 601, that is, the side of the gas diffusion layer 400 facing the gas flow plate 702. Since a gas (generally, an oxidant gas such as air) flows on the surface 400c, the water held in the hydrophilic portion 500 is carried to the gas downstream side by the gas. As a result, the discharge of water generated by the power generation reaction is improved, and the flooding phenomenon is suppressed.

  Also in this embodiment, since the entire hole portion of the communication hole 300 is closed with the hydrophilic portion 500, it is when the oxidant gas such as air flows through the oxidant gas passage 702x of the oxidant gas flow distribution plate 702. However, excessive drying of the electrolyte membrane 603 is suppressed.

  9 and 10 show a third embodiment. The third embodiment basically has the same configuration and operation effect as the first embodiment. Hereinafter, a description will be given centering on portions different from the first embodiment. In this embodiment, as shown in FIG. 9, a pressurizing body 800 having a plurality of needle-like members 801 is prepared. The needle-like member 801 has a conical surface 801f whose outer diameter decreases toward the tip, and can be formed using metal or ceramic as a base material. A plurality of communication holes 300 </ b> B were formed by pressing the pressure member 800 against the gas diffusion layer material 100 and inserting the needle-like member 801 of the pressure body 800 into the gas diffusion layer material 100. In this case, a plurality of communication holes 300B can be obtained and drilled. As shown in FIG. 10, as in the other embodiments, the hydrophilic portion 500 includes a first hydrophilic portion 501 provided in a hole portion on the opposite side of the communication hole 300 from the side facing the catalyst layer 601. And a film-like second hydrophilic portion 502 coated on the surface 400 c of the gas diffusion layer 400 so as to be integrated with the first hydrophilic portion 501. As shown in FIG. 10, the hydrophilic portion 500 faces at least the hole portion of the communication hole 300 </ b> B opposite to the side facing the catalyst layer 601 (that is, the gas distribution plate 702 in the gas diffusion layer 400. Since the surface side hole portion) is blocked, excessive drying of the electrolyte membrane 603 is suppressed.

  FIG. 11 shows a fourth embodiment. The fourth embodiment basically has the same configuration and operational effects as the first embodiment. Hereinafter, a description will be given centering on portions different from the first embodiment. In the present embodiment, as shown in FIG. 11, the hydrophilic portion 500 includes a first hydrophilic portion 501 embedded so as to close the entire communication hole 300, and a gas that is integrated with the first hydrophilic portion 501. And a film-like second hydrophilic portion 502 coated on the surface 400 c of the diffusion layer 400.

(Other examples)
According to each of the embodiments described above, the oxidant gas diffusion layer 401 has the gas passage 410 communicating in the thickness direction and the communication hole 300 communicating in the thickness direction, and the hydrophilic portion 500 having water absorption is formed in the communication hole 300. However, the present invention is not limited thereto, and a communication hole may be formed in the fuel gas diffusion layer 402 and a hydrophilic portion having water absorption may be provided in the communication hole. In addition, the present invention is not limited to the embodiments described above and shown in the drawings, and can be implemented with appropriate modifications without departing from the scope of the invention.

  The present invention can be used, for example, for a fuel cell for a vehicle, a fuel cell for an industrial device, a fuel cell for an electronic device, a fuel cell for an electrical device, and a fuel cell for home use.

It is sectional drawing which shows the state which laminated | stacked the catalyst layer and the gas diffusion layer on the electrolyte membrane. It is sectional drawing of the state which has irradiated the laser beam to the gas diffusion layer raw material. It is sectional drawing of the state which formed the communicating hole in the gas diffusion layer raw material by irradiation of the laser beam. It is sectional drawing of the state which provided the hydrophilic part in the communicating hole formed in the gas diffusion layer raw material by laser beam irradiation. It is a top view of a gas diffusion layer. It is sectional drawing of the fuel cell of a single cell. It is a graph which shows a current density and cell resistance. FIG. 6 is a cross-sectional view showing a state in which a catalyst layer and a gas diffusion layer are stacked on an electrolyte membrane according to Example 2. It is sectional drawing which concerns on Example 3 and shows the state which formed the communicating hole in the gas diffusion layer with the pressurization body which has a needle-shaped member. It is sectional drawing which concerns on Example 3 and shows the state which formed the communicating hole in the gas diffusion layer with the acicular member, and provided the hydrophilic part in the communicating hole. It is sectional drawing which concerns on Example 4 and shows the state which has embedded the hydrophilic part in the whole communicating hole formed in the gas diffusion layer. It is sectional drawing which concerns on a prior art and shows the discharge form of the produced water in a gas diffusion layer. It is sectional drawing which shows the discharge form of the produced water in the gas diffusion layer which concerns on a prior art and is related to the prior art in a high current density area | region.

Explanation of symbols

  In the figure, 100 is a gas diffusion layer material, 210 is a laser beam, 300 is a communication hole, 300A is a drain hole, 400 is a gas diffusion layer, 410 is a gas passage, 500 is a hydrophilic portion, 501 is a first hydrophilic portion, and 502 is The second hydrophilic portion, 600 is MEA, 401 is an oxidant gas diffusion layer, 402 is a fuel gas diffusion layer, 600 is an MEA, 601 is an oxidant catalyst layer, 603 is an electrolyte membrane, 605 is a fuel catalyst layer, Reference numeral 701 denotes a fuel gas distribution plate, 702 denotes an oxidant gas distribution plate, 800 denotes a pressurized body, and 801 denotes a needle-like member.

Claims (9)

In the membrane / electrode assembly formed by sequentially laminating an oxidant gas diffusion layer, an oxidant catalyst layer, an electrolyte membrane, a fuel catalyst layer, and a fuel gas diffusion layer,
At least one of the oxidant gas diffusion layer and the fuel gas diffusion layer is:
With a gas passage communicating in the thickness direction and a communication hole communicating in the thickness direction,
For the fuel cell, a hydrophilic portion having water absorption is provided in at least a hole portion of the communication hole opposite to the side facing the oxidant catalyst layer or the fuel catalyst layer. Membrane / electrode assembly.   2. The membrane / electrode for a fuel cell according to claim 1, wherein the gas passage has a three-dimensional hole structure communicating in the thickness direction, and the communication hole extends along the one thickness direction. Joined body.   3. The membrane / electrode assembly for a fuel cell according to claim 1, wherein the communication hole is formed by irradiation with a high energy density irradiation source or insertion of a needle-like member.   The membrane / electrode assembly for a fuel cell according to any one of claims 1 to 3, wherein the hydrophilic portion has water absorption and conductivity.   5. The hydrophilic portion according to claim 1, wherein the hydrophilic portion is a portion of the communication hole opposite to the side facing at least the oxidant catalyst layer or the fuel catalyst layer. A first hydrophilic portion provided on the first hydrophilic portion, and a surface of the first hydrophilic portion that is provided integrally with the first hydrophilic portion and that is opposite to the side facing the oxidant catalyst layer or the fuel catalyst layer. A membrane-electrode assembly for a fuel cell, comprising a second hydrophilic portion.   6. The hydrophilic portion according to claim 1, wherein the hydrophilic portion is a hole on a side opposite to at least a side of the communication hole facing the oxidant catalyst layer or the fuel catalyst layer. A membrane / electrode assembly for a fuel cell, wherein the portion is closed. In the manufacturing method of manufacturing a membrane-electrode assembly for a fuel cell by sequentially stacking an oxidant gas diffusion layer, an oxidant catalyst layer, an electrolyte membrane, a fuel catalyst layer, and a fuel gas diffusion layer,
At least one of the oxidant gas diffusion layer and the fuel gas diffusion layer is:
A first step of preparing a gas diffusion layer material to be one of the gas passages communicating in the thickness direction;
A second step of perforating the gas diffusion layer material with a communicating hole communicating in the thickness direction of the gas diffusion layer material;
By sequentially performing at least a third step of providing a hydrophilic portion having water absorption in a hole portion on the opposite side of the communication hole from the side facing the catalyst layer for oxidant or the catalyst layer for fuel. A method for producing a membrane-electrode assembly for a fuel cell, wherein the membrane-electrode assembly is formed. A gas diffusion layer for a fuel cell having one side in the thickness direction facing the catalyst layer, the other side in the thickness direction facing the gas distribution plate, and having gas permeability for supplying the gas from the gas distribution plate to the catalyst layer In
A gas passage that communicates in the thickness direction and a communication hole that communicates in the thickness direction, and a hydrophilic portion having water absorption is provided in at least a hole portion of the communication hole opposite to the side facing the catalyst layer. A gas diffusion layer for a fuel cell. A gas diffusion layer for a fuel cell having one side in the thickness direction facing the catalyst layer, the other side in the thickness direction facing the gas distribution plate, and having gas permeability for supplying the gas from the gas distribution plate to the catalyst layer In the manufacturing method of
A first step of preparing a gas diffusion layer material that has at least one of an oxidant gas diffusion layer and a fuel gas diffusion layer and has a gas passage communicating in the thickness direction;
A second step of perforating the gas diffusion layer material with a communicating hole communicating in the thickness direction of the gas diffusion layer material;
And a third step of sequentially providing a hydrophilic portion having water absorption on an inner wall surface of a portion of the communication hole opposite to the side facing the catalyst layer. A method for producing a gas diffusion layer.

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