JP2005216511A - Method of manufacturing gas diffusion member for fuel cell - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method of manufacturing gas diffusion member for fuel cell, which improves gas permeability of a gas diffusion member. <P>SOLUTION: The method includes a sheet-forming step for forming a sheet which holds a pore-forming agent inside a porous sheet body having a conductor with corrosion resistance as a substrate; and a pore-making step for heating the sheet after undergoing the sheet-forming step, and for transpiring the pore-forming agent with which the sheet is impregnated, and which has a fluidity. An agent containing a polymeric material such as polyvinyl alcohol as a main ingredient can be used as the pore-making agent with a fluidity. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

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

  Conventionally, as a method of manufacturing a joined body in which an electrode and an electrolyte membrane are joined, a solid powder of a metal such as zinc, aluminum, or chromium or a metal salt thereof and carbon carrying a catalyst on an outer surface are mixed. A sheet-like gas diffusion electrode is formed, and then the sheet-like gas diffusion electrode and the sheet-like polymer electrolyte membrane are joined and integrated with each other by hot pressing. Boiled in (sulfuric acid) to dissolve and remove the metal or metal salt contained in the gas diffusion electrode, thereby producing a joined body of the gas diffusion electrode and the electrolyte membrane having pores inside. A method has been proposed (Patent Document 1). In this case, a solid powder of a metal or a metal salt thereof can function as a pore forming agent.

In addition, as a method of manufacturing a joined body in which an electrode and an electrolyte membrane are joined, a solid pore-forming agent that is needle-shaped with iron is formed, and carbon carrying a catalyst on the outer surface is mixed with the pore-forming agent. A paste-like ink, and the ink is applied to form a sheet-like gas diffusion electrode, and then dried in a state in which a magnetic field perpendicular to the sheet surface is applied, and then the gas diffusion electrode and The sheet-like polymer electrolyte membrane is joined and integrated with each other by hot pressing, and then the gas diffusion electrode is immersed in a strongly acidic aqueous solution (dilute sulfuric acid) and boiled, and the metal contained in the gas diffusion electrode or A method has been proposed in which a metal salt is dissolved and removed, thereby producing a joined body of a gas diffusion electrode having pores and an electrolyte membrane (Patent Document 2).
Japanese Patent Laid-Open No. 10-189005 JP-A-10-189012

  According to the gas diffusion member for a fuel cell described above, further improvement in gas permeability in the gas diffusion member is required.

  This invention is made | formed in view of the above-mentioned situation, and makes it a subject to provide the manufacturing method of the gas diffusion member for fuel cells advantageous for improving the gas permeability in a gas diffusion member.

  The inventor has been eagerly developing a gas diffusion member for a fuel cell. And it was discovered that the use of a pore-forming agent having fluidity is advantageous for enhancing gas gas permeability in the gas diffusion member, and it was confirmed by a test to complete the present invention. In particular, we found that using a pore-forming agent having fluidity, which is mainly composed of a polymer material typified by polyvinyl alcohol, is advantageous in improving gas gas permeability in a gas diffusion member, and confirmed by tests. The present invention has been completed.

  The reason why the gas permeability in the gas diffusion member can be improved is not necessarily clear, but the pore-forming agent has fluidity with the required viscosity and fluidity, unlike the case where the pore-forming agent is solid particles. In the gas diffusion member, the pore former having fluidity is continuously extended for a long time and easily entangled, and the ratio of pores becoming isolated pores is reduced. This is presumed to be because continuous pores are easily formed.

  In addition, it is presumed that the pore-forming agent has fluidity mainly composed of a polymer material, and the polymer chain constituting the polymer material is continuously extended and easily entangled and easily becomes continuous pores. Is done.

  That is, the method for manufacturing a gas diffusion member for a fuel cell according to the first aspect of the present invention provides a sheet forming method in which a sheet holding a fluid pore forming agent is formed inside a sheet body having a corrosion-resistant conductor as a base material. And a pore-forming step of forming pores by heating the sheet that has undergone the sheet-forming step and evaporating the pore-forming agent held inside the sheet to the outside of the sheet It is.

  According to a second aspect of the present invention, there is provided a method of manufacturing a gas diffusion member for a fuel cell, in which a fluid pore former having a polymer material as a main component is held in a sheet body having a corrosion-resistant conductor as a base material. A sheet forming step for forming the sheet, and a hole forming step for heating the sheet that has undergone the sheet forming step to evaporate the polymer material inside the sheet to the outside of the sheet to form pores. To do.

  According to a third aspect of the present invention, there is provided a method for producing a gas diffusion member for a fuel cell, comprising: a sheet forming step of forming a sheet holding a fluid pore-forming agent inside a sheet body having a corrosion-resistant conductor as a base; An arrangement step of arranging a conductive layer containing a conductive material on the surface of the sheet that has undergone the sheet formation step, and heating the sheet that has undergone the arrangement step, and removing the pore-forming agent held inside the sheet from the outside of the sheet And a pore-forming step for forming pores by evaporation.

  According to the method of the present invention, in the sheet forming step, a sheet is formed by holding a fluid pore forming agent in the porous sheet body. The sheet body is made of a conductive material having corrosion resistance. The conductor having corrosion resistance is preferably in the form of a carbon material or fiber, and therefore, carbon fiber and carbon particles are typical.

  As the pore-forming agent having fluidity used in the method of the present invention, those which are thermally decomposed by heating and are evaporated are preferable. Therefore, as the pore-forming agent having fluidity, preferably, the pore-forming agent having fluidity whose main component is a polymer material can be employed. In this case, as the pore-forming agent having fluidity, one having fluidity obtained by dissolving or dispersing a polymer material in a solvent or a dispersion medium can be adopted. The polymer material is preferably a water-soluble polymer material.

  The polymer material described above can be at least one selected from polyvinyl alcohol (PVA), polyethylene oxide, polyvinyl pyrrolidone, polyethylene glycol, polyacrylamide, polyvinyl methyl ether, cellulose, starch, gelatin, and wax. Examples of cellulose include water-soluble fiber derivatives such as methyl cellulose, carboxymethyl cellulose, and hydroxyethyl cellulose.

  As the above-mentioned solvent or dispersion medium, an aqueous solvent or an organic solvent can be exemplified. For example, it can be at least one selected from water, methanol, ethanol, propanol, benzene, acetone, butanone, decalin, toluene, butyrolactone, formamide, n-hexane, ethylene glycol, dimethyl sulfoxide, and pentanediol. In general, polyvinyl alcohol is hardly soluble in an organic solvent, but is soluble in water.

  In general, the degree of polymerization (molecular weight) of a polymer material affects the solubility, dispersibility, viscosity, adhesiveness, etc. in a solvent or dispersion medium. If the degree of polymerization (molecular weight) and / or blending amount of the polymer material increases, the viscosity of the fluid pore-forming agent containing the polymer material as the main component increases, and the rate of adhesion to the exposed surface of the sheet increases. However, there may be a tendency that the impregnation property that the pore forming agent having fluidity impregnates the inside of the sheet is lowered.

  On the other hand, if the degree of polymerization (molecular weight) and / or blending amount of the polymer material is too small, the viscosity of the pore-forming agent having flowability mainly composed of the polymer material becomes low, and the polymer material Although the pore forming agent having fluidity as a main component impregnates the inside of the sheet, it may flow out of the sheet excessively due to the influence of gravity or the like. If the degree of polymerization (molecular weight) of the polymer material is appropriate, it is possible to suppress excessive adhesion to the exposed surface of the sheet and excessive outflow from the inside of the sheet due to the influence of gravity or the like. Furthermore, the entanglement of the solid content of the fluid pore former mainly composed of a polymer material and the entanglement of the polymer chain are good, which is advantageous for forming two-dimensional or three-dimensional continuous pores. is there. In consideration of such circumstances, it is preferable to adjust the degree of polymerization (molecular weight) and / or the amount of the polymer material.

  For polymer materials such as polyvinyl alcohol, if the degree of polymerization (molecular weight) increases, the solubility decreases, and the tendency of the sheet to impregnate decreases. Moreover, in order to improve the solubility or decomposability | degradability of polymer materials, such as polyvinyl alcohol, the temperature of a solvent or a dispersion medium can be raised from normal temperature. In this case, the amount of the polymer material such as polyvinyl alcohol, which is a pore-forming agent, is increased in the interior of the sheet, so that the proportion of pores is increased, which is advantageous in improving gas gas permeability. In this case, the temperature of the solvent or dispersion medium may be 100 ° C. or higher. When water is used as a solvent or dispersion medium for dissolving or dispersing the polymer material, warm water or hot water (70 ° C. or higher) at room temperature or higher can be used depending on circumstances.

  As for polyvinyl alcohol, the degree of polymerization may be 200 to 6000, and particularly 300 to 4000, 400 to 2500, and 450 to 1500, but is not limited thereto. Examples of the polyvinyl alcohol include those having a saponification degree of 55 to 99 mol%, particularly 75 to 99 mol%. The polyvinyl alcohol may be a modified polyvinyl alcohol obtained by copolymerizing a hydrophilic monomer in order to adjust solubility or the like.

  Further, the viscosity of the pore-forming agent having fluidity varies depending on the type of polymer material, the type of solvent or dispersion medium, the type of sheet, etc., but 1 to 50 cP or 1 to 30 cP (measurement method: A viscosity measuring method using a coaxial cylinder) can be exemplified, but is not limited thereto.

  As the concentration of the pore former having fluidity, when the pore former having fluidity is 100%, the concentration of the polymer material includes the kind of polymer material, the kind of solvent or dispersion medium, the sheet Although it differs depending on the type and the like, it can be exemplified by 0.1 to 30 wt%, 0.1 to 15 wt%, 0.2 to 10 wt%, and 0.3 to 5 wt%, but is not limited thereto.

  The sheet forming step according to the method of the present invention preferably uses a fluid pore former and a primary sheet based on a corrosion-resistant conductor, and uses the fluid pore former as the primary sheet. It is carried out by impregnating the inside of the. In this case, the primary sheet can be porous. The primary sheet is immersed in the fluid pore former, the fluid pore former is applied to the exposed surface of the primary sheet, or the fluid pore former is applied to the primary sheet exposed surface. Can be sprayed. In addition, after impregnating the inside of a primary sheet with the pore forming agent which has fluidity | liquidity, the drying operation which dries a primary sheet can be performed. This promotes the solidity of the pore former impregnated in the primary sheet. Therefore, even when the concentration of the pore-forming agent is low, it is advantageous for allowing the pore-forming agent to remain in the primary sheet and for forming pores.

  As described above, the pore former can contain a polymer material as a main component. As described above, the polymer material is preferably a water-soluble polymer material. In the case of a water-soluble polymer material, the solvent or dispersion medium becomes water, which is advantageous in terms of cost and operation. Examples of the primary sheet include carbon paper and carbon cloth. Carbon paper means a sheet in which a liquid component and a carbon fiber are separated from a raw material containing a carbon fiber, which is a conductor having corrosion resistance, and a liquid component by a papermaking process, and the carbon fibers are accumulated. Carbon cloth is meant to include woven and non-woven fabrics.

  In the sheet forming step according to the method of the present invention, the sheet may be formed directly from a raw material obtained by mixing a pore forming agent having fluidity and a conductor (such as carbon fiber) having corrosion resistance.

  According to the method of the present invention, a hole forming step is carried out in which the sheet having undergone the sheet forming step is heated to evaporate the pore forming agent held inside the sheet to the outside of the sheet to form pores. The heating temperature for heating the sheet may be any temperature that evaporates the pore-forming agent held inside the sheet to the outside of the sheet, and differs depending on the type of the pore-forming agent, for example, 280 ° C. or more, It can be 300 degreeC or more. As will be described later, pores can be formed by evaporating the pore former held inside the sheet to the outside of the sheet by sintering the water repellent material.

  An arrangement | positioning process is a process of arrange | positioning the electrically conductive layer containing an electrically conductive material on the exposed surface of the sheet | seat which passed through the sheet | seat formation process. As the conductive layer containing a conductive material, a conductive paste can be used. Examples of the conductive material include carbon materials such as carbon black. The conductive paste can be applied containing a conductive material. The conductive paste preferably contains a water repellent material in addition to the conductive material. Examples of the water repellent material include known fluororesins. When the pore-forming agent evaporates so as to penetrate through the conductive layer in the pore-forming step, pores that communicate with the pores of the gas diffusion member are also formed in the conductive layer, and the gas permeability can be improved.

  The fuel cell according to the present invention includes the fuel cell gas diffusion member formed in any one of the claims. According to this gas diffusion member, since gas permeability is good, it is advantageous for improving the power generation output of the fuel cell.

  According to the manufacturing method according to the present invention, gas permeability in the gas diffusion member is improved. In particular, the vertical gas permeability and the in-plane gas permeability in the gas diffusion member are improved.

  The reason why the gas permeability in the gas diffusion member can be improved is not necessarily clear, but as described above, unlike the case where the pore forming agent is solid particles, the fluidity having the required viscosity and fluidity is obtained. Therefore, it is presumed that the pore forming agent having fluidity is continuously extended and entangled, so that it is easy to form continuous pores. In addition, a fluid pore-forming agent mainly composed of a polymer material, and the polymer chains constituting the polymer material are continuously extended and intertwined, so that the ratio of pores to isolated pores is high. This is presumed to be due to a decrease in the formation of continuous pores.

  Embodiments according to the present invention will be specifically described based on respective examples with reference to the drawings.

(Example 1)
FIG. 1 is a flowchart showing a process for manufacturing a gas diffusion member. According to Example 1, 500 g of water (temperature: 80 to 90 ° C.) was mixed with 10 g of polyvinyl alcohol (corresponding to a water-soluble polymer material, Wako, polymerization degree 500). A molecular aqueous solution (polyvinyl alcohol aqueous solution, corresponding to a fluid pore-forming agent) was prepared. A blending amount of 10 g of polyvinyl alcohol corresponds to 2% with respect to 500 g of water ((10 g / (500 g + 10 g) × 100% ≈2 wt%)).

 In addition, when the blending amount of polyvinyl alcohol was 10 g, the viscosity of the polyvinyl alcohol aqueous solution was considerably low and was close to the viscosity of water.

  By immersing carbon paper in this polymer aqueous solution (temperature: normal temperature) in the air atmosphere, the polymer aqueous solution is made into carbon paper (Toray Industries, Inc., TORAYCA TGP-H-060, 200 mm x 250 mm, thickness 180 μm) Then, the carbon paper impregnated with polyvinyl alcohol was placed in a drying furnace (atmospheric pressure) maintained at a temperature of 70 ° C. and held for 30 minutes to dry the carbon paper. In this case, a solid content of an aqueous polyvinyl alcohol solution (corresponding to a fluid pore-forming agent having a polymer material as a main component) remains in the carbon paper.

  In addition, 106 g of dispersion stock solution (trade name: POLYFLON Dl grade) is added to 500 g of carbon black paste by weight (made by Gokoku, PSM black 12134, equivalent to conductive material), and the mixture is further stirred for a while. A paste (dispersion) was produced as a conductive paste. This dispersion stock solution has a content concentration of ethylene tetrafluoride (hereinafter referred to as PTFE, manufactured by Daikin Industries, Ltd., water repellent material) of 60 wt%.

  As described above, the carbon paste (carbon ink) was applied to both surfaces of the carbon paper in which the polyvinyl alcohol aqueous solution remained, and conductive layers were disposed on both surfaces of the carbon paper (see FIG. 3A). In this case, since the solid content of polyvinyl alcohol is present inside the carbon paper, the carbon paste is prevented from being impregnated from the exposed surface of the carbon paper, and the pores inside the gas diffusion member are closed. It is thought that it can be prevented.

  Next, carbon paper coated with carbon paste was placed in a drying furnace (atmospheric pressure) maintained at a temperature of 70 ° C. and held for 30 minutes, and the carbon paper was temporarily dried. Thereafter, this carbon paper was held at a sintering temperature of 380 ° C. for 60 minutes to sinter the carbon paste PTFE. As a result, pores were actively formed inside the carbon paper to produce a gas diffusion member.

  FIG. 4 schematically shows a state where the internal structure of the gas diffusion member manufactured as described above is observed. As shown in FIG. 4, the gas diffusion member (1) has a base material layer (10) made of carbon paper and a conductive layer (12) coated on both surfaces of the base material layer (10). In the base material layer (10) and the conductive layer (12), a large number of pores through which the fuel or oxidant gas passes are generated. In particular, when the cross section and the surface of the gas diffusion member are observed with a microscope, the pores in the base material layer (10) extend well in the in-plane direction of the base material layer (10). It seems that the air permeability is improved. Thereby, the uniformity of the gas permeability in the surface direction in the gas diffusion member is improved.

  And the carbon ink solid content of the gas diffusion member was measured by weight measurement. The carbon ink solid content α was determined as follows. The weight of the gas diffusion member after sintering PTFE was set to W1. The weight of the carbon paper before impregnating with polyvinyl alcohol was set to W2. And it calculated | required at (W1-W2 / W1) * 100%. The polyvinyl alcohol impregnated in the carbon paper is assumed to be completely evaporated by heating.

The gas diffusion member manufactured as described above was measured for vertical gas permeability and in-plane gas permeability. In this case, as shown in FIG. 5, the test piece S (diameter 40 millimeters, thickness 0.3 to 0.5 millimeters) is disposed along the direction perpendicular to the gas flow path 100, and the nitrogen cylinder 102 is connected to the mass flow controller. 104 is used to flow a gas (nitrogen gas) at a constant flow rate, and the differential pressure at the upstream point a immediately before the test piece S and the downstream point b immediately after the test piece S is measured with a differential pressure gauge. By calculating the gas flow rate per unit area, the vertical gas permeability of the test piece S was obtained. The gas permeation area of the test piece S was 6.15 cm ² . The vertical gas permeability was determined by K1 / K2. K1 was (gas flow rate / sample area). K2 was a differential pressure.

Further, as shown in FIG. 6, a container-shaped measuring jig 204 is brought into close contact with a test piece S (diameter 40 mm, thickness 0.3 to 0.5 mm) placed on a measuring surface 202 of a table 200 by a load F. In this state, a constant flow of gas (nitrogen gas) is caused to flow from the nitrogen cylinder 102 to the chamber 2061 of the measurement jig 204 using the mass flow controller 104, and the pressure at point c in the measurement jig 204. The in-plane gas permeability of the test piece S was determined by measuring the pressure difference between the point d and the outside point d with a differential pressure gauge and calculating the gas flow rate per unit area of the test piece S. The gas permeation area of the test piece S was 6.15 cm ² . The in-plane gas permeability was determined by M1 / M2. M1 was (gas flow rate × width of measurement jig 204). M2 is differential pressure × (peripheral length of the measuring jig 204). The circumference of the measurement jig 204 was a circumference of an intermediate diameter (29 mm) between the inner circumference diameter (28 mm) and the outer circumference diameter (30 mm) of the measurement jig 204.

  According to the present embodiment, polyvinyl alcohol as a pore-forming agent having fluidity existing inside the carbon paper is thermally decomposed by subsequent heating and evaporated to the outside of the carbon paper to form pores. For this reason, the gas permeability of a gas diffusion member improves. In particular, the vertical gas permeability and the in-plane gas permeability of the gas diffusion member are improved. Polyvinyl alcohol is present in the gas diffusion member as a pore-forming agent having fluidity, so it tends to exist two-dimensionally and three-dimensionally. Therefore, the pores are not formed like a pinhole, This is presumably because the pores are easily formed two-dimensionally or three-dimensionally, the ratio of isolated holes decreases, and the ratio of communication holes increases.

  Also, according to the present embodiment, before applying the carbon paste to the surface of the carbon paper as described above, the carbon paper is impregnated with polyvinyl alcohol, so that the carbon paste forming the conductive layer is It is considered that impregnation into the carbon paper while being applied to the exposed surface of the carbon paper is suppressed.

  Furthermore, according to this example, polyvinyl alcohol, which is a polymer material, functions as a pore-forming agent that forms pores in the gas diffusion member, and therefore has good transpiration, and In contrast, since a metal or a metal salt is not used as a pore-forming agent, it is possible to prevent a problem that the performance of the electrolyte membrane is deteriorated due to residual metal ions.

  Furthermore, according to the present embodiment, since metal ions are not dissolved in a strongly acidic aqueous solution, it is possible to avoid the influence of the metal ions on the performance of the electrolyte membrane. Furthermore, since the powdered metal or metal salt mixed as a pore-forming agent in the gas diffusion electrode is not removed by dissolving with a strong acidic aqueous solution, the metal ions remaining in the gas diffusion member are not separated from the functional groups of the electrolyte membrane. Bonding and affecting the performance of the electrolyte membrane can be avoided.

(Example 2)
Basically, a gas diffusion member was produced in the same manner as in Example 1. However, the blending amount of polyvinyl alcohol was set higher than that of Example 1 to 20 g. A blending amount of 20 g of polyvinyl alcohol is equivalent to 3.8% with respect to 500 g of water ((20 g / (500 g + 20 g) × 100% ≈3.8 wt%). Gas permeability was measured by the same method as in Example 1.

(Example 3)
Basically, a gas diffusion member was produced in the same manner as in Example 1. However, the blending amount of polyvinyl alcohol was higher than that of Example 1 to 30 g. A blending amount of 30 g of polyvinyl alcohol is equivalent to 5.7% with respect to 500 g of water ((30 g / (500 g + 30 g) × 100% ≈5.7 wt%). Gas permeability was measured by the same method as in Example 1.

Example 4
Basically, a gas diffusion member was produced in the same manner as in Example 1. However, the blending amount of polyvinyl alcohol was 40 g higher than that of Example 1. A blending amount of 40 g of polyvinyl alcohol corresponds to 7.4% with respect to 500 g of water ((40 g / (500 g + 40 g) × 100% ≈7.4 wt%)). Gas permeability was measured by the same method as in Example 1.

(Example 5)
Basically, a gas diffusion member was produced in the same manner as in Example 1. However, the blending amount of polyvinyl alcohol was higher than that of Example 1 to 50 g. A blending amount of 50 g of polyvinyl alcohol is equivalent to 9% with respect to 500 g of water ((50 g / (500 g + 50 g) × 100% ≈9
wt%). The carbon ink solid content and gas permeability of the gas diffusion member were measured by the same method as in Example 1.

(Example 6)
Basically, a gas diffusion member was produced in the same manner as in Example 1. However, the blending amount of polyvinyl alcohol was set higher than that of Example 1 to 60 g. The blending amount of polyvinyl alcohol 60g corresponds to 11% with respect to 500g of water ((60g / (500g + 60g) x 100% ≒ 11wt%). The viscosity was measured by the same method as in Example 1. When the blending amount of polyvinyl alcohol was 60 g, the viscosity of the polyvinyl alcohol aqueous solution was considerably high, and the tendency of the impregnation property of the polyvinyl alcohol aqueous solution to decrease was observed. The blending amount was up to 60 g.

(Example 7)
Basically, a gas diffusion member was produced in the same manner as in Example 1. However, although the degree of polymerization of polyvinyl alcohol was higher than that in Example 1, the blending amount of alcohol was reduced from 10 g to 5 g. That is, it was set to 5 g of polyvinyl alcohol (polymerization degree 1000). A blending amount of 5 g of polyvinyl alcohol is equivalent to 1% with respect to 500 g of water ((5 g / (500 g + 5 g) × 100% ≈1 wt%). The properties were measured in the same manner as in Example 1.

(Example 8)
Basically, a gas diffusion member was produced in the same manner as in Example 1. However, the polymerization degree and blending amount of polyvinyl alcohol were higher than in Example 1. That is, it was 15 g of polyvinyl alcohol (degree of polymerization 1000). That is, it was 15 g of polyvinyl alcohol (degree of polymerization 1000). A blending amount of 15 g of polyvinyl alcohol is equivalent to 3% with respect to 500 g of water ((15 g / (500 g + 15 g) × 100% ≈3 wt%)). The properties were measured in the same manner as in Example 1.

Example 9
Basically, a gas diffusion member was produced in the same manner as in Example 1. However, the polymerization degree and blending amount of polyvinyl alcohol were higher than in Example 1. That is, it was set to 15 g of polyvinyl alcohol (degree of polymerization 2000). A blending amount of 15 g of polyvinyl alcohol is equivalent to 3% with respect to 500 g of water ((15 g / (500 g + 15 g) × 100% ≈3 wt%)). The properties were measured in the same manner as in Example 1.

(Example 10)
Basically, a gas diffusion member was produced in the same manner as in Example 1. However, the polymerization degree and blending amount of polyvinyl alcohol were higher than in Example 1. That is, 15 g of polyvinyl alcohol (polymerization degree 2800) was used. A blending amount of 15 g of polyvinyl alcohol is equivalent to 3% with respect to 500 g of water ((15 g / (500 g + 15 g) × 100% ≈3 wt%).) The properties were measured in the same manner as in Example 1.

(Comparative Example 1)
According to Comparative Example 1, a gas diffusion member was produced in the same manner as in Example 1. However, the carbon paper was not impregnated with a polymer aqueous solution (polyvinyl alcohol aqueous solution) functioning as a pore-forming agent. The carbon ink solid content and gas permeability of the gas diffusion member were measured by the same method as in Example 1.

(Evaluation)
Table 1 shows the test results.

(Vertical gas permeability)
As shown in Table 1, the gas permeability in the vertical direction was good in Examples 1 to 10, exceeding 29 μm / [Pa · S]. Particularly, in Examples 3 to 6 and Example 10, it exceeded 100 μm / [Pa · S] and was good. Especially in Examples 4-6, it exceeded 500 micrometers / [Pa * S] and was favorable. In terms of vertical gas permeability, Example 6 was the best.

(In-plane direction gas permeability)
As shown in Table 1, in-plane gas permeability was excellent in Examples 1 to 10, exceeding 0.13 L / [min · MPa]. In particular, in Examples 2 to 6 and Example 10, it exceeded 1.0 L / [min · MPa] and was good. Especially in Examples 4-6, it exceeded 4L / [min * MPa] and was favorable. In terms of in-plane gas permeability, Example 6 was the best.

(Carbon ink solid content)
Regarding the carbon ink solid content, there was no significant difference between Examples 1 to 10 and Comparative Example 1.

  As described above, Example 6 was the best for both the vertical gas permeability and the in-plane gas permeability. It is presumed that polyvinyl alcohol that can function as a pore-forming material impregnates the inside of the carbon paper and is thermally decomposed and evaporated by subsequent heating.

(Pore distribution)
The pore distribution of the gas diffusion member produced as described above was measured by mercury porosimetry. The pore distribution was determined by gradually changing the pressure applied to mercury. FIG. 7 shows Comparative Example 1. FIG. 8 shows a second embodiment. FIG. 9 shows a fourth embodiment. FIG. 10 shows a tenth embodiment. As shown in FIG. 7, according to Comparative Example 1, in the range where the pore size exceeds 0.1 μm, the peak region of the pore size was not particularly recognized. The peak area of the pore size was about 19 to 26 μm in Example 2, about 21 to 30 μm and about 39 to 60 μm in Example 4, and about 10 to 22 μm in Example 10. When the polymerization degree of polyvinyl alcohol was the same, the tendency that the pore size increased as the blending amount of polyvinyl alcohol increased. As shown in FIGS. 7-10, according to the gas diffusion member which concerns on an Example, in the polyvinyl alcohol aqueous solution as a pore-forming agent which has fluidity, if the polymerization degree and / or compounding quantity of polyvinyl alcohol are adjusted, The peak of the pore size can be adjusted as appropriate.

(Application example)
FIG. 11 shows an application example. As shown in FIG. 11, the fuel cell includes an electrolyte membrane 50 having ion conductivity (proton conductivity), and a gas diffusion member 1A that forms a fuel electrode provided on one side in the thickness direction of the electrolyte membrane 50. Carbon or metal having a gas diffusion member 1B for forming an oxidant electrode provided on the other side in the thickness direction of the electrolyte membrane 50 and a fuel flow path 61 for supplying fuel to the gas diffusion member 1A for forming a fuel electrode And an oxidant flow plate 70 made of carbon or metal having an oxidant flow channel 71 for supplying an oxidant to the gas diffusion member 1B forming the oxidant electrode. Between the electrolyte membrane 50 and the gas diffusion member 1A, a catalyst layer 70A having a catalyst and an ion conductive material as main components is provided. Between the electrolyte membrane 50 and the gas diffusion member 1B, a catalyst layer 70B having a catalyst and an ion conductive material as main components is provided. According to the gas diffusion members 1A and 1B, since the gas permeability is good, it is advantageous for improving the power generation output.

(Other examples)
In addition, when the viscosity of the pore forming agent having fluidity formed with an aqueous polyvinyl alcohol solution is excessively high, the pore forming agent having fluidity may adhere excessively to the exposed surface of the carbon paper. In this case, the adhesion of the conductive layer to the exposed surface of the carbon paper may be reduced. Therefore, as shown in FIG. 3 (B), the pore forming agent having the fluidity excessively attached to the exposed surface of the carbon paper is removed while leaving the pore forming agent impregnated inside the carbon paper. The removal operation can be performed as necessary. Examples of the removal element include those having a function of scraping off the pore forming agent having the fluidity excessively attached to the exposed surface of the carbon paper and a function of scraping off the pore forming agent having the fluidity. Can do. As a result, the adhesion of the conductive layer to the exposed surface of the carbon paper is ensured.

  According to the above embodiment, polyvinyl alcohol is employed as the polymer material, but the present invention is not limited to this, and the above-described polymer material can be used as appropriate. 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 within a range not departing from the gist.

  The present invention can be used for gas diffusion members used in fuel cells for vehicles, stationary and portable.

It is a flowchart which shows the manufacture process of an Example. It is a block diagram which shows the concept of a manufacturing process. (A) is sectional drawing which shows typically the state which apply | coated the electrically conductive paste to carbon paper, (B) typically shows the state which removes the pore forming agent with the fluidity | liquidity which remains on the exposed surface of carbon paper. It is sectional drawing shown. It is sectional drawing which shows the internal structure of a gas diffusion member typically. It is a block diagram which shows the principle which measures the vertical direction gas permeability of a gas diffusion member. It is a block diagram which shows the principle which measures the in-plane direction gas permeability of a gas diffusion member. 5 is a graph showing a pore distribution according to Comparative Example 1. 6 is a graph showing a pore distribution according to Example 2. 10 is a graph showing a pore distribution according to Example 4. It is a graph which shows the pore distribution which concerns on Example 10. It is sectional drawing which shows typically the concept of the fuel cell which concerns on an application example.

Explanation of symbols

  In the figure, 1 is a gas diffusion member, 10 is a base material layer, and 12 is a conductive layer.

Claims (8)

A sheet forming step of forming a sheet holding a fluid pore-forming agent inside a sheet main body based on a conductor having corrosion resistance;
A hole forming step of heating the sheet that has undergone the sheet forming step and evaporating the pore forming agent held inside the sheet to the outside of the sheet to form pores. A method for manufacturing a gas diffusion member for a fuel cell. A sheet forming step of forming a sheet holding a fluid pore-forming agent having a polymer material as a main component inside a sheet main body based on a conductor having corrosion resistance;
A fuel cell gas comprising: a hole forming step of heating the sheet that has undergone the sheet forming step to evaporate a polymer material inside the sheet to the outside of the sheet to form pores. Manufacturing method of diffusion member. A sheet forming step of forming a sheet holding a fluid pore-forming agent inside a sheet main body based on a conductor having corrosion resistance;
An arranging step of arranging a conductive layer containing a conductive material on the exposed surface of the sheet that has undergone the sheet forming step;
A hole forming step of heating the sheet that has undergone the placement step and evaporating the pore forming agent held inside the sheet to the outside of the sheet to form pores. A method for producing a gas diffusion member for a fuel cell.   3. The method of manufacturing a fuel cell gas diffusion member according to claim 2, wherein the polymer material is a water-soluble polymer material.   5. The polymer material according to claim 2, wherein the polymer material is at least one selected from polyvinyl alcohol, polyvinyl pyrrolidone, polyvinyl methyl ether, polyethylene oxide, polyethylene glycol, polyacrylamide, cellulose, starch, gelatin, and wax. A method for producing a gas diffusion member for a fuel cell.   In any one of Claims 1-5, the said sheet | seat formation process uses the said pore forming agent which has the fluidity | liquidity, and the primary sheet | seat which uses the conductor which has the said corrosion resistance as a base material, A method for producing a gas diffusion member for a fuel cell, which is performed by impregnating the inside of the primary sheet with the pore forming agent having fluidity.   7. The fuel cell gas diffusion according to claim 6, wherein, in the sheet forming step, an operation of removing the fluid pore forming agent excessively attached to the exposed surface of the primary sheet by a removing element is performed. Manufacturing method of member.   The fuel cell which has the gas diffusion member for fuel cells formed in any one of Claims 1-7.

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