JP5322212B2 - Porous electrode substrate, method for producing the same, membrane-electrode assembly, and polymer electrolyte fuel cell - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a porous electrode substrate which has sufficient gas permeability, thickness and penetration direction resistance and exhibits high moisture control function with less fluctuation of cell performance when it is used for a fuel cell and a humidification condition fluctuates, a method for manufacturing the same, a membrane-electrode assembly and a solid polymer fuel cell. <P>SOLUTION: The following (A)-(D) processes are carried out in sequence for the method for manufacturing a porous electrode substrate. (A) A process for manufacturing a carbon fiber paper by dispersing carbon short fibers and binder short fibers, (B) a process for impregnating the carbon fiber paper with a solution in which a resin whose residual carbon ratio after carbonization is 20% or more is dissolved, immersing in a solvent which is a poor solvent against the resin whose residual carbon ratio is 20% or more and manufacturing a precursor sheet in which the resin whose residual carbon ratio is 20% or more is solidified, (C) a process for obtaining the precursor sheet from which the solvent is removed, (D) a process for obtaining a porous electrode substrate by carbonizing the resin whose residual carbon ratio is 20% or more in the precursor sheet. <P>COPYRIGHT: (C)2010,JPO&amp;INPIT

Description

  The present invention relates to a porous electrode substrate used for a polymer electrolyte fuel cell using a liquid fuel, a method for producing the same, and a membrane-electrode assembly and a polymer electrolyte fuel cell using the porous electrode substrate. It is about.

  A polymer electrolyte fuel cell is characterized by using a proton-conducting polymer electrolyte membrane, and is an apparatus for obtaining an electromotive force by electrochemically reacting a fuel gas such as hydrogen and an oxidizing gas such as oxygen. . The polymer electrolyte fuel cell can be used as a self-power generation device or a power generation device for a moving body such as an automobile.

  Such a polymer electrolyte fuel cell has a polymer electrolyte membrane that selectively conducts hydrogen ions (protons). Also, a structure in which a gas diffusion electrode having a catalyst layer mainly composed of carbon powder supporting a noble metal catalyst and a gas diffusion electrode base material is bonded to both surfaces of the polymer electrolyte membrane with the catalyst layer side inside It has become.

  Such a joined body composed of a polymer electrolyte membrane and two gas diffusion electrodes is called a membrane-electrode assembly (MEA: Membrane Electrode Assembly). In addition, separators are provided on both outer sides of the MEA so as to supply a fuel gas or an oxidizing gas and to form a gas flow path for the purpose of discharging generated gas and excess gas.

  The porous electrode substrate is fastened by a separator with a load of several MPa for the purpose of reducing electrical contact resistance and suppressing leakage of fuel gas or oxidizing gas supplied from the separator to the outside of the cell. Therefore, mechanical strength is required.

  Furthermore, the porous electrode substrate mainly needs to have the following three functions. The first function is to supply the fuel gas or the oxidizing gas uniformly to the noble metal catalyst in the catalyst layer from the gas flow path formed in the separator disposed outside the porous electrode substrate. The second function is to discharge water generated by the reaction in the catalyst layer. The third function is to conduct electrons necessary for the reaction in the catalyst layer or generated electrons to the separator. In order to impart these functions, it is generally effective to use a carbonaceous material for the porous electrode substrate.

  Therefore, the porous electrode base material needs to have a high reactive gas and oxidizing gas permeability, water discharge property, and electronic conductivity. In addition, the polymer electrolyte membrane used in a general solid polymer fuel cell exhibits proton conductivity in a water-containing state, so that the porous electrode substrate is not only a drainage of generated water, but also a polymer electrolyte. The contradictory function of retaining the membrane is required. When the gas permeability of the porous electrode substrate is increased to increase the drainage capacity of the generated water, the proton conduction resistance increases and the power generation performance decreases due to the drying of the polymer electrolyte membrane. On the contrary, in the case where the gas permeability of the porous electrode substrate is lowered and the water retention capacity of the polymer electrolyte membrane is increased, the power generation performance is improved by flooding in which the diffusion of the reaction gas and the oxidizing gas is hindered due to poor drainage of the generated water descend.

  Conventionally, in order to increase the mechanical strength, a porous electrode made of a paper-like carbon / carbon composite in which short carbon fibers are made with paper and then bound with an organic polymer and then fired at a high temperature to carbonize the organic polymer. Although the base material was obtained, there was a problem that it was difficult to maintain a balance between water retention and drainage of generated water because of the highly uniform structure. In addition, for the purpose of improving gas diffusibility and drainage, a porous electrode base material having through-holes has been proposed, but it is difficult to maintain mechanical strength because the through-holes are formed. There was a problem that it was difficult to maintain water retention.

  In Patent Document 1, the thickness is 0.05 to 0.5 mm, the bulk density is 0.3 to 0.8 g / cm, the strain rate is 10 mm / min, the distance between fulcrums is 2 cm, and the specimen width is 1 cm. Describes a porous carbon electrode substrate for a fuel cell, characterized in that the bending strength is 10 MPa or more and the bending deflection is 1.5 mm or more. However, this porous electrode base material has high mechanical strength, surface smoothness, sufficient conductivity, and a highly uniform structure, so it has water retention and drainage of generated water. There was a problem that it was difficult to maintain the balance.

Patent Document 2 includes a gas diffusion electrode comprising a carbon sheet having a catalyst layer formed on one surface, and a plurality of through holes formed from one surface to the other surface. Have been described. Although this porous electrode base material has high gas diffusibility, there is a problem that it is difficult to maintain mechanical strength and maintain water retention.
International Publication No. 2002/042534 Pamphlet JP 2002-110182 A

  The present invention provides a porous electrode substrate that has a sufficient moisture permeability, thickness, and resistance in the penetration direction, and exhibits a high moisture management function with little variation in cell performance due to variation in humidification conditions when used as a fuel cell. An object of the present invention is to provide a production method thereof, a membrane-electrode assembly, and a polymer electrolyte fuel cell.

The present invention is as follows.
(1) The manufacturing method of the porous electrode base material which performs the following (A)-(D) processes in order.
(A) Step of dispersing carbon short fibers and binder short fibers to produce carbon fiber paper (B) Residual carbon after carbonizing for 1 hour in a nitrogen gas atmosphere at 2000 ° C. After impregnating a solution in which a resin having a rate of 20% or more is dissolved, the resin having a carbonization rate after carbonization is immersed in a solvent that becomes a poor solvent for a resin having a carbonization rate of 20% or more. (C) A step of obtaining a precursor sheet from which the solvent has been removed (D) A step of obtaining a precursor sheet obtained by solidifying at least 20% of the resin. (D) A resin having a residual carbon ratio of 20% or more after carbonization in the precursor sheet. Step (2) for obtaining a porous electrode substrate by carbonization A method for producing a porous electrode substrate in which the following steps (a) to (d) are sequentially performed.
(A) Step of dispersing carbon short fibers and binder short fibers to produce carbon fiber paper (b) After impregnating the carbon fiber paper with a dimethylacetamide solution of polyacrylonitrile, it is immersed in water to solidify the polyacrylonitrile. (C) Step for obtaining a precursor sheet from which the solvent has been removed (d) Step for obtaining a porous electrode substrate by carbonizing polyacrylonitrile in the precursor sheet (3) (b) (D) The method for producing a porous electrode substrate according to (2), wherein the step (d) is replaced with the following steps (b ′) and (d ′), respectively.
(B ′) Step of producing a precursor sheet in which the carbon fiber paper is impregnated with a methanol solution of the phenol resin composition and then immersed in water to solidify the phenol resin composition (d ′) in the precursor sheet Step (4) to obtain a porous electrode substrate by carbonizing the phenol resin composition (4) Production of the porous electrode substrate according to any one of (1) to (3) that is heated and pressurized before carbonization in the step (D) Method.
(5) The method for producing a porous electrode base material according to (4), wherein the carbonization is performed after the heating and pressurization and then the oxidation treatment.
(6) A porous electrode substrate obtained by the method for producing a porous electrode substrate according to any one of (1) to (5).
(7) The porous electrode base material according to (6), in which dispersed short carbon fibers are joined together by porous carbon.
(8) A porous electrode base material in which dispersed carbon short fibers are joined by porous carbon.
(9) A membrane-electrode assembly using the porous electrode substrate according to any one of (6) to (8).
(10) A polymer electrolyte fuel cell using the membrane-electrode assembly according to (9).

  According to the present invention, a porous electrode substrate having sufficient gas permeability, thickness, and penetration direction resistance, and exhibiting a high moisture management function with little variation in cell performance even when the humidification conditions are varied when a fuel cell is obtained. A material, a manufacturing method thereof, a membrane-electrode assembly, and a polymer electrolyte fuel cell can be obtained.

<Short carbon fiber>
The carbon fiber that is a raw material of the short carbon fiber used in the present invention may be any of polyacrylonitrile-based carbon fiber, pitch-based carbon fiber, rayon-based carbon fiber, etc., but polyacrylonitrile-based carbon fiber is preferable. In particular, since the mechanical strength of the porous carbon electrode substrate can be made relatively high, it is preferable that the carbon fiber to be used is made of only polyacrylonitrile (PAN) based carbon fiber.
The diameter of the short carbon fiber is preferably 3 to 9 μm from the viewpoint of production cost and dispersibility of the short carbon fiber. From the aspect of smoothness of the finally obtained porous electrode substrate, it is more preferably 4 μm or more and 8 μm or less.
The fiber length of the short carbon fiber is preferably 2 to 12 mm from the viewpoint of dispersibility.

<Dispersion>
In the present invention, “dispersion” means that the carbon short fibers lie so as to form a single plane. Thereby, the short circuit by carbon short fiber and the breakage of carbon short fiber can be prevented. The orientation direction of the short carbon fibers may be substantially random, or the orientation in a specific direction may be high.

<Manufacturing method>
The manufacturing method of the porous electrode base material of this invention is a method of performing the process shown below in order. The porous electrode substrate can be suitably manufactured by the following method, for example.
(A) Step of dispersing carbon short fibers and binder short fibers to produce carbon fiber paper (B) Impregnating the carbon fiber paper with a solution in which a resin having a carbon residue ratio of 20% or more after carbonization is dissolved. After that, a precursor sheet is produced by immersing in a solvent that is a poor solvent for a resin having a carbon residue rate of 20% or more after carbonization, and solidifying a resin having a carbon residue rate of 20% or more after carbonization. Step (C) Obtaining a precursor sheet from which the solvent has been removed Step (D) Step of obtaining a porous electrode substrate by carbonizing a resin having a carbon residue ratio of 20% or more after carbonization in the precursor sheet

<Binder staple fiber>
The binder short fiber is used as a binder (glue) that holds the components together in a carbon short fiber paper containing carbon short fibers. As the binder short fiber, polyvinyl alcohol (PVA), polyvinyl acetate or the like can be used. In particular, polyvinyl alcohol is preferable as a binder because it has excellent binding power in the short carbon fiber paper making process, and the short carbon fibers do not fall off.

<Process for producing short carbon fiber paper>
Carbon short fiber and binder short fiber are dispersed to produce carbon short fiber paper. A wet method in which carbon short fiber and binder short fiber are dispersed in a liquid medium to make paper, or carbon in the air is used. A dry method in which short fibers and binder short fibers are dispersed and piled up can be applied. Among these, a wet method is preferable. The short carbon fibers can be dispersed into the single fibers, and the dispersed single fibers can be prevented from preventing convergence again.
As a method of mixing the short carbon fiber and the short binder fiber, there are a method of stirring and dispersing in water together with the carbon short fiber and a method of mixing directly, but a method of diffusing and dispersing in water is preferable for uniform dispersion. By mixing the binder short fibers in this way, the strength of the carbon fiber paper is maintained, and it is possible to prevent the carbon short fibers from being peeled off from the carbon fiber paper during the production or the orientation of the carbon short fibers from being changed. be able to.
In addition, short carbon fiber paper can be produced continuously or batchwise. The production of carbon short fiber paper in the present invention is particularly easy to control the basis weight, productivity and machine. From the viewpoint of mechanical strength, continuous is preferable. The basis weight of the short carbon fiber paper is preferably 10 to 200 g / m2.

<Resin with 20% or more carbon residue after carbonization>
The resin used as a resin having a carbon residue ratio of 20% or more after carbonization in the present invention is a substance that remains as a conductive substance even after carbonization, and preferably exhibits adhesiveness or fluidity at room temperature. Polyacrylonitrile, phenol resin, furan resin, epoxy resin, melamine resin, imide resin, urethane resin, aramid resin, pitch, etc. can be used as a single substance or as a mixture, and the type of resin used, impregnation during resin impregnation described later The amount of carbonization remaining varies depending on the amount, curing, and carbonization temperature.
As the phenol resin composition, a resol type phenol resin composition obtained by reaction of phenols and aldehydes can be used, but a novolac type phenol resin composition showing solid heat-fusibility can be mixed. preferable.

<Method of impregnating resin with a residual carbon ratio of 20% or more after carbonization>
The method for impregnating the carbon short fiber paper with a resin having a carbon residue ratio of 20% or more after carbonization is not particularly limited as long as the carbon short fiber paper can be impregnated with the resin. A method of uniformly coating a resin on the surface of fiber paper, a dip-nip method using a squeezing device, or a method of superposing carbon short fiber paper and a resin film and transferring the resin to a precursor sheet can be continuously performed. This is preferable in terms of productivity and production of long products.

<Amount of resin impregnated with carbonization rate of 20% or more after carbonization>
Porous carbon obtained by carbonizing a resin with a residual carbon ratio of 20% or more after carbonization in order to develop a moisture management function capable of maintaining a balance between drainage, moisture retention, and gas diffusibility in the porous electrode substrate However, since it is preferable that it is 20-50 mass parts with respect to 100 mass parts of carbon short fibers, the amount of resin whose carbon residue after carbonization to impregnate carbon short fiber paper is 20% or more is 100 mass of carbon short fibers. It is preferable to impregnate 70 to 120 parts by mass with respect to parts.

<Coagulation of resin with 20% or more carbon residue after carbonization>
The coagulation of the resin having a carbon residue of 20% or more after carbonization is performed after impregnating a carbon short fiber paper composed of carbon short fibers and binder short fibers with a resin solution having a carbon residue of 20% or more after carbonization. The resin having a residual carbon ratio after carbonization of 20% or more is immersed in a coagulation bath as a poor solvent, and the resin having a residual carbon ratio after carbonization of 20% or more is solidified. As the solvent used in the coagulation bath, an aqueous solvent can be generally used, but is not particularly limited as long as it becomes a poor solvent for the resin. Moreover, even if it is a single solvent, you may use the mixed solvent which mixed several solvent.
When polyacrylonitrile is used as a resin having a carbon residue ratio of 20% or more after carbonization, water, a water / dimethylacetamide mixed solvent, or the like can be used. When a phenol resin composition is used, water or a water / alcohol mixed solvent can be used.
A void can be formed by solidifying a resin having a carbon residue ratio of 20% or more after carbonization, and a resin having a carbon residue ratio of 20% or more after carbonization can be promoted to be porous.
Void formation depends on the rate of solidification in the coagulation bath. Since voids are easier to form when the coagulation speed is relatively high, the resin solution concentration, coagulation bath composition, coagulation bath temperature when carbon short fiber paper is impregnated with a resin having a carbon residue ratio of 20% or more after carbonization Precisely controlled by. The resin solution concentration is preferably 5 to 40% by mass in terms of workability during impregnation.
For example, when a resin having a carbon residue rate of 20% or more after carbonization is a polyacrylonitrile or phenol resin composition and a coagulation bath serving as a poor solvent is water, a preferable coagulation bath temperature is 10 ° C to 80 ° C.
Porous carbon is a carbonized resin that binds between short carbon fibers in the porous electrode base material and is itself porous. Porous control precisely controls the void size. In order to achieve this, it is preferable to make it porous in the solidification process after resin impregnation.

<Carbonization>
The precursor sheet obtained by solidifying a resin having a carbon residue rate of 20% or more after carbonization can be carbonized as it is. In addition, the precursor sheet can be carbonized after the heat and pressure molding, and further, the precursor sheet after the heat and pressure molding can be oxidized and then carbonized.
Carbonization of the precursor sheet is obtained by fusing carbon short fibers with a resin having a carbon residue ratio of 20% or more after carbonization and carbonizing a resin having a carbon residue ratio of 20% or more after carbonization. The purpose is to develop the mechanical strength and conductivity of the porous electrode substrate.
Carbonization is preferably performed in an inert gas in order to increase the conductivity of the porous electrode substrate. Carbonization is performed at a temperature of 1000 ° C. or higher. Carbonization is preferably performed in a temperature range of 1000 to 3000 ° C, and a temperature range of 1000 to 2200 ° C is more preferable. The porous electrode substrate obtained by carbonization at a temperature of less than 1000 ° C. does not have sufficient conductivity. Prior to carbonization, pretreatment by firing in an inert atmosphere of about 300 to 800 ° C. may be performed.
The time for carbonization can be, for example, 10 minutes to 1 hour.
When carbonizing the precursor sheet by continuous production, it is preferable from a viewpoint of cost reduction to perform carbonization continuously over the full length of a precursor sheet. If the porous electrode substrate is long, not only the productivity of the porous electrode substrate is increased, but also the subsequent MEA production can be performed continuously, which can greatly contribute to the cost reduction of the fuel cell. it can. Moreover, the porous electrode base material of the present invention can be continuously wound, and is preferable from the viewpoint of productivity and cost of the porous electrode base material and the fuel cell.

<Heating and pressing>
The precursor sheet obtained by solidifying a resin having a carbon residue rate of 20% or more after carbonization is heated and pressed at a temperature of less than 200 ° C. before carbonization, so that the carbon residue is carbonized from the carbon residue. It is preferable in terms of being able to be fused with a resin having a rate of 20% or more and reducing unevenness in the thickness of the porous electrode substrate. Any technique can be applied to the heat and pressure as long as the technique can uniformly heat and press the precursor sheet. As an example, there are a method of performing hot pressing with smooth rigid plates from both upper and lower surfaces, and a method of performing using a continuous belt press apparatus.
In the case where the precursor sheet by continuous production is heated and pressurized, a method using a continuous belt press apparatus is preferable in that a long porous electrode substrate can be formed. If the porous electrode substrate is long, not only the productivity of the porous electrode substrate is increased, but also the subsequent MEA production can be performed continuously, which greatly contributes to the cost reduction of the fuel cell. Can do. Moreover, the porous electrode base material of the present invention can be continuously wound, and is preferable from the viewpoint of productivity and cost of the porous electrode base material and the fuel cell. As a pressing method in the continuous belt device, there are a method of applying pressure to the belt by a roll press by a linear pressure and a method of pressing by a surface pressure by a hydraulic head press, but the latter is a smoother porous electrode substrate. It is preferable in that it is obtained.
In order to effectively smooth the surface, the heating temperature is preferably less than 200 ° C, more preferably 120 to 190 ° C.
The molding pressure is not particularly limited, but when the ratio of the resin having a residual carbon ratio after carbonization of 20% or more is large, it is easy to smooth the surface of the precursor sheet even if the molding pressure is low. If the press pressure is increased more than necessary at this time, there may be problems such as breaking the short carbon fibers during the pressurization or becoming too dense when the porous electrode base material is used. For example, pressurization can be performed at a pressure of 20 kPa to 10 MPa.
The time for heating and pressing can be, for example, 30 seconds to 10 minutes. When the precursor sheet is heated and pressed by a continuous belt device with a rigid plate sandwiched between the rigid plates and the belt, a release agent is used in advance so that a resin having a carbon residue rate of 20% or more after carbonization does not adhere to the rigid plate or belt. It is preferable to carry out coating or to put a release paper between the precursor sheet and the rigid plate or belt.

<Oxidation treatment>
The precursor sheet obtained by solidifying a resin having a carbon residue rate of 20% or more after carbonization is heat-press molded and then oxidized at a temperature of 200 ° C. or more and less than 300 ° C. to carbonize short carbon fibers. It is preferable in terms of further fusing with a resin having a residual carbon ratio of 20% or more and improving the carbonization ratio of a resin having a residual carbon ratio of 20% or more after carbonization.
The oxidation treatment is preferably performed at a temperature range of 200 to 300 ° C, more preferably at 240 to 270 ° C. The oxidation treatment is preferably performed in an air atmosphere.
The oxidation treatment time can be, for example, 30 minutes to 2 hours.
When oxidizing the precursor sheet by continuous manufacture, it is preferable from a viewpoint of cost reduction to perform continuously over the full length of a precursor sheet. If the porous electrode substrate is long, not only the productivity of the porous electrode substrate is increased, but also the subsequent MEA production can be performed continuously, which can greatly contribute to the cost reduction of the fuel cell. it can. Further, the porous electrode substrate of the present invention can be continuously wound, and is preferable from the viewpoints of productivity and cost of the porous electrode substrate and the fuel cell.

<Porous electrode substrate>
The thickness of the porous electrode substrate of the present invention is preferably 50 to 300 μm.

<Membrane-electrode assembly (MEA), polymer electrolyte fuel cell>
The porous electrode substrate of the present invention as described above can be suitably used for a membrane-electrode assembly. The membrane-electrode assembly using the porous electrode substrate of the present invention can be suitably used for a polymer electrolyte fuel cell.

  Hereinafter, the present invention will be described more specifically with reference to examples. Each physical property value in the examples was measured by the following method.

(1) Gas air permeability Based on JIS standard P-8117, the time required for 200 mL of air to permeate was measured using a Gurley densometer, and the gas air permeability was calculated.

(2) Thickness The thickness of the porous electrode substrate was measured using a thickness measuring device dial thickness gauge 7321 (trade name, manufactured by Mitutoyo Corporation). The size of the probe was 10 mm in diameter, and the measurement pressure was 1.5 kPa.

(3) Penetration direction resistance The thickness direction electrical resistance (penetration direction resistance) of the porous electrode substrate is obtained by sandwiching a sample between gold-plated copper plates and pressurizing at 1 MPa from above and below the gold-plated copper plate, and a current of 10 mA / cm ² . The resistance value when a current was passed at a density was measured and obtained from the following equation.

Penetration resistance (mΩ · cm ² ) = Measured resistance value (Ω) × Sample area (cm ² )

Example 1
As short carbon fibers, polyacrylonitrile (PAN) carbon fibers having an average fiber diameter of 7 μm and an average fiber length of 3 mm were prepared. Moreover, polyvinyl alcohol (PVA) short fibers (trade name: VBP105-1, manufactured by Kuraray Co., Ltd.) having an average fiber length of 3 mm were prepared as binder short fibers.

100 parts by mass of carbon short fibers are uniformly dispersed in water, defibrated into single fibers, and when sufficiently dispersed, 25 parts by mass of PVA short fibers are uniformly dispersed, and a standard square sheet machine (Kumaya Riki Kogyo) (Product name: No. 2555 standard square sheet machine, manufactured by Co., Ltd.) was used to manually produce carbon short fiber paper according to JIS P-8209 method, dried, and the basis weight was 25 g / m ^2. Carbon short fiber paper was obtained. The dispersion state of the short carbon fibers was good.
The carbon short fiber paper was impregnated with a dimethylacetamide solution of polyacrylonitrile containing 10% by mass of polyacrylonitrile, and then immersed in a coagulation bath made of water at room temperature to coagulate polyacrylonitrile having voids. Then, the precursor sheet | seat of 46 g / m < ² > of fabric weights was obtained by making it dry in 80 degreeC drying machine. This means that 105 parts by mass of polyacrylonitrile is attached to 100 parts by mass of the short carbon fibers.
Next, two precursor sheets that were overlapped were sandwiched between two sheets of paper coated with a silicone-based release agent, and then heated under pressure at 180 ° C. and 30 kPa for 3 minutes in a batch press apparatus.
The precursor sheet heated and pressurized was carbonized in a batch carbonization furnace in a nitrogen gas atmosphere at 2000 ° C. for 1 hour to obtain a porous electrode substrate. The obtained porous electrode base material had good gas permeability, thickness, and penetration direction resistance. The results are shown in Table 1.
In addition, the surface SEM photograph of the obtained porous electrode base material is shown in FIG. It was confirmed that the dispersed short carbon fibers were joined together with carbon made into carbon porous. The evaluation results are shown in Table 1.

(Example 2)
A porous electrode substrate was obtained in the same manner as in Example 1 except that the coagulation bath temperature was 57 ° C. In the obtained porous electrode base material, short carbon fibers dispersed by surface SEM observation are joined by carbon made into carbon porous, and the void size in the carbonized resin is increased as compared with Example 1. It was confirmed that Moreover, the gas permeability, thickness, and penetration direction resistance were also good results. The evaluation results are shown in Table 1.

(Example 3)
A porous electrode substrate was obtained in the same manner as in Example 1 except that the coagulation bath was a water / dimethylacetamide mixed solution containing 30% by mass of dimethylacetamide. In the obtained porous electrode base material, short carbon fibers dispersed by surface SEM observation are joined together by carbon made into carbon porous, and the void size in the carbonized resin is reduced as compared with Example 1. It was confirmed that Moreover, the gas permeability, thickness, and penetration direction resistance were also good results. The evaluation results are shown in Table 1.

Example 4
The precursor sheet heated under pressure was oxidized in a batch hot air oven in air at 250 ° C. for 1 hour, and then carbonized at 2000 ° C. for 1 hour in the same manner as in Example 1. A porous electrode substrate was obtained. In the obtained porous electrode base material, short carbon fibers dispersed by surface SEM observation are joined by carbon made carbon porous, and the void size in the carbonized resin is equivalent to that in Example 1. It was confirmed that there was. Moreover, the gas permeability, thickness, and penetration direction resistance were also good results. The evaluation results are shown in Table 1.

(Example 5)
The basis weight of the obtained carbon short fiber paper was 50 g / m ² , the basis weight of the precursor sheet after resin coagulation drying was 92 g / m ^2, and carbonized for 1 hour under the condition of 2000 ° C. without heating under pressure. Except for the above, a porous electrode substrate was obtained in the same manner as in Example 1. In the obtained porous electrode base material, short carbon fibers dispersed by surface SEM observation are joined by carbon made carbon porous, and the void size in the carbonized resin is equivalent to that in Example 1. It was confirmed that there was. Moreover, the gas permeability, thickness, and penetration direction resistance were also good results. The evaluation results are shown in Table 1.

(Example 6)
The resin solution was made into a methanol solution of a phenol resin composition containing 10% by mass of a phenol resin composition, and porous as in Example 1 except that the basis weight of the precursor sheet after coagulation and drying was 46 g / m ^2. An electrode substrate was obtained. In the obtained porous electrode base material, short carbon fibers dispersed by surface SEM observation are joined by carbon made carbon porous, and the void size in the carbonized resin is equivalent to that in Example 1. It was confirmed that there was. Moreover, the gas permeability, thickness, and penetration direction resistance were also good results. The evaluation results are shown in Table 1.

(Comparative Example 1)
A porous electrode substrate was obtained in the same manner as in Example 1 except that the precursor sheet after impregnation with resin in Example 1 was dried at 120 ° C. for 1 hour without being immersed in the coagulation bath. It was confirmed that the short carbon fibers dispersed by surface SEM observation were joined by carbon that was not made porous. The gas permeability, thickness, and penetration direction resistance were good results. The evaluation results are shown in Table 1.

(Comparative Example 2)
A porous electrode substrate was obtained in the same manner as in Example 6 except that the precursor sheet after resin impregnation of Example 6 was dried at room temperature for 8 hours without being immersed in the coagulation bath. It was confirmed by surface SEM observation that short carbon fibers dispersed in a two-dimensional plane were joined together by carbon that was not made porous. The gas permeability, thickness, and penetration direction resistance were good results. The evaluation results are shown in Table 1.

(Example 7)
(1) Production of membrane-electrode assembly (MEA) Two sets of the porous electrode base material obtained in Example 1 were prepared for the cathode and the anode. Perfluorosulfonic acid based catalyst in which a catalyst layer (catalyst layer area: 25 cm ² , Pt adhesion amount: 0.3 mg / cm ² ) composed of catalyst-supported carbon (catalyst: Pt, catalyst support amount: 50% by mass) is formed on both surfaces. A polymer electrolyte membrane (film thickness: 30 μm) was sandwiched between porous electrode substrates for cathode and anode, and these were joined to obtain MEA.

(2) Evaluation of MEA Fuel Cell Characteristics The MEA produced in (1) was sandwiched between two carbon separators having bellows-like gas flow paths to form a polymer electrolyte fuel cell (single cell).

The fuel cell characteristics were evaluated by measuring the current density-voltage characteristics of this single cell. Hydrogen gas was used as the fuel gas, and air was used as the oxidizing gas. The cell temperature was 80 ° C., the fuel gas utilization rate was 60%, and the oxidizing gas utilization rate was 40%. Gas humidification was performed by passing fuel gas and oxidizing gas through a bubbler.
The cell voltage of the fuel cell when the humidifier temperature was 80 ° C. and the current density was 0.8 A / cm ² was 0.648V.
In addition, the cell voltage of the fuel cell when the humidifier temperature is 60 ° C. and the current density is 0.8 A / cm ² is 0.608 V, which shows good characteristics, and the battery performance fluctuation is small even when the humidification condition changes. It was confirmed that it had a moisture management function.

(Comparative Example 3)
The fuel cell was evaluated in the same manner as in Example 7 except that the porous electrode substrate obtained in Comparative Example 1 was used.
The cell voltage of the fuel cell when the humidifier temperature was 80 ° C. and the current density was 0.8 A / cm ² was 0.637V.
In addition, when the humidifier temperature is 60 ° C. and the current density is 0.8 A / cm ² , the cell voltage of the fuel cell is 0.532 V, and the performance degradation due to the decrease in water retention in the fuel cell is noticeable. .

It is a surface SEM image of the porous electrode base material of this invention.

Claims (10)

The manufacturing method of the porous electrode base material which performs the following (A)-(D) processes in order.
(A) Step of dispersing carbon short fibers and binder short fibers to produce carbon fiber paper (B) Residual carbon after carbonizing for 1 hour in a nitrogen gas atmosphere at 2000 ° C. After impregnating a solution in which a resin having a rate of 20% or more is dissolved, the resin having a carbonization rate after carbonization is immersed in a solvent that becomes a poor solvent for a resin having a carbonization rate of 20% or more. (C) A step of obtaining a precursor sheet from which the solvent has been removed (D) A step of obtaining a precursor sheet obtained by solidifying at least 20% of the resin. (D) A resin having a residual carbon ratio of 20% or more after carbonization in the precursor sheet. Carbonization to obtain a porous electrode substrate The manufacturing method of the porous electrode base material which performs the following (a)-(d) process in order.
(A) Step of dispersing carbon short fibers and binder short fibers to produce carbon fiber paper (b) After impregnating the carbon fiber paper with a dimethylacetamide solution of polyacrylonitrile, it is immersed in water to solidify the polyacrylonitrile. (C) Step of obtaining a precursor sheet from which the solvent has been removed (d) Step of obtaining a porous electrode substrate by carbonizing polyacrylonitrile in the precursor sheet The method for producing a porous electrode substrate according to claim 2, wherein the steps (b) and (d) are replaced with the following steps (b ') and (d'), respectively.
(B ′) Step of producing a precursor sheet in which the carbon fiber paper is impregnated with a methanol solution of the phenol resin composition and then immersed in water to solidify the phenol resin composition (d ′) in the precursor sheet Process of carbonizing a phenol resin composition to obtain a porous electrode substrate   (D) The manufacturing method of the porous electrode base material as described in any one of Claims 1-3 which heat-presses before carbonization of a process.   The method for producing a porous electrode substrate according to claim 4, wherein the carbonization is performed after the heat and pressure followed by an oxidation treatment.   The porous electrode base material obtained by the manufacturing method of the porous electrode base material as described in any one of Claims 1-5.  The porous electrode base material according to claim 6, wherein the dispersed short carbon fibers are joined together by porous carbon.  A porous electrode base material in which dispersed short carbon fibers are joined by porous carbon.   The membrane-electrode assembly using the porous electrode base material as described in any one of Claims 6-8. A polymer electrolyte fuel cell using the membrane-electrode assembly according to claim 9.

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