JP2009076347A - Gas diffusion electrode substrate and its manufacturing method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a gas diffusion electrode substrate which has different gas permeability in surface direction in one sheet of gas diffusion electrode by a commercially viable method, and its manufacturing method. <P>SOLUTION: In order to provide an electrode substrate having different characteristics of a high gas permeability portion and a low gas permeability portion in one sheet of sheet material, application amount in width direction is changed by controlling the resin amount distribution to be given to a carbon fiber paper. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a porous carbon substrate preferably used as a material for a gas diffusion layer of a polymer electrolyte fuel cell and a method for producing the same.

  In the solid polymer fuel cell, one surface functions as an anode and the other surface functions as a cathode with the solid polymer membrane as a center. On the anode side, a fuel gas such as hydrogen is supplied to the catalyst layer through the pores of the gas diffusion layer, while on the cathode side, an oxidant gas such as air is supplied to the catalyst layer through the gas diffusion layer. A reaction occurs and power can be generated.

H ₂ → 2H ⁺ + 2e ⁻ (Anode side)
2H ⁺ + 1 / 2O ₂ + 2e ⁻ → H ₂ O (cathode side)
Since water is generated by the above-described electrochemical reaction on the cathode side, the oxidant gas supplied to the cathode has a higher water vapor partial pressure as it flows through the path in the separator, and water condensation tends to occur on the gas discharge side. Since the pores of the gas diffusion layer are blocked by the condensed water (hereinafter abbreviated as “flooding phenomenon”), the supply of the oxidant gas to the catalyst layer becomes insufficient and the power generation characteristics deteriorate.

  Although the flooding phenomenon can be suppressed by heating the fuel cell or increasing the porosity of the gas diffusion electrode substrate, in that case, drying of the solid polymer membrane is promoted on the gas supply side. As drying of the solid polymer membrane proceeds, proton transportability, which is a function of the solid polymer membrane, deteriorates and power generation characteristics deteriorate.

  In order to solve the above-mentioned flooding phenomenon on the gas discharge side and the drying of the solid polymer membrane on the gas supply side, the gas diffusion layer on the gas supply side is made to have low gas permeability, and the gas diffusion layer on the gas discharge side is A proposal for high gas permeability has been made (see Patent Document 1). However, in this method, two gas diffusion layers having a low carbon adhering amount (high gas permeability) and a gas diffusion layer having a high carbon adhering amount (low gas permeability) are bonded to the electrolyte. The purpose cannot be easily achieved in the process.

On the other hand, in the papermaking process under given conditions, areas with a large amount of fiber accumulation and areas with a small amount of fiber accumulation are created, an area with a large amount of fiber accumulation is arranged on the gas discharge side, and an area with a small amount of fiber accumulation is arranged on the gas supply side. A proposal has been made (see Patent Document 2). However, in this method, it is necessary to design a paper making process with the same width as the gas diffusion electrode base material in order to achieve the invention, and paper making with a narrower width than before, it is difficult to establish commercially. .
Japanese Patent Laid-Open No. 2001-6698 JP 2004-273392 A

  In view of the above-mentioned problems in the prior art, the present invention provides a porous carbon base material having different gas permeability in the in-plane direction among a single gas diffusion electrode base material and its production by a commercially established method. It is to provide a method.

  In the present invention, by controlling the distribution of the amount of resin applied in the resin impregnation step, it is possible to provide a gas diffusion electrode substrate having gas permeability that matches the use environment of the fuel cell, and the fuel cell characteristics It is possible to improve both stability and commerciality.

  That is, a gas diffusion electrode base material comprising a carbon fiber paper body and a resin carbide, wherein the carbon fiber paper body has a substantially uniform basis weight, and the resin carbide is It is a gas diffusion electrode base material having a weight distribution in the width direction.

Furthermore, the present invention provides
(1) A method for producing a gas diffusion electrode substrate including a step of resin curing and firing after spraying a resin on a carbon fiber paper body, wherein the amount of the resin is distributed in the width direction of the carbon fiber paper body Providing and spraying,
(2) A method for producing a gas diffusion electrode substrate including a step of resin curing and firing after resin is sprayed on a carbon fiber paper body, wherein the carbon fiber paper body is disposed at an angle with respect to a horizontal plane. And then spraying the resin,
(3) A method for producing a gas diffusion electrode substrate comprising a step of impregnating a carbon fiber papermaking body with a resin, followed by resin curing and firing, and before the resin curing and firing, a pair of gaps differing in the width direction Having a step of passing between the rolls of
It is characterized by.

  ADVANTAGE OF THE INVENTION According to this invention, it becomes possible to provide the gas diffusion electrode base material with distribution in gas permeability in one sheet | seat by giving the fabric distribution of the in-plane direction of a gas diffusion electrode base material. Moisture discharge is promoted by laying out a gas permeable electrode base with high gas permeability on the cathode gas discharge side, and a gas diffusion electrode base with low gas permeability on the cathode gas supply side By promoting the moisture retention by laying out the fuel cell, it becomes possible to provide a fuel cell with uniform moisture distribution in the cell and high power generation stability.

  The gas diffusion electrode substrate of the present invention is made by a method comprising paper making for forming a carbon fiber structure as a basic structure, resin impregnation and resin curing for binding carbon fibers, and firing for carbonizing the resin. It is obtained and has a basis weight distribution by intentionally distributing the amount of resin carbide that is a constituent element thereof.

  The substantially uniform basis weight means that the ratio between the maximum basis weight and the minimum basis weight within one electrode substrate is within 1.05, and that having a basis weight distribution means that the maximum basis weight is within one electrode substrate. It means that the basis weight ratio of the minimum basis weight is 1.05 or more.

Weight ratio = M1 ÷ M2
M1: Maximum basis weight g / m ²
M2: minimum basis weight g / m ² .

  In addition, the minimum basis weight and the maximum basis weight are obtained by taking four or more samples (10 cm × 10 cm) from arbitrary positions in the width direction in one electrode substrate, and dividing the sample mass by the area of the sample. Of these values, the largest basis weight M1 was the largest value and the smallest basis weight M2 was the smallest value. When the width direction occupation ratio is less than 75% with four samples, the number of samples is increased until the occupation ratio becomes 75% or more. Here, the width direction is a direction perpendicular to the roll winding direction (substantially the paper making winding direction) in the manufacturing process of the gas diffusion electrode substrate.

  The sloped basis weight distribution ideally means that when comparing any two basis weights between the maximum basis weight position and the minimum basis weight position, any two point basis weights can be compared. This means that the basis weight is larger than the basis weight on the minimum basis weight position side. In the present invention, the inclined basis weight distribution means that the basis weight between the maximum basis weight position and the minimum basis weight position is M2 + (M1-M2). A distribution in the range of × 0.25 to M2 + (M1−M2) × 0.75 is meant.

The basis weight is calculated by dividing the 10 cm × 10 cm square sample mass of the gas diffusion electrode substrate by the sample area as described above. If the width dimension is less than 40 cm and four samples cannot be collected, the sample dimensions should be set so that the four sample width direction occupancy is 75% or more and the area of one sample is 0.01 m ² or more. change. When the area of one sample is less than 0.01 m ² due to restrictions on the size of the gas diffusion electrode base material, the sample at the same position is cut out from the plurality of gas diffusion electrode base materials so that the total sample area is 0.01 m ² or more. Increase the number of samples so that

Weight per unit = W ÷ A
W: Sample mass g
A: Sample area m ² .

  In the present invention, the carbon fiber papermaking body is composed of carbon fibers serving as a skeleton and a papermaking binder that bonds the fibers, and is wound in a roll shape. The carbon fiber used as a raw material may be any of polyacrylonitrile (hereinafter abbreviated as PAN) carbon fiber, pitch carbon fiber, rayon carbon fiber, and phenolic carbon fiber. It is preferable to use a PAN-based carbon fiber or a pitch-based carbon fiber with high tensile strength, and it is more preferable to use a PAN-based carbon fiber. The papermaking binder is not particularly limited as long as it is a known one, and examples thereof include known organic binders such as acrylic resin, urethane resin, polyvinyl alcohol, water-soluble cellulose, and starch.

  The resin for binding the carbon fibers is applied by resin impregnation in which the carbon fiber papermaking body is passed through a tank containing a liquid resin or through a step of spraying the liquid resin. As the resin, a thermosetting resin such as a phenol resin or an epoxy resin can be used, and the amount of the resin is preferably a mass ratio of 0.5 to 4 with respect to the carbon fiber papermaking body. If the resin mass ratio relative to the carbon fiber papermaking body is less than 0.5, mechanical strength properties that can withstand the use environment cannot be obtained. When the resin mass ratio with respect to the carbon fiber papermaking body is 4 or more, the porosity of the carbon fiber papermaking body is lowered, and the gas diffusivity necessary for the use environment cannot be obtained. Moreover, in order to improve the electrical conductivity of the gas diffusion electrode substrate, a conductive filler such as graphite powder may be mixed with the resin and impregnated.

  The present invention is characterized by changing the gas permeability of the gas diffusion electrode base material by controlling the resin amount distribution in the width direction when continuously impregnating the carbon fiber paper body wound in a roll shape. is there. There are the following three methods as production methods for controlling the amount of resin.

  A 1st manufacturing method is a method of changing spraying resin amount in the width direction of a carbon fiber papermaking body. As a method of changing the spraying amount, there is a method of changing the hole diameter and / or pitch of the spraying port in the width direction. There is also a method of changing the concentration and / or flow rate of the resin to be sprayed in the width direction, but there is no limitation as long as it is a known one.

  And in the 1st manufacturing method, it is preferable to provide the gradient distribution in the said amount of spraying resin in the width direction of a carbon fiber papermaking body. The slanting spray resin amount is ideally any two spray resins when comparing the two spray resin amounts between the maximum spray resin amount position and the minimum spray resin amount position. Even if the amount is compared, it means that the amount of spray resin on the position side of the maximum spray resin amount is larger than the amount of spray resin on the position side of the minimum spray resin amount. The distribution of the amount means that the amount of spray resin between the position of the maximum spraying resin amount Q1 [g / min] and the middle position of the minimum spraying amount Q2 [g / min] is Q2 + (Q1-Q2) × 0.25. The distribution in the range of Q2 + (Q1-Q2) × 0.75 is meant.

  The second manufacturing method is a method in which the carbon fiber papermaking body to be delivered is installed at an angle with respect to a horizontal plane and the resin is sprayed. Here, the horizontal plane is a plane that is horizontal with respect to the ground, in other words, a water surface that is formed when water is allowed to stand still. The provision of an angle means that the surface of the carbon fiber paper body has an angle other than 0 ° with respect to the horizontal plane, and in order to effectively distribute the resin amount, an angle of 45 ° or more is preferably provided, and 90 ° More preferably.

  The third production method is a method in which a carbon fiber paper body impregnated with resin is passed between a pair of rolls having different gaps in the width direction. The angle formed by the pair of rolls is referred to as a taper angle. In the present invention, the taper angle is not limited at all. However, if the taper angle is too wide, local tension is applied to the carbon fiber papermaking body, causing problems of wrinkles and tearing. In order to generate | occur | produce, it is preferable that a taper angle shall be 0.2 degrees or less. In addition, the pair of rolls is provided with an angle with respect to the width direction of the carbon fiber paper body so that the resin squeezed by the pair of rolls flows from the roll part with a narrow gap toward the roll part with a wide gap. Also good.

  In the above manufacturing method, the resin is cured by heat treatment in order to fix the resin distributed in the width direction of the carbon fiber papermaking body. The curing method is not particularly limited as long as it is a known method, and includes a heat treatment under no pressure in a drying furnace and a heat treatment in a hot plate press.

  The firing process is performed in an inert atmosphere into which an inert gas such as nitrogen gas or argon gas is introduced. In the present invention, the treatment temperature is not limited at all, but the final firing temperature is preferably 1500 to 3000 ° C. from the balance of electrical conductivity and mechanical strength.

  Examples of the present invention and comparative examples will be described below.

Example 1
Polyacrylonitrile-based carbon fiber “Torayca (registered trademark)” T300-6K (average single fiber diameter: 7 μm, number of single fibers: 6,000 fibers) manufactured by Toray Industries, Inc. is cut to a length of 12 mm, and water is used as a papermaking medium. The paper was continuously made, further immersed in a 10% by weight aqueous solution of polyvinyl alcohol and dried to obtain a long carbon fiber paper having a carbon fiber basis weight of about 20 g / m ² and wound into a roll. The amount of polyvinyl alcohol attached corresponds to 20% by mass of the carbon fiber paper.

  A dispersion obtained by mixing scale-like graphite BF-5A (average particle size 5 μm), phenol resin, and methanol at a mass ratio of 1: 4: 40 manufactured by Chuetsu Graphite Industries Co., Ltd. was prepared. In the carbon fiber paper body of the process conceptual diagram of FIG. 1, resin spray ports are provided at a pitch of 1 cm at a portion 101, resin spray ports are provided at a distance of 1.5 cm at a portion 102, Resin spray ports were provided at intervals of 2 cm, and the dispersion was sprayed from the resin spray port, dried at 90 ° C. for 3 minutes, and wound into a roll. The phenol resin was adjusted so that the phenol resin was 125 parts by mass with respect to 100 parts by mass, and a resin in which a resol type phenol resin and a novolac type phenol resin were mixed at a mass ratio of 1: 1 was used.

Two dried resin-impregnated carbon paper bodies were stacked to form a molding material, and the following steps (1) to (3) were repeated to perform intermittent molding to cure the phenol resin.
(1) Open the pressing surface of the press (molding surface temperature 170 ° C.).
(2) The molding material is sent to a press machine and the molded product is taken (intermittent feed length 100 mm, required time about 5 seconds).
(3) The press machine pressurization surface is closed and heating and pressurization are performed (pressure 0.75 MPa, required time about 25 seconds).

  The carbon fiber papermaking body subjected to the heat treatment of the resin was introduced into a heating furnace having a maximum temperature of 2,000 ° C. maintained in a nitrogen gas atmosphere, and while continuously running in the heating furnace, about 500 ° C. / The gas diffusion electrode substrate was obtained by firing at a heating rate of 400 min / min (up to 650 ° C., 550 ° C./min for temperatures exceeding 650 ° C.).

(Example 2)
A dispersion obtained by mixing scale-like graphite BF-5A (average particle size 5 μm), phenol resin, and methanol at a mass ratio of 1: 4: 40 manufactured by Chuetsu Graphite Industries Co., Ltd. was prepared. The carbon fiber papermaking body is disposed at an angle of 90 ° with respect to a horizontal plane, and in the carbon fiber papermaking body of the process conceptual diagram of FIG. Provided at a pitch of 5 cm, the dispersion was sprayed from the resin spraying port, dried at 90 ° C. for 3 minutes, and wound up into a roll. The phenol resin was adjusted so that the phenol resin was 125 parts by mass with respect to 100 parts by mass, and a resin in which a resol type phenol resin and a novolac type phenol resin were mixed at a mass ratio of 1: 1 was used.

  Two dried resin-impregnated carbon paper bodies were laminated to form a molding material, and the subsequent resin curing and firing were carried out in the same manner as in Example 1 to obtain a gas diffusion electrode substrate.

(Example 3)
A dispersion obtained by mixing scale-like graphite BF-5A (average particle size 5 μm), phenol resin, and methanol at a mass ratio of 1: 4: 40 manufactured by Chuetsu Graphite Industries Co., Ltd. was prepared. After passing through the roll, after passing through the dipping tank containing the dispersion liquid so that the phenol resin becomes 125 parts by mass with respect to 100 parts by mass of the carbon fiber paper, the taper angle is 0.13 ° in the process conceptual diagram of FIG. It was passed between set rolls, dried at 90 ° C. for 3 minutes, and wound up into a roll. As the phenol resin, a resin obtained by mixing a resol type phenol resin and a novolac type phenol resin at a mass ratio of 1: 1 was used.

  Two dried resin-impregnated carbon paper bodies were laminated to form a molding material, and the subsequent resin curing and firing were carried out in the same manner as in Example 1 to obtain a gas diffusion electrode substrate.

(Comparative Example 1)
A gas diffusion electrode substrate was obtained in the same manner as in Example 1 except that the resin spray ports 101 and 103 were changed to a pitch of 1.5 cm.

(Comparative Example 2)
A gas diffusion electrode substrate was obtained in the same manner as in Example 3 except that the taper angle was changed to 0 °. The differential pressure generated when air of 14 cm ³ / cm ² / sec in the thickness direction was permeated through the gas diffusion electrode substrates of Examples and Comparative Examples thus obtained was measured as a gas permeability index. .

  Table 1 summarizes the basis weight, basis weight ratio, and gas permeability of the above examples and comparative examples.

  The basis weight ratio of the gas diffusion electrode base materials of Examples 1 to 4 is 1.05 or more, and the difference between the maximum basis weight and the minimum basis weight is large. Correspondingly, the differential pressure is high at the maximum basis weight, and the differential pressure is low at the minimum basis weight. As described above, according to the present invention, it is possible to provide a gas diffusion electrode substrate in which the gas permeability is changed in one gas diffusion electrode substrate by controlling the resin amount distribution in the resin impregnation step. it can.

  The porous carbon substrate according to the present invention can be preferably used as a material for a gas diffuser of a polymer electrolyte fuel cell, but its application range is not limited thereto.

2 is a process conceptual diagram of Example 1. FIG. FIG. 5 is a process conceptual diagram of Example 2. 6 is a process conceptual diagram of Example 3. FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 100: Carbon fiber papermaking body 101: Resin low weight part after impregnation 102: Resin middle weight part after impregnation 103: Resin high weight part after impregnation 111: Resin spraying port 131: Dipping tank 132: Roll 133: Taper angle

Claims (6)

A gas diffusion electrode base material comprising a carbon fiber paper body and a resin carbide, wherein the carbon fiber paper body has a substantially uniform basis weight, and the resin carbide is in a width direction. A gas diffusion electrode substrate having a basis weight distribution. The gas diffusion electrode substrate according to claim 1, wherein the distribution of the fabric weight in the width direction is an inclined distribution in which the fabric weight in the width direction continuously increases or decreases. A method of manufacturing a gas diffusion electrode substrate including a step of resin curing and firing after spraying a resin on a carbon fiber paper body, wherein the amount of the resin is distributed in the width direction of the carbon fiber paper body A method for producing a gas diffusion electrode substrate to be sprayed. The method for producing a gas diffusion electrode substrate according to claim 3, wherein the distribution in the width direction is an inclined distribution that increases or decreases the amount of resin sprayed in the width direction. A method for producing a gas diffusion electrode substrate including a step of resin curing and firing after spraying a resin on a carbon fiber paper body, wherein the carbon fiber paper body is disposed at an angle with respect to a horizontal plane. A method for producing a gas diffusion electrode substrate. A method for producing a gas diffusion electrode substrate comprising a step of resin curing and baking after impregnating a resin into a carbon fiber paper body, between a pair of rolls having different gaps in the width direction before resin curing and baking The manufacturing method of the gas diffusion electrode base material which has the process of passing through.

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