JP4461695B2 - Porous carbon electrode substrate and method for producing the same - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a porous carbon electrode substrate suitable for constituting a gas diffusion electrode of a fuel cell, particularly a polymer electrolyte fuel cell.
[0002]
[Prior art]
A gas diffusion electrode (hereinafter referred to as an electrode unless otherwise specified in the present specification) of a polymer electrolyte fuel cell (hereinafter referred to as a fuel cell unless otherwise specified in the present specification) has a high conductivity and a current collecting ability. It is required to have mechanical strength that can withstand handling, as well as the original functions such as being excellent in resistance and diffusion of substances that contribute to electrode reactions.
[0003]
As a base material constituting such an electrode, a composite sheet containing carbon short fibers dispersed in a substantially random direction in a substantially two-dimensional plane and a thermosetting resin such as a phenol resin is usually fired. Carbon fiber / carbon composite obtained by carbonizing carbon short fibers dispersed in a random direction in a substantially two-dimensional plane, obtained by carbonizing a thermosetting resin The thing made from material is used (for example, refer patent document 1).
[0004]
By the way, such an electrode base material generally has a bending elastic modulus as high as a dozen GPa in a three-point bending test, and it is extremely difficult to wind it in a roll shape. Therefore, although the baking is performed by a batch method, the temperature increase rate that can be taken by the batch method is at most about several degrees C / min. Therefore, the productivity is low and the manufacturing cost is high. In addition, the heating furnace is heavily consumed due to repeated heating and cooling.
[0005]
On the other hand, a method is also proposed in which a composite sheet containing short carbon fibers and thermosetting resin dispersed in a random direction in a substantially two-dimensional plane is fired while continuously running in a heating furnace. (For example, refer to Patent Document 2). This method can increase the rate of temperature rise compared to the batch method, and has high productivity because firing is performed continuously. However, on the other hand, unless conditions such as the basis weight of the thermosetting resin, the heating rate, and the maximum firing temperature are controlled in a well-balanced manner, the obtained electrode base material has low conductivity or low mechanical strength. It becomes a thing. If the conductivity is low, the power generation efficiency of a fuel cell using the conductivity is low. Moreover, when mechanical strength is low, a problem will arise in handling property.
[0006]
[Patent Document 1]
JP 7-48182 A
[0007]
[Patent Document 2]
WO 01/56103 Publication
[0008]
[Problems to be solved by the invention]
An object of the present invention is to solve the above-mentioned problems of the prior art, and have a high conductivity and mechanical strength, and excellent handling properties, and is a porous carbon electrode substrate suitable for constituting a fuel cell electrode. And providing a method for producing such a porous carbon electrode substrate with high productivity.
[0009]
  In order to achieve the above object, the present invention provides a carbon short fiber dispersed in a random direction in a substantially two-dimensional plane.Have cracksIt is bound with carbonized material, has a maximum load in a three-point bending test of at least 0.5 N, a bending elastic modulus in the range of 1 to 10 GPa, and a thickness in the range of 0.1 to 0.25 mm. Yes, electrical resistance in the thickness direction is 12 mΩ · cm²A porous carbon electrode substrate characterized by the following is provided.
[0010]
The short carbon fibers preferably have an average fiber diameter in the range of 5 to 20 μm and an average fiber length in the range of 3 to 20 mm. In addition, the basis weight of short carbon fiber is17~50g / m²It is preferable to be in the range of18~50g / m²It is preferable to be within the range. Furthermore, the electrode substrate of the present invention comprisesSodium is preferably contained within a range of 2,000 ppm or less, and the carbonized product is preferably graphite having a crystal size of 20 angstroms or more..
[0011]
The three-point bending test is performed in accordance with the method specified in JIS K 6911. At this time, the width of the test piece is 15 mm, the length is 40 mm, and the distance between fulcrums is 15 mm. Further, the radius of curvature of the fulcrum and the indenter is 3 mm, and the load application speed is 2 mm / min. When the electrode base material has anisotropy with respect to the maximum load and bending elastic modulus, the direction with the highest bending elastic modulus is the length direction of the test piece. The length direction of the strip-shaped electrode substrate obtained by the method is the length direction of the test piece. The maximum load and the flexural modulus of the electrode base material are indicators for the ease of winding into a roll and the quality of handling properties.
[0012]
In addition, the electrical resistance in the thickness direction is as follows: a 2.0 cm × 2.5 cm electrode substrate is used as a test piece, and the test piece is sandwiched between gold-plated stainless steel electrodes and pressed between electrodes under a pressure of 1.0 MPa. It is obtained from the voltage drop when a current of 1 A is passed by the following equation.
[0013]
R = V × 2.0 × 2.5 × 1,000
Where R: electrical resistance in the thickness direction (mΩ · cm²)
V: Voltage drop (V)
Furthermore, the thickness of the electrode substrate is determined by measuring the thickness when a surface pressure of 0.15 MPa is applied to the electrode substrate using a micrometer.
[0014]
The average fiber diameter of the short carbon fibers is determined as a simple average value by selecting any 10 short carbon fibers from an electron micrograph of 5,000 times the electrode substrate and measuring the fiber diameter. When the cross-sectional shape is not circular, for example, an elliptical diameter, the average value of the major axis and the minor axis is taken as the fiber diameter.
[0015]
Also, the average fiber length of the short carbon fibers is obtained by heating the short carbon fiber sheet used in the production of the electrode substrate at 600 ° C. in the atmosphere, and burning the other binders, etc., leaving the short carbon fibers. An optical microscope photograph of 5 times is taken for any 30 short carbon fibers thus obtained, the length of each short carbon fiber is measured from the photograph, and is determined as a simple average value.
[0016]
Furthermore, the basis weight of the short carbon fibers was obtained by heating the short carbon fiber sheet used in the production of the electrode substrate at 600 ° C. in the atmosphere, and burning the other binders and the like leaving the short carbon fibers. Obtained from the weight of short carbon fiber.
[0017]
Further, the basis weight of the carbonized material is obtained by subtracting the basis weight of the short carbon fiber obtained by the above-described method from the basis weight of the electrode base material.
[0018]
The porosity is calculated from the true density and the apparent density of the electrode substrate. The true density can be measured by a well-known floating method or pycnometer method. The apparent density is calculated from the thickness and basis weight of the electrode base material.
[0019]
In order to achieve the above-mentioned object, the present invention has a basis weight of 15 to 60 g / m.²Carbon short fibers dispersed in a random direction in a substantially two-dimensional plane, and a basis weight of 13 to 150 g / m.²The belt-shaped composite sheet containing the thermosetting resin in the range of 10 to 1,000 ° C./min at least at a speed while continuously running in the heating furnace maintained in an inert atmosphere. There is provided a method for producing a porous carbon electrode substrate, which is heated to 1,200 ° C., baked to carbonize the thermosetting resin, and then wound into a roll. The temperature increase rate in the temperature range up to 800 ° C. is preferably lower than that in the temperature range exceeding 800 ° C., and in that case, the temperature increase rate in the temperature range up to 800 ° C. is in the range of 10 to 800 ° C./min. It is preferable to be inside. Moreover, it is also preferable that the composite sheet be fired after being heated and pressure-molded.
[0020]
The temperature increase rate is obtained from the following equation from the temperature at the entrance of the heating furnace, the maximum temperature in the heating furnace, and the time required for the sheet introduced from the entrance of the heating furnace to move to the maximum temperature range (movement time). Here, the heating furnace inlet is a part on the heating furnace inlet side where the atmosphere is switched from the atmosphere to the inert atmosphere.
[0021]
V = (T2-T1) / t
V: Temperature increase rate (° C / min)
T1: Temperature at the furnace entrance (° C)
T2: Maximum temperature in the heating furnace (° C)
t: Travel time
Note that the number of heating furnaces need not be only one, and multistage baking can be performed using two or more heating furnaces. When two heating furnaces are used, the temperature increase rate of the first stage heating furnace is obtained from the above equation, and the temperature increase rate of the second stage heating furnace is determined by calculating T1 in the above equation with that of the preceding heating furnace. The maximum temperature, that is, the maximum temperature of the first stage furnace is obtained. The same applies when three or more heating furnaces are used.
[0022]
The electrode base material of the present invention can be a gas diffusion electrode by forming a conductive gas diffusion layer on at least one surface. Moreover, a polymer electrolyte fuel cell unit can be constituted by joining a gas diffusion electrode on at least one surface of a solid polymer electrolyte membrane having a catalyst layer on both sides on the gas diffusion layer side. Furthermore, a polymer electrolyte fuel cell can be configured by stacking a plurality of the fuel cell units.
[0023]
DETAILED DESCRIPTION OF THE INVENTION
The porous carbon electrode substrate of the present invention will be described in detail together with its production method. In the present invention, the basis weight is first 15 to 60 g / m.²In this range, a carbon short fiber sheet in which carbon short fibers are dispersed in a random direction in a substantially two-dimensional plane is prepared.
[0024]
As the carbon fiber constituting the short carbon fiber, carbon fiber such as polyacrylonitrile (PAN), pitch, or rayon can be used. Among them, it is preferable to use PAN-based or pitch-based, particularly PAN-based carbon fibers because an electrode base material having excellent mechanical strength and appropriate flexibility can be obtained.
[0025]
Such carbon fibers are preferably selected to have an average fiber diameter (average fiber diameter of single fibers) in the range of 5 to 20 μm. When the fiber having an average fiber diameter of less than 5 μm is used, the flexibility of the obtained electrode substrate may be lowered depending on the type of carbon fiber. Moreover, when a fiber having an average fiber diameter exceeding 20 μm is used, the mechanical strength of the obtained electrode substrate may be lowered. A more preferable range of the average fiber diameter is 6 to 13 μm, and a further preferable range is 6 to 10 μm.
[0026]
The short carbon fiber is obtained by cutting the carbon fiber described above, and it is preferable that the average fiber length is within the range of 3 to 20 mm. If the average fiber length is less than 3 mm, the mechanical properties such as the maximum load against bending and the elastic modulus of the obtained electrode substrate may be lowered. Moreover, when the fiber having an average fiber length exceeding 20 mm is used, the dispersibility during papermaking described later is deteriorated, and the variation in the basis weight of the short carbon fiber in the obtained electrode base material is increased, resulting in poor quality. is there. A more preferable range of the average fiber length is 4 to 17 mm, and a further preferable range is 5 to 15 mm.
[0027]
The carbon short fiber sheet can be obtained by a dry papermaking method, but is preferable because it is easy to use a wet papermaking method using water as a papermaking medium, and a uniform sheet with good dispersibility of carbon short fibers is obtained. . A belt-like sheet can be obtained by either a dry papermaking method or a wet papermaking method. In addition, if it is necessary to improve the form retainability and handling properties, the carbon short fiber sheet is within a range of about 1 to 30% by weight, and the polyvinyl alcohol, cellulose, polyester, epoxy resin, phenol resin, acrylic You may provide organic binders, such as resin.
[0028]
In the production of the carbon short fiber sheet, the basis weight of the carbon short fiber is 15 to 60 g / m.²It is preferable to be within the range. The basis weight is 15g / m²If it is less than this, the mechanical strength of the obtained electrode substrate may be insufficient. 60g / m²If it exceeds 1, the rigidity of the obtained electrode base material becomes high, and the flexibility may be impaired. On the other hand, the basis weight of the short carbon fibers determines the porosity of the electrode substrate obtained together with the basis weight of the thermosetting resin described later. In order to achieve a preferable porosity of 70 to 90%, the basis weight of the short carbon fibers should be within the above-mentioned range. A more preferable basis weight range is 17 to 50 g / m.²And a more preferable range is 20 to 40 g / m.²It is.
[0029]
In the present invention, the obtained short carbon fiber sheet is impregnated with a thermosetting resin that is carbonized by firing and binds the short carbon fibers together to obtain a composite sheet.
[0030]
As the thermosetting resin, phenol resin, epoxy resin, furan resin, melamine resin, or the like can be used. A mixed resin containing at least one of these may be used. Among these, it is preferable to use a phenol resin having a high carbonization yield.
[0031]
It is also preferable that a composite sheet of a carbon short fiber sheet and a thermosetting resin is molded by heating and pressing before firing. By this molding, the thickness and porosity can be made more appropriate. The temperature is 100 to 250 ° C, preferably 120 to 200 ° C, more preferably 140 to 180 ° C. The applied pressure is 0.01 to 2 MPa, preferably 0.05 to 1.5 MPa, more preferably 0.1 to 1 MPa.
[0032]
By the way, in continuous baking like this invention, since a temperature increase rate is quick, metals, such as sodium and calcium, remain easily on the electrode base material obtained compared with the case of a batch type. These metal ions cause a decrease in proton conductivity of the solid polymer electrolyte. Therefore, even when a phenol resin is used, it is preferable to select one produced using a metal-free catalyst. Examples of such phenol resins include ammonia resol type phenol resins and novolac type phenol resins. The amount of sodium and calcium contained in the electrode substrate can be measured by fluorescent X-ray analysis, but the amount of sodium is 2,000 ppm or less, preferably 1,000 ppm or less, more preferably 500 ppm or less. It is good to be. The amount of calcium is 100 ppm or less, preferably 70 ppm or less, and more preferably 50 ppm or less. By doing so, the fall of the proton conductivity of a solid polymer electrolyte can be suppressed.
[0033]
For thermosetting resins, carbon black, graphite powder, expanded graphite, carbonaceous milled fibers are used in the range of about 1 to 30% by weight in order to further improve the electrical properties such as conductivity of the obtained electrode substrate. It is also preferable to mix conductive powder such as. Among these, it is preferable to use carbon black or graphite powder. Most preferred is graphite powder.
[0034]
The thermosetting resin described above has a basis weight of 13 to 150 g / m on a carbon short fiber sheet.²Impregnation to be within range. The basis weight of the thermosetting resin is related to the basis weight of the carbonized material binding the short carbon fibers in the obtained electrode base material. If the basis weight of the carbonized material is too low, the mechanical strength of the obtained electrode base material becomes low, and if it is too high, the flexibility of the obtained electrode base material is lowered, so that 5 to 60 g / m.²In order to do so, the basis weight of the thermosetting resin is 13 to 150 g / m.²So as to be within the range of The basis weight of the carbonized product is 18 to 50 g / m.²However, the basis weight of the thermosetting resin necessary to do so is 45 to 125 g / m.²Is within the range. Most preferably, the basis weight of the carbonized material is 20 to 40 g / m.²However, the basis weight of the thermosetting resin necessary to do so is 50 to 100 g / m.²Is within the range. On the other hand, the basis weight of the thermosetting resin determines the porosity of the electrode substrate obtained together with the basis weight of the carbon short fibers described above. In order to achieve a preferable porosity of 70 to 90%, the basis weight of the thermosetting resin is preferably within the above range.
[0035]
In the present invention, a strip-shaped composite sheet, that is, a strip-shaped composite sheet containing short carbon fibers and a thermosetting resin, is led into a heating furnace maintained in an inert atmosphere, and the heating furnace is continuously provided. The temperature is raised to at least 1,200 ° C. at a speed in the range of 10 to 1,000 ° C./min while being run, and baked to carbonize the thermosetting resin. As a result, a porous carbon electrode substrate is obtained in which carbon short fibers dispersed in a random direction in a substantially two-dimensional plane are bound with a carbonized material. The obtained electrode substrate is wound into a roll.
[0036]
A so-called continuous firing furnace can be used as the heating furnace, and an inert atmosphere in the furnace can be obtained by circulating an inert gas such as nitrogen gas or argon gas in the furnace.
[0037]
In firing, the temperature raising rate is set within a range of 10 to 1,000 ° C./min, and the temperature is raised to at least 1,200 ° C. at that rate. If the rate of temperature increase is less than 10 ° C./min, the productivity is significantly reduced and the production cost is increased. Further, since the thermosetting resin is gradually carbonized, appropriate cracking of the carbonized product does not occur. The electrode substrate thus obtained has extremely low flexibility while maintaining conductivity. On the other hand, when the rate of temperature rise exceeds 1000 ° C./min, the thermosetting resin is abruptly carbonized, resulting in significant cracking of the carbonized material. Mechanical properties such as properties and strength are extremely low, and there are many wrinkles and warping. A preferable temperature increase rate range is 200 to 900 ° C./min, and a more preferable range is 300 to 800 ° C./min.
[0038]
Moreover, it is preferable to make the temperature increase rate in the temperature range up to 800 ° C. lower than that in the temperature range exceeding 800 ° C. This is because the weight loss in the process of carbonizing the thermosetting resin in the temperature range up to 800 ° C is much larger than that in the temperature range above 800 ° C, but the increase in the temperature range up to 800 ° C. If the temperature rate is lower than that in the temperature range exceeding 800 ° C., it is possible to further suppress deterioration of electrical characteristics such as conductivity and mechanical characteristics such as strength of the obtained electrode base material. is there.
[0039]
The firing temperature is required to be at least 1,200 ° C., but firing is preferably performed at a maximum firing temperature of 1,500 to 3,000 ° C. When the maximum firing temperature is 1,500 ° C. or more, graphitization of the thermosetting resin proceeds, impurities in the obtained electrode base material are reduced, and electrical characteristics such as conductivity are further improved. On the other hand, when the maximum firing temperature exceeds 3,000 ° C., not only the operating cost increases, but also the heating furnace is exhausted, its maintenance cost increases, and the production cost increases. A more preferable range of the maximum firing temperature is 1,600 to 2,500 ° C, and a more preferable range is 1,700 to 2,000 ° C. The degree of graphitization can be determined from the crystal size obtained from the half-value width of the carbon (002) peak measured by wide-angle X-ray diffraction by the transmission method. The crystal size of graphite is preferably 20 angstroms or more, more preferably 30 angstroms or more, and most preferably 40 angstroms or more. The fact that the crystal size is 20 angstroms or more means that graphitization of the thermosetting resin is progressing, and the proton conductivity of the solid polymer electrolyte is lowered due to less impurities in the obtained electrode substrate. And the conductivity of the obtained electrode base material is improved.
[0040]
Thus, carbon short fibers dispersed in a random direction in a substantially two-dimensional plane are bound with carbonized material, and the maximum load in a three-point bending test is at least 0.5 N and bending is performed. The elastic modulus is in the range of 1 to 10 GPa, the thickness is in the range of 0.1 to 0.25 mm, and the electric resistance in the thickness direction is 12 mΩ · cm.²The following porous carbon electrode substrate as shown in FIG. 1 is obtained. In FIG. 1, short carbon fibers appear to be linear, and a carbonized product of a thermosetting resin adheres to them.
[0041]
The maximum load in the three-point bending test of the electrode base material of the present invention is at least 0.5N. Such an electrode base material is hard to break and has excellent handling properties. The maximum load is preferably 0.6 N or more, and more preferably 0.7 N or more.
[0042]
The flexural modulus in the three-point bending test is related to the deformability and flexibility of the electrode base material, and those having a flexural modulus of less than 1 GPa are easily deformed when an external force is applied. End up. Moreover, the thing exceeding 10 GPa has very low flexibility, it becomes difficult to wind up into a roll shape, and handling properties deteriorate. A preferable range of the flexural modulus is 3 to 9 GPa, and a more preferable range is 5 to 8 GPa.
[0043]
The thickness of the electrode substrate is in the range of 0.1 to 0.25 mm. The thickness of the electrode substrate is related to cracking and flexibility when a shearing force is applied. If the thickness is less than 0.1 mm, when the electrode is constituted and the fuel cell is constituted, it is easily cracked when receiving a shearing force from the separator. Moreover, the thing exceeding 0.25 mm will reduce a softness | flexibility largely, and winding up to a roll shape will become difficult, or handling property will deteriorate. A preferable thickness range is 0.11 to 0.22 mm, and a more preferable range is 0.12 to 0.16 mm.
[0044]
The electric resistance in the thickness direction of the electrode substrate is 12 mΩ · cm.²It is as follows. The electric resistance in the thickness direction is related to the power generation efficiency when an electrode is formed and a fuel cell is formed. And the electric resistance in the thickness direction is 12 mΩ · cm²If it exceeds, the voltage drop due to ohmic loss increases, and the power generation efficiency decreases greatly. Electrical resistance is 9mΩ · cm²Or less, preferably 6 mΩ · cm²More preferably, it is as follows.
[0045]
The electrode substrate of the present invention preferably has a porosity in the range of 70 to 90%. When the porosity is within this range, when the electrode is configured and the fuel cell is configured, evaporation of water inside the fuel cell can be further suppressed, the solid polymer electrolyte is dried and proton conductivity is reduced. While being able to suppress that it falls, gas diffusibility improves and power generation efficiency comes to improve. A more preferable range of the porosity is 72 to 88%, and a further preferable range is 75 to 85%.
[0046]
It is also preferable to apply a water repellent treatment to the surface of the electrode substrate. When the surface has water repellency, it becomes possible to suppress clogging caused by water generated in the power generation reaction when an electrode is configured and a fuel cell is configured, and a substance necessary for the reaction can be sufficiently supplied. It becomes possible to improve power generation efficiency. Such water-repellent processing is performed on the surface of the electrode base material by using tetrafluoroethylene resin (PTFE), perfluoroalkoxy resin (PFA), fluorinated ethylene propylene resin (FEP), and fluorinated ethylene tetrafluoroethylene resin (ETFE). Can be carried out by applying about 1 to 50% by weight, preferably about 5 to 40% by weight, and more preferably about 10 to 30% by weight.
[0047]
Now, the electrode base material of the present invention can be formed into a gas diffusion electrode by forming a conductive gas diffusion layer on at least one surface. When the gas diffusion layer is provided, the unevenness on the surface is covered and smoothed, so that when the electrode is configured and the fuel cell is configured, it is easy to ensure electrical contact with the catalyst layer. In addition, damage to the solid polymer electrolyte membrane can be prevented more reliably. Such a gas diffusion layer is composed of the same fluorine-based resin as used in the above-described water-repellent processing on the surface of the electrode base material and the same conductive powder mixed in the above-described thermosetting resin. This can be done by applying the mixture. The mixing amount of the conductive powder is about 10 to 50% by weight, preferably about 15 to 45% by weight, and more preferably about 20 to 40% by weight.
[0048]
Such a gas diffusion electrode can constitute a fuel cell unit by bonding it to at least one side of a solid polymer electrolyte membrane having a catalyst layer on both sides on the gas diffusion layer side. In addition, a fuel cell can be configured by stacking a plurality of such fuel cell units. The catalyst layer is composed of a layer containing a solid polymer electrolyte and catalyst-supporting carbon. As the catalyst, platinum is usually used. In a fuel cell in which a reformed gas containing carbon monoxide is supplied to the anode side, it is preferable to use platinum and ruthenium as the catalyst on the anode side. As the solid polymer electrolyte, a material made of a perfluorosulfonic acid polymer having high proton conductivity, oxidation resistance and high heat resistance is preferably used. Such a fuel cell unit and the configuration of the fuel cell itself are well known.
[0049]
Examples and Comparative Examples
Example 1:
Polyacrylonitrile-based carbon fiber “Torayca” T-300-6K (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. Furthermore, it is immersed in a 10% by weight aqueous dispersion of polyvinyl alcohol and dried to give a carbon fiber weight of about 50 g / m.²A belt-like carbon short fiber sheet was obtained. The amount of polyvinyl alcohol attached corresponds to about 20% by weight.
[0050]
Next, the carbon short fiber sheet is impregnated with a phenol resin 10 wt% methanol solution so that the phenol resin is 125 parts by weight with respect to 100 parts by weight of the carbon short fiber sheet, and dried at 90 ° C. The phenol resin was cured by heating at 150 ° C. for 30 minutes under a pressure of 1.5 MPa. As the phenol resin, a mixed resin of 100 parts by weight of an alkali resol type phenol resin and the same part by weight of a novolac type phenol resin was used. The basis weight of the phenol resin adhering to the carbon short fiber sheet is about 63 g / m.²It becomes.
[0051]
Next, the composite sheet of short carbon fibers and phenol resin is introduced into a heating furnace having a maximum temperature of 2,000 ° C. maintained in a nitrogen gas atmosphere, and continuously running in the heating furnace, It was baked at a heating rate of 110 ° C./min up to 110 ° C./min. The specifications of the obtained porous carbon electrode substrate including those described above are shown below.
[0052]
Average fiber diameter of short carbon fibers: 7 μm
Average fiber length of short carbon fibers: 12 mm
Carbon short fiber basis weight: 50 g / m²
Maximum load in 3-point bending test: 1.1N
Flexural modulus in 3-point bending test: 6.6 GPa
Thickness: 0.21mm
Electrical resistance in the thickness direction: 8 mΩ · cm²
Carbonized product weight: 40 g / m²
Porosity: 80%
Graphite crystal size: 43 Å
Sodium content: 40 ppm
Calcium content: 50ppm
Example 2:
In Example 1, the pressure at which the phenol resin was cured was 0.5 MPa, and the rate of temperature increase was 380 ° C./min up to 800 ° C., and 500 ° C./min at temperatures exceeding 800 ° C. The specifications of the obtained porous carbon electrode substrate including those described above are shown below.
[0053]
Average fiber diameter of short carbon fibers: 7 μm
Average fiber length of short carbon fibers: 12 mm
Carbon short fiber basis weight: 50 g / m²
Maximum load in 3-point bending test: 0.8N
Flexural modulus in 3-point bending test: 5.0 GPa
Thickness: 0.22mm
Electrical resistance in the thickness direction: 10 mΩ · cm²
Carbonized product weight: 40 g / m²
Porosity: 80%
Graphite crystal size: 44 Å
Sodium content: 50ppm
Calcium content: 30ppm
Example 3:
In Example 1, the basis weight of the carbon fiber is 24 / m.²The carbon short fiber sheet was impregnated with a 10 wt% methanol solution of phenol resin so that the phenol resin was 125 parts by weight with respect to 100 parts by weight of the carbon short fiber sheet, and 90 ° C. After drying, the phenol resin was cured by heating at 150 ° C. for 30 minutes under a pressure of 0.5 MPa. Examples of the phenol resin include 100 parts by weight of an alkali resol type phenol resin, the same part by weight of a novolac type phenol resin, 75 parts by weight of graphite powder with respect to 100 parts by weight of these phenol resins, and 100 parts by weight of these phenol resins. A mixed resin obtained by mixing 75 parts by weight of carbon black was used. The basis weight of the phenol resin adhering to the carbon short fiber sheet is about 26 g / m.²It becomes.
[0054]
Next, the composite sheet of the short carbon fiber and the phenol resin is continuously introduced into a heating furnace having a maximum temperature of 2,000 ° C. maintained in a nitrogen gas atmosphere, and up to 800 ° C. at 380 ° C./min. At a temperature exceeding 800 ° C., it was fired at a heating rate of 500 ° C./min and wound up into a roll. The specifications of the obtained porous carbon electrode substrate including those described above are shown below.
[0055]
Average fiber diameter of short carbon fibers: 7 μm
Average fiber length of short carbon fibers: 12 mm
Carbon short fiber basis weight: 24 g / m²
Maximum load in 3-point bending test: 0.9N
Bending elastic modulus in three-point bending test: 9.0 GPa
Thickness: 0.17mm
Electrical resistance in the thickness direction: 4 mΩ · cm²
Carbonized product weight: 15 g / m²
Porosity: 80%
Graphite crystal size: 48 Angstrom
Sodium content: 20 ppm
Calcium content: 40ppm
Comparative example:
In Example 1, the pressure when curing the phenol resin was changed to 0.5 MPa. In addition, a batch-type heating furnace was used for firing, and the temperature increase rate was 1 ° C./min up to 800 ° C., and 2 ° C./min at temperatures exceeding 800 ° C. The specifications of the obtained porous carbon electrode substrate including those described above are shown below.
[0056]
Average fiber diameter of short carbon fibers: 7 μm
Average fiber length of short carbon fibers: 12 mm
Carbon short fiber basis weight: 50 g / m²
Maximum load in 3-point bending test: 1.3N
Flexural modulus in three-point bending test: 12.0 GPa
Thickness: 0.19mm
Electrical resistance in the thickness direction: 5 mΩ · cm²
Carbonized product weight: 40 g / m²
Porosity: 80%
Graphite crystal size: 49 Å
Sodium content: 10ppm
Calcium content: 40ppm
The porous carbon electrode substrates of Examples 1 to 3 have a large maximum load in a three-point bending test, a moderate bending elastic modulus, excellent handling properties, and high conductivity. On the other hand, the porous carbon electrode substrate of the comparative example has a bending elastic modulus that is too large and lacks flexibility and is inferior in handling properties.
[0057]
  The present invention provides a short carbon fiber dispersed in a random direction in a substantially two-dimensional plane.Have cracksIt is bound with carbonized material, and the maximum load in the three-point bending test is at least 0.5 N, the bending elastic modulus is in the range of 1 to 10 GPa, and the thickness is in the range of 0.1 to 0.25 mm. The electrical resistance in the thickness direction is 12 mΩ · cm²A porous carbon electrode substrate having a basis weight of 15 to 60 g / m²Carbon short fibers dispersed in a random direction in a substantially two-dimensional plane, and a basis weight of 13 to 150 g / m.²At least 1 at a speed in the range of 10 to 1000 ° C./min while continuously running a belt-like sheet containing a thermosetting resin in the range of 10 to 1,000 ° C./min while being continuously run in a heating furnace maintained in an inert atmosphere. , Heated to 200 ° C., baked to carbonize the thermosetting resin, and then wound into a roll. As is clear from the comparison between the examples and the comparative examples, the conductivity is High mechanical strength and excellent handling. Therefore, it is suitable for constituting a gas diffusion electrode of a fuel cell. Moreover, since continuous baking is performed, productivity is high and production cost can be reduced.
[Brief description of the drawings]
FIG. 1 is an electron micrograph (magnification: 60 times) of a porous carbon electrode substrate according to an embodiment of the present invention.

Claims (13)

Carbon short fibers dispersed in a random direction in a substantially two-dimensional plane are bound with carbonized material having cracks , and the bending load is elastic at a maximum load of at least 0.5 N in a three-point bending test. A porous carbon electrode substrate having a rate in the range of 1 to 10 GPa, a thickness in the range of 0.1 to 0.25 mm, and an electric resistance in the thickness direction of 12 mΩ · cm ² or less. .   The porous carbon electrode substrate according to claim 1, wherein the short carbon fibers have an average fiber diameter in the range of 5 to 20 µm and an average fiber length in the range of 3 to 20 mm. Basis weight of short carbon fibers is in the range of 17 ~ 50 g / m ^2, the porous carbon electrode substrate according to claim 1 or 2. Basis weight of the carbonized material is in the range of 18 ~ 50 g / ^{m 2,} the porous carbon electrode substrate according to any one of claims 1 to 3. The porous carbon electrode base material in any one of Claims 1-4 in which sodium is contained within the range of 2,000 ppm or less . The porous carbon electrode substrate according to any one of claims 1 to 5 , wherein the carbonized material is graphite having a crystal size of 20 angstroms or more . Basis weight in the range of 15 to 60 g / ^{m 2,} substantially heat that the short carbon fibers were dispersed in random directions in a two-dimensional plane, in a range having a basis weight of 13~150g / ^{m 2} The belt-shaped composite sheet containing the curable resin is raised to at least 1200 ° C. at a speed in the range of 10 to 1,000 ° C./min while continuously running in a heating furnace maintained in an inert atmosphere. A method for producing a porous carbon electrode substrate, which is heated and baked to carbonize the thermosetting resin and then wound into a roll.   The manufacturing method of the porous carbon electrode base material of Claim 7 which makes the temperature increase rate in the temperature range up to 800 degreeC lower than it in the temperature range over 800 degreeC.   The manufacturing method of the porous carbon electrode base material of Claim 8 which makes the temperature increase rate in the temperature range to 800 degreeC in the range of 10-800 degree-C / min.   The manufacturing method of the porous carbon electrode base material in any one of Claims 7-9 which bakes the composite sheet heat-pressed and shape | molded.   A gas diffusion electrode comprising an electrically conductive gas diffusion layer formed on at least one surface of the porous carbon electrode substrate according to claim 1.   A fuel cell unit comprising the gas diffusion electrode according to claim 11 bonded to at least one surface of a solid polymer electrolyte membrane having catalyst layers on both sides on the gas diffusion layer side.   A fuel cell comprising a plurality of the fuel cell units according to claim 12 stacked.

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