JP6477401B2 - Porous electrode substrate, membrane-electrode assembly using the same, and polymer electrolyte fuel cell using the same - Google Patents

Description

The present invention relates to a porous electrode substrate applied to a polymer electrolyte fuel cell, a membrane-electrode assembly using the same, and a polymer electrolyte fuel cell using the same.

  Solid polymer fuel cells are required to have high electrical conductivity, excellent current collection capability, and good mechanical strength to withstand various operations, and at the same time, diffusion of substances that contribute to electrode reactions It needs to be good. Therefore, a carbonized sheet is generally used for the electrode substrate. In applications that require high power density, such as automobiles, which have been attracting attention in recent years, the amount of water generated per unit reaction area increases because the fuel cell is operated in a region where the current density is high. Therefore, in such a case, the point is how to efficiently discharge water produced by the reaction, and the carbonized sheet used as the material of the gas diffuser of the fuel cell is required to have high drainage. Therefore, attempts have been made to improve drainage by controlling the pore distribution of the electrode substrate.

  For example, in Patent Document 1, an object is to provide a porous carbon material suitable for an electrode material having high mechanical strength and excellent electrical characteristics, and the pore distribution is unimodal (one mountain) and sharp. Although it is said that the peak is good, conversely in Patent Document 2, a hole is mechanically made in the sheet, and the gap formed between the yarns of the nonwoven fabric and the two types of holes of the holes are combined. Some are good to have. However, it was insufficient in terms of achieving both mechanical strength and drainage.

  Further, Patent Document 3 introduces mixing powders such as graphite and carbon black, but only a peak having a pore diameter of 1 μm or less was obtained, and drainage performance was not greatly improved. Patent Document 4 introduces porous carbon sheets with different pore distributions in the thickness direction by laminating sheets with different press molding conditions, but the problem of warping occurs because of the different structures on the front and back sides. To do. Also, these documents did not clearly describe how the pore distribution is improved to improve drainage and improve power generation performance.

  In patent document 5, the performance evaluation by the electric power generation test which is not described in patent documents 1-4 is performed. It is specified that the power generation performance is improved by making the pore distribution consisting of two peaks (two peaks) than the conventional one-peak pore distribution.

  In automobile applications, in addition to the condition of high power density where the accelerator is stepped on, it is necessary to keep the inside of the fuel cell cell stable even under low power driving conditions where the vehicle runs stably, and to generate power under a wide range of conditions. That is, it is required to generate power even under conditions of low temperature and low humidity, such as when the battery is started, and also generate power under conditions of high temperature and high humidity after the accelerator is depressed. In the method as disclosed in Patent Document 5, although the power generation performance is improved under the pinpoint power generation conditions, since there is no knowledge at other conditions, it cannot be directly applied to automobile applications.

  On the other hand, as a continuous molding method of carbonized sheets, there are widely known methods in which intermittent pressing is performed as in Patent Documents 3 and 4, and double belt press (DBP) is performed in Patent Documents 5 and 6. ing. In order to control the thickness, it is said that it is good to use a spacer or a cotter at the part that determines the thickness by pressurizing, but on the other hand, for controlling the pore distribution in these steps, Not specifically mentioned.

JP 10-167855 A JP-A-2005-317240 Japanese Patent No. 5055682 JP 2009-234851 Japanese Patent No. 5260581 JP 2004-134108 A

  The object of the present invention is to maintain the fuel cell in a stable state and to generate power in a wide range of conditions even under driving conditions with low power and stable driving, in addition to the conditions of high power density for stepping on the accelerator in automotive applications. It is to provide a porous electrode substrate.

  The reason why power generation performance deteriorates is that, in a relatively low temperature and high current density region, there is a problem called instantaneous flooding and plugging that power generation performance decreases instantaneously due to insufficient gas supply due to blockage of the base material or separator flow path. is there. On the other hand, under high-temperature and low-humidification conditions, there is a problem that power generation performance is lowered due to a decrease in proton conduction accompanying drying of the electrolyte membrane, which is called dry-up.

  Considering these phenomena from the viewpoint of porous electrode base materials, the conventional porous electrode base materials are mainly those with high symmetry of pore distribution peak regardless of whether they are paper type or cross type. there were. That is, the pore diameter is almost uniform over the entire substrate, and it is uncertain which route the fuel gas or generated water will diffuse and pass through. For this reason, when the path was blocked by the produced water, gas diffusion was inhibited, and once drying started, it accelerated and dried up.

  The present invention has been made in view of the above points, and an object thereof is to provide a porous electrode substrate that can be applied to a wide range of power generation conditions ranging from low temperature / high humidification conditions to high temperature / low humidification conditions.

  The present inventors have found that the above problems are solved by the following inventions (1) to (5).

(1) A porous electrode base material in which carbon fibers having a fiber diameter of 3 to 9 μm and a fiber length of 2 to 20 mm dispersed in a structure are bound with a resin carbide, and the porous electrode base material is made of mercury. A porous electrode base material characterized in that the pore distribution measured by the press-fitting method satisfies the following conditions.
<Conditions>
The horizontal axis is a logarithmic distribution curve with a common logarithm, and at least a section with a diameter of 1 to 100 μm is composed of 80 measurement points that are equally spaced in the common logarithm display. In the pore distribution, the skewness S of the pore distribution at a diameter of 1 to 100 μm is −1.0 <S <−0.5, the kurtosis K is 3.0 <K <4.5, and 1 to 20 μm. In the pore diameter range, one peak is also present in the pore diameter range of 20 to 100 μm, and the peak in the pore diameter range of 1 to 20 μm is lower than the peak in the pore diameter range of 20 to 100 μm.

(2) Using a porous electrode substrate subjected to only water repellent treatment, a cell temperature of 80 ° C. and a relative humidity of 42 with respect to a voltage value Va at a cell temperature of 80 ° C., a relative humidity of 100%, and a current density of 1.0 A / cm ² %, The ratio of the voltage value Vb at a current density of 1.0 A / cm ² is Vb / Va = 0.7 to 1.1.

  (3) A porous electrode substrate in which a coating layer composed of carbon powder and a water repellent is provided on one side and / or both sides of the porous electrode substrate according to (1) or (2).

  (4) A membrane-electrode assembly using the porous electrode substrate according to any one of (1) to (3).

  (5) A polymer electrolyte fuel cell using the membrane-electrode assembly according to (4).

  According to the present invention, it is possible to provide a porous electrode substrate that can be applied to a wide range of power generation conditions ranging from low temperature / high humidification conditions to high temperature / low humidification conditions. In addition, a membrane-electrode assembly and a polymer electrolyte fuel cell including the porous electrode substrate can be provided.

It is a figure which shows that the shape of the pore distribution obtained can be changed by the setting of a data point and a space | interval. In FIG. 1, the horizontal axis represents the pore diameter, and the vertical axis represents the cumulative pore volume curve representing the total volume of mercury injected into the pores, differentiated with the pore diameter as a variable . One peak in the pore diameter range of 1 to 20 μm, and one peak in the pore diameter range of 20 to 100 μm, and the peak in the pore diameter range of 1 to 20 μm is more than the peak in the pore diameter range of 20 to 100 μm It is a typical figure of low pore distribution. In FIG. 2, the horizontal axis represents the pore diameter, and the vertical axis represents the cumulative pore volume curve representing the total volume of mercury injected into the pores, differentiated with the pore diameter as a variable .

  Hereinafter, the present invention will be described in more detail.

<Porous electrode substrate>
The porous electrode substrate of the present invention is a porous electrode substrate in which carbon fibers dispersed in a structure have a diameter of 3 to 9 μm and a fiber length of 2 to 20 mm are bound with resin carbide, The pore distribution when the porous electrode substrate is measured by a mercury intrusion method satisfies the following condition.
(conditions)
The horizontal axis is a logarithmic distribution curve with a common logarithm, and at least a section with a diameter of 1 to 100 μm is composed of 80 measurement points that are equally spaced in the common logarithm display. In the pore distribution, the skewness S of the pore distribution at a diameter of 1 to 100 μm is −1.0 <S <−0.5, the kurtosis K is 3.0 <K <4.5, and 1 to 20 μm. In the pore diameter range, one peak is also present in the pore diameter range of 20 to 100 μm, and the peak in the pore diameter range of 1 to 20 μm is lower than the peak in the pore diameter range of 20 to 100 μm.

<Power generation performance of porous electrode substrate>
The power generation performance of the porous electrode substrate of the present invention is defined under the following conditions.

Porous electrode base material (PTFE adhesion amount 20 mass%) obtained by immersing, drying, and sintering a porous electrode base material in polytetrafluoroethylene (PTFE) dispersion is porous for cathode and anode Prepared as an electrode base material, a catalyst layer (catalyst layer area) comprising catalyst-supported carbon (catalyst: Pt, catalyst support amount: 50% by mass) on both sides of a perfluorosulfonic acid polymer electrolyte membrane (film thickness: 30 μm) : 25 cm ² , Pt adhesion amount: 0.3 mg / cm ² ) was prepared, and this laminate was sandwiched between porous electrode substrates for cathode and anode, and these were joined to form MEA (Membrane Electrode Assembly) is obtained. The MEA is sandwiched between two carbon separators having a bellows-like gas flow path to form a polymer electrolyte fuel cell (single cell). Hydrogen gas (utilization rate 60%) is used as fuel gas, and oxidizing gas is used as fuel gas. The current density-voltage characteristics are measured using air (utilization rate 40%). The voltage value at a current density of 1.0 A / cm ² when the cell temperature is 80 ° C. and the relative humidity is 100% (wet state) is Va, and the current density is 1 when the cell temperature is 80 ° C. and the relative humidity is 42% (dry state). The voltage value at 0.0 A / cm ² is Vb, and the ratio Vb / Va is obtained. The Vb / Va value is preferably 0.7 to 1.1. When the Vb / Va value is less than 0.7, it means that the conditions suitable for power generation are biased to a wet state, and it is not preferable because it is easy to dry up. On the other hand, when the Vb / Va value exceeds 1.1, it means that the conditions suitable for power generation are biased to the dry state, and it is not preferable because it easily floods.

<Carbon fiber>
Examples of the carbon fiber that is one fiber constituting the porous electrode substrate of the present invention include polyacrylonitrile-based carbon fiber (hereinafter referred to as “PAN-based carbon fiber”), pitch-based carbon fiber, and rayon-based carbon fiber. And the like obtained by cutting carbon fibers such as From the viewpoint of the mechanical strength of the porous electrode substrate, PAN-based carbon fibers are preferred.

  The average fiber length of the carbon fibers is preferably 2 to 20 mm from the viewpoint of dispersibility. The average fiber diameter of the carbon fibers is preferably 3 to 9 μm from the viewpoint of carbon fiber production cost and dispersibility, and more preferably 4 to 8 μm from the smoothness of the porous electrode substrate. . The average fiber length can be measured with a microscope such as a scanning electron microscope, and the carbon fiber is magnified 50 times or more, and 50 different single fibers are selected at random, and the length is measured. What is necessary is just to obtain | require an average value. The average fiber diameter of the carbon fibers is preferably 3 to 9 μm from the viewpoint of carbon fiber production cost and dispersibility, and more preferably 4 to 8 μm from the viewpoint of the smoothness of the porous electrode substrate. .

<Resin carbide>
In the present invention, the resin carbide is a substance formed by carbonizing a resin and binding carbon fibers together. The resin is preferably a resin having a strong binding force with carbon fibers such as a phenol resin and a large residual weight during carbonization, but is not particularly limited. Depending on the type of resin and the amount of impregnation into the carbon fiber paper, the ratio of the resin carbide remaining as a carbide on the porous carbon electrode base material varies.

<Mercury intrusion method>
The pore distribution in the present invention is obtained and defined by the following method.
The mercury intrusion method is used as a method for obtaining the pore distribution of the porous material. In the mercury intrusion method, the cumulative pore volume curve is the horizontal axis is the pore diameter of the sample converted from the pressure applied to the sample by the cylindrical approximation of the void, and the vertical axis is the total volume of mercury injected into the pores. Is a “pore distribution curve” that is obtained by differentiating the pore diameter as a variable.

<Pore distribution>
Usually, the pore distribution is often displayed in semilogarithm with the horizontal axis being logarithmic. On the other hand, in a given setting of the device manufacturer, the pressure applied to the sample (applied pressure) is set in advance to be uniform to some extent. When measured at such an applied pressure setting, the resulting pore diameter is uniquely determined by the applied pressure and the approximate cylinder equation, so the data points for drawing the pore distribution curve are those with smaller pore diameters in semilogarithmic display. It becomes dense on the (left side) and sparse on the larger pore size (right side). This indicates that the obtained pore distribution shape can be changed depending on how to take data points, that is, how to set the applied pressure. FIG. 1 shows an example of pore distribution obtained by using the same porous electrode substrate as a sample and changing the way of taking data points. Thus, the setting of the applied pressure is extremely important in evaluating the pore distribution.

  Therefore, we calculated the set value of the applied pressure by back-calculation so that the data points for drawing the pore distribution curve were equally spaced in semilogarithmic display. The smaller the data interval, the more accurate the shape, but about 80 points in the range of 1 to 100 μm are preferable so that the measurement time does not become too long. On the other hand, in order to accurately evaluate the pore distribution shape of the porous electrode substrate, it is preferable to acquire data also for regions having a pore diameter of less than 1 μm and more than 100 μm. In the present invention, a total of 144 applied pressures were set in the pressure range corresponding to about 0.08 μm to about 400 μm in pore diameter.

  In order to acquire such data, for a certain applied pressure setting value A, the next applied pressure setting value B is set so that B = 10 ^ 0.025 × A≈1.06 × A. To do. That is, the set value of the applied pressure forms a geometric sequence with a common ratio of 1.06 as a whole.

  When the number of data points is 80 in the range of 1 to 100 μm, the data interval in the semilogarithmic display is about 10 ^ 0.025≈1.06 [μm], and the pore distribution can be displayed with a resolution of about 1 μm.

<Distortion and kurtosis>
Since the pore distribution is a kind of frequency distribution from the viewpoint of statistics, the distribution shape can be defined by the “distortion” and “kurtosis” of the distribution, which are generally used in statistics.

  The skewness S (Skewness) is the expectation of the third power of the standard deviation of the distribution, and represents the bias of the distribution. From the definition of the skewness S, the normal distribution is S = 0, S> 0 when biased to the left, and S <0 when biased to the right.

  Kurtosis K is the expected value of the fourth power of the standard deviation of the distribution, and represents the sharpness of the distribution. Depending on how the kurtosis K is defined, the normal normal distribution is K = 3, K> 3 for the “sharp distribution” sharper than the normal distribution, and K for the “blunt distribution” rounded from the normal distribution <3.

  In the present invention, when performing statistical processing, the numerical value on the horizontal axis is read in advance as an index with 10 as the base. Specifically, since 1, 10 and 100 are 10 to the 0th power, 1st power and 2nd power, respectively, the position corresponding to 1 μm on the horizontal axis is “0”, 10 μm is “1”, and 100 μm is “2”. " In other respects, statistical processing is performed by replacing the index with a base of 10. In the case where the number of data points is 80 in the range of 1 to 100 μm, the data interval after rereading as an index is 2 ÷ 80 = 0.025.

Expressions (1) and (2) show definition expressions of the skewness S and the kurtosis K in the frequency distribution, respectively. When applying to the pore distribution, first, an expected value μ is obtained by dividing the sum of products of the pore diameter Xi indicated by the index and the corresponding frequency (strength) fi by the sum of the frequencies (strength). At this time, the expected value of the third power of Zi = Xi−μ is the skewness S, and the expected value of the fourth power is the kurtosis K from the definition formula.
... Formula (1)

... Formula (2)

  If the symmetry of the pore distribution peak breaks, that is, a peak that is distorted to the left or right can be created, the pore diameter is not uniform, and there are pores of various sizes. In the case of such a substrate, for example, the generated water passes preferentially through larger pores in terms of contact angle, while the fuel gas passes through smaller pores that are not clogged with water. Is expected to be divided to some extent. The symmetry of the pore distribution peak is preferably a shape that is slightly biased to the right side (having a tail on the left side). The pore distribution can be seen as a plot of the pore size that represents the total volume of voids corresponding to a certain pore size (mercury-inserted voids). If the volume on the left side is large (there is strength), the number of voids increases accordingly. That is, the balance between the gas path and the water path is improved, the drainage is excellent in a relatively low temperature and high current density region, and the moisture retention is excellent in a high temperature / low humidification condition.

When the long porous electrode substrate of the present invention is continuously produced, it is preferable to include the four main steps 1 to 4 described below. That is,
1. A step of producing a precursor carbon fiber sheet by dispersing the carbon fiber (A) in water (a precursor sheet production step 1),
2. Step of adding a phenol resin and / or a water-dispersible phenol resin to the precursor sheet (resin addition step 2)
3. Step of heating and pressurizing the precursor sheet at a temperature of 100 to 400 ° C. after the resin addition step 2 (heating and pressing step 3)
4). The process of carbonizing the precursor carbon fiber sheet (precursor) at a temperature of 1000 ° C. or higher after the heating and pressing process 3 (carbonization process 4).

  In the precursor sheet manufacturing step 1, deionized water may be used, and the carbon fiber (A), the carbon fiber precursor fiber (b) and / or the fibrillar fiber (b ′) are added to the water. Dispersing in water may also be included, and adding 5 to 15% by weight of polyvinyl alcohol to the mixed slurry and making paper may also be included. At this time, the sheet material for the precursor obtained by papermaking is preferably dried at 90 to 120 ° C. before the resin addition step 2 (first drying treatment step 6).

  In the precursor sheet manufacturing step 1, whether the carbon fiber (A), the carbon fiber precursor fiber (b) and / or the fibril fiber (b ′) is dispersed in water to obtain a sheet material. Alternatively, by including a step (entanglement treatment step 5) of entanglement of the sheet-like material between the precursor sheet manufacturing step 1 and the resin addition step 2, the carbon fiber (A) is opened to a single fiber. It helps to fiber and can increase the strength of the precursor carbon fiber sheet.

  Furthermore, a step of heating and pressing the precursor sheet at a temperature of 100 to 400 ° C. (heating and pressing step 3) may be included between the resin addition step 2 and the carbonization treatment step 4.

  Moreover, the 2nd drying process process 7 which dry-processes the sheet-like thing (entangled structure sheet | seat) after the said entanglement process can be further included. At that time, from the viewpoint of removing the dispersion medium from the entangled sheet material, the entangled sheet material may be dried again at 20 to 200 ° C.

  In the carbonization step 3, the carbonization treatment is preferably performed in a temperature range of 1000 ° C. to 2400 ° C. in an inert atmosphere from the viewpoint of imparting sufficient conductivity to the obtained porous electrode substrate. At this time, before performing a carbonization process, a pre-carbonization process can be performed in the temperature range of 300-1000 degreeC by inert atmosphere. By performing this pre-carbonization treatment, the decomposition gas containing a large amount of Na generated in the initial stage of carbonization can be easily exhausted, and various decomposition products adhere to or deposit on the inner wall of the carbonization furnace, or decomposition products thereof. It is possible to easily suppress the occurrence of pain such as corrosion and black spots.

  Hereinafter, each processing step and terms used in the processing step will be specifically described.

<Precursor sheet manufacturing process 1>
By dispersing the carbon fiber precursor fiber (b) and / or the fibrillar fiber (b ′) together with the carbon fiber (A) in water, the carbon fiber (A) and the carbon fiber precursor fiber (b) and / or By entangled with the fibrillar fibers (b ′), the strength of the sheet-like material is improved, and it can be made substantially binder-free.

In the present invention, an organic polymer compound may be used as a binder. The organic polymer compound used as the binder is not particularly limited, and examples thereof include polyvinyl alcohol (PVA) and polyester or polyolefin binders that are heat-sealed. The binder may be solid or liquid such as fibers or particles.

  Examples of the medium in which the fibrous material such as the carbon fiber (A), the carbon fiber precursor fiber (b), and / or the fibrillar fiber (b ′) is dispersed include a medium in which the fibrous material does not dissolve, such as water and alcohol. From the viewpoint of productivity, water is preferable.

Although the said sheet-like material can be manufactured by any of a continuous method and a batch method, it is preferable to manufacture by a continuous method from a viewpoint of productivity and mechanical strength of a sheet-like material. The basis weight of the sheet is preferably about 10 to ²⁰⁰ g / m2. Moreover, it is preferable that the thickness of a sheet-like material is about 20-400 micrometers.

<Resin addition process 2>
The thermosetting resin impregnated into the carbon fiber paper is preferably a resin that exhibits adhesiveness or fluidity at room temperature and remains as a conductive material even after carbonization, and a phenol resin, a furan resin, or the like is used. it can. As the phenol resin, a resol-type phenol resin obtained by a reaction between phenols and aldehydes in the presence of an alkali catalyst can be used. In addition, a novolac type phenolic resin which shows a solid heat-fusible property and is produced by the reaction of phenols and aldehydes under an acidic catalyst by a known method can be dissolved and mixed in the resol type flowable phenolic resin. . However, in this case, it is preferable to use a self-crosslinking type containing, for example, hexamethylenediamine as a curing agent. A commercially available product can be used as the phenol resin.

  As phenols, for example, phenol, resorcin, cresol, xylol and the like are used. As aldehydes, for example, formalin, paraformaldehyde, furfural and the like are used. Moreover, these can be used as a mixture.

  The content of the thermosetting resin in the resin-impregnated paper obtained by impregnating the carbon fiber paper with the thermosetting resin is preferably 30 to 70% by mass. By setting the content of the thermosetting resin to 30% by mass or more, the structure of the obtained porous carbon electrode substrate becomes dense and the strength becomes high. Moreover, the porosity and gas permeability of the obtained porous carbon electrode base material can be kept favorable by making the content rate of a thermosetting resin into 70 mass% or less. The resin-impregnated paper refers to a paper obtained by impregnating a carbon fiber paper with a thermosetting resin before heating and pressurization, but when the solvent is used at the time of resin impregnation, it means a paper from which the solvent has been removed.

  Carbon fiber paper may be impregnated with a mixture of a thermosetting resin and a conductive material. Examples of the conductive material include carbonaceous milled fiber, carbon black, acetylene black, and graphite powder. The mixing amount of the conductive material is preferably 1 to 50% by weight with respect to the thermosetting resin. By setting the mixing amount of the conductive substance to 1% by mass or more, the effect of improving the conductivity becomes sufficient. Moreover, since the effect of improving the conductivity tends to be saturated even when the amount of the conductive material exceeds 50% by mass, the increase in cost can be suppressed by setting the amount of the conductive material to 50% by mass or less. Can do.

  As a method for impregnating carbon fiber paper with a solution containing a thermosetting resin and optionally a conductive material, a method using a squeezing device or a method of superimposing a separately prepared thermosetting resin film on carbon fiber paper is preferable. In the method using the squeezing device, the impregnation solution is impregnated with carbon fiber paper so that the intake liquid is uniformly applied to the entire carbon fiber paper with the squeezing device, and the amount of liquid is adjusted by changing the roll interval of the squeezing device. Is the method. When the viscosity of the solution is relatively low, a spray method or the like can be used. In the method of superposing a thermosetting resin film on carbon fiber paper, first, a release paper is coated with a solution containing a thermosetting resin and optionally a conductive substance to obtain a thermosetting resin film. Thereafter, a thermosetting resin film is laminated on the carbon fiber paper, a heat and pressure treatment is performed, and the carbon fiber paper is impregnated with the thermosetting resin.

  The amount of the phenolic resin solid content is preferably 20 parts by mass or more from the viewpoint of the mechanical strength of the porous electrode substrate with respect to 100 parts by mass of the sheet-like material, and from the viewpoint of gas permeability of the porous electrode substrate. 150 mass parts or less are preferable and 20-120 mass parts is more preferable.

<Carbonization process 4>
As a method for carbonizing the precursor sheet, any method may be used as long as it is carbonized by continuous temperature rise from room temperature, and the temperature is 1000 ° C. or higher. In addition, it is preferable to perform a carbonization process in the temperature range of 1000 to 2400 degreeC by inert atmosphere from a viewpoint of sufficient electroconductivity provision. In addition, before performing a carbonization process, you may perform a precarbonization process in the temperature range of 300-1000 degreeC by inert atmosphere. By performing the pre-carbonization treatment, it is possible to easily take out the cracked gas generated in the initial stage of carbonization, so that it is possible to easily suppress the deposition and deposition of decomposition products such as Na and Ca on the inner wall of the carbonization furnace. Therefore, it becomes possible to suppress the corrosion of the furnace wall and the generation of black spots on the precursor sheet.

  When carbonizing the continuously manufactured precursor sheet, it is preferable to perform heat treatment continuously over the entire length of the precursor sheet from the viewpoint of manufacturing cost. If the porous electrode base material is long, the productivity of the porous electrode base material becomes high, and the subsequent membrane-electrode assembly (MEA) production can also be performed continuously. The manufacturing cost of the battery can be reduced. Moreover, it is preferable to wind up the manufactured porous electrode base material continuously from a viewpoint of productivity and manufacturing cost of a porous electrode base material and a fuel cell.

<Entanglement process 5>
By performing the entanglement treatment on the sheet-like material, a sheet (entangled structure sheet) having an entangled structure in which the carbon fibers (A) are entangled three-dimensionally can be formed. In the sheet-like product manufacturing step 1, when the carbon fiber precursor fiber (b) and / or the fibrillar fiber (b ′) is dispersed together with the carbon fiber (A), the sheet-like product is entangled, A sheet (entangled structure sheet) having an entangled structure in which the carbon fiber (A) and the carbon fiber precursor fiber (b) and / or the fibrillar fiber (b ′) are entangled three-dimensionally can be formed.

  The entanglement process can be selected as necessary from the method of forming the entangled structure, and is not particularly limited. A mechanical entanglement method such as a needle punching method, a high pressure liquid injection method such as a water jet punching method, a high pressure gas injection method such as a steam jet punching method, or a combination thereof can be used. The high-pressure liquid injection method is preferable in that the breakage of the carbon fiber (A) in the entanglement treatment step can be easily suppressed and appropriate entanglement can be easily obtained.

  Hereinafter, the high-pressure liquid injection method will be described in detail.

  The high-pressure liquid ejecting process is a process in which a sheet-like material is placed on a substantially smooth support member, and a liquid columnar flow, a liquid fan-shaped flow, a liquid slit flow, or the like ejected at a pressure of 1 MPa or more, for example, It is the processing method which entangles the carbon fiber (A) in a sheet-like material. When the carbon fiber precursor fiber (b) and / or the fibrillar fiber (b ′) is dispersed together with the carbon fiber (A) in the sheet-like product manufacturing step 1, the carbon fiber (A) and the carbon fiber precursor are dispersed. The fiber (b) and / or the fibrillar fiber (b ′) is entangled. Here, the support member having a substantially smooth surface is selected as necessary from the one in which the pattern of the support member is not formed on the resulting entangled structure and the ejected liquid is quickly removed. Can be used. Specific examples thereof include a 30-200 mesh wire net, a plastic net, or a roll.

  From the viewpoint of productivity, it is preferable to continuously perform a confounding process such as a high-pressure liquid injection process after producing a sheet-like material containing carbon fiber (A) on a substantially smooth support member. .

  The confounding process by high-pressure liquid injection of the sheet-like material may be repeated a plurality of times. That is, after performing the high-pressure liquid injection treatment of the sheet-like material, the sheet-like material may be further laminated and the high-pressure liquid injection treatment may be performed, or a sheet-like material having an entangled structure (entangled structure sheet shape) The object) may be turned over, and the high-pressure liquid injection process may be performed from the opposite side. These operations may be repeated.

  The liquid used for the high-pressure liquid jet treatment is not particularly limited as long as it is a solvent that does not dissolve the fiber to be treated, but it is usually preferable to use deionized water. The water may be warm water. In the case of a columnar flow, each jet nozzle hole diameter in the high-pressure liquid jet nozzle is preferably 0.06 to 1.0 mm, and more preferably 0.1 to 0.3 mm. The distance between the nozzle injection hole and the laminate is preferably 0.5 to 5 cm. The pressure of the liquid is preferably 1 MPa or more from the viewpoint of fiber entanglement, more preferably 1.5 MPa or more, and the entanglement treatment may be performed in one or more rows. When performing multiple rows, it is effective to increase the pressure in the second and subsequent high-pressure liquid ejection processes from the first row from the viewpoint of maintaining the sheet form.

  When the entangled structure sheet is continuously manufactured, a streak-like trajectory pattern is formed in the sheeting direction, and a dense structure may occur in the sheet. However, the trajectory pattern can be suppressed by vibrating a high-pressure liquid jet nozzle including one or more rows of nozzle holes in the width direction of the sheet. By suppressing the streaky trajectory pattern in the sheet forming direction, the tensile strength can be expressed in the sheet width direction. Further, when a plurality of high-pressure liquid jet nozzles having one or a plurality of rows of nozzle holes are used, the frequency of vibrating the high-pressure liquid jet nozzles in the width direction of the sheet and the phase difference thereof are controlled so that the entangled structure sheet It is also possible to suppress the periodic pattern appearing in.

  Since the tensile strength of the sheet is improved by the entanglement process, the tensile strength of the sheet can be maintained even in water or in a wet state. Thereby, it becomes possible to add water-dispersible resin or water-soluble resin continuously to the entangled sheet. Furthermore, since it is not necessary to recover the organic solvent by using a water-dispersible resin or a water-soluble resin, the manufacturing equipment can be simplified and the manufacturing cost can be reduced as compared with the conventional case.

<Heating and pressing step 3>
Conventionally, the thickness variation of the porous electrode substrate is reduced, and further, when entangled, the fluffy fiber on the sheet surface is suppressed in the vicinity of the sheet surface and incorporated as a fuel cell. The precursor sheet was heated and pressurized at a temperature of 100 to 400 ° C. from the viewpoint of suppressing short circuit current and gas leakage. This heating and pressurizing step 3 is a carbon fiber when the carbon fiber precursor fiber (b) and / or the fibrillar fiber (b ′) is dispersed together with the carbon fiber (A) in the sheet-like material manufacturing step 1. There is also an effect that (A) is fused with the carbon fiber precursor fiber (b) and / or the fibrillar fiber (b ′).

  As a method of heating and pressing, any technique can be applied as long as it is a technique that can uniformly heat and press with a pair of heating and pressing media for sandwiching the precursor sheet. For example, a method of hot pressing a flat rigid plate on both sides of the precursor sheet, a method of using a hot roll press device or a continuous belt press device can be mentioned. In the case of heating and pressurizing a continuously produced precursor sheet, a method using a hot roll press device or a continuous belt press device is preferable. Or the method of combining intermittent conveyance of a precursor sheet | seat and intermittent heat press with a smooth rigid board may be sufficient. By these methods, the carbonization process 4 mentioned above can be performed continuously.

  In the present invention, it is preferable to provide a certain clearance between the pair of heating and pressing media (smooth rigid plate, heat roll, belt) even in the preheating stage. This is because the mixed state (phase separation state) of the organic polymer compound binder and the resin can be controlled by adjusting the clearance. In the heating and pressurizing step, the cured thermosetting resin is formed while maintaining a mixed state (phase separation state) in which the organic polymer compound binder and the thermosetting resin are present. By subsequent carbonization, the organic polymer compound binder disappears, while the thermosetting resin remains as a resin carbide, thereby forming pores smaller in size than pores formed between carbon fibers.

  In other words, when the mixed state (phase separation state) of the organic polymer compound binder and the thermosetting resin changes, the distribution of the burned organic polymer compound binder also changes. The pore distribution also changes. Specifically, the change behavior is roughly divided into the following four <1> to <4>.

  <1> When the clearance between the pair of heating and pressurizing media is wider than about 200 μm, the organic polymer compound binder is not crushed by pressure, and phase separation proceeds completely between the thermosetting resin and the organic polymer compound binder. As a result, after carbonization, a mesh with a small diameter is formed with a constant size, so that two peaks with low distortion are formed.

  <2> When the clearance between the pair of heating and pressurizing media is about 150 μm, the phase separation proceeds in most part, but a part where the phase separation does not occur partly occurs. As a result, a two-peak peak having a high degree of distortion defined in the present invention is formed.

  <3> When the clearance between the pair of heating and pressurizing media is about 100 μm, phase separation partially occurs. As a result, only the portion where the phase separation has advanced is slightly reduced in pore diameter, and does not form a double peak.

  <4> When the clearance between the pair of heating and pressurizing media is narrower than about 50 μm, the thermosetting resin and the organic polymer compound cannot freely flow because a large pressure is applied to the sheet in the preheating stage. Therefore, a network structure is not formed, and a single peak having a low degree of distortion is formed.

  In the present invention, it is preferable that the clearance between the pair of heating and pressurizing media is 110 μm or more and 190 μm or less. More preferably, it is 125 μm or more and 175 μm or less. When the clearance between the pair of heating and pressurizing media is narrower than 110 μm, the organic polymer compound binder is crushed by the roll pressure, and phase separation occurs only partially, so that no two peaks are formed.

  In addition, when the clearance between the pair of heating and pressurizing media is wider than 190 μm, the organic polymer compound binder is not crushed by the roll pressure, phase separation proceeds completely, and a network having a small diameter is formed with a relatively fixed size. As a result, a two-peak peak with a low degree of distortion is formed.

  The pressure in heating and pressurization is not particularly limited, but when the content ratio of the carbon fiber precursor fiber (b) in the precursor sheet is high, the surface of the resin-added sheet can be easily smoothed even if the pressure is low. be able to. The pressure in the heating and pressing is preferably 20 kPa to 10 MPa. When the pressure is 10 MPa or less, it is possible to easily prevent the carbon fiber (A) from being destroyed during heating and pressurization, and it is possible to easily impart appropriate denseness to the porous electrode substrate. If the pressure is 20 kPa or more, the surface can be easily smoothed.

  When the precursor sheet is sandwiched between two rigid plates, or heated and pressed with a hot roll press or continuous belt press, a release agent should be applied in advance so that fibrous materials do not adhere to the rigid plate, roll, or belt. It is preferable to coat or release paper between a precursor sheet and a rigid plate, a heat roll, or a belt.

<First drying treatment step 6>
The production method of the present invention may further include a step 6 of drying the precursor sheet between the resin addition step 2 and the heating and pressing step 3. Thereby, the energy for removing the dispersion medium and unreacted monomer in the heating and pressurizing step 3 can be easily reduced, which is preferable.

  In that case, it is preferable to dry-process a precursor sheet | seat at the temperature of 90-120 degreeC from a viewpoint of removing a dispersion medium and an unreacted monomer from a precursor sheet | seat. The time for the drying treatment can be, for example, 1 minute to 24 hours.

  The drying method is not particularly limited, and heat treatment using a high-temperature atmosphere furnace or far-infrared heating furnace, direct heat treatment using a hot plate, a hot roll, or the like can be applied. The drying process by a high temperature atmosphere furnace or a far-infrared heating furnace is preferable at the point which can suppress adhesion of the thermosetting resin to a heating source. When drying the precursor sheet manufactured continuously, it is preferable to perform the drying process continuously over the entire length of the precursor sheet from the viewpoint of manufacturing cost. Thereby, the heating and pressurizing step 3 can be continuously performed following the first drying treatment step 6.

<Second drying treatment step 7>
The production method of the present invention can further include a second drying treatment step 7 for drying the entangled sheet-like material (entangled structure sheet) between the entanglement treatment step 5 and the resin addition step 2. At that time, from the viewpoint of removing the dispersion medium from the entangled sheet material, it is preferable to dry the entangled sheet material at 20 to 200 ° C. The time for the drying treatment can be, for example, 1 minute to 24 hours.

  The drying method is not particularly limited, and heat treatment using a high-temperature atmosphere furnace or far-infrared heating furnace, direct heat treatment using a hot plate, a hot roll, or the like can be applied. The drying process by a high temperature atmosphere furnace or a far-infrared heating furnace is preferable at the point which can suppress adhesion to the heating source of the fiber which comprises the sheet | seat which carried out the confounding process. In the case of drying the entangled sheet material produced continuously, it is preferable to continuously perform the drying treatment over the entire length of the entangled sheet material from the viewpoint of production cost. Thereby, the 2nd drying process 7 can be performed continuously after the confounding process 5.

<Carbon fiber precursor fiber (b)>
The carbon fiber precursor fiber (b) can be obtained by cutting long carbon fiber precursor fibers to an appropriate length. Moreover, this long-fiber-like carbon fiber precursor fiber can be comprised from the polymer (for example, acrylic polymer) mentioned later.

  The average fiber length of the carbon fiber precursor fiber (b) is preferably 2 to 20 mm from the viewpoint of dispersibility. The cross-sectional shape of the carbon fiber precursor fiber (b) is not particularly limited, but those having high roundness are preferred from the viewpoint of mechanical strength after carbonization and production cost. In addition, the average fiber diameter of the carbon fiber precursor fiber (b) is preferably 5 μm or less in order to easily suppress breakage due to shrinkage in the heating and pressurizing step 5 and the carbonization treatment step 3. From the viewpoint of spinnability, the average fiber diameter of the carbon fiber precursor fiber (b) is preferably 1 μm or more.

  From the viewpoint of maintaining the sheet form after carbonization, the polymer constituting the carbon fiber precursor fiber (b) preferably has a residual mass of 20% by mass or more in the carbonization process. Examples of such polymers include acrylic polymers, cellulose polymers, and phenolic polymers.

  The acrylic polymer used for the carbon fiber precursor fiber (b) may be a homopolymer of acrylonitrile or a copolymer of acrylonitrile and other monomers. The monomer copolymerized with acrylonitrile is not particularly limited as long as it is an unsaturated monomer constituting a general acrylic fiber. For example, methyl acrylate, ethyl acrylate, isopropyl acrylate, n-butyl acrylate, Acrylic esters represented by 2-ethylhexyl acrylate, 2-hydroxyethyl acrylate, hydroxypropyl acrylate, etc .; methyl methacrylate, ethyl methacrylate, isopropyl methacrylate, n-butyl methacrylate, isobutyl methacrylate, methacrylic acid Typical examples include t-butyl acid, n-hexyl methacrylate, cyclohexyl methacrylate, lauryl methacrylate, 2-hydroxyethyl methacrylate, hydroxypropyl methacrylate, diethylaminoethyl methacrylate and the like. Methacrylic acid esters; acrylic acid, methacrylic acid, maleic acid, itaconic acid, acrylamide, N-methylol acrylamide, diacetone acrylamide, styrene, vinyl toluene, vinyl acetate, vinyl chloride, vinylidene chloride, vinylidene bromide, vinyl fluoride, And vinylidene fluoride.

  In addition, the spinnability, the carbon fibers (A) can be bonded to each other from low temperature to high temperature, the remaining mass at the time of carbonization treatment is large, and the fiber elasticity and fiber strength at the time of performing the above-described entanglement treatment. In consideration, it is preferable to use an acrylic polymer containing 50% by mass or more of acrylonitrile units.

  The weight average molecular weight of the acrylonitrile-based polymer used for the carbon fiber precursor fiber (b) is not particularly limited, but is preferably 50,000 to 1,000,000. When the weight average molecular weight is 50,000 or more, the spinnability is improved and the yarn quality of the fiber tends to be good. When the weight average molecular weight is 1,000,000 or less, the polymer concentration that gives the optimum viscosity of the spinning dope increases, and the productivity tends to improve.

  Paper-like porous electrode base materials are rarely used as they are in fuel cells, and are usually mounted on the cells after being coated with a water repellent and carbon powder called MPL. Is done. Although the porous electrode base material of the present invention exhibits good power generation performance without MPL, MPL may be added. Moreover, it is preferable to perform the water-repellent treatment on the porous electrode substrate regardless of the presence or absence of MPL.

In the polymer electrolyte fuel cell, humidified fuel is supplied to suppress drying of the polymer electrolyte membrane and maintain appropriate proton conduction. Furthermore, water (water vapor) as an electrode reaction product is generated on the cathode side, but this may condense and become liquid water, which may block gas permeation by closing voids in the porous electrode substrate. Therefore, in order to ensure gas permeability, water repellent treatment is often performed with a water repellent.

  Examples of water repellents include fluorine-based resins and silicon resins (silicones) that are chemically stable and have high water repellency. Silicone is low in acid resistance and is in contact with a highly acidic polymer electrolyte membrane. Since it cannot be used, a fluororesin is exclusively used.

  The fluororesin is not particularly limited, but tetrafluoroethylene (TFE), hexafluoropropylene (HFP), vinylidene fluoride (VDF), chlorotrifluoroethylene (CTFE), vinyl fluoride, perfluoroalkyl vinyl ether, par Homopolymers or copolymers of fluorine monomers such as fluoro (allyl vinyl ether), perfluoro (butenyl vinyl ether) (PBVE), perfluoro (2,2-dimethyl-1,3-dioxole) (PDD) are used. be able to. Further, an ethylene-tetrafluoroethylene copolymer (ETFE), an ethylene-chlorotrifluoroethylene copolymer (ECTFE), or the like, which is a copolymer of these and olefins typified by ethylene, can also be used. As a form of these fluororesins, those dissolved in a solvent and those dispersed in a dispersion medium such as water or alcohol in a granular form are preferable from the viewpoint of impregnation. Commercially available products in the form of solutions, dispersions, or granules include polytetrafluoroethylene (PTFE), tetrafluoroethylene-hexafluoropropylene copolymer (FEP), and tetrafluoroethylene-perfluoroalkyl. There are vinyl ether (PFA), polyvinylidene fluoride (PVDF), etc., and it is preferable to use these from the viewpoints of handleability and manufacturing cost.

  As a method of water repellent treatment to the porous electrode base material, an impregnation method (dip method) in which the porous electrode base material is immersed in a dispersion liquid (dispersion) in which fine particles of fluororesin are dispersed, or a dispersion liquid is sprayed. A spray method or the like can be used. The concentration of the fluororesin dispersion is not particularly limited, but is preferably about 1 to 30% by weight in order to deposit the fluororesin uniformly without filling the voids of the porous electrode substrate. 10-30 weight% is more preferable, and 15-25 weight% is especially preferable.

  When PTFE is used as the fluororesin, it is preferable to sinter PTFE. The sintering temperature must be within a temperature range in which PTFE is softened and bound to carbon fiber or resin carbide, and PTFE is not thermally decomposed. 300-390 degreeC is more preferable, and 320-360 degreeC is especially preferable.

  The fluorine-based resin is applied so as to cover the macroscopic conductive path in the porous electrode base material in which the carbon fiber is bound by the resin carbide from the outside. That is, the fluororesin exists on the surface of the conductive path without dividing the conductive path made of carbon fiber and resin carbide. However, most of the fluorine-based resins are aggregated in the vicinity of the intersection of the fibers, and the surface of the carbon fiber or the resin carbide constituting the porous electrode base material is not necessarily covered with the fluorine-based resin without a gap. Therefore, even after the water repellent treatment, a conductive path that continues from the substrate surface to the inside of the substrate is secured, and both water repellency and conductivity can be achieved.

  The number of additions of the fluororesin is not particularly limited, but it is preferable to reduce the number of additions from the viewpoint of reducing the manufacturing cost. When the number of times of addition is multiple, the same fluororesin slurry may be used, or slurries with different slurry concentrations or different fluororesin types may be used. Further, the addition amount of the fluorine-based resin may be uniform in the thickness direction of the porous electrode substrate or may have a concentration gradient.

  As the carbon powder used for the coating layer, for example, graphite powder or carbon black can be used. For example, acetylene black (for example, Denka black manufactured by Denki Kagaku Kogyo Co., Ltd.), ketjen black (for example KetjenBlackEC manufactured by Lion Corporation), furnace black (for example, Vulcan XC72 manufactured by CABOT) and the like can be used. The proportion of the carbon powder used is preferably such that the concentration when the carbon powder is dispersed in a solvent is 5 to 30%. Examples of water repellents include fluorine-based resins and silicon resins (silicones) that are chemically stable and have high water repellency. Silicone is low in acid resistance and is in contact with a highly acidic polymer electrolyte membrane. Since it cannot be used, a fluororesin is exclusively used.

  The fluororesin is not particularly limited, but tetrafluoroethylene (TFE), hexafluoropropylene (HFP), vinylidene fluoride (VDF), chlorotrifluoroethylene (CTFE), vinyl fluoride, perfluoroalkyl vinyl ether, par Homopolymers or copolymers of fluorine monomers such as fluoro (allyl vinyl ether), perfluoro (butenyl vinyl ether) (PBVE), perfluoro (2,2-dimethyl-1,3-dioxole) (PDD) are used. be able to. Further, an ethylene-tetrafluoroethylene copolymer (ETFE), an ethylene-chlorotrifluoroethylene copolymer (ECTFE), or the like, which is a copolymer of these and olefins typified by ethylene, can also be used. As a form of these fluororesins, those dissolved in a solvent and those dispersed in a dispersion medium such as water or alcohol in a granular form are preferable from the viewpoint of impregnation. Commercially available products in the form of solutions, dispersions, or granules include polytetrafluoroethylene (PTFE), tetrafluoroethylene-hexafluoropropylene copolymer (FEP), and tetrafluoroethylene-perfluoroalkyl. There are vinyl ether (PFA), polyvinylidene fluoride (PVDF), etc., and it is preferable to use these from the viewpoints of handleability and manufacturing cost. The ratio of the water repellent used is preferably such that the concentration when the water repellent is dispersed in the solvent is 5 to 60%.

  Water or an organic solvent can be used as a solvent for dispersing the carbon powder and the water repellent. From the viewpoint of the risk of organic solvents, cost, and environmental load, it is preferable to use water. When an organic solvent is used, it is preferable to use a lower alcohol, acetone or the like that is a solvent that can be mixed with water. As a ratio of using these organic solvents, it is preferable to use them at a ratio of 0.5 to 2 with respect to water 1.

  The coating layer composed of carbon powder and a water repellent is a combination of carbon powder and a water repellent that is a binder. In other words, carbon powder is taken into the network formed by the water repellent and has a fine network structure. When forming the coating layer, it is difficult to define a clear boundary line between the coating layer and the porous electrode substrate because a part of the composition soaks into the porous electrode substrate. Only a portion of the coating layer composition where no penetration into the porous electrode substrate, that is, a layer composed of only carbon powder and a water repellent is defined as a coating layer.

  The porous electrode substrate of the present invention may further have a coating layer made of carbon powder and a water repellent on one side and / or both sides. Although coating layers may be provided on both sides, single-sided coating is more preferable because there is a possibility of lowering productivity and gas diffusibility and drainage due to increased processes as compared to single-sided coating.

  EXAMPLES The present invention will be specifically described below with reference to examples, but the present invention is not limited to these examples.

[Example 1]
Polyacrylonitrile-based carbon fiber cut to an average fiber length of 3 mm (Mitsubishi Rayon Co., Ltd., trade name: Pyrofil TR50S, average single fiber diameter: 7 μm), polyvinyl alcohol (PVA) fiber (Kuraray Co., Ltd., trade name: VPB105- 1, fiber length 3 mm), polyethylene pulp (manufactured by Mitsui Chemicals, trade name: SWP) was prepared. Polyacrylonitrile diameter carbon fiber, polyethylene pulp and polyvinyl alcohol fiber are put into a slurry tank of a wet short net continuous paper making machine in a ratio of 10: 8: 2, and water is further added to uniformly disperse and spread. When dispersed, the web is fed out, passed through a short mesh plate, dried with a dryer, and then a continuous sheet material (carbon) for a porous carbon electrode substrate precursor in a roll shape having a width of 1000 mm and a basis weight of 34 g / m ^2. Fiber paper).

Next, the carbon fiber paper is immersed in a methanol solution of a phenol resin (manufactured by DIC Corporation, trade name: Phenolite J-325), 90 parts by mass is attached to 100 parts by mass of the carbon fiber paper, and the width is further 850 mm. The resin-impregnated paper to which the phenol resin was made to adhere was obtained by slitting.
Two sheets of this resin-impregnated paper were laminated using a double belt press machine, and press molded. As the conditions at that time, preheating conditions were adjusted to a hot air temperature of 150 ° C., a preheating roll temperature of 228 ° C., and a clearance between the upper and lower sides of the preheating roll to 150 μm. Furthermore, the press roll temperature was 260 ° C., and the press pressure was 10.9 MPa. As a result, a cured resin sheet having a width of 850 mm and a length of 100 m was obtained. The conveyance speed was 0.8 m / min. Details are shown in Table 1.

  The obtained cured resin sheet is run in a firing furnace (width 1 m) in a nitrogen gas atmosphere, and then further is run in a firing furnace having a temperature region of 1600 ° C. or higher in a nitrogen gas atmosphere at a temperature of 6 m. Heat treatment was performed at a temperature of 2000 ° C. In addition, the sheet width | variety of the resin cured sheet at this time was 700 mm.

  The sample for pore distribution measurement was cut into a strip shape in order to first cut a porous electrode substrate into a 50 mm square and store it in a cell having a volume of 1.19 mL.

  The pore distribution measurement by the mercury intrusion method was carried out using AutoPore IV9500 (V1.07) manufactured by Shimadzu Corporation (Micrometrics) in a pressure range of about 80 nm to 400 μm in terms of pore diameter. The number of measurement points was 144 points, and the above range was set so as to cover the logarithmic display scale at equal intervals.

[Examples 2-6] Current NR series In Examples 2-6, polyacrylonitrile diameter carbon fiber, polyethylene pulp and polyvinyl alcohol fiber were made at a ratio of 10: 4: 2, and the basis weight of the base paper / DBP preheating roll temperature -Preheating roll clearance, curing temperature, curing pressure, and speed were set as shown in Table 1. The firing conditions were all the same as in Example 1.

[Comparative Example 1]
Polyacrylonitrile-based carbon fiber cut to an average fiber length of 3 mm (Mitsubishi Rayon Co., Ltd., trade name: Pyrofil TR50S, average single fiber diameter: 7 μm), polyvinyl alcohol (PVA) fiber (Kuraray Co., Ltd., trade name: VPB105- 1, fiber length 3 mm), polyethylene pulp (manufactured by Mitsui Chemicals, trade name: SWP) was prepared. Put the polyacrylonitrile diameter carbon fiber and polyethylene pulp and polyvinyl alcohol fiber in a ratio of 10: 8: 2 into the slurry tank of the wet short net continuous paper making machine, add water and spread it evenly, When dispersed, the web is fed out, passed through a short mesh plate, dried with a dryer, and then a continuous sheet-like material (carbon fiber) for a porous electrode substrate precursor in a roll shape having a width of 1000 mm and a basis weight of 20 g / m ^2. Paper).

  Next, the carbon fiber paper is immersed in a methanol solution of phenol resin (manufactured by DIC Corporation, trade name: Phenolite J-325), 100 parts by mass is adhered to 100 parts by mass of the carbon fiber paper, and the width is further 850 mm. The resin-impregnated paper to which the phenol resin was made to adhere was obtained by slitting. Two sheets of this resin-impregnated paper were laminated using a double belt press machine and press-molded. As conditions at that time, preheating conditions were adjusted to a hot air temperature of 150 ° C., a preheating roll temperature of 235 ° C., and a clearance between the upper and lower sides of the preheating roll (between a pair of heating and pressurizing media) were adjusted to 200 μm. Furthermore, the press roll temperature was 260 ° C. and the press pressure was 8.6 MPa. As a result, a cured resin sheet having a width of 850 mm and a length of 100 m was obtained. The conveyance speed was 0.8 m / min. Details are shown in Table 1. The firing conditions were the same as in Example 1.

[Comparative Example 2]
Adjust the mixing ratio of polyacrylonitrile diameter carbon fiber to polyethylene pulp and polyvinyl alcohol fiber to a ratio of 8: 0: 2, and the clearance between the upper and lower preheating rolls (between a pair of heating and pressurizing media) is zero (0 μm); The press pressure of the press roll was 5.0 MPa. Other than that was the same as Comparative Example 1.

  It was confirmed that the pore distribution can be controlled by adjusting the clearance between the pair of heating and pressurizing media in Examples and Comparative Examples of the present invention. When the clearance between the upper and lower preheating rolls is narrow as in Comparative Example 2, the polyethylene pulp is crushed by the roll pressure and cannot flow, and a network structure is not formed. Moreover, when the belt clearance is wider than 140 μm as in Comparative Example 1, it is assumed that phase separation proceeds and two peaks are formed. It was confirmed that a porous electrode substrate having a pore distribution as in the present invention was obtained by adjusting the clearance between the upper and lower preheating rolls to about 110 to 190 μm as in the examples of the present invention.

<Power generation test>
A power generation test was performed using the samples of Examples and Comparative Examples in the present invention. The test method is as follows.

(1) Manufacture of membrane-electrode assembly (MEA) The porous electrode base material obtained in the example was immersed in PTFE dispersion, dried and sintered to perform water repellent treatment. A water-repellent porous electrode substrate was prepared as a cathode electrode electrode and an anode electrode substrate. Further, a catalyst layer (catalyst layer area: 25 cm ² , Pt) composed of catalyst-supported carbon (catalyst: Pt, catalyst support amount: 50 mass%) on both surfaces of a perfluorosulfonic acid polymer electrolyte membrane (film thickness: 30 μm). The laminated body which formed the adhesion amount: 0.3 mg / cm < ² >) was made easy. This laminate was sandwiched between porous electrode substrates for cathode and anode, and joined to obtain an MEA.

(2) Fuel cell characteristic evaluation of MEA The obtained MEA 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 single cell temperature was 80 ° C., the fuel gas utilization rate was 60%, and the oxidizing gas utilization rate was 40%. Further, the humidification of the fuel gas and the oxidizing gas was performed by passing the fuel gas and the oxidizing gas through a bubbler at 80 ° C. (relative humidity 100%) or 60 ° C. (relative humidity 42%), respectively. Cell temperature 80 ° C., the voltage value is Va at a current density of 1.0A / cm ² in the case of a relative humidity of 100% cell temperature 80 ° C., the voltage value at a current density of 1.0A / cm ² in the case of a relative humidity of 42% Was Vb, and the ratio Vb / Va was obtained.

<Power generation test results and discussion>
Table 3 shows the power generation test results. It was confirmed that power generation was possible under various power generation conditions by using an electrode base material having a pore distribution as in the examples.

Claims (4)

A porous electrode base material in which carbon fibers having a fiber diameter of 3 to 9 μm and a fiber length of 2 to 20 mm dispersed in a structure are bound with resin carbide, and the porous electrode base material is formed by a mercury intrusion method. A porous electrode substrate characterized in that the pore distribution upon measurement satisfies the following conditions.
<Conditions>
The abscissa represents the pore diameter, the ordinate represents the cumulative pore volume curve representing the total volume of mercury injected into the pores , and the abscissa represents the common logarithm. In the pore distribution curve, at least a section having a diameter of 1 to 100 μm is composed of 80 measurement points that are equally spaced in a common logarithmic display. The skewness S of the pore distribution at 100 μm is −1.0 <S <−0.5, the kurtosis K is 3.0 <K <4.5, and a peak is observed in the pore diameter range of 1 to 20 μm. One peak is also present in the pore diameter range of 20 to 100 μm, and the peak in the pore diameter range of 1 to 20 μm is lower than the peak in the pore diameter range of 20 to 100 μm. The porous electrode base material which provided the coating layer which consists of carbon powder and a water repellent on one side or both surfaces of the porous electrode base material of Claim 1 . A membrane-electrode assembly using the porous electrode substrate according to claim 1 . A polymer electrolyte fuel cell using the membrane-electrode assembly according to claim 3 .