JP5694638B2 - Gas diffusion layer, membrane-electrode assembly and fuel cell - Google Patents

Description

  The present invention relates to a gas diffusion layer, a membrane-electrode assembly, and a fuel cell, and in particular, a gas diffusion layer, a membrane-electrode assembly, and a fuel cell capable of producing a fuel cell having excellent power generation performance even under low humidity. The present invention relates to a fuel cell excellent in power generation performance even under low humidity.

  Regarding energy used in various forms, exploring alternative fuels and conserving resources are important issues due to concerns over the depletion of petroleum resources. In the midst of this, active development has continued for fuel cells that convert various fuels into chemical energy and extract them as electric power.

  As disclosed in, for example, page 5 of “Technology Trend Survey on Fuel Cells” (Non-Patent Document 1), fuel cells are available depending on the type of electrolyte used, such as phosphoric acid fuel cells (PAFCs), molten carbonates. The fuel cell is classified into four types: a fuel cell (MCFC), a solid oxide fuel cell (SOFC), and a polymer electrolyte fuel cell (PEFC). These various fuel cells have a limited operating temperature range depending on the electrolyte, PEFC has a low temperature range of 100 ° C or lower, PAFC has a medium temperature range of 180-210 ° C, MCFC has a temperature of 600 ° C or higher, and SOFC has a temperature close to 1000 ° C. It is known to operate in the high temperature region. Among these, a general PEFC capable of outputting in a low temperature region takes out electric power generated by a combined reaction between hydrogen gas and oxygen gas (or air) as a fuel, but has a relatively small device configuration. There is an urgent need for practical use in that power can be efficiently extracted.

  FIG. 1 is a schematic diagram of a cross section of a main part of a fuel cell for showing a basic configuration of a conventionally known PEFC. In the figure, components having substantially the same configuration or function as materials are indicated by the same hatching. As shown in FIG. 1, the PEFC has a plurality of cell units in which a membrane-electrode assembly (MEA) composed of a negative electrode 17a, a solid polymer film 19 and a positive electrode 17c is sandwiched between a pair of bipolar plates 11a and 11c. Consists of structure. The negative electrode 17a includes a catalyst layer 15a that decomposes into protons and electrons, and a gas diffusion layer 13a that supplies fuel gas to the catalyst layer 15a. The positive electrode 17c includes a catalyst layer 15c that reacts protons, electrons, and oxygen gas. The gas diffusion layer 13c supplies oxygen gas to the catalyst layer 15c.

  Since the bipolar plate 11a has a groove capable of supplying fuel gas, when the fuel gas is supplied through the groove of the bipolar plate 11a, the fuel gas diffuses through the gas diffusion layer 13a and is supplied to the catalyst layer 15a. The supplied fuel gas is decomposed into protons and electrons, and the protons move through the solid polymer film 19 and reach the catalyst layer 15c. On the other hand, the electrons pass through an external circuit (not shown) and move to the positive electrode 17c. On the other hand, since the bipolar plate 11c has a groove capable of supplying an oxygen-containing gas, when the oxygen-containing gas is supplied through the groove of the bipolar plate 11c, the oxygen-containing gas diffuses through the gas diffusion layer 13c and is supplied to the catalyst layer 15c. . The supplied oxygen-containing gas reacts with protons that have moved through the solid polymer membrane 19 and electrons that have moved through the external circuit, thereby generating water.

  As a gas diffusion layer of such a membrane-electrode assembly (MEA), one having pores having a diameter of 17 to 90 μm (Patent Document 1), a first peak existing in the range of 1 μm to 100 μm, and 15 nm to One having a pore distribution having a second peak existing in the range of 1 μm (Patent Document 2), having a pore diameter peak between 5 μm and 50 μm, and a range of 100 μm and the vicinity thereof Further, there is known one having a peak of a pore diameter that serves as a gas diffusion path (Patent Document 3). Since any of these conventional gas diffusion layers has a large pore diameter exceeding 1 μm, the generated water or the water supplied by the humidified gas is easily discharged to the outside. As described above, in PEFC, since protons move through the solid polymer membrane, moisture is necessary for rapid movement of protons, but water is easily discharged to the outside in the conventional gas diffusion layer. In some cases, the solid polymer membrane is dried and protons hardly move, and sufficient power generation performance cannot be obtained. There is a concept of sufficiently humidifying the fuel gas and / or oxygen-containing gas so that protons can easily move, but this requires a large humidifier, which makes it difficult to reduce the weight and size. It was.

“Technological Trend Survey on Fuel Cells” (Edited by Technical Research Section, Patent Office, May 31, 2001, <URL> http://www.jpo.go.jp/shiryou/index.html) Japanese Patent No. 3929146 (Claim 2 etc.) JP 2000-182626 A (Claim 1 etc.) JP 2007-87651 A (Claim 2 etc.)

  The present invention has been made to solve the above-described problems, water generated in the positive electrode can be kept inside, the solid polymer film can be kept moist, and there is no need to supply a humidified gas, To provide a gas diffusion layer, a membrane-electrode assembly, and a light and small fuel cell that can be made into a light and small fuel cell by using a small humidifier even if necessary. Objective.

The invention according to claim 1 of the present invention is “a gas diffusion layer in which the entire fiber base material is filled with a fluororesin and a conductive agent, and in a range of pore diameters of 150 to 0.003 μm by a mercury intrusion method , In the Log differential pore volume distribution graph measured by applying pressure in the following order, the gas diffusion layer has only one peak defined below, and the peak exists in the range of pore diameter of 0.01 to 1 μm.
Record
Pressure; 1.5 psia, 2 psia, 2.5 psia, 3 psia, 3.5 psia, 4 psia, 5 psia, 6 psia, 7 psia, 8 psia, 9 psia, 10 psia, 12 psia, 14 psia, 16 psia, 18 psia, 20 psia, 25 psia, 30 psia, 40 psia, 30 psia, 40 psia, 60 psia, 70 psia, 80 psia, 90 psia, 100 psia, 120 psia, 140 psia, 170 psia, 200 psia, 250 psia, 300 psia, 350 psia, 400 psia, 450 psia, 500 psia, 600 psia, 700 psia, 800 psia, 900 psia, 900 psia, 900 psia, 900 psia sia, 2000 psia, 2400 psia, 2800 psia, 3200 psia, 3600 psia, 4000 psia, 4500 psia, 5000 psia, 5500 psia, 6000 psia, 6500 psia, 7000 psia, 8000 psia, a1000 psia, 1000 psia, 13000 psia, 12000 psia, 13000 psia, 12000 psia, 13000 psia, 12000 psia 25000 psia, 28000 psia, 32000 psia, 35000 psia, 38000 psia, 45000 psia, 50000 psia, 60000 psia
Peak; mean value I _AV of the slope represented by the following equation of peak inflection point P where 0.5 or more.

  The invention according to claim 2 of the present invention is “the gas diffusion layer according to claim 1, wherein the peak is present in a pore diameter range of 0.05 to 0.15 μm”.

The invention according to claim 3 of the present invention is “the gas diffusion layer according to claim 1 or 2, wherein the apparent density of the gas diffusion layer is 0.5 to 0.8 g / cm ³ ”.

Invention of Claim 4 of this invention is "the gas diffusion layer in any one of Claims 1-3 in which a fiber base material consists of a glass fiber nonwoven fabric."

The invention according to claim 5 of the present invention is "a membrane-electrode assembly including the gas diffusion layer according to any one of claims 1 to 4. "

The invention according to claim 6 of the present invention is “a fuel cell including a membrane-electrode assembly including the gas diffusion layer according to any one of claims 1 to 4 ”.

  Since the invention according to claim 1 of the present invention has only pores having a diameter of 0.01 to 1 μm, water generated at the positive electrode can be kept inside, and the solid polymer film can be kept moist, so that the humidified gas There is no need to supply or even if necessary, a small humidifier can be used, and a lightweight and small fuel cell can be manufactured.

  Since the invention according to claim 2 of the present invention has only pores having a diameter of 0.05 to 0.15 μm, water generated at the positive electrode can be kept inside, and the solid polymer film can be kept wet. There is no need to supply humidified gas or even if it is necessary, a small humidifier can be used, and a lightweight and small fuel cell can be manufactured.

  In the invention according to claim 3 of the present invention, since the fiber base material is filled with the fluororesin and the conductive agent, electric conductivity and appropriate water repellency can be imparted.

In the invention according to claim 4 of the present invention, since the apparent density of the gas diffusion layer is 0.5 to 0.8 g / cm ³ , the gas diffusion layer has a porosity that does not hinder gas permeation, supply, or diffusion. Have.

  The invention according to claim 5 of the present invention is excellent in chemical resistance against an acidic solution, alcohol or the like because the fiber base material is made of a glass fiber nonwoven fabric. Moreover, compared with the fiber base material comprised with carbon fiber, it has the extremely outstanding intensity | strength and processability. Furthermore, it is inexpensive.

  Since the invention according to claim 6 of the present invention is a membrane-electrode assembly including any one of the gas diffusion layers, water generated at the positive electrode can be retained inside and the solid polymer membrane can be kept wet. Therefore, it is not necessary to supply humidified gas, or even if necessary, a small humidifier can be used, and a lightweight and small fuel cell can be manufactured.

  Since the invention according to claim 7 of the present invention is a fuel cell including the membrane-electrode assembly including any one of the gas diffusion layers, water generated at the positive electrode is retained inside the cell, and the solid polymer membrane is wetted. Therefore, it is not necessary to supply humidified gas, or even if necessary, a small humidifier can be used, and a lightweight and small fuel cell can be obtained.

  The gas diffusion layer of the present invention has only one peak in the Log differential pore volume distribution graph measured by the mercury intrusion method, and the peak exists in the range of the pore diameter of 0.01 to 1 μm. Having only one peak in this way means that it is composed only of pores having the diameter and the diameter in the vicinity thereof, and the diameter is 0.01 to 1 μm, which is very unprecedented. Therefore, it is possible to keep water inside the battery and keep the solid polymer film moist. For example, having a peak larger than 1 μm means that the diameter of the pore is large, so that water is discharged to the outside and water is insufficient. Conversely, having a peak smaller than 0.01 μm means that the diameter of the pores is too small, so that water stays inside and clogs the pores, thereby inhibiting gas permeation, supply or diffusion. Is done. More preferably, only one peak is present in the pore diameter range of 0.05 to 0.15 μm.

The reason why the mercury intrusion method is employed in the present invention is that the preferred pore diameter is 0.01 to 1 μm, and this is a method suitable for measuring the pore diameter in this range. The mercury intrusion method can be performed with a mercury porosimeter. The measurement conditions by the mercury intrusion method are as follows.
1. Measurement range of pore diameter: 150 to 0.003 (μm)
2. Mercury contact angle: 130 (°)
3. Surface tension of mercury: 485 (mN / m)

  In the present invention, the peak is read based on the Log differential pore volume distribution graph. The Log differential pore volume distribution graph obtains a value obtained by dividing the differential pore volume (dV) by the logarithmic difference value d (logD) of the pore diameter, and plots this value against the average pore diameter of each section. It is a thing. Dividing by the logarithmic difference value d (logD) of the pore diameter in this way is that when dividing by the difference pore diameter, the denominator becomes small when the pore diameter is small, while the value is emphasized. This is because when the pore diameter is large, the denominator becomes large and the value is relaxed.

The “peak” in the present invention is the closest to the inflection point P on the left side of the inflection point P among the inflection points convex upward on the Log differential pore volume distribution graph. the measurement point is a, further right side of this inflection point P, when the B nearest measurement point to the inflection point P, a absolute value of the slope of the straight line L _a formed by connecting between the a-P B- If the average value of the absolute value of the slope of the straight line L _B formed by connecting between P is 0.5 or more, the inflection point P of "peak" (see FIG. 2). That is, the inflection point P when the average value I _{AV of the} slope represented by the following formula is 0.5 or more is called a peak.

If the average value _{I AV} of the inclination is 0.5 or more, because the peak of the inflection point P, as shown in FIG. 3-10, _visually, if _{I AV} is 0.5 or more This is because it can be recognized as a peak. 3 to 10, the pore diameter (logarithmic scale, range: 0.1 to 1 μm) is taken on the horizontal axis, and the Log differential pore volume (range: 0 to 1 cm ³ / g) is taken on the vertical axis. It is the graph which drawn the length of the axis equally.

In addition, the Log differential pore volume distribution graph in the present invention is obtained when pressure is applied in the following order in the mercury intrusion method. Note that the number and interval of plots on the graph are determined depending on how the pressure is applied.
1.5 psia, 2 psia, 2.5 psia, 3 psia, 3.5 psia, 4 psia, 5 psia, 6 psia, 7 psia, 8 psia, 9 psia, 10 psia, 12 psia, 14 psia, 16 psia, 18 psia, 20 psia, 25 psia, 30 psia, 30 psia, 40 psia, 50 psia, 40 psia, 50 psia 70 psia, 80 psia, 90 psia, 100 psia, 120 psia, 140 psia, 170 psia, 200 psia, 250 psia, 300 psia, 350 psia, 400 psia, 450 psia, 500 psia, 600 psia, 700 psia, 800 psia, 900 psia, 800 psia, 1000 psia, 1000 psia, 1000 psia 2000 psia, 2400 psia, 2800 psia, 3200 psia, 3600 psia, 4000 psia, 4500 psia, 5000 psia, 5500 psia, 6000 psia, 6500 psia, 7000 psia, 8000 psia, 9000 psia, 1000 psia, 1000 psia, 1000 psia, 13000 psia, 13000 psia, 13000 psia, 13000 psia, 13000 psia, 13000 psia. , 28000 psia, 32000 psia, 35000 psia, 38000 psia, 45000 psia, 50000 psia, 60000 psia

  Such a gas diffusion layer of the present invention can be composed of, for example, a fiber base material filled with a fluororesin and a conductive agent, or a molded product of a fluororesin and a conductive agent. Among these, a gas diffusion layer in which a fiber base material is filled with a fluororesin and a conductive agent is preferable because it has electrical conductivity and appropriate water repellency. The fiber base material is not particularly limited as long as it can impart strength to the gas diffusion layer. For example, glass fiber nonwoven fabric, carbon paper, acid-resistant organic fiber nonwoven fabric (for example, polytetrafluoroethylene fiber) , Polyvinylidene fluoride fiber, polyparaphenylene terephthalamide fiber, polyolefin fiber, polyphenylene sulfide fiber, polyester fiber represented by polyethylene terephthalate fiber and polytrimethylene terephthalate fiber, or a nonwoven fabric containing two or more types) be able to. Among these, glass fiber nonwoven fabrics are preferred because they are excellent in chemical resistance against acidic solutions, alcohols, etc., have excellent strength and processability, and are inexpensive.

  It is preferable that the glass fiber nonwoven fabric suitable as this fiber base material adhere | attaches glass fiber with the binder containing an acrylic resin, a vinyl acetate resin, and / or an epoxy resin. This is because the chlorine component and metal ions have adverse effects such as corrosivity in the fuel cell, but the resin is known as a resin with less impurities such as chlorine components and metal ions, and does not have the adverse effect. . In particular, it is preferable that the chlorine component is bonded with a binder of 20 ppm or less.

  In addition, when using an acrylic resin as resin which comprises a binder, it is preferable to use a self-crosslinking acrylic resin. In a fuel cell, protons are generated by a reaction in the catalyst layer, and the gas diffusion layer is exposed to a strong acid (about pH 2) atmosphere. Therefore, the gas diffusion layer preferably has acid resistance, and is cured by the self-crosslinking. This is because the acrylic resin exhibits excellent acid resistance. Here, “self-crosslinking acrylic resin” means an acrylic resin having one or two or more types of crosslinkable functional groups in the same or different monomer units, and a combination of these crosslinkable functional groups. For example, a combination of a carboxylic acid group and a vinyl group, a combination of a carboxylic acid group and a glycidyl group, a combination of a carboxylic acid group and an amine group, a combination of a carboxylic acid group and an amide group, a carboxylic acid group and a methylol group And a combination of a carboxylic acid group and an epoxy group. Among these, it does not contain nitrogen and is particularly excellent in oxidation resistance, a combination of a carboxylic acid group and a vinyl group, a combination of a carboxylic acid group and a glycidyl group, a combination of a carboxylic acid group and a methylol group, or a carboxylic acid group A combination with an epoxy group is preferred.

  Moreover, it is preferable that the solid content adhesion amount of the binder in a glass fiber nonwoven fabric exists in the range of 3-30 mass% on the basis of the mass of the whole glass fiber nonwoven fabric. When the solid content of the binder is less than 3% by mass, the mechanical strength as the glass fiber nonwoven fabric is low, and workability tends to be significantly impaired. On the other hand, when the solid content is more than 30% by mass, This is because the coating derived from the binder tends to be excessively formed and cannot be sufficiently filled with the fluororesin and the conductive agent.

Although such a glass fiber nonwoven fabric can be manufactured by a well-known method, it is preferable to manufacture by the wet method which can manufacture the glass fiber nonwoven fabric which has a uniform texture. The fiber diameter and fiber length of the glass fiber are 4 to 20 μm fiber diameter and 5 to 25 mm fiber length so that the glass fiber nonwoven fabric is excellent in dispersibility and mechanical strength when produced by a wet method. Is preferred. Further, as the glass fiber component, one or more kinds of E glass, C glass or Q glass having excellent chemical resistance (particularly acid resistance) can be used. The basis weight and thickness of the glass fiber nonwoven fabric are not particularly limited, but the basis weight is 4 so that the gas diffusion layer has an apparent density having a porosity that does not hinder gas permeation, supply or diffusion. The thickness is preferably ˜25 g / m ² , and the thickness is preferably 30 to 300 μm so that the strength can be secured. “Weight” refers to a value obtained by measuring the mass of a sample obtained by cutting a glass fiber nonwoven fabric into a 10 cm square and converting it to a mass of 1 m ^2. “Thickness” is a thickness gauge (manufactured by Mitutoyo Corporation): Code No. 547-321: measuring force 1.5N or less).

  In the gas diffusion layer of the present invention, the fiber base as described above is preferably filled with a fluororesin and a conductive agent. The gas diffusion layer is preferably filled with a conductive agent because it is necessary to conduct electrons in the thickness direction, and is preferably filled with a fluororesin in order to ensure appropriate water repellency. Examples of the conductive agent include carbon black and carbon nanotubes, and examples of the fluororesin include polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), tetrafluoroethylene and hexafluoropropylene. Examples thereof include a copolymer (FEP) and a tetrafluoroethylene / perfluoroalkyl vinyl ether copolymer (PFA).

  Such a fluororesin and a conductive agent are preferably filled in a fiber base material. However, as described above, the degree is only one peak in the Log differential pore volume distribution graph measured by the mercury intrusion method. And the peak is present in the pore diameter range of 0.01 to 1 μm. For example, if the filling of the fluororesin and the conductive agent into the fiber base material is insufficient, it is formed by a relatively large pore diameter peak exceeding 10 μm caused by the fiber base material, and the fluororesin and the conductive agent. As a result of having two peaks with a relatively small pore diameter of 1 μm or less due to the porous layer, water is discharged to the outside, the solid polymer membrane is not sufficiently wetted, and protons Becomes difficult to move, and sufficient power generation performance cannot be obtained. Therefore, it is necessary to fill the entire fiber base material with the fluororesin and the conductive agent sufficiently and uniformly.

  In order to fill the fiber base material with the fluororesin and the conductive agent sufficiently and uniformly in this manner, for example, it is preferable to apply a hot paste to the fiber base material by applying a conductive paste containing the fluororesin and the conductive agent. Further, the apparent density can be adjusted by hot pressing, and the surface can be smoothed. When the surface is smooth, the contact area between the gas diffusion layer, the catalyst layer, and the separator can be increased when a membrane-electrode assembly is produced. In addition, although the conditions of hot press are not specifically limited, For example, it is preferable to carry out for 10 to 180 seconds at the temperature of 50-250 degreeC and the pressure of 6-13 MPa.

  Moreover, it is preferable that it is 50-20: 50-80, and, as for the mass ratio of a fluororesin and a electrically conductive agent, it is more preferable that it is 40-25: 60-75.

The apparent density of the gas diffusion layer of the present invention is preferably 0.5 to 0.8 g / cm ³ . If the apparent density is higher than 0.8 g / cm ³ , gas permeation, supply, or diffusion, which is the original function of the gas diffusion layer, tends to deteriorate. On the other hand, the apparent density is higher than 0.5 g / cm ^3. If the packing density is low, the apparent density changes drastically when mounting as a gas diffusion layer of the fuel cell, and the gas is supplied to the bipolar plate gas supply groove, closing the groove, and supplying the gas efficiently. This is because, when the apparent density is low, the volume resistance increases and the electrical conductivity tends to deteriorate. The apparent density is a value obtained by dividing the basis weight (unit: g / cm ² ) by the thickness (unit: cm).

The basis weight and thickness of the gas diffusion layer are not particularly limited, but the basis weight is preferably 20 to 120 g / m ² and the thickness is 40 to 150 μm so as to reduce the volume resistance. Is preferred.

  The above is the case where the fiber base material is filled with a fluororesin and a conductive agent. The Log differential pore volume distribution graph measured by the mercury intrusion method has only one peak, and the peak is fine. As long as it exists in the range of 0.01-1 micrometer in pore diameter, it is not limited to the above-mentioned aspect, The gas diffusion layer which shape | molded the fluororesin and the electrically conductive agent with the shaping | molding die may be sufficient.

  Since the membrane-electrode assembly of the present invention includes the gas diffusion layer as described above, it is necessary to supply a humidified gas because water generated at the positive electrode is retained inside and the solid polymer membrane is easily kept moist. Even if necessary, a small humidifier can be used, and a lightweight and small fuel cell can be manufactured.

  The membrane-electrode assembly of the present invention can be exactly the same as the conventional membrane-electrode assembly except that it includes the gas diffusion layer as described above. For example, a gas diffusion electrode composed of a gas diffusion layer and a catalyst layer carries a catalyst (for example, a catalyst such as platinum) in a single or mixed solvent composed of ethyl alcohol, propyl alcohol, butyl alcohol, ethylene glycol dimethyl ether or the like. Carbon powder) is added and mixed, and then the ion exchange resin solution is added to it and mixed uniformly by ultrasonic dispersion to prepare a catalyst dispersion suspension. The catalyst dispersion suspension is coated on the surface of the gas diffusion layer. Alternatively, it can be produced by spraying and drying to form a catalyst layer. As the solid polymer film, for example, a perfluorocarbon sulfonic acid resin film, a sulfonated aromatic hydrocarbon resin film, an alkylsulfonated aromatic hydrocarbon resin film, or the like can be used. The membrane-electrode assembly can be produced, for example, by sandwiching a solid polymer membrane between the catalyst layers of a pair of gas diffusion electrodes and joining them by a hot press method.

  When the gas diffusion layer of the present invention is used for the positive electrode, water produced at the positive electrode can be kept inside to keep the solid polymer film moist, and when used for the negative electrode, Water that has been back-diffused from the inside can be kept inside, and the solid polymer membrane can be kept moist.

  Since the fuel cell of the present invention is a fuel cell including the membrane-electrode assembly having the gas diffusion layer described above, water generated at the positive electrode is retained inside, and the solid polymer membrane is easily kept moist. There is no need to supply or even if it is necessary, a small humidifier is sufficient, and it is a lightweight and small fuel cell.

  The fuel cell of the present invention can be exactly the same as a conventional fuel cell except that it includes a membrane-electrode assembly having a gas diffusion layer as described above. For example, it has a structure in which a plurality of cell units in which a membrane-electrode assembly as described above is sandwiched between a pair of bipolar plates are stacked. The bipolar plate is not particularly limited as long as it has a high conductivity, does not transmit gas, and has a flow path that can supply gas to the gas diffusion layer. For example, a carbon molding material, carbon- A resin composite material, a metal material, or the like can be used. A fuel cell can be manufactured by stacking a plurality of cell units each having a membrane-electrode assembly sandwiched between a pair of bipolar plates.

(Preparation of fiber base material)
First, the fiber base material used as the base of a gas diffusion layer was prepared. As this fiber base material, a glass fiber nonwoven fabric and a commercially available carbon paper (trade name: TGP-H-060, manufactured by Toray Industries, Inc.) were prepared. The glass fiber non-woven fabric is made of E glass (fiber diameter: 7 μm, fiber length: 13 mm) formed by a conventional wet papermaking method, and then a binder mainly composed of an acrylic resin and a polyvinyl acetate binder. Glass nonwoven fabric A (solid weight: 11 g / m ² , thickness: 110 μm) produced by impregnating a mixed binder mixed at a solid mass ratio of 1: 1 (solid content: 15 mass%) and drying, or similarly It is a glass nonwoven fabric B (weight per unit: 11 g / m ² , thickness: 110 μm) produced by impregnating an epoxy resin into the formed fiber web (solid content: 15 mass%) and drying.

(Preparation of conductive paste)
(1) Solid commercially available carbon black (manufactured by Electrochemical Industry Co., Ltd., trade name: Denka Black granular product) and commercially available PTFE dispersion “D-210C” (trade name, produced by Daikin Industries, Ltd.) Mixing at a mass / mass ratio of 60:40, stirring / dispersing with a water / ethanol mixed solution (volume ratio 2: 3) as a solvent, a conductive paste having a solid content of 10% by mass (hereinafter referred to as “first conductive paste”). Was prepared).
(2) After mixing the same commercially available carbon black as above and commercially available PTFE “Lublon L-5” (manufactured by Daikin Industries, Ltd., trade name) at a mass ratio of 60:40, A water / ethanol mixed solution (volume ratio 2: 3) was sufficiently stirred and dispersed as a solvent to prepare a conductive paste having a solid content of 5.7% by mass (hereinafter referred to as “second conductive paste”).
(3) The same commercially available carbon black as described above and commercially available PVDF (trade name: KF polymer, manufactured by Kureha Co., Ltd.) are mixed at a mass ratio of 75:25, and stirred and dispersed in an N-methylpyrrolidone solvent. A conductive paste having a content of 12% by mass (hereinafter referred to as “third conductive paste”) was prepared.

(Examples 1-7, Comparative Examples 1-3)
As shown in Table 1, a gas diffusion layer was manufactured by applying the first conductive paste, the second conductive paste, or the third conductive paste to the fiber base material.

  More specifically, when the first conductive paste is used, the paste is applied, dried by a hot air dryer having a temperature of 60 ° C., and then baked in a heating furnace at 350 ° C. for 1 hour in a nitrogen atmosphere. As a result, a hot diffusion was performed under the conditions of a pressure of 3 to 11 MPa, a temperature of 170 ° C., and a time of 30 seconds to adjust the apparent density and the pore diameter to produce a gas diffusion layer.

  In the case of using the second conductive paste, the paste is applied and dried by a hot air dryer at a temperature of 60 ° C., and then sintered in a heating furnace at 350 ° C. for 1 hour in a nitrogen atmosphere. A diffusion layer was produced.

  Further, when the third conductive paste is used, the paste is applied, immersed in a water bath for 30 minutes and substituted with a water solvent, and then dried with a hot air dryer at a temperature of 60 ° C., and a pressure of 8 to 15 MPa, a temperature Hot pressing was performed at 170 ° C. for 30 seconds to adjust the apparent density and the pore diameter, thereby producing a gas diffusion layer.

Table 1 summarizes the material composition, hot press conditions, basis weight, thickness, apparent density, and pore diameter (peaks in the Log differential pore volume distribution graph measured by mercury porosimetry) of these gas diffusion layers. It is. In the table, the glass fiber nonwoven fabric A is expressed as “glass A”, the glass fiber nonwoven fabric B is expressed as “glass B”, and the carbon paper is expressed as “carbon”. Furthermore, the first conductive paste is expressed as “first”, the second conductive paste is expressed as “second”, and the third conductive paste is expressed as “third”.

(Production of catalyst layer)
To 10.4 g of ethylene glycol dimethyl ether, 0.8 g of commercially available platinum-supported carbon particles (manufactured by Ishifuku Metal Co., Ltd., 40% by mass of platinum supported on carbon) are added and dispersed by ultrasonic treatment. 4.0 g of a 5 mass% Nafion solution (trade name, manufactured by Sigma-Aldrich, USA) was further dispersed by ultrasonic treatment, and further stirred with a stirrer to prepare a catalyst paste. Next, this catalyst paste was applied to a support (trade name: Naflon PTFE tape, manufactured by Nichias Co., Ltd., thickness: 0.1 mm) and dried at 60 ° C. by a hot air dryer, and the amount of platinum supported on the support was A catalyst layer of 0.5 mg / cm ² was prepared.

(Preparation of solid polymer membrane-catalyst layer assembly)
First, Nafion 112 (trade name, manufactured by DuPont, USA) was prepared as a solid polymer membrane. After the catalyst layers were laminated on both sides of the solid polymer membrane, the temperature was 135 ° C., the pressure was 2.6 MPa, The solid polymer membrane-catalyst layer assembly was manufactured by hot pressing under conditions of 2 minutes.

(Power generation evaluation using fuel cell evaluation cells)
After laminating the gas diffusion layers of Examples 1-7 or Comparative Examples 1-3 on both surfaces of the solid polymer membrane-catalyst layer assembly to form a membrane-electrode assembly (MEA), a clamping pressure of 3.0 N・ Assembled in a polymer electrolyte fuel cell “As-510-C25-1H” (trade name, manufactured by NF Circuit Design Block Co., Ltd.) at m, power generation performance was evaluated. This standard cell includes a bipolar plate and is used for MEA evaluation tests. In the same membrane-electrode assembly (MEA), the same gas diffusion layer was used on both the positive electrode side and the negative electrode side.

  Power generation was performed by supplying hydrogen gas on the negative side and oxygen gas on the positive electrode side at a flow rate of 500 mL / min, and the potential-current curve was measured by a power generation evaluation apparatus manufactured by NF Circuit Design Block Co., Ltd. At this time, the cell temperature was 80 ° C., and in order to humidify the negative electrode and the positive electrode, hydrogen gas and oxygen gas were passed through a humidifier filled with saturated water vapor at a temperature of 40 ° C. and then supplied into the fuel cell. . This potential-current curve was as shown in FIG.

From FIG. 11, in the Log differential pore volume distribution graph measured by the mercury intrusion method, the gas of Examples 1 to 7 having only one peak and the peak is in the range of the pore diameter of 0.01 to 1 μm. Compared with Comparative Examples 1 to 3, the membrane-electrode assembly provided with the diffusion layer has a pore diameter of less than 0.01 μm or more than 1 μm, and exhibits excellent power generation characteristics. Confirmed to get. In particular, in Examples 1 to 3 in which the pore diameter is 0.05 to 0.15 μm, the voltage when the current density is 1.5 A / cm ² is higher than those in Examples 4 to 7, and extremely excellent power generation. It was confirmed that the characteristics can be exhibited.

Schematic sectional view showing the schematic configuration of a polymer electrolyte fuel cell Log differential pore volume distribution graph explaining the concept of peak Log differential pore volume distribution graph with convex inflection point on average value I _{AV of} slope 0.3 Log differential pore volume distribution graph with convex inflection point on average value I _{AV of} slope 0.4 Log differential pore volume distribution graph with convex inflection point on average value I _{AV of} slope 0.5 Log differential pore volume distribution graph with convex inflection points on average value I _{AV of} slope 0.6 Log differential pore volume distribution graph with convex inflection point above mean value I _{AV of} slope 0.7 Log differential pore volume distribution graph with convex inflection point on average value I _{AV of} slope is 0.8 Log differential pore volume distribution graph with convex inflection point on mean value I _{AV of} slope 0.9 Log differential pore volume distribution graph with convex inflection point on average value I _{AV of} slope 1.0 Graph showing potential-current curve

Explanation of symbols

11a (negative electrode side) bipolar plate 11c (positive electrode side) bipolar plate 13a (negative electrode side) gas diffusion layer 13c (positive electrode side) gas diffusion layer 15a (negative electrode side) catalyst layer 15c (positive electrode side) catalyst layer 17a negative electrode 17c positive electrode 19 solid Polymer membrane

Claims (6)

This is a gas diffusion layer in which the entire fiber base material is filled with a fluororesin and a conductive agent. The log differential fineness is measured by applying pressure in the following order within the pore diameter range of 150 to 0.003 μm by the mercury intrusion method. In the pore volume distribution graph, a gas diffusion layer having only one peak defined below and having the peak in the range of pore diameter of 0.01 to 1 μm.
Record
Pressure; 1.5 psia, 2 psia, 2.5 psia, 3 psia, 3.5 psia, 4 psia, 5 psia, 6 psia, 7 psia, 8 psia, 9 psia, 10 psia, 12 psia, 14 psia, 16 psia, 18 psia, 20 psia, 25 psia, 30 psia, 40 psia, 30 psia, 40 psia, 60 psia, 70 psia, 80 psia, 90 psia, 100 psia, 120 psia, 140 psia, 170 psia, 200 psia, 250 psia, 300 psia, 350 psia, 400 psia, 450 psia, 500 psia, 600 psia, 700 psia, 800 psia, 900 psia, 900 psia, 900 psia, 900 psia sia, 2000 psia, 2400 psia, 2800 psia, 3200 psia, 3600 psia, 4000 psia, 4500 psia, 5000 psia, 5500 psia, 6000 psia, 6500 psia, 7000 psia, 8000 psia, a1000 psia, 1000 psia, 13000 psia, 12000 psia, 13000 psia, 12000 psia, 13000 psia, 12000 psia 25000 psia, 28000 psia, 32000 psia, 35000 psia, 38000 psia, 45000 psia, 50000 psia, 60000 psia
Peak; mean value I _AV of the slope represented by the following equation of peak inflection point P where 0.5 or more.

The gas diffusion layer according to claim 1, wherein the peak exists in the range of pore diameters of 0.05 to 0.15 µm. The gas diffusion layer according to claim 1 or 2, wherein the apparent density of the gas diffusion layer is 0.5 to 0.8 g / cm ³ . The gas diffusion layer according to any one of claims 1 to 3, wherein the fiber substrate is made of a glass fiber nonwoven fabric. A membrane-electrode assembly comprising the gas diffusion layer according to claim 1. A fuel cell comprising a membrane-electrode assembly comprising the gas diffusion layer according to claim 1.

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