JP4872202B2 - Fuel cell and fuel cell manufacturing method - Google Patents

Description

  The present invention relates to a fuel cell and a method for manufacturing the fuel cell.

  A fuel cell directly converts chemical energy into electrical energy by supplying fuel and an oxidant to two electrically connected electrodes and causing the fuel to be oxidized electrochemically. Unlike thermal power generation, it is not subject to the Carnot cycle, and exhibits high energy conversion efficiency. A fuel cell is usually configured by laminating a plurality of single cells having a basic structure in which an electrolyte membrane is sandwiched between a fuel electrode and an oxidant electrode, and among them, a solid polymer using a solid polymer electrolyte membrane as an electrolyte membrane Electrolytic fuel cells are particularly attracting attention as portable and mobile power sources because of their advantages such as easy miniaturization and operation at low temperatures.

  In the polymer electrolyte fuel cell, power is generated by the following electrochemical reaction by generating hydrogen in the fuel electrode or containing hydrogen and supplying an oxidant containing oxygen to the oxidant electrode.

Fuel electrode: H ₂ → 2H ⁺ + 2e ⁻ (1)
Oxidant electrode: 1 / 2O ₂ + 2H ⁺ + 2e ⁻ → H ₂ O (2)

  The electrons generated by the equation (1) reach the oxidant electrode after working with an external load via an external circuit. Then, protons generated by the equation (1) move from the fuel electrode side to the oxidant electrode side in the solid polymer electrolyte membrane.

  A fuel electrode and an oxidant electrode to which fuel or an oxidant is supplied in a gas state usually have a structure in which a catalyst layer and a gas diffusion layer are laminated in order from the solid polymer electrolyte membrane side. The gas diffusion layer is provided for the purpose of diffusing the supplied fuel or oxidant and supplying it to the catalyst layer as a place for the electrochemical reaction, and has a porous structure. In a state where the porosity of the porous structure is not kept high, gas diffusion is hindered, and the power generation performance of the fuel cell is deteriorated. Therefore, it is necessary to keep the porosity of the gas diffusion layer high. is there.

However, the pores of the gas diffusion layer are clogged by surplus water such as water vapor or moisture contained in the fuel or oxidant, moisture generated at the oxidizer electrode, or water that moves with protons. Therefore, even if the porosity is high, flooding may occur and drainage performance may be reduced. Therefore, it is important that the gas diffusion layer has a drainage property that allows excess water to be discharged out of the electrode without stagnation in the pores in the gas diffusion layer.
In addition, since the solid polymer electrolyte membrane and the catalyst layer usually need to be kept in a high humidity state to some extent, the gas diffusion layer sandwiching them is not only capable of draining excess water but also has a solid polymer electrolyte membrane. In addition, water retention that can maintain the wet state of the catalyst layer is also required.

  Conventionally, in order to improve the drainage property of the gas diffusion layer, a layer containing conductive particles such as carbon powder, a water repellent resin, and the like has been provided on the surface of the gas diffusion layer on the catalyst layer side. However, in the layer provided for the purpose of improving the drainage, the conductive powder aggregates, and it is difficult to form a sufficient space for gas diffusion and drainage. In addition, cracks were often generated on the surface and inside of the layer due to local aggregation of the conductive powder particles.

  As a technique for solving the above problems, for example, Patent Document 1 discloses that at least a part of a gas diffusion layer in contact with a catalyst layer includes a water-repellent resin and fibrous carbon, preferably further conductive particles. The thing including is described.

JP 2003-115302 A

  Like patent document 1, it is possible to create a space | gap suitable for gas diffusion by mixing an electroconductive granular material and a fiber. Moreover, these voids can be maintained in their shape without being completely crushed even in a crimping process such as hot pressing in the manufacture of fuel cells. However, in Patent Document 1, since carbon fibers that are hydrophilic are used as the fiber, excessive water in the electrode tends to accumulate in the formed pores, and drainage is insufficient.

  The present invention has been accomplished in view of the above circumstances, and an object thereof is to provide a fuel cell including a gas diffusion layer excellent in gas diffusibility and drainage and a method for manufacturing the same.

The fuel cell of the present invention is a fuel cell comprising an electrolyte membrane and a pair of electrodes on both sides of the electrolyte membrane, and at least one of the electrodes has a catalyst layer and a gas diffusion layer in order from the electrolyte membrane side. The gas diffusion layer has a laminated structure including at least a first gas diffusion layer and a second gas diffusion layer in order from the catalyst layer side, and the first gas diffusion layer is a water repellent resin. In addition, the conductive particles not subjected to hydrophobic treatment, and the fiber material that has been subjected to hydrophobic treatment in advance before forming the first gas diffusion layer, were measured by the following measurement method, and were subjected to the previously hydrophobic treatment. The fiber contact angle of water is 110 ° or more, the fiber diameter of the previously hydrophobized fiber is 5 to 600 nm, the aspect ratio is 10 to 500, and the prehydrophobic treated fiber is 10 to 10 for the conductive powder 0 that are contained by weight% and is characterized in.
Measurement method: A step of producing a press-molded body by applying a pressure of 500 kg / cm ^{2 to} the previously hydrophobized fiber material, and 2 μl of water are dropped on the press-molded body, and dropped by a contact angle meter The method which has the process of measuring the contact angle of water after 1 second.

According to the present invention, the catalyst layer side in which the moisture of the gas diffusion layer tends to stay is made to contain the fibrous material that has been previously hydrophobized , has a fiber diameter of 5 to 600 nm, and an aspect ratio of 10 to 500. As a result, pores having a size and a number sufficient for discharging excess moisture and diffusing gas are formed, and hydrophobicity is imparted to the pores. Therefore, if excessive moisture in the catalyst layer moves to the pores of the gas diffusion layer near the catalyst layer, the pores in the vicinity of the catalyst layer have hydrophobicity. Is quickly moved to another pore on the gas flow path side. Therefore, it is excellent in drainage.

Moreover, since the pores in the vicinity of the catalyst layer are less likely to be clogged with moisture due to such an action, the gas flow in the vicinity of the catalyst layer is not hindered and the gas diffusibility is excellent.
Furthermore, according to the present invention, when excess water moves to the pores of the gas diffusion layer in the vicinity of the catalyst layer, it is quickly discharged into the gas flow path by the above-described expelling action. When the amount of water is an appropriate amount, there is no action of attracting water from the catalyst layer, so that the water retention property for appropriately maintaining the wet state of the electrolyte membrane and the catalyst layer is also excellent.
Further, according to the present invention, a sufficient effect can be obtained by applying the hydrophobic treatment by setting the water contact angle of the previously hydrophobic treated fiber to 110 ° or more.
Furthermore, according to this invention, aggregation of the said electroconductive granular material is prevented by including the said textiles previously hydrophobically processed with the said electroconductive granular material. Moreover, according to this invention, electroconductivity can be provided to a 1st gas diffusion layer because the said electroconductive granular material is not given the hydrophobic process.

Further, the fuel cell manufacturing method of the present invention is hydrophobically treated by a method selected from the group consisting of fluorine gas treatment, fluorine resin coating treatment and hydrocarbon resin coating treatment , and has a fiber diameter of 5 to 600 nm, and , A step of preparing a fiber having an aspect ratio of 10 to 500 in advance, a first gas containing at least a water-repellent resin, a conductive granular material that has not been subjected to a hydrophobic treatment, and the fibrous material that has been subjected to a hydrophobic treatment in advance A step of applying the diffusion layer paste to at least the surface of the gas diffusion layer substrate that includes the layer to be the second gas diffusion layer, the surface facing the catalyst layer; and a gas diffusion layer substrate coated with the first gas diffusion layer paste. The fuel cell obtained by including the process of drying and / or baking is excellent in drainage property and gas diffusibility, and exhibits high power generation performance.

  The fuel cell obtained by the present invention has an excellent drainage property that allows excess water to be smoothly discharged while maintaining the wet state of the electrolyte membrane and the catalyst layer. Therefore, the gas diffusibility is high, the reaction gas can be supplied to the catalyst layer thoroughly, and the power generation can be efficiently performed under an appropriate wet condition. As a result, the power generation performance of the fuel cell can be improved.

  The fuel cell of the present invention is a fuel cell comprising an electrolyte membrane and a pair of electrodes on both sides of the electrolyte membrane, and at least one of the electrodes has a catalyst layer and a gas diffusion layer in order from the electrolyte membrane side. The gas diffusion layer has a laminated structure including at least a first gas diffusion layer and a second gas diffusion layer in order from the catalyst layer side, and the first gas diffusion layer is a water repellent resin. , Including conductive particles and selectively hydrophobically treated fibers, wherein the hydrophobically treated fibers are contained in an amount of 10 to 50% by weight based on the conductive particles. And

A configuration example of a polymer electrolyte fuel cell to which the present invention is applied will be described with reference to FIG. In FIG. 1, a fuel electrode catalyst layer 2a is provided on one side of the proton conductive solid polymer electrolyte membrane 1, and an oxidant electrode catalyst layer 2b is provided on the other side. Further, gas diffusion layers 5a and 5b having first gas diffusion layers 3a and 3b and second gas diffusion layers 4a and 4b are formed on the outer surfaces of the catalyst layers 2a and 2b. In this example, the electrode 6 (the fuel electrode 6 a and the oxidant electrode 6 b) is composed of the catalyst layer 2 and the gas diffusion layer 5. Usually, a reactive gas (fuel gas or oxidant gas) is supplied to each electrode of a membrane-electrode assembly composed of the electrolyte membrane 1 and a pair of electrodes 6 formed on both surfaces thereof, and is generated by an electrochemical reaction. A separator 8 that defines a gas flow path 7 is provided outside each electrode in order to discharge moisture and excess gas.
In addition, although the structural example of a polymer electrolyte fuel cell is demonstrated here, the fuel cell of this invention is not limited to a polymer electrolyte fuel cell. In addition, if the fuel or oxidant supplied to the electrode is gaseous, such as a direct methanol fuel cell using a liquid fuel such as a methanol solution or a gaseous oxidant such as air, The present invention can be applied.

In the fuel cell of the present invention, among the first and second gas diffusion layers constituting the gas diffusion layer 5, the first gas diffusion layer 3 disposed on the catalyst layer side where excess water tends to stay is repelled. An aqueous resin, a conductive powder, and a fiber that has been selectively subjected to hydrophobic treatment are included.
In the first gas diffusion layer, aggregation of the conductive particles is prevented by including the fibrous material together with the conductive particles. As a result, it is possible to secure a space required for reaction gas diffusion and moisture movement, and to prevent cracking of the first gas diffusion layer. At this time, as shown in FIG. 2, the fibrous material 9 is interposed between the particles of the conductive granular material 10 to prevent aggregation of the conductive granular material, and the pores 11 are formed around the fibrous material 9. Formation was observed with a scanning electron microscope. The pores 11 formed around the fiber 9 are larger than the pores 12 formed between the conductive particles 10 and have a diameter that allows gas and moisture to move smoothly. is doing. However, when the fibrous material 9 forming the pores 11 has a strong hydrophilicity, the moved water tends to stay in the pores, so that the pores are blocked and the gas diffusibility is lowered. There is.

  Therefore, in the present invention, the hydrophobic treated fiber is added to the inside of the pores 11 by including the hydrophobic treated fiber in the vicinity of the catalyst layer of the gas diffusion layer, particularly preferably at the interface with the catalyst layer. Made it possible to move quickly. That is, surplus moisture that has moved from the catalyst layer into the first gas diffusion layer located in the vicinity of the catalyst layer moves smoothly without remaining in the pores, and is discharged to the gas flow path side. Therefore, the fuel cell provided by the present invention has a gas diffusion layer excellent in drainage, and particularly in an electrode (in FIG. 1, the oxidant electrode 6b), a high current density region, etc. Even in a region where high drainage is required, clogging of the gas diffusion layer due to excess moisture is unlikely to occur and the gas diffusibility is excellent.

Furthermore, when excess water moves into the pores of the first gas diffusion layer located in the vicinity of the catalyst layer, it is quickly discharged to the gas flow path side by the expelling action as described above. When the amount of water in the catalyst layer is an appropriate amount, there is no action of attracting moisture, so that the wet state of the electrolyte membrane and the catalyst layer can be appropriately maintained.
Moreover, since the fiber is selectively subjected to the hydrophobic treatment, the powder that should originally function as the conductive powder does not deteriorate its conductivity by the hydrophobic treatment.
As described above, the fuel cell of the present invention has an excellent drainage property in which the excessive moisture to be discharged does not stay in the gas diffusion layer while keeping the wet state of the electrolyte membrane and the catalyst layer appropriately. In addition, conductivity is maintained. Therefore, it shows high battery characteristics.

  The fiber contained in the first gas diffusion layer is selectively subjected to a hydrophobic treatment. “Preferentially hydrophobized” means that the entire first gas diffusion layer is not hydrophobized but the position of the fiber contained therein is selectively hydrophobized. It is. However, as long as the effects of the present invention are not impaired, other materials subjected to hydrophobic treatment may be included in addition to the conductive material, the water-repellent resin, and the fiber treated by hydrophobic treatment.

  Whether the fiber contained in the first gas diffusion layer is selectively subjected to hydrophobic treatment, for example, only the fiber is subjected to a specific hydrophobic treatment or contained in the first gas diffusion layer. It can be determined by the fiber surface being covered with a resin different from the water repellent resin.

  Typically, the first gas diffusion layer may be formed using a fiber that has been previously hydrophobically treated. Here, the fiber material that has been hydrophobically treated in advance is typically the first gas diffusion layer formed by mixing other materials and the fiber material as described later before forming the first gas diffusion layer. Before the paste is prepared, it is a fiber that has been subjected to a hydrophobic treatment in advance.

  The hydrophobic treatment applied to the fiber material is not particularly limited as long as it can improve the hydrophobicity of the fiber material. For example, a fluorine gas treatment that heats the fiber material in a fluorine gas atmosphere to fluorinate the surface of the fiber material, Fluorine resin coating treatment for coating the fiber surface with a fluorine resin such as polytetrafluoroethylene (PTFE), tetrafluoroethylene-hexafluoropropylene copolymer (FEP), polyvinylidene fluoride (PVDF), or Examples thereof include a hydrocarbon resin coating treatment in which the fiber surface is coated with a hydrocarbon resin such as polypropylene and polyethylene. The method for the hydrophobic treatment is not particularly limited, and can be performed according to a general method.

As a measure of the hydrophobicity of the hydrophobic treatment, it is preferable that the water contact angle of the hydrophobically treated fiber is 110 ° or more, particularly 140 ° or more. By setting the contact angle of water after the hydrophobic treatment to 110 ° or more, a sufficient effect can be obtained by applying the hydrophobic treatment. Here, the water contact angle of the fiber material can be considered as the water contact angle of the surface of the press-molded body obtained by press-molding the fiber material, and can be measured by a contact angle meter. In addition, 2 μl of pure water is dropped on the pressed product of the fiber, and the value after 1 second is defined as the contact angle. Specifically, the press-molded body can be produced by putting an appropriate amount of fiber into a container and applying a pressure of 500 kg / cm ² from the top.

  The fiber material may have a fibrous shape, for example, a needle shape, a rod shape, a tube shape, or the like, or may be branched. Specifically, those having a fiber diameter of 5 to 600 nm, particularly 10 to 200 nm, and an aspect ratio of 10 to 500 are preferable. Here, when the fiber has a branch structure, the fiber length is the length from the branch point to the tip or from the branch point to the next branch point.

  As the material of the fiber material, it is only necessary to have the strength required as a material constituting the gas diffusion layer. For example, carbon fiber, metal fiber, noble metal fiber, carbon fiber coated with a noble metal coat, etc. There are no particular restrictions. Carbon fiber is preferable from the viewpoint of the strength, flexibility, weight and the like of the obtained gas diffusion layer. Examples of the carbon fiber include PAN-based carbon fiber, pitch-based carbon fiber, vapor-grown carbon fiber (VGCF), and carbon nanotube, and VGCF is particularly preferable. This is because VGCF is excellent in miscibility and durability with the conductive particles. VGCF is produced by gas phase thermal decomposition of hydrocarbon gases in the presence of a catalyst, and the specific production method thereof is various but not particularly limited.

The fiber material subjected to the hydrophobic treatment is contained in a proportion of 10 to 50% by weight with respect to the conductive powder. When the proportion of the fiber processed with hydrophobic treatment is less than 10% by weight with respect to the conductive particles, the effect of using the fiber processed with hydrophobic treatment is sufficiently obtained regardless of the hydrophobicity of the fiber. Absent. On the other hand, when the proportion of the fiber processed with hydrophobic treatment exceeds 50% by weight with respect to the conductive powder, the fiber processed with hydrophobic treatment has low conductivity or does not have gas diffusion. The conductivity of the layer is insufficient. By mixing the hydrophobically treated fiber with a proportion of 10 to 50% by weight with respect to the conductive powder, a gas diffusion layer in which drainage and conductivity are balanced can be obtained.
In addition, you may use the textiles which have not performed the hydrophobic treatment within the range which does not impair the effect of this invention with the textiles which performed the hydrophobic treatment for this invention.

  The conductive powder used in the present invention is not particularly limited as long as it is conductive, but a carbon material such as carbon black is preferable. Examples of the carbon black include oil furnace black, acetylene black, thermal black, channel black and the like, and among them, acetylene black is preferable. The primary particle diameter of the conductive powder is usually preferably 20 to 100 μm and particularly preferably 20 to 50 μm.

  The first gas diffusion layer may include the conductive particles that have been subjected to a hydrophobic treatment, but the conductivity of the first gas diffusion layer is provided by the conductive particles. In addition, since the conductive particles subjected to the hydrophobic treatment have low conductivity or do not show at all, the conductive particles are preferably not subjected to the hydrophobic treatment. When the conductive particles subjected to the hydrophobic treatment are included, it is necessary to determine the content in consideration of the conductivity of the first gas diffusion layer.

  The water-repellent resin is not particularly limited as long as it has a function as a binder when forming the first gas diffusion layer and can impart water repellency to the first gas diffusion layer. From the viewpoint of drainage of the first gas diffusion layer, the surface tension of the water repellent resin is preferably smaller than the surface tension of water (about 72 dyn / cm). Specific water-repellent resins that can be used include fluorine resins such as PTFE, FEP, and PVDF, and hydrocarbon resins such as polypropylene and polyethylene. The water-repellent resin may be about 20 to 80% by weight with respect to the total amount of the conductive particles and the hydrophobically treated fiber.

  The second gas diffusion layer has only to have pores (voids) necessary for gas diffusion and conductivity, and has the strength necessary to support the gas diffusion layer. Conductive porous materials such as paper, carbon cloth, carbon sheet, carbon nonwoven fabric, and carbon felt can be used. The conductive porous body is preferably subjected to a water repellent treatment by immersing in a fluororesin dispersion such as PTFE, FEP, or PVDF, or by applying such a dispersion. The thickness of the second gas diffusion layer is usually preferably about 100 to 400 μm.

  The gas diffusion layer only needs to have a laminated structure including at least the first gas diffusion layer and the second gas diffusion layer in order from the catalyst layer side, and within the range not impairing the effects of the present invention, Between the first gas diffusion layer, between the first gas diffusion layer and the second gas diffusion layer, or on the surface of the second gas diffusion layer opposite to the first gas diffusion layer. , May have additional layers or interfacial structures.

Hereinafter, the present invention will be described along with an example of a method for producing a fuel cell of the present invention.
First, the above-mentioned water-repellent resin, conductive powder, fibrous material that has been hydrophobically treated, and other components as necessary, such as organic solvents such as ethanol, propanol, propylene glycol, water, or a mixture thereof A first gas diffusion layer paste is prepared by mixing with a solvent. It is preferable to use a water-repellent resin that has been dispersed in a solvent such as water in advance from the viewpoint of dispersibility in the first gas diffusion layer paste.

Subsequently, the obtained gas diffusion layer paste is applied to at least the side facing the catalyst layer of the gas diffusion layer substrate including the second gas diffusion layer. At this time, the first gas diffusion layer paste may be impregnated inside the gas diffusion layer substrate. Here, the shape of the first gas diffusion layer is not particularly limited, and may be, for example, a shape that covers the entire surface of the gas diffusion layer base on the catalyst layer side or a shape having a predetermined pattern such as a lattice shape. . The thickness of the first gas diffusion layer (thickness from the surface of the gas diffusion layer substrate excluding the portion impregnated inside the gas diffusion layer substrate) is usually preferably about 5 to 30 μm.
The method for applying the first gas diffusion layer paste to the gas diffusion layer substrate is not particularly limited, and examples thereof include a screen printing method, a spray method, a doctor blade method, a gravure printing method, and a die coating method.
Even if the gas diffusion layer substrate including the second gas diffusion layer is composed of only the conductive porous body to be the second gas diffusion layer, an additional layer is provided on the conductive porous body. May be good.

Next, the gas diffusion layer substrate on which the first gas diffusion layer paste is applied is usually dried at 20 to 30 ° C. for about 120 minutes, and then baked at 320 to 380 ° C. for about 60 minutes, whereby the gas A diffusion layer sheet is completed. At this time, the drying step may be omitted.
The gas diffusion layer sheet obtained as described above is hot-pressed with the first gas diffusion layer and the catalyst layer facing each other on the solid polymer electrolyte membrane on which the catalyst layer is formed. Etc. to form a membrane-electrode assembly. In addition, a catalyst layer is formed on the surface of the first gas diffusion layer of the gas diffusion layer sheet, and the gas diffusion layer sheet and the electrolyte membrane are hot pressed in a state where the catalyst layer is sandwiched between the gas diffusion layer and the electrolyte membrane. May be joined together.

The catalyst layer usually contains an ion conductive material and a catalyst material. As the catalyst material, catalyst particles in which a catalyst component is supported on a conductive material such as a carbon material such as carbonaceous particles or carbonaceous fibers are preferably used. The catalyst component is not particularly limited as long as it has a catalytic action for the hydrogen oxidation reaction at the fuel electrode and the oxygen reduction reaction at the oxidant electrode. For example, platinum, ruthenium, iron, nickel, manganese And an alloy of a metal such as platinum and the like.
As the ion conductive material, it can be appropriately selected from materials used as an electrolyte membrane. Specifically, fluorine-based polymers represented by perfluorosulfonic acid polymers, sulfonic acid groups, carboxylic acid groups, Examples thereof include solid polymer electrolytes such as hydrocarbon-based polymers having an ion conductive group such as a boronic acid group in the side chain.

  The catalyst layer paste can be obtained by mixing and dispersing the above-mentioned ion conductive material and catalyst material and, if necessary, other materials such as a water repellent polymer and a binder in a solvent. As the solvent, a mixture of alcohols such as ethanol, methanol, propanol, propylene glycol and water can be used, but the solvent is not limited thereto. The concentration of each component in the catalyst layer paste is not particularly limited.

  The method for forming the catalyst layer on the electrolyte membrane or the gas diffusion layer may be a commonly used method. For example, the catalyst layer paste is directly applied and dried on the electrolyte membrane surface or the first gas diffusion layer. Or a catalyst layer sheet formed by applying and drying a catalyst layer paste on a substrate such as polytetrafluoroethylene to form a first gas diffusion layer in an electrolyte membrane or a gas diffusion layer. It can also be formed by transferring to the layer side. Although the film thickness of a catalyst layer is not specifically limited, What is necessary is just to be about 5-50 micrometers.

  The electrolyte membrane is not particularly limited, and the present invention can be applied to any electrolyte membrane that requires the presence of moisture for ionic conductivity in the electrolyte membrane. Specifically, for example, fluoropolymers represented by perfluorosulfonic acid polymers and solid polymers such as hydrocarbon polymers having ion conductive groups such as sulfonic acid groups, carboxylic acid groups, and boronic acid groups in the side chain. Examples thereof include molecular electrolyte membranes. The film thickness of the electrolyte membrane is not particularly limited, and may be about 15 to 60 μm.

  The membrane-electrode assembly obtained as described above is used as a fuel cell by being sandwiched between separators by a general method, and a fuel cell is obtained by stacking a plurality of fuel cells. According to the present invention, the electrolyte membrane and the catalyst layer can be maintained in an appropriate wet state, and the reaction gas can be supplied to the catalyst layer without any problem, so that it is possible to provide a fuel cell with high power generation performance. is there.

Example 1
<Fluorine treatment of carbon fiber>
Carbon fiber (VGCF) was placed in the reaction furnace, and the atmosphere in the reaction furnace was replaced with argon gas. Then, while flowing argon gas, it heated up to 400 degreeC, supplied fluorine gas, hold | maintained for 1 hour, and performed the fluorine treatment of carbon fiber. Subsequently, the fluorine gas was stopped, cooling was performed while supplying argon gas, and after the temperature became close to room temperature, the fluorine-treated carbon fiber was taken out from the reactor. The degree of fluorine treatment was adjusted by the fluorine gas concentration, treatment time, and treatment temperature.
Fluorine-treated carbon fiber is put in 10 g in a φ10 mm cylindrical container, and a pellet is produced by applying a pressure of 500 kg / cm ² from the top. The contact angle of water of the pellet is measured using a contact angle meter as follows. It measured on condition of this.

Drop volume: 2 μL
Time from dropping to measurement: 1 second Temperature: 25 ° C

<Manufacture of fuel cell>
Mixing 0.5 g of carbon particles carrying platinum, 0.15 g of a perfluorosulfonic acid resin solution (trade name Nafion, manufactured by DuPont), 5 ml of propylene glycol, and 3 ml of water, and dispersing them with an ultrasonic homogenizer and a stirrer. A catalyst paste was prepared. Next, the obtained catalyst paste is applied to both surfaces of a perfluorosulfonic acid resin membrane (trade name Nafion, manufactured by DuPont) by screen printing to form a catalyst layer, and the catalyst layer-electrolyte membrane-catalyst layer assembly is formed. Obtained. At this time, the amount of platinum was 0.3 mg / cm ² .

Subsequently, 3.6 g of carbon black, 4 g of a polytetrafluoroethylene (PTFE) dispersion solution (PTFE concentration: 60% by weight), 0.36 g of carbon fiber (water contact angle 116 °) pre-fluorinated (to carbon black) 10% by weight), 60 ml of water and 60 ml of propylene glycol were mixed and applied to a carbon paper (thickness: 200 μm, manufactured by Toray) as a second gas diffusion layer by screen printing, and the first gas diffusion layer was applied. Formed. Thereafter, the carbon paper on which the first gas diffusion layer was formed was dried (25 ° C., 120 minutes) and fired (350 ° C., 60 minutes) to obtain a gas diffusion layer sheet.
The obtained gas diffusion layer sheet was bonded by hot pressing (130 ° C., 3 MPa) on the catalyst layers on both sides of the catalyst layer-electrolyte membrane-catalyst layer assembly obtained above. Further, a separator was provided outside the gas diffusion layer to obtain a fuel cell.

(Example 2)
A fuel cell was prepared in the same manner as in Example 1 except that 3 g of carbon black and 0.9 g of carbon fiber having a water contact angle of 132 ° as a prefluorinated carbon fiber (30 wt% with respect to carbon black) were used. A cell was obtained.

(Example 3)
Except for using 2.6 g of carbon black and 1.3 g of carbon fiber having a water contact angle of 142 ° as a pre-fluorinated carbon fiber (50% by weight based on carbon black), the same as in Example 1, A fuel cell was obtained.

(Comparative Example 1)
Other than using 2.6 g of carbon black and 1.3 g of carbon fiber having a contact angle of 103 ° water with no fluorine treatment (50 wt% with respect to carbon black) instead of carbon fiber pre-fluorinated. In the same manner as in Example 1, a fuel cell was obtained.

(Comparative Example 2)
In the same manner as in Example 1, except that 3.7 g of carbon black and 0.3 g (8% by weight with respect to carbon black) of a pre-fluorinated carbon fiber having a water contact angle of 153 ° were used. A fuel cell was obtained.

(Comparative Example 3)
In the same manner as in Example 1, except that 3.7 g of carbon black and 0.3 g of carbon fiber having a water contact angle of 122 ° (8 wt% with respect to carbon black) as a pre-fluorinated carbon fiber were used. A fuel cell was obtained.

(Comparative Example 4)
Fuel was obtained in the same manner as in Example 1, except that 2.5 g of carbon black and 1.4 g of fluorine-treated carbon fiber having a water contact angle of 155 ° (56 wt% with respect to carbon black) were used. A battery cell was obtained.

(Comparative Example 5)
Other than using 3.7 g of carbon particles and 0.3 g (8 wt% with respect to carbon black) of carbon fibers having a contact angle of 103 ° water with no fluorine treatment instead of carbon fibers subjected to fluorine treatment, In the same manner as in Example 1, a fuel cell was obtained.

  About Examples 1-3 and Comparative Examples 1-5, the contact angle of water of carbon fibers (fibers), the mixing ratio of carbon fibers to carbon black (conductive particles) (carbon fiber amount / carbon black amount × 100 ) Is shown in Table 1.

[Power generation performance evaluation]
Using the obtained fuel cells of Examples 1 to 3 and Comparative Examples 1 to 5, an IV test was performed under the following conditions. 1.5A / cm ² at the voltage (V), and the resistance of at 0.1 A / cm ² and (milliohms) shown in Table 1.

<Test conditions>
Cell temperature: 80 ° C
Humidity: 100%
Fuel (hydrogen gas): 500 mL / min
Oxidizing agent (air): 1000 mL / min

  As can be seen from Table 1, the fuel cells of Examples 1 to 3 having a first gas diffusion layer in which carbon fiber pre-fluorinated was mixed with 10 to 50% by weight with respect to carbon black were compared with Comparative Example 1. High voltage was shown compared with ˜5 fuel cells. That is, in Comparative Example 1 and Comparative Example 5 using carbon fibers not subjected to fluorine treatment (hydrophobic treatment), the voltage was lower than that in Examples, regardless of the amount of carbon fiber mixed. This is presumably because the carbon fiber was not subjected to a hydrophobic treatment, so that the drainage in the pores formed by the carbon fiber and carbon black was insufficient.

Comparative Example 2 and Comparative Example 3 in which carbon fibers pre-fluorinated were mixed with carbon black in an amount of less than 10% by weight (8% by weight) are also the same as in Examples, regardless of the hydrophobicity of carbon fibers. The voltage was low compared. This is presumably because although the carbon fiber was subjected to hydrophobic treatment, the amount of carbon black mixed therein was too small, so that the effect of mixing the hydrophobic treated carbon fiber was not exhibited.
Further, in Comparative Example 4 in which carbon fiber pre-fluorinated was mixed in an amount of more than 50% by weight (56% by weight) with respect to the carbon black, the conductivity of the gas diffusion layer was lowered, so that the voltage drop and the resistance were significantly reduced. An increase was seen.

It is sectional drawing which showed one structural example of the polymer electrolyte fuel cell to which this invention is applied. It is a conceptual diagram of the pore formed in the 1st gas diffusion layer of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Proton conductive solid polymer electrolyte membrane 2 ... Catalyst layer 3 ... 1st gas diffusion layer 4 ... 2nd gas diffusion layer 5 ... Gas diffusion layer 6 ... Electrode 7 ... Gas flow path 8 ... Separator 9 ... Hydrophobic treatment Fiber material 10 ... Conductive powder 11 ... Pore (formed by fiber and conductive powder)
12 ... pores (formed between conductive particles)

Claims (2)

A fuel cell comprising an electrolyte membrane and a pair of electrodes on both surfaces of the electrolyte membrane, wherein at least one of the electrodes includes a catalyst layer and a gas diffusion layer in order from the electrolyte membrane side, wherein the gas diffusion layer Has a laminated structure including at least a first gas diffusion layer and a second gas diffusion layer in order from the catalyst layer side, and the first gas diffusion layer is subjected to a water repellent resin and a hydrophobic treatment. no conductive powder particles, and includes a pre-hydrophobic treated fibers product before the first gas diffusion layer formation,
The water contact angle of the previously hydrophobized fiber material measured by the following measurement method is 110 ° or more,
The fiber diameter of the previously hydrophobized fiber is 5 to 600 nm, and the aspect ratio is 10 to 500,
The fuel cell according to claim 1, wherein the fibrous material subjected to hydrophobic treatment in advance is contained in an amount of 10 to 50% by weight based on the conductive powder.
Measurement method: A step of producing a press-molded body by applying a pressure of 500 kg / cm ^{2 to} the previously hydrophobized fiber material, and 2 μl of water are dropped on the press-molded body, and dropped by a contact angle meter. The method which has the process of measuring the contact angle of water after 1 second. A fiber material that is hydrophobically treated by a method selected from the group consisting of fluorine gas treatment, fluorine resin coating treatment, and hydrocarbon resin coating treatment , and has a fiber diameter of 5 to 600 nm and an aspect ratio of 10 to 500. A step of preparing in advance, a first gas diffusion layer paste comprising at least a water-repellent resin, a conductive granular material that has not been subjected to a hydrophobic treatment, and the fiber material that has been subjected to a hydrophobic treatment in advance; A fuel cell comprising: a step of applying to at least a surface facing the catalyst layer of a gas diffusion layer substrate including a layer to be formed; and a step of drying and / or firing the gas diffusion layer substrate coated with the first gas diffusion layer paste. Manufacturing method.

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