JP2009238388A - Paste for micropore layer, membrane electrode assembly, and fuel cell - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To suppress occurrence of cracks in a porous layer constituting an electrode of a fuel cell. <P>SOLUTION: A membrane-electrode assembly 50 has a solid polyelectrolyte membrane 20, an anode 22, and a cathode 24. The anode 22 has a laminate composed of a catalyst layer 26 and a gas diffusion layer 28. The cathode 24 has the laminate composed of the catalyst layer 30 and the gas diffusion layer 32. The gas diffusion layer 28 has a micropore layer 29 contacting the catalyst layer 26. Moreover, the gas diffusion layer 32 has the micropore layer 33 contacting the catalyst layer 30. The micropore layer 29 and the micropore layer 33 are respectively kneaded pasty materials obtained by kneading conductive powders, a water repellent, and an insulating heat-curable resin. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a fuel cell that generates electricity by an electrochemical reaction between hydrogen and oxygen.

  In recent years, fuel cells that have high energy conversion efficiency and do not generate harmful substances due to power generation reactions have attracted attention. As one of such fuel cells, a polymer electrolyte fuel cell that operates at a low temperature of 100 ° C. or lower is known.

  A polymer electrolyte fuel cell has a basic structure in which a polymer electrolyte membrane, which is an electrolyte membrane, is disposed between a fuel electrode and an air electrode. The fuel electrode contains hydrogen and the air electrode contains oxygen. It is a device that supplies the agent gas and generates power by the following electrochemical reaction.

Fuel electrode: H ₂ → 2H ⁺ + 2e ⁻ (1)
^{_{Cathode: 1 / 2O 2 + 2H +}} + 2e - → H 2 O ··· (2)
The anode and cathode each have a structure in which a catalyst layer and a gas diffusion layer are laminated. The catalyst layers of the electrodes are arranged opposite to each other with the solid polymer film interposed therebetween, thereby constituting a fuel cell. The catalyst layer is a layer formed by binding carbon particles carrying a catalyst with an ion exchange resin. The gas diffusion layer becomes a passage for the oxidant gas and the fuel gas.

At the anode, hydrogen contained in the supplied fuel is decomposed into hydrogen ions and electrons as shown in the above formula (1). Among these, hydrogen ions move inside the solid polymer electrolyte membrane toward the air electrode, and electrons move to the air electrode through an external circuit. On the other hand, in the cathode, oxygen contained in the oxidant gas supplied to the cathode reacts with hydrogen ions and electrons that have moved from the fuel electrode, and water is generated as shown in the above formula (2). Thus, in the external circuit, electrons move from the fuel electrode toward the air electrode, so that electric power is taken out (see Patent Document 1).
Japanese Patent Laid-Open No. 2002-20369

  In a diffusion layer used in a conventional fuel cell, although there are differences depending on the type of electrode substrate and the microporous layer paste applied to the electrode substrate, large and small cracks have occurred on the surface of the microporous layer. This crack is presumed to result from the inability of the microporous layer to withstand the internal stress accompanying solvent evaporation when the microporous layer paste is dried.

  In order to suppress the occurrence of such cracks, if the kneading of the microporous layer paste is strengthened and the fiberization of a fluororesin such as PTFE in the microporous layer paste is strengthened, the paste viscosity increases and the paste applicability increases. The problem of being damaged arises.

  This invention is made | formed in view of such a subject, The objective is to provide the technique which suppresses the crack of the microporous layer which comprises a gas diffusion layer, without impairing the applicability | paintability to an electrode base material.

  One embodiment of the present invention is a paste for a microporous layer. The microporous layer paste is a microporous layer paste used for a microporous layer constituting a gas diffusion layer of a fuel cell, and includes conductive powder, a water repellent, an insulating thermosetting resin, It is characterized by providing.

  The fine pore layer paste of this aspect can be satisfactorily applied to the electrode substrate. After the fine pore layer paste is applied to the electrode substrate, a three-dimensional network structure is formed on the thermosetting resin by thermosetting. By forming it, it can suppress that a crack generate | occur | produces on the surface of a microporous layer.

  In the microporous layer paste of the above aspect, the thermal decomposition temperature of the thermosetting resin may be higher than the glass transition temperature of the water repellent. Further, the thermosetting start temperature of the thermosetting resin may be lower than the glass transition temperature of the water repellent.

  Further, the weight ratio of the thermosetting resin to the total weight of the conductive powder, the water repellent, and the thermosetting resin may be 1 wt% or more and 20 wt% or less. Further, the weight ratio of the thermosetting resin to the total weight of the conductive powder, the water repellent and the thermosetting resin may be 5 wt% or more and 20 wt% or less.

  The thermosetting resin may be selected from the group consisting of polyimide resin, phenol resin, melamine resin, urea resin, alkyd resin, unsaturated polyester resin, polyurethane, and epoxy resin.

  Another embodiment of the present invention is a membrane electrode assembly. The membrane electrode assembly includes an electrolyte membrane, an anode provided on one surface of the electrolyte membrane, and a cathode provided on the other surface of the electrolyte membrane, and at least one of the anode and the cathode is described above. It has the gas diffusion layer containing the microporous layer formed using the paste for microporous layers of either aspect.

  Yet another embodiment of the present invention is a fuel cell. The fuel cell includes the membrane electrode assembly described above.

  A combination of the above-described elements as appropriate can also be included in the scope of the invention for which patent protection is sought by this patent application.

  ADVANTAGE OF THE INVENTION According to this invention, it can suppress that a crack generate | occur | produces in the microporous layer which comprises the electrode of a fuel cell.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. In all the drawings, the same reference numerals are given to the same components, and the description will be omitted as appropriate.

(Embodiment 1)
FIG. 1 is a perspective view schematically showing the structure of the fuel cell according to Embodiment 1. FIG. FIG. 2 is a cross-sectional view taken along the line AA of FIG. The fuel cell 10 includes a flat membrane electrode assembly 50, and a separator 34 and a separator 36 are provided on both sides of the membrane electrode assembly 50. In this example, only one membrane electrode assembly 50 is shown, but a fuel cell stack may be configured by stacking a plurality of membrane electrode assemblies 50 via separators 34 and 36. The membrane electrode assembly 50 includes a solid polymer electrolyte membrane 20, an anode 22, and a cathode 24.

  The anode 22 has a laminate composed of a catalyst layer 26 and a gas diffusion layer 28. On the other hand, the cathode 24 has a laminate composed of a catalyst layer 30 and a gas diffusion layer 32. The catalyst layer 26 of the anode 22 and the catalyst layer 30 of the cathode 24 are provided to face each other with the solid polymer electrolyte membrane 20 interposed therebetween.

  A gas flow path 38 is provided in the separator 34 provided on the anode 22 side. Fuel gas is distributed to a gas flow path 38 from a fuel supply manifold (not shown), and the fuel gas is supplied to the membrane electrode assembly 50 through the gas flow path 38. Similarly, a gas flow path 40 is provided in the separator 36 provided on the cathode 24 side.

  The oxidant gas is distributed to the gas flow path 40 from the oxidant supply manifold (not shown), and the oxidant gas is supplied to the membrane electrode assembly 50 through the gas flow path 40. Specifically, when the fuel cell 10 is operated, a reformed gas containing a fuel gas, for example, hydrogen gas, flows through the gas flow path 38 along the surface of the gas diffusion layer 28 from the upper side to the lower side. The fuel gas is supplied to 22.

  On the other hand, during operation of the fuel cell 10, an oxidant gas, for example, air flows through the gas flow path 40 from the upper side to the lower side along the surface of the gas diffusion layer 32, whereby the oxidant gas is supplied to the cathode 24. The Thereby, a reaction occurs in the membrane electrode assembly 50. When hydrogen gas is supplied to the catalyst layer 26 via the gas diffusion layer 28, hydrogen in the gas becomes protons, and these protons move through the solid polymer electrolyte membrane 20 to the cathode 24 side. At this time, the emitted electrons move to the external circuit and flow into the cathode 24 from the external circuit. On the other hand, when air is supplied to the catalyst layer 30 through the gas diffusion layer 32, oxygen is combined with protons to become water. As a result, electrons flow from the anode 22 toward the cathode 24 in the external circuit, and power can be taken out.

  The solid polymer electrolyte membrane 20 exhibits good ion conductivity in a wet state, and functions as an ion exchange membrane that moves protons between the anode 22 and the cathode 24. The solid polymer electrolyte membrane 20 is formed of a solid polymer material such as a fluorine-containing polymer or a non-fluorine polymer, and is, for example, a sulfonic acid type perfluorocarbon polymer, a polysulfone resin, a phosphonic acid group or a carboxylic acid group-containing par A fluorocarbon polymer or the like can be used. Examples of the sulfonic acid type perfluorocarbon polymer include Nafion (manufactured by DuPont: registered trademark) 112. Examples of non-fluorine polymers include sulfonated aromatic polyetheretherketone and polysulfone. A typical film thickness of the solid polymer electrolyte membrane 20 is 50 μm.

  The catalyst layer 26 constituting the anode 22 is composed of an ion conductor (ion exchange resin) and carbon particles carrying a metal catalyst, that is, catalyst-carrying carbon particles. A typical film thickness of the catalyst layer 26 is 10 μm. The ion conductor connects the carbon particles carrying the alloy catalyst and the solid polymer electrolyte membrane 20, and has a role of transmitting protons between the two. The ionic conductor may be formed from the same polymer material as the solid polymer electrolyte membrane 20.

  Examples of the metal catalyst used for the catalyst layer 26 include an alloy catalyst made of a noble metal and ruthenium. Examples of the noble metal used in the alloy catalyst include platinum and palladium. Examples of the carbon particles supporting the metal catalyst include acetylene black, ketjen black, carbon nanotube, and carbon nano-onion.

  The gas diffusion layer 28 constituting the anode 22 has an anode gas diffusion base material and a microporous layer 29 applied to the anode gas diffusion base material. The anode gas diffusion base material is preferably composed of a porous body having electron conductivity, and for example, carbon paper, carbon woven fabric or nonwoven fabric can be used.

  The microporous layer 29 applied to the anode gas diffusion base material is a paste-like kneading obtained by kneading a conductive powder, a water repellent and an insulating thermosetting resin (hereinafter referred to as a thermosetting resin). It is a thing. For example, carbon black can be used as the conductive powder. In addition, as the water repellent, a fluorine resin such as tetrafluoroethylene resin (PTFE) or tetrafluoroethylene / hexafluoropropylene copolymer (FEP) can be used. It is preferable that the water repellent has a binding property. Here, the binding property refers to a property that can be made sticky (state) by joining things that are less sticky or those that tend to break apart. Since the water repellent has binding properties, a paste can be obtained by kneading the conductive powder, the water repellent and the insulating thermosetting resin.

  The thermosetting resin has a property of forming a polymer network structure by proceeding addition polymerization, condensation polymerization, addition condensation or cross-linking by heating, and cannot be restored to its original state.

  The thermal decomposition temperature of the thermosetting resin is preferably higher than the glass transition temperature (Tg) of a fluororesin (water repellent) such as PTFE used as the water repellent for the microporous layer 29. According to this, when the paste for the microporous layer is applied to a substrate such as carbon paper, and the heat treatment of the fluororesin, the thermosetting resin is thermally decomposed so that the cracks of the microporous layer 29 are reduced. It can suppress being weakened.

  Further, the thermosetting start temperature of the thermosetting resin is desirably higher than 30 ° C. and lower than the glass transition temperature of a fluororesin such as PTFE used for the microporous layer 29. According to this, it is possible to avoid thermosetting the thermosetting resin at room temperature, and after forming a three-dimensional network structure by thermosetting the thermosetting resin, the water repellent is heat-treated to cause cracks. Can be effectively suppressed.

  The weight ratio of the thermosetting resin to the entire solid content of the microporous layer 29 (the total importance of the thermosetting resin, the conductive powder and the water repellent) is desirably 1 wt% or more and 20 wt% or less, preferably 5 wt% or more and 20 wt%. % Or less is more desirable. By setting the weight ratio of the thermosetting resin to 1 wt% or more, the number of cracks generated on the surface of the gas diffusion layer is reduced, and the width and depth of the cracks can be reduced. Furthermore, when the weight ratio of the thermosetting resin is 5 wt% or more, almost no cracks are generated on the surface of the gas diffusion layer. On the other hand, when the weight ratio of the thermosetting resin is greater than 20 wt%, the resistance of the gas diffusion layer increases with the increase of the insulating component, which causes a decrease in cell voltage. For this reason, in order to keep the conductivity of the gas diffusion layer good, the weight ratio of the thermosetting resin is desirably 20 wt% or less.

  Examples of the thermosetting resin include insulating resins such as polyimide resin, phenol resin, melamine resin, urea resin, alkyd resin, unsaturated polyester resin, polyurethane, and epoxy resin. Of these, polyimide resin and epoxy resin are suitable as the thermosetting resin.

  The polyimide resin is stable at a high temperature, and thermal decomposition starts at a temperature higher than the glass transition temperature of PTFE (340 ° C.) and the glass transition temperature of PEP (260 ° C.). For example, as a polyimide resin, Kyocera Chemical Co., Ltd. imidaloy (KIR-30) is illustrated. Table 1 shows the general characteristics of imidaloy (KIR-30).

  Moreover, the curing temperature of the polyimide resin can be set so that thermosetting starts at around 80 to 100 ° C.

  In addition, the epoxy resin is almost stable up to about 300 ° C. and decomposes somewhat at the glass transition temperature of PTFE (340 ° C.), but is stable at the glass transition temperature of FEP (260 ° C.). Epoxy resins also have the advantage that there is a range of choices in cure speed. Further, the higher the temperature, the faster the curing rate. For example, the curing time at 100 ° C. is 400 seconds, and the curing time at 140 ° C. is 100 seconds.

  The catalyst layer 30 constituting the cathode 24 is composed of an ion conductor (ion exchange resin) and carbon particles carrying a catalyst, that is, catalyst-carrying carbon particles. The ionic conductor connects the carbon particles carrying the catalyst and the solid polymer electrolyte membrane 20, and has a role of transmitting protons between the two. The ionic conductor may be formed from the same polymer material as the solid polymer electrolyte membrane 20. For example, platinum or a platinum alloy can be used as the supported catalyst. Examples of the metal used for the platinum alloy include cobalt, nickel, iron, manganese, iridium and the like. Examples of the carbon particles supporting the catalyst include acetylene black, ketjen black, carbon nanotube, and carbon nano-onion.

  The gas diffusion layer 32 constituting the cathode 24 has a cathode gas diffusion base material and a microporous layer 33 applied to the cathode gas diffusion base material. The cathode gas diffusion base material is preferably composed of a porous body having electron conductivity, and for example, carbon paper, carbon woven fabric or nonwoven fabric can be used.

  The microporous layer 33 applied to the cathode gas diffusion base material is a paste-like kneaded material obtained by kneading the conductive powder, the water repellent and the insulating thermosetting resin, and the anode gas diffusion described above. This is the same as the microporous layer 29 applied to the substrate.

  According to the fuel cell 10 described above, it is possible to suppress the occurrence of cracks in the microporous layer constituting the gas diffusion layer, and to further smooth the microporous layer. As a result, the catalyst layer can be more uniformly applied on the microporous layer, so that it is possible to improve water management and reduce damage to the electrolyte membrane. Further, if it is attempted to suppress the occurrence of cracks in the microporous layer with a water repellent having a binding property such as PTFE, the paste viscosity becomes too high, causing a problem in applicability. According to the above, cracks can be suppressed by forming a polymer network structure during drying and heat treatment while maintaining an optimum paste state during application of the fine pore layer paste.

  In the fuel cell 10 described above, a thermosetting resin is used for both the microporous layers of the anode 22 and the cathode 24, but a thermosetting resin is used for one microporous layer of the anode 22 or the cathode 24. It may be done.

Example 1
<Cathode catalyst slurry preparation>
Platinum-supported carbon is used as the cathode catalyst, and Nafion (registered trademark) solution (DE2021 20 wt%) is used as the ion conductor. To 5 g of platinum-supporting carbon, 10 mL of ultrapure water is added and stirred, and then 15 mL of ethanol is added.

  The catalyst dispersion solution is subjected to ultrasonic stirring dispersion for 1 hour using an ultrasonic stirrer. Dilute a given Nafion solution with an equal volume of ultrapure water and stir with a glass rod for 3 minutes. Thereafter, ultrasonic dispersion is performed for 1 hour using an ultrasonic cleaner to obtain a Nafion aqueous solution. Thereafter, the aqueous Nafion solution is slowly dropped into the catalyst dispersion. During dropping, stirring is continuously performed using an ultrasonic stirrer. After completion of the Nafion aqueous solution dropwise addition, 10 g of a mixed solution of 1-propanol and 1-butanol (weight ratio 1: 1) is dropped, and the resulting solution is used as a catalyst slurry. During mixing, the water temperature is all adjusted to about 60 ° C., and ethanol is evaporated and removed.

<Cathode gas diffusion layer preparation>
Vulcan XC72 (carbon black) 17.3g, Terpineol (solvent) 130.1g, Triton x-100 (surfactant) 2.6g, Lubron fine powder 4.32g, PTFE fine powder 0.54g in a hybrid mixer 10 After mixing for 4 minutes, 4.42 g of polyimide resin (solid content ratio (weight ratio of polyimide resin to the total weight of carbon black, PTFE and polyimide resin) of 20%) is added, and further mixed for 3 minutes, and paste for microporous layer Is made. Thereafter, the prepared microporous layer paste is applied to a carbon substrate subjected to a water repellent treatment in a range of 1.92 to 2.24 mg / cm ² . Then, drying is performed at 120 ° C. for 2 hours in a heat treatment furnace. After drying, heat treatment is performed at 340 ° C. for 1 hour.

<Cathode fabrication>
The catalyst slurry prepared by the above method was applied by screen printing (150 mesh) to the cathode gas diffusion layer with a microporous layer prepared by the above method, dried at 80 ° C. for 3 hours, and 180 ° C. for 45 minutes. Heat treatment is performed.

<Preparation of anode catalyst slurry>
The method for preparing the catalyst slurry for the anode catalyst layer is the same as the method for preparing the cathode catalyst slurry, except that platinum ruthenium-supported carbon (TEC61E54, Tanaka Kikinzoku Kogyo Co., Ltd.) is used as the catalyst. Nafion is used as the ionic conductor.

<Preparation of anode gas diffusion layer>
The anode gas diffusion layer is the same as the method for producing the cathode gas diffusion layer described above.

<Anode fabrication>
The anode catalyst slurry produced by the above method is sequentially applied to the anode gas diffusion layer with a fine pore layer by screen printing (150 mesh), dried at 80 ° C. for 3 hours, and subjected to heat treatment at 180 ° C. for 45 minutes.

<Preparation of membrane electrode assembly>
Hot pressing is performed with the solid polymer electrolyte membrane sandwiched between the anode and cathode produced by the above method. Nafion is used as the solid polymer electrolyte membrane. A membrane electrode assembly is fabricated by hot pressing the anode, the solid polymer electrolyte membrane, and the cathode under the bonding conditions of 170 ° C. and 200 seconds.

  In the membrane electrode assembly thus obtained, it was confirmed that the viscosity of the fine pore layer paste was appropriate for application to the carbon base material of the gas diffusion layer. Further, it was confirmed that the microporous layer constituting the gas diffusion layers of the cathode and the anode was smooth with almost no cracks on the surface. Further, it was confirmed that the catalyst layer in contact with the microporous layer can be applied uniformly by smoothing the microporous layer.

  In Examples 2 to 4, an epoxy resin is used as the insulating thermosetting resin used for the microporous layer.

(Example 2)
In Example 2, the weight ratio of the epoxy resin is 1 wt%. Specifically, anode and cathode gas diffusion layers are produced by the following procedure.

Vulcan XC72 (carbon black) 17.3g, Terpineol (solvent) 130.1g, Triton x-100 (surfactant) 2.6g, Lubron fine powder 4.32g, PTFE fine powder 0.54g in a hybrid mixer 10 After mixing for 2 minutes, 0.22 g of epoxy resin (solid content ratio (weight ratio of the epoxy resin to the total weight of carbon black, PTFE and epoxy resin) is 1%) is added, and the mixture is further mixed for 3 minutes. Is made. Thereafter, the prepared microporous layer paste is applied to a carbon substrate subjected to a water repellent treatment in a range of 1.92 to 2.24 mg / cm ² . Then, drying is performed at 120 ° C. for 2 hours in a heat treatment furnace. After drying, heat treatment is performed at 340 ° C. for 1 hour.

  Using the anode and cathode gas diffusion layers thus obtained, a membrane / electrode assembly was produced in the same manner as in Example 1.

(Example 3)
In Example 3, the weight ratio of the epoxy resin is 5 wt%. Specifically, 1.11 g of epoxy resin is used as a thermosetting resin when the anode and cathode gas diffusion layers are produced in the same procedure as in Example 2. Using the obtained anode and cathode gas diffusion layers, a membrane electrode assembly was produced in the same manner as in Example 1.

Example 4
In Example 4, the weight ratio of the epoxy resin is 20 wt%. Specifically, when the anode and cathode gas diffusion layers are produced in the same procedure as in Example 2, 4.42 g of epoxy resin is used as the thermosetting resin. Using the obtained anode and cathode gas diffusion layers, a membrane electrode assembly was produced in the same manner as in Example 1.

(Comparative Example 1)
As Comparative Example 1, a gas diffusion layer with a microporous layer that did not use a conventional thermosetting resin was produced, and a membrane electrode assembly was produced. The manufacturing method of the membrane electrode assembly is the same as that of Example 1 except that a thermosetting resin is not used for the microporous layer.

(Comparative Example 2)
In Comparative Example 2, the weight ratio of the epoxy resin is 30 wt%. Specifically, when the anode and cathode gas diffusion layers are produced in the same procedure as in Example 2, 6.63 g of epoxy resin is used as the thermosetting resin. Using the obtained anode and cathode gas diffusion layers, a membrane electrode assembly was produced in the same manner as in Example 1.

  3A to 3D are microscopic images obtained by photographing the surface states of the porous layers of Comparative Example 1 and Examples 2 to 4, respectively.

  In the conventional type microporous layer according to Comparative Example 1, countless cracks are generated on the surface of the microporous layer. In contrast, in Example 2 in which the weight ratio of the epoxy resin was 1 wt%, it was confirmed that the number of cracks was reduced and the width and depth of the cracks were significantly reduced. Furthermore, in Example 3 and Example 4 in which the weight ratio of the epoxy resin was 5 wt% and 20 wt%, respectively, it was confirmed that almost no cracks occurred on the surface of the microporous layer, and the surface became smooth.

Using the gas diffusion layers of Examples 3 and 4 and Comparative Examples 1 and 2, the clamping pressure applied to the gas diffusion layer was changed, and the resistance was measured under each pressure. The clamping pressure actually applied to the gas diffusion layer is about 3.3 MPa. FIG. 4 is a graph showing the relationship between the clamping pressure applied to the gas diffusion layer and the resistance of the gas diffusion layer. As can be seen from FIG. 4, when the weight ratio of the epoxy resin is 30 wt%, it can be seen that the resistance of the gas diffusion layer rapidly increases due to the increase of the insulating component. For example, when the current density is 0.3 A / cm ² , a voltage drop of 10 mV or more may occur. For this reason, the weight ratio of the insulating resin is desirably 20 wt% or less in order to keep the conductivity of the gas diffusion layer good.

(Embodiment 2)
FIG. 5 is a cross-sectional view schematically showing the structure of the fuel cell according to the second embodiment. The fuel cell according to Embodiment 2 has the basic configuration of the fuel cell according to Embodiment 2 except that a multilayer microporous layer is provided in the gas diffusion layers that constitute the anode 22 and the cathode 24, respectively. It is the same.

  Specifically, the gas diffusion layer 28 constituting the anode 22 has a microporous layer having a two-layer structure including a microporous layer 29a and a microporous layer 29b. The microporous layer 29 a is provided on the catalyst layer 26 side, and one surface is in contact with the catalyst layer 26. The microporous layer 29b has one surface in contact with the microporous layer 29a and is provided on the gas flow path 38 side. The microporous layer 29a is the same as the microporous layer 29 of the first embodiment, and is a paste-like kneaded material obtained by kneading conductive powder, a water repellent, and an insulating thermosetting resin. On the other hand, the microporous layer 29b is a paste-like kneaded material obtained by kneading a conductive powder and a water repellent, which does not contain an insulating thermosetting resin.

  The gas diffusion layer 32 constituting the cathode 24 has a microporous layer having a two-layer structure including a microporous layer 33a and a microporous layer 33b. The microporous layer 33 a is provided on the catalyst layer 30 side, and one surface is in contact with the catalyst layer 30. One surface of the microporous layer 33b is in contact with the microporous layer 33a and is provided on the gas flow path 40 side. The microporous layer 33a is the same as the microporous layer 29 of the first embodiment, and is a paste-like kneaded material obtained by kneading a conductive powder, a water repellent, and an insulating thermosetting resin. On the other hand, the microporous layer 33b is a paste-like kneaded material obtained by kneading a conductive powder and a water repellent without containing an insulating thermosetting resin.

  According to the fuel cell of the present embodiment, by mixing an insulating thermosetting resin in the minimum necessary region of the microporous layer that contacts the catalyst layer, cracks are generated on the surface of the microporous layer that contacts the catalyst layer. While suppressing generation | occurrence | production, the electroconductivity of a gas diffusion layer can be kept favorable.

(Example 5)
A method for producing a gas diffusion layer according to Example 5 will be described. First, 17.3 g of Vulcan XC72 (carbon black), 130.1 g of terpineol (solvent), 2.6 g of Triton x-100 (surfactant), 4.32 g of Lubron fine powder, and 0.54 g of PTFE fine powder were used as a hybrid mixer. For 10 minutes to prepare a first microporous layer paste.

In addition, 17.3 g of Vulcan XC72 (carbon black), 130.1 g of terpineol (solvent), 2.6 g of Triton x-100 (surfactant), 4.32 g of Lubron fine powder, and 0.54 g of PTFE fine powder were used as a hybrid mixer. After mixing for 10 minutes, 4.42 g of polyimide resin (20% in terms of solid content (weight ratio of polyimide resin to the total weight of carbon black, PTFE and polyimide resin)) was added, and further mixed for 3 minutes. A paste for a microporous layer is prepared. Thereafter, the produced first microporous layer paste was applied to a carbon substrate that had been subjected to a water-repellent treatment, and after drying at 120 ° C. for 1 hour, the second microporous layer paste was applied, Dry again at 120 ° C. for 1 hour. The total coating charge is in the range of 1.92 to 2.24 mg / cm ² . Thereafter, heat treatment is performed at 340 ° C. for 1 hour.

  In the gas diffusion layer thus obtained, it was confirmed that almost no cracks were generated in the second microporous layer in contact with the catalyst layer, and the surface of the second microporous layer was smooth.

  In the above-described embodiment, the thermosetting resin and the solvent contained in the microporous layer paste are simultaneously cured at a constant temperature, but the thermosetting resin is cured at a low temperature ( For example, after being performed at 100 ° C., a two-stage heat treatment may be performed in which the solvent contained in the microporous layer paste is evaporated at a high temperature (for example, 120 ° C.). According to this, the formation of the three-dimensional network structure of the thermosetting resin by the thermosetting and the evaporation of the solvent can be more reliably performed, and as a result, the surface of the microporous layer is further hardly generated. be able to.

1 is a perspective view schematically showing the structure of a fuel cell according to an embodiment. It is sectional drawing on the AA line of FIG. 3A to 3D are microscopic images obtained by photographing the surface states of the porous layers of Comparative Example 1 and Examples 2 to 4, respectively. It is a graph which shows the relationship between the clamping pressure applied to a gas diffusion layer, and the resistance of a gas diffusion layer. 6 is a perspective view schematically showing the structure of a fuel cell according to Embodiment 2. FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Fuel cell, 20 Solid polymer electrolyte membrane, 22 Anode, 24 Cathode, 26,30 Catalyst layer, 28,32 Gas diffusion layer, 29,33 Microporous layer, 50 Membrane electrode assembly.

Claims (8)

A microporous layer paste used for a microporous layer constituting a gas diffusion layer of a fuel cell,
Conductive powder;
Water repellent,
An insulating thermosetting resin;
A paste for a fine pore layer, comprising:   The paste for a microporous layer according to claim 1, wherein a thermal decomposition temperature of the thermosetting resin is higher than a glass transition temperature of the water repellent.   The microporous layer paste according to claim 1 or 2, wherein a thermosetting start temperature of the thermosetting resin is lower than a glass transition temperature of the water repellent agent.   The weight ratio of the thermosetting resin to the total weight of the conductive powder, the water repellent, and the thermosetting resin is 1 wt% or more and 20 wt% or less. Item 2. A microporous layer paste according to item.   The weight ratio of the thermosetting resin to the total weight of the conductive powder, the water repellent, and the thermosetting resin is 5 wt% or more and 20 wt% or less. Item 2. A microporous layer paste according to item.   6. The thermosetting resin is selected from the group consisting of polyimide resin, phenol resin, melamine resin, urea resin, alkyd resin, unsaturated polyester resin, polyurethane, and epoxy resin. Item 2. A microporous layer paste according to item. An electrolyte membrane;
An anode provided on one surface of the electrolyte membrane;
A cathode provided on the other surface of the electrolyte membrane;
With
7. A film comprising at least one of the anode and the cathode having a gas diffusion layer including a microporous layer formed using the microporous layer paste according to claim 1. Electrode assembly.   A fuel cell comprising the membrane electrode assembly according to claim 7.