JP2008181834A - Manufacturing method of fuel cell diffusion layer, fuel cell diffusion layer, and fuel cell - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a fuel cell diffusion layer preventing or suppressing generation of flooding or drying-up in use for a long time. <P>SOLUTION: The manufacturing method of the fuel cell diffusion layer includes a reforming treatment process S102 performing reforming treatment by applying a reforming treatment solution containing a coupling agent to a substrate for the fuel cell diffusion layer and impregnating it, and a hydrophobic process S106 performing hydrophobic treatment by applying a water repellent solution to a reforming treatment part of the substrate for the fuel cell diffusion layer and impregnating it. The reforming treatment solution containing the coupling agent increases affinity between the substrate for the fuel cell diffusion layer and the water repellent solution, and prevents or suppresses drop in water repellency in the fuel cell diffusion layer. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a method for manufacturing a fuel cell diffusion layer, a fuel cell diffusion layer, and a fuel cell. Specifically, a method for producing a fuel cell diffusion layer comprising a step of hydrophobizing a fuel cell diffusion layer substrate with a water repellent treatment solution, a fuel cell diffusion layer produced by the production method, and further using the fuel cell diffusion layer The present invention relates to a fuel cell manufactured in this way.

  A general configuration of a general fuel cell will be described. As illustrated in FIG. 3, the cathode catalyst layer 14 (also referred to as a cathode electrode catalyst layer or an oxidation electrode catalyst layer) is formed on one surface of the electrolyte membrane 12, and the anode catalyst layer 16 (the anode electrode catalyst layer or film) is formed on the other surface. A cathode electrode diffusion layer 18 (also referred to as a cathode electrode diffusion layer or an oxidation electrode diffusion layer) on the outside of the cathode catalyst layer 14, and an anode. An anode diffusion layer 20 (also referred to as an anode electrode diffusion layer or a fuel electrode diffusion layer) is provided outside the catalyst layer 16 to form a so-called membrane electrode assembly (MEA) 40.

  In FIG. 3, a cathode side separator 22 in which an oxidizing gas channel 26 and a cell refrigerant channel (not shown) are formed is formed outside the cathode diffusion layer 18, and a fuel gas channel 28 and a cathode side separator 22 are formed outside the anode diffusion layer 20. The anode separator 24 in which a cell refrigerant flow path (not shown) is formed is provided so as to sandwich both surfaces of the MEA 40 and is united by an adhesive (not shown) to form the unit cell 10. By laminating a plurality of such unit cells 10, a fuel cell having desired output performance can be manufactured.

  In the unit cell 10 shown in FIG. 3, the electrolyte membrane 12 is required to function as a proton conductive electrolyte membrane in order to exhibit a predetermined function as a fuel cell. It is necessary to maintain more than the moisture content. For this reason, for example, the moisture content of the electrolyte membrane 12 can be maintained by supplying a fuel gas and / or an oxidizing gas (also referred to as a reaction gas) previously humidified to a predetermined moisture content into the unit cell 10. Generally done.

  On the other hand, the cathode catalyst layer 18 and the anode catalyst layer 20 provided on the oxidation electrode and the fuel electrode, respectively, are generally made of carbon fibers formed into a sheet shape, such as carbon paper or carbon cloth, and have desired air permeability and conductivity. In addition to ensuring floodability and preventing flooding due to moisture retention in the catalyst layer and diffusion layer, it is treated with a hydrophobic binder such as polytetraethylene (PTFE) to add hydrophobicity and enhance drainage. Are preferably used. Moreover, in order to prevent the electroconductive fall accompanying addition of a hydrophobic binder, electroconductive particles, such as carbon black and graphite, may be used together as needed.

  There are various methods for producing each diffusion layer. For example, a hydrophobic binder or conductive particles, and a dispersion medium such as a surfactant used as necessary, an aqueous medium such as water or alcohol. The dispersion or paste dispersed in is applied to one or both sides of the carbon fiber formed into a sheet shape, and dried to fix the hydrophobic binder or conductive particles on the carbon fiber, and then fired to make the hydrophobic Conventionally, a method of melting and binding a functional binder and thermally decomposing a dispersion medium has been employed.

  However, the adhesion of the hydrophobic binder to the diffusion layer substrate usually depends on the wettability of the substrate. For this reason, for example, there is a tendency to concentrate and adhere to a portion having a large surface area as enclosed by an ellipse in FIG. 4, that is, a portion where a plurality of fibers are intertwined. In the diffusion layer base material, the distribution of the hydrophobic binder generally corresponds to the distribution of the conductive particles, and the hydrophobic binder 18b is indeterminate when fired. For this reason, in FIG. 4, as a symbol of the variation of the hydrophobic binder 18 b, the hydrophobic binder 18 b is illustrated as a particle or dispersion 18 d that is attached to and integrated with the conductive particles 18 c. The individual distribution of the conductive particles 18c is not shown.

  Further, when the viscosity of the coating liquid is low, a phenomenon called so-called migration occurs in which the water-repellent binder or the conductive particles dispersed in the coating liquid move during drying, and further to the substrate. The distribution may vary. Therefore, when the wettability of the hydrophobic binder-containing dispersion with respect to the diffusion layer substrate is not good, for example, when carbon fibers having hydrophobicity are used as the diffusion layer substrate, the distribution of the hydrophobic binder in the diffusion layer As a result, unevenness may occur and flooding may occur in the catalyst layer or the diffusion layer. Also, in some cases, moisture in the catalyst layer or diffusion layer is excessively discharged, and the electrolyte membrane is dried, so that the so-called dry-up, in which the battery performance deteriorates due to the loss of proton conductivity, may occur. It was.

  Furthermore, when the distribution of the hydrophobic binder is uneven, there is a possibility that the conductive particles may drop off in some cases due to long-term use of the fuel cell. If the conductive particles fall off, the output may decrease due to a decrease in conductivity, and if the hydrophobic binder is peeled off, flooding may occur due to a decrease in drainage. In addition, it may be a factor that causes a remarkable defect in battery performance. For this reason, the long-term uniform distribution of the hydrophobic binder and / or conductive particles in the diffusion layer is one of the requirements regarding the durability of the fuel cell.

  In order to reduce the uneven application of the hydrophobic binder to the diffusion layer substrate, a method of increasing the viscosity of the dispersion or paste, a method of overcoating, or the like can be considered. However, there is a high possibility that the process takes too much time or becomes complicated, which is not preferable.

  By the way, Patent Documents 1 and 2 disclose a diffusion layer to which water-repellent and conductive properties are imparted by applying conductive particles whose surface has been subjected to a hydrophobic treatment with a water repellent. However, in a fuel cell including such a diffusion layer, a part of the water repellent may peel off from the surface of the conductive particles in some cases due to long-term use, and the water repellency may be deteriorated.

  In Patent Document 3, in order to eliminate the need for a surfactant that requires a baking step, a paste in which powder previously hydrophilized by plasma treatment is dispersed is applied and dried by irradiation with far-infrared rays. A diffusion layer is disclosed. However, depending on the labor of the plasma treatment, it may be considered that there is a case where there is no particular difference from the labor when the baking process is applied, although a special apparatus is required. Moreover, since it is necessary to prepare surface-treated conductive particles having different compositions that differ in the content of each material in accordance with the desired water repellency and conductivity, it may be assumed that this may be an obstacle to cost.

  Patent Document 4 discloses a diffusion layer in which hydrophilic micropores are formed by liquid phase oxidation using an oxidizing agent such as ammonium persulfate and then a water-repellent substance is uniformly applied.

JP 2003-208904 A JP 2003-208905 A JP 2004-273387 A JP 2006-73261 A

  However, since it is generally difficult to control the formation of uniform micropores by liquid phase oxidation, the fiber strength varies, and the overall strength of the diffusion layer substrate may be reduced. Moreover, when the oxidizing agent used for the liquid phase oxidation remains in the diffusion layer, it may be a factor of reducing the activity of the metal catalyst supported on the adjacent catalyst layer. For these reasons, the diffusion layer manufactured by the method described in Patent Document 4 is concerned with durability in some cases with respect to long-term use of the fuel cell.

  An object of the present invention is to provide a fuel cell diffusion layer that can prevent or suppress the occurrence of flooding and dry-up over a long period of use.

  Another object of the present invention is to provide a fuel cell diffusion layer capable of maintaining performance during manufacture over a long period of use.

  Furthermore, another object of the present invention is to provide a fuel cell capable of maintaining stable cell performance over a long period of use.

  The configuration of the present invention is as follows.

  (1) A first coating process in which a reforming treatment liquid containing a coupling agent is applied to a base material for a fuel cell diffusion layer and impregnated for reforming; A water-repellent treatment liquid is applied to the quality-treated portion and impregnated to make a hydrophobic treatment. The reforming treatment liquid includes the fuel cell diffusion layer base material and the water-repellent layer. A method for producing a fuel cell diffusion layer, comprising improving affinity with a treatment liquid.

  (2) The method for producing a fuel cell diffusion layer according to (1), further comprising a firing step.

  (3) The method for producing a fuel cell diffusion layer according to (1) or (2), wherein the base material for the fuel cell diffusion layer is a carbon-based fiber.

  (4) The method for producing a fuel cell diffusion layer according to any one of (1) to (3), wherein the water-repellent treatment liquid is an aqueous dispersion containing a fluororesin.

  (5) The method for producing a fuel cell diffusion layer according to any one of (1) to (4), wherein the modifying treatment liquid is an aqueous solution containing a silane coupling agent.

  (6) A fuel cell diffusion layer formed by the manufacturing method according to any one of (1) to (5) above.

  (7) Membrane / electrode assembly having an electrolyte membrane, a pair of catalyst layers formed so as to face each other with the electrolyte membrane interposed therebetween, and a pair of diffusion layers formed respectively outside the pair of catalyst layers And a pair of separators sandwiching both surfaces of the membrane electrode assembly and forming a gas flow path between each of the pair of diffusion layers, wherein at least one of the diffusion layers is the above (6) A fuel cell, which is the fuel cell diffusion layer described in 1.

  By preventing or suppressing the occurrence of flooding and dry-up, stable battery performance can be maintained over a long period of use.

  Hereinafter, it explains in detail using a drawing. In the embodiment of the present invention described below, the same reference numerals are given to the same components as those of the fuel cell shown in FIG. 3, and the description thereof will be omitted or only a brief description will be given. In addition, the dimensional ratio between the members in the drawing does not necessarily match the actual dimensional ratio between the members.

  FIG. 1 is a flowchart showing an example of a method for manufacturing a fuel cell diffusion layer according to an embodiment of the present invention. The method for producing the fuel cell diffusion layer will be described in detail below.

  First, a diffusion layer base material for forming a fuel cell diffusion layer is prepared. As the base material for the diffusion layer, for example, a fibrous (porous) woven or non-woven fabric made of a carbon-based material such as polyacrylonitrile or pitch is used. The base material for the diffusion layer made of a carbon-based material generally has high conductivity, and the electrical resistance in the base material surface direction can be, for example, about 5 to about 20 mΩ · cm, but is limited to this range. Do not mean. Further, diffusion layer base materials of various thicknesses may be used, but the same diffusion layer base materials used for the cathode diffusion layer 18 and / or the anode diffusion layer 20 shown in FIG. 3 can be used. It is. Specifically, the diffusion layer base material for forming the fuel cell diffusion layer 118 can have a thickness of, for example, about 100 μm to 300 μm, but is not limited to this range. More specifically, a diffusion layer substrate in which the thickness of the fuel cell diffusion layer 118 is about 100 μm to 300 μm can be applied. In addition, the shape of the above-mentioned diffusion layer base material assumes that the degree of expansion and / or contraction of the diffusion layer base material in the step of forming the fuel cell diffusion layer is very small and can be ignored. However, for example, even when the expansion and / or contraction of the diffusion layer base material is large, the shape of the diffusion layer base material can be appropriately determined according to the desired shape of the diffusion layer.

  First, as step S102, the above-mentioned diffusion layer base material is coated with a modification treatment liquid containing a coupling agent and impregnated to modify the fibers forming the diffusion layer base material (first). Coating process). As the modification treatment liquid, for example, a coupling agent such as a silane coupling agent or a titanate coupling agent is dissolved in an aqueous medium such as water or alcohol together with a dispersant or a viscosity modifier used as necessary. A dispersed aqueous solution can be used. Of the coupling agents, silane coupling agents are preferred, for example, γ- (2-aminoethyl) aminopropyltrimethoxysilane, γ- (2-aminoethyl) aminopropylmethyldimethoxysilane, γ-glycid. Examples include, but are not limited to, silane coupling agents having an alkoxy-Si bond by an alkoxy group such as methoxy group or ethoxy group, such as xylpropyltrimethoxysilane and γ-glycidoxypropylmethyldimethoxysilane. In another embodiment, an organic solvent or the like may be used instead of the aqueous medium, and there is no particular limitation as long as it is a composition that can be used as a diffusion layer.

  In the present embodiment, the coating amount of the coupling agent is not particularly limited as long as it can improve the affinity with the water repellent treatment agent described later with respect to the base material for the diffusion layer. For example, about 0.1 to 5%, more specifically about 0.1 to 3% can be set as a standard with respect to the dry weight of the layer base material.

  In the present embodiment, the concentration of the coupling agent in the modification treatment liquid can be appropriately set according to the application method of the modification treatment liquid so as to be the above-described application amount, and is particularly limited. It is possible to prepare without. As an example, it is possible to use a coupling agent concentration of, for example, about 0.1 to 5% with respect to the total weight of the reforming treatment liquid.

  After apply | coating and impregnating a modification process liquid to the base material for diffusion layers, as step S104, it is made to dry (1st drying process). The drying method may be any known method as long as it does not affect the base material for diffusion layer, such as natural drying, hot air drying, heat drying, and the like. In addition, here, it is not necessary to dry completely, and when it does not affect the next process, it is also possible to omit.

  Next, as step S106 shown in FIG. 1, a water repellent treatment liquid is applied to the modified diffusion layer base material, impregnated, and hydrophobized (second coating step). As the water repellent treatment liquid, for example, a fluororesin such as polytetrafluoroethylene (PTFE), tetrafluoroethylene / perfluoroalkyl vinyl ether copolymer (PEA), tetrafluoroethylene / hexafluoropropylene copolymer (FEP), Use a dispersion in which conductive particles such as carbon black and graphite used as necessary are dispersed or dissolved in an aqueous medium such as water and alcohol together with a surfactant (dispersant) used as necessary. be able to. As another embodiment, other water-repellent materials such as a hydrophobic binder may be used in place of the fluororesin, and a viscosity modifier may be further used as necessary, and used as a diffusion layer. There is no particular limitation as long as it is a possible composition. The size of the conductive particles can be, for example, about 0.1 μm to about 10 μm in outer dimensions. For example, highly conductive carbon particles such as Ketjen Black EC (trade name) are preferably used. . In addition, the size of the fluororesin or the water repellent material is preferably about 0.1 μm to about 10 μm in the outer dimensions in the coating liquid, but generally about 320 in the high temperature region, for example, PTFE. It is not limited to this because it melts and deforms when the temperature is higher than ° C.

  In the present embodiment, the application of the water-repellent treatment liquid can be carried out by, for example, an impregnation method, an applicator method, a spray method, a foam coating method, or any other known method, and is not particularly limited. It is also suitable to adjust the viscosity of the water-repellent treatment liquid as appropriate so as to obtain a preferable viscosity according to the coating method to be selected.

  A water repellent treatment liquid is applied to the base material for the diffusion layer and impregnated, and then dried as step S108 (second drying step). The drying method may be any known method as long as it does not affect the base material for diffusion layer, such as natural drying, hot air drying, heat drying, and the like. Further, the method may be the same as that in step S104 or may be different. It should be noted that it can be omitted if it does not affect the next step.

  After the second drying step (if omitted, after applying and impregnating the water repellent treatment liquid to the diffusion layer base material), the above-mentioned diffusion layer base material is fired as step S110 (firing step). ). By the baking process, a water repellent material such as a fluororesin is melted and bound to the base material for the diffusion layer. In addition, the coupling agent is cross-linked, and taken in, for example, the base material for the diffusion layer to form a silica layer (in the case of a silane coupling agent) or a titanate layer (in the case of a titanate coupling agent), and is fixed. Furthermore, organic components such as surfactants contained in the modification treatment liquid and the water repellent treatment liquid and remaining in the base material for the diffusion layer are decomposed and removed. In order to realize these, baking is performed at a high temperature of about 340 to about 400 ° C. for about 60 minutes to about 8 hours, for example.

  After completion of the firing step, the mixture is allowed to cool and cut into a desired shape as necessary to complete the fuel cell diffusion layer 118.

  In the present embodiment, the fiber surface forming the diffusion layer base material is treated with the modifying treatment liquid, so that the affinity with the water repellent treatment liquid containing the water repellent material is improved. Therefore, as shown in FIG. 2, the diffusion layer base material 18a is subjected to the modification treatment liquid as compared with the case where the direct water repellency treatment is performed without performing the modification treatment as shown in FIG. By performing the water-repellent treatment after the modification treatment, the dispersion 18d in the water-repellent treatment liquid containing the water-repellent material 18b and the conductive particles 18c is uniformly distributed over the entire base material for the diffusion layer. It becomes possible. The fuel cell diffusion layer 118 obtained in this way is used in place of the cathode diffusion layer 18 and / or the anode diffusion layer 20 shown in FIG. 3, thereby preventing or suppressing the occurrence of flooding and dry-up. A battery can be manufactured. In FIG. 2, the thin layer formed by applying the modifying treatment liquid is omitted.

  In another embodiment of the present invention, the modification treatment liquid may be applied to the diffusion layer base material in advance at a predetermined location prior to the application of the water repellent treatment liquid. There is no need. For example, when there is a demand for making the surface layer portion of the fuel cell diffusion layer hydrophilic, it is not necessary to apply the reforming treatment liquid to the surface layer portion. In addition, it is not necessary to apply a water-repellent treatment liquid to the entire area subjected to the modification treatment in the diffusion layer base material, but from the viewpoint of effective use of a chemical solution (modification treatment liquid and / or water-repellent treatment liquid), It is preferable to apply the water-repellent treatment liquid to the entire portion subjected to the modification treatment with the modification treatment liquid and perform the water-repellent treatment.

  The fuel cell diffusion layer 118 shown in FIG. 2 was manufactured, and the durability was compared with that of the conventional diffusion layer 18 shown in FIG. Unless otherwise specified, both “part” and “%” are based on mass.

<Base material for diffusion layer>
As the base material for the diffusion layer, carbon paper (TGP-H-060, manufactured by Toray Industries, Inc.) having a size of 3.5 cm × 3.5 cm square and a thickness of 190 μm was used.

[Production of Diffusion Layer 1]
<Modification process (S102)>
A 2% -ethanol solution of γ-glycidoxypropyltrimethoxysilane (SH6040 (trade name), manufactured by Toray Dow Corning), which is a silane coupling agent, was prepared as a modification treatment liquid. This modification treatment liquid was dip-coated on the diffusion layer substrate and impregnated.

<First drying step (S104)>
Drying was performed at 100 ° C. for 1 hour by hot air drying. From the measurement of the substrate weight, it was found that 0.5% of the silane coupling agent was adhered to the substrate weight.

<Hydrophobicization step (S106)>
PTFE with an average particle diameter of 0.2 μm was used as the water repellent material, and acetylene black with an average primary particle diameter of 35 nm was used as the conductive particles, respectively, and deionized water with PTFE / acetylene black = 40/60 (dry weight ratio). A water repellent coating solution having a solid content of 20% was prepared. The viscosity of this water repellent treatment liquid was 500 mPa · s. Means of a die coater as a coating apparatus, the diffusion layer base material, water-repellent liquid of 1 cm ² per 10mg (dry weight 2 mg / cm ²⁾ was applied and impregnated.

<Second drying step (S108)>
Drying was performed at 100 ° C. for 1 hour by hot air drying.

<Firing step (S110)>
Firing was performed at 350 ° C. for 8 hours using a firing furnace. After firing, the mixture was allowed to cool to obtain a diffusion layer 1.

[Production of Diffusion Layer 2]
Diffusion layer 2 was obtained by the same method as diffusion layer 1 except that a 1.2% ethanol solution of SH6040 (trade name) was used as the modification treatment liquid.

[Production of Diffusion Layer 3]
Diffusion layer 3 was obtained by the same method as diffusion layer 1 except that a 0.4% ethanol solution of SH6040 (trade name) was used as the modification treatment liquid.

[Production of Diffusion Layer 4]
Diffusion layer 4 was obtained by the same method as diffusion layer 1 except that the modification treatment liquid was not used.

  The produced diffusion layers 1 to 4 are summarized in Table 1.

[Evaluation]
The presence or absence of a change in the drainage properties of the diffusion layer immediately after production of the fuel cell and after long-term use was evaluated by the following hot water test and cell voltage measurement.

[Example 1]
<Heat resistance test>
The diffusion layer 1 is immersed in hot water adjusted to 80 ° C. for a predetermined time (500 hours and 1000 hours), and compared with the water repellency immediately after production. confirmed.

[Trolling angle measurement]
When the diffusion layer in which 2 μg of droplet (5% ethanol aqueous solution) is dropped on the surface is gradually tilted, the droplet flows and falls at a predetermined angle. The water repellency was evaluated by measuring this angle (falling angle). The results are shown in Table 2. A smaller falling angle means higher water repellency. For example, a diffusion layer having a falling angle of 10 ° or less is suitable. In addition, the measurement result shown in Table 2 is an average value by three measurements.

[Tape peeling test]
A commercially available cellophane tape (manufactured by Nichiban) was pressure-bonded to the surface of the diffusion layer 1, peeled off, and visually evaluated whether or not carbon black particles adhered to the adhesive surface of the adhesive tape. Table 2 shows the results. The evaluation criteria in Table 2 are as follows. ◎: Adherence is not observed, ○: Adherence is slightly recognized (adhesion area less than 5%), Δ: Considerable adhesion is observed (adhesion area is less than 5 to 80%), X: Adhesion is observed over almost the entire surface (Attached area 80% or more).

<Cell voltage measurement test>
A unit cell 10 shown in FIG. 3 was produced. In the production of the fuel cell described below, the reference numerals shown in parentheses correspond to the reference numerals shown in FIG.

<Electrolyte membrane>
Nafion (registered trademark) 112 (manufactured by DuPont), which is a fluorine-based electrolyte membrane, was cut into a 5 cm × 5 cm square and used as the electrolyte membrane (12).

<Preparation of catalyst layer>
A catalyst having 50% platinum supported on the weight of carbon black (Ketjen Black EC600, obtained from Lion Corporation) was prepared. This catalyst was mixed and dispersed using a 20% Nafion (registered trademark) solution (20% Nafion (registered trademark) Dispersion Solution DE2020, manufactured by DuPont) and a 50% aqueous ethanol solution as a dispersion medium to prepare a catalyst ink. . The mixing ratio of the catalyst and Nafion (registered trademark) was set to catalyst: Nafion (registered trademark) (solid content) = 1: 0.5.

The catalyst ink was transferred onto both surfaces of the electrolyte membrane (12) by using a decal method to prepare a cathode catalyst layer (14) and an anode catalyst layer (16). More specifically, a sheet obtained by applying a predetermined amount of catalyst ink on another sheet (which uses an ETFE film in this embodiment) is prepared in advance, and this is transferred and bonded to the electrolyte membrane (12) by a thermocompression press. Thus, a method for producing the cathode catalyst layer (14) and the anode catalyst layer (16) was employed. Here, the amount of catalyst ink applied is such that the amount of catalyst applied on the cathode catalyst layer (14) side is 0.8 mg / cm ² and the amount of catalyst applied on the anode catalyst layer (16) side is 0.5 mg / cm ^2. Each was adjusted. As another embodiment, the same catalyst layer can be obtained by applying the catalyst ink directly on both surfaces of the electrolyte membrane (12) by spraying.

<Bonding to diffusion layer (production of MEA)>
A cathode catalyst layer (14) is formed on one surface of the electrolyte membrane (12) and an anode catalyst layer (16) is formed on the other surface, respectively. The diffusion layer (18) and the anode diffusion layer (20) were sandwiched and joined from both sides by a thermocompression press to produce an MEA (40). In the present embodiment, the bonding conditions are 120 ° C. and 3 MPa, but are not limited to this, and can be set arbitrarily.

<Production of unit cell (fuel cell)>
As a cathode separator (22) and an anode separator (24), a carbon separator (4.5 cm × 4.5 cm square, a 5 mm thick Nisshinbo separator, a gas channel and a refrigerant channel, a width of 1.8 mm, a depth of A unit cell 1 was formed by pressing and sandwiching a 0.5 mm-thick channel groove on both sides.

In order to evaluate the battery performance, the cell voltage in the fuel cell 1 was measured under the following conditions. Oxidizing gas: air (dew point 65 ° C., utilization rate arbitrary), fuel gas: pure hydrogen (dew point 65 ° C., utilization rate 80%), cell temperature 65 ° C., oxidizing gas so that the current density is 0.7 A / cm ^2. The battery was evaluated by arbitrarily changing the utilization rate. The average value of the cell voltage for 60 minutes and its deviation (3σ) were determined and shown in Table 3.

  On the other hand, in the diffusion layer 1, a fuel cell similar to the above fuel cell 1 was produced using a 1000 hour hot water resistance test, and the average value of the cell voltage for 60 minutes and its deviation were determined. This result showed the same result as what operated the fuel cell 1 continuously for 1000 hours on the above-mentioned electric power generation conditions.

[Example 2]
A hot water resistance test was conducted in the same manner as in Example 1 except that the diffusion layer 2 was used in place of the diffusion layer 1. The results are shown in Table 2.

  A fuel cell 2 was fabricated in the same manner as the fuel cell 1 except that the diffusion layer 2 was used instead of the diffusion layer 1 as the cathode diffusion layer (18) and the anode diffusion layer (20). Similarly, a cell voltage measurement test was conducted. The results are shown in Table 3.

  On the other hand, in the diffusion layer 2, a fuel cell similar to the fuel cell 2 was produced using a 1000-hour hot water resistance test, and a cell voltage measurement test was performed in the same manner as in Example 1. The same results as those obtained when the fuel cell 2 was continuously operated for 1000 hours under the power generation conditions were shown.

[Example 3]
A hot water resistance test was conducted in the same manner as in Example 1 except that the diffusion layer 3 was used in place of the diffusion layer 1. The results are shown in Table 2.

  A fuel cell 3 was fabricated in the same manner as the fuel cell 1 except that the diffusion layer 3 was used instead of the diffusion layer 1 as the cathode diffusion layer (18) and the anode diffusion layer (20). Similarly, a cell voltage measurement test was conducted. The results are shown in Table 3.

  On the other hand, in the diffusion layer 3, a fuel cell similar to the fuel cell 3 was produced using a 1000-hour hot water resistance test, and a cell voltage measurement test was performed in the same manner as in Example 1. The same results as those obtained when the fuel cell 3 was continuously operated for 1000 hours under the power generation conditions were shown.

[Comparative Example 1]
A hot water resistance test was conducted in the same manner as in Example 1 except that the diffusion layer 4 was used in place of the diffusion layer 1. The results are shown in Table 2.

  A fuel cell 4 was produced in the same manner as the fuel cell 1 except that the diffusion layer 4 was used instead of the diffusion layer 1 as the cathode diffusion layer (18) and the anode diffusion layer (20). Similarly, a cell voltage measurement test was conducted. The results are shown in Table 3.

  On the other hand, in the diffusion layer 4, a fuel cell similar to the fuel cell 4 was manufactured using the one subjected to the hot water resistance test for 1000 hours, and the cell voltage measurement test was performed in the same manner as in Example 1. The same results as those obtained when the fuel cell 4 was continuously operated for 1000 hours under the power generation conditions were shown.

  From the results of the hot water resistance test shown in Table 2, in the diffusion layer not subjected to the modification treatment shown in Comparative Example 1, the water repellency decreases with the elapse of the immersion time in hot water, and the carbon particles easily fall off. I understand that On the other hand, in the diffusion layers shown in Examples 1 to 3, it can be seen that the water repellency is maintained over a long period of time and the dropping of the carbon particles is suppressed.

  Further, from the results of the cell voltage measurement test shown in Table 3, at the beginning of the diffusion layer production, there is no significant difference in battery performance depending on the presence or absence of the modification treatment, and almost equivalent results are obtained. Comparative Example 1 It has been found that the diffusion layer 4 shown in FIG. 1 deteriorates by immersion in hot water for 1000 hours, and the output of the fuel cell 4 decreases and the stability of the cell voltage also decreases. On the other hand, in the diffusion layers shown in Examples 1 to 3, it is understood that generation of flooding is suppressed by maintaining water repellency, and stable battery performance is exhibited over a long period of time.

  The present invention is effective for any fuel cell, but can be used particularly for a fuel cell that is subjected to a highly humidified operation.

It is a flowchart which shows an example of the manufacturing method of the fuel cell diffusion layer in embodiment of this invention. It is an enlarged view which shows the outline of a structure of the fuel cell diffusion layer produced by the method shown in FIG. It is a figure shown about the outline of the composition of the fuel cell which can apply the fuel cell diffusion layer in the embodiment of the invention. It is an enlarged view which shows the outline of a structure of the conventional fuel cell diffusion layer.

Explanation of symbols

  10 unit cell, 12 electrolyte membrane, 14 cathode catalyst layer, 16 anode catalyst layer, 18 cathode diffusion layer, 18a diffusion layer substrate, 18b water repellent material (hydrophobic binder), 18c conductive particles, 20 anode diffusion layer , 22 Cathode side separator, 24 Anode side separator, 26 Oxidizing gas flow path, 28 Fuel gas flow path, 40 Membrane electrode assembly (MEA), 118 Diffusion layer.

Claims (7)

A first coating step in which a reforming treatment liquid containing a coupling agent is applied to a base material for a fuel cell diffusion layer, impregnated and reformed;
A second coating step of applying a water repellent treatment liquid to the modified treatment portion of the base material for the fuel cell diffusion layer and impregnating the hydrophobic treatment solution;
Have
The method for producing a fuel cell diffusion layer, wherein the reforming treatment liquid improves the affinity between the fuel cell diffusion layer base material and the water-repellent treatment liquid.   The method for manufacturing a fuel cell diffusion layer according to claim 1, further comprising a firing step. In the manufacturing method of Claim 1 or 2,
The method for producing a fuel cell diffusion layer, wherein the base material for the fuel cell diffusion layer is a carbon fiber. In the manufacturing method of any one of Claim 1 to 3,
The method for producing a fuel cell diffusion layer, wherein the water repellent treatment liquid is an aqueous dispersion containing a fluororesin. In the manufacturing method according to any one of claims 1 to 4,
The method for producing a fuel cell diffusion layer, wherein the reforming treatment liquid is an aqueous solution containing a silane coupling agent.   A fuel cell diffusion layer formed by the manufacturing method according to claim 1. A membrane electrode assembly having an electrolyte membrane, a pair of catalyst layers formed to face each other with the electrolyte membrane interposed therebetween, and a pair of diffusion layers formed respectively outside the pair of catalyst layers;
A pair of separators sandwiching both surfaces of the membrane electrode assembly and forming a gas flow path between each of the pair of diffusion layers;
Have
The fuel cell according to claim 6, wherein at least one of the diffusion layers is the fuel cell diffusion layer according to claim 6.

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