JP2006318824A - Slurry for forming catalyst membrane, catalyst membrane for solid polymer fuel cell, its manufacturing method, membrane-electrode assembly, and solid polymer fuel cell - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a slurry capable of forming a catalyst membrane for a solid polymer type fuel cell in which the power generation capability of the fuel cell can be enhanced, and a power generation capability cannot be degraded easily even if it is operated for a long time; a catalyst membrane for a solid polymer fuel cell a membrane-electrode assembly and a solid polymer type fuel cell, in which power generation capability cannot be degraded easily even if it is operated for a long time with a high power generation capability. <P>SOLUTION: In this slurry for forming the catalyst membrane; a graphite, a water-repellent resin, catalyst particle, and ion conductivity resin are dispersed into water and/or alcohol. This catalyst membrane for the solid polymer fuel cell is applied by the slurry for forming the catalyst membrane and formed. This membrane-electrode assembly 2 has an electrolyte layer 20, and catalyst membranes for the solid polymer fuel cell which are laminated on the both surfaces of the electrolyte layer 20. The one or both catalyst membranes 10a and 10b for the solid polymer fuel cells are the catalyst membrane for the solid polymer fuel cells. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a catalyst film forming slurry for forming a catalyst film for a polymer electrolyte fuel cell. The present invention also relates to a catalyst membrane for a polymer electrolyte fuel cell, a production method thereof, a membrane-electrode assembly, and a polymer electrolyte fuel cell.

A fuel cell is a power generation system that continuously supplies fuel and an oxidant and extracts chemical energy as electric power when they react. Depending on the type of electrolyte used, there are two types of fuel cells: alkaline type, phosphoric acid type, and solid polymer type, which have relatively low operating temperatures, and molten carbonate type and solid oxide electrolyte type that operate at high temperatures. Separated.
Among these, the polymer electrolyte fuel cell has a five-layer structure in which a catalyst membrane is disposed on both surfaces of an ion conductive electrolyte layer, and a gas diffusion layer made of a porous material is disposed outside the catalyst membrane. It is common to have a single cell in which a MEA (Membrane Electrode Assembly) is used and a separator is disposed outside the gas diffusion layer. In this polymer electrolyte fuel cell, one side of the electrolyte layer is a fuel electrode, the other side is an oxidant electrode, and both gas diffusion layers are electrically connected via an external load circuit. .
The catalyst film in the polymer electrolyte fuel cell must have a function of causing an electrochemical reaction and a function of draining or retaining water generated by the reaction between the fuel and the oxidant. This is a particularly important configuration in a molecular fuel cell.

Conventionally, an MEA (membrane-electrode assembly) has been applied to both surfaces of an electrolyte layer with a coating liquid in which catalyst particles comprising a catalyst component or a catalyst component and a carbon material supporting the catalyst component are dispersed, and a gas diffusion layer thereon. It was manufactured by pasting together. According to such a production method, the production efficiency can be increased, but when the dispersion medium in the coating liquid is removed by drying, wrinkles are easily generated in the electrolyte layer, so that it is difficult to form a smooth catalyst film. (For example, see Patent Document 1).
Thus, a method of applying a coating liquid on a porous gas diffusion layer made of carbon paper or the like has been proposed (see, for example, Patent Document 2). The coating liquid in this method is composed of catalyst-supporting carbon, an ion conductive resin (for example, trade name: Nafion manufactured by DuPont) and a dispersion medium, and the ion conductive resin is used as a binder for the catalyst particles.
JP-A-5-29005 JP-A-7-130376

However, when a coating liquid is applied onto the gas diffusion layer of the porous body, it is difficult to form a uniform catalyst film because the catalyst particles enter the pores of the porous body. . In addition, in the catalyst film formed by coating, since the catalyst particles are easily embedded in the binder, a so-called three-phase interface composed of an electrode material-electrolyte-catalyst that causes an electrochemical reaction is efficiently arranged. It wasn't. That is, in the method of Patent Document 2, the arrangement of the catalyst component inside the catalyst film is not optimized, and the electrochemical efficiency is low, so that it is necessary to use a large amount of the catalyst component. In particular, in a polymer electrolyte fuel cell using methanol, ethanol, or the like as a direct fuel, since the separation efficiency of hydrogen ions from fuel by the catalyst component is low, a larger amount of catalyst component is required. Therefore, there has been a demand for a catalyst membrane that can efficiently use hydrogen as a catalyst component and ionize hydrogen with high efficiency and increase the power generation capability of the fuel cell.
In addition, although the catalyst-carrying carbon bound with the ion conductive resin as described above has a porous structure, the pore diameter is as small as 1 μm or less, so that the generated water and the feed water are condensed to form pores. There was a case of obstruction. For this reason, the power generation capacity may decrease when operated for a long time.

  The present invention has been made in order to solve the above-mentioned problems, and the catalyst component can be used with high efficiency, the power generation capacity of the fuel cell can be increased, and the power generation capacity is not easily lowered even when operated for a long time. It is an object of the present invention to provide a slurry for forming a catalyst film that can form a catalyst film for a polymer fuel cell. In addition, the catalyst component can be used with high efficiency, the power generation capacity is high, and the power generation capacity is not easily lowered even if the catalyst is operated for a long time, and the production method thereof, the membrane-electrode assembly, and An object of the present invention is to provide a polymer electrolyte fuel cell.

The slurry for forming a catalyst film of the present invention is characterized in that graphite, a water repellent resin, catalyst particles, and an ion conductive resin are dispersed in water and / or alcohol.
In the slurry for forming a catalyst film of the present invention, the water repellent resin is preferably a fluororesin.
In the slurry for forming a catalyst film of the present invention, the fluororesin is polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), polyhexafluoropropylene (PHFP), ethylene-tetrafluoroethylene copolymer (ETFE). And at least one selected from these copolymers.
In the slurry for forming a catalyst film of the present invention, the graphite is preferably at least one selected from scale-like, flaky graphite, flaky graphite, and expanded graphite.
In the slurry for forming a catalyst film of the present invention, it is preferable that a conductive additive is further dispersed.
In that case, it is preferable that the said conductive support agent is carbon black and / or carbon fiber, Furthermore, it is preferable that the said carbon fiber is a carbon nanotube.
The catalyst membrane for a polymer electrolyte fuel cell of the present invention is formed by applying the above-described slurry for forming a catalyst membrane.
The catalyst membrane for a polymer electrolyte fuel cell of the present invention preferably has a porous structure.
When it has a porous structure, it is preferable that the porous structure is formed of graphite.
In the catalyst membrane for a polymer electrolyte fuel cell of the present invention, the water repellent resin, the catalyst particles, and the ion conductive resin are preferably held on the graphite surface.
When the catalyst film-forming slurry contains a conductive additive, the catalyst film for a polymer electrolyte fuel cell of the present invention is formed by applying the catalyst film-forming slurry, and the water-repellent resin and the catalyst It is preferable that the particles, the ion conductive resin, and the conductive auxiliary agent are held on the graphite surface.
The method for producing a catalyst membrane for a polymer electrolyte fuel cell according to the present invention includes a film forming step of coating the above-described catalyst film-forming slurry on a substrate to form a coating film, and drying the coating film. And a drying step.
The membrane-electrode assembly of the present invention is a membrane-electrode assembly comprising an electrolyte layer and a catalyst membrane for a polymer electrolyte fuel cell laminated on both surfaces of the electrolyte layer,
One or both of the polymer membranes for a polymer electrolyte fuel cell are the aforementioned polymer membranes for a polymer electrolyte fuel cell.
The polymer electrolyte fuel cell of the present invention is characterized by comprising the membrane-electrode assembly described above.

According to the slurry for forming a catalyst film of the present invention, the catalyst component is used with high efficiency, the power generation capacity of the fuel cell can be increased, and the power generation capacity is not easily lowered even if operated for a long time. A catalyst membrane can be formed.
The catalyst membrane for a polymer electrolyte fuel cell of the present invention uses a catalyst component with high efficiency, can increase the power generation capability of the fuel cell, and does not easily decrease the power generation capability even if operated for a long time.
According to the method for producing a catalyst membrane for a polymer electrolyte fuel cell of the present invention, the catalyst component can be used with high efficiency, the power generation capability of the fuel cell can be increased, and the power generation capability is reduced even if operated for a long time. A difficult catalyst membrane can be produced.
In the membrane-electrode assembly and the polymer electrolyte fuel cell of the present invention, the catalyst component is used with high efficiency, the power generation capacity is high, and the power generation capacity is not easily lowered even when operated for a long time.

Hereinafter, preferred embodiments of the present invention will be described.
<Slurry for forming a catalyst film>
The slurry for forming a catalyst film of the present invention is one in which graphite, a water repellent resin, catalyst particles, and an ion conductive resin are dispersed in water and / or alcohol as a dispersion medium.
The catalyst film forming slurry is preferably water as a dispersion medium, and more preferably ion-exchanged water. If the dispersion medium is ion-exchanged water, there are few impurities, and the dispersibility of graphite, water-repellent resin, catalyst particles, and conductive additive can be increased. If the dispersion medium is aqueous, it is good for the environment.
Examples of the alcohol used as the dispersion medium include methanol, ethanol, propanol, butanol and the like.

[graphite]
Although it does not restrict | limit especially as graphite, It is preferable that it is any 1 or more types chosen from flaky graphite, flaky graphite, and expanded graphite. If the graphite is flaky graphite, flaky graphite, or expanded graphite, a catalyst film having a porous structure can be formed more easily, and the utilization efficiency of catalyst particles can be further increased. As a result, it is possible to form a catalyst film with higher current collecting ability and to manufacture a polymer electrolyte fuel cell with higher power generation capacity.

  The average particle size of graphite is preferably 0.1 to 200 μm. If the average particle size of the graphite is less than 0.1 μm, the contact resistance between the graphite tends to increase and the conductivity tends to decrease, and if it exceeds 200 μm, it tends to be difficult to form a paint or film. .

[Water repellent resin]
As the water repellent resin, a resin having no hydrophilic group such as a hydroxyl group, a carboxy group, an amino group, and an amide group and having a hydrocarbon or halogen, particularly a fluorine resin having high water repellency is preferable. Among fluororesins, polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), polyhexafluoropropylene (HFP), ethylene-tetrafluoroethylene copolymer (ETFE), and copolymers thereof are stable. It is preferable in terms of economy. These resins can be used alone or in admixture of two or more. These resins are used in the form of powder (fine particles).

[Catalyst particles]
The catalyst particles may be particles composed only of the catalyst component or may be particles in which the catalyst component is supported on the carbon material. However, since the catalyst component can be used with higher efficiency, Particles carrying components are preferred.
As the catalyst component, when a catalyst film on the fuel electrode side is formed, an alloy catalyst made of platinum and ruthenium is preferable because hydrogen ions can be generated with high efficiency. In the case of forming the catalyst film on the oxidant electrode side, a platinum catalyst is preferable because oxygen ions can be generated with high efficiency.

When the catalyst particles are particles in which a catalyst component is supported on a carbon material, the carbon material is an inorganic material having carbon atoms as a main component and having conductivity, and having resistance to an oxidizing atmosphere. There is no particular limitation. As a specific carbon material, carbon black such as furnace black or channel black can be used.
Any grade of carbon black can be used regardless of the specific surface area and particle size, but it has a large specific surface area and secondary agglomeration in terms of both catalyst membrane performance and productivity. A high structure having a large particle size is preferred. Examples of the high-structure carbon black include Lion Akzo's trade name: Ketchen EC, Cabot's trade name: Vulcan XC72R, and the like. These high structure carbon blacks are preferably used because of their high dispersibility in the coating liquid and low resistance when used in the catalyst film.
Examples of carbon materials other than carbon black include acetylene black and graphite, as well as carbon fibers and fullerenes. The carbon fiber includes carbon nanotubes.

[Ion conductive resin]
Examples of the ion conductive resin include those having a proton (hydrogen ion) exchange group. Here, examples of the proton exchange group include a sulfonic acid group, a carboxylic acid group, and a phosphoric acid group. Among the ion conductive resins, a resin having a proton exchange group composed of a fluoroalkyl ether side chain and a fluoroalkyl main chain, for example, a product name: Nafion manufactured by DuPont is preferable.

[Conductive aid]
In the slurry for forming the catalyst film, it is preferable that the conductive additive is further dispersed because the power generation capacity can be further increased.
The conductive auxiliary agent is not particularly limited as long as it is an inorganic material having carbon atoms as a main component and having conductivity and resistance to an oxidizing atmosphere. That is, the same carbon material used for the catalyst particles can be used. Among the carbon materials, carbon black and carbon fiber are preferable, and carbon nanotubes with high conductivity are more preferable because the conductivity between graphites is higher and the power generation characteristics are further improved.

[concentration]
The concentration of the catalyst film-forming slurry can be appropriately selected in consideration of target characteristics such as mechanical strength and ease of coating. For example, it is preferable to lower the concentration when it is desired to reduce the film thickness and to increase the concentration when it is desired to increase the thickness.

[Preparation method]
Examples of the method for preparing the slurry for forming a catalyst film include a method of adding and dispersing a solution containing ion conductive resin, graphite, water-repellent resin, and catalyst particles in water and / or alcohol. The order of addition is not particularly limited, but first, water and / or alcohol and a solution containing an ion conductive resin are mixed to obtain a resin slurry, and then graphite and water repellent resin are added to the resin slurry. After obtaining the carbon slurry, it is preferable to add catalyst particles to the carbon slurry. In this order, the catalyst particles are easily held on the surface of the catalyst film, and the utilization efficiency of the catalyst component can be further improved.
In the dispersion, a commercially available mixer can be used. For example, a homomixer, a hybrid mixer, or the like is preferably used.

Since the slurry for forming a catalyst film described above contains graphite, water repellent resin, and ion conductive resin, it is porous and a three-phase interface is efficiently formed. As a result, it is possible to form a catalyst film for a polymer electrolyte fuel cell that uses the catalyst component with high efficiency and has high power generation capacity. In addition, since it has water repellency and can be prevented from being blocked by supply water or generated water, it is possible to form a catalyst film for a polymer electrolyte fuel cell in which the power generation capacity is not easily lowered even when operated for a long time.
In addition, since water and / or alcohol is used as the dispersion medium, the dispersibility of graphite, water repellent resin, ion conductive resin, and conductive additive can be increased. If the slurry is highly dispersed, a catalyst film with high dispersibility of catalyst particles can be formed. This is another factor that can increase power generation capacity.

<Catalyst membrane for polymer electrolyte fuel cell>
FIG. 1 shows an embodiment of the catalyst membrane for a polymer electrolyte fuel cell (hereinafter abbreviated as “catalyst membrane”) of the present invention.
The catalyst film 10 of the present embodiment is formed by applying the catalyst film-forming slurry, and has a graphite 11 having a porous structure, and a water-repellent resin 12 held on the surface of the graphite 11. The catalyst particles 13, the ion conductive resin 14, and the conductive assistant 15 are included.

[Composition ratio of catalyst membrane]
The content (mass) of each component in the catalyst membrane 10 is 250 to 750% for graphite 11 and 25 to 250 for water repellent resin 12 when the blending amount (mass) of the ion conductive resin 14 is 100%. %, The catalyst particles 13 are preferably 25 to 250%, and the conductive assistant 15 is preferably 25 to 250%.
When the amount of graphite 11 is less than 250%, the conductivity tends to decrease, and when it is more than 750%, it tends to be difficult to form a paint or a film.
When the water repellent resin 12 is less than 25%, the water repellency tends to be insufficient. When the water repellent resin 12 exceeds 250%, the water repellent resin 12 closes the pores and tends to deteriorate the performance as a catalyst film.
If the catalyst particle 13 is less than 25%, proton generation from the fuel tends to be insufficient, and if it exceeds 250%, the proton generation amount is saturated, which is uneconomical.
If the amount of the conductive assistant 15 is less than 25%, the effect of improving the conductivity may be insufficient, and if it is more than 250%, it tends to be difficult to form a paint or a film.
If the ion conductive resin 14 is too small relative to the other components, hydrogen ion transmission may be insufficient. If it is too much, the catalyst particles 13 held on the surface of the graphite 11 are completely covered. Therefore, there is a tendency to reduce the catalytic performance and power generation characteristics.

[Catalyst membrane pore size]
The pore diameter of the catalyst membrane 10 is preferably 1 μm or more, and more preferably 5 μm or more. When the pore diameter is as large as 1 μm or more and the catalyst membrane 10 has a high porosity, the fluid resistance becomes small and the fuel and generated water can more easily permeate, so that the power generation capacity can be further prevented from decreasing. Further, if the pore diameter of the catalyst membrane 10 is 1 μm or more, the amount of the catalyst component used when taking out hydrogen ions from the liquid fuel such as alcohol can be greatly reduced.

[Catalyst film thickness]
The thickness of the catalyst film 10 is preferably 1 to 400 μm, more preferably 5 to 200 μm, and particularly preferably 10 to 150 μm. When the thickness of the catalyst film 10 is less than 1 μm, the amount of the catalyst particles 13 is reduced, so that the power generation characteristics may be lowered. In addition, when the thickness of the catalyst film 10 exceeds 400 μm, the electrical contact resistance increases and the passage distance of the fuel fluid becomes long, so that the fuel supply is likely to be delayed and the discharge efficiency of the generated water is reduced. In addition, the elasticity of the film tends to be lowered and easily broken.

The catalyst film 10 described above includes graphite 11 and easily forms a porous structure. Further, the catalyst particles and the ion conductive resin 14 are held on the surface of the porous graphite 11. 13 and the arrangement of the ion conductive resin 14 are optimized. According to the catalyst film 10 having such a structure, the contact efficiency between the catalyst component and the fuel is increased, and hydrogen ions generated from the fuel by the action of the catalyst component are transmitted with high efficiency. Therefore, since the utilization efficiency of the catalyst component is high and the current collecting property is high, the power generation capacity is high. Further, since the catalyst film 10 contains the water-repellent resin 12 and has water repellency, the pores of the porous structure can be prevented from being blocked by generated water or supplied water, and the power generation capacity can be prevented from being lowered.
Further, the catalyst film 10 has an advantage that the catalyst particles 13 are not easily dropped when the fuel cell is manufactured.

<Method for producing catalyst membrane for polymer electrolyte fuel cell>
The method for producing a catalyst membrane for a polymer electrolyte fuel cell of the present invention comprises a film forming step of coating the catalyst film-forming slurry on a substrate to form a coating film, and drying the coating film. And a drying step.

[Film forming process]
As a base material used in a film formation process, what can peel from a coating film after drying a coating film is preferable. As a preferable base material, for example, a film made of polyethylene terephthalate, polytetrafluoroethylene, polyimide, polyethylene naphthalate (PEN), or the like can be given. Moreover, the resin film by which the surface was mold release-processed can also be used.
When the catalyst film and the electrolyte layer are integrated, heat transfer is performed from the side of the base material laminated on the catalyst film, and therefore, among the above preferable base materials, those having high heat resistance are preferable. Specifically, a PEN film and a polyimide film are preferable.

  The coating method is not particularly limited, and for example, a dip coating method, a spray coating method, a roll coating method, a doctor blade method, a gravure coating method, a screen printing method and the like can be adopted. Moreover, it is preferable to select a coating method as appropriate depending on the viscosity of the slurry for forming the catalyst film.

[Drying process]
Drying in the drying step may be natural drying or forced drying using a dryer or the like.

According to the manufacturing method of the catalyst film 10 described above, a catalyst film in which a porous structure is formed of graphite and the catalyst particles and the ion conductive resin are held on the graphite surface can be manufactured. Therefore, according to this production method, it is possible to produce a catalyst film that can use the catalyst components with high efficiency and has high power generation capability, and that is less likely to have lower power generation capability even when operated for a long time.
In addition, since the coating method is applied in this manufacturing method, the thickness of the catalyst film can be easily controlled. Further, productivity can be increased and production can be enlarged at a low cost.

<Membrane-electrode assembly, polymer electrolyte fuel cell>
One embodiment of the membrane-electrode assembly and polymer electrolyte fuel cell of the present invention will be described.
FIG. 2 shows a membrane-electrode assembly and a polymer electrolyte fuel cell according to this embodiment. The membrane-electrode assembly 2 of this embodiment includes an electrolyte layer 20, catalyst films 10a and 10b stacked on both surfaces of the electrolyte layer 20, and gas diffusion layers 30a stacked on the catalyst films 10a and 10b, respectively. , 30b, which are joined together. That is, it is a five-layer assembly of gas diffusion layer 30a-catalyst membrane 10a-electrolyte layer 20-catalyst membrane 10b-gas diffusion layer 30b.
In this membrane-electrode assembly 2, one gas diffusion layer 30a side is a fuel electrode, and the other gas diffusion layer 30b side is an oxidant electrode.
A polymer electrolyte fuel cell 1 according to this embodiment includes a membrane-electrode assembly 2 and separators 3, 3 provided outside the gas diffusion layers 30 a, 30 b of the membrane-electrode assembly 2. Is. In the polymer electrolyte fuel cell 1, both catalyst films 10 a and 10 b are electrically connected via an external load circuit 40.

As the electrolyte layer 20 of the membrane-electrode assembly 2, one made of a solid polymer electrolyte can be used, and examples thereof include trade names: Nafion 117, Nafion 112, etc. manufactured by DuPont.
Examples of the gas diffusion layers 30a and 30b include carbon paper and carbon cloth.
Examples of the separator 3 include those made of graphite and metal.

  The membrane-electrode assembly 2 is obtained by preparing a three-layer laminate of catalyst membrane 10a-electrolyte layer 20-catalyst membrane 10b and laminating gas diffusion layers 30a, 30b on both sides of the three-layer laminate. As a method for producing a three-layer laminate, for example, a method in which the catalyst films 10a and 10b are stacked on both surfaces of the electrolyte layer 20 and pressure-bonded by hot pressing or the like, and a method in which the catalyst film forming slurry is applied on both surfaces of the electrolyte layer 20 Etc.

An example of a power generation method using this polymer electrolyte fuel cell will be described. First, hydrogen as a fuel is supplied to the gas diffusion layer 30a on the fuel electrode side and introduced into the catalyst film 10a on the fuel electrode side, and oxygen as an oxidant is supplied to the gas diffusion layer 30b on the oxidant electrode side. The catalyst is introduced into the catalyst film 10b on the oxidant electrode side. Hydrogen introduced into the fuel electrode-side catalyst membrane 10a is separated into hydrogen ions and charges by a catalyst component such as platinum, and then the hydrogen ions are guided to the oxidant electrode-side catalyst membrane 10b through the electrolyte layer 20. . On the other hand, the charge is guided to the catalyst film 10b on the oxidant electrode side through the external load circuit 40. Further, oxygen introduced into the catalyst film 10b on the oxidant electrode side combines with the hydrogen ions and charges to generate water.
Thus, by reacting hydrogen and oxygen, charge can be passed through the external load circuit 40, so that it can function as a battery.

Since the membrane-electrode assembly 2 and the polymer electrolyte fuel cell 1 described above include the catalyst membranes 10a and 10b described above, the catalyst components can be used with high efficiency, the power generation capacity is high, and the operation is continued for a long time. The power generation capacity is unlikely to decrease even if it is used.
Since such a polymer electrolyte fuel cell 1 has a high power generation capacity per unit catalyst amount and can realize a long-life fuel cell without increasing costs, it can be applied to electric vehicles, personal computers, and the like. it can.

The polymer electrolyte fuel cell of the present invention is not limited to the above-described embodiment example. For example, since the catalyst membrane described above can also exhibit the function of a gas diffusion layer, the membrane-electrode assembly of the present invention may not include the gas diffusion layer. That is, what is necessary is just to have comprised the 3 layer laminated body of the catalyst membrane-electrolyte layer-catalyst membrane. In that case, a separator is disposed outside each catalyst membrane. As described above, if the membrane-electrode assembly does not include the gas diffusion layer, the member can be simplified and the cost can be reduced.
Moreover, it is not necessary for both catalyst membranes to be the catalyst membrane of the present invention, and either one may be the catalyst membrane of the present invention. If the catalyst membrane of the present invention is installed on the fuel electrode side, the fuel supply performance is improved, and if it is installed on the oxidant electrode side, the generated water is excellently discharged.

<Example 1>
(Manufacture of fuel electrode catalyst membrane)
First, 20 g of water and 10 g of a solution containing an ion conductive resin (trade name: Nafion 20 mass% solution manufactured by DuPont) were mixed to obtain a resin slurry. Next, 8 g of scaly graphite, 1 g of PTFE particles, and 1 g of carbon black as a conductive assistant were added to the resin slurry to obtain a carbon slurry. Subsequently, 2 g of catalyst-supported carbon black (produced by Tanaka Kikinzoku Kogyo Co., Ltd .; particles in which 54% by mass of platinum / ruthenium was supported on 46% by mass of carbon black as a catalyst) was added to the carbon slurry to form a catalyst film-forming slurry A was prepared.

  The obtained slurry A for forming a catalyst film was applied to a PEN film using an applicator to obtain a coated film. Thereafter, the coated film was dried to obtain a catalyst film A having a thickness of 50 μm. This catalyst film A was used as a fuel electrode catalyst film in a fuel cell.

  Except that catalyst-supported carbon black (manufactured by Tanaka Kikinzoku Kogyo; particles in which 46% by mass of platinum was supported on 54% by mass of carbon black) was used as the catalyst particles, the same procedure as in the preparation of slurry A for forming a catalyst film was used. Thus, a slurry B for forming a catalyst film was prepared. Then, using the catalyst film forming slurry B, a catalyst film B having a thickness of 50 μm was obtained in the same manner as the method for forming the catalyst film A. This catalyst film B was used as a catalyst film for an oxygen electrode in a fuel cell.

(Observation of catalyst membrane)
When the detailed structures of the cross sections of the obtained fuel electrode catalyst film and oxygen electrode catalyst film were observed using a scanning electron microscope (SEM), each catalyst film was porous by graphite 11 as shown in FIG. It was confirmed that the water-repellent resin 12, the catalyst particles 13, the ion conductive resin 14, and the conductive auxiliary agent 15 are held on the surface of the graphite 11.

<Example 2>
A fuel electrode catalyst film (thickness: 50 μm) and an oxygen electrode catalyst film (thickness: 50 μm) were the same as in Example 1 except that the carbon black as the conductive auxiliary agent in Example 1 was changed to carbon nanotubes. Respectively.

<Comparative Example 1>
2 g of catalyst-supported carbon black supporting the platinum-ruthenium alloy used in Example 1 was prepared, mixed with 20 g of butyl acetate, and dispersed for 10 minutes with an ultrasonic cleaner to prepare a fuel electrode catalyst dispersion. 22 g was obtained. Next, 8 g of a solution containing an ion conductive resin (trade name: Nafion 5 mass% solution manufactured by DuPont) is mixed with 22 g of the fuel electrode catalyst dispersion, and further dispersed for 30 minutes with an ultrasonic cleaner. A slurry C for forming a catalyst film containing no graphite was prepared. This catalyst film-forming slurry C was applied to one surface of an electrolyte layer (trade name: Nafion 117, manufactured by DuPont) using an applicator and dried to form a fuel electrode catalyst film having a thickness of 50 μm.
Further, a catalyst film forming slurry D was prepared in the same manner as the catalyst film forming slurry C except that a catalyst supporting carbon black supporting a platinum alloy was used instead of the catalyst supporting carbon black. The catalyst film-forming slurry D was applied to the other surface of the electrolyte layer (trade name: Nafion 117, manufactured by DuPont) using an applicator and dried to form a catalyst film for an oxygen electrode having a thickness of 50 μm.
When the cross section of each catalyst film was observed by SEM, the catalyst film was not porous.

<Comparative Example 2>
A fuel electrode catalyst membrane and an oxygen electrode catalyst membrane were obtained in the same manner as in Example 1 except that the PTFE particles were not added.

Next, the polymer membranes of Examples 1 and 2 and Comparative Examples 1 and 2 were provided on both the fuel electrode side and the oxygen electrode side of the electrolyte layer as described below to produce solid polymer fuel cells.
<Example 3>
The fuel electrode catalyst membrane and the oxygen electrode catalyst membrane of Example 1 were laminated on both surfaces of an electrolyte layer made of an ion exchange membrane (trade name: Nafion 117 manufactured by DuPont), and then carbon as a gas diffusion layer on each catalyst membrane. Paper was laminated and these were integrated by hot pressing (120 ° C.) to obtain a membrane-electrode assembly. Next, this membrane-electrode assembly was incorporated into a single cell to obtain a polymer electrolyte fuel cell.

<Example 4>
After the lamination of the gas diffusion layer in Example 3 was omitted to obtain a membrane-electrode assembly of a three-layer laminate, the membrane-electrode assembly was incorporated into a single cell to obtain a polymer electrolyte fuel cell.
<Example 5>
A polymer electrolyte fuel cell was obtained in the same manner as in Example 3, except that the fuel electrode catalyst film and the oxygen catalyst film of Example 2 were used.
<Example 6>
A polymer electrolyte fuel cell was obtained in the same manner as in Example 4 except that the fuel electrode catalyst film and the oxygen catalyst film of Example 2 were used.

<Comparative Example 3>
A fuel cell was obtained in the same manner as in Example 3 except that the fuel electrode catalyst film and the oxygen catalyst film of Comparative Example 1 were used.
<Comparative example 4>
A fuel cell was obtained in the same manner as in Example 3 except that the fuel electrode catalyst film and the oxygen catalyst film of Comparative Example 2 were used.
<Comparative Example 5>
A fuel cell was obtained in the same manner as in Example 4 except that the fuel electrode catalyst film and the oxygen catalyst film of Comparative Example 2 were used.

<Fuel cell power generation characteristics>
The power generation characteristics of the fuel cells of Examples 3 to 6 and Comparative Examples 3 to 5 were evaluated as follows. First, hydrogen and oxygen humidified by bubbling (each supply pressure 2.5 atm (2.53 × 10 ⁵ Pa)) are supplied to a solid polymer fuel cell, and the temperature is maintained at 80 ° C. The fuel cell was activated. Then, after 5 hours, after 500 hours and after 1000 hours of operation, the voltage at which the current density was 1 A / cm ² was measured. The results are shown in Table 1.

As is clear from Table 1, the fuel cells of Examples 3 to 6 using the catalyst film containing graphite, water-repellent resin, catalyst particles, and ion conductive resin all have a voltage drop even when operated for a long time. It was suppressed. Moreover, since the fuel cells of Examples 3 to 6 had high water repellency, flooding was suppressed and the voltage was high.
In contrast, the fuel cell of Comparative Example 3 containing no graphite and water-repellent resin had a low voltage, and the voltage decreased when operated for a long time. Further, the fuel cells of Comparative Examples 4 and 5 that did not contain the water repellent resin had a low voltage.

  For the fuel cells of Examples 3 to 6 and Comparative Examples 3 to 5, power generation was performed in the same manner as when hydrogen was used as the fuel, except that a methanol dilution with water (5% by mass of methanol) was used as the fuel. Characteristics were evaluated. The results are shown in Table 2.

  As is clear from Table 2, even when the fuel was a methanol liquid system, the fuel cells of Examples 3 to 6 had a high voltage, and the voltage drop was prevented. On the other hand, the voltage of the fuel cell of Comparative Example 3 was low and the voltage dropped when operated for a long time. Moreover, the voltage of the fuel cells of Comparative Examples 4 and 5 was low.

1 is a cross-sectional view showing an embodiment of a catalyst membrane for a polymer electrolyte fuel cell of the present invention. It is a figure showing typically an example of an embodiment of a polymer electrolyte fuel of the present invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Polymer electrolyte fuel cell 2 Membrane-electrode assembly 10, 10a, 10b Catalyst membrane (catalyst membrane for polymer electrolyte fuel cell)
11 Graphite 12 Water repellent resin 13 Catalyst particles 14 Ion conductive resin 15 Conductive aid 20 Electrolyte layer 30a, 30b Gas diffusion layer 40 External load circuit

Claims (15)

  A slurry for forming a catalyst film, characterized in that graphite, a water-repellent resin, catalyst particles, and an ion conductive resin are dispersed in water and / or alcohol.   The slurry for forming a catalyst film according to claim 1, wherein the water-repellent resin is a fluororesin.   The fluororesin is selected from polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), polyhexafluoropropylene (PHFP), ethylene-tetrafluoroethylene copolymer (ETFE), and copolymers thereof. The slurry for forming a catalyst film according to claim 2, wherein the slurry is at least one kind.   The catalyst film forming slurry according to any one of claims 1 to 3, wherein the graphite is at least one selected from scale-like, scale-like graphite, flaky graphite, and expanded graphite.   The catalyst film-forming slurry according to any one of claims 1 to 4, wherein a conductive additive is further dispersed.   6. The slurry for forming a catalyst film according to claim 5, wherein the conductive additive is carbon black and / or carbon fiber.   The slurry for forming a catalyst film according to claim 6, wherein the carbon fibers are carbon nanotubes.   A catalyst film for a polymer electrolyte fuel cell, which is formed by applying the slurry for forming a catalyst film according to any one of claims 1 to 7.   The catalyst membrane for a polymer electrolyte fuel cell according to claim 8, which has a porous structure.   The catalyst membrane for a polymer electrolyte fuel cell according to claim 9, wherein the porous structure is made of graphite.   The catalyst film for a polymer electrolyte fuel cell according to any one of claims 8 to 10, wherein the water-repellent resin, the catalyst particles, and the ion conductive resin are held on the surface of the graphite. .   The slurry for forming a catalyst film according to claim 5 is applied and formed, and the water-repellent resin, the catalyst particles, the ion conductive resin, and the conductive auxiliary agent are held on the graphite surface. A catalyst membrane for a polymer electrolyte fuel cell, wherein A film forming step of coating the slurry for forming a catalyst film according to any one of claims 1 to 7 on a substrate to form a coated film;
A method for producing a catalyst membrane for a polymer electrolyte fuel cell, comprising: a drying step of drying the coated film. A membrane-electrode assembly comprising an electrolyte layer and a catalyst membrane for a polymer electrolyte fuel cell laminated on both surfaces of the electrolyte layer,
A membrane-electrode assembly, wherein one or both of the polymer membranes for a polymer electrolyte fuel cell is the catalyst membrane for a polymer electrolyte fuel cell according to any one of claims 8 to 12. A polymer electrolyte fuel cell comprising the membrane-electrode assembly according to claim 14.

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