JP5430079B2 - Manufacturing method of membrane electrode assembly - Google Patents

Description

  The present invention relates to a method for manufacturing a membrane electrode assembly, a method for manufacturing a fuel cell, a membrane electrode assembly, and a fuel cell. The membrane electrode assembly according to the production method of the present invention can be suitably used as a membrane electrode assembly for a fuel cell.

  The polymer electrolyte fuel cell is expected as a future energy generation device because of its high energy conversion efficiency, cleanliness, and quietness. Since polymer electrolyte fuel cells have high energy density and low operating temperature, in recent years, they are not only used for automobiles and household power generators, but also for small electric devices such as mobile phones, laptop computers, digital cameras, etc. The use of is also being studied. Solid polymer fuel cells are attracting attention because they may be able to be driven for a longer time than conventional secondary batteries.

  While the polymer electrolyte fuel cell has the advantage that it can be driven even at an operating temperature of 100 ° C. or lower, it has the problem that the voltage gradually decreases with the lapse of the power generation time and the power generation stops at the end. Yes.

  Such a problem is that the water generated by the reaction stays in the gap of the catalyst layer, and the gap in the catalyst layer is blocked by water, and the supply of the fuel gas, which is a reactant, is hindered. This is due to a so-called “flooding phenomenon” in which the power generation reaction stops. In particular, flooding is likely to occur in the catalyst layer on the cathode side where water is generated.

  Moreover, in order to put it to practical use as a small fuel cell for electric equipment, it is essential to make the entire system compact. In particular, when the fuel cell is mounted on a small electric device, it is necessary to downsize not only the entire system but also the battery itself. For this reason, a method (Air Breathing) in which air is supplied to the air electrode (cathode) by natural diffusion without using a pump or a blower is considered promising.

  When such a method is used, the generated water is discharged out of the fuel cell only by natural evaporation, so that the generated water stays in the catalyst layer and flooding often occurs.

  From the above, it is considered that improving the gas diffusibility of the catalyst layer, particularly the generated water dissipation, and suppressing flooding are important factors affecting the performance stability of the fuel cell.

  In this regard, Patent Documents 1 and 2 disclose techniques for improving gas diffusibility and generated water dissipation by providing a drainage groove in the catalyst layer.

  On the other hand, Patent Document 3 discloses a method of forming a porous catalyst layer having a dendritic shape using a sputtering method or an ion plating method. In Patent Document 3, the thickness of the catalyst layer is several μm, which is thinner than that of the conventional platinum-supported carbon catalyst (several tens of μm), and the material diffusion path of gas and water droplets is shortened. Disclosed is a technique for improving the performance.

In Non-Patent Document 1, when forming a catalyst layer by an ion beam assisted deposition (IBAD) method, the catalyst layer is patterned to be divided into a catalyst formation region and a catalyst non-formation region by using a mask. doing. Non-Patent Document 1 states that the dissipating property of the generated water is thereby improved and the output of the fuel cell is improved.
JP 2004-327358 A JP 2004-039474 A JP 2006-49278 A M.M. S. Saha A.B. F. Gulla, R .; J. et al. Allen and S.M. Mukerjee, Electrochim. Acta, 51 (2006) 4680.

  In the example of Patent Document 3, a porous catalyst layer is formed by a vapor deposition method using a PTFE (polytetrafluoroethylene) transfer sheet as a substrate, and then transferred to a solid polymer electrolyte membrane to form a membrane electrode A joined body (hereinafter referred to as “MEA”) is produced.

  However, as a result of intensive studies by the inventors of the present invention, in the case of the example of Patent Document 3, in the vicinity of the PTFE sheet side of the porous catalyst layer, a dense layer having a thickness of about 0.1 to 0.2 μm. Was found to form. In addition, in this invention and this specification, a dense layer is a layered area | region which is porous, but has a low porosity compared with the other area | region in a porous catalyst layer.

  Furthermore, the inventors have found that when the fuel cell is assembled, the dense layer inhibits the material diffusibility between the porous catalyst layer and the gas diffusion layer.

  Furthermore, when producing MEA, it discovered that many cracks with a width of 1 micrometer or more were produced in the random shape in the catalyst layer by the swelling action of the electrolyte membrane. In this porous catalyst layer, it is considered that gas and water droplets diffuse in the catalyst layer in the in-plane direction and are exchanged with the gas diffusion layer through this crack.

  That is, conventionally, there are many places where the length of the substance diffusion path is larger than the thickness of the catalyst layer, and this has been a factor of reducing the substance diffusibility of the porous catalyst layer. .

  Here, even if the manufacturing method described in Patent Documents 1 and 2 is simply combined with the catalyst layer manufacturing method described in Patent Document 3 and a drainage groove is provided, a dense layer is still formed near the transfer sheet of the catalyst layer. Since it is formed, the material diffusibility is hindered and the problem cannot be solved.

  Further, in the case of the manufacturing method described in Patent Document 2, a non-transfer portion of the catalyst, that is, a groove is formed by bending the transfer sheet with a mold. For this reason, the width and interval of the grooves that can be formed are larger than twice the thickness of the transfer sheet. Patent Document 2 describes that the strength of the manufacturing operation cannot be obtained unless the thickness of the transfer sheet is 10 μm or more. Therefore, there is a problem that the width and interval of the grooves are limited to those larger than 20 μm. .

  In order to improve the material diffusibility of the catalyst layer described in Patent Document 3, it is necessary to make the groove interval substantially equal to the thickness (several μm) of the catalyst layer, so the method described in Patent Document 2 is simply Combining them does not solve the problem.

  Further, when the groove width is as large as several hundreds of micrometers, the capillary force is weakened, and thus there is a problem that the generated water tends to stay in the groove, which is not preferable, and the problem cannot be solved.

  On the other hand, as described in Non-Patent Document 1, it is a simple method to provide a non-catalyst formation region (this region is functionally a drainage groove) using a mask film formation method. Since the catalyst formed on the mask is wasted, there is a problem in terms of cost. Even if the catalyst formed on the mask is recovered and reused, the recovery cost cannot be ignored. In addition, the mask manufacturing cost also contributes to the cost increase.

  The prior art has the above-mentioned problems, and a practical technique for improving the material diffusibility and generated water dissipation of the catalyst layer having a dendritic shape described in Patent Document 3 and improving the catalyst utilization efficiency is demanded. It was done.

  This invention is comprised in view of the above situations, and it aims at providing the manufacturing method of the membrane electrode assembly which improved the material diffusibility and the catalyst utilization efficiency.

  Another object of the present invention is to provide a fuel cell having high output and stable power generation characteristics at low cost using the membrane electrode assembly produced by the above production method.

  Furthermore, an object of the present invention is to provide a membrane electrode assembly excellent in substance diffusibility and catalyst utilization efficiency and a fuel cell using the same.

Therefore, the present invention provides a method for producing a membrane electrode assembly having a catalyst layer on both sides of a solid polymer electrolyte membrane,
A first film forming step of forming a first layer comprising a catalyst or a catalyst precursor on the surface of the sheet by a vapor phase film forming method;
Forming a through hole in the first layer;
A second film forming step of forming a second layer made of a catalyst or a catalyst precursor on the surface of the first layer in which the through holes are formed by a vapor phase film forming method;
Bonding a solid polymer electrolyte membrane to the surface of the second layer;
Peeling the sheet from the first layer;
Is a method for producing a membrane electrode assembly, comprising: Through these steps, at least one of the catalyst layers is formed on the solid polymer electrolyte membrane.

  The step of forming the through hole in the first layer is preferably a step of forming the through hole so that the opening ratio of the surface of the first layer in contact with the sheet is 8% or more and 40% or less. .

The step of forming the through hole in the first layer is a step of forming the through hole so that the catalyst or the catalyst precursor in the first layer remains at 50 μg or more per 1 cm ² of the surface area of the sheet after the through hole is formed. It is preferable that

Before the first film forming step, it is preferable to have a step of providing irregularities on the surface of the sheet, and depositing the first layer on the surface having the irregularities. As such irregularities, streaky irregularities are preferable. As the step of providing irregularities on the surface of the sheet, rubbing treatment or polishing treatment is preferably used. The step of bonding the solid polymer electrolyte membrane to the surface of the second layer includes at least a second layer formed on the concave and convex portions and a second layer formed on the concave and convex portions. It is preferable to be a step of joining a part and the solid polymer electrolyte membrane.

  Various methods for providing the through hole are conceivable, but a dry etching method is preferable.

  Providing a layer made of platinum or platinum oxide as the first layer, providing a layer made of PtOx (X ≧ 2) as the second layer, and reducing the PtOx (X ≧ 2). preferable. It is preferable to form a catalyst layer having a dendritic shape by reducing the PtOx (X ≧ 2).

  Further, the present invention provides a method for producing a fuel cell comprising at least a step of producing a membrane electrode assembly by any one of the production methods described above and a step of forming a gas diffusion layer on both sides of the membrane electrode assembly. It is.

Furthermore, the present invention provides a membrane electrode assembly having a catalyst layer on both sides of a solid polymer electrolyte membrane, wherein at least one of the catalyst layers is a catalyst layer having a dendritic shape,
The catalyst layer having the dendritic shape has macro cracks and through holes, and the through hole in the region surrounded by the macro cracks of the catalyst layer having the dendritic shape is opposite to the solid polymer electrolyte membrane. The membrane electrode assembly is characterized in that the aperture ratio at the surface is 8% or more and 40% or less.

  The weighted average of the equivalent circle diameter in the region surrounded by the macro cracks is preferably 35 μm or less, and the standard deviation of the equivalent circle diameter is preferably 50% or less of the weighted average.

  Further, the present invention is a fuel cell having at least such a membrane electrode assembly and gas diffusion layers present on both sides thereof.

  According to the method for manufacturing a membrane electrode assembly and the method for manufacturing a fuel cell of the present invention, it is possible to improve the material diffusibility of the obtained membrane electrode assembly and to suppress a decrease in the output of the fuel cell due to flooding of the catalyst layer. Thus, a fuel cell that can be stably driven for a long time can be obtained. Moreover, since the catalyst utilization efficiency can be improved, the amount of catalyst can be reduced, and the cost of the membrane electrode assembly and the fuel cell can be reduced. According to the membrane electrode assembly and the fuel cell of the present invention, a fuel cell that improves the material diffusibility of the membrane electrode assembly, suppresses the output decrease of the fuel cell due to the flooding of the catalyst layer, and can be driven stably for a long time. Can be obtained.

  As a result of intensive studies by the present inventors, in order to solve the above-mentioned problem, the material diffusibility in the dense layer is improved and / or the catalyst is island-shaped surrounded by the cracks. It came to the idea that shortening the in-plane material diffusion path length in the catalyst layer by reducing the equivalent circle diameter of the region (hereinafter sometimes referred to as “catalyst grain”) is effective. .

  In addition, it has been found that the material diffusibility of the catalyst layer can be improved by reducing the variation in the equivalent circle diameter of the catalyst grains.

  Hereinafter, preferred embodiments of a method for producing a membrane electrode assembly according to the present invention, preferred embodiments of a method for producing a fuel cell according to the present invention, and a membrane electrode assembly according to the present invention will be described with reference to the drawings. A preferred embodiment and a preferred embodiment of a fuel cell using the same will be described. However, the scope of the present invention is determined by the scope of claims, and the following description does not limit the scope of the present invention. For example, the materials, dimensions, shapes, arrangements, manufacturing conditions, and the like described below do not limit the scope of the present invention.

  First, preferred embodiments of the membrane electrode assembly and the fuel cell manufactured by the manufacturing method of the present invention will be described.

  The membrane electrode assembly (MEA) referred to in this specification has a catalyst layer on both sides of a solid polymer electrolyte membrane.

  FIG. 1 is a schematic diagram showing an example of a cross-sectional configuration of a fuel cell single cell using a membrane electrode assembly produced by the present invention. In FIG. 1, reference numeral 1 denotes a solid polymer electrolyte membrane, and a pair of catalyst layers, that is, an anode-side catalyst layer 2 and a cathode-side catalyst layer 3 are arranged with this sandwiched therebetween. An integral body of the solid polymer electrolyte membrane 1, the anode side catalyst layer 2, and the cathode side catalyst layer 3 is an MEA8.

  In this example, an example is shown in which the catalyst layer according to the production method of the present invention is arranged only on the cathode side electrode (air electrode) side, but the arrangement configuration of the catalyst layer is not limited to this. For example, the catalyst layer according to the present invention may be disposed on the anode side, or may be disposed only on the anode side. However, in view of the fact that flooding is likely to occur in the cathode-side catalyst layer where water is generated, it is preferable to dispose a catalyst layer according to the production method of the present invention at least on the cathode side.

  An anode side gas diffusion layer 4 and an anode side electrode (fuel electrode) 6 are disposed outside the anode side catalyst layer 2. The anode electrode 6 has at least one through hole through which fuel gas (typically hydrogen gas) can pass. The anode-side gas diffusion layer 4 is composed of a microporous layer (microporous layer, hereinafter abbreviated as MPL) 9 and a gas diffusion base material 10 that supports the MPL 9.

  On the outside of the catalyst layer 3 on the cathode side, a cathode side gas diffusion layer 5, a cathode side electrode (air electrode) 7 and a foam metal 12 are arranged. The cathode-side gas diffusion layer 5 is also composed of MPL 9 and a gas diffusion base material 10 that supports MPL 9.

  Moreover, as the material of the electrodes 6 and 7, a material excellent in conductivity and oxidation resistance is preferably used. Specific examples of suitable materials include platinum, titanium, carbon, SUS (stainless steel), SUS coated with gold, SUS coated with carbon, aluminum coated with gold, and aluminum coated with carbon.

  As the material of the foam metal 12, like the electrodes 6 and 7, a material excellent in conductivity and oxidation resistance is suitable. Specifically, SUS, nickel chromium alloy, and titanium are preferably used. As an example of the nickel chromium alloy foam metal, Celmet (registered trademark, manufactured by Toyama Sumitomo Electric Co., Ltd.) can be mentioned. From the viewpoint of improving corrosion resistance and reducing contact resistance, any of these materials may be coated with gold. The foam metal 12 is not necessarily used, but if not used, it is necessary to provide a through hole in the electrode 7 and to provide a function of allowing at least oxygen and water vapor gas to pass. The foam metal 12 is not necessarily installed only on the cathode side, but may be used only on the anode side or on both electrodes. The pore diameter and porosity of the foam metal 12 are not particularly limited as long as they do not hinder the diffusion of reaction gas, water vapor and the like.

  As the solid polymer electrolyte membrane (hereinafter sometimes simply referred to as “electrolyte membrane”) 1, a perfluorocarbon polymer having a sulfonic acid group can be suitably used. An example of a perfluorosulfonic acid polymer is Nafion (registered trademark, manufactured by DuPont).

When proton H ⁺ moves in the electrolyte membrane toward the cathode side, the electrolyte membrane also has a function of retaining water molecules because water molecules are often used to move the hydrophilic portion in the electrolyte. It is preferable.

As a function of the solid polymer electrolyte membrane, it is preferable that the proton H ⁺ generated on the anode side is transmitted to the cathode side, unreacted reaction gases (hydrogen and oxygen) are not passed, and a predetermined water retention function is provided. Any material having such a function can be selected and used for the solid polymer electrolyte membrane in consideration of various conditions.

  The gas diffusion layers 4 and 5 preferably have the following functions. First, in order to perform an electrode reaction efficiently, it is a function which supplies fuel gas or air uniformly and sufficiently in a plane to the electrode reaction region in the fuel electrode or the catalyst layer of the air electrode. In addition, it is a function for releasing the charge generated by the electrode reaction to the outside of the single cell. Further, it is a function for efficiently discharging reaction product water and unreacted gas to the outside of the single cell.

  As the gas diffusion layer having such a function, a porous body having electron conductivity can be preferably used. For example, a carbon fine particle layer using carbon cloth or carbon paper as the gas diffusion base material 10 and PTFE as a binder as the MPL 9 can be preferably used. As the carbon fine particles, acetylene black, ketjen black, vapor-grown fibrous carbon, carbon nanotube, or the like can be used. The cathode side catalyst layer 3 is preferably a porous catalyst layer, and is preferably composed of an aggregate of platinum nanoparticles. Among them, it is particularly preferable to use as the cathode-side catalyst layer 3 a dendritic shape obtained by reducing PtOx (X ≧ 2: typically platinum dioxide). The catalyst layer having a dendritic shape is an excellent porous catalyst layer having a large specific surface area.

  Here, the dendritic shape in the present specification refers to a structure in which a large number of rod-like or flake (thin pieces) -like structures composed of catalyst nanoparticles are gathered with branch points. When the cross section of the catalyst layer having a dendritic shape is observed with a tunnel microscope or the like, it looks like a tree that is branched by a plurality of rod-like structures or flake-like structures made of catalyst particles.

  One rod-like or flake-like structure preferably has a short-side length of 5 nm to 200 nm. Here, the length in the short direction means the minimum dimension in the virtual projection plane of one rod-like structure or flake-like structure. With respect to the aggregate of dendritic platinum nanoparticles, for example, a technique disclosed in JP-A-2006-49278 can be applied to the present invention.

In the present specification, the term “platinum dioxide” simply means PtOx (X ≧ 2), that is, not only that represented by the chemical formula PtO ₂ generally called platinum dioxide, but also the chemical formula PtOx ( X> 2) is included. Even if what is represented by the chemical formula PtOx (X> 2) is used, the effect of the present invention can be sufficiently obtained. There is no particular upper limit for X, but considering the properties of platinum, the upper limit for X is actually considered to be 2.5. Further, from the viewpoint of obtaining a catalyst layer having a dendritic shape, it is desirable to reduce platinum dioxide defined in this way. Furthermore, in order to obtain a dendritic structure, it is preferable to reduce hexagonal crystalline platinum dioxide or amorphous platinum dioxide. However, platinum oxide other than platinum dioxide or platinum is also preferably used for the first layer. This is because the influence of the composition of the first layer on the formation of the dendritic shape is extremely small, but it is possible to form a through-hole without using platinum dioxide.

  The platinum nanoparticles having a diameter of 2 nm or more and 20 nm or less are preferable because of high catalytic activity, and those having a diameter of 2 nm or more and 10 nm or less are particularly preferable because of a large surface area.

  When the diameter exceeds 20 nm, the catalytic activity may be lowered, and the performance of the fuel cell may be lowered accordingly. On the other hand, those having a diameter of less than 2 nm are difficult to produce.

  The cathode catalyst layer 3 preferably contains a hydrophobic agent.

  In order to add a hydrophobic agent to the cathode side catalyst layer 3, a method of adding a fluororesin fine particle dispersion (for example, Polyflon (registered trademark, manufactured by Daikin Industries)) or the like to the cathode side catalyst layer 3 is disclosed in JP-A-2006-332041. Known methods such as those described can be used. From the viewpoint of spreading the hydrophobic agent to the details of the pores of the catalyst layer 3, it is particularly preferable to use the method described in JP-A-2006-332041.

  Specifically, the method described in JP-A-2006-332041 includes the following steps. First, an Si compound having a hydrophobic substituent that generates a polymerizable group by causing a hydrolysis reaction by the catalytic action of platinum oxide is brought into contact with platinum oxide. Next, the Si compound is subjected to a polymerization reaction to produce a hydrophobic agent on the surface of the platinum oxide. Thereafter, the platinum oxide is reduced.

  According to this method, a hydrophobic agent made of methylsiloxane or the like can be easily added only to the cathode side catalyst layer 3.

  All of the techniques related to the cathode side catalyst layer 3 described above can be applied to the anode side catalyst layer 2 as well. However, considering that flooding is likely to occur in the cathode-side catalyst layer 3 and not in the anode-side catalyst layer 2, a general catalyst such as platinum black or platinum-supported carbon should be used as the anode-side catalyst layer 2. You can also.

  Next, an embodiment of a manufacturing method according to the present invention will be described.

  In the first embodiment of the present invention, a catalyst layer or a catalyst precursor layer (first layer) is formed on the surface of a sheet (hereinafter referred to as a “transfer sheet” for the sake of clarity) by a vapor deposition method. A first film forming step, a step of forming a through hole in the catalyst layer or the catalyst precursor layer, and a catalyst layer or a catalyst precursor further on the surface of the catalyst layer or the catalyst precursor layer in which the through hole is formed. And a second film formation step for forming a body layer (second layer).

  As the vapor deposition method, a sputtering method such as reactive sputtering or an ion plating method is preferably used.

  As a material for the transfer sheet used in the present invention, a material having a heat resistant temperature of 130 ° C. or higher is preferably used. This is because, in the transfer step when forming the MEA, hot pressing is performed at a temperature equal to or higher than the glass transition temperature (130 ° C. in Nafion (registered trademark)) of the solid polymer electrolyte membrane. In addition, when a material having a high heat-resistant temperature is used, it is possible to reduce a possibility that the transfer sheet is damaged when the temperature of the transfer sheet is increased during vapor deposition. More specifically, it is preferable to use a resin substrate having a high heat resistant temperature such as PTFE, polycarbonate, polyimide, etc. as the transfer sheet.

  When the center line average roughness of these transfer sheets is 10 nm or less, when a platinum dioxide layer is formed by a vapor phase film forming method such as an ion plating method or a reactive sputtering method, usually 0.02 to A dense layer having a thickness of about 0.2 μm is formed, and a porous layer is formed thereon. These as a whole become a catalyst precursor layer. The thickness of the dense layer varies depending on the total pressure of the atmosphere during film formation, and the thickness is reduced as the total pressure is increased, and is increased as the total pressure is decreased. For example, a dense layer having a thickness of 0.02 μm at a total pressure of 8 Pa, a thickness of 0.1 μm at a total pressure of 5 Pa, and a thickness of 0.2 μm at a total pressure of 3 Pa is formed.

  When such a catalyst precursor layer is transferred to the electrolyte membrane and then reduced, or a catalyst layer obtained by reducing such a catalyst precursor layer is transferred to the electrolyte membrane to form an MEA, a dense layer in the catalyst layer is obtained. (Not shown) is exposed on the surface of the catalyst layer on the MPL 9 side. As a result, in the single fuel cell, this dense layer is located between the porous layer (not shown) in the catalyst layer and the MPL 9, and the material diffusibility between the catalyst layer and the gas diffusion layer. Is inhibited.

  If the center line average roughness of the transfer sheet is 10 nm or more, the dense layer is not formed, but if the roughness is large, even if a PTFE sheet having excellent releasability is used, transfer is performed from the catalyst layer after transfer. There is a problem that it becomes difficult to peel off the sheet.

  4 and 5 show the surface (MPL side) of the catalyst layer produced by the conventional production method. From FIG. 5, it can be seen that the surface of the catalyst layer is quite dense although there are minute cracks.

  Further, as can be seen from FIG. 4, a large number of large cracks having a width of several μm are present on the surface of the conventional catalyst layer. This is considered to be formed with the swelling of the electrolyte membrane.

  In the conventional catalyst layer, it is considered that the movement of gas and water droplets is mainly performed through this large crack. Since the gap between the large cracks is wide, when the reaction gas or generated water tries to move in the thickness direction of the catalyst layer, there is a distance that the reaction gas or generated water must move in the in-plane direction in the catalyst layer. It will be long. Therefore, it is estimated that the conventional catalyst layer has a low material diffusibility in the thickness direction.

  On the other hand, according to the first embodiment of the present invention, a through hole is formed in the dense layer. Since the through hole exists in the dense layer, the moving distance in the in-plane direction when the reaction gas or generated water tries to move in the thickness direction of the catalyst layer can be shortened. For this reason, the material diffusibility in the thickness direction of the catalyst layer is greatly improved as compared with the conventional case.

  Here, it is preferable that the opening ratio of the through holes on the surface in contact with the transfer sheet of the first layer be 8% or more and 40% or less. When the aperture ratio is less than 8%, the effect of the present invention is drastically reduced. When the aperture ratio is larger than 40%, the effect of the present invention is almost saturated. On the other hand, the adhesion between the transfer sheet and the first layer is reduced and the film is easily peeled off. It becomes difficult.

  In addition, the shape of the through hole as referred to in the present invention does not need to have a cross section close to a circle. For example, a microcrack formed by connecting a plurality of through-holes having a substantially circular cross section is also included in the through-hole referred to in the present invention. In the present specification, a microcrack refers to a crack having a width of 1 μm or less. On the other hand, in the present invention and the present specification, a crack having a width exceeding 1 μm is called a macro crack. A typical example of a macro crack is a streak crack. In the present invention and the present specification, the term “streak crack” means that a crack having a width of 1 μm or more is substantially linear over a length of at least 100 μm or more.

  In addition, the aperture ratio of the through hole as used in the field of this invention refers to the occupation rate of the opening part of the through hole in one catalyst grain in the surface of a layer. Here, one catalyst grain is a region surrounded by macro cracks. In the stage where the through holes are formed in the first layer, such macro cracks are scarcely present, and therefore the area occupied by the openings of the macro cracks can be ignored in calculating the aperture ratio. The definition of such an opening is substantially meaningful when a membrane electrode assembly or a fuel cell is finally formed. Hereinafter, how to obtain the aperture ratio of the through hole will be described in such a case.

  First, the main plane of the catalyst layer after the formation of the membrane electrode assembly (reverse treatment to the solid polymer electrolyte membrane when the catalyst precursor layer is used in the production process is reduced to a catalyst layer) The side surface: the surface appearing in the table) is photographed with a scanning electron microscope. At the time of shooting, the shooting position and magnification are appropriately adjusted so that macro cracks (that is, cracks other than through holes (including micro cracks)) do not enter the screen. When photographing, the aperture is dark, and the others (the portion where the catalyst is present on the surface) are photographed brightly. Therefore, it is preferable to adjust the image quality so that the contrast is as high as possible.

  Next, by using image analysis software (for example, trade name “A image kun” manufactured by Asahi Kasei Engineering Co., Ltd.), the obtained electron micrograph is subjected to black and white binarization processing and image analysis processing of the image, It is possible to determine the occupancy ratio of the opening portion of the through hole in each catalyst grain (that is, the opening ratio of the through hole in the present invention).

  It is preferable that the thickness of the layer formed in the first film forming step of forming a catalyst layer or a catalyst precursor layer on the surface of the transfer sheet by a vapor phase film forming method is 50 to 500 nm. If the thickness is less than 50 nm, it is difficult to form through holes so that the catalyst layer or catalyst precursor layer remaining after the next through hole forming step does not become too small. On the other hand, if the thickness is greater than 500 nm, the amount of platinum dioxide that must be removed in the through-hole forming step becomes too large, resulting in an increase in wasted platinum.

In the through hole forming step, it is preferable to use an etching method, especially a dry etching method.
In the through hole forming step, it is preferable to appropriately select conditions (for example, etching conditions) such that the opening ratio of the through holes is 8% or more and 40% or less. After the through holes are formed, it is preferable that 50 μg / cm ² or more of the catalyst layer or the catalyst precursor layer remains per transfer sheet area.

If the remaining amount is less than 50 μg / cm ² , the area where the catalyst layer or the catalyst precursor layer covers the substrate becomes too small and the exposed area of the substrate becomes large. Therefore, in the next second film forming step, the dense layer is formed again. In that case, the effects of the present invention may not be sufficiently obtained.

It is preferable to appropriately select through-hole forming conditions (for example, etching conditions) such that 50 μg or more of the catalyst or catalyst precursor in the first layer remains per 1 cm ² of the surface area of the sheet after forming the through-holes.

  Moreover, it is preferable that the porosity of the first layer after forming the through-hole is 35% or more and 45% or less.

  By setting the porosity to be 35% or more, the material diffusibility and the generated water dissipation can be further improved. On the other hand, although it is possible for the porosity to exceed 45%, even if the porosity is increased in a range where the porosity is greater than 45%, the degree of improvement in material diffusibility and generated water dissipation is On the other hand, since the adhesive force between the transfer sheet and the first layer becomes small and easily peels off, care must be taken in handling during production.

  The porosity here is calculated as follows. First, the MEA is cut using a focused ion beam (FIB) (hereinafter referred to as “FIB processing”), and the cross section is observed with a scanning electron microscope (SEM) to take a photograph. A line parallel to the main plane of the first layer is drawn in the first layer in the obtained cross-sectional photograph. In the SEM photograph, the hole portion is observed as black and the catalyst portion is observed as white. Therefore, the ratio of the black pixels on this line to all the pixels on the line is defined as the porosity of the first layer.

  Here, when performing the FIB processing, the incident angle of the FIB is set to 20 to 40 ° with respect to the main plane of the catalyst layer, rather than being cut by causing the FIB to enter at a 90 ° angle with respect to the main plane of the catalyst layer. By making the degree, it is preferable that the main plane is cut at an angle other than a right angle so that the oblique section of the catalyst layer is exposed. By cutting in this way, an image including three-dimensional information in which plane information is added to cross-sectional information can be obtained, so that a more accurate porosity can be obtained.

  Prior to FIB processing, if the catalyst layer is immersed in ink or the like and the pores of the catalyst layer are filled with carbon, adhesion of scattered matter during FIB processing can be prevented, and the contrast between the pores and the catalyst during SEM observation. Since the ratio becomes high, an accurate porosity can be calculated, which is preferable. However, in this method, the ink easily spreads over the first layer, but it is difficult to spread the ink over the entire catalyst layer. For this reason, in the cross-sectional observation image of the sample manufactured by this method, although the first layer can obtain a high-contrast image, the second layer may obtain only an inaccurate image. In the observation image obtained by this method, it is preferable that only the region of the first layer is an analysis target.

  Hereinafter, an example of a method for manufacturing a fuel cell (single cell) using the first embodiment of the present invention will be described more specifically along the order of steps.

In addition, you may perform the reduction process of the process of the following (3) after the process of the following (5).
(1) A platinum dioxide layer (catalyst precursor layer) is formed.

  As a first film forming step, a platinum dioxide layer is formed on the surface of a PTFE (polytetrafluoroethylene) sheet as a transfer sheet by a reactive sputtering method.

  Thereafter, dry etching is performed in an Ar atmosphere as a through hole forming step.

Thereafter, as a second film formation step, a platinum dioxide layer is formed on the surface of the platinum dioxide layer subjected to dry etching by a reactive sputtering method.
(2) Hydrophobizing the catalyst layer.

Subsequently, the catalyst layer is hydrophobized according to a known technique described in JP-A-2006-332041. That is, a hydrophobic agent is formed on the catalyst surface by bringing the obtained porous platinum oxide layer into contact with a gas of an Si compound containing a hydrophobic substituent. Then, you may accelerate | stimulate the polymerization reaction of a hydrophobic agent by heating.
(3) The platinum dioxide layer is reduced.

  Subsequently, the platinum dioxide layer is subjected to hydrogen reduction treatment to obtain a porous platinum catalyst layer as a cathode side catalyst layer.

  Furthermore, an appropriate amount of an IPA (isopropyl alcohol) solution of Nafion, which is a proton conductive electrolyte, is dropped on the obtained catalyst layer, and then the solvent is volatilized in a vacuum to form a proton path on the catalyst surface. .

In this way, a cathode side catalyst layer is obtained.
(4) An anode side catalyst layer is prepared.

An anode-side catalyst layer is obtained by forming a platinum-supported carbon catalyst layer on the surface of the PTFE sheet using a doctor blade. The thickness of the catalyst layer is preferably in the range of 20 to 40 μm. The catalyst slurry used here is a mixture of platinum-supported carbon (manufactured by Johnson Matthey, HiSPEC 4000), Nafion, PTFE, IPA, and water.
(5) Create an MEA.

A solid polymer electrolyte membrane (Dupont) is formed by using the PTFE sheet with the cathode side catalyst layer obtained in the step (3) and the PTFE sheet with the anode side catalyst layer obtained in the step (4) so that each catalyst layer is inside. Made by NRE 211) and hot pressing. Thereafter, the PTFE sheet outside the cathode side catalyst layer and the PTFE sheet outside the anode side catalyst layer are peeled off to obtain an MEA having the catalyst layer of the present invention.
(6) Create a single fuel cell.

  The MEA obtained in the step (5) is converted into the gas diffusion layers 4 and 5 made of carbon cloth (LT1400-W manufactured by E-TEK), the anode side electrode 6, the foam metal 12, and the cathode side electrode 7 as shown in FIG. A fuel cell single cell is produced by sandwiching between the two.

  It is also possible to produce a fuel cell in which a plurality of single cells produced in this way are stacked.

  Moreover, 2nd embodiment of this invention adds the process of providing an unevenness | corrugation in the said transfer sheet before said 1st film-forming process. In this way, in the produced MEA, macro cracks (for example, streak cracks) are formed in the catalyst layer in addition to the through-holes, which is preferable because the substance diffusibility is further improved. More specifically, it is as follows.

  When unevenness is provided on the surface of the transfer sheet, unevenness is formed in the catalyst layer or the catalyst precursor layer. By controlling the height difference of the unevenness of this catalyst layer or the catalyst precursor layer and the space interval (minimum distance in the recesses between steps: that is, the minimum width of the recesses), the catalyst layer (the catalyst precursor layer is reduced) When transferring the catalyst precursor layer or the catalyst precursor layer to the electrolyte membrane, the electrolyte membrane can be brought into contact with the recess, and the catalyst layer in the recess is electrolyted together with the catalyst layer in the recess. It becomes possible to transfer to a film. If it does in this way, a catalyst layer or a catalyst precursor layer will shear-break in the uneven | corrugated level | step difference part at the time of transcription | transfer (at the time of a hot press). Thereby, the crack of the shape reflecting the uneven shape (step) is formed in the dense layer of the catalyst layer or the catalyst precursor layer. As the electrolyte membrane swells after hot pressing, the width of the crack expands, and many macro cracks having a width exceeding 1 μm are formed. A suitable example of control will be described later.

  The macro cracks thus formed finally function as a drainage groove in the catalyst layer. That is, the membrane electrode assembly and the fuel cell can be manufactured at low cost without wasting the catalyst as compared with the mask film forming method.

  In the second embodiment, the step of forming the through hole in the dense layer is necessary. This is because when the through hole is not formed in the dense layer, the mechanical strength of the dense layer becomes high, so that shear fracture cannot be caused, and macro cracks reflecting the uneven shape are not formed.

As a specific method of the second embodiment, the steps (1) to (6) of the first embodiment described above may be performed after the step (A) shown below. In the second embodiment, the step (3) may be performed after the step (5).
(A) Concavities and convexities are formed on the transfer sheet.

  Unevenness is formed on the surface of the PTFE sheet as a transfer sheet using polishing treatment, rubbing treatment, imprinting or the like.

  The method for forming the unevenness is not particularly limited. For example, by imprinting, polishing with abrasive paper, rubbing with a rubbing cloth, various pressing treatments, melting the sheet to form an irregular surface, laser irradiation, etc., the molecules on the sheet surface are thermally decomposed or light Decomposition or partial melting of the vicinity of the surface of the sheet to form a recess, use of a photolithography process, or the like can be used. From the viewpoint of production cost, rubbing treatment or polishing treatment is preferable. When a rubbing process or a polishing process is used, irregularities having various shapes can be formed on the transfer sheet. In this case, the uneven shape formed on the transfer sheet preferably has a center line average roughness (Ra) of 0.38 μm or more and 30 μm or less. By setting Ra to 0.38 μm or more, macro cracks that finally reflect the uneven shape are easily formed in the catalyst layer. Further, when Ra is set to 30 μm or less, the contact between the catalyst layer in the recess and the electrolyte membrane becomes good during transfer to the electrolyte membrane, and waste of the catalyst or catalyst precursor can be suppressed.

  The concavo-convex shape can be precisely controlled using an imprinting method or a photolithography process. In this case, it is preferable that the height difference of the unevenness is 0.1 μm or more. By making the unevenness height difference to be 0.1 μm or more, a sufficient height difference is given to the dense layer compared to the thickness of the dense layer (0.02 μm to 0.2 μm), resulting in shear failure in the transfer process. It can be made easier.

  Regardless of the method of forming the unevenness, the height difference of the unevenness is preferably equal to or less than the sum of the penetration depth of the electrolyte membrane into the recess and the thickness of the catalyst layer or the catalyst precursor layer in the transfer step. By making such a relationship, the transfer of the catalyst layer or catalyst precursor layer in the recess can be improved.

  The depth of penetration of the electrolyte membrane into the recess depends on the temperature of the transfer process. That is, in the transfer step, the electrolyte membrane can be easily heated to the softening point or more to easily enter the recess of the electrolyte membrane. Since the penetration depth depends on the physical properties of the electrolyte membrane, it is desirable to design in advance the height difference of the irregularities on the transfer sheet surface according to the electrolyte membrane to be used. For example, when NRE212 (manufactured by Dupont, thickness: 50 μm) is used as the electrolyte membrane, and the thickness of the catalyst layer is 2 μm, the height difference of the unevenness on the surface of the transfer sheet is preferably 20 μm or less.

The above-described space interval is preferably 5 μm or more and 200 μm or less. By setting the space interval to 5 μm or more, the electrolyte membrane can easily enter the recess in the transfer process. Moreover, the macro crack which reflected the uneven | corrugated shape can be increased by making space space into 200 micrometers or less. As for the space interval, the optimum range varies depending on the physical properties of the electrolyte membrane, so it is desirable to design in advance according to the electrolyte membrane to be used. For example, when NRE212 (manufactured by Dupont, thickness: 50 μm) is used as the electrolyte membrane, and the thickness of the catalyst layer is 2 μm, the preferable spacing of the transfer sheet according to the unevenness of the transfer sheet is as follows. is there.
When uneven height difference ≦ 2 μm: 5 μm <space interval ≦ 50 μm
When uneven height difference> 2 μm: 10 μm <space interval ≦ 50 μm
Examples of the shape of the projections and depressions provided on the transfer sheet include streaks (straight, curved, zigzag), dots, holes, or a mixed shape thereof. Even if any uneven shape is adopted, the catalyst layer or catalyst precursor layer in the concave portion is transferred to the electrolyte membrane during the transfer process, and finally, the macro crack reflecting the adopted uneven shape is formed. Formed in the catalyst layer.

  Many cracks also exist in the catalyst layer produced without providing irregularities on the transfer sheet. For example, when a platinum oxide layer, which is a catalyst precursor layer, is reduced to obtain a catalyst layer, cracks (hereinafter referred to as crack A) due to volume shrinkage due to reduction or swelling of the electrolyte membrane occur. Cracks (hereinafter referred to as cracks B) exist.

  In addition to these cracks, the catalyst grains can be made smaller by forming cracks reflecting the uneven shape (hereinafter referred to as cracks C) by the steps described above as the second embodiment. Thereby, the substance diffusibility in the catalyst layer can be further improved. This is because the reaction gas and generated water existing in the catalyst layer diffuse through the dense layer (mainly through holes) in the catalyst layer and diffuse in the in-plane direction via the crack C. This is because the smaller the catalyst grain, the shorter the material diffusion distance in the in-plane direction of the catalyst layer.

  Here, the weighted average D of the equivalent circle diameter of the region (catalyst grain) surrounded by macro cracks in the catalyst layer is preferably 35 μm or less.

  By setting D to 35 μm or less, the material diffusibility in the catalyst layer can be further improved.

  In addition, D can be calculated | required with the following numerical formula.

(In (Formula 1), N is the total number of catalyst grains, and S (n) represents the perimeter of the nth catalyst grain.)

  The method for obtaining S (n) is as follows.

First, the main plane of the catalyst layer after the formation of the membrane electrode assembly (the catalyst layer after the reduction treatment when the catalyst precursor layer is reduced) (surface opposite to the solid polymer electrolyte membrane), that is, appears on the table The surface is taken with a scanning electron microscope. The imaging area is preferably 0.08 mm ² or more. In order to capture the correct shape by photographing cracks and catalyst grains with high resolution, photograph a plurality of locations on the catalyst layer at a magnification of 500 times or more so that the total photographing area is 0.08 mm ² or more. It is preferable to do. In this case, it is preferable to perform the particle analysis process individually for each image.

  When photographing, the crack portion and the opening of the through hole are dark, and the other catalyst grain portions are photographed brightly. Therefore, it is preferable to adjust the image quality so that the contrast is as high as possible.

  Next, by using image analysis software (for example, trade name “A image kun” manufactured by Asahi Kasei Engineering Co., Ltd.), the obtained electron micrograph is subjected to black and white binarization processing and image analysis processing of the image, The perimeter length S (n) of each catalyst grain can be determined. Note that grains that are present at the edge of the image and do not show the entire catalyst grain are excluded from the analysis target.

  In the analysis process, various parameters are set so that catalyst grains can be accurately extracted as particles from the obtained image.

  In addition, when unevenness is given to the transfer sheet by rubbing treatment or polishing treatment, cracks are stopped in the middle of the catalyst grains, and one large catalyst grain in which a plurality of catalyst grains are partially connected may be observed. is there. For such a large catalyst grain, if the minimum width of the connecting portion is 5 μm or less, it is considered that the catalyst grain is substantially broken, and the particle analysis process is performed as a separate catalyst grain. This is because, in consideration of the function of macro cracks for improving material diffusivity, even if the cracks do not completely divide the grains, if the connecting portion has a sufficiently small width, the surrounding catalyst layer This is because substantially the same effect as in the case where cracks completely divide the grains is considered to be obtained.

  The above-described measurement for determining the perimeter can be performed simultaneously with the above-described measurement for determining the aperture ratio of the through hole.

  The smaller the weighted average D of the equivalent circle diameter of the region (catalyst grains) surrounded by macro cracks in the catalyst layer, the better the material diffusibility.

  However, when a rubbing process or a polishing process is used, irregularities having various shapes are formed, so there is a limit to reducing the value of D. According to the experiments by the present inventors, the lower limit value of D in this case was 16 μm.

  On the other hand, if the imprinting method or the photolithography method is used, the concavo-convex shape can be precisely controlled with a dimensional accuracy of 1 μm or less. Even in that case, D is preferably 5 μm or more. This is because it is preferable to set the space interval of the transfer sheet and the minimum width of the convex portions to 5 μm or more in order to transfer to the catalyst or catalyst precursor in the concave portions.

  When the space interval of the transfer sheet and the minimum width of the convex portion are 5 μm or more and 50 μm or less, the interval between the cracks C is 5 μm or more and 50 μm or less. In this case, stress relaxation of the catalyst layer occurs, and other cracks (crack A and crack B) are hardly formed. That is, the effect of reducing D due to crack A and crack B is difficult to expect. For this reason, even if the space interval of the transfer sheet and the minimum width of the convex portion are 5 μm, it is difficult to make D less than 5 μm.

  Further, when the standard deviation of the equivalent circle diameter of the region (catalyst grains) surrounded by macro cracks in the catalyst layer is σ, σ / D should be 50% (0.5) or less. It is preferable from a viewpoint of an improvement, and it is more preferable that it is 40% (0.4) or less. Although there is no lower limit to the value of σ / D, when rubbing treatment or polishing treatment was used, the lower limit value of σ / D confirmed experimentally was 37% (0.37). If the cost is not considered, σ / D can be set to 3% or less by using an imprinting method or a photolithography method.

  Various methods can be adopted as a method for manufacturing the MEA and the fuel cell according to the above embodiments.

  Next, specific examples will be shown to describe the present invention in detail.

Example 1
In this example, a polymer electrolyte fuel cell having the structure shown in FIG. 1 was produced using the first embodiment of the present invention.

  Hereinafter, the manufacturing process of the polymer electrolyte fuel cell according to the present embodiment will be described in detail.

(Process 1)
First, as a first film forming step, a platinum oxide layer is formed on the surface of a PTFE sheet (manufactured by Nitto Denko, Nitoflon: hereinafter sometimes referred to as “substrate”) by RF reactive sputtering using a Pt (4N) target. A film was formed to a thickness of 300 nm. As a reactive sputtering apparatus, CS-200 manufactured by ULVAC was used. Here, in the reactive sputtering, the total pressure is 5 Pa, the oxygen flow rate ratio (Q _O2 / (Q _Ar + Q _{O 2} ) is 90%, the substrate heater temperature is 40 ° C., and the RF (13.56 MHz high frequency) input power is 5 .4 W / cm ² was performed.

Thereafter, as a through hole forming step, the inside of the vacuum chamber was replaced with an Ar atmosphere (0.67 Pa), RF was applied to the substrate at a power of 2.8 mW / cm ² , and plasma etching was performed for 7 minutes. Here, the platinum oxide remaining on the substrate was 50 μg / cm ² per substrate area.

  Further, as a second film formation step, a platinum dioxide layer was formed with a thickness of 2 μm. The reactive sputtering conditions were the same as those in the first film formation step. The O / Pt molar ratio in the platinum oxide layer was about 2.4.

(Process 2)
A hydrophobic agent was formed on the surface of the platinum oxide according to a known technique described in JP-A-2006-332041. That is, the platinum oxide layer obtained in (Step 1) is brought into contact with the vapor of 2,4,6,8-tetramethyltetracyclosiloxane at room temperature (vapor pressure 1.2 kPa) for 4 minutes in a closed container. Thus, an appropriate amount of hydrophobic agent was formed on the surface of the platinum oxide. The Si / Pt molar ratio in the platinum oxide layer was 0.18.

(Process 3)
Subsequently, the obtained platinum oxide layer was subjected to a reduction treatment by exposing it to a 2% H ₂ / He atmosphere for 30 minutes to obtain a porous platinum catalyst layer having a dendritic shape on the surface of the PTFE sheet. The amount of Pt supported was 0.65 mg / cm ² .

Thereafter, 8 μl of a 1 wt% Nafion solution (5% Nafion dispersion solution manufactured by Wako Pure Chemical Industries, Ltd. diluted to 1% with IPA) was dropped on the obtained catalyst layer per 1 cm ² of catalyst area, and the solvent was removed in a vacuum. By volatilizing, a proton path was formed on the catalyst surface.

  In this way, a porous platinum catalyst layer as a cathode side catalyst layer was obtained.

(Process 4)
In order to form the anode catalyst layer, a platinum-supporting carbon layer was formed on the surface of the PTFE sheet by a doctor blade method so that the amount of Pt supported was 0.3 mg / cm ² . The catalyst slurry used here is a kneaded product of 1 part by mass of platinum-supported carbon (manufactured by Johnson Matthey, HiSPEC 4000), 0.07 part by mass of Nafion, 1 part by mass of IPA, and 0.4 part by mass of water.

(Process 5)
With the catalyst layer on the inside, the PTFE sheet with the catalyst layer prepared in (Step 3) and (Step 4) sandwiched the solid polymer electrolyte membrane (Dupont Nafion 112, thickness 50 μm), 4 MPa, 150 ° C. Hot pressing was performed under pressing conditions of 10 min. Thereafter, the PTFE sheet was peeled off from both the anode and cathode catalyst layers to remove the PTFE sheet, thereby obtaining an MEA. In this MEA, the cathode side catalyst layer is the catalyst layer of the present invention, and the anode side catalyst layer is the platinum-supported carbon catalyst layer.

(Step 6)
The MEA obtained in (Step 5) is formed by the gas diffusion layers 4 and 5 made of carbon cloth with MPL (LT1400-W manufactured by E-TEK), the anode side electrode 6, the foamed metal 12 and the cathode side electrode 7 in FIG. A fuel cell single cell was formed by sandwiching in this order. Although not shown in FIG. 1, the periphery of the gas diffusion layers 4 and 5 is sealed with an O-ring 11.

(Comparative Example 1)
A single cell was produced in the same manner as in Example 1 except that the through hole forming step was not performed in (Step 1). The amount of Pt supported on the cathode side catalyst layer was 0.61 mg / cm ² .

  Scanning electron microscope of the cathode side catalyst layer surface of Example 1 after removing the PTFE sheet in (Step 5) (surface on the side facing the MPL: the same applies to the following Examples and Comparative Examples unless otherwise specified) The photographs are shown in FIGS. Further, scanning electron micrographs of the cathode side catalyst layer surface of Comparative Example 1 are shown in FIGS.

  As can be seen from these figures, in Comparative Example 1, the surface of the catalyst layer was formed from a relatively dense portion, and a large crack having a width of several μm was present in a mesh form between the catalyst layers.

  On the other hand, in Example 1, there were few big cracks, many through-holes were formed in the catalyst layer surface, and it was observed that it was more porous than Comparative Example 1. This is the difference in shape brought about by the etching step (step 1).

(Example 2)
In this example, a polymer electrolyte fuel cell having the structure shown in FIG. 1 was produced using the first embodiment of the present invention.

A single cell prepared in the same manner as in Example 1 was prepared except that the platinum oxide layer was formed to a thickness of 1 μm in the second film forming step in (Step 1). The amount of Pt supported on the cathode catalyst layer was 0.35 mg / cm ² .

(Comparative Example 2)
A single cell was produced in the same manner as in Example 2 except that the through hole forming step was not performed in (Step 1). The amount of Pt supported on the cathode catalyst layer was 0.31 mg / cm ² .

(Evaluation of Examples 1 and 2 and Comparative Examples 1 and 2)
As shown in FIG. 6, an electronic load device and a hydrogen gas pipe were connected to each single fuel cell produced by the above process, and the power generation characteristics of the fuel cell were evaluated. At that time, the anode electrode side was filled with hydrogen gas at a dead end of 0.2 MPa, and the cathode electrode side was opened to the air. The evaluation of power generation characteristics was performed at a battery temperature of 25 ° C. and a relative humidity of the external environment of 50%.

FIG. 7 shows the time change of the cell voltage when continuous power generation is performed at a current density of 400 mA / cm ² .

  In FIG. 7, when Example 1 and Comparative Example 1 are compared, the voltage of the single cell using the catalyst layer of Example 1 was still 0.62 V or more on average even after 30 minutes. In the single cell of Example 1, it was 0.56 V, which was about 60 mV lower than Example 1. Note that “average” means that the voltage is averaged by removing the influence of short-term voltage fluctuation (noise) in the measurement result.

The amount of Pt in Example 1 is 40 μg / cm ² greater than that in Comparative Example 1, but this difference is very small, so it is not considered to be a factor that gives a voltage difference of 60 mV.

  Further, when Example 2 and Comparative Example 2 were compared, the voltage of the single cell using the catalyst layer of Example 2 was still 0.58 V or more on average even after 30 minutes, whereas Comparative Example 2 In the single cell, the average voltage was 0.52 V, which was about 60 mV lower than Example 2.

  As a result, the fuel cells (single cells) of Examples 1 and 2 are much more excellent in output and output stability (power generation stability) than the fuel cells (single cells) of Comparative Examples 1 and 2. It shows that. The reason why such a result is obtained is that the cathode side catalyst layers of Examples 1 and 2 have through-holes, so that compared to the cathode side catalyst layers of Comparative Examples 1 and 2, the generated water dissipation is It is thought that it is excellent in drainage.

  Furthermore, when Example 2 and Comparative Example 1 are compared in FIG. 7, the catalyst layer of Example 2 has a Pt amount of about 60% as compared with the catalyst layer of Comparative Example 1, but it is more than that of Comparative Example 1. The high voltage could be maintained for a long time.

  This shows that the catalyst utilization efficiency is improved by the production method of the present invention, and a higher fuel cell output can be obtained with a smaller amount of Pt.

Next, FIG. 8 shows changes in cell voltage over time when continuous power generation is performed on the single cell of Example 1 and the single cell of Comparative Example 1 at a current density of 450 mA / cm ² .

  In FIG. 8, when Example 1 was compared with Comparative Example 1, the average voltage of the single cell using the catalyst layer of Example 1 was 0.52 V or more even after 1 hour (3600 seconds). On the other hand, the average value of the single cell of Comparative Example 1 was 0.46 V, which was about 60 mV lower than Example 1.

  Furthermore, in Comparative Example 1, the voltage decreased with the lapse of power generation time, whereas in the single cell of Example 1, the voltage did not decrease after 3000 seconds.

This is because when continuous power generation was performed at a current density of 450 mA / cm ² , the amount of generated water in the catalyst layer exceeded the amount of dissipation in Comparative Example 1, and the amount of retained water increased with the lapse of power generation time. On the other hand, in Example 1, since the generated water dissipation amount was larger than that in Comparative Example 1, it is considered that the accumulated water did not increase more than a certain level.

(Example 3)
In this example, a polymer electrolyte fuel cell having the configuration shown in FIG. 1 was produced using the second embodiment of the present invention.

(Process A)
A substantially linear unevenness having a depth of about 1 μm was formed on a PTFE sheet (manufactured by Nitto Denko, trade name Nittolon) by rubbing. The cloth (cloth) used for the rubbing treatment is a carbon cloth (LT1400-W, E-TEK Co.). Formed.

  Subsequent steps were the same as those in Example 1 (Step 1) and thereafter, and a single fuel cell was produced.

Example 4
A fuel cell single cell was prepared in the same manner as in Example 3 except that the plasma etching time was 8 minutes in (Step 1).

(Comparative Example 3)
A fuel cell single cell was produced in the same manner as in Example 3 except that the through hole forming step was not performed.

  9 and 10 show scanning electron micrographs of the cathode-side catalyst layer surface after the PTFE sheet of Example 3 was removed. Further, FIG. 11 shows a scanning electron micrograph of the surface of the cathode side catalyst layer after removing the PTFE sheet of Comparative Example 3.

  As can be seen from FIG. 9, in Example 3, a large number of substantially linear cracks having a width of several μm were formed in the catalyst layer together with the mesh cracks. Further, as can be seen from FIG. 10, in Example 3, the surface of the catalyst layer was formed with a large number of through holes in the same manner as in Example 1.

  On the other hand, as can be seen from FIG. 11, no streak crack was observed in Comparative Example 3, and only a mesh crack was formed. In Comparative Example 3, the surface of the catalyst layer was formed from a relatively dense portion as in Comparative Example 1.

  Since the shape of the unevenness imparted to the transfer sheet was substantially linear, the substantially linear crack observed in Example 3 is considered to be a crack (crack C) reflecting the uneven step. The other network cracks are considered to be cracks (crack A, crack B) formed by volume shrinkage due to reduction of the catalyst layer or swelling of the electrolyte membrane. From the comparison between FIG. 10 and FIG. 11, it is considered that the step of forming the through hole in the dense layer contributes to the formation of the crack C on the surface of the catalyst layer.

(Evaluation of Examples 3 and 4 and Comparative Example 3)
Similar to the evaluation of Example 1 and the like, the time change of the cell voltage of the single fuel cell of Example 3 and Example 4 when continuous power generation was performed at a current density of 400 mA / cm ² was compared with Example 1. FIG. 12 shows the results of the fuel cell single cells of Example 1 and Comparative Example 3 together with the results.

  When Example 3 and Comparative Examples 1 and 3 were compared, the single cell using the catalyst layer of Example 3 had an average voltage of 0.65 V or more after 30 minutes, whereas Comparative Example The voltages of the single cells 1 and 3 were both about 0.57 V and about 80 mV lower than Example 3.

  When Example 4 was compared with Comparative Examples 1 and 3, the voltage of the single cell using the catalyst layer of Example 4 was still 0.60 V or more after 30 minutes, whereas Comparative Example 1 The voltage of the single cells 3 and 3 was about 0.57 V, which was about 30 mV lower than Example 4.

  Further, comparing Example 3 and Example 1, the voltage after 30 minutes was 20 mV higher in Example 3 than in Example 1. Further, when compared with the maximum voltage, Example 3 was 0.7 V, which was 60 mV higher than 0.64 V which is the maximum voltage of Example 1.

  Furthermore, when Example 4 and Example 1 were compared by the maximum voltage, Example 4 was 0.67V, 30 mV higher than 0.64V which is the maximum voltage of Example 1.

  As a result, the fuel cells (single cells) of Example 3 and Example 4 are more excellent in output and output stability (power generation stability) than the fuel cell (single cell) of Example 1. It is shown that. The reason why such a result is obtained is that the cathode side catalyst layers of Example 3 and Example 4 have cracks C in addition to the through-holes. It is considered that the drainage is more excellent. In other words, by combining the process of forming irregularities on the transfer sheet and the process of forming through-holes in the dense layer of the catalyst layer, the water dissipation of the catalyst layer is greatly improved, and the fuel cell output and output stability are stabilized. Can be improved.

(Example 5)
In this example, a polymer electrolyte fuel cell having the configuration shown in FIG. 1 was produced using the second embodiment of the present invention.

(Process A)
A substantially linear unevenness was formed on a PTFE sheet (Nitto Denko, Nitoflon) as a transfer sheet by polishing treatment. As the polishing sheet used for the polishing treatment, an alumina polishing sheet (WA400-75FEZ-A, manufactured by Nihon Micro Coating Co., Ltd.) is used, and a rubber roll is pressed on the polishing sheet to polish the PTFE sheet in a certain direction. A substantially linear unevenness was formed. The applied pressure at this time was 2 kg / cm ² , the rubber roll hardness was 60 degrees, and the polishing sheet moving speed was 1400 mm / min. Ra of the PTFE sheet after the polishing treatment was 0.46 μm.

  Subsequent steps were the same as those in Example 1 (Step 1) and thereafter, and a single fuel cell was produced.

(Example 6)
A fuel cell single cell was produced in the same manner as in Example 5 except that the polishing sheet was changed to WA1000-75FEZ-A in Example 5. Ra of the PTFE sheet after the polishing treatment was 0.26 μm.

  FIG. 13 shows a scanning electron micrograph of the cathode side catalyst layer surface of Example 5 after removing the PTFE sheet. FIG. 14 shows a scanning electron micrograph of the cathode-side catalyst layer surface of Example 6 after the PTFE sheet was removed.

  As can be seen from FIG. 13, in Example 5, a large number of substantially linear cracks having a width of several μm were formed in the catalyst layer together with the mesh cracks. Although not clearly shown in the figure, a large number of through holes were formed on the surface of the catalyst layer of Example 5 as in Example 1.

  On the other hand, as can be seen from FIG. 14, substantially straight cracks were not seen on the surface of the catalyst layer of Example 6, and only mesh cracks were formed. Such a result shows that when the unevenness is imparted to the transfer sheet by the polishing treatment, the crack C is not formed unless Ra is 0.3 μm or more.

(Evaluation of Example 5 and Example 6)
Similar to the evaluation of Example 1 and the like, the time change of the cell voltage of the single fuel cell of Example 5 when continuous power generation is performed at a current density of 400 mA / cm ² is the same as the fuel of Example 6 and Example 1. It shows in FIG. 15 with the result of a battery single cell.

  Comparing Example 5 and Example 6, the single cell using the catalyst layer of Example 5 had an average voltage of 0.66 V or more even after 30 minutes, whereas Example 6 The voltage of the single cell was about 0.625 V, and Example 5 was about 35 mV higher than Example 6.

  Further, when compared with the maximum voltage, Example 5 was about 0.69 V, which was 30 mV higher than about 0.66 V which is the maximum voltage of Example 6. When Example 6 and Example 1 were compared, Example 6 and Example 1 became the same voltage after 30 minutes although Example 6 had a maximum voltage higher by about 20 mV than Example 1.

  That is, in this example, when the unevenness was imparted to the transfer sheet by the polishing treatment, the effect of the second embodiment was sufficiently obtained by setting Ra to 0.3 μm or more.

Next, the relationship between the weighted average D of the equivalent circle diameters of the catalyst grains of Examples 1 and 3 to 6 and the maximum voltage of the single fuel cell when continuous power generation is performed at a current density of 400 mA / cm ² is shown in FIG. Shown in

Similarly, FIG. 17 shows a fuel cell when continuous power generation is performed at a ratio σ / D of standard deviation σ and D of the equivalent circle diameter of catalyst grains of Examples 1 and 3 to 6 and a current density of 400 mA / cm ^2. The relationship with the maximum voltage of a single cell is shown.

Here, for the calculation of D and σ, image analysis software (A image-kun, manufactured by Asahi Kasei Corporation) was used. When observing with an electron microscope, an arbitrary place of the catalyst layer was photographed at a magnification of 500 times at four locations of 0.02 mm ^{2 and} subjected to particle analysis processing individually, and the perimeter of each catalyst grain S (n ) In addition, for catalyst grains in which only a part of the catalyst grains is slightly connected, it is considered that the crack is effectively cut off from the catalyst grains only when the minimum width of the connecting portion is 5 μm or less. The analysis process was carried out as a grain.

  16-17, it turns out that the maximum voltage of a single cell voltage tends to become large, so that D and (sigma) / D are small. In particular, in Examples 3 to 5 in which D <35 μm and σ / D <50%, it can be seen that the single cell voltage is significantly improved as compared with Examples 1 and 6.

  The reason why such a result is obtained is that the cathode side catalyst layers of Examples 3 to 5 have catalyst grains formed by forming cracks C in addition to the formation of through holes in the dense catalyst layer according to the first embodiment. It is considered that the material diffusibility is improved as compared with Examples 1 and 6 because the size and the variation thereof are small.

  That is, by combining the step of forming irregularities on the transfer sheet and the step of forming through holes in the dense layer of the catalyst layer, the generated water dissipation of the catalyst layer is greatly improved and the output of the fuel cell is improved. be able to.

(Example 7)
This example is an example in which the membrane electrode assembly 8 illustrated in FIG. 1 was produced using the second embodiment of the present invention.

(Process A)
By a photolithography process and a dry etching process, a concavo-convex pattern having three types of regular shapes such as a line shape, a dot shape, and a hole shape as shown in FIGS. 18 to 20 was formed on the Si substrate. Here, the space between the concave and convex portions was 10 μm, and the minimum width of the convex portion was also 10 μm. The uneven height difference was 2 μm.

  Next, using CYTOP (trade name, manufactured by Asahi Glass Co., Ltd.), a fluororesin film (thickness of 0.1 μm or less) as a release layer was formed on the Si substrate.

  A Si substrate having this release layer was used as a transfer sheet, and the subsequent steps were the same as those in Example 1 (Step 1) to (Step 5), and a membrane electrode assembly was produced.

(Example 8)
A membrane / electrode assembly was produced in the same manner as in Example 7 except that the uneven space interval was 50 μm and the minimum width of the convex portion was 50 μm.

Example 9
A membrane / electrode assembly was produced in the same manner as in Example 8 except that the unevenness height difference was 10 μm.

(Example 10)
A membrane / electrode assembly was produced in the same manner as in Example 7 except that the uneven spacing was 5 μm and the minimum width of the convex portion was 5 μm.

(Example 11)
A membrane / electrode assembly was fabricated in the same manner as in Example 7 except that the uneven space interval was 1 μm and the minimum width of the convex portion was 1 μm.

(Example 12)
A membrane / electrode assembly was produced in the same manner as in Example 9 except that the uneven space interval was 5 μm and the minimum width of the convex portion was also 5 μm.

(Example 13)
A membrane / electrode assembly was fabricated in the same manner as in Example 9 except that the uneven space interval was 1 μm and the minimum width of the protrusion was 1 μm.

(Example 14)
A membrane / electrode assembly was produced in the same manner as in Example 7 except that the unevenness height difference was 10 μm.

  Tables 1 and 2 show the uneven shape conditions of Examples 7 to 14 and the results of the presence or absence of a catalyst layer remaining on the Si substrate after the transfer step.

  As can be seen from these tables, in Examples 7 to 9, almost no catalyst layer remained on the Si substrate after the transfer step except in the case of the hole shape.

  On the other hand, in the case of the hole-shaped uneven shape of Example 7 and Examples 10 to 14, in the transfer process, the catalyst layer in the recess was hardly transferred, and many catalysts were formed in the recess in the Si substrate after the transfer process. The layer remained.

  These results show that when the concave / convex depth of the Si substrate is 2 μm, and the concave / convex shape is a line or a dot, if the space interval is larger than 5 μm, along with the catalyst layer on the convex portion, almost all the concave portions This shows that the catalyst layer is transferred to the electrolyte membrane.

  These results also indicate that, when the uneven depth is 10 μm, if the space interval is larger than 10 μm, the catalyst layer on the convex portion and the catalyst layer on the concave portion are transferred to the electrolyte membrane regardless of the uneven shape.

  21 and 22 show the surface of the cathode catalyst layer after removing the release sheet of each membrane electrode assembly obtained in Examples 7 and 8 (uneven shape = line shape) (surface on the side facing the MPL). ) Shows a scanning electron micrograph.

  As can be seen from these figures, in these catalyst layers, white lines were observed at locations corresponding to the uneven step positions. This was observed in common with other uneven shapes.

  FIG. 23 is an enlarged view of a portion that appears as a white line when the uneven shape is a dot shape in the eighth embodiment. As can be seen from FIG. 23, the portions shown as white lines in FIGS. 21 and 22 were cracks reflecting uneven steps. This was common even in the case of other uneven shapes.

  That is, in all cases where the catalyst layer was transferred to the concave portion, cracks C were formed in the catalyst layer at the uneven step portion.

  As can be seen from FIGS. 21 and 22, only cracks C were observed under such uneven dimension conditions, and cracks A and B other than that were hardly observed. This is considered to indicate that the cracks A and B are hardly formed because the stress relaxation of the catalyst layer occurs due to the crack C when the interval between the cracks C is 50 μm or less.

(Example 15)
A single cell was prepared in the same manner as in Example 1 except that the plasma etching time was set to 1 minute in (Step 1). The platinum oxide remaining on the sheet after forming the through-hole was 84 μg / cm ² per substrate area.

(Example 16)
A single cell was prepared in the same manner as in Example 1 except that the plasma etching time was 3 minutes in (Step 1). The platinum oxide remaining on the sheet after forming the through-hole was 75 μg / cm ² per substrate area.

(Example 17)
A single cell prepared in the same manner as in Example 1 was prepared except that the plasma etching time was 8 minutes in (Step 1). The platinum oxide remaining on the sheet after forming the through-hole was 52 μg / cm ² per substrate area.

(Example 18)
A single cell was prepared in the same manner as in Example 1 except that the total pressure in the first film formation step was 3 Pa and the plasma etching time in the through hole formation step was 8 minutes in (Step 1). did. The platinum oxide remaining on the sheet after forming the through hole was 56 μg / cm ² per substrate area.

(Example 19)
A single cell produced in the same manner as in Example 1 except that the total pressure in the first film formation step was 8 Pa and the plasma etching time in the through-hole formation step was 8 minutes in (Step 1). did. The platinum oxide remaining on the sheet after forming the through holes was 40 μg / cm ² per substrate area.

(Evaluation of Examples 15 to 19)
As shown in FIG. 6, an electronic load device and a hydrogen gas pipe were connected to each single fuel cell produced by the above process, and the power generation characteristics of the fuel cell were evaluated. At that time, the anode electrode side was filled with hydrogen gas at a dead end of 0.2 MPa, and the cathode electrode side was opened to the air. The evaluation of power generation characteristics was performed at a battery temperature of 25 ° C. and a relative humidity of the external environment of 100%.

The test method is the open circuit voltage (OCV) to a current density of 1A / cm ^2, and sweep to 0V at 1mA ^/ cm 2 ^/ sec after the sweep in the current sweep rate 0.1mA ^/ cm 2 ^/ sec, the The voltage-current density characteristics of the cell were evaluated.

  Under this condition, since the anode side is a dead end, water evaporation from the anode side does not occur. Furthermore, since the air humidity on the cathode side is 100% RH, the amount of water evaporation from the cathode side is also small. That is, under this condition, moisture movement outside the cell is suppressed, so flooding at the cathode tends to occur. Furthermore, since the current value sweep plate at the time of measurement is small, the power generation time at the time of measurement is increased and a lot of water is generated, so that the fuel cell is likely to be flooded at a high current density. By comparing the membrane electrode assemblies of each Example and Comparative Example under conditions where flooding is likely to occur in this way, the magnitude of material diffusibility in the cathode catalyst layer of each membrane electrode assembly can be evaluated. It becomes easier to judge the effect.

  The results of the voltage-current density characteristics of the fuel cell single cells of Examples 15 to 17 are shown in FIG. 24 together with the results of the fuel cell single cells of Example 1 and Comparative Example 1. Moreover, the result of the voltage-current density characteristic of the fuel cell single cell of Examples 18 and 19 is shown in FIG.

24 and as can be seen from 25, with respect to the output current density was Comparative Example 1 about 410mA / cm ² at 0.4V, Example 1 and Examples 15 to 17 In about 440 mA / cm ² or more Yes, 20 mA / cm ² or more. Especially Example 17 In 490mA / cm ² and 70 mA / cm ² was high.

The current density of Example 19 was 450 mA / cm ^2, which was larger than that of Comparative Example 1, but smaller than those of Examples 1 and 18 despite the same etching time. This is presumably because, in Example 19, the dense layer was thin, and in the etching for 8 minutes, the Pt oxide remaining on the sheet after the formation of the through hole was too small. That is, in Example 19, the Pt oxide after the through hole forming step was less than 50 μg / cm ² , so that a dense layer was formed again in the subsequent second film forming step, and the through hole opening was larger than in Examples 11 and 12. It is presumed that the output current density has decreased with the decrease in the rate.

  FIG. 26 shows a correlation diagram between the through hole opening ratio in the cathode catalyst layer and the output current density at 0.4 V in the membrane electrode assemblies of Example 1, Comparative Example 1, and Examples 15 to 19. From this figure, it can be seen that the output current density is greatly improved when the aperture ratio in the surface opposite to the solid polymer electrolyte membrane of the through hole in the region surrounded by macro cracks is in the range of 8% to 40%. From this figure, it can be seen that the output current density rapidly decreases at 8% or less, and is almost saturated at 30% or more.

  FIG. 27 shows a scanning electron micrograph of the catalyst layer cross section of Example 17 and FIG. 28 of Comparative Example 1. Here, the beam incident angle during FIB processing was set to 28 ° with respect to the main plane of the catalyst layer.

  A line (width 7 nm) parallel to the main plane of the first layer 13 is drawn in the first layer 13 in FIGS. 27 and 28, and black pixels on this line occupy all the pixels on the line. The percentage was calculated as the porosity of the first layer.

  In addition, when drawing a line, it was made to pass near the film thickness direction center of a 1st layer. This is because in the observation sample, the first layer is not a perfect flat plate shape, and the boundary between the first layer and the other is not a straight line. This is because there is a possibility that the line cannot pass through the portion that is not the first layer and the accurate porosity cannot be calculated.

  The porosity of the first layer in the catalyst layer of Example 17 (FIG. 27) is 43%, which is 10% higher than the porosity (33%) of the first layer in Comparative Example 1 (FIG. 28). It was. When considered together with the result of FIG. 26, it can be seen that the first layer in Example 17 has higher through-hole opening ratio and porosity than in Comparative Example 1. Due to the structure of this first layer, the catalyst layer of Example 17 is estimated to have higher gas diffusibility and generated water dissipation than the catalyst layer of Comparative Example 1, and as a result, it can output a high current density.

  In the second layer 14 shown in FIGS. 27 and 28, there may be a region where the porosity seems to be lower than that of the first layer 13. In this region, the ink added during sample preparation is filled. It may not be sufficient, so it is not accurate information and can therefore be ignored here.

It is an example of the schematic diagram showing the cross-sectional structure of the single cell of a polymer electrolyte fuel cell. 2 is a scanning electron micrograph (magnification 1000 times) showing the catalyst layer surface of Example 1. FIG. 2 is a scanning electron micrograph (magnification 60,000 times) showing the surface of the catalyst layer of Example 1. FIG. 2 is a scanning electron micrograph (magnification 1000 times) showing the surface of a catalyst layer of Comparative Example 1. 2 is a scanning electron micrograph (magnification 60,000 times) showing the surface of a catalyst layer of Comparative Example 1. It is a schematic diagram of the evaluation apparatus of a polymer electrolyte fuel cell. It is a figure which shows the time change of the voltage in the output current density of 400 mA / cm < ² > of the polymer electrolyte fuel cell of Example 1, 2 and Comparative Example 1,2. It is a figure which shows the time change of the voltage in the output current density of 450 mA / cm < ² > of the polymer electrolyte fuel cell of Example 1 and Comparative Example 1. FIG. 4 is a scanning electron micrograph (magnification 1000 times) showing the catalyst layer surface of Example 3. FIG. 4 is a scanning electron micrograph (magnification of 30,000 times) showing the surface of a catalyst layer of Example 3. FIG. 4 is a scanning electron micrograph (magnification 1000 times) showing the surface of a catalyst layer of Comparative Example 3. It is a figure which shows the time change of the voltage in the output current density of 400 mA / cm < ² > of the polymer electrolyte fuel cell of Example 3 and Comparative Examples 1 and 3. FIG. 6 is a scanning electron micrograph (magnification 500 times) showing the surface of a catalyst layer of Example 5. FIG. 6 is a scanning electron micrograph (magnification 500 times) showing the surface of a catalyst layer of Example 6. FIG. It is a figure which shows the time change of the voltage in the output current density of 400 mA / cm < ² > of the polymer electrolyte fuel cell of Example 5 and Example 6. FIG. It is a figure which shows the relationship between the weighted average value of the circle equivalent diameter of a catalyst grain, and the maximum output voltage of a fuel cell. It is a figure which shows the relationship between the ratio ((sigma) / D) of the weighted average value of a circle equivalent diameter of a catalyst grain, and a standard deviation, and the highest output voltage of a fuel cell. It is a schematic diagram which shows the uneven | corrugated shape provided on Si substrate in Example 7. FIG. It is a schematic diagram which shows the uneven | corrugated shape provided on Si substrate in Example 7. FIG. It is a schematic diagram which shows the uneven | corrugated shape provided on Si substrate in Example 7. FIG. 6 is a view showing the surface of a cathode side catalyst layer of a membrane electrode assembly of Example 7. FIG. (1000x magnification) 6 is a view showing the surface of a cathode side catalyst layer of a membrane electrode assembly in Example 8. FIG. (1000x magnification) It is a figure (magnification 30,000 times, tilt angle 15 degrees) which shows the enlarged image of the catalyst layer of Example 8. 6 is a graph showing voltage-current density characteristics of fuel cells of Example 1, Examples 15 to 17, and Comparative Example 1. FIG. It is a figure which shows the voltage-current density characteristic of the fuel battery cell of Example 18 and Example 19. It is a figure which shows the correlation of the through-hole opening rate in the cathode catalyst layer of the membrane electrode assembly of Example 1, Comparative Example 1, and Examples 15 thru | or 19, and the output current density in 0.4V. 10 is a scanning electron microscope (magnification: 35,000 times) showing a cross section of the catalyst layer of Example 17. 3 is a scanning electron microscope (magnification 35,000 times) showing a cross section of a catalyst layer of Comparative Example 1. FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Solid polymer electrolyte membrane 2 Anode side catalyst layer 3 Cathode side catalyst layer 4 Anode side gas diffusion layer 5 Cathode side gas diffusion layer 6 Anode side electrode 7 Cathode side electrode 8 MEA (membrane electrode assembly)
9 MPL
DESCRIPTION OF SYMBOLS 10 Gas diffusion base material 11 O ring seal 12 Foam metal 13 1st layer 14 2nd layer

Claims (8)

In the method for producing a membrane electrode assembly having a catalyst layer on both sides of a solid polymer electrolyte membrane,
A first film forming step of forming a first layer comprising a catalyst or a catalyst precursor on the surface of the sheet by a vapor phase film forming method;
Forming a through hole in the first layer;
A second film forming step of forming a second layer made of a catalyst or a catalyst precursor on the surface of the first layer in which the through holes are formed by a vapor phase film forming method;
Bonding a solid polymer electrolyte membrane to the surface of the second layer;
Peeling the sheet from the first layer;
A method for producing a membrane electrode assembly, comprising:   The step of forming a through hole in the first layer is a step of forming a through hole so that an opening ratio of a surface of the first layer in contact with the sheet is 8% or more and 40% or less. The manufacturing method of the membrane electrode assembly of Claim 1.   The step of forming a through hole in the first layer is a step of forming the through hole so that the catalyst or catalyst precursor in the first layer remains after 50 μg or more per 1 cm 2 of the surface area of the sheet after the through hole is formed. The method for producing a membrane electrode assembly according to claim 1, wherein the membrane electrode assembly is provided.   The method according to claim 1, further comprising a step of providing unevenness on the surface of the sheet before the first film forming step, and forming the first layer on the surface provided with the unevenness. The manufacturing method of the membrane electrode assembly in any one.   The method for producing a membrane electrode assembly according to claim 4, wherein the step of providing irregularities on the surface of the sheet is a step of providing streaky irregularities on the surface of the sheet. 6. The method for producing a membrane / electrode assembly according to claim 5, wherein the step of providing streaky irregularities on the surface of the sheet is a rubbing treatment or a polishing treatment. The step of bonding a solid polymer electrolyte membrane to the surface of the second layer includes at least a second layer formed on the concave / convex convex portion and a second layer formed on the concave / convex concave portion. The method for producing a membrane electrode assembly according to any one of claims 4 to 6, wherein a part of the membrane electrode assembly is a step of joining both to the solid polymer electrolyte membrane.   The method of manufacturing a membrane electrode assembly according to claim 1, wherein the through hole is formed by dry etching.

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