JP2008234941A - Manufacturing method of porous catalyst layer, manufacturing method of membrane-electrode assembly, and manufacturing method of polymer electrolyte fuel cell - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a manufacturing method of a porous catalyst layer capable of forming pores in a self-organization manner without causing loss of a catalyst. <P>SOLUTION: This manufacturing method of a porous catalyst layer for a polymer electrolyte fuel cell includes a process of reducing the oxide of a catalyst material with any of phosphine, ammonia, hydrogen sulfide, SO<SB>2</SB>and HCHO. Platinum oxide is reduced in the reduction reaction. In the reduction reaction, platinum oxide is immersed in a phosphine acid aqueous solution, and heated to a value above a temperature at which phosphine acid is thermally decomposed to produce phosphine. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a method for producing a porous catalyst layer of a polymer electrolyte fuel cell, a method for producing a membrane electrode assembly using the method for producing a porous catalyst layer, and a method for producing a polymer electrolyte fuel cell. .

  The polymer electrolyte fuel cell is expected as a future energy generation device in applications such as automobiles and household generators because of its high energy conversion efficiency, cleanliness, and quietness.

  In recent years, polymer electrolyte fuel cells have high energy density and low operating temperature, so it is possible to drive small electric devices such as mobile phones, notebook computers, and digital cameras for a long time compared to conventional secondary batteries. There is sex and attracts attention.

However, although the polymer electrolyte fuel cell can be driven even at an operating temperature of 100 ° C. or lower, there is a problem that the voltage gradually decreases with the lapse of the power generation time and the power generation stops at the end.
This is because the water generated by the reaction stays in the gap of the catalyst layer, and the power generation reaction stops by blocking the gap in the catalyst layer and preventing the supply of the fuel gas as the reactant. "Phenomenon" is the cause. In particular, flooding is likely to occur in the catalyst layer on the cathode side where water is generated.

  Also, for practical use as a fuel cell for small electrical equipment, it is essential to make the entire system compact. In particular, when the fuel cell is mounted on a small electric device, the cell itself needs to be downsized, and air is supplied from the vent hole to the air electrode by natural diffusion without using a pump or a blower (Air Breathing). Many are taken. In such a case, the produced water is discharged out of the fuel cell only by natural evaporation, so that the produced water is often retained in the catalyst layer and flooding often occurs. For this reason, improving the dispersibility of the generated water in the catalyst layer is an important factor that affects the performance stability of the fuel cell.

  For this reason, generally known is a method of increasing the hydrophobicity of the catalyst layer by mixing fluororesin fine particle powder such as polytetrafluoroethylene (PTFE) as a hydrophobic agent in the catalyst layer together with a solvent and a surfactant.

  Further, in order to improve the dispersibility of the generated water, the catalyst layer has a hydrophobic concentration distribution in the thickness direction of the catalyst layer (Patent Document 1), or the catalyst support particle has a particle size distribution in the thickness direction of the catalyst layer ( Patent Document 2) discloses a method.

  However, in a fuel cell or a stack type fuel cell in which a membrane-electrode assembly (MEA) is sandwiched by a separator having a gas flow groove, the diffusion distance of water vapor from the outside of the cell differs depending on each position in the electrode surface. Therefore, it is known that a water vapor partial pressure distribution is generated in the plane of the catalyst layer.

  In this case, when the fuel cell is driven at a high load for a long time, the difference in the water vapor partial pressure distribution in the catalyst layer surface becomes large, and a portion locally close to the saturated water vapor pressure is formed. As a result, water vapor generated by power generation condenses inside the pores of the catalyst layer and closes the pores, and local flooding occurs in the catalyst layer.

  In order to avoid such a local flooding condition, when the humidity of the supply gas is lowered, a region where the humidity is too low (local dryout region) is created in the catalyst layer surface, contrary to the above case. Thus, there is a problem that the proton resistance of the solid polymer electrolyte in that region increases, and the battery performance decreases.

  Thus, in order to prevent the nonuniformity of the moisture distribution in the catalyst layer surface, in the method of changing the composition of the catalyst layer described in Patent Documents 1 and 2 in the film thickness direction, the composition is in the in-plane direction of the catalyst layer. Due to the constant, the condensed water does not diffuse efficiently in the in-plane direction of the catalyst layer, which is insufficient.

  Therefore, a method of providing a groove for drainage on the surface of the catalyst layer in contact with the gas diffusion layer (Patent Documents 3 and 4), a method of unevenly imparting hydrophobicity in the catalyst layer surface (Patent Document 5), A method of providing a catalyst layer non-formation region is proposed (Patent Document 6).

According to these methods, even if a difference in moisture distribution occurs in the catalyst layer surface, an effect of spontaneously making the moisture distribution constant in the catalyst layer surface by natural diffusion can be obtained.
Japanese Patent No. 3245929 JP-A-1996-162123 JP 2004-327358 A JP 2005-38780 A JP 2004-171847 A JP 2004-039474 A

  However, in any of the methods conventionally used as described above, since the catalyst layer is composed of catalyst particles or catalyst-supported particles, the main supply path of the reaction gas is randomly connected by voids between the particles. It is formed in the shape of a ant nest that is branched and connected.

  Therefore, the diffusion distance with respect to the film thickness direction of the reaction gas is longer than the thickness of the catalyst layer. For this reason, there existed a problem that the diffusion time of reaction gas and produced | generated water vapor | steam was long and the output of a fuel cell was restrained low.

Further, each of the above prior arts has the following problems.
That is, in the method of providing drainage grooves on the surface of the catalyst layer in contact with the gas diffusion layer described in Patent Documents 3 and 4 (Patent Documents 3 and 4), the grooves do not reach the interface between the catalyst layer and the electrolyte membrane. In the catalyst layer in the vicinity of the electrolyte membrane, there is a problem that the in-plane moisture distribution is difficult to be made uniform.

  Furthermore, in the method in which the hydrophobicity-providing portion described in Patent Document 5 is unevenly distributed in the catalyst layer surface, there is an effect of preventing local flooding, but the movement of water depends on the difference in the degree of hydrophilicity / hydrophobicity in the catalyst layer. Therefore, when local dryout occurs in a highly hydrophobic region, there is a problem that moisture does not move there and the dryout cannot be eliminated.

  Moreover, in the method of providing the catalyst layer non-formation region in the catalyst layer described in Patent Document 6, the catalyst layer non-formation region is formed in order to press the uneven mold from above the transfer film when the catalyst is thermally transferred to the electrolyte membrane. Therefore, there is a problem that a loss of the catalyst layer is inevitably generated and extra cost is required.

  Furthermore, in principle, a catalyst non-formation region and a catalyst formation region that are smaller than twice the thickness of the transfer film and the sum of the mold protrusions cannot be formed separately. Since the thickness of the transfer film is required to be at least 10 μm due to handling problems, a pattern smaller than 20 μm cannot be formed in principle by this method. For this reason, there is a case where the distance that surplus water reaches to the non-catalyst formation region is long, and there is a problem that the moisture distribution in the catalyst layer surface is difficult to be made uniform.

The prior art has the above-described problems, and a technique has been demanded in which the gas diffusion time of the catalyst layer is short and the moisture distribution in the catalyst layer surface can be made uniform quickly.

The present invention also provides a method for producing the above porous catalyst layer that can form pores in a self-organized manner without loss of the catalyst.
The present invention also provides a membrane electrode assembly and a polymer electrolyte fuel cell having stable power generation characteristics at a low cost.

A method for producing a porous catalyst layer that solves the above problems is a method for producing a porous catalyst layer for a polymer electrolyte fuel cell, wherein the oxide of the catalyst material is phosphine, ammonia, hydrogen sulfide, SO ₂ , It includes the step of reducing with any of HCHO.

In the reduction reaction, it is preferable that platinum oxide is immersed in an aqueous phosphinic acid solution and heated to a temperature at which the phosphinic acid is thermally decomposed to produce phosphine.
When using ammonia, hydrogen sulfide, SO ₂ , or HCHO, it is preferable to directly expose platinum oxide to a gas or a dilution gas.

  A method for producing a membrane / electrode assembly that solves the above problems includes a step of forming a solid polymer electrolyte membrane, an electrode, and a porous catalyst layer between the solid polymer electrolyte membrane and the electrode by the method described above. It is characterized by having.

  A method for producing a polymer electrolyte fuel cell that solves the above-described problems includes a step of forming a membrane electrode assembly by the above-described method.

The present invention provides a method for producing a porous catalyst layer capable of forming pores in a self-organized manner without loss of the catalyst.
In addition, the present invention can provide a membrane electrode assembly and a polymer electrolyte fuel cell having stable power generation characteristics at a low cost.

Hereinafter, the present invention will be described in detail.
Hereinafter, an embodiment of the porous catalyst layer of the present invention will be described with reference to the drawings. However, the materials, dimensions, shapes, arrangements, and the like described in this embodiment do not limit the scope of the present invention unless otherwise specified. The manufacturing method described below is also the same.

  FIG. 1 is a schematic diagram showing an example of a cross-sectional configuration of a single cell of a polymer electrolyte fuel cell using the porous catalyst layer of 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 porous catalyst layer 3 are arranged therebetween.

  In this embodiment, an example in which the porous catalyst layer of the present invention is disposed only on the cathode (air electrode) side is shown, but the arrangement configuration of the catalyst layer is not limited thereto. For example, the porous catalyst layer of the present invention may be disposed on both electrodes or only on the anode side.

  The cathode side catalyst layer is composed of a porous catalyst layer 3 having substantially columnar pores, and is composed of a porous catalyst 4 and a catalyst carrier 5 that supports the porous catalyst layer 4. A cathode side gas diffusion layer 7 and a cathode side electrode (air electrode) 9 are arranged outside the catalyst layer 3 on the cathode side.

  The anode-side catalyst layer 2 is composed of a catalyst 11 and a catalyst carrier 5, and an anode-side gas diffusion layer 6 and an anode-side electrode (fuel electrode) 8 are disposed on the outside thereof.

  The solid polymer electrolyte membrane 1 is formed of a polymer material such as a perfluorocarbon polymer having a sulfonic acid group or a non-fluorine polymer. For example, a sulfonic acid type perfluorocarbon polymer, a polysulfone resin, a phosphonic acid group or a carboxyl group is used. A perfluorocarbon polymer having an acid group can be preferably used.

  An example of a perfluorosulfonic acid polymer is Nafion (manufactured by DuPont) 112. Examples of non-fluorine polymers include sulfonated directional group polyether ketones and aromatic polysulfones.

When proton H ⁺ moves through the electrolyte membrane toward the cathode, the hydrophilic portion of the electrolyte moves using water molecules as a medium, and therefore the electrolyte membrane must also have a function of retaining water molecules. I must. Therefore, the function of the solid polymer electrolyte membrane is to transmit proton H ⁺ generated on the anode side to the cathode side and not to pass unreacted reaction gases (hydrogen and oxygen) and to have a predetermined water retention function. is necessary. Any one satisfying this condition can be selected and used.

  The gas diffusion layers 6 and 7 supply the fuel gas or air uniformly and sufficiently in the plane to the electrode reaction region in the catalyst layer of the fuel electrode or the air electrode in order to perform the electrode reaction efficiently, and the anode The charge generated by the electrode reaction is released to the outside of the single cell, and the reaction product water and unreacted gas are efficiently discharged to the outside of the single cell.

As the gas diffusion layer, a porous body having electron conductivity such as carbon cloth or carbon paper can be preferably used.
The role of the catalyst carrier 5 includes improving the catalytic activity as a co-catalyst, maintaining the shape of the porous catalyst 4 or the catalyst 11, ensuring the electron conduction channel, increasing the specific surface area, etc., for example, carbon black, platinum fine particle layer or gold fine particle A layer can be preferably used. Note that the catalyst carrier 5 does not necessarily have to be provided in the single fuel cell according to the present invention.

The porous catalyst 4 and the catalyst 11 are porous. As a method for forming the porous catalyst 4, platinum oxide is used as a strong reducing gas, specifically, phosphine, ammonia ammonia, hydrogen sulfide, SO ₂ , HCHO. It is preferable to use and reduce.

  The porous catalyst 4 and the catalyst 11 are made of a solid polymer electrolyte, a hydrophobic agent, and a catalyst material. As the solid polymer electrolyte contained in the porous catalyst 4 and the catalyst 11, it is preferable to use the same material as that of the solid polymer electrolyte membrane 1. As the hydrophobic agent, a fluororesin such as polytetrafluoroethylene (PTFE) or an alkylsiloxane resin such as methylsiloxane can be preferably used.

  As a method for adding the hydrophobic agent, a known hydrophobizing method in which the porous catalyst 4 and the catalyst 11 are impregnated in a fluororesin solution can be used. However, in particular, in order to add a hydrophobic agent to the porous catalyst 4, it is particularly preferable to use a known technique described in JP-A-2006-332041. In this method, a Si compound having a hydrophobic substituent that generates a polymerizable group by causing a hydrolysis reaction by the catalytic action of the platinum oxide is brought into contact with the platinum oxide, and then the Si compound is adjacent to the platinum oxide. In this method, a hydrophobic agent is generated on the surface of the platinum oxide by the polymerization reaction, and then the platinum oxide is reduced. According to this method, a hydrophobic agent made of methylsiloxane or the like can be easily added to the pores of the porous catalyst 4.

  As the catalyst material, platinum, a multielement metal containing platinum, a mixture of platinum and an oxide of a metal element other than platinum, or a mixture of a multielement metal containing platinum and an oxide of a metal element other than platinum is used.

  The metal elements other than platinum are Al, Si, Ti, V, Cr, Fe, Co, Ni, Cu, Zn, Ge, Zr, Nb, Mo, Ru, Rh, Pd, Ag, In, Sn, Hf, At least one metal element selected from Ta, W, Os, Ir, Au, La, Ce, and Nd.

  The pore shape in the porous catalyst layer 4 is substantially columnar, and two types of pores are formed: a small pore having a pore diameter of 0.03 μm to 1 μm and a large pore having a pore diameter of 2 μm to 10 μm. Has been. With this structure, the diffusion time of the reaction gas in the catalyst layer is short, and the moisture distribution in the catalyst layer surface can be made uniform quickly.

  In general, the pore diameter measurement method includes Hg injection method, image analysis from SEM image, etc., but Hg injection method requires a relatively large amount of sample and is not suitable for the catalyst layer of the present invention. Since measurement is difficult, a method based on image analysis from an SEM image is preferable.

  FIG. 2 is a schematic diagram showing an example of a pore structure of the porous catalyst 4 in the porous catalyst layer of the present invention. In FIG. 2, the pore shape of the porous catalyst 4 is of two types, a substantially columnar small hole 12 and a substantially columnar large hole 13 that extend in the film thickness direction of the catalyst layer.

  In the present specification, “substantially columnar holes” means a shape in which one continuous hole does not branch in the film thickness direction of the catalyst layer and continues from the upper end to the lower end of the catalyst layer in the film thickness direction. Means vacancies. The pore diameter may vary from the upper end to the lower end, and the pores may extend in a direction perpendicular to, substantially perpendicular to, or inclined from the surface of the catalyst layer.

  4 to 6 show SEM images of the porous catalyst layer. From these figures, the small pores 12 have a pore diameter ranging from 0.03 μm to 1 μm, and the large pores 13 have a pore diameter of 1 μm to 10 μm. Range. The large holes 13 may be continuous in a groove shape, in which case the minimum value of the width of the series of grooves is 1 μm or more and 10 μm or less.

Moreover, the distance (for example, A in FIG. 2) from the small hole 12 to the large hole 13 is as short as 10 μm or less.
Due to the pore structure and the effect of the hydrophobic agent contained in the catalyst layer, the water generated on the small pore 12 side in the catalyst layer is promptly guided to the large pore 13 by the capillary force, and the water is absorbed in the small pore. It is prevented that the gas supply path stays and is blocked.

  In addition, even when a surplus or deficiency of water locally occurs in the catalyst layer, the water moves through the large holes 13 having a small movement resistance, and moisture is distributed autonomously and quickly within the catalyst layer surface. Therefore, the moisture distribution in the catalyst layer surface is quickly made uniform.

  As a method for forming the pore structure of the porous catalyst 4, it is preferable to use a reduction reaction of platinum oxide. At this time, the platinum oxide is preferably reduced with a strong reducing gas such as phosphine or ammonia. The platinum oxide immersed in the phosphinic acid aqueous solution is heated to a temperature equal to or higher than the temperature at which the phosphinic acid is thermally decomposed to form phosphine, preferably 200. It is particularly preferable to heat at a temperature of from ℃.

If the temperature is lower than 200 ° C., the decomposition of phosphinic acid does not occur. If the temperature exceeds 250 ° C., the catalyst particles such as platinum nanoparticles generated by reduction in the catalyst layer grow and the catalytic activity decreases.
By reducing platinum oxide with phosphine at about 200 ° C., a large volume shrinkage occurs, and a pore structure as shown in FIG. 2 is formed in a self-organizing manner. For this reason, unlike the technique of removing the groove portion after forming the catalyst layer once as in the prior art, the catalyst loss and the number of manufacturing steps are small, and the manufacturing cost can be suppressed.

In addition to the method using the above sodium phosphonate solution, the following method can also be used as a method for reducing platinum oxide.
(1) A method in which the generation reaction of phosphine (PH ₃ ) is carried out by the reaction shown in the following reaction formula (1).

(2) A method using a reducing agent other than phosphine, for example, a method using ammonia.
Various methods can be used as the method for producing the porous catalyst layer of the present invention, and the case where phosphine is used as a reducing agent in the configuration shown in FIG. 1 will be described as an example. . In addition, this invention is not limited to the following manufacturing method at all.

(1) A catalyst layer on the cathode side is prepared.
A porous platinum oxide catalyst layer is formed on a PTFE (polytetrafluoroethylene) sheet as a transfer layer to the solid polymer electrolyte membrane by reactive sputtering.
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. Thereafter, the polymerization reaction of the hydrophobic agent may be promoted by heating.

(2) The catalyst layer is reduced.
An appropriate amount of an aqueous solution of sodium phosphinate of 0.3% by mass to 2.0% by mass is collected with a micropipette and dropped onto the catalyst layer obtained in (1). Subsequently, this is placed in a furnace heated to 200 ° C. in a nitrogen atmosphere, phosphine is generated on the catalyst by thermal decomposition of phosphinic acid, platinum oxide is reduced, and a porous catalyst layer is obtained.

  Here, since the generated phosphine reacts with oxygen in the atmosphere and ignites, for safety reasons, it is preferable to maintain the inside of the furnace in an inert atmosphere during the heat treatment, and exhaust the exhaust after sufficiently diluting with nitrogen or the like. .

  Thereafter, an appropriate amount of Nafion solution (5 wt%, manufactured by Wako Pure Chemical Industries) is dropped on the obtained catalyst layer, and then the solvent is volatilized in a vacuum to form an electrolyte channel on the catalyst surface.

(4) A catalyst layer on the anode side is prepared.
A platinum-supporting carbon catalyst layer or a platinum black catalyst layer is formed on the PTFE sheet using a doctor blade. The thickness of the catalyst layer is preferably in the range of 20 μm to 40 μm. The catalyst slurry used here is a mixture of platinum-supported carbon (manufactured by Johnson Matthey, HiSPEC 4000) or platinum black (manufactured by Johnson Matthey, HiSPEC 1000), Nafion, PTFE, IPA (isopropyl alcohol), and water.

  (4) Hot pressing is performed by sandwiching a solid polymer electrolyte membrane (manufactured by Dupont, Nafion 112) with the pair of catalyst layers produced as described above so that the PTFE sheet faces outside. Further, by peeling the PTFE sheet, the pair of catalyst layers are transferred to the solid polymer electrolyte membrane, and the electrolyte membrane and the pair of catalyst layers are joined to obtain a membrane-electrode assembly (MEA).

(5) A single cell is manufactured by sandwiching the MEA with a carbon cloth (manufactured by E-TEK, LT1400-W) as a gas diffusion layer, and a fuel electrode and an air electrode.
The method for producing a catalyst layer of the present invention is not limited to the solid polymer type fuel cell having a single cell configuration, but can be applied to a solid polymer type fuel cell having a configuration in which a plurality of single cells are stacked.

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 configuration shown in FIG. 1 in the embodiment was produced.

Hereinafter, the manufacturing process of the polymer electrolyte fuel cell according to the present embodiment will be described in detail.
(Process 1)
As a transfer layer to the polymer electrolyte membrane, a porous platinum oxide layer having a thickness of 2.4 μm was formed on a PTFE sheet (manufactured by Nitto Denko, Nitoflon) by reactive sputtering. The reactive sputtering was performed under the conditions of a total pressure of 5 Pa, an oxygen flow rate ratio (Q _O2 / (Q _Ar + Q _O2 ) of 70%, a substrate temperature of 25 ° C., and an RF input power of 5.4 W / cm ² .

(Process 2)
Subsequently, according to a known technique described in JP-A-2006-332041, this porous platinum oxide layer and carbon paper composite was subjected to vaporization of 2,4,6,8-tetramethylcyclotetrasiloxane vapor (partial pressure) at 25 ° C. 0.05 Pa) for 5 minutes to form a methylsiloxane polymer on the platinum oxide surface.

A 1.5% by mass aqueous solution of sodium phosphinate was collected with a micropipette, and 9 μL was added dropwise per 1 cm ^{2 of} the catalyst layer obtained in (1). Subsequently, this was put in an electric furnace heated to 200 ° C. in a nitrogen atmosphere, phosphine was generated by thermal decomposition of phosphinic acid, and platinum oxide was reduced. Here, the amount of platinum supported in the obtained porous catalyst layer was about 0.6 mg / cm ² .

  The form of the obtained catalyst layer is shown in FIG. 4, FIG. 5 and FIG. FIG. 4 is a scanning electron micrograph (5000 times magnification) of the surface of the porous catalyst layer of Example 1 of the present invention. FIG. 5 is a scanning electron micrograph (magnification 2500 times) of the surface of the porous catalyst layer of Example 1 of the present invention. FIG. 6 is a scanning electron micrograph (magnification 5000 times) showing a bird's-eye view of the porous catalyst layer of Example 1 of the present invention.

  As can be seen from these figures, the catalyst layer has a small pore having a pore diameter of 1 μm or less and two large and small columnar pores having a pore diameter of about 3 to 5 μm from the upper end of the catalyst layer. It had a continuous structure to the lower end. Many large holes are connected to form a groove, and the minimum width of the groove is about 3 μm.

  Further, the minimum width of the series of grooves was 1 μm or more and 10 μm or less, and the longest distance to the large holes in all the small holes was 10 μm or less.

(Process 3)
Thereafter, 8 μl of 1 wt% Nafion solution (5% Nafion solution manufactured by Wako Pure Chemical Industries, diluted to 1% with IPA) was dropped into 1 cm ² of the catalyst layer, and the solvent was volatilized in vacuum. As a result, the electrolyte was added to the catalyst surface.

(Process 4)
In this step, a platinum-supported carbon catalyst layer was produced as a catalyst layer that forms a pair with the catalyst layer produced in (Step 3). A platinum-supported carbon catalyst layer was formed on a PTFE sheet as a transfer layer to the polymer electrolyte membrane using a doctor blade.

The catalyst slurry used here is a kneaded mixture of 1 part by mass of platinum-supporting 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. The amount of platinum supported at this time was 0.35 mg / cm ² .

(Process 5)
The solid polymer electrolyte membrane (manufactured by Dupont, Nafion 112) was sandwiched between the two catalyst layers prepared in (Step 3) and (Step 4), and hot pressing was performed under pressing conditions of 8 MPa, 150 ° C., and 1 min. By peeling the PTFE sheet, the pair of catalyst layers was transferred to the polymer electrolyte membrane, and the electrolyte membrane and the pair of catalyst layers were joined.

(Step 6)
The porous catalyst layer of the present invention is the cathode side, the platinum-supporting carbon catalyst layer is the anode side, and the bonded body is a carbon cloth (manufactured by E-TEK, LT-1400W) as a gas diffusion layer, and further, a fuel electrode and an air electrode A single cell was formed sandwiched between electrodes.

  With respect to the single cell manufactured by the above steps, the characteristics were evaluated using the evaluation apparatus having the configuration shown in FIG. Although not shown in FIG. 7, the anode side electrode 8 and the cathode side electrode 9 are provided with a number of slits for gas permeation.

  When the anode electrode side was filled with hydrogen gas at the dead end and the cathode electrode side was opened to air at 25 ° C.-50% RH and a discharge test was conducted at a battery temperature of 25 ° C., a current as shown in FIG. -Voltage characteristics were obtained.

As a comparative example, an example of using MEA prepared in the same manner except that the reduction treatment of the porous platinum oxide layer in step (2) was performed using a 2% H ₂ / He mixed gas. This is shown in FIG. The amount of platinum supported in the catalyst layer was about 0.8 mg / cm ² as in Example 1.

The form of the catalyst layer used in the comparative example is shown in FIG. As can be seen from this figure, the catalyst layer of the comparative example had a structure with a uniform pore diameter.
Since the effect of the porous catalyst layer of the present invention is a reduction in diffusion polarization, in the low current density region where diffusion polarization is small in principle, the difference between the example and the comparative example was not so much seen. However, the effect of the porous catalyst layer of the present invention becomes more remarkable as the current density region becomes higher, that is, the diffusion polarization-controlled region.

When the voltage at 500 mA / cm ² , which is the diffusion polarization controlling region, is compared, the single cell of this example can obtain a voltage of 0.43 V or higher, whereas the comparative example can obtain only a voltage of about 0.35 V. . That is, in the porous catalyst layer of this example, the deterioration of battery characteristics due to diffusion polarization was significantly suppressed as compared with the catalyst layer of the comparative example. This indicates that the porous catalyst layer of the present invention is superior in water dispersibility to the catalyst layer of the comparative example.

  As shown in the above examples, by using the porous catalyst layer according to this example as the catalyst layer of the polymer electrolyte fuel cell, the dispersibility of the generated water in the catalyst layer is greatly improved, and excellent A fuel cell having cell characteristics was obtained.

  Furthermore, the method for producing the catalyst layer according to this example is a simple, inexpensive and highly reproducible process, so that a polymer electrolyte fuel cell having stable power generation characteristics can be realized at low cost.

Since the porous catalyst layer obtained by the production method of the present invention can improve the water dispersibility in the catalyst layer, it can be used as a catalyst layer of a polymer electrolyte fuel cell.
The polymer electrolyte fuel cell having the catalyst layer can be used as a fuel cell for small electric devices such as a mobile phone, a notebook computer, and a digital camera.

It is a schematic diagram showing the structure of the single cell of the polymer electrolyte fuel cell using the porous catalyst layer of this invention. It is a schematic diagram which shows an example of the porous catalyst in the porous catalyst layer of this invention. It is explanatory drawing explaining an example of distribution of the diameter of the transversal direction of the hole of a porous catalyst. It is a scanning electron micrograph (5000-times multiplication factor) of the surface of the porous catalyst layer of Example 1 of this invention. It is a scanning electron micrograph (2500 times magnification) of the surface of the porous catalyst layer of Example 1 of this invention. It is a scanning electron micrograph (magnification 5000 times) which shows a mode that the porous catalyst layer of Example 1 of this invention was looked down on. It is a schematic diagram of the evaluation apparatus of a polymer electrolyte fuel cell. It is a figure which shows the characteristic of the polymer electrolyte fuel cell of Example 1 of this invention and a comparative example. It is a scanning electron micrograph (5000-times multiplication factor) of the surface of the catalyst layer of the comparative example of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Solid polymer electrolyte membrane 2 Anode side catalyst layer 3 Cathode side porous catalyst layer 4 Porous catalyst 5 Catalyst carrier 6 Anode side gas diffusion layer 7 Cathode side gas diffusion layer 8 Anode side electrode (fuel electrode)
9 Cathode side electrode (air electrode)
DESCRIPTION OF SYMBOLS 10 Membrane-electrode assembly 11 Catalyst 12 Substantially columnar small hole 13 Substantially columnar large hole 14 Mixture of solid polymer electrolyte, hydrophobic agent and catalyst material

Claims (5)

A method for producing a porous catalyst layer for a polymer electrolyte fuel cell, comprising a step of reducing an oxide of a catalyst material with any one of phosphine, ammonia, hydrogen sulfide, SO ₂ , and HCHO. A method for producing a porous catalyst layer.   The method for producing a porous catalyst layer according to claim 1, wherein platinum oxide is reduced in the reduction reaction.   3. The production of a porous catalyst layer according to claim 1, wherein, in the reduction reaction, platinum oxide is immersed in an aqueous phosphinic acid solution and heated to a temperature at which the phosphinic acid is thermally decomposed to produce phosphine. Method.   The method according to any one of claims 1 to 3, wherein the solid polymer electrolyte membrane, the electrode, and the membrane electrode assembly having a porous catalyst layer between the solid polymer electrolyte membrane and the electrode are produced. A process for producing a membrane electrode assembly, comprising the step of forming a porous catalyst layer by the method.   A method for producing a polymer electrolyte fuel cell, comprising the step of forming a membrane electrode assembly by the method according to claim 4.