JP2007194197A - Catalyst electrode and its manufacturing method, and polymer electrolyte fuel cell - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a catalyst electrode which can form a good three-phase interface and prevent flooding of an electrode by product water, and improve performance of a polymer electrolyte fuel cell. <P>SOLUTION: The catalyst electrode is composed of catalyst 2 and a porous carbon frame 3 which carries the catalyst 2. The catalyst 2 has a dendritic structure or a laminate structure, and the porous carbon frame 3 has fine holes with a diameter of 0.5μm or more and 10μm or less in a mode diameter, and moreover, with a porosity ratio of the catalyst electrode 4 in a range of 12% or more and 80% or less. The polymer electrolyte fuel cell is provided with the above catalyst electrode. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a catalyst electrode, a method for producing the same, and a polymer electrolyte fuel cell.

  The polymer electrolyte fuel cell is expected as a future energy generation device because of its high energy conversion efficiency and cleanliness. In recent years, not only for applications such as automobiles and household generators, but also because of its high energy density, it can be installed in small electrical devices such as mobile phones, laptop computers, and digital cameras, compared to conventional secondary batteries. There is a possibility that it can be driven for a long time, attracting attention. However, for in-vehicle use and home use, it is still necessary to reduce the cost, and it is desired to reduce the amount of catalyst used as one method. Moreover, for practical use as a small electric device, it is necessary to make the entire system compact and improve the power generation efficiency.

  Until now, attempts have been made to increase the surface area and increase the utilization efficiency of the catalyst by making the catalyst fine particles, supporting them on carbon particles and dispersing them three-dimensionally. Further, attempts have been made to improve the gas diffusibility in the catalyst layer by providing pores in the catalyst layer to improve the material transport. In particular, when a fuel cell is mounted on a small electric device, the cell itself needs to be miniaturized, and air is supplied from the vent hole to the air electrode by natural diffusion without using a pump or a blower (air breathing). ) Is often taken. In such a case, mass transport at the air electrode is often the rate-limiting reaction, and it is considered that improving the gas diffusibility of the catalyst layer is an effective means.

As a method for improving the gas diffusibility and solving the catalyst utilization rate, Patent Document 1 discloses a configuration of a catalyst electrode for a polymer electrolyte fuel cell comprising a catalyst electrode in which a catalyst is supported on fibrous carbon. Yes. Patent Document 2 discloses a fuel cell electrode formed by supporting catalyst fine particles on the surface of a carbon nanofiber.
JP2003-200052 JP 2002-298661

  However, the problem of obtaining a catalyst electrode that is more versatile and that can be produced by a simple method and that further improves the catalyst utilization rate has not been sufficiently studied so far. .

  Therefore, an object of the present invention is to provide a catalyst electrode having a high catalyst utilization rate and a fuel cell using the catalyst electrode.

  The present invention comprises a catalyst and a porous carbon frame supporting the catalyst, the catalyst has a dendritic structure or a flaky structure, and the porous carbon frame has a mode diameter of 0.5 μm or more in mode diameter. It has pores of 10 μm or less, and the porosity in the catalyst electrode is in the range of 12% or more and 80% or less.

The catalyst is preferably supported in a three-dimensionally dispersed manner on the surface of the porous carbon frame and inside the frame.
The catalyst is composed of platinum oxide, a composite oxide of platinum and a metal element other than platinum, platinum obtained by reducing the platinum oxide or composite oxide, or a multi-element metal containing platinum, or a metal element other than platinum and platinum. It is preferably one of a mixture with an oxide and a mixture of a multi-element metal containing platinum and an oxide of a metal element other than platinum. Here, as metal elements other than platinum, Al, Si, Ti, V, Cr, Fe, Co, Ni, Cu, Zn, Ge, Zr, Nb, Mo, Ru, Rh, Pd, Ag, In, Sn , Hf, Ta, W, Os, Ir, Au, La, Ce, and Nd can be preferably used.

The average thickness of the branched branches or flakes of the catalyst having the dendritic structure or flaky structure is preferably 5 nm or more and 50 nm or less.
The porous carbon frame is preferably made of carbon powder and a binder made of a solid polymer electrolyte.

The catalyst electrode of the present invention is suitably used as a catalyst electrode of a polymer electrolyte fuel cell.
The present invention also relates to a method for producing a catalyst electrode comprising a catalyst and a porous carbon frame carrying the catalyst, the catalyst being porous in the gas phase by sputtering, vacuum deposition or ion plating. It has the process of forming in the surface of a carbon frame, and the inside of a flame | frame.

  The present invention also provides a solid polymer fuel cell comprising any of the catalyst electrodes described above and a solid polymer electrolyte membrane adjacent to the catalyst electrode.

According to the catalyst electrode of the present invention, the formation of a good three-phase interface and the flooding of the electrode with generated water are suppressed, and the performance of the polymer electrolyte fuel cell can be improved.
In addition, since the catalyst electrode of the present invention can be manufactured by a simple method having versatility, it is possible to realize performance stabilization and improvement in uniformity of the membrane-catalyst electrode.

  Further, the present invention can provide a polymer electrolyte fuel cell having a uniform and stable power generation characteristic over a long period of time at a low cost.

  Hereinafter, with reference to the drawings, preferred embodiments of the catalyst electrode of the polymer electrolyte fuel cell of the present invention and the manufacturing method thereof will be described in detail by way of example. However, the materials, dimensions, shapes, relative arrangements, and the like of the constituent members described in this embodiment are not intended to limit the scope of the present invention only to those unless otherwise specified. Absent. Similarly, the manufacturing method described below is not the only one.

  FIG. 1 is a schematic diagram showing an example of a cross-sectional configuration of a single cell of a solid polymer fuel cell using a catalyst electrode. In the catalyst electrode, a dendritic or flaky catalyst is three-dimensionally distributed on the surface of the porous carbon frame and inside the frame.

  In FIG. 1, reference numeral 1 denotes a solid polymer electrolyte membrane, and a pair of cathode catalyst electrode 4 and anode catalyst electrode 5 are arranged on both sides of the membrane, and a cathode gas diffusion layer 6, anode gas diffusion layer 7 and cathode collector are disposed on the outside thereof. An electric body 8 and an anode current collector 9 are disposed.

  In this embodiment, an example in which a catalyst electrode in which a catalyst having a dendritic or lamellar structure is three-dimensionally dispersed on the surface of a porous carbon frame and inside the frame is used only for the cathode catalyst electrode. However, the arrangement is not limited to this. For example, it includes a case where the catalyst electrode of the present invention is disposed on both electrodes, or a case where the catalyst electrode of the present invention is disposed only on the anode side, and various configurations can be preferably selected.

Furthermore, in FIG. 1, 2 is a catalyst, 3 is a catalyst carrier, and in this embodiment is a porous carbon frame, from which a catalyst electrode 4 is constructed.
The catalyst 2 is composed of platinum oxide, a composite oxide of platinum and a metal element other than platinum, platinum obtained by reducing the platinum oxide or the composite oxide or a multi-element metal containing platinum, and a metal element other than platinum and platinum. It is preferably one of a mixture with an oxide and a mixture of a multi-element metal containing platinum and an oxide of a metal element other than platinum.

  Examples of metal elements other than platinum include Al, Si, Ti, V, Cr, Fe, Co, Ni, Cu, Zn, Ge, Zr, Nb, Mo, Ru, Rh, Pd, Ag, In, Sn, and Hf. , Ta, W, Os, Ir, Au, La, Ce, and Nd can be preferably used.

  The catalyst 2 has a dendritic structure or a flaky structure. The dendritic structure is, for example, a large number of dendritic shapes in a scanning electron microscope (SEM) photograph (FIG. 3A: magnification 10,000 times, FIG. 3B: magnification 30,000 times) of the catalyst electrode of Example 2 of the present invention shown in FIG. What is shown by is a catalyst, and represents the structure which consists of the aggregate | assembly of the dendritic material.

  The flaky structure is, for example, a scanning electron microscope (SEM) photograph of the catalyst electrode of Example 1 of the present invention shown in FIG. 2 (FIG. 2A: magnification 10,000 times, FIG. 2B: magnification 30,000 times, FIG. 2C: magnification 300,000) 2), a catalyst having a large number of flakes represents a structure composed of aggregates of the flakes.

  When the catalyst is formed using a method of reducing after sputtering as described later, a flaky structure is likely to occur when the amount of catalyst is small, and a dendritic structure is likely to occur when the amount of catalyst is large. When the dendritic structure is observed in detail, it may have a flaky nanostructure unit. Such a case is also conceptually included in the dendritic structure.

  The average thickness of the branched branches or flakes of the catalyst having the dendritic structure or flaky structure is preferably in the range of 5 nm to 50 nm, more preferably 5 nm to 20 nm.

  The catalyst having the form, composition, configuration, and dimensions described above can be suitably formed by a physical vapor deposition method such as sputtering, vacuum vapor deposition or ion plating, or a reactive vacuum vapor deposition method in a gas phase. For example, a platinum oxide having a dendritic structure or a flaky structure can be easily coated on the surface of a porous carbon frame by reactive sputtering using a platinum target. Can be distributed.

  In FIG. 1, a porous carbon frame 3 represents a carbon sheet having pores 11 and three-dimensionally connecting the pores. The pores in the porous carbon frame preferably have a mode diameter of 0.5 to 10 μm, preferably 1.0 to 10 μm in mode diameter.

  Further, the porosity of the porous carbon frame is 12% or more and 80% or less, preferably 40% or more and 80% or less. In addition, the porosity indicates the ratio of the pore volume in the sample volume obtained by the sample area × sample thickness.

The thickness of the catalyst electrode is 5 μm or more and 30 μm or less, preferably 10 μm or more and 25 μm or less.
As carbon, carbon nanotubes, ketjen black, Showa Denko: VGCF, Nippon Graphite: flake carbon, Cabot: Vulcan XC-72R can be suitably selected or used in combination.

  The method for producing the porous carbon frame uses carbon suitably selected or combined from carbon nanotubes, ketjen black, Showa Denko: VGCF, Nippon Graphite: flake carbon, Cabot: Vulcan XC-72R, and the like. The carbon is made into a slurry together with a solid polymer electrolyte or a binder such as Teflon (registered trademark) and a dispersion solvent such as IPA, and is applied to a Teflon (registered trademark) sheet to obtain a porous carbon frame. At this time, a method may be employed in which the slurry is directly applied onto the gas diffusion layer to form a porous carbon frame.

  The catalyst electrode in which the catalyst having a dendritic structure or a flake-like structure is three-dimensionally dispersed and arranged on the surface of the porous carbon frame and the inside of the frame is joined to the solid polymer electrolyte membrane by a transfer method. be able to. In that case, a method of dropping a solid polymer electrolyte solution as a proton conductive material onto the catalyst electrode may be used, or transfer using the solid polymer electrolyte used in the preparation of the porous carbon frame and driving as a battery. Is also possible. However, when transferring and generating electricity using the solid polymer electrolyte in the porous carbon frame, the solid polymer electrolyte contracts in the high vacuum atmosphere of sputtering, and the carbon in the frame is disconnected. There is a problem that the electrode strength is weakened and the electrode is cracked during transfer. Furthermore, since the proton conduction path is cut off, there arises a problem that the utilization rate of the catalyst is remarkably lowered. Therefore, in order to transfer and generate electric power with the above-described configuration, an organic solvent such as IPA or ethanol is dropped on the catalyst electrode after sputtering, and the solid polymer electrolyte in the porous carbon frame is dissolved and dried for rebinding. There is a need.

Further, by forming a porous carbon frame again on the formed catalyst electrode and forming the catalyst by sputtering, the catalyst electrodes can be stacked. At that time, it is possible to improve the water retention and proton conductivity of the electrolyte membrane by including more solid polymer electrolyte in the porous carbon frame of the electrode close to the solid polymer electrolyte. In addition, the porous carbon frame of the electrode close to the gas diffusion layer may be inclined to the functionality of the catalyst electrode by including more Teflon (registered trademark) to improve water repellency and flooding resistance. Is possible.

As the solid polymer electrolyte membrane, a perfluorosulfonic acid polymer having a structure in which a side chain having a sulfonic acid group at the end is bonded to a fluorocarbon skeleton can be preferably used. The perfluorosulfonic acid polymer has a fluorocarbon skeleton that is not crosslinked, and forms a crystal in which the skeleton is bonded by van der Waals force. Furthermore, some sulfonic acid groups are aggregated to form a reverse micelle structure, which is a conduction channel for proton H ⁺ .

When proton H ⁺ moves in the electrolyte membrane toward the cathode side, it moves using water molecules as a medium. Therefore, the electrolyte membrane preferably has a function of holding water molecules.
Therefore, the solid polymer electrolyte membrane transmits proton H ⁺ generated on the anode side to the cathode side, does not pass unreacted reaction gases (hydrogen and oxygen), and has a predetermined water retention function. preferable. Any one satisfying this condition can be selected and used.

  The gas diffusion layers 6 and 7 have a function of supplying 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. It is preferable. Furthermore, the charge generated by the anode 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.

  There are various methods for producing the catalyst electrode of this embodiment and the polymer electrolyte fuel cell, and an example of a method for producing the catalyst electrode will be described below using the catalyst electrode shown in FIGS. 2A to 2C as an example.

  Specifically, the catalyst electrode shown in FIGS. 2A to 2C is formed by three-dimensionally applying a catalyst by sputtering on the surface of a porous carbon frame produced using carbon powder (made by Showa Denko: VGCF) and inside the frame. It is distributed.

(1) Production of porous carbon frame as catalyst carrier Carbon powder (made by Showa Denko: VGCF), solid polymer electrolyte solution (made by Dupont: 5% Nafion solution), IPA (made by Kishida Chemical) are mixed at a predetermined ratio. Into a slurry. The obtained slurry is applied on a PTFE sheet as a transfer layer to the polymer electrolyte membrane using a doctor blade to obtain a porous carbon frame.

(2) Formation of catalyst on porous carbon frame Next, the substrate produced by the above process is moved to a sputtering apparatus to form a platinum oxide catalyst having a dendritic and flaky structure into a film of about 0.25 mg / cm ² . .

After the sputtering chamber pressure is evacuated to 1.0 × 10 ⁻⁴ Pa, Ar and O ₂ are introduced to 2.5 and 20.0 sccm, respectively, and the total pressure is adjusted to 6.0 Pa at the orifice.
Reactive sputtering is performed at an RF input power of 4.0 W / cm ^{2 to} form about 0.25 mg / cm ^{2 of} platinum oxide having a dendritic or flaky structure.

  At this time, since the substrate has sufficient pores and holes, the sputtered platinum oxide is formed not only on the surface of the porous carbon frame but also on the inside of the frame, and is three-dimensionally distributed. Formed.

The substrate after film formation is easily reduced by exposure to 10 kPa of 2% H ₂ / He to obtain a cathode catalyst electrode.
(3) Production of anode electrode Platinum-supported carbon (manufactured by Johnson Matthey: HiSPEC 4000) is used as a catalyst for the anode electrode of the counter electrode, and a solid polymer electrolyte solution (manufactured by Dupont: 5% Nafion solution) and IPA are mixed at a predetermined ratio. Into a slurry. The obtained slurry is applied on a PTFE sheet as a transfer layer to the polymer electrolyte membrane using a doctor blade to obtain an anode catalyst electrode.

(4) Preparation of MEA (membrane-electrode assembly) Hot pressing is performed by sandwiching a solid polymer electrolyte membrane (manufactured by Dupont, Nafion 112) between the cathode catalyst electrode and the anode catalyst electrode obtained as described above. Further, by peeling the PTFE sheet, the pair of catalyst electrodes is transferred to the polymer electrolyte membrane, and the electrolyte membrane and the pair of catalyst electrodes are joined. A single cell is produced by sandwiching the joined body between 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 single cell of the polymer electrolyte fuel cell has been described above by taking the case of the catalyst electrode shown in FIG. 2 as an example. However, the present invention is limited to the polymer electrolyte fuel cell having this single cell configuration. It is not intended to include a solid polymer fuel cell having a configuration in which a plurality of single cells are stacked.

Next, more specific examples based on the above embodiment will be described in detail.
Example 1
In this example, the catalyst is three-dimensionally dispersed by sputtering on the surface of the porous carbon frame using carbon powder (made by Showa Denko: VGCF) and inside the frame.

Hereinafter, the manufacturing process of the polymer electrolyte fuel cell according to the present embodiment will be described in detail.
(Process 1)
First, a porous carbon frame is prepared as a catalyst carrier.

  Carbon powder (manufactured by Showa Denko: VGCF), solid polymer electrolyte solution (manufactured by Dupont: 5% Nafion solution), and IPA are mixed and dispersed at a predetermined ratio to form a slurry. The obtained slurry is applied onto a PTFE sheet as a transfer layer to the polymer electrolyte membrane by using a doctor blade to obtain a porous carbon frame having a thickness of 20 μm.

(Process 2)
Next, the substrate produced by the above process is moved to a sputtering apparatus, and a platinum oxide catalyst having a dendritic or flaky structure is formed to a film thickness of about 0.25 mg / cm ² .

After the sputtering chamber pressure is evacuated to 1.0 × 10 ⁻⁴ Pa, Ar and O ₂ are introduced to 2.5 and 20.0 sccm, respectively, and the total pressure is adjusted to 6.0 Pa at the orifice.
Reactive sputtering was performed at an RF input power of 4.0 W / cm ^{2 to} form about 0.25 mg / cm ^{2 of} platinum oxide having a dendritic or flaky structure on a porous carbon frame.

  At this time, since the substrate has sufficient pores and holes, the sputtered platinum oxide is formed not only on the surface of the porous carbon frame but also on the inside of the frame, and is three-dimensionally distributed. Formed.

The substrate after film formation is easily reduced by exposure to 10 kPa of 2% H ₂ / He. After the reduction, 0.3 cc of IPA per 1 cm ^{2 of} the substrate is dropped to dissolve Nafion in the porous carbon frame, and then dried in the air atmosphere to rebound to obtain a cathode catalyst electrode.

(Process 3)
Next, an anode catalyst electrode as a counter electrode is produced. Platinum-supported carbon (manufactured by Johnson Matthey: HiSPEC 4000) is used as the anode catalyst, and a solid polymer electrolyte solution (manufactured by Dupont: 5% Nafion solution) and IPA are mixed in a predetermined ratio to form a slurry. The obtained slurry is applied on a PTFE sheet as a transfer layer to the polymer electrolyte membrane using a doctor blade to obtain an anode catalyst electrode.

(Process 4)
A solid polymer electrolyte membrane (Dupont Nafion 112) is sandwiched between the cathode catalyst electrode and the anode catalyst electrode obtained as described above, and hot pressing is performed. Further, by peeling the PTFE sheet, the pair of catalyst electrodes is transferred to the polymer electrolyte membrane, and the electrolyte membrane and the pair of catalyst electrodes are joined. A single cell is produced by sandwiching the joined body between a carbon cloth (LT1400-W manufactured by E-TEK) as a gas diffusion layer, and a fuel electrode and an air electrode. In this example, since power generation is performed using the solid polymer electrolyte (manufactured by Dupont: Nafion) used at the time of producing the porous carbon frame, it is not necessary to add the solid polymer electrolyte after applying the catalyst to the porous carbon frame. is there.

  With respect to the single cell manufactured through the above steps, the characteristics were evaluated using the evaluation apparatus having the configuration shown in FIG. A discharge test was conducted at a battery temperature of 80 ° C. by flowing hydrogen gas to the anode electrode side and air to the cathode electrode side.

  At this time, as Comparative Example 1, a similar test was performed on a single cell manufactured using a catalyst electrode obtained by sputtering platinum oxide directly on a gas diffusion layer without using a porous carbon frame carrier as a cathode.

First, the shapes of the electrodes of Example 1 and Comparative Example 1 are compared using SEM images.
2A to 2C are scanning electron microscope (SEM) photographs showing the particle structure of the catalyst of the catalyst electrode of Example 1 (FIG. 2A: magnification 10,000 times, FIG. 2B: magnification 30,000 times, FIG. 2C: magnification 300,000) Times).

4A to 4B are scanning electron microscope (SEM) photographs (FIG. 4A: magnification 10,000 times, FIG. 4B: magnification 30,000 times) showing the particle structure of the catalyst of the catalyst electrode of Comparative Example 1. FIG.
In the catalyst of Comparative Example 1, a dendritic morphology opened in the direction of the polymer electrolyte membrane was observed. In spite of the same platinum amount being sputtered, the catalyst of Example 1 was in the form of a flake with an average thickness at the initial dendritic formation of 5 nm to 50 nm. In Example 1, it is considered that the sputter area was increased because of the three-dimensionally distributed arrangement not only on the surface of the porous carbon frame but also inside the frame, resulting in a flaky shape.

Next, the IV characteristics of Example 1 and Comparative Example 1 are shown in FIG. Comparing the limiting current at which the cell voltage becomes 0 V, Comparative Example 1 was 0.212 A / cm ² , while Example 1 was 0.327 A / cm ² . Further, the cell voltage at 0.1 A / cm ² and 0.2 A / cm ² of Comparative Example 1 each 0.542V, while a which was 0.310V, respectively In Embodiment 1 0.617V, 0. It improved to 499V.

Further, in this example, the limit current was 0.0048 mA / cm ² which was an extremely low value when no IPA was dropped after sputtering when the catalyst electrode was produced. From this, it can be seen that in the catalyst electrode having the structure as in Example 1, the steps of Nafion dissolution and rebinding by dropping IPA after sputtering are indispensable.

  As described above, the catalyst is three-dimensionally distributed on the surface of the porous carbon frame and inside the frame, so that good gas diffusibility and sufficient water discharge are ensured, and a good three-phase interface is formed. And the performance improvement was made possible by suppressing flooding of the electrode by the generated water.

  As described above, by using the catalyst electrode according to the present embodiment as the catalyst layer of the polymer electrolyte fuel cell, a fuel having excellent cell characteristics by forming a good three-phase interface and suppressing flooding of the electrode by generated water. A battery was obtained. Furthermore, since the catalyst electrode manufacturing method according to this example is a simple, inexpensive, and reproducible process, a solid polymer fuel cell having stable characteristics can be realized at low cost.

Example 2
This example is an example of a catalyst electrode in the case where carbon powder (manufactured by Nippon Graphite: flake carbon GR-15) is used as the material of the porous carbon frame. In the following, the manufacturing process of the polymer electrolyte fuel cell according to this example is the same as that of Example 1. In the following, only the step (step 1) that differs from the first embodiment in terms of configuration and manufacturing method will be described in detail.

(Process 1)
First, a porous carbon frame is prepared as a catalyst carrier.
Carbon powder (manufactured by Nippon Graphite: flake carbon GR-15), solid polymer electrolyte solution (manufactured by Dupont: 5% Nafion solution), and IPA are mixed and dispersed at a predetermined ratio to form a slurry. The obtained slurry is applied onto a PTFE sheet as a transfer layer to the polymer electrolyte membrane by using a doctor blade to obtain a porous carbon frame having a thickness of 20 μm.

  With respect to the single cell manufactured through the above steps, the characteristics were evaluated using the evaluation apparatus having the configuration shown in FIG. A discharge test was conducted at a battery temperature of 80 ° C. by flowing hydrogen gas to the anode electrode side and air to the cathode electrode side. At this time, as Comparative Example 1, a similar test was conducted on a single cell manufactured using a catalyst electrode obtained by sputtering platinum oxide directly on a gas diffusion layer without using a carrier.

First, the electrode shapes of Comparative Example 1 and Example 2 are compared using SEM images.
3A to 3B are scanning electron microscope (SEM) photographs (FIG. 3A: magnification 10,000 times, FIG. 3B: magnification 30,000 times) showing the particle structure of the catalyst of the catalyst electrode of Example 2. FIG.

4A to 4B are scanning electron microscope (SEM) photographs (FIG. 4A: magnification 10,000 times, FIG. 4B: magnification 30,000 times) showing the particle structure of the catalyst of the catalyst electrode of Comparative Example 1. FIG.
Unlike the case of Example 1, the shape of the catalyst of Example 2 was dendritic like that of Comparative Example 1. The average diameter of the branched branches of the dendritic structure of Example 2 is 20 nm.

  The difference between the dendritic catalyst of Example 2 and Comparative Example 1 is that Comparative Example 1 has a shape in which the branch of the tree grows vertically and opens in the direction of the electrolyte membrane, whereas Example 2 has a branch of the dendritic catalyst. The shape grows in the horizontal direction.

Next, the IV characteristics of Example 2 and Comparative Example 1 are shown in FIG. Comparing the limiting current at which the cell voltage becomes 0 V, Comparative Example 1 was 0.212 A / cm ² , whereas in Example 2, it was 0.229 A / cm ² . Further, the cell voltage at 0.1 A / cm ² and 0.2 A / cm ² of Comparative Example 1 each 0.542V, while was 0.310V, respectively in Example 2 0.527V, 0. It was 390V. Although a slight increase was confirmed in the limit current, the improvement was slight compared with Example 1.

  Table 1 below shows the results of the characteristics of the polymer electrolyte fuel cells produced using the catalyst electrodes of Examples 1 and 2 and the polymer electrolyte fuel cell of Comparative Example 1.

  Moreover, the pore distribution of the porous carbon frames of Example 1 and Example 2 is shown in FIG. 7, and the results of comparing the pore diameters obtained thereby and the porosity in the catalyst electrode are shown in the following table. It is shown in 2.

From the results of Example 2, the effect as a porous carbon frame is exhibited even when the pore diameter is 0.5 μm or more and 10 μm or less in the mode diameter and the porosity is 12% or more and 80% or less. The porous carbon frame preferably has a pore diameter of 1.0 μm to 10 μm and a porosity of 40% to 80% in terms of mode diameter. By using such a porous carbon frame, the catalyst formed by sputtering is three-dimensionally distributed not only on the surface layer of the porous carbon frame but also inside the layer. As a result, the formation of a good three-phase interface and the flooding of the electrode due to the produced water are suppressed by the good gas diffusibility and water discharge property, and the performance is greatly improved.

  The catalyst electrode of the present invention can be used for a polymer electrolyte fuel cell having uniform and stable power generation characteristics over a long period of time because formation of a good three-phase interface and flooding of the electrode due to generated water are suppressed. Can do.

It is a schematic diagram which shows an example of the cross-sectional structure of the single cell of the polymer electrolyte fuel cell using a catalyst electrode. It is a scanning electron microscope (SEM) photograph (FIG. 2A: Magnification 10,000 times) which shows the particle structure of the catalyst of the catalyst electrode of Example 1. FIG. It is a scanning electron microscope (SEM) photograph (FIG. 2B: magnification 30,000 times) which shows the particle structure of the catalyst of the catalyst electrode of Example 1. FIG. It is a scanning electron microscope (SEM) photograph (FIG. 2C: 300,000 times magnification) which shows the particle structure of the catalyst of the catalyst electrode of Example 1. FIG. It is a scanning electron microscope (SEM) photograph (FIG. 3A: magnification 10,000 times) which shows the particle structure of the catalyst of the catalyst electrode of Example 2. FIG. It is a scanning electron microscope (SEM) photograph (FIG. 3B: 30,000 times magnification) which shows the particle structure of the catalyst of the catalyst electrode of Example 2. FIG. It is a scanning electron microscope (SEM) photograph (Drawing 4A: magnification 10,000 times) which shows the particle structure of the catalyst of the catalyst electrode of comparative example 1. It is a scanning electron microscope (SEM) photograph (FIG. 4B: 30,000 times magnification) which shows the particle structure of the catalyst of the catalyst electrode of the comparative example 1. It is a schematic diagram of the evaluation apparatus of a polymer electrolyte fuel cell. FIG. 3 is a graph showing characteristics of a polymer electrolyte fuel cell produced using catalyst electrodes of Examples 1 and 2 and a polymer electrolyte fuel cell of Comparative Example 1. It is the figure which showed the pore distribution of the porous carbon frame of Example 1,2.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Solid polymer electrolyte membrane 2 Catalyst 3 Porous carbon frame 4 Catalyst electrode 5 Anode catalyst electrode 6 Cathode gas diffusion layer 7 Anode gas diffusion layer 8 Cathode current collector 9 Anode current collector 10 Membrane-electrode assembly 11 Pore

Claims (7)

  A catalyst and a porous carbon frame supporting the catalyst. The catalyst has a dendritic structure or a flaky structure, and the porous carbon frame has a pore diameter of 0.5 μm or more and 10 μm or less in mode diameter. A catalyst electrode having pores and a porosity in the catalyst electrode in a range of 12% to 80%.   The catalyst electrode according to claim 1, wherein the catalyst is supported in a three-dimensionally dispersed manner on the surface of the porous carbon frame and inside the frame.   The catalyst is composed of platinum oxide, a composite oxide of platinum and a metal element other than platinum, platinum obtained by reducing the platinum oxide or composite oxide, or a multi-element metal containing platinum, or a metal element other than platinum and platinum. 3. The catalyst electrode according to claim 1, wherein the catalyst electrode is any one of a mixture of an oxide and a mixture of a multicomponent metal containing platinum and an oxide of a metal element other than platinum.   4. The catalyst electrode according to claim 1, wherein an average thickness of the branched branches or flakes of the catalyst having the dendritic structure or the flaky structure is 5 nm or more and 50 nm or less.   The catalyst electrode according to any one of claims 1 to 4, wherein the porous carbon frame is composed of carbon powder and a binder made of a solid polymer electrolyte.   A method for producing a catalyst electrode comprising a catalyst and a porous carbon frame carrying the catalyst, wherein the surface of the porous carbon frame and the frame are formed by sputtering, vacuum deposition or ion plating of the catalyst in the gas phase. The manufacturing method of the catalyst electrode characterized by having the process formed in an inside.   A solid polymer fuel cell comprising the catalyst electrode according to claim 1 and a solid polymer electrolyte membrane adjacent to the catalyst electrode.