JP6798102B2 - Method for manufacturing electrode catalyst layer, membrane electrode assembly, polymer electrolyte fuel cell, and electrode catalyst layer - Google Patents

Description

The present invention relates to an electrode catalyst layer provided in a fuel cell, a membrane electrode assembly provided with the electrode catalyst layer, a polymer electrolyte fuel cell provided with the membrane electrode assembly, and a method for producing the electrode catalyst layer.

A fuel cell uses a chemical reaction between a fuel such as hydrogen and an oxidant such as oxygen to generate electric power. Since power generation by a fuel cell has advantages such as high efficiency, low environmental load, and low noise, the fuel cell is attracting attention as a source of clean energy. In particular, since the polymer electrolyte fuel cell can be used near room temperature, it is expected to be used as an in-vehicle power source, a stationary power source for home use, etc., and in recent years, various researches and developments on the polymer electrolyte fuel cell have been made. Is being done. Above all, improvement of power generation characteristics is an important theme for enhancing the practicality of polymer electrolyte fuel cells.

In a polymer electrolyte fuel cell, an electrode catalyst layer forming an air electrode as a cathode, an electrode catalyst layer forming a fuel electrode as an anode, and a polymer electrolyte membrane sandwiched between these two electrode catalyst layers are provided. It has a membrane electrode assembly. Further, the polymer electrolyte fuel cell includes two separators in which a gas flow path for supplying gas to the membrane electrode assembly is formed, and the membrane electrode assembly is sandwiched between these two separators.

Oxidizing agent gas containing oxygen is supplied to the electrode catalyst layer constituting the cathode through the gas flow path, and fuel gas containing hydrogen is supplied to the electrode catalyst layer constituting the anode through the gas flow path. To. Then, these gases react in the presence of a catalyst, and a chemical reaction accompanied by conduction of protons in the polymer electrolyte membrane proceeds, and as a result, an electromotive force is generated between the cathode and the anode.

Since the configuration of the electrode catalyst layer affects the power generation characteristics of the polymer electrolyte fuel cell, attempts have been made to improve the power generation characteristics by improving the electrode catalyst layer. For example, Patent Document 1 states that the initial characteristics and durability of a polymer electrolyte fuel cell are improved, that is, an increase in discharge voltage at the initial stage of use of a polymer electrolyte fuel cell and use for a certain period of time. The composition of the electrode catalyst layer capable of suppressing the decrease in the discharge voltage later is disclosed.

Japanese Unexamined Patent Publication No. 2003-115299

By the way, in addition to the above-mentioned initial characteristics and durability, the power generation characteristics in a low humidification environment are also one of the power generation characteristics that are desired to be improved in the polymer electrolyte fuel cell.

In order to ensure the proton conductivity and conductivity of the polymer electrolyte membrane and the electrode catalyst layer, it is necessary to humidify the membrane electrode assembly. However, the need for a large amount of humidification leads to an increase in the cost required for installing and driving the humidifier, and as a result, the cost required for operating the power generation system using the polymer electrolyte fuel cell is increased. Increase.

Therefore, a polymer electrolyte fuel cell that exhibits high power generation characteristics not only in a highly humidified environment but also in a low humidified environment is desired. It should be noted that such a requirement is common not only to polymer electrolyte fuel cells but also to fuel cells having the same structure as polymer electrolyte fuel cells and generating electric power by a chemical reaction accompanied by conduction of protons.

The present invention provides a method for producing an electrode catalyst layer, a membrane electrode assembly, a polymer electrolyte fuel cell, and an electrode catalyst layer capable of obtaining good power generation characteristics in both a high humidification environment and a low humidification environment. The purpose is to provide.

The electrode catalyst layer that solves the above problems is an electrode catalyst layer containing a polymer electrolyte having a tetrafluoroethylene skeleton, a carbon carrier that is a conductive carrier made of carbon, and a catalytic substance supported on the carbon carrier. When the carbon atom concentration of the electrode catalyst layer obtained by energy-dispersed X-ray spectroscopic analysis is Xc and the fluorine atom concentration is Xf, 85 at% <Xc <90 at% and 3 at% <Xf <7 at%. Yes, the thickness of the electrode catalyst layer is 1 μm or more and 15 μm or less.

According to the above configuration, the electrode catalyst layer can achieve both improvement of proton conductivity in a low humidification environment and improvement of gas and water diffusivity in a high humidification environment. Therefore, in the fuel cell provided with this electrode catalyst layer, the power generation performance in both the high humidification environment and the low humidification environment is enhanced.
In the above configuration, the mass ratio of the polymer electrolyte to the carbon carrier contained in the electrode catalyst layer is preferably 0.8 or more and 1.6 or less.
According to the above configuration, the composition of the electrode catalyst layer is determined as the mass ratio of the polymer electrolyte to the carbon carrier, so that the electrode catalyst layer can be easily formed.

The film electrode joints that solve the above problems include a cathode catalyst layer that is an electrode catalyst layer used for the cathode of a fuel cell, an anode catalyst layer that is an electrode catalyst layer used for the anode of the fuel cell, and the cathode catalyst layer. A polymer electrolyte membrane sandwiched between the above and the anode catalyst layer, and the cathode catalyst layer includes a polymer electrolyte having a tetrafluoroethylene skeleton, a carbon carrier which is a conductive carrier made of carbon, and the carbon. When the carbon atom concentration of the cathode catalyst layer obtained by energy-dispersed X-ray spectroscopic analysis is Xc and the fluorine atom concentration is Xf, which contains the catalyst substance supported on the carrier, 85 at% <Xc <90 at% and 3, 3 at% <Xf <7 at%, and the thickness of the cathode catalyst layer is 1 μm or more and 15 μm or less.

According to the above configuration, in the cathode catalyst layer provided in the membrane electrode assembly, it is possible to achieve both improvement of proton conductivity in a low humidification environment and improvement of gas and water diffusivity in a high humidification environment. Therefore, the fuel cell provided with this membrane electrode assembly can improve the power generation performance in both a high humidification environment and a low humidification environment.
The polymer electrolyte fuel cell that solves the above problems includes the membrane electrode assembly and a pair of separators that sandwich the membrane electrode assembly.
According to the above configuration, in the polymer electrolyte fuel cell, the power generation performance in both the high humidification environment and the low humidification environment is enhanced.

In a method for producing an electrode catalyst layer that solves the above problems, a polymer electrolyte having a tetrafluoroethylene skeleton, a carbon carrier that is a conductive carrier made of carbon, and a catalyst substance supported on the carbon carrier are dispersed in a solvent. A first step of producing a catalyst ink and a second step of forming an electrode catalyst layer by applying the catalyst ink to a base material and drying the catalyst ink are included. In the first step, the catalyst ink is contained. The catalyst ink is adjusted so that the mass ratio of the polymer electrolyte to the carbon carrier is 0.8 or more and 1.6 or less, and energy is dispersed in the electrode catalyst layer formed in the second step. When the carbon atom concentration of the electrode catalyst layer obtained by type X-ray spectroscopic analysis is Xc and the fluorine atom concentration is Xf, 85 at% <Xc <90 at% and 3 at% <Xf <7 at%, and the electrode The thickness of the catalyst layer is 1 μm or more and 15 μm or less.

According to the above method, the fuel cell can form an electrode catalyst layer in which the power generation performance is enhanced in both a high humidification environment and a low humidification environment. Then, since such an electrode catalyst layer can be formed by controlling the mass ratio of the polymer electrolyte to the carbon carrier in the catalyst ink, the formation of the electrode catalyst layer is easy.

According to the present invention, in a fuel cell, good power generation characteristics can be obtained in both a high humidification environment and a low humidification environment.

A cross-sectional view showing a cross-sectional structure of a membrane electrode assembly according to an embodiment of the membrane electrode assembly. The plan view which shows the planar structure of the membrane electrode assembly of one Embodiment. The cross-sectional view which shows the cross-sectional structure of the membrane electrode assembly of the modification. The figure which shows an example of the spectrum obtained by performing the qualitative analysis of the cross section of the electrode catalyst layer by the energy dispersive X-ray spectroscopic analysis about one Embodiment of an electrode catalyst layer. The exploded perspective view which shows the perspective structure of the fuel cell disassembled about one Embodiment of a polymer electrolyte fuel cell.

An embodiment of a method for manufacturing an electrode catalyst layer, a membrane electrode assembly, a polymer electrolyte fuel cell, and an electrode catalyst layer will be described with reference to FIGS. 1 to 5.

[Electrode catalyst layer and membrane electrode assembly]
The configuration of the electrode catalyst layer and the membrane electrode assembly including the electrode catalyst layer will be described with reference to FIGS. 1 to 3.
As shown in FIG. 1, the membrane electrode assembly 10 includes a polymer electrolyte membrane 11 and two electrode catalyst layers, a cathode catalyst layer 12C and an anode catalyst layer 12A. The cathode catalyst layer 12C is an electrode catalyst layer used for the cathode of the fuel cell, and the anode catalyst layer 12A is an electrode catalyst layer used for the anode of the fuel cell.

The polymer electrolyte film 11 is sandwiched between the cathode catalyst layer 12C and the anode catalyst layer 12A, the cathode catalyst layer 12C is in surface contact with one of the two surfaces of the polymer electrolyte film 11, and the anode catalyst layer 12A is in surface contact. It is in surface contact with the other of the two surfaces of the polymer electrolyte membrane 11.

As shown in FIG. 2, when viewed from the direction facing one surface of the polymer electrolyte membrane 11, the outer shape of the cathode catalyst layer 12C and the outer shape of the anode catalyst layer 12A are substantially the same shape, and these catalyst layers 12C , The outer shape of the polymer electrolyte membrane 11 is larger than the outer shape of 12A. The outer shape of the polymer electrolyte membrane 11 and the outer shape of the catalyst layers 12C and 12A are not particularly limited, and may be rectangular, for example.

As shown in FIG. 3, the membrane electrode assembly 10 may further include a gasket 13. The gasket 13 surrounds the outer periphery of the laminate composed of the polymer electrolyte membrane 11, the cathode catalyst layer 12C, and the anode catalyst layer 12A, and prevents gas and the like supplied to the catalyst layers 12C and 12A from leaking from the fuel cell. It has a function to suppress. Although FIG. 3 shows an example in which the membrane electrode assembly 10 includes one gasket, the membrane electrode assembly 10 has a gasket surrounding the outer periphery of the cathode catalyst layer 12C and an anode catalyst layer instead. It may be provided with two gaskets, one with a gasket surrounding the outer periphery of the 12A.

The membrane electrode assembly 10 may include the polymer electrolyte membrane 11 and the catalyst layers 12C and 12A, and the configuration other than these is not particularly limited. For example, the membrane electrode assembly 10 may include two gas diffusion layers having a function of diffusing the gas supplied to the catalyst layers 12C and 12A. One of the gas diffusion layers covers the surface of the cathode catalyst layer 12C opposite to the surface in contact with the polymer electrolyte membrane 11, and the other of the gas diffusion layer is the surface of the anode catalyst layer 12A in contact with the polymer electrolyte membrane 11. Covers the opposite side.

The polymer electrolyte membrane 11 contains a polymer electrolyte, and each of the cathode catalyst layer 12C and the anode catalyst layer 12A includes a polymer electrolyte, a carbon carrier which is a conductive carrier made of carbon, and a catalyst supported on the carbon carrier. Contains substances.

The polymer electrolyte contained in the catalyst layers 12C and 12A is a polymer electrolyte having proton conductivity and a tetrafluoroethylene skeleton, and preferably has a perfluoro side chain containing a sulfonic acid group. Examples of such polymer electrolytes include Nafion (registered trademark) manufactured by DuPont, Flemion (registered trademark) manufactured by Asahi Glass, Aciplex (registered trademark) manufactured by Asahi Kasei, and GORE-SELECT (registered trademark) manufactured by Gore. .. Among these materials, in order to increase the output voltage of the polymer electrolyte fuel cell, it is preferable to use a Nafion (registered trademark) -based material manufactured by DuPont.

The polymer electrolyte used in the polymer electrolyte film 11 may be any polymer electrolyte having proton conductivity. For example, in addition to the above-mentioned fluorine-based polymer electrolyte, a hydrocarbon-based polymer electrolyte may be used. .. However, it is preferable that the polymer electrolyte contained in the polymer electrolyte membrane 11 and the polymer electrolyte contained in the catalyst layers 12C and 12A are the same. The reason is that the interfacial resistance between the polymer electrolyte membrane 11 and the catalyst layers 12C and 12A increases, and the difference in the dimensional change rate between the polymer electrolyte membrane 11 and the catalyst layers 12C and 12A when the humidity changes. This is because it is possible to suppress the increase in size.

Examples of the catalytic material include platinum group elements such as platinum, palladium, ruthenium, iridium, rhodium, and osmium, metals such as iron, lead, copper, chromium, cobalt, nickel, manganese, vanadium, molybdenum, gallium, and aluminum, and , These alloys, oxides, compound oxides, carbides and the like are used. In particular, it is preferable to use platinum as the catalyst substance.

The carbon carrier may be a carrier that is in the form of a fine powder, has conductivity, and is not affected by the catalyst. For example, carbon black, graphite, graphite, activated carbon, carbon nanotubes, and fullerenes are preferably used.

The composition of the catalyst layers 12C and 12A is 85 at% <Xc <90 at% when the carbon atom concentration of the catalyst layers 12C and 12A obtained by energy dispersive X-ray spectroscopic analysis (EDX) is Xc and the fluorine atom concentration is Xf. And, 3 at% <Xf <7 at% is satisfied.

When the carbon atom concentration Xc is higher and the fluorine atom concentration Xf is lower than the above range, the proton conductivity of the catalyst layers 12C and 12A is insufficient and the resistance of the catalyst layers 12C and 12A is increased, so that the output of the fuel cell is increased. descend. Further, when the carbon atom concentration Xc is lower than the above range and the fluorine atom concentration Xf is high, the conductivity due to the carbon carrier is lowered, so that the output of the fuel cell is lowered. Further, when the carbon atom concentration Xc is lower and the fluorine atom concentration Xf is higher than the above range, the proportion of the pores contained in the catalyst layers 12C and 12A is small, so that the pores are clogged with water and supplied to the catalyst layers 12C and 12A. It is easy to block the path of the gas to be produced, and as a result, the output of the fuel cell is reduced.

That is, when each of the carbon atom concentration Xc and the fluorine atom concentration Xf of the catalyst layers 12C and 12A are within the above ranges, the proton conductivity in the catalyst layers 12C and 12A and the conductivity due to the carbon carrier are enhanced, and the gas And the diffusivity of water is enhanced.

Since the polymer electrolyte must contain water in order for the polymer electrolyte to pass protons, the proton conductivity of the catalyst layers 12C and 12A in a low humidification environment is such that the catalyst layers 12C and 12A in a high humidification environment. It is lower than the proton conductivity of. In the present embodiment, when each of the carbon atom concentration Xc and the fluorine atom concentration Xf of the catalyst layers 12C and 12A are within the above ranges, the catalyst layer 12C can obtain sufficient proton conductivity even in a low humid environment. , 12A proton conductivity is enhanced. That is, the catalyst layers 12C and 12A of the present embodiment show good proton conductivity in both a highly humidified environment and a low humidified environment.

On the other hand, if the amount of the polymer electrolyte in the catalyst layers 12C and 12A is increased too much in order to increase the proton conductivity, the number of pores contained in the catalyst layers 12C and 12A may decrease or the pores may become narrow. In particular, in a highly humid environment, the pores are clogged with water, making it difficult for the gas supplied to the catalyst layers 12C and 12A to reach the inside of the catalyst layers 12C and 12A. Further, in the cathode catalyst layer 12C, water is generated by power generation, so that such a phenomenon becomes remarkable. On the other hand, in the present embodiment, the ratio of the pores contained in the catalyst layers 12C and 12A is sufficiently ensured by setting each of the carbon atom concentration Xc and the fluorine atom concentration Xf of the catalyst layers 12C and 12A within the above ranges. Therefore, the diffusivity of gas and water is enhanced.

Therefore, according to the catalyst layers 12C and 12A of the present embodiment, it is possible to improve the proton conductivity in a low humidification environment and the diffusivity of gas and water in a high humidification environment at the same time. The output of the fuel cell is increased in both the environment and the low humidification environment.

The carbon atom concentration Xc and the fluorine atom concentration Xf of the catalyst layers 12C and 12A are determined by using the energy dispersive X-ray spectroscopic analysis (EDX) apparatus attached to the scanning electron microscope (SEM). It is obtained by performing elemental analysis of the cross section of. For example, using a scanning electron microscope (FE-SEM S-4800) and an energy dispersive X-ray spectroscopic analyzer (EDAX Genesis2000) manufactured by Hitachi High-Technology Co., Ltd., qualitative analysis and quantification of the cross section of each catalyst layer 12C, 12A. You just have to analyze it.

FIG. 4 shows an example of the spectrum obtained by performing a qualitative analysis of the cross section of the electrode catalyst layer using the above apparatus. In the spectrum shown in FIG. 4, a carbon peak is confirmed in the vicinity of 0.28 keV, and a fluorine peak is confirmed in the vicinity of 0.68 keV. By performing a quantitative analysis for correcting this peak intensity, a carbon atom concentration Xc in the electrode catalyst layer and a fluorine atom concentration Xf in the electrode catalyst layer can be obtained.

When the above apparatus is used, the observation magnification of the scanning electron microscope when performing the above analysis is preferably about 100,000 to 300,000 times. The size of the analysis region, which is the region targeted for elemental analysis in the cross section of the catalyst layers 12C and 12A, is expressed as the length in the thickness direction of the electrode catalyst layer × the length in the direction orthogonal to the thickness direction. , The size may be from 0.3 μm × 0.4 μm to 1.0 μm × 1.5 μm. Since the catalyst layers 12C and 12A are formed by applying and drying the catalyst ink in which the constituent materials of the catalyst layers 12C and 12A are uniformly dispersed, the composition thereof is substantially uniform in the entire catalyst layers 12C and 12A. ..

Further, the catalyst layers 12C and 12A may contain metal atoms constituting the catalyst substance in addition to carbon atoms and fluorine atoms, and may also contain oxygen atoms and sulfur atoms contained in the side chain of the polymer electrolyte. However, the influence of the oxygen atom density and the sulfur atom density on the difference in the power generation performance of the fuel cell due to the difference in the degree of humidification is small. Although the metal atomic density affects the conductivity of the catalyst layers 12C and 12A, it contributes to the improvement of proton conductivity in a low-humidity environment and the improvement of gas and water diffusivity in a high-humidity environment. small. Therefore, even if the oxygen atom density, the sulfur atom density, and the metal atom density constituting the catalyst substance change, if each of the carbon atom concentration Xc and the fluorine atom concentration Xf is within the above ranges, the output of the fuel cell can be increased. It is possible.

As a method for exposing the cross section of the electrode catalyst layer, a known method such as ion milling or ultramicrotome can be used. When processing to expose the cross section, it is preferable to perform processing while cooling the membrane electrode assembly in order to reduce damage to the polymer electrolyte constituting the electrode catalyst layer.

The thickness of the cathode catalyst layer 12C is 1 μm or more and 15 μm or less, preferably 5 μm or more and 15 μm or less, and more preferably 10 μm or more and 15 μm or less. If the thickness of the cathode catalyst layer 12C is 15 μm or less, the surface of the catalyst layer 12C will be cracked, the gas supplied to the cathode catalyst layer 12C and the diffusion of water generated by power generation will be hindered, and the conductivity will be reduced. The deterioration of sex is suppressed. As a result, the decrease in the output of the fuel cell is suppressed. Further, when the thickness of the cathode catalyst layer 12C is not more than the lower limit of the above range, the uniformity of the concentration of the catalyst substance and the polymer electrolyte in the catalyst layer 12C is enhanced.

The thickness of the anode catalyst layer 12A is preferably 1 μm or more and 15 μm or less, and preferably 2 μm or more and 5 μm or less. When the thickness of the anode catalyst layer 12A is not more than the upper limit of the above range, it is possible to prevent the supply of fuel such as hydrogen gas from being hindered inside the anode catalyst layer 12A. As a result, the decrease in the output of the fuel cell is suppressed. Further, when the thickness of the anode catalyst layer 12A is at least the lower limit of the above range, the uniformity of the concentration of the catalyst substance and the polymer electrolyte in the catalyst layer 12A is enhanced.

The thickness of the catalyst layers 12C and 12A is measured by the following method. The cross section of the electrode catalyst layer is observed using a scanning electron microscope, and five or more measurement regions are set in the cross section. The measurement region is, for example, a region having a size including the entire electrode catalyst layer in the thickness direction of the electrode catalyst layer and a predetermined size within a range of 15 μm or more and 25 μm or less in the direction orthogonal to the thickness direction. Is. For each measurement area, the thickness of three or more points is measured, and the average value of these measured values is used as the representative value of each measurement area. Then, the average value of the representative values of each measurement region is taken as the thickness of the electrode catalyst layer.

As the scanning electron microscope, for example, a scanning electron microscope (FE-SEM S-4800) manufactured by Hitachi High-Technology Co., Ltd. is used, and the cross section of the electrode catalyst layer is observed at a magnification of about 3000 to 10,000 times. It should be done.

With respect to the carbon carrier and the polymer electrolyte contained in the catalyst layers 12C and 12A, the mass ratio of the polymer electrolyte to the carbon carrier is preferably 0.8 or more and 1.6 or less.

When the mass ratio is 1.6 or less, the output of the fuel cell is increased because the proton path network is sufficiently constructed by the polymer electrolyte in the catalyst layers 12C and 12A. Further, when the mass ratio is 0.8 or more, the pores contained in the catalyst layers 12C and 12A are suppressed from being blocked by the polymer electrolyte, so that the diffusion of gas and water is suppressed. As a result, the output of the fuel cell is increased.

[Manufacturing method of electrode catalyst layer and membrane electrode assembly]
The method for producing the catalyst layers 12C and 12A and the membrane electrode assembly 10 described above will be described.
The catalyst layers 12C and 12A are formed by applying a catalyst ink containing the constituent materials of the catalyst layers 12C and 12A to a substrate to form a coating film, and drying the coating film to remove the solvent of the catalyst ink. ..

When the polymer electrolyte membrane 11 is used as the base material, the catalyst layers 12C and 12A can be directly formed on the surface of the polymer electrolyte membrane 11. Alternatively, a base material different from the polymer electrolyte membrane 11 may be used as a base material for forming the catalyst layers 12C and 12A, and the catalyst layers 12C and 12A may be transferred from the base material to the polymer electrolyte membrane 11. .. In this case, each of the cathode catalyst layer 12C and the anode catalyst layer 12A formed on the different base materials is brought into contact with the polymer electrolyte membrane 11, and the laminated body is heated and pressurized to heat and pressurize the catalyst layer. 12C and 12A are bonded to the polymer electrolyte membrane 11. Then, by peeling off the base material, a laminate of the polymer electrolyte membrane 11 and the catalyst layers 12C and 12A is formed. The above-mentioned gas diffusion layer may be used as the base material. In this case, the base material functions as a gas diffusion layer without being separated from the catalyst layers 12C and 12A.

The catalyst ink includes the above-mentioned polymer electrolyte having a tetrafluoroethylene skeleton, the above-mentioned carbon carrier, a catalyst substance supported on the carbon carrier, and an ink solvent. The catalyst ink is produced by adding a polymer electrolyte and a carbon carrier carrying a catalyst substance to an ink solvent, mixing them, and performing a dispersion treatment.

Here, with respect to the carbon carrier contained in the ink solvent and the polymer electrolyte, the mass ratio of the polymer electrolyte to the carbon carrier is preferably 0.8 or more and 1.6 or less. According to such a configuration, the catalyst layers 12C and 12A in which the mass ratio of the polymer electrolyte to the carbon carrier is 0.8 or more and 1.6 or less can be formed. Then, by adjusting the catalyst ink so that the mass ratio is within the above range, each of the carbon atom concentration Xc and the fluorine atom concentration Xf of the formed catalyst layers 12C and 12A can be easily contained within the above range. ..
For the dispersion treatment, for example, a planetary ball mill, a bead mill, an ultrasonic homogenizer, or the like may be used.

The ink solvent used as a dispersion medium for the catalyst ink is particularly limited as long as it is a solvent that does not erode the catalyst substance or the polymer electrolyte and can dissolve the polymer electrolyte or disperse it as a fine gel in a highly fluid state. Not done.

The ink solvent may contain water having a high affinity with the polymer electrolyte. Further, the ink solvent preferably contains a volatile organic solvent, but when a lower alcohol is used as the organic solvent, the ink solvent is an organic solvent and water in order to raise the ignition temperature of the ink solvent. It is preferable to use a mixed solvent of. The ratio of water in the ink solvent is not particularly limited as long as the polymer electrolyte does not separate from the ink solvent to cause white turbidity or the polymer electrolyte does not gel.

A base material different from the polymer electrolyte membrane 11 is used as a base material for forming the catalyst layers 12C and 12A, and this base material is peeled off after the polymer electrolyte membrane 11 and the catalyst layers 12C and 12A are bonded. When forming the catalyst layers 12C and 12A, a film made of the following materials may be used as the base material. That is, examples of such a substrate include ethylene tetrafluoroethylene copolymer (ETFE), tetrafluoroethylene-hexafluoropropylene copolymer (FEP), tetrafluoroperfluoroalkyl vinyl ether copolymer (PFA), and polytetra. Films made of fluororesin with excellent transferability such as fluoroethylene (PTFE), polyimide, polyethylene terephthalate, polyamide (nylon), polysulfone, polyether sulfone, polyphenylene sulfide, polyether ether ketone, polyetherimide , Polyallylate, polyethylene naphthalate and other polymer films are used.

As a method of applying the catalyst ink to the base material, for example, a coating method such as die coat, slit die coat, roll coat, curtain coat, spray coat, squeegee or the like is used. In particular, the die coat is a catalyst because the film thickness of the portion of the coating film formed in the middle portion from the start to the end of the application of the catalyst ink is stable and it can be applied intermittently. It can be suitably used as an ink application method.
Further, for drying the coating film, for example, a warm air oven, IR drying, vacuum drying and the like are used.

When the catalyst layers 12C and 12A formed on the base material are bonded to the polymer electrolyte membrane 11 by heating and pressurizing, the pressure applied to the catalyst layers 12C and 12A affects the power generation performance of the fuel cell. Therefore, the pressure applied to the laminate during pressurization is preferably 0.5 MPa or more and 20 MPa or less, and preferably 2 MPa or more and 15 MPa or less. When the pressure is equal to or lower than the upper limit of the above range, the catalyst layers 12C and 12A are suppressed from being over-compressed, and when the pressure is equal to or higher than the lower limit of the above range, the catalyst layers 12C and 12A and the polymer electrolyte membrane 11 are formed. Since sufficient bondability is obtained, deterioration of the power generation performance of the fuel cell can be suppressed.

Further, the heating temperature is preferably set near the glass transition point of the polymer electrolyte contained in the catalyst layers 12C and 12A. As a result, the bondability between the catalyst layers 12C and 12A and the polymer electrolyte membrane 11 is improved, and the increase in interfacial resistance is suppressed.

As a result, the membrane electrode assembly 10 including the polymer electrolyte membrane 11 and the catalyst layers 12C and 12A is formed. When the membrane electrode assembly 10 includes a gasket 13 and a gas diffusion layer, these members are appropriately assembled after the above steps.

[Proton electrolyte fuel cell]
The configuration of the polymer electrolyte fuel cell including the above-mentioned membrane electrode assembly 10 will be described with reference to FIG.
As shown in FIG. 5, the polymer electrolyte fuel cell 20 includes a membrane electrode assembly 10 having a pair of gas diffusion layers 14C and 14A, and a pair of separators 21C and 21A. The membrane electrode assembly 10 is sandwiched between the separator 21C and the separator 21A. In the separator 21C, the gas flow path 22C is recessed on the surface facing the membrane electrode assembly 10, and the cooling water flow path 23C is recessed on the surface opposite to the membrane electrode assembly 10. ing. In the separator 21A, a gas flow path 22A is recessed on the surface facing the membrane electrode assembly 10, and a cooling water flow path 23A is recessed on the surface opposite to the membrane electrode assembly 10. ing.

In the above configuration, the cathode catalyst layer 12C and the gas diffusion layer 14C laminated on the cathode catalyst layer 12C form an air electrode as a cathode, and the gas diffusion laminated on the anode catalyst layer 12A and the anode catalyst layer 12A. A fuel electrode, which is an anode, is formed from the layer 14A.

Separators 21C and 21A are assembled to the membrane electrode assembly 10, and a supply mechanism for an oxidant gas and a fuel gas is further provided to manufacture a single-cell polymer electrolyte fuel cell 20. The polymer electrolyte fuel cell 20 may be used in a single cell state, or may be used as one fuel cell by stacking a plurality of polymer electrolyte fuel cells 20 and connecting them in series. ..

When the polymer electrolyte fuel cell 20 is used, an oxidant gas such as oxygen flows through the gas flow path 22C of the separator 21C on the cathode side, and a fuel gas such as hydrogen flows through the gas flow path 22A of the separator 21A on the anode side. Is done. Further, cooling water is flowed through the cooling water flow paths 23C and 23A of the separators 21C and 21A. Then, the gas is supplied from the gas flow path 22C to the cathode, and the gas is supplied from the gas flow path 22A to the anode, so that the electrode reaction accompanied by proton conduction in the polymer electrolyte membrane 11 proceeds. , An electromotive force is generated between the cathode and the anode.

[Example]
The above-mentioned electrode catalyst layer, membrane electrode assembly, polymer electrolyte fuel cell, and method for producing the electrode catalyst layer will be described with reference to specific examples and comparative examples.

(Example 1)
A polymer electrolyte (Nafion (registered trademark), manufactured by DuPont) dispersion, a platinum-supported carbon catalyst (TEC10E50E, manufactured by Tanaka Kikinzoku Kogyo Co., Ltd.), and a mixed solvent of water and ethanol are mixed, and a planetary ball mill is used. A dispersion treatment was performed to prepare a catalytic ink. At that time, the mixing amount of the polymer electrolyte and the platinum-supported carbon catalyst was determined so that the mass ratio of the polymer electrolyte to the carbon carrier was 1.0.

The adjusted catalyst ink was applied to a rectangular area on the surface of the PTFE film by a slit die coater. Subsequently, the PTFE film coated with the catalyst ink is placed in a warm air oven at 80 ° C. until the catalyst ink is no longer tacked, that is, until the catalyst ink does not adhere to the fingertips even if the coating film is lightly touched with the fingertips. After drying, a cathode catalyst layer was formed on the surface of the PTFE film.
Further, the anode catalyst layer was formed on the surface of the PTFE film by the same step as the step of forming the cathode catalyst layer except that the amount of the catalyst ink applied in the thickness direction of the coating film was halved.

Then, the cathode catalyst layer formed on the PTFE film faces one surface of the polymer electrolyte membrane (Nafion (registered trademark) 212, manufactured by DuPont), and the anode catalyst layer formed on the PTFE film is the polymer electrolyte membrane. The laminate was placed so as to face the other surface of the structure, and the laminate was hot pressed. Then, the PTFE film was peeled off from each of the cathode catalyst layer and the anode catalyst layer to obtain a membrane electrode assembly of Example 1.

A laminate composed of a polymer electrolyte membrane, a cathode catalyst layer, and an anode catalyst layer was sandwiched between two gas diffusion layers, and a gasket was assembled. Further, this structure was sandwiched between two separators and tightened so as to apply a predetermined surface pressure to obtain a polymer electrolyte fuel cell of Example 1.

(Example 2)
The membrane electrode assembly and Examples of Example 2 were subjected to the same steps as in Example 1 except that the amount of catalyst ink applied in the thickness direction of the coating film was increased by 1.5 times when the cathode catalyst layer was formed. 2 solid polymer fuel cells were obtained.

(Example 3)
The membrane electrode assembly and Examples of Example 3 were subjected to the same steps as in Example 1 except that the amount of catalyst ink applied in the thickness direction of the coating film was reduced to 1/5 when forming the anode catalyst layer. 3 solid polymer fuel cells were obtained.

(Example 4)
In the preparation of the catalyst ink, the same steps as in Example 1 except that the mixing amount of the polymer electrolyte and the platinum-supported carbon catalyst was determined so that the mass ratio of the polymer electrolyte to the carbon carrier was 0.8. Obtained a membrane electrode assembly of Example 4 and a polymer electrolyte fuel cell of Example 4.

(Example 5)
In the preparation of the catalyst ink, the same steps as in Example 1 except that the mixing amount of the polymer electrolyte and the platinum-supported carbon catalyst was determined so that the mass ratio of the polymer electrolyte to the carbon carrier was 1.6. The membrane electrode assembly of Example 5 and the polymer electrolyte fuel cell of Example 5 were obtained.

(Comparative Example 1)
In the preparation of the catalyst ink, the same steps as in Example 1 except that the mixing amount of the polymer electrolyte and the platinum-supported carbon catalyst was determined so that the mass ratio of the polymer electrolyte to the carbon carrier was 0.7. A membrane electrode assembly of Comparative Example 1 and a polymer electrolyte fuel cell of Comparative Example 1 were obtained.

(Comparative Example 2)
In the preparation of the catalyst ink, the same steps as in Example 1 except that the mixing amount of the polymer electrolyte and the platinum-supported carbon catalyst was determined so that the mass ratio of the polymer electrolyte to the carbon carrier was 1.7. The membrane electrode assembly of Comparative Example 2 and the polymer electrolyte fuel cell of Comparative Example 2 were obtained.

(Comparative Example 3)
The membrane electrode assembly of Comparative Example 3 and Comparative Example 3 were subjected to the same steps as in Example 1 except that the amount of the catalyst ink applied in the thickness direction of the coating film was doubled when the cathode catalyst layer was formed. A polymer electrolyte fuel cell was obtained.

(Evaluation)
For the membrane electrode assembly of each Example and each Comparative Example, the thickness of each of the cathode catalyst layer and the anode catalyst layer was measured, and the carbon atom concentration Xc and the fluorine atom concentration Xf in the cathode catalyst layer were analyzed. In addition, the power generation performance of each example and each comparative example of the polymer electrolyte fuel cell was evaluated in a high humidification environment and a low humidification environment.

(Measurement of the thickness of the electrode catalyst layer)
The thickness of each of the cathode catalyst layer and the anode catalyst layer was measured by observing the cross section of the electrode catalyst layer using a scanning electron microscope.
Specifically, first, a cross section polisher (SM-09010) manufactured by JEOL Ltd. was used to expose the cross section of the electrode catalyst layer. Next, the obtained cross section was observed at a magnification of 5000 times using a scanning electron microscope (FE-SEM S-4800) manufactured by Hitachi High Technology, Inc., and in the field of view, that is, the thickness of the electrode catalyst layer. Thicknesses were measured at three locations within a measurement region having a size of 20 μm in a direction orthogonal to the direction, and the average value was used as a representative value in this measurement region. The above representative values were calculated for the five measurement regions, and the average value of the representative values of each measurement region was taken as the thickness of the electrode catalyst layer.

(Analysis of carbon atom concentration and fluorine atom concentration)
The carbon atom concentration Xc and the fluorine atom concentration Xf of the cathode catalyst layer were obtained by energy dispersive X-ray spectroscopic analysis.
Specifically, using the cross section used for measuring the thickness of the electrode catalyst layer described above, energy dispersive X-ray spectroscopy incidental to a scanning electron microscope (FE-SEM S-4800) manufactured by Hitachi High Technology Co., Ltd. The carbon atom concentration Xc and the fluorine atom concentration Xf were determined by performing qualitative analysis and quantitative analysis using an analyzer (EDAX Genesis2000). The observation magnification of the scanning electron microscope at the time of analysis was set to 200,000 times. The size of the analysis region at this time was 0.6 μm × 0.8 μm in the length in the thickness direction × the length in the direction orthogonal to the thickness direction in the electrode catalyst layer.

(Evaluation of power generation performance)
Using the polymer electrolyte fuel cells of each example and each comparative example as a single cell for evaluation, the New Energy and Industrial Technology Development Organization (NEDO) solid polymer fuel cell practical application promotion technology development basic technology development: cell The IV measurement was carried out according to the method described in the common basic technology "cell evaluation analysis protocol" for evaluation analysis. The relative humidity of the cassette and the relative humidity of the anode are changed from the conditions described in the "cell evaluation analysis protocol", and high humidification is performed when each of the relative humidity of the cassette and the relative humidity of the anode is set to 100% RH. Under the environment, the case where each of the relative humidity of the cassette and the relative humidity of the anode was set to 25% RH was defined as a low humidification environment.

(result)
In Table 1, for each Example and each Comparative Example, the mass ratio X of the polymer electrolyte to the carbon carrier used in the preparation of the catalyst ink, the thickness of each of the cathode catalyst layer and the anode catalyst layer, and the thickness of each of the cathode catalyst layer and the cathode catalyst layer. The evaluation of the power generation performance of the polymer electrolyte fuel cell with carbon atom concentration Xc and fluorine atom concentration Xf is shown. Regarding the power generation performance, in a highly humidified environment, the case where the current at a voltage of 0.6 V was larger than 20 A was evaluated as ◯, and the case where the current was 20 A or less was evaluated as x. Further, in a low humidification environment, the case where the current at a voltage of 0.6 V was greater than 10 A was evaluated as ◯, and the case where the current was 10 A or less was evaluated as x.

As shown in Table 1, for the cathode catalyst layer, the carbon atom concentration Xc and the fluorine atom concentration Xf are 85 at% <Xc <90 at% and 3 at% <Xf <7 at%, and the thickness is 1 μm or more and 15 μm or less. It was shown that in each of Examples 1 to 5, good power generation performance can be obtained in both a high humidification environment and a low humidification environment. Since the composition of the anode catalyst layer is the same as that of the cathode catalyst layer, it is suggested that the above conditions are also satisfied for the anode catalyst layers of Examples 1 to 5. On the other hand, in Comparative Examples 1 to 3 in which the above conditions were not satisfied for the cathode catalyst layer, the power generation performance was low in both a low humidification environment or both a high humidification environment and a low humidification environment.

Further, when the substances used in each example are used as the carbon carrier and the polymer electrolyte, the catalyst ink is adjusted so that the mass ratio of the polymer electrolyte to the carbon carrier is 0.8 or more and 1.6 or less. It was shown that an electrode catalyst layer having a carbon atom concentration Xc and a fluorine atom concentration Xf within the above ranges can be formed.

The electrode catalyst layer in which the carbon atom concentration in the electrode catalyst layer and the thickness of the electrode catalyst layer are the same is not limited to the polymer electrolyte used in each example, but a polymer electrolyte having a tetrafluoroethylene skeleton can be used. If the electrode catalyst layer contains the electrode catalyst layer, the same tendency can be obtained for the characteristics that affect the difference in power generation performance due to the degree of humidification. Therefore, not only when the substance used in each example is used as the polymer electrolyte, but also the carbon atom concentration of the electrode catalyst layer containing the polymer electrolyte having a tetrafluoroethylene skeleton and the carbon carrier carrying the catalyst substance. If the above conditions regarding the Xc and fluorine atom concentrations Xf and the layer thickness are satisfied, it is possible to obtain good power generation performance in both a high humidification environment and a low humidification environment.

As described above, the present inventor has conducted intensive research on the power generation performance in the low humidification environment, and as a result, the ratio of the carbon atom concentration and the fluorine atom concentration in the electrode catalyst layer is large in the power generation performance in the low humidification environment. I found that it was influential. Furthermore, in order to obtain good power generation performance in both a high-humidified environment and a low-humidified environment, the carbon atom density is excessive and the fluorine atom density is too low, and the carbon atom density is too low and the fluorine atom density is low. I found that it was necessary to avoid both being excessive. Based on these findings, it was found that the carbon atom concentration and the fluorine atom concentration in the electrode catalyst layer can be obtained in a range in which good power generation performance can be obtained in both a high-humidified environment and a low-humidified environment.

In the above-described embodiments and examples, both the cathode catalyst layer and the anode catalyst layer are electrode catalyst layers that satisfy the conditions of the carbon atom concentration Xc and the fluorine atom concentration Xf and the thickness of the layer. It was.

In the polymer electrolyte fuel cell, since the reaction barrier of the reaction at the cathode is larger than the reaction barrier of the reaction at the anode, the activity of the reaction at the cathode catalyst layer has a greater influence on the progress of the electrode reaction. Further, since water is generated by such a chemical reaction in the cathode catalyst layer, increasing the diffusibility of gas and water in the cathode catalyst layer greatly contributes to the improvement of power generation performance. Therefore, if at least the cathode catalyst layer satisfies the above conditions, good power generation performance can be obtained in both a high humidification environment and a low humidification environment.

Further, it is not limited to the polymer electrolyte fuel cell, and has a membrane electrode assembly structure similar to that of the polymer electrolyte fuel cell, such as a direct methanol fuel cell, and is powered by a chemical reaction accompanied by conduction of protons. When the electrode catalyst layer of the above embodiment is used for the fuel cell that produces the fuel cell, good power generation performance can be obtained in both a high humidification environment and a low humidification environment by the same operation as in the case of the polymer electrolyte fuel cell. .. In a direct methanol fuel cell, since the fuel supplied to the anode is a liquid, increasing the diffusibility of the gas or liquid in the anode catalyst layer also greatly contributes to the improvement of power generation performance. Therefore, in the direct methanol fuel cell, the electrode catalyst layer of the above embodiment may be used only for either the cathode or the anode.

As described above, the electrode catalyst layer of the above embodiment is not limited to the electrode catalyst layer of the polymer electrolyte fuel cell, and may be used as the electrode catalyst layer of the direct methanol fuel cell, or may be used as the cathode catalyst layer. It may be used as an anode catalyst layer.

As described above with reference to the examples, according to the above-described embodiment, the effects listed below can be obtained.
(1) The carbon atom concentration Xc and the fluorine atom concentration Xf of the electrode catalyst layer obtained by energy dispersive X-ray spectroscopic analysis satisfy 85 at% <Xc <90 at% and 3 at% <Xf <7 at%, and the electrode catalyst. The thickness of the layer is 1 μm or more and 15 μm or less. According to such a configuration, the electrode catalyst layer can achieve both improvement of proton conductivity in a low humidification environment and improvement of gas and water diffusivity in a high humidification environment. Therefore, in the fuel cell provided with this electrode catalyst layer, the power generation performance in both the high humidification environment and the low humidification environment is enhanced.

(2) The mass ratio of the polymer electrolyte to the carbon carrier contained in the electrode catalyst layer is 0.8 or more and 1.6 or less. According to such a configuration, the composition of the electrode catalyst layer is determined as the mass ratio of the polymer electrolyte to the carbon carrier, so that the electrode catalyst layer can be easily formed.

(3) The catalyst ink is adjusted so that the mass ratio of the polymer electrolyte to the carbon carrier contained in the catalyst ink is 0.8 or more and 1.6 or less, and the catalyst ink is used to satisfy the above conditions. According to the method for forming the layer, the electrode catalyst layer satisfying the above conditions can be formed by controlling the mass ratio of the polymer electrolyte to the carbon carrier in the catalyst ink, so that the electrode catalyst layer can be easily formed.

10 ... Membrane electrode assembly, 11 ... Polymer electrolyte membrane, 12C ... Cathode catalyst layer, 12A ... Anode catalyst layer, 13 ... Gasket, 14C, 14A ... Gas diffusion layer, 20 ... Solid polymer fuel cell, 21C, 21A … Separator.

Claims (5)

And a polymer electrolyte having a tetrafluoroethylene backbone with a carbon carrier is a conductive carrier made of carbon, viewed contains a catalyst substance supported on the carbon support, the electrodes used in combination to the anode catalyst layer and cathode catalyst layer It is a catalyst layer
When the carbon atom concentration of the electrode catalyst layer obtained by the energy dispersive X-ray spectroscopic analysis is Xc and the fluorine atom concentration is Xf, 85 at% <Xc <90 at% and 3 at% <Xf <7 at%.
The electrode catalyst layer having a thickness of 1 μm or more and 15 μm or less. The electrode catalyst layer according to claim 1, wherein the mass ratio of the polymer electrolyte to the carbon carrier contained in the electrode catalyst layer is 0.8 or more and 1.6 or less. A cathode catalyst layer, which is an electrode catalyst layer used for the cathode of a fuel cell,
An anode catalyst layer, which is an electrode catalyst layer used for the anode of the fuel cell,
A polymer electrolyte membrane sandwiched between the cathode catalyst layer and the anode catalyst layer,
With
Each catalyst layer contains a polymer electrolyte having a tetrafluoroethylene skeleton, a carbon carrier which is a conductive carrier made of carbon, and a catalyst substance supported on the carbon carrier, and is obtained by energy dispersion type X-ray spectroscopic analysis. when the carbon atom concentration in the catalyst layer Xc, and Xf fluorine atom concentration to be, 85at% <Xc <90at% , and a 3at% <Xf <7at%,
A membrane electrode assembly in which the thickness of each catalyst layer is 1 μm or more and 15 μm or less. The membrane electrode assembly according to claim 3 and
A pair of separators sandwiching the membrane electrode assembly,
A solid polymer fuel cell equipped with. A method for manufacturing an electrode catalyst layer used in combination with an anode catalyst layer and a cathode catalyst layer.
The first step of producing a catalyst ink by dispersing a polymer electrolyte having a tetrafluoroethylene skeleton, a carbon carrier which is a conductive carrier made of carbon, and a catalyst substance supported on the carbon carrier in a solvent.
The second step of forming the electrode catalyst layer by applying the catalyst ink to the substrate and drying it, and
Including
In the first step, the catalyst ink is adjusted so that the mass ratio of the polymer electrolyte to the carbon carrier contained in the catalyst ink is 0.8 or more and 1.6 or less.
With respect to the electrode catalyst layer formed in the second step, when the carbon atom concentration of the electrode catalyst layer obtained by energy dispersion type X-ray spectroscopic analysis is Xc and the fluorine atom concentration is Xf, 85 at% <Xc <90 at. %, 3 at% <Xf <7 at%, and the thickness of the electrode catalyst layer is 1 μm or more and 15 μm or less. A method for producing an electrode catalyst layer.