JP2003109643A - Fuel cell - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a fuel cell capable of keeping an electrolyte material in a desirable wet environment without cutting an electron conductive passage inside a catalyst layer, and achieving the efficient cell performance. SOLUTION: In this fuel cell including a pair of catalyst layers holding a proton conductive electrolyte film therebetween, at least one of the catalyst layers is composed of a mixture including a catalyst component, the electrolyte material and a carbon material, which has a water vapor adsorption of 100 ml/g or less at 25 deg.C under relative humidity of 90%.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a fuel cell,
In particular, it operates under conditions where water tends to aggregate in the catalyst layer,
For example, the present invention relates to a fuel cell such as a polymer electrolyte fuel cell having an improved catalyst layer.

[0002]

2. Description of the Related Art A general polymer electrolyte fuel cell has a polymer electrolyte membrane sandwiched between one side and a catalyst layer which serves as a positive electrode on the other side and a negative electrode on the other side. It has a basic structure in which water-repellent carbon paper or the like is in contact as a gas diffusion layer.

In order to extract an electric current from a fuel cell having such a basic structure, an oxidizing gas such as oxygen or air is supplied to the positive electrode side, a reducing gas such as hydrogen is supplied to the negative electrode side, and a reducing gas such as hydrogen is supplied from the outside through a gas diffusion layer. Supply each. For example, when using hydrogen gas and oxygen gas, it occurs on the negative electrode catalyst.

[0004]

[Chemical 1]

The chemical reaction of and takes place on the cathode catalyst

[0006]

[Chemical 2]

An electric current is taken out by utilizing the energy difference of the chemical reaction. For this purpose, a gas diffusion path capable of supplying oxygen gas or hydrogen gas to the catalyst inside the catalyst layer, a proton conduction path and an electron transfer path capable of respectively transmitting the protons and electrons generated on the negative electrode catalyst to the positive electrode catalyst, At least the electric current cannot be taken out unless they are connected in the catalyst layer without being divided. Inside the catalyst layer, generally, pores formed in the gap of the material as a gas diffusion path, an electrolyte material as a proton conduction path,
The carbon material functions as an electron conduction path by making each network function.

In particular, an ion exchange resin such as a perfluorosulfonic acid polymer or styrenedivinylbenzenesulfonic acid is used as a polymer electrolyte material in the proton conducting path. These commonly used ion exchange resins exhibit high proton conductivity for the first time in a wet environment,
In a dry environment, the proton conductivity will decrease. It is considered that this is because water molecules are essential for the transfer of protons. Therefore, in order to operate the fuel cell efficiently, it is essential that the electrolyte material is always in a wet state, and it is necessary to constantly supply water vapor together with the gas supplied to both electrodes.

Generally, for the purpose of supplying water to the electrolyte material, a method of humidifying the gas supplied to the cell and operating the cell below the dew point is adopted. According to this method, the water vapor supplied into the cell partially aggregates to form droplets of aggregated water. In addition, water is produced on the positive electrode catalyst by the positive electrode reaction described above. Depending on the operating conditions of the cell, the generated water aggregates when the water vapor in the catalyst layer becomes supersaturated and becomes aggregated water droplets.

The water generated by these reactions coagulates, or the water vapor supplied for humidification coagulates in the catalyst layer to form droplets that block the gas diffusion path. This phenomenon is called flooding, and it is remarkable in the positive electrode in which a large amount of water is generated at the time of discharging a large current, which causes an extreme voltage drop.

As described above, in order to stably operate the fuel cell, it is necessary to sufficiently condense the inside of the catalyst layer while satisfying the contradictory requirements of promptly discharging the condensed water out of the system. For this reason, carbon materials conventionally used for catalyst layers have been changed to polytetrafluoroethylene (hereinafter referred to as PTFE).
)) Or a silane coupling agent.

In Japanese Patent Laid-Open No. 5-36418, PTFE is used.
The powder is a PTFE colloid in JP-A-4-264367, and the PTFE colloid in JP-A-7-183035.
The water-repellent carbon powder prepared by
Japanese Patent No. 404 has proposed a device to increase the water repellency inside the catalyst layer and quickly discharge the condensed water out of the system by incorporating a carbon material which has been subjected to a water repellent treatment with a silane coupling agent into the catalyst layer. .

[0013]

In the conventionally proposed catalyst layer, since a compound such as PTFE or a silane coupling agent that divides the electron conduction path of the catalyst layer is used, there is a problem in performance such as deterioration of battery performance, Since the process is complicated and a relatively expensive compound is used, there are problems that the manufacturing cost is increased.

Further, these silane coupling agents and PT
Since the water repellency of a water repellent substance such as FE is extremely high, the wet environment suitable for the electrolyte material cannot be maintained inside the catalyst layer using these compounds, and the conventional catalyst layer does not always realize efficient battery characteristics. could not. Therefore, conventionally, there is no proposal of a material that maintains a suitable wet environment for an electrolyte material, and a quantitative index regarding the hydratability of a material that maintains a suitable wet environment useful for catalyst layer design is clearly shown. Was not done.

Therefore, an object of the present invention is to provide a fuel cell which can maintain a suitable wet environment without dividing the electron conduction path in the catalyst layer of the fuel cell and can exhibit extremely efficient cell performance. .

[0016]

[Means for Solving the Problems] As a result of repeated studies to solve the above problems, it is confirmed that the hydratability of the carbon material, which is one of the main components of the catalyst layer, has an appropriate range. The carbon material which is the main component is divided into a carbon material supporting a catalyst component (hereinafter, catalyst supporting carbon material) and a carbon material not supporting a catalyst component (hereinafter, gas diffusion carbon material),
When it is contained in the catalyst layer, it is possible to prevent clogging of the gas diffusion path due to condensed water, in particular, it is possible to significantly improve the battery characteristics during large current discharge, and further, the optimum range for the content ratio of the gas diffusion carbon material is The present invention has been completed, and the inventors have found that the gas diffusion carbon material exists in a range suitable for hydration, and have completed the present invention.

That is, the gist of the present invention is that
It is as follows.

(1) A fuel cell comprising a pair of catalyst layers sandwiching a proton-conducting electrolyte membrane, wherein at least one catalyst layer comprises a catalyst component, an electrolyte material and a carbon material. A fuel cell having a water vapor adsorption amount of 100 ml / g or less at 25 ° C. and a relative humidity of 90%.

(2) The carbon material constitutes a catalyst-supporting carbon material that supports the catalyst component and a gas-diffusing carbon material that does not support the catalyst component, and the gas-diffusing carbon material is 5 mass% in the catalyst layer. % Or more and 50% by mass or less, The fuel cell according to (1).

(3) The gas diffusion carbon material is 25 ° C.,
The fuel cell according to (2), which comprises one or more kinds of carbon materials having a water vapor adsorption amount of 1 ml / g or more and 100 ml / g or less at a relative humidity of 90%.

(4) The gas diffusion carbon material is 25 ° C.
The fuel cell according to (3), which comprises one or more kinds of carbon materials having a water vapor adsorption amount of 1 ml / g or more and 50 ml / g or less at a relative humidity of 90%.

[0022]

BEST MODE FOR CARRYING OUT THE INVENTION The fuel cell of the present invention has a catalyst layer containing a catalyst component, a carbon material, and an electrolyte material, and the carbon material, which is one of the main components of the catalyst layer, has a temperature of 25 ° C. The water vapor adsorption amount at a relative humidity of 90% is 100 ml / g or less.

The amount of water vapor adsorbed at 25 ° C. and 90% relative humidity, which is an index, can be measured by using a commercially available apparatus for measuring the amount of water vapor adsorption. Alternatively, the dried carbon material can be allowed to stand for a sufficient time in a thermo-hygrostat at 25 ° C. and a relative humidity of 90%, and the mass change can be measured. When a plurality of carbon materials are used in the catalyst layer, the amount of water vapor adsorbed in the mixture obtained by mixing the carbon materials at the content rates of the carbon materials should be measured.

When the amount of water vapor adsorbed at 25 ° C. and 90% relative humidity of the carbon material is 100 ml / g or less, the blockage of the gas diffusion path at the time of large current discharge can be suppressed, and a stable current can be taken out. If it is more than 100 ml / g, condensed water is retained in the catalyst layer, the gas diffusion path is easily blocked, and the voltage behavior during large current discharge becomes unstable.

A carbon material having a water vapor adsorption amount of 100 ml / g or less at 25 ° C. and a relative humidity of 90% can be selected from generally existing carbon materials using the water vapor adsorption amount as an index.
Alternatively, even in the case of a carbon material having an excessive amount of water vapor adsorption, the amount of water vapor adsorption can be reduced to a suitable range by firing in an inert atmosphere. Although the conditions are not particularly limited, the amount of water vapor adsorption can be reduced to a desired range by performing heat treatment in an atmosphere such as argon, nitrogen, helium, or vacuum.

The type of carbon material used for the catalyst layer included in the fuel cell of the present invention is not particularly limited as long as it is a carbon material having electron conductivity which is generally present, but is originally required. Cause a chemical reaction other than the reaction,
A material in which a substance constituting a carbon material is eluted by contact with condensed water is not preferable, and a chemically stable carbon material is preferable. The primary particle diameter of the carbon material is preferably 1 μm or less, and a carbon material larger than this can be crushed and used. When the primary particle diameter is more than 1 μm, the gas diffusion path and the proton conduction path are likely to be divided, and the distribution of the carbon material in the catalyst layer tends to be nonuniform, which is not preferable. Carbon black can be mentioned as a preferable carbon material.

The carbon material, which is one of the main components of the catalyst layer included in the fuel cell of the present invention, preferably constitutes a catalyst supporting carbon material and a gas diffusion carbon material. By including a carbon material in which no catalyst component is supported, that is, a gas diffusion carbon material in the catalyst layer, it is possible to develop a path through which gas can diffuse in the catalyst layer, and hydrogen or hydrogen is mainly used for the negative electrode. In the case of a mixed gas or a positive electrode, oxygen, air, or the like is likely to diffuse into the catalyst layer, and can come into contact with many catalyst surfaces. Therefore, the reaction in the catalyst layer is efficiently advanced, and high battery performance is obtained.

Further, it is more preferable that the content of the gas diffusion carbon material in the catalyst layer is within the range of 5% by mass or more and 50% by mass or less. If it is less than 5% by mass, the gas diffusion path cannot be sufficiently expanded, and the effect of including the gas diffusion carbon material becomes unclear. If it exceeds 50% by mass, the proton conduction path becomes poor and the IR drop becomes large, so that the battery performance deteriorates. Although it depends on the type and form of the carbon material used, 10% by mass to 40% by mass is most preferable. Within this range, the gas diffusion path can be developed without impairing the proton conduction path and the electron conduction path.

In order to obtain a higher effect, a gas diffusion carbon material having a surface hydration property, that is, a water vapor adsorption amount in an appropriate range is used. Specifically, the water vapor adsorption amount at 25 ° C. and relative humidity 90% is 1 ml / g or more and 100 m.
A carbon material having a ratio of 1 / g or less is selected as the gas diffusion carbon material. If the amount of water vapor adsorbed at 25 ° C. and relative humidity of 90% is less than 1 ml / g, the water repellency becomes too strong, making it difficult for the electrolyte material coexisting in the catalyst layer to maintain a wet state, resulting in a decrease in proton conductivity. Therefore, the effect of adding the gas diffusion carbon material may be reduced. If the amount of water vapor adsorbed at 25 ° C. and relative humidity of 90% is 1 ml / g or more, the wet state suitable for the electrolyte material coexisting in the catalyst layer can be maintained, so that the gas diffusion path can be maintained without impairing the proton conductivity. Can be expanded. If the carbon material has a water vapor adsorption amount of 1 ml / g or more at 25 ° C. and a relative humidity of 90%, it is 2
It is also possible to mix more than one kind of carbon material and use it as a gas diffusion carbon material. On the other hand, 25 ° C, relative humidity 90%
When the amount of water vapor adsorbed in the catalyst exceeds 100 ml / g, discharge of water generated inside the catalyst layer at the time of high-current discharge may not catch up, and the gas diffusion path may be blocked. Therefore, the effect of adding the gas diffusion carbon material May be low.

The amount of water vapor adsorbed on the gas diffusion carbon material at 25 ° C. and relative humidity of 90% is 1 ml / g or more and 50 m or more.
It is more preferably 1 / g or less. Within this range, even during a small current discharge in which a small amount of water is generated inside the positive electrode, it is possible to prevent the electrolyte material in the positive electrode from being dried, a suitable wet state can be maintained, and even during a large current discharge, the catalyst Since the water generated inside the layer can be efficiently diffused to the outside of the catalyst layer, an efficient battery can be obtained over the entire range from low load to high load regardless of load conditions. 25
Adsorption amount of water vapor is 50ml / at 90 ℃, relative humidity 90%
If it exceeds g, the discharge of water generated inside the catalyst layer at the time of high-current discharge may not catch up, and the gas diffusion path may be blocked, so the effect of adding the gas diffusion carbon material may be reduced.

The control of the hydration property of the gas diffusion carbon material surface is
This can be achieved by selecting the amount of water vapor adsorption as an index from the carbon materials that generally exist. Alternatively, even in the case of a carbon material having a water vapor adsorption amount less than the preferred range, the water vapor adsorption amount can be reduced by treating the carbon material surface with an acid or a base or exposing the carbon material to an oxidizing atmosphere environment. It can be increased to a suitable range. Although the conditions are not particularly limited, for example, treatment in heated concentrated nitric acid, immersion in a hydrogen peroxide aqueous solution, heat treatment in an ammonia stream, or heating in a sodium hydroxide aqueous solution. The amount of water vapor adsorbed can be increased by immersion or by heat treatment in dilute oxygen, dilute NO, or NO ₂ . vice versa,
When the amount of adsorbed water vapor is too large, the amount of adsorbed water vapor can be reduced to a suitable range by firing in an inert atmosphere as described above. Although not particularly limited, the amount of adsorbed water vapor can be reduced by performing heat treatment in an atmosphere such as argon, nitrogen, helium, or vacuum.

The catalyst layer included in the fuel cell of the present invention exerts an effect regardless of the type and form of the electrolyte membrane and the electrolyte material used, and is not particularly limited thereto.

The fuel cell in which the catalyst layer included in the fuel cell of the present invention is most effective is a fuel cell that operates under conditions in which water tends to agglomerate in the catalyst layer. The effect of the catalyst layer of the present invention is not dependent. For example, it is preferably used for a polymer electrolyte fuel cell and the like.

The electrolyte material used in the electrolyte membrane or catalyst layer used in the fuel cell of the present invention is a polymer having a phosphoric acid group, a sulfonic acid group or the like introduced therein, such as a perfluorosulfonic acid polymer or benzenesulfonic acid. Examples thereof include polymers having introduced thereinto. However, the present invention is not limited to polymers and may be used for fuel cells using an electrolyte membrane of an inorganic type, an inorganic-organic hybrid type or the like. To exemplify a particularly suitable operating temperature range, room temperature to 150 ° C.
Fuel cells that operate within the range are preferred. The mass ratio of the catalyst-supporting carbon material and the electrolyte material in the catalyst layer is 1:
2-5: 1 is preferred. When the amount of the catalyst-supporting carbon material is less than 1: 2, the surface of the catalyst is excessively covered with the electrolyte material, and the area where the reaction gas can contact the catalyst component becomes small, which is not preferable. When the material contains, the electrolyte network becomes poor,
It is not preferable because the proton conductivity becomes low.

The catalyst-supporting carbon material used in the catalyst layer of the present invention is a catalyst if the catalyst material effective for the kind of gas supplied is supported and the electron conductivity is good. It does not limit the types of components and carbon materials. Examples of the catalyst component include noble metals such as platinum, palladium, ruthenium, gold, rhodium, osmium, and iridium, noble metal composites and alloys of two or more of these noble metals, and noble metals with organic compounds and inorganic compounds. Examples thereof include a complex, a transition metal, and a complex of a transition metal with an organic compound or an inorganic compound. The amount of these catalyst components supported on the catalyst-supporting carbon material cannot be generally stated because each of them has its own proper range. For example, in the case of platinum, it is 5 to 60 mass in terms of platinum based on the carbon material. It is preferable to support in the range of%. Further, a composite of two or more of these may also be used. The method for supporting such a catalyst component on the catalyst-supporting carbon material may be any method known in the art and is not particularly limited, but it should be appropriately selected according to the carbon material and the catalyst component. is there.

Carbon black is the most common example of the carbon material supporting the catalyst, but in addition to this, graphite, carbon fiber and the like, pulverized products thereof, carbon compounds such as carbon nanofiber and carbon nanotube, etc. Can be used. Also, two or more of these can be used.

The method for forming the catalyst layer included in the fuel cell of the present invention is not particularly limited. For example, a catalyst-supporting carbon material and a gas diffusion carbon material are mixed, a solution in which an electrolyte such as a perfluorosulfonic acid polymer is dissolved or dispersed is added to this, and water or an organic solvent is added as necessary to prepare an ink. . This ink can be dried into a film and used as a catalyst layer.

However, in order for the catalyst layer included in the fuel cell of the present invention to function effectively, it is preferable to select a method of making the surface of the gas diffusion carbon material so that the electrolyte material does not come into contact as much as possible. In particular, a preferable catalyst layer forming method will be described below.

A) A solution obtained by pulverizing and mixing a catalyst-supporting carbon material and an electrolyte material in a good solvent for the electrolyte material, and then adding a poor solvent for the electrolyte material, and heterocoagulating the electrolyte material and the catalyst-supporting carbon material. , A liquid B obtained by crushing a gas diffusion carbon material not supporting a catalyst component in a poor solvent of an electrolyte material, and a liquid C obtained by mixing the liquid A and the liquid B
The liquid is dried into a film to form a catalyst layer.

In this method, when the catalyst-supporting carbon material is pulverized and mixed with the electrolyte material in a good solvent for the electrolyte material,
The catalyst-supporting carbon material, which was a large agglomerate, is crushed into fine agglomerates, and the electrolyte material is dissolved and present in the vicinity of the surface. When a poor solvent for the electrolyte material is added to this to coagulate the electrolyte material, the catalyst-supporting particles and the electrolyte material particles cause heterocoagulation, and the electrolyte material is fixed to the surface of the catalyst-supporting carbon material. When a fine gas-diffusing carbon material is further added to this solution, the electrolyte material is fixed on the catalyst-supporting carbon material surface, so the surface of the gas-diffusing carbon material is hard to be covered by the electrolyte material, and the surface of the gas-diffusing carbon material is You can take advantage of the surface texture that you have. In particular, this method is effective when a gas diffusion carbon material whose surface hydration is controlled is used.

B) Obtained by crushing and mixing the catalyst-supporting carbon material and the electrolyte material in a good solvent for the electrolyte material, then solidifying by drying, and adding a poor solvent for the electrolyte material to this, and crushing the resulting solid material. A liquid and a gas diffusion carbon material not supporting a catalyst component are pulverized in a poor solvent of an electrolyte material to prepare a liquid B, and a liquid C is obtained by mixing the liquid A and the liquid B.
The liquid is dried into a film to form a catalyst layer.

Also in this method, when the catalyst-supporting carbon material is pulverized and mixed with the electrolyte material in a good solvent for the electrolyte material and then dried, the electrolyte material is fixed in a film form on the surface of the catalyst-supporting carbon material. When this is pulverized in a poor solvent for the electrolyte material, most of the electrolyte material is atomized while being fixed to the catalyst-supporting carbon material. Furthermore, when a fine gas-diffusing carbon material is added to this solution, the electrolyte material is fixed to the catalyst-supporting carbon material surface as in the method A, so that the gas-diffusing carbon material surface is hard to be covered with the electrolyte material. ,
The surface texture originally possessed by the surface of the gas diffusion carbon material can be utilized. This method is also particularly effective when using a gas diffusion carbon material whose surface hydration property is controlled.

The good solvent for the electrolyte material used in these catalyst layer forming methods is a solvent that substantially dissolves the electrolyte material used, and cannot be limited because it depends on the type and molecular weight of the electrolyte material. To give a specific example, methanol, ethanol, isopropyl alcohol and the like can be given as good solvents for the perfluorosulfonic acid polymer contained in the commercially available 5% Nafion solution manufactured by Aldrich.

The poor solvent for the electrolyte material used in these preferable catalyst layer forming methods is a solvent that does not substantially dissolve the electrolyte material used, and the solvent varies depending on the type and molecular weight of the electrolyte material. Therefore, it cannot be specified. For example, 5 commercially available from Aldrich
Examples of the poor solvent for the perfluorosulfonic acid polymer contained in the% Nafion solution include hexane, toluene, benzene, ethyl acetate and butyl acetate.

As a method of pulverizing or pulverizing and mixing in the above-mentioned preferable method for preparing a catalyst layer of A) or B), a catalyst-supporting carbon material or a gas-diffusing carbon material which is a large aggregate is pulverized and at least 1 μm. The means is not limited as long as it can achieve the purpose of crushing into the following aggregates. As a general method, for example, a method of using ultrasonic waves, a method of mechanically crushing using a ball mill, glass beads or the like can be used.

When the ink is dried in the form of a film, a generally proposed method can be applied and is not particularly limited. For example, it is applied on carbon paper which is a gas diffusion layer and dried, and then the perfluorosulfonic acid polymer Such as hot pressing to the electrolyte membrane, a method of applying to the electrolyte membrane such as perfluorosulfonic acid polymer and then drying, once applied to a Teflon (registered trademark) sheet and the like, then dried, perfluoro Examples thereof include a method of transferring to an electrolyte membrane such as a sulfonic acid polymer by hot pressing or the like. In this way, the fuel cell of the present invention can be prepared.

[0047]

EXAMPLES <Measurement of Water Vapor Adsorption Amount of Gas Diffusion Carbon Material> As carbon materials contained in the catalyst layer, carbon blacks A, B, C, D, E, F, G and H having different water vapor adsorption amounts, eight kinds in total Prepared. C and G are commercially available carbon blacks, A is C heat-treated in argon, D and H are C and G treated in warm concentrated nitric acid,
Those washed with water and dried, and those of B, E, and F were those in which G was heat-treated in argon to change the temperature and the heating time. The amount of water vapor adsorbed on these carbon blacks is measured by measuring the amount of water vapor by a constant volume water vapor adsorber (Bell Japan, BE
LSORPIS), and the amount of water vapor adsorbed on the sample when the sample that had been degassed and pretreated at 120 ° C. and 1 Pa for 2 hours was kept at a constant temperature of 25 ° C. and the water vapor partial pressure was gradually increased. Was measured. An adsorption isotherm diagram was drawn from the obtained measurement results, and the amount of water vapor adsorbed at a relative humidity of 90% was read from the diagram. The results are shown in Table 1.

[0048]

[Table 1]

<Preparation of catalyst-supporting carbon material> Carbon black G was dispersed in an aqueous solution of chloroplatinic acid, and the solvent was dried under reduced pressure using a rotary evaporator to obtain a catalyst precursor, which was used as a 10% hydrogen-90% Ar stream. Medium, 300 ° C for 3 hours,
A reduction treatment was performed to obtain a catalyst-supporting carbon material α having a platinum loading rate of 20% by mass in terms of platinum and a catalyst-supporting carbon material β having a platinum loading rate of 30% by weight in terms of platinum. For carbon blacks C and H, the platinum loading rate is 2 in terms of platinum by the same procedure.
0% by mass of catalyst-supporting carbon materials γ and δ were obtained.

Further, carbon black G was dispersed in a chloroplatinic acid aqueous solution, kept at 50 ° C., hydrogen peroxide solution was added while stirring, and then Na ₂ S ₂ O ₄ aqueous solution was added to the catalyst precursor. Got This catalyst precursor was filtered, washed with water, dried, and then subjected to a reduction treatment in a 100% H ₂ gas stream at 300 ° C. for 3 hours to obtain a catalyst-supporting carbon material ε having a platinum supporting rate of 20 mass% in terms of platinum.

When observing the catalyst-supporting carbon materials prepared with a transmission electron microscope and comparing the particle sizes of the supported platinum,
The platinum particle size distributions of α, β, γ, and δ are all 2 to 50 n
Although it was as wide as m, the platinum particle size distribution of ε was 2 to 6 nm.
The particle size distribution was fine and uniform compared to α, β, γ and δ.

<Preparation of Catalyst Electrolyte Mixed Solution> The catalyst-supporting carbon material α was placed in a container, and a 5% Nafion solution (manufactured by Aldrich) was added thereto so that the mass ratio of the catalyst-supporting carbon material and Nafion was 1/1. In addition, glass beads were added for the purpose of crushing the carbon material, and the mixture was crushed and mixed by stirring, and ethanol was added so that the solid content concentration of the catalyst-supporting carbon material and Nafion was 6% by mass, and further stirred. A catalyst electrolyte mixed solution α1 was obtained. In the same manner, catalyst-supported carbon materials β, γ, δ, ε were used to obtain a catalyst electrolyte mixed solution β1, γ1, δ1, ε1.

<Preparation of Gas Diffusion Carbon Material Solution> Carbon black C is placed in a container, ethanol is added thereto, glass beads are added for the purpose of crushing the carbon material, and the mixture is crushed and mixed by stirring to carry a catalyst component. A gas diffusion carbon material solution C1 containing 6% by mass of carbon black C was obtained.

Also, take carbon black A in a container,
Butyl acetate was added to this, glass beads were added for the purpose of crushing the carbon material, and the mixture was crushed and mixed by stirring to obtain a gas diffusion carbon material solution A2 containing 6% by mass of carbon black A not supporting a catalyst component. It was Gas diffusion carbon material solutions B2, C2, D2, E2, F2, G using carbon blacks B, C, D, E, F, G, H in the same manner.
2, H2 was obtained.

Further, the carbon black C is placed in a container, hexane is added thereto, glass beads are added for the purpose of crushing the carbon material, and the mixture is crushed and mixed by stirring to obtain 6 carbon black C which does not carry a catalyst component. A gas diffusion carbon material solution C3 containing mass% was obtained.

<Preparation of Ink> An ink was prepared by stirring and mixing the catalyst electrolyte mixed solution and the gas diffusion carbon material solution in the ratios shown in Table 2 below.

[0057]

[Table 2]

For example, in the ink 4, 3.2 g of the catalyst electrolyte mixed solution α1 was placed in a container, 5 g of ethanol was added as a solvent while stirring, and after sufficient stirring, 0.8 g of gas diffusion carbon was stirred. It was prepared by adding the material solution C1. Inks 1 to 3 and 14 to 16 were also prepared by the same procedure. In addition, the gas diffusion carbon material solution was not added to the inks 1 to 3.

For the ink 6, the catalyst-electrolyte mixed solution α1 (3.8 g) was placed in a container, 5 g of butyl acetate, which is a poor solvent for the electrolyte, was added to the container with stirring, and the mixture was stirred for 24 hours or longer. After hetero-aggregating the electrolyte material with the electrolyte material, 0.2 g of the gas diffusion carbon material solution C2 with stirring.
Was added to prepare. Ink 5, 7-13, 17-32,
37 and 38 were similarly prepared. The ink 18,
Hexane was used as the poor solvent added when 25 was prepared.
The gas diffusion carbon material solution was not added to the inks 5, 17, 18, 37.

Further, for the ink 35, 2.8 g of the catalyst / electrolyte mixed solution β1 was placed in a container and dried overnight at 100 ° C., and then 7.6 g of butyl acetate and glass beads, which are poor solvents for the electrolyte material, were added. And thoroughly pulverize and mix by stirring, and while stirring, 1.2 g of the gas diffusion carbon material solution C2
Was added to prepare. Inks 33, 34, and 36 were also created in the same manner. Hexane was used as the poor solvent added when the inks 34 and 36 were prepared. In addition, the ink 33, 34
No gas diffusion carbon material solution was added to the.

<Preparation of Catalyst Layer and Performance Evaluation (Part 1)> First, catalyst layers containing catalyst-supporting carbon materials prepared by using carbon blacks having different water vapor adsorption amounts were prepared, and the battery performances were compared. As the ink, Inks 1 to 4 using a good solvent for the electrolyte material as a solvent were used. Table 3 below shows the types of ink used for the negative electrode and the positive electrode, the type of catalyst-supporting carbon material contained in the finished catalyst layer, and the type and content of the gas diffusion carbon material, together with the battery performance evaluation results. It was

The method of making electrodes and the method of evaluation will be described below.

A carbon paper preliminarily treated to be water-repellent with PTFE was cut into a 2.5 cm × 2.5 cm square, and ink was repeatedly applied and dried on the carbon paper to form a catalyst layer bonded to the carbon paper. At this time, the platinum content was determined by measuring the change in mass of the carbon paper before and after coating and the composition of the ink used, and the conditions were adjusted so as to be 0.5 mg / cm ² . Using two catalyst layers bonded to this carbon paper, an electrolyte membrane (Nafion 11
2) was sandwiched and hot pressed for 5 minutes at 140 ° C. and 100 kg / cm ² to obtain a bonded body of carbon paper-catalyst layer-electrolyte membrane-catalyst layer-carbon paper.

Further, the obtained joined body was incorporated into a fuel cell measuring device and the cell performance was measured. Battery performance is measured from open voltage (usually 0.9 to 1.0V) to 0.2
The voltage was gradually changed to V and the current density flowing at 0.5 V was measured. The electrode area is 6.25 cm ^2.
And Gas was supplied with pure oxygen for the positive electrode and pure hydrogen for the negative electrode so that the utilization rates were 50% and 80%, respectively, and the pressure of each gas was adjusted by a back pressure valve provided at the downstream of the cell to obtain 0.1 MPa. Set to. The cell temperature is set to 80 ° C, and the supplied pure oxygen and pure hydrogen are 75 ° C and 85 ° C, respectively.
Bubbling was performed in distilled water kept at ℃ to humidify.

[0065]

[Table 3]

As shown in Table 3, 25 ° C. and 90% relative humidity
%, The battery performance of Examples 1 to 3 using a carbon material having a water vapor adsorption amount of 100 ml / g or less is 100 m
It was superior to Comparative Example 1 using a carbon material of more than 1 / g. In addition, the battery performance of Example 3 in which 20% of the gas diffusion carbon material C was contained in the catalyst layer was particularly excellent.

<Preparation of Catalyst Layer and Performance Evaluation (Part 2)> Next, the catalyst-supporting carbon material was fixed to α, and the catalyst layers in which the kind of the gas diffusion carbon material and the content in the catalyst layer were changed were prepared. Prepared and compared the battery performance. That is, the inks used were inks 5 to 13 containing α as the catalyst supporting carbon material and using the poor solvent of the electrolyte material as the solvent. Table 4 below shows the type of ink used for each of the negative electrode and the positive electrode, the type of catalyst-supporting carbon material contained in the finished catalyst layer, and the type and content of the gas diffusion carbon material, together with the battery performance evaluation results. It was

The electrode was prepared and evaluated in the same procedure as in <Preparation of catalyst layer and performance evaluation (1)>.

[0069]

[Table 4]

As shown in Table 4, the battery performance of Examples 5 to 11 in which the gas diffusion carbon material was contained in the catalyst layer in an amount of 5% by mass or more and 50% by mass or less was particularly excellent. In Example 12 containing more than 50% by mass of the gas diffusion carbon material, the battery performance was slightly inferior. When measuring the resistance of the battery by the current interrupt method while measuring the battery performance,
Since the resistance value of Example 12 was larger than the resistance values of Examples 4 to 11, the gas diffusion carbon material became excessive, the network of the electrolyte material was divided, and the proton conductivity became low, so that the battery performance deteriorated. It is thought that it was done.

Further, comparing Examples 7 to 10 in which the content of the gas diffusion carbon material is 20% by mass, 25 ° C.
The amount of water vapor adsorbed when the relative humidity is 90% is 1 ml / g or more 1
Examples 9 and 10 containing the gas diffusion carbon materials C and G of 00 ml / g or less are particularly excellent, and the water vapor adsorption amount at 25 ° C. and relative humidity of 90% is 1 ml / g or more and 50 or more.
Example 9 containing the gas diffusion carbon material C having an amount of ml / g or less was the most excellent.

<Preparation of Catalyst Layer and Performance Evaluation (Part 3)> Next, the catalyst-supporting carbon material was fixed to β, and the catalyst layers were prepared by changing the kind of the gas diffusion carbon material, and at least one electrode was prepared. The battery performances when the batteries were arranged in the above were compared. That is, the ink contains inks β as a catalyst supporting carbon material, and inks 14 to 1 using a good solvent of an electrolyte material as a solvent.
6 was used. Table 5 below shows the types of ink used for the negative electrode and the positive electrode, the type of catalyst-supporting carbon material contained in the finished catalyst layer, and the type and content of the gas diffusion carbon material, together with the battery performance evaluation results. It was

The electrode evaluation method was the same as in <Preparation of catalyst layer and performance evaluation (No. 1)>, but the electrode was prepared according to the following procedure.

The ink is applied to a thin Teflon (registered trademark) sheet and dried repeatedly, and this is 2.5 cm × 2.5 c.
It cut | disconnected to the square of m, and created the catalyst layer-Teflon (trademark) sheet joined body. After sandwiching the electrolyte membrane (Nafion 112) using the two catalyst layer-Teflon (registered trademark) sheet joined bodies prepared, hot pressing was performed for 3 minutes at 140 ° C. and 100 kg / cm ² , and then Teflon (registered trademark) ) Only the sheet was peeled off to prepare a catalyst layer-electrolyte membrane-catalyst layer assembly. At this time, the mass of the catalyst layer transferred to the electrolyte membrane was determined by the mass difference between the catalyst layer-Teflon (registered trademark) sheet joined body and the peeled Teflon (registered trademark) sheet, and this and the composition of the ink Obtain the platinum content, and the platinum content is 0.05 in terms of platinum.
The amount of coating and the number of coatings were adjusted so as to be mg / cm ² . Furthermore, the carbon paper that has been made water repellent with PTFE is cut into 2.5 cm × 2.5 cm squares, and 2
The catalyst layer-electrolyte membrane-catalyst layer assembly is sandwiched by using one sheet, and 1
Hot pressing was further performed for 3 minutes under the conditions of 40 ° C. and 100 kg / cm ² to obtain a bonded body of carbon paper-catalyst layer-electrolyte membrane-catalyst layer-carbon paper.

[0075]

[Table 5]

As shown in Table 5, Example 1 in which a gas diffusion carbon material was contained in at least one catalyst layer in the catalyst layer
The battery performance of Nos. 4 to 16 was particularly excellent.

<Preparation of Catalyst Layer and Performance Evaluation (Part 4)> Next, the catalyst-supporting carbon material was fixed to β, and the catalyst layers in which the kind of the gas diffusion carbon material and the content in the catalyst layer were changed were prepared. Prepared and compared the battery performance. That is, the inks used were inks 17 to 32 containing β as the catalyst-carrying carbon material and basically the poor solvent of the electrolyte material as the solvent, and the ink 14 partially using the good solvent. Table 6 below shows the types of ink used for the negative electrode and the positive electrode, the type of the catalyst-supporting carbon material contained in the finished catalyst layer, the type and the content rate of the gas diffusion carbon material, together with the battery performance evaluation results. It was The electrode was prepared and evaluated in the same procedure as in <Preparation of catalyst layer and performance evaluation (No. 3)>.

[0078]

[Table 6]

As shown in Table 6, 25 ° C., relative humidity 90
%, The battery performance of Examples 17 to 34 using a carbon material having a water vapor adsorption amount of 100 ml / g or less is 10
It was superior to Example 30 using more than 0 ml / g of carbon material. It was also found that the battery performance of Examples 19 to 33 in which the gas diffusion carbon material was contained in the catalyst layer on at least one side in an amount of 5% by mass or more and 50% by mass or less was excellent.

In comparison with Examples 22 to 29 in which the content ratio of the gas diffusion carbon material is 30% by mass, 25
Gas diffusion carbon materials C and D having a water vapor adsorption amount of 1 ml / g or more and 100 ml / g or less at a temperature of 90 ° C. and a relative humidity of 90%.
Examples 24 to 29 containing E, F and G are excellent,
Among them, Examples 24 to 28 containing the gas diffusion carbon materials C, D, E and F having a water vapor adsorption amount of 1 ml / g or more and 50 ml / g or less at 25 ° C. and a relative humidity of 90% are particularly excellent. I found out.

<Preparation of Catalyst Layer and Performance Evaluation (Part 5)> Next, electrodes were prepared using inks 34 to 37 prepared so as to form a thin film of an electrolyte material on a catalyst-supporting carbon material, and batteries were prepared. The performance was compared. Table 7 below shows the types of ink used for the negative electrode and the positive electrode, the type of catalyst-supporting carbon material contained in the finished catalyst layer, and the type and content of the gas diffusion carbon material, together with the battery performance evaluation results. It was

Further, the method of forming the electrode and the evaluation method are as follows.
Preparation of Catalyst Layer and Performance Evaluation (Part 3)>

[0083]

[Table 7]

As shown in Table 7, even when the catalyst layer was prepared by using the ink prepared so as to form a thin electrolyte material film on the catalyst-supporting carbon material, the catalyst layer contained the gas diffusion carbon material. It was found that the battery performance of Examples 37 and 38 thus prepared was particularly excellent.

<Preparation of Catalyst Layer and Performance Evaluation (Part 6)> Here, electrodes were prepared using inks 37 and 38 containing the catalyst-supporting carbon material ε on which fine platinum was supported, and battery performances were compared. did. Table 8 below shows the type of ink used for each of the negative electrode and the positive electrode, the type of catalyst-supporting carbon material contained in the finished catalyst layer, and the type and content of the gas diffusion carbon material, together with the battery performance evaluation results. It was

The method of making and evaluating the electrodes is as follows.
The procedure was the same as in <Preparation of Catalyst Layer and Performance Evaluation (3)>.

[0087]

[Table 8]

As shown in Table 8, even when the catalyst-supporting carbon material supporting fine platinum was used, the battery performance of Example 40 in which the catalyst layer contained the gas diffusion carbon material was particularly excellent. I found out that

[0089]

As described above, since the fuel cell of the present invention does not use a compound such as PTFE or a silane coupling agent in the catalyst layer, it does not divide the electron conduction path and is suitable for the electrolyte material. The environment can be maintained, and extremely efficient battery performance can be exhibited. Also, P
Since no compound such as TFE or a silane coupling agent is used, the cost for producing the catalyst layer can be reduced, and an inexpensive and high-performance catalyst layer can be stably supplied.

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Tsutomu Sugiura             20-1 Shintomi, Futtsu-shi, Chiba Nippon Steel shares             Company Technology Development Division F-term (reference) 5H018 AA06 AS01 BB01 BB03 BB06                       BB11 BB12 BB13 BB17 EE03                       EE05 EE06 EE08 EE18 HH05                       HH08                 5H026 AA06 CX05 EE05 HH05 HH08                 5H027 AA06 KK31 KK41

Claims (4)

[Claims] 1. A fuel cell comprising a pair of catalyst layers sandwiching a proton-conducting electrolyte membrane, wherein at least one catalyst layer comprises a catalyst component, an electrolyte material, and a carbon material. A fuel cell having a water vapor adsorption amount of 100 ml / g or less at 25 ° C. and a relative humidity of 90%. 2. The carbon material constitutes a catalyst-supporting carbon material supporting the catalyst component and a gas-diffusing carbon material not supporting the catalyst component, and the gas-diffusing carbon material is 5% by mass in a catalyst layer. The fuel cell according to claim 1, wherein the fuel cell is contained in an amount of 50% by mass or more and 50% by mass or less. 3. The gas-diffusing carbon material has a water vapor adsorption amount of 1 ml / g or more at 25 ° C. and a relative humidity of 90%.
The fuel cell according to claim 2, wherein the fuel cell is made of one or more kinds of carbon materials of 0 ml / g or less. 4. The gas-diffusing carbon material has a water vapor adsorption amount of 1 ml / g or more at 25 ° C. and a relative humidity of 90%.
The fuel cell according to claim 3, wherein the fuel cell is made of one or more kinds of carbon materials having an amount of ml / g or less.