JP2003132900A - Metal dispersed carbon film structure, fuel cell electrode, electrode joint body, and fuel cell - Google Patents

Abstract

PROBLEM TO BE SOLVED: To enhance the performance of a fuel cell by manufacturing, especially, a fuel cell electrode from a material in which metal fine particles are carried in a porous carbon structure, which is used to control a transportation path of electrons, fuel gas, and protons in an electrolyte film-gas diffusion electrode joint body for a fuel cell. SOLUTION: There are provided a carbon film structure which has a porous structure containing fine communication holes, with average bore being 0.05-10 μm and porosity being 25-85%, a metal dispersion carbon film structure having such structure as metal fine particles are dispersed, and a fuel cell electrode, electrode joint body, and fuel cell using the same.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a member for a fuel cell and a fuel cell.

[0002]

2. Description of the Related Art In recent years, fuel cells have been developed and put into practical use. For example, in the case of a solid polymer electrolyte fuel cell, the polymer solid electrolyte layer has a thickness of 0.1 to 0.3 m on both sides.
A porous carbon plate made of m carbon fiber paper is provided, and a platinum-based catalyst as an electrode catalyst is supported on the surface of the porous carbon plate to form a gas diffusion electrode.
A battery cell is formed by providing a separator made of a dense carbon plate of 3 mm. Further, in the case of a phosphoric acid fuel cell, a porous carbon plate made of a carbon fiber paper body having a thickness of 0.1 to 0.3 mm is provided on both sides of the electrolyte layer in which the phosphoric acid holder holds phosphoric acid, A platinum catalyst as an electrode catalyst is supported on the surface to form a gas diffusion electrode, and a separator having a thickness of 1 to 3 mm with a gas flow channel groove is provided on the outside thereof to form a battery cell.

Conventionally, a powdery material typified by carbon black has been used as a carbon material of a noble metal catalyst carrier, and an electrode which is a constituent material of a reaction part of a polymer electrolyte fuel cell is also noble metal. It is produced by using a paste composed of carbon powder on which is carried, a binder such as a resin, and a solvent. (For example, Japanese Patent Laid-Open No. 5-36418) However, the structure control of the electrode produced by using the powder as a starting material is limited, and a support structure capable of effectively utilizing an expensive noble metal catalyst is formed. Things were difficult.

DISCLOSURE OF THE INVENTION According to the present invention, a material in which fine metal particles are supported on a porous carbon structure, particularly an electrode for a fuel cell, is prepared, and by using this, an electron, a fuel gas and a proton are produced. By preparing an electrolyte membrane-fuel cell gas diffusion electrode assembly in which the transport path of
The purpose is to achieve high performance of the fuel cell.

[0004]

The present invention has a porous structure having fine communicating pores and an average pore diameter of 0.05 to 10.
The present invention relates to a metal-dispersed carbon film structure having a structure in which fine metal particles are dispersed in a carbon film structure having a porosity of 25 to 85% in μm.

The present invention also relates to the above metal-dispersed carbon film structure, wherein the average size of the metal fine particles is 1 to 10 nm.

The present invention also relates to the above metal-dispersed carbon film structure, wherein at least one kind of the fine metal particles is a noble metal or an alloy containing a noble metal element.

The present invention also relates to an electrode for a fuel cell, which uses the above metal-dispersed carbon membrane structure.

The present invention also relates to an electrolyte membrane-fuel cell gas diffusion electrode assembly having the fuel cell electrode as a constituent element.

The present invention also relates to a fuel cell including the above fuel cell electrode as a constituent element.

[0010]

BEST MODE FOR CARRYING OUT THE INVENTION The metal-dispersed carbon membrane structure of the present invention has a porous structure having fine communicating pores, an average pore diameter of 0.05 to 10 μm, and a porosity of 25 to 85%. The film structure is a structure in which fine metal particles are dispersed. The carbon film structure has a porous structure having fine communication holes, and is a carbon film structure having a smooth surface other than the open holes.

In the present specification, the porous structure having fine communication holes is a so-called open hole in which pores are continuous from any surface to other surfaces in a passage form, and the space between adjacent pores is a wall. The pores have a linear structure and the pores extend non-linearly while bending.

That is, when the gas flows, the carbon film structure is guided by the passage-like pores extending non-linearly and is distributed non-linearly, so that a short path does not occur. Furthermore, the surface of the carbon membrane structure having a porous structure of the present invention has a smooth surface except for the open pores formed by the pores extending from the inside of the membrane to reach the surface, and when laminated with a separator or the like. The interface with another layer is in surface contact with the smooth surface.

In order to further explain the above-mentioned porous structure and surface smoothness, a typical example of a carbon membrane structure having a porous structure forming the fuel cell electrode base material of the present invention will be described. Scanning electron micrographs of the cross section are shown in Fig. 1 and Fig. 1, respectively.
As shown in FIG. Since the surface of the carbon film structure of the present invention other than the open pores has the smoothness as shown in FIG. 1, when the laminated body is formed, it becomes surface contact at the interface.

Further, the carbon membrane structure as the electrode base material of the present invention has an average pore diameter of 0.05 to 10 μm, preferably 0.1.
It is 05-2 micrometers. When the average pore diameter of the surface is less than the above range, pressure loss occurs, so that the gas cannot be distributed efficiently, and when the average pore diameter exceeds the above range, the gas tends to flow linearly and the gas is evenly distributed over a wide range. It is not preferable because distribution becomes difficult.

The porosity of the carbon film structure is 25 to 85.
%, Preferably 30 to 70%. When the porosity is less than the above range, the gas flow rate becomes small, and when the porosity exceeds the above range, the mechanical strength of the film becomes small, which is not preferable.

The carbon film structure has a graphitization ratio of 3
0% or more, preferably 60% or more, particularly preferably 90
% Or more is preferable. When the graphitization ratio is 60% or more, the mechanical strength of the film is increased and the flexibility is improved, which is preferable, and the electrical conductivity and the thermal conductivity are also improved, which is preferable.

The carbon membrane structure of the present invention has a porous structure having fine communicating pores, and is suitably manufactured by heating and carbonizing a high heat resistant polymer membrane having a smooth surface other than open pores in an anaerobic atmosphere. can do. It is preferable to use a high heat resistant polymer because it can retain a porous structure when heated.

The high heat-resistant polymer is capable of forming a porous film having fine communication holes, and is capable of retaining a porous structure composed of fine communication holes even when carbonized by heating. It is not particularly limited. Polymers such as polyimide-based, cellulose-based, furfural resin-based, and phenol resin-based polymers can be preferably mentioned, but aromatic polyimide is particularly preferable because it can easily obtain a carbon structure having high mechanical strength by heating and carbonization. Is. Here, the aromatic polyimide also includes a polyamic acid that is a precursor of the aromatic polyimide and a partially imidized polyamic acid.

The highly heat-resistant polymer film having a porous structure having fine communication holes and having a smooth surface other than the open holes is
It can be suitably produced by a phase inversion method using a polymer solution. A solution prepared by dissolving a polymer in an organic solvent (solvent) is cast on a glass plate, for example, and the cast film is compatible with the organic solvent and the polymer is insoluble in an organic solvent or water (non-solvent). It can be obtained by a so-called phase inversion method in which pores are formed by utilizing a phase separation phenomenon caused by the substitution of the solvent with the non-solvent at that time. However, the usual phase inversion method forms a dense layer on the surface.

[0020] Japanese Patent Application Laid-Open No. 11-310658 and Japanese Patent Application No. 11-11, which are explicitly cited as a part of the specification of the present invention.
No. 6178, Japanese Patent Application No. 2000-284651,
The phase inversion method in which the solvent replacement rate adjusting material is used to adjust the solvent replacement rate is preferable because a porous polymer membrane having fine communication holes can be easily obtained.

Specifically, first, a casting film of a polymer solution having a smooth surface is formed, then a solvent substitution rate adjusting material (porous film) is laminated on the surface of the casting membrane, and then the laminated body. Is brought into contact with a non-solvent to form pores by phase separation to deposit a porous polymer film. Since the surface of the porous polymer film formed by this method (the surface other than the open pores) retains the surface smoothness of the original casting film, the surface other than the open pores has a porous structure having communicating pores. A smooth porous polymer film can be easily obtained.

By heating and carbonizing a highly heat-resistant polymer film having a porous structure having fine communication holes and having a smooth surface other than open pores in an anaerobic atmosphere, it has a porous structure having fine communication holes. A carbon film structure having a smooth surface other than the open pores can be obtained.

The anaerobic atmosphere is not particularly limited, but an inert gas such as nitrogen gas, argon gas or helium gas, or vacuum is suitable. Carbonization by heating may undesirably cause structural defects, because decomposition products may be dissipated or carbon content may be distilled off to reduce the carbon yield when the temperature is rapidly raised. Therefore, the temperature rising rate is 20 ° C./min or less, particularly 1 to 1
It is preferable to raise the temperature at a sufficiently slow rate of about 0 ° C./minute to gradually carbonize. The heating temperature and heating time may be any temperature or time as long as sufficient carbonization is performed. Further, in order to increase the graphitization rate of the obtained carbon structure to increase the mechanical strength, electrical conductivity and thermal conductivity, 2400-3500 ° C.,
Particularly, the range of 2600 to 3000 ° C. is preferable, and the temperature range is preferably 20 to 180 minutes.

Further, it is preferable to pressurize at the time of heating during the heating and carbonization because a carbon film structure having a high graphitization rate and high mechanical strength and high electrical conductivity and thermal conductivity can be obtained. Pressurization suppresses changes in shape due to shrinkage during heating carbonization, and promotes graphitization by enhancing the orientation of the carbon portion that is being carbonized, so mechanical strength, conductivity, heat conduction A carbon film structure having high properties can be obtained. Pressure is 1-250MPa, especially 10-250MP
It is better to apply at a. Pressurization is suitably performed using a high temperature compressor or an isotropic hot press (HIP).

Further, in order to promote graphitization, a compound having an effect of promoting graphitization such as a boron compound is previously added to a highly heat-resistant polymer film having a porous structure having fine communication holes to be heated. Is preferred. Fine powders of these compounds are uniformly dispersed in a polymer solution as a raw material, and when the solution is used to produce a high heat-resistant polymer film having a porous structure by the above-mentioned method, the compound is obtained. A highly heat resistant polymer film having a uniformly dispersed porous structure can be produced.

Further, in the present invention, the high heat-resistant polymer film having a porous structure having fine communication holes and having a smooth surface other than the open holes has a target thickness after being individually carbonized by heating. It may be used by stacking so as to be small, but it is not preferable because an interface is formed between the respective layers and it becomes necessary to control the contact resistance of each interface, which makes the handling complicated. In the method of adhering with an adhesive, the adhesive may reduce the battery performance. There is also a method of adhering with a phenol-based adhesive or the like and heating again to carbonize the adhesive to integrate it, but it is not preferable because complicated treatment is required. When a laminated body in which a plurality of high heat-resistant polymer membranes having a porous structure having fine communicating pores and a surface other than open pores is smooth is carbonized by heating, they are carbonized and integrated to form the carbon membrane structure of the present invention. It is particularly preferable because it can be obtained. By this method, carbon film structures having various film thicknesses can be obtained from the same thin polymer film.

The metal-dispersed carbon film structure of the present invention comprises a structure in which fine metal particles are dispersed in the carbon film structure.

The size of the fine metal particles is, for example, 1 to 10 n.
It is preferably m.

The fine metal particles are preferably noble metals. Examples of the noble metal include platinum, palladium,
Examples thereof include nickel, and platinum is particularly preferable.

Examples of the method of dispersing the metal fine particles in the carbon film structure include a method of utilizing a vapor phase such as vacuum deposition and a method of supporting using a metal precursor solution.
Specifically, the porous carbon membrane structure is immersed in a metal precursor solution and dried as it is to carry a platinum precursor,
Then, the platinum precursor is reduced by performing heat treatment in an inert gas atmosphere, and the metal-supported porous carbon membrane structure can be obtained by washing and drying.

The above-mentioned metal precursor solution is dissolved in, for example, a water / methanol mixed solvent (weight ratio 1: 1) of the platinum acetylacetonato complex, preferably, the concentration is 0.1.
It can be prepared with a precursor solution of 1 to 5% by weight.

The heat treatment in the above inert gas atmosphere is preferably carried out at a temperature of 180 to 1000.degree.

The metal-dispersed carbon membrane structure of the present invention can be suitably used as an electrode for fuel cells.

In the fuel cell electrode, for example, the carbon membrane structure in which platinum is dispersed is a commercially available Nafion solution [DuPont perfluorocarbon sulfonic acid resin solution [Nafion 5012: resin concentration; 5 wt%, solvent: methanol + It can be produced by immersing in isopropanol + water]]. Since the electrode of the present invention has a large number of fine communication holes, it is suitable as an electrode of a high-performance fuel cell that can provide a reaction field for cell reaction that is widely and uniformly dispersed.

The electrolyte membrane-fuel cell gas diffusion electrode assembly having the fuel cell electrode of the present invention as a constituent element can be suitably produced. The above electrode assembly can be manufactured by a usual method. For example, the above electrode and a commercially available Nafion membrane (Nafion 117 manufactured by DuPont)
By hot pressing at 120 to 150 ° C., an electrolyte membrane-fuel cell gas diffusion electrode assembly can be produced.

A fuel cell containing the above electrolyte membrane-gas diffusion electrode assembly for a fuel cell of the present invention as a constituent element can be suitably manufactured.

The above fuel cell can be manufactured by a usual method. For example, a polymer electrolyte fuel cell can be manufactured by sandwiching the above-mentioned joined body with a general fuel cell separator in which a fuel gas channel is formed on one surface of a carbon plate.

[0038]

EXAMPLES Next, the present invention will be described with reference to examples in which an aromatic polyimide suitable as a high heat resistant polymer is used. However, the present invention is not limited to the following examples. In the present invention, air permeability, porosity, average pore diameter, graphitization rate, and performance evaluation of fuel cells were measured by the following methods.

Air permeability Measured according to JIS P8117. A B-type Gurley Densometer (manufactured by Toyo Seiki Co., Ltd.) was used as a measuring device. The film of the sample is clamped in a circular hole having a diameter of 28.6 mm and an area of 645 mm ² , and the air in the cylinder is passed from the test circular hole portion to the outside of the cylinder by the inner cylinder weight of 567 g. The time taken for 100 cc of air to pass was measured and was taken as the air permeability (Gurley value).

Porosity The film thickness, area and weight of a film cut into a predetermined size were measured, and the porosity was calculated from the weight per unit area by the following formula. S of the following formula
Is the film area, d is the film thickness, w is the measured weight, D is the density, polyimide is 1.34, and for the carbon film structure, the density is determined for each sample in consideration of the graphitization ratio obtained by the method described below. It was calculated. Porosity = (1-W / (S * d * D)) * 100

Average Pore Size A scanning electron micrograph of the surface of the membrane was taken, the pore area was measured for 50 or more openings, and the average pore area was determined to be a perfect circle according to the following formula: The average diameter was calculated. Sa in the following equation means the average value of the pore area. Average pore size = 2 x (Sa / π) ^1/2

Graphitization rate The X-ray diffraction was measured and determined by the Ruland method.

Evaluation of fuel cell The operating temperature of the fuel cell is 70 ° C., and the humidity is 70 as fuel gas.
% Of hydrogen and air, the current-potential characteristics were measured at a fuel gas supply / discharge pressure difference of 0.1 kgf / cm ² . The measurement was performed after the fuel cell was operated in a steady state for 1 hour to confirm that the fuel cell was sufficiently stable.

The size of the metal fine particles dispersed in the carbon film structure was evaluated by TEM and SEM observation.

Production of Porous Polyimide Membrane (Reference Example 1) 3,3 ′ as a tetracarboxylic acid component,
Using 4,4′-biphenyltetracarboxylic dianhydride (hereinafter, sometimes abbreviated as s-BPDA) and paraphenylenediamine (hereinafter, sometimes abbreviated as PPD) as a diamine component, PPD for S-BPDA Has a molar ratio of 0.999 and a content of the monomer component of 8.5.
It is dissolved in N-methyl-2-pyrrolidone (hereinafter sometimes abbreviated as NMP) so that the weight% thereof becomes 40 ° C.,
Polymerization was carried out for 15 hours to obtain a polyamic acid solution as a polyimide precursor. The solution viscosity of this polyamic acid solution (temperature: 25 degrees, E-type rotational viscometer) was 600 poises.

The polyamic acid solution was cast on a mirror-polished stainless steel plate to a thickness of about 100 μm, and the surface of the cast film of the polyamic acid solution was permeated by a solvent replacement rate adjusting material. 550 seconds / 100 cc polyolefin microporous membrane (Upore UP2 manufactured by Ube Industries, Ltd.)
The surface was covered with 015) so as not to cause wrinkles. By immersing the laminate in 1-propanol for 7 minutes and performing solvent substitution through a solvent substitution rate adjusting material, a polyamic acid having a porous structure having fine communicating pores and having a smooth surface other than open pores. The film was deposited.

Then, the polyamic acid film is submerged in water.
After soaking for 0 minutes, peel it off from the stainless steel plate, fix it on a pin tenter, and in the air at a temperature of 400 ° C.
Heat treatment was performed for 20 minutes. The imidation ratio of the obtained porous polyimide film was 70%, the film thickness was 27 μm, the air permeability was 360 seconds / 100 cc, the porosity was 51%, and the average pore size was 0.
It was 17 μm.

The above porous polyimide film was heated to 1400 at a rate of 10 ° C./min under an inert gas stream,
It was carbonized by holding it for 1.5 hours to obtain a porous carbon membrane structure. Add this to water of platinum acetylacetonato complex /
The platinum precursor was supported by immersing it in a 1 wt% platinum precursor solution prepared by dissolving it in a solvent mixed with methanol (weight ratio 1: 1), and then drying it at room temperature. Subsequently, the platinum precursor is reduced by performing a heat treatment at 1100 ° C. in an inert gas atmosphere, and then sufficiently washed with a mixed solvent of pure water and methanol and dried to obtain a platinum-supporting porous carbon membrane structure. Obtained. As a result of SEM and TEM observation, it was confirmed that platinum fine particles were supported. From the elemental analysis by ICP, the film thickness of the porous carbon, and the like, the amount of platinum per square cm was calculated to be 0.02 mg.

A commercially available Nafion solution [Perfluorocarbon sulfonic acid resin solution manufactured by DuPont [Nafion 5012: resin concentration; 5
wt%, solvent: methanol + isopropanol + water]] and dried to coat the Nafion thin film on the surface of the porous carbon to form an electrode. Further, this electrode was combined with a commercially available Nafion 117 membrane (manufactured by DuPont)
Bonding was performed by hot pressing at a temperature of 10 to 150 ° C. to obtain an electrolyte membrane-electrode assembly. This was assembled into a fuel cell and the current-potential characteristics were measured.

Comparative Example 1 Commercially available 20% by weight platinum-supported carbon fine powder, commercially available 5% by weight Nafion solution and polytetrafluoroethylene (PTFE) dispersion were used.
The mixture was mixed at a weight ratio of 4: 3: 2 to prepare a paste. This paste was uniformly applied to both sides of a commercially available Nafion 117 membrane so that the amount of platinum per square cm was 0.5 mg, and dried at 110 ° C. to obtain an electrolyte membrane-electrode assembly. This was assembled into a fuel cell using the same members as those used in Example 1, and the current-potential characteristics were measured.

(Example 2) The electrolyte membrane-electrode assembly produced in Example 1 and Comparative Example 1 was incorporated into a fuel cell and the current-potential characteristics were measured. As a result, in Example 1,
An output of 80 mA / cm @ 2 at 0.35 V and an output of 430 mA / cm @ 2 at 0.35 V were obtained in Comparative Example 1. Converting this into a current value per unit amount of platinum catalyst, 4000 A / g in Example 1 and 860 A / g in Comparative Example 1,
The apparent activity per unit amount of the platinum catalyst in Example 1 could be estimated to be 4.5 times or more that of Comparative Example 1.

[0052]

EFFECTS OF THE INVENTION According to the present invention, it is possible to produce a membrane-electrode assembly in which the electrode reaction sites are three-dimensionalized by reliably securing the paths of electrons, protons and fuel gas, and an expensive precious metal catalyst. The apparent activity of can be significantly improved. Further, it is possible to realize a polymer electrolyte fuel cell with high power generation efficiency per unit area.

[Brief description of drawings]

FIG. 1 is a scanning electron micrograph of the surface of a typical example of an electrode base material for a fuel cell of the present invention.

FIG. 2 is a scanning electron microscope photograph of a cross section of a typical example of the electrode substrate for a fuel cell of the present invention.

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Claims (6)

[Claims] 1. A porous structure having fine communication holes,
Average pore size is 0.05-10μm and porosity is 25-85%
A metal-dispersed carbon film structure comprising a structure in which fine particles of at least one kind of metal or alloy are dispersed in the carbon film structure. 2. The average size of the fine metal particles is 1 to 10 n.
The metal dispersed carbon film structure according to claim 1, wherein the metal dispersed carbon film structure is m. 3. The metal dispersed carbon film structure according to claim 1, wherein at least one kind of the metal fine particles is a noble metal or an alloy containing a noble metal element. 4. A fuel cell electrode comprising the metal-dispersed carbon membrane structure according to any one of claims 1 to 3. 5. An electrolyte membrane-fuel cell gas diffusion electrode assembly having the fuel cell electrode according to claim 4 as a constituent element. 6. A fuel cell comprising the fuel cell electrode according to claim 4 as a constituent element.