JPH1092439A - Gas diffusion electrode based on polyether sulfone carbon blend - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide the gas diffusion electrode to be used for a fuel cell. SOLUTION: This invention is concerned with the electric catalyst gas diffusion electrode for a fuel cell, which includes an anisotropic gas diffusion layer formed out of porous carbon matrix, and a catalyst layer made out of solidified 'ink' suspended matters including catalytic carbon particles and thermal plastic polymer, carbon particles and polyether sulfone are distributed all over the aforesaid porous carbon matrix in such a way that the aforesaid matrix is uniformly porous in the lateral direction against the direction of a gas flow, and that it is also porous with respect to gas asymmetrically against the direction of a gas flow, the porosity rate of the aforesaid gas diffusion layer is gradually lowered toward the end of a gas flow, the thickness of the aforesaid gas diffusion layer is roughly 50μm to 300μm, the surface low in a porosity rate of the gas diffusion layer is covered by the aforesaid catalyst layer, and the catalyst layer is roughly 7μm to 300μm in thickness, and is also provided with metallic catalyst of roughly 0.2mg/cm<2> to 0.5mg/cm<2> .

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

FIELD OF THE INVENTION The present invention relates to the manufacture of gas diffusion electrodes for use in solid polymer electrolyte fuel cells, a gas comprising polyethersulfone ("PESF") blended with carbon and platinum metal electrocatalysts. It relates to a diffusion electrode.

[0002]

2. Description of the Related Art A fuel cell is an electrochemical device that directly converts a part of energy of a chemical reaction into DC electric energy. The direct conversion of energy to DC electrical energy eliminates the need to convert energy to heat,
Avoids the limitations of the Carno-cycle efficiency of conventional methods of generating electricity. Thus, without being subjected to Carno-cycle limitations, fuel cell technology offers the potential for efficiency 2-3 times higher than the fuel efficiency of traditional generators (eg, internal combustion engines). Other benefits of fuel cells include quiet,
There is cleaning (no air contamination) and reduced or complete removal of moving parts.

[0003] Typically, fuel cells are referred to as electrodes.
It contains a plurality of porous electrical terminals and an electrolyte disposed between these electrodes. In a typical fuel cell operation,
The reductant gas passes through the gas diffusion electrode to the catalyst layer, where it reacts to form two protons and two electrons. These protons are transferred to the electrolyte layer (elect
transfer to the cathode via a trolley). Electrons are conducted from the anode to the cathode via an external resistor that produces an electric force. The oxidant permeates the anode electrode and combines with the electrons in the cathode catalyst layer. Fuel cell reactants are classified into oxidants and reductants based on their electron acceptor or electron donating properties. Oxidants include pure oxygen, oxygen-containing gases (eg, air) and halogens (eg, chlorine). Reductants include hydrogen, carbon monoxide, natural gas, methane, ethane, formaldehyde and methanol.

[0004] The electrolyte of a fuel cell acts as an electrochemical connection between the electrodes that provides a path for the flow of ions in the circuit, while electrodes made of carbon or metal provide an electrical path. In addition, the electrolyte prevents migration of reactants away from the respective electrodes where the formation of an explosive mixture can occur. The electrolytes that can be used should not directly react to an appropriate extent with the reactants or reaction products formed during operation of the fuel cell. In addition, the electrolyte must allow for the transfer of ions formed during operation of the fuel cell. Examples of electrolytes used are aqueous solutions of strong bases such as alkali metal hydroxides, aqueous solutions of acids such as sulfuric acid and hydrochloric acid, water-soluble salt electrolytes such as seawater, molten salt electrolytes and ion exchange polymer membranes. is there.

[0005] One type of fuel cell is a polymer electrolyte (PE).
M) Fuel cells, based on proton exchange polymer membranes. This PEM fuel cell contains a solid polymer membrane that is an "ion exchange membrane" that acts as an electrolyte. The ion exchange membrane is sandwiched between two "gas diffusion" electrodes (anode and cathode), each of which generally contains a metal catalyst supported by a conductive material. Each of these gas diffusion electrodes is exposed to a reactant gas (reductant gas and oxidant gas). The electrochemical reaction occurs at each of two junctions (three-phase boundaries) at one of the electrodes, the electrolyte polymer membrane and the reactant gas interface.

For example, when oxygen is an oxidizing gas and hydrogen is a reducing gas, hydrogen is supplied to the anode,
Oxygen is supplied to the cathode. The overall chemical reaction in this process is: 2H ₂ + O ₂ → 2H ₂ O. The electrochemical reaction occurring at the metal catalyst site of the electrode is as follows.

[0007]

Embedded image During operation of the fuel cell, hydrogen penetrates the anode,
Interacts with the metal catalyst to generate electrons and protons. Electrons are guided from the conductive material to the cathode through an electron path and an external circuit, and at the same time, protons move to the cathode through an ionic path by the polymer electrolyte. At the same time, oxygen penetrates the catalytic site of the cathode, where it gains electrons and reacts with protons to obtain water. Consequently, the products of the PEM fuel cell reaction are water and electricity. In PEM fuel cells,
Current flows simultaneously in the ion path and the electron path. PEM
The efficiency of a fuel cell largely depends on its ability to minimize both ionic and electronic resistivity with respect to current.

[0008] Gas diffusion electrodes play an important role in fuel cells. During fuel cell operation, the fuel gas interacts with the fuel cell electrode, causing a heterogeneous reaction at the catalytic site of the electrode. In order to undergo these reactions, the electrocatalyst must be in contact with conductive carbon, electrolyte and fuel gas. Therefore, the electrodes must meet the following criteria: 1) low gas diffusion resistance to the reaction site; 2) high electronic conductivity: 3) mechanical strength during long-term operation; 4) proper hydrophilic / hydrophobic balance; And 5) stability.

Gas diffusion electrodes for fuel cells are conventionally formed from carbon black and platinum metal supported on a polymer carrier. The polymer acts as a binder for the carbon black particles and ensures physical integrity, ie, the mechanical strength of the electrode. Carbon is used to minimize the electronic resistance of the electrode, while platinum acts as a catalyst for electrochemical reactions.

[0010] Most gas diffusion electrodes for fuel cells use polytetrafluoroethylene ("PTF") as a binder.
E "). This polymer has high thermal stability and is resistant to chemical degradation. However, PTFE does not dissolve in any of the known solvents and must be used as a suspension. This complicates the process of fabricating the electrode, and more specifically, when using PTFE as a binder for carbon, it is difficult to control the structure of the electrode, the porosity and pore size of the electrode. is there.

A Teflon (registered trademark) type gas diffusion electrode for a fuel cell is conventionally produced by mixing PTFE and carbon or graphite powder and compressing the mixture into a sheet. Acts as a binder. This sheet is heated at a sintering temperature, for example, 300
C. to 350.degree. C., where the binder partially decomposes, creating a porous matrix through which gases can pass and interact with the carbon. US Patent No. 4,847,1
No. 73 describes a process for producing carbon and polymer matrices by combining and mixing PTFE with other polymers or combining PTFE with a binder of other polymers. U.S. Pat. No. 3,899,354 discloses that carbon paper is sprayed with a suspension of a mixture of PTFE and carbon until a thin layer is obtained which forms an electrode matrix, and the matrix is then coated as described above. Another method of making a matrix of carbon and PTFE or other polymeric binder by heating to the sintering temperature is described.

[0012] Proceeding, Int. Powe
r Source Symposium (1990)
In, Cabasso and Manassen describe another method of making fuel cell electrodes. Instead of compressing or spraying the polymer binder and carbon to form a matrix and then sintering the matrix to form a gas diffusion layer, a carbon-containing platinum catalyst is mixed with a polyvinylidene fluoride (PVF ₂ ) solution. , cast, then, is immersed in dimethylformamide (non-solvent to precipitate the PVF _2). Cabasso and others
Many other soluble polymers are used under the fuel cell conditions used, ie, low operating currents of up to 200 mA / cm ² , relatively low operating temperatures (25 ° C. to 35 ° C.) and pressures slightly above atmospheric pressure. It also states that it is resistant under the conditions. In fact, most polymers degrade due to the high acidic nature of the membrane, high operating temperatures up to 95 ° C., and currents up to a few A / cm ² through the matrix.

Have reported two methods of making an electrode matrix containing a platinum catalyst therein.
In one method, an electrode matrix is prepared by uniformly casting a solution containing a mixture of a platinum catalyst, carbon, PVF ₂ and a solvent on a glass plate. By doing so, the platinum catalyst is spread evenly throughout the electrode matrix. In another method, a solution of a mixture of carbon, a platinum catalyst, a polymer and a solvent is cast on a glass plate, and then a graphite cloth is carefully placed on top of the film mixture, on which the carbon polymer without platinum catalyst is placed. Cast mixture. It is immersed in water, and has a three-layer structure of a carbon catalyzed polymer with one layer of carbon adhered to the other.

Most work in the last few decades has focused on PTFE as a binder for carbon supports in gas diffusion electrodes.
(Teflon-type electrodes) and the focus was on using as much catalyst as possible in the electrodes. Platinum-supported carbon / electrode catalyst carbon blended as a component of a gas diffusion electrode of the H ₂ / O ₂ fuel cells -
The function of PTFE mixtures is well known. Platinum-loaded carbon PTFE mixtures are generally prepared by (precisely) mixing platinum black or platinum-loaded carbon with a negatively charged hydrophobic dispersion of an aqueous colloid of PTFE particles, and depositing the mixture on a carbon cloth support. Prepared (Rep
ort No. AFML-TR-77-68). Thin porous carbon paper with anti-wetting treatment is also disclosed in US Pat.
As disclosed in U.S. Pat. No. 12,538, a gas diffusion electrode is manufactured using a support instead of carbon cloth. This electrode solves the "flooding" problem during fuel cell operation.

Several techniques have been developed to increase the availability of platinum catalysts. A method of reducing catalyst by a factor of 10 by using an improved electrode structure is disclosed in Los et al.
Alamos National Laboratory
y (Gothesfield et al., J. Applied
Electrochemistry, Vol. 22, (19)
92) 1st page) Los Alamos, New Me
xico and Texas A & M Universal
site, College Station, Texa
s, developed on the basis of electrodes from Prototech (US Pat. No. 4,826,742). In those methods, Protot containing 0.4 mg / cm ² Pt is used.
The electrode manufactured by ech was then sputter deposited with Pt to provide Pt (0.05 m
g / cm ² ). These electrodes and Naf
The fuel cell assembled with the ion 112 membrane showed 1 A / cm ² at 0.5 V using H ₂ —O ₂ as the reactant gas, and there was no significant loss of performance after 50 days of operation. G
othesfield and the like contain Pt content of 0.15 mg /
A method for reducing to cm ² is described. This method uses P
Organic solvent, Pt-C and Nafio on TFE membrane sheet
and applying an ink made from the n solution.

For good performance, the fuel cell electrodes must have a suitable morphology and catalyst distribution. Fuel cell electrodes require a porous structure that provides a free path for gas permeation and that distributes gas permeation over the entire surface area of the electrocatalyst. How efficiently the fuel gas is distributed over the electrocatalyst largely depends on the porosity in the electrode, which is an essential parameter that determines the efficiency of the electrode.

[0017]

Accordingly, it is an object of the present invention to provide an inexpensive and easy way to produce gas diffusion electrodes having favorable chemical and electrical properties for fuel cells and other electrochemical applications. To provide.

It is another object of the present invention to provide a gas diffusion electrode having a controlled electrode structure, porosity and pore size.

It is an object of the present invention to use a blend of polyethylene sulfone and activated carbon that is soluble in an organic solvent and subsequently to form the blend as a porous membrane in a non-solvent at low temperatures in a phase inversion manner. It is an object of the present invention to provide a method for producing a gas diffusion electrode having a controlled porosity and pore size by solidification.

Yet another object of the present invention is to provide a method of manufacturing a gas diffusion electrode in which a gas diffusion layer and a catalyst layer are separately formed, and each structure has characteristics which are most suitable for its function. It is configured so that

Yet another object of the present invention is to provide a simple method of manufacturing a gas diffusion electrode using a one-stage phase change technique.

[0022]

SUMMARY OF THE INVENTION The objects and criteria for gas diffusion electrodes described above and their manufacture can be achieved by the practice of the present invention. In one aspect, the invention relates to an electrocatalytic gas diffusion electrode for a fuel cell, wherein the electrocatalytic gas diffusion electrode is (a) manufactured from a porous carbon matrix in which carbon particles and polyether sulfone are distributed. The distribution is such that the matrix is homogeneously porous in the transverse direction to the gas flow and is porous so that the gas can permeate asymmetrically in the gas flow direction. The porosity of the gas diffusion layer decreases in the gas flow direction, and the thickness of the gas diffusion layer is about 50 μm to about 30 μm.
0 μm and (b) a catalyst layer made from a solidified “ink” suspension containing catalytic carbon particles and a thermoplastic polymer, said catalyst layer covering the small porosity surface of the gas diffusion layer. , From about 7 μm to about 50 μm thick, and from about 0.2 mg / cm ² to about 0.2 μm of metal catalyst.
(A) and (b) having 5 mg / cm ² .

In another aspect, the invention relates to a method of making a gas diffusion electrode suitable for a fuel cell, the method comprising:
(A) preparing an anisotropic gas diffusion layer produced from a porous carbon matrix, wherein the porous carbon matrix is coated with carbon particles and polyether sulfone, It is homogeneously porous in the lateral direction and is distributed so as to allow gas to penetrate asymmetrically in the direction of gas flow, and the porosity of the gas diffusion layer increases in the direction of gas flow. And the gas diffusion layer is about 50
μm to about 300 μm, and the diffusion layer is
Using a doctor knife, cast a blend of polyethersulfone and carbon particles dissolved in a solvent for the polyethersulfone and carbon particles on the carbon support to form a layer of film on the carbon support,
Here, the blend penetrates at least a portion of the carbon support, 2) coagulates the film in a coagulating liquid that is a non-solvent for the polyethersulfone and carbon particles, and 3) removes the coagulating solvent. Prepared by
And b. A step of coating a catalyst layer produced from an aqueous ink suspension containing catalytic carbon particles and a thermoplastic polymer on the small porosity surface of the gas diffusion layer, wherein the suspension is 0.5 to 2% thermoplastic polymer, wherein the thermoplastic polymer is selected from the group consisting of polyethersulfone, poly (vinylidene fluoride) and sulfonated polysulfone, wherein the catalyst layer covers the small porosity surface of the gas diffusion layer And the catalyst layer is about 7 μm to about 50 μm
And has a metal catalyst of about 0.2 mg / cm ² to about 0.5 mg / cm ² .

The polymer material serves many functions simultaneously in the gas diffusion electrode of a fuel cell. The polymer material acts as a binder to hold with the carbon catalyst, imparting electrode integrity and imparting hydrophobicity. The platinum metal (Pt) catalyst in the electrode works best when it comes into contact with carbon, electrolyte and reactant gases simultaneously. Increase the availability of Pt,
To reduce ohmic losses and eliminate flooding, the electrode matrix must be configured to accommodate these conditions. The structure should be manufactured such that the ion and electron paths are short with minimal bends, while the catalyst has maximum exposure and availability of reactant gases without wetting and leaching. Platinum is an expensive catalyst and should be used in the smallest possible amount with the highest possible efficiency. Therefore, it has been found that localization of Pt near the surface of the electrode adjacent to the reactant gas is most advantageous for electrode performance. Bacon's double layer model electrode structure (GB 667,298) is widely accepted. The bilayer model structure has an asymmetric anisotropic structure with one side opening facing the gas side and other relatively small pores facing the electrolyte side. The former facilitates the transfer of gas and the latter fills the electrolyte. Therefore, the crossover (crossov)
er) Prevent further gas diffusion which would cause problems.

Applicants can use an inexpensive thermoplastic polymer, polyethersulfone, to form a blend with carbon particles suitable as an electronic matrix material. Polyethersulfone is an amorphous polymer having a hydrophobic, high glass transition temperature. It is resistant to oxidizing and reducing environments. In addition, low pH
With good durability and operating capacity. Polyethersulfone is available from Gas Separation (I. Cabasso, "Enc"
Cyclopedia Polymer Science
and Engineering ", 2nd edition, Joh
n Willy & Sons, Inc. Issue 9, pp. 509 (1987)) and have proven to have outstanding building blocks for various porous membranes for ultrafiltration. Suitable polyethersulfones according to the present invention have an average molecular weight of about 25,000 to about 100,000.
0, including those having the following repeating units:

[0026]

Embedded image In the present invention, when polyether sulfone and carbon particles are mixed at a polymer to carbon weight ratio of about 20:80 to about 45:65, polyether sulfone by itself is an excellent binder for the carbon in the blend. Function. As a result, polyethersulfone
It can be used satisfactorily as a matrix building unit for binders and gas diffusion electrodes instead of the more expensive PTFE polymers. The polyethersulfone polymer in the blend provides an electrode structure with the properties essential for producing high quality fuel cell electrodes.

The gas diffusion electrode of the present invention is manufactured by a two-step method.

The first step is to use a phase inversion method,
Thickness, preferably greater than about 75 μm and about 300 μm.
An anisotropic gas diffusion layer of the invention is made having a thickness of less than μm, preferably less than about 150 μm. The phase inversion method includes the following steps. That is, 1) a blend of polyethersulfone and carbon particles dissolved in a solvent for polyethersulfone is cast on a carbon support or a glass plate using a doctor knife to form a layer of film on the carbon support. 2) coagulating the film in a coagulating liquid which is a non-solvent for the polyethersulfone; and 3)
The film is dried to remove the coagulating liquid.

The second step is to apply a layer of catalyst-carbon-polymer "ink" onto the carbon-polymer gas diffusion layer using an airbrush to produce a catalyst layer, wherein the catalyst "ink" is More than about 7μm, about 50μm
Less than about 10, preferably less than about 10 μm. The weight ratio of metal catalyst on carbon to polymer in the ink is from 25:75 to 40:60. The electrodes of the present invention have higher porosity in the gas diffusion layer, lower catalyst loading, and higher catalyst availability. The performance of a fuel cell incorporating this electrode is high.

The conductive carbon support is greater than about 7 μm, preferably greater than about 10 μm, less than about 35 μm,
Preferably, it is a fibrous or porous sheet having a thickness of less than 25 μm. Suitable conductive carbon supports include carbon paper, highly conductive carbon cloth, highly conductive carbon felt, carbon tape, and the like.

The finely divided carbon is, for example, B.I. of about 50 to about 2000 m ² / g. E. FIG. T. It is a carbon black having a surface area by the method. Suitable finely divided carbon is activated carbon or carbon black, ie carbon powder in a very finely divided state. B. E. FIG. T. Commercially available carbon black powders useful in the present invention, as measured by the method, are from about 50 m ² / g to about 2000 m ²
/ G surface area. Such powders include furnace black, lamp black, acetylene black, channel black, and thermal black. About 200m ² / g~ B. of about 600m ² / g E. FIG. Furnace black having a T surface area is preferred. The particle size of these activated carbon materials can range from about 5 nanometers to as high as about 1000 nanometers, but preferably is less than about 300 nanometers in average particle size.

B. E. FIG. The T method uses Bru to determine the surface area.
It relates to the naver-Emmett-Teller method.

The term "carbon black" refers to So
U.S. Pat. No. 4,440,167 to Lomon
Used as defined in the issue description.

From about 50 to about 300 m ² / g of B.I. E. FIG. T.
Commercially available carbon blacks having surface areas can be steam activated to increase their surface area, if desired, thereby increasing their B.I. up to about 600 m ² / g.
E. FIG. T. The value can be increased.

The surface characteristics of carbon black can vary. Certain of these carbon blacks have surface functionality, such as, for example, surface carboxyl groups (and other types of oxygen-containing groups) or fluorine-containing groups. Physicochemical properties and ash can also vary. further,
The carbon black can be graphitized (whereby the carbon black powder acquires some of the structural properties of the graphite) or graphitized and then treated to restore or enhance surface functionality.

Suitable commercially available carbon blacks include, for example, BLACK PEARLS ™, such as BLACK PEARL 2000, VULCA
N (trademark, for example, Vulcan VX-72), KE
TJEN BLACK EC300J (Akzo Chemie Americo ofB, New York)
urt trademark), activated carbon, acetylene black C-10
0, or a mixture thereof. Available KET
JEN BLACK material is about 900 to about 1000 m ²
B./g. E. FIG. T. Oil furnace black with surface area, and especially EC300J is 950
It appears to have a surface area of m ² / g. KETJEN
BLACK EC 300J is mesophase carbon (mes
of carbose, and thus has a region on the long range. These areas are
Carbon can be made more corrosion resistant which is important for cathode applications.

According to US Pat. No. 4,461,814 to Klinedienst, KETJEN
BLACK oil furnace black has a surface area (90
0 m ² / g) and dibutyl phthalate (“D
BP ") Both absorption numbers are high. Klinedienst
Determines the DBP absorption according to ASTM test D-2414-70, the absorption number is preferably greater than 125 cm ³ per 100 g of carbon black (for example,
230 cm ^3/100 g greater than) and should be, the surface area should exceed 250 meters ² / g, giving a carbon black cathode collector with optimum properties. K
ETJEN BLACK DBP absorption number is Klined
It has been reported to be 340cm ³ / 100g by ienst. Acetylene black has high DBP absorption but low B.P. E. FIG. T. Tends to surface area. vice versa,
Lurgi Carbon Black (Lurgi Umive
tt and available from Chemotechnik GmbH). E. FIG. T. Surface area (1
200 m ² / g), low DBP absorption number (100
Less than). "CSX" carbon black (Bi
Cabot Corporation of llerica, MA
ion) (also available from ION). E. FIG. T. It is reported that the surface area has a high DBP absorption number.

Suitable solvents for the polyethersulfone and carbon blend include N, N-dimethylformamide ("DMF"), N, N-dimethylacetamide,
Some are selected from the group consisting of N-methylpyrrolidone and dimethylsulfoxide. The amount of solvent required to dissolve the polyethersulfone can vary depending on the solvent. For example, 10-20% by weight dissolves in DMF.

Suitable coagulating liquids which are non-solvents for blending the polyethersulfone and carbon particles include water,
It is selected from the group consisting of isopropanol and hexane and a mixture of water and isopropanol.

Vulcan XC-72, acetylene black C-100 and BlackPearl 200
A porous carbon material, such as 0, can be used to make the gas diffusion electrode of the method of the present invention without causing the water flooding problem commonly encountered when such carbon is used in fuel cell electrodes. . Such carbon materials absorb such large amounts of liquid that would result in flooding of the gas electrode when the carbon is cast in a blended state. Vulcan XC-72
When using carbon with a low surface area such as
These carbons do not absorb too much liquid and too much liquid is necessary to produce a composition that can be cast as a film. In conclusion, even a few hundred micrometers thick film produced in this way does not contain enough active carbon material for the electrodes. In addition, carbon materials such as charcoal have high electrical resistance, and because of their dimensions, the high porosity matrix they form is subject to the high pressures encountered by standard fuel cell assemblies, i.e., 20 psi to 100 psi.
Can not withstand the pressure of. Therefore, charcoal was not used in the manufacture of fuel cell electrodes.

By using high frequency ultrasound,
It has been unexpectedly found that the flooding problem can be solved and that such a carbon material can be cast in a solvent. Therefore, organic solvents (DMF) and polyethersulfone are treated with the carbon material to solve the problem of absorption of large amounts of liquid by carbon materials such as Vulcan XC-72, which are commonly used in the manufacture of fuel cell electrodes. And mix well with an ultrasonic device to obtain a suspension. High frequency ultrasound results in a slurry that can be cast at the desired thickness on a carbon cloth support. Ultrasound does not appear to cause the carbon to absorb enough liquid to interfere with the formation of electrodes during the casting process. It has been found that sonication of a mixture of polyether sulfone, a platinum catalyst and a carbon material results in a slurry that can be cast to a smaller thickness with less solvent hindering the casting process. Thus, the present invention can cast common carbon for fuel cell electrodes.

The formation of a good gas diffusion electrode requires that the reactant gas spread evenly within the matrix of the gas diffusion electrode. Gas is a fluid and behaves like a fluid flowing along the path of least resistance. In fuel cells,
Reactant gases flow toward the catalyst bed where they are consumed. One problem with fuel cell devices, especially electrodes, is the homogeneity of the passages. If the electrode matrix is dense in one area and low in another area, most of the gas flow will go to the less dense area. As a result, the catalyst is underutilized. The gas diffusion electrode of the present invention has an electrode matrix that is laterally homogeneous and asymmetric in the direction of gas flow. This is because when the gas enters the electrode, the gas penetrates from the surface of the gas diffusion electrode, which is "open" with low resistance, and as the gas diffuses, the electrode matrix progresses toward the other surface. As the density increases, the pores of the matrix become smaller. Therefore, the electrode matrix of the present invention has an anisotropic porous structure with two asymmetric surface layers as shown in the photograph of FIG.

As described in the 1990 article by Cabasso et al., Mixtures such as PVF ₂ , carbon materials and platinum catalysts are not sonicated and when cast as a solution on a glass support. Due to the way the glass interacts with the polymer carbon mixture, a dual density surface forms. Surprisingly, to ensure the anisotropic structure of the electrode, which facilitates the penetration of the penetrating gas,
It has been found that the sonicated slurry has to be cast on carbon cloth or carbon paper. The sonicated slurry ensures anisotropic structure when cast on a carbon cloth and subsequently submerged in water.

Gas diffusion and distribution in the matrix is important for electrode performance. The prediction of the gas layer on the carbon cloth was studied diligently. It has also been found that when the cast slurry solidifies at low temperature in a coagulating liquid that is a non-solvent for the slurry, it results in higher quality gas diffusion electrodes and a laterally homogeneous anisotropic porous structure. .

[0045] Suitable coagulation bath temperatures can range from room temperature to -30 ° C. When the coagulating liquid comprises a mixture of water and alcohol, a temperature below 0C, preferably above -20C is used. When the coagulating liquid is water, a temperature of 25C to 4C is preferably used.

Suitable coagulating liquids which are non-solvents for the casting slurry are water and alcohols and / or mixtures of water and inorganic salts, aqueous solutions made in a volume ratio of 99: 1 to 1:99. is there. Preferably, water is used as the coagulating liquid. When the coagulating liquid is a mixture, it is a mixture of water and alcohol or water and salt, and is 90:10 to 10: 9.
Those having a capacity ratio of 0 are preferred. Suitable alcohols include ethanol, isopropanol and methanol. Suitable salts include LiCl, LiNO ₃ and Na
NO _{3 and the} like.

As mentioned above, suitable thermoplastic polymers in the catalyst layer are those selected from the group consisting of polyethersulfone, poly (vinylidene fluoride) and sulfonated polysulfone. Sulfonated polyethersulfone and sulfonated poly (phenylene oxide) also seem to be suitable as thermoplastic polymers for the catalyst layer.

[0048]

The following examples are illustrative of the present invention but should not be construed as limiting the invention. (Example 1) High surface area (DP-5, 200; 200)
m ² ) carbon black (Cabot, Inc. to V
Gas diffusion electrodes were produced by wet phase inversion using commercially available ulcan VX-72R) and polyethersulfone. Carbon black is mixed with 12 to 15 wt% of polyether sulfone and N, N-dimethylformamide.
% To form a suspension. The suspension is converted to a slurry by sonication to form a slurry.
Mix well for minutes. Using a doctor blade knife, apply the resulting slurry to a 0.015 mm thick hydrophobic, carbon cloth support (Zoltek to Panex PWB).
(Commercially available as -3)) until one layer of 0.50 μm thick film was formed on the support. Care was taken during casting to ensure that the slurry at least partially penetrated the fabric. Next, the film was immersed in a deionized water bath to coagulate the film. The coagulated film was washed very well with deionized water and placed in a drying box and dried for at least 24 hours. The dried film forms the gas diffusion layer of the gas diffusion electrode, which has small pores on the surface (see TEM pictures). Next, the gas diffusion layer of the electrode was heated at 250 ° C. for 1 hour.

An aqueous "ink" suspension of the catalyst layer was prepared as follows. That is, 0.06 g of polyvinylidene fluoride (PFV ₂ ) was suspended in 4 g of 2-propanol and 6 g of water by an ultrasonic device. Then, 0.05 g of a nonionic surfactant (Triton-X
-100) and was added 20 wt% Pt of 0.3g on Vulcan VX-72 carbon black PFV ₂ colloidal solution. The mixture was mixed again by sonication to form the final "ink" suspension. This "ink" was then applied on the surface of the gas diffusion electrode on average using an art air brush. The application procedure is 7.0
g of the "ink" suspension was applied to a 88 cm ² gas diffusion layer. The resulting electrode, as illustrated in FIG. 2, has a 20 μm thick catalyst layer of 0.35 mg /
cm ² of platinum. The size of the platinum particles is 20-40
It is within the range of Å. The electrodes are then applied for at least 2 hours 3
Heated at 00 ° C.

The gas diffusion electrode manufactured by the above method was evaluated in a H ₂ / O ₂ fuel cell. Set the catalyst side of this electrode to 0.
Brushed with 5 wt% protonated 117 Nafion solution and hot pressed to Nafion 112 or Nafion 117 membrane. An open cell voltage of 1.0 V was measured. FIG. 3 shows a polarization curve of a fuel cell using a gas diffusion electrode manufactured according to Example 1 and a Nafion 112 membrane. FIG. 4 shows the electrode of Example 1 and Nafio.
Figure 3 shows polarization curves for fuel cell electrodes using n112 membrane at different reactant pressures. 1 A / c at 0.5 V
m ² current can be drawn, indicating good performance of this electrode. (Example 2) The method of Example 1 was repeated except that the gas diffusion layer was manufactured by dry phase inversion. Polyethersulfone and acetylene black C-100 carbon were converted to DM
F to form a paste. The paste was cast on a carbon cloth support, and then dried in air to completely evaporate the solvent to form a cast film layer. Next, this film was passed through two rollers at room temperature to produce a gas diffusion layer of an electrode. This electrode and Nafio
The fuel cell manufactured using the n112 membrane had an open cell voltage of 1.0 V and at 0.5 V the current density was 800 mA / cm ² . Example 3 The method of Example 1 was repeated except that a gas diffusion layer was produced using a mixture of water and DMF as a coagulating solvent. Sulfonated polysulfone was used instead of PVF ₂ as the polymer in the catalyst layer “ink” suspension. Fuel cells made using this electrode and the Nafion 112 membrane had a higher platinum catalyst utilization of about 35%. At 0.5V, 2 for fuel cell
The current density of A / cm ² was measured. (Example 4) 0.5 g of platinum on activated carbon (10 wt% P
t, Fluka Chemical, Inc. ) To 1.
6g DMF and 1.6g 15wt% PES in DMF
It was suspended in a mixture with the F solution by an ultrasonic device. The suspension was then cast on a carbon cloth support using a doctor knife to form a layer of film. The film was immersed in a deionized water bath for 30 seconds to coagulate the film. The solidified film was then removed from the water bath, washed very well and placed in a drying box and dried for 24 hours. The platinum content of the catalyst layer was 0.5 mg / cm ² . The thickness of the formed gas diffusion electrode was about 150 μm. A fuel cell manufactured using the gas diffusion electrode and the Nafion 117 membrane has an overresistance of 0.69 Ω / cm ^{2 and} 110 mV / cm ^2.
It had a Decade Tafel gradient. The maximum current density was 800 mA / cm ² . (Example 5) highly hydrophobic, carbon black (5-20% range) of the low surface area of 60 m ² / g, acetylene black C-100 (Chevron Chemica
lCo. The method of Example 4 was repeated, except for the addition of ()).
In this example, the surface concentration of platinum in the catalyst layer was 0.1 mg /
cm ² . When the amount of secondary carbon is increased from 0 to 10%, the maximum current density is from 800 mA / cm ² to 1
A / cm ² . Example 6 The method of Example 4 was repeated except that poly (vinylpyrrolidone) PVP was used as a pore filter to control the porosity of the gas diffusion layer and to obtain the required open pore structure. PVP was mixed with the polymer solution before casting the gas diffusion layer. Subsequently, the PVP was removed by rinsing the electrodes with water for 3 days. This gas diffusion electrode and Nafion
117 cell voltage (ov)
erall cell voltage) is about 200 mV
Increased.

[Brief description of the drawings]

FIG. 1 is a scanning electron microscope (SEM) photograph showing a cross section of a PESF-carbon diffusion electrode of the present invention.
A is 200 times and B is 500 times.

FIG. 2 is a 400 × scanning electron micrograph showing a cross section of a PESF-carbon diffusion electrode of the present invention.
a is the secondary image and b is the pt x-ray map.

FIG. 3 shows a gas diffusion electrode and Naf prepared as described in Example 1 at 80 ° C., 300 psig.
Cell potential (cell voltage (V)) vs. current density (A /) for the fuel cell assembly of the present invention containing an in 112 membrane.
cm ² ).

FIG. 4 shows various hydrogen-oxygen gas pressures: (○) 1.
(●); and (▼) a gas diffusion electrode manufactured as described in Example 1 at 30 psig and N
5 is a graph of cell potential (cell voltage (V)) versus current density (A / cm ² ) for a fuel cell assembly of the present invention containing an afin 112 membrane.

 ────────────────────────────────────────────────── ─── Continuing on the front page (72) Inventor, Cabasso, Israel 13210, Syracuse, Buckingham Avenue 131, New York, United States of America Inventor Yushin Yuan 13210, Syracuse, Buckingham Avenue 131, New York, United States 131 (72) Inventor Xiao Xue, United States 94555, California, Montague Avenue, Fremont 4862

Claims (21)

[Claims] 1. A fuel comprising an anisotropic gas diffusion layer composed of a porous carbon matrix and a catalyst layer made from a solidified "ink" suspension containing catalytic carbon particles and a thermoplastic polymer. An electrocatalytic gas diffusion electrode for a battery, wherein the porous carbon matrix is made of carbon particles and polyether sulfone,
The matrix is uniformly porous in the transverse direction to the gas flow, and is distributed so as to allow gas to penetrate asymmetrically in the gas flow direction. Rate decreases in the direction of gas flow, and the thickness of the gas diffusion layer ranges from about 50 μm to about 3 μm.
00 μm, and the catalyst layer covers the small porosity surface of the gas diffusion layer, and the catalyst layer has a thickness of about 7 μm to about 5 μm.
0 μm thick and about 0.2 mg / cm 2 of metal catalyst
^The electrode above, having from ² to about 0.5 mg / cm ² . 2. The electrode of claim 1, wherein said catalyst layer comprises about 5 to about 25% by weight of said polyether sulfopolymer, with the balance being said carbon particles. 3. The method according to claim 2, wherein the gas diffusion layer is about 20:80 to about 4
The electrode of claim 1 having a polymer to carbon ratio of 5:65. 4. The method according to claim 1, wherein the carbon particles are selected from the group consisting of activated carbon, carbon black and acetylene black. E. FIG. T. Surface area is about 50m ^2
2. The electrode of claim 1, wherein said electrode is between about 2000 m2 / g and about 2000 m2 / g. 5. The electrode according to claim 1, wherein the gas diffusion layer further contains poly (vinylpyrrolidone). 6. The thermoplastic polymer in the catalyst layer is PV
F _2, sulfonated polysulfone, sulfonated polyethersulfone, and is selected from the group consisting of sulfonated poly (phenylene oxide) electrode according to claim 1. 7. The catalyst carbon particles have a particle size of about 200 m ² / g.
B. to about 2000m ² / g E. FIG. T. High surface area carbon carrier particles having a large surface area (carboncarr)
The electrode of claim 1, comprising catalytic metal particles adhered to the outer particles. 8. The catalyst metal particles include precious metal particles uniformly deposited on the carbon carrier particles,
The electrode according to claim 7, wherein the noble metal is selected from the group consisting of platinum, palladium, rhodium and iridium, and is present in an amount of 10-20% based on the weight of the carbon carrier particles. 9. The electrode according to claim 1, wherein said gas diffusion layer has a thickness of about 75 μm to about 150 μm. 10. The catalyst layer has a thickness of 7 μm to 10 μm.
0.15 mg / cm ² -0.5 mg of platinum catalyst
The electrode according to claim 1, wherein the electrode has a density of / cm ² . Wherein said catalyst layer is comprised of 5 to 30% PVF ₂ and 70% to 95% carbon particles mixed with a platinum alloy electrode according to claim 1. 12. A method of manufacturing a gas diffusion electrode suitable for use in a fuel cell, comprising: a. A step of preparing an anisotropic gas diffusion layer composed of a porous carbon matrix, wherein the porous carbon matrix is coated with carbon particles and polyether sulfone in a direction transverse to the gas flow. The gas diffusion layer is homogeneously porous and is distributed so as to allow gas to penetrate asymmetrically in the direction of gas flow, and the porosity of the gas diffusion layer increases in the direction of gas flow. The thickness of the gas diffusion layer is about 50 μm to about 300 μm;
1) Using a doctor knife, cast a blend of polyethersulfone and carbon particles dissolved in a solvent for polyethersulfone on a carbon support to form a film on the carbon support, A) by coagulating the film in a coagulating liquid that is a non-solvent for the polyether sulfone, and 3) removing the coagulating solvent, and b. A step of coating a catalyst layer composed of an ink suspension containing catalytic carbon particles and a thermoplastic polymer on the small porosity surface of the gas diffusion layer, wherein the suspension is 0.5 to 2% thermoplastic polymer, wherein the thermoplastic polymer is selected from the group consisting of polyethersulfone, poly (vinylidene fluoride) and sulfonated polysulfone, wherein the catalyst layer covers the small porosity surface of the gas diffusion layer And the thickness of the catalyst layer is about 7 μm to about 5 μm.
0. The method of claim 1 wherein said metal catalyst is about 0.2 mg / cm < ² > to about 0.5 mg / cm < ² >. 13. The method according to claim 1, wherein in the step (a) (1), the gas diffusion layer is formed in N, N′-dimethylformamide by 5 to 2 hours.
13. The method of claim 12, wherein the method is produced using a solution comprising 5 wt% PESF. 14. In step (a) (1), the carbon particles are selected from the group consisting of activated carbon, carbon black, acetylene black and mixtures thereof,
B. E. FIG. T. Surface area of about 50m ² / g~2000m ² / g
13. The method of claim 12, wherein 15. In step (a) (1), a blend of polyethersulfone and carbon particles dissolved in a solvent for polyethersulfone is sufficient to uniformly mix polyethersulfone and carbon particles. 15. The method of claim 14, wherein sonication is performed over a period of time. 16. (a) In (1), the solvent for the polyethersulfone is selected from the group consisting of N, N-dimethylformamide, N, N-dimethylacetamide, N-methylpyrrolidone and dimethylsulfoxide. The method of claim 14, wherein 17. In the step (a) and the step (2), the gas diffusion layer is made of water, hexane, ethanol, water / N, N′-.
13. The method of claim 12, wherein the method is produced using a coagulating liquid selected from the group consisting of dimethylformamide, water / ethanol, water / methanol, water / isopropanol, tetrahydrofuran, and mixtures thereof. 18. The method of claim 17, wherein in step (a) (2), the temperature of the coagulating liquid is between ambient temperature and −30 ° C. 19. The method of claim 12, wherein in step (b), the catalyst layer contains a non-ionic surfactant. 20. 200 ° C. for 15 minutes to 2 hours
The method according to any of claims 12 to 19, further comprising the step (c) of sintering the final electrode at 300C. 21. The method according to claim 12, wherein in step (b), the coating is performed by an air brush coating method.