JP2001273907A - Gas diffusion electrode and its manufacturing method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent a stay of water, and obtain a gas diffusion electrode which is superior in gas diffusion property without cutting off a proton conduction path between a catalyst layer and a proton electro-conductive solid polyelectrolyte membrane, and between the electronic conduction path between the catalyst layer and a gas diffusion layer. SOLUTION: In the gas diffusion electrode, a porous resin having a communicating hole in the catalyst layer and gas diffusion layer is equipped, and the porous resin equipped in the catalyst layer and the porous resin equipped in the gas diffusion layer are successively continued.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a gas diffusion electrode and a method for manufacturing the same.

[0002]

2. Description of the Related Art A solid polymer electrolyte fuel cell uses a solid ion exchange membrane as an electrolyte and supplies, for example, hydrogen as a fuel to an anode and oxygen, for example, as an oxidant to a cathode to perform an electrochemical reaction. Is a device for obtaining

The electrochemical reaction at each electrode in this case is shown below.

Anode: H ₂ → 2H ⁺ + 2e ⁻ Cathode: 1 / 2O ₂ + 2H ⁺ + 2e ⁻ → H ₂ O Total reaction: H ₂ + 1 / 2O ₂ → H ₂ O As shown in the above formula, at the anode and cathode The reaction requires the supply of oxygen and hydrogen gases, the transfer of protons (H ⁺ ) and electrons (e ⁻ ), and the reaction takes place at the three-phase interface in the electrode where they are simultaneously filled, ie, the reaction gas, the catalyst, and the solid. It proceeds only at the electrolyte interface. Therefore, in the fuel cell, a gas supply path from the catalyst layer surface to the three-phase interface, a proton conduction path from the three-phase interface of the anode to the three-phase interface of the cathode through the solid electrolyte membrane,
An electron conduction path from the three-phase interface to the current collector needs to be formed.

Therefore, a membrane-electrode assembly is used in which a gas diffusion electrode composed of a catalyst layer and a gas diffusion layer is bonded to both surfaces of a solid polymer electrolyte membrane as an anode and a cathode. Here, the catalyst layer contains catalyst particles such as carbon carrying a catalyst, and the gas diffusion layer is made of a conductive porous material such as carbon paper.

The catalyst layer is composed of catalyst particles, a solid polymer electrolyte and, if necessary, polytetrafluoroethylene (PTF).
E) is a place where an electrode reaction is performed, and the gas diffusion layer is formed by applying PTFE or the like to a conductive porous body to impart water repellency.

[0007]

As described above, in order to promote the reaction in a fuel cell, a continuous gas flow path, a proton conduction path, and an electron conduction path are required in the catalyst layer. However, when the fuel cell is operated at a high current density, because the humidified gas is supplied, and water is generated by the reaction at the cathode,
Water accumulates on the surface and in the pores of the catalyst layer, which causes a problem that gas diffusivity is hindered and output is significantly reduced.

[0008] Generally, in order to prevent stagnation of water due to generation and movement of water, PTFE particles are mixed in the catalyst layer or PTFE is applied to the surface of the conductive porous body by applying PTFE. Gives water. In order to prevent water from staying in the electrode during high current density operation, it is necessary to increase the amount of PTFE mixed to increase water repellency, but PTFE has strong water repellency, but the particles themselves are large, Since there is no gas diffusion property, if the mixing ratio of PTFE is increased in order to increase water repellency, the proton conduction path, the electron conduction path, and the gas diffusion path are cut off, and the output of the fuel cell is rather lowered.

The present inventor has manufactured an electrode in which PTFE is sufficiently arranged in the catalyst layer in order to impart strong water repellency. However, it is necessary to provide strong water repellency while maintaining good proton conductivity and electron conductivity. It was confirmed that sufficient performance could not be obtained.

In view of the above, the present invention provides a proton conduction path between a catalyst layer and a proton conductive solid polymer electrolyte membrane,
An object of the present invention is to obtain a gas diffusion electrode having excellent gas diffusivity by preventing water from staying without interrupting an electron conduction path between a catalyst layer and a gas diffusion layer.

The gas diffusion electrode of the present invention is mainly used for a solid polymer electrolyte fuel cell, but can also be used for other fuel cells, batteries, sensors and the like.

[0012]

According to a first aspect of the present invention, there is provided a gas diffusion electrode comprising a porous resin having a communication hole between a catalyst layer and a gas diffusion layer. The porous resin provided in the gas diffusion layer is continuous.

According to a second aspect of the present invention, in the gas diffusion electrode, the porosity of the porous resin is 30% or more and 95% or less.

According to a third aspect of the present invention, in the gas diffusion electrode, the porous resin has an average pore diameter of 50 nm or more and 5 μm or less.

The invention of claim 4 relates to a method for producing a porous resin for the gas diffusion electrode, wherein the resin is phase-separated from a solution in which the resin is dissolved in a solvent.

A fifth aspect of the present invention relates to a method for producing a porous resin for the gas diffusion electrode, wherein a solution obtained by dissolving a resin in a first solvent is insoluble in the resin and the first solvent is dissolved in the first solvent. The method is characterized in that a step of removing the second solvent is performed by replacing the first solvent with the second solvent to cause the resin to undergo phase separation using a second solvent compatible with the second solvent.

According to a sixth aspect of the present invention, in the method for manufacturing a gas diffusion electrode, after the gas diffusion electrode including the catalyst layer and the gas diffusion layer contains a solution obtained by dissolving a resin in a solvent,
It is characterized by passing through a step of phase-separating the resin from this solution.

According to a seventh aspect of the present invention, in the method for manufacturing a gas diffusion electrode, a membrane-electrode assembly in which a gas diffusion electrode including a catalyst layer and a gas diffusion layer is joined to at least one of the solid polymer electrolyte membranes, After a solution in which the resin is dissolved in a solvent is included, a step of phase-separating the resin from the solution is performed.

The invention according to claim 8 is the method for manufacturing a gas diffusion electrode, wherein the step of disposing the gas diffusion electrode including the catalyst layer and the gas diffusion layer with a solution in which a resin is dissolved in a solvent is performed. It is characterized by being performed below.

[0020]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, a structural example of a gas diffusion electrode according to the present invention will be described more specifically with reference to the drawings.

FIG. 1 is a schematic view showing the structure of a gas diffusion electrode according to the present invention, and FIG. 2 is a conventional gas diffusion electrode in which PTFE is arranged on the surface of a conductive porous material constituting a gas diffusion layer and in a catalyst layer. It is a schematic diagram which shows the structure of. 1 and 2, 1 is a catalyst layer, 2 is a gas diffusion layer, 3 is a porous resin, 4 is a solid polymer electrolyte, and 5 is PTFE particles.

As shown in FIG. 1, the gas diffusion electrode of the present invention comprises a porous catalyst layer 1 and a gas diffusion layer 2 provided with a porous resin 3 having communication holes. Resin 3 provided for the gas diffusion layer 2 and porous resin 3 provided for the gas diffusion layer 2
Is a novel electrode having both good proton conductivity and high gas diffusivity. The gas diffusion layer contains a conductive porous body, and the catalyst layer contains catalyst particles.

That is, the gas diffusion electrode according to the present invention comprises:
A porous resin having pores communicating with the pores of the catalyst layer and the surface layer is provided, and a porous resin having pores communicating with the gas diffusion layer is also provided. Since the porous resin of the diffusion layer is continuous, the pores of the porous resin of the catalyst layer and the pores of the porous resin of the gas diffusion layer are continuous.

With the gas diffusion electrode having such a structure, it is possible to prevent gas diffusibility into the pores of the catalyst layer, the surface layer, and the gas diffusion layer from being impaired. Then, water is prevented from staying in the pores of the catalyst layer and in the surface layer, the reaction gas is sufficiently supplied to the three-phase interface, and a highly active gas diffusion electrode can be obtained even at a high current density.

Here, in order for the gas to be smoothly supplied to the catalyst layer and for the water to be smoothly discharged from the catalyst layer, it is necessary to use a porous resin having communication holes arranged in the gas diffusion electrode. The pore diameter is preferably 5 nm or more and 5 μm or less, more preferably 1 μm or less.

The porosity of the porous resin is 30% or more and 9% or more.
It is preferably 5% or less, and particularly preferably 50% or more and 95% or less in order to sufficiently diffuse gas.

The average pore size and porosity are as follows:
It can be analyzed by an electron microscope or measured by a mercury porosimeter.

The catalyst particles contained in the catalyst layer include platinum, rhodium, ruthenium, iridium, palladium,
It is suitable to use platinum group metals such as osmium and alloy particles thereof, or catalyst-supporting carbon carrying these catalysts.

As the solid polymer electrolyte, a cation exchange resin is used. Among them, it is preferable to use a perfluorocarbon sulfonic acid or a styrene-divinylbenzene sulfonic acid type cation exchange resin.

Further, the porous resin used in the present invention includes polyethers such as polyvinyl chloride, polyacrylonitrile, polyethylene oxide, and polypropylene oxide, polyacrylonitrile, vinylidene fluoride polymer, polyvinylidene chloride, polymethyl methacrylate, and polymethyl methacrylate. Methyl acrylate, polyvinyl alcohol, polymethacrylonitrile, polyvinyl acetate, polyvinylpyrrolidone, polyethyleneimine, polybutadiene, polystyrene, polyisoprene, or derivatives thereof may be used alone or in combination, and also constitute the above resin. Although a resin obtained by copolymerizing various monomers may be used,
Preferably, a fluororesin having high water repellency, for example, ethylene trifluoride chloride copolymer (PCTFE), vinylidene fluoride polymer (PVdF), vinyl fluoride polymer (PVF)
Or a fluorine-containing copolymer such as an ethylene / tetrafluoroethylene copolymer, or a mixture thereof.

The gas diffusion layer used in the present invention is:
Although a foamed nickel or titanium fiber sintered body may be used, it is preferable to use a conductive porous body made of a carbon material that is a sintered body such as carbon fiber in terms of acid resistance and electron conductivity.

In the method for producing a gas diffusion electrode of the present invention, it is preferable to use a phase separation as a method of including a porous resin in the gas diffusion electrode. The term “phase separation” generally refers to a phenomenon in which, in a completely mixed two-component solution or solid solution, the solubility decreases as the temperature changes, and the two-phase solution or solid solution separates into two liquid or solid phases. (Chemistry Dictionary, Tokyo Chemical Doujin Co., Ltd., issued in 1994). "
It means a method of separating a resin from a solution in which the resin is dissolved in a solvent.

As a specific method of phase separation, there are a solvent extraction method and a method using a change in concentration, and as a method using a change in concentration, there are a method using a change in solubility with temperature and a method using evaporation of a solvent. . In the present invention, these phase separation methods can be used to obtain a porous resin.

Among these phase separation methods, it is preferable to use a solvent extraction method since dense and continuous pores are formed. The phase separation by the solvent extraction method means that a first solvent is dissolved from a solution in which a resin is dissolved in a first solvent by using a second solvent which is insoluble in the resin and compatible with the first solvent. Is replaced with a second solvent to separate the resin. After the resin undergoes phase separation, the second
By removing the solvent, a porous resin can be obtained.

The phase separation method utilizing the change in solubility with temperature refers to a method of increasing the temperature in a combination of a solvent and a resin in which the resin is hardly dissolved at a low temperature and easily dissolved when the temperature is increased. When a solution is prepared by completely dissolving the resin in the solvent, and then the temperature of the solution is lowered, the solubility of the solvent in the resin decreases, and the resin is separated in the solution. The porous resin can be obtained by removing the solvent from the solution of the resin and the solvent having undergone such phase separation.

Further, the phase separation method using solvent evaporation refers to a phenomenon in which a solution in which a resin is completely dissolved in a solvent is prepared, and then the solvent is evaporated from the solution to separate the resin in the solution. In some cases, a porous resin can be obtained by further removing the solvent from a solution of the resin and the solvent that has undergone such phase separation, but this method does not always result in a porous resin. Absent.

As a resin used in the production of a porous resin by phase separation, fine and uniform pores are obtained, so that a PVdF homopolymer, vinylidene fluoride.
Polyvinylidene fluoride (PVdF) resin such as propylene hexafluoride polymer (P (VdF-HEP)) or vinylidene fluoride / tetrafluoroethylene copolymer (P (VdF-TFP)) is preferable. Among them, a vinylidene fluoride polymer (PVdF) excellent in water repellency or a vinylidene fluoride-propylene hexafluoride copolymer (P (VdF-HFP)) which is soft and easy to handle is preferable.

The solvent for dissolving the resin used for phase separation utilizing the change in concentration or the first solvent used for phase separation by the solvent extraction method may be any solvent that dissolves the resin, such as methyl ethyl ketone and acetone. Ketone, propylene carbonate, ethylene carbonate, dimethyl carbonate, diethyl carbonate, carbonates such as ethyl methyl carbonate, dimethyl ether, diethyl ether, ethyl methyl ether, ethers such as tetrahydrofuran, dimethylformamide, dimethylacetamide, 1-methyl-pyrrolidinone, n- Methyl-pyrrolidone and the like.

In the phase separation using the solvent extraction method described above, the first solvent for dissolving the resin may be, for example, n-
Use of methyl-pyrrolidone (NMP) is more preferable because fine and uniform pores can be obtained. In addition, as the second solvent compatible with the first solvent, water or a mixed solution of water and alcohol is preferable at a low cost.

In the above-described method for producing a porous resin by phase separation utilizing a change in concentration, the solvent that dissolves the resin is such that the resin is unlikely to dissolve in the solvent at low temperatures.
Solvents that readily dissolve when the temperature is raised are preferred.

In the gas diffusion electrode of the present invention, the catalyst layer and the gas diffusion layer were previously integrated in order to make the porous resin provided in the catalyst layer and the porous resin provided in the gas diffusion layer continuous. It is preferable to go through a step of including a resin in the gas diffusion electrode.

More preferably, a step of providing a resin in a gas diffusion electrode portion of a membrane-electrode assembly in which a gas diffusion electrode including a catalyst layer and a gas diffusion layer is bonded to at least one of the solid polymer electrolyte membranes. Is good.

The gas diffusion electrode manufactured by this method has not only high water repellency due to a porous resin having communication holes, but also the resin distribution after forming an electron conduction network between the catalyst layer and the gas diffusion layer. Therefore, both high gas diffusivity and high electron conductivity can be obtained. In particular,
At least one of the solid polymer electrolyte membrane, a membrane in which a gas diffusion electrode including a catalyst layer and a gas diffusion layer is bonded-a gas diffusion electrode manufactured through a step of providing a resin in a gas diffusion electrode portion of an electrode assembly, A sufficient proton conduction network is formed between the catalyst layer and the solid polymer electrolyte membrane.

As a method of providing a porous resin in a gas diffusion electrode provided with a catalyst layer and a gas diffusion layer, a method in which a solution in which a resin is dissolved in a solvent is added to the gas diffusion electrode, and then the resin is added There is a manufacturing method through a step of separating layers.

Further, as a method of providing a porous resin in a gas diffusion electrode having a catalyst layer and a gas diffusion layer, there is a solvent extraction method. In this method, a solution in which a resin is dissolved in a first solvent is included in a gas diffusion electrode, and the resin is insoluble and the first
It is preferable that the first solvent is replaced with the second solvent using a second solvent compatible with the above-mentioned solvent, the resin is subjected to phase separation, and then a step of removing the second solvent is performed.

Further, in the method in which the gas diffusion electrode having the catalyst layer and the gas diffusion layer is provided with a porous resin, the step of including a solution obtained by dissolving the resin in a solvent is performed at 50 Torr or less, more preferably 1 Torr or less. It is preferably performed under reduced pressure.

In the present invention, as a method for providing the gas diffusion electrode with a porous resin, for example, polyvinylidene fluoride (PVdF) is replaced with n-methylpyrrolidone (NMP).
Is preferably placed on a gas diffusion electrode under reduced pressure, and NMP is replaced with water, from the viewpoints of water repellency, uniformity of pore size, and the like.

As described above, in order to manufacture the gas diffusion electrode of the present invention, for example, the catalyst-supporting carbon particles and the solid polymer electrolyte solution and, if necessary, PTFE
A conventional catalyst layer manufactured by a method such as heating and drying after forming a catalyst paste containing a particle dispersion solution on a substrate such as a polymer film, or a dispersion of platinum-supported carbon and PTFE particles as required. After forming the catalyst paste containing the solution on a substrate such as a polymer film and drying, apply a solid polymer electrolyte solution from above,
A solution in which a resin is dissolved in a solvent in a gas diffusion electrode in which the catalyst layer manufactured by the method of disposing is transferred to a gas diffusion layer, or a membrane-electrode assembly in which the gas diffusion electrode is bonded to a solid polymer electrolyte membrane. The gas diffusion electrode provided with the porous resin is obtained by a method in which the resin is phase-separated after disposing.

In order to manufacture the gas diffusion electrode of the present invention, for example, a paste containing carbon particles and a solid polymer electrolyte solution and, if necessary, a PTFE particle dispersion solution is added to a substrate such as a polymer film. After being formed into a film, one manufactured by a method of heating and drying,
A gas diffusion electrode can also be manufactured by a method in which a porous resin is disposed on a gas diffusion electrode obtained by integrating a conductive porous body as a gas diffusion layer with a porous resin by the above-described method, and then catalyst particles are supported. .

The gas diffusion layer manufactured by using these methods contains a porous resin up to the deep portion of the fine pores of the catalyst layer. Since the holes communicate from the catalyst layer to the gas diffusion layer, good gas diffusivity can be provided.

[0051]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below with reference to preferred embodiments.

First, an embodiment of the present invention will be described.
First, platinum supported carbon (Tanaka Kikinzoku, TEC-1
0V-30E: 30 platinum on Valcan XC-72
wt.%) and a solid polymer electrolyte solution (5% by weight of Nafion, manufactured by Aldrich) were prepared.

Next, the catalyst paste was applied to a polymer film (FEP film: tetrafluoroethylene-hexafluoropropylene copolymer sheet, manufactured by Daikin Industries, Ltd.).
A catalyst layer obtained by applying a 300-mesh stainless screen on a 25-μm-thick stainless steel screen and naturally drying at room temperature for about 1 hour was subjected to hot pressing (95 ° C.) using a solid polymer electrolyte membrane (manufactured by DuPont). , Nafion, thickness 150μm)
And a gas diffusion layer (carbon paper: 0.5 mm thick) is hot-pressed (135
° C) to obtain a membrane-electrode assembly.

The obtained membrane-electrode assembly was fixed with a jig for preventing contraction of the solid polymer electrolyte membrane due to drying.
Dried at 0 ° C. for 30 minutes. Thereafter, the PVdF / NMP solution was impregnated under a reduced pressure of 1 Torr (PVdF concentration: 6 wt%). Immediately, the excess PVdF / NMP solution was removed. I got The gas diffusion electrode A had a structure in which a porous resin was continuously provided from inside the catalyst layer hole to the gas diffusion layer.

The platinum amount of the gas diffusion electrode A is about 1.0 mg.
/ Cm ² , the amount of platinum-supported carbon during paste production was adjusted. The obtained gas diffusion electrode A was incorporated into a single cell of a fuel cell to obtain a cell A.

Further, a comparative example will be described. First, platinum supported carbon (Tanaka Kikinzoku, TEC-10V
-30E: 30 wt% platinum on Valcan XC-72
% Supported) and a solid polymer electrolyte solution (manufactured by Aldrich,
Nafion 5 wt% solution) and PTFE particle dispersion solution (manufactured by DuPont-Mitsui Fluorochemicals, Teflon 30)
A catalyst paste consisting of J) was prepared.

Next, the catalyst paste was applied to a polymer film (FEP film: tetrafluoroethylene-hexafluoropropylene copolymer sheet, manufactured by Daikin Industries, Ltd.):
The catalyst layer obtained by applying the solution on a film having a thickness of 25 μm and naturally drying at room temperature for about 1 hour was subjected to hot pressing (95 ° C.) using a solid polymer electrolyte membrane (Dupont, Nafion, 150 μm thick).
m), and a gas diffusion layer (carbon paper: 0.5 mm thick) is hot-pressed (13
(5 ° C.) to obtain a gas diffusion electrode B.

The platinum amount of the gas diffusion electrode B is about 1.0 mg
/ Cm ² , the amount of platinum-supported carbon during paste production was adjusted. Then, the gas diffusion electrode B was incorporated into a single cell of a fuel cell to obtain a cell B.

FIG. 3 shows the current-voltage characteristics of these cells when hydrogen was used as the anode-side supply gas and oxygen was used as the cathode-side supply gas, and hydrogen was used as the anode-side supply gas and air was used as the cathode-side supply gas. Current when
FIG. 4 shows the voltage characteristics. The operating conditions were as follows: the supply gas pressure was 1 atm, and each was humidified by bubbling in a closed water tank at 70 ° C. The operating temperature of the cell was set to 60 ° C., and the holding time at the time of measurement at each current value was set to 2 minutes.

In FIGS. 3 and 4, the symbol (記号) indicates the characteristic of the cell A, and the symbol (▲) indicates the characteristic of the cell B. As is clear from FIGS. 3 and 4, the cell A of the example according to the present invention obtained a higher output voltage at each current density than the cell B of the comparative example. In particular, as shown in FIG. 4, the difference was remarkable when air was used as the cathode-side supply gas.

[0061]

According to the gas diffusion electrode of the present invention, since the porous resin having the communication hole is provided continuously with the catalyst layer and the gas diffusion layer, the resin has high gas diffusion and repellency of the resin. The retention of water is prevented by the aqueous solution, and high gas diffusivity is ensured even inside the catalyst layer.

Further, by disposing the porous resin after integrating the gas diffusion layer, the catalyst layer, and the solid polymer electrolyte membrane, it has high electron conductivity and proton conductivity. Oxygen can be supplied to the inside of the hole even when air with a low partial pressure is used, so that the output is greatly increased as compared with a conventional electrode, and a high-performance fuel cell can be manufactured even in a region with a high current density.

[Brief description of the drawings]

FIG. 1 is a schematic view showing the structure of a gas diffusion electrode according to the present invention.

FIG. 2 is a schematic view showing the structure of a conventional gas diffusion electrode.

FIG. 3 is a diagram showing current-voltage characteristics of a cell when hydrogen is used for an anode and oxygen is used for a cathode.

FIG. 4 is a diagram showing current-voltage characteristics of a cell when hydrogen is used for an anode and air is used for a cathode.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 catalyst layer 2 gas diffusion layer 3 porous resin 4 solid polymer electrolyte membrane 5 PTFE particles

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) H01M 8/10 H01M 8/10

Claims (8)

[Claims] 1. A porous resin having communication holes between a catalyst layer and a gas diffusion layer, wherein the porous resin provided in the catalyst layer and the porous resin provided in the gas diffusion layer are continuous. A gas diffusion electrode. 2. The porosity of the porous resin is 30% or more and 95% or more.
The gas diffusion electrode according to claim 1, wherein: 3. The porous resin has an average pore diameter of 50 nm or more.
3. The gas diffusion electrode according to claim 1, wherein the diameter is not more than μm. 4. The method for producing a porous resin according to claim 1, wherein the resin is phase-separated from a solution in which the resin is dissolved in a solvent. 5. A method of dissolving a resin in a first solvent, using a second solvent in which the resin is insoluble and compatible with the first solvent, and converting the first solvent into a second solvent. The method for producing a porous resin according to claim 1, wherein the second solvent is removed after the resin is subjected to phase separation by substitution. 6. The method according to claim 1, further comprising a step of causing a gas diffusion electrode provided with a catalyst layer and a gas diffusion layer to contain a solution obtained by dissolving the resin in a solvent and then phase-separating the resin. 4. The method for producing a gas diffusion electrode according to 2 or 3. 7. A solution obtained by dissolving a resin in a solvent is applied to a gas diffusion electrode portion of a membrane-electrode assembly in which a gas diffusion electrode including a catalyst layer and a gas diffusion layer is bonded to at least one of solid polymer electrolyte membranes. 4. The method for producing a gas diffusion electrode according to claim 1, further comprising a step of phase-separating the resin after being included. 8. The method according to claim 6, wherein the step of including a solution obtained by dissolving the resin in the solvent in the gas diffusion electrode including the catalyst layer and the gas diffusion layer is performed under reduced pressure.
A method for producing the gas diffusion electrode according to the above.