JP2001160401A - Gas diffusion electrode for polymer electrolyte fuel cell and method for producing the same - Google Patents

Abstract

(57) Abstract: A gas diffusion electrode for a fuel cell having excellent proton conductivity and excellent gas diffusion. In a gas diffusion electrode for a solid polymer electrolyte fuel cell, a catalyst layer comprises a proton conductive solid polymer electrolyte having communication holes with catalyst particles and a porous resin having no proton conductivity. Including.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a gas diffusion electrode for a solid polymer electrolyte fuel cell and a method for producing 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 hydrogen, for example, as a fuel to an anode, and oxygen, for example, as an oxidant to a cathode, and causes an electrochemical reaction to be performed. Is a device for obtaining

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

Anode: H ₂ → 2H ⁺ + 2e ⁻ Cathode: 1/2 O ₂ + 2H ⁺ + 2e ⁻ → H ₂ O Total reaction: H ₂ +1/2 O ₂ → H ₂ O As shown in the above formula In addition, reactions at the anode and cathode require the supply of oxygen and hydrogen gases, the transfer of protons (H ⁺ ) and electrons (e ⁻ ), and all reactions take place simultaneously at the three-phase interface in the electrode. ,
That is, it proceeds only at the interface between the reaction gas, the catalyst, and the solid electrolyte. Therefore, the fuel cell has a gas supply path from the catalyst layer surface to the three-phase interface, a proton conduction path from the anode three-phase interface to the cathode three-phase interface through the solid electrolyte membrane, and an electron transfer path from the three-phase interface to the current collector. A conduction path must be formed.

Therefore, a membrane-electrode assembly in which a gas diffusion electrode comprising a catalyst layer and a conductive porous substrate serving as a current collector is joined to both surfaces of a solid polymer electrolyte membrane as an anode and a cathode. Used. The catalyst layer is a mixture of carbon carrying a catalyst, a solid polymer electrolyte, and a water repellent such as PTFE, and is a place where an electrode reaction is performed.

[0006] Among them, gas diffusivity and proton conductivity are major problems that affect the performance of a fuel cell, and in order to manufacture a fuel cell with higher performance, it is essential to improve them. . Totsuka et al. Formed a solid polymer electrolyte with three-dimensional communication holes,
We have developed a porous solid polymer electrolyte with significantly improved gas diffusivity and proton conductivity, and have proposed to apply it to fuel cell electrodes.
69-170). However, considering that a fuel cell is mounted on an electric vehicle, the current output is not sufficient, and further higher output is desired.

[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. Therefore, the present inventors first attempted to improve proton conductivity and gas diffusivity by using the electrode provided with a solid polymer electrolyte having a communication hole by the method of Totsuka et al.

However, although good results were obtained with respect to the performance of the fuel cell in the low current density region, when the fuel cell was operated in the high current density region, it was necessary to supply water to the solid polymer electrolyte membrane. Due to humidification and generation of water at the cathode, there has been a problem that water stays inside the communication holes of the solid polymer electrolyte having the above-described original communication holes and on the surface, and gas diffusibility is inhibited, and the output is significantly reduced. .

Generally, in order to prevent water from staying due to generation and movement of water, polytetrafluoroethylene (PTFE) particles are mixed in the catalyst layer, or PTFE is added to the surface of the conductive porous substrate. Is applied to impart water repellency. However, although PTFE has strong water repellency, the particles themselves are large and do not have gas diffusivity. Therefore, if the mixing ratio of PTFE is increased to further increase the water repellency, the proton conduction path, the electron conduction path, and the gas diffusion Block the route.

The present inventor manufactured an electrode in which PTFE was added to an electrode provided with the above-mentioned solid polymer electrolyte having a communication hole, but although good proton conductivity was obtained, PTF was obtained.
E did not contribute to the improvement of water repellency in the communication hole, and it was confirmed that sufficient performance could not be obtained due to insufficient gas diffusivity.

In view of the above, an object of the present invention is to provide a gas diffusion electrode for a fuel cell having excellent proton conductivity and excellent gas diffusion.

[0012]

According to the gas diffusion electrode for a fuel cell electrode of the present invention, the catalyst layer is composed of a proton conductive solid polymer electrolyte having communication holes with catalyst particles and a porous material having no proton conductivity. And a porous resin, and more preferably, the porous resin is provided in a communication hole of a proton conductive solid polymer electrolyte.

[0013] The method for producing a solid polymer electrolyte having a communicating hole is characterized in that a solution a 'obtained by dissolving a proton conductive solid polymer electrolyte in a solvent a is immersed in a solvent b having a polar group other than an alcoholic hydroxyl group. By replacing the solvent a with the solvent b, a step of removing the solvent b is performed.

Further, the method for producing a porous resin having no proton conductivity is as follows: a solution c ′ obtained by dissolving a resin having no proton conductivity in a solvent c is insoluble in the resin and the solvent c It is characterized in that a step of replacing the solvent c with the solvent d by immersing it in a solvent d which is compatible with the solvent d and then removing the solvent d is performed.

In the following, "proton conductive solid polymer electrolyte" is abbreviated as "solid polymer electrolyte (SPE)", and "porous resin having no proton conductivity" is referred to as "porous resin." Resin (R) ".

[0016]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, a structural example of a gas diffusion electrode for a fuel cell according to the present invention will be described more specifically with reference to the drawings.

1 to 4 show the structure of a gas diffusion electrode for a fuel cell according to the present invention. In FIGS. 1 to 4, 1 is a solid polymer electrolyte (SPE), 2 is carbon particles, and 3 is The communication holes of the solid polymer electrolyte (SPE), 4 is a porous resin (R), and 5 are catalyst particles.

FIG. 1 shows the structure before the porous resin (R) is provided in the communication hole of the solid polymer electrolyte (SPE), and FIG. 2 shows the structure of the porous resin in the communication hole of the solid polymer electrolyte (SPE). (R)
1 shows a structure provided with: As shown in FIG. 1, the electrode according to the present invention is a solid polymer electrolyte (SP) having a communication hole.
E) A porous resin (R) 4 is provided in a communicating hole 3 of a solid polymer electrolyte (SPE) including a carbon particle 2 carrying platinum in a highly dispersed state as a catalyst particle and having the communicating hole. This is a novel electrode having both high proton conductivity and gas diffusivity.

The porous resin (R) 4 may be arranged only in the communicating hole of the solid polymer electrolyte (SPE) as shown in FIG. 2, but as shown in FIG. By disposing the porous resin (R) on the surface of the electrolyte (SPE) or on the entire catalyst layer as shown in FIG. 4, higher gas diffusivity is provided. Further, if necessary, PTFE particles can be provided in the conductive porous substrate and the catalyst layer as before.

That is, according to the present invention, by forming a solid polymer electrolyte (SPE) having communication holes, high proton conductivity is obtained, and catalyst particles inside the pores, that is, up to the three-phase interface, are obtained. A continuous proton conduction path can be secured, and the porous resin (R) disposed in the communication hole prevents water from staying in the communication hole and allows the reaction gas to reach the three-phase interface. When supplied sufficiently, a gas diffusion electrode for a fuel cell which is highly active even at a high current density can be obtained.

If these porous resins (R) are arranged in at least a part of the communicating holes of the solid polymer electrolyte (SPE), all of the porous resins (R) are formed in the communicating holes of the solid polymer electrolyte (SPE). Alternatively, it may be disposed on the entire surface of the solid polymer electrolyte (SPE) and on a part of the surface.

In the present invention, platinum is used as the catalyst particles.
It is suitable to use platinum group metals such as rhodium, ruthenium, iridium, palladium and osmium and alloy particles thereof, or a catalyst-carrying carbon carrying these catalysts.

As the solid polymer electrolyte (SPE), a proton exchange membrane is used, and among them, perfluorocarbonsulfonic acid or styrene-divinylbenzene sulfonic acid type solid polymer electrolyte is preferably used.

Further, the porous resin (R) used in the present invention
Are polyvinyl chloride, polyacrylonitrile, polyethylene oxide, polyether such as polypropylene oxide, polyacrylonitrile, vinylidene fluoride polymer,
Polyvinylidene chloride, polymethyl methacrylate, polymethyl acrylate, polyvinyl alcohol, polymethacrylonitrile, polyvinyl acetate, polyvinylpyrrolidone, polyethyleneimine, polybutadiene, polystyrene, polyisoprene, or a derivative thereof, alone or mixed A resin obtained by copolymerizing various monomers constituting the above resin may be used, but a fluororesin having high water repellency, for example, ethylene trifluoride chloride copolymer (PCTFE), vinylidene fluoride polymer is preferable. Fluorine-containing homopolymers such as coalesced (PVdF) and vinyl fluoride polymers (PVF) or fluorine-containing copolymers such as ethylene-tetrafluoroethylene copolymer are preferable, and a mixture thereof may be used.

The conductive porous substrate used in the present invention may be a foamed nickel or titanium fiber sintered body. However, in terms of acid resistance and electronic conductivity, the conductive porous substrate is made of a sintered body such as carbon fiber. An object made of a certain carbon material is desirable.

The solid polymer electrolyte (SPE) having a communication hole used for the gas diffusion electrode for a fuel cell of the present invention is a solution a ′ obtained by dissolving the solid polymer electrolyte (SPE) in a solvent a.
Is immersed in a solvent b having a polar group other than an alcoholic hydroxyl group, whereby the solvent a is replaced with the solvent b, and then the solvent b is removed.

Here, the solvent a used in the present invention includes:
Alcohol or a mixed solvent of alcohol and water can be used, and among them, alcohol is preferably used as the solvent a. Also, as the solid polymer electrolyte (SPE), a proton exchange membrane is used,
Among them, it is preferable to use perfluorocarbon sulfonic acid or a styrene-divinylbenzene-based sulfonic acid type solid polymer electrolyte, and as the solid polymer electrolyte solution a ′, a solution in which a perfluorocarbon sulfonic acid resin is dissolved in alcohol is preferable. .

Further, as the solvent b having a polar group other than the alcoholic hydroxyl group used in the present invention, an organic solvent having an alkoxycarbonyl group in the molecule and having 1 to 7 carbon atoms, such as propyl formate, formic acid Butyl, isobutyl formate, ethyl acetate, propyl acetate, isopropyl acetate, allyl acetate, butyl acetate, isobutyl acetate, pentyl acetate, isopentyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl acrylate, butyl acrylate, acrylic Isobutyl acrylate, methyl butyrate, methyl isobutyrate, ethyl butyrate, ethyl isobutyrate, methyl methacrylate, propyl butyrate, isopropyl isobutyrate, 2-ethoxyethyl acetate, 2- (2-ethoxyethoxy) ethyl acetate, or a mixture thereof, It is preferable to use

The porous resin (R) used for the fuel cell electrode of the present invention is preferably formed by, for example, a solvent extraction method since dense and continuous terms are formed. That is, the solution c ′ obtained by dissolving the resin in the solvent c is immersed in a solvent d insoluble in the resin and compatible with the solvent c, thereby replacing the solvent c with the solvent d.
It is preferable to manufacture by passing through the step of removing.

The resin used in the production of the porous resin (R) of the present invention includes polyethers such as polyvinyl chloride, polyacrylonitrile, polyethylene oxide and polypropylene oxide, polyacrylonitrile, vinylidene fluoride polymer, and poly (vinylidene fluoride). Vinylidene chloride, polymethyl methacrylate, polymethyl acrylate, polyvinyl alcohol, polymethacrylonitrile, polyvinyl acetate,
Polyvinylpyrrolidone, polyethyleneimine, polybutadiene, polystyrene, polyisoprene, or derivatives thereof may be used alone or in combination, or a resin obtained by copolymerizing various monomers constituting the above resin may be used. , Preferably a highly water-repellent fluororesin, for example, ethylene trifluoride chloride copolymer (PCTF
E), fluorine-containing homopolymers such as vinylidene fluoride polymer (PVdF) and vinyl fluoride polymer (PVF) or fluorine-containing copolymers such as ethylene / tetrafluoroethylene copolymer, and mixtures thereof. Good.

In the production of the porous fluororesin by the solvent extraction method, fine and uniform pores are obtained, so that PVdF homopolymer, vinylidene fluoride / propylene hexafluoride polymer (P (VdF- HEP)) or
Vinylidene fluoride / tetrafluoroethylene copolymer (P (V
dF-TFP)) and other polyvinylidene fluorides (PVd
F) -based resins are preferred. Above all, a vinylidene fluoride polymer (PVdF) excellent in water repellency or a vinylidene fluoride / propylene hexafluoride copolymer (P (VdF-TFP)) which is soft and easy to handle is preferable.

The solvent c for dissolving the resin may be any solvent capable of dissolving the resin, such as carbonic esters such as dimethylformamide, propylene carbonate, ethylene carbonate, dimethyl carbonate, diethyl carbonate and ethyl methyl carbonate, dimethyl ether, diethyl ether, and the like. Examples thereof include ethers such as ethyl methyl ether and tetrahydrofuran, dimethylacetamide, 1-methyl-pyrrolidinone, and n-methyl-pyrrolidone.

As the solvent d compatible with the solvent c, water or a mixed solution of water and an alcohol is preferable at a low cost.

In the present invention, when the porous resin (R) is filled into the communication holes of the solid polymer electrolyte (SPE) of the catalyst layer, for example, polyvinylidene fluoride (PVdF)
Is dissolved in n-methylpyrrolidone (NMP), and extracted with water is preferable in terms of water repellency, uniformity of pore size, and the like.

As described above, in order to manufacture an electrode including a solid polymer electrolyte (SPE) having a communication hole, for example, a solvent containing an alcohol is used as the solvent a, and the solid polymer electrolyte (SPE) is used. After dissolving a solution a ′ in a solvent a and a catalyst paste obtained by mixing catalyst particles and carbon as a conductive agent, applying the conductive paste on a conductive porous substrate,
The conductive porous substrate coated with the catalyst paste is immersed in a solvent b having a polar group other than the alcoholic hydroxyl group, and the solvent a
Is preferably replaced by a solvent b, and then a step of removing the solvent b is preferable.

Further, in order to manufacture a catalyst layer in which a porous resin (R) is provided in the communication hole of the solid polymer electrolyte (SPE) having the communication hole, for example, a solid polymer having the communication hole is used. After a solution c ′ obtained by dissolving a resin in a solvent c is contained in a conductive porous substrate provided with a catalyst layer containing an electrolyte (PSE), the conductive porous substrate is insoluble in the resin and the solvent c Dipped in a solvent d compatible with
And then passing through a step of removing the solvent d.

[0037]

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

[Examples] Platinum-supported carbon (TEC-10V-30E, Valcan XC-72, manufactured by Tanaka Kikinzoku)
A catalyst paste comprising a solid polymer electrolyte solution (Aldrich, Nafion 5 wt% solution) and a solid polymer electrolyte solution (30 wt% platinum) is prepared.

The catalyst paste was applied on a conductive porous carbon electrode substrate (0.5 mm) using a stainless steel screen of 300 mesh, and the carbon electrode substrate was immersed in butyl acetate for 10 minutes. After replacing the solvent of the solid polymer electrolyte solution with butyl acetate, take out and dry the butyl acetate at room temperature, and a carbon electrode substrate provided with a catalyst layer containing platinum-supported carbon and a solid polymer electrolyte having communication holes. A was obtained.

A PVdF / NMP solution (PVdF) was applied to a carbon electrode substrate provided with the obtained porous solid polymer electrolyte.
(Concentration: 6 wt%) after vacuum impregnation, and excess PV on the surface
The dF / NMP solution was wiped off, immersed in ion-exchanged water for 10 minutes to replace NMP with water, and then dried to remove water, thereby obtaining a fuel cell electrode A.

The electrode A has a structure in which a porous resin (R) is provided in the inside, the surface, and the conductive porous body of the communication hole of the solid polymer electrolyte (SPE). The amount of platinum-carrying carbon at the time of paste production was adjusted so that the platinum amount of electrode A was about 1.0 mg / cm ² .

The obtained electrode A was hot-pressed (120
(C), and bonded to both surfaces of a solid polymer electrolyte membrane (manufactured by DuPont, Nafion, film thickness 150 μm), and assembled into a single cell of a fuel cell to obtain Cell A.

[Comparative Example 1] Platinum-supported carbon (TEC-10V-30E manufactured by Tanaka Kikinzoku, Valcan XC-7
2, a paste comprising a solid polymer electrolyte solution (manufactured by Aldrich, Nafion 5 wt% solution) and a PTFE particle dispersion solution (manufactured by Du Pont-Mitsui Fluorochemicals, Teflon 30J) was provided with water repellency. Conductive porous carbon electrode substrate (0.5 m
m), and dried at 120 ° C. for 1 hour in a nitrogen atmosphere to obtain an electrode B.

The platinum amount of the electrode B is about 1.0 mg / cm ²
The amount of platinum-carrying carbon during the production of the paste was adjusted so that The obtained electrode B is hot-pressed (120
(C) at both sides of a solid polymer electrolyte membrane (Dupont, Nafion, 150 μm in thickness) and assembled into a single cell of a fuel cell to obtain a cell B.

Comparative Example 2 Platinum-supported carbon (TEC-10V-30E, Valcan XC-7, manufactured by Tanaka Kikinzoku)
A catalyst paste composed of a solid polymer electrolyte solution (5% by weight of Nafion, manufactured by Aldrich) and platinum (30 wt% supported on 2) is prepared.

The catalyst paste was applied on a conductive porous carbon electrode substrate (0.5 mm) using a stainless steel screen of 300 mesh, and the carbon electrode substrate was immersed in butyl acetate for 10 minutes. Then, the butyl acetate was taken out and dried at room temperature to obtain a carbon electrode substrate C provided with a catalyst layer containing catalyst particles, carbon, and a solid polymer electrolyte having three-dimensional communication holes.

The platinum amount of the electrode C is about 1.0 mg / cm ²
The amount of platinum-carrying carbon during the production of the paste was adjusted such that Hot pressing (120 ° C) the obtained electrode C
At solid polymer electrolyte membrane (Dupont, Nafion,
A cell C was obtained by bonding to both surfaces having a thickness of 150 μm) and assembling into a single cell of a fuel cell.

FIG. 5 shows the current-voltage characteristics when hydrogen was used as the anode side supply gas and oxygen was used as the cathode side supply gas using these cells. FIG. 5 shows hydrogen as the anode side supply gas and air as the cathode side supply gas. FIG. 6 shows the current-voltage characteristics when using. 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. And the operating temperature of the cell is 60
° C, and the holding time at the time of measurement at each current value was 2 minutes.

As is clear from FIGS. 5 and 6, the cell A according to the present invention obtained a higher output voltage at each current density than the conventional cells B and C. Particularly, as shown in FIG. 6, the difference was remarkable when air was used as the cathode side supply gas.

This is because, in a cell A using an electrode A in which porous PVdF is arranged in the pores and on the surface of a solid polymer electrolyte (SPE) having a communicating hole, a solid polymer electrolyte having a communicating hole (SPE) is used. SPE) has high proton conductivity, and furthermore, by arranging water-repellent porous PVdF in the through-holes and on the surface thereof, stagnation of water in the through-holes and on the surface is prevented, and oxygen content is reduced. Oxygen can be supplied to the inside of the hole even when low-pressure air is used, and the output is improved as compared with a conventional electrode.

[0051]

According to the fuel cell electrode of the present invention, the proton conductive solid polymer electrolyte in the catalyst layer has many communication holes, and the proton conductive solid polymer electrolyte having the communication holes has a large diameter. By disposing a porous resin having no proton conductivity in the pores and on the surface, a gas diffusion electrode for a fuel cell having high proton conductivity and high gas diffusivity can be obtained, and in a region where the current density is high. In addition, a high-performance fuel cell can be manufactured.

[Brief description of the drawings]

FIG. 1 is a schematic view showing a structure of a fuel cell electrode according to the present invention before a porous resin (R) is provided in pores of a solid polymer electrolyte (SPE).

FIG. 2 is a schematic view showing a structure of a fuel cell electrode according to the present invention in which a porous resin (R) is provided in pores of a solid polymer electrolyte (SPE).

FIG. 3 is a schematic diagram showing a structure of a fuel cell electrode according to the present invention in which a surface of a solid polymer electrolyte (SPE) is also provided with a porous resin (R).

FIG. 4 is a schematic view showing a structure (R) of a fuel cell electrode according to the present invention in which a porous resin (R) is provided on the entire catalyst layer.

FIG. 5 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. 6 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]

 DESCRIPTION OF SYMBOLS 1 Solid polymer electrolyte (SPE) 2 Carbon particles 3 Communication hole of solid polymer electrolyte (SPE) 4 Porous resin (R) 5 Catalyst particles

Claims (4)

[Claims] 1. A gas diffusion electrode for a solid polymer electrolyte fuel cell, wherein the catalyst layer comprises a proton conductive solid polymer electrolyte having communication holes with catalyst particles and a porous resin having no proton conductivity. A gas diffusion electrode for a fuel cell, comprising: 2. The gas diffusion electrode for a fuel cell according to claim 1, wherein the porous resin is provided in a communication hole of a proton conductive solid polymer electrolyte. 3. A solvent a having a proton-conductive solid polymer electrolyte dissolved in a solvent a is immersed in a solvent b having a polar group other than an alcoholic hydroxyl group, whereby the solvent a is replaced with the solvent b. 3. The method for producing a proton conductive solid polymer electrolyte having communication holes according to claim 1, further comprising a step of removing the solvent b. 4. A resin having no proton conductivity is dissolved in a solvent c.
The solution c ′ dissolved in the solvent c is immersed in a solvent d that is insoluble in the resin and compatible with the solvent c, thereby replacing the solvent c with the solvent d and then removing the solvent d The method for producing a porous resin according to claim 1 or 2, wherein: