JP7187798B2 - Catalyst layers and membrane electrode assemblies for polymer electrolyte fuel cells - Google Patents

Description

TECHNICAL FIELD The present invention relates to a catalyst layer that is a constituent member of a polymer electrolyte fuel cell.

In recent years, in order to solve environmental problems such as global warming, the development of new power sources for _CO2 reduction has been demanded. Fuel cells, which do not emit _CO2 , have attracted attention as a power source. A fuel cell uses a fuel (eg, hydrogen) and an oxidant (eg, oxygen) to oxidize to produce harmless water. The chemical energy obtained by producing water is converted into electrical energy and used as a power source or power source.
Since fuel cells are classified according to the type of electrolyte, they strongly depend on the operating temperature, and a suitable fuel cell is used depending on the temperature range in which the mounted object operates. A polymer electrolyte fuel cell (PEFC) operates at a low temperature, has a high output density, and can be made compact and lightweight. Therefore, it is being developed as a power source for home use and a power source for vehicles.

A polymer electrolyte fuel cell (PEFC) has a structure (membrane electrode assembly) in which a polymer electrolyte membrane is sandwiched between a fuel electrode (anode) and an air electrode (cathode). By supplying air gas containing oxygen to the air electrode side, electricity is generated by the following electrochemical reaction.
Anode: H ₂ → 2H ⁺ + 2e ^- (Reaction 1)
Cathode: 1/2O ₂ + 2H ⁺ + 2e ⁻ → H ₂ O (Reaction 2)

The anode and cathode each consist of a laminated structure of a catalyst layer and a gas diffusion layer. Protons and electrons are generated by the electrode catalyst from the hydrogen supplied to the anode-side catalyst layer (reaction 1). Protons pass through the polymer electrolyte in the anode-side catalyst layer and the polymer electrolyte membrane to move to the cathode. Electrons travel through an external circuit to the cathode. In the cathode-side catalyst layer, protons, electrons, and oxygen contained in air supplied from the outside react to produce water (reaction 2).

In order to reduce the cost of fuel cells, efforts are being made to develop fuel cells that exhibit high output characteristics. However, there is a problem that the power generation performance is lowered due to the phenomenon (flooding) that the gas supply to the catalyst layer and the gas diffusion layer is interrupted due to excessive generation of water due to the high output operation.
In order to solve the above problems, Patent Documents 1 and 2 propose catalyst layers containing not only platinum-supported carbon but also carbon fibers.

JP-A-10-241703 Japanese Patent No. 5537178

In Patent Literatures 1 and 2, it is presumed that inclusion of carbon fibers in the catalyst layer created voids in the catalyst layer, leading to improved drainage. However, although the structure and content of carbon fibers are specified, the structure of the catalyst layer exhibiting high power generation performance is not clarified.
Therefore, we clarify the range in which the ion exchange capacity of the ionomer, which strongly affects the structure of the catalyst layer, exhibits good power generation performance.
The present invention has been made in view of the above circumstances, and provides a polymer electrolyte fuel cell catalyst layer and a membrane electrode assembly capable of improving drainage and gas diffusibility and capable of high output. for the purpose.

One aspect of the present invention is a catalyst layer for a polymer electrolyte fuel cell. In order to solve the above problems, the catalyst layer is composed of catalyst-supporting carbon particles, a polymer electrolyte and carbon fibers, and the ion exchange capacity (IEC) of the polymer electrolyte satisfies the formula (1). characterized by
1.5≧IEC≧1.1 [meq/g] Expression (1)
Further, a membrane electrode assembly according to one aspect of the present invention has the catalyst layer on at least one of the anode and the cathode.

ADVANTAGE OF THE INVENTION According to one aspect of the present invention, it is possible to provide a polymer electrolyte fuel cell catalyst layer that exhibits improved drainage and gas diffusibility and high power generation performance.

1 is a configuration diagram of a catalyst layer for a polymer electrolyte fuel cell according to an embodiment of the present invention; FIG. 1 is a configuration diagram of a membrane electrode assembly according to an embodiment of the present invention; FIG.

An embodiment of the present invention will be described with reference to the drawings. In addition, the present invention is not limited to the embodiments described below, and it is possible to add modifications such as design changes based on the knowledge of those skilled in the art. Embodiments are also included in the scope of embodiments of the present invention.
FIG. 1 shows a catalyst layer (cathode catalyst layer 6, anode catalyst layer 7). FIG. 2 shows a membrane electrode assembly according to one embodiment of the present invention comprising a polymer electrolyte membrane 5, a cathode catalyst layer 6, an anode catalyst layer 7, a gasket material 8 and a gas diffusion layer 9. FIG.

Next, the configuration of the catalyst layers (cathode catalyst layer 6, anode catalyst layer 7) will be described with reference to FIG.
The catalyst particles 1 used in the present embodiment include platinum group elements such as platinum, palladium, ruthenium, iridium, rhodium, and osmium, as well as iron, lead, copper, chromium, cobalt, nickel, manganese, vanadium, molybdenum, gallium, and aluminum. or alloys thereof can be used. In addition, oxides, composite oxides, and the like can also be used. Further, the particle size of these catalysts is, for example, about 0.1 nm or more and 1 μm or less, preferably 0.5 nm or more and 100 nm or less, more preferably about 1 nm or more and 10 nm or less.

Carbon particles are generally used for the conductive carrier 2 that supports these catalyst particles 1 . Any kind of carbon particles may be used as long as they are particulate, conductive, and not affected by the catalyst particles 1. Carbon black, graphite, black lead, activated carbon, fullerene, etc. can be used.
The polymer electrolyte 3 used in this embodiment may be any material as long as it has proton conductivity, and the same material as the polymer electrolyte membrane 5 (see FIG. 2) can be used. A hydrogen-based polymer electrolyte or the like can be used. As the fluorine-based polymer electrolyte, for example, a Nafion (registered trademark)-based material manufactured by DuPont can be used.

The ratio I/(C+CF) between the mass C of the conductive carrier 2 and the mass CF of the carbon fiber 4 supported by the catalyst particles 1 and the mass I of the polymer electrolyte 3 is 0.2 or more and 1.5 or less. and good.
In particular, when the IEC (ion exchange capacity of the polymer electrolyte) is 1.1 or more and less than 1.3, I/(C+CF) is more preferably 0.2 or more and less than 0.8. Moreover, when IEC is 1.3 or more and less than 1.5, I/(C+CF) is more preferably 0.8 or more and 1.5 or less. This is because the lower the IEC, the more likely the polymer electrolyte 3 and the carbon fibers 4 are entangled, and the effective range of I/(C+CF) with respect to power generation performance changes depending on the IEC.
When I/(C+CF) is less than 0.2, the proton pass is poor and the power generation performance is significantly impaired. On the other hand, when I/(C+CF) exceeds 1.5, the drainage performance of the catalyst layer is deteriorated, which significantly impairs the power generation performance of the fuel cell.

Carbon fibers, carbon nanofibers, carbon nanotubes, and the like can be used as the carbon fibers 4 used in this embodiment. Carbon nanofibers and carbon nanotubes are preferred. For example, a material such as VGCF (registered trademark) manufactured by Showa Denko KK can be used. The fiber diameter of the carbon fibers 4 is preferably 0.5 to 500 nm, more preferably 10 to 300 nm. By setting it within the above range, the voids in the catalyst layer can be increased, and high power generation performance can be exhibited. The fiber length of the carbon fibers 4 is preferably 1-200 μm, more preferably 1-50 μm. By setting the content within the above range, the strength of the catalyst layer can be increased, and the occurrence of cracks during formation can be suppressed. Moreover, the voids in the catalyst layer can be increased, and high power generation performance is exhibited.
Further, the solvent used as the dispersion medium of the catalyst ink does not erode the conductive carrier 2 supporting the catalyst particles 1, the polymer electrolyte 3 and the carbon fiber 4, and keeps the polymer electrolyte 3 in a state of high fluidity. There is no particular limitation as long as it can be dissolved or dispersed as a fine gel with .

The solvent preferably contains a volatile organic solvent or water, and the organic solvent is not particularly limited, but methanol, ethanol, 1-propanol, 2-propanol, 1 -butanol, 2-butanol, isobutyl alcohol, tert-butyl alcohol, pentanol and other alcohols, acetone, methyl ethyl ketone, pentanone, methyl isobutyl ketone, heptanone, cyclohexanone, methylcyclohexanone, acetonylacetone, diisobutyl Ketone solvents such as ketones, ether solvents such as tetrahydrofuran, dioxane, diethylene glycol dimethyl ether, anisole, methoxytoluene, dibutyl ether, other dimethylformamide, dimethylacetamide, N-methylpyrrolidone, ethylene glycol, diethylene glycol, diacetone alcohol, 1- A polar solvent such as methoxy-2-propanol is used. A mixture of two or more of these solvents and water can also be used. A dispersant may be included.

Next, the fabrication and construction of the membrane electrode assembly will be described with reference to FIG.
The membrane electrode assembly has catalyst layers (a cathode catalyst layer 6 on the front side and an anode catalyst layer 7 on the back side), a gasket material 8 and a gas diffusion layer 9 on the front and back surfaces of the polymer electrolyte membrane 5 . The gasket material 8 and the gas diffusion layer 9 are laminated in this order from the polymer electrolyte membrane 5 side. The gasket material 8 is arranged so as to surround the catalyst layers (cathode catalyst layer 6, anode catalyst layer 7).

As the polymer electrolyte membrane 5 used in the above-mentioned membrane electrode assembly, any material having proton conductivity may be used, and fluorine-based polymer electrolytes, hydrocarbon-based polymer electrolytes, and the like can be used. As the fluorine-based polymer electrolyte, for example, Nafion (registered trademark) manufactured by DuPont can be used. As the hydrocarbon-based polymer electrolyte membrane, for example, electrolyte membranes such as sulfonated polyetherketone, sulfonated polyethersulfone, sulfonated polyetherethersulfone, sulfonated polysulfide, and sulfonated polyphenylene can be used. Among them, a material containing perfluorosulfonic acid as a fluorine-based polymer electrolyte can be preferably used for the polymer electrolyte membrane 5 .

The plastic film having the gasket material 8 and the adhesive layer may have heat resistance to such an extent that it does not melt when heated and pressurized. Polymers such as polyethylene naphthalate, polyethylene terephthalate, polyimide, polyparvanic aramid, polyamide (nylon), polysulfone, polyethersulfone, polyethersulfone, polyphenylene sulfide, polyetheretherketone, polyetherimide, and polyacrylate A film can be used. Heat-resistant fluororesins such as ethylenetetrafluoroethylene copolymer, tetrafluoroethylene-hexafluoropropylene copolymer, tetrafluoroperfluoroalkylvinylether copolymer, and polytetrafluoroethylene can also be used. As the base material of the gasket material 8, polyethylene naphthalate is particularly preferable in consideration of gas barrier properties and heat resistance.

The adhesive layer of the plastic film having the gasket material 8 and the adhesive layer may be an adhesive such as acrylic, urethane, silicone, or rubber. Considering the heat resistance at the time of hot pressing, it is more preferable to be acrylic. The adhesiveness of the adhesive layer of the plastic film having the gasket material 8 and the adhesive layer is such that if the adhesive strength between the polymer electrolyte membrane 5 and the gasket material 8 is greater than the adhesive strength between the gasket material and the plastic film having the adhesive layer, It is preferable because it is easy to apply the gasket material 8 to the membrane electrode assembly.

Next, the production of the above catalyst layer and membrane electrode assembly will be described.
Dispersion treatment in preparing the catalyst ink can be performed using various devices. Examples of the dispersion treatment include treatment with a ball mill or roll mill, treatment with a shear mill, treatment with a wet mill, ultrasonic dispersion treatment, and the like. Alternatively, a homogenizer or the like that agitates by centrifugal force may be used.
Examples of the coating method for forming the catalyst ink on the substrate for coating include a die coater method, a roll coater method, and a spray method, but are not limited to the present invention.
The substrate for coating on which the catalyst layer, which is a component of the membrane electrode assembly, is formed is the polymer electrolyte membrane 5 and the transfer substrate, but is not limited in the present invention.

When the substrate is produced by the transfer method, any material can be used as long as it can form a catalyst layer on its surface and transfer the catalyst layer to the polymer electrolyte membrane 5 . Polymers such as polyimide, polyethylene terephthalate, polyparvanic acid aramid, polyamide (nylon), polysulfone, polyethersulfone, polyethersulfone, polyphenylene sulfide, polyetheretherketone, polyetherimide, polyacrylate, and polyethylene naphthalate A film can be used. Heat-resistant fluororesins such as ethylenetetrafluoroethylene copolymer, tetrafluoroethylene-hexafluoropropylene copolymer, tetrafluoroperfluoroalkylvinylether copolymer, and polytetrafluoroethylene can also be used.

Assuming that the ion exchange capacities of the cathode catalyst layer 6 and the anode catalyst layer 7 are IEC, the IEC is preferably 1.1 or more and 1.5 or less. Within this range, the gas diffusibility and drainage properties of the catalyst layer are enhanced, and good power generation performance is obtained. On the other hand, when the IEC is less than 1.1, the entanglement between the polymer electrolyte 3 and the carbon fibers 4 is suppressed, and the polymer electrolyte 3 aggregates, which is not preferable. Further, if the IEC exceeds 1.5, the bond between the polymer electrolyte 3 and the conductive carrier 2 or the carbon fiber 4 becomes strong, and the drainage performance deteriorates, which is not preferable.
From the above, it can be seen that a membrane electrode assembly having a carbon fiber-containing catalyst layer with an IEC of 1.1 or more and 1.5 or less exhibits high power generation performance.

A membrane electrode assembly, which is one of the embodiments of the present invention, is provided with the catalyst layer on at least one of the anode and the cathode. be done.
According to the method for manufacturing the membrane electrode assembly described above, it is possible to manufacture a membrane electrode assembly in which the catalyst layers are bonded to both surfaces of the polymer electrolyte membrane 5 in good shape.
EXAMPLES The present invention will be specifically described below with reference to Examples. However, the invention is not limited to only these examples.

(Preparation of catalyst ink)
The catalyst ink for forming the catalyst layer is composed of a fluorine-based polymer electrolyte dispersion solution, platinum-supported carbon, carbon fiber (VGCF-H, "VGCF" is a registered trademark), 1-propanol, and water. The catalyst ink for the catalyst layer was prepared by mixing with a ball mill.

(Formation of catalyst layer and manufacture of membrane electrode assembly)
An anode and a cathode were formed on the polymer electrolyte membrane 5 by die coating to produce a membrane electrode assembly.
(Power generation evaluation)
The carbon paper used as the gas diffusion layer 9 was adhered so as to sandwich the membrane electrode assemblies produced in Examples and Comparative Examples, and placed in a power generation evaluation cell. Using a fuel cell measuring device, the cell temperature was set to 80° C., and the current and voltage were measured. Hydrogen was used as the fuel gas, and air was used as the oxidant gas.

[Example 1]
A catalyst ink that uses platinum-supported carbon (TEC10E50E), carbon fiber (VGCF-H), and polymer electrolyte (Aquivion830, IEC1.1) and has an I/(C+CF) of 0.2, supporting platinum on the catalyst layer. A polymer electrolyte membrane Nafion 212 was coated with the coating so that the amount was 0.2 mg/cm ² to prepare a membrane electrode assembly.
[Example 2]
A membrane electrode assembly was produced in the same manner as in Example 1, except that I/(C+CF) was 0.7.

[Example 3]
A membrane electrode assembly was produced in the same manner as in Example 1, except that a polymer electrolyte (Aquivion 950, IEC 1.2) was used.
[Example 4]
A membrane electrode assembly was produced in the same manner as in Example 3, except that I/(C+CF) was 0.7.

[Example 5]
A catalyst ink that uses platinum-supported carbon (TEC10E50E), carbon fiber (VGCF-H), and polymer electrolyte (Aquivion700, IEC1.4) and has an I/(C+CF) of 0.8, supporting platinum on the catalyst layer. A polymer electrolyte membrane Nafion 212 was coated with the coating so that the amount was 0.2 mg/cm ² to prepare a membrane electrode assembly.
[Example 6]
A membrane electrode assembly was produced in the same manner as in Example 5, except that I/(C+CF) was 1.5.

[Comparative Example 1]
A membrane electrode assembly was produced in the same manner as in Example 1, except that no carbon fiber was used.
[Comparative Example 2]
A membrane electrode assembly was produced in the same manner as in Example 5, except that no carbon fiber was used.

[Comparative Example 3]
A membrane electrode assembly was produced in the same manner as in Example 1, except that a polymer electrolyte (Nafion, IEC 0.99) was used.
[Comparative Example 4]
A membrane electrode assembly was produced in the same manner as in Example 1, except that a polymer electrolyte (Nafion 117, IEC 2.0) was used.
(Evaluation results)
The results of Examples and Comparative Examples are summarized in Table 1.

From the above results, according to the present embodiment, the power generation performance of the membrane electrode assembly is improved by having the catalyst layer that satisfies the formulas (1), (2) and (3). As a result, it is possible to provide a polymer fuel cell catalyst layer capable of improving drainage and gas diffusibility and capable of high output.

DESCRIPTION OF SYMBOLS 1... Catalyst particle 2... Conductive carrier 3... Polymer electrolyte 4... Carbon fiber 5... Polymer electrolyte membrane 6... Cathode catalyst layer 7... Anode catalyst layer 8... Gasket material 9... Gas diffusion layer

Claims (2)

A polymer electrolyte fuel cell catalyst layer comprising platinum particles, carbon particles, a polymer electrolyte and a fibrous material,
the fibrous substance is a carbon nanotube or carbon nanofiber,
When the ion exchange capacity IEC of the polymer electrolyte satisfies the following formula (1), the ratio of the mass C of the carbon particles supporting the platinum particles and the mass CF of the fiber material to the mass I of the polymer electrolyte A catalyst layer for a polymer electrolyte fuel cell, wherein I/(C+CF) is 0.8 or more and 1.5 or less.
1.5>IEC≧1.3 [meq/g] Expression (1) 2. A membrane electrode assembly, wherein the polymer electrolyte fuel cell catalyst layer according to claim 1 is provided on at least one of an anode and a cathode.

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