JP2022165779A - Electrode catalyst layer, membrane electrode assembly, and polymer electrolyte fuel cell - Google Patents

Abstract

To improve power generation performance under both high humidification and low humidification operating conditions.SOLUTION: A first electrode catalyst layer 20 includes catalyst-supporting particles 21 having a hydrophobic coating, a polymer electrolyte 22, and a hydrophilized carbon fiber 23 with an average fiber length of 0.7 μm or more and 20 μm or less. The catalyst-supporting particles 21 include a carrier and a catalyst supported on the carrier. When the content of the carrier is 100 parts by mass, the content of the hydrophilized carbon fibers 23 is 5 parts by mass or more and 30 parts by mass or less.SELECTED DRAWING: Figure 2

Description

TECHNICAL FIELD The present invention relates to an electrode catalyst layer, a membrane electrode assembly, and a polymer electrolyte fuel cell.

As a countermeasure against the global environmental burden, which increases year by year, there is a growing demand for the creation of cleaner energy. A fuel cell is a power generation system that generates electrical energy through a chemical reaction between hydrogen and oxygen and discharges only water, and high expectations are placed on the fuel cell as a future energy source.

Fuel cells are classified into alkaline type, phosphoric acid type, solid polymer type, molten carbonate type, solid oxide type, etc. according to the type of electrolyte. Since polymer electrolyte fuel cells can be used at around room temperature, they are expected to be widely used for automotive power sources and household stationary power sources. Therefore, in order to commercialize polymer electrolyte fuel cells, research and development are actively being conducted to improve power generation characteristics and durability, and to reduce costs.

A polymer electrolyte fuel cell includes a polymer electrolyte membrane having proton conductivity, a fuel electrode as an anode, and an air electrode as a cathode. The polymer electrolyte membrane is sandwiched between the fuel electrode and the air electrode in the thickness direction of the polymer electrolyte membrane. The anode has an electrode catalyst layer that separates the fuel gas into protons and electrons. The air electrode has an electrode catalyst layer that oxidizes protons transported through the polymer electrolyte membrane with an oxygen-containing oxidant and receives electrons from an external circuit. The electrode catalyst layers of the fuel electrode and the air electrode include a catalyst material such as a platinum-based noble metal, a carrier supporting the catalyst material, and a polymer electrolyte.

A polymer electrolyte fuel cell has a basic configuration of a single cell, in which a gas diffusion layer and a separator are arranged on the opposite side of the polymer electrolyte membrane of the electrode catalyst layer of each of the fuel electrode and the air electrode. A plurality of cells are laminated. The gas diffusion layer is a layer that is electrically conductive and for uniformly diffusing the reaction gas. The separator is a member that has a gas channel and a cooling water channel and plays a role of extracting electrons to an external circuit, and is arranged outside the gas diffusion layer. Hereinafter, a polymer electrolyte membrane having fuel electrodes and air electrodes formed on both sides thereof will be referred to as a membrane electrode assembly.

In a polymer electrolyte fuel cell, a fuel gas containing hydrogen is supplied to the fuel electrode, and an oxidant gas containing oxygen is supplied to the air electrode. The electrode reaction shown occurs and electricity is generated.

Fuel electrode: H ₂ →2H ⁺ +2e ^- (Formula 1)
Air electrode: 1/2O ₂ +2H ⁺ +2e ⁻ →H ₂ O (Formula 2)
As shown in Equation 1, the fuel gas supplied to the fuel electrode is separated into protons and electrons by the catalyst material contained in the electrode catalyst layer of the fuel electrode. The separated protons move to the air electrode through the humidified polymer electrolyte and polymer electrolyte membrane contained in the electrode catalyst layer of the fuel electrode. The separated electrons are extracted from the anode to an external circuit and travel through the external circuit to the cathode. As shown in Equation 2, at the air electrode, the oxidant gas reacts with the protons and electrons that have moved from the fuel electrode to produce water. An electric current is generated by electrons passing through an external circuit.

By the way, in order to increase the proton conductivity in the membrane electrode assembly, it is necessary to humidify the inside of the membrane electrode assembly to a relatively high level. Therefore, a humidifier is used to replenish the moisture in the system. However, from the viewpoint of cost reduction, which is a barrier to widespread use of fuel cells, it is desirable to reduce the number of humidifiers. If the number of humidifiers is reduced, a membrane electrode assembly that can exhibit power generation performance under low humidification conditions without using a humidifier is required.

Techniques disclosed in Patent Literature 1 and Patent Literature 2 are known as techniques relating to such membrane electrode assemblies. Patent Literature 1 discloses a technique for improving power generation performance under low humidity conditions by providing a predetermined water retention layer and a hydrophobic moisture management layer between an electrode catalyst layer and a gas diffusion layer. Further, Patent Document 2 discloses a technique for improving power generation performance under low humidification conditions by subjecting the constituent material of the gas diffusion layer to hydrophilic treatment.

JP 2019-169315 A JP 2004-031325 A

Conventional fuel cells using the electrode catalyst layers disclosed in Patent Documents 1 and 2 have room for improvement in terms of improving power generation performance under both high and low humidity operating conditions. .

The electrode catalyst layer for solving the above problems is an electrode catalyst layer bonded to a polymer electrolyte membrane in a membrane electrode assembly, comprising catalyst-carrying particles having a hydrophobic coating, a polymer electrolyte, and an average fiber length of Hydrophilized carbon fibers having a diameter of 0.7 μm or more and 20 μm or less, and the catalyst-supporting particles include a carrier and a catalyst supported on the carrier, and when the content of the carrier is 100 parts by mass, The content of the hydrophilized carbon fiber is 5 parts by mass or more and 30 parts by mass or less.

In the electrode catalyst layer, when the content of the carrier is 100 parts by mass, the content of the polymer electrolyte may be 40 parts by mass or more and 100 parts by mass or less.
In the electrode catalyst layer, the hydrophilized carbon fibers may have an average fiber diameter of 10 nm or more and 300 nm or less.

A membrane electrode assembly for solving the above problems includes a polymer electrolyte membrane and the electrode catalyst layer, and the electrode catalyst layer is bonded to the polymer electrolyte membrane.
A polymer fuel cell for solving the above problems comprises the membrane electrode assembly, a pair of gas diffusion layers sandwiching the membrane electrode assembly in the thickness direction of the membrane electrode assembly, and the membrane electrode assembly and a pair of separators sandwiching the membrane electrode assembly and the pair of gas diffusion layers in the thickness direction of.

According to the present invention, it is possible to improve power generation performance under both high humidification conditions and low humidification conditions.

FIG. 2 is a cross-sectional view showing the structure of a membrane electrode assembly in one embodiment; FIG. 2 is a schematic diagram schematically showing the structure of the first electrode catalyst layer in one embodiment. FIG. 4 is a cross-sectional view showing the structure of catalyst-supporting particles contained in the first electrode catalyst layer in one embodiment. 1 is an exploded perspective view showing the configuration of a polymer electrolyte fuel cell according to one embodiment; FIG.

An embodiment of an electrode catalyst layer, a membrane electrode assembly, and a polymer electrolyte fuel cell will be described with reference to FIGS. 1 to 4. FIG. Each figure in the drawings is appropriately exaggerated to facilitate understanding. Further, the configurations and materials of the electrode catalyst layer, membrane electrode assembly, polymer electrolyte fuel cell, and method for producing them of the present invention are not limited to the configurations and materials described below, and the same functions Including all materials and configurations that can be inferred to have

[Membrane electrode assembly]
As shown in FIG. 1, the membrane electrode assembly 10 includes a polymer electrolyte membrane 11, a cathode side electrode catalyst layer 12C, and an anode side electrode catalyst layer 12A.

The polymer electrolyte membrane 11 is a solid polymer electrolyte membrane. The polymer electrolyte membrane 11 is made of, for example, a polymer material having proton conductivity. Polymer materials having proton conductivity include, for example, fluorine-based resins and hydrocarbon-based resins. Examples of fluorine-based resins include Nafion (manufactured by DuPont, registered trademark), Flemion (manufactured by AGC, registered trademark), and Gore-Select (manufactured by Gore, registered trademark). Hydrocarbon-based resins include, for example, engineering plastics and engineering plastics into which sulfonic acid groups have been introduced.

The cathode-side electrode catalyst layer 12</b>C is an electrode catalyst layer forming an air electrode, which is a cathode, and is bonded to one side surface of the polymer electrolyte membrane 11 . The cathode-side electrode catalyst layer 12C is a layer for oxidizing protons transported through the polymer electrolyte membrane 11 with an oxygen-containing oxidizing agent and receiving electrons from an external circuit. The anode-side electrode catalyst layer 12A is an electrode catalyst layer that constitutes a fuel electrode, which is an anode, and is bonded to the surface of the polymer electrolyte membrane 11 opposite to the surface to which the cathode-side electrode catalyst layer 12C is bonded. The anode-side electrode catalyst layer 12A is a layer for separating fuel gas into protons and electrons. Moreover, below, it may describe as an electrode catalyst layer as a concept including the cathode side electrode catalyst layer 12C and the anode side electrode catalyst layer 12A.

[Electrode catalyst layer]
The first electrode catalyst layer and the second electrode catalyst layer as electrode catalyst layers will be described below. Both the cathode side electrode catalyst layer 12C and the anode side electrode catalyst layer 12A are first electrode catalyst layers. Alternatively, one of the cathode-side electrode catalyst layer 12C and the anode-side electrode catalyst layer 12A is the first electrode catalyst layer, and the other is the second electrode catalyst layer. That is, at least one of the cathode side electrode catalyst layer 12C and the anode side electrode catalyst layer 12A is used as the first electrode catalyst layer. As a result, it is possible to obtain the effect of improving the power generation performance under both the high humidification condition and the low humidification condition. From the viewpoint of enhancing the above effects, when only one of the cathode-side electrode catalyst layer 12C and the anode-side electrode catalyst layer 12A is used as the first electrode catalyst layer, the cathode-side electrode catalyst layer 12C constituting the air electrode is used as the first electrode catalyst layer. It is preferable to use one electrode catalyst layer.

(First electrode catalyst layer)
As shown in FIG. 2 , the first electrode catalyst layer 20 includes catalyst-carrying particles 21 , polymer electrolyte 22 , and hydrophilic carbon fibers 23 . In addition, the first electrode catalyst layer 20 may contain, as optional components, other known components contained in the electrode catalyst layer of a fuel cell.

<Catalyst-carrying particles>
As shown in FIG. 3, the catalyst-carrying particles 21 include a catalyst 21a, a carrier 21b that carries the catalyst 21a, and a hydrophobic coating 21c that coats the catalyst 21a and the carrier 21b.

As the catalyst 21a, for example, a metal contained in the platinum group, a metal other than the platinum group, or an alloy, oxide, multiple oxide, or carbide thereof can be used. Examples of metals included in the platinum group include platinum, palladium, ruthenium, iridium, rhodium, and osmium. Examples of non-platinum group metals include gold, iron, lead, copper, chromium, cobalt, nickel, manganese, vanadium, molybdenum, gallium, and aluminum. Among these, platinum, gold, palladium, rhodium, ruthenium, and alloys thereof are highly active as catalysts and are suitable. Incidentally, the catalyst 21a constituting the catalyst-carrying particles 21 may be of only one type in the above examples, or may be a combination of two or more types.

The average particle size of the catalyst 21a is, for example, preferably 0.5 nm or more and 20 nm or less, more preferably 1 nm or more and 5 nm or less. A decrease in stability can be suppressed by setting the average particle size of the catalyst 21a to 0.5 nm or more. Also, by setting the average particle size of the catalyst 21a to 20 nm or less, the decrease in activity can be suppressed. In addition, in this specification, the arithmetic mean particle diameter calculated|required from the particle size measurement is defined as an average particle diameter.

As the carrier 21b, a material that has electrical conductivity, is not affected by the catalyst 21a, and is capable of supporting the catalyst 21a is used. Examples of the substance constituting the carrier 21b include carbon materials such as carbon black, graphite, graphite, activated carbon, carbon nanotubes, carbon nanofibers, and fullerene. In addition, the carrier 21b constituting the catalyst-carrying particles 21 may be of only one type in the above examples, or may be a combination of two or more types.

The shape of the carrier 21b is not particularly limited, and may be, for example, a particle shape or a fiber shape. From the viewpoint of smoothly transmitting electrons generated on the surface of the catalyst 21a to the outside of the system, the carrier 21b preferably has a shape that allows the catalyst 21a to be supported on its outer surface.

The average particle size of the carrier 21b is, for example, preferably 10 nm or more and 1000 nm or less, more preferably 10 nm or more and 100 nm or less. By setting the average particle size of the carrier 21b to 10 nm or more, an electron conduction path is easily formed in the electrode catalyst layer. Further, by setting the average particle size of the carrier 21b to 1000 nm or less, an increase in resistance due to an increase in the thickness of the first electrode catalyst layer 20 can be suppressed.

As the hydrophobic coating 21c, for example, a coating formed from a fluorine-based compound having at least one polar group can be used. Polar groups include, for example, hydroxyl groups, alkoxy groups, carboxyl groups, ester groups, ether groups, carbonate groups, and amide groups. Due to the presence of the polar group, the fluorine-based compound can be immobilized on the outermost surface of the carrier 21b supporting the catalyst 21a. The portion other than the polar group in the fluorine-based compound preferably has a structure composed of fluorine and carbon because of its high hydrophobicity and chemical stability. However, if the hydrophobic coating 21c has sufficient hydrophobicity and chemical stability, it is not limited to such a structure.

The film thickness of the hydrophobic film 21c is preferably a film thickness sufficient to allow reaction gas to pass through. The film thickness of the hydrophobic film 21c is preferably 40 nm or less, for example. In this case, the reactant gas can be sufficiently permeated, and inhibition of the supply of the reactant gas to the active sites can be suppressed.

Moreover, the film thickness of the hydrophobic film 21c is preferably, for example, 2 nm or more. In this case, sufficient hydrophobicity can be imparted to the catalyst-supporting particles 21, and water generated in the electrode by the cell reaction can be sufficiently repelled. Further, in this case, it is possible to suppress the retention of the generated water, and as a result, it is possible to suppress the inhibition of the supply of the reaction gas to the active sites by the retained generated water.

<Polymer electrolyte>
A substance having proton conductivity is used as the polymer electrolyte 22 . Examples of substances having proton conductivity include fluorine-based polymer electrolytes and hydrocarbon-based polymer electrolytes. Examples of fluorine-based polymer electrolytes include those having a tetrafluoroethylene skeleton typified by Nafion (registered trademark) manufactured by DuPont. Hydrocarbon polymer electrolytes include, for example, sulfonated polyetherketone, sulfonated polyethersulfone, sulfonated polysulfide, and sulfonated polyphenylene. In addition, the polymer electrolyte 22 constituting the first electrode catalyst layer 20 may be of one type in the above examples, or may be a combination of two or more types.

The content of the polymer electrolyte in the first electrode catalyst layer 20 is preferably 40 parts by mass or more and 100 parts by mass or less, for example, when the content of the carrier 21b in the first electrode catalyst layer 20 is 100 parts by mass. . By setting the content of the polymer electrolyte to 40 parts by mass or more, it is possible to suppress a decrease in proton conductivity due to a defect in the conduction path of protons. As a result, it becomes easier to ensure a balance between proton conductivity and electron conductivity in the first electrode catalyst layer 20 . By setting the content of the polymer electrolyte to 100 parts by mass or less, the catalyst 21a of the catalyst-carrying particles 21 can be suitably exposed. As a result, catalytic activity in the first electrode catalyst layer 20 is improved.

<Hydrophilic carbon fiber>
As the hydrophilic carbon fiber 23, for example, a hydrophilic carbon fiber manufactured to have hydrophilicity, or a hydrophilic carbon fiber treated to impart hydrophilicity to non-hydrophilic carbon fibers may be used. can be done. The treatment for imparting hydrophilicity includes, for example, ozone or oxygen plasma treatment, electrolytic oxidation treatment, and mixed acid treatment.

The shape of the hydrophilic carbon fiber 23 is not particularly limited, and may be, for example, a hollow structure or a solid structure. Specific examples of the hydrophilic carbon fiber 23 include VGCF (Vapor Grown Carbon Fiber) and CNT (Carbon Nano Tube). The hydrophilic carbon fibers 23 constituting the first electrode catalyst layer 20 may be of one type in the above examples, or may be a combination of two or more types.

The average fiber length of the hydrophilized carbon fibers 23 is 0.7 μm or more and 20 μm or less. By setting the average fiber length of the hydrophilized carbon fiber 23 within the above range, it is possible to improve the power generation performance of the fuel cell while improving the moisture retention of the first electrode catalyst layer 20 due to the use of the hydrophilized carbon fiber 23. can.

More specifically, the main effects obtained by including the hydrophilic carbon fiber 23 in the first electrode catalyst layer 20 are moisture retention in the first electrode catalyst layer 20 and an electron conduction path in the first electrode catalyst layer 20. and structural reinforcement of the first electrode catalyst layer 20 . By setting the average fiber length of the hydrophilized carbon fibers 23 to 0.7 μm or more, a network between the hydrophilized carbon fibers 23 is easily formed. As a result, the electron conduction paths in the first electrode catalyst layer 20 can be sufficiently constructed and the structure of the first electrode catalyst layer 20 can be sufficiently strengthened, thereby improving the power generation performance of the fuel cell. By setting the average fiber length of the hydrophilized carbon fibers 23 to 20 μm or less, the dispersibility of the hydrophilized carbon fibers 23 can be improved when the first electrode catalyst layer 20 is formed using the catalyst ink described later.

Further, in the fuel cell, the amount of water produced in the electrode catalyst layer as a result of the cell reaction is proportional to the amount of chemical reaction. Therefore, when power is generated at a high current density, the amount of water produced increases. If the generated water is not sufficiently drained out of the electrode catalyst layer, the generated water remaining in the electrode catalyst layer may clog the gas diffusion path. In this case, flooding occurs, which is a phenomenon in which the reaction gas cannot reach the active point and the power generation performance is remarkably lowered.

By setting the average fiber length of the hydrophilized carbon fiber 23 to 20 μm or less, sufficient voids can be secured in the first electrode catalyst layer 20, and the drainage performance of the first electrode catalyst layer 20 is improved. As a result, flooding is less likely to occur even when power is generated at a high current density, and the power generation performance of the fuel cell is improved.

The average fiber diameter of the hydrophilized carbon fibers 23 is preferably, for example, 10 nm or more and 300 nm or less. In this case, gaps of an appropriate size can be formed in the first electrode catalyst layer 20, so that gas diffusibility in the first electrode catalyst layer 20 is improved.

The content of the hydrophilic carbon fiber 23 in the first electrode catalyst layer 20 is 5 parts by mass or more and 30 parts by mass or less when the content of the carrier 21b in the first electrode catalyst layer 20 is 100 parts by mass. Also, the content of the hydrophilic carbon fiber 23 is preferably 5 parts by mass or more and 20 parts by mass or less.

By setting the content of the hydrophilized carbon fibers 23 to 5 parts by mass or more, a network between the hydrophilized carbon fibers 23 is easily formed. As a result, it is possible to sufficiently construct an electron conduction path in the electrode catalyst layer and to structurally strengthen the electrode catalyst layer. As a result, the power generation performance of the fuel cell is improved. By setting the content of the hydrophilic carbon fiber 23 to 30 parts by mass or less, an increase in resistance due to an increase in the thickness of the first electrode catalyst layer 20 can be suppressed.

(Second electrode catalyst layer)
As the second electrode catalyst layer, a known electrode catalyst layer applied to a membrane electrode assembly can be used. The second electrode catalyst layer differs from the first electrode catalyst layer 20 in that, for example, the catalyst-supporting particles 21 that do not have the hydrophobic coating 21c are used and that the hydrophilic carbon fiber 23 is not included. An electrode catalyst layer having a configuration similar to that of the first electrode catalyst layer 20 can be used.

Regarding the above materials used for the components of the first electrode catalyst layer and the second electrode catalyst layer, the materials used for the cathode side electrode catalyst layer 12C and the materials used for the anode side electrode catalyst layer 12A may be the same or at least partially different.

[Polymer electrolyte fuel cell]
Next, the configuration of a polymer electrolyte fuel cell having the membrane electrode assembly 10 will be described. A single-cell polymer electrolyte fuel cell will be described below as an example of a polymer electrolyte fuel cell. The polymer electrolyte fuel cell is not limited to a single cell structure, and may have a structure in which a plurality of single cells are provided and a plurality of single cells are stacked.

As shown in FIG. 4, a polymer electrolyte fuel cell 30 includes a membrane electrode assembly 10, a pair of gas diffusion layers 31a and 31b, and a pair of separators 32a and 32b.
The gas diffusion layers 31a and 31b are layers for uniformly diffusing the reaction gas. The gas diffusion layer 31a is arranged so as to face the cathode side electrode catalyst layer 12C of the membrane electrode assembly 10 . The gas diffusion layer 31b is arranged so as to face the anode-side electrode catalyst layer 12A of the membrane electrode assembly 10 . The pair of gas diffusion layers 31 a and 31 b sandwich the membrane electrode assembly 10 in the thickness direction of the membrane electrode assembly 10 . Also, the cathode-side electrode catalyst layer 12C and the gas diffusion layer 31a form an air electrode, which is a cathode. The anode-side electrode catalyst layer 12A and the gas diffusion layer 31b form a fuel electrode, which is an anode.

The gas diffusion layers 31a and 31b are made of a material having electronic conductivity and gas diffusibility. Porous carbon material, for example, can be used as the material forming the gas diffusion layers 31a and 31b. Porous carbon materials include, for example, carbon cloth, carbon paper, and non-woven fabric.

The separators 32a and 32b are members that take out electrons to an external circuit, and are arranged outside the gas diffusion layer 31b. The pair of separators 32 a and 32 b sandwich the membrane electrode assembly 10 and the pair of gas diffusion layers 31 a and 31 b in the thickness direction of the membrane electrode assembly 10 .

The separators 32a, 32b have gas channels 33a, 33b and cooling water channels 34a, 34b. The gas channels 33a and 33b are channels for circulating reaction gases, and are formed on the surfaces of the separators 32a and 32b facing the gas diffusion layers 31a and 31b. The cooling water channels 34a and 34b are channels for circulating cooling water, and are formed on the surfaces of the separators 32a and 32b opposite to the surfaces facing the gas diffusion layers 31a and 31b.

The separators 32a, 32b are made of a material that is electrically conductive and impermeable to gas. Examples of materials forming the separators 32a and 32b include carbon materials and metal materials. Moreover, it is preferable that the material constituting the separators 32a and 32b has a certain degree of strength and good formability.

An oxidant gas as a reaction gas is supplied to the gas flow path 33a of the separator 32a facing the gas diffusion layer 31a constituting the air electrode. The oxidant gas is, for example, air or oxygen gas. A fuel gas as a reaction gas is supplied to the gas flow path 33b of the separator 32b facing the gas diffusion layer 31b constituting the fuel electrode. The fuel gas is, for example, hydrogen gas.

In the polymer electrolyte fuel cell 30, a fuel gas containing hydrogen is supplied to the fuel electrode, and an oxidant gas containing oxygen is supplied to the air electrode, so that the following equations 1 and 2 are satisfied at the fuel electrode and the air electrode. The electrode reaction shown in occurs and electricity is generated. Moreover, polymer electrolyte fuel cells are used in combination with accompanying devices such as a gas supply device and a cooling device.

Fuel electrode: H ₂ →2H ⁺ +2e ^- (Formula 1)
Air electrode: 1/2O ₂ +2H ⁺ +2e ⁻ →H ₂ O (Formula 2)
[Method for manufacturing membrane electrode assembly]
A method for manufacturing the membrane electrode assembly 10 will be described below.

The method for manufacturing the membrane electrode assembly 10 includes a preparation step of preparing a catalyst ink and a formation step of forming an electrode catalyst layer using the catalyst ink.
(Preparation process)
In the preparation step, the catalyst ink is prepared by mixing each component constituting the electrode catalyst layer using a dispersion medium.

The dispersion medium is not particularly limited as long as it can disperse each component constituting the electrode catalyst layer. Dispersion media include, for example, water, alcohols, ketones, and mixtures thereof. Specifically, water, alcohols such as methanol, ethanol, 1-propanol, 2-propanol, 1-butanol, 2-butanol, isobutyl alcohol, tert-butyl alcohol, acetone, methyl ethyl ketone, methyl propyl ketone, methyl Ketones such as butyl ketone, methyl isobutyl ketone, methyl amyl ketone, pentanone, heptanone, cyclohexanone, methylcyclohexanone, acetonylacetone, diethyl ketone, dipropyl ketone, and diisobutyl ketone can be used as appropriate.

Further, the catalyst ink may contain a dispersant for good dispersion of each component constituting the electrode catalyst layer. Dispersants include, for example, anionic surfactants, cationic surfactants, amphoteric surfactants, and nonionic surfactants.

Examples of anionic surfactants include alkyl ether carboxylate, ether carboxylate, alkanoyl sarcosine, alkanoyl glutamate, acyl glutamate, oleic acid/N-methyltaurine, potassium oleate/diethanolamine salt, alkyl ether sulfate/ Triethanolamine salt, polyoxyethylene alkyl ether sulfate/triethanolamine salt, amine salt of special modified polyether ester acid, amine salt of higher fatty acid derivative, amine salt of special modified polyester acid, amine of high molecular weight polyether ester acid Salt, amine salt of special modified phosphoric acid ester, amide amine salt of high molecular weight polyester acid, amide amine salt of special fatty acid derivative, alkylamine salt of higher fatty acid, amide amine salt of high molecular weight polycarboxylic acid, sodium laurate, sodium stearate, olein Carboxylic acid surfactants such as sodium phosphate, dialkylsulfosuccinate, dialkyl sulfosuccinate, 1,2-bis(alkoxycarbonyl)-1-ethanesulfonate, alkylsulfonate, alkylsulfonate, paraffin sulfonate , α-olefin sulfonate, linear alkylbenzene sulfonate, alkylbenzene sulfonate, polynaphthyl methanesulfonate, polynaphthyl methanesulfonate, naphthalene sulfonate-formalin condensate, alkylnaphthalene sulfonate, alkanoyl methyl tauride, lauryl sulfate sodium salt, cetyl sulfate Sulfonic acid type surfactants such as ester sodium salt, stearyl sulfate sodium salt, oleyl sulfate sodium salt, lauryl ether sulfate ester salt, alkylbenzene sodium sulfonate, oil-soluble alkylbenzene sulfonate, α-olefin sulfonate, alkyl Sulfate ester salts, alkyl sulfate salts, alkyl sulfates, alkyl ether sulfates, polyoxyethylene alkyl ether sulfates, alkyl polyethoxy sulfates, polyglycol ether sulfates, alkyl polyoxyethylene sulfates, sulfated oils, highly sulfated oils, etc. Sulfuric acid ester type surfactant, (mono or di) alkyl phosphate, (mono or di) alkyl phosphate, (mono or di) alkyl phosphate, alkyl polyoxyethylene phosphate, alkyl ether phosphate, alkyl poly Etoki Phosphate, polyoxyethylene alkyl ether, alkylphenyl phosphate, polyoxyethylene salt, alkylphenyl ether phosphate, alkylphenyl polyethoxy phosphate, polyoxyethylene alkylphenyl ether phosphate, higher alcohol phosphorus Acid monoester disodium salt, higher alcohol phosphate diester disodium salt, phosphate ester surfactant such as zinc dialkyldithiophosphate.

Examples of cationic surfactants include benzyldimethyl{2-[2-(P-1,1,3,3-tetramethylbutylphenoxy)ethoxy]ethyl}ammonium chloride, octadecylamine acetate, tetradecylamine acetate, Salt, octadecyltrimethylammonium chloride, beef tallow trimethylammonium chloride, dodecyltrimethylammonium chloride, coconut trimethylammonium chloride, hexadecyltrimethylammonium chloride, behenyltrimethylammonium chloride, coconutdimethylbenzylammonium chloride, tetradecyldimethylbenzylammonium chloride, octadecyldimethylbenzylammonium chloride Chloride, dioleyldimethylammonium chloride, 1-hydroxyethyl-2-tallow imidazoline quaternary salt, 2-heptadecenyl-hydroxyethylimidazoline, stearamidoethyldiethylamine acetate, stearamidoethyldiethylamine hydrochloride, triethanolamine monostea rateformates, alkylpyridium salts, higher alkylamine ethylene oxide adducts, polyacrylamideamine salts, modified polyacrylamideamine salts, and perfluoroalkyl quaternary ammonium iodides.

Amphoteric surfactants include, for example, dimethyl coconut betaine, dimethyl lauryl betaine, sodium laurylaminoethylglycine, sodium laurylaminopropionate, stearyldimethylbetaine, lauryldihydroxyethyl betaine, amidobetaine, imidazolinium betaine, lecithin, 3- sodium [ω-fluoroalkanoyl-N-ethylamino]-1-propanesulfonate, N-[3-(perfluorooctanesulfonamido)propyl]-N,N-dimethyl-N-carboxymethylene ammonium betaine.

Nonionic surfactants include, for example, coconut fatty acid diethanolamide (1:2 type), coconut fatty acid diethanolamide (1:1 type), bovine fatty acid diethanolamide (1:2 type), bovine fatty acid diethanolamide (1: type 1), oleic acid diethanolamide (1:1 type), hydroxyethyllaurylamine, polyethylene glycol laurylamine, polyethylene glycol coconut amine, polyethylene glycol stearylamine, polyethylene glycol beef tallow amine, polyethylene glycol beef tallow propylene diamine, polyethylene glycol dioleylamine , dimethyllaurylamine oxide, dimethylstearylamine oxide, dihydroxyethyllaurylamine oxide, perfluoroalkylamine oxide, polyvinylpyrrolidone, higher alcohol ethylene oxide adduct, alkylphenol ethylene oxide adduct, fatty acid ethylene oxide adduct, polypropylene glycol ethylene oxide adduct fatty acid esters, glycerin fatty acid esters, pentaerythrityl fatty acid esters, sorbit fatty acid esters, sorbitan fatty acid esters, and sugar fatty acid esters.

Among the above surfactants, sulfonic acid-type surfactants such as alkylbenzenesulfonic acid, oil-soluble alkylbenzenesulfonic acid, α-olefinsulfonic acid, sodium alkylbenzenesulfonate, oil-soluble alkylbenzenesulfonate, and α-olefinsulfonate The agent can be suitably used as a dispersant because it has an excellent carbon dispersing effect and is less likely to cause a change in catalytic performance due to residual dispersant.

The dispersion method in the preparation process is not particularly limited as long as it can disperse each component contained in the catalyst ink, and a known dispersion method can be used. Known dispersion methods include, for example, a method using a planetary ball mill, a bead mill, or an ultrasonic homogenizer. In addition, the blending ratio of each component and the dispersion medium in the catalyst ink can be appropriately selected according to coatability and required power generation performance.

(Formation process)
In the formation step, after the catalyst ink obtained in the preparation step is applied to the base material, a drying treatment is performed to volatilize the dispersion medium, thereby forming a coated electrode catalyst layer. As the substrate, the polymer electrolyte membrane 11, the transfer substrate, or the gas diffusion layers 31a and 31b can be used.

The coating method for applying the catalyst ink to the base material is not particularly limited, and a known coating method that is applied to apply a slurry mixture to a uniform film thickness on the base material can be used. can. Known coating methods include, for example, die coating, bar coating, spray coating, dipping, and screen printing. Among these, it is preferable to use the die coating method because the viscosity range of the catalyst ink that can be applied is relatively wide and the coating can be performed with high film thickness uniformity.

The drying method used in the drying treatment is not particularly limited as long as it is a method capable of volatilizing the dispersion medium, and known drying methods such as an oven, a hot plate, and a method using far infrared rays can be used. . Moreover, the drying temperature and drying time in the drying treatment can be appropriately selected according to the materials used for the electrode catalyst layer and the substrate.

Further, when a transfer base material is used as the base material, a process of transferring the electrode catalyst layer formed on the transfer base material from the transfer base material to the polymer electrolyte membrane 11 is performed. As a transfer method at that time, for example, a transfer method using thermocompression can be used.

The substrate for transfer is not particularly limited as long as it can release the formed electrode catalyst layer and transfer it to the polymer electrolyte membrane. For example, a fluororesin film can be used as the transfer substrate. The fluororesin film has excellent transferability. Examples of fluorine-based resins constituting the fluorine-based resin film include ethylenetetrafluoroethylene copolymer (ETFE), tetrafluoroethylene-hexafluoropropylene copolymer (FEP), tetrafluoroperfluoroalkyl vinyl ether copolymer ( PFA), polytetrafluoroethylene (PTFE).

When the polymer electrolyte membrane 11 or the transfer substrate is used as the transfer substrate, the membrane electrode assembly 10 is obtained by providing electrode catalyst layers on both sides of the polymer electrolyte membrane 11 . Then, the polymer electrolyte fuel cell 30 is obtained by laminating the obtained membrane electrode assembly 10, the gas diffusion layers 31a and 31b, and the separators 32a and 32b.

Further, when the gas diffusion layers 31a and 31b are used as the transfer base material, gas diffusion is achieved by laminating the polymer electrolyte membrane 11 and the gas diffusion layers 31a and 31b on which the electrode catalyst layers are formed. A membrane electrode assembly 10 having layers 31a, 31b is obtained. Then, by laminating the separators 32 a and 32 b on the obtained membrane electrode assembly 10 , the polymer electrolyte fuel cell 30 is obtained.

The electrode catalyst layer manufacturing method for manufacturing the cathode side electrode catalyst layer 12C and the electrode catalyst layer manufacturing method for manufacturing the anode side electrode catalyst layer 12A may be the same or different. may

EXAMPLES Next, the above embodiments will be described more specifically with reference to examples and comparative examples. It should be noted that the present invention is not limited to the configurations described in Examples.
[Example 1]
A catalyst ink was prepared by subjecting a liquid mixture obtained by mixing catalyst-carrying particles, a polymer electrolyte, carbon fibers, and a dispersion medium to dispersion treatment. The blending amount of the polymer electrolyte was set to 70 parts by mass with respect to the blending amount of the carrier contained in the catalyst-carrying particles, that is, 100 parts by mass of the catalyst-carrying particles in terms of carrier. The blending amount of the carbon fiber was set to 20 parts by mass with respect to 100 parts by mass of the catalyst-supporting particles in terms of the carrier. The blending amount of the dispersion medium was such that the solid content concentration of the catalyst ink was 10% by mass. The dispersion treatment was carried out for 60 minutes at a rotation speed of 600 rpm using zirconia balls with a diameter of 3 mm and a planetary ball mill. Details of each component used in the catalyst ink are as follows.

Catalyst-carrying particles: platinum-carrying carbon catalyst with a hydrophobic coating formed from a fluorine-based compound (carrying density: 50% by mass, thickness of hydrophobic coating: 25 nm)
Polymer electrolyte: fluorine-based polymer electrolyte (Nafion (registered trademark) dispersion manufactured by Wako Pure Chemical Industries, Ltd.)
Carbon fiber: Carbon fiber (average fiber length 6 μm, average fiber diameter 150 nm) obtained by hydrophilizing carbon fiber (VGCF-H (registered trademark) manufactured by Showa Denko Co., Ltd.) that is not hydrophilized by oxygen plasma treatment.
Dispersion medium: a mixture of water and 1-propanol at a mass ratio of 1:1 Next, using a die coater, a prepared catalyst is applied to one side of a polymer electrolyte membrane (Nafion (registered trademark) 211 manufactured by Dupont) By applying the ink, a square coating film of 50 mm long×50 mm wide was formed. The amount of catalyst ink applied was such that the amount of supported platinum was 0.3 mg/cm ² . Then, a drying process was performed using an oven at 80° C. to volatilize the dispersion medium contained in the coating film, thereby forming a cathode-side electrode catalyst layer.

Next, the prepared catalyst ink was applied to the surface of the polymer electrolyte membrane opposite to the surface on which the cathode-side electrode catalyst layer was formed, thereby forming a square coating film of 50 mm long×50 mm wide. . The amount of catalyst ink applied was such that the amount of supported platinum was 0.1 mg/cm ² . Then, a drying treatment was performed using an oven at 80° C. to volatilize the dispersion medium contained in the coating film to form an anode-side electrode catalyst layer, thereby obtaining a membrane electrode assembly of Example 1.

[Comparative Example 1]
A membrane electrode assembly of Comparative Example 1 was obtained in the same manner as in Example 1, except that the type of catalyst-carrying particles was changed. The details of the catalyst-supporting particles used in Comparative Example 1 are as follows.

Catalyst-carrying particles: platinum-carrying carbon catalyst without hydrophobic coating (carrying density: 50% by mass)
[Comparative Example 2]
A membrane electrode assembly of Comparative Example 2 was obtained in the same manner as in Example 1, except that the type of carbon fiber was changed. Details of the carbon fiber used in Comparative Example 2 are as follows.

Carbon fiber: non-hydrophilized carbon fiber (VGCF-H (registered trademark) manufactured by Showa Denko, average fiber length 6 μm, average fiber diameter 150 nm)
[Comparative Example 3]
A membrane electrode assembly of Comparative Example 3 was obtained in the same manner as in Example 1, except that the type of catalyst-carrying particles and the type of carbon fiber were changed. The details of the catalyst-supporting particles and carbon fiber used in Comparative Example 3 are as follows.

Catalyst-carrying particles: platinum-carrying carbon catalyst without hydrophobic coating (carrying density: 50% by mass)
Carbon fiber: non-hydrophilized carbon fiber (VGCF-H (registered trademark) manufactured by Showa Denko, average fiber length 6 μm, average fiber diameter 150 nm)
[Comparative Example 4]
A membrane electrode junction of Comparative Example 4 was prepared in the same manner as in Example 1, except that the amount of carbon fiber compounded was 70 parts by mass with respect to the compounded amount of catalyst-supporting particles of 100 parts by mass in terms of carrier. got a body

[Comparative Example 5]
A membrane electrode junction of Comparative Example 5 was prepared in the same manner as in Example 1, except that the amount of carbon fiber was 2 parts by mass with respect to 100 parts by mass of the catalyst-supporting particles in terms of the carrier. got a body

[Evaluation of power generation performance]
For each of the membrane electrode assemblies of Example 1 and Comparative Examples 1 to 5, a sample was prepared by laminating carbon paper as a gas diffusion layer so as to sandwich the membrane electrode assembly. Each sample was placed in a power generation evaluation cell, and current-voltage measurement was performed using a fuel cell measuring device. The cell temperature during measurement was set at 80°C. As operating conditions, the following high humidification conditions and low humidification conditions were adopted. Hydrogen was used as the fuel gas, and air was used as the oxidant gas. At this time, hydrogen was flowed at a flow rate at which the hydrogen utilization rate was 80%, and air was flowed at a flow rate at which the oxygen utilization rate was 40%. In addition, the back pressure was set to 50 kPa.

(Operating conditions)
High humidification conditions: relative humidity anode 90% RH, cathode 80% RH
Low humidification conditions: relative humidity anode 90% RH, cathode 30% RH
The measured power generation performance of each sample is shown in the power generation performance column of Table 1. In Table 1, the case where the voltage is 0.65 V or more when the current density is 2.0 A/cm ² is indicated by "◯", and the case where the same voltage is less than 0.65 V is indicated by "x". ing.

表１に示すように、実施例１を用いた場合には、高加湿条件及び低加湿条件のいずれの運転条件においても良好な発電性能を示した。また、高加湿条件の発電性能の評価が「〇」であることから、実施例１を用いた場合は、高加湿条件においてもフラッディングは生じておらず、生成水を十分に排水できていると考えられる。

As shown in Table 1, when Example 1 was used, good power generation performance was exhibited under both high humidification conditions and low humidification conditions. In addition, since the evaluation of the power generation performance under high humidification conditions is "O", when Example 1 is used, flooding does not occur even under high humidification conditions, and it can be said that the generated water can be sufficiently drained. Conceivable.

On the other hand, in the case of using Comparative Example 1 in which the catalyst-carrying particles without the hydrophobic coating were used, the power generation performance under high humidification conditions was lowered. In the case of using Comparative Example 2, which employs carbon fibers that have not been hydrophilized, the power generation performance deteriorated under low humidification conditions. When using Comparative Example 3, which employs catalyst-supporting particles without a hydrophobic coating and carbon fibers that have not been hydrophilized, the power generation performance deteriorated under both high and low humidification conditions.

From the results of Example 1 and Comparative Examples 1 to 3, by using a combination of catalyst-supporting particles with a hydrophobic coating and hydrophilized carbon fibers, power generation under both high and low humidification operating conditions. It was shown that the effect of improving the performance can be obtained. The mechanism by which this effect is obtained is presumed as follows. In Example 1, the catalyst ink that forms the electrode catalyst layer contains catalyst-carrying particles with a hydrophobic coating, which are hydrophobic substances, and hydrophilic carbon fibers, which are hydrophilic substances. ing. As a result, when the applied catalyst ink is dried to form the electrode catalyst layer, the configuration such as the shape and distribution of the voids formed in the electrode catalyst layer can be changed during power generation to allow gaseous water to enter the layer. The structure is suitable for discharging liquid water out of the layer while leaving it. As a result, power generation performance is improved under both high humidification and low humidification operating conditions.

Further, when using Comparative Examples 4 and 5 in which the content of the hydrophilized carbon fiber is outside the range of 5 parts by mass or more and 30 parts by mass or less, the power generation performance under both high humidification conditions and low humidification conditions is low. Decreased. From the results of Comparative Examples 4 and 5, the effect of improving the power generation performance under high humidification conditions and low humidification conditions obtained by Example 1 was confirmed by the catalyst-supporting particles provided with a hydrophobic coating and the hydrophilized carbon fiber. It was shown that it cannot be obtained by simply combining and using. In order to obtain the above effect, it is necessary to set the content of the hydrophilized carbon fiber to a specific range in addition to using the catalyst-carrying particles provided with a hydrophobic coating and the hydrophilized carbon fiber. It has been shown.

DESCRIPTION OF SYMBOLS 10... Membrane electrode assembly 11... Polymer electrolyte membrane 12C... Cathode side electrode catalyst layer 12A... Anode side electrode catalyst layer 20... First electrode catalyst layer 21... Catalyst carrying particles 21a... Catalyst 21b... Carrier 21c... Hydrophobic coating 22 Polymer electrolyte 23 Hydrophilic carbon fiber 30 Solid polymer fuel cell 31a, 31b Gas diffusion layer 32a, 32b Separator 33a, 33b Gas channel 34a, 34b Cooling water channel

Claims (5)

An electrode catalyst layer bonded to a polymer electrolyte membrane in a membrane electrode assembly,
Catalyst-supporting particles having a hydrophobic coating, a polymer electrolyte, and hydrophilic carbon fibers having an average fiber length of 0.7 μm or more and 20 μm or less,
The catalyst-supporting particles comprise a carrier and a catalyst supported on the carrier,
The electrode catalyst layer, wherein the content of the hydrophilized carbon fiber is 5 parts by mass or more and 30 parts by mass or less when the content of the carrier is 100 parts by mass. The electrode catalyst layer according to claim 1, wherein the content of the polymer electrolyte is 40 parts by mass or more and 100 parts by mass or less when the content of the carrier is 100 parts by mass. 3. The electrode catalyst layer according to claim 1, wherein the hydrophilic carbon fibers have an average fiber diameter of 10 nm or more and 300 nm or less. a polymer electrolyte membrane;
An electrode catalyst layer according to any one of claims 1 to 3,
A membrane electrode assembly, wherein the electrode catalyst layer is bonded to the polymer electrolyte membrane. a membrane electrode assembly according to claim 4;
a pair of gas diffusion layers sandwiching the membrane electrode assembly in the thickness direction of the membrane electrode assembly;
A polymer electrolyte fuel cell comprising a pair of separators sandwiching the membrane electrode assembly and the pair of gas diffusion layers in the thickness direction of the membrane electrode assembly.

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