JP5585036B2 - How to use catalyst ink for fuel cell - Google Patents

Description

  The present invention relates to a method for storing and using a catalyst ink for a polymer electrolyte fuel cell, and a solid catalyst ink stored by this storage method.

  A fuel cell is a power generation engine that generates electricity from an electrochemical reaction between hydrogen and oxygen, has high power generation efficiency, and discharges only water during power generation, and is expected as a next-generation power source. A membrane electrode assembly of a polymer electrolyte fuel cell has a structure in which electrode catalyst layers are bonded to both surfaces of a polymer electrolyte membrane. A fuel cell is used in which a gas diffusion layer is disposed outside the electrode catalyst layer of the membrane electrode assembly and is further sandwiched between separators.

  As a method for producing a membrane / electrode assembly, a method using a catalyst ink containing at least a catalyst-supporting carbon, a dispersion solvent, and a polymer electrolyte is known. These are mixed and dispersed to produce a catalyst ink, the catalyst ink is applied onto the substrate, the solvent is removed, and a transfer sheet having an electrode catalyst layer provided on the substrate is produced. This is a polymer electrolyte membrane. The membrane / electrode assembly is manufactured by hot-pressing on the top.

  Platinum is mainly used as the catalyst-supporting carbon catalyst because of its high catalytic activity. In addition to water, various organic solvents such as alcohols, ketones, ethers, and esters are used as the dispersion solvent for the catalyst ink. However, since the catalyst-supporting carbon and the polymer electrolyte can be well dispersed, the alcohols Is often used.

  Such a catalyst ink has a problem that the storage period after preparation is as short as about 1-2 days. When the catalyst ink is stored at room temperature, platinum as a catalyst oxidizes alcohols as a dispersion solvent to generate carboxylic acid. Since the membrane electrode assembly manufactured using the catalyst ink in which the dispersion solvent is oxidized and denatured may deteriorate the power generation performance, the catalyst ink after the storage period has been discarded. A method capable of storing a catalyst ink containing expensive platinum for a long period of time is also necessary from the viewpoint of cost reduction.

  As a method for storing the catalyst ink for a long period of time, Patent Document 1 discloses a method using a photocatalyst. This method is a method in which photocatalyst particles are mixed in catalyst ink and stored while irradiating light to prevent oxidation of the dispersion solvent. The catalyst ink stored by this method needs to be used after removing the photocatalyst particles before use. However, since the catalyst ink using the catalyst-supporting carbon is black and does not easily transmit light, it is considered difficult to sufficiently prevent oxidation by the method using the photocatalyst.

JP 2005-85574 A

  The present invention is intended to solve the above-described conventional problems, and a method for storing and using a catalyst ink for a fuel cell capable of extending the storage period of the catalyst ink, and a solid stored by this storage method. An object is to provide a catalyst ink.

  The present inventor has found that the following storage method solves the above problem.

According to the first aspect of the present invention, a solid catalyst ink that has been cooled and solidified containing a catalyst-supporting carbon, a dispersion solvent, and a polymer electrolyte is heated to a liquid state. A method for using a catalyst ink is characterized in that a coating film is formed by coating on a substrate, and a dispersion solvent contained in the coating film is dried and removed to form an electrode catalyst layer.

The invention according to claim 2 of the present invention is heated is obtained by the use of a catalyst ink according to claim 1, characterized in that to a temperature of 30 ° C. or less than 1 ° C..

  According to the method for storing a catalyst ink of the present invention, the oxidation of the dispersion solvent can be suppressed as long as the catalyst ink is cooled and solidified. Therefore, according to the present invention, the membrane electrode assembly produced using the catalyst ink stored as the solid catalyst ink can maintain the power generation performance even after the catalyst ink has been stored for a long period of time.

  Therefore, according to the above method, the storage period of the catalyst ink can be extended, and therefore, the catalyst ink to be discarded can be reduced.

FIG. 1 is a diagram showing a method for storing and using a catalyst ink according to the present invention.

  Hereinafter, a method for storing and using the catalyst ink according to the present invention will be described.

  FIG. 1 shows a schematic diagram of a method for storing and using a catalyst ink according to the present invention. In the method for storing a catalyst ink of the present invention, a catalyst ink is prepared and stored as a solid catalyst ink solidified by cooling at a temperature that does not melt. In this solidified state, oxidation of the dispersion solvent can be suppressed, so that it can be stored for a long period of time. When using the catalyst ink, the solid catalyst ink can be used in a liquid state by raising the temperature to room temperature.

  Here, room temperature specifically refers to 1 ° C. or higher and 30 ° C. or lower. This is because when the temperature is lower than 1 ° C., the dispersion solvent may not melt, and when the temperature is higher than 30 ° C., the solvent volatilizes and the composition of the catalyst ink may change. Further, the method for raising the temperature of the solid catalyst ink to room temperature may be any method as long as the solid catalyst ink is heated from the outside to raise the temperature to room temperature. In particular, in order to prevent a change in the composition of the solid catalyst ink due to a rapid temperature change, it is preferable to raise the temperature of the solid catalyst ink to room temperature by standing at room temperature.

  The catalyst ink contains at least catalyst-carrying carbon carrying a catalyst substance, a polymer electrolyte, and a dispersion solvent.

  The catalyst-supported carbon catalyst used in the present invention includes platinum, palladium, ruthenium, iridium, rhodium, osmium, platinum group elements, iron, lead, copper, chromium, cobalt, nickel, manganese, vanadium, molybdenum in addition to platinum. Further, a metal such as gallium or aluminum or an alloy thereof, an oxide, a double oxide, or the like may be used. The particle size of these catalysts is preferably 0.5 nm or more and 20 nm or less because the activity of the catalyst is lowered when it is larger than 20 nm, and the stability of the catalyst is lowered when it is smaller than 0.5 nm. More preferably, it is 1 nm or more and 5 nm or less.

  The type of carbon particles for supporting the catalyst may be any particle as long as it is in the form of fine particles and has electrical conductivity and is not affected by the catalyst. Carbon black, graphite, graphite, activated carbon, carbon fiber, Carbon nanotubes and fullerenes may be used. If the particle size of the carbon particles is smaller than 10 nm, it is difficult to form an electron conduction path. If the particle size is larger than 1000 nm, the gas diffusibility of the electrode catalyst layer may be lowered, or the utilization rate of the catalyst may be lowered. About 10 nm or more and 1000 nm or less are preferable. More preferably, it is 10 nm or more and 100 nm or less.

  Any polymer electrolyte may be used as long as it has proton conductivity, and a fluorine-based polymer electrolyte or a hydrocarbon-based polymer electrolyte may be used. Among these, Nafion (registered trademark) manufactured by Dupont and Flemion (registered trademark) material manufactured by Asahi Glass Co., Ltd. may be suitably used as the fluorine-based polymer electrolyte.

  As the dispersion solvent, organic solvents such as water, alcohols, ketones, ethers, and esters are used alone or in combination. Among them, alcohols may be preferably used because the catalyst-supporting carbon and the polymer electrolyte can be dispersed well. As alcohols, for example, alcohols such as methanol, ethanol, 1-propanol, 2-propanol, 1-butanol, 2-butanol, isobutyl alcohol, and tert-butyl alcohol may be used.

  Other organic solvents can be mixed with the alcohols. Other organic solvents include acetone, methyl ethyl ketone, methyl propyl ketone, methyl butyl ketone, methyl isobutyl ketone, methyl amyl ketone, pentanone, heptanone, cyclohexanone, methyl cyclohexanone, acetonyl acetone, diethyl ketone, dipropyl ketone, diisobutyl. Ketones such as ketones, tetrahydrofuran, tetrahydropyran, dioxane, diethylene glycol dimethyl ether, anisole, methoxytoluene, diethyl ether, dipropyl ether, dibutyl ether and other ethers, isopropylamine, butylamine, isobutylamine, cyclohexylamine, diethylamine, aniline, etc. Amines, propyl formate, isobutyl formate, amyl formate, methyl acetate, ethyl acetate, Use esters such as propyl acetate, butyl acetate, isobutyl acetate, pentyl acetate, isopentyl acetate, methyl propionate, ethyl propionate, butyl propionate, and other acetic acid, propionic acid, dimethylformamide, dimethylacetamide, N-methylpyrrolidone, etc. May be. Examples of the glycol and glycol ether solvents include ethylene glycol, diethylene glycol, propylene glycol, ethylene glycol monomethyl ether, ethylene glycol dimethyl ether, ethylene glycol diethyl ether, diacetone alcohol, 1-methoxy-2-propanol, and 1-ethoxy-2. -Propanol or the like may be used.

  The catalyst ink may be obtained by mixing a catalyst-supporting carbon, a polymer electrolyte, and a dispersion solvent and applying a dispersion treatment. Examples of the dispersion method include ball mill, bead mill, roll mill, shear mill, wet mill, ultrasonic dispersion treatment, and homogenizer.

  The cooling temperature and cooling method may be any method as long as it can be cooled below the melting point of the dispersion solvent and the catalyst ink is solidified, and the cooling rate is not limited. For example, there is a method of bringing the catalyst ink into contact with liquid nitrogen. If the solid catalyst ink is not melted during storage, it can be stored for 1 to 2 weeks.

  In order to use the catalyst ink stored in a solid state, the solid catalyst ink may be heated to room temperature and made liquid. The catalyst ink that has been liquefied again after storage is immediately used for the production of the electrode catalyst layer so as not to change its quality. The electrode catalyst layer may be manufactured by an application step of applying a catalyst ink on a substrate and a drying step of removing a solvent of a coating film made of the catalyst ink applied on the substrate. The membrane / electrode assembly is produced by transferring an electrode catalyst layer formed on a substrate onto a polymer electrolyte membrane.

  In addition to the gas diffusion layer, a transfer film may be used as the substrate used in the coating process. The transfer film may be made of any material having good transferability, such as ethylene tetrafluoroethylene copolymer (ETFE), tetrafluoroethylene-hexafluoropropylene copolymer (FEP), tetrafluoroperfluoroalkyl vinyl ether copolymer. Fluorine resins such as (PFA) and polytetrafluoroethylene (PTFE) may be used. Further, a polymer film such as polyimide, polyethylene terephthalate, polyamide (nylon), polysulfone, polyethersulfone, polyphenylene sulfide, polyether ether ketone, polyetherimide, polyarylate, polyethylene naphthalate may be used. You may use what processed the release layer etc. to these base materials.

  As a gas diffusion layer, you may use what is used for the normal fuel cell. Specifically, a porous carbon material such as carbon cloth, carbon paper, and nonwoven fabric may be used as the gas diffusion layer. The gas diffusion layer may be used as a substrate.

  As a method for applying the catalyst ink, a doctor blade method, a screen printing method, a roll coating method, a spray method, or the like may be used.

  The temperature of the drying process is not particularly limited, but it is preferable to carry out at a room temperature or higher and 150 ° C. or lower. If the temperature is higher than 150 ° C., it is not appropriate because the generation of uneven drying of the electrode catalyst layer and the effect of heat treatment on the polymer electrolyte increase. When the boiling point of the solvent in the catalyst ink is not lower than the boiling point of the solvent, the evaporation rate is remarkably increased.

  A membrane electrode assembly is obtained by bonding the electrode catalyst layer formed on the base material to both surfaces of the polymer electrolyte membrane. As a joining method, electrode catalyst layers formed on a base material are arranged on both surfaces of a polymer electrolyte membrane, and these can be joined by heating and pressurizing them. When a transfer film is used as the substrate, the transfer film may be peeled off after bonding, and a membrane electrode assembly including catalyst layers on both sides of the polymer electrolyte membrane may be used. Moreover, when a gas diffusion layer is used for the base material, it is not necessary to peel off the base material that is the gas diffusion layer after the transfer step.

  The polymer electrolyte membrane only needs to have proton conductivity, and a fluorine-based polymer electrolyte or a hydrocarbon-based polymer electrolyte may be used. Examples of the fluorine-based polymer electrolyte include Nafion (registered trademark) manufactured by Dupont, Flemion (registered trademark) manufactured by Asahi Glass Co., Ltd., and Nile (registered trademark) manufactured by Asahi Kasei Co., Ltd., Gore Select (registered trademark) manufactured by Gore. Etc. may be used. As the hydrocarbon polymer electrolyte membrane, electrolyte membranes such as sulfonated polyether ketone, sulfonated polyethersulfone, sulfonated polyetherethersulfone, sulfonated polysulfide, and sulfonated polyphenylene may be used. Among them, a Nafion (registered trademark) material manufactured by Dupont can be suitably used as the polymer electrolyte membrane.

<Preparation of catalyst ink>
A planetary ball mill comprising a platinum-supported carbon catalyst (support: Ketjen) having a platinum support amount of 30% by mass, a 20% by mass polymer electrolyte solution (Nafion (registered trademark), manufactured by Dupont), and a dispersion solvent. Then, a dispersion treatment was performed to prepare a catalyst ink. The dispersion solvent was a mixed solvent of water and ethanol.

<Storage of catalyst ink>
The prepared catalyst ink was transferred into a heat insulating container containing liquid nitrogen to obtain a solid catalyst ink. Cooling was continued and the state of the solid catalyst ink was maintained and stored for 1 week.

<Use of catalyst ink, production of membrane electrode assembly>
The solid catalyst ink was taken out into a sealed container and allowed to stand at room temperature. The solid catalyst ink changed to a liquid state. Using PTFE sheet as a base material, the catalyst ink changed into a liquid state was applied using a doctor blade and dried in an oven set at 80 ° C. for 5 minutes to prepare an electrode catalyst layer on the transfer film. A set of this was punched out into a square shape, and a laminated body was arranged so as to face both surfaces of the polymer electrolyte membrane (Nafion 212 (registered trademark), manufactured by Dupont), and hot pressing was performed at 130 ° C. for 10 minutes. After hot pressing, the membrane electrode assembly was produced by peeling off the PTFE of the base material.

<Power generation performance measurement>
The membrane electrode assemblies of Examples and Comparative Examples were bonded together so as to sandwich a carbon cloth as a gas diffusion layer, and installed in a power generation evaluation cell. This was measured at a cell temperature of 80 ° C. using a fuel cell measuring device. The humidification condition was 25% RH for both the anode and the cathode. Hydrogen was used as the fuel gas and air was used as the oxidant gas. The back pressure was 100 kPa.

(result)
The membrane / electrode assembly produced from the catalyst ink stored for one week showed the same power generation performance as the membrane / electrode assembly produced from the catalyst ink which was used immediately without being stored. Therefore, it was confirmed that the membrane electrode assembly manufactured using the catalyst ink stored by the storage method according to the present invention does not change the power generation performance even after storing the catalyst ink for a long time.

  The membrane electrode assembly of the present invention has uniform power generation performance. Therefore, the present invention can be suitably used for a fuel cell using a polymer electrolyte membrane, particularly a stationary cogeneration system and an electric vehicle.

Claims (2)

The solid catalyst ink that has been cooled and solidified containing the catalyst-supporting carbon, the dispersion solvent, and the polymer electrolyte is heated to a liquid state,
Applying the liquid catalyst ink on a substrate to form a coating film,
A method for using a catalyst ink, comprising drying and removing the dispersion solvent contained in the coating film to form an electrode catalyst layer. The method of using a catalyst ink according to claim 1 , wherein the temperature rise is performed to a temperature of 1 ° C or higher and 30 ° C or lower.

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