JP2022158098A - Method for manufacturing electrode sheet - Google Patents

Abstract

To provide a method for manufacturing an electrode sheet, by which time for a MEA fabrication step can be shortened.SOLUTION: A method for manufacturing an electrode sheet to be used for a membrane-electrode assembly, and having a catalyst layer formed on a sheet member comprises the steps of: applying the catalyst layer to a first sheet member in such a way that a peripheral edge of the first sheet member is left, thereby forming the electrode sheet having the catalyst layer on the first sheet member; heating the electrode sheet; and cooling the electrode sheet. At least in the step of cooling the electrode sheet, a second sheet member larger having an area larger than that of the catalyst layer is disposed on a face of the first sheet member on a side where the catalyst layer is formed with the electrode sheet depressurized, and the second sheet member is caused to adhere to the peripheral edge of the first sheet member.SELECTED DRAWING: Figure 1

Description

The present disclosure relates to a method for manufacturing an electrode sheet.

A fuel cell (FC) is composed of a fuel cell stack (hereinafter sometimes simply referred to as a stack) in which one single cell or a plurality of single cells (hereinafter sometimes referred to as cells) are stacked, and hydrogen It is a power generation device that extracts electrical energy through an electrochemical reaction between a fuel gas such as gas and an oxidant gas such as oxygen. It should be noted that the fuel gas and oxidant gas that are actually supplied to the fuel cell are often mixtures with gases that do not contribute to oxidation/reduction. In particular, the oxidant gas is often air containing oxygen.
In the following, the fuel gas and the oxidant gas may be simply referred to as "reactant gas" or "gas" without particular distinction. Also, both a single cell and a fuel cell stack in which single cells are stacked may be referred to as a fuel cell.
A single cell of this fuel cell usually includes a membrane electrode assembly (MEA).
A membrane electrode assembly has a catalyst layer and a gas diffusion layer (GDL, hereinafter sometimes simply referred to as a diffusion layer) on both sides of a polymer electrolyte membrane (hereinafter also simply referred to as "electrolyte membrane"). It has a structure formed in order. Therefore, the membrane electrode assembly is sometimes called a membrane electrode gas diffusion layer assembly (MEGA).
A single cell has two separators sandwiching both sides of the membrane electrode gas diffusion layer assembly, if necessary. The separator usually has a structure in which grooves are formed as flow paths for the reaction gas on the surface in contact with the gas diffusion layer. This separator has electronic conductivity and also functions as a current collector for the generated electricity.
At the fuel electrode (anode) of the fuel cell, hydrogen (H ₂ ) as fuel gas supplied from the gas flow path and the gas diffusion layer is protonated by the catalytic action of the catalyst layer, passes through the electrolyte membrane, and reaches the oxidant electrode ( cathode). The co-generated electrons do work through an external circuit and travel to the cathode. Oxygen (O ₂ ) as an oxidant gas supplied to the cathode reacts with protons and electrons in the catalyst layer of the cathode to produce water. The produced water gives moderate humidity to the electrolyte membrane, and excess water permeates the gas diffusion layer and is discharged out of the system.

BACKGROUND ART Various studies have been made on constituent materials of fuel cells mounted on fuel cell vehicles (hereinafter sometimes referred to as "vehicles").
For example, Patent Literature 1 discloses a method for manufacturing an electrode sheet, which is used for a membrane electrode assembly and in which a catalyst layer containing an electrolyte is formed on a sheet member.

In Patent Document 2, the green sheet laminate can be easily removed from the suction head without causing deformation on the surface of the green sheet laminate, and the difference in thermal contraction between the holding substrate and the green sheet laminate is disclosed. A green sheet stacking method capable of preventing the occurrence of warpage due to

JP 2017-037759 A Japanese Patent Application Laid-Open No. 2003-203823

As an example of manufacturing a membrane electrode assembly (MEA), there is a technique in which an electrode sheet having a catalyst layer formed on a transfer sheet is dried and heat-treated, and the catalyst layer of the electrode sheet is transferred to an electrolyte membrane. After the heat treatment, the catalyst layer applied to the transfer sheet is cooled to room temperature. During the cooling, the catalyst layer and the transfer sheet may warp due to thermal effects. When the catalyst layer is warped in this way, there is a problem that it takes time to align the anode and the cathode with the electrolyte membrane.
The transfer sheet (resin film) is a reinforcing material used only during manufacturing, and is not a component of the final MEA. There is a problem that it is more likely to be thermally deformed. According to FIG. 4 of the above Patent Document 1, cooling is performed while constraining one direction vertically or horizontally, but there is a possibility that deformation in the direction not constrained cannot be suppressed by constraining only one direction as described above. .

The present disclosure has been made in view of the above circumstances, and a main object of the present disclosure is to provide a method of manufacturing an electrode sheet that can shorten the time required for the MEA manufacturing process.

A method for manufacturing an electrode sheet according to the present disclosure is a method for manufacturing an electrode sheet used for a membrane electrode assembly, in which a catalyst layer is formed on a sheet member,
forming the electrode sheet having the catalyst layer on the first sheet member by applying the catalyst layer to the first sheet member so as to leave the peripheral edge portion of the first sheet member;
heating the electrode sheet;
a step of cooling the electrode sheet,
In the step of at least cooling the electrode sheet, in a state in which the electrode sheet is decompressed, a second cooling layer having an area larger than that of the catalyst layer is formed on the surface of the first sheet member on which the catalyst layer is formed. are placed, and the peripheral portion of the first sheet member and the second sheet member are bonded together.

According to the electrode sheet manufacturing method of the present disclosure, the time required for the MEA manufacturing process can be shortened.

FIG. 1 is a flow chart showing an example of the manufacturing method of the present disclosure. FIG. 2 shows a perspective image (upper figure) and a side view image (lower figure) of an electrode sheet, which is a work manufactured by the manufacturing method of the present disclosure. FIG. 3 shows a perspective image (upper figure) and a side view image (lower figure) of an electrode sheet, which is a work manufactured by a conventional manufacturing method.

A method for manufacturing an electrode sheet according to the present disclosure is a method for manufacturing an electrode sheet used for a membrane electrode assembly, in which a catalyst layer is formed on a sheet member,
forming the electrode sheet having the catalyst layer on the first sheet member by applying the catalyst layer to the first sheet member so as to leave the peripheral edge portion of the first sheet member;
heating the electrode sheet;
a step of cooling the electrode sheet,
In the step of at least cooling the electrode sheet, in a state in which the electrode sheet is decompressed, a second cooling layer having an area larger than that of the catalyst layer is formed on the surface of the first sheet member on which the catalyst layer is formed. are placed, and the peripheral portion of the first sheet member and the second sheet member are bonded together.

According to the present disclosure, the catalyst layer of the electrode sheet is sandwiched between separate resin sheets, sealed in a vacuum (reduced pressure), and isotropically restrained using the pressure difference. As a result, the electrode sheet can be isotropically restrained, and anisotropic deformation is also suppressed. Alignment becomes easy, leading to shortening of the MEA manufacturing process.
Specifically, the electrode sheet is covered with a non-adhesive sheet (such as a Teflon sheet) that is a second sheet member, and the non-adhesive sheet is vacuum-sucked with a suction pallet, thereby fixing the work (processing target) in vacuum, It is possible to suppress thermal deformation of the work that occurs when heat is input. Since the thermal deformation of the work is suppressed even after thermal bonding, the work can be kept in a state of less deformation such as warping.

In addition, in the FC manufacturing process, there is a process of integrating the resin sheet (three-layer sheet) and MEGA by thermal bonding, but heat is also transferred to the resin sheet side, and the melting point of the resin sheet and the temperature at the time of thermal bonding is close, the resin sheet is thermally deformed and the entire work is warped, and there is a problem that the drawing standard value (a warp amount of 10 mm or less) cannot be satisfied.
According to the present disclosure, in the FC manufacturing process, when heat is input to thermally bond the resin sheet (three-layer sheet) and MEGA, a thin non-adhesive sheet (second sheet) is placed on the easily deformable resin sheet. (equivalent to a member) is covered and fixed together with the work by suction, even if heat is input, thermal deformation of the resin sheet can be reduced.

Electrode sheets are used in membrane electrode assemblies, and are formed by forming a catalyst layer on a sheet member.

FIG. 1 is a flow chart showing an example of the manufacturing method of the present disclosure.
The manufacturing method of the electrode sheet of the present disclosure has (1) a coating step, (2) a heating step, and (3) a cooling step.

(1) Application step In the application step, the catalyst layer is applied to the first sheet member so as to leave the peripheral edge portion of the first sheet member, thereby forming the catalyst layer on the first sheet member. It is a step of forming the electrode sheet.
The catalyst layer to be applied may be in the form of a catalyst ink. The catalyst ink contains a catalyst that promotes an electrochemical reaction, an electrolyte with proton conductivity, a carrier with electron conductivity, a solvent, and the like.

Examples of catalysts that can be used include platinum (Pt) and alloys of Pt and other metals (for example, Pt alloys containing cobalt, nickel, etc.).

The electrolyte may be one having proton conductivity, or may be a fluororesin or the like. As the fluorine-based resin, for example, a perfluorosulfonic acid-based resin such as Nafion (registered trademark) may be used. The ionomer may be, for example, a perfluorosulfonic acid resin such as Nafion (registered trademark).

The support may be carbon (carbon support). Carbon (carbon support) may be, for example, a commercially available carbon material. Carbon materials include, for example, Ketjen Black (trade name: manufactured by Ketjen Black International), Vulcan (trade name: manufactured by Cabot), Norit (trade name: manufactured by Norit), Black Pearl (trade name: Cabot (manufactured by Chevron), acetylene black (trade name: manufactured by Chevron), carbon nanotubes, carbon nanohorns, carbon nanowalls, carbon nanofibers, carbon alloys, and the like.
The carbon support may be carbon support particles that are particulate in shape.
The average particle size of the carbon carrier particles is not particularly limited, but may be 10 nm to 10 μm.

The solvent is not particularly limited, and may be appropriately selected depending on the electrolyte used and the like. Examples of solvents that can be used include water, methanol, ethanol, propanol, propylene glycol, N,N-dimethylformamide, N,N-diethylformamide, N,N-dimethylacetamide, N,N-diethylacetamide, and the like. . As a solvent, a mixture of two or more kinds may be used.

A method for applying the catalyst ink is not particularly limited, and a conventionally known method can be adopted. Methods of applying the catalyst ink include a doctor blade method, a metal mask printing method, an electrostatic coating method, a dip coating method, a spray coating method, a roll coating method, a gravure coating method, and a screen printing method.

As the first sheet member, one having self-supporting properties can be appropriately selected and used, and for example, a resin such as polytetrafluoroethylene (PTFE) can be used.

(2) Heating step The heating step is a step of heating the electrode sheet.
The heating method is not particularly limited as long as the first sheet member and the catalyst layer can be thermally bonded, and the electrode sheet may be heated using a heater or the like. Moreover, in the heating step, the catalyst ink may be dried.

(3) Cooling Step The cooling step is a step of cooling the electrode sheet.
The cooling method is not particularly limited, and the electrode sheet may be cooled by leaving it at room temperature, under reduced pressure using a decompression pump or the like, or under vacuum for a predetermined time.

In the present disclosure, at least in the cooling step, the second sheet member having an area larger than the area of the catalyst layer is arranged on the surface of the first sheet member on which the catalyst layer is formed while the electrode sheet is decompressed. Then, the peripheral portion of the first sheet member and the second sheet member are adhered. Therefore, the electrode sheet is cooled while the peripheral portion of the first sheet member and the second sheet member are adhered to each other under reduced pressure.
Specifically, the surface of the electrode sheet, which is the workpiece, on which the catalyst layer is formed is covered with the Teflon sheet, which is the second sheet member, and is covered with the first sheet member and the second sheet member by adsorption with the adsorption palette. The inside may be evacuated, and the catalyst layer may be pressed by external air pressure in a state in which the peripheral edge portion of the first sheet member and the second sheet member are adhered under reduced pressure.
If necessary, a second sheet member having an area larger than that of the catalyst layer is placed on the surface of the first sheet member on which the catalyst layer is formed, while the electrode sheet is depressurized even in the heating step. , the peripheral portion of the first sheet member and the second sheet member may be adhered. Therefore, the electrode sheet may be heated while the peripheral portion of the first sheet member and the second sheet member are adhered to each other under reduced pressure.

Examples of the decompression method for the electrode sheet include methods such as adsorption using an adsorption palette and decompression using a decompression pump.
The state in which the electrode sheet is decompressed means that the inside covered with the first sheet member and the second sheet member is evacuated by the adsorption of the peripheral portion of the first sheet member and the second sheet member by the adsorption palette. It may be in a state where
The electrode sheet is cooled at least in a state in which the peripheral edge portion of the first sheet member and the second sheet member are adhered to each other under a reduced pressure during cooling, thereby preventing the catalyst layer from warping, thereby preventing the anode and the electrode sheet from being warped. Positioning of the cathode to the electrolyte membrane, etc. can be performed with high accuracy.
The second sheet member may be a non-adhesive sheet such as a Teflon sheet. By using a non-adhesive sheet. The catalyst layer can be sealed and adhered under reduced pressure, and can be easily separated from the first sheet member after cooling.
The thicknesses of the first sheet member and the second sheet member are not particularly limited, and may be 50 μm.

After cooling the electrode sheet, the second sheet member is separated from the electrode sheet, and the catalyst layer is transferred and joined from the first sheet member of the electrode sheet to both surfaces of the electrolyte membrane to form a membrane electrode assembly. good. The catalyst layer may be a cathode catalyst layer or an anode catalyst layer.
A membrane electrode assembly using an electrode sheet has an anode catalyst layer, an electrolyte membrane, and a cathode catalyst layer in this order.
The cathode (oxidant electrode) includes a cathode catalyst layer.
The anode (fuel electrode) includes an anode catalyst layer.
The cathode catalyst layer and the anode catalyst layer are collectively referred to as catalyst layers.
The catalyst layer may include, for example, a catalyst that promotes the electrochemical reaction, an electrolyte with proton conductivity, and a carrier with electron conductivity.
The electrolyte membrane may be a solid polymer electrolyte membrane. Examples of solid polymer electrolyte membranes include fluorine-based electrolyte membranes such as perfluorosulfonic acid thin films containing water, and hydrocarbon-based electrolyte membranes. As the electrolyte membrane, for example, a Nafion membrane (manufactured by DuPont) may be used.

FIG. 2 shows a perspective image (upper figure) and a side view image (lower figure) of an electrode sheet, which is a work manufactured by the manufacturing method of the present disclosure. The electrode sheet of the present disclosure is subjected to the coating step, the heating step, and the cooling step, and in a state in which the electrode sheet is depressurized during the cooling step, the catalyst layer is formed on the side of the first sheet member on which the catalyst layer is formed. A second sheet member having an area larger than that of the second sheet member was arranged, and the electrode sheet was cooled while the peripheral edge portion of the first sheet member and the second sheet member were adhered under reduced pressure.
As shown in FIG. 2, it can be seen that the maximum amount of warpage of the workpiece due to thermal deformation is reduced to 7 mm.
FIG. 3 shows a perspective image (upper figure) and a side view image (lower figure) of an electrode sheet, which is a work manufactured by a conventional manufacturing method. The conventional electrode sheet was manufactured in the same manner as the manufacturing method of the present disclosure, except that the second sheet member was not placed on the electrode sheet during the cooling process and the electrode sheet was not decompressed. manufactured.
As shown in FIG. 3, due to thermal deformation, the maximum amount of warpage of the work is as large as 31 mm, which does not satisfy the drawing standard value.

Claims (1)

A method for manufacturing an electrode sheet used in a membrane electrode assembly and having a catalyst layer formed on a sheet member, comprising:
forming the electrode sheet having the catalyst layer on the first sheet member by applying the catalyst layer to the first sheet member so as to leave the peripheral edge portion of the first sheet member;
heating the electrode sheet;
a step of cooling the electrode sheet,
In the step of at least cooling the electrode sheet, in a state in which the electrode sheet is decompressed, a second cooling layer having an area larger than that of the catalyst layer is formed on the surface of the first sheet member on which the catalyst layer is formed. and bonding the peripheral portion of the first sheet member to the second sheet member.

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