WO2008102578A1

WO2008102578A1 - Fuel cell, laminate for fuel cell, and method of manufacturing the same

Info

Publication number: WO2008102578A1
Application number: PCT/JP2008/050474
Authority: WO
Inventors: Julien Roussel
Original assignee: Toyota Jidosha Kabushiki Kaisha
Priority date: 2007-02-19
Filing date: 2008-01-09
Publication date: 2008-08-28
Also published as: JP2008204710A

Abstract

A fuel cell including a laminate having a flat surface and high gas permeability is disclosed. The fuel cell includes: an electrolyte membrane (31); an air electrode (32b) provided on one surface of the electrolyte membrane; a fuel electrode (32a) provided on the other surface of the electrolyte membrane, laminates each having a three-dimensional metal mesh sheet (34) and a water repellent paste (33) provided on one surface thereof so as to be filled into a part of the three-dimensional mesh sheet in the thickness direction thereof; and separators (20a, 20b. In the laminates, the three-dimensional mesh sheets (34) come into contact with the corresponding separators (20a, 20b), and the water repellent pastes (33) come into contact with the air electrode (32b) and the fuel electrode (32a).

Description

DESCRIPTION

FUEL CELL, LAMINATE FOR FUEL CELL, AND METHOD OF

MANUFACTURING THE SAME

BACKGROUND OF THE INVENTION

Field of the Invention

The present invention relates to a fuel cell, a laminate for a fuel cell, and a method of manufacturing the same .

Description of Related Art A fuel cell is formed by laminating a plurality of cells each having an electrolyte membrane-electrode assembly, which includes an electrolyte membrane, an air electrode, and a fuel electrode, interposed between separators that have gas grooves. The separators are provided with flow passages for fuel, an oxidizing agent, and a coolant and manifolds for supplying or discharging fuel, the oxidizing agent, and the coolant to or from the cell.

Conventionally, there has been proposed a gas diffuser including a layer containing an electrically conductive web, carbon black particles, and binder particles (for example, refer to Japanese Patent Application Laid-Open No. 11-273688) . SUMMARY OF THE INVENTION

However, since the conventionally proposed gas diffuser is manufactured by applying a mixture of carbon black particles and binder particles onto the electrically conductive web, the mixture drops down into the conductive web by gravity, which makes it difficult to form a uniform mixture layer on the conductive web. As a result, it is difficult to obtain a sufficient performance of the coated mixture layer.

Accordingly, an object of the invention is to provide a fuel cell including a laminate having a flat surface and high gas permeability, a laminate for a fuel cell, and a method of manufacturing the same.

(1) According to an aspect of the invention, there is provided a fuel cell including: an electrolyte membrane; an air electrode that is provided on one surface of the electrolyte membrane; a fuel electrode that is provided on the other surface of the electrolyte membrane; laminates each having a three-dimensional metal mesh sheet and a water repellent paste that is provided on one surface of the three-dimensional metal mesh sheet, wherein the water repellent is filled into a part of the three-dimensional mesh sheet in the thickness direction thereof; and separators, wherein, in the laminates, the three- dimensional mesh sheets come into contact with the corresponding separators, and the water repellent pastes come into contact with the air electrode and the fuel electrode. (2) In the fuel cell according to the above- mentioned aspect, preferably, the separators are flat separators without gas grooves. (3) According to another aspect of the invention, there is provided a laminate for a fuel cell having a three-dimensional metal mesh sheet and a water repellent paste that is provided on one surface of the three-dimensional metal mesh sheet so as to be filled into a part of the three-dimensional mesh sheet in the thickness direction thereof. (4) According to still another aspect of the invention, there is provided a method of manufacturing a laminate of a three-dimensional metal mesh sheet and a water repellent paste, including the steps of: bonding a flexible film to one surface of the three- dimensional metal mesh sheet and pressing the flexible film into a part of the three-dimensional mesh sheet in a thickness direction thereof; applying the water repellent paste onto the other surface of the three-dimensional mesh sheet opposite to the one surface having the flexible film bonded thereto and drying the water repellent paste; and peeling off the flexible film from the three-dimensional mesh sheet. (5) According to yet another aspect of the invention, there is provided a fuel cell, including: an electrolyte membrane; an air electrode that is provided on one surface of the electrolyte membrane; a fuel electrode that is provided on the other surface of the electrolyte membrane; water repellent pastes each of which has one surface coming into contact with the air electrode or the fuel electrode and the other surface having uneven portions therein; and three-dimensional mesh sheets each of which has one surface coming into contact with the corresponding water repellent paste and the other surface coming into contact with a corresponding separator, wherein each of the three-dimensional mesh sheets has openings in a mesh and convex portions of the water repellent paste are formed in a part of the three-dimensional mesh sheet in the thickness direction thereof in the mesh.

According to the above-mentioned aspects of the invention, it is possible to provide a fuel cell including a laminate having high gas permeability, a laminate for a fuel cell, and a method of manufacturing the same.

BRIEF DESCRIPTION OF THE DRAWINGS

Fig. 1 is a cross-sectional view illustrating the structure of a cell forming a fuel cell according to an embodiment of the invention.

Fig. 2 is a diagram illustrating a method of manufacturing a laminate for the fuel cell according to the embodiment of the invention. Fig. 3 is graph illustrating a result of measuring a contact resistance according to an example. DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

Hereinafter, exemplary embodiments of the invention will be described below. The following embodiments are just illustrative, but the invention is not limited thereto. In addition, various modifications and changes of the invention can be made without departing from the scope and spirit of the invention. (Fuel cell) A fuel cell according to the invention includes an electrolyte membrane, an air electrode that is provided on one surface of the electrolyte membrane, a fuel electrode that is provided on the other surface of the electrolyte membrane, laminates each having a three-dimensional metal mesh sheet and a water repellent paste that is provided on one surface of the three-dimensional metal mesh sheet so as to be filled into a part of the three-dimensional mesh sheet in the thickness direction thereof, and separators, wherein, in the laminates, the three-dimensional mesh sheets come into contact with the corresponding separators, and the water repellent pastes come into contact with the air electrode and the fuel electrode.

According to the invention, it is possible to provide a fuel cell including laminates each having a flat surface and high gas permeability by using the laminates each of which includes the three-dimensional metal mesh sheet and the water repellent paste that is provided on one surface of the three-dimensional metal mesh sheet so as to be filled into a part of the three-dimensional mesh sheet in the thickness direction thereof.

That is, in the laminate, the water repellant paste is provided on one surface of the three-dimensional mesh sheet so as to be filled into a part of the three- dimensional mesh sheet in the thickness direction thereof. Therefore, the other part of the three-dimensional mesh sheet in the thickness direction serves as openings, thereby achieving high gas permeability in the laminate. In addition, in the laminates, the water repellent pastes come into contact with the air electrode and the fuel electrode, respectively, -which makes it possible to prevent a membrane-electrode assembly from being damaged. Further, the other surface of the three-dimensional mesh sheet opposite to the surface having the water repellent paste provided thereon is planarized, which makes it possible to improve the contact between the three- dimensional mesh sheet and the separator. According to this structure of the invention, it is possible to achieve a simple fuel cell. In addition, since the number of parts is reduced, it is possible to reduce the thickness of the fuel cell and thus reduce the contact resistance between parts. Hereinafter, exemplary embodiments of the invention will be described below with reference to the accompanying drawings. Fig. 1 is a cross-sectional view illustrating the structure of a cell forming a fuel cell according to an embodiment of the invention.

As shown in Fig. 1, a cell includes an electrolyte membrane 31, an anode electrode 32a that is provided on one surface of the electrolyte membrane 31, a cathode electrode 32b that is provided on the other surface of the electrolyte membrane 31, a pair of laminates 40 each including a three-dimensional metal mesh sheet 34 and a water repellent paste 33 and supporting the anode electrode 32a and the cathode electrode 32b, and a pair of separators 20a and 20b further supporting the laminates 40.

A plurality of cells are laminated to form a polymer electrolyte fuel cell, as a cell stack.

Each of the laminates 40 of the three-dimensional mesh sheet 34 and the water repellent paste 33 is formed by providing the water repellent paste 33 on one surface of the three-dimensional metal mesh sheet 34. In the laminates 40, the three-dimensional mesh sheets 34 come into contact with the separators 20a and 20b, and the water repellent pastes 33 come into contact with the anode electrode 32a and the cathode electrode 32b.

Since the water repellent paste 33 is filled into a part of the three-dimensional mesh sheet 34 in the thickness direction thereof, the other part of the three- dimensional mesh sheet 34 in the thickness direction thereof serves as openings 36, and the openings 36 and the separators 20a and 20b form gas flow passages. In this way, the laminates 40 can maintain high gas permeability.

The term 'thickness direction of the three- dimensional mesh sheet' means the direction in which the components of the fuel cell (for example, an anode and a cathode) are laminated. The term 'filling the water repellent paste into a part of the three-dimensional mesh sheet in the thickness direction thereof means that the water repellent paste is substantially uniformly filled into the meshes of each of three-dimensional mesh sheets in the direction in which the sheet expends.

In this embodiment, the thickness of the water repellent paste filled into the mesh of each of three- dimensional mesh sheets is substantially constant, but the invention is not limited thereto. The thickness of the water repellent paste filled into the mesh of each of three-dimensional mesh sheets may be non-uniform.

Specifically, the water repellent paste is filled into the mesh of the three-dimensional mesh sheet in a concave shape in the thickness direction (in the direction from the three-dimensional mesh sheets to the electrodes) , and the concave portions of the water repellent paste come into contract with the openings 36.

Since the three-dimensional mesh sheets 34, the water repellent pastes 33, and the separators 20a and 20b form gas flow passages, flat separators without the gas grooves shown in Fig. 1 can be 'used as the separators 20a and 20b. The three-dimensional metal mesh sheet 34 may be formed of metal mesh, expanded metal, metal foam, or punching metal .

The water repellent paste 33 may be a mixture of a conductive filler, a binder, a water repellent agent, a surface active agent, and a reinforcing agent. The water repellent paste 33 does not contain a catalyst, such as platinum or carbon containing platinum.

The rigidity of the water repellent paste 33 is preferably lower than that of the three-dimensional mesh sheet 34. In addition, the water repellent paste 33 may have openings that have a smaller diameter than some of the openings 36 of the three-dimensional mesh sheet 34 so as to have gas diffusibility. The conductive filler may be formed of carbon fiber, vapor growth carbon fiber (VGCF) , or carbon black.

For example, fluorine resin or silicon (Si) may be used as the binder.

The electrolyte membrane 31 is made of a polymer ion exchange membrane.

The anode electrode 32a and the cathode electrode 32b are formed of, for example, a porous carbon material (diffusing layer) containing a catalyst, such as platinum, adhered to its surface. A fuel gas is supplied to the anode electrode 32a, and an oxidation gas is supplied to the cathode electrode 32b. The supply of the reactant gases causes an electrochemical reaction in an electrolyte membrane-electrode assembly, thereby obtaining an electromotive force.

The fuel gases include liquid fuels, such as hydrogen gas, methanol, ethanol, gasoline, diesel oil, and liquefied hydrogen, and gas fuels, such as reformed gas, hydrogen containing gas, and natural gas.

For example, air may be used as the oxidation gas. The separators 20a and 20b are formed of a gas- impermeable conductive material. For example, carbon, a conductive rigid resin, and metallic materials, such as aluminum and stainless steel, may be used as the conductive material .

In the above, an electrolyte membrane-electrode assembly is interposed between a pair of laminates 40, which is further interposed between a pair of flat separators. The invention, however, is not limited thereto. Also included in the invention are a fuel cell having the laminate 40 and the flat separator only on the anode electrode 32a (a normal separator is provided on the cathode electrode 32b) and a fuel cell having the laminate 40 and the flat separator only on the cathode electrode 32b (a normal separator is provided on the anode electrode 32a) .

Further, the fuel cell according to the invention includes an electrolyte membrane, an air electrode that is provided on one surface of the electrolyte membrane, a fuel electrode that is provided on the other surface of the electrolyte membrane, water repellent pastes each of which has one surface coming into contact with the air electrode or the fuel electrode and the other surface having uneven portions therein, and three-dimensional mesh sheets each of which has one surface coming into contact with the water repellent paste and the other surface coming into contact with a separator. The three-dimensional mesh sheet has openings in the mesh, and convex portions of the water repellent paste are formed in a part of the three- dimensional mesh sheet in the thickness direction thereof in the mesh.

The term 'the formation of the convex portions of the water repellent paste' means that the convex portions of the water repellent paste are tightly fitted into the mesh of the three-dimensional mesh sheet. Preferably, the fuel cell according to the invention is a polymer electrolyte fuel cell. The fuel cell can be applied to, for example, an in-vehicle power generation system of a fuel cell hybrid vehicle (FCHV) , but the invention is not limited thereto. For example, the fuel cell can be used as a power generation system mounted on an automotive body including various movable bodies (for example, ships and airplanes) and robots and further as a stationary fuel cell.

(Laminate for fuel cell) As described above, the laminate for a fuel cell according to the invention includes the three-dimensional metal mesh sheet and the water repellent paste that is provided on one surface of the three-dimensional metal mesh sheet so as to be filled into a part of the three- dimensional mesh sheet in the thickness direction thereof.

(Method of manufacturing laminate for fuel cell) A method of manufacturing the laminate for a fuel cell according to the invention includes the steps of: bonding a flexible film on one surface of the three- dimensional metal mesh sheet and pressing the flexible film into a part of the three-dimensional mesh sheet in the thickness direction thereof; applying a water repellent paste onto the other surface of the three-dimensional mesh sheet opposite to the one surface having the flexible film bonded thereto and drying the water repellent paste; and peeling off the flexible film from the three-dimensional mesh sheet.

This manufacturing method can provide a laminate for a fuel cell that has high gas permeability and a flat surface.

The manufacturing method will be described in detail with reference to the accompanying drawings. Fig. 2 is a diagram illustrating a method of manufacturing the laminate for a fuel cell according to this embodiment.

As shown in Fig. 2A, first, a flexible film 35 is bonded to one surface of the three-dimensional metal mesh sheet 34. Then, pressure is applied to the bonded structure in the direction of arrows as shown in Fig. 2A. Subsequently, as shown in Fig. 2B, the flexible film 35 is pressed into a part of the three-dimensional mesh sheet 34 in the thickness direction thereof.

For example, the flexible film 35 may be a plastic elastic film, a paraffin film, a polycarbonate film, or a silicon (Si) film.

Then, as shown in Fig. 2C, a water repellent paste 33 (for example, carbon paste) is applied onto the other surface of the three-dimensional mesh sheet 34 opposite the one surface having the flexible film 35 bonded thereto, and then dried.

Next, as shown in Fig. 2D, the flexible film 35 is peeled off from the three-dimensional mesh sheet 34, and a ^■ heat treatment is performed on the three-dimensional mesh sheet 34 and the water repellent paste 33 to obtain the laminate 40 for a fuel cell composed of the three- dimensional mesh sheet 34 and the water repellent paste 33. This manufacturing method using the flexible film 35 makes it possible to obtain the laminate 40 having high gas permeability in which a part of the three-dimensional mesh sheet 34 in the thickness direction thereof serves as openings.

Further, according to this manufacturing method, unlike a method of simply applying a water repellent paste onto the three-dimensional mesh sheet, the water repellent paste 33 does not drip to the other side of the three- dimensional mesh sheet 34, and the other surface of the three-dimensional mesh sheet 34 opposite to the one surface having the water repellent paste 33 applied thereto is planarized. As a result, it is possible to improve the contact between the laminate 40 and the separators 20a and 20b. Examples

As Example, the laminate 40 of the three-dimensional mesh sheet 34 and the water repellent paste 33 shown in Fig. 2 is manufactured by the above-mentioned manufacturing method. In this case, a titanium mesh is used as the three-dimensional mesh sheet 34, a paraffin film having a size of 5 cm x 5 cm is used as the flexible film 35, and a pressure of 1 ton is applied.

As Comparative example, a water repellent paste is applied onto a three-dimensional mesh sheet, without using the flexible film, such that it is fully filled into the three-dimensional mesh sheet, thereby manufacture a laminate .

Then, relative values are obtained by measuring contact resistance per unit area for the laminates in the usual manner, and the measured results are shown in Fig. 3. As can be seen from Fig. 3, the contact resistance of the laminate according to Example is considerably lower than that according to Comparative example. For example, at a pressure of 'a', the contact resistance is improved by about 35%, and at a pressure of ^!b', the contact resistance is improved by about 40%.

Further, according to Example, the surface of the laminate 40 opposite to the surface having the water repellent paste 33 applied thereto is planarized.

Claims

1. A fuel cell comprising: an electrolyte membrane; an air electrode that is provided on one surface of the electrolyte membrane; a fuel electrode that is provided on the other surface of the electrolyte membrane; laminates each having a three-dimensional metal mesh sheet and a water repellent paste that is provided on one surface of the three-dimensional metal mesh sheet so as to be filled into a part of the three-dimensional mesh sheet in the thickness direction thereof; and separators, wherein, in the laminates, the three-dimensional mesh sheets come into contact with the corresponding separators and the water repellent pastes come into contact with the air electrode and the fuel electrode.

2. The fuel cell according to claim 1, wherein the separators are flat separators without gas grooves.

3. A laminate for a fuel cell having a three- dimensional metal mesh sheet and a water repellent paste that is provided on one surface of the three-dimensional metal mesh sheet, wherein the water repellent paste is filled into a part of the three-dimensional mesh sheet in the thickness direction thereof.

4. A method of manufacturing a laminate for a fuel cell, the method comprising the steps of: bonding a flexible film to one surface of a three- dimensional metal mesh sheet and pressing the flexible film into a part of the three-dimensional mesh sheet in a thickness direction thereof; applying a water repellent paste onto the other surface of the three-dimensional mesh sheet opposite to the one surface having the flexible film bonded thereto and drying the water repellent paste; and peeling off the flexible film from the three- dimensional mesh sheet.

5. A fuel cell comprising: an electrolyte membrane; an air electrode that is provided on one surface of the electrolyte membrane; a fuel electrode that is provided on the other surface of the electrolyte membrane; water repellent pastes each of which has one surface coming into contact with the air electrode or the fuel electrode and the other surface having uneven portions therein; and three-dimensional mesh sheets each of which has one surface coming into contact with the corresponding water repellent paste and the other surface coming into contact with a corresponding separator, wherein each of the three-dimensional mesh sheets has openings in a mesh and convex portions of the water repellent paste are formed in a part of the three- dimensional mesh sheet in the thickness direction thereof in the mesh.