JP2024053505A - Unit cell of polymer electrolyte fuel cell (PEMFC) and its manufacturing method - Google Patents

Abstract

[Problem] To provide a new method for manufacturing a unit cell of a polymer electrolyte membrane electrochemical battery (PEMFC) and a unit cell obtained by the method. [Solution] A method for manufacturing a unit cell (10) of an electrochemical battery (100) comprising a membrane electrode assembly (3) and bipolar plates (4) on both sides of the membrane electrode assembly (3), comprising the steps of: (a1) providing a sealing frame (5) on the outer periphery of the membrane electrode assembly (3) to form a frame-integrated membrane electrode assembly (3); (a) placing a UV-curable adhesive on the surface of the bipolar plate (4) that faces the sealing frame (5) when the bipolar plate (4) is placed on both sides of the membrane electrode assembly (3); and (b) forming a joint (A) that joins the frame-integrated membrane electrode assembly (3) and the bipolar plate (4) by curing the UV-curable adhesive. [Selected Figure] FIG. 4

Description

The present invention relates to a unit cell of a polymer electrolyte fuel cell (PEMFC) and a method for manufacturing the same.

There are several types of fuel cells (hereinafter, in the specification, claims, or abstract, they may be referred to as "electrochemical cells"), but among them, polymer electrolyte fuel cells (PEMFCs) have a polymer electrolyte membrane and operate at relatively low temperatures (room temperature to approximately 100°C), making them a fuel cell with a wide range of applicability.

A PEMFC has a structure called a unit cell, which is stacked in series. A unit cell generally includes a membrane electrode assembly (MEA) where an electrochemical reaction occurs, and a bipolar plate (BPP) or a separator. In order to avoid misalignment and maintain airtightness due to the need to stack the cells in series, the MEA and BPP are integrated with a rubber material by injection molding to manufacture the unit cell (see, for example, Patent Document 1).

U.S. Patent Application Publication No. 2021/0083304

However, when performing injection molding, the rubber material must first be heated to its melting point, and residual heat can cause the BPP to deform. Also, the pressure generated during injection molding can damage the BPP. Furthermore, because the MEA is very thin and brittle, the difference in the thermal expansion coefficients of the BPP and MEA can cause excessive pressure to be applied to the MEA, damaging the membrane and resulting in gas leakage. Also, the difference in thermal expansion coefficients can cause misalignment when stacking the cells, resulting in gas leakage.

The present invention aims to manufacture PEMFC unit cells while avoiding the above problems that arise when integrating unit cells.

According to one aspect of the present invention, there is provided a method for manufacturing a unit cell (10) of an electrochemical cell (fuel cell) (100) comprising a membrane electrode assembly (3) and bipolar plates (4) on both sides of the membrane electrode assembly (3), the method including the steps of (a1) providing a sealing frame (5) on the outer periphery of the membrane electrode assembly (3) to form a frame-integrated membrane electrode assembly (3), (a) placing a UV-curable adhesive on the surface of the bipolar plate (4) that faces the sealing frame (5) when the bipolar plate (4) is placed on both sides of the membrane electrode assembly (3), and (b) forming a joint (A) that joins the frame-integrated membrane electrode assembly (3) and the bipolar plate (4) by curing the UV-curable adhesive.

According to one aspect of the present invention, there is provided a unit cell (10) of an electrochemical cell (fuel cell) (100) comprising a membrane electrode assembly (3) and bipolar plates (4) on both sides of the membrane electrode assembly (3), the unit cell (10) comprising a sealing frame (5) on the outer periphery of the membrane electrode assembly (3) and a joint (A) for joining the sealing frame (5) and the bipolar plate (4), the joint (A) being disposed between the membrane electrode assembly (3) and the bipolar plate (4), and a UV-curable adhesive being used for the joint (A).

The present invention provides a method for manufacturing a PEMFC unit cell that avoids problems that arise when integrating unit cells, and a unit cell obtained by this method.

1 is a cross-sectional view showing the configuration of a PEMFC according to an embodiment of the present invention. 1 is a cross-sectional view showing the configuration of a unit cell of a PEMFC according to an embodiment of the present invention. 4 is a flowchart illustrating a method for manufacturing a unit cell according to the present embodiment. 5A to 5C are schematic diagrams illustrating a method for manufacturing a unit cell according to the present embodiment.

The following describes an embodiment of a PEMFC unit cell and a method for manufacturing the unit cell of the present invention with reference to the drawings. The configuration described below is an example (representative example) of the present invention, and is not limited thereto. Note that the "fuel cell" described below is an example of an "electrochemical cell" described in the claims, etc.

(PEMFC)
FIG. 1 shows the configuration of a polymer electrolyte fuel cell (PEMFC) 100 according to this embodiment.
The PEMFC100 of this embodiment is mounted on a moving object such as a vehicle, and supplies driving power to the moving object by generating electricity through a chemical reaction of fuel gas. However, the present invention can be applied not only to moving objects, but also to fuel cells in stationary power generation systems and the like.

As shown in FIG. 1, the PEMFC 100 includes a plurality of unit cells 10 stacked in series, a pair of current collector plates 11, a pair of insulator plates 12, and a pair of end plates 13 arranged on both sides of each cell 10 in the stacking direction. The PEMFC 100 also includes a gas pipe 14 attached to at least one of the end plates 13. The gas pipe 14 communicates with a manifold (not shown).

The unit cells 10, the collector plate 11 on the gas pipe 14 side, the insulator plate 12, and the end plate 13 are connected to the gas pipe 14 and have six through holes P1 to P6 that penetrate the unit cells 10 in the stacking direction. Fuel gas, oxidant gas, and cooling water are supplied and discharged through these through holes P1 to P6.

The PEMFC100 includes seals 15 between each of the components, the collector plate 11, the insulator plate 12, the end plate 13, and the gas pipe 14. The seals 15 are, for example, O-rings that surround the outside of the through-holes P1 to P6, and are made of an elastomer material. The seals 15 come into contact with the adjacent components to seal the outer peripheries of the through-holes P1 to P6, thereby preventing gas leakage and cooling water leakage from the through-holes P1 to P6.

The pair of end plates 13 are fastened by fastening members such as bolts and nuts, and a fastening force acts on the PEMFC100 in the stacking direction of each component of the PEMFC100 sandwiched between the end plates 13. This fastening force fixes the stacking structure of each component between the end plates 13, and seals the fuel gas, oxidizer gas, and coolant water inside the PEMFC100.

(Unit Cell 10)
FIG. 2 shows the configuration of a unit cell 10 .
The unit cell 10 includes a membrane electrode assembly (MEA) 3 in which an electrochemical reaction occurs, a pair of bipolar plates (BPP: Bi-Polar Plates) 4 arranged on both sides of the MEA 3, and a sealing frame 5 integrated with the MEA so as to surround the outer periphery of the MEA 3. The sealing frame 5 may include a sealing lip structure 5a at a position surrounding the outer periphery of the MEA 3. The MEA 3 functions as an electrode and includes a catalyst coated electrolyte membrane (CCM: Catalyst Coated Membrane) 1 and a pair of gas diffusion layers (GDL: Gas Diffusion Layer) 2. The CCM 1 includes a catalyst layer 1a and an electrolyte membrane 1b. The pair of GDLs 2 sandwich the CCM 1. In addition, the pair of GDLs 2 are further sandwiched from the outside by the BPP 4.

The electrolyte membrane 1b of the CCM1 is an ion-conductive polymer electrolyte membrane, and the polymer electrolyte membrane is coated on its periphery with a catalyst layer 1a. Examples of polymer electrolytes that can be used for the electrolyte membrane 1b include perfluorosulfonic acid polymers such as Nafion (registered trademark) and Aquivion (registered trademark); aromatic polymers such as sulfonated polyether ether ketone (SPEEK) and sulfonated polyimide; and aliphatic polymers such as polyvinyl sulfonic acid and polyvinyl phosphoric acid.

From the viewpoint of improving durability, the electrolyte membrane 1b can be a composite membrane in which a porous substrate is impregnated with a polymer electrolyte. The porous substrate is not particularly limited as long as it has pores capable of supporting the polymer electrolyte, and a membrane in a porous, woven, nonwoven, fibril, or other form can be used. The material of the porous substrate is also not particularly limited, but from the viewpoint of increasing ion conductivity, the above-mentioned polymer electrolytes can be used. Among them, fluorine-based polymers such as polytetrafluoroethylene, polytetrafluoroethylene-chlorotrifluoroethylene copolymer, and polychlorotrifluoroethylene have excellent strength and shape stability.

The MEA 3 functions as an electrode. One side of the MEA 3 is the anode, also called the fuel electrode. The other side is the cathode, also called the air electrode. Hydrogen gas is supplied to the anode as the fuel gas, and air containing oxygen gas is supplied to the cathode as the oxidant gas.

At the anode, a reaction occurs in which hydrogen gas (H ₂ ) produces electrons (e ^- ) and protons (H ⁺ ). The electrons move to the cathode via an external circuit (not shown). This movement of electrons generates a current at the external electrode. The protons move to the cathode via the CCM1.

At the cathode, oxygen ions (O ^2- ) are generated from oxygen gas (O ₂ ) by electrons transferred from an external circuit. The oxygen ions combine with protons (2H ⁺ ) transferred from the CCM1 to become water (H ₂ O).

The catalyst layer 1a of the CCM1 coats the electrolyte membrane 1b from the outside, promoting the reaction of hydrogen gas and oxygen gas with a catalyst. The catalyst layer 1a includes a catalyst, a carrier that supports the catalyst, and an ionomer that covers these.

Examples of catalysts include metals such as platinum (Pt), ruthenium (Ru), iridium (Ir), rhodium (Rh), palladium (Pd), and tungsten (W), as well as mixtures and alloys of these metals. Among these, platinum, mixtures and alloys containing platinum are preferred from the standpoint of catalytic activity, resistance to poisoning by carbon monoxide, heat resistance, and the like.

Examples of carriers include conductive porous carbon with fine pores, such as mesoporous carbon and acetylene black. Mesoporous carbon is preferred from the viewpoints of good dispersibility, large surface area, and little particle growth at high temperatures even when a large amount of catalyst is supported.

As the ionomer, an ionically conductive polymer electrolyte similar to CCM1 can be used.

The GDL2 can diffuse the fuel gas and oxidant gas supplied to the unit cell 10 uniformly over the entire surface of the catalyst layer 1a.

The GDL 2 can be formed by placing a gas diffusion layer sheet (GDL sheet) as the outermost layer of the MEA 3. Examples of gas diffusion layer sheets include porous fiber sheets such as carbon fibers that have electrical conductivity, gas permeability, and gas diffusivity, as well as metal sheet materials such as foamed metal and expanded metal.

The sealing frame 5 is integrated with the MEA 3 by injection molding to form a frame-integrated MEA. The sealing frame 5 is provided to surround the outer periphery of the MEA 3. Since the MEA 3 is very thin and fragile, the sealing frame 5 functions as a support for the MEA 3. The sealing frame 5 also functions as a sealant that seals the fuel gas and oxidant gas between the lower unit cell and the upper unit cell.

A resin with low electrical conductivity can be used as the material for the sealing frame 5. There are no particular limitations on the resin material, and examples include polyphenylene sulfide (PPS), glass-filled polypropylene (PP-G), polystyrene (PS), silicone resin, and fluorine-based resin.

The sealing frame 5 functions as a sealant and is preferably provided with a convex sealing lip structure 5a at a position surrounding the outer periphery of the MEA 3. The sealing lip structure 5a maintains airtightness between the MEA 3 and the BPP 4 when multiple unit cells 10 are stacked in series.

When multiple unit cells 10A and 10B are stacked in series as shown in FIG. 2, the BPP4 of another unit cell 10B is adjacent to the upper part of the frame-integrated MEA of the unit cell 10A. It is preferable that the sealing lip structure 5a protrudes from the cathode side surface of the BPP4 of the unit cell 10B. Here, the sealing lip structure 5a of the unit cell 10A is arranged so as to contact the BPP4 of the other unit cell 10B, maintaining the airtightness of the MEA3 "between" both unit cells 10A and 10B.

Meanwhile, a joint A formed from a UV-curable adhesive is placed between the MEA 3 and BPP 4 of each unit cell 10. During the manufacturing stage, the UV-curable adhesive is placed on the upper surface of the BPP 4 (facing the MEA 3), and in a subsequent step, UV irradiation is performed using a UV irradiation device to form the joint A. This joint A integrates the BPP 4 and the frame-integrated MEA, maintaining airtightness between the MEA 3 and BPP 4 "inside" each unit cell 10.

From the viewpoint of avoiding misalignment, it is preferable to arrange the sealing lip structure 5a so that it overlaps with the arrangement position of the joint A made of UV-curable adhesive on the BPP when viewed from the stacking direction. In other words, there is a joint A formed so as to be sandwiched between the sealing frame 5 and the BPP 4 directly below the sealing lip structure 5a.

In order to facilitate easy alignment, the sealing frame 5 may be made of a transparent material. From the same viewpoint, the UV-curable adhesive A may also be made of a transparent material.

UV-curing adhesives are adhesives that polymerize and harden in a short time due to ultraviolet (UV) energy emitted from an ultraviolet irradiation device. There are no particular limitations on the material of the UV-curing adhesive, so long as it can maintain sufficient airtightness when the joint is formed.

Examples of UV-curable adhesives include acrylic resins and epoxy resins. When acrylic resins are irradiated with ultraviolet light, they begin to polymerize and harden through a radical reaction. When epoxy resins are irradiated with ultraviolet light, they generate cations (acids) and begin to polymerize and harden.

Regarding the relative positions of the sealing lip structure 5a, the joint, the MEA 3, and the BPP 4, the sealing lip structure 5a is positioned so as to maintain airtightness of the reactant gas at either the cathode or the anode of the MEA 3. At the other electrode, a joint made of a UV-curable resin is positioned so as to maintain airtightness of the reactant gas.

From the viewpoint of preventing gas leakage, it is preferable to provide a sealing lip structure 5a on the cathode of the MEA 3 and a joint on the anode. If gas leakage occurs, gas that is not consumed in power generation will leak to the outside, and the gas consumption efficiency will decrease, so it is important to consider gas leakage. Since hydrogen gas (H ₂ ) passing through the anode has a smaller molecular weight than oxygen gas (O ₂ ), arranging a joint that maintains better airtightness on the anode side makes it less likely for gas leakage to occur.

Here, from the viewpoint of performing UV irradiation from above for a predetermined time and amount to form a joint during manufacturing, it is preferable that the sealing frame 5 has light transmission properties. Also, from the viewpoint of alignment, it is preferable that the sealing frame 5 has light transmission properties. Also, the UV-curable adhesive may be colored. When viewed from above the sealing frame 5 having light transmission properties, it is easy to identify the colored UV-curable adhesive, and it is easy to align the sealing lip structure 5a of the sealing frame 5 with the UV-curable adhesive.

The light transmission characteristic of the sealing frame 5 is not particularly limited with respect to light transmittance, so long as it is suitable for UV irradiation from above the sealing frame 5 to pass through the sealing frame 5 and harden the curable adhesive to form joint A. The sealing frame 5 and joint A are aligned so that they overlap when viewed from the stacking direction. If the sealing frame 5 has a high light transmittance, it is easy to confirm the position of the UV curable adhesive on the BPP 4 below. This makes alignment easier.

(BPP4)
The BPP4 is also called a separator. The BPP4 has the functions of separating air containing oxygen gas ( _O2 ) from hydrogen gas ( _H2 ), conducting electrons, discharging water produced by the reaction, and removing heat generated by power generation by circulating cooling water.

A plurality of recesses 4a communicating with the through holes P1 to P6 are provided on the surface of the BPP 4. Among the recesses 4a of the BPP 4, the recesses 4a on the side facing the MEA 3 serve as fuel gas supply paths, supplying hydrogen gas (H ₂ ) to the anode side of the MEA 3 and oxygen gas (O ₂ ) to the cathode side. The recesses 4a on the side not facing the MEA 3 are also used as passages for cooling water when cooling water is used to cool the PEMFC 100.

A conductive material is used as the material for BPP4. Examples of conductive materials include metals such as stainless steel, or carbon.

(Method of Manufacturing Unit Cell 10)
FIG. 3 is a flow chart showing a method for manufacturing the unit cell 10.
Referring to FIG. 3, the operation is as follows: in step S1001, the MEA 3 is integrated with the sealing frame 5 by injection molding to prepare a frame-integrated MEA.

In step S1002, BPP4 is fabricated. In step S1002, after BPP4 is fabricated, a UV-curable adhesive is placed on one end of the fabricated BPP4. Note that the operations in steps S1001 and S1002 are different processes (separate processes), and there is no chronological order to the operations. Either operation may be performed first, or they may be performed in parallel.

Next, in step S1003, the frame-integrated MEA produced in step S1001 and the BPP4 produced in step S1002 are assembled, and then the UV-curable adhesive is irradiated with UV to form a joint A for integration. By forming the joint A, airtightness is generated between the BPP4 and the MEA3 in the unit cell 10. Here, when assembling the frame-integrated MEA and the BPP4, they are aligned so that the sealing lip structure 5a of the sealing frame 5 and the UV-curable adhesive overlap when viewed from the stacking direction.
Through the above operations, the unit cell 10 is manufactured.

FIG. 4 is a schematic diagram illustrating a method for manufacturing a unit cell according to this embodiment.
The upper left, lower left, and right diagrams in Fig. 4 correspond to steps S1001, S1002, and S1003, respectively, in Fig. 3. The left ends of the frame-integrated MEA fabricated in step S1001, the BPP4 fabricated in step S1002, and the unit cell 10 fabricated in step S1003 are each omitted.

After the operations of steps S1001 and S1002, in step S1003, both components are assembled and then irradiated with UV from above onto the UV-curable adhesive to form a joint and integrate the components to produce the unit cell 10. The time of UV irradiation is adjusted by the speed of the belt conveyor, but as described above, the irradiation time can be shortened by using the UV-curable adhesive and sealing frame 5 that have light-transmitting properties.

In this way, by assembling the two assemblies obtained in steps S1001 and S1002 in step S1003, it is possible to avoid the problems that arise in the process of manufacturing a unit cell by integrating the MEA and BPP by injection molding, as in the conventional technology.

In other words, when the MEA and BPP are injection molded at the same time as in the conventional technology, problems such as deformation and damage of the BPP caused by residual heat of the rubber material, damage to the MEA membrane due to differences in thermal expansion coefficient, gas leakage, and misalignment can be avoided by the manufacturing method of the unit cell 10 described above.

(Method of manufacturing PEMFC100)
The PEMFC 100 is manufactured by disposing the BPP 4 on both sides of the MEA 3. As shown in Figures 2 to 4, the unit cell 10 in an actual production line has the BPP 4 disposed on one side of the MEA 3, so that the MEA 3 sandwiched "between" a plurality of unit cells 10 has the BPP 4 disposed on both sides. The MEA 3 is obtained, for example, by coating both sides of the electrolyte membrane with ink containing a catalyst layer 1a and drying it to produce a CCM 1, and then bonding a gas diffusion layer sheet to the catalyst layer 1a of the CCM 1 to form a gas diffusion layer (GDL) 2.

The above describes preferred embodiments of the present invention, but the present invention is not limited to these embodiments, and various modifications and variations are possible within the scope of the gist of the invention.

1: CCM, 1a: catalyst layer, 1b: electrolyte membrane, 2: GDL, 3: MEA, 4: BPP, 4a: recess, 5: sealing frame, 5a: sealing lip structure, 10: unit cell, A: joint

Claims (7)

A method for manufacturing a unit cell (10) of an electrochemical cell (100) comprising a membrane electrode assembly (3) and bipolar plates (4) on both sides of the membrane electrode assembly (3), comprising the steps of:
a step (a1) of providing a sealing frame (5) on an outer peripheral edge of the membrane electrode assembly (3) to form a frame-integrated membrane electrode assembly (3);
(a) placing a UV-curable adhesive on a surface of the bipolar plate (4) that faces the sealing frame (5) when the bipolar plate (4) is placed on both sides of the membrane electrode assembly (3);
(b) forming a joint (A) for joining the frame-integrated membrane electrode assembly (3) and the bipolar plate (4) by curing the UV-curable adhesive;
A manufacturing method comprising: The manufacturing method according to claim 1, in which the step (a1) of forming the frame-integrated membrane electrode assembly (3) and the step (a) of placing the UV-curable adhesive are performed in separate steps, and then, in the step (b) of forming the joint (A), the joint (A) is formed by irradiating the UV-curable adhesive with UV light. The sealing frame (5) has a sealing lip structure (5a) protruding from the cathode side surface of the bipolar plate (4).
The method of claim 1 . The position of the sealing lip structure (5a) overlaps with the position of the joint portion (A) when viewed from the stacking direction.
The method according to claim 3. The UV-curable adhesive is disposed on the anode side surface of the bipolar plate (4).
The method of claim 1 . The manufacturing method according to claim 1, wherein the sealing frame (5) has light-transmitting properties. A unit cell (10) of an electrochemical cell (100) comprising a membrane electrode assembly (3) and bipolar plates (4) on both sides of the membrane electrode assembly (3),
a sealing frame (5) on the outer periphery of the membrane electrode assembly (3);
a joint (A) for joining the sealing frame (5) and the bipolar plate (4), the joint (A) being disposed between the membrane electrode assembly (3) and the bipolar plate (4);
A UV-curable adhesive is used for the joint (A),
Unit cell (10).

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