JP2024066263A - Solid polymer electrolyte fuel cell and method for producing solid polymer electrolyte fuel cell - Google Patents

Abstract

[Problem] To provide a polymer electrolyte fuel cell with improved durability while maintaining the proton transport resistance of the polymer electrolyte membrane. [Solution] A polymer electrolyte fuel cell according to an embodiment has a proton-conductive polymer electrolyte membrane, a fuel electrode disposed adjacent to one side of the polymer electrolyte membrane, and an oxidizer electrode disposed adjacent to the other side of the polymer electrolyte membrane. The polymer electrolyte membrane is a composite membrane comprising a first membrane containing a first electrolyte material and a second membrane containing a second electrolyte material. The second membrane covers a portion of the first membrane. The oxygen permeability of the second membrane is smaller than that of the first membrane. The tensile strength of the second membrane is greater than that of the first membrane. [Selected Figure] Figure 1

Description

Embodiments of the present invention relate to a polymer electrolyte fuel cell and a method for manufacturing a polymer electrolyte fuel cell.

In a fuel cell, a fuel gas containing hydrogen is introduced to the fuel electrode, and an oxidant gas containing oxygen is introduced to the oxidant electrode, and electricity and heat are obtained by an electrochemical reaction. In a solid polymer electrolyte fuel cell, a polymer membrane is used as the electrolyte, and electrodes are placed on both sides of the membrane. The electrodes are obtained by applying a catalyst layer onto a gas diffusion layer. The catalyst used is a precious metal such as platinum supported on carbon particles (see Patent Document 7, etc.).

Conventional polymer electrolyte membranes are made of perfluorosulfonic acid and have a thickness of 15 to 100 μm (Patent Document 1). Both the main chain and the side chain of perfluorosulfonic acid are fluorinated, that is, hydrogen bonded to carbon is replaced with fluorine, so it is chemically stable but has the disadvantage of being expensive. In solid polymer electrolyte fuel cells, the polymer electrolyte membrane serves as a proton conductor and also has a sealing function for reactant gases. If the polymer electrolyte membrane is damaged, cross leakage of reactant gases occurs, making the system inoperable. To put fuel cell systems into practical use, highly durable polymer electrolyte membranes that can withstand long-term operation are required.

Completely unfluorinated hydrocarbon-based membranes have been developed for perfluorosulfonic acid. To improve chemical stability, it is common to use compounds containing aromatics in the main chain, such as polyether ether ketone (see Patent Document 2). Patent Document 3 reports a polymer electrolyte membrane made of a polyether sulfone copolymer. These hydrocarbon-based membranes can be produced inexpensively because they are not fluorinated, and are said to cost 1/10 of the cost of perfluorosulfonic acid membranes. However, they have low resistance to hydrogen peroxide generated during the reduction reaction of oxygen, and the polymer membrane can be damaged after several thousand hours of operation, causing cross leakage, so improvements are desired.

Many researchers have studied and reported on the mechanism by which polymer membranes deteriorate. It is believed that the main cause is chemical deterioration due to OH radicals that are generated when hydrogen peroxide dissociates (see Patent Document 4). Hydrogen peroxide is thought to be generated by oxygen leaking from the oxidizer electrode to the fuel electrode, and by a two-electron reaction at the oxidizer electrode. This is explained in detail below.

In a typical fuel cell reaction at the oxidizer electrode, protons react with oxygen to produce water, as shown in formula (1). This reaction is called a four-electron reaction because four electrons are involved.
4H ⁺ +O ₂ +4e ⁻ → 2H ₂ O (1)

Although the polymer membrane has a gas sealing function, even when it is healthy, there are small gas leaks. This occurs when the reactive gas dissolves in the moisture contained in the polymer membrane and diffuses. When oxygen leaks from the oxidizer electrode to the fuel electrode, it reacts with hydrogen in the presence of the fuel electrode catalyst, producing hydrogen peroxide through the reaction shown in formula (2) as an elementary process of the reaction shown in formula (1). This reaction is called a two-electron reaction because two electrons are involved.
2H ⁺ +O ₂ +2e ⁻ → H ₂ O ₂ (2)

One of the techniques for preventing the generation of hydrogen peroxide from cross-leaked oxygen and hydrogen in these reactions is the application of a reactive gas permeation prevention layer (see Patent Document 5). This prevents oxygen cross-leaking and suppresses the generation of hydrogen peroxide by consuming cross-leaked oxygen in the catalyst in the reactive gas permeation prevention layer. It has also been found that applying the reactive gas permeation prevention layer, especially to the fuel electrode side, is even more effective.

Patent Document 6 also introduces a technique for preventing the enlargement of pinholes by laminating multiple polymer electrolyte membranes. With regard to chemical deterioration, even if the same type of membrane is laminated together, the durability can be expected to be improved due to the membrane thickness effect. Patent Document 7 introduces a method for suppressing the amount of methanol permeation and improving mechanical strength by laminating polymer electrolyte membranes in a fuel cell that uses liquid organic fuel such as methanol as fuel. In this Patent Document 7, a polymer electrolyte membrane of a fluorocarbon resin is laminated with a polyindole membrane or polyaniline membrane having an NH group, or a hydrocarbon polymer membrane such as polystyrene sulfonic acid. The hydrocarbon polymer membrane has the advantage of being able to suppress the amount of oxygen permeation more than a polymer electrolyte membrane of a fluorocarbon resin, and the advantage of the superior mechanical strength of the fluorocarbon polymer electrolyte membrane.

Japanese Patent Application Laid-Open No. 6-342665 Japanese Patent Application Laid-Open No. 6-93114 Japanese Patent Application Laid-Open No. 10-21943 Patent No. 3271801 JP 2005-149859 A Japanese Patent Application Laid-Open No. 6-84528 JP 2004-335250 A JP 2008-47315 A

In solid polymer fuel cells, the performance and durability of polymer electrolyte membranes are an issue. Perfluorosulfonic acid membranes have high proton conductivity and low humidity dependency, but they also have high gas permeability and are prone to chemical degradation due to radical species generated by oxygen cross-leakage. On the other hand, non-fluorinated aromatic hydrocarbon-based membranes can suppress oxygen cross-leakage, which is the cause of radical species generation, due to intermolecular interactions with aromatics, but their proton conductivity is highly humidity-dependent, resulting in high proton transport resistance under low humidity conditions. In addition, aromatic hydrocarbon-based membranes are poor in flexibility and difficult to make into thin films.
In the case of immersion of a polymer electrolyte membrane as described in Patent Document 8, a perfluorosulfonic acid membrane is formed on the front surface of a hydrocarbon electrolyte, so that an increase in the electrolyte membrane thickness at the location where the electrode reaction occurs is an issue. In other words, there is a problem that the increase in membrane thickness accompanying the composite increases the proton transport resistance, resulting in a decrease in battery characteristics.

An embodiment of the present invention provides a polymer electrolyte fuel cell that has improved durability while maintaining the proton transport resistance of the polymer electrolyte membrane.

The solid polymer electrolyte fuel cell according to the embodiment has a proton-conductive polymer electrolyte membrane, a fuel electrode disposed adjacent to one side of the polymer electrolyte membrane, and an oxidizer electrode disposed adjacent to the other side of the polymer electrolyte membrane, and the polymer electrolyte membrane is a composite membrane including a first membrane containing a first electrolyte material and a second membrane containing a second electrolyte material, the second membrane covers a part of the first membrane, the oxygen permeability of the second membrane is smaller than the oxygen permeability of the first membrane, and the tensile strength of the second membrane is greater than the tensile strength of the first membrane.

According to an embodiment of the present invention, it is possible to provide a polymer electrolyte fuel cell that has improved durability while maintaining the proton transport resistance of the polymer electrolyte membrane.

FIG. 1 is a perspective view showing an example of a polymer electrolyte fuel cell according to an embodiment. FIG. 2 is an exploded perspective view showing a polymer electrolyte membrane, a fuel electrode, and an oxidizer electrode in the solid polymer fuel cell of the first embodiment. FIG. 3 is an exploded perspective view showing a polymer electrolyte membrane and a fuel electrode in a solid polymer fuel cell according to a second embodiment. FIG. 4 is an exploded perspective view showing a polymer electrolyte membrane and an oxidizer electrode in a solid polymer fuel cell according to a third embodiment. FIG. 5 is an exploded perspective view showing a polymer electrolyte membrane, an oxidizer electrode, and a separator in a solid polymer fuel cell according to a fourth embodiment. 6A and 6B are perspective views illustrating a method for manufacturing a polymer electrolyte fuel cell in a fifth embodiment, in which (A) shows a state in which a first membrane is pressed with a mold, (B) shows a first membrane having a recess formed on one surface, (C) shows a state in which a second membrane is fitted into the first membrane, and (D) shows a polymer electrolyte membrane which is a composite membrane of the first membrane and the second membrane. 7A and 7B are perspective views illustrating a method for manufacturing a polymer electrolyte fuel cell in a sixth embodiment, in which (A) shows a state in which a first membrane having a recess formed on one surface is covered with a mask material, (B) shows a state in which a coating liquid is sprayed onto the first membrane partially covered with the mask material, and (C) shows a polymer electrolyte membrane which is a composite membrane of the first membrane and the second membrane.

Various embodiments will be described below with reference to the drawings. Each figure is a schematic diagram to facilitate understanding of the embodiment, and the shapes, dimensions, ratios, etc. may differ from the actual ones in some places, but these can be appropriately modified in design by taking into account the following explanations and known technologies.

Figure 1 is a perspective view showing an example of a solid polymer fuel cell according to an embodiment. As shown in Figure 1, the solid polymer fuel cell 1 has a proton-conductive polymer electrolyte membrane 10, a fuel electrode 20 arranged adjacent to one side of the polymer electrolyte membrane 10, and an oxidizer electrode 30 arranged adjacent to the other side of the polymer electrolyte membrane 10. That is, the fuel electrode 20 and the oxidizer electrode 30 are thermally compressed to both sides of the polymer electrolyte membrane 10.

The fuel electrode 20 preferably includes a hydrogen inlet 2A for introducing hydrogen from outside the polymer electrolyte fuel cell 1. The oxidizer electrode 30 preferably includes an air inlet 3 for introducing air from outside the polymer electrolyte fuel cell 1. Such a polymer electrolyte fuel cell 1 is configured to introduce hydrogen and air from the outside and generate electricity using the hydrogen and oxygen in the air.

The fuel electrode 20 and the oxidizer electrode 30 include, for example, a carbon support carrying catalytic metal particles, and an ionomer. Platinum and platinum alloys can be used as catalytic metal particles. More specifically, platinum, platinum-ruthenium alloy, platinum-nickel alloy, platinum-cobalt alloy, etc. can be used.

Representative examples of ionomers include polymer electrolytes with proton conductivity. Particularly preferred examples include Nafion (registered trademark), Flemion (registered trademark), and Aciplex (registered trademark). In addition, the ionomers can be composed of electrolytes capable of transporting protons, such as copolymers of trifluorostyrene derivatives, polybenzimidazole impregnated with phosphoric acid, aromatic polyether ketone sulfonic acid, and aliphatic hydrocarbon resins. Among these, Nafion (registered trademark) is particularly preferred.

The polymer electrolyte membrane 10 is a composite membrane comprising a first membrane 11 and a second membrane 12. The first membrane 11 and the second membrane 12 are described below.

The first membrane 11 includes a first electrolyte material. The first electrolyte material is preferably a polymer compound having a fluorocarbon as a main skeleton. A specific example of a polymer compound having a fluorocarbon as a main skeleton is perfluorosulfonic acid. Perfluorosulfonic acid is a polymer obtained by copolymerizing tetrafluoroethylene and perfluorosulfonyl ethoxyvinyl ether, followed by hydrolysis. Specific examples of perfluorosulfonic acid include Nafion (registered trademark), Flemion (registered trademark), and Aciplex (registered trademark). Among them, Nafion (registered trademark) is preferred.
Perfluorosulfonic acid has a high dissociation degree of sulfonic acid group due to the high electronegativity of fluorine. Therefore, when perfluorosulfonic acid is used, it has the characteristics of having high proton conductivity and low humidity dependency of proton transport resistance. That is, by using perfluorosulfonic acid for the first membrane 11, the proton transport resistance in the first membrane 11 can be kept small, and the proton transport resistance in the first membrane 11 can be kept small even under low humidity conditions.

The second membrane 12 contains a second electrolyte material. The second electrolyte material is preferably a polymer compound having an aromatic main skeleton. Such a second electrolyte material has the property that oxygen is unlikely to pass between molecules due to intermolecular interactions in the aromatic portion. Therefore, the gas barrier property of the second membrane 12 is improved, and cross leakage of oxygen in the second membrane 12 can be suppressed. As a result, the generation of hydrogen peroxide in the fuel electrode 20 can be suppressed.
Furthermore, since the second membrane 12 contains the second electrolyte material, the tensile strength of the second membrane 12 is increased. That is, the mechanical strength of the polymer electrolyte membrane 10 including the second membrane 12 can be increased.

Specific examples of polymer compounds having an aromatic backbone include sulfonated aromatic polymers and polyether ether ketones. Among them, sulfonated aromatic polymers are preferred. Sulfonated aromatic polymers have higher proton transport capacity than non-sulfonated polymer compounds, and can maintain a low proton transport resistance in the second membrane 12. In addition, membranes of sulfonated aromatic polymers have better dimensional stability against dry-wet cycles than membranes of polymer compounds having a fluorocarbon backbone. Therefore, in the polymer electrolyte membrane 10 in the embodiment, since it is a composite membrane of the first membrane 11 and the second membrane 12, mechanical deterioration can be suppressed more than when the electrolyte membrane is made of the first membrane 11 alone.

In the polymer electrolyte membrane 10, the second membrane 12 covers a portion of the first membrane 11. As described above, the first electrolyte material contained in the first membrane 11 has high proton conductivity. By having the second membrane 12 cover only a portion of the first membrane 11, an increase in the proton transport resistance in the polymer electrolyte membrane 10 can be suppressed compared to a case in which the second membrane 12 covers the entire surface of the first membrane 11. In other words, the proton transport resistance of the polymer electrolyte membrane 10 as a whole can be kept small.
Furthermore, by adopting a structure in which the second membrane 12 covers a portion of the first membrane 11, the thickness of the polymer electrolyte membrane 10 can be made smaller than when the second membrane 12 covers the entire surface of the first membrane 11. That is, it is possible to make the polymer electrolyte membrane 10 thinner. The thickness of the polymer electrolyte membrane 10 is preferably 200 μm or less, more preferably 100 μm or less, and even more preferably 50 μm or less. On the other hand, from the viewpoint of maintaining the mechanical strength of the polymer electrolyte membrane 10, the thickness of the polymer electrolyte membrane 10 is preferably 1 μm or more, more preferably 5 μm or more, and even more preferably 10 μm or more.

From the viewpoint of maintaining a small proton transport resistance of the polymer electrolyte membrane 10, the thickness of the second membrane 12 is preferably 50 μm or less, more preferably 30 μm or less, and even more preferably 10 μm or less. Furthermore, from the viewpoint of maintaining the mechanical strength of the polymer electrolyte membrane 10, the thickness of the second membrane 12 is preferably 0.1 μm or more, more preferably 1 μm or more, and even more preferably 5 μm or more.

From the viewpoint of maintaining a small proton transport resistance of the polymer electrolyte membrane 10, the ratio of the thickness of the second membrane 12 to the thickness of the polymer electrolyte membrane 10 is preferably 50% or less, more preferably 30% or less, and even more preferably 20% or less. Furthermore, from the viewpoint of maintaining the mechanical strength of the polymer electrolyte membrane 10, the ratio of the thickness of the second membrane 12 to the thickness of the polymer electrolyte membrane 10 is preferably 0.1% or more, more preferably 1% or more, and even more preferably 10% or more.

In the polymer electrolyte membrane 10, the oxygen permeability of the second membrane 12 is smaller than that of the first membrane 11. That is, a portion of the first membrane 11 is covered with the second membrane 12, which has a smaller oxygen permeability. In this way, the polymer electrolyte membrane 10 can suppress oxygen cross-leakage compared to a case where the first membrane 11 is used as an electrolyte membrane alone.

Oxygen permeability can be measured in accordance with "Gas permeability test method for plastic films and sheets (JIS K7126-2:2006 Method B (isobaric method))" at a temperature of 23°C and a relative humidity of 60%. The measurement device used is an oxygen permeability measuring device (OX-TRAN 2/20, manufactured by Modern Controls).

In the polymer electrolyte membrane 10, the tensile strength of the second membrane 12 is greater than that of the first membrane 11. That is, a portion of the first membrane 11 is covered with the second membrane 12, which has a greater tensile strength. In this way, the polymer electrolyte membrane 10 has superior dimensional stability and is less susceptible to mechanical deterioration, compared to an electrolyte membrane consisting of the first membrane 11 alone. The details are as follows.

The power generation reaction causes the polymer electrolyte fuel cell 1 to reach a temperature of 60 to 80°C, and the humidity also becomes high due to the water produced. Some of the first electrolyte materials contained in the first membrane 11 have the property of swelling when they absorb moisture. The swelling of the first membrane 11 causes the fuel electrode 20 or the oxidizer electrode 30 to be pushed outward, and therefore in the polymer electrolyte fuel cell 1 whose exterior is constrained by the separator 40 or the like, stress is generated between the fuel electrode 20 and the separator 40, etc. When the polymer electrolyte fuel cell 1 repeatedly starts and stops generating power, and the temperature and humidity repeatedly change, stress is repeatedly generated and released, and mechanical deterioration progresses.
Therefore, by covering a part of the first membrane 11 having a low tensile strength with the second membrane 12 having a high tensile strength, the dimensional stability of the polymer electrolyte membrane 10 can be improved and mechanical deterioration can be suppressed.

In this embodiment, the material used for the separator 40 is preferably conductive porous carbon. By using such a material, the cooling water can be circulated inside the separator 40 under negative pressure. This allows the water generated by the power generation reaction to be forcibly drawn into the cooling water flow path 4B, preventing flooding.

The tensile strength can be measured by carrying out a tensile test as follows.
The first film 11 is cut into a width of 20 mm to prepare a sample. Both ends of the cut sample are clamped in the chuck of a Shimadzu Autograph AG 10kNX (manufactured by Shimadzu Corporation). The sample is pulled at a pulling speed of 1 m/min, and the maximum stress value of the stress-strain curve is taken as the tensile strength of the first film 11.
The tensile strength of the second film 12 can be measured in the same manner as the tensile strength of the first film 11 .

The proton transport resistance of the polymer electrolyte membrane 10 at low humidity increases by the amount that the first membrane 11 is covered with the second membrane 12. Therefore, from the viewpoint of maintaining a small proton transport resistance, it is preferable to make the area of the first membrane 11 covered with the second membrane 12 as small as possible. Specifically, the ratio of the area occupied by the second membrane 12 to the surface area of the polymer electrolyte membrane 10 is preferably 50% or less, more preferably 30% or less, and even more preferably 10% or less.
Furthermore, since the first membrane 11 is covered with the second membrane 12, cross leakage of oxygen can be prevented and the dimensional stability of the polymer electrolyte membrane 10 can be improved. From these viewpoints, the area of the first membrane 11 covered with the second membrane 12 needs to be large to a certain extent. Specifically, the ratio of the area occupied by the second membrane 12 to the surface area of the polymer electrolyte membrane 10 is preferably 0.1% or more, more preferably 1% or more, and even more preferably 5% or more.
The surface area of the polymer electrolyte membrane 10 means the sum of the area of one side (the surface in contact with the fuel electrode 20) and the area of the other side (the surface in contact with the oxidizer electrode 30). Similarly, the area occupied by the second membrane 12 means the sum of the area occupied by the second membrane 12 on one side (the surface in contact with the fuel electrode 20) and the area occupied by the second membrane 12 on the other side (the surface in contact with the oxidizer electrode 30).

Next, each embodiment of the polymer electrolyte membrane 10 will be described.

[First embodiment]
2 , the second film 12 covers the first film 11 at the peripheral portions of both faces of the polymer electrolyte membrane 10 (the face adjacent to the fuel electrode 20 and the face adjacent to the oxidizer electrode 30).
The peripheral portions on both sides of the polymer electrolyte membrane 10 are susceptible to stress accompanying the swelling of the first membrane 11. By covering the peripheral portions with the second membrane 12, which has excellent dimensional stability, the swelling of the polymer electrolyte membrane 10 can be suppressed, and mechanical deterioration of the solid polymer fuel cell 1 can be effectively prevented.

Although not shown, it is also preferable that the second membrane 12 covers the first membrane 11 at the periphery of one of the faces of the polymer electrolyte membrane 10 (the face adjacent to the fuel electrode 20 or the face adjacent to the oxidizer electrode 30). By covering one of the faces with the second membrane 12, mechanical deterioration of the solid polymer electrolyte fuel cell 1 can be similarly prevented.

[Second embodiment]
In the second embodiment, as shown in Fig. 3, a second membrane 12 is formed on a part of the surface of the polymer electrolyte membrane 10 adjacent to the fuel electrode 20. The second membrane 12 and the hydrogen inlet port 2A are arranged so as to overlap in a plan view. That is, the part of the first membrane 11 adjacent to the hydrogen inlet port 2A is covered with the second membrane 12. Note that the oxidizer electrode 30 is omitted in Fig. 3.
In this specification, a plan view refers to observing one of the surfaces of the polymer electrolyte membrane 10 (the surface adjacent to the fuel electrode 20 or the surface adjacent to the oxidizer electrode 30) from above.
In the solid polymer electrolyte fuel cell 1, if the second membrane 12 is not present, cross leakage is likely to occur near the hydrogen inlet portion 2A, and chemical deterioration due to radical species is also likely to occur. In the second embodiment, by covering the portion of the first membrane 11 that is close to the hydrogen inlet portion 2A with the second membrane 12, which has low oxygen permeability, cross leakage in the portion close to the hydrogen inlet portion 2A can be effectively prevented and the durability of the polymer electrolyte membrane 10 against chemical deterioration can be improved.

In the second embodiment, as shown in FIG. 3, multiple hydrogen flow paths 2B are provided in a straight line, and the multiple hydrogen flow paths 2B are arranged in parallel. Hydrogen enters the inside of the fuel electrode 20 from the hydrogen inlet portion 2A, and then exits the fuel electrode 20 from the opposite side. The hydrogen passes through an externally installed manifold (not shown) and is then introduced back into the fuel electrode 20. In this way, hydrogen can be repeatedly introduced into and out of the fuel electrode 20, allowing hydrogen to be efficiently introduced into the fuel electrode 20.

Although not shown, the second membrane 12 may be present in other areas in addition to the vicinity of the hydrogen inlet portion 2A. For example, the second membrane 12 may cover the first membrane 11 on a portion of the surface that contacts the oxidizer electrode 30.

[Third embodiment]
In the third embodiment, as shown in Fig. 4, the second membrane 12 is formed on a part of the surface of the polymer electrolyte membrane 10 adjacent to the oxidizer electrode 30. The second membrane 12 and the air inlet portion 3A are arranged to overlap in a plan view. That is, the part of the first membrane 11 adjacent to the air inlet portion 3A is covered with the second membrane 12. Note that the fuel electrode 20 is omitted in Fig. 3.
In the solid polymer electrolyte fuel cell 1, the oxygen partial pressure is highest at the air inlet 3A, and in the absence of the second membrane 12, chemical deterioration due to oxygen is likely to occur in the vicinity of the air inlet 3A. In the third embodiment, by covering the portion of the first membrane 11 close to the air inlet 3A with the second membrane 12, the first membrane 11 can be protected from chemical deterioration, thereby improving the durability of the polymer electrolyte membrane 10 against chemical deterioration. In addition, the second membrane 12 has a low oxygen permeability, and can prevent cross leakage in the portion where the oxygen partial pressure is high.

In the third embodiment, as shown in FIG. 4, multiple air flow paths 3B are provided in a straight line, and the multiple air flow paths 3B are arranged in parallel. Air enters the inside of the oxidizer electrode 30 from the air inlet portion 3A, and then exits the oxidizer electrode 30 from the opposite side. Oxygen is turned back through a manifold (not shown) installed outside, and is introduced back into the oxidizer electrode 30. In this way, air is repeatedly passed in and out of the oxidizer electrode 30, allowing air to be efficiently introduced into the oxidizer electrode 30.

Although not shown, the second film 12 may be present in other areas in addition to the vicinity of the air inlet portion 3A. For example, the second film 12 may cover the first film 11 on a portion of the surface that contacts the fuel electrode 20.

[Fourth embodiment]
In the fourth embodiment, as shown in Fig. 5, the polymer electrolyte membrane 10 has a second membrane 12 formed on a part of the surface adjacent to the oxidizer electrode 30. The solid polymer electrolyte fuel cell 1 also has a separator 40 on the surface of the oxidizer electrode 30 opposite to the polymer electrolyte membrane 10. The separator 40 also has a cooling water inlet 4A for introducing cooling water from the outside of the solid polymer electrolyte fuel cell 1. The second membrane 12 and the cooling water inlet 4A are arranged to overlap in a plan view. That is, the part of the first membrane 11 adjacent to the cooling water inlet 4A is covered with the second membrane 12. Note that the fuel electrode 20 is omitted in Fig. 5.
In the solid polymer electrolyte fuel cell 1, the vicinity of the cooling water inlet 4A is most likely to be cooled, and in the absence of the second membrane 12, this area is likely to be mechanically deteriorated due to sudden contraction of the polymer electrolyte membrane 10. In the fourth embodiment, the portion of the first membrane 11 adjacent to the cooling water inlet 4A is covered with the second membrane 12, which has excellent dimensional stability, thereby improving the durability of the polymer electrolyte membrane 10 against mechanical deterioration.
Furthermore, the cooling water may contain dissolved substances (e.g., iron ions, etc.) that chemically deteriorate the first film 11. Even in such a case, in the fourth embodiment, the second film 12 can suppress the chemical deterioration of the first film 11.

In the fourth embodiment, as shown in FIG. 5, the cooling water flow path 4B is provided so as to meander inside the separator 40. By making the cooling water meander inside the separator 40, the solid polymer fuel cell 1 that generates heat due to the power generation reaction can be efficiently cooled.

Although not shown, the cooling water may be introduced into the separator 40 as well as into the member adjacent to the outside of the fuel electrode 20 (the side opposite to the surface where the fuel electrode 20 is adjacent to the polymer electrolyte membrane 10). This allows the solid polymer fuel cell 1 to be cooled more efficiently.

Next, we will explain the manufacturing method for solid polymer fuel cells.

[Fifth embodiment]
The manufacturing method of the fifth embodiment includes, in this order, a step of applying pressure to a part of a surface of a first membrane while heating the part, thereby forming a recess in the surface of the first membrane (hereinafter referred to as a "pressurizing step"), and a step of heating the first membrane and the second membrane in a state in which the second membrane is fitted into the recess, thereby forming a polymer electrolyte membrane (hereinafter referred to as a "bonding step"). The fifth embodiment will be described below with reference to FIG. 6.

In the pressurizing step, for example, a heated mold 51 is pressed against the surface of the first membrane 11 containing the first electrolyte material (FIG. 6(A)). At this time, by heating the mold 51 so that the temperature is equal to or higher than the melting point or glass transition point of the first electrolyte material, the first membrane 11 is plastically deformed, and the thickness of the pressurized portion is reduced. As a result, a recess 13 can be provided on the surface of the first membrane 11 (FIG. 6(B)). In this specification, the recess means a portion having a thinner thickness than the surroundings, and includes a portion having a thinner thickness at the periphery of the membrane as well as a portion having a thinner thickness near the center of the membrane.
Furthermore, by appropriately changing the shape of the mold 51, it is possible to provide the recesses 13 of a desired shape on the surface of the first film 11.
In the pressing step, a known hot press can be used.

In the bonding step after the pressurizing step, for example, the second membrane 12 cut out to fit the shape of the recess 13 is fitted into the recess 13 on the surface of the first membrane 11 (FIG. 6(C)). In this state, the first membrane 11 and the second membrane 12 are heated. At this time, by heating to a temperature above the melting point or glass transition point of the first electrolyte material and above the melting point or glass transition point of the second electrolyte material, the first membrane 11 and the second membrane 12 are bonded at the interface to form an integrated composite membrane (FIG. 6(D)). In this way, a polymer electrolyte membrane 10 in which a part of one side of the first membrane 11 is covered with the second membrane 12 of a desired shape can be manufactured.
In the bonding step, the first membrane 11 and the second membrane 12 can be bonded together without using an adhesive. Therefore, it is possible to prevent the proton conductivity of the polymer electrolyte membrane 10 from being reduced by the adhesive between the first membrane 11 and the second membrane 12.

The other surface of the first membrane 11 can be covered with a second membrane 12 having a desired shape in the same manner. As a result, a polymer electrolyte membrane 10 as shown in FIG. 2 can be produced.
Moreover, by appropriately changing the shape of the mold 16 and the shape of the second membrane 12 from those shown in FIG. 6, it is also possible to produce the polymer electrolyte membrane 10 shown in FIGS.

[Sixth embodiment]
The manufacturing method of the sixth embodiment includes, in this order, a step of applying pressure to a part of the surface of the first film while heating the part, thereby forming a recess in the surface of the first film (pressurizing step), a step of applying a coating liquid in which a second electrolyte material is dissolved, to the recess (hereinafter referred to as a "coating step"), and a step of drying the coating liquid to form the second film (hereinafter referred to as a "drying step"). The sixth embodiment will be described below with reference to FIG. 7.
The pressurizing step in the sixth embodiment is similar to the pressurizing step in the fifth embodiment, and therefore a description thereof will be omitted.

In the coating step after the pressurizing step, for example, the portion of the surface of the first film 11 that was not pressurized in the pressurizing step is covered in advance with a mask material 52 of a predetermined shape ( FIG. 7(A) ). In this state, a coating liquid in which the second electrolyte material is dissolved is sprayed from a spray nozzle 53 to perform spray coating ( FIG. 7(B) ). By spray coating, the coating liquid can be applied to the recess 13. At that time, the coating liquid is applied to the mask material 52 as well as the recess 13.
Instead of spray coating, other wet coating methods may be used, such as spin coating, doctor blade coating, and die coater coating.

In the drying step after the coating step, for example, the mask material 52 is removed from the first film 11, and the first film 11 is heated and dried by a heating device. The heating and drying removes the solvent from the coating liquid applied to the recesses 13, and a second film 12 made of the second electrolyte material is formed in the recesses 13 ( FIG. 7(C) ). In this manner, a polymer electrolyte membrane 10 can be manufactured in which a portion of one side of the first film 11 is covered with the second film 12 having a desired shape.
The mask material 52 may be removed after drying rather than before drying.

In the sixth embodiment, the thickness of the second film 12 to be formed can be adjusted by appropriately controlling the concentration of the second electrolyte material in the coating liquid, the coating time of the coating liquid, and the like.
From the viewpoint of shortening the drying time in the drying step, the concentration of the second electrolyte material in the coating liquid is preferably 0.001 g/mL or more, more preferably 0.005 g/mL or more, and even more preferably 0.01 g/mL or more. From the viewpoint of ease of handling of the coating liquid, the concentration of the second electrolyte material in the coating liquid is preferably 0.1 g/mL or less, more preferably 0.05 g/mL or less, and even more preferably 0.03 g/mL or less.
From the viewpoint of reliably forming the second film 12, the application time of the coating liquid is preferably 5 seconds or more, more preferably 30 seconds or more, and even more preferably 60 seconds or more. From the viewpoint of shortening the drying time in the drying step, the application time of the coating liquid is preferably 600 seconds or less, more preferably 300 seconds or less, and even more preferably 150 seconds or less.

When heat drying is performed in the drying process, the heating temperature is preferably less than the melting point or glass transition point of the first electrolyte material in order to prevent deformation of the first film 11.

Although several embodiments of the present invention have been described, these embodiments are presented as examples and are not intended to limit the scope of the invention. These novel embodiments can be implemented in various other forms, and various omissions, substitutions, and modifications can be made without departing from the gist of the invention. These embodiments and their modifications are included in the scope and gist of the invention, and are included in the scope of the invention and its equivalents described in the claims.

REFERENCE SIGNS LIST 1 Solid polymer electrolyte fuel cell 2A Hydrogen inlet 2B Hydrogen flow path 3A Air inlet 3B Air flow path 4A Cooling water inlet 4B Cooling water flow path 10 Polymer electrolyte membrane 11 First membrane 12 Second membrane 13 Recess 20 Fuel electrode 30 Oxidizer electrode 40 Separator 51 Mold 52 Mask material 53 Spray nozzle

Claims (9)

A solid polymer electrolyte fuel cell having a proton-conductive polymer electrolyte membrane, a fuel electrode disposed adjacent to one surface of the polymer electrolyte membrane, and an oxidizer electrode disposed adjacent to the other surface of the polymer electrolyte membrane,
the polymer electrolyte membrane is a composite membrane comprising a first membrane containing a first electrolyte material and a second membrane containing a second electrolyte material;
the second film covers a portion of the first film;
the oxygen permeability of the second membrane is smaller than the oxygen permeability of the first membrane,
A polymer electrolyte fuel cell, wherein the second membrane has a tensile strength greater than the tensile strength of the first membrane. The solid polymer electrolyte fuel cell according to claim 1, wherein the first electrolyte material is a polymer compound having a fluorocarbon as a main skeleton. The solid polymer electrolyte fuel cell according to claim 1 or 2, wherein the second electrolyte material is a hydrocarbon-based polymer compound having an aromatic main skeleton. The solid polymer electrolyte fuel cell according to claim 1 or 2, wherein the second membrane covers the first membrane at the periphery of the polymer electrolyte membrane. the fuel electrode has a hydrogen inlet port through which hydrogen is introduced from outside the polymer electrolyte fuel cell;
3. The polymer electrolyte fuel cell according to claim 1, wherein the second membrane adjacent to the fuel electrode and the hydrogen inlet port overlap each other in a plan view. the oxidizer electrode has an air inlet portion for introducing air from the outside of the polymer electrolyte fuel cell,
3. The polymer electrolyte fuel cell according to claim 1, wherein the second membrane adjacent to the oxidizer electrode and the air inlet portion overlap in a plan view. the solid polymer electrolyte fuel cell has a separator arranged on a surface of the oxidizer electrode opposite to the polymer electrolyte membrane,
the separator has a cooling water inlet portion for introducing cooling water from the outside of the polymer electrolyte fuel cell;
3 . The polymer electrolyte fuel cell according to claim 1 , wherein the second membrane adjacent to the oxidizer electrode and the cooling water inlet portion overlap in a plan view. 3. The method for producing a polymer electrolyte fuel cell according to claim 1,
applying pressure to a portion of a surface of the first film while heating the portion to form a recess in the surface of the first film;
heating the first membrane and the second membrane in a state in which the second membrane is fitted into the recess to form the polymer electrolyte membrane;
The method for producing a polymer electrolyte fuel cell comprises the steps of: 3. The method for producing a polymer electrolyte fuel cell according to claim 1,
applying pressure to a portion of a surface of the first film while heating the portion to form a recess in the surface of the first film;
applying a coating liquid in which the second electrolyte material is dissolved to the recess;
drying the coating liquid to form the second film;
The method for producing a polymer electrolyte fuel cell comprises the steps of:

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