Solid polymer electrolyte membrane, electrolyte membrane-electrode assembly, and solid polymer electrolyte fuel cell

Abstract

To improve the mechanical durability of the outer periphery of an electrode sandwiched between separators when applied to a solid polymer electrolyte fuel cell.SOLUTION: A solid polymer electrolyte membrane 2 for a fuel cell is sandwiched between an anode electrode catalyst layer 6 and a cathode electrode catalyst layer 7, and an outer electrode portion 2a protruding outward from the anode electrode catalyst layer 6 and the cathode electrode catalyst layer 7 is sandwiched between separators. The solid polymer electrolyte membrane 2 is made of a polymer containing sulfonic groups, and the sulfonic groups of the outer electrode portion 2a are crosslinked with Mg or Ca.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a solid polymer electrolyte membrane suitable for use in a solid polymer electrolyte fuel cell mounted on an electric vehicle or the like, an electrolyte membrane-electrode assembly using the same, and a solid polymer electrolyte fuel cell using the same. [Background technology]

[0002] Fuel cells, which generate electricity by electrochemically oxidizing hydrogen, have high power generation efficiency, clean exhaust gases, and minimal environmental impact. In recent years, technological development has been underway for a variety of applications, including power generation and power sources for electric vehicles. One such fuel cell is a solid polymer electrolyte fuel cell, which operates at relatively low temperatures. A solid polymer electrolyte fuel cell comprises a membrane electrode assembly (MEA). An MEA consists of a solid polymer electrolyte membrane (also referred to as the "electrolyte membrane") sandwiched between an anode electrode catalyst layer (fuel electrode) that supplies fuel gas such as hydrogen or hydrocarbons, and a cathode electrode catalyst layer (oxygen electrode) that supplies oxidant gas such as oxygen or air. A solid polymer electrolyte fuel cell has a structure in which the exposed portions of the electrolyte membrane in the MEA that extend beyond the outer periphery of both catalyst layers (hereinafter referred to as the "electrode outer periphery") are sandwiched between separators via a gasket.

[0003] Even in fuel cells with a structure in which the outer periphery of the electrode of the electrolyte membrane in the MEA is sandwiched between separators, various technologies have been proposed to improve the performance and durability of the fuel cell itself, the electrolyte membrane, and the MEA used therein. For example, to prevent gas leakage from the outer periphery of the electrode of the electrolyte membrane, one technology involves pressurizing a sealant between the outer periphery of the electrode and a gasket inside the separator to prevent gas leakage. However, with this technology, stress fluctuations occur in the outer periphery of the electrode due to the electrolyte membrane repeatedly swelling with water generated during power generation and drying out during non-power generation, resulting in reduced power generation performance and reduced durability of the outer periphery of the electrode.

[0004] Patent Document 1 focuses on this point and discloses an MEA technology that prevents gas leakage to avoid a decrease in power generation performance due to leakage, and also suppresses drying of the electrolyte membrane to prevent membrane rupture due to compressive stress associated with stress fluctuations at the outer periphery of the electrodes. In this technology, the MEA includes seals that prevent gas leakage from the sides of the anode catalyst layer, the cathode catalyst layer, and the electrolyte membrane, and gaskets provided on both sides of these seals. Parts of the seals form adhesive joints that bond the solid polymer electrolyte membrane to the gaskets. The adhesive joints are located on the outer peripheries of the anode catalyst layer and the cathode catalyst layer in the planar direction so as to prevent gas leakage from the sides of the anode catalyst layer and the cathode catalyst layer. This is said to suppress gas leakage and electrolyte membrane drying, thereby achieving the above-mentioned objectives. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] International Publication No. 2007 / 026797 Summary of the Invention [Problem to be solved by the invention]

[0006] The technology of Patent Document 1 mentioned above is a technology that aims to improve the durability and performance of MEAs and fuel cells by sealing the periphery of the electrode periphery of the electrolyte membrane to prevent the electrode periphery from drying out, thereby suppressing stress fluctuations and ultimately stress increases caused by repeated swelling and drying at the electrode periphery. This technology is effective in resolving issues that arise when the electrode periphery is pressurized and sealed with a sealant. In contrast to this technology, if the physical properties (material characteristics) of the electrode periphery of the fuel cell electrolyte membrane could be changed to improve mechanical durability, it would be possible to improve the durability and performance of MEAs using fuel cell electrolyte membranes and fuel cells using these MEAs.

[0007] This invention was conceived by focusing on such problems, and when applied to a solid polymer electrolyte fuel cell, it is possible to improve the mechanical durability by changing the physical properties of the outer peripheral portion of the electrode sandwiched by the separator. One of the objectives is to provide a solid polymer electrolyte membrane, an electrolyte membrane - electrode assembly using the same, and a solid polymer electrolyte fuel cell using the same. In addition to this objective, it is also another objective of this invention to achieve operational effects derived from each configuration shown in the "Modes for Carrying Out the Invention" described later, which are operational effects not achievable with conventional technologies.

Means for Solving the Problems

[0008] The disclosed solid polymer electrolyte membrane, electrolyte membrane - electrode assembly, and solid polymer electrolyte fuel cell can be realized as the following disclosed modes (application examples), and can solve at least a part of the above problems. Mode 2 is an additionally selectable mode that can be omitted. Mode 2 does not disclose essential modes or configurations for this invention.

[0009] Mode 1. The disclosed solid polymer electrolyte membrane is a solid polymer electrolyte membrane for a fuel cell that is sandwiched between an anode electrode catalyst layer and a cathode electrode catalyst layer, and the outer peripheral portion of the electrode protruding outward from the anode electrode catalyst layer and the cathode electrode catalyst layer is sandwiched by a separator. This solid polymer electrolyte membrane is made of a polymer containing a sulfonic group, and the sulfonic groups in the outer peripheral portion of the electrode are cross - linked by Mg or Ca.

[0010] Mode 2. In the mode including the above Mode 1, it is preferable that the density EW of the sulfonic group is 500 < EW < 1200.

[0011] Mode 3. The disclosed electrolyte membrane - electrode assembly includes the solid polymer electrolyte membrane described in the above Mode 1 or 2, and anode electrode catalyst layer and cathode electrode catalyst layer arranged so as to sandwich the solid polymer electrolyte membrane.

[0012] Aspect 4. The disclosed solid polymer electrolyte fuel cell comprises the electrolyte membrane-electrode assembly described in Aspect 3 above, and separators that sandwich the outer periphery of the electrodes of the solid polymer electrolyte membrane. [Effects of the Invention]

[0013] The disclosed solid polymer electrolyte membrane, electrolyte membrane-electrode assembly, and solid polymer electrolyte fuel cell can improve the mechanical durability of the outer periphery of the electrode sandwiched between separators. [Brief explanation of the drawings]

[0014] [Figure 1] 1 is a cross-sectional view of a membrane-electrode assembly including a solid polymer electrolyte membrane according to an embodiment. [Figure 2] 2 is a cross-sectional view showing a unit cell of a solid polymer electrolyte fuel cell equipped with the electrolyte membrane-electrode assembly shown in FIG. 1. FIG. DETAILED DESCRIPTION OF THE INVENTION

[0015] With reference to the drawings, a solid polymer electrolyte membrane as an embodiment, an electrolyte membrane-electrode assembly using the same, and a solid polymer electrolyte fuel cell using the same will be described. The embodiments described below are merely examples, and are not intended to exclude various modifications or applications of techniques not explicitly stated in the following embodiments. The configurations of the embodiments can be implemented with various modifications within the scope of their spirit. Furthermore, they can be selected or combined as needed.

[0016] [1. Overall structure] As shown in FIG. 2, a unit cell 1S of a solid polymer electrolyte fuel cell 1 (hereinafter simply referred to as "fuel cell 1") according to this embodiment includes a membrane electrode assembly 3 (hereinafter simply referred to as "MEA 3") including a solid polymer electrolyte membrane 2 (hereinafter simply referred to as "electrolyte membrane 2"), a separator 4, and a gasket 5. The fuel cell 1 is configured as an assembly (stack) of several tens to several hundreds of unit cells 1S connected in series. Note that the planar shapes of the fuel cell 1 or unit cell 1S are not shown, but they can be formed into various shapes, such as rectangular or square.

[0017] The MEA 3 is constructed by sandwiching an electrolyte membrane 2 between an anode electrode catalyst layer (fuel electrode) 6 that supplies a fuel gas such as hydrogen or a hydrocarbon, and a cathode electrode catalyst layer (oxygen electrode) 7 that supplies an oxidant gas such as oxygen or air. The electrolyte membrane 2 is a thin film having a thickness of about 10 to 100 microns, and the catalyst layers 6 and 7 are formed to have a thickness that is approximately the same as or smaller than the electrolyte membrane 2. For convenience, the thickness of the MEA 3 is shown greatly exaggerated in FIG. 2 and FIG. 1, which will be described later.

[0018] 1 and 2, the outer peripheral portion 3a of the MEA 3 has a structure in which the outer peripheral portion 2a (thickly hatched portion) of the electrolyte membrane 2 protrudes outward beyond the outer peripheral portions 6a, 7a of both catalyst layers 6, 7. The outer peripheral portion 2a of the electrolyte membrane 2 protruding beyond the outer peripheral portions 6a, 7a of both catalyst layers 6, 7 (hereinafter also referred to as "electrode outer peripheral portion 2a") is sandwiched between separators 4 via a gasket 5. The catalyst layers 6, 7 are connected to an external device 8, whereby the fuel cell 1 is used as a power source. An example of this external device 8 is a plug-in hybrid vehicle (PHEV) that can be externally charged or externally powered.

[0019] [2. Solid polymer electrolyte membrane] The electrolyte membrane 2 has a sulfonic acid group (-SO3) -It is composed of a polymer having a structural unit represented by the following general formula (I) containing. The density of this sulfonic acid group (the weight (molecular weight) of the polymer in the ionomer per sulfonic acid group) EW is 500 < EW < 1200. In the electrolyte membrane 2 of the present embodiment, the sulfonic acid groups in the electrode outer peripheral portion 2a that do not contribute to power generation are crosslinked by Mg (magnesium) or Ca (calcium). That is, the electrode outer peripheral portion 2a of the electrolyte membrane 2 is a polymer having a structural unit represented by the following general formula (II) or (III).

[0020]

Chemical formula

[0021]

Chemical formula

[0022]

Chemical formula

[0023] The sulfonic acid group (-SO3) constituting the electrolyte membrane 2 - To crosslink with Mg or Ca, for example, the following method can be applied. First, add MeOH (methanol) to an aqueous solution of magnesium nitrate Mg(NO3) or calcium nitrate Ca(NO3)2, and immerse the portion corresponding to the electrode outer peripheral portion 2a of the electrolyte membrane 2. The concentration of the aqueous solution of magnesium nitrate or calcium nitrate, the concentration of methanol, and the temperature and immersion time during immersion are appropriately set to be necessary and sufficient. When the predetermined immersion time required for the reaction has elapsed, wash the surface of the electrode outer peripheral portion 2a of the electrolyte membrane 2 with pure water to remove the Mg or Ca adhering to the surface.

[0024] In order to partially immerse only the outer electrode portion 2a of the electrolyte membrane 2, the portion of the electrolyte membrane 2 other than the outer electrode portion 2a (i.e., the central portion 2b that comes into contact with the catalyst layers 6, 7 when constructing the MEA 3) may be masked or otherwise treated to prevent it from coming into contact with the aqueous solution of magnesium nitrate or calcium nitrate.

[0025] During immersion, the sodium ions Na in the aqueous solution of magnesium nitrate or calcium nitrate migrate from the surface of the electrolyte membrane 2 to the inside due to the swelling action of methanol. 2+ or calcium ion Ca 2+ enters and two sulfonic acid groups (-SO3) - hydrogen ion 2H bonded to + is sodium ion Na 2+ or calcium ion Ca 2+ and two sulfonic acid groups (-SO3) - is cross-linked by Mg or Ca.

[0026] Although this reaction takes some time to proceed, since the thickness of the electrolyte membrane 2 is extremely thin, about 10 to 100 microns, the reaction proceeds in the thickness direction within a certain time, and two sulfonic acid groups (-SO3) are formed throughout the entire thickness direction. - At this time, the reaction also proceeds in the extending direction of the electrolyte membrane 2 (the direction perpendicular to the thickness direction), but this reaction is limited to the thickness of the electrolyte membrane 2 or less, so that the sulfonic acid group (-SO3) is limited to the outer periphery 2a of the electrode. - can be cross-linked with Mg or Ca.

[0027] [3. Actions and Effects] The solid polymer electrolyte membrane 2, the electrolyte membrane-electrode assembly 3, and the solid polymer electrolyte fuel cell 1 according to this embodiment are configured as described above, and therefore provide the following actions and effects. The electrode outer periphery 2a of the electrolyte membrane 2 (the thickly hatched area in FIGS. 1 and 2) is formed by a sulfonic acid group (-SO3) -is cross-linked by Mg or Ca, a change in the physical properties (material characteristics) occurs, and swelling is prevented or suppressed. As a result, membrane shrinkage due to drying of the outer electrode portion 2a is prevented or suppressed, damage such as breakage caused by membrane expansion and shrinkage is suppressed, and durability is improved. As a result, gas leaks caused by damage to the electrolyte membrane 2 are prevented or suppressed, and a decrease in power generation efficiency caused by gas leaks is prevented or suppressed.

[0028] That is, the electrode outer periphery 2a of the electrolyte membrane 2 is sandwiched between the separator 4 via the gasket 5. When the electrode outer periphery 2a repeatedly swells and shrinks due to drying, stress fluctuations occur, which can lead to damage such as breakage. However, according to the configuration of this embodiment, as described above, swelling of the electrode outer periphery 2a of the electrolyte membrane 2 due to changes in physical properties is prevented or suppressed. This prevents or suppresses expansion and shrinkage of the membrane in the electrode outer periphery 2a, thereby preventing or suppressing the occurrence of stress fluctuations. Therefore, damage such as breakage caused by membrane expansion and shrinkage can be suppressed, thereby improving the mechanical durability of the electrode outer periphery 2a. This makes it possible to configure the electrolyte membrane 2 thinner while maintaining its mechanical durability. By thinning the electrolyte membrane 2, the internal resistance of the battery can be reduced and the output can be increased.

[0029] The outer periphery 2a of the electrode is filled with hydrogen ions 2H + is sodium ion Na 2+ or calcium ion Ca 2+ However, the outer electrode portion 2a is not sandwiched between the catalyst layers 6 and 7 and is not responsible for power generation, so this does not affect power generation performance. On the other hand, in the part of the electrolyte membrane 2 other than the outer electrode portion 2a, that is, in the central portion 2b of the electrolyte membrane 2 sandwiched between the catalyst layers 6 and 7, the hydrogen ions 2H + Since the reactor remains in place, power generation can be performed without any problems, and power generation performance is ensured.

[0030] [4. Other] The configurations of the above-described solid polymer electrolyte membrane 2, electrolyte membrane-electrode assembly 3, and solid polymer electrolyte fuel cell 1 are examples. In the above embodiment, a simpler configuration is exemplified. However, for example, in the unit cell 1S of the solid polymer electrolyte fuel cell 1, an adhesive or a sealing material may be used as necessary to enhance the interlayer bonding property and the sealing property.

[0031] Also, although the method of crosslinking the sulfonic acid group (-SO3) - constituting the electrolyte membrane 2 with Mg or Ca has been described, this is an example, and it is not limited to this as long as the sulfonic acid group (-SO3) - can be crosslinked with Mg or Ca. The equivalent weight EW of the sulfonic acid group density is not limited to 500 < EW < 1200.

Industrial Applicability

[0032] This case is applicable to the manufacturing industry of solid polymer electrolyte fuel cells provided with a solid polymer electrolyte membrane containing at least a sulfonic acid group, and is also applicable to the manufacturing industries of various products using this solid polymer electrolyte fuel cell as a power source.

Explanation of Reference Numerals

[0033] 1 Solid polymer electrolyte fuel cell (fuel cell) 1S Unit cell 2 Solid polymer electrolyte membrane (electrolyte membrane) 2a Outer peripheral portion of the electrode (outer peripheral portion of the electrolyte membrane 2) 2b Central portion of the electrolyte membrane 2 3 Electrolyte membrane-electrode assembly (MEA) 3a Outer peripheral portion of MEA3 4 Separator <​​​​​​​​​​​

Claims

1. A solid polymer electrolyte membrane for a fuel cell, which is sandwiched between an anode electrode catalyst layer and a cathode electrode catalyst layer, and in which outer peripheral portions of the electrodes protruding outward from the anode electrode catalyst layer and the cathode electrode catalyst layer are sandwiched between separators, comprising a polymer containing a sulfonic acid group, The sulfonic acid groups on the outer periphery of the electrode are crosslinked with Mg or Ca. A solid polymer electrolyte membrane characterized by:

2. The density EW of the sulfonic acid group is 500<EW<1200. The solid polymer electrolyte membrane according to claim 1 .

3. The solid polymer electrolyte membrane according to claim 1; an anode electrode catalyst layer and a cathode electrode catalyst layer disposed so as to sandwich the solid polymer electrolyte membrane, An electrolyte membrane-electrode assembly characterized by:

4. The electrolyte membrane-electrode assembly according to claim 3; and a separator that sandwiches the outer periphery of the electrode of the solid polymer electrolyte membrane. A solid polymer electrolyte fuel cell comprising:

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