JP2021190176A - Membrane electrode gas diffusion layer assembly for fuel battery cell - Google Patents

Abstract

To provide a membrane electrode gas diffusion layer assembly (MEGA) which can prevent peeling between a catalyst layer and a microporous layer due to swelling and contraction of an electrolyte membrane.SOLUTION: An MEGA 2 for a fuel battery cell includes: a membrane electrode assembly 4 having an electrolyte membrane 5 and a pair of catalyst layers 6 and 6 joined to each other so as to sandwich both surfaces of the electrolyte membrane 5; and a pair of gas diffusion layers 7 and 7 joined to each other so as to sandwich both surfaces of the membrane electrode assembly 4. At least one of the pair of gas diffusion layers 7 and 7 has a microporous layer 72 in contact with the catalyst layer 6, the catalyst layer 6 contains an ionomer, and the microporous layer 72 contains a polytetrafluoroethylene resin. When a basis weight of the ionomer contained per unit area of the catalyst layer 6 is represented by A and a basis weight of the polytetrafluoroethylene resin contained per unit area of the microporous layer 72 is represented by B, 0.20≤A/B is satisfied.SELECTED DRAWING: Figure 2

Description

The present invention relates to a membrane electrode gas diffusion layer junction for a fuel cell.

Conventionally, a polymer electrolyte fuel cell has a structure in which a plurality of fuel cell cells are laminated. The fuel cell includes a membrane electrode assembly composed of an ion-permeable electrolyte membrane and an anode catalyst layer and a cathode catalyst layer bonded so as to sandwich the electrolyte membrane. Gas diffusion layers are formed on both sides of the membrane electrode assembly to supply fuel gas or oxidant gas and to collect electricity generated by an electrochemical reaction. A membrane electrode gas diffusion layer assembly (Membrane Electrode & Gas Diffusion Layer Assembly, hereinafter "MEGA") in which gas diffusion layers are arranged on both sides of the membrane electrode assembly is sandwiched by a pair of separators.

In the MEGA membrane electrode assembly, hydrogen gas as a fuel is supplied to the anode catalyst layer, oxygen gas (air) as an oxidizing agent is supplied to the cathode in the cathode layer, and hydrogen is oxidized to protons in the anode catalyst layer. , Oxidation is reduced to water in the cathode catalyst layer, and the fuel cell generates electricity.

In such MEGA, it is known that the gas diffusion layer has a microporous layer. For example, Patent Document 1 discloses MEGA including a gas diffusion layer having a microporous layer in contact with a catalyst layer. The microporous layer described in Patent Document 1 contains a polytetrafluoroethylene resin, which ensures that the microporous layer has water repellency to repel the generated water generated in the membrane electrode assembly. ..

Japanese Unexamined Patent Publication No. 2018-190584

By the way, for example, the electrolyte membrane tends to swell and contract in the plane direction (direction orthogonal to the thickness direction) due to the generation of water in the membrane electrode junction and the movement of the water. Therefore, in MEGA, the expansion and contraction of the electrolyte membrane is suppressed by integrally restraining the electrolyte membrane with the catalyst layer and the gas diffusion layer.

However, in the membrane electrode gas diffusion layer junction exemplified in Patent Document 1 and the like, the adhesion between the catalyst layer and the microporous layer may not be ensured, and due to the swelling and contraction of the electrolyte membrane, the catalyst layer and the catalyst layer may not be secured. There is a risk of peeling from the microporous layer.

The present invention has been made in view of these points, and as the present invention, the membrane electrode gas diffusion capable of preventing the separation between the catalyst layer and the microporous layer due to the swelling and contraction of the electrolyte membrane can be prevented. A layered body is provided.

In view of the above problems, the membrane electrode gas diffusion layer assembly according to the present invention includes a membrane electrode assembly having an electrolyte membrane and a pair of catalyst layers bonded so as to sandwich both sides of the electrolyte membrane. A membrane electrode gas diffusion layer assembly for a fuel cell, comprising a pair of gas diffusion layers bonded so as to sandwich both sides of the membrane electrode assembly, wherein at least one of the pair of gas diffusion layers is , The catalyst layer has a microporous layer in contact with the catalyst layer, the catalyst layer contains an ionoma, the microporous layer contains a polytetrafluoroethylene (hereinafter, "PTFE") resin, and is a unit of the catalyst layer. When the amount of the ionoma contained per area is A and the amount of the polytetrafluoroethylene resin contained per unit area of the microporous layer is B, the following formula (1) is used. It is characterized by satisfying.
0.20 ≤ A / B ... Equation (1)

According to the present invention, the basis weight (A) of the ionoma of the catalyst layer and the basis weight (B) of the PTFE resin of the microporous layer satisfy the relationship of the above formula (1), whereby the catalyst layer and the microporous layer are satisfied. The adhesion with the layer can be enhanced.

Here, when A / B is less than 0.20, the amount of PTFE resin present at the interface of the microporous layer per unit area is relative to the amount of ionoma present at the interface of the catalyst layer per unit area. Becomes excessive. Here, the interface of the catalyst layer is a surface where the catalyst layer is in contact with the microporous layer, and the interface of the microporous layer is a surface where the microporous layer is in contact with the catalyst layer. Since the releasable (non-adhesive) PTFE resin is difficult to adhere to the ionoma, the presence of excess PTFE resin makes it difficult for the ionomer at the interface of the catalyst layer to adhere to the microporous layer, and the catalyst layer and the microporous layer are difficult to adhere to. Adhesion with and will decrease.

Therefore, in the present invention, as described above, by satisfying the relationship of the above formula (1), it is possible to enhance the adhesion between the catalyst layer and the microporous layer, and the catalyst layer caused by the swelling and contraction of the electrolyte membrane. And the microporous layer can be prevented from peeling off.

It is a schematic cross-sectional view of the fuel cell provided with the membrane electrode gas diffusion layer junction (MEGA) which concerns on embodiment of this invention. It is a schematic cross-sectional view of MEGA shown in FIG. It is a schematic cross-sectional view of the test body which concerns on Reference Example 1 to Reference Example 7. It is a graph which shows the relationship between the ratio of the ionomer basis weight to the basis weight of a polytetrafluoroethylene resin, and the adhesion of a catalyst layer and a microporous layer.

Hereinafter, embodiments according to the present invention will be described with reference to FIGS. 1 and 2. In the following, as an example, a case where the present invention is applied to a fuel cell mounted on a fuel cell vehicle will be described as an example, but the scope of application is not limited to such an example.

The membrane electrode gas diffusion layer junction (MEGA) 2 of the present embodiment is applied to the fuel cell 1. As shown in FIG. 1, a fuel cell 10 is formed by stacking a plurality of fuel cell 1s, which are basic units. Each fuel cell 1 is a solid polymer fuel cell that generates electromotive force by an electrochemical reaction between an oxidant gas (for example, oxygen gas, usually air gas) and a fuel gas (for example, hydrogen gas). First, with reference to FIG. 1, the fuel cell 1 provided with the MEGA 2 of the present embodiment will be outlined.

The fuel cell 1 shown in FIG. 1 includes a MEGA 2 and a pair of separators 3 and 3 sandwiching both sides of the MEGA 2. The MEGA 2 is a power generation unit of the fuel cell 1, and the configuration of the MEGA 2 will be described later.

In the present embodiment, each separator 3 is a plate-shaped member based on a metal having excellent conductivity, gas impermeableness, etc., and has an isosceles trapezoidal corrugated shape, and one side thereof is MEGA2. It is in contact with (gas diffusion layer 7), and the other surface side is in contact with the other surface side of the adjacent separator 3.

A gas flow path 21 for fuel gas is formed between the separator 3 and MEGA 2 on one side (anode side), and a gas flow path for oxidant gas is formed between the separator 3 and MEGA 2 on the other side (cathode side). 22 is formed. A flow path 23 for a refrigerant (for example, water) for cooling the fuel cell 1 is formed between the separators 3 and 3 that are in surface contact with each other between the two adjacent fuel cell 1s. When the fuel gas is supplied to the gas flow path 21 and the oxidant gas is supplied to the gas flow path 22, an electrochemical reaction occurs in the fuel cell 1 to generate an electromotive force. ^{In this electrochemical reaction, protons (H +} ) generated in the catalyst layer 6 on the anode side and water permeate through the electrolyte membrane 5 in a hydrated state, and generated water is generated in the catalyst layer 6 on the cathode side. To.

Next, MEGA2 of the present embodiment will be described with reference to FIG. As shown in FIG. 2, MEGA 2 includes a membrane electrode assembly 4 and a pair of gas diffusion layers 7 and 7 bonded so as to sandwich both sides of the membrane electrode assembly 4. The membrane electrode assembly 4 has an electrolyte membrane 5 and a pair of catalyst layers 6 and 6 bonded so as to sandwich both sides of the electrolyte membrane 5.

The electrolyte membrane 5 is not limited as long as it is a proton-conducting ion exchange membrane formed of a solid polymer material, but for example, a thin film of a perfluorosulfonic acid polymer (Nafion (trade name) manufactured by DuPont). ) Can be mentioned.

In the pair of catalyst layers 6 and 6, the catalyst layer 6 arranged on one side of the electrolyte membrane 5 serves as an anode, and the catalyst layer 6 on the other side serves as a cathode. Each catalyst layer 6 contains a polyelectrolyte, ionoma, and catalyst-supported carrier particles in which a catalyst is supported on carrier particles.

The ionomer is a polymer electrolyte having proton conductivity, and the following reference example uses a perfluoro-based proton exchange resin of a fluoroalkyl copolymer having a fluoroalkyl ether side chain and a perfluoroalkyl main chain. ing. For example, Nafion (trade name) manufactured by DuPont, Aciplex (trade name) manufactured by Asahi Kasei, Flemion (trade name) manufactured by Asahi Glass, Gore-Select (trade name) manufactured by Japan Goretex, etc. are exemplified. There are polymers of trifluorostyrene sulfonic acid and those in which a sulfonic acid group is introduced into polyvinylidene fluoride. Further, there are hydrocarbon-based proton exchange resins such as styrene-divinylbenzene copolymers and polyimide-based resins in which a sulfonic acid group is introduced.

The carrier particles of the catalyst-supported carrier particles may be carrier particles having conductivity. For example, in the following reference examples, carbon black is used, but in addition, carbon nanotubes, carbon nanofibers, or mesoporous Examples include carbon materials such as carbon. On the other hand, examples of the catalyst of the catalyst-supporting carrier particles include catalyst metals such as platinum, platinum alloys, and palladium. The catalyst may be supported on the surface of the carrier particles, or may be encapsulated and supported in the pores of the carrier particles.

The pair of gas diffusion layers 7 and 7 are layers that provide a fuel gas or an oxidant gas and collect electricity generated by an electrochemical reaction. Fuel gas is provided from the gas diffusion layer 7 arranged on the anode side, and oxidant gas is provided from the gas diffusion layer 7 arranged on the cathode side.

Each gas diffusion layer 7 has a diffusion layer base material 71 that is relatively rigid and has thickness and deformation performance, and a microporous layer 72 formed on the diffusion layer base material 71. The microporous layer 72 is in contact with the catalyst layer 6.

The diffusion layer base material 71 is not particularly limited as long as it has low electrical resistance and can collect electricity, but is not particularly limited, but is conductive such as a carbon fiber base material such as carbon paper, a graphite fiber base material, or a foamed metal. Examples include porous substrates with properties and gas diffusivity.

The microporous layer 72 is a porous layer and contains carbon particles as conductive particles and polytetrafluoroethylene (PTFE) resin as a water repellent. The PTFE resin can repel the generated water generated in the membrane electrode assembly 4. Further, the microporous layer 72 may contain a cerium compound such as cerium oxide, whereby cerium ions can be supplied to the membrane electrode assembly 4 to detoxify hydrogen hydrogen radicals generated during power generation.

The PTFE resin is not particularly limited as long as it has water repellency, and may be fibrous or granular.

As a result of repeated experiments, the inventor found that the ratio of ionomer contained in the catalyst layer 6 to the PTFE resin contained in the microporous layer 72 was the ratio between the catalyst layer 6 and the microporous layer under the same material physical characteristics. It was found that it greatly contributed to the adhesion with 72. The inventor has clarified from the following reference examples that the condition for ensuring these adhesions is that the following formula (1) is satisfied.
0.20 ≤ A / B ... Equation (1)

Here, A (mg / cm ² ) is the basis weight of ionoma contained in the unit area of the catalyst layer 6 (hereinafter, simply “the basis weight of ionoma”), and B (mg / cm ² ) is. , The basis weight of the PTFE resin contained in the unit area of the microporous layer 72 (hereinafter, simply "the basis weight of the PTFE resin"). The “unit area” is a unit area (specifically, 1 cm × 1 cm) in a plane orthogonal to the thickness direction of the catalyst layer 6 or the microporous layer 72. The basis weight of ionomer is the amount of all ionomer contained when the catalyst layer 6 is cut off in the region of this unit area. On the other hand, the basis weight of the PTFE resin is the amount of all the PTFE resin contained when the microporous layer 72 is cut off in the region of this unit area.

Here, the amount of ionomer and the amount of PTFE resin are determined by the catalyst layer 6 or the microporous layer 72 formed after the solvent in the ink containing the ionomer and the PTFE resin is removed by drying, as described later. It is the amount contained per unit area. Since the thickness of the catalyst layer 6 and the microporous layer 72 is thin, the amount of ionoma and the amount of PTFE resin, respectively, are the amount of ionoma present at the interface of the catalyst layer 6 per unit area and the micro per unit area. It corresponds to the amount of PTFE resin present at the interface of the porous layer 72. Therefore, A / B corresponds to the occupancy rate (area ratio) of ionomer and PTFE resin at these interfaces.

Here, when A / B is less than 0.20, as will be described later, the interface of the microporous layer 72 per unit area is relative to the amount of ionoma existing at the interface of the catalyst layer 6 per unit area. The amount of PTFE resin present in is excessive. Since the PTFE resin, which is difficult to adhere to the ionomer, is excessively present, the ionomer at the interface of the catalyst layer 6 is difficult to adhere to the microporous layer 72, and the adhesion between the catalyst layer 6 and the microporous layer 72 is reduced. As will be clear from the reference examples described later, more preferably, the A / B may be 0.23 or more, and the upper limit of the A / B may be 0.40 or less.

In the present embodiment, by satisfying the relationship of the above formula (1), it is possible to increase the adhesion between the catalyst layer 6 and the microporous layer 72, and the catalyst layer is caused by the swelling and contraction of the electrolyte membrane 5. It is possible to prevent the 6 and the microporous layer 72 from peeling off. As a result, the durability of the electrolyte membrane 5 can be improved.

Next, the manufacturing method of MEGA2 of the present embodiment will be outlined. In the method for producing MEGA2, first, a membrane electrode assembly 4 and a pair of gas diffusion layers 7 and 7 are prepared. When forming the prepared membrane electrode assembly 4, the catalyst-supported carrier particles, ionoma, and a solvent (for example, water, alcohol, etc.) are mixed to prepare a catalyst ink.

Next, the prepared catalyst ink is applied to both surfaces of the electrolyte membrane 5 and then dried in a warm air drying furnace or the like to form the catalyst layer 6. As a coating method, a spray method, a coater method, a doctor blade method, or the like may be applied. In the present embodiment, after the catalyst ink is applied and dried, the basis weight A (mg / cm ² ) of the ionomer is adjusted so as to satisfy the above formula (1). As described above, the basis weight of ionomer is the amount contained in the unit area of the catalyst layer 6 formed after the solvent of the catalyst ink is blown off by drying. In this way, a membrane electrode assembly 4 in which the catalyst layers 6 and 6 are bonded to both surfaces of the electrolyte membrane 5 is formed.

Each of the pair of gas diffusion layers 7 and 7 can be formed in the same manner. Specifically, carbon particles, PTFE resin, a solvent (for example, water, etc.), and, if necessary, a surfactant are mixed to prepare an ink for a microporous layer. The ink for the microporous layer may further contain cerium oxide.

Next, the prepared ink for the microporous layer is applied onto the diffusion layer base material 71, dried using a hot plate or the like, and fired to form the microporous layer 72. As the coating method, the same method as the above-mentioned catalyst ink may be applied. In the present embodiment, when the ink for the microporous layer is applied and dried, the basis weight of the PTFE resin is adjusted so as to satisfy the above formula (1). As described above, the basis weight of the PTFE resin is the amount contained in the unit area of the microporous layer 72 formed after the solvent of the ink for the microporous layer is blown off by drying. In this way, the gas diffusion layer 7 to which the microporous layer 72 is bonded is formed on the diffusion layer base material 71.

Next, both sides of the prepared membrane electrode assembly 4 are joined so as to be sandwiched between the prepared pair of gas diffusion layers 7 and 7. At the time of bonding, both sides of the membrane electrode assembly 4 are formed by a pair of gas diffusion layers 7 and 7 so that the catalyst layer 6 of the membrane electrode assembly 4 and the microporous layer 72 of the gas diffusion layer 7 face each other. It is sandwiched and hot-pressed in this state. The conditions of the hot pressure press are not particularly limited as long as the catalyst layer 6 and the microporous layer 72 can be bonded. In this way, MEGA2 is manufactured. The fuel cell 1 can be manufactured by arranging the separators 3 and 3 on both sides of the MEGA 2.

As shown in FIG. 3, the inventors prepared the test pieces according to Reference Examples 1 to 7 in which the catalyst layer and the microporous layer were bonded, and in terms of the adhesion between the catalyst layer and the microporous layer, the inventors prepared the test specimens. The relationship between the basis weight of ionomer and the basis weight of PTFE resin was specified.

<Reference example 1>
A catalyst layer basis weight of the ionomer is 0.14 mg / cm ^2, and basis weight of the PTFE resin is produced respectively a microporous layer is 0.35 mg / cm ^2, the catalyst layer and the microporous layer prepared Was heat-bonded to prepare a test piece shown in FIG. Next, a 90 ° peeling test method was carried out on the test piece, and the adhesion between the catalyst layer and the microporous layer was measured.

<Reference Example 2 to Reference Example 4>
Reference Example 2 to Reference Example 4 are test specimens in which the basis weight of ionomer is constant and the basis weight of PTFE resin is shaken. Specifically, the test pieces of Reference Examples 2 to 4 were prepared in the same manner as in Reference Example 1 except for the basis weight of the PTFE resin, and the 90 ° peeling test method was carried out to measure the adhesion. Basis weight of the PTFE resin of Reference Example 2 to Reference Example 4, ^{respectively, 0.53mg / cm 2, 0.70mg /} cm 2, is 1.40 mg / cm ^2.

<Reference Example 5 to Reference Example 7>
Reference Examples 5 to 7 are test specimens in which the basis weight of the PTFE resin is constant and the basis weight of ionomer is shaken. Specifically, the test pieces of Reference Examples 5 to 7 were prepared in the same manner as in Reference Example 2 except for the basis weight of ionomer, and the 90 ° peeling test method was carried out to measure the adhesion. Basis weight of the ionomer of Example 5 to Example 7, ^{respectively, 0.12mg / cm 2, 0.15mg /} cm 2, is 0.17 mg / cm ^2.

Table 1 shows the basis weight of ionoma (A), the basis weight of PTFE resin (B), the ratio of the basis weight of ionoma to the basis weight of PTFE resin (A / B), and the adhesion according to Reference Examples 1 to 7. Shown in. Further, FIG. 4 shows a graph showing the relationship between the ratio of the basis weight of ionomer to the basis weight of the PTFE resin and the adhesion between the catalyst layer and the microporous layer. As will be described later, Reference Examples 1 to 3 and Reference Examples 5 to 7 correspond to Reference Examples, and Reference Example 4 corresponds to Reference Comparative Example.

As can be seen from FIG. 4, when the ratio (A / B) of the ionomer basis weight A to the basis weight B of the PTFE resin is in the range of 0.20 or more, the adhesion between the catalyst layer and the microporous layer increased. .. On the other hand, when the A / B was less than 0.20, the adhesion was reduced. When A / B is less than 0.20, the amount of PTFE resin present at the interface of the microporous layer per unit area is larger than the amount of ionoma present at the interface of the catalyst layer per unit area. Too much. Since the water-repellent PTFE resin is difficult to adhere to the ionomer, the presence of excess PTFE resin makes it difficult for the ionomer at the interface of the catalyst layer to adhere to the microporous layer, and the adhesion between the catalyst layer and the microporous layer is reduced. It is thought that.

Therefore, by satisfying the relationship of the above formula (1), it is possible to enhance the adhesion between the catalyst layer and the microporous layer, and due to the swelling and contraction of the electrolyte membrane, the catalyst layer and the microporous layer are separated from each other. It is possible to prevent peeling. As a result, the durability of the electrolyte membrane can be improved.

Since the PTFE resin and carbon particles are mainly present at the interface of the microporous layer, when the amount of PTFE resin per unit area increases at this interface, the amount of carbon particles per unit area decreases. do. Therefore, as the amount of PTFE resin increases, the adhesion between the catalyst layer and the microporous layer decreases. Therefore, the ionomer at the interface of the catalyst layer adheres to the carbon particles at the interface of the microporous layer, so that the catalyst layer and the microporous layer adhere to each other. It is considered that the adhesion with the layer is developed.

Although one embodiment of the present invention has been described in detail above, the present invention is not limited to the above-described embodiment, and various aspects are described within the scope of the claims as long as the spirit of the present invention is not deviated. It is possible to make design changes.

For example, in the above embodiment, an example in which both of the pair of gas diffusion layers have a microporous layer in contact with the catalyst layer has been described, but the present invention is not limited to this, and at least one of the pair of gas diffusion layers is described. One may have a microporous layer in contact with the catalyst layer.

1: Fuel cell, 2: Membrane electrode gas diffusion layer assembly (MEGA), 4: Membrane electrode assembly, 5: Electrolyte membrane, 6: Catalyst layer, 7: Gas diffusion layer, 72: Microporous layer

Claims (1)

A membrane electrode assembly having an electrolyte membrane and a pair of catalyst layers bonded so as to sandwich both sides of the electrolyte membrane.
A pair of gas diffusion layers bonded so as to sandwich both sides of the membrane electrode assembly,
Membrane electrode gas diffusion layer junction for fuel cell with
At least one of the pair of gas diffusion layers has a microporous layer in contact with the catalyst layer.
The catalyst layer contains ionomer.
The microporous layer contains a polytetrafluoroethylene resin and contains.
When the amount of the ionoma contained in the unit area of the catalyst layer is A and the amount of the polytetrafluoroethylene resin contained in the unit area of the microporous layer is B, the following A membrane electrode gas diffusion layer bonded body characterized by satisfying the formula (1).
0.20 ≤ A / B ... Equation (1)

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