JP2008112598A - Membrane-electrode assembly for fuel cell - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a membrane-electrode assembly for a fuel cell excellent in adhesion between an electrolyte membrane and a catalyst layer and high in power generation performance. <P>SOLUTION: The membrane-electrode assembly includes a hydrocarbon polymer electrolyte membrane 1 and catalyst layers 4a, 4b arranged on both surfaces of the hydrocarbon polymer electrolyte membrane and containing a catalyst and a first fluorinated polymer electrolyte, and an intermediate layer 9 interposing between the hydrocarbon polymer electrolyte membrane and at least one catalyst layer, and the intermediate layer contains a second fluorinated polymer electrolyte and a polymer A having a glass transition temperature of 100°C-150°C and containing no proton acid group. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a membrane / electrode assembly for a fuel cell.

  A fuel cell directly converts chemical energy into electrical energy by supplying fuel and an oxidant to two electrically connected electrodes and causing the fuel to be oxidized electrochemically. Unlike thermal power generation, fuel cells are not subject to the Carnot cycle and thus exhibit high energy conversion efficiency. A fuel cell is usually formed by laminating a plurality of single cells having a basic structure of a membrane / electrode assembly in which an electrolyte membrane is sandwiched between a pair of electrodes. Among them, a solid polymer electrolyte fuel cell using a solid polymer electrolyte membrane as an electrolyte membrane has advantages such as being easy to downsize and operating at a low temperature. It is attracting attention as a power source for the body.

In the solid polymer electrolyte fuel cell, the reaction of the formula (1) proceeds at the anode (fuel electrode).
H ₂ → 2H ⁺ + 2e ⁻ (1)
The electrons generated by the equation (1) reach the cathode (oxidant electrode) after working with an external load via an external circuit. Then, the proton generated in the formula (1) moves in the solid polymer electrolyte membrane from the anode side to the cathode side by electroosmosis while being hydrated with water.
On the other hand, the reaction of the formula (2) proceeds at the cathode.
4H ⁺ + O ₂ + 4e ⁻ → 2H ₂ O (2)

  As solid polymer electrolyte membranes (hereinafter sometimes referred to as polymer electrolyte membranes), Nafion (trade name, manufactured by DuPont) has been used since it has excellent properties required for electrolyte membranes such as proton conductivity and chemical stability. ), Aciplex (trade name, manufactured by Asahi Kasei) and Flemion (trade name, manufactured by Asahi Glass), and other fluoropolymer electrolyte membranes such as perfluorocarbon sulfonic acid resin membranes have been used.

  However, the fluorine-based polymer electrolyte membrane is very expensive and is one of the factors hindering the cost reduction of the fuel cell. Further, since the fluorine-based polymer electrolyte membrane contains fluorine, there is also a problem that the environmental load is large. Therefore, research and development of polymer electrolyte membranes that are less expensive than fluorine-based polymer electrolyte membranes and have a low fluorine content are underway. For example, proton conducting groups such as sulfonic acid groups, carboxyl groups, and phosphoric acid groups on hydrocarbon polymers such as polyether ether ketone (PEEK), polyether ketone, polyether sulfone (PES), and polyphenylene sulfide (PPS). The thing using the hydrocarbon type polymer electrolyte which introduce | transduced is mentioned.

Usually, the electrodes (usually the catalyst layers) provided on both surfaces of the polymer electrolyte membrane also ensure proton conductivity in the electrode, ensure the bondability between the polymer electrolyte membrane and the electrode, catalyst particles contained in the electrode, etc. A polymer electrolyte is contained for the purpose of securing the binding property of the resin.
In general, by using a polymer electrolyte that is the same as or the same as the polymer electrolyte membrane as the polymer electrolyte for electrodes, sufficient bondability can be obtained between the polymer electrolyte membrane and the catalyst layer (electrode). In other words, the hydrocarbon polymer electrolyte membrane is used in the case of hydrocarbon polymer electrolyte membranes, and the fluorine polymer electrolyte is used in the case of fluorine polymer electrolyte membranes, thereby ensuring the bondability between the polymer electrolyte membrane and the electrode. can do.

JP 2004-253399 A JP 2004-335270 A

When using a hydrocarbon-based polymer electrolyte as the polymer electrolyte for electrodes, the hydrocarbon-based polymer electrolyte is generally inferior in oxygen permeability to the fluorine-based polymer electrolyte, thus inhibiting gas diffusion in the catalyst layer. It's easy to do. In addition, part of the molecular structure of the hydrocarbon-based polymer electrolyte and an organic solvent used as a solvent may be strongly adsorbed on a catalyst such as Pt, and the catalytic activity may be reduced. From this viewpoint, it is considered that a fluorine-based polymer electrolyte is suitable as the polymer electrolyte for electrodes.
Therefore, a combination of a hydrocarbon polymer electrolyte membrane and a fluorine polymer electrolyte (polymer electrolyte for electrodes) is used from the viewpoint of cost reduction of the fuel cell, gas diffusibility of the catalyst layer, and catalytic activity. Is being considered.

  However, when the hydrocarbon-based polymer electrolyte membrane is combined with the fluorine-based polymer electrolyte as the electrode polymer electrolyte in this way, the bondability between the electrolyte membrane and the catalyst layer tends to be insufficient.

  In order to ensure the bonding between the hydrocarbon polymer electrolyte membrane and the catalyst layer containing the fluorine polymer electrolyte, it is necessary to simultaneously soften the hydrocarbon polymer electrolyte and the fluorine polymer electrolyte. Hydrocarbon polymer electrolytes have a high glass transition point and are not easily softened by heating. Therefore, it is difficult to fuse a hydrocarbon polymer electrolyte membrane and a catalyst layer containing a fluorine polymer electrolyte by heating. is there. When the thermocompression bonding of the hydrocarbon-based polymer electrolyte membrane is carried out at a high temperature to sufficiently soften, the fluorine-based polymer electrolyte is decomposed or the proton-conducting group of the fluorine-based polymer electrolyte or the hydrocarbon-based polymer electrolyte is changed. There is a high possibility of detachment. Also, under the conditions where the catalyst coexists, the decomposition of the hydrocarbon polymer electrolyte and the fluorine polymer electrolyte tends to proceed without heating to a temperature as high as the glass transition temperature of the hydrocarbon polymer electrolyte. There is.

  Furthermore, the catalyst layer containing the fluorine-based polymer electrolyte is isotropic in dimensional change at the time of swelling, that is, in the thickness direction and the surface direction, whereas the hydrocarbon-based polymer electrolyte membrane is swollen. There is a tendency that the dimensional change at the time is large in the thickness direction and hardly changes in the surface direction. Therefore, when the catalyst layer containing the hydrocarbon polymer electrolyte membrane and the fluorine polymer electrolyte swells under high humidity conditions such as the operating condition of the fuel cell, the catalyst layer containing the fluorine polymer electrolyte The hydrocarbon polymer electrolyte membrane cannot follow the dimensional change in the surface direction, and the electrolyte membrane and the catalyst layer are peeled off.

  The bondability between the electrolyte membrane and the catalyst layer greatly affects the proton conductivity and water mobility between the electrolyte membrane and the catalyst layer, and is very important from the viewpoint of improving the performance and stabilizing the performance of the fuel cell. It is desired to improve the bondability between the electrolyte electrolyte resin membrane and the catalyst layer containing the fluorine electrolyte resin.

  In Patent Document 1, for the purpose of enhancing the adhesion at the interface between the electrode surface and the electrolyte membrane, a catalyst electrode containing a first solid polymer electrolyte and a catalyst substance, a solid polymer electrolyte membrane, and the catalyst electrode, A fuel cell having an adhesive layer including a second polymer electrolyte provided between the solid polymer electrolyte membrane has been proposed. In Patent Document 1, there is a description that the adhesive layer may contain a polymer electrolyte such as the first polymer electrolyte in addition to the second polymer electrolyte, but the adhesive formed only by the polymer electrolyte. The layer may swell greatly when water is absorbed, such as when the fuel cell is operated, and may peel off from the electrolyte membrane and the electrode.

  Further, in Patent Document 2, for the purpose of providing a membrane / electrode assembly having strong adhesion between an electrolyte membrane and an electrode, the polymer electrolyte (A) having a solid polymer electrolyte membrane having at least a glass transition temperature of 140 ° C. or higher There has been proposed a solid polymer fuel cell comprising a mixture of polymers (B) having a glass transition temperature of less than 140 ° C., wherein the polymer (A) is a non-fluorinated hydrocarbon polymer. However, in Patent Document 2, a polymer that does not have proton conductivity is included in the electrolyte membrane, and there is a possibility that sufficient proton conductivity may not be obtained. Further, when the dispersibility of the polymer (A) and the polymer (B) is poor, the polymer (A) and the polymer (B) may be unevenly distributed in the film, and in the plane of the electrolyte film or in the thickness direction. There is also a possibility that a portion showing proton conductivity and a portion not showing are distributed.

  The present invention has been accomplished in view of the above circumstances, and an object of the present invention is to provide a membrane / electrode assembly for a fuel cell that has excellent bondability between an electrolyte membrane and a catalyst layer and has high power generation performance.

  The fuel cell membrane / electrode assembly of the present invention is provided with a hydrocarbon polymer electrolyte membrane and both surfaces of the hydrocarbon polymer electrolyte membrane, and contains a catalyst and a first fluorine polymer electrolyte. A fuel cell membrane / electrode assembly comprising an intermediate layer interposed between the hydrocarbon-based polymer electrolyte membrane and at least one of the catalyst layers, the intermediate layer comprising: It contains a second fluorine-based polymer electrolyte and a polymer A having a glass transition temperature of 100 ° C. to 150 ° C. and having no proton acid group.

The membrane / electrode assembly of the present invention is provided with the above-described intermediate layer, thereby ensuring the proton conductivity of the intermediate layer with the second fluorine-based polymer electrolyte, and the hydrocarbon-based with the polymer A. This achieves improvement in the bondability between the polymer electrolyte membrane and the catalyst layer. Further, an intermediate layer containing the polymer A and a fluorine-based polymer electrolyte is interposed between the hydrocarbon-based polymer electrolyte membrane and the catalyst layer containing a fluorine-based polymer electrolyte, whereby the electrolyte The difference in dimensional change in the bonding surface direction when the membrane and the catalyst layer swell can be alleviated, and separation between the electrolyte membrane and the catalyst layer can be prevented.
Therefore, according to the present invention, there is provided a membrane / electrode assembly for a fuel cell that ensures the bondability between the electrolyte membrane and the catalyst layer over a long period of time, exhibits excellent proton conductivity and water mobility, and exhibits high power generation performance. Obtainable.

  From the viewpoint of ensuring the bonding property between the catalyst layer and the electrolyte membrane by the intermediate layer and ensuring the proton conductivity in the intermediate layer, the content of the polymer A in the intermediate layer is such that the polymer A and the second fluorine are contained. The total weight of the polymer electrolyte is preferably 5 wt% to 30 wt%.

  From the viewpoint of the affinity with the second fluorine-based polymer electrolyte and the bonding property between the catalyst layer containing the fluorine-based polymer electrolyte and the intermediate layer, the polymer A is a partially fluorinated hydrocarbon-based polymer. Molecules are preferred. From the viewpoint of glass transition temperature and ease of production of the intermediate layer, the polymer A preferably does not contain an aromatic ring.

  ADVANTAGE OF THE INVENTION According to this invention, it is possible to provide the membrane electrode assembly which is excellent in the joining property between an electrolyte membrane and a catalyst layer, and expresses high power generation performance.

  The fuel cell membrane / electrode assembly of the present invention is provided with a hydrocarbon polymer electrolyte membrane and both surfaces of the hydrocarbon polymer electrolyte membrane, and contains a catalyst and a first fluorine polymer electrolyte. A fuel cell membrane / electrode assembly comprising an intermediate layer interposed between the hydrocarbon-based polymer electrolyte membrane and at least one of the catalyst layers, the intermediate layer comprising: It contains a second fluorine-based polymer electrolyte and a polymer A having a glass transition temperature of 100 ° C. to 150 ° C. and having no proton acid group.

Hereinafter, a fuel cell membrane-electrode assembly (hereinafter, simply referred to as a membrane-electrode assembly) provided by the present invention will be described with reference to FIG. FIG. 1 is a cross-sectional view schematically showing one embodiment (unit cell 100) of a unit cell provided with the membrane-electrode assembly of the present invention.
The unit cell 100 is a membrane in which a fuel electrode (anode) 2 and an oxidant electrode (cathode) 3 are provided on one surface side of a hydrocarbon polymer electrolyte membrane (hereinafter sometimes referred to simply as an HC electrolyte membrane) 1. -It has the electrode assembly 6. The fuel electrode 2 has a fuel electrode side catalyst layer 4a on the surface facing the HC electrolyte membrane 1, and a fuel electrode side gas diffusion layer 5a is laminated adjacent to the catalyst layer 4a. Similarly, the oxidant electrode 3 has an oxidant electrode side catalyst layer 4b on the surface facing the HC electrolyte membrane 1, and an oxidant electrode side gas diffusion layer 5b is laminated adjacent to the catalyst layer 4b. It has become.

Each catalyst layer 4 (4a, 4b) includes a catalyst having catalytic activity for the electrode reaction in each electrode (2, 3), and a fluorine-based polymer electrolyte (first fluorine) that imparts proton conductivity to the electrode. -Based polymer electrolyte (hereinafter sometimes referred to as a first F-based electrolyte). In addition to imparting proton conductivity, the fluorine-based polymer electrolyte in the catalyst layer has functions such as securing the bondability between the electrolyte membrane and the electrode and immobilizing the catalyst.
In this embodiment, each electrode (fuel electrode, oxidant electrode) has a structure in which a catalyst layer and a gas diffusion layer are laminated, but has a single-layer structure composed of only the catalyst layer. Alternatively, a structure in which a functional layer is provided in addition to the catalyst layer and the gas diffusion layer may be used.

A surface facing each of the electrodes 2 and 3 that faces the HC electrolyte membrane and containing the first F electrolyte, the fuel electrode side catalyst layer 4a and the oxidant electrode side catalyst layer 4b, and the HC electrolyte membrane 1 And a glass transition temperature of 100 ° C. to 150 ° C., respectively, with a fluorine-based polymer electrolyte (second fluorine-based polymer electrolyte; hereinafter sometimes referred to as a second F-based electrolyte). An intermediate layer 9 containing a polymer A having no proton acid group (hereinafter sometimes simply referred to as polymer A) is provided.
In the present embodiment, the fuel electrode side catalyst layer 4a and the HC electrolyte membrane 1 (between the fuel electrode 2 and the HC electrolyte membrane 1) and the oxidant electrode side catalyst layer 4b and the HC electrolyte membrane 1 are used. The intermediate layer 9 is provided in both of the gaps (between the oxidant electrode 3 and the HC electrolyte membrane 1). The intermediate layer is provided between the fuel electrode side catalyst layer 4a and the HC electrolyte membrane 1 or It may be provided only in either one between the oxidant electrode side catalyst layer 4b and the HC electrolyte membrane 1.

  The membrane / electrode assembly 6 is sandwiched between two separators 7 a and 7 b to form a single cell 100. On one side of each of the separators 7a and 7b, grooves for forming a flow path of the reaction gas (fuel gas and oxidant gas) are provided. The fuel is formed by these grooves and the outer surfaces of the fuel electrode 2 and the oxidant electrode 3. A gas flow path 8a and an oxidant gas flow path 8b are defined. The fuel gas channel 8 a is a channel for supplying a fuel gas (a gas containing hydrogen or generating hydrogen) to the fuel electrode 2, and the oxidant gas channel 8 b is an oxidant gas to the oxidant electrode 3. It is a flow path for supplying (a gas containing or generating oxygen).

  Like the membrane / electrode assembly of the present invention, the polymer electrolyte constituting the electrolyte membrane is an HC electrolyte, and the polymer electrolyte contained in the catalyst layer provided adjacent to the electrolyte membrane is an F electrolyte. In this case, as described above, it has been difficult to secure the bonding property between the electrolyte membrane and the catalyst layer (electrode) due to the low softness of these HC electrolyte membranes. If the bonding property between the electrolyte membrane and the catalyst layer is poor, the proton conductivity at the interface between the electrolyte membrane and the catalyst layer is lowered and the cell resistance is increased. Furthermore, water mobility between the electrolyte membrane and the catalyst layer is reduced, and water stays in the catalyst layer or at the interface between the catalyst layer and the electrolyte membrane, thereby causing flooding, dry-up, etc. In this case, the water balance is lost, or separation between the electrolyte membrane and the electrode occurs. As a result, there arises a problem that not only the power generation performance is lowered but also the durability is lowered and stable power supply is impossible.

  Furthermore, while the catalyst layer containing the F-based electrolyte undergoes dimensional change isotropically when swollen, the HC-based electrolyte membrane produces a dimensional change mainly in the thickness direction and a small dimensional change in the plane direction. Tend. That is, when the catalyst layer containing the HC-based electrolyte membrane and the F-based electrolyte swells under highly humid conditions such as operating conditions of the fuel cell, the dimensional change in the surface direction of the catalyst layer containing the F-based polymer electrolyte In addition, the HC polymer electrolyte membrane cannot follow, and the electrolyte membrane and the catalyst layer are easily separated. Therefore, in an environment where a highly wet state and a dry state are repeated as in a fuel cell, it has been difficult to exhibit stable performance for a long period of time.

  In contrast, the membrane / electrode assembly of the present invention has an F-based electrolyte (second F-based electrolyte) between an HC electrolyte membrane and a catalyst layer containing an F-based electrolyte (first F-based electrolyte). Electrolyte) and an intermediate layer containing a specific polymer A are interposed between the HC electrolyte membrane and a catalyst layer containing an F electrolyte (hereinafter sometimes referred to as an F electrolyte containing catalyst layer). Improved bondability.

  The intermediate layer is given proton conductivity by the second F-based electrolyte. In addition, since the second F-based electrolyte has a high affinity with the first F-based electrolyte, it improves the bondability between the catalyst layer containing the first F-based electrolyte and the intermediate layer together with the polymer A. To contribute.

  On the other hand, the polymer A having a glass transition temperature of 100 ° C. to 150 ° C. functions to ensure the bondability between the intermediate layer and the HC-based electrolyte membrane and between the intermediate layer and the catalyst layer, and as a result, the HC-based electrolyte membrane. And the catalyst layer containing the F-based electrolyte are enhanced. An intermediate layer containing a polymer having a glass transition temperature of 100 to 150 ° C. is interposed between the HC electrolyte membrane and the catalyst layer containing an F electrolyte, and simultaneously with pressurization, the glass transition temperature of the polymer A By heating to the above temperature, the polymer A is softened, and the HC electrolyte membrane and catalyst layer that are in contact with the intermediate layer are bonded to the intermediate layer. At this time, even if it is not heated to a high temperature at which the HC electrolyte membrane is softened, if it is heated above the glass transition temperature of the polymer A having a glass transition temperature in the above range, the HC electrolyte membrane-intermediate layer-catalyst Interlayers can be joined.

  Furthermore, the membrane / electrode assembly of the present invention has the intermediate layer interposed between the HC-based electrolyte membrane and the catalyst layer containing the F-based electrolyte, so that the electrolyte membrane and the catalyst layer are peeled at the time of swelling. Prevention was realized.

The intermediate layer does not have a proton acid group, and has a low swelling property as compared with the HC electrolyte or F electrolyte, and a second that causes an isotropic dimensional change upon swelling. Fluorine-based electrolyte is contained. Therefore, the magnitude of the dimensional change in the surface direction during swelling is HC-based electrolyte membrane <intermediate layer <F-based electrolyte-containing catalyst layer. In this way, by interposing a layer having an intermediate degree of dimensional change between the HC electrolyte membrane and the F-type electrolyte-containing catalyst layer having greatly different dimensional changes in the plane direction, the HC electrolyte membrane during swelling And the stress generated on the joint surface of the F-based electrolyte-containing catalyst layer can be relaxed, and peeling between these layers can be prevented.
At this time, in the conventional membrane / electrode assembly in which the HC electrolyte membrane and the F-based electrolyte-containing catalyst layer are directly bonded, the bonding between the electrolyte membrane and the catalyst layer is not secured. In the invention, since the bondability is ensured by the intermediate layer, the stress relaxation effect as described above is sufficiently exerted, and peeling between the electrolyte membrane and the catalyst layer can be prevented.

  As described above, the membrane / electrode assembly of the present invention has ensured bondability between the HC electrolyte membrane and the F electrolyte containing catalyst layer, expresses high power generation performance, and has excellent durability. Stable power supply over a long period of time is possible.

  Here, the fluorine-based polymer electrolyte (F-based electrolyte) is a perfluorocarbon sulfone represented by Nafion (trade name, manufactured by DuPont), Aciplex (trade name, manufactured by Asahi Kasei), and Flemion (trade name, manufactured by Asahi Glass). Fluorine-containing polymer electrolyte such as acid resin. The first F-based electrolyte and the second F-based electrolyte may be different or the same.

  Further, the hydrocarbon polymer electrolyte (HC electrolyte) typically does not contain fluorine at all, but since the effects of the present invention can be sufficiently obtained, it is more than the electrolyte resin used as the F electrolyte. It may be partially fluorine-substituted within the range of a small fluorine content. Specific examples of hydrocarbon polymer electrolytes include polyether ether ketone, polyether ketone, polyether sulfone, polyphenylene sulfide, polyphenylene ether, polyparaphenylene, and other engineering plastics, polyethylene terephthalate, polyethylene, polypropylene, polystyrene, etc. Examples thereof include those obtained by introducing proton acid groups (proton conductive groups) such as sulfonic acid groups, carboxylic acid groups, phosphoric acid groups, and boronic acid groups into these general-purpose plastics, and copolymers thereof.

  The HC electrolyte membrane is composed mainly of the HC electrolyte as described above, and may be composed of only the HC electrolyte, or may contain other components. . Moreover, you may contain multiple types of HC type electrolyte. The film thickness of the HC electrolyte membrane is not particularly limited, and is usually about 10 to 100 μm.

  The polymer A having a glass transition temperature in the range of 100 ° C. to 150 ° C. and having no proton acid group has a glass transition temperature in the above range and does not have a proton acid group. If it is, it will not specifically limit. Here, the proton acid group is a group capable of dissociating protons and exhibits proton conductivity. Specific examples include a sulfonic acid group, a carboxylic acid group, a phosphoric acid group, and a boronic acid group.

If the glass transition temperature of the polymer A is less than 100 ° C., the polymer A softens under the conditions during power generation of the fuel cell, and the configuration of the membrane / electrode assembly may not be maintained. On the other hand, if the glass transition temperature of the polymer A is higher than 150 ° C., it is necessary to heat and pressure bond at a high temperature in order to ensure the bonding property between the electrolyte membrane and the catalyst layer, so that the electrolyte in the electrolyte membrane and the catalyst layer deteriorates. May occur.
The glass transition temperature of the polymer A may be in the range of 100 ° C. to 150 ° C., but particularly from the viewpoints of modification, decomposition, etc. due to heat of the electrolyte resin constituting the polymer A, the catalyst layer, and the electrolyte membrane. It is preferable that it exists in the range of 100 to 140 degreeC.

  Examples of the polymer A having the glass transition temperature as described above include those having no aromatic ring in the main chain and / or side chain. Engineering plastics, which are typical examples of polymers having aromatic rings, generally have a high glass transition temperature exceeding 200 ° C. Further, many polymers having an aromatic ring have poor solvent solubility. As will be described later, the intermediate layer is formed by using a solution in which the second F-based electrolyte and the polymer A are dissolved in a solvent. Therefore, when the solvent solubility is low, the intermediate layer exhibits sufficient performance. Difficult to form.

  Since the affinity with the first F-based electrolyte contained in the catalyst layer adjacent to the intermediate layer and the second F-based electrolyte contained in the intermediate layer is high, the polymer A includes a fluorine-containing polymer. Particularly preferred are partially fluorinated hydrocarbon polymers. By using the polymer A having high affinity with the first and second F-based electrolytes, the effect of improving the bondability between the intermediate layer and the catalyst layer is high, and the film formability of the intermediate layer is also improved. Because it can be expected. Among them, the hydrocarbon polymer partially substituted with fluorine is excellent in affinity with the first and second F electrolytes and also in affinity with the HC electrolyte membrane. It can be expected that the bondability between the membrane-F-based electrolyte-containing catalyst layer is further enhanced.

The partially fluorinated hydrocarbon polymer may contain hetero atoms other than carbon and hydrogen in addition to fluorine.
Specific examples of the polymer A include polystyrene, polycarbonate, and polyvinylidene fluoride (PVdF), and PVdF is particularly preferable.

The amount of the second F-based electrolyte and polymer A contained in the intermediate layer is not particularly limited, but the amount of polymer A relative to the total weight of the second F-based electrolyte and polymer A [polymer A / (Polymer A + second F-based electrolyte) × 100] is preferably 5 to 30 wt%, particularly preferably 5 to 20 wt%.
When the amount of the polymer A is 30 wt% or less, the proton conductivity in the intermediate layer can be sufficiently secured, and the power generation performance of the membrane / electrode assembly can be maintained. On the other hand, when the amount of the polymer A is 5 wt% or more, a sufficient effect of improving the bonding property between the HC-based electrolyte membrane, the intermediate layer, and the catalyst layer by the polymer A can be obtained.

  From the viewpoint of proton conductivity and water mobility, the thickness of the intermediate layer should be as thin as possible within the range that can secure the bonding property between the HC-based electrolyte membrane and the catalyst layer. Specifically, it is 5 μm or less, particularly 2 μm or less. It is preferable that it is usually about 0.5 to 2 μm.

  The method for producing the intermediate layer in the membrane / electrode assembly of the present invention is not particularly limited. Usually, first, an intermediate layer solution containing the polymer A constituting the intermediate layer and the second F-based electrolyte is prepared. To do.

  The solvent for dissolving the polymer A and the second F-based electrolyte constituting the intermediate layer as described above is not particularly limited, and is appropriately determined in consideration of the solubility of the fluorine-based electrolyte to be used and the polymer A, and the like. Just choose. Specifically, alcohols such as ethanol, propanol, propylene glycol, butanol, organic solvents such as N-methyl-2-pyrrolidone (NMP), dimethyl sulfoxide (DMSO), tetrahydrofuran (THF), water, or a mixture thereof Etc.

The polymer A, the F-based electrolyte, and the solvent may be added and mixed at the same time, but from the viewpoint of the solubility of the polymer A and the F-based electrolyte in the solvent, the polymer A in which the polymer A is dissolved in advance. It is preferable to prepare an intermediate layer solution by preparing a solution and an F-based electrolyte solution in which the F-based electrolyte is dissolved, and mixing the polymer A solution and the F-based electrolyte solution.
At this time, the solvent of the polymer A solution and the F-based electrolyte solution may be different or the same. However, it is preferable to select the amount and type of each solvent in consideration of the solubility of each of the polymer A and the second F-based electrolyte.

As a method for preparing the intermediate layer solution containing the polymer A, the F-based electrolyte, and the solvent, a general method can be adopted, for example, a stirring means such as a roll mill, a ball mill, an ultrasonic homogenizer, and a jet mill. Can be used.
In addition to the polymer A, the F-based electrolyte and the solvent, the intermediate layer solution may contain other components as necessary within the range not impairing the effects of the present invention.

  The intermediate layer solution may be applied to a suitable substrate surface (for example, HC electrolyte membrane surface, F electrolyte containing catalyst layer surface, transfer substrate surface, etc.) and dried to form the intermediate layer. it can. For example, (1) an intermediate layer solution was applied to the surface of the HC electrolyte membrane and dried to form an intermediate layer, and then a catalyst ink was applied to the surface of the intermediate layer and dried to form a catalyst layer. Method of thermocompression bonding electrolyte membrane-intermediate layer-catalyst layer laminate, (2) Apply intermediate layer solution on HC electrolyte membrane surface, dry to form intermediate layer, and separately apply catalyst ink on transfer substrate surface (3) First, a catalyst ink is applied to the surface of a transfer substrate and dried to form a catalyst layer using a catalyst layer transfer sheet formed by coating Subsequently, a catalyst layer / intermediate layer transfer sheet is prepared by applying an intermediate layer solution on the surface of the catalyst layer and drying to form an intermediate layer. The HC electrolyte membrane and the catalyst layer / intermediate layer transfer sheet are It is a method to thermally transfer the intermediate layer-catalyst layer laminate to the surface of the HC electrolyte membrane by thermocompression bonding. , And the like. Here, in the methods (2) and (3), the intermediate layer, the catalyst layer, and the electrolyte membrane are joined by thermocompression bonding when the transfer sheet is thermally transferred.

  In addition, after applying the intermediate layer solution on the surface of the F-based electrolyte-containing catalyst layer and drying to form an intermediate layer, the obtained catalyst layer-intermediate layer laminate and the HC-based electrolyte membrane are thermocompression-bonded, The intermediate layer solution is applied to the surface of the transfer substrate and dried to form an intermediate layer transfer sheet. The transfer sheet is superposed on the F-based electrolyte-containing catalyst layer or the HC-based electrolyte membrane and thermocompression bonded. First, an intermediate layer was formed on the surface of the F-based electrolyte-containing catalyst layer or HC-based electrolyte membrane, and then the HC-based electrolyte membrane or the intermediate layer was formed on the F-based electrolyte-containing catalyst layer on which the intermediate layer was formed. By providing the F-based electrolyte-containing catalyst layer on the HC-based electrolyte membrane, a membrane / electrode assembly including an intermediate layer between the electrolyte membrane and the electrode (catalyst layer) can be obtained.

  The method for applying the intermediate layer solution is not particularly limited, and examples thereof include a spray method, a screen printing method, a doctor blade method, a gravure printing method, a die coating method, a spin coating method, and a dip coating method. The drying conditions for the intermediate layer solution are not limited, and general methods such as heat drying, vacuum drying, and heat vacuum drying can be employed.

  As the gas diffusion layer sheet for forming the gas diffusion layer, a gas diffusion property that can efficiently supply gas to the catalyst layer, conductivity, and strength required as a material constituting the gas diffusion layer, for example, Carbonaceous porous bodies such as carbon paper, carbon cloth, carbon felt, titanium, aluminum, copper, nickel, nickel-chromium alloy, copper and its alloys, silver, aluminum alloy, zinc alloy, lead alloy, titanium, niobium , Tantalum, iron, stainless steel, gold, platinum, and the like, and those made of a conductive porous material such as a metal mesh or a metal porous material. The thickness of the conductive porous body is preferably about 50 to 500 μm.

  The gas diffusion layer sheet may be composed of a single layer of the conductive porous body as described above, but a water repellent layer may be provided on the side facing the catalyst layer. The water-repellent layer usually has a porous structure containing conductive particles such as carbon particles and carbon fibers, water-repellent resin such as polytetrafluoroethylene (PTFE), and the like. The water-repellent layer is not necessarily required, but it can improve the drainage of the gas diffusion layer while maintaining an appropriate amount of water in the catalyst layer and the electrolyte membrane. There is an advantage that electrical contact can be improved.

  The method for forming the water repellent layer on the conductive porous body is not particularly limited. For example, water repellent obtained by mixing conductive particles such as carbon particles, water repellent resin, and other components as necessary with an organic solvent such as ethanol, propanol, propylene glycol, water or a mixture thereof. The layer ink may be applied to at least the side of the conductive porous body facing the catalyst layer, and then dried and / or fired. The thickness of the water repellent layer may usually be about 1 to 50 μm. Examples of the method for applying the water repellent layer ink to the conductive porous body include a screen printing method, a spray method, a doctor blade method, a gravure printing method, and a die coating method.

  In addition, the conductive porous body is formed by impregnating and applying a water-repellent resin such as polytetrafluoroethylene to the side facing the catalyst layer with a bar coater, etc. It may be processed so as to be discharged well.

The catalyst layer can be formed using a catalyst ink containing at least a first F-based electrolyte and a catalyst.
As the catalyst, usually, a catalyst component supported on conductive particles is used. The catalyst component is not particularly limited as long as it has catalytic activity for the oxidation reaction of the fuel at the fuel electrode or the reduction reaction of the oxidant at the oxidant electrode, and is generally used for solid polymer fuel cells. Can be used. For example, platinum or an alloy of platinum and a metal such as ruthenium, iron, nickel, and manganese can be used.
As the conductive particles as the catalyst carrier, carbon particles such as carbon black, conductive carbon materials such as carbon fibers, and metal materials such as metal particles and metal fibers can also be used.

  The catalyst ink is obtained by dissolving or dispersing the above catalyst and the first F-based electrolyte in a solvent. The solvent for the catalyst ink may be appropriately selected. For example, alcohols such as methanol, ethanol, and propanol, a mixture thereof, and a mixture of these with water can be used. In addition to the catalyst and the first F-based electrolyte, the catalyst ink may contain other components such as a binder and a water-repellent resin as necessary.

  The method for forming the catalyst layer is not particularly limited. For example, the catalyst layer may be formed on the surface of the gas diffusion layer sheet by applying and drying the catalyst ink on the surface of the gas diffusion layer sheet, or the intermediate layer. The catalyst layer may be formed on the intermediate layer on the surface of the HC-based electrolyte membrane by applying and drying the catalyst ink on the intermediate layer of the HC-based electrolyte membrane on which is formed. Alternatively, a transfer sheet is prepared by applying and drying catalyst ink on the surface of the transfer substrate, and the transfer sheet is bonded to the HC electrolyte membrane or gas diffusion sheet on which the intermediate layer is formed by thermocompression bonding or the like. Alternatively, a catalyst layer may be formed on the intermediate layer on the surface of the HC-based electrolyte membrane, or an F-based catalyst layer having a catalyst layer formed on the surface of the gas diffusion layer sheet may be produced.

A method for applying the catalyst ink, a drying method, and the like can be appropriately selected. For example, examples of the coating method include a spray method, a screen printing method, a doctor blade method, a gravure printing method, a die coating method, and the like. Examples of the drying method include reduced pressure drying, heat drying, and reduced pressure heat drying. There is no restriction | limiting in the specific conditions in reduced pressure drying and heat drying, What is necessary is just to set suitably.
The amount of catalyst ink applied varies depending on the composition of the catalyst ink and the catalyst performance of the catalyst metal used for the electrode catalyst, but the amount of catalyst component per unit area is about 0.1 to 1.0 mg / cm ^2. What should I do? The film thickness of the catalyst layer is not particularly limited, but may be about 1 to 30 μm.

As a transfer substrate on which a polymer electrolyte mixed solution for forming an intermediate layer or a catalyst ink for forming a catalyst layer is applied, a general substrate can be used, for example, polytetrafluoroethylene (PTFE). ), Polypropylene, tetrafluoroethylene-ethylene copolymer (ETFE), or the like can be used.
The electrolyte membrane and the gas diffusion layer sheet on which the intermediate layer and the catalyst layer are formed by the above-described method are appropriately overlapped and thermocompression-bonded, and bonded to each other to obtain a membrane / electrode assembly.

  In the membrane-electrode assembly of the present invention, at least one of the oxidant electrode side catalyst layer and the fuel electrode side catalyst layer provided on the surface of the HC electrolyte membrane has an intermediate layer between the HC electrolyte membrane. However, it is sufficient to improve the power generation performance by improving the bonding properties between the two catalyst layers and the HC electrolyte membrane. It is preferable to provide an intermediate layer between both the electrode catalyst layer and the HC electrolyte membrane. When an intermediate layer is provided only between one electrode (catalyst layer) and the HC electrolyte membrane, the electrode (catalyst layer) and the HC electrolyte membrane are joined in a process that omits the intermediate layer formation step. That's fine.

  The produced membrane / electrode assembly is further sandwiched between separators to form a single cell. As the separator, for example, a carbon separator containing a high concentration of carbon fiber and made of a composite material with a resin, a metal separator using a metal material, or the like can be used. Examples of the metal separator include those made of a metal material excellent in corrosion resistance, and those coated with a coating that enhances the corrosion resistance by coating the surface with carbon or a metal material excellent in corrosion resistance. .

(Example 1)
<Preparation of intermediate layer solution>
A solution in which PVdF (polymer A) is dissolved in NMP and a solution in which perfluorocarbon sulfonic acid resin (second fluorine-based electrolyte) is dissolved in a mixed solution of water and alcohol are combined with PVdF: perfluorocarbon sulfonic acid resin. (Weight ratio) = 25: 75 [PVdF / (PVdF + perfluorocarbon sulfonic acid resin) × 100 = 25%] was mixed to prepare an intermediate layer solution A.

<Production of membrane / electrode assembly>
An intermediate layer solution A is spray-coated on one surface of a hydrocarbon-based polymer electrolyte membrane (7 cm × 7 cm, film thickness 30 μm), dried at 70 ° C., and a 0.5 μm thick intermediate layer (13 cm ² , PVdF And the total amount of perfluorocarbon sulfonic acid resin: 0.25 mg / cm ² ).

  On the other hand, a commercially available Pt / C catalyst (Pt supporting rate: 50 wt%), a perfluorocarbon sulfonic acid resin (first fluorine-based electrolyte, trade name: Nafion), and a solvent (mixture of water, ethanol and propanol) Was mixed with stirring so that Pt: perfluorocarbon sulfonic acid resin: carbon (weight ratio) = 1: 1: 1 to prepare a catalyst ink.

The catalyst ink was spray-coated on the surface of the intermediate layer provided on one surface of the hydrocarbon-based polymer electrolyte membrane and on the other surface without the intermediate layer. At this time, the catalyst ink was applied so that the amount of Pt per unit area of the catalyst layer was 0.5 mg / cm ² . The ink was dried at 70 ° C. to form a catalyst layer (13 cm ² ).

The obtained catalyst layer / intermediate layer / electrolyte membrane / catalyst layer assembly was sandwiched by two carbon cloths for gas diffusion layer, and thermocompression-bonded (pressing pressure: 3 MPa, pressing temperature: 140 ° C.) An electrode assembly was obtained.
The obtained membrane electrode assembly was sandwiched between two separators (made of carbon) to produce a single cell.

(Example 2)
In Example 1, a solution in which PVdF is dissolved in NMP and a solution in which perfluorocarbon sulfonic acid resin is dissolved in a mixture of water and alcohol are PVdF: perfluorocarbon sulfonic acid resin (weight ratio) = 50: 50. A single cell was produced in the same manner as in Example 1 except that the intermediate layer solution B mixed so that [PVdF / (PVdF + perfluorocarbon sulfonic acid resin) × 100 = 50%] was used.

(Comparative Example 1)
A single cell was produced in the same manner as in Example 1 except that the intermediate layer was not formed in Example 1.

(Comparative Example 2)
Example 1 except that an intermediate layer (total amount of perfluorocarbon sulfonic acid resin: 0.25 mg / cm ² ) was formed using a solution obtained by dissolving perfluorocarbon sulfonic acid resin in a mixed solution of water and alcohol. Similarly, a single cell was produced.

[Power generation evaluation]
About the single cell of Example 1, Example 2, Comparative Example 1, and Comparative Example 2 produced above, power generation evaluation was performed under the following conditions. The results are shown in FIG. In the single cells of Example 1, Example 2, and Comparative Example 2, the side on which the intermediate layer was formed was an air electrode.
<Power generation evaluation conditions>
・ Fuel (hydrogen gas): 500ml / min (60RH%)
・ Oxidizing agent (air): 900ml / min (60RH%)
-Cell temperature: 80 ° C

As shown in FIG. 2, Example 1 in which an intermediate layer containing PVdF and perfluorocarbon sulfonic acid resin is provided between a hydrocarbon polymer electrolyte membrane and a catalyst layer containing a fluorine-based electrolyte includes the intermediate layer Compared with the comparative example 1 which does not provide, a high voltage was exhibited from the low current density region to the high current density region, and the cell resistance was also reduced. Further, in Comparative Example 2 in which the intermediate layer made of only the perfluorocarbon sulfonic acid resin was provided, the cell resistance was reduced as compared with Example 1, but the cell voltage was the same as that of Example 1. This is presumably because in the single cell of Example 1, the adhesion between the electrolyte membrane and the catalyst layer was improved by PVdF contained in the intermediate layer.
Example 2 in which the content of PVdF exceeds 30 wt% with respect to the total amount of the perfluorocarbonsulfonic acid resin and PVdF is lower in voltage than Example 1 in which the content of PVdF is 30 wt% or less, Cell resistance also increased. This is presumably because the proton conductivity of the intermediate layer decreased with an increase in the content of PVdF.

(Reference experiment)
When drying a sulfonated poly (4-phenoxybenzoyl-1,4-phenylene) [hereinafter referred to as S-PPBP] film represented by the following formula and a perfluorocarbon sulfonic acid resin film (Nafion: trade name) (at 60 ° C. The state of vacuum drying for 10 minutes) and the length of the side (in-plane direction and thickness direction) in 25 ° C. water were measured, and the expansion coefficient in 25 ° C. water was determined based on the time of drying. The results are shown in Table 1.

  According to Table 1, the membrane made of perfluorocarbon sulfonic acid resin, which is a fluorine-based polymer electrolyte, has the same coefficient of expansion in the in-plane direction and in the thickness direction when dry-wet, In the film made of S-PPBP, which is a molecular electrolyte, the expansion coefficient in the thickness direction greatly exceeded the expansion coefficient in the in-plane direction. And it turns out that the expansion coefficient in the in-plane direction of perfluorocarbon sulfonic acid resin has reached about twice with respect to the expansion coefficient in the in-plane direction of S-PPBP. As a result, when the S-PPBP membrane (hydrocarbon polymer electrolyte membrane) and the catalyst layer containing the perfluorocarbon sulfonic acid resin (fluorine polymer electrolyte) are joined, these joint interfaces are caused by the fluctuation of the wet state. It can be inferred that a large stress is generated in.

It is a conceptual diagram which shows one example of a single cell containing the membrane-electrode assembly for fuel cells of this invention. It is a graph which shows the result of the electric power generation evaluation test of an Example and a comparative example.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Electrolyte membrane 2 ... Fuel electrode (anode)
3 ... Oxidant electrode (cathode)
4a ... Anode side catalyst layer 4b ... Cathode side catalyst layer 5a ... Anode side gas diffusion layer 5b ... Cathode side gas diffusion layer 6 ... Membrane / electrode assembly 7a ... Anode side separator 7b ... Cathode side separator 8a ... Anode side gas flow path 8b ... Cathode side gas flow path 9 ... Intermediate layer 100 ... Single cell

Claims (4)

Membrane / electrode joint for a fuel cell comprising a hydrocarbon polymer electrolyte membrane and a catalyst layer provided on both sides of the hydrocarbon polymer electrolyte membrane and containing a catalyst and a first fluorine polymer electrolyte Body,
An intermediate layer interposed between the hydrocarbon-based polymer electrolyte membrane and at least one of the catalyst layers,
The intermediate layer contains a second fluorine-based polymer electrolyte and a polymer A having a glass transition temperature of 100 ° C. to 150 ° C. and having no proton acid group, Membrane / electrode assembly for fuel cells.   2. The fuel cell according to claim 1, wherein a content of the polymer A in the intermediate layer is 5 wt% to 30 wt% with respect to a total weight of the polymer A and the second fluorinated polymer electrolyte. Membrane / electrode assembly.   The membrane / electrode assembly for a fuel cell according to claim 1 or 2, wherein the polymer A is a partially fluorinated hydrocarbon polymer.   The membrane / electrode assembly for a fuel cell according to any one of claims 1 to 3, wherein the polymer A does not contain an aromatic ring.

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